[
{
"id": "authors:q5czm-0ss33",
"collection": "authors",
"collection_id": "q5czm-0ss33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180117-125209725",
"type": "article",
"title": "Thermodynamically complete equation of state of MgO from true radiative shock temperature measurements on samples preheated to 1850 K",
"author": [
{
"family_name": "Fat'yanov",
"given_name": "O. V.",
"clpid": "Fat'yanov-O-V"
},
{
"family_name": "Asimow",
"given_name": "P. D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Plate impact experiments in the 100\u2013250 GPa pressure range were done on a \u27e8100\u27e9 single-crystal MgO preheated before compression to 1850 K. Hot Mo(driver)-MgO targets were impacted with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 7.5 km/s. Radiative temperatures and shock velocities were measured with 3%\u20134% and 1%\u20132% uncertainty, respectively, by a six-channel pyrometer with 3-ns time resolution, over a 500\u2013900-nm spectral range. MgO shock front reflectivity was determined in additional experiments at 220 and 248 GPa using \u224850/50 high-temperature sapphire beam splitters. Our measurements yield accurate experimental data on the mechanical, optical, and thermodynamic properties of B1 phase MgO from 102 GPa and 3900 K to 248 GPa and 9100 K, a region not sampled by previous studies. Reported Hugoniot data for MgO initially at ambient temperature, T=298 K, and the results of our current Hugoniot measurements on samples preheated to 1850 K were analyzed using the most general methods of least-squares fitting to constrain the Gr\u00fcneisen model. This equation of state (EOS) was then used to construct maximum likelihood linear Hugoniots of MgO with initial temperatures from 298 to 2400 K. A parametrization of all EOS values and best-fit coefficients was done over the entire range of relevant particle velocities. Total uncertainties of all the EOS parameters and correlation coefficients for these uncertainties are also given. The predictive capabilities of our updated Mie-Gr\u00fcneisen EOS were confirmed by (1) the good agreement between our Gr\u00fcneisen data and five semiempirical \u03b3(V) models derived from porous shock data only or from combined static and shock data sets, (2) the very good agreement between our 1-bar Gr\u00fcneisen values and \u03b3(T) at ambient pressure recalculated from reported experimental data on the adiabatic bulk modulus K_s(T), and (3) the good agreement of the brightness temperatures, corrected for shock reflectivity, with the corresponding values calculated using the current EOS or predicted by other groups via first-principles molecular dynamics simulations. Our experiments showed no evidence of MgO melting up to 250 GPa and 9100 K. The highest shock temperatures exceed the extrapolated melting curve of Zerr and Boehler by >3300 K and the upper limit for the melting boundary predictions of Aguado and Madden by >2600 K and those of Strachan et al. by >2100 K. We show that the potential for superheating in our shock experiments is negligible and therefore out data put a lower limit on the melting curve of B1 phase MgO in P\u2212T space close to the set of consistent independent predictions by Sun et al., Liu et al., and de Koker and Stixrude.",
"doi": "10.1103/PhysRevB.97.024106",
"issn": "2469-9950",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2018-01-01",
"series_number": "2",
"volume": "97",
"issue": "2",
"pages": "Art. No. 024106"
},
{
"id": "authors:8sf86-93y07",
"collection": "authors",
"collection_id": "8sf86-93y07",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130531-104225510",
"type": "article",
"title": "Moderate velocity oblique impact sliding: Production of shocked meteorite textures and palaeomagnetically important metallic spherules in planetary regoliths",
"author": [
{
"family_name": "Potter",
"given_name": "David K.",
"clpid": "Potter-D-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We detail the production of metallic spherules in laboratory oblique shock impact experiments, and their applicability (1) to textures in a partly shock-melted chondritic meteorite and (2) to the occurrence of palaeomagnetically important fine iron or iron alloy particles in the lunar regolith. Samples recovered from 29\u201344 GPa, 800 ns, experiments revealed melting and textures reminiscent of metallic spherules in the Yanzhuang H-chondrite, including \"dumbbell\" forms and other more complex morphologies. Our experiments demonstrate that metallic spherules can be produced via oblique impact sliding at lower velocities (1.85 km s^(\u22121)) than are generally assumed in previous work associated with bulk-shock melting, and that oblique impact sliding is a viable mechanism for producing spherules in shock-induced veins in moderately shocked meteorites. Significantly, our experiments also produced fine metallic (iron alloy) spherules within the theoretical narrow size range (a few tens of nanometers for slightly ellipsoidal particles) for stable single-domain (SSD) particles, which are the most important palaeomagnetically, since they can record lunar and planetary magnetic fields over geological time periods. The experiments also produced spherules consistent with superparamagnetic (SP) and multidomain (MD) particle sizes. The fine SSD and SP particles on the lunar surface are currently thought to have been formed predominantly by space weathering processes. Our experiments suggest that oblique shock impact sliding may be a further means of producing the SSD and SP iron or iron alloy particles observed in the lunar regolith, and which are likely to occur in the regoliths of Mercury and other planetary bodies.",
"doi": "10.1111/maps.12081",
"issn": "1086-9379",
"publisher": "Meteoritical Society",
"publication": "Meteoritics and Planetary Science",
"publication_date": "2013-04",
"series_number": "4",
"volume": "48",
"issue": "4",
"pages": "656-664"
},
{
"id": "authors:hhe00-0ph98",
"collection": "authors",
"collection_id": "hhe00-0ph98",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120529-090456353",
"type": "article",
"title": "Time-of-flight mass spectrometry of mineral volatilization: Toward direct composition analysis of shocked mineral vapor",
"author": [
{
"family_name": "Austin",
"given_name": "Daniel E.",
"clpid": "Austin-D-E"
},
{
"family_name": "Shen",
"given_name": "Andy H. T.",
"clpid": "Shen-Andy-H-T"
},
{
"family_name": "Beauchamp",
"given_name": "J. L.",
"orcid": "0000-0001-8839-4822",
"clpid": "Beauchamp-J-L"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We have developed an orthogonal-acceleration time-of-flight mass spectrometer to study the volatiles produced when a mineral's shock-compressed state is isentropically released, as occurs when a shock wave, driven into the mineral by an impact, reflects upon reaching a free surface. The instrument is designed to use a gun or explosive-launched projectile as the source of the shock wave, impact onto a flange separating a poor vacuum and the high vacuum (10^(\u22127) Torr) interior of the mass spectrometer, and transmission of the shock wave through the flange to a mineral sample mounted on the high-vacuum side of the flange. The device extracts and analyzes the neutrals and ions produced from the shocked mineral prior to the possible occurrence of collateral instrument damage from the shock-inducing impact. The instrument has been tested using laser ablation of various mineral surfaces, and the resulting spectra are presented. Mass spectra are compared with theoretical distributions of molecular species, and with expected distributions from laser desorption.",
"doi": "10.1063/1.4705745",
"issn": "0034-6748",
"publisher": "American Institute of Physics",
"publication": "Review of Scientific Instruments",
"publication_date": "2012-04",
"series_number": "4",
"volume": "83",
"issue": "4",
"pages": "Art. No. 044502"
},
{
"id": "authors:b6kpn-wdv92",
"collection": "authors",
"collection_id": "b6kpn-wdv92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101129-141006829",
"type": "article",
"title": "Shock compression of liquid silicates to 125 GPa: The anorthite\u2010diopside join",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "We determined the equation of state (EOS) of three silicate liquid compositions by shock compression of preheated samples up to 127 GPa. Diopside (Di; Ca_2Mg_2SiO_6)\nat 1773 K, anorthite (An; CaAl_2Si_2O_8) at 1923 K and the eutectic composition Di_(64)An_(36) at 1673 K were previously studied by shock compression to 38 GPa. The new data extend the EOS of each composition nearly to the Earth's core-mantle boundary. The previously reported anomaly at 25 GPa for Di_(64)An_(36) eutectic was not reproduced; rather all data for this composition fit within error a straight line Hugoniot in particle velocity vs. shock velocity. Di also displays a linear Hugoniot consistent with ultrasonic data and a third-order finite strain EOS. The full anorthite data set is complex; we examine a model with a transition between two structural states and a fourth\u2010order finite strain model\nexcluding two points that may not display relaxed behavior. We also report an experiment on room-temperature solid Di_(64)An_(36) aggregate that clearly demonstrates increase upon compression of the Gr\u00fcneisen parameter of this liquid, much as experiment and theory have shown for forsterite and enstatite liquids. We construct isentropes and isotherms from our Hugoniots using Mie-Gr\u00fcneisen thermal pressure and evaluate the model of ideal mixing of volumes. Volume may mix almost linearly at high temperature, but deviates\nstrongly when calculated along an isotherm; it remains difficult to reach a firm conclusion. We compare the densities of liquids to lower mantle solids. Our results suggest that basaltic liquids rich in CaO and Al_2O_3 are notably denser than liquids in the MgO-SiO_2 binary and, subject to uncertainties in the behavior of FeO and in corrections for thermal pressure, such liquids may be the most likely candidates for achieving negative buoyancy in the lowermost mantle.",
"doi": "10.1029/2009JB007145",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "2010-10-26",
"volume": "115",
"pages": "Art. No. B10209"
},
{
"id": "authors:b8bca-70a59",
"collection": "authors",
"collection_id": "b8bca-70a59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090908-083701874",
"type": "article",
"title": "Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes",
"author": [
{
"family_name": "Tschauner",
"given_name": "Oliver",
"orcid": "0000-0003-3364-8906",
"clpid": "Tschauner-O"
},
{
"family_name": "Kostandova",
"given_name": "Natalya",
"clpid": "Kostandova-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Ma",
"given_name": "Chi",
"orcid": "0000-0002-1828-7033",
"clpid": "Ma-Chi-Geology"
},
{
"family_name": "Sinogeikin",
"given_name": "Stanislas",
"clpid": "Sinogeikin-S"
},
{
"family_name": "Liu",
"given_name": "Zhenxian",
"clpid": "Liu-Zhenxian"
},
{
"family_name": "Fakra",
"given_name": "Sirine",
"clpid": "Fakra-S"
},
{
"family_name": "Tamura",
"given_name": "Nobumichi",
"orcid": "0000-0002-3698-2611",
"clpid": "Tamura-Nobumichi"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "We observed micrometer-sized grains of wadsleyite, a high-pressure phase of (Mg,Fe)_2SiO_4, in the recovery products of a shock experiment. We infer these grains crystallized from shock-generated melt over a time interval of <1 \u03bcs, the maximum time over which our experiment reached and sustained pressure sufficient to stabilize this phase. This rapid crystal growth rate (\u22481 m/s) suggests that, contrary to the conclusions of previous studies of the occurrence of high-pressure phases in shock-melt veins in strongly shocked meteorites, the growth of high-pressure phases from the melt during shock events is not diffusion-controlled. Another process, such as microturbulent transport, must be active in the crystal growth process. This result implies that the times necessary to crystallize the high-pressure phases in shocked meteorites may correspond to shock pressure durations achieved on impacts between objects 1\u20135 m in diameter and not, as previously inferred, \u22481\u20135 km in diameter. These results may also provide another pathway for syntheses, via shock recovery, of some high-value, high-pressure phases.",
"doi": "10.1073/pnas.0905751106",
"pmcid": "PMC2728955",
"issn": "0027-8424",
"publisher": "National Academy of Sciences",
"publication": "Proceedings of the National Academy of Sciences of the United States of America",
"publication_date": "2009-08-18",
"series_number": "33",
"volume": "106",
"issue": "33",
"pages": "13691-13695"
},
{
"id": "authors:z784k-s5586",
"collection": "authors",
"collection_id": "z784k-s5586",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090701-113819858",
"type": "article",
"title": "Shock compression of preheated molybdenum to 300 GPa",
"author": [
{
"family_name": "Sun",
"given_name": "Daoyuan",
"orcid": "0000-0003-4461-4664",
"clpid": "Sun-Daoyuan"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "Shock compression experiments on samples at elevated initial temperature provide a test of the Mie-Gr\u00fcneisen method of predicting off-principal Hugoniot states. Pure molybdenum, preheated to 1673 K, was shocked to peak pressures up to 300 GPa, double the compression range previously studied for this material at elevated temperature. The data lie strictly below the cold Hugoniot of Mo in shock velocity vs. particle velocity space, with some downward curvature. Previous approximations and extrapolations from lower-compression data fail to match these results, but the data are well fit by a Mie-Gr\u00fcneisen correction to the cold Hugoniot. However, the data are insufficiently precise and the phases obtained in the shock experiments too uncertain to discriminate among different functional forms of the density dependence of the Gr\u00fcneisen parameter.",
"doi": "10.1016/j.pepi.2008.08.004",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "2009-05",
"series_number": "1-4",
"volume": "174",
"issue": "1-4",
"pages": "302-308"
},
{
"id": "authors:d6nqy-pqt71",
"collection": "authors",
"collection_id": "d6nqy-pqt71",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MOSjgrb09",
"type": "article",
"title": "The MgSiO_3 system at high pressure: Thermodynamic properties of perovskite, postperovskite, and melt from global inversion of shock and static compression data",
"author": [
{
"family_name": "Mosenfelder",
"given_name": "Jed L.",
"clpid": "Mosenfelder-J-L"
},
{
"family_name": "Frost",
"given_name": "Daniel J.",
"clpid": "Frost-D-J"
},
{
"family_name": "Rubie",
"given_name": "David C.",
"clpid": "Rubie-D-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "We present new equation-of-state (EoS) data acquired by shock loading to pressures up to 245 GPa on both low-density samples (MgSiO_3 glass) and high-density, polycrystalline aggregates (MgSiO_3 perovskite + majorite). The latter samples were synthesized using a large-volume press. Modeling indicates that these materials transform to perovskite, postperovskite, and/or melt with increasing pressure on their Hugoniots. We fit our results together with existing P-V-T data from dynamic and static compression experiments to constrain the thermal EoS for the three phases, all of which are of fundamental importance to the dynamics of the lower mantle. The EoS for perovskite and postperovskite are well described with third-order Birch-Murnaghan isentropes, offset with a Mie-Gr\u00fcneisen-Debye formulation for thermal pressure. The addition of shock data helps to distinguish among discrepant static studies of perovskite, and for postperovskite, constrain a value of K' significantly larger than 4. For the melt, we define for the first time a single EoS that fits experimental data from ambient pressure to 230 GPa; the best fit requires a fourth-order isentrope. We also provide a new EoS for Mg_2SiO_4 liquid, calculated in a similar manner. The Gr\u00fcneisen parameters of the solid phases decrease with pressure, whereas those of the melts increase, consistent with previous shock wave experiments as well as molecular dynamics simulations. We discuss implications of our modeling for thermal expansion in the lower mantle, stabilization of ultra-low-velocity zones associated with melting at the core-mantle boundary, and crystallization of a terrestrial magma ocean.",
"doi": "10.1029/2008JB005900",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "2009-01-14",
"volume": "114",
"pages": "B01203"
},
{
"id": "authors:gns65-qza81",
"collection": "authors",
"collection_id": "gns65-qza81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-114335915",
"type": "article",
"title": "Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 2. Kaersutitic amphibole experiments",
"author": [
{
"family_name": "Minitti",
"given_name": "Michelle E.",
"orcid": "0000-0003-4715-4544",
"clpid": "Minitti-M-E"
},
{
"family_name": "Leshin",
"given_name": "L. A.",
"clpid": "Leshin-L-A"
},
{
"family_name": "Dyar",
"given_name": "M. Darby",
"orcid": "0000-0003-4272-793X",
"clpid": "Dyar-M-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Guan",
"given_name": "Yunbin",
"orcid": "0000-0002-7636-3735",
"clpid": "Guan-Yunbin"
},
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-Sheng-Nian"
}
],
"abstract": "To constrain the influence of impact shock on water and hydrogen isotope signatures of Martian meteorite kaersutites, we conducted shock recovery experiments on three terrestrial kaersutite crystals. Homogeneous impact shock to 32 GPa, commensurate with shock levels experienced by Martian meteorite kaersutites, led to increases in kaersutite water contents (\u0394H_2O = 0.25\u20130.89 wt.%), decreases in Fe^3+/\u03a3Fe (4\u201320%), and enrichments in hydrogen isotope composition (\u0394D = + 66 to + 87\u2030) relative to pre-shock values. The latter values represent the largest shock-induced hydrogen isotope fractionations measured to date. These observations are explained most completely by a two-step shock process. First, shock-induced devolatilization led to hydrogen isotope enrichment through preferential loss of H relative to D. Second, reaction of the kaersutite with the ambient atmosphere led to increased water contents and reduced Fe. Fe reduction and water addition via the reaction Fe^2+ + OH^\u2212 \u2194 Fe^3+ + O_2\u2212 + \u00bdH_2 explain the Fe^3+/\u03a3Fe data and some of the water data. Further water addition mechanisms (irreversible adsorption, shock implantation) are necessary to fully explain the increased water contents. Addition of water from the terrestrial atmosphere, which is isotopically light relative to the experimental kaersutite compositions, means the measured hydrogen isotope enrichments are likely minima. The measured (minimum) levels of hydrogen isotope enrichment are relevant to the hydrogen isotope variability within and among Martian kaersutites, but are minor relative to their absolute \u03b4D values. Alternatively, addition of water from the enriched Martian atmosphere could explain both Martian kaersutite hydrogen isotope variability and absolute \u03b4D values. However, the low Martian kaersutite water contents leave little room for significant water addition. The importance of the ambient atmosphere to the outcome of the shock experiments makes it difficult to translate our results to Mars given the unknown influence of its more tenuous atmosphere on the processes observed in the experiments. Our results suggest that shock is a feasible mechanism for influencing Martian kaersutite water contents and hydrogen isotope compositions but that its complex signature precludes precise determination of that influence.",
"doi": "10.1016/j.epsl.2007.11.012",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2008-02-28",
"series_number": "3-4",
"volume": "266",
"issue": "3-4",
"pages": "288-302"
},
{
"id": "authors:3vc88-rmk70",
"collection": "authors",
"collection_id": "3vc88-rmk70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120905-095738686",
"type": "article",
"title": "Thermodynamic properties of Mg_2SiO_4 liquid at ultra-high\n pressures from shock measurements to 200 GPa on forsterite and wadsleyite",
"author": [
{
"family_name": "Mosenfelder",
"given_name": "Jed L.",
"clpid": "Mosenfelder-J-L"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "Polycrystalline samples of Mg_2SiO_4 forsterite and wadsleyite were synthesized and then dynamically loaded to pressures of 39\u2013200 GPa. Differences in initial density and internal energy between these two phases lead to distinct Hugoniots, each characterized by multiple phase regimes. Transformation to the high-pressure phase assemblage MgO + MgSiO_3 perovksite is complete by 100 GPa for forsterite starting material but incomplete for wadsleyite. The datum for wadsleyite shocked to 136 GPa, however, is consistent with the assemblage MgO + MgSiO_3 post-perovksite. Marked increases in density along the Hugoniots of both phases between \u223c130 and 150 GPa are inconsistent with any known solid-solid phase transformation in the Mg_2SiO_4 system but can be explained by melting. Density increases upon melting are consistent with a similar density increase observed in the MgSiO_3 system. This implies that melts with compositions over the entire Mg/Si range likely for the mantle would be negatively or neutrally buoyant at conditions close to the core-mantle boundary, supporting the partial melt hypothesis to explain the occurrence of ultra-low velocity zones at the base of the mantle. From the energetic difference between the high-pressure segments of the two Hugoniots, we estimate a Gr\u00fcneisen parameter (\u03b3) of 2.6 \u00b1 0.35 for Mg_2SiO_4-liquid between 150 and 200 GPa. Comparison to low-pressure data and fitting of the absolute pressures along the melt Hugoniots both require that \u03b3 for the melt increases with increasing density. Similar behavior was recently predicted in MgSiO_3 liquid via molecular dynamics simulations. This result changes estimates of the temperature profile, and hence the dynamics, of a deep terrestrial magma ocean.",
"doi": "10.1029/2006JB004364",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "2007-06-30",
"series_number": "B6",
"volume": "112",
"issue": "B6",
"pages": "Art. No. B06208"
},
{
"id": "authors:qmmy5-qtn08",
"collection": "authors",
"collection_id": "qmmy5-qtn08",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-085054442",
"type": "article",
"title": "Effects of shock-induced cracks on the ultrasonic velocity and attenuation in granite",
"author": [
{
"family_name": "Ai",
"given_name": "Huirong A.",
"clpid": "Ai-H-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Measurements of the compressional wave velocity and the attenuation coefficients of 1-cm cubes were conducted. Samples were taken at various radii and depths beneath a 20 \u00d7 20 \u00d7 15 cm San Marcos granite block, impacted by a lead bullet at a velocity of 1200 m/s. The damage parameters of the cubes are calculated from the measured preimpact and postimpact P wave velocities, V_(p0) and V_p, and the crack density is inverted from the measured P wave velocities. The anisotropic orientation of cracks is more obvious from the attenuation than crack density and damage parameters calculated from the ultrasonic velocity. P wave velocity and the normalized distance from the impact point follow an exponential decay relation. Other properties, such as the damage parameter, crack density, and attenuation coefficient, are expressed by a power law decay with distance. The damage parameter and attenuation coefficients are approximately linearly related. The slope of the linear fitting results in directions normal to the crack orientation is about twice the value in direction along the crack orientation. The attenuation coefficient is found to be a more useful parameter than elastic velocity in describing the anisotropic orientation of cracks.",
"doi": "10.1029/2006JB004353",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "2007-01-09",
"series_number": "B1",
"volume": "112",
"issue": "B1",
"pages": "Art. No. B01201"
},
{
"id": "authors:49e0p-a9d28",
"collection": "authors",
"collection_id": "49e0p-a9d28",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110120-142722360",
"type": "article",
"title": "Simulation of dynamic response of granite: A numerical\n approach of shock-induced damage beneath impact craters",
"author": [
{
"family_name": "Ai",
"given_name": "H. A.",
"clpid": "Ai-H-A"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The mechanical response of rocks to dynamic loading is complex. It is not well understood because of the difficulty of\ndefining an effective shear and tensile strength model. Recently AUTODYN-2D from Century Dynamics is used to\nsimulate the shock-induced damage in granite targets impacted by projectiles at different velocities. The simulated results\nare compared with experiment data. Johnson\u2013Holmquist shock damage constitutive model for brittle materials is applied\nto describe the damage and shear strain achieved in a confined volume of granite. A tensile crack softening model is\ncoupled with the JH model to simulate the propagation of radial tensile cracks generated by the principal tensile stress\nperpendicular to the shock front. The tensile stress is assumed to be equal to the deviatoric stress at radii that experience\nless than the Hogoniot elastic limit stress. Instead of traditional grid-based methods, a smooth particle hydrodynamics is\nused to define damaged regions in brittle media.",
"doi": "10.1016/j.ijimpeng.2006.09.046",
"issn": "0734-743X",
"publisher": "Elsevier",
"publication": "International Journal of Impact Engineering",
"publication_date": "2006-12",
"series_number": "1-12",
"volume": "33",
"issue": "1-12",
"pages": "1-10"
},
{
"id": "authors:fj48w-gc048",
"collection": "authors",
"collection_id": "fj48w-gc048",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120830-160334838",
"type": "article",
"title": "Recovery of stishovite-structure at ambient conditions out of shock-generated amorphous silica",
"author": [
{
"family_name": "Tschauner",
"given_name": "Oliver",
"orcid": "0000-0003-3364-8906",
"clpid": "Tschauner-O"
},
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "We show that bulk amorphous silica recovered from shock-wave experiments on quartz to 57 GPa is not a true glass but rather keeps a large degree of long-range structural information that can be recovered by static cold recompression to 13 GPa. At this pressure, shock-retrieved silica assumes the structure of crystalline stishovite. A minor amount of material recovers the structure of a recently discovered new silica polymorph.",
"doi": "10.2138/am.2006.2015",
"issn": "0003-004X",
"publisher": "Mineralogical Society of America",
"publication": "American Mineralogist",
"publication_date": "2006-11",
"series_number": "11-12",
"volume": "91",
"issue": "11-12",
"pages": "1857-1862"
},
{
"id": "authors:2d6cx-prr46",
"collection": "authors",
"collection_id": "2d6cx-prr46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100319-092501259",
"type": "article",
"title": "Surface motion of a fluid planet induced by impacts",
"author": [
{
"family_name": "Ni",
"given_name": "Sidao",
"orcid": "0000-0003-2988-4850",
"clpid": "Ni-Sidao"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "In order to approximate the free-surface motion of an Earth-sized planet subjected to a giant impact, we have described the excitation of body and surface waves in a spherical compressible fluid planet without gravity or intrinsic material attenuation for a buried explosion source. Using the mode summation method, we obtained an analytical solution for the surface motion of the fluid planet in terms of an infinite series involving the products of spherical Bessel functions and Legendre polynomials. We established a closed form expression for the mode summation excitation coefficient for a spherical buried explosion source, and then calculated the surface motion for different spherical explosion source radii a (for cases of a/R= 0.001 to 0.035, R is the radius of the Earth) We also studied the effect of placing the explosion source at different radii r_0 (for cases of r_0/R= 0.90 to 0.96) from the centre of the planet. The amplitude of the quasi-surface waves depends substantially on a/R, and slightly on r_0/R. For example, in our base-line case, a/R= 0.03, r_0/R= 0.96, the free-surface velocity above the source is 0.26c, whereas antipodal to the source, the peak free surface velocity is 0.19c. Here c is the acoustic velocity of the fluid planet. These results can then be applied to studies of atmosphere erosion via blow-off caused by asteroid impacts.",
"doi": "10.1111/j.1365-246X.2006.03072.x",
"issn": "0956-540X",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal International",
"publication_date": "2006-10",
"series_number": "1",
"volume": "167",
"issue": "1",
"pages": "445-452"
},
{
"id": "authors:sevqc-kd942",
"collection": "authors",
"collection_id": "sevqc-kd942",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-082051842",
"type": "article",
"title": "In situ dust measurements in the inner Saturnian system",
"author": [
{
"family_name": "Srama",
"given_name": "R.",
"clpid": "Srama-R"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "In July 2004 the Cassini\u2013Huygens mission reached the Saturnian system and started its orbital tour. A total of 75 orbits will be carried out during the primary mission until August 2008. In these four years Cassini crosses the ring plane 150 times and spends approx. 400 h within Titan's orbit. The Cosmic Dust Analyser (CDA) onboard Cassini characterises the dust environment with its extended E ring and embedded moons. Here, we focus on the CDA results of the first year and we present the Dust Analyser (DA) data within Titan's orbit. This paper does investigate High Rate Detector data and dust composition measurements. The authors focus on the analysis of impact rates, which were strongly variable primarily due to changes of the spacecraft pointing. An overview is given about the ring plane crossings and the DA counter measurements. The DA dust impact rates are compared with the DA boresight configuration around all ring plane crossings between June 2004 and July 2005. Dust impacts were registered at altitudes as high as 100 000 km above the ring plane at distances from Saturn between 4 and 10 Saturn radii. In those regions the dust density of particles bigger than 0.5 \u00b5m can reach values of 0.001 m^(-3).",
"doi": "10.1016/j.pss.2006.05.021",
"issn": "0032-0633",
"publisher": "Elsevier",
"publication": "Planetary and Space Science",
"publication_date": "2006-08",
"series_number": "9-10",
"volume": "54",
"issue": "9-10",
"pages": "967-987"
},
{
"id": "authors:d4r7j-4x114",
"collection": "authors",
"collection_id": "d4r7j-4x114",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-080700248",
"type": "article",
"title": "Bugbuster \u2014 survivability of living bacteria upon shock compression",
"author": [
{
"family_name": "Willis",
"given_name": "M. J.",
"clpid": "Willis-M-J"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Bertani",
"given_name": "L. E.",
"clpid": "Bertani-L-E"
},
{
"family_name": "Nash",
"given_name": "C. Z.",
"clpid": "Nash-C-Z"
}
],
"abstract": "Shock recovery experiments were conducted on suspensions of 10^6/ml E. coli bacteria contained in a water-based medium that is emplaced within stainless steel containers. The water is shocked and recovered. These experiments simulate the environment of bacteria residing either in surface bodies of water or in subsurface water-filled cracks in rocks. Early Earth life is likely to have existed in such environments. However, the E. coli are not believed to be representative of early life and are merely used here for initial experiments. Some 10^(\u2212 2) to 10^(\u2212 4) of the bacteria population survived initial (800 ns duration) shock pressures in water of 220 and 260 MPa. TEM images of shock recovered bacteria indicate cell wall rupture and delamination. This appears to be the mortality mechanism.\nThe TEM images indicate cell wall indentations may be occurring as would be consistent with Rayleigh\u2013Taylor or Richtmyer\u2013Meshkov fluid instabilities. In the present case, we consider the experiments as representing three layers of fluids: (1) The water-based medium, a stronger and possibly denser cell wall medium, and the interior of the cell cytoplasm. Variations of only 10\u201315% are expected in density. (2) A second mechanism that may cause cell wall failure is the multiple shock (nearly isentropic) compression freezing of liquid water medium into ice VI or ice VII high pressure phase that are 20% to 25% denser than the liquid. The decrease in volume associated with the transformation is expected to induce overpressures in the still liquid cell cytoplasm.\nCell dynamic tensile wall strength thus appears to be a critical parameter from either of the above failure modes. Because the strain rate dependence of cell wall tensile strength is unstudied, we utilize the Grady and Lipkin [D.E. Grady, L. Lipkin, Criteria for impulsive rock fracture, Geophys. Res. Lett. 7 (1980) 255\u2013258] model of tensile failure versus time scale (strain rate). Our single datum is fit to this law and we assume that at low strain rates, overpressures exceeding the cell Turgor pressure require on the order of \u223c10^3 s. This model which has been applied to brittle media and metals for describing failure may permit application of short duration laboratory experiments as in the present ones to infer responses of organisms to much lower shock pressures, but for longer time scales (10^0 to 10^3 s) of planetary impacts.\nUsing the present data for E. coli and applying the Grady and Lipkin model, we find that a 1.5 km diameter impactor will cause mortality of bacteria within a radius of 10^2 km but upon stress related attenuation the subsurface bacteria outside of this radius should survive.",
"doi": "10.1016/j.epsl.2006.03.054",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2006-07-30",
"series_number": "3-4",
"volume": "247",
"issue": "3-4",
"pages": "185-196"
},
{
"id": "authors:84dyy-hpq69",
"collection": "authors",
"collection_id": "84dyy-hpq69",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-092814393",
"type": "article",
"title": "Decreased values of cosmic dust number density estimates in the Solar System",
"author": [
{
"family_name": "Willis",
"given_name": "M. J.",
"clpid": "Willis-M-J"
},
{
"family_name": "Burchell",
"given_name": "M. J.",
"clpid": "Burchell-M-J"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Kr\u00fcger",
"given_name": "H.",
"clpid": "Kr\u00fcger-H"
},
{
"family_name": "Gr\u00fcn",
"given_name": "E.",
"clpid": "Gr\u00fcn-E"
}
],
"abstract": "Experiments to investigate the effect of impacts on side-walls of dust detectors such as the present NASA/ESA Galileo/Ulysses instrument are reported. Side walls constitute 27% of the internal area of these instruments, and increase field of view from 140\u00b0 to 180\u00b0. Impact of cosmic dust particles onto Galileo/Ulysses Al side walls was simulated by firing Fe particles, 0.5\u20135 \u03bcm diameter, 2\u201350 km\u2009s^(\u22121), onto an Al plate, simulating the targets of Galileo and Ulysses dust instruments. Since side wall impacts affect the rise time of the target ionization signal, the degree to which particle fluxes are overestimated varies with velocity. Side-wall impacts at particle velocities of 2\u201320 km\u2009s^(\u22121) yield rise times 10\u201330% longer than for direct impacts, so that derived impact velocity is reduced by a factor of \u223c2. Impacts on side wall at 20\u201350 km\u2009s^(\u22121) reduced rise times by a factor of \u223c10 relative to direct impact data. This would result in serious overestimates of flux of particles intersecting the dust instrument at velocities of 20\u201350 km\u2009s^(\u22121). Taking into account differences in laboratory calibration geometry we obtain the following percentages for previous overestimates of incident particle number density values from the Galileo instrument [Gr\u00fcn et al., 1992. The Galileo dust detector. Space Sci. Rev. 60, 317\u2013340]: 55% for 2 km\u2009s^(\u22121) impacts, 27% at 10 km\u2009s^(\u22121) and 400% at 70 km\u2009s^(\u22121). We predict that individual particle masses are overestimated by \u223c10\u201390% when side-wall impacts occur at 2\u201320 km\u2009s^(\u22121), and underestimated by \u223c10\u2013^(102)\u223c10\u2013102 at 20\u201350 km\u2009s^(\u22121). We predict that wall impacts at 20\u201350 km\u2009s^(\u22121) can be identified in Galileo instrument data on account of their unusually short target rise times. The side-wall calibration is used to obtain new revised values [Kr\u00fcger et al., 2000. A dust cloud of Ganymede maintained by hypervelocity impacts of interplanetary micrometeoroids. Planet. Space Sci. 48, 1457\u20131471; 2003. Impact-generated dust clouds surrounding the Galilean moons. Icarus 164, 170\u2013187] of the Galilean satellite dust number densities of 9.4\u00d7^(10\u22125), 9.9\u00d7^(10\u22125), 4.1\u00d7^(10\u22125), and 6.8\u00d7^(10\u22125) m^(\u22123) at 1 satellite radius from Io, Europa, Ganymede, and Callisto, respectively. Additionally, interplanetary particle number densities detected by the Galileo mission are found to be 1.6\u00d7^(10\u22124), 7.9\u00d7^(10\u22124), 3.2\u00d7^(10\u22125), 3.2\u00d7^(10\u22125), and 7.9\u00d7^(10\u22124) m^(\u22123) at heliocentric distances of 0.7, 1, 2, 3, and 5 AU, respectively. Work by Burchell et al. [1999b. Acceleration of conducting polymer-coated latex particles as projectiles in hypervelocity impact experiments. J. Phys. D: Appl. Phys. 32, 1719\u20131728] suggests that low-density \"fluffy\" particles encountered by Ulysses will not significantly affect our results\u2014further calibration would be useful to confirm this.",
"doi": "10.1016/j.icarus.2005.02.018",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "2005-08",
"series_number": "2",
"volume": "176",
"issue": "2",
"pages": "440-452"
},
{
"id": "authors:bjfsq-6z269",
"collection": "authors",
"collection_id": "bjfsq-6z269",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150427-082615873",
"type": "article",
"title": "Thermodynamics of the lowermost mantle",
"author": [
{
"family_name": "Sun",
"given_name": "D.",
"orcid": "0000-0003-4461-4664",
"clpid": "Sun-Daoyuan"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "P. D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "Seismic observations of the region above the core mantle boundary (CMB), including Ultra-Low Velocity Zones (ULVZ) and D\" discontinuities, and recent mineral physics data suggest the bottom of the mantle may be chemically heterogeneous, possibly, on account of the occurrence of the recently discovered post-perovskite (CaIrO_3) structure. Moreover, the large decrease in shear wave velocity in selected areas (ULVZ) in the lowermost 40 km of the mantle indicates the likely presence of partially molten material. To provide a complete petrologic and mineral physics model of this region, it is important to define both constituent material properties and phase equilibria including melting behavior. We expect to describe models that encompass the entire MgOFeO-CaO-Al_2O_3-SiO_2 system and to define complete mineral physics equations of state, employing thermochemical data to obtain complete phase diagrams. Our mineral physics-based seismic models are to be obtained using global inversion methods. Initial model results are reported for the SiO_2-MgO system.",
"doi": "10.1016/j.gca.2005.03.027",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2005-05-15",
"series_number": "10",
"volume": "69",
"issue": "10",
"pages": "A253"
},
{
"id": "authors:s9jes-hxw78",
"collection": "authors",
"collection_id": "s9jes-hxw78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-103932604",
"type": "article",
"title": "Shock properties of H_2O ice",
"author": [
{
"family_name": "Stewart",
"given_name": "Sarah T.",
"clpid": "Stewart-S-T"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "To understand the mechanics and thermodynamics of impacts on, and collisions between, icy planetary bodies, we measured the dynamic strength and shock states in H2O ice. Here, we expand upon previous analyses and present a complete description of the phases, temperature, entropy, and sound velocity along the ice shock Hugoniot. Derived from shock wave measurements centered at initial temperatures (T_0) of 100 K and 263 K, the Hugoniot is composed of five regions: (1) elastic shocks in ice Ih, (2) ice Ih deformation shocks, and shock transformation to (3) ice VI, (4) ice VII, and (5) liquid water. In each region, data obtained at different initial temperatures are described by a single U_S \u2013 \u0394u_p shock equation of state. The dynamic strength of ice Ih is strongly dependent on initial temperature, and the Hugoniot Elastic Limit varies from 0.05 to 0.62 GPa, as a function of temperature and peak shock stress. We present new bulk sound velocity measurements and release profiles from shock pressures between 0.4 and 1.2 GPa. We report revised values for the shock pressures required to induce incipient melting (0.6 \u00b1 0.05, 1.6 \u00b1 0.3 GPa) and complete melting (2.5 \u00b1 0.1, 4.1 \u00b1 0.3 GPa) upon isentropic release from the shock state (for T_0 = 263, 100 K). On account of the >40% density increase upon transformation from ice Ih to ices VI and VII, the critical shock pressures required for melting are factors of 2 to 10 lower than earlier predicted. Consequently, hypervelocity impact cratering on planetary surfaces and mutual collisions between porous cometesimals will result in abundant shock-induced melting throughout the solar system.",
"doi": "10.1029/2004JE002305",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "2005-03",
"series_number": "E3",
"volume": "110",
"issue": "E3",
"pages": "Art. No. E03005"
},
{
"id": "authors:e7hcz-7p994",
"collection": "authors",
"collection_id": "e7hcz-7p994",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120905-093417118",
"type": "article",
"title": "Shock-synthesized glassy and solid silica: Intermediates between four- and six-fold coordination",
"author": [
{
"family_name": "Tschauner",
"given_name": "O.",
"orcid": "0000-0003-3364-8906",
"clpid": "Tschauner-O"
},
{
"family_name": "Luo",
"given_name": "S. N.",
"clpid": "Luo-S-N"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Swift",
"given_name": "D. C.",
"clpid": "Swift-D-C"
},
{
"family_name": "Tierney",
"given_name": "T. E.",
"clpid": "Tierney-T-E"
},
{
"family_name": "Paisley",
"given_name": "D. L.",
"clpid": "Paisley-D-L"
},
{
"family_name": "Chipera",
"given_name": "S. J.",
"clpid": "Chipera-S-J"
}
],
"abstract": "Upon compression, many materials undergo major reconstructions of their structure and bonding, including increases in coordination of atoms and changes in bonding character. While transforming, the materials pass through intermediate states, which are often too transient to be captured and examined. Here we discuss the coordination change in silica as an example of a system where such interesting intermediate structural states have been quenched from shock-experiments. On the basis of these results we suggest a relation between the formation of one of these phases and the extension of the liquid\u2013liquid transition boundary into the stability field of solid silica. We report Raman spectra of shock-retrieved vitreous silica which indicate different compression mechanisms for shock-generated amorphous silica and vitreous silica compressed at 300 K. Static recompression of shock-generated glass leads to an amorphous-crystal transition above 13 GPa.",
"doi": "10.1080/08957950412331331754",
"issn": "0895-7959",
"publisher": "Taylor and Francis",
"publication": "High Pressure Research",
"publication_date": "2004-12",
"series_number": "4",
"volume": "24",
"issue": "4",
"pages": "471-479"
},
{
"id": "authors:gbm6p-9mm15",
"collection": "authors",
"collection_id": "gbm6p-9mm15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-132004810",
"type": "article",
"title": "The Cassini Cosmic Dust Analyzer",
"author": [
{
"family_name": "Srama",
"given_name": "R.",
"clpid": "Srama-R"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The Cassini-Huygens Cosmic Dust Analyzer (CDA) is intended to provide direct observations of dust grains with masses between 10^(\u221219) and 10^(\u22129) kg in interplanetary space and in the jovian and saturnian systems, to investigate their physical, chemical and dynamical properties as functions of the distances to the Sun, to Jupiter and to Saturn and its satellites and rings, to study their interaction with the saturnian rings, satellites and magnetosphere. Chemical composition of interplanetary meteoroids will be compared with asteroidal and cometary dust, as well as with Saturn dust, ejecta from rings and satellites. Ring and satellites phenomena which might be effects of meteoroid impacts will be compared with the interplanetary dust environment. Electrical charges of particulate matter in the magnetosphere and its consequences will be studied, e.g. the effects of the ambient plasma and the magnetic field on the trajectories of dust particles as well as fragmentation of particles due to electrostatic disruption.\nThe investigation will be performed with an instrument that measures the mass, composition, electric charge, speed, and flight direction of individual dust particles. It is a highly reliable and versatile instrument with a mass sensitivity 10^6 times higher than that of the Pioneer 10 and 11 dust detectors which measured dust in the saturnian system. The Cosmic Dust Analyzer has significant inheritance from former space instrumentation developed for the VEGA, Giotto, Galileo, and Ulysses missions. It will reliably measure impacts from as low as 1 impact per month up to 10^4 impacts per second. The instrument weighs 17 kg and consumes 12 W, the integrated time-of-flight mass spectrometer has a mass resolution of up to 50. The nominal data transmission rate is 524 bits/s and varies between 50 and 4192 bps.",
"doi": "10.1007/s11214-004-1435-z",
"issn": "0038-6308",
"publisher": "Springer",
"publication": "Space Science Reviews",
"publication_date": "2004-09",
"series_number": "1-4",
"volume": "114",
"issue": "1-4",
"pages": "465-518"
},
{
"id": "authors:zf1c3-sjd76",
"collection": "authors",
"collection_id": "zf1c3-sjd76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120831-143626223",
"type": "article",
"title": "Shock-induced melting of MgSiO_3 perovskite and implications for melts in Earth's lowermost mantle",
"author": [
{
"family_name": "Akins",
"given_name": "Joseph A.",
"clpid": "Akins-J-A"
},
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "New shock wave equation of state (EOS) data for enstatite and MgSiO_3 glass constrain the density change upon melting of Mg-silicate perovskite up to 200 GPa. The melt becomes denser than perovskite near the base of Earth's lower mantle. This inference is confirmed by shock temperature data suggesting a negative pressure-temperature slope along the melting curve at high pressure. Although melting of Earth's mantle involves multiple phases and chemical components, this implies that the partial melts invoked to explain anomalous seismic velocities in the lowermost mantle may be dynamically stable.",
"doi": "10.1029/2004GL020237",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2004-07-30",
"series_number": "14",
"volume": "31",
"issue": "14",
"pages": "Art. No. L14612"
},
{
"id": "authors:y6yf5-skw51",
"collection": "authors",
"collection_id": "y6yf5-skw51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-125925807",
"type": "article",
"title": "Shock-induced superheating and melting curves of geophysically important minerals",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock-state temperature and sound-speed measurements on crystalline materials, demonstrate superheating-melting behavior distinct from equilibrium melting. Shocked solid can be superheated to the maximum temperature, T_c\u2032. At slightly higher pressure, P_c, shock melting occurs, and induces a lower shock temperature, T_c. The Hugoniot state, (P_c,T_c), is inferred to lie along the equilibrium melting curve. The amount of superheating achieved on Hugoniot is, \u0398_H+=T_c\u2032/T_c\u22121. Shock-induced superheating for a number of silicates, alkali halides and metals agrees closely with the predictions of a systematic framework describing superheating at various heating rates [Appl. Phys. Lett. 82 (12) (2003) 1836]. High-pressure melting curves are constructed by integration from (P_c,T_c) based on the Lindemann law. We calculate the volume and entropy changes upon melting at (P_c,T_c) assuming the R ln 2 rule (R is the gas constant) for the disordering entropy of melting [J. Chem. Phys. 19 (1951) 93; Sov. Phys. Usp. 117 (1975) 625; Poirier, J.P., 1991. Introduction to the Physics of the Earth's Interior. Cambridge University Press, Cambridge, 102 pp.].\n(P_c,T_c) and the Lindemann melting curves are in excellent accord with diamond-anvil cell (DAC) results for NaCl, KBr and stishovite. But significant discrepancies exist for transition metals. If we extrapolate the DAC melting data [Phys. Rev. B 63 (2001) 132104] for transition metals (Fe, V, Mo, W and Ta) to 200\u2013400 GPa where shock melting occurs, shock temperature measurement and calculation would indicate \u0398_H+\u223c0.7\u20132.0. These large values of superheating are not consistent with the superheating systematics. The discrepancies could be reconciled by possible solid\u2013solid phase transitions at high pressures. In particular, this work suggests that Fe undergoes a possible solid\u2013solid phase transition at \u223c200 GPa and melts at \u223c270 GPa upon shock wave loading, and the melting temperature is \u223c6300 K at 330 GPa.",
"doi": "10.1016/j.pepi.2003.04.001",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "2004-06-15",
"volume": "143-144",
"pages": "369-386"
},
{
"id": "authors:9ex1w-0bg58",
"collection": "authors",
"collection_id": "9ex1w-0bg58",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120830-153419650",
"type": "article",
"title": "Petrology of the lowermost mantle",
"author": [
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
},
{
"family_name": "Sun",
"given_name": "D",
"orcid": "0000-0003-4461-4664",
"clpid": "Sun-Daoyuan"
},
{
"family_name": "Akins",
"given_name": "J. A.",
"clpid": "Akins-J-A"
},
{
"family_name": "Luo",
"given_name": "S. N.",
"clpid": "Luo-Sheng-Nian"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Seismic observations of the thermal boundary layer above\nthe core-mantle boundary (CMB), including Ultra-Low\nVelocity Zones and D\" discontinuities with velocity jumps of\neither sign, suggest that the bottom of the mantle may be\ncompositionally distinct and, in places, partially molten[1].\nOur new shock-wave data constrain the melting curve and\nliquid equation of state (EOS) of the key lower mantle\ncomponent MgSiO_3 perovskite and suggest neutral or negative\nbuoyancy of this melt at CMB pressure.",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "2004-06",
"series_number": "11",
"volume": "68",
"issue": "11",
"pages": "A561"
},
{
"id": "authors:p9qpv-y7v79",
"collection": "authors",
"collection_id": "p9qpv-y7v79",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120905-142013132",
"type": "article",
"title": "Shock-compressed MgSiO_3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Akins",
"given_name": "Joseph A.",
"clpid": "Akins-J-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "Optical emission of MgSiO_3 glass, enstatite, olivine, and quartz under shock wave compression was investigated with optical pyrometry at discrete wavelengths ranging from visible to near infrared. We develop a new analysis of optical emission that does not require a gray body assumption. Instead, at each wavelength, the optical linear absorption coefficients (\u03b1) and blackbody spectral radiances (L_(\u03bbb)) of shocked and unshocked materials were obtained by nonlinear fitting to the time-resolved radiance from the target assembly. The absorption spectra of unshocked samples corresponding to the measured values of \u03b1 reproduce those from independent static optical spectroscopic measurements. The measured values of \u03b1 (ranging from 7 to 56 mm^(\u22121)) for shocked samples indicate that shock-induced high-pressure phases (including melt) can be regarded essentially as black bodies in the optical range investigated, although starting phases such as enstatite and olivine have band-like spectra at ambient conditions. The effect of emission from the air gap at the driver sample interface on the recorded radiance can be resolved, but \u03b1 and L_(\u03bbb) cannot be separated for this component of the signal. The shock velocity-particle velocity relationships of these silicates derived from radiance history are in accord with previous investigations using independent techniques. Given the limited amount of shock wave data, possible high-pressure melting curves of Mg-perovskite and its assemblage with periclase are deduced; their melting temperatures near the core-mantle boundary (CMB) being 6000 \u00b1 500 K and 4000 \u00b1 300 K, respectively. It is proposed that Mg-perovskite melts with density increase at the CMB pressure.",
"doi": "10.1029/2003JB002860",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "2004-05-11",
"series_number": "B5",
"volume": "109",
"issue": "B5",
"pages": "Art. No. B05205"
},
{
"id": "authors:5exk7-9kw86",
"collection": "authors",
"collection_id": "5exk7-9kw86",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-104950483",
"type": "article",
"title": "Dynamic tensile strength of terrestrial rocks and application to impact cratering",
"author": [
{
"family_name": "Ai",
"given_name": "Huirong-Anita",
"clpid": "Ai-H-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Dynamic tensile strengths and fracture strengths of 3 terrestrial rocks, San Marcos gabbro, Coconino sandstone, and Sesia eclogite were determined by carrying out flat-plate (PMMA and aluminum) impact experiments on disc-shaped samples in the 5 to 60 m/sec range. Tensile stresses of 125 to 300 MPa and 245 to 580 MPa were induced for gabbro and eclogite, respectively (with duration time of ~1 \u03bcs). For sandstone (porosity 25%), tensile stresses normal to bedding of ~13 to 55 MPa were induced (with duration times of 2.4 and ~1.4 \u03bcs). Tensile crack failure was detected by the onset of shock-induced (damage) P and S wave velocity reduction.\n\nThe dynamic tensile strength of gabbro determined from P and S wave velocity deficits agrees closely with the value of previously determined values by post-impact microscopic examination (~150 MPa). Tensile strength of Coconino sandstone is 20 MPa for a 14 \u03bcs duration time and 17 MPa for a 2.4 \u03bcs duration time. For Sesia eclogite, the dynamic tensile strength is ~240 MPa. The fracture strength for gabbro is ~250 MPa, ~500 MPa for eclogite, and ~40 MPa for sandstone. Relative crack-induced reduction of S wave velocities is less than that of post-impact P wave velocity reductions for both gabbro and eclogite, indicating that the cracks were predominantly spall cracks.\n\nImpacts upon planetary surfaces induce tensile failure within shock-processed rocks beneath the resulting craters. The depth of cracking beneath impact craters can be determined both by seismic refraction methods for rocks of varying water saturation and, for dry conditions (e.g., the Moon), from gravity anomalies. In principle, depth of cracking is related to the equations-of-state of projectile and target, projectile dimension, and impact velocity. We constructed a crack-depth model applicable to Meteor Crater. For the observed 850 m depth of cracking, our preferred strength scaling model yields an impact velocity of 33 km/s and impactor radius of 9 m for an iron projectile.",
"doi": "10.1111/j.1945-5100.2004.tb00338.x",
"issn": "1086-9379",
"publisher": "Meteoritical Society",
"publication": "Meteoritics and Planetary Science",
"publication_date": "2004-02",
"series_number": "2",
"volume": "39",
"issue": "2",
"pages": "233-246"
},
{
"id": "authors:knqkr-p6739",
"collection": "authors",
"collection_id": "knqkr-p6739",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120830-094450477",
"type": "article",
"title": "A new dense silica polymorph: A possible link between tetrahedrally and octahedrally coordinated silica",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Tschauner",
"given_name": "Oliver",
"orcid": "0000-0003-3364-8906",
"clpid": "Tschauner-O"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "We present the discovery of a novel dense silica polymorph retrieved from shock-wave and diamond-anvil cell experiments. This polymorph is the first observed silicate composed of face-sharing polyhedra and it has a density similar to stishovite. Sterical constraints on the bond angles induce an intrinsic disorder of Si positions, such that the Si-coordination is transitional between four-and sixfold. The structure provides a mechanism for this coordination change in silica and other silicates at high temperature that is fundamentally different from mechanisms at 300 K. The new polymorph also illustrates how the face-sharing polyhedra, naturally occurring along previously proposed compression mechanisms for dense silicate melts, can be constructed without inferring unphysically small bond angles.",
"issn": "0003-004X",
"publisher": "Mineralogical Society of America",
"publication": "American Mineralogist",
"publication_date": "2004-02",
"series_number": "2-3",
"volume": "89",
"issue": "2-3",
"pages": "455-461"
},
{
"id": "authors:ccakd-phh08",
"collection": "authors",
"collection_id": "ccakd-phh08",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LUOprb03",
"type": "article",
"title": "Maximum superheating and undercooling: Systematics, molecular dynamics simulations, and dynamic experiments",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-Sheng-Nian"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "\u00c7a\u011fin",
"given_name": "Tahir",
"orcid": "0000-0002-3665-0932",
"clpid": "\u00c7a\u011fin-T"
},
{
"family_name": "Strachan",
"given_name": "Alejandro",
"orcid": "0000-0002-4174-9750",
"clpid": "Strachan-Alejandro"
},
{
"family_name": "Goddard",
"given_name": "William A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
},
{
"family_name": "Swift",
"given_name": "Damian C.",
"clpid": "Swift-Damian-C"
}
],
"abstract": "The maximum superheating and undercooling achievable at various heating (or cooling) rates were investigated based on classical nucleation theory and undercooling experiments, molecular dynamics (MD) simulations, and dynamic experiments. The highest (or lowest) temperature Tc achievable in a superheated solid (or an undercooled liquid) depends on a dimensionless nucleation barrier parameter beta and the heating (or cooling) rate Q. beta depends on the material: beta[equivalent]16pigammasl3/(3kTmDeltaHm2) where gammasl is the solid-liquid interfacial energy, DeltaHm the heat of fusion, Tm the melting temperature, and k Boltzmann's constant. The systematics of maximum superheating and undercooling were established phenomenologically as beta= (A0\u2013b log10Q)thetac(1\u2013thetac)2 where thetac = Tc/Tm, A0 = 59.4, b = 2.33, and Q is normalized by 1 K/s. For a number of elements and compounds, beta varies in the range 0.2\u20138.2, corresponding to maximum superheating thetac of 1.06\u20131.35 and 1.08\u20131.43 at Q~1 and 10^12 K/s, respectively. Such systematics predict that a liquid with certain beta cannot crystallize at cooling rates higher than a critical value and that the smallest thetac achievable is 1/3. MD simulations (Q~10^12 K/s) at ambient and high pressures were conducted on close-packed bulk metals with Sutton-Chen many-body potentials. The maximum superheating and undercooling resolved from single- and two-phase simulations are consistent with the thetac-beta-Q systematics for the maximum superheating and undercooling. The systematics are also in accord with previous MD melting simulations on other materials (e.g., silica, Ta and epsilon-Fe) described by different force fields such as Morse-stretch charge equilibrium and embedded-atom-method potentials. Thus, the thetac-beta-Q systematics are supported by simulations at the level of interatomic interactions. The heating rate is crucial to achieving significant superheating experimentally. We demonstrate that the amount of superheating achieved in dynamic experiments (Q~10^12 K/s), such as planar shock-wave loading and intense laser irradiation, agrees with the superheating systematics.",
"doi": "10.1103/PhysRevB.68.134206",
"issn": "0163-1829",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2003-10-01",
"series_number": "13",
"volume": "68",
"issue": "13",
"pages": "Art. No. 134206"
},
{
"id": "authors:zecxp-1qh89",
"collection": "authors",
"collection_id": "zecxp-1qh89",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120905-141101974",
"type": "article",
"title": "Polymorphism, superheating, and amorphization of silica upon shock wave loading and release",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
}
],
"abstract": "We present a detailed and quantitative examination of the thermodynamics and phase change mechanisms (including amorphization) that occur upon shock wave loading and unloading of silica. We apply Debye-Gr\u00fcneisen theory to calculate both the Hugoniot of quartz and isentropic release paths. Quartz converts to stishovite (or a stishovite-like phase) between 15 and 46 GPa, and persistence of the solid phase above its liquidus (i.e., superheating) is confirmed between 77 and 110 GPa. Calculations compare favorably to measurements of shock and post-shock temperatures. For silica, the method of measuring post-shock temperature is insensitive to predicting whether phase transitions actually occur during release. Measurements of release states in pressure-particle velocity space are compared to computed frozen-phase release paths. This comparison suggests transformation of a stishovite-like phase to lower density phases including quartz, liquid, or dense amorphous glass. Transformations to liquid or glass occur upon release from peak pressure of 26 GPa and above. The isentropic release assumption appears to be approximately valid. A shock pressure-temperature scale relating metamorphism of silica in shock-loaded quartz is proposed. Neither recovery of coesite nor substantial quantities of crystalline stishovite-like phases upon shock loading of quartz is predicted. Trace amounts of crystalline stishovite-like phases from shock loading between 15 and 26 GPa are expected.",
"doi": "10.1029/2002JB002317",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "2003-09-10",
"series_number": "B9",
"volume": "108",
"issue": "B9",
"pages": "Art. No. 2421"
},
{
"id": "authors:c2hx9-02170",
"collection": "authors",
"collection_id": "c2hx9-02170",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-085618121",
"type": "article",
"title": "Hypervelocity microparticle impact studies using a novel cosmic dust mass spectrometer",
"author": [
{
"family_name": "Austin",
"given_name": "Daniel E.",
"clpid": "Austin-D-E"
},
{
"family_name": "Grimm",
"given_name": "Ronald L.",
"orcid": "0000-0003-0407-937X",
"clpid": "Grimm-R-L"
},
{
"family_name": "Manning",
"given_name": "Heidi L. K.",
"clpid": "Manning-H-L-K"
},
{
"family_name": "Bailey",
"given_name": "Carl L.",
"clpid": "Bailey-C-L"
},
{
"family_name": "Farnsworth",
"given_name": "James E.",
"clpid": "Farnsworth-J-E"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Beauchamp",
"given_name": "J. L.",
"orcid": "0000-0001-8839-4822",
"clpid": "Beauchamp-J-L"
}
],
