[ { "id": "authors:3davr-01x82", "collection": "authors", "collection_id": "3davr-01x82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-073900966", "type": "book_section", "title": "Physics of intact capture of cometary coma dust samples", "book_title": "Shock compression of condensed matter 2011", "author": [ { "family_name": "Anderson", "given_name": "W. W.", "clpid": "Anderson-W-W" }, { "family_name": "Ahrens", "given_name": "Thomas", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Elert", "given_name": "Mark", "clpid": "Elert-M-L" } ], "abstract": "The physics of hypervelocity impact into foams are of interest because of application to\ncomet dust capture during flyby encounters. Particles much larger than the foam cells behave as if the\nfoam were a continuum, so that standard equations of fluid mechanics describe the effects of drag and\nablation. Calculations based on these arguments accurately reproduce experimental results.", "doi": "10.1063/1.3686417", "isbn": "978-0-7354-1006-0", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2012", "pages": "875-878" }, { "id": "authors:tzz94-7s316", "collection": "authors", "collection_id": "tzz94-7s316", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100621-092634935", "type": "book_section", "title": "Shock temperatures of preheated MgO", "book_title": "Shock-induced spall in copper: The effects of anisotropy, temperature, defects and loading pulse", "author": [ { "family_name": "Fat'yanov", "given_name": "Oleg V.", "clpid": "Fat'yanov-O-V" }, { "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": "Shock temperature measurements via optical pyrometry are being conducted on <100> single-crystal MgO preheated before compression to 1905\u20131924 K. Planar shocks were generated by impacting hot Mo(driver plate)-MgO targets with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 6.6 km/s. Quasi-brightness temperature was measured with 2\u20133% uncertainty by a 6-channel optical pyrometer with 3 ns time resolution, over 500\u2013900 nm spectral range. A high-power, coiled irradiance standard lamp was adopted for spectral radiance calibration accurate to 5%. In our experiments, shock pressure in MgO ranged from 102 to 203 GPa and the corresponding temperature varied from 3.78 to 6.53 kK. For the same particle velocity, preheated MgO Hugoniot has about 3% lower shock velocity than the room temperature Hugoniot. Although model shock temperatures calculated for the solid phase exceeded our measurements by ~5 times the uncertainty, there was no clear evidence of MgO melting, up to the highest compression achieved.", "doi": "10.1063/1.3295277", "isbn": "978-0-7354-0732-9", "publisher": "American Institute of Physics", "publication_date": "2009-12-28", "pages": "855-858" }, { "id": "authors:zxkq7-s0g50", "collection": "authors", "collection_id": "zxkq7-s0g50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100618-105854615", "type": "book_section", "title": "Advances in Shock Compression of Mantle Materials and Implications", "book_title": "Shock Compression of Condensed Matter - 2009", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Mosenfelder", "given_name": "Jed L.", "clpid": "Mosenfelder-J-L" }, { "family_name": "Asimow", "given_name": "Paul D.", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" } ], "abstract": "Hugoniots of lower mantle mineral compositions are sensitive to the conditions where they cross phase boundaries including both polymorphic phase transitions and partial to complete melting. For SiO_2, the Hugoniot of fused silica passes from stishovite to partial melt (73 GPa, 4600 K) whereas the Hugoniot of crystal quartz passes from CaCi_2 structure to partial melt (116 GPa, 4900 K). For Mg_2SiO_4, the forsterite Hugoniot passes from the periclase +MgSiO_3 (perovskite) assemblage to melt before 152 GPa and 4300 K, whereas the wadsleyite Hugoniot transforms first to periclase +MgSiO_3 (post-perovskite) and then melts at 151 GPa and 4160 K. Shock states achieved from crystal enstatite are molten above 160 GPa. High-pressure Gr\u00fcneisen parameters for molten states of MgSiO_3 and Mg_2SiO_4 increase markedly with compression, going from 0.5 to 1.6 over the 0 to 135 GPa range. This gives rise to a very large (>2000 K) isentropic rise in temperature with depth in thermal models of a primordial deep magma ocean within the Earth. These magma ocean isentropes lead to models that have crystallization initiating at mid-lower mantle depths. Such models are consistent with the suggestion that the present ultra-low velocity zones, at the base of the lowermost mantle, represent a dynamically stable, partially molten remnant of the primordial magma ocean. The new shock melting data for silicates support a