"abstract": "Micron-sized iron and copper particles accelerated to 2\u201320 km/s in a 2 MV van de Graaff electrostatic accelerator were used to test the performance of our recently developed cosmic dust mass spectrometer. This compact in situ dust analyzer, known as the Dustbuster, is designed to determine the elemental composition of cosmic dust particles through impact ionization and subsequent time-of-flight mass spectrometry. Results from 750 laboratory impacts show high mass resolution, typically 150\u2013350 (m/\u0394m) for projectile components and 300\u2013600 for the target material (tantalum). Peaks corresponding to H, C, O, Na, and K ions are also observed, consistent with previous microparticle impact experiments. Field-induced emission of electrons immediately before impact is a possible cause of ion formation from species with high ionization potentials. The high mass resolution, large sensitive target area, and small size make the Dustbuster an ideal instrument for inclusion on a spacecraft payload.",
"doi": "10.1029/2002JE001947",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "2003-05-14",
"series_number": "E5",
"volume": "108",
"issue": "E5",
"pages": "Art. No. 5038"
},
{
"id": "authors:qd5f1-gdb70",
"collection": "authors",
"collection_id": "qd5f1-gdb70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SHEjap03",
"type": "article",
"title": "Shock wave induced vaporization of porous solids",
"author": [
{
"family_name": "Shen",
"given_name": "Andy H.",
"clpid": "Shen-A-H"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
}
],
"abstract": "Strong shock waves generated by hypervelocity impact can induce vaporization in solid materials. To pursue knowledge of the chemical species in the shock-induced vapors, one needs to design experiments that will drive the system to such thermodynamic states that sufficient vapor can be generated for investigation. It is common to use porous media to reach high entropy, vaporized states in impact experiments. We extended calculations by Ahrens [J. Appl. Phys. 43, 2443 (1972)] and Ahrens and O'Keefe [The Moon 4, 214 (1972)] to higher distentions (up to five) and improved their method with a different impedance match calculation scheme and augmented their model with recent thermodynamic and Hugoniot data of metals, minerals, and polymers. Although we reconfirmed the competing effects reported in the previous studies: (1) increase of entropy production and (2) decrease of impedance match, when impacting materials with increasing distentions, our calculations did not exhibit optimal entropy-generating distention. For different materials, very different impact velocities are needed to initiate vaporization. For aluminum at distention (m)<2.2, a minimum impact velocity of 2.7 km/s is required using tungsten projectile. For ionic solids such as NaCl at distention <2.2, 2.5 km/s is needed. For carbonate and sulfate minerals, the minimum impact velocities are much lower, ranging from less than 1 to 1.5 km/s.",
"doi": "10.1063/1.1563035",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "2003-05-01",
"series_number": "9",
"volume": "93",
"issue": "9",
"pages": "5167-5174"
},
{
"id": "authors:cjqcs-m8m87",
"collection": "authors",
"collection_id": "cjqcs-m8m87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-084531903",
"type": "article",
"title": "Shock Hugoniot of H_2O ice",
"author": [
{
"family_name": "Stewart",
"given_name": "Sarah T.",
"clpid": "Stewart-S-T"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The outcome of impacts onto and between icy planetary bodies is controlled by the material response defined by the shock Hugoniot. New Lagrangian shock wave profile measurements in H_2O ice at initial temperatures (T_0) of 100 K, together with previous T_0 = 263 K data, define five distinct regions on the ice Hugoniot: elastic shocks in ice Ih, ice Ih deformation shocks, and shock transformation to ices VI, VII and liquid water. The critical pressures required to induce incipient melting (0.6, 4.5 GPa) and complete melting (3.7, >5.5 GPa) upon isentropic release from the shock state (for T_0 = 263, 100 K) were revised using calculated shock temperatures and entropy. On account of the >40% density increase upon transformation from ice Ih to ices VI and VII, the critical shock pressures required for melting are factors of 2 to 5 lower than earlier predicted. Consequently, hypervelocity impact cratering on planetary surfaces and mutual collisions between porous cometesimals will result in abundant shock-induced melting throughout the solar system.",
"doi": "10.1029/2002GL016789",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2003-03-27",
"series_number": "6",
"volume": "30",
"issue": "6",
"pages": "Art. No. 1332"
},
{
"id": "authors:27055-sag25",
"collection": "authors",
"collection_id": "27055-sag25",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LUOapl03.912",
"type": "article",
"title": "Superheating systematics of crystalline solids",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Systematics of superheating (theta= T/Tm\u20131) of crystalline solids as a function of heating rate (Q) are established as beta= A(Q)(theta+ 1)theta2, where the normalized energy barrier for homogeneous nucleation is beta= 16pigammasl3/(3kTmDeltaHm2), T is temperature, Tm melting temperature, A a Q-dependent parameter, gammasl interfacial energy, DeltaHm heat of fusion, and k Boltzmann's constant. For all elements and compounds investigated, beta varies between 0.2 and 8.2. At 1 and 10^12 K/s, A = 60 and 31, theta= 0.05\u20130.35 and 0.06\u20130.45, respectively. Significant superheating is achievable via ultrafast heating. We demonstrate that the degree of superheating achieved in shock-wave loading and intense laser irradiation as well as in molecular dynamics simulations (Q~10^12 K/s) agrees with the theta\u2013beta\u2013Q systematics.",
"doi": "10.1063/1.1563046",
"issn": "0003-6951",
"publisher": "Applied Physics Letters",
"publication": "Applied Physics Letters",
"publication_date": "2003-03-24",
"series_number": "12",
"volume": "82",
"issue": "12",
"pages": "1836-1838"
},
{
"id": "authors:df672-wjc35",
"collection": "authors",
"collection_id": "df672-wjc35",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-101106717",
"type": "article",
"title": "Mass spectrometer calibration of Cosmic Dust Analyzer",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Gupta",
"given_name": "Satish C.",
"clpid": "Gupta-S-C"
},
{
"family_name": "Jyoti",
"given_name": "G.",
"clpid": "Jyoti-G"
},
{
"family_name": "Beauchamp",
"given_name": "J. L.",
"orcid": "0000-0001-8839-4822",
"clpid": "Beauchamp-J-L"
}
],
"abstract": "The time-of-flight (TOF) mass spectrometer (MS) of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft is expected to be placed in orbit about Saturn to sample submicrometer-diameter ring particles and impact ejecta from Saturn's satellites. The CDA measures a mass spectrum of each particle that impacts the chemical analyzer sector of the instrument. Particles impact a Rh target plate at velocities of 1-100 km/s and produce some 10^(\u22128) to 10^(\u22125) times the particle mass of positive valence, single-charged ions. These are analyzed via a TOF MS. Initial tests employed a pulsed N2 laser acting on samples of kamacite, pyrrhotite, serpentine, olivine, and Murchison meteorite induced bursts of ions which were detected with a microchannel plate and a charge sensitive amplifier (CSA). Pulses from the N_2 laser (10^(11) W/cm^2) are assumed to simulate particle impact. Using aluminum alloy as a test sample, each pulse produces a charge of \u223c4.6 pC (mostly Al^(+1)), whereas irradiation of a stainless steel target produces a \u223c2.8 pC (Fe^(+1)) charge. Thus the present system yields \u223c10^(\u22125)% of the laser energy in resulting ions. A CSA signal indicates that at the position of the microchannel plate, the ion detector geometry is such that some 5% of the laser-induced ions are collected in the CDA geometry. Employing a multichannel plate detector in this MS yields for Al-Mg-Cu alloy and kamacite targets well-defined peaks at 24 (Mg^(+1)), 27(Al^(+1)), and 64 (Cu^(+1)) and 56 (Fe^(+1)), 58 (Ni^(+1)), and 60 (Ni^(+1)) dalton, respectively.",
"doi": "10.1029/2002JE001912",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "2003-02-14",
"series_number": "E2",
"volume": "108",
"issue": "E2",
"pages": "Art. No. 5007"
},
{
"id": "authors:mb8hh-m1x10",
"collection": "authors",
"collection_id": "mb8hh-m1x10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120823-103324201",
"type": "article",
"title": "Shock-wave equation of state of molten and solid fayalite",
"author": [
{
"family_name": "Chen",
"given_name": "George Q.",
"clpid": "Chen-George-Q"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Stolper",
"given_name": "E. M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
}
],
"abstract": "Shock-wave equations of state (EOS) of initially solid (300 K) and molten (1573 K) fayalite (Fe_2SiO_4, Fa) are measured over the pressure ranges of 23\u2013212 and 5\u201347 GPa, respectively. The 300 K data indicates that Fa undergoes a phase change from the low-pressure olivine structure (Lpp) over the 35\u201355 GPa range. In agreement with earlier analyses of Rockport fayalite shock data and diamond cell recovery experiments, the high pressure phase (Hpp) data are consistent with an oxide (2FeO+SiO_2, stishovite) mixture. A fit to the Hpp Hugoniot data in the shock velocity (u_S)\u2013particle velocity (u_P) plane yields: u_S = 4.07 (0.22)km/s + 1.43 (0.06)u_P. Here, the initial density, \u03c1_0 is 4.375 (0.027) Mg/m^3.\nThe 1573 K data yields: u_S = 2.63(0.02) km/s + 1.59 (0.01)u_P. Initial density calculated from temperature data is 3.750 (0.018) Mg/m^3 and K_(0S)=25.9\u00b10.4 GPa, and K_(0S)\u2032=5.36\u00b10.04 GPa. The bulk modulus, K_(0S), compares favorably with Agee's result [Geophys. Res. Lett. 19 (1992a) 1169], 24.4 GPa, but the pressure derivative is much less than the K_(0T)\u2032=10.1 GPa previously reported.\nMolten Fa compression data >40 GPa are closely fit with an ideal mixture of oxides, SiO_2 (stishovite) + 2FeO (Lpp), in support of the hypothesis of Rigden et al. [J. Geophys. Res. 94 (1989) 9508].\nA model molten basalt incorporating previous molten anorthite (An)\u2013diopside (Di) eutectic and the present molten Fa (EOS) data implies that a zone of basic silicate liquid, could be neutrally buoyant at a depth of \u223c250\u2013400 km, upon partial melting of a peridotite mantle as discussed by Rigden et al. [Science 226 (1984) 1071]. This conclusion is based on comparison of the density of the model basalt: (An_(0.36)Di_(0.64))_(0.85)Fa_(0.15), with Dziewonski and Anderson's Preliminary Reference Earth model [Phys. Earth Planet. Inter. 25 (1981) 297].",
"doi": "10.1016/S0031-9201(02)00080-8",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "2002-11-28",
"series_number": "1-2",
"volume": "134",
"issue": "1-2",
"pages": "35-52"
},
{
"id": "authors:9ze7j-njq41",
"collection": "authors",
"collection_id": "9ze7j-njq41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-080304073",
"type": "article",
"title": "Molecular dynamics modeling of stishovite",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-Sheng-Nian"
},
{
"family_name": "\u00c7a\u011fin",
"given_name": "Tahir",
"orcid": "0000-0002-3665-0932",
"clpid": "\u00c7a\u011fin-T"
},
{
"family_name": "Strachan",
"given_name": "Alejandro",
"orcid": "0000-0002-4174-9750",
"clpid": "Strachan-Alejandro"
},
{
"family_name": "Goddard",
"given_name": "William A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A Morse-stretch potential charge equilibrium force field for silica system has been employed to simulate the thermodynamics of stishovite with the molecular dynamics (MD) method. The equation of state, thermal expansivity and melting curve of stishovite have been obtained. This simple force field yielded results in accordance with the static and dynamic experiments. The stishovite melting simulation appears to validate the interpretation of superheating of the solid along the Hugoniot in the shock melting experiments. MD simulations show that the thermal expansivity of stishovite at lowermost mantle conditions is a weak function of temperature. The phase diagram of silica up to the mega bar regime is proposed based on the experimental and theoretical studies. The related physical and geophysical implications are addressed.",
"doi": "10.1016/S0012-821X(02)00749-5",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2002-08-30",
"series_number": "1",
"volume": "202",
"issue": "1",
"pages": "147-157"
},
{
"id": "authors:04dxw-m1p84",
"collection": "authors",
"collection_id": "04dxw-m1p84",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120905-135949010",
"type": "article",
"title": "Direct shock wave loading of Stishovite to 235 GPa: Implications for perovskite stability relative to an oxide assemblage at lower mantle conditions",
"author": [
{
"family_name": "Luo",
"given_name": "Sheng-Nian",
"clpid": "Luo-S-N"
},
{
"family_name": "Mosenfelder",
"given_name": "J. L.",
"clpid": "Mosenfelder-J-L"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Pure stishovite and coesite samples with zero porosity and dimensions appropriate for planar shock wave experiments have been synthesized with multi-anvil high-pressure techniques. The equation of state of stishovite is obtained by direct shock wave loading up to 235 GPa: K_(0T) = 306 \u00b1 5 GPa and K'_(0T) = 5.0 \u00b1 0.2 where K_(0T) and K'_(0T) are ambient bulk modulus and its pressure derivative, respectively. The Hugoniots (shock equations of state) for stishovite, coesite and quartz achieve widely differing internal energy states at equal volume and therefore allow us to determine the Gruneisen parameter of stishovite. On the basis of the resulting P-V-T equation of state for stishovite and previous studies on other phases on the MgO-SiO_2 binary, the breakdown reaction of MgSiO_3-perovskite to MgO and SiO_2 was calculated. Our calculations show that perovskite is thermodynamically stable relative to the stishovite and periclase assemblage at lower mantle conditions. We obtain similar results for a range of models, despite the appreciable differences among these experiment-based thermodynamic parameters.",
"doi": "10.1029/2002GL015627",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2002-07-15",
"series_number": "14",
"volume": "29",
"issue": "14",
"pages": "Art. No. 1691"
},
{
"id": "authors:hsx5e-nyb81",
"collection": "authors",
"collection_id": "hsx5e-nyb81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-075611973",
"type": "article",
"title": "Shock temperature in calcite (CaCO_3) at 95\u2013160 GPa",
"author": [
{
"family_name": "Gupta",
"given_name": "Satish C.",
"clpid": "Gupta-S-C"
},
{
"family_name": "Love",
"given_name": "Stanley G.",
"clpid": "Love-S-G"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The temperatures induced in crystalline calcite (CaCO_3) upon planar shock compression (95\u2013160 GPa) are reported from two-stage light gas gun experiments. Temperatures of 3300\u20135400 K are obtained by fitting six-channel optical pyrometer radiances in the 450\u2013900 nm range to the Planck gray-body radiation law. Thermodynamic calculations demonstrate that these temperatures are some 400\u20131350 K lower than expected for vibronic excitations of the lattice with a 3R/mole-atom specific heat (R is gas constant). The temperature deficit along the Hugoniot is larger than that expected from only melting. In addition to melting, it appears likely that shock-induced decomposition of calcite occurs behind the shock front. We modeled disproportionation of calcite into CaO (solid) plus CO_2 (gas). For temperature calculations, specific heat at constant volume for 1 mole of CO_2 is taken to be 6.7R as compared to 9R in the solid state; whereas a mole of calcite and a mole of CaO have their solid state values 15R and 6R, respectively. Calculations suggest that the calcite decomposes to CaO and CO_2 at \u223c110\u00b110 GPa along the Hugoniot. Recent reanalysis of earlier VISAR measurements of particle velocity profiles [1] indicates that calcite shocked to 18 GPa undergoes disproportionation at much lower pressures upon isentropic expansion.",
"doi": "10.1016/S0012-821X(02)00685-4",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2002-07-15",
"series_number": "1",
"volume": "201",
"issue": "1",
"pages": "1-12"
},
{
"id": "authors:1g2ev-kmy12",
"collection": "authors",
"collection_id": "1g2ev-kmy12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LIUjap02",
"type": "article",
"title": "Effect of phase change on shock wave attenuation in GeO2",
"author": [
{
"family_name": "Liu",
"given_name": "C.",
"clpid": "Liu-Cangli"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Brar",
"given_name": "N. S.",
"clpid": "Brar-N-S"
}
],
"abstract": "Stress-wave profiles in vitreous GeO2 induced by planar and spherical projectile impact were measured using piezoresistance gauges in the 4 to 18 GPa shock pressure range. The planar experiments demonstrate the response of vitreous GeO2. This response can be divided into three regimes: (1) An elastic shock regime with ramp 4 GPa Hugoniot elastic limit (HEL) precursor. Shock propagation velocity decreases from an initial longitudinal elastic wave speed of 3.5 to 2.8 km/s at 4 GPa. (2) A transition wave regime where the ramp wave is superimposed on the precursor with an additional amplitude of 0 to 2 GPa followed by a sharp increase in shock pressure achieving peak loading pressures of 8 to 14 GPa. Above 4 GPa the ramp wave velocity decreases to a value below 2.5 km/s (the speed of the bulk wave, at the HEL). (3) A shock wave achieving the final shock state forms when peak pressure is >6 GPa specified by linear shock-particle velocity relation D=0.917+1.71 u (km/s) over the 6-40 GPa range for an initial density of 3.655 g/cm(3). The Hugoniots of GeO2 and SiO2, both initially vitreous, are found to be virtually coincident if pressure in SiO2 is calculated by multiplying the GeO2 pressure by the ratio of the initial densities of vitreous GeO2 to fused SiO2. The volume axes are translated by aligning the specific volumes for onset and completion of the four- to six-fold coordination phase change. Although only limited spherical impactor spherically diverging shock experiments were conducted, our present results demonstrate (1) The supported elastic shock in fused SiO2 decays less rapidly than a linear elastic wave when elastic wave stress amplitude is higher than 4 GPa. A supported elastic precursor in vitreous GeO2 decays faster with radius than a linear elastic wave; (2) in GeO2 (vitreous) unsupported shock waves decay with peak pressure in a phase transition range (4-15 GPa) with propagation radius (r) as proportional tor(-3.35).",
"doi": "10.1063/1.1469663",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "2002-06-01",
"series_number": "11",
"volume": "91",
"issue": "11",
"pages": "9136-9146"
},
{
"id": "authors:m0eka-ghv33",
"collection": "authors",
"collection_id": "m0eka-ghv33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-083721362",
"type": "article",
"title": "Dynamic compression of SiO_2: A new interpretation",
"author": [
{
"family_name": "Akins",
"given_name": "Joseph A.",
"clpid": "Akins-J-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "In light of recent discoveries of post-stishovite phases of SiO_2, with the CaCl_2 and \u03b1-PbO_2 structures, we have reassigned the regimes along the Hugoniots for initial quartz, coesite, cristobalite, porous coesite, and fused silica. Calculated Hugoniots for fused silica, cristobalite and porous coesite indicate transition to stishovite, and then melt. Hugoniots for crystal quartz and coesite indicate that transition occurs to stishovite, then the CaCl2 structure and finally to melt.",
"doi": "10.1029/2002GL014806",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2002-05-15",
"series_number": "10",
"volume": "29",
"issue": "10",
"pages": "Art. No. 1394"
},
{
"id": "authors:j2w6z-t0926",
"collection": "authors",
"collection_id": "j2w6z-t0926",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-110225653",
"type": "article",
"title": "Phase diagram of iron, revised-core temperatures",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Holland",
"given_name": "Kathleen G.",
"clpid": "Holland-K-G"
},
{
"family_name": "Chen",
"given_name": "George Q.",
"clpid": "Chen-G-Q"
}
],
"abstract": "Shock-wave experiments on iron preheated to 1573 K from 14 to 73 GPa, yield sound velocities of the \u03b3- and liquid-phases. Melting is observed in the highest pressure (\u223c71 \u00b1 2 GPa) experiments at calculated shock temperatures of 2775 \u00b1 160 K. This single crossing of the \u03b3-liquid boundary agrees with the \u03b3-iron melting line of Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This \u03b3-iron melting curve is \u223c300\u00b0C lower than that of Shen et al. [1998] at 80 GPa. In agreement with Brown [2001] the discrepancy between the diamond cell melting data and the iron shock temperatures require the occurrence of yet another sub-solidus phase along the principal Hugoniot at \u223c200 GPa. This would reconcile the static and dynamic data for iron's melting curve. Upward pressure and temperature extrapolation of the \u03b3-iron melting curve to 330 GPa yields 5300 \u00b1 400 K for the inner core-outer core boundary temperature.",
"doi": "10.1029/2001GL014350",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2002-04-01",
"series_number": "7",
"volume": "29",
"issue": "7",
"pages": "Art. No. 1150"
},
{
"id": "authors:dbx6k-p3a43",
"collection": "authors",
"collection_id": "dbx6k-p3a43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120906-113903468",
"type": "article",
"title": "Stishovite and its implications in geophysics: new results from shock-wave experiments and theoretical modeling",
"author": [
{
"family_name": "Luo",
"given_name": "S.-N.",
"clpid": "Luo-S-N"
},
{
"family_name": "Mosenfelder",
"given_name": "J. L.",
"clpid": "Mosenfelder-J-L"
},
{
"family_name": "Asimow",
"given_name": "Paul D.",
"orcid": "0000-0001-6025-8925",
"clpid": "Asimow-P-D"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Abstract Unavailable.",
"doi": "10.1070/PU2002v045n04ABEH001155",
"issn": "1063-7869",
"publisher": "IOP",
"publication": "Physics-Uspekhi",
"publication_date": "2002-04",
"series_number": "4",
"volume": "45",
"issue": "4",
"pages": "435-439"
},
{
"id": "authors:tbv58-yxw15",
"collection": "authors",
"collection_id": "tbv58-yxw15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AUSrsi02",
"type": "article",
"title": "Dustbuster: a compact impact-ionization time-of-flight mass spectrometer for in situ analysis of cosmic dust",
"author": [
{
"family_name": "Austin",
"given_name": "Daniel E.",
"clpid": "Austin-D-E"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Beauchamp",
"given_name": "J. L.",
"orcid": "0000-0001-8839-4822",
"clpid": "Beauchamp-J-L"
}
],
"abstract": "We report on the design and testing of a compact impact-ionization time-of-flight mass spectrometer for analysis of cosmic dust, suitable for use on deep space missions. The instrument, Dustbuster, incorporates a large target area with a reflectron, simultaneously optimizing mass resolution, particle detection, and ion collection. Dust particles hit the 65-cm2 target plate and are partially ionized by the impact. The resulting ions, with broad energy and angular distributions, are accelerated through a modified reflectron, focusing ions of specific m/z in space and time to produce high-resolution mass spectra. The cylindrically symmetric instrument is 10 cm in diameter and 20 cm in length, considerably smaller than previous in situ dust analyzers, and can be easily scaled as needed for specific mission requirements. Laser desorption ionization of metal and mineral samples embedded in the impact plate simulated particle impacts for evaluations of instrument performance. Mass resolution in these experiments ranged from 60\u2013180, permitting resolution of isotopes. The mass spectrometer can be combined with other instrument components to determine dust particle trajectories and sizes.",
"doi": "10.1063/1.1427762",
"issn": "0034-6748",
"publisher": "American Institute of Physics",
"publication": "Review of Scientific Instruments",
"publication_date": "2002-01",
"series_number": "1",
"volume": "73",
"issue": "1",
"pages": "185-189"
},
{
"id": "authors:vr0ve-zgf40",
"collection": "authors",
"collection_id": "vr0ve-zgf40",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-080006635",
"type": "article",
"title": "Damage and rock-volatile mixture effects on impact crater formation",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Stewart",
"given_name": "Sarah T.",
"clpid": "Stewart-S-T"
},
{
"family_name": "Lainhart",
"given_name": "Michael E.",
"clpid": "Lainhart-M-E"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We explored simple geologic strength and material response models to determine which have the capability to simulate impact-induced faulting, complicated ejecta patterns and complex crater shapes. This led us to develop models for material damage, dilatancy, and inhomogeneous materials (mixtures). We found that a strength degradation (damage) model was necessary to produce faulting in homogeneous materials. Both normal and thrust ring faults may occur and extend relatively deeply into the planet during the transient cavity radial expansion. The maximum depth of fault development is about the depth of maximum penetration by the projectile. Dilatancy in geologic materials may reduce the final bulk density compared to the pristine state because of irreversible fracturing. When we include the effects of dilatancy, the radial position of faulting is displaced because of greater upward motions. In addition, the late time crater profile is shallower and the expression of features such as central peaks and rings may be more pronounced. Both damage and rock-ice mixtures effect the distribution of ejecta. The excavation flow field within the heavily damaged region is similar to flow fields in Mohr-Coulomb materials with no zero-pressure strength. In the outer, less damaged zone within the excavation cavity, the material trajectories collapse back into the crater. This effect creates a zone of reduced ejecta emplacement near the edge of the final crater. In the case of rock-ice mixtures, energy is preferentially deposited in the more compressible volatile component and the ejecta pattern is dependent upon the location of shock-induced phase changes in the volatile material.",
"doi": "10.1016/S0734-743X(01)00112-9",
"issn": "0734-743X",
"publisher": "Elsevier",
"publication": "International Journal of Impact Engineering",
"publication_date": "2001-12",
"series_number": "1-10",
"volume": "26",
"issue": "1-10",
"pages": "543-553"
},
{
"id": "authors:v9yck-sd834",
"collection": "authors",
"collection_id": "v9yck-sd834",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-074802268",
"type": "article",
"title": "Wave Generation from Explosions in Rock Cavities",
"author": [
{
"family_name": "Liu",
"given_name": "Cangli",
"clpid": "Liu-Cangli"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We have developed a measurement method to monitor P- and S-waves generated from laboratory-scale explosions in meter-sized rock samples at a series of stations, as well as invented a device to drill spherical cavities in rock, with diameters up to 10\u2009centimeters. We applied these to experiments in Bedford limestone in which spherical/cylindrical explosives (0.2 to 1.9\u2009g) were centrally placed in 1.2- to 3-cm diameter cavities. Stress waves generated by the explosions were recorded within a radius of 25\u2009cm. The radial stress wave records and post-explosion studies demonstrate that S-waves are generated from explosions in cavities as a result of both wave mode-conversion from the cavity wall and crack propagation in rocks. The experimental results of wave generation from the explosions in spherical and cylindrical cavities demonstrate the cavity geometrical effect on the resulting wave pattern. The P- and S-waves generated by explosions and crack propagation in rocks are analyzed. A simple analytic model for P-wave generation is proposed to explain the differences of P-wave-induced displacement histories between the observed waveforms and those predicted by a step-pressure source. Generally, the qualitative predictions of this model fit the observations. The present results demonstrate the importance of rock cracking and cavities in P- and S-wave generation.",
"doi": "10.1007/PL00001137",
"issn": "0033-4553",
"publisher": "Springer",
"publication": "Pure and Applied Geophysics",
"publication_date": "2001-10",
"series_number": "11",
"volume": "158",
"issue": "11",
"pages": "1909-1949"
},
{
"id": "authors:r39kf-dfj37",
"collection": "authors",
"collection_id": "r39kf-dfj37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130625-093912540",
"type": "article",
"title": "Shock-induced devolatilization and isotopic\n fractionation of H and C from Murchison meteorite:\n some implications for planetary accretion",
"author": [
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Xu",
"given_name": "Xiaomei",
"clpid": "Xu-Xiaomei"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Epstein",
"given_name": "Samuel",
"clpid": "Epstein-S"
}
],
"abstract": "Incipient shock-induced devolatilization of Murchison meteorite occurs upon subjecting samples to a minimum\nshock stress, or pressure, of about 5 GPa. This pressure is similar to that required to initiate devolatilization of 20%\nporous serpentine. Upon low velocity impact (61.5 km/s) the solid shocked products were combusted and isotopic\nanalysis of the resulting H_2O and CO_2 was performed. H and ^(13)C are partitioned preferentially over D and ^(12)C,\nrespectively, into the released gas suggesting that the inorganic (mineral) portion of Murchison is devolatilized\npreferentially over the organic (kerogen) fraction (which is relatively enriched in D and ^(12)C) at the shock pressures\nstudied. These results are combined with previous results on serpentine devolatilization to derive an empirical H\nfractionation versus devolatilization relation that is used to evaluate the extent of impact-induced isotopic fractionation\nduring planetary accretion. During accretion of the Earth, impact-induced devolatilization and formation of the early\nprimitive atmosphere would have begun at a point where the `growing' Earth achieved a radius in the 480-800 km\nrange. The present experimental results suggest that the Earth's early atmosphere would have been enriched in\nhydrogen (relative to D) compared to the residual solid, with a fractionation factor of -18 to -23\u2030. Assuming that\ncurrent planetary atmospheres have resulted from degassing of planetary interiors after loss of the earliest H-enriched\natmosphere, the above degree of isotopic fractionation is not sufficient by itself to explain the large positive \u03b4D values of\nthe present Martian and Venusian atmospheres. However, this mechanism in conjunction with tectonic recycling over\ngeologic time could contribute to preferential H loss for Earth and Mars.",
"doi": "10.1016/S0012-821X(01)00429-0",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2001-09-30",
"series_number": "1",
"volume": "192",
"issue": "1",
"pages": "23-30"
},
{
"id": "authors:cmd6j-9y356",
"collection": "authors",
"collection_id": "cmd6j-9y356",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-082941787",
"type": "article",
"title": "Impact induced damage beneath craters",
"author": [
{
"family_name": "Xia",
"given_name": "Kaiwen",
"clpid": "Xia-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Ackermann et al. (1975) described the subsurface structure of Meteor Crater and identified a fractured rock zone extending to about 1 km deep. The depth of the fractured/damage zone can be used to extract information about the impact cratering process. We impacted rock samples (San Marcos gabbro) in the laboratory and imaged the damage structure using both dicing and tomography methods. We propose a simple model to describe the damage zone depth based on the laboratory measurements. The model agrees well with other methods for the estimation of the projectile size of Meteor Crater and it may be used for estimates of damage around craters of other planets and moons.",
"doi": "10.1029/2001GL013001",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "2001-09-15",
"series_number": "18",
"volume": "28",
"issue": "18",
"pages": "3525-3527"
},
{
"id": "authors:hen1n-meh51",
"collection": "authors",
"collection_id": "hen1n-meh51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141027-165633583",
"type": "article",
"title": "An instrument for in situ comet nucleus surface density profile measurement by gamma ray attenuation",
"author": [
{
"family_name": "Ball",
"given_name": "Andrew J.",
"clpid": "Ball-A-J"
},
{
"family_name": "Gadomski",
"given_name": "Stanislaw",
"clpid": "Gadomski-S"
},
{
"family_name": "Banaszkiewicz",
"given_name": "Marek",
"clpid": "Banaszkiewicz-M"
},
{
"family_name": "Spohn",
"given_name": "Tilman",
"clpid": "Spohn-T"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Whyndham",
"given_name": "Matthew",
"clpid": "Whyndham-M"
},
{
"family_name": "Zarnecki",
"given_name": "John C.",
"clpid": "Zarnecki-J-C"
}
],
"abstract": "The MUPUS experiment on the Rosetta Lander will measure thermal and mechanical properties as well as the bulk density of the cometary material at and just below the surface of the nucleus of comet 46P/Wirtanen. A profile of bulk density vs. depth will be obtained by measuring the attenuation of 662 keV gamma rays emitted by a ^(137)Cs source. Compton scattering is the dominant interaction process at this energy, the attenuation depending directly on the total number of electrons along the source\u2013detector path. This in turn is approximately proportional to the column density. We report here on the design of the bulk density instrument and the results of related Monte Carlo simulations, laboratory tests and calculations of the instrument's performance. The ^(137)Cs radioisotope source is mounted in the tip of the MUPUS thermal probe\u2014a 10 mm diameter rod, to be hammered into the surface of the nucleus to a depth of ~ 370 mm. Two cadmium zinc telluride (CZT) detectors mounted at the top of the probe will monitor the count rate of 662keV photons. Due to the statistics of photon counting, the integration time required to measure column density to a particular accuracy varies with depth as well as with bulk density. The required integration time is minimised for a material thickness equal to twice the exponential attenuation length. At shallower depths the required time rises due to the smaller fractional change in count rate with varying depth, while at greater depths the reduced count rate demands longer integration times. The former effect and the fact that the first 45 mm of the source\u2013detector path passes not through the comet but through the material of the probe, mean that the first density measurement cannot be made until the source has reached a depth of perhaps 100 mm. The laboratory experiments indicate that at this depth an integration time no less than 348 s (falling to 93.9 s at full penetration) would be required to measure a bulk density of 1000 kg m^(-3) to 5% accuracy, assuming a source activity of 1.48 mCi (decayed from an initial 2 mCi). Although solutions involving feedback of the measured bulk density into a time-budgeting algorithm are conceivable, a simple approach where equal time is spent per unit depth may be best, providing an accuracy in bulk density of around 5\u201320%, for 25 mm slices and the expected range of parameters.",
"doi": "10.1016/S0032-0633(01)00041-1",
"issn": "0032-0633",
"publisher": "Elsevier",
"publication": "Planetary and Space Science",
"publication_date": "2001-08",
"series_number": "9",
"volume": "49",
"issue": "9",
"pages": "961-976"
},
{
"id": "authors:1hk8g-01q87",
"collection": "authors",
"collection_id": "1hk8g-01q87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-075042221",
"type": "article",
"title": "Shock-induced vaporization of anhydrite and global cooling from the K/T impact",
"author": [
{
"family_name": "Gupta",
"given_name": "Satish C.",
"clpid": "Gupta-S-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Yang",
"given_name": "Wenbo",
"clpid": "Yang-W"
}
],
"abstract": "Discovery of abundant anhydrite (CaSO_4) and gypsum (CaSO_4\u20222H_2O) in the otherwise carbonate sediment comprising the upper 3 km thick layer of the target rock at the K/T impact site has prompted research on these minerals. Evaluation of the severity of the proposed extinction mechanism involving injection of impact-generated SO_2 and SO_3 into the stratosphere entails determination of criteria for shock-induced vaporization of these minerals. In the present work we present new data on the vaporization criteria of anhydrite. These are based on the reanalysis of the shock wave experiments of Yang and Ahrens [Earth Planet. Sci. Lett. 156 (1998) 125\u2013140], conducted on material with 30% porosity, in which the shock- (fully or partially) vaporized sample interacts with an overlying LiF window. The velocity histories, monitored using a velocity interferometer, are compared with numerical simulations employing an improved equation of state for porous anhydrite and its vaporization products. We also employ the 'entropy criterion' for vaporization of material under shock compression. The values of the entropies of incipient and complete vaporization for anhydrite are determined to be 1.65\u00b10.12 and 3.17\u00b10.12 kJ (kg K)^(\u22121), respectively, and the corresponding pressures for incipient and the complete vaporization along the Hugoniot for the solid material are 32.5\u00b12.5 and 122\u00b113 GPa, respectively as compared with 81\u00b17 and 155\u00b113 GPa previously reported by Yang and Ahrens. Along with these criteria, the use of the recent estimate of diameter (100 km) for the Chicxulub transient crater [O'Keefe and Ahrens, J. Geophys. Res. 104 (E11) (1999) 27091\u201327104; Morgan et al., Nature 390 (1997) 472\u2013476] that is smaller than previously assumed, along with Ivanov et al.'s [Geol. Soc. Am. Spec. Pap. 307 (1996) 125\u2013142] 2-D hydrodynamic simulation to determine the shock attenuation and Pope et al.'s [J. Geophys. Res., 102 (E9) (1997) 21645\u201321664] radiative transfer model, yields the maximum decrease in the average global surface temperature of 12\u201319 K for 9.0\u20139.5 years at the K/T boundary. Thus, the global cooling is inferred to have been less severe than that indicated by the upper limit of the range of 5\u201331 K decrease lasting for \u223c12 years calculated by Pope et al. Because ambient global surface temperatures at K/T time were \u223c18\u201320\u00b0C warmer than present values, this cooling event produced cold, but not freezing conditions at the Earth's surface.",
"doi": "10.1016/S0012-821X(01)00327-2",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "2001-06-15",
"series_number": "3-4",
"volume": "188",
"issue": "3-4",
"pages": "399-412"
},
{
"id": "authors:zcegn-faz96",
"collection": "authors",
"collection_id": "zcegn-faz96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-132337515",
"type": "article",
"title": "Mass spectrometer calibration of high velocity impact ionization based cosmic dust analyzer",
"author": [
{
"family_name": "Jyoti",
"given_name": "G.",
"clpid": "Jyoti-G"
},
{
"family_name": "Gupta",
"given_name": "Satish C.",
"clpid": "Gupta-S-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Kossakovski",
"given_name": "Dmitri",
"clpid": "Kossakovski-D-A"
},
{
"family_name": "Beauchamp",
"given_name": "J. L.",
"orcid": "0000-0001-8839-4822",
"clpid": "Beauchamp-J-L"
}
],
"abstract": "We are calibrating the time of flight mass spectrometer of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft. The CDA measures the flux of particles in the 10^(\u221215) to 10^(\u22129) g range at intersection velocities of up to 100 km/s. Of special interest are the chemical composition of the particles in orbit about Saturn and/or its satellites that are expected to be captured by CDA during ring plane crossings and upon close encounter with the satellites. Upon impacting a rhodium plate, particles are expected to partially ionize and their chemical composition is expected to be determined from mass analysis of the positive ions. In order to optimize impact ionization calibration experiments using a light gas-gun launched microspheric particles, we have done initial testing with a short duration pulsed laser (4 ns duration nitrogen laser (337 nm)). The beam is focused to deliver the 300\u03bcJ energy per laser pulse onto a 33 \u03bcm^2. The laser power density (\u224810^10 W/cm^2) simulates the impact of particles with various combinations of density and velocities, e.g., 8 g/cm^3 (Fe) projectile at 23 km/s or 1 g/cm^3 projectile at 65 km/s. The CDA spectrometer will operate in the near vacuum of Saturnian zone environment is housed in a laboratory chamber at 10^(\u22126) mbar. The ions and electrons are separated by 680 V between target and grid. The laser ionization produces charge of 4.6pC (mostly Al^(+1)) in aluminum and 2.8pC (Fe^(+1)) in stainless steel. Estimating that each Al^(+1) and Fe^(+1) ion requires an energy of 5.98 and 7.90 eV/ion implies that \u223c10\u22125 % of the laser pulse energy produces ions and the present system has a 10% detection efficiency. Using multi-channel plate detector to detect ions from aluminum alloy and kamacite yields well defined peaks at 24(Mg^(+1)), 27(Al^(+1)) and 64 (Cu^(+1)), and, 56(Fe^(+1)), 58(Ni^(+1)) and 60(Ni^(+1)) amu, respectively. Also contaminant ions at 23 (Na^(+1)) and 39(K^(+1)) amu are detected.",
"doi": "10.1016/S0734-743X(99)00090-1",
"issn": "0734-743X",
"publisher": "Elsevier",
"publication": "International Journal of Impact Engineering",
"publication_date": "1999-12",
"series_number": "1",
"volume": "23",
"issue": "1",
"pages": "401-408"
},
{
"id": "authors:y4my6-0mg83",
"collection": "authors",
"collection_id": "y4my6-0mg83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-113231744",
"type": "article",
"title": "Complex craters: Relationship of stratigraphy and rings to impact conditions",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "One of the key issues associated with the understanding of large scale impacts is how the observable complex crater structural features (e.g., central peaks and pits, flat floors, ring shaped ridges and depressions, stratigraphic modifications, and faults) relate to the impactor's parameters (e.g., radius, velocity, and density) and the nonobservable transient crater measures (e.g., depth of penetration and diameter at maximum penetration). We have numerically modeled large-scale impacts on planets for a range of impactor parameters, gravity and planetary material strengths. From these we found that the collapse of the transient cavity results in the development of a tall, transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary strength to produce a wide range of the observed surface features. In addition, we found that the underlying stratigraphy is inverted outside of the transient cavity diameter (overturned flap region), but not inside. This change in stratigraphy is observable by remote sensing, drilling, seismic imaging and gravity mapping techniques. We used the above results to develop scaling laws and to make estimates of the impact parameters for the Chicxulub impact and also compared the calculated stratigraphic profile with the internal structure model developed by Hildebrand et. al. [1998], using gravity, seismic and other field data. For a stratigraphy rotation diameter of 90 km, the maximum depth of penetration is \u223c43 km. The impactor diameter was also calculated. From the scaling relationships we get for a 2.7 g/cm^3 asteroid impacting at 20 km/s, or a 1.0 g/cm^3 comet impacting at 40 km/s, an impactor diameter of \u223c13 km, and for a comet impacting at 60 km/s, an impactor diameter of \u223c10 km.",
"doi": "10.1029/1998JE000596",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1999-11-25",
"series_number": "E11",
"volume": "104",
"issue": "E11",
"pages": "27091-27104"
},
{
"id": "authors:2r3b7-xwv25",
"collection": "authors",
"collection_id": "2r3b7-xwv25",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141021-124357929",
"type": "article",
"title": "Effect of irreversible phase change on shock-wave propagation",
"author": [
{
"family_name": "Chen",
"given_name": "G. Q.",
"clpid": "Chen-G-Q"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Yang",
"given_name": "W.",
"clpid": "Yang-W"
},
{
"family_name": "Knowles",
"given_name": "J. K.",
"clpid": "Knowles-J-K"
}
],
"abstract": "New release adiabat data for vitreous GeO_2 are reported up to \u223c25 GPa using the VISAR technique. Numerical modeling of isentropic release wave induced dynamic states achieved from one dimensional strain\u2013stress waves is consistent with a phase change that induce an increase in zero-pressure density from 3.7\u20136.3 Mg/m^3 starting at \u223c8 GPa. The first release adiabat data for SiO_2 ( fused quartz) are presented (obtained with immersed foil technique) . Above 10 GPa, the SiO_2 release isentropes, in analogy with GeO_2, are steeper than the Hugoniot in the volume-pressure space, indicating the presence of an irreversible phase transition (to a stishovite-like phase). We simulate propagation of shock-waves in GeO_2, in spherical and planar symmetries, and predict enhanced attenuation for shock pressures ( p) above the phase change initiation pressure (8 GPa) . The pressure from a spherical source decays with propagation radius r, p \u223c r^x, where x is the decay coefficient. Modeling hysteresis of the phase change gives x = \u22122.71, whereas without the phase change, x = \u22121.15. An analytical model is also given.",
"doi": "10.1016/S0022-5096(98)00090-8",
"issn": "0022-5096",
"publisher": "Elsevier",
"publication": "Journal of the Mechanics and Physics of Solids",
"publication_date": "1999-04",
"series_number": "4",
"volume": "47",
"issue": "4",
"pages": "763-783"
},
{
"id": "authors:11rqv-b8b92",
"collection": "authors",
"collection_id": "11rqv-b8b92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-094917470",
"type": "article",
"title": "Impact Erosion of Planetary Atmospheres: Some Surprising Results",
"author": [
{
"family_name": "Newman",
"given_name": "William I.",
"clpid": "Newman-W-I"
},
{
"family_name": "Symbalisty",
"given_name": "Eugene M. D.",
"clpid": "Symbalisty-E-M-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Jones",
"given_name": "Eric M.",
"clpid": "Jones-E-M"
}
],
"abstract": "We have investigated by analytical and computational means the effect of Cretaceous\u2013Tertiary (K/T) size impacts (5\u00d710^(30)erg, 9-km-radius bolide of 10^(19)g) on terrestrial atmospheres. We have extended analytically the approximate solution due to A. S. Kompaneets (1960,Sov. Phys. Dokl. Engl. Transl.5, 46\u201348) for the blast wave obtained for atmospheric nuclear explosions (idealized to isothermal atmospheres) to ideal adiabatic atmospheres and to data-based models of the Earth's atmosphere. For the first time, we have been able to obtain analytically the particle trajectories in an isothermal atmosphere. The outcome of this nonlinear analysis is that a massive impact (without the subsequent ejection of substantial mass) would only influence a column of \u224830-km radius in the Earth's atmosphere and that the shocked gas would be propelled up and against the column \"wall,\" but would not escape from the planet. We examined the validity of \"hemispheric blowoff,\" the hypothesis that all material in a hemisphere lying above a plane tangent to the point of impact radially accelerated outward and, if sufficiently energetic, would also be ejected. We adapted and used a state-of-the-art code (CAVEAT), a hybrid Los Alamos\u2013Sandia Lagrangian\u2013Eulerian finite difference scheme for multimaterial flow problems with large distortion and internal slip. In our CAVEAT calculations, the vapor cloud produced by the impact produces a shock that is orders of magnitude stronger than any previous use of such codes. We developed new methods to test the accuracy and convergence of CAVEAT for K/T size impact events, and it proved to be a robust tool. We explored a K/T size impact where the 9-km-radius bolide was vaporized and injected into the atmosphere and found no radial outflow in agreement with the analytic model but, instead, a 50-km-radius vertical column formed with only a small fraction of material reaching escape velocity\u2014no more than about 7% of the vaporized bolide plus atmospheric mass will escape the gravitation of the Earth.",
"doi": "10.1006/icar.1999.6076",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1999-04",
"series_number": "2",
"volume": "138",
"issue": "2",
"pages": "224-240"
},
{
"id": "authors:qgphe-5km71",
"collection": "authors",
"collection_id": "qgphe-5km71",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-085211644",
"type": "article",
"title": "Barringer medal acceptance address - 1997 July 23, Maui, Hawaii",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Officers and Members of the Meteoritical Society, Professor\nPepin, ladies and gentlemen, it is a great honor to receive the Barringer\nAward. My first trip to a meteor crater was to Meteor Crater,\nor, as it has been historically called, Barringer Crater. Since the\ncrater was surrounded to a radius of more than 10 km by fragments\nof the iron-nickel meteorite, Canyon Diablo, I never could understand\nwhy some geologists insisted that it was volcanic! What volcano\nemits iron-nickel? The 1 km in diameter Barringer Crater, Arizona\nis, of course, named after the mining engineer Daniel Barringer and\nhis heirs who run the crater as a high-quality science exhibit. They\nare a scientifically appreciative family-run company who both support\nmeteorite research, sponsor a wonderful interpretive program at the\nMeteor Crater Museum as well as support this meeting and this award.\nTheir interest and support is appreciated by their community. My\nfirst trip to Barringer Crater was led by Eugene Shoemaker in 1972.\nGene mapped the crater in 1960 for his Ph.D. thesis, figured out\nhow planetary cratering worked, and went on to explain it to the rest\nof the world as he participated in exploring the Moon and then virtually\nall the solid planets and satellites in the solar system. Although\nI was an associate professor when Gene Shoemaker and Don Anderson\nbrought me to Caltech, I learned much from Shoemaker and was\ndevastated last Friday when I learned of his accidental death during\nhis annual trek to Australia to map preserved craters on this desert\ncontinent.",
"doi": "10.1111/j.1945-5100.1998.tb01326.x",
"issn": "1086-9379",
"publisher": "Meteoritical Society",
"publication": "Meteoritics and Planetary Science",
"publication_date": "1998-07",
"series_number": "S4",
"volume": "33",
"issue": "S4",
"pages": "A6"
},
{
"id": "authors:q2y3r-cmj06",
"collection": "authors",
"collection_id": "q2y3r-cmj06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-123254590",
"type": "article",
"title": "Shock vaporization of anhydrite and global effects of the K/T bolide",
"author": [
{
"family_name": "Yang",
"given_name": "Wenbo",
"clpid": "Yang-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock vaporization experiments were carried out for 30% porous anhydrite up to 76 GPa. Shocked fully or partially vaporized samples interact with overlying LiF windows whose velocity histories are monitored using a velocity interferometer to obtain pressure bounds for incipient and complete vaporization for CaSO_4. Experimental data and thermodynamic calculations indicate that these shock pressures are 81 \u00b1 7 and 155 \u00b1 13 GPa for crystal anhydrite, and 27 \u00b1 1 and 67 \u00b1 6 GPa for porous anhydrite, respectively. A one-dimensional finite-difference code was used to simulate the measured velocity profiles. The vaporized products can be described by a simple Gr\u00fcneisen thermal equation of state where the effective Gr\u00fcneisen parameter varies from 1.5 to 0.73 upon release from 76 to 25 GPa. Using the above criteria, and recent lithic models of the impact site, the mass of degassed S has been estimated from the Chicxulub impact. For asteroids of 10 and 20 km in diameter impacting the Earth at 20 km/s, the mass of degassed S in SO_2 or SO_3 is found to be 0.5 \u00d7 10^(17) to 2 \u00d7 10^(17) g. Simple extrapolation of Sigurdsson's [H. Sigurdsson, Assessment of the atmospheric impact of volcanic eruptions, in: V.L. Sharpton, P.D. Ward (Eds.), Global Catastrophes in Earth History: An Interdisciplinary Conference on Impact, Volcanism, and Mass Mortality, Geol. Soc. Am. Spec. Pap. 247 (1990) 99\u2013110.] formula yields a global cooling prediction of \u227310\u00b0C.",
"doi": "10.1016/S0012-821X(98)00006-5",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1998-03-30",
"series_number": "3-4",
"volume": "156",
"issue": "3-4",
"pages": "125-140"
},
{
"id": "authors:4jzvm-rjc75",
"collection": "authors",
"collection_id": "4jzvm-rjc75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-155251695",
"type": "article",
"title": "Shock-wave equation of state of rhyolite",
"author": [
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Yang",
"given_name": "Wenbo",
"clpid": "Yang-W"
},
{
"family_name": "Chen",
"given_name": "George",
"clpid": "Chen-G-Q"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We have obtained new shock-wave equation of state (EOS) and release adiabat data for rhyolite. These data are combined with those of Swegle (1989, 1990) to give an experimental Hugoniot which is described by U_s = 2.53(\u00b10.08) + 3.393(\u00b10.37)u_p for u_p < 0.48 km s^(\u22121), U_s = 3.85(\u00b10.05) + 0.65(\u00b10.03)up for 0.48 \u2264 u_p < 2.29 km s^(\u22121), U_s = 1.52(\u00b10.08) + 1.67(\u00b10.02)u_p for 2.29 \u2264 u_p < 4.37 km s^(\u22121), and U_s = 3.40(\u00b1034) + 1.24(\u00b10.06)u_p for u_p \u2265 4.37 km s^(\u22121), with \u03c1_0 = 2.357 \u00b1 0.052 Mg m^(\u22123). We suggest that the Hugoniot data give evidence of three distinct phases\u2014both low- and high-pressure solid phases and, possibly, a dense molten phase. EOS parameters for these phases are \u03c1_0 = 2.494 \u00b1 0.002 Mg m^(\u22123), K_(S0) = 37 \u00b1 2 GPa, K\u2032 = 6.27 \u00b1 0.25, and \u03b3 = 1.0(V/V_0) for the low-pressure solid phase; \u03c1_0 = 3.834 \u00b1 0.080 Mg m^(\u22123), K_(S0) = 128 \u00b1 20 GPa, K\u2032 = 3.7 \u00b1 1.4, and \u03b3 = 1.5 \u00b1 0.5 for the solid high-pressure phase; and \u03c1_0 = 3.71 \u00b1 0.10 Mg m^(\u22123), K_(S0) = 127 \u00b1 25 GPa, K\u2032 = 2.1 \u00b1 1.0, and \u03b3 = 1.5 \u00b1 1.0 for the dense liquid. Transition regions of the Hugoniot cover the ranges of 9\u201334 GPa for the low-pressure\u2014high-pressure solid transition and 90\u2013120 GPa for the high-pressure solid\u2014liquid transition. Release paths from high-pressure states, calculated from the EOS parameters, suggest that the material remains in the high-pressure solid phase upon release. Release paths from both the high-pressure solid and liquid fall above the Hugoniot until the Hugoniot enters the low-pressure\u2014high-pressure mixed phase region, when the release paths then cross the Hugoniot and fall below it, ending at significantly higher zero-pressure densities than that of the low-pressure phase. The low-pressure release paths fall very close to the Hugoniot. Estimates of residual heat deposition, based on shock-release path hysteresis, range from 20 to 60 per cent of the shock Hugoniot energy.",
"doi": "10.1046/j.1365-246x.1998.00389.x",
"issn": "0956-540X",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal International",
"publication_date": "1998-01",
"series_number": "1",
"volume": "132",
"issue": "1",
"pages": "1-13"
},
{
"id": "authors:kza3h-f3t52",
"collection": "authors",
"collection_id": "kza3h-f3t52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:DUFjap97",
"type": "article",
"title": "Dynamic compression of an Fe\u2013Cr\u2013Ni alloy to 80 GPa",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Wave profiles were measured in an Fe\u2013Cr\u2013Ni alloy (stainless steel 304) shock compressed to Hugoniot stresses between 7 and 80 GPa. A single-stage propellant gun was used to generate shock states and time histories were recorded by velocity interferometry. The particle velocity measurements are generally consistent with impedance match calculations to \u00b12%. Unloading wave velocities were obtained from analysis of the release wave profiles. Using Eulerian finite strain theory and under the assumption of fully elastic initial release, the first and second pressure derivatives of the longitudinal modulus are given by: 7.9(0.5) and \u20130.16(0.06) GPa\u20131, where the numbers in parentheses are one standard deviation uncertainties. The first and second pressure derivatives of the adiabatic bulk modulus are: 6.4(1.0) and \u20130.17(0.08) GPa\u20131. The unloading wave velocities are generally consistent with extrapolated trends from low-pressure ultrasonic data as well as with higher stress shock measurements on an alloy of similar composition. From 1 bar to 80 GPa, Poisson's ratio, nu, increases with Hugoniot stress, sigma (in GPa), according to the relation: nu =0.29 + 0.0008 sigma. The Hugoniot elastic limit of 304 steel was found to be 0.35(0.12) GPa, and the initial yield stress is 0.21(0.07) GPa. The elastic precursor velocity was 5.8(0.1) km/s. Numerical simulations of the wave profiles using a constitutive model that incorporates a Bauschinger effect and stress relaxation reproduced the main features observed in the profiles. Release adiabats were also calculated from the measured wave profiles. The shear stress at unloading was determined to vary with stress according to the relation: tau0+tauc=0.149+0.018 sigma, where sigma is given in GPa.",
"doi": "10.1063/1.366233",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1997-11-01",
"series_number": "9",
"volume": "82",
"issue": "9",
"pages": "4259-4269"
},
{
"id": "authors:62a6c-yn418",
"collection": "authors",
"collection_id": "62a6c-yn418",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-091742470",
"type": "article",
"title": "Eugene M. Shoemaker (1928-97) - Founder of the scientific study of impact cratering - Obituary",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Eugene Shoemaker, who died on 18 July,\nfounded the scientific study of planetary\nimpact cratering on the Earth, Moon,\nplanets and their satellites, as well as\npioneering surveys of near-Earth asteroids\nand comets, often in collaboration with\nhis wife Carolyn. His most important\nscientific legacy was recognizing how\npervasive the impact cratering process was\nin the early Solar System.",
"doi": "10.1038/38145",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1997-09-11",
"series_number": "6647",
"volume": "389",
"issue": "6647",
"pages": "132"
},
{
"id": "authors:3865y-03f56",
"collection": "authors",
"collection_id": "3865y-03f56",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-085238827",
"type": "article",
"title": "Ahrens Receives the Hess Medal",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Tom Ahrens was awarded the Harry H.\nHess Medal at the AGU Fall Meeting Honor\nCeremony on December 17, 1996, in San\nFrancisco. The Hess Medal recognizes outstanding\nachievements in research in the constitution\nand evolution of Earth and its sister\nplanets. The award citation and Ahren's response\nare given here.",
"doi": "10.1029/97EO00210",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "Eos",
"publication_date": "1997-08-05",
"series_number": "31",
"volume": "78",
"issue": "31",
"pages": "319-323"
},
{
"id": "authors:289tt-69m18",
"collection": "authors",
"collection_id": "289tt-69m18",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-091729022",
"type": "article",
"title": "The crystal structure of calcite III",
"author": [
{
"family_name": "Smyth",
"given_name": "Joseph R.",
"clpid": "Smyth-J-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The crystal structure of calcite III has been deduced from existing high pressure powder X-ray diffraction patterns, based on the assumption that it is a displacive modification of the calcite I structure. The structure is monoclinic with space group C2 and a Z of 6. There are two Ca and two C positions, and five O positions, and atom coordinates have been refined by distance-least-squares methods to give reasonable octahedral coordination for Ca and parallel, planar CO_3 groups. Unit cell parameters refined from a published powder diffraction pattern at 4.1 GPa are: a = 8.746(8)\u00c5; b = 4.685(5)\u00c5; c = 8.275(8)\u00c5; and \u03b2= 94.4\u00b0. The structure has a calculated density of 2.949 Mg/m\u00b3 at 4.1 GPa which is less than that of aragonite at this pressure and consistent with early piston cylinder studies. This implies that calcite III is indeed a metastable intermediary between calcite I and aragonite.",
"doi": "10.1029/97GL01603",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1997-07-01",
"series_number": "13",
"volume": "24",
"issue": "13",
"pages": "1595-1598"
},
{
"id": "authors:71ytn-95496",
"collection": "authors",
"collection_id": "71ytn-95496",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-084053866",
"type": "article",
"title": "Dynamically Induced Phase Transitions and the Modeling of Comminution in Brittle Solids",
"author": [
{
"family_name": "Knowles",
"given_name": "James K.",
"clpid": "Knowles-J-K"
},
{
"family_name": "Winfree",
"given_name": "Nancy A.",
"clpid": "Winfree-N-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Some experiments suggest the presence of a sharp interface between comminuted and uncomminuted regimes in a ceramic subject to impact by a penetrator. This in turn suggests that one might model the associated dynamical process with the help of recently developed continuum models of the macroscopic response of solids undergoing phase transitions. A highly idealized phase transition model of such a com- minuted process is analyzed here. The model accounts for the kinetics of the phase transition. If the shear wave speed in the comminuted material is small compared to that in the uncomminuted portion, it is found that the energy reaching the uncomminuted portion of the target is greatly reduced in comparison to its value in the absence of the phase transition.",
"doi": "10.1177/108128659700200201",
"issn": "1081-2865",
"publisher": "SAGE Publications",
"publication": "Mathematics and Mechanics of Solids",
"publication_date": "1997-06",
"series_number": "2",
"volume": "2",
"issue": "2",
"pages": "99-116"
},
{
"id": "authors:t0x68-5qf40",
"collection": "authors",
"collection_id": "t0x68-5qf40",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-085011066",
"type": "article",
"title": "Melting of (Mg,Fe)_2SiO_4 at the Core-Mantle Boundary of the Earth",
"author": [
{
"family_name": "Holland",
"given_name": "Kathleen G.",
"clpid": "Holland-K-G"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The lower mantle of the Earth is believed to be largely composed of (Mg,Fe)O (magnesiow\u00fcstite) and (Mg,Fe)SiO_3 (perovskite). Radiative temperatures of single-crystal olivine [(Mg_(0.9),Fe_(0.1))_2SiO_4] decreased abruptly from 7040 \u00b1 315 to 4300 \u00b1 270 kelvin upon shock compression above 80 gigapascals. The data indicate that an upper bound to the solidus of the magnesiow\u00fcstite and perovskite assemblage at 4300 \u00b1 270 kelvin is 130 \u00b1 3 gigapascals. These conditions correspond to those for partial melting at the base of the mantle, as has been suggested occurs within the ultralow-velocity zone beneath the central Pacific.",
"doi": "10.1126/science.275.5306.1623",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1997-03-14",
"series_number": "5306",
"volume": "275",
"issue": "5306",
"pages": "1623-1625"
},
{
"id": "authors:6709h-22d95",
"collection": "authors",
"collection_id": "6709h-22d95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-102735165",
"type": "article",
"title": "Origin of asteroid rotation rates in catastrophic impacts",
"author": [
{
"family_name": "Love",
"given_name": "Stanley G.",
"clpid": "Love-S-G"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The rotation rates of asteroids, which are deduced from periodic fluctuations in their brightnesses, are controlled by mutual collisions. The link between asteroid spin and collision history is usually made with reference to impact experiments on centimetre-scale targets, where material strength governs the impact response. Recent work, however, indicates that for objects of the size of most observed asteroids (\u22651 km in diameter), gravity rather than intrinsic strength controls the dynamic response to collisions. Here we explore this idea by modelling the effect of impacts on large gravitating bodies. We find that the fraction of a projectile's angular momentum that is retained by a target asteroid is both lower and more variable than expected from laboratory experiments, with spin evolution being dominated by 'catastrophic' collisions that eject ~50 per cent of the target's mass. The remnant of an initially non-rotating silicate asteroid that suffers such a collision rotates at a rate of ~2.9 per day, which is close to the observed mean asteroid rotation rate of ~2.5 d^(\u20131). Moreover, our calculations suggest that the observed trend in the mean spin frequency for different classes of asteroids (2.2 d^(\u20131)for C-type asteroids, 2.5 d^(\u20131) for S-type, and 4.0 d^(\u20131) for M-type) is due to increasing mean density, rather than increasing material strength.",
"doi": "10.1038/386154a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1997-03-13",
"series_number": "6621",
"volume": "386",
"issue": "6621",
"pages": "154-156"
},
{
"id": "authors:3ravt-g9096",
"collection": "authors",
"collection_id": "3ravt-g9096",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-142109125",
"type": "article",
"title": "Stress wave attenuation in shock-damaged rock",
"author": [
{
"family_name": "Liu",
"given_name": "Cangli",
"clpid": "Liu-Cangli"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The velocity and attenuation of ultrasonic stress waves in gabbroic rock samples (San Marcos, California) subjected to shock loading in the 2 GPa range were studied. Prom P wave velocity measurements we determined the damage parameter D_p and crack density \u03b5 of the samples and related these to the attenuation coefficient (quality factor) under dynamic strains of 2\u00d710^(\u22127) and at a frequency of 2 MHz using the ultrasonic pulse-echo method. A fit to the data yields the P wave spatial attenuation coefficient at a frequency of 2 MHz, \u03b1_p(D_p) = 1.1 + 28.2D_P (decibels per centimeter). From the relation between the attenuation coefficient and quality factor, the quality factor Q is given by Q^(\u22121) = 0.011(1 + 25.6D_p)(1 \u2212 Dp)^\u00bd. Using O'Connell-Budiansky theory relating crack density to velocity, the parameter in Walsh's theory was determined based on experimental data. An approximate method is also proposed to estimate the average half-length of cracks based on the attenuation measurements.",
"doi": "10.1029/96JB03891",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1997-03-10",
"series_number": "B3",
"volume": "102",
"issue": "B3",
"pages": "5243-5250"
},
{
"id": "authors:x6fzx-7nr83",
"collection": "authors",
"collection_id": "x6fzx-7nr83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-153746932",
"type": "article",
"title": "Special issue - Physical and chemical evolution of the Earth - Preface",
"author": [
{
"family_name": "Ohtani",
"given_name": "Eiji",
"clpid": "Ohtani-E"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "This Special Issue represents a portion of the\npapers presented at the interassociation (International\nAssociation of Seismology and Physical Properties\nof the Earth's Interior and International Association\nof Volcanology and Geochemistry of the Earth's\nInterior) joint symposium, 'Physical and Chemical\nEvolution of the Earth', held at the International\nUnion of Geodesy and Geophysics meeting in Boulder,\nColorado, in July 1995. It covers a wide range\nof topics on accretion, core formation, and dynamics\nof the Earth's interior. Some 31 papers presented by\nauthors from 11 countries contributed to the Symposium.",
"doi": "10.1016/S0031-9201(97)90019-4",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1997-03",
"series_number": "1-4",
"volume": "100",
"issue": "1-4",
"pages": "1-2"
},
{
"id": "authors:qjvj3-vmn90",
"collection": "authors",
"collection_id": "qjvj3-vmn90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-152738598",
"type": "article",
"title": "Erosion of terrestrial planet atmosphere by surface motion after a large impact",
"author": [
{
"family_name": "Chen",
"given_name": "George Q.",
"clpid": "Chen-G-Q"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The history of atmosphere accretion has a large significance in the evolution of the Earth and other planets. Here we present a quantitative analysis of the Earth's response to large impacts (in the 10^(32)\u201310^(38) erg energy range), and the resulting atmosphere loss owing to the global radial surface motion. Our results show that it is possible to deplete the Earth's atmosphere via this mechanism in very large (lunar-sized, \u223c 10^(38) erg) impacts.",
"doi": "10.1016/S0031-9201(96)03228-1",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1997-03",
"series_number": "1-4",
"volume": "100",
"issue": "1-4",
"pages": "21-26"
},
{
"id": "authors:phdbg-60f32",
"collection": "authors",
"collection_id": "phdbg-60f32",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-113544833",
"type": "article",
"title": "Impact of Comet Shoemaker\u2013Levy 9\u2014Size, Origin, and Plumes: Comparison of Numerical Analysis with Observations",
"author": [
{
"family_name": "Takata",
"given_name": "Toshiko",
"clpid": "Takata-Toshiko"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Numerical results of impact of Comet Shoemaker\u2013Levy 9 (SL9) on Jupiter are compared with observational phenomena to investigate the size and origin of SL9 and impact features. Plume evolution is simulated numerically for 0.4- and 2.0-km-diameter (D) impactors. Analytical estimates indicate that the maximum plume heights are proportional to (D/lnD)^3. This relation is also confirmed by the extrapolation of numerical simulations. From the correlation between maximum plume heights and impactor diameters, the diameters of large SL9 fragments and the parent body are estimated as \u223c2 and 4\u20135 km, respectively. The plume induced by the impact of fragments of SL9 consists of atmospheric gas and impactor material. The chemical abundances of the plumes, especially their high CO abundances, indicate that they contain primitive materials from fragments and thus SL9 is probably of cometary origin. The lateral expansion of plume is also examined. Our simulations suggest that the energy source required to produce the observable waves should be located in the stratospheric region, rather than in the deep troposphere. Finally, the ejecta pattern observed by Hubble Space Telescope [Hammel et al. (1995) Science 267, 1288\u20131296] is simulated by a simple particle model. The results suggest that the ejection of atmospheric gas and cometary materials from a narrow \u223c30\u00b0 cone region along the trajectory spreads out and yields the ejecta patterns observed by Hubble Space Telescope overlying the clouds.",
"doi": "10.1006/icar.1996.5616",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1997-02",
"series_number": "2",
"volume": "125",
"issue": "2",
"pages": "317-330"
},
{
"id": "authors:dw1rm-x3x29",
"collection": "authors",
"collection_id": "dw1rm-x3x29",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-151622756",
"type": "article",
"title": "Catastrophic impacts on gravity dominated asteroids",
"author": [
{
"family_name": "Love",
"given_name": "Stanley G.",
"clpid": "Love-S-G"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We use the smoothed particle hydrodynamics method to simulate catastrophic collisions on silicate bodies whose impact response is dominated by gravity rather than material strength. Encounter speeds of 3, 5, and 7 km sec^(\u22121), impact angles of 15\u00b0, 45\u00b0, and 75\u00b0, and target diameters of 10 to 1000 km are investigated. The projectile and target materials are modelled using the Tillotson equation of state for granite. Our model treats gravity rigorously, but neglects strength and fracture effects. We calculate the initial hydrodynamic phase of each event; after the impact shock wave crosses the target, particle motions are nearly ballistic and can be treated analytically. Material that does not escape may reaccrete \u223c1 hr to \u223c1 yr after the impact. The partitioning of impact energy into heat and motion of projectile and target material favors kinetic energy at higher speeds and larger projectile:target diameter ratios, but does not depend on the absolute size scale of the event. After the impact, most of the kinetic energy is carried by a small amount of fast ejecta. Particle velocity distributions are not sensitive to size scale and have complex, evolving shapes that are poorly represented by simple approximations. The catastrophic threshold (impact energy per unit target mass required to permanently eject 50% of the target against gravity) ranges from 8 \u00d7 10^3J kg^(\u22121) at 10 km diameter to 1.5 \u00d7 10^6J kg^(\u22121) at 1000 km, varying as target diameter to the 1.13 \u00b1 0.01 power. Extrapolating these results suggests that gravity dominance extends to stony bodies as small 250 \u00b1 150 m in diameter, smaller than previously believed. This result implies that asteroids as small as a few hundred meters across may be \"rubble piles.\" Nearly catastrophic impacts can exhume target core material and catapult surface rocks to the antipodes (\"scrambling\" the target), but selective removal of the outer layers is inefficient. Most material strongly heated in these impacts escapes, limiting globally averaged heating from a single collision to \u226450\u00b0C for asteroids \u22641000 km in diameter.",
"doi": "10.1006/icar.1996.0195",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1996-11",
"series_number": "1",
"volume": "124",
"issue": "1",
"pages": "141-155"
},
{
"id": "authors:mch12-qdn60",
"collection": "authors",
"collection_id": "mch12-qdn60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-115404323",
"type": "article",
"title": "Emplacement of penetrators into planetary surfaces",
"author": [
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Gibson",
"given_name": "Andrew",
"clpid": "Gibson-A-D"
},
{
"family_name": "Scott",
"given_name": "Ronald",
"clpid": "Scott-R-F"
},
{
"family_name": "Suzuki",
"given_name": "Kojiro",
"clpid": "Suzuki-K"
}
],
"abstract": "We present experimental data and a model for the low-velocity (subsonic, 0\u20131000 m/s) penetration of brittle materials by both solid and hollow (i.e., coring) penetrators. The experiments show that penetration is proportional to momentum/frontal area of the penetrator. Because of the buildup of a cap in front of blunt penetrators, the presence or absence of a streamlined or sharp front end usually has a negligible effect for impact into targets with strength. The model accurately predicts the dependence of penetration depth on the various parameters of the target-penetrator system, as well as the qualitative condition of the target material ingested by a corer. In particular, penetration depth is approximately inversely proportional to the static bearing strength of the target. The bulk density of the target material has only a small effect on penetration, whereas friction can be significant, especially at higher impact velocities, for consolidated materials. This trend is reversed for impacts into unconsolidated materials. The present results suggest that the depth of penetration is a good measure of the strength, but not the density, of a consolidated target. Both experiments and model results show that, if passage through the mouth of a coring penetrator requires initially porous target material to be compressed to <26% porosity, the sample collected by the corer will be highly fragmented. If the final porosity remains above 26%, then most materials, except cohesionless materials, such as dry sand, will be collected as a compressed slug of material.",
"doi": "10.1029/96JE01421",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1996-09-25",
"series_number": "E9",
"volume": "101",
"issue": "E9",
"pages": "21137-21149"
},
{
"id": "authors:40yk2-me636",
"collection": "authors",
"collection_id": "40yk2-me636",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-155620346",
"type": "article",
"title": "High-pressure melting of iron: New experiments and calculations",
"author": [
{
"family_name": "Chen",
"given_name": "George Q.",
"clpid": "Chen-G-Q"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The melting curve of \u03b5-iron in the pressure range of 100 GPa to 300 GPa has been derived by computing Gibbs free energies at high pressures and high temperatures from equation of states (EOS) of the \u03b1-, \u03b5- and liquid phases. Our calculations indicate that the melting curve of iron is very sensitive to the EOS of both the solid (\u03b5) and melt phases. Optimal EOS parameters for \u03b5-iron are presented as well as new data for sound velocities in \u03b3- and liquid phases. The latter provides a value for the Gruneisen parameter for liquid iron of 2.55 at 9.7 Mg m^(-3) at a pressure of 74 GPa. Preliminary shock-wave experiments on pure iron preheated to 1300 \u00b0C were conducted in the 17-74 GPa range. Melting was observed in the highest pressure (74 GPa) experiment. This result supports our theoretically derived melting curve, which is close to those measured by Boehler (1993) and Saxena et al. (1993).",
"doi": "10.1098/rsta.1996.0047",
"issn": "1364-503X",
"publisher": "Royal Society of London",
"publication": "Philosophical Transactions A: Mathematical, Physical and Engineering Sciences",
"publication_date": "1996-06-15",
"series_number": "1711",
"volume": "354",
"issue": "1711",
"pages": "1251-1263"
},
{
"id": "authors:chzj7-gy951",
"collection": "authors",
"collection_id": "chzj7-gy951",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-093136350",
"type": "article",
"title": "Shock temperature and melting in iron sulfides at core pressures",
"author": [
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The temperatures of shock-compressed FeS and FeS_2 in the pressure ranges 125\u2013170 GPa and 100\u2013244 GPa, respectively, are reported and used to constrain the melting curves and thermodynamic properties to core pressures. A fit of the Lindemann law parameters corresponding to the usual functional form for the lattice Gr\u00fcneisen parameter gives \u03b3_L = 1.17 \u00b1 0.13 and n_L = 0.5 \u00b1 0.5 for the high-pressure phase of FeS at \u03c1 = 5340 kg/m^3 and \u03b3_L = 2.18 \u00b1 0.32 and n_L = 1.6 \u00b1 0.7 for FeS_2 at \u03c1 = 5011 kg/m^3. The entropies of fusion are \u223c203 J kg\u22121 K\u22121 for FeS at 120 GPa and \u223c180 J kg^\u22121 K^\u22121 for FeS_2 at 220 GPa. We find that the melting temperature of FeS is 3240\u00b1200 K, 4210 \u00b1 700 K, and 4310 \u00b1 750 K at 136 GPa, 330 GPa, and 360 GPa, respectively. For FeS_2, the melting temperatures are 3990 \u00b1 300 K, 5310 \u00b1 700 K, and 5440 \u00b1 750 K, respectively, for the same pressures. The electronic specific heat for FeS is given by C_e = \u03b2_0 (\u03c1_0/\u03c1)\u03b3e with \u03b20 = 0.25 \u00b1 0.10 J kg^\u22121 K^\u22122 and \u03b3_e = 1.34 for \u03c10 = 5340 kg/m3 for the high-pressure solid phase and \u03b2_0 \u2248 0.05 J kg\u22121 K^\u22122 and \u03b3e = 1.34 for \u03c1_0 = 5150 kg/m^3 for the liquid phase. For FeS_2, there is no detectable electronic contribution, and the lattice specific heat is only 67% of the Dulong-Petit limit, possibly implying tight S-S binding in S_2 units. A reexamination of all shock wave melting data for Fe indicates these approximately agree, but they do not resolve the disagreement between the extrapolated static diamond anvil cell data sets. Fe should melt at \u223c6600 K at 243 GPa and 6900 \u00b1 750 K at 330 GPa (the pressure of the inner core-outer core boundary). Because the FeS melting curve falls well below that of FeS_2, FeS may eventually undergo peritectic melting at high pressures, while FeS_2 melts congruently.",
"doi": "10.1029/95JB01972",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1996-03-10",
"series_number": "B3",
"volume": "101",
"issue": "B3",
"pages": "5627-5642"
},
{
"id": "authors:pmj51-zh604",
"collection": "authors",
"collection_id": "pmj51-zh604",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-092917436",
"type": "article",
"title": "Atmospheric effects on cratering on Venus",
"author": [
{
"family_name": "Takata",
"given_name": "T.",
"clpid": "Takata-Toshiko"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Phillips",
"given_name": "R. J.",
"clpid": "Phillips-R-J"
}
],
"abstract": "A paraboloidal bow shock model is developed in order to estimate the surface distribution of gas shock-induced modifications surrounding Venusian impact craters. We apply two-dimensional oblique shock dynamics to describe a three-dimensional paraboloidal-shaped bow shock impinging upon an assumed incompressible Venusian surface. The effects of the hypersonic atmospheric shock acting on the Venusian surface are considered in terms of induced maximum gas pressure, density, particle velocity, and temperature, for varying angles and velocities of impact. The maximum boulder size that can be saltated by the shock wave induced gas flow and the degree of mutual collision of the surface materials are also considered. The present calculations quantitatively predict the areal extent of the gas shock perturbed surface for normal and oblique impact as a function of impact angle and velocity, and radii of impactors. For a 1-km radius stony meteorite impacting normally at 20 km/s, the radius of the disturbed area extends \u223c10\u201317 times the 3\u20135 km crater radius. The perturbed surface affects the surface radar properties, and the present results can provide an explanation of the wide \"dark/bright halos\" surrounding some of the Venusian impact craters observed via Magellan imagery. For example, a \u223c50-km radius bright halo surrounding a \u223c20-km dark halo is observed around the 3.1-km radius crater located at 16.5\u00b0 north latitude and 334.4\u00b0 longitude. The average value of the radar backscatter cross section of the \u223c20-km radius dark halo indicates that \u223c50-cm-thick layer of porous lithologic material is superimposed upon an assumed undisturbed basement rock surface. The bright halo indicates that the surface roughness in this region is \u223c30 % greater than that of the surrounding original surface. These features can be induced by atmospheric shock waves. The present model can relate the observed crater halo radii to the impact parameters, such as projectile radius and density, and the impact velocity and angle.",
"doi": "10.1029/95JE02641",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1995-11-25",
"series_number": "E11",
"volume": "100",
"issue": "E11",
"pages": "23329-23348"
},
{
"id": "authors:jwgf1-zsj24",
"collection": "authors",
"collection_id": "jwgf1-zsj24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-154659867",
"type": "article",
"title": "Structure, Composition and Evolution of the Earth's Interior \u2013 Introduction",
"author": [
{
"family_name": "Franck",
"given_name": "Siegfried",
"clpid": "Franck-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "This Special Issue developed out of two symposia of the 27th General Assembly of the International Association of Seismology and Physics of the Earth's Interior (IASPEI) which was held at Victoria University of Wellington, Wellington, New Zealand, on 10-21 January 1994. It contains papers from Symposium S4 'Deep Earth Discontinuities: Configuration and Dynamics' convened by F. D. Stacey (Australia), T. Lay (USA) and U. Christensen (Germany) and from the Symposium S5 'Structure and Composition of the Earth's Interior and their Relation to Planetary Evolution' convened by the undersigned. Both symposia were joint with the 'Study of the Earth's Interior' (SEDI), Committee of the International Union of Geodesy and Geophysics (IUGG). The present papers in this Special Issue are divided into five groups: seismology; geodesy; numerical modeling; mineral physics; and petrophysics. As Guest Editors, we believe this Special Issue is a good example of communication between the individual research communities.",
"doi": "10.1016/0031-9201(95)90013-6",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1995-11",
"series_number": "1-2",
"volume": "92",
"issue": "1-2",
"pages": "1"
},
{
"id": "authors:q9wyf-fwc03",
"collection": "authors",
"collection_id": "q9wyf-fwc03",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-143200471",
"type": "article",
"title": "Comet Shoemaker-Levy 9: Fragment and progenitor impact energy",
"author": [
{
"family_name": "Takata",
"given_name": "Toshiko",
"clpid": "Takata-Toshiko"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Harris",
"given_name": "Alan W.",
"orcid": "0000-0001-7431-2013",
"clpid": "Harris-A-W"
}
],
"abstract": "Initial observational data from the impact of fragments of Comet Shoemaker-Levy 9 (SL9) are compared with smoothed particle hydrodynamic (SPH) calculations to determine their pre-impact diameters and the equivalent diameter of the SL9 progenitor. Diameters (solid ice) of 2.0\u00b10.1, 2.0\u00b10.05, 2.1\u00b10.04 and 1.9\u00b10.05 km for fragments A, E, G1, and W are obtained from impact-induced plume heights from the Hubble Space Telescope (HST) data. Applying these values to scale apparent diameters for the balance of 18 SL fragments in Weaver et al.'s [1995] catalog of 22 objects yields a SL9 progenitor diameter of 5.0\u00b11.8 km. This corresponds to total impact energy of 1.2 (+1.8\u22120.8) \u00d7 10^(30) erg. Such an energetic event occurs on Jupiter and Earth at least every 4,900 +4,700, \u22122,700, and \u223c0.5 \u00d7 10^8 years, respectively.",
"doi": "10.1029/95GL02237",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1995-09-01",
"series_number": "17",
"volume": "22",
"issue": "17",
"pages": "2433-2436"
},
{
"id": "authors:wqpdn-08n13",
"collection": "authors",
"collection_id": "wqpdn-08n13",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-144147208",
"type": "article",
"title": "Impact Jetting of Geological Materials",
"author": [
{
"family_name": "Yang",
"given_name": "Wenbo",
"clpid": "Yang-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "To understand jetting of earth materials, gabbro slabs (5 mm thick) were accelerated to 1.5-2 km sec^(-1) and impacted gabbro (5-10 mm thick), novaculite (10 mm thick), and porous sandstone (12 mm thick) targets at inclination angles of 30\u00b0-60\u00b0. The ejecta were collected using a catcher box filled with styrofoam and the particles are extracted using chloroform. Jetting angles are determined by the relative positions of the target and the crater produced by the ejecta. The mass of the ejected particles per unit area (\u223c50 mg cm^(-2)) of the impactor remains almost independent of the impact velocity, inclination angle, thickness of the target and sample mineralogy, and density. Hydrodynamic models are used to calculate the jetting mass, angle, and velocity. Theoretical models predict \u223c6 times more ejecta than the experimentally measured as the inclination angle increases. X-ray diffraction of the recovered ejecta shows that it is still in crystalline form, which agrees with thermodynamic calculations. Because the experimental results indicate that the theoretical jetting model for thin metal plates provides a poor description of the experiments, the application of metal plate theory to planet-sized objects appears to be questionable.",
"doi": "10.1006/icar.1995.1125",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1995-08",
"series_number": "2",
"volume": "116",
"issue": "2",
"pages": "269-274"
},
{
"id": "authors:2nvj4-bs165",
"collection": "authors",
"collection_id": "2nvj4-bs165",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-104858972",
"type": "article",
"title": "Fractionation of ruthenium from iridium at the Cretaceous-Tertiary boundary",
"author": [
{
"family_name": "Evans",
"given_name": "Noreen Joyce",
"clpid": "Evans-Noreen-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Gregoire",
"given_name": "D. C.",
"clpid": "Gregoire-D-C"
}
],
"abstract": "New data on Ru/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman River, Saskatchewan) and marine Cretaceous-Tertiary boundary sites (Brazos River, Texas; Beloc, Haiti; DSDP 577 and DSDP 596). The Ru/Ir ratio varies from 0.5 to 1 within 4000 km of Chicxulub and increases to 2\u20133 at paleodistances (65 Ma) of up to 12,000 km from the impact site. For CI chondrites, Ru/Ir= 1.5. A ballistic model of ejecta cloud cooling and expansion, which employs the available vapor-pressure versus temperature data for Ru and Ir, predicts qualitatively similar global variation in the Ru/Ir ratio but by only a factor of 1.5. We infer that several other factors, such as remobilization of PGE during diagenesis, preferential oxidation of Ru, condensation kinetics and atmospheric chemical and circulation processes, may account for the observed larger Ru/Ir variation.",
"doi": "10.1016/0012-821X(95)00117-U",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1995-08",
"series_number": "1-2",
"volume": "134",
"issue": "1-2",
"pages": "141-153"
},
{
"id": "authors:d2pht-npw35",
"collection": "authors",
"collection_id": "d2pht-npw35",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141027-154816617",
"type": "article",
"title": "Impact Jetting of Geological Materials",
"author": [
{
"family_name": "Yang",
"given_name": "Wenbo",
"clpid": "Yang-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "To understand jetting of earth materials, gabbro slabs (5 mm thick) were accelerated to 1.5-2 km sec^(-1) and impacted gabbro (5-10 mm thick), novaculite (10 mm thick), and porous sandstone (12 mm thick) targets at inclination angles of 30\u00b0-60\u00b0. The ejecta were collected using a catcher box filled with styrofoam and the particles are extracted using chloroform. Jetting angles are determined by the relative positions of the target and the crater produced by the ejecta. The mass of the ejected particles per unit area (\u223c50 mg cm^(-2)) of the impactor remains almost independent of the impact velocity, inclination angle, thickness of the target and sample mineralogy, and density. Hydrodynamic models are used to calculate the jetting mass, angle, and velocity. Theoretical models predict \u223c6 times more ejecta than the experimentally measured as the inclination angle increases. X-ray diffraction of the recovered ejecta shows that it is still in crystalline form, which agrees with thermodynamic calculations. Because the experimental results indicate that the theoretical jetting model for thin metal plates provides a poor description of the experiments, the application of metal plate theory to planet-sized objects appears to be questionable.",
"doi": "10.1006/icar.1995.1125",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1995-08",
"series_number": "2",
"volume": "116",
"issue": "2",
"pages": "269-274"
},
{
"id": "authors:r9x4t-wk771",
"collection": "authors",
"collection_id": "r9x4t-wk771",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-123034988",
"type": "article",
"title": "Hypervelocity Impacts and Magnetization of Small Bodies in the Solar System",
"author": [
{
"family_name": "Chen",
"given_name": "Guangqing",
"clpid": "Chen-G-Q"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Hide",
"given_name": "Raymond",
"clpid": "Hide-R"
}
],
"abstract": "The observed magnetism of asteroids such as Gaspra and Ida (and other small bodies in the solar system including the Moon and meteorites) may have resulted from an impact-induced shock wave producing a thermodynamic state in which iron-nickel alloy, dispersed in a silicate matrix, is driven from the usual low-temperature, low-pressure, \u03b1, kaemacite, phase to the paramagnetic, epsilon (hcp), phase. The magnetization was acquired upon rarefaction and reentry into the ferromagnetic, \u03b1, structure. The degree of remagnetization depends on the strength of the ambient field, which may have been associated with a Solar-System-wide magnetic field. A transient held induced by the impact event itself may have resulted in a significant, or possibly, even a dominant contribution, as well. The scaling law of Housen et al. (Housen, K. R., R. M. Schmidt, and K. A. Holsapple 1991. Icarus 94, 180-190) for catastrophic asteroid impact disaggregation imposes a constraint on the degree to which small planetary bodies may be magnetized and yet survive fragmentation by the same event. Our modeling results show it is possible that Ida was magnetized when a large impact fractured a 125 +/- 22-km-radius protoasteroid to form the Koronis family. Similarly, we calculate that Gaspra could be a magnetized fragment of a 45 +/- 15 km-radius protoasteroid.",
"doi": "10.1006/icar.1995.1080",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1995-05",
"series_number": "1",
"volume": "115",
"issue": "1",
"pages": "86-96"
},
{
"id": "authors:h345z-h0477",
"collection": "authors",
"collection_id": "h345z-h0477",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-091644578",
"type": "article",
"title": "Shock compression and isentropic release of granite",
"author": [
{
"family_name": "Sekine",
"given_name": "Toshimori",
"clpid": "Sekine-Toshimori"
},
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Rubin",
"given_name": "Allan M.",
"clpid": "Rubin-A-M"
},
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New equation of state data for a weathered granite shocked to about 125 GPa are reported and combined with the Westerly granite data of McQueen, Marsh & Fritz (1967). The shock velocity (U_s)-particle velocity (U_p) relations can be fitted with two linear regressions: U_s= 4.40 + 0.6U_p for a range of U_p up to about 2 km s^(-1) and U_s= 2.66 + 1.49U_p for a range of about 2 to 5 km s^(-1). The third-order Birch-Murnaghan equation of state parameters are K_(os) = 51-57 GPa and K'_(os) = 1.4-1.8 for the low-pressure regime and K_(os) = 251 \u00b1 30 GPa and an assumed K'_(os) = 4 for the high-pressure regime. Compressive waveforms in dry and water-saturated granite were measured at 10-15 GPa using the VISAR technique. The measured wave profiles were successfully modelled using a Maxwellian stress-relaxation material model. Water-saturated granite is characterized by a ~25 per cent lower yield strength and a ~75 per cent longer material relaxation time than dry granite.",
"doi": "10.1111/j.1365-246X.1995.tb01817.x",
"issn": "0956-540X",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal International",
"publication_date": "1995-02",
"series_number": "2",
"volume": "120",
"issue": "2",
"pages": "247-261"
},
{
"id": "authors:atce8-t7k52",
"collection": "authors",
"collection_id": "atce8-t7k52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-122651904",
"type": "article",
"title": "Compressional sound velocity, equation of state, and constitutive response of shock-compressed magnesium oxide",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Wave profile and equation of state (EOS) data are reported for low-porosity polycrystalline magnesium oxide under shock compression. The Hugoniot equation of state between 14 and 133 GPa is U_S = 6.87(10) + 1.24(4)u_p, where the numbers in parentheses are one standard deviation uncertainties in the last digit(s). Reverse-impact wave profiles constrain the compressional sound velocity, V_p, at 10\u201327 GPa to \u00b12%. Measured V_p values are consistent with ultrasonic data extrapolated from 3 GPa. By combining the Hugoniot results with ultrasonic data, the adiabatic bulk modulus and its first and second pressure derivatives at constant entropy are 162.5(2) GPa, 4.09(9), and \u22120.019(4) GPa^(\u22121). The shear modulus and its first and second pressure derivatives are 130.8(2) GPa, 2.5(1), \u22120.026(45) GPa^(\u22121). Polycrystalline MgO has a compressive yield strength of 1\u20131.5 GPa at the elastic limit which increases to 2.7(8) GPa along the Hugoniot and is similar at unloading. Wave profiles for MgO at 10\u201339 GPa are described using a modified elastic-plastic model. There are significant differences in the dynamic response of single-crystal and polycrystalline MgO.",
"doi": "10.1029/94JB02065",
"issn": "2169-9313",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research. Solid Earth",
"publication_date": "1995-01-10",
"series_number": "B1",
"volume": "100",
"issue": "B1",
"pages": "529-542"
},
{
"id": "authors:ww1nh-yr168",
"collection": "authors",
"collection_id": "ww1nh-yr168",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-161334039",
"type": "article",
"title": "Equations of state of \u03b1, \u03f5 and liquid iron and Iron's melting curve \u2014thermodynamic calculations",
"author": [
{
"family_name": "Chen",
"given_name": "Guangqing",
"clpid": "Chen-G-Q"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The melting curve between \u03f5 and liquid iron (100GPa< P <300GPa) has been derived by computing Gibbs free energies at high pressures and high temperatures from equations of state of the \u03b1, \u03f5 and liquid phases. The most uncertainty lies in the equation of state (EOS) of the \u03f5 phase. By comparing the calculations to experimental data, the internal thermodynamic consistency of the three phases are examined. The best fits to the melting curves of Boehler [1993] and Williams et al. [1987] can be obtained with lower bulk moduli than determined by static compression. Using available equations of state of the iron phases, our calculations indicate that if sub-solidus iron is of the \u03f5 phase, Boehler's melting curve is thermodynamically more consistent than Williams et al.'s. The problem is complicated by the possible existence of a new phase between the \u03f5 and the liquid fields.",
"doi": "10.1029/94GL02892",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1995-01-01",
"series_number": "1",
"volume": "22",
"issue": "1",
"pages": "21-24"
},
{
"id": "authors:jtkvy-zys22",
"collection": "authors",
"collection_id": "jtkvy-zys22",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-112455494",
"type": "article",
"title": "Shock-induced devolatilization of calcium sulfate and implications for K-T extinctions",
"author": [
{
"family_name": "Chen",
"given_name": "Guangqing",
"clpid": "Chen-G-Q"
},
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The devolatilization of calcium sulfate, which is present in the target rock of the Chicxulub, Mexico impact structure, and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. We measured the amount of SO_2 produced from two shock-induced devolatilization reactions of calcium sulfate up to 42 GPa in the laboratory:\nCaSO_4 + SiO_2 \u2192 CaSiO_3 + SO_3\u2191\nCaSO_4 \u2192 CaO + SO_2\u2191 + 1/2O_2\u2191\nWe found both to proceed to a much lower extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be \u223c 10^(\u22122) times those calculated for equilibrium. Upon modeling the quantity of sulfur oxides degassed into the atmosphere from shock devolatilization of CaSO_4 in the Chicxulub lithographic section, the resulting 9 \u00d7 10^(16) to 6 \u00d7 10^(17) g (in sulfur mass) is lower by a factor of 10\u2013100 than previous upper limit estimates, the related environmental stress arising from the resultant global cooling and fallout of acid rain is insufficient to explain the widespread K-T extinctions.",
"doi": "10.1016/0012-821X(94)90174-0",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1994-12",
"series_number": "3-4",
"volume": "128",
"issue": "3-4",
"pages": "615-628"
},
{
"id": "authors:545td-1y484",
"collection": "authors",
"collection_id": "545td-1y484",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141027-113407423",
"type": "article",
"title": "Mechanical properties of shock-damaged rocks",
"author": [
{
"family_name": "He",
"given_name": "Hongliang",
"clpid": "He-H"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Stress-strain tests were performed both on shock-damaged gabbro and limestone. The effective Young's modulus decreases with increasing initial damage parameter value, and an apparent work-softening process occurs prior to failure. To further characterize shock-induced microcracks, the longitudinal elastic wave velocity behavior of shock-damaged gabbro in the direction of compression up to failure was measured using an acoustic transmission technique under uniaxial loading. A dramatic increase of velocity was observed for the static compressive stress range of 0\u201350 MPa. Above that stress range, the velocity behavior of lightly damaged (D_0<0.1) gabbro is almost equal to unshocked gabbro. The failure strength of heavily damaged (D_0>0.1) gabbro is \u223c100\u2212150 MPa, much lower than that of lightly damaged and unshocked gabbros (\u223c230\u2212260 MPa). Following Nur's theory, the crack shape distribution was analyzed. The shock-induced cracks in gabbro appears to be largely thin penny-shaped cracks with c/a values below 5 \u00d7 10^(\u22124). Moreover, the applicability of Ashby and Sammis's theory relating failure strength and damage parameter of shock-damaged rocks was examined and was found to yield a good estimate of the relation of shock-induced deficit in elastic modulus with the deficit in compressive strength.",
"doi": "10.1016/0148-9062(94)90154-6",
"issn": "0148-9062",
"publisher": "Elsevier",
"publication": "International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts",
"publication_date": "1994-10",
"series_number": "5",
"volume": "31",
"issue": "5",
"pages": "525-533"
},
{
"id": "authors:rhknm-y5988",
"collection": "authors",
"collection_id": "rhknm-y5988",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-151639123",
"type": "article",
"title": "The Origin of the Earth",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The question of the origin of the blue planet pictured in figure 1 is related to other questions about our beginnings. These include the origin of the universe, the evolution of galaxies and stars, the origin of life and the ascent of humankind. In the late 1700s both Pierre\u2010Simon Laplace and Immanuel Kant suggested that Earth and the other planets in the solar system had condensed from a flattened nebular disk surrounding the Sun. Since these astute hypotheses were suggested, a series of well\u2010known physical scientists including James Jeans, Gerald Kuiper and Harold Urey have developed a now widely accepted theory of the accretion of the Earth and planets. Their theory, which I describe below, was based on telescopic observations of the solar system,theoretical calculations and the study of meteorites. Now referred to as the Schmidt theory (after Otto Yu. Schmidt of the Institute of the Earth, Moscow), it explains the formation of the planets as resulting from the accretion of already solid bodies.",
"doi": "10.1063/1.881436",
"issn": "0031-9228",
"publisher": "American Institute of Physics",
"publication": "Physics Today",
"publication_date": "1994-08",
"series_number": "8",
"volume": "47",
"issue": "8",
"pages": "38-45"
},
{
"id": "authors:qeknp-jad69",
"collection": "authors",
"collection_id": "qeknp-jad69",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-145845649",
"type": "article",
"title": "Dynamic response of molybdenum shock compressed at 1400\u00b0C",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Wave profile measurements are reported for pure molybdenum initially heated to 1400\u2009\u00b0C and shock compressed to stresses between 12 and 81 GPa. The Hugoniot states are consistent with previous results and all data can be described by the parameters: c_0=4.78(2) km/s and s=1.42(2), where the numbers in parentheses are one standard deviation uncertainties in the last digits. The amplitude of the Hugoniot elastic limit is 1.5\u20131.7 GPa at 1400\u2009\u00b0C compared with 25\u2009\u00b0C values of 2.3\u20132.8 GPa. Unloading wave velocities range from 6.30(22) km/s at 12.0 GPa to 7.91(24) km/s at 80.7 GPa and are 4%\u20138% below extrapolated ultrasonic values and Hugoniot measurements from a room temperature initial state. These differences can be explained by the effect of temperature on the compressional elastic wave velocity. No temperature dependence of the dynamic tensile strength can be resolved from the present data.",
"doi": "10.1063/1.357758",
"issn": "0021-8979",
"publisher": "American Institute of Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1994-07-15",
"series_number": "2",
"volume": "76",
"issue": "2",
"pages": "835-842"
},
{
"id": "authors:ng663-stb90",
"collection": "authors",
"collection_id": "ng663-stb90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-160015910",
"type": "article",
"title": "Radiative signatures from impact of comet Shoemaker-Levy-9 on Jupiter",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Takata",
"given_name": "Toshiko",
"clpid": "Takata-Toshiko"
}
],
"abstract": "The visible optical power emitted from the expansion plumes from 0.4 and 2 km diameter fragments of Shoemaker-Levy are expected to be, \u223c25% and comparable to, the visible solar flux reflected from Jupiter, respectively, for several minutes, and could be easily observed by sensors on the Galileo spacecraft. Earth-based observers can detect these plumes as these expand over the SW limb of Jupiter and come into earth view some minutes after impact!",
"doi": "10.1029/94GL01578",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1994-07-01",
"series_number": "14",
"volume": "21",
"issue": "14",
"pages": "1551-1553"
},
{
"id": "authors:w5pgk-qv996",
"collection": "authors",
"collection_id": "w5pgk-qv996",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-092020236",
"type": "article",
"title": "Impact of comet Shoemaker-Levy 9 on Jupiter",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Takata",
"given_name": "Toshiko",
"clpid": "Takata-Toshiko"
},
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Orton",
"given_name": "Glenn S.",
"orcid": "0000-0001-7871-2823",
"clpid": "Orton-G-S"
}
],
"abstract": "Three-dimensional numerical simulations of the impact of Comet Shoemaker-Levy 9 on Jupiter and the resulting vapor plume expansion were conducted using the Smoothed Particle Hydrodynamics (SPH) method. An icy body with a diameter of 2 km can penetrate to an altitude of -350 km (0 km = 1 bar) and most of the incident kinetic energy is transferred to the atmosphere between -100 km to -250 km. This energy is converted to potential energy of the resulting gas plume. The unconfined plume expands vertically and has a peak radiative power approximately equal to the total radiation from Jupiter's disc. The plume rises a few tens of atmospheric scale heights in \u223c10\u00b2 seconds. The rising plume reaches the altitude of \u223c3000 km, but no atmospheric gas is accelerated to the escape velocity (\u223c60 km/s).",
"doi": "10.1029/94GL01325",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1994-06-01",
"series_number": "11",
"volume": "21",
"issue": "11",
"pages": "1087-1090"
},
{
"id": "authors:qx901-9zv78",
"collection": "authors",
"collection_id": "qx901-9zv78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:RULrsi94",
"type": "article",
"title": "Inward electrostatic precipitation of interplanetary particles",
"author": [
{
"family_name": "Rulison",
"given_name": "Aaron J.",
"clpid": "Rulison-Aaron-J"
},
{
"family_name": "Flagan",
"given_name": "Richard C.",
"orcid": "0000-0001-5690-770X",
"clpid": "Flagan-R-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "An inward precipitator collects particles initially dispersed in a gas throughout either a cylindrical or spherical chamber onto a small central planchet. The instrument is effective for particle diameters greater than about 1 \u00b5m. One use is the collection of interplanetary dust particles which are stopped in a noble gas (xenon) by drag and ablation after perforating the wall of a thin-walled spacecraft-mounted chamber. First, the particles are positively charged for several seconds by the corona production of positive xenon ions from inward facing needles placed on the chamber wall. Then an electric field causes the particles to migrate toward the center of the instrument and onto the planchet. The collection time (of the order of hours for a 1 m radius spherical chamber) is greatly reduced by the use of optimally located screens which reapportion the electric field. Some of the electric field lines terminate on the wires of the screens so a fraction of the total number of particles in the chamber is lost. The operation of the instrument is demonstrated by experiments which show the migration of carbon soot particles with radius of approximately 1 \u00b5m in a 5-cm-diam cylindrical chamber with a single field enhancing screen toward a 3.2 mm central collection rod.",
"doi": "10.1063/1.1144832",
"issn": "0034-6748",
"publisher": "American Institute of Physics",
"publication": "Review of Scientific Instruments",
"publication_date": "1994-06",
"series_number": "6",
"volume": "65",
"issue": "6",
"pages": "1839-1846"
},
{
"id": "authors:scxkj-95b23",
"collection": "authors",
"collection_id": "scxkj-95b23",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-082304930",
"type": "article",
"title": "Comet Shoemaker-Levy 9: Impact on Jupiter and Plume Evolution",
"author": [
{
"family_name": "Takata",
"given_name": "Toshiko",
"clpid": "Takata-Toshiko"
},
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The impact of fragments of Comet Shoemaker-Levy 9 on Jupiter and the resulting vapor plume expansion are investigated by conducting three-dimensional numerical simulations using the smoothed particle hydrodynamics (SPH) method. An icy body, representing the cometary fragments, with a velocity of 60 km/sec and a diameter of 2 km can penetrate to 350 km below the 1-bar pressure level in the atmosphere. Most of the initial kinetic energy of the fragment is transferred to the atmosphere between 50 km and 300 km below the 1-bar pressure level. The shock-heated atmospheric gas in the wake is totally dissociated and partially ionized. Scaling our SPH results to other sizes indicates that fragments larger than \u223c100 m in diameter can penetrate to below the visible cloud decks. The energy deposited in the atmosphere is explosively released in the upward expansion of the resulting plume. The plume preferentially expands upward rather than horizontally due to the density gradient of the ambient atmosphere. It rises \u226510^2 km in \u223c10^2 sec. Eventually the total atmospheric mass ejected to above 1 bar is \u226540 times the initial mass of the impactor. The plume temperature at a radius \u223c10^3 km is >10^3 K for 10^3 sec for a 2-km fragment. We predict that impact-induced plumes will be observable with the remote sensing instruments of the Galileo spacecraft. As the impact site rotates into the view of Earth some 20 min after the impact, the plume expansion will be observable using the Hubble Space Telescope and from visible and infrared instruments on groundbased telescopes. The rising plume reaches \u223c3000 km altitude in \u223c10 min and will be visible from Earth.",
"doi": "10.1006/icar.1994.1074",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1994-05",
"series_number": "1",
"volume": "109",
"issue": "1",
"pages": "3-19"
},
{
"id": "authors:3er96-86a28",
"collection": "authors",
"collection_id": "3er96-86a28",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-151913992",
"type": "article",
"title": "Shock induced formation of MgAl_2O_4 spinel from oxides",
"author": [
{
"family_name": "Potter",
"given_name": "David K.",
"clpid": "Potter-D-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The physics of mineral grain sliding, which occurs upon dynamic compression of rocks, is investigated by shock loading single crystals of corundum (Al_2O_3) and periclase (MgO) in contact obliquely in impact experiments. Energy dispersive X-ray analysis and X-ray diffraction studies of samples recovered from 26\u201336 GPa, 800 ns experiments indicated that under certain conditions a spinel phase of composition MgAl_2O_4 and thickness \u226420 \u00b5m was produced at the interface between the two crystals. Although the computed shock (continuum) temperatures were below those necessary to melt the initial oxides, the spinel nonetheless appears to have formed as a result of localised melting, via grain boundary sliding friction, followed by rapid quenching. Scanning electron microscopy (SEM) revealed some evidence for such melting. Moreover, the timescale of the experiments is too short for solid state diffusion (during the shock state) to explain the observed spinel thickness, although defect enhanced solid state diffusion, subsequent to loading and unloading, remains a possibility. The results also reinforce other recent observations and theories of heterogeneous deformation in minerals.",
"doi": "10.1029/94GL00079",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1994-04-15",
"series_number": "8",
"volume": "21",
"issue": "8",
"pages": "721-724"
},
{
"id": "authors:g52r8-zjk29",
"collection": "authors",
"collection_id": "g52r8-zjk29",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-122757198",
"type": "article",
"title": "Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage",
"author": [
{
"family_name": "Polanskey",
"given_name": "Carol A.",
"clpid": "Polanskey-C-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Carbonate samples from the 8.9-Mt nuclear (near-surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen and Kaibab limestone, which had been shocked to known pressures. Analysis of the OAK Crater borehole samples has identified a thin zone of allocthonous highly shocked (10\u201313 GPa) carbonate material underneath the apparent crater floor. This \u223c5- to 15-m-thick zone occurs at a maximum depth of \u223c125 m below current seafloor at the borehole, sited at the initial position of the OAK explosive, and decreases in depth towards the apparent crater edge. Because this zone of allocthonous shocked rock delineates deformed rock below, and a breccia of mobilized sand and collapse debris above, it appears to outline the transient crater. The transient crater volume inferred in this way is found to be 3.2\u00b10.2\u00d710^6 m^3, which is in good agreement with a volume of 5.3\u00d710^6 m^3 inferred from gravity scaling of laboratory experiments [Schmidt et al., 1986]. A layer of highly shocked material is also found near the surface outside the crater. The latter material could represent a fallout ejecta layer. The ejecta boulders recovered from the present crater floor experienced a range of shock pressures from \u223c0 to 15 GPa with the more heavily shocked samples all occurring between radii of 360 and \u223c600 m. Moreover, the fossil content, lithology, and Sr isotopic composition all demonstrate that the initial position of the bulk of the heavily shocked rock ejecta sampled was originally near surface rock at initial depths in the 32 to 45-m depth (below sea level) range. The EPR technique is also sensitive to prehistoric shock damage. This is demonstrated by our study of shocked Kaibab limestone from the 49,000-year-old Meteor (Barringer) Crater Arizona. We found shock damage present in the \u03b2 member of the Kaibab Formation exposed in the crater walls corresponding to peak shock stress in the 0.3- to 0.6 GPa range. Carbonate ejecta recovered from within the crater experienced shock pressures of up to 0.6 GPa. Assuming shock damage levels of 0.3 to 0.6 GPa for the lightly shocked carbonate on the walls of the Meteor crater, combined with the shock pressure versus distance model of Moss [1988] and Lamb et al. [1991], Meteor Crater impact energies of 2.4 to 8.9 Mt are obtained. This approximately agrees with energies of 3.3 to 7.1 Mt calculated from the crater scaling of Schmidt and Housen [1987].",
"doi": "10.1029/93JE03574",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1994-03-25",
"series_number": "E3",
"volume": "99",
"issue": "E3",
"pages": "5621-5638"
},
{
"id": "authors:1cat2-pjw57",
"collection": "authors",
"collection_id": "1cat2-pjw57",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-155133504",
"type": "article",
"title": "The temperature sensitivity of elastic wave velocity at high pressure: New results for molybdenum",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A new experimental technique is described whereby a material is heated to very high temperature (T), shock compressed to high pressure (P) (and higher T), and the compressional elastic wave velocity of the high P and T state is measured. This method has been applied to the high-pressure standard molybdenum at pressures between 12 and 81 GPa and at an initial temperature of 1400\u00b0C. The compressional velocity of Mo at 2450\u00b0C and 81 GPa is found to be 7.91 km/s, compared to a calculated value of 8.36 km/s at 81 GPa along the 25\u00b0C isotherm. Data for molybdenum, a number of other metals, and a silicate yield a consistent trend which can be used to determine the scaling coefficient between compressional velocity and temperature at geophysically relevant conditions.",
"doi": "10.1029/94GL00223",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1994-03-15",
"series_number": "6",
"volume": "21",
"issue": "6",
"pages": "473-476"
},
{
"id": "authors:k8rpn-b5w21",
"collection": "authors",
"collection_id": "k8rpn-b5w21",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-165134717",
"type": "article",
"title": "An equation of state for liquid iron and implications for the Earth's core",
"author": [
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "An equation of state is presented for liquid iron based on published ultrasonic, thermal expansion, and enthalpy data at 1 bar and on pulse-heating and shock wave compression and sound speed data up to 10 Mbar. The equation of state parameters, centered at 1 bar and 1811 K (the normal melting point of iron), are density, \u03c1_0 = 7019 kg/m^3, isentropic bulk modulus, K_(S0) = 109.7 GPa, and the first- and second-pressure derivatives of K_S, K\u2032_(S0) = 4.66 and K\u2033_(S0) = \u22120.043 GPa^(\u22121). A parameterization of the Gr\u00fcneisen parameter \u03b3 as a function of density \u03c1 and specific internal energy E is \u03b3 = \u03b3_0 + \u03b3\u2032(\u03c1/\u03c1_0)^n(E - E_0) where \u03b3_0 = 1.735, \u03b3\u2032 = \u22120.130 kg/MJ, n = \u22121.87, and E_0 is the internal energy of the liquid at 1 bar and 1811 K. The model gives the temperature dependence of \u03b3 at constant volume as (\u2202\u03b3/\u2202T)_(v|1bar,1811K) = \u22128.4 \u00d7 10^(\u22125) K^(\u22121). The constant volume specific heat of liquid Fe at core conditions is 4.0\u20134.5 R. The model gives excellent agreement with measured temperatures of Fe under shock compression. Comparison with a preliminary reference Earth model indicates that the light component of the core does not significantly affect the magnitude of the isentropic bulk modulus of liquid Fe but does decrease its pressure derivative by \u223c10%. Pure liquid Fe is 3\u20136% more dense than the inner core, supporting the presence of several percent of light elements in the inner core.",
"doi": "10.1029/93JB03158",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1994-03-10",
"series_number": "B3",
"volume": "99",
"issue": "B3",
"pages": "4273-4284"
},
{
"id": "authors:rncgv-zv781",
"collection": "authors",
"collection_id": "rncgv-zv781",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-111703905",
"type": "article",
"title": "Observations of impact-induced molten metal-silicate partitioning",
"author": [
{
"family_name": "Rowan",
"given_name": "Linda R.",
"clpid": "Rowan-L-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Observations of molten mid-ocean ridge basalt (MORB)-molybdenum (Mo) interactions produced by shock experiments provide insight into impact and differentiation processes involving metal-silicate partitioning. Analysis of fragments recovered from experiments (achieving MORB liquid shock pressures from 0.8 to 6 GPa) revealed significant changes in the composition of the MORB and Mo due to reaction of the silicate and metal liquids on a short time scale ( < 13 s). The FeO concentration of the shocked liquid de creases systematically with increasing pressure. In fact, the most highly shocked liquid (6 GPa) contains only 0.1 wt% FeO compared to an initial concentration of 9 wt% in the MORB. We infer from the presence of micrometer-sized Fe-, Si- and Mo-rich metallic spheres in the shocked glass that the Fe and Si oxides in the MORB were reduced in an estimated oxygen fugacity of 10^(\u221217) bar and subsequently alloyed with the Mo.\n\nThe in-situ reduction of FeO in the shocked molten basalt implies that shock-induced reduction of impact melt should be considered a viable mechanism for the formation of metallic phases. Similar metallic phases may form during impact accretion of planets and in impacted material found on the lunar surface and near terrestrial impact craters. In particular, the minute, isolated Fe particles found in lunar soils may have formed by such a process. Furthermore, the metallic spheres within the shocked glass have a globular texture similar to the textures of metallic spheroids from lunar samples and the estimated, slow cooling rate of \u2a7d 140\u00b0C/s for our spheres is consistent with the interpretation that the lunar spheroids formed by slow cooling within a melted target.",
"doi": "10.1016/0012-821X(94)90052-3",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1994-03",
"series_number": "1-2",
"volume": "122",
"issue": "1-2",
"pages": "71-88"
},
{
"id": "authors:3rx0w-q4441",
"collection": "authors",
"collection_id": "3rx0w-q4441",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-121808902",
"type": "article",
"title": "Physics of interplanetary dust capture via impact into organic polymer foams",
"author": [
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The physics of hypervelocity impacts into foams is of interest because of the possible application to interplanetary dust particle (IDP) capture by spacecraft. We present a model for the phenomena occurring in such impacts into low-density organic polymer foams. Particles smaller than foam cells behave as if the foam is a series of solid slabs and are fragmented and, at higher velocities, thermally altered. Particles much larger than the foam cells behave as if the foam were a continuum, allowing the use of a continuum mechanics model to describe the effects of drag and ablation. Fragmentation is expected to be a major process, especially for aggregates of small grains. Calculations based on these arguments accurately predict experimental data and, for hypothetical IDPs, indicate that recovery of organic materials will be low for encounter velocities greater than 5 km s^(\u22121). For an organic particle 100 \u03bcm in diameter, \u223c35% of the original mass would be collected in an impact at 5 km s^(\u22121), dropping to \u223c10% at 10 km s^(\u22121) and \u223c0% at 15 km s^(\u22121). For the same velocities the recovery ratios for troilite (FeS) are \u223c95%, 65%, and 50%, and for olivine (Mg_2SiO_4) they are \u223c98%, 80%, and 65%, demonstrating that inorganic materials are much more easily collected. The density of the collector material has only a second-order effect, changing the recovered mass by <10% of the original mass.",
"doi": "10.1029/93JE03147",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1994-01-25",
"series_number": "E1",
"volume": "99",
"issue": "E1",
"pages": "2063-2071"
},
{
"id": "authors:6awdq-7fp73",
"collection": "authors",
"collection_id": "6awdq-7fp73",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-110049204",
"type": "article",
"title": "Pressure-temperature range of reactions between liquid iron in the outer core and mantle silicates",
"author": [
{
"family_name": "Song",
"given_name": "Xi",
"clpid": "Song-X"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The possibility of reaction between the liquid iron of the Earth's outer core and crystalline silicates ((Mg, Fe)SiO_3) of the mantle, Mg_(0.9), Fe_(0.1)SiO_3(pv) + 0.15 Fe (\u03f5) = 0.9MgSiO_3 (pv) + 0.2FeO (hpp) + 0.05 FeSi (\u03f5) + 0.05 SiO_2 (st), was proposed by Knittle and Jeanloz (1989,1991) on the basis of exploratory experiments. We calculate Gibbs free-energies for the reactants and the products of the above reaction in order to constrain the pressure-temperature range. Upon application of thermal expansion, equation of state and heat capacity data, we demonstrate that this reaction can occur at pressures as low as 30 GPa at 3500 K, and at temperatures as low as 900 K at the 130 GPa pressure of the present core-mantle boundary. Furthermore, we propose a modified equation of reaction at the core-mantle boundary: Mg_(0.9)Fe_(0.1)SiO_3 (pv) + 0.3Fe (\u03f5) = 0.9MgSiO_3 (pv) + 0.3FeO(hpp) + 0.1FeSi. Our results imply that similar reactions may occur during the early accretion history of the Earth.",
"doi": "10.1029/93GL03262",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1994-01-15",
"series_number": "2",
"volume": "21",
"issue": "2",
"pages": "153-156"
},
{
"id": "authors:9qq7d-pn333",
"collection": "authors",
"collection_id": "9qq7d-pn333",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-115404267",
"type": "article",
"title": "Planetary Cratering Mechanics",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The objective of this study was to obtain a quantitative understanding of the cratering process over a broad range of conditions. Our approach was to numerically compute the evolution of impact induced flow fields and calculate the time histories of the key measures of crater geometry (e.g. depth, diameter, lip height) for variations in planetary gravity (0 to 10^9 cm/s^2), material strength (0 to 2400 kbar), and impactor radius (0.05 to 5000 km). These results were used to establish the values of the open parameters in the scaling laws of Holsapple and Schmidt (1987). We describe the impact process in terms of four regimes: (1) penetration, (2) inertial, (3) terminal and (4) relaxation. During the penetration regime, the depth of impactor penetration grows linearly for dimensionless times \u03c4 = (Ut/a) <5.1. Here, U is projectile velocity, t is time, and a is projectile radius. In the inertial regime, \u03c4 > 5.1, the crater grows at a slower rate until it is arrested by either strength or gravitational forces. In this regime, the increase of crater depth, d, and diameter, D, normalized by projectile radius is given by d/a = 1.3 (Ut/a)^(0.36) and D/a = 2.0(Ut/a)^(0.36). For strength-dominated craters, growth stops at the end of the inertial regime, which occurs at \u03c4 = 0.33 (Y_(eff)/\u03c1U^2)^(\u22120.78), where Y_(eff) is the effective planetary crustal strength. The effective strength can be reduced from the ambient strength by fracturing and shear band melting (e.g. formation of pseudo-tachylites). In gravity-dominated craters, growth stops when the gravitational forces dominate over the inertial forces, which occurs at \u03c4 = 0.92 (ga/U^2)^(\u22120.61). In the strength and gravity regimes, the maximum depth of penetration is d_p/a = 0.84 (Y/\u03c1 U^2)^(\u22120.28) and d_p/a = 1.2 (ga/U^2)^(\u22120.22), respectively. The transition from simple bowl-shaped craters to complex-shaped craters occurs when gravity starts to dominate over strength in the cratering process. The diameter for this transition to occur is given by D_t = 9.0 Y/\u03c1g, and thus scales as g^(\u22121) for planetary surfaces when strength is not strain-rate dependent. This scaling result agrees with crater-shape data for the terrestrial planets [Chapman and McKinnon, 1986]. We have related some of the calculable, but nonobservable parameters which are of interest (e.g. maximum depth of penetration, depth of excavation, and maximum crater lip height) to the crater diameter. For example, the maximum depth of penetration relative to the maximum crater diameter is 0.6, for strength dominated craters, and 0.28 for gravity dominated craters. These values imply that impactors associated with the large basin impacts penetrated relatively deeply into the planet's surface. This significantly contrasts to earlier hypotheses in which it had been erroneously inferred from structural data that the relative transient crater depth of penetration decreased with increasing diameter. Similarly, the ratio of the maximum depth of excavation relative to the final crater diameter is a constant \u22430.05, for gravity dominated craters, and \u2243 0.09 for strength dominated craters. This result implies that for impact velocities less than 25 km/s, where significant vaporization begins to take place, the excavated material comes from a maximum depth which is less than 0.1 times the crater diameter. In the gravity dominated regime, we find that the apparent final crater diameter is approximately twice the transient crater diameter and that the inner ring diameter is less than the transient crater diameter.",