model of the primordial magma ocean that is concordant with the Berkeley-Caltech iron core model [1] for the temperature at the center of the Earth.", "doi": "10.1063/1.3295278", "isbn": "978-0-7354-0732-9", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2009-12-28", "pages": "859-862" }, { "id": "authors:eej03-g0h02", "collection": "authors", "collection_id": "eej03-g0h02", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AIHaipcp06", "type": "book_section", "title": "Numerical Modeling of Shock-Induced Damage for Granite under Dynamic Loading", "book_title": "Shock compression of condensed matter--2005 : proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter held at Baltimore, MD 31 July-5 August, 2005", "author": [ { "family_name": "Ai", "given_name": "H. A.", "clpid": "Ai-H-A" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Furnish", "given_name": "M. D." }, { "family_name": "Elert", "given_name": "Mark" }, { "family_name": "Russell", "given_name": "Thomas P." }, { "family_name": "White", "given_name": "Carter T." } ], "abstract": "Johnson-Holmquist constitutive model for brittle materials, coupled with a crack softening model, is used to describe the deviatoric and tensile crack propagation beneath impact crater in granite. Model constants are determined either directly from static uniaxial strain loading experiments, or indirectly from numerical adjustment. Constants are put into AUTODYN-2D from Century Dynamics to simulate the shock-induced damage in granite targets impacted by projectiles at different velocities. The agreement between experimental data and simulated results is encouraging. Instead of traditional grid-based methods, a Smooth Particle Hydrodynamics solver is used to define damaged regions in brittle media.", "doi": "10.1063/1.2263593", "isbn": "0-7354-0341-4", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2006-07-28", "pages": "1431-1434" }, { "id": "authors:9dfxv-xdq36", "collection": "authors", "collection_id": "9dfxv-xdq36", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150202-103603719", "type": "book_section", "title": "Giant impact-induced blow-off of primordial atmosphere", "book_title": "Large Meteorite Impacts III", "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" } ], "contributor": [ { "family_name": "Kenkmann", "given_name": "Thomas", "clpid": "Kenkmann-T" }, { "family_name": "H\u00f6rz", "given_name": "Friedrich", "clpid": "H\u00f6rz-F" }, { "family_name": "Deutsch", "given_name": "Alexander", "clpid": "Deutsch-A" } ], "abstract": "The surface motion from a large impact upon an attenuation-free fluid sphere was studied and numerically simulated. An analytic solution for the free-surface velocity shows that close to the source, the acoustic wave due to the free-surface interaction (a \"quasi-surface wave\") is not separable from the direct wave. At >90\u00b0, the quasi-surface wave separates and has a larger amplitude than the direct body wave. Near the antipode the quasi-surface wave amplitude is much larger than the direct body wave and is comparable to the direct wave amplitude immediately near the source at 0\u00b0. The resulting solution covers both the wave interference range as defined in the asymptotic theory of near-surface wave propagation developed by Russian physicist V.S. Buldyrev reported in 1968, as well as in the geometric ray range. The geometric range theory was described in several papers in terms of multi-geometry reflection by R. Burridge, H. Jeffreys, and E.R. Lapwood in England in 1957 through 1963. For a large surface excitation (e.g., giant \u223c10^(27) J impact) a portion of the atmosphere above a plane tangent to Earth at the impact point is launched to velocities greater than the escape velocity. The resulting antipodal free-surface velocity achieved is \u223c1.9 km/s, which is sufficient to launch a comparable fraction of the atmosphere to escape.", "doi": "10.1130/0-8137-2384-1.427", "isbn": "9780813723846", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "2005", "pages": "427-432" }, { "id": "authors:n7rms-z3g45", "collection": "authors", "collection_id": "n7rms-z3g45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AHRaipcp04", "type": "book_section", "title": "Giant Impact Induced Atmospheric Blow-Off", "book_title": "Shock Compression of Condensed Matter -- 2003: Proceedings of the 13th Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Shen", "given_name": "Andy H.", "clpid": "Shen-Andy-H-T" }, { "family_name": "Ni", "given_name": "Sidao", "orcid": "0000-0003-2988-4850", "clpid": "Ni-Sidao" } ], "abstract": "Previous calculations indicate that the Earth suffered impacts from objects up to Mars size. Such a giant impact may have produced a temporary ejecta-based ring that accreted to form the Moon. To simulate the surface waves from such events we approximated the cratering source as a buried pressurized sphere. For a 10^27 J impactor we calculated the resulting surface wave using the mode summation method of Sato et al.. For such an impact, the solid Earth free-surface velocity above, and antipodal to, the source achieves 2.6 and 1.9 km/s. Such large ground motions pump the atmosphere and result in upward particle motions which cause the atmosphere to be accelerated to excess of the escape velocity (11.2 km/s) at high altitudes. For a 1.3 \u00d7 10^32 J Moon-forming impact we calculate that ~50% of the Earth's atmosphere is accelerated to escape.", "doi": "10.1063/1.1780504", "isbn": "0-7354-0181-0", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2004-07-20", "pages": "1419-1422" }, { "id": "authors:bge30-m0j75", "collection": "authors", "collection_id": "bge30-m0j75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LUOaipcp04a", "type": "book_section", "title": "Melting at the Limit of Superheating", "book_title": "Shock Compression of Condensed Matter - 2003: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter", "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": "Swift", "given_name": "Damian C.", "clpid": "Swift-D-C" } ], "contributor": [ { "family_name": "Furnish", "given_name": "Michael D." }, { "family_name": "Gupta", "given_name": "Yogendra M." }, { "family_name": "Forbes", "given_name": "Jerry W." } ], "abstract": "Theories on superheating-melting mostly involve vibrational and mechanical instabilities, catastrophes of entropy, volume and rigidity, and nucleation-based kinetic models. The maximum achievable superheating is dictated by nucleation process of melt in crystals, which in turn depends on material properties and heating rates. We have established the systematics for maximum superheating by incorporating a dimensionless nucleation barrier parameter and heating rate, with which systematic molecular dynamics simulations and dynamic experiments are consistent. Detailed microscopic investigation with large-scale molecular dynamics simulations of the superheating-melting process, and structure-resolved ultrafast dynamic experiments are necessary to establish the connection between the kinetic limit of superheating and vibrational and mechanical instabilities, and catastrophe theories.", "doi": "10.1063/1.1780210", "isbn": "0735401810", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2004-07-20", "pages": "172-175" }, { "id": "authors:9zke0-tbj14", "collection": "authors", "collection_id": "9zke0-tbj14", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:STEaipcp04b", "type": "book_section", "title": "Impact-Induced Melting of Near-Surface Water Ice on Mars", "book_title": "Shock Compression of Condensed Matter - 2003: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter", "author": [ { "family_name": "Stewart", "given_name": "Sarah T.", "clpid": "Stewart-S-T" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "O'Keefe", "given_name": "John D.", "clpid": "O'Keefe-J-D" } ], "contributor": [ { "family_name": "Furnish", "given_name": "Michael D." }, { "family_name": "Gupta", "given_name": "Yogendra M." }, { "family_name": "Forbes", "given_name": "Jerry W." } ], "abstract": "All fresh and many older Martian craters with diameters greater than a few km are surrounded by ejecta blankets which appear fluidized, with morphologies believed to form by entrainment of liquid water. We present cratering simulations investigating the outcome of 10 km s\u20131 impacts onto models of the Martian crust, a mixture of basalt and ice at an average temperature of 200 K. Because of the strong impedance mismatch between basalt and ice, the peak shock pressure and the pressure decay profiles are sensitive to the mixture composition of the surface. For typical impact events, about 50% of the excavated ground ice is melted by the impact-induced shock. Pre-existing subsurface liquid water is not required to form observed fluidized ejecta morphologies, and the presence of rampart craters on different age terranes is a useful probe of ground ice on Mars over time.", "doi": "10.1063/1.1780519", "isbn": "0735401810", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2004-07-20", "pages": "1484-1487" }, { "id": "authors:7wx36-fs640", "collection": "authors", "collection_id": "7wx36-fs640", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:STEaipcp04a", "type": "book_section", "title": "A New H2O Ice Hugoniot: Implications for Planetary Impact Events", "book_title": "Shock Compression of Condensed Matter - 2003: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter", "author": [ { "family_name": "Stewart", "given_name": "S. T.", "clpid": "Stewart-S-T" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Furnish", "given_name": "Michael D." }, { "family_name": "Gupta", "given_name": "Yogendra M." }, { "family_name": "Forbes", "given_name": "Jerry W." } ], "abstract": "Collisions on icy planetary bodies produce impact melt water, redistribute ground ice, and deposit thermal energy available for chemical reactions. The amount of melt generated from an impact is sensitive to the initial temperature, which ranges from the 273 K on Earth and Mars to 40 K on the surface of Pluto. Previous shock wave studies, centered at ~263 K for terrestrial applications, had difficulty defining the onset of phase transformations on the ice Hugoniot, and consequently, the criteria for shock melting was poorly constrained. Because ices on most planetary surfaces exist at ambient temperatures much below 263 K, we conducted a detailed study of the shock response of solid ice at 100 K and ~40 % porous ice at ~150 K to derive Hugoniots and critical pressures for shock-induced melting that are applicable to most of the solar system. New Hugoniots for solid and ~40 % porous ice are defined, and the critical pressures required to induce incipient melting and complete melting upon isentropic release from the shock state are revised using calculated shock temperatures and entropy. The critical pressures required for incipient melting of solid ice are only 0.6 and 4.5 GPa for 263 and 100 K respectively, and pressures between 0.1\u20130.5 GPa initiate melting of porous ice between 250 and 150 K. Therefore, hypervelocity impact cratering on planetary surfaces, with peak shock pressures >100 GPa, and mutual collisions between porous cometesimals in the outer solar system, with peak pressures of ~1 GPa, will generate prodigious amounts of shock-induced melt water.", "isbn": "0735401810", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2004-07-20", "pages": "1478-1483" }, { "id": "authors:af48b-bdf28", "collection": "authors", "collection_id": "af48b-bdf28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:AHRaipcp02", "type": "book_section", "title": "Depth of Cracking beneath Impact Craters: New Constraint for Impact Velocity", "book_title": "Shock Compression of Condensed Matter -- 2001: Proceedings of the 12th Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Xia", "given_name": "Kaiwen", "clpid": "Xia-Kaiwen" }, { "family_name": "Coker", "given_name": "Demirkan", "orcid": "0000-0001-7385-7089", "clpid": "Coker-Demirkan" } ], "contributor": [ { "family_name": "Furnish", "given_name": "Michael D." }, { "family_name": "Horie", "given_name": "Yasuyuki" }, { "family_name": "Thadhani", "given_name": "Naresh N." } ], "abstract": "Both small-scale impact craters in the laboratory and less than 5 km in diameter bowl-shaped craters on the Earth are strength (of rock) controlled. In the strength regime, crater volumes are nearly proportional to impactor kinetic energy. The depth of the cracked rock zone beneath such craters depends on both impactor energy and velocity. Thus determination of the maximum zone of cracking constrains impact velocity. We show this dependency for small-scale laboratory craters where the cracked zone is delineated via ultrasonic methods. The 1 km-deep cracked zone beneath Meteor Crater is found to be consistent with the crater scaling of Schmidt (1) and previous shock attenuation calculations.", "doi": "10.1063/1.1483799", "isbn": "0-7354-0068-7", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2002-07-08", "pages": "1393-1396" }, { "id": "authors:sekn6-1q428", "collection": "authors", "collection_id": "sekn6-1q428", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LIUaipcp00b", "type": "book_section", "title": "Vitreous GeO2 response to shock loading", "book_title": "Shock compression of condensed matter--1999 : proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter held at Snowbird, Utah, June 27-July 2, 1999", "author": [ { "family_name": "Liu", "given_name": "C.", "clpid": "Liu-Cangli" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Brar", "given_name": "N. S.", "clpid": "Brar-N-S" } ], "contributor": [ { "family_name": "Furnish", "given_name": "Michael D." }, { "family_name": "Chhabildas", "given_name": "Lalit C." }, { "family_name": "Hixson", "given_name": "Robert S." } ], "abstract": "Shock wave profiles in vitreous GeO2 (6.56 Mg/m^3) under planar loading were measured using stress gauges to 14 GPa. New and previous data yield Hugoniot: D=0.974 (km/s)+1.711 u for shocks of 6 to 40 GPa. We show that the phase change from 4- to 6-fold coordination of Ge+4 with O\u20132 in vitreous GeO2 occurs from 4 to 15 GPa. Hugoniots of vitreous GeO2 and SiO2 are found to approximately coincide if the pressure in SiO2 is scaled