"doi": "10.1029/93JE01330",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1993-09-25",
"series_number": "E9",
"volume": "98",
"issue": "E9",
"pages": "17011-17028"
},
{
"id": "authors:3q95h-rcb34",
"collection": "authors",
"collection_id": "3q95h-rcb34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-151127738",
"type": "article",
"title": "Thermal expansion of mantle and core materials at very high pressures",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The thermal expansivities (\u03b1) of MgO and high-pressure phases of CaO, CaMgSi_2O_6, and Fe at ultrahigh pressure are obtained by comparing existing shock compression and temperature measurements to 300 K compression curves constructed from ultrasonic elasticity and static compression data. For MgO, \u03b1 can be represented by: \u03b1 = \u03c1_o\u03b3_oC_V(\u03c1_o/\u03c1)^(0.5\u00b10.5)/K_T where \u03b3 is the Gr\u00fcneisen parameter, C_V is the constant volume specific heat, K_T is the isothermal bulk modulus, and \u03c1 is the density. Using this expression, the thermal expansivity of MgO is 28-32\u00d710^(\u22126)K^(\u22121) at the pressure of the top of the lower mantle and 10-16\u00d710^(\u22126)K^(\u22121) at its base (at 2000 K). New data for \u03b1 of \u03b5-Fe, together with an inner core temperature of 6750 K, constrain the density of the inner core to be 5\u00b12% less than the density of \u03b5-Fe, implying the inner core contains a light element.",
"doi": "10.1029/93GL00479",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1993-06-07",
"series_number": "11",
"volume": "20",
"issue": "11",
"pages": "1103-1106"
},
{
"id": "authors:y35bv-1xn42",
"collection": "authors",
"collection_id": "y35bv-1xn42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-085837803",
"type": "article",
"title": "Impact Erosion of Terrestrial Planetary Atmospheres",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The idea that planetary atmospheres can erode as a result of impact, and\nthus lose mass along with solid and molten high velocity ejecta during\naccretional infall of planetesimals follows from such early thoughtful\nworks as that of Arrhenius et al (1974), Benlow & Meadows (1977),\nRingwood (1979), and Cameron (1983). Ahrens et al (1989) describe how\nplanetary impact accretion (and impact erosion) concepts lead naturally,\nfrom the idea that atmospheres form and erode during planetary growth.",
"doi": "10.1146/annurev.ea.21.050193.002521",
"issn": "0084-6597",
"publisher": "Annual Reviews",
"publication": "Annual Review of Earth and Planetary Sciences",
"publication_date": "1993-05",
"volume": "21",
"pages": "525-555"
},
{
"id": "authors:yw98j-mws82",
"collection": "authors",
"collection_id": "yw98j-mws82",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-113853415",
"type": "article",
"title": "Impact-induced tensional failure in rock",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Rubin",
"given_name": "Allan M.",
"clpid": "Rubin-A-M"
}
],
"abstract": "Planar impact experiments were employed to induce dynamic tensile failure in Bedford limestone. Rock discs were impacted with aluminum and polymethyl methacralate flyer plates at velocities of 10 to 25 m/s. This resulted in tensile stresses in the range of \u223c11 to 160 MPa. Tensile stress durations of 0.5 and 1.3 \u03bcs induced microcrack growth which in many experiments were insufficient to cause complete spalling of the samples. Ultrasonic P and S wave velocities of recovered targets were compared to the velocities prior to impact. Velocity reduction, and by inference microcrack production, occurred in samples subjected to stresses above 35 MPa in the 1.3-\u03bcs PMMA experiments and 60 MPa in the 0.5-\u03bcs aluminum experiments. Apparent fracture toughnesses of 2.4 and 2.5 MPa m^(1/2) are computed for the 1.3- and 0.5-\u03bcs experiments. These are a factor of \u223c2 to 6 greater than quasi-static determinations. Three-dimensional impact experiments were conducted on 20 cm-sized blocks of Bedford limestone and San Marcos gabbro. Compressional wave velocity deficits up to 50\u201360% were observed in the vicinity of the crater. These damage levels correspond to O'Connell and Budiansky damage parameters of 0.4 as compared to the unshocked rock. The damage decreases as \u223cr^(\u22121.5) from the crater indicating a dependence on the magnitude and duration of the tensile pulse. Using the observed variation in damage with tensile stress from the one-dimensional experiments, and estimates of the variation of peak dynamic tensile stress and tensile stress duration with distance from an impact on an elastic half-space, the observed dependence of damage with radius in the three-dimensional experiments are theoretically predicted and compare favorably to experimental data.",
"doi": "10.1029/92JE02679",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research E",
"publication_date": "1993-01-25",
"series_number": "E1",
"volume": "98",
"issue": "E1",
"pages": "1185-1203"
},
{
"id": "authors:c7wfm-xkb44",
"collection": "authors",
"collection_id": "c7wfm-xkb44",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-104517295",
"type": "article",
"title": "Deflection and fragmentation of near-Earth asteroids",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Harris",
"given_name": "Alan W.",
"orcid": "0000-0001-7431-2013",
"clpid": "Harris-A-W"
}
],
"abstract": "The collision with Earth of near-Earth asteroids or comet nuclei poses a potential threat to mankind. Objects about 100 m in diameter could be diverted from an Earth-crossing trajectory by the impact of a rocket-launched mass, but for larger bodies nuclear explosions seem to be the only practical means of deflection. Fragmentation of the body by nuclear charges is less efficient or secure.",
"doi": "10.1038/360429a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1992-12-03",
"series_number": "6403",
"volume": "360",
"issue": "6403",
"pages": "429-433"
},
{
"id": "authors:mqdvp-mv898",
"collection": "authors",
"collection_id": "mqdvp-mv898",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-132440425",
"type": "article",
"title": "Dynamic consolidation of superhard materials",
"author": [
{
"family_name": "Yang",
"given_name": "Wenbo",
"clpid": "Yang-Wenbo"
},
{
"family_name": "Bond",
"given_name": "G. M.",
"clpid": "Bond-G-M"
},
{
"family_name": "Tan",
"given_name": "Hua",
"clpid": "Tan-Hua"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Liu",
"given_name": "G.",
"clpid": "Liu-G"
}
],
"abstract": "Shock consolidation experiments were conducted via flyer impact on synthetic diamond (6\u201312 \u03bcm) and cubic boron nitride (c-BN) (4\u20138 \u03bcm) admixed with SiC whisker (SCW), Si_3N_4 whisker (SNW), SiC powder, and Si powder contained in stainless steel capsules under the shock pressure range of 10\u201330 GPa. Scanning electron microscopy and transmission electron microscopy imaging of the samples revealed no plastic deformation or melting of diamond and virtually no deformation of c-BN, whereas the SCW and SNW were extensively melted and recrystallized into bundle-shaped crystallites. In contrast, SiC powder mixed with diamond was also melted but demonstrated equant grain growth. A new method to calculate the shock temperature and melt fraction is formulated on the basis of Milewski's sphere-rod packing data. The new method assigns excess bulk volume to the zone around whiskers and yields a better description of the energy deposition mechanism of the consolidation of powder-whisker systems. Some of the experiments employed Sawaoka's post-shock annealing technique, in which the sample is sandwiched between two layers of a mixture of titanium powder plus carbon. Very well consolidated samples were obtained with post-shock heating under shock pressures of only about 11 GPa. Micro-Vickers hardness values up to 27 GPa were obtained for c-BN plus SCW at a low impact velocity of 1.45 km/s with post-shock heating. This hardness is similar to that obtained at a higher impact velocity of 1.95 km/s without post-shock heating. To understand the post-shock heating process, one-dimensional time dependent temperature profile calculations were conducted for the sample and Ti + C layers. Post-shock heating appears to be very important in the consolidation of powder and whisker admixture. The calculated optimum Ti + C thickness is about 0.8\u20131.7 mm at a porosity of 40% for a typical sample thickness of 2 mm. The heating and cooling time is a few milliseconds. Good compacts with micro-Vickers hardness values up to 28 GPa were also obtained upon shock consolidation of diamond plus Si admixtures.",
"doi": "10.1557/JMR.1992.1501",
"issn": "0884-2914",
"publisher": "Materials Research Society",
"publication": "Journal of Materials Research",
"publication_date": "1992-06",
"series_number": "6",
"volume": "7",
"issue": "6",
"pages": "1501-1518"
},
{
"id": "authors:hamxb-0ya55",
"collection": "authors",
"collection_id": "hamxb-0ya55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-093208227",
"type": "article",
"title": "Sound Velocities at High Pressure and Temperature and Their Geophysical Implications",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Temperature coefficients of compressional and bulk sound velocities at pressures on the order of 100 GPa are obtained from Hugoniot sound velocity measurements for solid Al, W, Cu, Ta, and Mg_2SiO_4. The Hugoniot velocities are compared to third-order finite strain extrapolations of velocities along the principal isentrope using ultrasonically determined coefficients. At low pressure, where thermal effects are minor, good agreement is found between the Hugoniot velocities and finite strain extrapolations. At high pressures, differences in velocities and temperatures are used to constrain temperature coefficients of velocity. For all materials studied except W, the temperature coefficients of velocity at pressures above 1 Mbar are a factor of 2 to 8 smaller in magnitude than zero-pressure values. In shock-melted materials, the Hugoniot sound velocities are close to finite strain velocities calculated from low-pressure properties of the solid phase for Mo, Ta, Pb, Fe, and alkali halides. The temperature coefficient determined for the high-pressure phases of forsterite above 100 GPa (| (\u2202V_P/\u2202T)_P| = 0.1 \u00b1 0.1 m/s/K) is in agreement with estimates based on elastic and thermodynamic properties for the Earth. Our results indicate that |(\u2202VP/\u2202T)_P| is a decreasing function of pressure in contrast to residual sphere studies which suggest |(\u2202V_P/\u2202T)_P| is nearly constant with depth in the Earth. In combination with mineral physics estimates of thermal expansivity at High pressure, it is estimated that (\u2202V_P/\u2202\u03c1)_P = 2 (km/s)/(g/cm^3) for P > 100 GPa, with acceptable values ranging from 0 to 8. This overlaps the range of estimated lower mantle values based on seismic and geodetic data. Tomographic and free oscillation data require large increases in the parameter \u03bd = (\u2202 ln V_S/\u2202 ln VP)_P under lower mantle conditions, relative to laboratory values. Available data for tungsten and aluminum yield \u03bd values along the Hugoniot that are consistent with zero-pressure values for these materials, although uncertainties are \u00b1 50%. Temperature coefficients of velocity at high pressure are used to make improved estimates of the magnitude of thermal heterogeneities sampled by seismic tomography. Long-wavelength compressional velocity anomalies at pressures in the 100\u2013127 GPa range (2271\u20132891 km depth) in the lower mantle correspond to temperature variations of 120 \u00b1 100 K, whereas those in the D\u2033 region are likely to be a factor of 3 to 4 larger.",
"doi": "10.1029/91JB02650",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1992-04-10",
"series_number": "B4",
"volume": "94",
"issue": "B4",
"pages": "4503-4520"
},
{
"id": "authors:z36ke-gmm97",
"collection": "authors",
"collection_id": "z36ke-gmm97",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-093138361",
"type": "article",
"title": "Shock-Induced Transformations in the System NaAISiO_4 -SiO_2 :\n a new Interpretation",
"author": [
{
"family_name": "Sekine",
"given_name": "Toshimori",
"clpid": "Sekine-Toshimori"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New internally consistent interpretations of the phases represented by the high pressure phase shock wave data for an albite-rich rock, Jadeite, and nepheline in the system NaAlSiO_4-SiO_2, are obtained using the results of static high pressure investigations, and the recent discovery of the hollandite phase in a shocked meteorite. We conclude that nepheline transforms directly to the calcium ferrite structure, whereas albite transforms possibly to the hollandite structure. Shock Hugoniots for the other plagioclase and alkali feldspars also indicate that these transform to hollandite structures. The pressure-volume data at high pressure could alternatively represent the compression of an amorphous phase. Moreover, the shock Hugoniot data are expected to reflect the properties of the melt above shock stresses of 60\u201380 GPa. The third order Birch-Murnaghan equation of state parameters are: K_(os) = 275\u00b138 GPa and K\u2032_(os) = 1.6\u00b11.5 for the calcium ferrite type NaAlSiO_4, K_(os) = 186\u00b133 GPA and K\u2032_(os) = 2.6\u00b11.7 for the albite-rich hollandite, K_(os) = 236\u00b145 GPa and K\u2032_(os) = 2.3\u00b12.0 for the orthoclase-rich hollandite, and K_(os) = 190 to 210 GPa and K\u2032_(os) \u2248 2.2 for the anorthite-rich hollandite.",
"doi": "10.1007/BF00199416",
"issn": "0342-1791",
"publisher": "Springer",
"publication": "Physics and Chemistry of Minerals",
"publication_date": "1992-02",
"series_number": "6",
"volume": "18",
"issue": "6",
"pages": "359-364"
},
{
"id": "authors:ze64r-89193",
"collection": "authors",
"collection_id": "ze64r-89193",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-132140835",
"type": "article",
"title": "The fate of organic matter during planetary accretion: preliminary studies of the organic chemistry of experimentally shocked Murchison meteorite",
"author": [
{
"family_name": "Tingle",
"given_name": "Tracy N.",
"clpid": "Tingle-T-N"
},
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Becker",
"given_name": "Christopher H.",
"clpid": "Becker-C-H"
}
],
"abstract": "It is possible that Earth's biologic precursors were delivered by late-impacting asteroids or comets, and it is possible that these objects were a source of Earth's volatile inventory. To understand the behavior of organic matter in carbonaceous meteorites during hypervelocity impact (1\u20132 km s^(\u22121)), three samples of the Murchison (CM2) carbonaceous chondrite were shocked to 19, 20 and 36 GPa and analyzed by very sensitive thermal-desorption photoionization mass spectrometry (SALI). Thermal-desorption (25\u2013800 \u00b0C) SALI mass spectra of unshocked Murchison reveal indigenous aliphatic, aromatic, sulfur and organosulfur compounds. Samples shocked to \u224820 GPa exhibit little or no loss of organic matter relative to the unshocked material. This is consistent with the earlier work of Tyburczyet al. (1986) which showed that incipient devolatilization of Murchison occurs at peak shock pressures near 20 GPa. The small amount of organic matter lost appears to have occurred by volatilization of elemental sulfur, amines and aliphatic compounds. In the sample shocked to 36 GPa, approximately 70% of the organic matter was volatilized as a result of impact. The residual organic matter desorbed at somewhat higher temperatures and displayed a different chemical signature. In particular, the shocked material has a lower alkene/alkane ratio than that of the starting material. The preliminary data suggest that it is unlikely that the indigenous organic matter in carbonaceous chondrite-like planetesimals could have survived impact on the Earth in the later stages of Earth's accretion. However, chemical reactions that produce organic compounds with greater thermal stabilities may occur during impact or subsequent to impact by condensation of the impact-produced vapor plume.",
"doi": "10.1007/BF01808309",
"issn": "0169-6149",
"publisher": "Springer",
"publication": "Origins of life and evolution of the biosphere",
"publication_date": "1992",
"series_number": "5-6",
"volume": "21",
"issue": "5-6",
"pages": "385-397"
},
{
"id": "authors:6c6qp-e1173",
"collection": "authors",
"collection_id": "6c6qp-e1173",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141027-101823852",
"type": "article",
"title": "Angular momentum transfer in low velocity oblique impacts: Implications for asteroids",
"author": [
{
"family_name": "Yanagisawa",
"given_name": "Masahisa",
"clpid": "Yanagisawa-Masahisa"
},
{
"family_name": "Eluszkiewicz",
"given_name": "Janusz",
"clpid": "Eluszkiewicz-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The efficiency of angular momentum transfer \u03b6 in low velocity oblique impacts was studied experimentally. \u03b6 is defined as the fraction of incident angular momentum transferred to the rotation of the target. Plaster, mortar, cement, and one granite target were studied. Lead and aluminum projectiles were used. Only cratering impacts were considered. \u03b6 was found to decrease with increasing incidence angle \u03c6 (relative to the surface normal). For example, for impacts into cylindrical mortar targets a least-squares fit of the form \u03b6 = A(cos \u03c6)\u03b2 with A = 0.9 and \u03b2 = 1.7 was found to match the data points reasonably well. In addition, \u03b2 decreased from 1.9 to 1.4 as the kinetic energy density \u03f5 (= kinetic energy of the projectile/projectile volume) increased from 0.5 to 1.8 \u00d7 10^9 J m^(\u22123). This suggests that more energetic impacts transfer angular momentum more efficiently. \u03b6 decreased as the indentation hardness H of the target increased: at \u03c6 \u223c 35\u00b0, \u03b6 = 0.07 for granite (H = 850 kg mm^(\u22122) and \u03b6 = 0.7 for plaster (H = 7.5 kg mm^(\u22122)). Cement and mortar (H = 76 kg mm^(\u22122)) yielded intermediate values, although the values for cement (\u03b6 \u223c 0.3) were appreciably lower than for mortar (\u03b6 \u223c 0.6). In all cases where the velocity of the ricochetted projectile was determined, the fraction of angular momentum carried away by ejecta was found to be less than 30%. Finally, the results were only weakly dependent on the material of the projectile.",
"doi": "10.1016/0019-1035(91)90227-K",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1991-12",
"series_number": "2",
"volume": "94",
"issue": "2",
"pages": "272-282"
},
{
"id": "authors:9n72f-qn374",
"collection": "authors",
"collection_id": "9n72f-qn374",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-164402827",
"type": "article",
"title": "Shock wave equation of state of muscovite",
"author": [
{
"family_name": "Sekine",
"given_name": "Toshimori",
"clpid": "Sekine-Toshimori"
},
{
"family_name": "Rubin",
"given_name": "Allan M.",
"clpid": "Rubin-A-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock wave data to provide an equation of state of muscovite (initial density: 2.835 g/cm^3) were determined up to a pressure of 141 GPa. The shock velocity (Us) versus particle velocity (Up) data are fit with a single linear relationship: U_s=4.62(\u00b10.12) +1.27(\u00b10.04)U_p (km/s). Third-order Birch-Murnaghan equation of state parameters (isentropic bulk modulus and isentropic pressure derivative of bulk modulus) are K_(os)=52\u00b14GPa and K'_(os)=3.2\u00b10.3. The pressure-temperature relation along the Hugoniot suggests that muscovite may dehydrate to KAlSi_3O_8 (hollandite), corundum, and water, with a small volume change, above 80 GPa. Thermodynamic calculations of the equilibrium pressure for the dehydration yields a significantly lower value. Observed unloading paths from shock pressures up to about 80 GPa are steeper in a density-pressure plane than the Hugoniot and become shallower with increasing shock pressure above that pressure. The changing slope may indicate that devolatilization occurs during unloading above 80 GPa. The present equation of state data for muscovite are compared with results of previously reported recovery experiments.",
"doi": "10.1029/91JB02253",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1991-11-10",
"series_number": "B12",
"volume": "96",
"issue": "B12",
"pages": "19675-19680"
},
{
"id": "authors:8y0sb-z9c53",
"collection": "authors",
"collection_id": "8y0sb-z9c53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-163719837",
"type": "article",
"title": "Shock wave equation of state of serpentine to 150 GPa: Implications for the occurrence of water in the Earth's lower mantle",
"author": [
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
}
],
"abstract": "The shock equation of state of serpentine has been determined to 150 GPa. Four distinct regions occur along the Hugoniot: a low-pressure phase, a mixed phase region, a high-pressure phase, and a very high pressure phase. The low-pressure phase (LPP) exists under shock pressures to about 40 GPa. This material exhibits shock properties that are partially consistent with those of low pressure serpentine, but steep release paths and a low value of K\u2032 = 2.77 suggest transformation to another, possibly amorphous, assemblage. Thermodynamic calculations indicate that under equilibrium conditions, serpentine would decompose to oxides plus water at conditions below 10 GPa along the Hugoniot. A mixed phase region begins at 40 GPa with complete transition to a high-pressure phase occurring by about 55 GPa. The high-pressure phase (HPP) occurs at shock pressures between 55 GPa and 125 GPa. Model Hugoniots based on perovskite plus periclase plus water and brucite plus periclase plus stishovite reproduce the serpentine HPP Hugoniot within experimental error, so definitive identification of the HPP as a distinct hydrous mineral phase or as a free water containing mixture is not possible. Above 125 GPa a transition to a very compressible phase, possibly a hydrous partial melt, occurs. The serpentine HPP Hugoniot is about 15\u201320 % less dense than the Earth's lower mantle. Models of the lower mantle based on shock equations of state for olivine, pyroxene, and serpentine indicate that for an atomic Mg/(Mg+Fe) ratio of 0.80, the presence of 2 wt % H_2O is consistent with seismically determined lower mantle density estimates. Greater amounts of H_2O can be accommodated if accompanied by an increase in Fe content. Calculated Hugoniot sound speeds of the serpentine HPP, although poorly constrained, are broadly consistent with lower mantle sound speeds. Thus the high-pressure density and sound speed of an H_2O-rich magnesium silicate determined from shock equation of state experiments indicate that the observed seismic properties of the lower mantle allow the existence of several weight percent of water in the lower mantle.",
"doi": "10.1029/91JB01573",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1991-10-10",
"series_number": "B11",
"volume": "96",
"issue": "B11",
"pages": "18011-18027"
},
{
"id": "authors:0mzfg-vq949",
"collection": "authors",
"collection_id": "0mzfg-vq949",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MILrmp91",
"type": "article",
"title": "Shock-wave viscosity measurement",
"author": [
{
"family_name": "Miller",
"given_name": "Gregory H.",
"clpid": "Miller-G-H"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The problem of measuring the viscosity of fluids under shock-loading conditions is discussed. The authors examine in detail the method of Sakharov et al. (1965) and Zaidel' (1967) for measuring shear viscosity from the decay of perturbations on a corrugated shock front. The relevance of initial conditions, finite shock amplitude, bulk viscosity, and the sensitivity of the measurements to the shock boundary conditions are discussed. The validity of the viscous perturbation approach is examined by numerically solving the second-order Navier-Stokes equations. These numerical experiments indicate that shock instabilities may occur even when the Kontorovich-D'yakov stability criteria are satisfied. The corrugated shock front induces mixing of the shocked sample. This mixing is particularly vigorous in viscous materials and may be responsible for the rapid rate of some shock-induced chemical reactions. The experimental results for water at 15 GPa are discussed, and several possibilities are considered to explain why the viscosity obtained by these experiments is so different from those obtained by other methods. Two possible reasons are favored: (1) the analytic method may be inappropriate because it ignores possible complications at the onset of the shock perturbations, and (2) the large effective viscosity determined by this method may reflect the existence of ice VII on the Rayleigh path of the Hugoniot. The latter interpretation reconciles the experimental results with estimates and measurements obtained by other means and is consistent with pressure-volume-temperature Hugoniot data and the phase diagram of H2O.",
"doi": "10.1103/RevModPhys.63.919",
"issn": "0034-6861",
"publisher": "Reviews of Modern Physics",
"publication": "Reviews of Modern Physics",
"publication_date": "1991-10-01",
"series_number": "4",
"volume": "63",
"issue": "4",
"pages": "919-948"
},
{
"id": "authors:kpngv-yws77",
"collection": "authors",
"collection_id": "kpngv-yws77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-162846493",
"type": "article",
"title": "The shock wave equation of state of brucite Mg(OH)_2",
"author": [
{
"family_name": "Duffy",
"given_name": "Thomas S.",
"clpid": "Duffy-T-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
}
],
"abstract": "New equation of state (EOS) data for brucite Mg(OH)_2 shocked between 12 and 60 GPa are reported. When combined with earlier data of Simakov et al. (1974), it is found that brucite EOS data between 12 and 97 GPa can be fit with a single linear U_s-u_p relationship: U_s = 4.76(0.11) + 1.35(0.05) u_p. The third order Birch-Murnaghan equation parameters are: K_(os) = 51 \u00b1 4 GPa and K\u2032_(os) = 5.0 \u00b1 0.4. The lack of a U_s-u_p discontinuity indicates that no phase transformation with a significant volume change occurs to at least 97 GPa. However, thermodynamic and theoretical Hugoniot calculations suggest brucite may dehydrate with only a small volume change. A lower bound for this dehydration pressure under shock conditions is inferred to be 26 GPa. We report the first partial release states measured for this material. The data are in quantitative agreement with earlier shock recovery experiments (Lange and Ahrens, 1984). Volatilization upon release begins at pressures as low as 12 GPa, much less than predicted by the shock entropy method. Calculated phase boundaries using the present EOS data are consistent with experimental data and indicate that brucite is unlikely to be stable under lower mantle conditions. However, brucite data, in conjunction with data for silicates and oxides, can be used to infer the effect of H_2O on lower mantle properties. At high pressure, bulk sound velocities calculated for MgO and Mg(OH)_2 are very similar, indicating that the presence of hydrous assemblages in the lower mantle may not produce anomalous bulk seismic velocities. Comparison of densities in brucite and other high-pressure phases under mantle conditions indicates that the water content of the lower mantle is between 0 and 3 wt %.",
"doi": "10.1029/91JB00987",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1991-08-10",
"series_number": "B9",
"volume": "96",
"issue": "B9",
"pages": "14319-14330"
},
{
"id": "authors:bzx33-6wp59",
"collection": "authors",
"collection_id": "bzx33-6wp59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120823-134021457",
"type": "article",
"title": "The Equation of State of a Molten Komatiite. 2. Application to Komatiite Petrogenesis and the Hadean Mantle",
"author": [
{
"family_name": "Miller",
"given_name": "Gregory H.",
"clpid": "Miller-G-H"
},
{
"family_name": "Stolper",
"given_name": "Edward M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New experimental data for the equation of state of a komatiitic liquid were used to model adiabatic melting in a peridotitic mantle. If komatiites are formed by >30% partial melting of a peridotitic mantle, then komatiites generated by adiabatic melting come from source regions that began their unmelted ascent in the lower transition zone (\u2248500\u2013670 km) or the lower mantle (>670 km). The great depth of incipient melting implied by this model suggests that komatiitic liquids may form in a pressure regime where they are denser than their coexisting crystals, possibly the bulk mantle. Although komatiitic magmas are thought to separate from residual crystals in the mantle at a temperature \u2248200\u00b0C greater than modem mid-ocean ridge basalts (MORBs), their ultimate sources are predicted to be diapirs that, if adiabatically decompressed from initially solid mantle, were more than 700\u00b0C hotter than the sources of MORBs and were derived from great depth. We also studied the evolution of an initially molten mantle, i.e., a magma ocean. Our model considers the thermal structure of the magma ocean, density constraints on crystal segregation, and approximate phase relationships for a nominally chondritic mantle. Crystallization will begin at the core-mantle boundary. Perovskite buoyancy at >70 GPa may lead to a compositionally stratified lower mantle with iron-enriched magnesiow\u00fcstite content increasing with depth. Large convective velocities in the magma ocean would prohibit crystal-liquid fractionation by settling or flotation until quiescent boundary layers form. Such boundary layers could form when the crystal content of the magma reaches a critical value (near 44 vol %) and, in the late stages of crystallization, around unmelted blocks of foundered protocrust. Matrix compaction and diapirism could also lead to fractionation effects. The upper mantle could be depleted or enriched in perovskite components relative to the bulk mantle. Olivine neutral buoyancy may lead to the formation of a dunite septum in the upper mantle, partitioning the ocean into upper and lower reservoirs, but this septum must be permeable.",
"doi": "10.1029/91JB01203",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1991-07-10",
"series_number": "B7",
"volume": "96",
"issue": "B7",
"pages": "11,849-11,864"
},
{
"id": "authors:m5hzs-7d909",
"collection": "authors",
"collection_id": "m5hzs-7d909",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120823-134339056",
"type": "article",
"title": "The Equation of State of a Molten Komatiite. 1. Shock Wave Compression to 36 GPa",
"author": [
{
"family_name": "Miller",
"given_name": "Gregory H.",
"clpid": "Miller-G-H"
},
{
"family_name": "Stolper",
"given_name": "Edward M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The equation of state (EOS) of an initially molten (1550\u00b0C) komatiite (27 wt % MgO) was determined in the 5\u201336 GPa pressure range via shock wave compression. Shock wave velocity U_s and particle velocity U_p (kilometers/second) follow the linear relationship U_s = 3.13(\u00b10.03) + 1.47(\u00b10.03) U_p . Based on a calculated density at 1550\u00b0C, 0 bar of 2.745\u00b10.005 g/cm^3, this U_s -U_p relationship gives the isentropic bulk modulus K_s = 27.0 \u00b1 0.6 GPa, and its first and second isentropic pressure derivatives, K\u2032_s = 4.9 \u00b10.1 and K\u2033_s = \u22120.109 \u00b1 0.003 GPa^(\u22121). The calculated liquidus compression curve agrees within error with the static compression results of Agee and Walker (1988) to 6 GPa but is less dense than their extrapolated values at higher pressures. We determine that olivine (FO_(94)) will be neutrally buoyant in komatiitic melt of the composition that we studied near 8.2 GPa. Clinopyroxene would also be neutrally buoyant near this pressure. Liquidus garnet-majorite may be less dense than this komatiitic liquid in the 20\u201324 GPa interval; however, pyropic-garnet and perovskite phases are denser than this komatiitic liquid in their respective liquidus pressure intervals to 36 GPa. Liquidus perovskite may be neutrally buoyant near 70 GPa. At 40 GPa, the density of shock-compressed molten komatiite would be approximately equal to the calculated density of an equivalent mixture of dense solid oxide components. This observation supports the model of Rigden et al. (1989) for compressibilities of liquid oxide components. Using their theoretical EOS for liquid forsterite and fayalite, we calculate the densities of a spectrum of melts from basaltic through peridotitic that are related to the experimentally studied komatiitic liquid by addition or subtraction of olivine. At low pressure, olivine fractionation lowers the density of basic magmas, but above 13\u201314 GPa this trend is reversed. All of these basic to ultrabasic liquids are predicted to have similar densities at 13\u201314 GPa, and this density is approximately equal to the density of the bulk (preliminary reference Earth model) mantle in this pressure range. This suggests that melts derived from a peridotitic mantle may be inhibited from ascending from depths greater than 400 km.",
"doi": "10.1029/91JB01204",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1991-07-10",
"series_number": "B7",
"volume": "96",
"issue": "B7",
"pages": "11831-11848"
},
{
"id": "authors:ptnw1-n9g14",
"collection": "authors",
"collection_id": "ptnw1-n9g14",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-110741314",
"type": "article",
"title": "Solution and shock-induced exsolution of argon in vitreous carbon",
"author": [
{
"family_name": "Gazis",
"given_name": "Carey",
"clpid": "Gaziz-C-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Carbon has been shown by several researchers to be the main noble-gas carrier in chondritic meteorites. To add to our knowledge of noble gas solution and exsolution in carbonaceous material, experiments were performed on vitreous carbon, a type of amorphous carbon. Ar-rich vitreous carbon samples were prepared under vapor-saturated conditions using argon as the pressurizing medium. Solubility data were obtained for temperatures of 773 to 973K and pressures of 250 to 1500 bars. Up to 7 wt.% Ar was dissolved in the carbon. The solubility data were compared to a thermodynamic model of argon atoms dissolving into a fixed population of \"holes\" in the carbon. Two variations of the model yielded estimates of the enthalpy of solution of Ar in vitreous carbon (\u0394H\u00b0_(Ar)) of \u2248 \u22124700 cal/mole.\n\nPreliminary shock experiments showed that 28% of the total argon was released by driving 4 GPa^* shocks into the argon-rich carbon. It was demonstrated that shock-induced argon loss is not simply caused by the impact-induced diminution of grain size. The present value of shock pressure required for partial impact devolatilization of Ar from carbon is below the range (5\u201330 GPa) that H_2O is released from phyllosilicates.",
"doi": "10.1016/0012-821X(91)90214-3",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1991-06",
"series_number": "2-4",
"volume": "104",
"issue": "2-4",
"pages": "337-349"
},
{
"id": "authors:9h9y1-6a616",
"collection": "authors",
"collection_id": "9h9y1-6a616",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-150745567",
"type": "article",
"title": "Displacements from relief of In situ stress by a cylindrical hole",
"author": [
{
"family_name": "Smither",
"given_name": "C. L.",
"clpid": "Smither-C-L"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The holographic in situ stressmeter is an instrument which records the displacement field on a borehole wall induced by the drilling of a small, stress-relieving sidehole. The data is in the form of double-exposure holograms; the patterns of interference fringes on these holograms may be analyzed to yield the state of stress at a location on the borehole wall. A set of at least three of these holograms, properly spaced around the borehole at a given depth, can in turn be analyzed to reveal the far-field state of stress. Previous work with this instrument has modelled the borehole wall as a thin flat elastic plate through which a hole is drilled. This model, while adequate, was not capable of fitting the observed fringe data within two radii of the sidehole in every case. Several previous holograms were obtained, generally from locations in the borehole which had low levels of borehole wall stress, which could not be modelled satisfactorily. This work improves the model by using the analytic approach of Youngdahl and Sternberg for the displacements on the free surface of a half space with a through-going hole subjected to a plane state of stress at infinity. This model relaxes the assumption inherent in the thin plate model that the body is in a state of plane stress everywhere in its interior. To test the effectiveness of this model, we re-analyzed holograms obtained from field deployment of the holographic in situ stressmeter. The new analysis gives approximately the same result as the old model; however, the errors corresponding to this solution are significantly reduced. We believe that the Youngdahl and Sternberg model may also be applied in other situations. The in situ state of stress of a rock wall could be determined by drilling a stress-relieving hole, measuring the resulting displacements or strains, and analyzing the data with the technique described in this paper.",
"doi": "10.1016/0148-9062(91)92165-U",
"issn": "0148-9062",
"publisher": "Elsevier",
"publication": "International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts",
"publication_date": "1991-05",
"series_number": "2-3",
"volume": "28",
"issue": "2-3",
"pages": "175-186"
},
{
"id": "authors:7dnex-6f010",
"collection": "authors",
"collection_id": "7dnex-6f010",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-100048909",
"type": "article",
"title": "Ablation of silicate particles in high-speed continuum and transition flow with application to the collection of interplanetary dust particles",
"author": [
{
"family_name": "Rulison",
"given_name": "Aaron J.",
"clpid": "Rulison-A-J"
},
{
"family_name": "Flagan",
"given_name": "Richard C.",
"orcid": "0000-0001-5690-770X",
"clpid": "Flagan-R-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Miller",
"given_name": "Wayne F.",
"clpid": "Miller-W-F"
}
],
"abstract": "A model for the ablation and deceleration of spheres in continuum and slip flow is presented. Experiments\nwere conducted in which initially spherical 7.1 micron diameter soda-lime glass particles were launched from\nvacuum at ~4500 m s^(-1) through a 0.5 mil (13 micron) plastic film into a capture chamber containing xenon\nat 0.1 and 0.2 atm and 295 K. Samples of ablated particles were collected and inspected using scanning electron\nmicroscopy (SEM). It was found that the ratio of the ablated particle radius (R_f) to the initial radius (R_0)\ndepends on the gas pressure such that at 0.1 atm, R_f/R_0 = 0.67 \u00b1 0.08, and at 0.2 atm, R_f/R_0 = 0.88 \u00b1 0.08.\nThe model agrees with these results if the heat of ablation Q is set to 1.5 \u00b1 0.2 MJ kg^(-1). This value of Q\napproximately corresponds to the energy needed to raise the particle temperature from 295 to 1300 K, the\nworking point of soda-lime glass. This indicates that the mechanism of ablation is melting and blowing of\nmaterial from the particle's surface.",
"doi": "10.1086/169905",
"issn": "0004-637X",
"publisher": "American Astronomical Society",
"publication": "Astrophysical Journal",
"publication_date": "1991-04-10",
"series_number": "1",
"volume": "371",
"issue": "1",
"pages": "432-442"
},
{
"id": "authors:dtfvf-zcf05",
"collection": "authors",
"collection_id": "dtfvf-zcf05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-090958603",
"type": "article",
"title": "Dynamic tensile-failure-induced velocity deficits in rock",
"author": [
{
"family_name": "Rubin",
"given_name": "Allan M.",
"clpid": "Rubin-A-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Planar impact experiments were employed to induce dynamic tensile failure in Bedford limestone. Rock discs were impacted with aluminum and polymethyl methacralate (PMMA) flyer plates at velocities of 10 to 25 m/s. Tensile stress magnitudes and duration were chosen so as to induce a range of microcrack growth insufficient to cause complete spalling of the samples. Ultrasonic P- and S-wave velocities of recovered targets were compared to the velocities prior to impact. Velocity reduction, and by inference microcrack production, occurred in samples subjected to stresses above 35 MPa in the 1.3 \u03bcs PMMA experiments and 60 MPa in the 0.5 \u03bcs aluminum experiments. Using a simple model for the time-dependent stress-intensity factor at the tips of existing flaws, apparent fracture toughnesses of 2.4 and 2.5 MPa m^(\u00bd) are computed for the 1.3 and 0.5 \u03bcs experiments. These are a factor of \u223c 2 to 3 greater than quasi-static values. The greater dynamic fracture toughness observed may result from microcrack interaction during tensile failure. Data for water-saturated and dry targets are indistinguishable.",
"doi": "10.1029/91GL00214",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1991-02",
"series_number": "2",
"volume": "18",
"issue": "2",
"pages": "219-222"
},
{
"id": "authors:dkyr0-e1z11",
"collection": "authors",
"collection_id": "dkyr0-e1z11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-162056912",
"type": "article",
"title": "Shock temperature measurements in metals: New results for an Fe alloy",
"author": [
{
"family_name": "Bass",
"given_name": "Jay D.",
"clpid": "Bass-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Abelson",
"given_name": "John R.",
"clpid": "Abelson-J-R"
},
{
"family_name": "Hua",
"given_name": "Tan",
"clpid": "Hua-T"
}
],
"abstract": "The temperature of a Fe-Cr-Ni alloy (304 stainless steel) has been measured during shock compression using a high-speed radiometric technique. Experiments were performed on high-quality thick films deposited on sapphire and LiF windows. The samples had no observable porosity or defects and closely meet the ideal criteria for shock temperature measurements. Data obtained with both Al_2O_3 and LiF windows are internally consistent, indicating that they remain transparent to high pressures and are thus suitable windows for shock temperature measurements. Our data yield stainless steel melting temperatures ranging from 4570\u00b1310K at 138 GPa to 5710\u00b1340 K at 215 GPa, and additionally provide bounds on the initial Hugoniot temperatures of the sample between 5600\u00b1340 K at 234 GPa (near the solidus) and 6580\u00b1440 K at 283 (in the liquid field). Taken together, these data define a smooth curve for melting of the alloy up to 271 GPa and 5860 K, which should represent a point on the Iiquidus. Melting along the Hugoniot begins at approximately 234 GPa and 5600 K, as compared with 242 GPa and 6400 K for pure Fe. At the pressure of the inner core-outer core boundary, the melting point of 304 stainless steel is lower than that of pure Fe by \u2248 1450 K, as compared with only 110 K at 1 atm. These results demonstrate that upon alloying with Ni and Cr the melting point depression of Fe and thus material likely to comprise the inner core increases with increasing pressure.",
"doi": "10.1029/JB095iB13p21767",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1990-12-10",
"series_number": "B13",
"volume": "95",
"issue": "B13",
"pages": "21767-21776"
},
{
"id": "authors:j77yw-04q75",
"collection": "authors",
"collection_id": "j77yw-04q75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-150539202",
"type": "article",
"title": "Studies of the Earth's Deep Interior: Goals and Trends",
"author": [
{
"family_name": "Lay",
"given_name": "Thorne",
"orcid": "0000-0003-2360-4213",
"clpid": "Lay-T"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Olson",
"given_name": "Peter",
"clpid": "Olson-P"
},
{
"family_name": "Smyth",
"given_name": "Joseph",
"clpid": "Smyth-J-R"
},
{
"family_name": "Loper",
"given_name": "David",
"clpid": "Loper-D"
}
],
"abstract": "The deep interior of planet Earth has long fascinated philosophers, scientists and fantasy writers, yet it remains inaccessible to direct scrutiny and thus largely enigmatic. Romantic notions about the interior are provocative, with crystal\u2010filled chambers and pitchfork\u2010bearing devils. However, the more scientifically based visions are just as alluring.\nProfound opportunities for understanding the mysteries of the inner Earth lie within reach. But it will take a concerted interdisciplinary research effort to model the total dynamic Earth system.",
"doi": "10.1063/1.881240",
"issn": "0031-9228",
"publisher": "American Institute of Physics",
"publication": "Physics Today",
"publication_date": "1990-10",
"series_number": "10",
"volume": "43",
"issue": "10",
"pages": "44-52"
},
{
"id": "authors:6vy3j-ymw05",
"collection": "authors",
"collection_id": "6vy3j-ymw05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-081532814",
"type": "article",
"title": "Impact Spallation Experiments: Fracture Patterns and Spall Velocities",
"author": [
{
"family_name": "Polanskey",
"given_name": "Carol A.",
"clpid": "Polanskey-C-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Spall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4-g lead bullet to a 0.04-g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small-scale experiments is considered in detail. The targets were also bisected to observe the pattern of internal fractures. The series of fractures was observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical \"near-surface zone\" predicted by the spallation model. According to the model, between this boundary and the free surface, the target material is expected to have received reduced levels of compressive stress as compared to the more highly shocked region below.",
"doi": "10.1016/0019-1035(90)90025-5",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1990-09",
"series_number": "1",
"volume": "87",
"issue": "1",
"pages": "140-155"
},
{
"id": "authors:pecw5-t7b82",
"collection": "authors",
"collection_id": "pecw5-t7b82",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141024-124437010",
"type": "article",
"title": "Shock-induced temperatures of CaMgSi_2O_6",
"author": [
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Optical radiation from CaMgSi_2O_6 crystal (diopside) shock-compressed to 145\u2013170 GPa yields shock-induced temperatures of 3500\u20134800 K, while that from CaMgSi_2O_6 glass, with a density 86% that of CaMgSi_2O_6 crystal, shock-compressed to 96\u201398 GPa, yields shock-induced temperatures of 3700\u20133900 K. The observed radiation histories of of the targets containing CaMgSi_2O_6 crystal and glass imply that the shock-compressed states of both are highly absorptive, with effective absorption coefficients of \u2265 500\u20131000 m^(\u22121). Calculated shock-compressed states for both CaMgSi_2O_6 crystal and glass, when compared to experimental results, imply the presence of a high-pressure phase (HPP) along both Hugoniots over the respective pressure ranges. The CaMgSi_2O_6 crystal experimental results are consistent with a standard temperature and pressure (STP) HPP mass density of 4100\u00b1100 kg/m^3, a STP HPP bulk modulus of 250\u00b150 GPa, and a difference in specific internal energy (SIE) between (metastable) HPP and the CaMgSi_2O_6 crystal states at STP (\"energy of transition\") of 2.2\u00b10.5 MJ/kg. The CaMgSi_2O_6 glass results are \"best-fit\" by the same (median) values of all three parameters; except for the STP SIE difference between the CaMgSi_2O_6 glass and HPP states, however, they are less sensitive to parameter variations than the crystal results because they are at lower pressure. All these model constraints are insensitive to the range of values (1\u20132) assumed for the STP HPP Gruneisen's parameter. The relatively high value of the STP SIE difference between HPP and CaMgSi_2O_6 crystal or glass most likely implies that CaMgSi_2O_6 glass and crystal experience both solid-solid and solid-liquid phase transformations along their respective Hugoniots below 96 and 144 GPa, respectively. The HPP CaMgSi_2O_6 Hugoniot constrained by the crystal experimental results lies between 2500\u20133000 K in the pressure range (110\u2013135 GPa) of the lowermost mantle (D\u2032\u2032)] our results imply that CaMgSi_2O_6 is at least partly molten at these pressures and temperatures. Seismically constrained compositional models for this region of Earth's lower mantle suggest that it could contain a significant amount of Ca (25\u201330 wt % CaO). If so, our results imply that the temperature of the D\u2032\u2032 region must be below \u2248 3000 K, since the finite S-wave velocity of the D\u2032\u2032 region implies that it must be (at least at seismic frequencies) predominantly solid.",
"doi": "10.1029/JB095iB05p06943",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1990-05-10",
"series_number": "B5",
"volume": "95",
"issue": "B5",
"pages": "6943-6953"
},
{
"id": "authors:k06qd-4gn63",
"collection": "authors",
"collection_id": "k06qd-4gn63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130820-110805297",
"type": "article",
"title": "Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: Implications for planetary accretion",
"author": [
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Krishnamurthy",
"given_name": "R. V.",
"clpid": "Krishnamurthy-R-V"
},
{
"family_name": "Epstein",
"given_name": "Samuel",
"clpid": "Epstein-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The degree of impact-induced devolatilization of nonporous serpentine, porous serpentine, and deuterium-enriched serpentine was investigated using two independent experimental methods, the gas recovery method and the solid recovery method, yielding consistent results. The gas recovery method enables determination of the chemical and hydrogen isotopic composition of the recovered gases. Experiments on deuterium-enriched serpentine unambiguously identify the samples as the source of the recovered gases, as opposed to other possible contaminants. For shock pressures near incipient devolatilization (P_(initial) = 5.0 GPa), the hydrogen isotopic composition of the evolved gas is similar to that of the starting material. For higher shock pressures the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H_2O to H_2 in gases recovered at higher shock pressures, probably caused by reaction of evolved H_2O with the metal gas recovery fixture. The hydrogen isotopic fractionation between the evolved gas and the residual solid indicates nonequilibrium, kinetic control of gas-solid isotopic ratios. In contrast, gaseous H_2O-H_2 isotopic fractionation suggests high temperature (800\u20131300 K) isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition (i.e., shear bands). Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can affect the distribution of hydrogen isotopes of planetary bodies during accretion, leaving the interiors enriched in deuterium. The significance of this process for planetary development depends on the models used for extrapolation of the observed isotopic fractionation to devolatilizations greater than those investigated experimentally and assumptions about timing and rates of protoatmosphere loss, frequency of multiple impacts, and rates of gas-solid or gas-melt isotopic re-equilibration. A simple model indicates that substantial planetary interior enrichments of D/H relative to that of the incident material can result from impact-induced hydrogen fractionation during accretion.",
"doi": "10.1016/0012-821X(90)90063-4",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1990-05",
"series_number": "2",
"volume": "98",
"issue": "2",
"pages": "245-260"
},
{
"id": "authors:8bb6k-ta614",
"collection": "authors",
"collection_id": "8bb6k-ta614",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:TANjap90",
"type": "article",
"title": "Shock induced polymorphic transition in quartz, carbon, and boron nitride",
"author": [
{
"family_name": "Tan",
"given_name": "Hua",
"clpid": "Tan-Hua"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A theory describing the polymorphism induced by shock waves in silicates, oxides, sulfides, and many inorganic solids is presented. Shock wave experiments conducted on these and other materials indicate that many transformations to high-pressure phases are triggered via the production of shear bands and, in some cases, formation of high-density amorphous phases. Shock states in the mixed phase regimes, of quartz, carbon, and boron nitride, are quantitatively described in terms of the properties of both their low- and high-pressure phases. Good agreement between the calculated results and measured Hugoniot data in the mixed phase regime is obtained. By fitting the pressures of the onset of the phase transition from graphite to diamond, and associating its triggering with crossing the extension of the metastable melting line of graphite, we obtain a similar shaped curve to the metastable melting line obtained by Bundy [J. Geophys. Res. 85, 6930 (1980)]. Similarly, the transition from quartz to stishovite is associated with the metastable melting line of coesite. The present theory, when fit to the onset of the mixed phase regime of graphitelike boron nitride transforming to cubic boron nitride Hugoniot, predicts the standard entropy for cubic BN to be 0.4\u20130.5 J/g K.",
"doi": "10.1063/1.345282",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1990-01-01",
"series_number": "1",
"volume": "67",
"issue": "1",
"pages": "217-224"
},
{
"id": "authors:4gx1p-1xc15",
"collection": "authors",
"collection_id": "4gx1p-1xc15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BOSrsi89",
"type": "article",
"title": "A sensitive time-resolved radiation pyrometer for shock-temperature measurements above 1500 K",
"author": [
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "An optical system has been developed which can determine time-resolved temperatures in shocked materials by measuring the spectral radiance of light emitted from shocked solid samples in the visible and near-infrared wavelength range (0.5\u20131.0 \u00b5m). It can measure temperatures as low as 1500 K and has been successfully used to observe shock-induced chemical reactions in powder samples. The high sensitivity of this radiation pyrometer can be attributed to the large angular aperture (0.06 sr), the large bandwidth per channel (up to 0.1 \u00b5m), the large photodiode detection areas (1.0 cm^2), and the small number of calibrated channels (4) among which light is divided. Improved calibration techniques, as well as the layout of the instrument, eliminate certain sources of error encountered in previous shock-temperature experiments. Errors in the measured spectral radiance were reduced by: (1) recalibration before every experiment to account for changes in optical components; (2) direct calibration of voltage recorded at each digitizer to prevent transfer error by an intermediate step; (3) use of a spectral irradiance calibration lamp to exclude errors due to spatial inhomogeneities associated with spectral radiance sources; and (4) obtaining a large spatial average of light at each wavelength from the same portion of the sample to eliminate errors from possible inhomogeneities in the sample. The magnitude each of these errors could previously contribute was 1%\u20132% of the total signal. Absolute temperature uncertainties, determined from the standard deviation of the measured spectral radiances from the least-squares-fit values, are typically about 5%. Emissivities are poorly constrained by spectral radiance data because of a weak functional dependence, and uncertainties can easily exceed 50% for temperatures of around 2000 K.",
"doi": "10.1063/1.1140480",
"issn": "0034-6748",
"publisher": "Review of Scientific Instruments",
"publication": "Review of Scientific Instruments",
"publication_date": "1989-12",
"series_number": "12",
"volume": "60",
"issue": "12",
"pages": "3711-3716"
},
{
"id": "authors:arckp-qhk54",
"collection": "authors",
"collection_id": "arckp-qhk54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-113046471",
"type": "article",
"title": "Water storage in the mantle",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The origins of the oceans and Earth's volatile atmosphere are major unsolved problems in earth sciences. The recent study by Finger et al. of the crystal chemistry of a water-bearing mineral phase, cryptically named phase B and grown under conditions equivalent to a depth in the Earth of 360 km, dramatically demonstrates that several times the Earth's visible water budget could be stored in the mantle.",
"doi": "10.1038/342122a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1989-11-09",
"series_number": "6246",
"volume": "342",
"issue": "6246",
"pages": "122-123"
},
{
"id": "authors:545c8-enc61",
"collection": "authors",
"collection_id": "545c8-enc61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-083454168",
"type": "article",
"title": "Optical radiation from shock-compressed materials and interfaces",
"author": [
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Bass",
"given_name": "Jay D.",
"clpid": "Bass-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Recent observations of shock-induced radiation from oxides, silicates and metals of geophysical interest constrain the shock-compressed temperature of these materials. In these experiments, a projectile impacts a target consisting of a metal driver plate, a metal film or foil layer, and a transparent window. We investigate the relationship between the temperature inferred from the observed radiation, and the temperatures of different high-pressures states (e.g. shocked state) of the shock-compressed film (or foil) and window. Deviations of the temperature in each target component away from that of their respective shock-compressed states occur because of (1) shock-impedance mismatch between target components, (2) thermal mismatch between target components, (3) surface roughness at target interfaces, and (4) conduction within and between target components. In particular, conduction may affect the temperature of the film/foil material at the film/foil-window interface, a major thermal radiation source in the target, on the time scale of the experiments.\n\nTo be observed, radiation from sources at the film/foil-window interface or in the shocked window material must propagate through (1) the shocked window material, (2) the shock front, (3) the unshocked window material, and (4) the unshocked window free surface. Consequently, the observed intensity of target radiation sources is affected by the optical properties of each region. In particular, the source radiation intensity may be greatly reduced due to absorption in the shocked and/or unshocked window material, and/or only partial transmission through the film/foil-window interface, shock front and/or unshocked window free surface.\n\nTo illustrate various aspects of the model, we apply it to radiation data from targets composed of an Fe driver plate, and Fe film or foil layer, and either an Al_2O_3 or LiF window layer.",
"doi": "10.1016/0370-1573(89)90092-6.",
"issn": "0370-1573",
"publisher": "Elsevier",
"publication": "Physics Reports",
"publication_date": "1989-09",
"series_number": "6",
"volume": "180",
"issue": "6",
"pages": "333-416"
},
{
"id": "authors:zgfvm-3qv65",
"collection": "authors",
"collection_id": "zgfvm-3qv65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120824-090218887",
"type": "article",
"title": "High-Pressure Equation of State of Molten Anorthite and Diopside",
"author": [
{
"family_name": "Rigden",
"given_name": "Sally M.",
"clpid": "Rigden-S-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Stolper",
"given_name": "E. M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
}
],
"abstract": "New Hugoniot equation of state data for molten diopside (at 1773 K) and molten anorthite (at 1923 K) are reported to 38 and 35 GPa, respectively. The diopside data (initial density, 2.61 Mg/m^3) are described by a straight-line fit to the shock velocity-particle velocity results of U_s = 3.30 + 1.44 U_p km s^(\u22121), and our preferred fit to the anorthite data (initial density, 2.55 Mg/m^3) is given by U_s = 2.68 + 1.42 U_p km s^(\u22121). Reduction of the data to a third-order Birch-Murnaghan isentrope assuming the Gruneisen ratio times the density is a constant, and the Mie-Gruneisen equation of state gives K_(0s) = 22.4 GPa and K\u2032_s = 6.9 for diopside. For anorthite we calculate K_(0S) = 17.9 GPa and K\u2032_s = 5.3. The present data for diopside are used to calculate the diopside solidus at high pressures. We expect the solidus to be shallow above \u223c 10 GPa, but the lack of data on the variation of either the Gruneisen parameters of the liquid and crystal or the heat capacity and thermal expansion at elevated pressures makes extrapolation of fusion curves uncertain. Solidus temperatures of 2400\u20132500 K and 2560\u20132705 K for diopside are calculated at 10 and 20 GPa, respectively. The new data are combined with those of Rigden et al. [1988] for the Di_(0.64)A_(0.36) eutectic composition to examine the degree to which such liquids mix ideally with respect to volume up to \u223c 25 GPa. For the eutectic composition at 1400\u00b0C we calculate the volumes of the An and Di mix nearly ideally to 25 GPa. We find that the ratio of the partial molar volumes of the oxides in silicate melts to that of the crystal oxides at 1673 K and 1 atm is 1.0 \u00b1 0.1 for a wide range of oxide components. For the low-pressure tetrahedrally coordinated oxides (e.g., SiO_2, Al_2O_3, Fe_2O_3) the ratio is >1.3 with respect to oxides such as stishovite, corundum, and hematite in which the cations are octahedrally coordinated by oxygens. If changes in coordination of Al and Si from tetrahedral at low pressures to octahedral at high pressures occur in melts, they do so gradually over an interval of \u223c 40 GPa. Although 1 atm bulk moduli for a wide compositional range of silicate melts are similar, the differences in integrated compression to mixed oxide-like high-pressure configurations are reflected mainly by variations in K^\u2032_T. K^\u2032_T is found to vary inversely with fraction of network forming initially tetrahedrally coordinated cations (e.g., Al^(3+), Si^(4+)). Thus K^\u2032_T, which may be uncertain by \u00b11.5, is estimated to vary from \u22727 for molten anorthite, enstatite, and diopside to \u223c 8 for molten ferrosilite to \u223c 10 for molten forsterite and to \u223c 11 for molten fayalite.",
"doi": "10.1029/JB094iB07p09508",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1989-07-10",