by the ratio of SiO2 to GeO2 initial density.", "doi": "10.1063/1.1303472", "isbn": "1-56396-923-8", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2000-04-18", "pages": "275-278" }, { "id": "authors:0hkne-qr249", "collection": "authors", "collection_id": "0hkne-qr249", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:LIUaipcp00a", "type": "book_section", "title": "Penetration depth time history measurement method", "book_title": "Shock compression of condensed matter--1999 : proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter held at Snowbird, Utah, June 27-July 2, 1999", "author": [ { "family_name": "Liu", "given_name": "C.", "clpid": "Liu-Cangli" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Furnish", "given_name": "Michael D." }, { "family_name": "Chhabildas", "given_name": "Lalit C." }, { "family_name": "Hixson", "given_name": "Robert S." } ], "abstract": "A new method for measuring the depth time history of rigid body penetration into brittle materials under a deceleration of ~10^5 g. The method includes: sabot-projectile, sabot-projectile separation and penetration depth detection systems. Relatively small intrinsic time error (3%) and depth error (0.3\u20130.7 mm) results. Penetration depth time history in a series of 4140 steel projectile penetrations into a mortar are measured at velocities of 100 to 500 m/sec with sufficient accuracy such that differentiation with respect to time yields stopping force, via Newton's second law.", "doi": "10.1063/1.1303645", "isbn": "1-56396-923-8", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2000-04-18", "pages": "1039-1042" }, { "id": "authors:g1dz0-ksy08", "collection": "authors", "collection_id": "g1dz0-ksy08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:JYOaipcp00", "type": "book_section", "title": "Mass spectrometer calibration of Cosmic Dust Analyzer", "book_title": "Shock compression of condensed matter--1999 : proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter held at Snowbird, Utah, June 27-July 2, 1999", "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": "T. 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" } ], "contributor": [ { "family_name": "Furnish", "given_name": "M. D.", "clpid": "Furnish-M-D" }, { "family_name": "Chhabildas", "given_name": "L. C.", "clpid": "Chhabildas-L-C" }, { "family_name": "Hixson", "given_name": "R. S.", "clpid": "Hixson-R-S" } ], "abstract": "The time of flight mass spectrometer of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft, is expected to be placed in orbit about Saturn to sample the ring material and satellite impact ejecta. Upon impact of an incident dust particle against the target plate at velocities of 5-100 km/s, some 10\u20138 to 10\u20135 times the particle mass of positive valence, single-charged ions is induced. These are analyzed via a time-of-flight mass spectrometer. Initial experiments employing a pulsed N2 laser (>300 \u00b5J/pulse, 4ns, 337nm) acting on a suite of samples are described. The laser beam is focussed to deliver the light pulses onto a laser power density (1011 W/cm2) to simulate the impact of particles. Laser ionization produced a charge of 4.6 pC per pulse for aluminum alloy. Estimating that each Al+1 ion require energy of 5.98 eV ionization energy/ion implies that 10\u20135% of the laser energy produced ions and the present system has a 5% efficiency of collecting the laser-irradiation induced ions. Employing a multi-channel plate detector in this mass spectrometer yields for Al-Mg-Cu alloy and kamacite (Fe-Ni mineral) 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.", "isbn": "1-56396-923-8", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2000-04-18", "pages": "967-970" }, { "id": "authors:sr33n-97716", "collection": "authors", "collection_id": "sr33n-97716", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:STEaipcp00", "type": "book_section", "title": "Shock wave propagation in porous ice", "book_title": "Shock compression of condensed matter--1999 : proceedings of the Conference of the American Physical Society Topical Group on Shock COmpression of Condensed Matter held at Snowbird, Utah, June 27-July 2, 1999", "author": [ { "family_name": "Stewart", "given_name": "Sarah T.", "clpid": "Stewart-S-T" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Furnish", "given_name": "M. D." }, { "family_name": "Chhabildas", "given_name": "L. C." }, { "family_name": "Hixson", "given_name": "R. S." } ], "abstract": "We present data on shock wave propagation in porous ice under conditions applicable to the outer solar system. The equation of state of porous ice under low temperature and low pressure conditions agrees well with measurements under terrestrial conditions implying that data on terrestrial snow may be applicable to the outer solar system. We also observe rarefaction waves from small regions of increased porosity and calculate release wave velocities.", "doi": "10.1063/1.1303686", "isbn": "1-56396-923-8", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2000-04-18", "pages": "1243-1246" }, { "id": "authors:d9tm0-md570", "collection": "authors", "collection_id": "d9tm0-md570", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GUPaipcp00b", "type": "book_section", "title": "Shock induced vaporization of anhydrite CaSO4 and calcite CaCO3", "book_title": "Shock compression of condensed matter--1999 : proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter held at Snowbird, Utah, June 27-July 2, 1999", "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" } ], "contributor": [ { "family_name": "Furnish", "given_name": "M. D." }, { "family_name": "Chhabildas", "given_name": "L. C." }, { "family_name": "Hixson", "given_name": "R. S." } ], "abstract": "Discovery of abundant anhydrite (CaSO4) and gypsum (CaSO4.2H2O) in the otherwise carbonate sediments comprising the upper portion of the rocks contained within the Chicxulub impact crater has prompted research on the shock-induced vaporization of these minerals. We use a vaporization criterion determined by shock-induced entropy. We reanalyze the shock wave experiments of Yang [1]. He shocked 30% porous anhydrite and 46% porous calcite. Post-shock adiabatic expansion of the sample across a 5 mm-thick gap and then impact upon an aluminum witness plate backed by LiF window that is monitored with a VISAR. Reanalysis uses Herrman's P-alpha model [2] for porous materials, and a realistic interpolation gas equation-of-state for vaporization products. Derived values of the entropies for incipient and complete vaporization for anhydrite are 1.65\u00b10.12 and 3.17\u00b10.12 kJ(kg.K)\u20131, and for calcite these are 0.99\u00b10.11 and 1.93\u00b10.11 kJ(kg.K)\u20131. Corresponding pressures for incipient and complete vaporization along the Hugoniot of non-porous anhydrite are 32.5\u00b12.5 and 122\u00b113 GPa and for non-porous calcite are 17.8\u00b12.9 and 54.1\u00b15.3 GPa, respectively. These pressures are a factor of 2\u20133 lower than reported earlier by Yang.", "isbn": "1-56396-923-8", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2000-04-01", "pages": "1259-1262" }, { "id": "authors:wr4rs-7e602", "collection": "authors", "collection_id": "wr4rs-7e602", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GUPaipcp00a", "type": "book_section", "title": "Shock temperatures in calcite (CaCO3): Implication for shock induced decomposition", "book_title": "Shock compression of condensed matter--1999 : proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter held at Snowbird, Utah, June 27-July 2, 1999", "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" } ], "contributor": [ { "family_name": "Furnish", "given_name": "M. D." }, { "family_name": "Chhabildas", "given_name": "L. C." }, { "family_name": "Hixson", "given_name": "R. S." } ], "abstract": "The temperatures induced in crystalline calcite upon planar shock compression (95\u2013160 GPa) are reported from two-stage light gas-gun experiments. The temperatures are obtained fitting 6-channel optical pyrometer radiances in the 450 to 900 nm range, to a Planck radiation law temperature varied from 3300 to 5400 K. Calculations demonstrate that the temperatures are some 400 to 1350 K lower than if either shock-induced melting and/or disproportionation of calcite behind the shock front was not occurring. Here calcite is modeled as disproportionating into a molecular liquid, or a solid CaO plus CO2 gas. For temperature calculations, specific heat at constant volume for one mole of CO2 is taken to be 6.7R as compared to 9R in the solid state; whereas calcite and CaO have their solid state values (15R and 6R). Calculations also suggest that the onset of decomposition in calcite to CaO and CO2 during loading occurs at ~75\u00b110 GPa, along the Hugoniot whereas decomposition begins upon unloading from 18 GPa. The 18 GPa value is based on comparison of VISAR measurements of particle velocity profiles induced upon isentropic expansion with one-dimensional numerical simulation.", "doi": "10.1063/1.1303691", "isbn": "1-56396-923-8", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2000-04-01", "pages": "1263-1266" }, { "id": "authors:j7k5n-cr110", "collection": "authors", "collection_id": "j7k5n-cr110", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-145102241", "type": "book_section", "title": "Shock temperatures and the melting point of iron", "book_title": "Shock compression of condensed matter 