"series_number": "B7",
"volume": "94",
"issue": "B7",
"pages": "9508-9522"
},
{
"id": "authors:hzymr-mrb16",
"collection": "authors",
"collection_id": "hzymr-mrb16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-134725686",
"type": "article",
"title": "Physical Properties of Solid and Molten Earth Materials - Foreword",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The study of the physics of solid and molten Earth materials as a scientific subfield of solid Earth geophysics continues to grow rapidly. Much of the research is motivated by the many new observations of the geophysics of the crust, mantle, and core that requires explanation in terms of such variables as composition, temperature, and rheology.",
"doi": "10.1016/0031-9201(89)90067-8",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1989-06",
"series_number": "3-4",
"volume": "55",
"issue": "3-4",
"pages": "v"
},
{
"id": "authors:y2kbz-gz307",
"collection": "authors",
"collection_id": "y2kbz-gz307",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141112-124004006",
"type": "article",
"title": "Phase relations in iron-rich systems and implications for the Earth's core",
"author": [
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Recent experimental data concerning the properties of iron, iron sulfide, and iron oxide at high pressures are combined with theoretical arguments to constrain the probable behavior of the Fe-rich portions of the Fe-O and Fe-S phase diagrams. We infer that a solid solution exists between \u03f5-Fe and S at high pressures. This is based on the similarity in the atomic radii of Fe and S (rFe/rS \u22480.97), and on the observation that S apparently does not form a solid solution with the \u03b3-phase of Fe. We suggest that the \u03f5-Fe S system may, to first order, be modeled as an ideal solid solution and, therefore, will not have a eutectic. The solid solution probably is not ideal, but there are insufficient data to constrain the non-ideal behavior. The \u03f5-Fe-O system, on the other hand, probably has very little solid solution (rO/rFe \u22480.84), although there is recent evidence that a highly non-ideal solid solution does exist between \u03b3-Fe and O. Experimental data extending to > 100 GPa suggest that solid FeO may remain a stable compound at high pressures, with a possible miscibility gap between FeO and Fe. This is based on the observation that FeO melts at higher temperatures than either Fe or O at high pressures. Theoretical extrapolation of the melting curve of FeO indicates that this behavior should continue throughout the pressure range relevant to the Earth's core. Thus, the Fe-rich portion of the Fe-O phase diagram is predicted to display a eutectic between \u03f5-Fe and FeO at core pressures. Comparison of the predicted composition of the Fe-FeO eutectic at inner core pressures with the amount of oxygen required to give the outer core its observed density (28 at. % O) indicates that, if the only light element in the core were oxygen, the core composition would lie significantly toward the FeO side of the eutectic and FeO would be the solid phase of the inner core. This is inconsistent with the properties of the inner core. This argument indicates that, although oxygen is probably present in non-trivial quantities, it cannot be the only light element in the core, and may not even be the most abundant light element in the core. The results of our analysis are compatible with sulfur as another major light element in the core, as the Fe-S solidus is always more Fe-rich than the coexisting liquidus.",
"doi": "10.1016/0031-9201(89)90069-1",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1989-06",
"series_number": "3-4",
"volume": "55",
"issue": "3-4",
"pages": "208-220"
},
{
"id": "authors:9dnsy-zcw63",
"collection": "authors",
"collection_id": "9dnsy-zcw63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-162859690",
"type": "article",
"title": "Shock temperatures in silica glass: Implications for modes of shock-induced deformation, phase transformation, and melting with pressure",
"author": [
{
"family_name": "Schmitt",
"given_name": "Douglas R.",
"clpid": "Schmitt-D-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Gray body temperatures and emittances of silica glass under shock compression between 10 and 30 GPa are determined. Observed radiative temperatures are higher than computed continuum temperatures for shock-compressed silica glass; however, below \u223c26 GPa observed emittances are <0.02. This suggests that fused quartz deforms heterogeneously in this shock pressure range as has been observed in other minerals. Between 10 and 16 GPa, radiative temperatures decrease from 4400 K to 3200 K, whereas above 16\u201330 GPa, gray body temperatures of \u223c3000 K with low emittances are observed. The emittances increase with pressure from 0.02 to 0.9. The pressure range from 10 to 16 GPa coincides with the permanent densification region, while the 16\u201330 GPa range coincides with the inferred mixed phase region along the silica glass Hugoniot. The differing radiative behaviors may relate to these modes of deformation. Based upon earlier shock recovery experiments and a proposed model of heterogeneous deformation under shock compression, the temperatures associated with low emittances in the mixed phase region probably represent the melting temperature of the high-pressure phase, stishovite, which can be expected to crystallize from a melt in hot zones. Above 20 GPa the melting temperature of stishovite would therefore be 3000 K\u00b1200 K and almost independent of pressure to 30 GPa. The effects of pressure on melting relations for the system SiO_2\u2013Mg_2SiO_4 are considered together with the proposed stishovite melting curve and suggested maximum solidus temperatures within the mantle of \u223c2370 K at 12.5 GPa and \u223c2530 K at 20.0 GPa. Using the proposed stishovite melting temperatures Tm and estimates of upper mantle temperatures T, the effective viscosity, which can be considered a function of the homologous temperature T/T_m, appears to remain nearly constant from 200 to 600 km depth in the Earth.",
"doi": "10.1029/JB094iB05p05851",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1989-05-10",
"series_number": "B5",
"volume": "94",
"issue": "B5",
"pages": "5851-5871"
},
{
"id": "authors:8axnr-bp741",
"collection": "authors",
"collection_id": "8axnr-bp741",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-153042630",
"type": "article",
"title": "Ideal Fe\u2014FeS, Fe\u2014FeO phase relations and Earth's core",
"author": [
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Anderson",
"given_name": "William W.",
"clpid": "Anderson-W-W"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Bass",
"given_name": "Jay D.",
"clpid": "Bass-J-D"
}
],
"abstract": "Liquid-state and solid-state model fits to melting data for Fe, FeS and FeO provide constraints for calculating ideal phase relations in Fe-FeS and Fe-FeO systems in the pressure range corresponding to the Earth's outer core. The liquid-state model fit to the Fe melting data of Williams and Jeanloz places constraints on the temperature and other properties of Fe along the liquidus beyond the range of their data. The temperature along the best-fit Fe liquidus reaches 5000 K at 136 GPa and 7250 K at 330 GPa, which is somewhat lower than that implied by the Hugoniot results (\u223c7800 K at 330 GPa). This discrepancy may be due to reshock in experimental targets, or some inaccuracy in the extrapolation, presuming the Hugoniot results represent the equilibrium melting behavior of Fe. Constraints on the solidi of FeS and FeO from the comparison of data and solid-state model calculations imply that FeS and FeO melt at \u223c4610 and 5900 K, respectively, at 136 GPa, and \u223c6150 and 8950 K, respectively, at 330 GPa.\n\nCalculations for the equilibrium thermodynamic properties of solid and liquid Fe along the coincident solidus and liquidus imply that the entropy of melting for Fe is approximately independent of pressure at a value of approximately R (where R is the gas constant), while the change in the molar heat capacity across the transition increases with pressure from \u223c0.5R to 4R between standard pressure and 330 GPa. We use these constraints to construct ideal-mixing phase diagrams for Fe-FeS and Fe-FeO systems at outer core pressures, assuming that Fe and FeS, or Fe and FeO, respectively, are the solid phases in equilibrium with the liquid Fe-FeS or Fe-FeO mixtures, respectively. Calculated Fe-FeO eutectic compositions at 330 GPa (15\u201320 mol% O) are <25 mol% O, while calculated Fe-FeS eutectic compositions at 330 GPa (23\u201330 mol% S) are generally >25 mol% S. Combined with density considerations, these calculations imply that an O-rich outer core is more likely to lie on the FeO-rich side of the Fe-FeX eutectic, while an S-rich outer core is more likely to lie on the Fe-rich side of the Fe-FeX eutectic. In addition, eutectic temperatures in both systems are \u22735000 K at 330 GPa. Widely accepted temperature profiles for the outer core, ranging from \u22723000 K at the 136 GPa, the core-mantle boundary, to \u22724200 K at 330 GPa, the outer-inner core boundary, are \u2a7e800 K below this value. In the context of the outer-inner core boundary-phase boundary hypothesis, this discrepancy implies that at least one boundary layer of \u2a7e1000 K exists in the mantle, possibly at its base in the D\u2033 region.",
"doi": "10.1016/0031-9201(89)90241-0",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1989-05",
"series_number": "1-2",
"volume": "55",
"issue": "1-2",
"pages": "154-186"
},
{
"id": "authors:a3wzn-kcy47",
"collection": "authors",
"collection_id": "a3wzn-kcy47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-073217994",
"type": "article",
"title": "In-situ holographic elastic moduli measurements from boreholes",
"author": [
{
"family_name": "Schmitt",
"given_name": "Douglas R.",
"clpid": "Schmitt-D-R"
},
{
"family_name": "Smither",
"given_name": "Catherine",
"clpid": "Smither-C-L"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We have developed a unique technique employing\noptical holography to measure the static Young's modulus\n(E) from a borehole. In the experiment, a known\npoint force induces micron scale displacements on the\nborehole wall which are recorded by a double-exposure\nhologram. Raw data consist of dark fringes superimposed\non the three-dimensional image whose pattern is\nmodeled to find E directly. In the laboratory, the holographic\ntechnique determined E on rock and metal samples\nto an uncertainty better than 10 percent. For example,\ndouble exposure holograms of a saw-cut sample of\ndolomitic marlstone gave an E of 16.8 \u00b1 2.8 GPa in\nagreement with 17.2 \u00b1 2.0 GPa predicted by published\ndensity-modulus relationships. Field tests of a holographic\ntool in a horizontal mine pillar borehole gave\nin-situ Es which range from 26.9 to 36.0 GPa. Although\nthese data could be interpreted as localized elastic heterogeneity\nwithin the rock mass, elastic anisotropy of\nthe rock is a possible explanation for this variation.",
"doi": "10.1190/1.1442673",
"issn": "0016-8033",
"publisher": "Society of Exploration Geophysicists",
"publication": "Geophysics",
"publication_date": "1989-04",
"series_number": "4",
"volume": "54",
"issue": "4",
"pages": "468-477"
},
{
"id": "authors:cm5p6-qyp45",
"collection": "authors",
"collection_id": "cm5p6-qyp45",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-110311009",
"type": "article",
"title": "Impact production of CO_2 by the Cretaceous/Tertiary extinction bolide and the resultant heating of the Earth",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Evidence at the Cretaceous/Tertiary boundary suggests that the proposed 'extinction' bolide struck a continental or shallow marine terrane. This evidence includes: shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types; a high ^(87)Sr/^(86)Sr ratio in some planktonic fossils which could reflect continental-derived Sr(ref.5); and evidence that the platinum-group-element-rich clay layer is underlain (at some localities) by a deposit of possible tsunamic origin. These observations and data demonstrate that sea level at the end of the Cretaceous was ~150-200 m higher than at present, suggesting the possibility that the extinction bolide struck a shallow marine carbonate-rich sedimentary section. Here we show that the impact of such a bolide (~5km in radius) onto a carbonate-rich terrane would increase the CO_2 content of the atmosphere by a factor of\ntwo to ten. Additional dissolution of CO_2 from the ocean's photic zone could release much larger quantities of CO_2. The impact induced release of CO_2, by itself, would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 K to 10 K for periods of 10^4 to 10^5 years.",
"doi": "10.1038/338247a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1989-03-16",
"series_number": "6212",
"volume": "338",
"issue": "6212",
"pages": "247-249"
},
{
"id": "authors:sz6mb-tkd03",
"collection": "authors",
"collection_id": "sz6mb-tkd03",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-080541722",
"type": "article",
"title": "Analysis and modelling of holographic measurements of in situ stress",
"author": [
{
"family_name": "Smither",
"given_name": "C. L.",
"clpid": "Smither-C-L"
},
{
"family_name": "Schmitt",
"given_name": "D. R.",
"clpid": "Schmitt-D-R"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Holographic in situ stress measurements were made at five azimuths at a single depth in a horizontal borehole in a mine pillar. For the first time, all six components of the stress tensor were determined by this technique. The stressmeter data indicate a vertical stress of \u221210.2MPa (compressive), in good agreement with the predicted vertical stress for the mine pillar depth and dimensions. The maximum horizontal stress is in ,an approximate E-W direction. The minimum principal stress is 3.2 MPa (tensile) and is oriented in an approximate N-S direction, along the axis of the borehole. The principal stresses are not strongly aligned in the horizontal and vertical directions relative to the borehole. Analysis of holographic stress data uses the analytic solution for displacements induced by drilling a small stress-relief hole in an infinite plate subjected to plane stress. Two-dimensional finite element analysis was conducted in order to compare the displacement of a thin plate to the displacements in a thicker body more closely resembling the situation in the borehole. The results suggest that the values of stress predicted by the current method of analysis may be overestimated for some states of stress of the borehole wall.",
"doi": "10.1016/0148-9062(88)90975-8",
"issn": "0148-9062",
"publisher": "Elsevier",
"publication": "International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts",
"publication_date": "1988-12",
"series_number": "6",
"volume": "25",
"issue": "6",
"pages": "353-362"
},
{
"id": "authors:67yhy-gfg24",
"collection": "authors",
"collection_id": "67yhy-gfg24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-125804354",
"type": "article",
"title": "Elements, Oxides, Silicates: High Pressure Phases With Implications for the Earth's Interior [Book Review]",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A vitally important aspect of understanding the composition, structure, and processes acting within the solid Earth is obtaining a complete as possible knowledge of the fields of stability of the Earth's component minerals and their high-pressure polymorphs with respect to pressure and temperature. Liu and Bassett's book is the first effort which has focused on bringing together the available phase diagrams for the elements, oxides, and silicates that are relevant to the understanding of Earth's and the other terrestrial planetary interiors. Since the book also covers the elements and compounds important to the shallow region of the mantles of the major planets (e.g., H_2 , He, C, and H_2O), it is an invaluable source of data for scientists studying the interiors of these planets as well.\nAn initial introductory chapter lays out, in very condensed form, the relation of phase diagrams to thermodynamic properties. Crystal chemical principles are summarized, as well as the main features of the techniques and apparatus employed to obtain the data summarized in the remainder of the book. Although references to apparatus papers are numerous and well chosen, references to works which relate thermodynamic properties to construction of phase diagrams are lacking. Table 1.3, a summary of the ionic radii of elements in different coordinations appears to me to be the most valuable part of Chapter 1.",
"doi": "10.1029/88EO01157",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "Eos",
"publication_date": "1988-10-18",
"series_number": "42",
"volume": "69",
"issue": "42",
"pages": "964"
},
{
"id": "authors:8ssbp-8wg39",
"collection": "authors",
"collection_id": "8ssbp-8wg39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-144144345",
"type": "article",
"title": "Dynamic consolidation of cubic boron nitride and its admixtures",
"author": [
{
"family_name": "Tan",
"given_name": "Hua",
"clpid": "Tan-Hua"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Cubic boron nitride (C\u2013BN)' powders admixed with graphite-structured boron nitride powder (g-DN), silicon carbide whisker (SCW), or silicon nitride whisker (SNW) were shock compacted to pressures up to 22 GPa. Unlike previous work with diamond and graphite [D. K. Potter and T. J. Ahrens, J. Appl. Phys. 63, 910 (1987) it was found that the addition of g-BN inhibited dynamic consolidation. Good consolidation was achieved with a 4\u20138 \u03bcm particle size C\u2013BN powder admixed with 15 wt.% SNW or 20 wt.% SCW whereas a 37\u201344 \u03bcm particle size C\u2013BN mixture was only poorly consolidated. Scanning electron microscopy (SEM) analysis demonstrates that SCW and SNW in the mixtures were highly deformed and indicated melt textures. A skin heating model was used to describe the physics of consolidation. Model calculations are consistent with SEM analysis images that indicate plastic deformation of SCW and SNW. Micro-Vickers hardness values as high as 50 GPa were obtained for consolidated C\u2013BN and SNW mixtures. This compares to 21 GPa for single-crystal Al_2O_3 and 120 GPa for diamond.",
"doi": "10.1557/JMR.1988.1010",
"issn": "0884-2914",
"publisher": "Materials Research Society",
"publication": "Journal of Materials Research",
"publication_date": "1988-09",
"series_number": "5",
"volume": "3",
"issue": "5",
"pages": "1010-1020"
},
{
"id": "authors:wshfh-krw39",
"collection": "authors",
"collection_id": "wshfh-krw39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120615-163116316",
"type": "article",
"title": "The equation of state of molybdenum at 1400\u2009\u00b0C",
"author": [
{
"family_name": "Miller",
"given_name": "Gregory H.",
"clpid": "Miller-G-H"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Stolper",
"given_name": "Edward M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
}
],
"abstract": "Shock compression data to 96 GPa for pure molybdenum, initially heated to 1400\u2009\u00b0C, are presented. Finite strain analysis of the data gives a bulk modulus at 1400\u2009\u00b0C, K_(0S), of 244 \u00b1 2 GPa and its pressure derivative, K\u2032_(0S), of 4. A fit of shock velocity to particle velocity gives the coefficients of U_S = c_0 + sU_P to be c_0 = 4.77 \u00b1 0.06 km/s and s = 1.43 \u00b1 0.05. From the zero\u2010pressure sound speed c_0, a bulk modulus of 232 \u00b1 6 GPa is calculated which is consistent with extrapolation of ultrasonic elasticity measurements. The temperature derivative of the bulk modulus at zero pressure, \u2202K_(0S)/\u2202T|_P, is approximately \u22120.012 GPa/K. A thermodynamic model is used to show that the thermodynamic Gr\u00fcneisen parameter is proportional to the density and independent of temperature. The Mie\u2013Gr\u00fcneisen equation of state adequately describes the high\u2010temperature behavior of molybdenum under the present range of shock loading conditions.",
"doi": "10.1063/1.341124",
"issn": "0021-8979",
"publisher": "American Institute of Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1988-05-01",
"series_number": "9",
"volume": "63",
"issue": "9",
"pages": "4469-4475"
},
{
"id": "authors:m1vdb-13q80",
"collection": "authors",
"collection_id": "m1vdb-13q80",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:POTjap88",
"type": "article",
"title": "Shock consolidation of diamond and graphite mixtures to fused polycrystalline diamond",
"author": [
{
"family_name": "Potter",
"given_name": "David K.",
"clpid": "Potter-D-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The production of fused compacts of polycrystalline diamond was achieved by subjecting porous (35%\u201349% porosity) mixtures of diamond crystals plus graphite (13\u201316 wt. %) to dynamic shock pressures of 10\u201318 GPa. The recovered material from an initial mixture of 4\u20138-\u00b5m diamond crystals plus graphite revealed a very homogeneous texture with little evidence of original grain boundaries. The preconsolidation addition of graphite also allowed ultrafine (<5 \u00b5m) diamond crystals to be consolidated; this was not previously possible with the use of diamond crystals alone. The results are consistent with calculations which suggest that a thin layer of graphite surrounding a diamond crystal delays thermal equilibrium between the surface and interior of the diamond crystal, thus allowing greater surface heating. Consolidation is also probably enhanced by conversion of graphite to diamond, possibly via the liquid state.",
"doi": "10.1063/1.340032",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1988-02-01",
"series_number": "3",
"volume": "63",
"issue": "3",
"pages": "910-914"
},
{
"id": "authors:d50kg-nny90",
"collection": "authors",
"collection_id": "d50kg-nny90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120822-113026741",
"type": "article",
"title": "Shock compression of molten silicate: results for a model basaltic composition",
"author": [
{
"family_name": "Rigden",
"given_name": "S. M.",
"clpid": "Rigden-S-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Stolper",
"given_name": "E. M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
}
],
"abstract": "A technique has been developed for measurement of the shock wave, pressure-density equation of state of molten silicates initially at temperatures of up to \u223c2000 K. A 40-mm propellant gun apparatus accelerates metal flyer plates to speeds of up to 2.5 km s^(\u22121); these flyer plates are capable of driving shock waves with amplitudes of 35\u201340 GPa (350\u2013400 kbar) into molten silicate samples. Modifications to the standard equation of state experiments that are described here include design of a molybdenum sample container for the molten silicate; use of a 10-kW radio frequency induction heater to melt the sample prior to impact; implementation of shuttering systems to protect the optical system and prevent preexposure of the film in the rotating-mirror, continuously writing, streak camera; and reduction of Hugoniot data taking into account the effect of the sample capsule. Data for a model basaltic liquid (36 mol % anorthite, 64 mol % diopside) at an initial temperature of 1673 K and initial density of 2.61 Mg m^(\u22123), yield a shock velocity-particle velocity (U_(S)-U_(P)) relation given by U_S = 3.06 + 1.36 UP km s^(\u22121) up to values of U_P = 1.7 km s^(\u22121). The zero-pressure, bulk sound speed is in good agreement with ultrasonic measurements. The best fit Birch-Murnaghan equation of state for this model basaltic liquid is K_(0S) = 24.2 GPa and K\u2032 = 4.85 based on Hugoniot points at low pressures (<25 GPa). Within the resolution of our data set, density increases smoothly with pressure over the 0\u201325 GPa pressure range, suggesting that structural rearrangements take place gradually in response to pressure in this pressure interval. At high pressures (\u2273 25 GPa) the Hugoniot data suggest that the liquid stiffens considerably. This may indicate that the gradual structural changes characteristic of the lower-pressure regime, such as changes of Al3+ and Si4+ coordination by oxygen from fourfold to sixfold, are essentially complete by \u223c25 GPa. These high-pressure Hugoniot data are fit by US = 0.85 + 2.63 Up km s^(\u22121). The high-pressure regime is similar to that obtained in initially solid silicates upon shock compression. Shock temperature calculations yield values of 2400\u20132600 K at 25 GPa, and the states achieved are believed to lie metastably in the liquid field.",
"doi": "10.1029/JB093iB01p00367",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1988-01-10",
"series_number": "B1",
"volume": "93",
"issue": "B1",
"pages": "367-382"
},
{
"id": "authors:8fs17-x9r58",
"collection": "authors",
"collection_id": "8fs17-x9r58",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SCHMjap88",
"type": "article",
"title": "Shock-induced melting and shear banding in single-crystal NaCl",
"author": [
{
"family_name": "Schmitt",
"given_name": "Douglas R.",
"clpid": "Schmitt-D-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
}
],
"abstract": "Radiative color temperatures were measured in single-crystal sodium chloride under shock compression parallel to [100] over a pressure range from 20 to 35 GPa. Color temperatures from 2500 to 4500 K and emittances from 0.003 to 0.3 were determined by fitting observed spectra (450\u2013850 nm) to the Planck greybody radiation law. These data support a heterogeneous shock deformation model of shocked halite in this pressure range. A 2500-K temperature rise, of unknown origin, is observed over the B1\u2013B2 mixed phase region from 25 to 30 GPa. Assuming that shock deformation occurs via yielding in localized planar zones which become melt and the melting temperature at high pressure controls the temperature, we infer that the temperature of the B2 fusion curve from 30 to 35 GPa rises from 3200 to 3300 K. The B1\u2013B2-liquid triple point is predicted to be at a temperature of 2250 K and 23.5 GPa.",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1988-01-01",
"series_number": "1",
"volume": "63",
"issue": "1",
"pages": "99-106"
},
{
"id": "authors:yqeff-6bh72",
"collection": "authors",
"collection_id": "yqeff-6bh72",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-105941472",
"type": "article",
"title": "Shock-induced temperatures of MgO",
"author": [
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock-compressed MgO radiates thermally at temperatures between 2900 and 3700 K in the 170\u2013200 GPa pressure range. A simple energy-transport model of the shocked-MgO-targets distinguishes between different shock-induced radiation sources in these targets and provides estimates of spectral absorption-coefficients, \u03b1_(\u03bbMgO), for shocked MgO (e.g. at 203 GPa, \u03b1_(\u03bbMgO) ~ 630, 7500, 4200 and 3800 m^(\u22121), at 450, 600, 750 and 900 nm, respectively). The experimentally inferred temperatures of the shock-compressed states of MgO are consistent with temperatures calculated for MgO assuming that (1) it deforms as an elastic fluid, (2) has a Dulong-Petit value for specific heat at constant volume in its shocked state, and (3) undergoes no phase transformation below 200 GPa.",
"doi": "10.1111/j.1365-246X.1987.tb01664.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1987-12",
"series_number": "3",
"volume": "91",
"issue": "3",
"pages": "667-691"
},
{
"id": "authors:2n2dm-f1h52",
"collection": "authors",
"collection_id": "2n2dm-f1h52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-103531844",
"type": "article",
"title": "Microstructural modifications in a dynamically consolidated microcrystalline nickel titanium alloy powder",
"author": [
{
"family_name": "Thadhani",
"given_name": "Naresh N.",
"clpid": "Thadhani-N-N"
},
{
"family_name": "Vreeland",
"given_name": "Thad, Jr.",
"clpid": "Vreeland-T-Jr"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Spherically shaped, microcrystalline NiTi alloy powder with both nonhomogeneous particle-size distribution (2 to 60\u03bcm diameter) and chemical composition, was consolidated with a shock input energy of 316 kJ kg%^(\u22121). Upon shock compaction, the two-phase NiTi powder particles (containing 45wt% Ti and 65 wt% Ti) were bonded together, generally by interparticle melting and subsequent welding. The melted material at interparticle regions was observed to have rapidly solidified to largely amorphous and/or microcrystalline phases. Particle interiors were also subjected to extensive plastic deformation which resulted in deformation twinning, grain elongation and some recrystallization to defect-free grains. Unique microstructural modifications occurring due to inhomogeneous thermal and mechanical processing during the dynamic consolidation process, are reported here.",
"doi": "10.1007/BF01132045",
"issn": "0022-2461",
"publisher": "Springer",
"publication": "Journal of Materials Science",
"publication_date": "1987-12",
"series_number": "12",
"volume": "22",
"issue": "12",
"pages": "4446-4452"
},
{
"id": "authors:bg0wr-dn009",
"collection": "authors",
"collection_id": "bg0wr-dn009",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120820-094201788",
"type": "article",
"title": "On the nature of pressure\u2010induced coordination changes in silicate melts and glasses",
"author": [
{
"family_name": "Stolper",
"given_name": "Edward M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Progressive decreases in the Si\u2010O\u2010Si angles between corner\u2010shared silicate tetrahedra in glasses and melts with increasing pressure can lead to arrangements of oxygen atoms that can be described in terms of edge\u2010 or face\u2010shared octahedra. This mechanism of compression can account for the gradual, continuous increases in melt and glass densities from values at low pressure that indicate dominantly tetrahedral coordination of Si to values at several tens of GPa that suggest higher coordination. It also can explain the unquenchable nature of octahedrally coordinated Si in glasses, the absence of spectroscopically detectable octahedrally coordinated Si in glasses until they are highly compressed, the gradual and reversible transformation from tetrahedral to octahedral coordination in glasses once the transformation is detectable spectroscopically, and the fact that this transformation takes place in glass at room temperature. It may also have relevance to pressure\u2010induced transformations from crystalline to glassy phases, the difficulty in retrieving some metastable high pressure crystalline phases at low pressure, and the observed differences between the pressures required for phase transformations in shock wave experiments on glasses and crystals.",
"doi": "10.1029/GL014i012p01231",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1987-12",
"series_number": "12",
"volume": "14",
"issue": "12",
"pages": "1231-1233"
},
{
"id": "authors:8yc7g-sxp32",
"collection": "authors",
"collection_id": "8yc7g-sxp32",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-105941387",
"type": "article",
"title": "Pyrite: Shock compression, isentropic release, and composition of the Earth's core",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
}
],
"abstract": "New shock wave data (to 180 GPa) for pyrite (FeS_2) shocked along (001) demonstrate that this mineral, in contrast to other sulfides and oxides, does not undergo a major pressure-induced phase change over the entire pressure range (320 GPa) now explored. (This is probably so because of the initial, low-spin 3-d, orbital configuration of Fe^(+2)). The primary evidence which indicates that a large phase change does not occur is the approximate agreement of the shock velocity when extrapolated to zero particle velocity, 5.4 km/s, with the expected zero-pressure bulk sound speed of pyrite (5.36 to 5.43 km/s on the basis of previous ultrasonic data). Pyrite displays a prominent elastic shock (or Hugoniot elastic limit) of 8 \u00b1 1 GPa. The velocity of the elastic shock approaches 8.72 km/s with decreasing shock pressure, the longitudinal elastic wave velocity. As shock pressure increases, the elastic shock velocity approaches 9.05 km/s and the elastic shock becomes overdriven for shock pressures greater than about 120 GPa. Analysis of release isentrope data obtained via the pressure-particle velocity buffer method indicates that buffer particle velocities in all experiments are from 1.7% to 20% greater than expected for a Gr\u00fcneisen ratio given by 1.56 (V/V_o)^(1.0). This discrepancy appears to result from volume increases upon pressure release of 0.04% to 4.5% which may result from shock-induced partial melting. The normalized pressure, finite-strain formalism for reducing Hugoniot data is extended to take into account initial porosity and shock-induced phase transitions. A least squares fit to the present and previous shock data for pyrite yields an isentropic bulk modulus, K_s, of 162 \u00b1 9 GPa and a value of dK_s/dP = 4.7 \u00b1 0.3. This is close to the 145 \u00b1 3 GPa bulk modulus observed ultrasonically. If the slight discrepancy in zero-pressure modulus is taken into account in the normalized pressure finite-strain formalism, a zero-pressure density of the shock-induced high-pressure phase having a density some 2% to 3% less than pyrite is inferred to occur in the high-pressure shocked state. We suggest from this result, the release isentrope results, and limited phase diagram data that the Hugoniot states probably correspond to material which is partially to completely melted. Using the above derived equation of state and previous shock wave data for iron, both the seismologically determined density and bulk modulus distribution in the outer core are fit to models with various temperature distributions and varying weight percent sulfur. Good agreement between the shock wave derived equation of state and the density/bulk modulus relations of the liquid outer core are obtained for temperatures of \u223c3000 K at the core/mantle boundary extending to 4400 K at the outer core-inner core boundary. For this thermal model a calculated sulfur content of 11 \u00b1 2% is obtained.",
"doi": "10.1029/JB092iB10p10363",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1987-09-10",
"series_number": "B10",
"volume": "92",
"issue": "B10",
"pages": "10363-10375"
},
{
"id": "authors:zn5kz-00j59",
"collection": "authors",
"collection_id": "zn5kz-00j59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:POTapl87",
"type": "article",
"title": "Dynamic consolidation of diamond powder into polycrystalline diamond",
"author": [
{
"family_name": "Potter",
"given_name": "David K.",
"clpid": "Potter-D-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The formation of a polycrystalline solid compact, by fusing an initially porous aggregate of diamond crystals under dynamic shock pressure (7.5\u201318 GPa), is shown to depend critically on the size of the initial crystals. Porous aggregates of 100\u2013150 \u00b5m diameter crystals upon shock compaction produced compacts. These exhibited pronounced fracturing of the individual crystals and showed no evidence of fusion. Aggregates consisting of ultrafine crystals (<5 \u00b5m) also exhibited minimal consolidation. However, samples composed of crystals in the range 4\u20138 \u00b5m produced strong fused compacts of polycrystalline diamond. A model calculation indicates that at 10 GPa less than 0.07 mass fraction of the diamond powder can be melted and this molten material is quenched in 0.8 ns for 8-\u00b5m-diam crystals.",
"doi": "10.1063/1.98427",
"issn": "0003-6951",
"publisher": "Applied Physics Letters",
"publication": "Applied Physics Letters",
"publication_date": "1987-08-03",
"series_number": "5",
"volume": "51",
"issue": "5",
"pages": "317-319"
},
{
"id": "authors:v0d76-f3g51",
"collection": "authors",
"collection_id": "v0d76-f3g51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-090949803",
"type": "article",
"title": "The Melting Curve of Iron to 250 Gigapascals: A Constraint on the Temperature at Earth's Center",
"author": [
{
"family_name": "Williams",
"given_name": "Quentin",
"clpid": "Williams-Q"
},
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Bass",
"given_name": "Jay",
"clpid": "Bass-J-D"
},
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The melting curve of iron, the primary constituent of Earth's core, has been measured to pressures of 250 gigapascals with a combination of static and dynamic techniques. The melting temperature of iron at the pressure of the core-mantle boundary (136 gigapascals) is 4800 \u00b1 200 K. whereas at the inner core-outer core boundary (330 gigapascals), it is 7600 \u00b1 500 K. Corrected for melting point depression resulting from the presence of impurities, a melting temperature for iron-rich alloy of 6600 K at the inner core-outer core boundary and a maximum temperature of 6900 K at Earth's center are inferred. This latter value is the first experimental upper bound on the temperature at Earth's center, and these results imply that the temperature of the lower mantle is significantly less than that of the outer core.",
"doi": "10.1126/science.236.4798.181",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1987-04-10",
"series_number": "4798",
"volume": "236",
"issue": "4798",
"pages": "181-182"
},
{
"id": "authors:a5520-km458",
"collection": "authors",
"collection_id": "a5520-km458",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-115544788",
"type": "article",
"title": "Impact experiments in low-temperature ice",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New results of low-velocity impact experiments in cubic and cylindrical (20 cm) water-ice targets initially at 257 and 81 \u00b0K are reported. Impact velocities and impact energies vary between 0.1 and 0.64 km/sec and 10^9 and 10^(10) ergs, respectively. Observed crater diameters range from 7 to 15 cm and are two to three times larger than values found for equal-energy impacts in basaltic targets. Crater dimensions in ice targets increase slightly with increasing target temperatures. Crater volumes of strength-controlled ice craters are about 10 to 100 times larger than those observed for craters in crystalline rocks. Based on similarity analysis, general scaling laws for strength-controlled crater formation are derived and are applied to crater formation on the icy Galilean and Saturnian satellites. This analysis indicates that surface ages, based on impact-crater statistics on an icy crust, will appear greater than those for a silicate crust which experienced the same impact history. The greater ejecta volume for cratering in ice versus cratering in silicate targets leads to accelerated regolith production on an icy planet.",
"doi": "10.1016/0019-1035(87)90020-0",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1987-03",
"series_number": "3",
"volume": "69",
"issue": "3",
"pages": "506-518"
},
{
"id": "authors:z73qb-wpy96",
"collection": "authors",
"collection_id": "z73qb-wpy96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-091822400",
"type": "article",
"title": "Shock-induced volatile loss from a carbonaceous chondrite: implications for planetary accretion",
"author": [
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Frisch",
"given_name": "Benjamin",
"clpid": "Frisch-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Solid-recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that for an impact of a given velocity, H_2O and total volatiles are driven from the sample in the same proportion as present initially. We infer that the volatiles other than H_2O driven from the meteorite also have the same bulk composition as those of the starting material. Thus, the early bulk composition of an impact-induced atmosphere of a planet growing by accretion from material like Murchison would be the same as the volatile composition of the incident planetesimals. Incipient devolatilization of Murchison occurs at an initial shock pressure of about 11 GPa and complete devolatilization occurs at a pressure of about 30 GPa. If an Earth-sized planet were formed from the infall of planetesimals of Murchison composition, incipient and complete devolatilization of accreting planetesimals would occur when the planet reached approximately 12% and 27%, respectively, of its final radius. Thus, impact-induced devolatilization of accreting planetesimals and of the hydrated surface would profoundly affect the distribution of volatiles within the accreting planet. For example, for a cold, homogeneous accretion of a planet, prior to metallic core formation and internal differentiation, the growing planet would have a very small core with the same volatile content as the incident material, a volatile-depleted \"mantle\", and an extremely volatile-rich surface.",
"doi": "10.1016/0012-821X(86)90104-4",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1986-11",
"series_number": "3-4",
"volume": "80",
"issue": "3-4",
"pages": "201-207"
},
{
"id": "authors:78cpd-x4847",
"collection": "authors",
"collection_id": "78cpd-x4847",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-104852507",
"type": "article",
"title": "Oblique Impact: A Process for Obtaining Meteorite Samples from Other Planets",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Cratering flow calculations for a series of oblique to normal (10\u00b0 to 90\u00b0) impacts of silicate projectiles onto a silicate halfspace were carried out to determine whether or not the gas produced upon shock-vaporizing both projectile and target material would form a downstream jet that could entrain and propel SNC meteorites from the Martian surface. The difficult constraints that the impact origin hypothesis for SNC meteorites has to satisfy are that these meteorites are lightly to moderately shocked and yet have been accelerated to speeds in excess of the Martian escape velocity (more than 5 kilometers per second). Two-dimensional finite difference calculations were performed that show that at highly probable impact velocities (7.5 kilometers per second), vapor plume jets are produced at oblique impact angles of 25\u00b0 to 60\u00b0 and have speeds as great as 20 kilometers per second. These plumes flow nearly parallel to the planetary surface. It is shown that upon impact of projectiles having radii of 0.1 to 1 kilometer, the resulting vapor jets have densities of 0.1 to 1 gram per cubic centimeter. These jets can entrain Martian surface rocks and accelerate them to velocities greater than 5 kilometers per second. This mechanism may launch SNC meteorites to earth.",
"doi": "10.1126/science.234.4774.346",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1986-10-17",
"series_number": "4774",
"volume": "234",
"issue": "4774",
"pages": "346-349"
},
{
"id": "authors:1rj18-ys620",
"collection": "authors",
"collection_id": "1rj18-ys620",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-112207870",
"type": "article",
"title": "Shock wave equation of state of enstatite",
"author": [
{
"family_name": "Watt",
"given_name": "J. Peter",
"clpid": "Watt-J-P"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock compression data are reported for hot-pressed Bamble bronzite (En_(86)) loaded to pressures between 104 and 161 GPa. When compared to earlier shock wave data on En_(90) at lower pressures and to static compression data, our data require the presence of a phase change. In P-\u03c1 space the data yield two distinct trajectories, which cannot be explained by experimental error. The higher-density data, corrected for porosity and a small amount of metallic iron impurity, agree with a theoretical En_(86) high-pressure phase Hugoniot calculated from static compression equation of state data for perovskite (pv) structure silicates when experimental errors and uncertainties in the equation of state parameters are considered. All the En86 data can be described by a calculated Hugoniot if the first pressure derivative of the MgSiO_3 (pv) bulk modulus is taken as 4.5 \u00b1 1.0. Combining the present preferred data with recent shock wave data for single-crystal forsterite, we find that En_(86) is slightly more dense than Fo86 at pressures above 110 GPa. Comparison of the forsterite and enstatite data with the Preliminary Reference Earth Model (PREM) lower mantle densities, with corrections applied for the higher shock temperatures relative to lower mantle temperatures, shows that PREM densities are satisfied by olivine or pyroxene stoichiometries with Mg mole fractions from 0.82 to 0.90. These values are lower than estimates of 0.90 to 0.95 developed from extrapolating static compression data to lower mantle conditions.",
"doi": "10.1029/JB091iB07p07495",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1986-06-10",
"series_number": "B7",
"volume": "91",
"issue": "B7",
"pages": "7495-7503"
},
{
"id": "authors:wv0wy-6yn12",
"collection": "authors",
"collection_id": "wv0wy-6yn12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181207-111946085",
"type": "article",
"title": "High-Pressure Research Applications Seminar",
"author": [
{
"family_name": "Manghnani",
"given_name": "Murli H.",
"clpid": "Manghnani-M-H"
},
{
"family_name": "Akimoto",
"given_name": "Syun-iti",
"clpid": "Akimoto-Syun-iti"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Syono",
"given_name": "Yasuhiko",
"clpid": "Syono-Yasuhiko"
},
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Yagi",
"given_name": "Takehiko",
"clpid": "Yagi-Takehiko"
}
],
"abstract": "The United States\u2010Japan seminar on \"High\u2010Pressure Research Applications in Geophysics and Geochemistry\" was held in Honolulu, Hawaii, January 13\u201316, 1986, under the auspices of the National Science Foundation (NSF) and the Japan Society for the Promotion of Science (JSPS). The seminar, the third in a series, was cocovened by Murli H. Manghnani (University of Hawaii, Honolulu) and Syun\u2010iti Akimoto (University of Tokyo). Coming together for this symposium were 25 researchers from Japan, 22 from the United States, and four others, from Australia, the People's Republic of China, the Netherlands, and the Federal Republic of Germany. Of the 52 papers presented, 38 were presented orally at seven scientific sessions, and the rest were displayed at a poster session.",
"doi": "10.1029/eo067i017p00427-03",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "Eos",
"publication_date": "1986-04-29",
"series_number": "17",
"volume": "67",
"issue": "17",
"pages": "427-428"
},
{
"id": "authors:bpxhn-51610",
"collection": "authors",
"collection_id": "bpxhn-51610",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-113320685",
"type": "article",
"title": "Dynamic compression and volatile release of carbonates",
"author": [
{
"family_name": "Tyburczy",
"given_name": "James A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Particle velocity profiles upon shock compression and adiabatic release were measured for polycrystalline calcite (Solenhofen limestone) to 12\u201324 GPa and for porous calcite (Dover chalk, \u03c1_o = 1.40 g/cm^3, 49% porosity) to between 5 and 11 GPa. The electromagnetic particle velocity gauge method was used. Upon shock compression of Solenhofen limestone, the Hugoniot elastic limit was determined to vary from 0.36 to 0.45 GPa. Transition shocks at between 2.5 and 3.7 GPa, possibly arising from the calcite II-III transition, were observed. For the Solenhofen limestone, the release paths lie relatively close to the Hugoniot. Evidence for the occurrence of the calcite III-II transition upon release was observed, but no rarefaction shocks were detected. Initial release wave speeds suggest retention of shear strength up to at least 20 GPa, with a possible loss of shear strength at higher pressures. The measured equation of state is used to predict the fraction of material devolatilized upon adiabatic release as a function of shock pressure. The effect of ambient partial pressure of CO_2 on the calculations is demonstrated. P_(CO_2) should be taken into account in models of atmospheric evolution by means of impact-induced mineral devolatilization. Mass fractions of CO_2 released expected on the basis of a continuum model are much lower than determined experimentally. This discrepancy, and radiative characteristics of shocked calcite, indicate that localization of thermal energy (shear banding) occurs under shock compression even though no solid-solid transitions occur in this pressure range. Release adiabatic data indicate that Dover chalk loses its shear strength when shocked to 10 GPa pressure. At 5 GPa the present data are ambiguous regarding shear strength. For Dover chalk, continuum shock entropy calculations result in a minimum estimate of 90% devolatilization upon complete release from 10 GPa. For calcite, isentropic release paths from calculated continuum Hugoniot temperatures cross into the CaO (solid) + CO_2 (vapor) field at improbably low pressures (for example, 10 GPa for a shock pressure of 25 GPa). However, calculated isentropic release paths originating from PT points corresponding to previous color temperature under shock measurements cross into the melt plus vapor field at pressures greater than 0.5 GPa, suggesting that devolatilization is initiated at the shear banding sites.",
"doi": "10.1029/JB091iB05p04730",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1986-04-10",
"series_number": "B5",
"volume": "91",
"issue": "B5",
"pages": "4730-4744"
},
{
"id": "authors:zktwp-88c17",
"collection": "authors",
"collection_id": "zktwp-88c17",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-165732729",
"type": "article",
"title": "Shock-induced CO_2 loss from CaCO_3; implications for early planetary atmospheres",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We report new results of shock recovery experiments on single crystal calcite. Recovered samples are subjected to thermogravimetric analysis. This yields the maximum amount of post-shock CO_2, the decarbonization interval, \u0394T, and the energy of association (or vaporization), \u0394EV, for the removal of remaining CO_2 in shock-loaded calcite. Comparison of post-shock CO_2 with that initially present determines shock-induced CO_2 loss as a function of shock pressure. Incipient to complete CO_2 loss occurs over a pressure range of \u223c 10to\u223c 70GPa. The latter pressure should be considered a lower bound. Comparable to results on hydrous minerals, \u0394T and \u0394EV decrease systematically with increasing shock pressure. This indicates that shock loading leads to both the removal of structural volatiles and weakening of bonds between the volatile species and remainder of the crystal lattice.\nOptical and scanning electron microscopy (SEM) reveal structural changes, which are related to the shock-loading. Comparable to previous findings on shocked antigorite is the occurrence of dark, diffuse areas, which can be resolved as highly vesicular areas as observed with a scanning electron microscope. These areas are interpreted as representing quenched partial melts, into which shock-released CO_2 has been injected.\nThe experimental results are used to place bonds on models of impact production of CO_2 during accretion of the terrestrial planets.",
"doi": "10.1016/0012-821X(86)90150-0",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1986-04",
"series_number": "3-4",
"volume": "77",
"issue": "3-4",
"pages": "409-418"
},
{
"id": "authors:rcgbs-85m84",
"collection": "authors",
"collection_id": "rcgbs-85m84",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-114001644",
"type": "article",
"title": "Holographic in situ stress measurements",
"author": [
{
"family_name": "Bass",
"given_name": "Jay D.",
"clpid": "Bass-J-D"
},
{
"family_name": "Schmitt",
"given_name": "Douglas",
"clpid": "Schmitt-D-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A new instrument for measuring the in situ level of stress in boreholes has been developed. The instrument operates on the principle of locally relieving the stresses acting on a rock mass by drilling a small hole into the borehole surface and recording the resultant displacement field by holographic interferometry. Because the recording technique is optical, the entire displacement field due to stress relief is obtained. A description of the stressmeter, theory of the interferometric technique, data reduction methodology, and results of laboratory stress relief calibration tests are presented. In addition, we present results from a field deployment of the instrument in an underground shale mine in Garfield County, Colorado using a test borehole within a support pillar. Sufficient data were obtained to constrain five of six stress components at a shallow level of the test borehole, thereby demonstrating the viability of the holographic technique. The holographic stress-relief data yield an approximate EW maximum horizontal stress direction. By comparison with previous hydrofracture measurements of Bredehoeft et al., our results indicate substantial stress-relief near the pillar face, thus masking any relicts of the far-field tectonic stress.",
"doi": "10.1111/j.1365-246X.1986.tb05170.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1986-04",
"series_number": "1",
"volume": "85",
"issue": "1",
"pages": "13-41"
},
{
"id": "authors:7gg1p-52m16",
"collection": "authors",
"collection_id": "7gg1p-52m16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-115645217",
"type": "article",
"title": "Shock temperatures in anorthite glass",
"author": [
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Mitchell",
"given_name": "Arthur C.",
"clpid": "Mitchell-A-C"
}
],
"abstract": "Temperatures of CaAl_2Si_2O_8 (anorthite glass) shocked to pressures between 48 and 117 GPa have been measured in the range from 2500 to 5600 K, using optical pyrometry techniques. The pressure dependence of the shock temperatures deviates significantly from predictions based on a single high-pressure phase. Either a variable specific heat, or the existence of three phase transitions, at pressures of about 55, 85 and 100 GPa and with transition energies of about 0.5 MJ kg^(\u22121) each (\u2248 1.5 MJ kg^(\u22121) total) can explain the shock-temperature data. The proposed phase transition at 100 GPa can possibly be identified with the stishovite melting transition. Theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive properties of the shocked material yield good agreement with observations, indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases. Observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm^(\u22121) to greater than 24 mm^(\u22121) \u2014 an increasing function of shock pressure. The assumption that the shocked material radiates as a black body is supported by the theoretical model, and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength.",
"doi": "10.1111/j.1365-246X.1986.tb04367.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1986-03",
"series_number": "3",
"volume": "84",
"issue": "3",
"pages": "475-489"
},
{
"id": "authors:gx7dv-dje92",
"collection": "authors",
"collection_id": "gx7dv-dje92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-120258959",
"type": "article",
"title": "Hugoniot equation of state of anorthite glass and lunar anorthosite",
"author": [
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Rigden",
"given_name": "Sally M.",
"clpid": "Rigden-S-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Twenty-one Hugoniot experiments were conducted on an amorphous material of anorthite composition, in the pressure range 8\u2013120 GPa, using both routine and new methods. Two Hugoniot measurements at about 120 GPa were made on lunar gabbroic anorthosite (Apollo 15, 418). Theoretical Hugoniots are constructed for both materials assuming they are disproportionate to their component oxides. These accurately predict the P-\u03c1 behaviour of the lunar anorthosite Hugoniot at 120 GPa and the anorthite glass Hugoniot above 50 GPa, but overestimate the shock temperatures of anorthite glass. The mixed oxide model fails to predict the release paths of either material. We conclude that the mixed oxide model is a good description of the bulk properties of the high-pressure phases of anorthite, but does not represent the actual phases. A significant enrichment of calcic refractory material in the Earth's lower mantle is not precluded by the bulk properties of the anorthite high-pressure phases.",
"doi": "10.1111/j.1365-246X.1986.tb04366.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1986-03",
"series_number": "3",
"volume": "84",
"issue": "3",
"pages": "455-473"
},
{
"id": "authors:tabtn-gt169",
"collection": "authors",
"collection_id": "tabtn-gt169",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-122404790",
"type": "article",
"title": "Shock wave properties of anorthosite and gabbro",
"author": [
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock wave experiments have been conducted on San Gabriel anorthosite and San Marcos gabbro to peak stresses between 5 and 11 GPa using a 40-mm-bore propellant gun. Particle velocity wave profiles were measured directly at several points in each target by means of electromagnetic gauges, and Hugoniot states were calculated by determining shock transit times from the gauge records. The particle velocity profiles yielded sound velocities along the release adiabats which indicate a retention of shear strength upon shock compression for anorthosite, with a loss of strength upon release to nearly zero stress. Sound velocities of anorthosite shocked to peak stresses between 6 and 10 GPa were measured to be between 5.1 and 5.3 km/s upon release to nearly zero stress as compared to \u223c6.9 and 5.4 km/s for the expected longitudinal and bulk wave speeds. Stress density release paths in the anorthosite indicate possible transformation of albite to Jadeite + (quartz or coesite), with the amount of albite transformed ranging from as low as 0.05 to as much as 0.19 mass fraction in the 6\u201310 GPa shock stress range. Electrical interference effects precluded the determination of accurate release paths for San Marcos gabbro. Because of the apparent loss of shear strength during unloading from the shocked state, the fluidlike rheology of anorthosite which is indicated implies that calculations of energy partitioning due to impact onto planetary surfaces based on elastic-plastic models will underestimate the amount of internal energy deposited in the impacted surface material.",
"doi": "10.1029/JB090iB09p07814",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1985-08-10",
"series_number": "B9",
"volume": "90",
"issue": "B9",
"pages": "7814-7820"
},
{
"id": "authors:5t49h-f0f68",
"collection": "authors",
"collection_id": "5t49h-f0f68",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-145418595",
"type": "article",
"title": "Shock effects on hydrous minerals and implications for carbonaceous meteorites",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Lambert",
"given_name": "Philippe",
"clpid": "Lambert-P"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New infrared absorption spectra, thermo-gravimetric analyses and optical-and scanning electron microscopy of shock-recovered specimens of antigorite serpentine (Mg_3Si_2O_5(OH)_4) from the pressure range between 25 to 59 GPa are reported. The infrared spectra show systematic changes in absorption peaks related to structural and molecular surface absorbed water. H_2O absorption peaks increase at the expense of OH peaks with increasing shock pressure. Changes in SiO bond vibrational modes with increasing shock pressure parallel those seen for other, non-hydrous minerals. Thermogravimetric analyses of shock-recovered samples determine the amount of shock-induced water loss. For samples shocked in vented assemblies, the data define a relation between shock-induced water loss versus shock pressure. Results for samples shocked in sealed assemblies demonstrate a dependence of water loss on shock pressure and target confinement. For the vented assembly samples, a linear relation between shock pressure and both the length of dehydration interval and the effective activation energy for releasing post-shock structural water in antigorite is found. Optical and scanning electron miscroscopy of shocked antigorite reveal a number of textures thought to be unique to shock loading of volatile-bearing minerals. Gas bubbles, which probably are the result of shock-released H_2O appear to be injected into zones of partial melting. This process may produce the vesicular dark veins which are distributed throughout heavily shocked samples. The present observations suggest several criteria which may constrain possible shock histories of the hydrous matrix phases of carbonaceous condrites. A model is proposed for explaining hydrous alteration processes occurring on carbonaceous chondrite parent bodies in the course of their accretion. We speculate that shock loading of hydrous minerals would release and redistribute free water in the regoliths of carbonaceous chondrite parent bodies giving rise to the observed hydrous alterations.",
"doi": "10.1016/0016-7037(85)90142-5",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "1985-08",
"series_number": "8",
"volume": "49",
"issue": "8",
"pages": "1715-1726"
},
{
"id": "authors:arpeh-fga92",
"collection": "authors",
"collection_id": "arpeh-fga92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120821-070838359",
"type": "article",
"title": "Densities of Liquid Silicates at High Pressures",
"author": [
{
"family_name": "Rigden",
"given_name": "Sally M.",
"clpid": "Rigden-S-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Stolper",
"given_name": "Edward M.",
"orcid": "0000-0001-8008-8804",
"clpid": "Stolper-E-M"
}
],
"abstract": "Densities of molten silicates at high pressures (up to \u223c230 kilobars) have been measured for the first time with shock-wave techniques. For a model basaltic composition (36 mole percent anorthite and 64 mole percent diopside), a bulk modulus K_s, of \u223c230 kilobars and a pressure derivative (dK_s/dP) of \u223c4 were derived. Some implications of these results are as follows: (i) basic to ultrabasic melts become denser than olivine-and pyroxene-rich host mantle at pressures of 60 to 100 kilobars; (ii) there is a maximum depth from which basaltic melt can rise within terrestrial planetary interiors; (iii) the slopes of silicate solidi [(dT_m/dP), where T_m is the temperature] may become less steep at high pressures; and (iv) enriched mantle reservoirs may have developed by downward segregation of melt early in Earth history.",
"doi": "10.1126/science.226.4678.1071",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1984-11-30",
"series_number": "4678",
"volume": "226",
"issue": "4678",
"pages": "1071-1074"
},
{
"id": "authors:m946r-n0x15",
"collection": "authors",
"collection_id": "m946r-n0x15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141023-163940308",
"type": "article",
"title": "FeO and H_2O and the homogeneous accretion of the earth",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We present new shock devolatilization recovery data for brucite (Mg(OH)_2) shocked to 13 and 23 GPa. These data combined with previous data for serpentine (Mg_3Si_2O_5(OH)_4) are used to constrain the minimum size terrestrial planet for which planetesimal infall will result in an impact-generated water atmosphere. Assuming a chondritic abundance of minerals including 3\u20136%, by mass water, in hydrous phyllosilicates, we carried out model calculations simulating the interaction of metallic iron with impact-released free water on the surface of the accreting Earth. We assume that the reaction of water with iron in the presence of enstatite is the prime source of the terrestrial FeO component of silicates and oxides. Lower and upper bounds on the terrestrial FeO budget are based on mantle FeO content and possible incorporation of FeO in the outer core. We demonstrate that the iron-water reaction would result in the absence of atmospheric/hydrospheric water, if homogeneous accretion is assumed. In order to obtain ~10^(25) g of atmospheric water by the end of accretion, slightly heterogeneous accretion with initially 36% by mass iron planetesimals, as compared to a homogeneous value of 34% is required. Such models yield final FeO budgets, which either require a higher FeO content of the mantle (17 wt.%) or oxygen as a light element in the outer core of the Earth.",