1997", "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" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Dandekar", "given_name": "D. P.", "clpid": "Dandekar-D-P" }, { "family_name": "Forbes", "given_name": "J. W.", "clpid": "Forbes-J-W" } ], "abstract": "New measurements of the ratio of Fe to LiF and Al_2O_3 anvil thermal diffusivities are used to obtain revised shock temperatures for Fe. New results match Brown and McQueen's (1) calculations of the temperatures of 5000 and 5800K at the 200 and 243 GPa transitions in Fe. New sound speed measurements along the Hugoniot of \u03b3-Fe, centered at 1573K, demonstrate that this phase melts at \u223c70 GPa and \u223c2800 K and the \u03b3 phase does not occur above \u223c93 GPa. At higher pressures, perhaps over the entire pressure range of the Earth's molten outer core (132 to 330 GPa), the \u03b2 (dhcp) phase, and not the \u03b5 phase, appears to be the solidus phase of pure Fe.", "doi": "10.1063/1.55518", "isbn": "1-56396-833-9", "publisher": "American Institute of Physics", "place_of_publication": "Woodbury, NY", "publication_date": "1998", "pages": "133-136" }, { "id": "authors:5jvvj-mqh32", "collection": "authors", "collection_id": "5jvvj-mqh32", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-144202210", "type": "book_section", "title": "Shock wave equations of state of chondritic meteorites", "book_title": "Shock compression of condensed matter 1997", "author": [ { "family_name": "Anderson", "given_name": "William W.", "clpid": "Anderson-W-W" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Dandekar", "given_name": "D. P.", "clpid": "Dandekar-D-P" }, { "family_name": "Forbes", "given_name": "J. W.", "clpid": "Forbes-J-W" } ], "abstract": "We have obtained shock compression data for Murchison and Bruderheim chondritic meteorites. Data for Murchison suggest that the Hugoniot states are described by a smooth curve to \u226590 GPa, having \u03c1_0=2.656\u200aMg/m^3, K_(S0)=24.2\u00b1.7\u200aGPa, K\u2032=4.17\u00b1.10, and constant \u03b3=1.0. The data for Bruderheim suggest more complicated behavior. A mineral mixture model consistent with the Bruderheim data suggests that the Hugoniot state is a low pressure phase below 25 GPa, with \u03c1_0=3.555\u200aMg/m^3, K_(S0)=146\u200aGPa, K\u2032=2.53, and constant \u03c1\u03b3=7.11\u200aMg/m^3; and a high pressure phase above 65 GPa, with \u03c1_0=4.40\u200aMg/m^3, K_(S0)=225\u200aGPa, K\u2032=3.25, and constant \u03c1\u03b3=7.485\u200aMg/m^3.", "doi": "10.1063/1.55475", "isbn": "1-56396-833-9", "publisher": "American Institute of Physics", "place_of_publication": "Woodbury, NY", "publication_date": "1998", "pages": "115-118" }, { "id": "authors:nxz1h-x3131", "collection": "authors", "collection_id": "nxz1h-x3131", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-093003466", "type": "book_section", "title": "Properties of LiF and Al_2O_3 to 240 GPa for Metal Shock Temperature Measurements", "book_title": "Properties of Earth and Planetary Materials at High Pressure and Temperature", "author": [ { "family_name": "Holland", "given_name": "Kathleen G.", "clpid": "Holland-K-G" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "Shock temperature experiments employing a six-channel pyrometer were conducted on 200, 500, and 1000 A thick films of Fe sandwiched between 3-mm-thick anvils of Al203 and LiF to measure the thermal diffusivity ratios\nAl_20_3/Fe and LiF / Fe at high temperatures and pressures. Temperature decays of 3000 \u00b1 800 K in 250 ns were observed at Fe pressures of 194 - 303 GPa, which reflect the conduction of heat from the thin metal films into the anvil material. These results were achieved via experiments employing LiF anvils at conditions of 164 - 165 GPa and 4190 - 4220 K and Al_2O_3 anvils at conditions of 156 - 304 GPa and 1290 - 2740 K. Thermal modeling of interface temperature versus time yields best fit thermal diffusivity\nratios of 4 - 19 \u00b1 1 (Fe/anvil) over the pressure and temperature range of the experiments. Calculated thermal conductivities for Fe, using electron gas theory, of 111 - 181 W /mK are used to calculate thermal conductivities\nfor the anvil materials ranging from 2 to 13 W /mK. Debye theory predicts higher values of 8 to 35 W /mK. Data from previous experiments on thick (\u2265l00\u03bcm) films of Fe and stainless steel are combined with our present results from experiments on thin (\u22641000 A) films to infer a 5860 \u00b1 390\nK Hugoniot temperature for the onset of melting of iron at 243 GPa. Our results address the question of whether radiation observed in shock temperature experiments on metals originates from the metal at the metal/anvil\ninterface or from the shocked anvil. We conclude that the photon flux from the shocked assemblies recorded in all experiments originates from the