"doi": "10.1016/0012-821X(84)90057-8",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1984-11",
"series_number": "1",
"volume": "71",
"issue": "1",
"pages": "111-119"
},
{
"id": "authors:m3m3c-hfd46",
"collection": "authors",
"collection_id": "m3m3c-hfd46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-123016605",
"type": "article",
"title": "Shock temperatures in CaO",
"author": [
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Mitchell",
"given_name": "Arthur C.",
"clpid": "Mitchell-A-C"
}
],
"abstract": "Blackbody temperatures of CaO shocked to pressures from 140 to 182 GPa have been measured in the 3750 to 6000 K range using the Lawrence Livermore National Laboratory light gas gun. These shock temperatures, along with Hugoniot data for single crystal and porous CaO and isothermal data, are used to construct equations of state for the high pressure (B2) phase of CaO. The zero-pressure density of the B2 phase is between 3.8 and 4.0 Mg/m^3 and the B1-B2 transition energy is 2.1 to 2.3 MJ/kg. The density and bulk modulus at pressures from 70 to 135 GPa are similar to seismically determined values for the lower mantle of the earth. Thus the lower mantle could have a substantial inventory of Ca-bearing minerals, and mixed oxide models, for the composition of the lower mantle will be insensitive to the quantity of CaO assumed.",
"doi": "10.1029/JB089iB09p07845",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1984-09-10",
"series_number": "B9",
"volume": "89",
"issue": "B9",
"pages": "7845-7851"
},
{
"id": "authors:2psm6-m5103",
"collection": "authors",
"collection_id": "2psm6-m5103",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-111705334",
"type": "article",
"title": "Shock wave equations of state using mixed-phase regime data",
"author": [
{
"family_name": "Watt",
"given_name": "J. Peter",
"clpid": "Watt-J-P"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A method is given that uses Hugoniot data in the mixed-phase regime to constrain further equation of state (EOS) parameters of low- and high-pressure phases of materials under-going phase transformations on shock loading. We compute the relative proportion of low- and high-pressure phases present in the mixed-phase region and apply additional tests to the EOS parameters of the separate low- and high-pressure phases by invoking two simple requirements: the fraction of high-pressure phase (1) must increase with increasing shock pressure, and (2) must approach one at the high-pressure end of the mixed-phase regime. We apply our analysis to previously published data for potassium thioferrite, KfeS_2, and pyrrhotite, Fe_(0.9)S. We find that including the mixed-phase regime data in the KfeS_2 analysis requires no change in the published high-pressure EOS parameters. For Fe_(0.9)S we must modify the high-pressure phase EOS parameters to account for both the mixed-phase and high-pressure phase Hugoniot data. Our values of zero-pressure density, bulk modulus and first pressure derivative of the bulk modulus of the high-pressure phase of Fe_(0.9)S are 5.3 Mg/m^3, 106 GPa, and 4.9, respectively.",
"doi": "10.1029/JB089iB09p07836",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1984-09-10",
"series_number": "B9",
"volume": "89",
"issue": "B9",
"pages": "7836-7844"
},
{
"id": "authors:cg8ft-9jz14",
"collection": "authors",
"collection_id": "cg8ft-9jz14",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:TYBrsi84",
"type": "article",
"title": "Streak camera recording of shock wave transit times at large distances using laser illumination",
"author": [
{
"family_name": "Tyburczy",
"given_name": "J. A.",
"clpid": "Tyburczy-J-A"
},
{
"family_name": "Blayney",
"given_name": "J. L.",
"clpid": "Blayney-J-L"
},
{
"family_name": "Miller",
"given_name": "W. F.",
"clpid": "Miller-W-F"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A pulsed laser illumination system for streak camera recording of impact-induced shock wave transit times (~1 \u00b5s) during impact experiments is described. Laser illumination of centimeter-sized subjects offers many advantages over diffuse illumination techniques for streak photography. Source-to-sample and sample-to-camera distances of ~10^0 to 10^1 m can be employed. Light filtering, and simultaneous recording of both the impact event and the camera streak rate calibration, can be carried out easily. For use in such a system we describe a Pockels cell controller in which the reference 10-MHz oscillator signal is synchronously divided down to 38 Hz to provide a trigger signal for laser and streak camera testing.",
"doi": "10.1063/1.1137947",
"issn": "0034-6748",
"publisher": "Review of Scientific Instruments",
"publication": "Review of Scientific Instruments",
"publication_date": "1984-09-01",
"series_number": "9",
"volume": "55",
"issue": "9",
"pages": "1452-1454"
},
{
"id": "authors:cyrqr-fhd75",
"collection": "authors",
"collection_id": "cyrqr-fhd75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-115302418",
"type": "article",
"title": "A theory for the shock-wave consolidation of powders",
"author": [
{
"family_name": "Schwarz",
"given_name": "R. B.",
"clpid": "Schwarz-R-B"
},
{
"family_name": "Kasiraj",
"given_name": "P.",
"clpid": "Kasiraj-P"
},
{
"family_name": "Vreeland",
"given_name": "T., Jr.",
"clpid": "Vreeland-T-Jr"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A model for the shock consolidation of powders is developed which predicts, for a given powder density, the regimes of shock pressure P and shock duration t_d expected to yield fully densified compacts of near optimum strength. Most of the densification work is assumed deposited near particle boundaries, leading to partial melting. The model gives an upper bound to the amount of melt. The condition that the melt between particles must exceed a critical thickness and must solidify within the duration of the shocked state leads to necessary conditions for P and t_d.These requirements are presented in \"maps of shock consolidation,\" using normalized parameters. The model predicts that for a shock energy (normalized to that required to heat iron to the melting point) of 0.7, a minimum shock duration of 2\u03bcs is required to consolidate 60\u03bcm diameter iron-based powder.",
"doi": "10.1016/0001-6160(84)90131-7",
"issn": "0001-6160",
"publisher": "Elsevier",
"publication": "Acta Metallurgica",
"publication_date": "1984-08",
"series_number": "8",
"volume": "32",
"issue": "8",
"pages": "1243-1252"
},
{
"id": "authors:7e03m-9vn27",
"collection": "authors",
"collection_id": "7e03m-9vn27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-104135464",
"type": "article",
"title": "Shock consolidation of a rapidly solidified steel powder",
"author": [
{
"family_name": "Kasiraj",
"given_name": "P.",
"clpid": "Kasiraj-P"
},
{
"family_name": "Vreeland",
"given_name": "T., Jr.",
"clpid": "Vreeland-T-Jr"
},
{
"family_name": "Schwarz",
"given_name": "R. B.",
"clpid": "Schwarz-R-B"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Rapidly solidified AISI 9310 steel powders were consolidated by shock waves produced from the impact of high velocity flyers. Dependence of the microhardness and the ultimate tensile strength of the compacts on the initial shock pressure (from 3.6 to 17.9 GPa) and the maximum shock pressure (from 6 to 37 GPa) was measured for an initial powder density 0.6 of the bulk density and a shock duration of 2\u20133 s. Photomicrographs and SEM fractographs were used to study the interparticle bonding in the compacts. Results show that for initial shock pressures below 4 GPa, the compacts have negligible strength. However, above this threshold the strength of the compact rises rapidly until a maximum value of 1.3 \u00b1 0.1 GPa is reached for an initial shock pressure of 12.4 GPa. The strength then remains constant before decreasing at the highest initial shock pressure. In marked contrast, with increasing shock pressure, the diamond pyramid hardness increases very gradually from a value of about 340 for the powder to about 500 at the highest shock pressure. The maximum strength obtained correlates reasonably well with the strength-expected from microhardness measurements.",
"doi": "10.1016/0001-6160(84)90130-5",
"issn": "0001-6160",
"publisher": "Elsevier",
"publication": "Acta Metallurgica",
"publication_date": "1984-08",
"series_number": "8",
"volume": "32",
"issue": "8",
"pages": "1235-1241"
},
{
"id": "authors:a9hbr-hg715",
"collection": "authors",
"collection_id": "a9hbr-hg715",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-124108087",
"type": "article",
"title": "Hugoniot data for pyrrhotite and the Earth's core",
"author": [
{
"family_name": "Brown",
"given_name": "J. Michael",
"clpid": "Brown-J-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Shampine",
"given_name": "Dennis L.",
"clpid": "Shampine-D-L"
}
],
"abstract": "New shock wave Hugoniot data for pyrrhotite (Fe_(0.9S)) now describe the equation of state to nearly twofold compression at a maximum pressure of 274 GPa. A minor discontinuity on the Hugoniot between 100 and 150 GPa is interpreted as the melting transition. While not tightly constrained, the inferred melting point lies below lower-bound temperature estimates based on the Lindemann criterion. The highest-pressure Hugoniot data (representing the melted phase) are used to model the equation of state for liquid iron sulfide. A density for liquid pyrrhotite of 7.80\u00b10.20 Mg/m^3 under core-mantle boundary conditions (P = 135 GPa, T = 4000 K) is calculated. Assuming that sulfur is the primary alloying element in a predominately iron core, the present data are consistent with a homogeneous outer core containing 10\u00b14 wt % sulfur.",
"doi": "10.1029/JB089iB07p06041",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1984-07-10",
"series_number": "B7",
"volume": "89",
"issue": "B7",
"pages": "6041-6048"
},
{
"id": "authors:s8jtx-hby56",
"collection": "authors",
"collection_id": "s8jtx-hby56",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-121624888",
"type": "article",
"title": "Impact cratering and spall failure of gabbro",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
}
],
"abstract": "Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro to examine the relation between spall strength and maximum spall ejecta thickness. The impact experiments carried out with 0.04- to 0.2-g, 5- to 6-km/sec projectiles produced decimeter- to centimeter-sized craters and demonstrated crater efficiencies of 6 \u00d7 10^(\u22129) g/erg, an order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 g yield values of b = d(log N_f)/d log(m) \u22120.5 \u22120.6, where N is the cumulative number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejecta resides in a few large fragments. The large fragments are plate-like with mean values of B/A and C/A 0.8 0.2, respectively (A = long, B = intermediate, and C = short fragment axes). The small equant-dimensioned fragments (with mass < 0.1 g and B \u223c 0.1 mm) represent material which has been subjected to shear failure. The dynamic tensile strength of San Marcos gabbro was determined at strain rates of 10^4 to 10^5 sec^(\u22121) to be 147 \u00b1 9 MPa. This is 3 to 10 times greater than inferred from quasi-static (strain rate 10^0 sec^(\u22121)) loading experiments. Utilizing these parameters in a continuum fracture model predicts a tensile strength of \u03c3_ m \u03c7^[0.25-0.3], where \u03b5 is strain rate. It is suggested that the high spall strength of basic igneous rocks gives rise to enhanced cratering efficiencies due to spall in the <10^2-m crater diameter strength-dominated regime. Although the impact spall mechanism can enhance cratering efficiencies it is unclear that resulting spall fragments achieve sufficient velocities such that fragments of basic rocks can escape from the surfaces of planets such as the Moon or Mars.",
"doi": "10.1016/0019-1035(84)90084-8",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1984-06",
"series_number": "3",
"volume": "58",
"issue": "3",
"pages": "383-395"
},
{
"id": "authors:rzbyv-bts78",
"collection": "authors",
"collection_id": "rzbyv-bts78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-121755731",
"type": "article",
"title": "Shock wave consolidation of an amorphous alloy",
"author": [
{
"family_name": "Kasiraj",
"given_name": "P.",
"clpid": "Kasiraj-P"
},
{
"family_name": "Kostka",
"given_name": "D.",
"clpid": "Kostka-D"
},
{
"family_name": "Vreeland",
"given_name": "T., Jr.",
"clpid": "Vreeland-T-Jr"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Irregular flakes prepared from \u223c 50 \u03bcm thick melt spun ribbons of an amorphous Markomet 1064 alloy (Ni_(55\u20228)Mo_(25\u20227)B_(8\u20228)) were consolidated by shock waves produced from stainless steel flyer plate impact in the 0.9 to 1.4 Km/s velocity range. Recovered samples were observed to have a bulk density of 8.9\u00b1.2 g/cm^3. The compacts remained amorphous for shock energies of less than 450 KJ/Kg. Metallographs indicate that moderately good interparticle bonding can be achieved with shock waves at stress levels below those which can induce recrystallization from shock heating.",
"doi": "10.1016/0022-3093(84)90668-9",
"issn": "0022-3093",
"publisher": "Elsevier",
"publication": "Journal of Non-Crystalline Solids",
"publication_date": "1984-01",
"series_number": "Pt. 2",
"volume": "61-62",
"issue": "Pt. 2",
"pages": "967-971"
},
{
"id": "authors:r3ana-bzr59",
"collection": "authors",
"collection_id": "r3ana-bzr59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-122339769",
"type": "article",
"title": "Shock compression of single-crystal forsterite",
"author": [
{
"family_name": "Watt",
"given_name": "J. Peter",
"clpid": "Watt-J-P"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Dynamic compression results are reported for single-crystal forsterite loaded along the orthorhombic a and c axes to pressures from 130 to 165 GPa. Hugoniot states for the two axes are well described by a single curve offset to densities 0.15\u20130.20 g/cm^3 lower than earlier data for single-crystal forsterite shocked along the b axis above 100 GPa. Earlier data of Syono et al. [1981a] show marginal support for similar b-axis behavior in the mixed-phase region from 50 to 92 GPa. Thus shocked forsterite is most compressible in the b direction for the mixed-phase and high-pressure regimes (P > 50 GPa). These data represent the highest pressures for which shock properties have been observed to depend on crystal orientation. Theoretical Hugoniots for mixed-oxide and perovskite-structure high-pressure assemblages of forsterite calculated from recent experimental data are virtually identical and agree with the b-axis data. The a- and c-axis data are also consistent with both high-pressure assemblages because uncertainties in equation of state parameters produce a broad range of computed Hugoniots. Our calculated \"average\" Hugoniot is up to 0.13 g/cm^3 less dense than the preferred theoretical Hugoniots, in agreement with earlier measurements on dense polycrystalline forsterite. Interpolation between the single-crystal forsterite Hugoniots and Hugoniots for fayalite and Fo_(45) gives Fo_(88) Hugoniots bracketing Twin Sisters dunite data not previously well fit by systematics. Release paths are steep for the a and b axes but c-axis release paths are much shallower. Hugoniot elastic limits measured for the a and b axes are in good agreement with previous data of Syono et al.; however, the present data for the a axis reveal a triple wave structure: two deformational shock waves as well as the elastic shock, a feature not previously found. The second shock, with amplitude about 9 GPa and a shock temperature of about 350\u00b0K, could perhaps be explained by the forsterite \u03b1\u2192\u03b2 or \u03b3 phase transformation.",
"doi": "10.1029/JB088iB11p09500",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1983-11-10",
"series_number": "B11",
"volume": "88",
"issue": "B11",
"pages": "9500-9512"
},
{
"id": "authors:3bbr7-qt561",
"collection": "authors",
"collection_id": "3bbr7-qt561",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-133535637",
"type": "article",
"title": "Temperatures of shock-induced shear instabilities and their relationship to fusion curves",
"author": [
{
"family_name": "Schmitt",
"given_name": "Douglas R.",
"clpid": "Schmitt-D-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New emission spectra for MgO and CaAl_2Si_2O_8 (glass) are observed from 430 to 820 nm. Taken with previous data, we suggest that transparent solids display three regimes of light emission upon shock compression to successively higher pressures: (1) characteristic radiation such as observed in MgO and previously in other minerals, (2) heterogeneous hot spot (greybody) radiation observed in CaAl_2Si_2O_8 and previously in all transparent solids undergoing shock-induced phase transformations, and (3) blackbody emission observed in the high pressure phase regime in NaCl, SiO_2, CaO, CaAl_2Si_2O_8, and Mg_2SiO_4. The onset of regime (2) may delineate the onset of shock-induced polymorphism whereas the onset of regime (3) delineates the Hugoniot pressure required to achieve local thermal equilibrium in the shocked solid. We also propose that the hot spot temperatures and corresponding shock pressures determined in regime (2) delineate points on the fusion curves of the high pressure phase.",
"doi": "10.1029/GL010i011p01077",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1983-11",
"series_number": "11",
"volume": "10",
"issue": "11",
"pages": "1077-1080"
},
{
"id": "authors:m9c5h-q6q82",
"collection": "authors",
"collection_id": "m9c5h-q6q82",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-090502017",
"type": "article",
"title": "Preface",
"author": [
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Tozer",
"given_name": "D. C.",
"clpid": "Tozer-D-C"
}
],
"abstract": "These papers are approximately half of those presented at a special symposium on \"Lateral Heterogeneity in the Lithosphere\" held as part of the Leeds meeting of the European Geophysical Society, August 1982.",
"doi": "10.1016/0031-9201(83)90116-4",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1983-10",
"series_number": "3",
"volume": "33",
"issue": "3",
"pages": "R3"
},
{
"id": "authors:c2md9-12z27",
"collection": "authors",
"collection_id": "c2md9-12z27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:KONjap83",
"type": "article",
"title": "Shock-induced radiation spectra of fused quartz",
"author": [
{
"family_name": "Kondo",
"given_name": "Ken-ichi",
"clpid": "Kondo-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Sawaoka",
"given_name": "Akira",
"clpid": "Sawaoka-A"
}
],
"abstract": "An optical multichannel analyzer is applied to observe shock-induced radiation spectra of fused quartz in the 23\u201331 GPa shock-pressure range. Characteristics of sample-driver interface strongly influence both intensity and profile of the observed spectra. Brightness and color temperature are determined by an integration of spectral radiance and a fit to the greybody radiation spectrum, respectively. The resultant brightness and color temperature are lower and considerably higher than those estimated by the theoretical calculation, respectively. Some broad but strong line spectra are, however, superimposed onto the continuous greybody radiation spectrum even though the influences of the interface are reduced as much as possible. The line spectra are probably caused by electroluminescence and/or triboluminescence.",
"doi": "10.1063/1.332676",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1983-08-01",
"series_number": "8",
"volume": "54",
"issue": "8",
"pages": "4382-4385"
},
{
"id": "authors:9xep1-azv58",
"collection": "authors",
"collection_id": "9xep1-azv58",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-134932344",
"type": "article",
"title": "Dynamic compression of diopside and salite to 200 GPa",
"author": [
{
"family_name": "Svendsen",
"given_name": "Bob",
"clpid": "Svendsen-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New Hugoniot data on single crystal diopside, CaMgSi_2O_6 (Di), suggest that transformation to a high-pressure thermomechanical state begins at \u223c50 GPa and is complete above 100 GPa, in agreement with other pyroxenes and silicates of geophysical interest. Comparison of the new high pressure phase (HPP) data for Di and salite, CaMg_(0.82)Fe_(0.18)Si_2O_6 (Sa) with appropriate mixed oxide and perovskite models implies compatibility between either model and the data. Conversely, least-squares fits to the HPP Di data favor lower (3.6 - 3.9 Mg/m\u00b3) values of zero-pressure, room-temperature density than the models (4.0 - 4.1 Mg/m\u00b3). Similar comments apply to porosity-corrected HPP hedenbergite (Hd) data. The HPP Di, Sa, and Hd data also imply much larger density differences between these compositions in the HPP regime (e.g., \u22480.8 Mg/m\u00b3 between Di and Hd) than at STP (0.38 Mg/m\u00b3). This may represent the influence of multiple transition processes (e.g., polymorphism and Fe^(2+) high-low spin) as a function of Fe content across the Di-Hd series. The new HPP Sa data closely parallel (\u22480.1 Mg/m\u00b3 less dense) the lower mantle density profile from \u223c90 GPa to 136 GPa. Our results are consistent with the speculations of Jeanloz and Ahrens on the possibility of significant Ca in the lower mantle.",
"doi": "10.1029/GL010i007p00501",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1983-07",
"series_number": "7",
"volume": "10",
"issue": "7",
"pages": "501-504"
},
{
"id": "authors:n1pzm-7ym85",
"collection": "authors",
"collection_id": "n1pzm-7ym85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-140016808",
"type": "article",
"title": "Shock compression of diamond crystal",
"author": [
{
"family_name": "Kondo",
"given_name": "Ken-ichi",
"clpid": "Kondo-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Two shock wave experiments employing inclined mirrors have been carried out to determine the Hugoniot elastic limit (HEL), final shock state at 191 and 217 GPa, and the post-shock state of diamond crystal, which is shock-compressed along the intermediate direction between the <111> and <110> crystallographic axes. The HEL wave has a velocity of 19.9 \u00b1 0.3 mm/\u00b5sec and an amplitude of 63 \u00b1 28 GPa. An alternate interpretation of the inclined wedge mirror streak record suggests a ramp precursor wave and then another HEL value. The maximum post-shock density achieved upon release from the \u223c200 GPa shock state is \u223c3.95 Mg/m\u00b3, which compares to the initial density 3.52 Mg/m\u00b3. This result suggests an elastic unloading effect or shock-induced transition to a denser (possibly metallic) phase.",
"doi": "10.1029/GL010i004p00281",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1983-04",
"series_number": "4",
"volume": "10",
"issue": "4",
"pages": "281-284"
},
{
"id": "authors:btk10-pe835",
"collection": "authors",
"collection_id": "btk10-pe835",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-124350963",
"type": "article",
"title": "Shock temperatures of SiO_2 and their geophysical implications",
"author": [
{
"family_name": "Lyzenga",
"given_name": "Gregory A.",
"clpid": "Lyzenga-G-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Mitchell",
"given_name": "Arthur C.",
"clpid": "Mitchell-A-C"
}
],
"abstract": "The temperature of SiO_2 in high-pressure shock states has been measured for samples of single-crystal \u03b1-quartz and fused quartz. Pressures between 60 and 140 GPa have been studied using projectile impact and optical pyrometry techniques at Lawrence Livermore National Laboratory. Both data sets indicate the occurrence of a shock-induced phase transformation at \u223c70 and \u223c50 GPa along the \u03b1- and fused quartz Hugoniots, respectively. The suggested identification of this transformation is the melting of shock-synthesized stishovite, with the onset of melting delayed by metastable superheating of the crystalline phase. Some evidence for this transition in conventional shock wave equation of state data is given, and when these data are combined with the shock temperature data, it is possible to construct the stishovite-liquid phase boundaries. The melting temperature of stishovite near 70 GPa pressure is found to be 4500 K, and melting in this vicinity is accompanied by a relative volume change and latent heat of fusion of \u223c2.7% and \u223c2.4 MJ/kg, respectively. The solid stishovite Hugoniot centered on \u03b1-quartz is well described by the linear shock velocity-particle velocity relation, u_s = 1.822 up + 1.370 km/s, while at pressures above the melting transition, the Hugoniot centered on \u03b1-quartz has been fit with u_s = 1.619 u_p + 2.049 km/s up to a pressure of \u223c200 GPa. The melting temperature of stishovite near 100 GPa suggests an approximate limit of 3500 K for the melting temperature of SiO_2-bearing solid mantle mineral assemblages, all of which are believed to contain Si^(4+) in octahedral coordination with O^(2\u2212). Thus 3500 K is proposed as an approximate upper limit to the melting point and the actual temperature in the earth's mantle. Moreover, the increase of the melting point of stishovite with pressure at 70 GPa is inferred to be \u223c11 K/GPa. Using various adiabatic temperature gradients in the earth's mantle and assuming creep is diffusion controlled in the lower mantle, the current results could preclude an increase of viscosity by more than a factor of 10^3 with depth across the mantle.",
"doi": "10.1029/JB088iB03p02431",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1983-03-10",
"series_number": "B3",
"volume": "88",
"issue": "B3",
"pages": "2431-2444"
},
{
"id": "authors:5mvv0-d2414",
"collection": "authors",
"collection_id": "5mvv0-d2414",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-144857284",
"type": "article",
"title": "Heterogeneous shock-induced thermal radiation in minerals",
"author": [
{
"family_name": "Kondo",
"given_name": "Ken-ichi",
"clpid": "Kondo-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A 500 channel optical imaging intensifying and spectral digital recording system is used to record the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. Initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range demonstrate greybody emission spectra corresponding to temperatures in the 3,000 to 4,000 K range and emissivities ranging from 0.003 to 0.02. In the case of gypsum and calcite, distinctive line spectra, are superimposed on the thermal radiation. The observed color temperatures are a factor of 2 to 10 greater than the Hugoniot temperature, calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are believed to be real. We conclude that we are detecting a large number of closed spaced high temperature shear-band regions immediately behind the shock front. A shear instability model, such as proposed independently by Grady (1977, 1980), Ananin et al. (1974), and Horie (1980), in which small zones of highly deforming and melted material are produced which are the source of the detected thermal radiation and have a fractional effective area approximately numerically equal to the measured emissivity, can be used to predict an effective emissivity of 0.0065 directly behind the shock front. If shear band instability arises from viscous flow processes, Grady's model and mineral thermal properties yield for the shocked mineral viscosities values in the range of 10^9 to 10^(15) P immediately behind the shock front.",
"doi": "10.1007/BF00308375",
"issn": "0342-1791",
"publisher": "Springer",
"publication": "Physics and Chemistry of Minerals",
"publication_date": "1983-03",
"series_number": "3-4",
"volume": "9",
"issue": "3-4",
"pages": "173-181"
},
{
"id": "authors:0k7cx-pks63",
"collection": "authors",
"collection_id": "0k7cx-pks63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-145443115",
"type": "article",
"title": "Preface [to SEASAT II]",
"author": [
{
"family_name": "Kirwan",
"given_name": "A. D.",
"clpid": "Kirwan-A-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Born",
"given_name": "George H.",
"clpid": "Born-G-H"
}
],
"abstract": "No abstract is available for this article.",
"doi": "10.1029/JC088iC03p01529",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research C",
"publication_date": "1983-02-28",
"series_number": "C3",
"volume": "88",
"issue": "C3",
"pages": "1529"
},
{
"id": "authors:tcc9t-dr455",
"collection": "authors",
"collection_id": "tcc9t-dr455",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-132713052",
"type": "article",
"title": "The dynamic tensile strength of ice and ice-silicate mixtures",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We determined the dynamic tensile strength of ice and ice silicate mixtures at strain rates of \u223c10^4 s^(\u22121). At these strain rates, ice has a tensile strength of \u223c17 MPa, and ice-silicate mixtures with 5 and 30 wt % sand content have strengths of \u223c20 and 22 MPa, respectively. These values lie significantly above tensile strengths of \u223c1.6 MPa for ice and of \u223c5\u22126 MPa for frozen silt, measured at strain rates of \u223c10^(\u22122) to 10\u00b0 s^(\u22121), but markedly below values found for a variety of rocks at comparable strain rates. Results of the present experiments are used to derive parameters for continuum fracturing models in icy media, which are used to determine relations between tensile strength and strain rate, and to predict stress and damage histories as well as size frequency distributions for ice and ice-silicate fragments. It is found that tensile strength \u03c3_M is related to strain rate by \u03c3_M \u221d \u03b5_0^[0.25\u20130.3], similar to results obtained for other geological materials. The increase of small fragments relative to larger fragments with increasing strain rate, as predicted by the continuum model, is a result which parallels findings in laboratory impact experiments.",
"doi": "10.1029/JB088iB02p01197",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1983-02-10",
"series_number": "B2",
"volume": "88",
"issue": "B2",
"pages": "1197-1208"
},
{
"id": "authors:md9wk-m0v24",
"collection": "authors",
"collection_id": "md9wk-m0v24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-152831902",
"type": "article",
"title": "Shock-induced color changes in nontronite: Implications for the Martian fines",
"author": [
{
"family_name": "Weldon",
"given_name": "Ray J.",
"clpid": "Weldon-R-J"
},
{
"family_name": "Thomas",
"given_name": "Warren M.",
"clpid": "Thomas-W-M"
},
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Riverside nontronite, a candidate for the major mineral in the Martian fines, becomes both redder and darker upon shock loading between 180 and 300 kbar. The change from olive-yellow (2.5 Y 6/6) to strong brown (7.5 YR 4/6) in the 300-kbar sample brackets the range of color observed at the Viking lander sites. Optical microscopy, X-ray diffraction, optical, infrared, and ^(57)Fe M\u00f6ssbauer spectroscopy were applied to understand the physical basis of the color change. The Riverside nontronite experienced partial dehydroxylation, probably due to shock-induced heating, that changed the coordination of the Fe3+ in the octahedral layer of the clay to a mixture of 4- and 6-fold or a distorted 5-fold coordination. These changes in the clay cause the O^(2\u2212)-Fe^(3+) charge transfer absorption edge to shift from the near ultraviolet into the visible, producing a redder and darker phase. The absorption spectra of both impacted and nonimpacted Riverside nontronite contains the basic features of the reflectance spectra of the bright regions of Mars: a steep drop in absorption from the near UV into the visible and a featureless near IR region. Calculations indicate that significant impact induced color changes (and dehydration) can occur on Mars, though it seems likely that the mechanism would be more effective, volumetrically, at producing variations in color rather than affecting the absolute color.",
"doi": "10.1029/JB087iB12p10102",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1982-11-30",
"series_number": "B12",
"volume": "87",
"issue": "B12",
"pages": "10102-10114"
},
{
"id": "authors:7qvmy-na059",
"collection": "authors",
"collection_id": "7qvmy-na059",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-141152834",
"type": "article",
"title": "Impact induced dehydration of serpentine and the evolution of planetary atmospheres",
"author": [
{
"family_name": "Lange",
"given_name": "M. A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock recovery experiments in the 25 to 45 GPa range on antigorite serpentine determine the amount of shock-induced loss of structural water as a function of shock pressure. Infrared absorption spectra of shock recovered samples demonstrate systematic changes in the amount of structural water and molecular, surface adsorbed water. These yield qualitative estimates of shock-induced water loss and demonstrate that a portion of the shock released structural water is readsorbed on interfacial grain surfaces. Determination of the post-shock water content of the shocked samples relates shock-induced water loss and shock pressure. Based on the present results and theoretical predictions, we conclude that shock pressures of from 20 to \u223c60 GPa induce incipient to complete water loss, respectively. This result agrees closely with theoretical estimates for total dehydration. The dehydration interval and the activation energies for dehydration in shocked samples decrease systematically with increasing shock pressure as experienced by the sample. We believe the present experiments are applicable to describing dehydration processes of serpentine-like minerals in the accretional environment of the terrestrial planets. We conclude that complete loss of structural water in serpentine could have occurred from accretional impacts of \u223c3 km/sec when earth and Venus have grown to about 50% of their final size. Accreting planetesimals, impacting Mars, never reached velocities sufficient for complete dehydration of serpentine. Our results support a model in which an impact generated atmosphere/hydrosphere forms while the earth is accreting.",
"doi": "10.1029/JB087iS01p0A451",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1982-11-15",
"series_number": "S1",
"volume": "87",
"issue": "S1",
"pages": "A451-A456"
},
{
"id": "authors:ybw2k-1ve10",
"collection": "authors",
"collection_id": "ybw2k-1ve10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130820-111438190",
"type": "article",
"title": "Shock-induced devolatilization of calcite",
"author": [
{
"family_name": "Boslough",
"given_name": "Mark B.",
"clpid": "Boslough-M-B"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Vizgirda",
"given_name": "Joana",
"clpid": "Vizgirda-J"
},
{
"family_name": "Becker",
"given_name": "Richard H.",
"clpid": "Becker-R-H"
},
{
"family_name": "Epstein",
"given_name": "Samuel",
"clpid": "Epstein-S"
}
],
"abstract": "The amounts of CO_2 and CO evolved upon shock compression and decompression of calcite to 18 GPa (180 kbar) have been determined using a new gas phase shock recovery technique and gas source mass spectrometry. The data demonstrate that from \u223c0.03 to 0.3 mole percent of calcite is devolatilized at shock pressures significantly lower than those predicted (30 GPa) for the onset of volatilization by continuum thermodynamic theory and are in qualitative agreement with release adiabat data for calcite and aragonite. Carbon and oxygen isotope ratios in the shock-released CO_2 are the same as those in the unshocked (hydrothermal) calcite, demonstrating that the CO_2 comes from the calcite rather than other potential sources.",
"doi": "10.1016/0012-821X(82)90049-8",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1982-11",
"series_number": "1",
"volume": "61",
"issue": "1",
"pages": "166-170"
},
{
"id": "authors:s0c4c-6ha04",
"collection": "authors",
"collection_id": "s0c4c-6ha04",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-142818323",
"type": "article",
"title": "Constraints on Core Composition from Shock-Wave Data",
"author": [
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Seismic data demonstrate that the density of the liquid core is some 8-10 % less than\npure iron. Equations of state of Fe-Si, C, FeS_2, FeS, KFeS_2 and FeO, over the\npressure interval 133-364 GPa and a range of possible core temperatures (3500-5000 K), can be used to place constraints on the cosmochemically plausible light\nelement constituents of the core (Si, C, S, K and O). The seismically derived density\nprofile allows from 14 to 20 % Si (by mass) in the outer core. The inclusion of Si, or\npossibly C (up to 11 %), in the core is possible if the Earth accreted inhomogeneously\nwithin a region of the solar nebulae in which a C:O (atomic) ratio of about 1 existed,\ncompared with a C:O ratio of 0.6 for the present solar photosphere. In contrast, homogeneous\naccretion permits Si, but not C, to enter the core by means of reduction of\nsilicates to metallic Fe-Si core material during the late stages of the accumulation of\nthe Earth. The data from the equation of state for the iron sulphides allow up to\n9-13 % S in the core. This composition would provide the entire Earth with a S:Si\nratio in the range 0.14-0.3, comparable with meteoritic and cosmic abundances.\nShock-wave data for KFeS_2 give little evidence for an electronic phase change from\n4s to 3d orbitals, which has been suggested to occur in K, and allow the Earth to store\na cosmic abundance of K in the metallic core.",
"doi": "10.1098/rsta.1982.0064",
"issn": "1364-503X",
"publisher": "Royal Society of London",
"publication": "Philosophical Transactions A: Mathematical, Physical and Engineering Sciences",
"publication_date": "1982-08-20",
"series_number": "1492",
"volume": "306",
"issue": "1492",
"pages": "37-47"
},
{
"id": "authors:epz9e-yxt73",
"collection": "authors",
"collection_id": "epz9e-yxt73",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-150026899",
"type": "article",
"title": "Cometary and meteorite swarm impact on planetary surfaces",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The velocity flow fields, energy partitioning, and ejecta distributions resulting from impact of porous (fragmented) icy cometary nuclei with silicate planetary surfaces at speeds from 5 to 45 km/s are different than those resulting from the impact of solid ice or silicate meteorites. The impact of 1 g/cm^3 ice spheres onto an atmosphereless anorthosite planetary surface induces cratering flows that appear similar to those induced by normal density anorthosite meteorite impact. Both of these impactors lead to deep transient crater cavities for final crater diameters less than \u223c1 to \u223c10 km and for escape velocities \u227210^5 cm/s. Moreover the fraction of internal energy partitioned into the planetary surface at the cratering site is 0.6 for both ice and anorthosite impactors at 15 km/s. As the assumed density of the hypothetical cometary nucleus or fragment cloud from a nucleus decreases to 0.01 g/cm^3, the fraction of the impact energy partitioned into planetary surface internal energy decreases to less than 0.01, and the flow field displays a toroidal behavior in which the apparent source of the flow appears to emanate from a disc or ringlike region rather than from a single point, as in the explosive cratering case. The edges of the crater region are in several cases depressed and flow downward, whereas the center of the crater region is uplifted. Moreover, the resultant postimpact particle velocity flow in some cases indicates the formation of concentric ridges, a central peak, and a distinct absence of a deep transient cavity. In contrast, transient cavities are a ubiquitous feature of nearly all previous hypervelocity impact calculations. The calculations of the flow fields for low density (0.01 g/cm^3) impactors exhibited surface interface (comet-planet) instabilities. These are attributed to both the Rayleigh-Taylor and Helmholtz instability conditions, and we believe that these occur in all flows involving volatile low-density (0.01 g/cm^3) projectiles. It is speculated that these hydrodynamic instabilities can give rise to concentric rings in the inner crater region in large-scale impacts on planetary surfaces, although other mechanisms for their production may also act. The ejecta mass loss versus planetary escape velocity was computed, and these results imply that the critical escape velocity, at which as much material is lost as is being accreted from a planet, ranges from 1.2 to 2.75 km/s for encounter speeds of 5 to 15 kms/s, with cometary impactors having a density of 0.01 to 1 g/cm^3. These values compare to 0.83 and 1.5 km/s for silicate impactors, thereby indicating that it is more difficult for volatiles than silicates to be accreted onto objects with escape velocities similar to the Moon, Mercury, and Mars. For objects with escape velocities in the 0.1 to 1 km/s range the accretional efficiency for silicate and various porosity ices are similar, whereas for objects with escape velocities <0.1 km/s the accretional efficiency of icy impactors becomes significantly lower than for silicate impactors.",
"doi": "10.1029/JB087iB08p06668",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1982-08-10",
"series_number": "B8",
"volume": "87",
"issue": "B8",
"pages": "6668-6680"
},
{
"id": "authors:90xqd-5s266",
"collection": "authors",
"collection_id": "90xqd-5s266",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-151200534",
"type": "article",
"title": "The role of iron partitioning in mantle composition, evolution, and scale of convection",
"author": [
{
"family_name": "Watt",
"given_name": "J. Peter",
"clpid": "Watt-J-P"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The effect on composition and evolution of the mantle of the recently-observed strong concentration of iron in (Mg, Fe)O-magnesiow\u00fcstite (mw) at the expense of (Mg, Fe)SiO_3-perovskite (pv) structure is studied by calculating a temperature- and pressure-dependent iron partitioning coefficient for the lower mantle. The value of the standard entropy for MgSiO_3-perovskite is found to be 69.4\u00b110.3 J/mole deg from the recently determined phase diagram of forsterite. Iron remains concentrated in (Mg, Fe)O throughout the entire lower mantle if account is taken of an FeO phase change, with the partitioning coefficient (x^(pv)_(Fe)/x^(pv)_(Mg))/(x^(mw)_(Fe)/x^(mw)_(Mg)) increasing from 0.04 to 0.8 between 670 Km a the core-mantle boundary. Partitioning has negligible effect on gross density and elastic properties Of the lower mantle. By using recent shock wave and static compression results for FeO and MgSiO_3-perovskite, we find that the lower mantle is more pyroxene-rich than the upper mantle and as iron-rich, or somewhat less so, than the upper mantle. Mg/(Mg + Fe) = 0.93\u20130.95 for the lower mantle compared with 0.85\u20130.90 for the uppermost mantle. The lower mantle Mg/Si ratio is closer to chondritic values (0.99\u00b1 0.03) (\u22481.5 for a peridotite with px/ol = 0.4(molar)), thus supporting the idea of a chemically layered mantle with implications for the style of mantle convection. While partitioning of iron has no significant effect on gross lower mantle density, we find that the (Mg, Fe)O and perovskite components of the lower mantle have essentially the same densities. Mantles with higher bulk iron contents have (Mg, Fe)O denser than the perovskite component; for a bulk magnesium mole fraction of, 0.80, the density difference is 0.7\u20130.8 g/cm^3. We investigate the feasibility of the Mao, Bell, and Yagi gravitational separation hypothesis of mantle evolution in which a mantle more iron-rich than present loses iron through gravitational sinking of the denser (Mg, Fe) O, and we conclude that the process cannot successfully compete with solid state convection unless implausibly large grain sizes or unacceptably low viscosities are invoked. A likely explanation for removal of iron from an initially iron rich lower mantle is upward extraction of FeO-enriched basalts or picrites and concentration of iron in upper mantle garnets during accretion of the earth or subsequent convection with the entire mantle passing through the partial melt zone. Thus the lower mantle was depleted of iron relative to both the upper mantle and the mantles of the small terrestrial planets and satellites, which do not have mantle pressures sufficient to form perovskite-structure silicates, or which had lower accretional temperatures and less extensive melting. On this basis, Venus would be expected to have a mantle similarly depleted in iron.",
"doi": "10.1029/JB087iB07p05631",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1982-07-10",
"series_number": "B7",
"volume": "87",
"issue": "B7",
"pages": "5631-5644"
},
{
"id": "authors:yyasy-yxz50",
"collection": "authors",
"collection_id": "yyasy-yxz50",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-075615370",
"type": "article",
"title": "Impact mechanics of the Cretaceous-Tertiary extinction bolide",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "On Earth impact of ~ 10 km diameter, asteroidal or cometary objects the vaporized, melted and (< 1 mm) solid ejecta transfer ~40\u201350% of their energy to the atmosphere, giving rise to a short possibly lethal (to large animals) heating pulse. Some 1\u201320 projectile masses of early, high-speed and highly shocked (diameter, <1 \u00b5m) extraterrestrial-rich ejecta is lofted to altitudes of 10 km where it can be globally distributed. It is proposed that this material represents the global Cretaceous\u2013Tertiary boundary layer. When in the upper atmosphere it may have caused decreases in solar tropospheric insolation and resulting major extinctions in biota.",
"doi": "10.1038/298123a0",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "1982-07-08",
"series_number": "5870",
"volume": "298",
"issue": "5870",
"pages": "123-127"
},
{
"id": "authors:2bwar-2z163",
"collection": "authors",
"collection_id": "2bwar-2z163",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-161911139",
"type": "article",
"title": "The evolution of an impact-generated atmosphere",
"author": [
{
"family_name": "Lange",
"given_name": "Manfred A.",
"clpid": "Lange-M-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock wave and thermodynamic data for rock-forming and volatile-bearing minerals are used to determine minimum impact velocities (v_(cr)) and minimum impact pressures (p_(cr)) required to form a primary H_2O atmosphere during planetary accretion from chondritelike planetesimals. The escape of initially released water from an accreting planet is controlled by the dehydration efficiency. Since different planetary surface porosities will result from formation of a regolith, v_(cr) and p_(cr) can vary from 1.5 to 5.8 km/sec and from 90 to 600 kbar, respectively, for target porosities between 0 and \u223c45%. On the basis of experimental data, hydration rates for forsterite and enstatite are derived. For a global regolith layer on the Earth's surface, the maximum hydration rate equals 6 \u00d7 10^(10) g H_2O sec^(\u22121) during accretion of the Earth. Attenuation of impact-induced shock pressure is modeled to the extent that the amount of released water as a function of projectile radius, impact velocity, weight fraction of water in the target, target porosity, and dehydration efficiency can be estimated. The two primary processes considered are the impact release of water bound in hydrous minerals (e.g., serpentine) and the subsequent reincorporation of free water by hydration of forsterite and enstatite. These processes are described in terms of model calculations for the accretion of the Earth. Parameters which lead to a primary atmosphere/hydrosphere are: an accretion time of \u2a85 1.6 \u00d7 10^8years, the use of an accretion model defined by Weidenschilling (1974, 1976), a mean planetesimal radius of 0.5 km, a hydration rate of 6 \u00d7 10^(10) g H_2O sec^(\u22121) inferred from a mean porosity of \u223c 10% for the upper 1 km of the accreting Earth, and values for the dehydration efficiency, DE, of 0.55 and 0.07 for the maximum and minimum pressure decay model, respectively. Conditions which prohibit the formation of a primary atmosphere include an accretion time much longer than 1.6 \u00d7 10^8 years, a hydration rate for forsterite and enstatite well in excess of 6 \u00d7 10^(10) g H_2O sec^(\u22121), and a dehydration efficiency DE < 0.07. We conclude that the concept of dehydration efficiency is of dominant importance in determining the degree to which an accreting planet acquires an atmosphere during its formation.",
"doi": "10.1016/0019-1035(82)90031-8",
"issn": "0019-1035",
"publisher": "Elsevier",
"publication": "Icarus",
"publication_date": "1982-07",
"series_number": "1",
"volume": "51",
"issue": "1",
"pages": "96-120"
},
{
"id": "authors:t9vbc-xza54",
"collection": "authors",
"collection_id": "t9vbc-xza54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LYZjcp82",
"type": "article",
"title": "The temperature of shock-compressed water",
"author": [
{
"family_name": "Lyzenga",
"given_name": "G. A.",
"clpid": "Lyzenga-G-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Nellis",
"given_name": "W. J.",
"clpid": "Nellis-W-J"
},
{
"family_name": "Mitchell",
"given_name": "A. C.",
"clpid": "Mitchell-A-C"
}
],
"abstract": "Temperatures from 3300\u20135200 K were measured in liquid H2O shocked to 50\u201380 GPa (500\u2013800 kbar). A six-channel, time-resolved optical pyrometer was used to perform the measurements. Good agreement with the data is obtained by calculating the temperature with a volume-dependent Gr\u00fcneisen parameter derived from double-shock data and a heat capacity at constant volume of 8.7 R per mol of H2O.",
"doi": "10.1063/1.443031",
"issn": "0021-9606",
"publisher": "Journal of Chemical Physics",
"publication": "Journal of Chemical Physics",
"publication_date": "1982-06-15",
"series_number": "12",
"volume": "76",
"issue": "12",
"pages": "6282-6286"
},
{
"id": "authors:61ynf-n3t48",
"collection": "authors",
"collection_id": "61ynf-n3t48",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-152204008",
"type": "article",
"title": "Shock compression of aragonite and implications for the equation of state of carbonates",
"author": [
{
"family_name": "Vizgirda",
"given_name": "Joana",
"clpid": "Vizgirda-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Hugoniot equation of state and release adiabat results are presented for c cut crystals of aragonite, the high-pressure polymorph of calcite, shocked to pressures of up to 40 GPa. A Hugoniot elastic limit is observed at 2.5\u00b10.8 GPa and is similar to that of calcite, which, depending on orientation, ranges from 1.5 to 2.5 GPa. A phase transition, possibly displacive, occurs between 5.5 and 7.6 GPa. Above shock pressures of \u223c10 GPa, the aragonite and calcite Hugoniots are nearly coincident, suggesting transformation of both polymorphs to the same phase. Model calculations, attempting to characterize the high pressure CaCO_3 phase are presented. Aragonite release adiabats centered at pressures between 9 and 14 GPa indicate that states with apparent zero-pressure densities from 2.9 to 3.2 g/cm^3 are achieved upon decompression from progressively greater shock pressures. Observed unloading paths from shock pressures above 17 GPa are significantly and consistently shallower (in a density-pressure plane) than those from lower pressures, and zero-pressure densities up to 20% below that of the initial aragonite density are achieved upon unloading; these features suggest that vaporization is occurring upon unloading. According to theoretical shock temperature and entropy calculations, however, the minimum shock pressure for vaporization upon release for aragonite is 55 GPa (and 33 GPa for calcite), significantly higher than the observed value.",
"doi": "10.1029/JB087iB06p04747",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1982-06-10",
"series_number": "B6",
"volume": "87",
"issue": "B6",
"pages": "4747-4758"
},
{
"id": "authors:95zet-cb760",
"collection": "authors",
"collection_id": "95zet-cb760",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-154051250",
"type": "article",
"title": "The equation of state of Mg_(0.6)Fe_(0.4)O to 200 GPa",
"author": [
{
"family_name": "Vassiliou",
"given_name": "M. S.",
"clpid": "Vassiliou-M-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New Hugoniot data on polycrystalline (avg.porosity 6.9%) samples of the magnesiowustite Mg_(0.6)Fe_(0.4)O are presented, covering the pressure range up to 200 GPa. When our data are fit by a single 3rd order Eulerian Hugoniot with K_0 constrained to its ultrasonic value of 161.5 GPa, the required isentropic pressure derivative K_0\u2032 is 4.37 +/\u2212 0.37. This value is significantly lower than the ultrasonic one of 6.18; existing isothermal compression data, however, are in agreement with our value rather than the ultrasonic one. Our data are adequately explained without phase transitions. There is some marginal evidence for a possible phase transition around 120 GPa. If such a transition indeed occurs it is probably of small volume change compared to the transition observed in FeO; we place an extreme upper bound of 3% on the density change such a transformation could involve and still be consistent with the data. Contrary to earlier hypotheses, we believe that a phase transition in magnesiowustite is not a likely explanation of the seismic effects in the D\u2033 region of the lower mantle. The wustite transition may be a more complex phenomenon than initially supposed \u2014 perhaps an effect of nonstoichiometry localized to the iron-rich end of the solid solution series.",
"doi": "10.1029/GL009i002p00127",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1982-02",
"series_number": "2",
"volume": "9",
"issue": "2",
"pages": "127-130"
},
{
"id": "authors:dza4c-0hy58",
"collection": "authors",
"collection_id": "dza4c-0hy58",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120717-132851875",
"type": "article",
"title": "Limited aperture light source streak photography",
"author": [
{
"family_name": "Vassiliou",
"given_name": "M. S.",
"clpid": "Vassiliou-M-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "In shock wave equation\u2010of\u2010state experiments employing inclined mirror techniques, limited aperture light sources such as the xenon flash lamp are generally more convenient to use than extended light sources employing explosives, but can create alignment problems when mirror inclination angles are large. These problems can be solved by employing a wedge\u2010shaped inclined mirror in place of a flat one.",
"doi": "10.1063/1.1136807",
"issn": "0034-6748",
"publisher": "American Institute",
"publication": "Review of Scientific Instruments",
"publication_date": "1982-01",
"series_number": "1",
"volume": "53",
"issue": "1",
"pages": "108-109"
},
{
"id": "authors:nfxdf-eyn83",
"collection": "authors",
"collection_id": "nfxdf-eyn83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120717-155256329",
"type": "article",
"title": "Electrical measurements on fused quartz under shock compression",
"author": [
{
"family_name": "Kondo",
"given_name": "Ken-ichi",
"clpid": "Kondo-K"
},
{
"family_name": "Sawaoka",
"given_name": "Akira",
"clpid": "Sawaoka-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The resistivities of specimens of SiO_2 (fused quartz) singly and doubly shocked in the 10\u201345 and 27\u201390 GPa ranges, respectively, demonstrate a marked decrease from values of \u223c10\u20130.1 \u03a9\u22c5m at a single\u2010shock pressure of \u223c40 and a double\u2010shock pressure of \u223c74 GPa. These states correspond to calculated shock temperatures of \u223c3300 and \u223c3600 K, respectively. At shock pressures below 36 GPa the measured resistivity versus calculated shock temperature agrees closely with ambient\u2010pressure and high\u2010temperature resistivity data. This suggests that the ionic conduction mechanisms inferred to control electrical properties at ambient pressure also act under shock\u2010induced high temperatures in quartz and the presumed high\u2010pressure phase, stishovite into which fused quartz appears to transform above 20 GPa. At 36\u201340 GPa the rapid decrease in resistivity by a factor of 10^2 suggests a further transformation to an unknown phase which may correspond to the onset of melting. The existing pressure\u2010density Hugoniot data do not demonstrate any anomalous density change associated with this phase change.",
"doi": "10.1063/1.329459",
"issn": "0021-8979",
"publisher": "American Institute of Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1981-08",
"series_number": "8",
"volume": "52",
"issue": "8",
"pages": "5084-5089"
},
{
"id": "authors:hs8s8-qyy54",
"collection": "authors",
"collection_id": "hs8s8-qyy54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181219-080606901",
"type": "article",
"title": "Highlights: Spring Council Meeting",
"author": [
{
"family_name": "Walker",
"given_name": "James C. G.",
"clpid": "Walker-J-C-G"
},
{
"family_name": "Cicerone",
"given_name": "Ralph J.",
"clpid": "Cicerone-R-J"
},
{
"family_name": "Prinn",
"given_name": "Ronald G.",
"clpid": "Prinn-R-G"
},
{
"family_name": "Russell",
"given_name": "Christopher T.",
"orcid": "0000-0003-1639-8298",
"clpid": "Russell-C-T"
},
{
"family_name": "Southwood",
"given_name": "David",
"orcid": "0000-0001-6483-9241",
"clpid": "Southwood-D-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Weidner",
"given_name": "Donald J.",
"clpid": "Weidner-D-J"
}
],
"abstract": "Council members present at the May 24, 1981, meeting were Keiiti Aki, Steven Burges (for Jim Wallis), Peter S. Eagleson, E. R. Engdahl, Charles E. Helsley, James R. Heirtzler, Carl Kisslinger, Leslie H. Meredith, Chris N. K. Mooers, Norman F. Ness, Marcia M. Neugebauer, James J. O'Brien, Richard Rapp, Carl Sagan, James C. Savage, Joseph V. Smith, Fred Spilhaus, Donald L. Turcotte, James A. Van Allen, J. Tuzo Wilson, and Jay Winston (for Elmar R. Reiter until his arrival at 6:50 P.M.). David Strangway, representing the Canadian Geophysical Union, and Peter Steinhauser, representing the European Geophysical Society, were special observers at the meeting. Council meetings are open, and a number of section secretaries, committee chairmen, journal editors, and other members attended. The following major actions were adopted by the Council:\n\nThe experiment of publishing oceanography and lower\u2010atmosphere papers in JGR Green issues alternate to those containing upper\u2010atmosphere papers will be continued through 1982. From preliminary indications the experiment seems to be working, but a full year of data, including a renewal cycle, is needed to assess the success of the experiment. Final decision will be made prior to the 1983 dues notices.",
"doi": "10.1029/EO062i029p00588-01",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "Eos",
"publication_date": "1981-07-21",
"series_number": "29",
"volume": "62",
"issue": "29",
"pages": "588-590"
},
{
"id": "authors:7by3k-2qs16",
"collection": "authors",
"collection_id": "7by3k-2qs16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141103-155129976",
"type": "article",
"title": "Hugoniot equation of state of periclase to 200 GPa",
"author": [
{
"family_name": "Vassiliou",
"given_name": "M. S.",
"clpid": "Vassiliou-M-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New shock wave data on {100} oriented single crystal periclase covering the pressure range from 160 to 200 GPa suggest that MgO is described by a single Hugoniot up to 200 GPa, with no displacive phase transitions of volume change greater than 1-1.5 per cent. For a third order finite strain fit, with K_0 constrained to its ultrasonically determined value of 162.7 GPa, the implied K_0\u2032 of 4.27 \u00b1 0.24 is in agreement with ultrasonically determined value of 4.17 \u00b1 0.14. The new data indicate a somewhat steeper Hugoniot than that suggested by previously published shock wave results under 120 GPa. A previously published result at 258 GPa shows more compression in the light of the present data than would be expected for MgO in the B1 structure, and may signal the onset of a phase transition, although we cannot confidently make this interpretation. If MgO forms an ideal solid solution with FeO, our data does not support the occurrence of a significant transition in magnesiowustite at lower mantle pressures.",
"doi": "10.1029/GL008i007p00729",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1981-07",
"series_number": "7",
"volume": "8",
"issue": "7",
"pages": "729-732"
},
{
"id": "authors:25etv-cwk31",
"collection": "authors",
"collection_id": "25etv-cwk31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141104-144451015",
"type": "article",
"title": "Dynamic Tensile Strength of Lunar Rock Types",
"author": [
{
"family_name": "Cohn",
"given_name": "Stephen N.",
"clpid": "Cohn-S-N"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The dynamic tensile strengths of four rocks have been determined. A flat plate impact experiment is used to generate \u223c1-\u03bcs-duration tensile stress pulses in rock samples by superposing rarefaction waves to induce fracture. A gabbroic anorthosite and a basalt were selected because they are the same rock types as occur on the lunar highlands and mare, respectively. Although these have dynamic tensile strengths which lie within the ranges 153\u2013174 MPa and 157\u2013179 \u2013MPa, whereas Arkansas novaculite and Westerly granite exhibit dynamic tensile strengths of 67\u201388 MPa and 95\u2013116 MPa, respectively, the effect of chemical weathering and other factors, which may affect application of the present results to the moon, have not been explicitly studied. The reported tensile strengths are based on a series of experiments on each rock where determination of incipient spallation is made by terminal microscopic examination. These data are generally consistent with previous determinations, at least one of which was for a significantly chemically altered (hydroxylated) but physically coherent rock. The tensile failure data do not bear a simple relation to compressive results and imply that any modeling involving rock fracture consider the tensile strength of igneous rocks under impulse loads distinct from the values for static tensile strength. Generally, the dynamic tensile strengths of nonporous igneous rocks range from \u223c 100 to 180 MPa, with the more basic, and even amphibole-bearing samples, yielding the higher values.",
"doi": "10.1029/JB086iB03p01794",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1981-03-10",
"series_number": "B3",
"volume": "86",
"issue": "B3",
"pages": "1794-1802"
},
{
"id": "authors:957eh-4ta53",
"collection": "authors",
"collection_id": "957eh-4ta53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141104-143322617",
"type": "article",
"title": "Impact cratering: The effect of crustal strength and planetary gravity",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Upon impact of a meteorite with a planetary surface the resulting shock wave both 'processes' the material in the vicinity of the impact and sets a larger volume of material than was subjected to high pressure into motion. Most of the volume which is excavated by the impact leaves the crater after the shock wave has decayed. The kinetic energy which has been deposited in the planetary surface is converted into reversible and irreversible work, carried out against the planetary gravity field and against the strength of the impacted material, respectively. By using the results of compressible flow calculations prescribing the initial stages of the impact interaction (obtained with finite difference techniques) the final stages of cratering flow along the symmetry axis are described, using the incompressible flow formalism proposed by Maxwell. The fundamental assumption in this description is that the amplitude of the particle velocity field decreases with time as kinetic energy is converted into heat and gravitational potential energy. At a given time in a spherical coordinate system the radial velocity is proportional to R^(\u2212z), where R is the radius (normalized by projectile velocity) and z is a constant shape factor for the duration of flow and a weak function of angle. The azimuthal velocity, as well as the streamlines, is prescribed by the incompressibility condition. The final crater depth (for fixed strength Y) is found to be proportional to R_0[2(z + 1)u_(or)\u00b2/g]^(1/(z+1)), where u_(or) is the initial radial particle velocity at (projectile normalized) radius R_0, g is planetary gravity, and z (which varied from 2 to 3) is the shape factor. The final crater depth (for fixed gravity) is also found to be proportional to [\u03c1u_(or)^2/Yz]^(1/(z+1)), where \u03c1 and Y are planetary density and yield strength, respectively. By using a Mohr-Coulomb yield criterion the effect of varying strength on transient crater depth and on crater formation time in the gravity field of the moon is investigated for 5-km/s impactors with radii in the 10- to 10^7-cm range. Comparison of crater formation time and maximum transient crater depth as a function of gravity yields dependencies proportional to g^(\u22120.58) and g^(\u22120.19), respectively, compared to g^(\u22120.618) and g^(\u22120.165) observed by Gault and Wedekind for hypervelocity impact craters in the 16- to 26-cm-diameter range in a quartz sand (with Mohr-Coulomb type behavior) carried out over an effective gravity range of 72\u2013980 cm/s\u00b2.",
"doi": "10.1029/RG019i001p00001",
"issn": "8755-1209",
"publisher": "American Geophysical Union",
"publication": "Reviews of Geophysics",
"publication_date": "1981-02",
"series_number": "1",
"volume": "19",
"issue": "1",
"pages": "1-12"
},
{
"id": "authors:0mtqc-1eg58",
"collection": "authors",
"collection_id": "0mtqc-1eg58",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141104-145449462",
"type": "article",
"title": "Shock compression of KFeS_2 and the question of potassium in the core",
"author": [
{
"family_name": "Somerville",
"given_name": "Malcolm",
"clpid": "Somerville-M"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The Hugoniot equation of state of KFeS_2 (initial density 2.663 g/cm^3) has been determined for pressures up to 110 GPa. The Hugoniot data demonstrate a transformation at 13\u00b11 GPa to a phase with an apparent zero-pressure density of 3.7\u00b10.2 g/cm^3. A comparison of the inferred isentrope of KFeS_2 (high-pressure phase) with those of Fe, FeS_(0.9), and FeS_2 indicates that the atomic volume of potassium in KFeS_2 is approximately twice that of iron at 75 GPa. In the temperature and pressure range of the experiments, potassium fails to meet the empirical Hume-Rothery and Raynor (HRR) criterion for solubility of an element in iron, namely, that the molar volume of the element should not exceed that of iron by a factor greater than \u223c1.4. However, both the applicability of the HRR solubility criterion and the inferred isentrope of KFeS_2 at high pressure are uncertain. Thermochemical calculations of the partitioning of K between a sulfide and silicate phase (e.g., KFeS_2 and KAlSiO_4 or KAlSi_3O_8 (hollandite)) indicate that pressure does not have a pronounced effect on the relative stability of solid KFeS_2 and potassium aluminosilicate high-pressure phases. The calculations suggest that the high-pressure phase of KFeS_2 would not be stable in relation to KAlSiO_4 (kalsilite) in the upper mantle, or in relation to KAlSi_3O_8 (hollandite) in the lower mantle. However, the calculations do not bear directly on the question of partitioning of K into an iron sulfide melt from lower mantle aluminosilicate phases. Although the present results cannot absolutely rule out the hypothesis that a large fraction of the terrestrial potassium budget has dissolved into a molten iron sulfide-bearing core, the present analysis of the pressure-volume relation for potassium, iron, iron sulfides, potassium aluminosilicate, and potassium iron sulfide yields no evidence in support of this hypothesis.",
"doi": "10.1029/JB085iB12p07016",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1980-12-10",
"series_number": "B12",
"volume": "85",
"issue": "B12",
"pages": "7016-7024"
},
{
"id": "authors:yjj62-xw564",
"collection": "authors",
"collection_id": "yjj62-xw564",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-120845960",
"type": "article",
"title": "Anorthite: thermal equation of state to high pressures",
"author": [
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We present shock-wave (Hugoniot) data on single-crystal and porous anorthite (CaAl_2Si_2O_8) to pressures of 120 GPa. These data are inverted to yield values of the Gr\u00fcneisen parameter (\u03b3), adiabatic bulk modulus (K_s) and coefficient of thermal expansion (\u03b1) over a broad range of pressures and temperatures which in turn are used to reduce the raw Hugoniot data and construct an experimentally-based, high-pressure thermal equation of state for anorthite. We find surprisingly high values of \u03b3 which decrease from about 2.2 to 1.2 over the density range 3.4 to 5.0 Mg m^(\u22123). Our data clearly indicate that whereas the zeroth order anharmonic (quasi-harmonic) properties such as \u03b3 and \u03b1 decrease upon compression of a single phase, these properties apparently increase dramatically (200 per cent or more) in going from a low to a high pressure phase. The results for anorthite also support the hypothesis that higher-order anharmonic contributions to the thermal properties decrease more rapidly upon compression than the lowest order anharmonicities. We find an initial density p_0 ~ 3.4 Mg m^(\u22123) for the 'high-pressure phase' portion of the Hugoniot, with an initial value of Ks essentially identical to that of anorthite at zero pressure (90 GPa). This is surprising in light of recently documented candidate high-pressure assemblages for anorthite with significantly higher densities, and it raises the question of the non-equilibrium nature of Hugoniot data. By correcting the properties of anorthite to lower mantle conditions we find that although the density of anorthite is comparable to that of the lowermost mantle, its bulk modulus is considerably less, hence making enrichment in the mantle implausible except perhaps near its base.",
"doi": "10.1111/j.1365-246X.1980.tb02589.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1980-09",
"series_number": "3",
"volume": "62",
"issue": "3",
"pages": "529-549"
},
{
"id": "authors:g2e1f-pmf43",
"collection": "authors",
"collection_id": "g2e1f-pmf43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-121410226",
"type": "article",
"title": "Equations of state of FeO and CaO",
"author": [
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New shock-wave (Hugoniot) and release-adiabatic data for Fe_(0.94)O and CaO, to 230 and 175 GPa (2.3 and 1.75 Mbar) respectively, show that both oxides transform from their initial B1 (NaCl-type) structures at about 70 (\u00b110) GPa. CaO transforms to the B2 (CsCl-type) structure and FeO is inferred to do the same. Alternatively, FeO may undergo an electronic transition, but it probably does not disproportionate under shock to Fe and Fe_2O_3 or Fe_3O_4. The Hugoniot data for the B1 phases of FeO and CaO agree with the ultrasonically-determined bulk moduli (K_0= 185, 112 GPa, respectively) and with the ultrasonically-determined pressure derivative for CaO (K\u2032_0= 4.8); K\u2032_0\u223c 3.2 for FeO is determined from the present data. The Hugoniot data for both FeO and CaO are consistent with low- and high-pressure phases having identical K_0 and K\u2032_0. Volume changes for B1/B2 transitions in oxides agree with theoretical expectations and with trends among the halides: -\u0394V/V_1 ~ 4 per cent and 11 per cent for FeO and CaO respectively. Also, the transition pressures increase with decreasing cation/anion radius ratio for the oxides. The Hugoniot data show that the density of the outer core is equal to that of a 50\u201350 mix (by weight) of Fe and FeO (\u223c10 wt per cent oxygen), consistent with geochemical arguments for the presence of oxygen in the core. In terms of a mixture of simple oxides, the density of the lower mantle is satisfied by Fe/(Mg + Fe) \u223c 0.12, however, arbitrarily large amounts of CaO can be present; an enrichment of refractory components in the lower mantle is allowed by the shock-wave data. Because of the relatively low transition pressure in FeO, a B1/B2 transition in (Mg, Fe)O is likely to occur in the lower mantle even if MgO transforms at 150\u2013170 GPa. Such a transition may contribute to the scattering of seismic waves and change in velocity gradient found near the base of the mantle.",
"doi": "10.1111/j.1365-246X.1980.tb02588.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1980-09",
"series_number": "3",
"volume": "62",
"issue": "3",
"pages": "505-528"
},
{
"id": "authors:zkq1j-6v648",
"collection": "authors",
"collection_id": "zkq1j-6v648",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-140819748",
"type": "article",
"title": "Shock-induced effects in calcite from Cactus Crater",
"author": [
{
"family_name": "Vizgirda",
"given_name": "J.",
"clpid": "Vizgirda-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Tsay",
"given_name": "Fun-Dow",
"clpid": "Tsay-F-D"
}
],
"abstract": "Shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into the rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll, has been detected and quantified using electron spin resonance (ESR). ESR spectra of Mn^(2+), present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. A similar variation was observed in coral samples experimentally shocked to progressively higher pressures. It is speculated that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting and hence, small (< 0.01 \u00c5) increases in cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models are suggested by the ESR results. One depicts a steady decay of the shock wave, from a maximum stress level of 4.5 GPa, at a rate, calculated in terms of post-flow co-ordinates, of d^(\u22125.7); this high attenuation rate may be due to the rocks underlying Cactus Crater having been displaced downward 5\u20136 m. The second delineates a breccia lens, possibly stratified, with a breccia-bedrock interface at 20 \u00b1 5 m.",
"doi": "10.1016/0016-7037(80)90059-9",
"issn": "0016-7037",
"publisher": "Elsevier",
"publication": "Geochimica et Cosmochimica Acta",
"publication_date": "1980-08",
"series_number": "8",
"volume": "44",
"issue": "8",
"pages": "1059-1069"
},
{
"id": "authors:v9d3a-qxn06",
"collection": "authors",
"collection_id": "v9d3a-qxn06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130416-114115408",
"type": "article",
"title": "Absorption spectrum of shock-compressed Fe^(2+)-bearing MgO and the radiative conductivity of the lower mantle",
"author": [
{
"family_name": "Goto",
"given_name": "Tsuneaki",
"clpid": "Goto-T"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Rossman",
"given_name": "George R.",
"orcid": "0000-0002-4571-6884",
"clpid": "Rossman-G-R"
},
{
"family_name": "Syono",
"given_name": "Yasuhiko",
"clpid": "Syono-Y"
}
],
"abstract": "New shock wave measurements of the optical absorption spectrum from 410 to 580 nm of 0.14 and 0.26 mole percent Fe^(2+)-bearing MgO (synthetic periclase) have been carried out to pressures of 42 GPa, and demonstrate considerably lower opacities at short wavelengths than inferred from static high pressure measurements on more Fe^(2+)-rich samples. Although the spectra obtained under dynamic pressure conditions demonstrate a marked increase in the absorption coefficient at 410 nm (e.g., from 0.3 to 0.65 cm\u22121 for 0.26 mole percent Fe^(2+)), in qualitative agreement with the effect of pressure on more Fe^(2+)-rich samples, the absolute values of the absorptivity coefficients observed are \u223c10^2 lower than those inferred from static high pressure spectral data for iron-rich materials probably containing relatively more ferric iron. The spectra for (Mg_(0.9), Fe_(0.1))O inferred from Mao and Bell's (1977) static results to 31 GPa imply that radiative thermal conductivity for the lower mantle (\u223c3000 K) is effectively blocked by significant opacity in the optical range. When the present shock-wave results, for which the Fe^(3+) content is believed to be less than 5% of the total iron, are extrapolated to a typical mantle Fe^(2+) composition, temperatures of \u223c3000 K and pressure of 31 GPa, a significant radiative thermal conductivity, 4 J (s K m)^(\u22121) is calculated, implying that significant radiative thermal conductivity of the lower mantle may take place in Fe^(2+)-depleted minerals under highly reducing conditions.",
"doi": "10.1016/0031-9201(80)90044-8",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1980-06",
"series_number": "3-4",
"volume": "22",
"issue": "3-4",
"pages": "277-288"
},
{
"id": "authors:3q6b9-fwx23",
"collection": "authors",
"collection_id": "3q6b9-fwx23",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141110-134218113",
"type": "article",
"title": "Identification of Ice VI on the Hugoniot of Ice I_h",
"author": [
{
"family_name": "Gaffney",
"given_name": "Edward S.",
"clpid": "Gaffney-E-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Ice VI has been produced by shock compression of ice I_h to about 2 GPa. This is the second high-pressure polymorph of water observed in shock loading. These experiments point out the ease with which high-pressure phases can form when ice I_h is impacted. The new shock data, combined with previous static measurements, provide preliminary equation of state parameters for ice VI.",
"doi": "10.1029/GL007i005p00407",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1980-05",
"series_number": "5",
"volume": "7",
"issue": "5",
"pages": "407-409"
},
{
"id": "authors:rr4as-k5418",
"collection": "authors",
"collection_id": "rr4as-k5418",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181219-075122266",
"type": "article",
"title": "Electrical conductivity measurement of fayalite under shock compression up to 56 GPa",
"author": [
{
"family_name": "Mashimo",
"given_name": "Tsutomu",
"clpid": "Mashimo-Tsutomu"
},
{
"family_name": "Kondo",
"given_name": "Ken-ichi",
"clpid": "Kondo-Ken-ichi"
},
{
"family_name": "Sawaoka",
"given_name": "Akira",
"clpid": "Sawaoka-Akira"
},
{
"family_name": "Syono",
"given_name": "Yasuhiko",
"clpid": "Syono-Yasuhiko"
},
{
"family_name": "Takei",
"given_name": "Humihiko",
"clpid": "Takei-Humihiko"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The electrical conductivity measurements of single\u2010crystal fayalite are performed under shock wave compression in the pressure range 19.5\u201356 GPa. The electrical conductivity under shock compression increases by a factor of more than 10^(10) from 0 to 40 GPa. Over the range 19.5\u201342 GPa the specific conductivity \u03c3 can be closely described by log_(10)\u03c3 (S/m) = \u22124.65 + 0.15P (GPa). The conductivity versus pressure relation at room temperature is calculated by using measured values of the activation energy to correct the high\u2010temperature shock data to room temperature. After the effect of temperature is removed, the increase in conductivity with pressure approximately agrees with that measured under static pressure using a diamond anvil cell by Mao and Bell. Above pressures of \u223c42 GPa the conductivity remains at a relatively high level of \u223c100 S/m from 40 to 55 GPa.",
"doi": "10.1029/jb085ib04p01876",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research: Solid Earth",
"publication_date": "1980-04-10",
"series_number": "B4",
"volume": "85",
"issue": "B4",
"pages": "1876-1881"
},
{
"id": "authors:gzj41-x7k77",
"collection": "authors",
"collection_id": "gzj41-x7k77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141104-075902335",
"type": "article",
"title": "Dynamic Compression of Earth Materials",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock wave techniques have been used to investigate the pressuredensity relations of metals, silicates, and oxides over the entire range of pressures present in the earth (3.7 x 10^6 bars at the center). In many materials of geophysical interest, such as iron, w\u00fcstite, calcium oxide, and forsterite, major shock-induced phase changes dominate the compression behavior below pressures of 10^6 bars. The shock wave data for the high-pressure phases of these minerals lead to important inferences about the composition of the lower mantle and outer, liquid core of the earth. The lower mantle of the earth appears to have a slightly higher density than is inferred to correspond to the behavior of an olivine-rich assembiage of the same composition as the upper mantle. The core has a density some 10 percent less than that of pure iron and may have 9 to 12 percent sulfur or about 8 percent oxygen by weight.",
"doi": "10.1126/science.207.4435.1035",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1980-03-07",
"series_number": "4435",
"volume": "207",
"issue": "4435",
"pages": "1035-1041"
},
{
"id": "authors:b6c77-xe454",
"collection": "authors",
"collection_id": "b6c77-xe454",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141110-163422745",
"type": "article",
"title": "Shock temperature measurements in Mg_2SiO_4 and SiO_2 at high pressures",
"author": [
{
"family_name": "Lyzenga",
"given_name": "Gregory A.",
"clpid": "Lyzenga-G-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Temperatures in the high pressure shock state have been determined by measurement of optical radiation from pure samples of forsterite (Mg_2SiO_4), \u03b1-quartz, and fused silica. Shock waves of known amplitude were produced by tantalum flyer impact using a two-stage light gas gun. Shock pressures in the ranges 150-175 GPa and 70-115 GPa for Mg_2SiO_4 and SiO_2 respectively were achieved, and temperatures in the range 4500-6800 K were measured. The observed temperatures in Mg_2SiO_4 are consistent with the occurrence of a shock-induced phase transition with a transition energy of \u223c 1.5 MJ/kg. Measured Hugoniot temperatures versus pressure in both fused and crystalline SiO_2 shocked to the stishovite regime suggest the occurrence of a previously unknown transition, beginning at pressures of approximately 107 GPa and 70 GPa for \u03b1-quartz and fused quartz, respectively. The energies and temperatures appear to be consistent with the onset of melting of stishovite under shock loading.",
"doi": "10.1029/GL007i002p00141",
"issn": "0094-8276",
"publisher": "American Geophysical Union",
"publication": "Geophysical Research Letters",
"publication_date": "1980-02",
"series_number": "2",
"volume": "7",
"issue": "2",
"pages": "141-144"
},
{
"id": "authors:n8czq-tjk93",
"collection": "authors",
"collection_id": "n8czq-tjk93",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-150851681",
"type": "article",
"title": "Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages",
"author": [
{
"family_name": "Croft",
"given_name": "S. K.",
"clpid": "Croft-S-K"
},
{
"family_name": "Kieffer",
"given_name": "S. W.",
"clpid": "Kieffer-S-W"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "We produced a series of decimeter-sized impact craters in blocks of ice near 0\u00b0C and \u221270\u00b0C and in ice-saturated sand near \u221270\u00b0C as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar system satellites. The projectiles used were standard 0.22 and 0.30 caliber bullets fired at velocities between 0.3 and 1.5 km/s, with kinetic energies at impact between 10^9 and 4\u00d710^(10) ergs. Crater diameters in the ice-saturated sand were \u223c2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were \u223c3 times larger. If this dependence of crater size on strength persists to large hypervelocity impact craters, then surfaces of geologic units composed of ice or ice-saturated soil would have greater crater count ages than rocky surfaces with identical influx histories. The magnitude of the correction to crater counts required by this strength effect is comparable to the magnitudes of corrections required by variations in impact velocity and surface gravity used in determining relative interplanetary chronologies. The relative sizes of craters in ice and ice-saturated sand imply that the tensile strength of ice-saturated sand is a strong inverse function of temperature. If this is true, then Martian impact crater energy versus diameter scaling may also be a function of latitude.",
"doi": "10.1029/JB084iB14p08023",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1979-12-30",
"series_number": "B14",
"volume": "84",
"issue": "B14",
"pages": "8023-8032"
},
{
"id": "authors:fsk2p-vrx88",
"collection": "authors",
"collection_id": "fsk2p-vrx88",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-151537075",
"type": "article",
"title": "Release adiabat measurements on minerals: The effect of viscosity",
"author": [
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The current inversion of pressure-particle velocity data for release from a high-pressure shock state to a pressure-density path usually depends critically upon the assumption that the release process is isentropic. It has been shown by Kieffer and Delaney that for geological materials below stresses of \u223c150 GPa, the effective viscosity must be \u227210^3kg m^(\u22121) s^(\u22121) (10^4 P) in order that the viscous (irreversible) work carried out on the material in the shock state remains small in comparison to the mechanical work recovered upon adiabatic rarefaction. The available data pertaining to the offset of the Rayleigh line from the Hugoniot curve for minerals, the magnitude of the shear stress in the high-pressure shock state for minerals, and the direct measurements of the viscosities of several engineering materials shocked to pressures below 150 GPa yield effective viscosities of \u223c10^3kg m^(\u22121) s^(\u22121) or less. We infer that this indicates that the conditions for isentropic release of minerals from shock states are achieved, at least approximately, and we conclude that the application of the Riemann integral to obtain pressure-density states along the release adiabats of minerals in shock experiments is valid.",
"doi": "10.1029/JB084iB13p07545",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1979-12-10",
"series_number": "B13",
"volume": "84",
"issue": "B13",
"pages": "7545-7548"
},
{
"id": "authors:vbgp0-wz430",
"collection": "authors",
"collection_id": "vbgp0-wz430",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151109-152245770",
"type": "article",
"title": "B1-B2 Transition in Calcium Oxide from Shock-Wave and Diamond-Cell Experiments",
"author": [
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Mao",
"given_name": "H. K.",
"clpid": "Mao-H-K"
},
{
"family_name": "Bell",
"given_name": "P. M.",
"clpid": "Bell-P-M"
}
],
"abstract": "Volume and structural data obtained by shock-wave and diamond-cell techniques demonstrate that calcium oxide transforms from the B1 (sodium chloride type) to the B2 (cesium chloride type) structure at 60 to 70 gigapascals (0.6 to 0.7 megabar) with a volume decrease of 11 percent. The agreement between the shockwave and diamond-cell results independently confirms the ruby-fluorescence pressure scale to about 65 gigapascals. The shock-wave data agree closely with ultrasonic measurements on the B1 phase and also agree satisfactorily with equations of state derived from ab initio calculations. The discovery of this B1-B2 transition is significant in that it allows considerable enrichment of calcium components in the earth's lower mantle, which is consistent with inhomogeneous accretion theories.",
"doi": "10.1126/science.206.4420.829",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1979-11-16",
"series_number": "4420",
"volume": "206",
"issue": "4420",
"pages": "829-830"
},
{
"id": "authors:1atem-n8v45",
"collection": "authors",
"collection_id": "1atem-n8v45",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LYZrsi79",
"type": "article",
"title": "Multiwavelength optical pyrometer for shock compression experiments",
"author": [
{
"family_name": "Lyzenga",
"given_name": "G. A.",
"clpid": "Lyzenga-G-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A system for measurement of the spectral radiance of materials shocked to high pressures (~100 GPa) by impact using a light gas gun is described. Thermal radiation from the sample is sampled at six wavelength bands in the visible spectrum, and each signal is separately detected by solid-state photodiodes, and recorded with a time resolution of ~10 ns. Interpretation of the records in terms of temperature of transparent sample materials is discussed. Results of a series of exploratory experiments with metals are also given. Shock temperatures in the range 4000\u20138000 K have been reliably measured. Spectral radiance and temperatures have been determined with uncertainties of 2%.",
"doi": "10.1063/1.1135731",
"issn": "0034-6748",
"publisher": "Review of Scientific Instruments",
"publication": "Review of Scientific Instruments",
"publication_date": "1979-11-01",
"series_number": "11",
"volume": "50",
"issue": "11",
"pages": "1421-1424"
},
{
"id": "authors:bf5n3-cdc24",
"collection": "authors",
"collection_id": "bf5n3-cdc24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141222-101655990",
"type": "article",
"title": "Shock-wave compression of vitreous and rutile-type GeO_2: A comparative study",
"author": [
{
"family_name": "Jackson",
"given_name": "Ian",
"clpid": "Jackson-I"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The dynamic compression of both vitreous and rutile-type GeO_2 has been studied throughout the pressure range 0\u2013160 GPa (1.6 Mbar). At sufficiently high pressures (respectively >35 GPa and >70 GPa) both materials attain densities greater than those expected for the rutile phase at the same pressure. These results may be explained in terms of transformation of both vitreous and rutile-type GeO_2 to a common high-pressure phase or state with a zero-pressure density \u223c5% greater than that of the rutile polymorph. The vastly different thermal regimes associated with the two Hugoniots allow important deductions to be made concerning the elastic and thermodynamic properties of shocked germanium dioxide. In particular, an effective Gr\u00fcneisen parameter of 1.24 \u00b1 0.1 is required at a density of 7.4 g/cm^3. Inconsistency between this value and those calculated from the Vashchenko-Zubarev model suggests that the latter may not provide an adequate description of the thermal properties of close-packed germanates and silicates.",
"doi": "10.1016/0031-9201(79)90108-0",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1979-09",
"series_number": "1",
"volume": "20",
"issue": "1",
"pages": "60-70"
},
{
"id": "authors:p5j25-6fm42",
"collection": "authors",
"collection_id": "p5j25-6fm42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141111-152226628",
"type": "article",
"title": "Post-shock temperatures in minerals",
"author": [
{
"family_name": "Raikes",
"given_name": "Susan A.",
"clpid": "Raikes-S-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "An experimental technique has been developed for the measurement of post-shock temperatures in a wide variety of materials, including those of geophysical interest such as silicates. The technique uses an infrared radiation detector to determine the brightness temperature of samples shocked to pressures in the range 5 to \u223c 30 GPa; in these experiments measurements have been made in two wavelength ranges (4.5 to 5.75 \u03bcm; 7 to 14 \u03bcm). Reproducible results, with the temperatures in the two wavelength bands generally in excellent agreement, have been obtained for aluminium-2024 (10.5 to 33 GPa; 125 to 260\u00b0C), stainless steel-304 (11.5 to 50 GPa; 80 to 350\u00b0C), crystalline quartz (5.0 to 21.5 GPa; 80 to 250\u00b0C), forsterite (7.5 to 28.0 GPa; \u223c 30 to 160\u00b0C) and Bamble bronzite (6.0 to 26.0 GPa; \u223c 30 to 225\u00b0C). \n\nThese results are generally much higher at low pressures (where they may even be in excess of the calculated shock temperatures) than the values calculated assuming a hydrodynamic rheology and isentropic release parallel to the Hugoniot but tend towards them at higher pressures. In aluminium-2024, the theoretical post-shock temperatures, assuming a fluid-like rheology, are 35 to 218\u00b0C, for the pressure range 10.5 to 33 GPa. However, the results are in considerably better agreement with values calculated assuming elasto-plastic behaviour (80 to 270\u00b0C) which probably also causes the high measured temperatures for stainless steel. In forsterite the measured values ranged from 65\u00b0C at 9.6 GPa (there was no detectable rise at 7.5 GPa) to 156\u00b0 at 28.0 GPa, whereas the 'hydrodynamic values' were 30 to 120\u00b0C. Values obtained for quartz were in excellent agreement with those calculated by Mashimo et al. using release adiabat data. It is concluded that release adiabat data should be used, wherever available, for calculations of residual temperature, and that adequate descriptions of the shock and release processes in minerals need to be more complex than generally assumed.",
"doi": "10.1111/j.1365-246X.1979.tb04804.x",
"issn": "0016-8009",
"publisher": "Royal Astronomical Society",
"publication": "Geophysical Journal of the Royal Astronomical Society",
"publication_date": "1979-09",
"series_number": "3",
"volume": "58",
"issue": "3",
"pages": "717-747"
},
{
"id": "authors:p77qh-4pe09",
"collection": "authors",
"collection_id": "p77qh-4pe09",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140226-100654164",
"type": "article",
"title": "Absorption Spectra of Cr^(3+) in Al_2O_3 Under Shock Compression",
"author": [
{
"family_name": "Goto",
"given_name": "Tsuneaki",
"clpid": "Goto-T"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Rossman",
"given_name": "George R.",
"orcid": "0000-0002-4571-6884",
"clpid": "Rossman-G-R"
}
],
"abstract": "Unpolarized absorption spectra of single crystals of Cr^(3+) doped Al_2O_3 (synthetic ruby) have measured using a new, time-resolving, dispersive, streak photographic system over the range \u223c350 to \u223c700 nm during a series of shock loading experiments. The crystal field absorptions assigned to the transition ^4A_(2g) \u2192 ^4T_(2g) were observed to shift in a series of experiments from 555\u00b11 nm at atmospheric pressure to 503\u00b15 nm at 46 GPa. In a single experiment at 32 GPa the ^4A_(2g) \u2192 4 T_(1g) transition was observed to shift from 405\u00b11 to 386\u00b15 nm. The present data extrapolate downwards in compression toward the 10 GPa data of Stephens and Drickamer (1961) although both crystal field absorption energies increase considerably less with compression than predicted by the simple ionic point charge model. The single datum observed for the Racah parameter B, 588\u00b138 cm^(\u22121) at 32 GPa, is consistant with previous results to 10 GPa and the trend of decreasing B, with compression expected from the divergence of the data from the point charge model due to increasing covalancy.",
"doi": "10.1007/BF00307949",
"issn": "0342-1791",
"publisher": "Springer",
"publication": "Physics and Chemistry of Minerals",
"publication_date": "1979-07-16",
"series_number": "3",
"volume": "4",
"issue": "3",
"pages": "253-263"
},
{
"id": "authors:py2da-jp807",
"collection": "authors",
"collection_id": "py2da-jp807",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-123329621",
"type": "article",
"title": "Shock wave compression of single-crystal forsterite",
"author": [
{
"family_name": "Jackson",
"given_name": "Ian",
"clpid": "Jackson-I"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Hugoniot equation of state measurements have been performed on pure synthetic single-crystal forsterite (Mg_2SiO_4) in the pressure range 70\u2013160 GPa (0.7\u20131.6 Mbar). These and earlier data for polycrystalline forsterite are compared with theoretical Hugoniots for the assemblages 2MgO (rocksalt) + SiO_2 (stishovite) and MgO (rocksalt) + MgSiO_3 (perovskite). The densities attained by single-crystal forsterite at pressures in excess of 120 GPa are greater than those expected in the event of shock-induced transformation to the isochemical oxide mixture. A similar test of the hypothesis of shock-induced transformation to the perovskite-bearing assemblage is sensitive to the choice of MgSiO_3 (perovskite) bulk modulus. Recent static compression measurements of Yagi et al. (1978) yield a K_(0T) of 286 GPa (for K_(0T)\u2032 = 5), which, along with other elastic and thermodynamic parameters, suggests that shocked forsterite may be more dense than the perovskite-bearing assemblage. Crystalline phases of up to 5% greater zeropressure density or equally dense short-range-order-only phases may well be involved. Alternatively, the use of an isentropic bulk modulus of 250 GPa (estimated by Liebermann et al., 1977) for MgSiO_3 (perovskite) allows consistency between the data and the calculated MgO + MgSiO_3 (perovskite) Hugoniot for a reasonable choice (\u223c3.8) of K_(0s)\u2032 for the latter phase. The new forsterite data along with high-pressure Hugoniot data for other olivines and olivinitic rocks define a smooth isobaric variation of Hugoniot density with composition. It is shown that an estimated pyrolite (Ringwood, 1975) Hugoniot density of 5.31 g/cm^3 at 120 GPa is \u223c2% less dense than inferred from typical lower mantle density profiles.",
"doi": "10.1029/JB084iB06p03039",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1979-06-10",
"series_number": "B6",
"volume": "84",
"issue": "B6",
"pages": "3039-3048"
},
{
"id": "authors:0x8tq-wvc03",
"collection": "authors",
"collection_id": "0x8tq-wvc03",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-153212340",
"type": "article",
"title": "Equations of state of iron sulfide and constraints on the sulfur content of the Earth",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New shock and release wave data for pyrrhotite (Fe_(0.9)S) obtained over the pressure range of 3\u2013158 GPa (0.03\u20131.58 Mbar) suggest that this mineral undergoes a major shock-induced phase change(s) with an onset in the range 2.7\u20133.8 GPa. Free-surface velocities of Fe_(0.9)S released from states between 8.9 and 24.7 GPa indicate a maximum postshock density of \u223c5.54 g/cm^3. A pressure of \u223c25 GPa appears to be required to drive the phase transition(s) to completion. A density for the high-pressure phase (hpp) consistent with present static high-pressure X ray data, \u223c5.34 g/cm^3, was used to calculate a zero-pressure, adiabatic bulk modulus of 126\u2013128 GPa for the hpp. Release adiabat measurements centered at 152 and 158 GPa are consistent with the assumption that the Hugoniot curve in the 25- to 158-GPa range reflects the properties of a denser polymorph, possibly with eight-fold coordination, which may be similar to the local bonding of sulfur in the liquid core of the earth. Similar, but less well constrained, reductions are presented for pyrite, FeS_2, based on the three data points of Simakov et al. (1974) in the pressure range 88\u2013320 GPa. These are inferred to represent the behavior of an unknown hpp (approximate zero-pressure density of 5.3 g/cm^3) and indicate that this phase forms at a pressure above \u223c29 GPa. Reduction of these data yields a zero-pressure bulk modulus for the hpp in the range 205\u2013244 GPa. The raw Hugoniot data for Fe_(0.9)S, FeS_2, and Fe when constrained to the seismologically obtained density-pressure profiles of the outer core of the earth indicate a systematic decrease of apparent sulfur content from 10 to 6.5% with depth. When the shock data are reduced to isotherms, a nearly constant sulfur content in the range 9\u201312% is inferred. Using these bounds on the sulfur content of the core, and depending on whether an olivine or pyroxene mantle stoichiometry is assumed, the earth can be modeled as being depleted in S by a factor ranging from 1.7 to 3.2 with respect to the abundances of Si and from 2.8 to 7.5 relative to the abundance of Fe, in CCl carbonaceous chondrites. It is concluded that although the shock wave data permit the major light element in the core to be sulfur, the earth can be modeled as being depleted in sulfur, along with other volatile elements. A systematic relation, C_0(km/s) = 7.15 - 0.47 [V bar], was also discovered upon comparison of the inferred densities and bulk sound speeds (C_0) of the hpp's of the iron sulfides with other measurements for 12 sulfides and elemental sulfur. Here inline image is the volume (in cubic centimeters) per mole of atoms.",
"doi": "10.1029/JB084iB03p00985",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research B",
"publication_date": "1979-03-10",
"series_number": "B3",
"volume": "84",
"issue": "B3",
"pages": "985-998"
},
{
"id": "authors:0268n-9nh20",
"collection": "authors",
"collection_id": "0268n-9nh20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181219-081601423",
"type": "article",
"title": "Editorial",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "As your new editor for JGR-Red, one of my highest priorities is to reduce the publication delay of interesting and good papers in geophysics and related solid earth science. These papers, even the\u00b7 speculative ones, are the lifeblood of solid earth science, and I would like to attract a higher percentage of these than previously seen in the journal. Moreover, I would like to encourage the submission of short reports and comments (three to five manuscript pages), which comment on recent papers, present new or additional data, analysis, or theory, that do not fit the format of a longer paper or are not appropriate for submission to a letter journal.",
"doi": "10.1029/JB084iB01p00145",
"issn": "2169-9313",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research. Solid Earth",
"publication_date": "1979-01-10",
"series_number": "B1",
"volume": "84",
"issue": "B1",
"pages": "145"
},
{
"id": "authors:srq89-v4671",
"collection": "authors",
"collection_id": "srq89-v4671",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151110-092051331",
"type": "article",
"title": "The B1/B2 Transition in CaO from Shock-Wave and Diamond-Cell Experiments",
"author": [
{
"family_name": "Jeanloz",
"given_name": "R.",
"clpid": "Jeanloz-R"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Bell",
"given_name": "P. M.",
"clpid": "Bell-P-M"
},
{
"family_name": "Mao",
"given_name": "H. K.",
"clpid": "Mao-H-K"
}
],
"abstract": "There is considerable interest in B1/B2 transitions in theoretical studies of oxide structures (Tosi and Arai, 1966; Cohen and Gordon, 1976; Demarest et al., 1977), and interest also in their possible occurrence in the earth's lower mantle. Volume and crystal-structure data obtained by both dynamic shockwave and static diamond-cell techniques indicate that CaO transforms from the B1 (NaCl-type) to the B2 (CsCl-type) structure at 0.6-0.7 Mbar with a volume decrease of 11 %.",
"issn": "0069-066X",
"publisher": "Carnegie Institution of Washington",
"publication": "Year Book Carnegie Institution of Washington",
"publication_date": "1979",
"series_number": "78",
"issue": "78",
"pages": "627-630"
},
{
"id": "authors:dzeh2-63d22",
"collection": "authors",
"collection_id": "dzeh2-63d22",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141222-135223089",
"type": "article",
"title": "Impact flows and crater scaling on the moon",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The axisymmetric distribution of stress, internal energy and particle velocity resulting from the impact of an iron meteoroid with a gabbroic anorthosite lunar crust has been calculated for the regime in which shock-induced melting and vaporization takes place. Comparison of impact flow fields, with phase changes in silicates taken into account, with earlier results demonstrate that in the phase change case when the 15-km/s projectile has penetrated some two projectile radii into the moon, the peak stress in the flow is \u223c0.66 Mbar at a depth of 66 km, and the stress has decayed to \u223c66 kbar at a depth of 47 km. Rapid attenuation occurs because of the high rarefaction velocity of the high-pressure phases associated with a 35% (zero-pressure) density increase. This feature of the phase-change flow tends to strongly concentrate the maximum shock pressures along the meteoroid trajectory (axis) and makes the conical zone along which high internal energy deposition occurs, both shallow and narrow. Examination of the gravitational energies required to excavate larger craters on the moon indicates the importance of gravity forces acting during the excavation of craters having radii in the range greater than \u223c2 \u2013 \u223c140 km. It is observed that the \"hydrodynamic\" energy vs. crater radius relation approaches those for various \"gravitational\" energy vs. radius relations at the radii values corresponding to the larger mare basins. Cratering energy values in the range of (1.0 \u2013 9.4) \u2022 10^(32) erg are inferred on this basis for the Imbrium crater. Using these values and the criteria that all rocks exposed to \u223c100 kbar or greater shock pressures are included in the ejecta (some of which falls back) implies that the maximum depth of sampling expected to be represented within the Apollo collection lies in the range 148\u2013328 km.",
"doi": "10.1016/0031-9201(78)90072-9",
"issn": "0031-9201",
"publisher": "Elsevier",
"publication": "Physics of the Earth and Planetary Interiors",
"publication_date": "1978-05",
"series_number": "4",
"volume": "16",
"issue": "4",
"pages": "341-351"
},
{
"id": "authors:myzd0-ma427",
"collection": "authors",
"collection_id": "myzd0-ma427",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LYZjap78",
"type": "article",
"title": "The relation between the shock-induced free-surface velocity and the postshock specific volume of solids",
"author": [
{
"family_name": "Lyzenga",
"given_name": "Gregory A.",
"clpid": "Lyzenga-G-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The release of solids from a state of shock compression at a free surface is examined. For isentropic release, the postshock specific volume V[prime]0 is shown to be constrained by V[prime]0? (Ufs\u2013Up)2/P1+V1, where (P1,V1) is the pressure-volume Hugoniot state of shock compression and Ufs and Up are the free-surface and shock particle velocities, respectively. When a sudden phase change occurs during the release process, this lower bound is increased, subject to simplifying assumptions about the phase transition.",
"doi": "10.1063/1.324323",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1978-01-01",
"series_number": "1",
"volume": "49",
"issue": "1",
"pages": "201-204"
},
{
"id": "authors:3xvj5-rew72",
"collection": "authors",
"collection_id": "3xvj5-rew72",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151116-133940996",
"type": "article",
"title": "Meteorite Impact Ejecta: Dependence of Mass and Energy Lost on Planetary Escape Velocity",
"author": [
{
"family_name": "O'Keefe",
"given_name": "John D.",
"clpid": "O'Keefe-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The calculated energy efficiency of mass ejection for iron and anorthosite\nobjects striking an anorthosite planet at speeds of 5 to 45 kilometers per second\ndecreases with increasing impact velocity at low escape velocities. At escape velocities\nof > 10^5 and > 2 x 10^4 centimeters per second, respectively, the slower impactors\nproduce relatively less ejecta for a given impact energy. The impact velocities at\nwhich ejecta losses equal meteorite mass gains are found to be approximately 20, 35,\nand 45 kilometers per second for anorthosite objects and approximately 25, 35, and\n40 kilometers per second for iron objects striking anorthosite surfaces for the gravity\nfields of the moon, Mercury, and Mars.",
"doi": "10.1126/science.198.4323.1249-a",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1977-12-23",
"series_number": "4323",
"volume": "198",
"issue": "4323",
"pages": "1249-1251"
},
{
"id": "authors:82e6a-ysj59",
"collection": "authors",
"collection_id": "82e6a-ysj59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150729-140034932",
"type": "article",
"title": "Shock-Produced Olivine Glass: First Observation",
"author": [
{
"family_name": "Jeanloz",
"given_name": "Raymond",
"clpid": "Jeanloz-R"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Lally",
"given_name": "J. S.",
"clpid": "Lally-J-S"
},
{
"family_name": "Nord",
"given_name": "G. L., Jr.",
"clpid": "Nord-G-L-Jr"
},
{
"family_name": "Christie",
"given_name": "J. M.",
"clpid": "Christie-J-M"
},
{
"family_name": "Heuer",
"given_name": "A. H.",
"clpid": "Heuer-A-H"
}
],
"abstract": "Transmission electron microscope (TEM) observations of an experimentally shock-deformed single crystal of natural peridot, (Mg_(0.88)Fe_(0.12))_2SiO_4, recovered from peak pressures of about 56 x 10^9 pascals revealed the presence of amorphous zones located within crystalline regions with a high density of tangled dislocations. This is the first reported observation of olivine glass. The shocked sample exhibits a wide variation in the degree of shock deformation on a small scale, and the glass appears to be intimately associated with the highest density of dislocations. This study suggests that olivine glass may be formed as a result of shock at pressures above about 50 to 55 x 10^9 pascals and that further TEM observations of naturally shocked olivines may demonstrate the presence of glass.",
"doi": "10.1126/science.197.4302.457",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "1977-07-29",
"series_number": "4302",
"volume": "197",
"issue": "4302",
"pages": "457-459"
},
{
"id": "authors:r3vd4-k4k31",
"collection": "authors",
"collection_id": "r3vd4-k4k31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-141708778",
"type": "article",
"title": "Longitudinal elastic velocities in MgO to 360 kbar",
"author": [
{
"family_name": "Meier",
"given_name": "Lyle D.",
"clpid": "Meier-L-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Numerical descriptions of shock wave induced flows obtained with a two-dimensional Lagrangian finite difference code are compared in detail with experimental data obtained via the lateral relaxation method for polycrystalline magnesium oxide (MgO) to a pressure of 360 kbar. The equation of state used for MgO was assumed to be of the Mie-Gr\u00fcneisen form, and detailed comparison of experimental and calculated data was used to obtain refined values of the shear strength and shear modulus of MgO at high pressures. The best fitting rheological model for MgO was characterized by a shear strength which decreased from a value of 26 kbar at 16.5-kbar mean stress to 13.5 kbar at 360-kbar mean stress along the principal Hugoniot curve. The first and second pressure derivatives of the shear modulus, when the shear modulus is evaluated as a quadratic function of pressure, yield (\u2202\u03bc/\u2202P) = 2.44 and \u03bc(\u2202^2\u03bc/\u2202P^2) = 1.7\u00b13.0. The uncertainties in the determination of \u03bc(\u2202^2\u03bc/\u2202P^2) have been reduced by a factor of 5 over previous estimates.",
"doi": "10.1029/JB082i017p02523",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1977-06-10",
"series_number": "17",
"volume": "82",
"issue": "17",
"pages": "2523-2528"
},
{
"id": "authors:bkmks-33098",
"collection": "authors",
"collection_id": "bkmks-33098",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151110-090926285",
"type": "article",
"title": "Impact processess",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A major conclusion resulting from U.S. and Soviet imaging and sampling missions to the Moon is that all the soils and many near-surface rocks are impact ejecta, and that even pristine rock surfaces, when examined under all resolvable scales, are covered with impact craters. New results reported, pertaining to cratering on the Moon and the other terrestrial planets, range from data on the dynamic strength of a rock to energy partitioning and crater-stability calculations. New ideas on the role of volatiles in crater formation and criteria for recognition of impact melts were presented. New constraints on the size and flux rate of impacting objects in the zones of the terrestrial planets over the last 3 X 10^9 years were given.",
"issn": "0016-8556",
"publisher": "American Geological Institute",
"publication": "Geotimes",
"publication_date": "1977-05",
"volume": "22",
"pages": "24-26"
},
{
"id": "authors:j4tas-qab07",
"collection": "authors",
"collection_id": "j4tas-qab07",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151110-071232930",
"type": "article",
"title": "Effects of Shock Pressures on Calcic Plagioclase",
"author": [
{
"family_name": "Gibbons",
"given_name": "Rex V.",
"clpid": "Gibbons-R-V"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Samples of single crystal calcic plagioclase (labradorite, An63, from Chihuahua, Mexico) have been shock-loaded to pressures up to 496 kbar. Optical and electron microscopic studies of the recovered samples show the effects of increasing shock pressures on this mineral. At pressures up to 287 kbar, the recovered specimens are still essentially crystalline, with only a trace amount of optically unresolvable glass present at 287 kbar. Samples recovered after shock-loading to pressures between 300 and 400 kbar are almost 100% diaplectic glasses; that is formed by shock transformation presumably in the solid-state. Above about 400 kbar, glasses with refractive indices similar to thermally fused glass were produced. The general behavior of the index of refraction with shock pressures agrees closely with previous work, however, the absence of planar features is striking. At pressures less than 300 kbar, the most prominent physical feature is the pervasive irregular fracturing caused by the shock crushing, although some (001) and (010) cleavages are observed. No fine-scale shock deformation structures, i.e. planar features, were noted in any of the specimens. We conclude, in contrast to previous studies of shocked rocks that planar features are not necessarily definitive shock indicators, in contrast to diaplectic glass (e.g., maskelynite) and high-pressure phases, but are rather likely indicative of the local heterogeneous dynamic stress experienced by plagioclase grains within shocked rocks.",
"doi": "10.1007/BF00307982",
"issn": "0342-1791",
"publisher": "Springer",
"publication": "Physics and Chemistry of Minerals",
"publication_date": "1977-03",
"series_number": "1",
"volume": "1",
"issue": "1",
"pages": "95-107"
},
{
"id": "authors:sv0da-bwq31",
"collection": "authors",
"collection_id": "sv0da-bwq31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150708-105329578",
"type": "article",
"title": "Measurements of the longitudinal modulus of Pierre clay shale at varying strain rates",
"author": [
{
"family_name": "Bless",
"given_name": "Stephan J.",
"clpid": "Bless-S-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The propagation speed of finite-amplitude compressional waves of strain-rate 10^3 - 10^4 sec^(-1) in Pierre clay shale have been measured using shock wave techniques. The inferred longitudinal modulus perpendicular to the bedding is approximately a factor of four higher than that measured by others in uniaxial strain tests at strain rates of 1-5 sec^(-1). The present shock wave speeds measured in the laboratory and in-situ finite-amplitude explosive experiments measured by others correlate more closely with field seismic velocities than with laboratory uniaxial strain measurements. Elastic properties of this highly saturated friable material measured parallel to the bedding are less sensitive to sampling disturbances than those measured in the perpendicular direction.",
"doi": "10.1190/1.1440710",
"issn": "0016-8033",
"publisher": "Society of Exploration Geophysicists",
"publication": "Geophysics",
"publication_date": "1977-02-01",
"series_number": "1",
"volume": "42",
"issue": "1",
"pages": "34-40"
},
{
"id": "authors:g6x6j-exv11",
"collection": "authors",
"collection_id": "g6x6j-exv11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151119-082244245",
"type": "article",
"title": "Electrical Conductivity Induced in Insulators by Pulsed Radiation",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Wooten",
"given_name": "Frederick",
"clpid": "Wooten-F"
}
],
"abstract": "The minimum prompt photoconductivity induced by pulses of x rays, gamma rays, and energetic electrons in various amorphous and disordered insulating organic and inorganic materials is predicted on the basis of data for the scattering of hot electrons in solids and the band gap for insulators. For total doses of 3 x 10^4 to 30 x 10^4 rad or greater, the minimum prompt photoconductivity is predicted to be linear with dose rate, \u03b3, and is given by \u03c3(\u03a9^(-1)cm^(-1))=5 x 10^(-19) \u03c1_0\u03b3/E_g^2, where \u03c1_0 is the density (g/cm^3) and Eg is the optical band gap (eV). This formula agrees well with data for a variety of plastics, mica, and borosilicate glass under widely different irradiation conditions. The formula considerably underestimates absolute values of prompt conductivities observed for Al_2O_3, MgO, and certain plastics, because the model does not hold for ordered materials.",
"doi": "10.1109/TNS.1976.4328451",
"issn": "0018-9499",
"publisher": "IEEE",
"publication": "IEEE Transactions on Nuclear Science",
"publication_date": "1976-06",
"series_number": "3",
"volume": "23",
"issue": "3",
"pages": "1268-1272"
},
{
"id": "authors:dz8pj-3r724",
"collection": "authors",
"collection_id": "dz8pj-3r724",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-144021446",
"type": "article",
"title": "Measurement of release wave speed in shock-compressed polycrystalline alumina and aluminum",
"author": [
{
"family_name": "Bless",
"given_name": "Stephan J.",
"clpid": "Bless-S-J"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Values of release wave speed in shock-compressed polycrystalline alumina and aluminum (2024) have been measured to 400 and 260 kbar, respectively. These values, as well as previous data for aluminum and iron, have been compared with fourth-order finite strain extrapolations of the longitudinal sound speed V_p. For alumina in the pressure range 200\u2013300 kbar and for \u03b1 iron and \u2208 iron the observed release wave speeds fall below any reasonable extrapolation of V_p. In the range 360\u2013400 kbar the data for alumina indicate that M(\u2202^2M/\u2202 P^2) \u2243 \u221250 (where M and P are longitudinal modulus and pressure, respectively); this value is in approximate agreement with Graham's \u223c200-kbar data on elastic shock compression of single-crystal aluminum oxide. For aluminum the data indicate a value for M(\u2202^2M/\u2202 P^2) of 2.7\u00b15.7.",
"doi": "10.1029/JB081i011p01935",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1976-04-10",
"series_number": "11",
"volume": "81",
"issue": "11",
"pages": "1935-1942"
},
{
"id": "authors:e179d-g7592",
"collection": "authors",
"collection_id": "e179d-g7592",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-144823605",
"type": "article",
"title": "Shock compression of ilmenite",
"author": [
{
"family_name": "King",
"given_name": "David A.",
"clpid": "King-D-A"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Single- and reflected-shock compression measurements on single-crystal ilmenite (FeTiO_3) to pressures of 635 and 930 kbar, respectively, demonstrate anomalously large compressions above \u223c320 kbar and imply the onset of one or more major phase changes at this pressure level which continue to occur to at least \u223c600 kbar. The phase change onset pressure is considerably above the calculated upper bound of 193 kbar for the stability of ilmenite with respect to breakdown into wustite and rutile. Over the 300- to 600-kbar range, samples shocked along the c axis are consistently more compressible than those shocked along the perpendicular direction; at a given density the Hugoniot curves differ by 40 kbar. The observed density (6.25 g/cm^3) of the highest-pressure single-shock state implies that the shock-induced high-pressure phase has a zero-pressure density of at least 5.4 g/cm^3, or a density 13% greater than that of ilmenite. The reflected-shock data have a larger experimental uncertainty but indicate an even greater zero-pressure density for the high-pressure phase. The large density increase inferred restricts the possible nature of the high-pressure phase. These data are consistent with the 1300-kbar datum reported by Simakov et al. (1974) and with the disproportionment of ilmenite into mixed oxides in the rock salt (FeO) and fluorite (TiO_2) phases as observed (Liu, 1975) in static recovery experiments.",
"doi": "10.1029/JB081i005p00931",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1976-02-10",
"series_number": "5",
"volume": "81",
"issue": "5",
"pages": "931-935"
},
{
"id": "authors:9p4bd-bvw10",
"collection": "authors",
"collection_id": "9p4bd-bvw10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181219-082107636",
"type": "article",
"title": "James B. Macelwane Award to Dan McKenzie, Gerald Schubert and Vytenis M. Vasyliunas",
"author": [
{
"family_name": "Menard",
"given_name": "H. W.",
"clpid": "Menard-H-W"
},
{
"family_name": "McKenzie",
"given_name": "Dan",
"clpid": "McKenzie-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Schubert",
"given_name": "Gerald",
"clpid": "Schubert-G"
},
{
"family_name": "Dessler",
"given_name": "Alexander J.",
"clpid": "Dessler-A-J"
},
{
"family_name": "Vasyliunas",
"given_name": "Vytenis M.",
"clpid": "Vasyliunas-V-M"
}
],
"abstract": "To those earth scientists who have followed the revolutionary development of plate tectonics from its dawning, it may come as a surprise that Dan McKenzie can have done so much and still be young enough to qualify for the James B. Macelwane Award. Nonetheless it is so. He was born on February 21, 1941. He received his advanced education at King's College, Cambridge University, and was awarded a B.A. in 1963 and a Ph.D. in 1966. He became a Fellow of the college in 1965. He was fortunate enough to be a student in Edward Bullard's Department of Geodesy and Geophysics just in those exciting years when the validity of sea floor spreading was demonstrated. McKenzie was one of the first to realize the broader implications of the computer fitting of continents by Bullard and others which assumed that the drifting crust is rigid.",
"doi": "10.1029/eo056i011p00922",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "Eos",
"publication_date": "1975-11",
"series_number": "11",
"volume": "56",
"issue": "11",
"pages": "922-926"
},
{
"id": "authors:xm20a-1qz74",
"collection": "authors",
"collection_id": "xm20a-1qz74",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151110-071232613",
"type": "article",
"title": "Compaction by impact of unconsolidated lunar fines",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "New Hugoniot and release adiabate data for 1.8 g cm^(\u22123) lunar fines (sample, 70051) in the ~2 to ~70 kbar range demonstrate that upon shock compression intrinsic crystal density (~3.1 g cm^(\u22123)) is achieved undershock stresses of 15 to 20 kbar. Release adiabate determinations indicate that measurable irreversible compaction occurs upon achieving shock pressures above ~4 kbar. For shocks in the ~7 to 15 kbar range, the inferred,post-shock, specific volumes observed decrease nearly linearly with increasing peak shock pressures. Upon shocking to ~15 kbar the post-shock density is approximately that of the intrinsic minerals. If the present data for sample 70051 are taken to be representative of the response to impact of unconsolidated regolith material on the Moon, it is inferred that the formation of appreciable quantities of soil breccia can be associated with the impact of meteoroids or ejecta at speeds of as low as ~1 km s^(\u22121).",
"doi": "10.1007/BF00565328",
"issn": "0027-0903",
"publisher": "Springer",
"publication": "The Moon",
"publication_date": "1975-10",
"series_number": "2",
"volume": "14",
"issue": "2",
"pages": "291-299"
},
{
"id": "authors:2jcg9-mx776",
"collection": "authors",
"collection_id": "2jcg9-mx776",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130430-081835615",
"type": "article",
"title": "Spectra of shock-affected rhodonite: A reply",
"author": [
{
"family_name": "Gibbons",
"given_name": "Rex V.",
"clpid": "Gibbons-R-V"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Rossman",
"given_name": "George R.",
"orcid": "0000-0002-4571-6884",
"clpid": "Rossman-G-R"
}
],
"abstract": "The Gaussian resolution procedure of Faye (1975)\nleading to the conclusion that the spectral changes in\na shock-loaded rhodonite are the result of a broadening\nor intensification of the ultraviolet charge-transfer\nabsorption and that the 540 nm band is\npresent with comparable intensity in both pre- and\npost-shock samples is not physically meaningful\nbecause it has ignored the dominant process which\ngives rise to the rising baseline \"absorption\" throughout\nthe near-infrared and visible spectral regions.\nThat process is wavelength-dependent scattering.",
"issn": "0003-004X",
"publisher": "Mineralogical Society of America",
"publication": "American Mineralogist",
"publication_date": "1975-09",
"series_number": "9-10",
"volume": "60",
"issue": "9-10",
"pages": "942-943"
},
{
"id": "authors:j9ykg-v6985",
"collection": "authors",
"collection_id": "j9ykg-v6985",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141217-105232664",
"type": "article",
"title": "Rapid formation of eclogite in a slightly wet mantle",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Schubert",
"given_name": "Gerald",
"clpid": "Schubert-G"
}
],
"abstract": "A model, in which dissolved ions migrate through water films surrounding mineral grains to sites of reaction, predicts the geologically rapid occurrence of the gabbro-eclogite phase change in the earth's mantle at temperatures less than 600\u2013800\u00b0C. In a water-undersaturated mantle, interstices within the rock can contain water vapor in equilibrium with small amounts of hydrous phases such as chlorite, tremolite or talc and in the presence of other gases such as CO_2, at H_2O pressures less than the lithostatic pressure of the rock. The solubility of ions in this interstitial water vapor is strongly dependent on pressure and is the rate-limiting process in the model; reaction occurs rapidly if the water pressure is at least 0.5\u20131 kbar. The 5 km of oceanic gabbroic crust can transform to eclogite upon subduction into the mantle at depths of several tens of kilometers, depending on the rate of heating of the descending crustal material and the nature of the minor hydrous phases present. The downward body force on the descending slab due to the eclogitization of oceanic crust is comparable to the downward forces associated with thermal contraction of the slab and the elevation of the olivine-spinel phase boundary.",
"doi": "10.1016/0012-821X(75)90165-X",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1975-08",
"series_number": "1",
"volume": "27",
"issue": "1",
"pages": "90-94"
},
{
"id": "authors:3ctxd-tzr39",
"collection": "authors",
"collection_id": "3ctxd-tzr39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-094219192",
"type": "article",
"title": "Equations of state of the Earth",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The major results of research in the United States for 1971\u20131974 in the areas of static, high-pressure X ray, ultrasonic and shock wave measurements, and progress in theoretical equations of state are summarized. This 4-year period has seen the massive accumulation of new data pertinent to describing the properties, and to some extent geodynamic processes, of the upper mantle as well as exposing the gauntlet of scientific challenge with regard to our lack of detailed understanding of the major changes in crustal seismic velocities, which seem to offer so much promise for earthquake prediction. In the area of very high pressure geophysics, another challenging problem uncovered is the question of explaining the low adiabatic gradient in the outer core, which seems to be required to retain liquid iron alloy material at the melting point. Important advances in what until recently has been quite empirical elastic moduli 'systematics' have demonstrated how ionic radii and ionic packing densities may be quantitatively employed to predict unmeasured equations of state as well as tie together an ever increasing body of data for the elasticity of compounds which are crystal-chemical analogs of mantle minerals.",
"doi": "10.1029/RG013i003p00335",
"issn": "8755-1209",
"publisher": "American Geophysical Union",
"publication": "Reviews of Geophysics",
"publication_date": "1975-07",
"series_number": "3",
"volume": "13",
"issue": "3",
"pages": "335-339"
},
{
"id": "authors:0ncz0-pad51",
"collection": "authors",
"collection_id": "0ncz0-pad51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150107-133010454",
"type": "article",
"title": "Solidified gas samples for shock wave experimentation",
"author": [
{
"family_name": "Lagus",
"given_name": "P. L.",
"clpid": "Lagus-P-L"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Giles",
"given_name": "S. L.",
"clpid": "Giles-S-L"
},
{
"family_name": "Westphal",
"given_name": "J. A.",
"clpid": "Westphal-J-A"
}
],
"abstract": "A cryogenic vacuum system suitable for use with a propellant or light gas gun for performing dynamic compression experiments on solidified gases is described. An optical recording system allows the sample target (suspended in a vacuum of 10^(\u22125) torr) to be monitored until shortly before impact. These experimental techniques have been used to measure Hugoniot data for solid argon and the first Hugoniot data for solid hydrogen.",
"doi": "10.1016/0011-2275(75)90110-1",
"issn": "0011-2275",
"publisher": "Elsevier",
"publication": "Cryogenics",
"publication_date": "1975-05",
"series_number": "5",
"volume": "15",
"issue": "5",
"pages": "246-248"
},
{
"id": "authors:5j4b3-d8w70",
"collection": "authors",
"collection_id": "5j4b3-d8w70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141105-095608913",
"type": "article",
"title": "Gabbro-eclogite reaction rate and its geophysical significance",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Schubert",
"given_name": "Gerald",
"clpid": "Schubert-G"
}
],
"abstract": "The gabbro-garnet granulite-eclogite transformation may play a significant role in driving the motions of terrestrial lithospheric plates. Whether or not this transformation is in fact important as a driving mechanism for plate tectonics depends on the relationship of the reaction time to geologic time. Solid state diffusion under completely dry conditions is investigated as a possible model for the gabbro-eclogite reaction, with the result that it could not produce the transition in geologically meaningful times at temperatures less than circa 600\u00b0\u2013800\u00b0C in the earth's upper mantle. Other reaction mechanisms must exist for the geologically rapid occurrence of the phase change at lower temperatures. It is found that one of these mechanisms can be grain interstitial diffusion in a mantle with minute amounts of water. In this model, dissolved ions migrate through water films surrounding mineral grains to sites of reaction. A water-undersaturated mantle contains a small quantity of hydrous phases, such as chlorite, amphibole, or talc, the presence of which implies that interstices within the rock can contain water in equilibrium with these minerals and at a pressure P_(H_2O) which is less than the pressure in the rock. Implicit then is the presence of other gases and/or structural rock integrity. This P_(H_2O) is calculated for serpentine, tremolite, and talc as a function of temperature and rock pressure. Various pertinent cations are sufficiently mobile in aqueous solution that at high temperature and high pressure, diffusion through water will not significantly slow the reaction. Rather, pressure-induced solubility of ions in this water vapor is the important rate-limiting process in the model. Rock pressure and temperature must be such as to generate at least \u223c0.5-1 kbar of P_(H_2O) in the presence of the hydrous phases for geologically short reaction times. Under ambient conditions P_(H_2O) is quite small, the cations are relatively insoluble, and the reaction time is geologically long. Upon subduction of a basaltic upper crust or lithosphere, for example, an increase in P_(H_2O) occurs, and with increasing pressure the mineral solubility in this supercritical water increases dramatically, yielding geologically short reaction times; for example, \u223c20 m.y. for chlorite-containing rocks with \u223c10^(\u22125)-cm film thickness for ion diffusion at depths of \u223c15-30 km and at temperatures of \u223c150\u00b0\u2013300\u00b0C for different heating models of the descending slab. For gabbros in which amphibole (tremolite)-pyroxene equilibria buffer the partial pressure of water, depths of \u223c55\u201370 km and temperatures of 400\u00b0\u2013550\u00b0C are required for rapid eclogitization, again for different slab heating models. Thus contrary to previous suggestions, the gabbro-eclogite transformation, as it probably occurs in the descending or spreading lithosphere, is not simply rate-controlled by temperature but depends heavily on pressure and on the nature of the minor hydrous minerals present.",
"doi": "10.1029/RG013i002p00383",
"issn": "0034-6853",
"publisher": "American Geophysical Union",
"publication": "Reviews of Geophysics and Space Physics",
"publication_date": "1975-05",
"series_number": "2",
"volume": "13",
"issue": "2",
"pages": "383-400"
},
{
"id": "authors:9m550-s5324",
"collection": "authors",
"collection_id": "9m550-s5324",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130513-091545950",
"type": "article",
"title": "A Spectrographic Interpretation of the Shock-Produced Color\n Change in Rhodonite (MnSiO_3): The Shock-Induced Reduction\n of Mn(lll) to Mn(II).",
"author": [
{
"family_name": "Gibbons",
"given_name": "Rex V.",
"clpid": "Gibbons-R-V"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Rossman",
"given_name": "George R.",
"orcid": "0000-0002-4571-6884",
"clpid": "Rossman-G-R"
}
],
"abstract": "Samples of rhodonite (MnSiO_3-pyroxenoid from Franklin, New Jersey) have been shockloaded to pressures up to 496 kilobars. Optical spectral studies of four recovered samples show a decreasing Mn^(3+) content upon recovery from successively higher shock pressures; after shock-loading to 496 kbar, the Mn^(3+) has essentially disappeared. No corresponding change in the optical spectrum results from heating rhodonite to 1250\u00b0C for 3.5 hours in a reducing atmosphere. Rhodonite heated to 1360\u00b0 under the same conditions melts incongruently to manganese-rich glass and silica with disappearance of the 540 nm Mn^(3+) absorption band. The color change in the shocked rhodonite arises from irreversible reduction of Mn3+ during high shock pressures and possible high shock temperatures. It is suggested that Mn^(3+) is reduced to Mn^(2+) by water present in the sample during the shock event.",
"issn": "0003-004X",
"publisher": "Mineralogical Society of America",
"publication": "American Mineralogist",
"publication_date": "1974-01",
"series_number": "1-2",
"volume": "59",
"issue": "1-2",
"pages": "177-182"
},
{
"id": "authors:w8r3s-yj417",
"collection": "authors",
"collection_id": "w8r3s-yj417",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-152822340",
"type": "article",
"title": "Measurement of elastic velocities of MgO under shock compression to 500 kilobars",
"author": [
{
"family_name": "Davies",
"given_name": "Geoffrey F.",
"clpid": "Davies-G-F"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The velocities of rarefaction waves in shock-compressed MgO have been measured by observing the reduction of the shock front velocity near the sample edges due to the rarefaction waves propagating from the edges. The extent of this 'edge effect' is difficult to determine accurately because of its emergent nature. Arrangements sensitive to differences in shock front velocity yielded rarefaction wave velocities close to predicted longitudinal velocities in the high-pressure shock state. Velocities closer to the hydrodynamic sound speed in the shock state were obtained from less sensitive arrangements. These results can be interpreted in terms of a two-stage elastoplastic model of the decompression. The longitudinal velocities measured in shock states up to 528 kb imply second pressure derivatives of the elastic moduli c_(ij)\u2033, given by K_0c_(ij)\u2033 = \u22121 \u00b1 15, where K is the bulk modulus.",
"doi": "10.1029/JB078i032p07596",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1973-11-10",
"series_number": "32",
"volume": "78",
"issue": "32",
"pages": "7596-7601"
},
{
"id": "authors:hd3q9-7ed49",
"collection": "authors",
"collection_id": "hd3q9-7ed49",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-160955809",
"type": "article",
"title": "Optical absorption spectra of ruby and periclase at high shock pressures",
"author": [
{
"family_name": "Gaffney",
"given_name": "Edward S.",
"clpid": "Gaffney-E-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A spectrographic system is described that is capable of measuring optical absorption spectra in solids to shock pressures of several hundred kilobars. The system utilized light from a 'point' source at about 60,000\u00b0K. Spectra have a resolution of about 40 A and cover the visible range. With a streak camera, time resolution of about 75 nsec can be obtained. The spectrum of MgO is observed to remain featureless at 450 kb and upon unloading from this pressure. The color centers observed in shock-recovered material must result from either higher pressures or other processes. The optical absorption spectra of ruby under shock compressions of almost 15% have been measured in the range 375\u2013600 nm. Below the elastic limit the large anisotropic strains are evident from the splitting of the ^4A_2 \u2192 ^4T_2 (F) absorption band by 3730 cm^(\u22121). Above the elastic limit this splitting is not resolved (but must be less than 800 cm^(\u22121)), indicating considerable loss of shear strength in such cases. Above the Hugoniot elastic limit up to pressures of 530 kb (15% volume compression) the measured value of the crystal field parameter agrees, within experimental error, with the value calculated from a point charge model (Dq \u03b1 r^(\u22125)) if the local compressibility is equal to the bulk compressibility. This result agrees with Stephens and Prickamer's absorption data up to 150 kb and suggests that the point charge model is useful in predicting crystal field effects in mantle minerals, especially those having similar oxygen anion packings such as corundum.",
"doi": "10.1029/JB078i026p05942",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1973-10-09",
"series_number": "26",
"volume": "78",
"issue": "26",
"pages": "5942-5953"
},
{
"id": "authors:twf81-pg844",
"collection": "authors",
"collection_id": "twf81-pg844",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-153705662",
"type": "article",
"title": "Shock-induced transition of quartz to stishovite",
"author": [
{
"family_name": "Kleeman",
"given_name": "John D.",
"clpid": "Kleeman-J-D"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The transformation of quartz to stishovite has been studied by X-ray and optical examination of a series of experimentally shock-loaded specimens of a quartz-copper mixture. Shock pressures of 68 to 260 kb and peak temperatures of 320\u00b0 to 870\u00b0K were achieved. Stishovite was identified from quartz shock-loaded above 90 kb; the quantity increases with increasing pressure, but is not dependent on temperature. The formation of stishovite under shock conditions appears to be intimately related to a short-range order phase.",
"doi": "10.1029/JB078i026p05954",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1973-10-09",
"series_number": "26",
"volume": "78",
"issue": "26",
"pages": "5954-5960"
},
{
"id": "authors:n8m18-wjw05",
"collection": "authors",
"collection_id": "n8m18-wjw05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LAGjcp73",
"type": "article",
"title": "Shock wave measurements on solid hydrogen and argon",
"author": [
{
"family_name": "Lagus",
"given_name": "Peter L.",
"clpid": "Lagus-P-L"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Hugoniot data for solid argon (initially at 77\u00b0K and 1 bar) and solid hydrogen (initially at 5\u00b0K and 1 bar) have been obtained to 143 kbar and 6.4 kbar, respectively, using the projectile impact method. The argon data (at volumes of 15.28, 14.84, and 14.64 cm3/mole) are in fair agreement with previous shock data, and in excellent agreement with the most recent theoretically predicted Hugoniot. The hydrogen data (at volumes of 17.10, 15.32, 15.27, 15.11 cm3/mole) are compared with Hugoniots calculated from published isothermal compression data. For both argon and hydrogen, the shock and isothermal data are self-consistent under the assumption \u03b3/V is constant. To compressions of V/V0\u22480.65, the previous isothermal compression measurements on solid hydrogen are consistent with the present shock data.",
"doi": "10.1063/1.1680513",
"issn": "0021-9606",
"publisher": "American Institute of Physics",
"publication": "Journal of Chemical Physics",
"publication_date": "1973-10-01",
"series_number": "7",
"volume": "59",
"issue": "7",
"pages": "3517-3522"
},
{
"id": "authors:w9876-y4856",
"collection": "authors",
"collection_id": "w9876-y4856",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151106-101705516",
"type": "article",
"title": "Shock Compression of Iron Sulphide and the Possible Sulphur Content of the Earth's Core",
"author": [
{
"family_name": "King",
"given_name": "D. A.",
"clpid": "King-D-A"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A light component in the Earth's outer core could account for its apparent lower density and higher seismic parameter than pure iron. On the basis of shock data for iron and iron\u2013nickel, Birch and McQueen and Marsh concluded that the outer core was less dense than pure iron by 10 and 8 weight %, respectively. To account for these discrepancies both sulphur and silicon have been proposed as alloying elements with iron in the outer core.",
"doi": "10.1038/physci243082a0",
"issn": "0300-8746",
"publisher": "Nature Publishing Group",
"publication": "Nature Physical Science",
"publication_date": "1973-06-04",
"series_number": "127",
"volume": "243",
"issue": "127",
"pages": "82-84"
},
{
"id": "authors:c5wfs-9da63",
"collection": "authors",
"collection_id": "c5wfs-9da63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-163454928",
"type": "article",
"title": "A shock-induced phase change in orthoclase",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Liu",
"given_name": "Hsi-Ping",
"clpid": "Liu-H-P"
}
],
"abstract": "New shock compression data to 340 kb for single-crystal orthoclase (along (001)) demonstrate the onset of a shock-induced phase change at \u223c115 kb. Along the Hugoniot a mixed-phase region extends to \u223c300 kb, above which the data are believed to correspond to the properties of a high-pressure phase having the hollandite structure (zero pressure density of 3.84 g/cm^3) reported by Ringwood et al. If the hollandite value for the zero pressure density is used, the zero pressure bulk modulus of this phase is approximately 2.8 \u00b1 0.2 Mb.",
"doi": "10.1029/JB078i008p01274",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1973-03-10",
"series_number": "8",
"volume": "78",
"issue": "8",
"pages": "1274-1278"
},
{
"id": "authors:06ymf-dwe51",
"collection": "authors",
"collection_id": "06ymf-dwe51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141106-164106515",
"type": "article",
"title": "Shock wave compression of iron-silicate garnet",
"author": [
{
"family_name": "Graham",
"given_name": "Earl K.",
"clpid": "Graham-E-K"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock wave Hugoniot data have been obtained for almandine-garnet of composition (Fe_(0.79), Mg_(0.14), Ca_(0.04), Mn_(0.03)) Al_2Si_3O_(12) to pressures of >650 kb. The Hugoniot data indicate the onset of a high-pressure phase at 195 \u00b1 20 kb. Equation-of-state systematics and crystal chemical data (stemming largely from analog compounds) suggest that the high-pressure phase occurs in an 'ilmenitelike' structure with an initial density of 4.44 \u00b1 0.04 g/cm^3. This value represents an increase of about 6% over the initial garnet density of 4.180 \u00b1 0.005 g/cm^3. The adiabatic bulk modulus K_0^s and its first pressure derivative (\u2202K^s/\u2202P)_T were calculated for the high-pressure phase and found to be 3.19 \u00b1 0.39 Mb and 2.6 \u00b1 0.7, respectively. The major source of probable error in these values results from the indicated uncertainty in the initial density of the high-pressure phase. These results strongly suggest that upper mantle minerals are likely to occur in the ilmenite structure over a substantial part of the lower mantle.",
"doi": "10.1029/JB078i002p00375",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1973-01-10",
"series_number": "2",
"volume": "78",
"issue": "2",
"pages": "375-392"
},
{
"id": "authors:hk98e-pjb36",
"collection": "authors",
"collection_id": "hk98e-pjb36",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120724-082317999",
"type": "article",
"title": "Shock Melting and Vaporization of Metals",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The effect of initial porosity on shock induction of melting and vaporization is investigated for Ba, Sr, Li, Fe, Al, U, and Th. For the less compressible of these metals, it is found that for a given strong shock\u2010generation system (explosive in contact, or flyer\u2010plate impact) an optimum initial specific volume exists such that the total entropy production, and hence the amount of metal liquid or vapor, is a maximum. Initial volumes from 1.4 to 2.0 times crystal volumes, depending on the metal sample and shock\u2010inducing system, will result in optimum postshock entropies.",
"doi": "10.1063/1.1661519",
"issn": "0021-8979",
"publisher": "American Institute of Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1972-05-01",
"series_number": "5",
"volume": "43",
"issue": "5",
"pages": "2443-2445"
},
{
"id": "authors:0n873-cgw68",
"collection": "authors",
"collection_id": "0n873-cgw68",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141222-100758080",
"type": "article",
"title": "The state of mantle minerals",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The static pressure-volume, high-pressure X-ray, shock, and ultrasonic equation of state data are used to describe the seismic properties in terms of the mineralogy of the upper mantle, the spinel-zone, and the post-spinel or lower mantle. For the upper mantle, elastic properties have been measured for olivines, pyroxenes, and garnets. The effect of pressure, temperature and the Fe/Mg ratio on elasticity is less well known for pyroxene and garnet than for olivine. In the spinel zone, ~ 400- ~ 650 km depth, the major minerals include \u03b2- and \u03b3-(Mg,Fe)_2SiO_4 and a complex garnet, largely composed of aluminum-silicate garnet and pyroxene components. The zero-pressure bulk moduli of these phases lie in the range 1.8\u20132.1 Mbar. Although the high-pressure X-ray measurements of the bulk moduli of the Fe-rich \u03b3- or spinel phase (ringwoodite) are reported, the shear properties of the silicate spinels are unmeasured, as are all the properties of the distorted spinel, \u03b2-phase. The bulk modulus of the complex-garnet phase is known approximately from shock-wave data for pyroxene, but since standard specific volumes are unknown, reduction of these data to adiabats is uncertain. The major minerals of the lower, or post-spinel, mantle are thought to be (Mg,Fe)_2SiO_4 in the close-packed Sr_2PbO_4-structure, and the pyroxene and garnet component, initially in the close-packed ilmenite structure, and at greater depths probably transforming to the perovskite structure. Only shock-wave data and results inferred from the elasticity of the close-packed oxides are available in this regime. Except for garnet, the zero-pressure densities of the shock-induced high-pressure phases are not known; this difficulty, and the lack of data or a theory for the Gr\u00fcneisen parameter make reduction of these data difficult.",
"doi": "10.1016/0040-1951(72)90020-0",
"issn": "0040-1951",
"publisher": "Elsevier",
"publication": "Tectonophysics",
"publication_date": "1972-04",
"series_number": "1-4",
"volume": "13",
"issue": "1-4",
"pages": "189-219"
},
{
"id": "authors:aejdw-s3d28",
"collection": "authors",
"collection_id": "aejdw-s3d28",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150107-133724965",
"type": "article",
"title": "A shock-induced phase change in iron-silicate garnet",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Graham",
"given_name": "E. K.",
"clpid": "Graham-E-K"
}
],
"abstract": "Hugoniot measurements on iron-silicate garnet (Fe_(0.79), Mg_(0.14), Ca_(0.04), Mn_(0.03))_3 Al_2Si_3O_(12) initial density 4.18 g/cm^3, demonstrate that above a shock pressure of 205 \u00b1 20 kbar transition to a high-pressure phase(s), having an apparent zero-pressure density and bulk modulus of 4.44 \u00b1 0.06g/cm^3 and 3.3 \u00b1 0.3 Mbar, occurs. Crystal chemical systematics and Debye-Scherrer X-ray patterns of a recovered phase(s), which may be the shock-induced high-pressure form, suggest possible formation of a phase with a density of\u223c 4.48/cm^3. Occurrence of such a polymorph of garnet in the mantle would give rise to an increase in density and seismic velocity below \u223c 600km in the earth.",
"doi": "10.1016/0012-821X(72)90086-6",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1972-02",
"series_number": "1",
"volume": "14",
"issue": "1",
"pages": "87-90"
},
{
"id": "authors:anc8r-y2b17",
"collection": "authors",
"collection_id": "anc8r-y2b17",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140912-094451326",
"type": "article",
"title": "Generation of seismic waves by explosions in prestressed media",
"author": [
{
"family_name": "Toks\u00f6z",
"given_name": "M. Nafi",
"clpid": "Toks\u00f6z-M-N"
},
{
"family_name": "Thomson",
"given_name": "Ker C.",
"clpid": "Thomson-K-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The mechanisms of generation of seismic waves by an explosion in prestressed media are studied using both field seismograms and controlled laboratory experiments. LRSM seismograms from the underground nuclear explosion BILBY are analyzed to determine the source parameters from the radiated Love and Rayleigh waves. From the normalized amplitudes of Rayleigh waves as well as the Love-Rayleigh amplitude ratios, a composite source consisting of an isotropic explosion and a double couple is synthesized for the explosion and the associated tectonic strain release. From BILBY and other explosions studied by similar techniques, it is found that the tectonic strain energy release strongly depends on the medium properties in the immediate vicinity of the explosion. For \"harder\" media (such as granite) the tectonic strain energy release and the relative amplitude of Love waves are significantly higher than for softer media such as alluvium. Source-time functions of Love waves associated with the explosions are closer to time functions of earthquakes than to those of explosions.\n\nThe mechanisms of the pre-existing strain energy release by explosive sources are studied in two separate laboratory experiments. In a one-dimensional experiment where an explosive source is detonated in a rod stressed in torsion, the S-wave amplitudes are found to be linearly proportional to prestrain. In the second experiment, radiation of seismic waves and the near-source phenomena of explosive sources in prestressed plates are studied by photoelastic as well as strain gauge observations. The generation of S-waves is greatly enhanced by the prestress condition. It is found that extended cracking (faulting) occurs along directions determined by the prestress field. The transverse (SH) waves are generated primarily by the relaxation of the stress field along these cracks. The explosion-generated cavity alone could not account for the radiated transverse seismic energy.",
"issn": "0037-1106",
"publisher": "Seismological Society of America",
"publication": "Bulletin of the Seismological Society of America",
"publication_date": "1971-12",
"series_number": "6",
"volume": "61",
"issue": "6",
"pages": "1589-1623"
},
{
"id": "authors:9wfed-q3260",
"collection": "authors",
"collection_id": "9wfed-q3260",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141107-083037852",
"type": "article",
"title": "Dynamic compression of enstatite",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Gaffney",
"given_name": "Edward S.",
"clpid": "Gaffney-E-S"
}
],
"abstract": "New shock wave data for Bamle enstatite (Mg_(0.86),Fe_(0.14))SiO_3 in the range from 60\u2013480 kb indicate a Hugoniot elastic limit of 67\u00b110 kb and a possible phase-transition-produced shock front of 135\u00b110 kb amplitude. Above the latter shock pressure, states in a mixed-phase regime are achieved up to \u223c350 kb, above which the Hugoniot states are believed to represent the equation of state of a shock-induced phase, probably having the majorite (garnet) structure with a zero-pressure density of \u223c3.67 g/cm^3. The present data, representing the high-pressure phase, agree closely with those of R. G. McQueen, S. P. Marsh, and J. N. Fritz above 610 kb for a Stillwater bronzitite of similar mineralogy. It is suggested that the formation of majorite from enstatite in naturally impacted rocks and meteorites requires dynamic pressures of at least \u223c135 kb.",
"doi": "10.1029/JB076i023p05504",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1971-08-10",
"series_number": "23",
"volume": "76",
"issue": "23",
"pages": "5504-5513"
},
{
"id": "authors:1fm7j-rws42",
"collection": "authors",
"collection_id": "1fm7j-rws42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141107-084805316",
"type": "article",
"title": "Shock metamorphism of silicate glasses",
"author": [
{
"family_name": "Gibbons",
"given_name": "Rex V.",
"clpid": "Gibbons-R-V"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The changes in refractive index caused by shock compression have been determined for tektite, soda-lime, and silica glasses shocked to pressures up to 460 kb. For shock compression below 80 kb for fused silica and 40 kb for tektite and soda-lime glasses, compression is reversible as the refractive indices are within 0.0025 of the starting values. Index increases of 0.01, 0.04, and 0.06 are observed for soda-lime, tektite, and silica glasses shocked to pressures of 80, 130, and 140 kb respectively. For soda-lime glass subjected to shock pressures between 80 and 230 kb there is a decrease in the postshock refractive index to n=1.5211 at 230 kb. For fused silica shocked to pressures of 140 to 460 kb, refractive index drops from 1.52 to 1.47. The reasons for these decreases in index are not obvious. New values for postshock temperatures for fused silica based on release adiabat data, e.g. \u223c1000\u00b0C for a shock state at 250 kb, suggest that the decreases in refractive index are caused by a combination of decompression along release adiabats and reconstructive transformation from a shock-induced stishovitelike phase to a low-density glass. Postshock densities calculated from the refractive index data agree closely with those calculated from the release adiabat data.",
"doi": "10.1029/JB076i023p05489",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1971-08-10",
"series_number": "23",
"volume": "76",
"issue": "23",
"pages": "5489-5498"
},
{
"id": "authors:39d35-gw043",
"collection": "authors",
"collection_id": "39d35-gw043",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151106-104454513",
"type": "article",
"title": "Static and dynamic compression of Earth materials",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Takahashi",
"given_name": "Taro",
"clpid": "Takahashi-Taro"
}
],
"abstract": "The triennium, 1967\u20131970, has been a period of marked increase in acquisition of pressure-volume data for minerals, rocks, and compounds of geophysical interest. A wide assortment of data has been obtained by the conventional dilatometric techniques as well as by the more recently developed X-ray diffraction and shock-wave techniques. Highlights of progress during the last 3 years include hydrostatic compression measurements for Apollo 11 lunar samples [Stephens and Lilley, 1970; Schreiber et al., 1970], static compression measurements of the spinel phase of (Mg,Fe)_2SiO_4 solid solutions, which are likely constituents of the transition zone of the earth's mantle [Mao et al., 1969], and Hugoniot data for high-pressure phases of ferromagnesian silicates, which may represent the constituents of the lower mantle [McQueen et al., 1967b].",
"doi": "10.1029/EO052i005pIU147",
"issn": "0096-3941",
"publisher": "American Geophysical Union",
"publication": "Eos",
"publication_date": "1971-05",
"series_number": "5",
"volume": "52",
"issue": "5",
"pages": "147-153"
},
{
"id": "authors:z4p8c-5ra60",
"collection": "authors",
"collection_id": "z4p8c-5ra60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AHRjap71",
"type": "article",
"title": "Explosive Gas Blast: The Expansion of Detonation Products in Vacuum",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Allen",
"given_name": "Charles F.",
"clpid": "Allen-C-F"
},
{
"family_name": "Kovach",
"given_name": "Robert L.",
"clpid": "Kovach-R-L"
}
],
"abstract": "A series of 0.2- to 3-gm HNS charges were detonated in vacuums of 10^\u22123 to 10^\u22125 Torr. The resultant freely expanding, detonation product, gas blast achieves terminal velocities of 8 to 12 km/sec within 3 to 5 \u00b5sec after the detonation wave arrives at the free surface. Measured pressure profiles display rise times to maximum stagnation (``reflected shock'') pressure varying from ~30 \u00b5sec, 20-cm away from a 2.6-gm charge, to ~185 \u00b5sec, 127-cm away from 0.2-gm charge at 10\u22125 Torr. Rise times were generally shorter at 10\u22123 and 10\u22124 Torr; the 10\u22125 Torr values agree with numerical calculations. Using cube root scaling of charge mass, the observed peak reflected pressure as a function of range may be represented by\n\np = 6.5 x 10^5 (bar) r'^-3.5,\n\nwhere r[prime] the ratio of the range to the equivalent charge radius.",
"doi": "10.1063/1.1660099",
"issn": "0021-8979",
"publisher": "American Institute of Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1971-02",
"series_number": "2",
"volume": "42",
"issue": "2",
"pages": "815-829"
},
{
"id": "authors:fa7st-qqg49",
"collection": "authors",
"collection_id": "fa7st-qqg49",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141107-090405434",
"type": "article",
"title": "Equation of state of forsterite",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Lower",
"given_name": "John H.",
"clpid": "Lower-J-H"
},
{
"family_name": "Lagus",
"given_name": "Peter L.",
"clpid": "Lagus-P-L"
}
],
"abstract": "Shock wave data for pure forsterite with initial bulk densities of 2.6 and 3.1 g/cm^3 are obtained to 0.370 Mb by impacting series of specimens with tungsten alloy plates that are launched at speeds of up to 2.3 km/sec with a high-performance propellant gun. The onset of a shock-induced phase change, probably corresponding to the forsterite-'post spinel' phase change is observed at 0.280\u00b10.025 Mb. Because of the low shock temperatures, the transition is believed to be limited by the reaction rate and this pressure value should be taken only as an upper limit. Adiabats derived from the Hugoniot data for the forsterite phase are fit to the two-parameter finite strain Birch-Murnaghan equation and to two simple ionic equations of state. The Birch-Murnaghan form of the equation of state gives a zero-pressure bulk modulus (1.29 Mb) that agrees more closely with the ultrasonic data than the modulus obtained from the ionic equations of state. An unusual relaxation effect, in which the elastic shock precursor velocity varies from 5.8 to 9.5 km/sec, is also observed. The characteristic time of the relaxation process appears to be less than 1 \u03bcsec.",
"doi": "10.1029/JB076i002p00518",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1971-01-10",
"series_number": "2",
"volume": "76",
"issue": "2",
"pages": "518-528"
},
{
"id": "authors:n3aa7-00d34",
"collection": "authors",
"collection_id": "n3aa7-00d34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150210-152040091",
"type": "article",
"title": "Erasure of fission tracks in glasses and silicates by shock waves",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Fleischer",
"given_name": "Robert L.",
"clpid": "Fleischer-R-L"
},
{
"family_name": "Price",
"given_name": "P. Buford",
"clpid": "Price-P-B"
},
{
"family_name": "Woods",
"given_name": "Richard T.",
"clpid": "Woods-R-T"
}
],
"abstract": "Shock loading experiments have been carried out to determine the effect of dynamic pressures and associated temperatures on fission tracks in tektite (indochinite) and soda-lime glasses, biotite, and apatite. Below shock pressures of 83 \u00b1 4 and 31 \u00b1 3 kb, track densities remain unaltered in the tektite and soda-lime glass, respectively. In the tektite glass, partial and complete erasure of tracks is observed in samples recovered from 112 \u00b1 2 and 133 \u00b1 10 kb. In the soda-lime glass, partial erasure is observed in samples recovered from 33 \u00b1 3 and 42 \u00b1 3 kb. Shock temperature calculations indicate that the temperatures achieved upon shocking the glasses are appreciably lower than those at which tracks would be annealed out under static conditions. Single-crystals of apatite retain tracks when shocked to 45 \u00b1 5 kb. apatite recovered from shock pressures above 82 \u00b1 5 kb is granulated to micron-sized particles which preclude recognition of tracks. Single-crystal biotite specimens shocked to pressure up to 173 \u00b1 5 kb show no appreciable loss in fission track density.",
"doi": "10.1016/0012-821X(70)90145-7",
"issn": "0012-821X",
"publisher": "Elsevier",
"publication": "Earth and Planetary Science Letters",
"publication_date": "1970-07",
"series_number": "6",
"volume": "8",
"issue": "6",
"pages": "420-426"
},
{
"id": "authors:j649f-fwa84",
"collection": "authors",
"collection_id": "j649f-fwa84",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150708-103900362",
"type": "article",
"title": "Explosive Seismic Sources for the Moon",
"author": [
{
"family_name": "Kovach",
"given_name": "Robert L.",
"clpid": "Kovach-R-L"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The coupling of seismic energy under vacuum conditions, such as the moon, using an untamped surface charge is different from coupling in air. In vacuum, the explosive gas blast and the detonation products continuously expand out ward and interact with the solid surface. A series of model experiments was performed to investigate the effect\nof vacuum on coupling seismic energy.",
"doi": "10.1190/1.1440079",
"issn": "0016-8033",
"publisher": "Society of Exploration Geophysicists",
"publication": "Geophysics",
"publication_date": "1970-02-01",
"series_number": "1",
"volume": "35",
"issue": "1",
"pages": "33-44"
},
{
"id": "authors:cdpp0-n0d61",
"collection": "authors",
"collection_id": "cdpp0-n0d61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141107-104321219",
"type": "article",
"title": "A proposed equation of state of stishovite",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Takahashi",
"given_name": "Taro",
"clpid": "Takahashi-T"
},
{
"family_name": "Davies",
"given_name": "Geoffrey F.",
"clpid": "Davies-G-F"
}
],
"abstract": "The available shock-wave data for solid \u03b1 quartz in the stishovite pressure regime are reduced to a 25\u00b0C isotherm and an adiabat, centered at standard conditions, using recent standard density, enthalpy, and coefficient of thermal expansion data. The calculated isothermal bulk modulus, 3 Mb, as determined from the Birch-Murnaghan equation, depends critically on the value of (dK/dP)T at zero pressure and to a yet unknown extent on the form of the equation of state. The high-temperature value of Gr\u00fcneisen's ratio (0.8 to 0.9) along the a quartz (stishovite regime) Hugoniot was obtained from the pressure offsets of the fused quartz and porous quartz Hugoniot. The high value for \u03b3 obtained from thermochemical data at standard conditions (1.5\u00b10.3) suggests that a marked decrease in the value of \u03b3 to 0.8 occurs with increasing temperature.",
"doi": "10.1029/JB075i002p00310",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1970-01-10",
"series_number": "2",
"volume": "75",
"issue": "2",
"pages": "310-316"
},
{
"id": "authors:a2mz2-khr65",
"collection": "authors",
"collection_id": "a2mz2-khr65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151120-132936753",
"type": "article",
"title": "Deformation of experimentally shocked biotite",
"author": [
{
"family_name": "Horz",
"given_name": "Friedrich",
"clpid": "Horz-F"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Shock experiments (10-40 kb) on lepidomelane show that kinking occurs at pressures as low as 9 kb; the intensity is related to peak pressure and shock pulse duration (0.7-0.3\u00b5 sec.), and is produced by shocks propagated along [hk0] and not along [001]. The shock-induced kinks have a wider range of their angle of external rotation (19-121\u00b0) than their static counterparts (40-60\u00b0). The ratio of the kink angles, \u03b5 and \u03b4, scatters widely, indicating shock induced kinking is highly asymmetrical. A marked decrease of 2V from 24 to 7\u00b0 with increasing pressure is observed. Laue transmission patterns show that permanent angular rotations as great as 4.4\u00b0 are induced by shock pressures of 37.5 kb. In individual samples the increase in permanent angular rotations and decrease in 2V can be closely correlated.",
"doi": "10.2475/ajs.267.10.1213",
"issn": "0002-9599",
"publisher": "American Journal of Science",
"publication": "American Journal of Science",
"publication_date": "1969-12",
"series_number": "10",
"volume": "267",
"issue": "10",
"pages": "1213-1229"
},
{
"id": "authors:khn6a-y9j30",
"collection": "authors",
"collection_id": "khn6a-y9j30",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140423-112327460",
"type": "article",
"title": "Equations of State and Crystal Structures of High-Pressure Phases of Shocked Silicates and Oxides",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Anderson",
"given_name": "Don L.",
"clpid": "Anderson-D-L"
},
{
"family_name": "Ringwood",
"given_name": "A. E.",
"clpid": "Ringwood-A-E"
}
],
"abstract": "Shock-wave data are now available for a variety of rocks, minerals, and oxides of geophysical interest in the pressure range appropriate for the lower mantle. These data are analyzed to obtain equation-of-state parameters with emphasis on the shock-induced high-pressure phases. Of twenty-four materials for which Hugoniot data are analyzed, all but MgO, Al_2O_3, and MnO_2 undergo at least one shock-induced phase change below 800 kb. Birch-Murnaghan parameters for the raw Hugoniots, metastable Hugoniots, adiabats, and 25\u00b0C isotherms are obtained for the high-pressure phases. On correcting the raw Hugoniot data for MgO and Al_2O_3 for strength effects, we find that the calculated adiabatic equations of state are in good agreement with recent ultrasonic data. The zero-pressure densities of high-pressure phases are obtained by constraining the adiabats calculated from the Hugoniot data such that the zero-pressure densities and the zero-pressure slopes of the adiabats satisfy Anderson's seismic equation of state.\nProbable crystallographic structures of the high-pressure phases are inferred from the classical laws of crystal chemistry and, in some cases, from static high-pressure recovery experiments on analog compounds. Shock data for SiO_2 (stishovite) indicate that transformation to the fluorite-type structure (observed in TiO_2) does not take place under shock, at least to \u223c2000 kb. Fe_2O_3 probably transforms to either the perovskite or B rare earth structure with a zero-pressure density of 5.96 g/cm^\u00b3. MgAl_2O_4 (spinel) may transform to the CaFe_2O_4 structure with a zero-pressure density of 4.19 g/cm_\u00b3. Feldspars transform to the hollandite structure (density, of \u223c3.85 g/cm^\u00b3). Olivine-rich rocks containing greater than 10% FeO either disproportionate to the ilmenite and rock salt structure or transform to a new post-spinel polymorph having the Sr_2PbO_4 structure. Pyroxenes containing greater than 10% FeO probably transform to the ilmenite structure. High-pressure forms of sillimanite and andalusite have calculated densities of 4.00 and 3.95 g/cm^\u00b3, respectively. This probably represents disproportionation reaction products, Al_2O_3 + SiO_2 (stishovite), which would give a density of 4.09 g/cm^\u00b3. The Birch-Murnaghan second-order parameter \u03be is nearly zero for MgO and Al_2O_3. 0.73 for stishovite, and \u223c1 for the high-pressure phases of the olivines and pyroxenes. The values of K\u2032 = dK/dP are calculated along the Hugoniots and adiabats and are found to decrease at a rate of \u22120.5 to \u22121.6 cm\u00b3/g when the density is increased either by compression or by iron substitution.",
"doi": "10.1029/RG007i004p00667",
"issn": "8755-1209",
"publisher": "American Geophysical Union",
"publication": "Reviews of Geophysics",
"publication_date": "1969-11",
"series_number": "4",
"volume": "7",
"issue": "4",
"pages": "667-707"
},
{
"id": "authors:1ynam-qwq46",
"collection": "authors",
"collection_id": "1ynam-qwq46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151120-085359033",
"type": "article",
"title": "Dynamic Photoelastic Studies of P and S Wave Propagation in Prestressed Media",
"author": [
{
"family_name": "Thomson",
"given_name": "Ker C.",
"clpid": "Thomson-K-C"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Toks\u00f6z",
"given_name": "M. Nafi",
"clpid": "Toks\u00f6z-M-N"
}
],
"abstract": "The occasional existence of very pronounced, anomalous, horizontally polarized seismic waves from underground nuclear bomb blasts has been reported by several investigators. In order to further understanding of this phenomenon and the processes of mechanical radiation from explosions, particularly in prestressed media, a model study has been undertaken. Experimental apparatus has been developed which permits the generation and propagation of body waves from explosions in transparent plate models prestressed to various two-dimensional stress configurations. High-speed framing camera sequences are presented showing the explosion process and the resulting plate compressional and shear wave propagation in prestressed models. These are compared to theoretical calculations of isochromatic and \u03c0/4 isoclinic fringe patterns associated with the wave propagation in stress-free plates and plates prestressed in tension and shear. The following distinctive optical phenomena were predicted theoretically and observed in the high-speed photoelastic patterns: a \u03c0/4 discontinuity between P and S wave isoclinics for the unstressed case; a tendency for the isoclinics to broaden and envelope the isochromatics in regions where the P and S waves are superimposed; development of serrations in the dynamic isoclinics in the presence of a prestressing field (yielding a pseudo-isochromatic appearance to isoclinics when viewed monochromatically); and finally, a general similarity between the dynamic optical effects in media under tensile and shear prestress.",
"doi": "10.1190/1.1440041",
"issn": "0016-8033",
"publisher": "Society of Exploration Geophysicists",
"publication": "Geophysics",
"publication_date": "1969-10",
"series_number": "5",
"volume": "34",
"issue": "5",
"pages": "696-712"
},
{
"id": "authors:cdnh8-agz90",
"collection": "authors",
"collection_id": "cdnh8-agz90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GAFjcp69",
"type": "article",
"title": "Heat of Formation of O2\u2013",
"author": [
{
"family_name": "Gaffney",
"given_name": "Edward S.",
"clpid": "Gaffney-E-S"
},
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A series of Born\u2013Mayer-type calculations are used to calculate the lattice energies of simple oxides (MgO, BeO, CaO, and ZnO). Repulsion and other non-Coulombic contributions to the lattice energy are obtained using thermodynamic and recent ultrasonic data for the bulk moduli and the isothermal pressure and temperature derivatives of the elastic constants. Using thermochemical data for the heat of formation of MgO, CaO, and BeO and their cations, the heat of formation of O2\u2013, DeltaHf\u00b0(O2\u2013), is calculated to be 197 \u00b1 5 kcal/mole. Using the largest value of DeltaHf\u00b0(O2\u2013), obtained for MgO, presumably the most ionic of the crystals treated, a value of 202.3 kcal/mole is obtained. These values are believed to be more accurate than earlier values given by Morris and by Huggins and Sakamoto who obtained 210 \u00b1 6 and 221 \u00b1 15 kcal/mole. The anomalously low value calculated for DeltaHf\u00b0(O2\u2013) for ZnO is believed to result from a substantial covalent contribution in the Zn[Single Bond]O bond in this oxide.",
"doi": "10.1063/1.1672107",
"issn": "0021-9606",
"publisher": "Journal of Chemical Physics",
"publication": "Journal of Chemical Physics",
"publication_date": "1969-08-01",
"series_number": "3",
"volume": "51",
"issue": "3",
"pages": "1088-1091"
},
{
"id": "authors:907ky-hza29",
"collection": "authors",
"collection_id": "907ky-hza29",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141107-114927211",
"type": "article",
"title": "Shock compression of feldspars",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Petersen",
"given_name": "C. F.",
"clpid": "Petersen-C-F"
},
{
"family_name": "Rosenberg",
"given_name": "J. T.",
"clpid": "Rosenberg-J-T"
}
],
"abstract": "Hugoniot data for oligoclase and microcline to 670 and 580 kb and release adiabat data for oligoclase were obtained by means of the inclined mirror and immersed-foil-reflected-light techniques, respectively. Oligoclase and microcline have Hugoniot elastic limits in the range of 40\u201355 and 80\u201385 kb. These limits increase slightly with increasing driving shock pressure. Above the elastic limit, extending to \u223c300 and \u223c400 kb, transition regions of anomalously high compression are observed for microcline and oligoclase. These data and the data of McQueen, Marsh, and Fritz for albitite and anorthosite indicate that at successively higher shock pressures within this region, the feldspars gradually transform to a high-pressure, high-density polymorph. This polymorph probably corresponds to the rutile-like hollandite structure obtained in high-pressure quenching experiments by Kume, Matsumoto, and Koizumi (in KAlGe_3O_8) and by Ringwood, Reid, and Wadsley (in KAlSo_3O_8, microcline). In the hollandite structure germanium or silicon is in octahedral coordination with oxygen. The zero-pressure density and the Birch-Murnaghan equation of state parameters for the adiabat and isotherm are calculated for the high-pressure polymorphs of oligoclase, microcline, anorthosite, and albitite. The release adiabat centered at 180 kb indicates that at this shock pressure some (\u223c15%) of the hollandite phase forms but apparently reverts to a lower-density phase on pressure release. Release adiabat curves centered at 272 and 417 kb and calculated postshock temperatures indicate that material of feldspar composition recovered from meteorite and laboratory impacts is converted to the hollandite structure upon shock compression; upon pressure release this material probably reverts to the low-density maskelynite form.",
"doi": "10.1029/JB074i010p02727",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1969-05-15",
"series_number": "10",
"volume": "74",
"issue": "10",
"pages": "2727-2746"
},
{
"id": "authors:qt0qx-zsg16",
"collection": "authors",
"collection_id": "qt0qx-zsg16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AHRrsi69",
"type": "article",
"title": "Calibration of an Image-Converter Streak Camera",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Spetzler",
"given_name": "Hartmut",
"clpid": "Spetzler-H"
}
],
"abstract": "A new technique for time calibrating an image-converter streak camera by repetitively photographing a standard signal displayed on a wide-band sweep-delay oscilloscope is described.",
"doi": "10.1063/1.1683934",
"issn": "0034-6748",
"publisher": "Review of Scientific Instruments",
"publication": "Review of Scientific Instruments",
"publication_date": "1969-02-01",
"series_number": "2",
"volume": "40",
"issue": "2",
"pages": "354-355"
},
{
"id": "authors:jysaj-ahy75",
"collection": "authors",
"collection_id": "jysaj-ahy75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AHRjap68",
"type": "article",
"title": "Material Strength Effect in the Shock Compression of Alumina",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Gust",
"given_name": "W. H.",
"clpid": "Gust-W-H"
},
{
"family_name": "Royce",
"given_name": "E. B.",
"clpid": "Royce-E-B"
}
],
"abstract": "The Hugoniot elastic limits (HEL) of a high-density aluminum oxide ceramic (Lucalox) and a slightly lower-density ceramic (porosity approximately 4%) were determined to be 112\u00b113 and 83\u00b15 kbar, respectively. Above the HEL, the shock-stress-volume Hugoniot curves for both materials are offset by 40 kbar or more above their hydrostatic-pressure-volume curves. These results indicate that shear stresses with magnitudes of about 30\u201340 kbar persist in aluminum oxide to shock-pressure levels of at least 300 kbar.",
"doi": "10.1063/1.1655810",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1968-09-01",
"series_number": "10",
"volume": "39",
"issue": "10",
"pages": "4610-4616"
},
{
"id": "authors:jbja4-bbv29",
"collection": "authors",
"collection_id": "jbja4-bbv29",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150811-165610837",
"type": "article",
"title": "Thermodynamics of the Adiabatic Expansion of a Mixture of Two Phases",
"author": [
{
"family_name": "Cowperthwaite",
"given_name": "M.",
"clpid": "Cowperthwaite-M"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "The thermodynamics of the adiabatic expansion of a mixture of two phases capable of interchanging heat and matter across the phase boundary is presented. The law of conservation of energy is applied to each phase considered as an open system and to the mixture of phases considered as a closed system. Expressions for the entropy production resulting from internal irreversible processes demonstrate the difference between adiabatic and isentropic changes and specify conditions under which the expansion of a closed two-phase system is isentropic. Three such possible isentropic processes are defined, and expressions are derived for the temperature-pressure-volume states achieved in them. The thermodynamic treatment is useful in studies of the adiabatic release of a shock-induced mixture of phases.",
"doi": "10.1119/1.1973649",
"issn": "0002-9505",
"publisher": "American Association of Physics Teachers",
"publication": "American Journal of Physics",
"publication_date": "1967-10",
"series_number": "10",
"volume": "35",
"issue": "10",
"pages": "951-955"
},
{
"id": "authors:spry1-4tt31",
"collection": "authors",
"collection_id": "spry1-4tt31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141107-162252871",
"type": "article",
"title": "Calculated mineral reactions in the Earth's mantle",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Syono",
"given_name": "Yasuhiko",
"clpid": "Syono-Y"
}
],
"abstract": "Thermochemical and compressibility data are used to calculate the approximate pressures and temperatures required for the reaction of clinoenstatite to Mg_2SiO_4 (spinel or olivine) or to periclase and stishovite, the reaction of forsterite to Mg_2SiO_4 (spinel) or periclase and stishovite, and the breakdown of Mg_2SiO_4 (spinel) to periclase and stishovite. The calculated reaction lines for Mg_2SiO_4 (olivine) \u2192 2 MgO + SiO_2 and MgSiO_3 \u2192 MgO + SiO_2 are p = 199\u00b117 + 0.021T and p = 182\u00b117 + 0.024T (p in kilobars and T in degrees Celsius). These reaction lines lie at higher pressures than previously estimated. Because of the formation of Mg_2SiO_4 (spinel) these two reactions probably do not take place in the earth's mantle. It appears, rather, that the reactions Mg_2SiO_4 (olivine) \u2192 Mg_2SiO_4 (spinel), Mg_2SiO_4 (spinel) \u2192 2 MgO + SiO_2, and 2 MgSiO_3 \u2192 Mg_2SiO_4 (spinel) + SiO_2 take place along p = 110\u00b111 + 0.024T, p = 321\u00b138 \u2212 0.013T, and p = 133\u00b119 + 0.039 T, respectively.",
"doi": "10.1029/JZ072i016p04181",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1967-08-15",
"series_number": "16",
"volume": "72",
"issue": "16",
"pages": "4181-4188"
},
{
"id": "authors:cphq0-vem83",
"collection": "authors",
"collection_id": "cphq0-vem83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150811-134908613",
"type": "article",
"title": "Immersed-Foil Method for Measuring Shock Wave Profiles in Solids",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Ruderman",
"given_name": "M. H.",
"clpid": "Ruderman-M-H"
}
],
"abstract": "A new technique is described for measuring, essentially directly, a complex shock front profile that is transmitted into a transparent liquid from a solid material. The image of a grid light source, reflected from a Mylar foil immersed within the liquid, is recorded with a streak camera.Index of refraction data for liquids in the high\u2010pressure shocked state (required for calculating particle velocities from image displacements) are reported for glycerol, ethanol, water, and hexane to 220, 135, 58, and 41 kbar, respectively. The increase of index of refraction with density for water agrees with that reported by Zel'dovich, Sinitsyn, and Kormer, but is considerably less (as are also the results for the other liquids) than that predicted by the Lorentz\u2010Lorenz formula. Hugoniot data obtained concurrently with the refractive index data agree closely with those of Rice and Walsh. Applications of the immersed\u2010foil method are discussed for: (a) determining the release adiabats from shock states produced by a double shock front in a solid; (b) the study of shock wave attenuation in solids; and (3) measurement of the adiabatic sound velocity of liquids in the high\u2010pressure shocked state.",
"doi": "10.1063/1.1708133",
"issn": "0021-8979",
"publisher": "American Institute of Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1966-12-01",
"series_number": "13",
"volume": "37",
"issue": "13",
"pages": "4758-4765"
},
{
"id": "authors:hrvq1-vmg85",
"collection": "authors",
"collection_id": "hrvq1-vmg85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141110-092500399",
"type": "article",
"title": "Stress relaxation behind elastic shock waves in rocks",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Duvall",
"given_name": "George E.",
"clpid": "Duvall-G-E"
}
],
"abstract": "The amplitude of elastic shock waves in Arkansas novaculite is observed to decrease at a rate of \u22483.3 kb/mm for shock propagation path lengths of 6 to 12 mm. The amplitude of the final shock state in the experiments is held near the 155-kb pressure level. A total variation of elastic shock wave amplitude (Hugoniot elastic limit) of \u224840 kb (from 110 to 70 kb) is observed in \u22481 cm of shock travel. The intrinsic attenuation term in a constitutive equation for a stress-relaxing elastoplastic material is found to account for \u224890% of the observed peak pressure attenuation of the elastic shock, as compared with the \u224810% which is predicted from the instantaneous elastic shock profile. The Hugoniot elastic limits of Sioux and Eureka quartzites, which were not as intensively studied as the Arkansas novaculite, are also found to decrease with shock propagation path length.",
"doi": "10.1029/JZ071i018p04349",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1966-09-15",
"series_number": "18",
"volume": "71",
"issue": "18",
"pages": "4349-4360"
},
{
"id": "authors:y76yq-wm109",
"collection": "authors",
"collection_id": "y76yq-wm109",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AHRjap66",
"type": "article",
"title": "High-pressure electrical behavior and equation of state of magnesium oxide from shock wave measurements",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "A decrease in resistivity of MgO from >10^(5) to ~10^(3)\u03a9\u00b7cm is observed when thin single crystals are shocked in the [001] direction to 920\u00b170 kbar. This effect may be produced by several electronic processes, or by ionic transport in which the effective O= or Mg++ diffusion constants are increased by perhaps a factor of 10^39 from those calculated at high pressure (according to Zener strain-energy model). Voltages are observed during passage of various-strength (70 to 936 kbar) shock fronts through the specimen. These voltages approximately scale as the inverse of the specimen thickness and may arise from net volume polarization (~0.2 to ~9 V/cm). Some Hugoniot data to 660 kbar (including measurement of elastic-shock amplitude varying from 35 to 89 kbar) are presented.",
"doi": "10.1063/1.1782080",
"issn": "0021-8979",
"publisher": "Journal of Applied Physics",
"publication": "Journal of Applied Physics",
"publication_date": "1966-06-01",
"series_number": "7",
"volume": "37",
"issue": "7",
"pages": "2532-2541"
},
{
"id": "authors:tfvf6-n5g25",
"collection": "authors",
"collection_id": "tfvf6-n5g25",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141110-110955993",
"type": "article",
"title": "Shock compression of crustal rocks: Data for quartz, calcite, and plagioclase rocks",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Gregson",
"given_name": "V. G., Jr.",
"clpid": "Gregson-V-G-Jr"
}
],
"abstract": "Hugoniot data in the 4- to 250-kb stress range were obtained for quartzite and novaculite, sandstones of varying porosity, single-crystal calcite, marble, porous and nonporous limestone, several plagioclases of varying composition, and a basalt. Conventional plane-wave, in-contact explosive assemblies were used; the shock state was computed from measured shock velocities; particle velocities are inferred from either specimen or driver plate free-surface motion. Impedence-match solutions were obtained for porous rock. High values of the Hugoniot elastic limit were observed in nonporous rocks\u2014approximately 40 to 90 kb in quartzite and novaculite, 40 to 50 kb in the plagioclase rocks, and 15 to 25 kb in calcite and marble. Reduced values were found for porous rocks, approximately 5 kb in sandstone and limestone. Phase transitions are inferred at 30, 45, and 95 kb in calcite, and 22, 45, and 90 kb in marble and limestone. For calcite these are indicated by multiple shock fronts. Anomalously low volumes achieved by sandstone shocked to above approximately 40 kb, and high calculated shock temperatures, suggest partial conversion to coesite or stishovite. High-pressure states observed in basalt and plagioclase agree with previously reported states for gabbro [Hughes and McQueen, 1958] above 300 kb when both data are plotted in terms of relative volume. The previously observed slope-change of the gabbro Hugoniot is believed to result from an elastic wave of perhaps 50-kb amplitude which is overdriven at 300 kb.",
"doi": "10.1029/JZ069i022p04839",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1964-11-15",
"series_number": "22",
"volume": "69",
"issue": "22",
"pages": "4839-4874"
},
{
"id": "authors:agb7w-0te86",
"collection": "authors",
"collection_id": "agb7w-0te86",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150811-133418821",
"type": "article",
"title": "Elasticity of selected rocks and minerals",
"author": [
{
"family_name": "Woeber",
"given_name": "A. F.",
"clpid": "Woeber-A-F"
},
{
"family_name": "Katz",
"given_name": "Samuel",
"clpid": "Katz-S"
},
{
"family_name": "Ahrens",
"given_name": "T. J.",
"clpid": "Ahrens-T-J"
}
],
"abstract": "Elastic constants of selected rocks and minerals are listed, as obtained from measured values of density and of compressional and rotational wave velocities along 3 orthogonal directions. Density-velocity correlation and velocity-anisotropy are discussed.",
"doi": "10.1190/1.1439242",
"issn": "0016-8033",
"publisher": "Society of Exploration Geophysicists",
"publication": "Geophysics",
"publication_date": "1963-08",
"series_number": "4",
"volume": "28",
"issue": "4",
"pages": "658-663"
},
{
"id": "authors:nfsjb-r3e67",
"collection": "authors",
"collection_id": "nfsjb-r3e67",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141110-111613014",
"type": "article",
"title": "Ultrasonic observation of the calcite-aragonite transition",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Katz",
"given_name": "Samuel",
"clpid": "Katz-S"
}
],
"abstract": "Elastic-wave velocities were measured as a function of pressure by ultrasonic pulse interferometry in Solenhofen and Manlius limestone specimens to pressures of 27 and 38 kb. Longitudinal velocities decrease sharply from 5.3 km/sec at a mean pressure of 4 kb to a minimum of 4.8 km/sec at 8 kb. Transverse velocities decrease from 3.1 to 2.9 km/sec. At the minimum, bulk and rigidity moduli are 25 and 10 per cent below their 4-kb values. A density increase of 1.7 per cent is associated with this minimum. The observed effects are attributed to the calcite-aragonite transition, and they may be due to an inherent property of the material, a major component of which undergoes a polymorphic transition, the low- and high-pressure phases coexisting over a considerable pressure range. This may be an additional mechanism to account for low-velocity zones in the earth's interior.",
"doi": "10.1029/JZ068i002p00529",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1963-01-15",
"series_number": "2",
"volume": "68",
"issue": "2",
"pages": "529-537"
},
{
"id": "authors:jncs5-ak687",
"collection": "authors",
"collection_id": "jncs5-ak687",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141110-112952333",
"type": "article",
"title": "An ultrasonic interferometer for high-pressure research",
"author": [
{
"family_name": "Ahrens",
"given_name": "Thomas J.",
"clpid": "Ahrens-T-J"
},
{
"family_name": "Katz",
"given_name": "Samuel",
"clpid": "Katz-S"
}
],
"abstract": "A new method in which ultrasonic interferometry is used to measure the pressure dependence of elastic constants and the density of solids has been applied to polycrystalline KCl to pressures of 36 kilobars. Simultaneous measurement of longitudinal and transverse wave velocities in a specimen of initial thickness of approximately 0.2 mm, compressed between two tungsten carbide anvils, yields the adiabatic pressure derivative of density, which is numerically integrated to give the pressure-density relation, permitting direct comparison with Bridgman's data. Densities obtained by the present method are within 0.7 per cent of Bridgman's throughout the pressure range studied. The 19.7-kb phase transition of KCl is marked by a 6 and 12 per cent increase in bulk and shear moduli, the former in good agreement with Bridgman. Extension of the present method to higher pressures and high temperatures and to a variety of materials appears feasible.",
"doi": "10.1029/JZ067i007p02935",
"issn": "0148-0227",
"publisher": "American Geophysical Union",
"publication": "Journal of Geophysical Research",
"publication_date": "1962-07",
"series_number": "7",
"volume": "67",
"issue": "7",
"pages": "2935-2944"
}
]