metal. Within the uncertainties of the shock temperature data, the uncertainties in shock temperatures resulting from the radiation from the anvils is negligible. This is in direct disagreement with the conclusions of previous work by\nKondo.", "doi": "10.1029/GM101p0335", "isbn": "9780875900834", "publisher": "American Geophysical Union", "publication_date": "1998", "pages": "335-343" }, { "id": "authors:09k84-g0g51", "collection": "authors", "collection_id": "09k84-g0g51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141028-133541926", "type": "book_section", "title": "Radio frequency heating coils for shock wave experiments", "book_title": "High-pressure materials research : symposium held December 1-4, 1998, Boston, Massachusetts, U.S.A.", "author": [ { "family_name": "Chen", "given_name": "George Q.", "clpid": "Chen-G-Q" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Wentzcovitch", "given_name": "R. M.", "clpid": "Wentzcovitch-R-M" }, { "family_name": "Hemley", "given_name": "Russell J.", "clpid": "Hemley-R-J" }, { "family_name": "Nellis", "given_name": "W. J.", "clpid": "Nellis-W-J" }, { "family_name": "Yu", "given_name": "P. Y.", "clpid": "Yu-P-Y" } ], "abstract": "Radio-frequency eddy current heating of metallic samples in shock wave, ultrasonic and diamond anvil apparatus provides a methodology for obtaining hot samples or hot metallic gaskets (containing a sample) and yet not heating the entire target, ultrasonic assembly or diamond cell. Analysis of a previous design of a radio-frequency (\u223c0.5 MHz) coil demonstrated that the center of 13 mm diameter shock wave experiment sample discs were underheated and the experimental temperatures achieved resulted from conduction of heat from the overheated sample edges relative to the center of the sample. We show, using the Biot-Savant law, that the ratio of magnetic field in the center to that at the edge of the sample, f, can be maximized to a value of f=1.8, by decreasing the radius of the heater coil, relative to the 13 mm diameter of sample. A simple analysis provides the thermal gradient across the sample thickness. An electric skin depth for iron of \u223c1 mm for the 0.45 MHz frequency of the heater power supply of our system is obtained. This leads to a maximum temperature gradient of \u223c52 K over the 4 mm thickness of the shock wave sample discs.", "doi": "10.1557/PROC-499-63", "isbn": "1-55899-404-1", "publisher": "Materials Research Society", "place_of_publication": "Warrendale, PA", "publication_date": "1998", "pages": "63-71" }, { "id": "authors:gn34n-xzd62", "collection": "authors", "collection_id": "gn34n-xzd62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-145439867", "type": "book_section", "title": "Wave generations from confined explosions in rocks", "book_title": "Shock compression of condensed matter 1997", "author": [ { "family_name": "Liu", "given_name": "C. L.", "clpid": "Liu-C-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Dandekar", "given_name": "D. P.", "clpid": "Dandekar-D-P" }, { "family_name": "Forbes", "given_name": "J. W.", "clpid": "Forbes-J-W" } ], "abstract": "In order to record P- and S-waves generated from confined explosions in rocks in the laboratory, a method is developed based on the interactions between incident P- and SV-waves and free-surfaces of rocks. The relations between particle displacements of incident P- and SV-waves, and the strains measured using strain gauges attached on free-surfaces of rocks are analytically derived. P- and SV-waves generated from confined explosions in Bedford limestone are recorded.", "doi": "10.1063/1.55601", "isbn": "1-56396-833-9", "publisher": "American Institute of Physics", "place_of_publication": "Woodbury, NY", "publication_date": "1998", "pages": "859-862" }, { "id": "authors:symmq-z1433", "collection": "authors", "collection_id": "symmq-z1433", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141029-092819848", "type": "book_section", "title": "High pressure and high temperature equation of state of gamma and liquid iron", "book_title": "High-pressure materials research : symposium held December 1-4, 1998, Boston, Massachusetts, U.S.A.", "author": [ { "family_name": "Chen", "given_name": "George Q.", "clpid": "Chen-G-Q" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Hemley", "given_name": "R. J.", "clpid": "Hemley-R-J" }, { "family_name": "Nellis", "given_name": "W. J.", "clpid": "Nellis-W-J" }, { "family_name": "Wentzcovitch", "given_name": "R. M.", "clpid": "Wentzcovitch-R-M" }, { "family_name": "Yu", "given_name": "P. Y.", "clpid": "Yu-P-Y" } ], "abstract": "Shock-wave experiments on pure iron preheated to 1573 K were conducted in the 17\u201373 GPa range. The shock-wave equation of state of \u03b3-iron at an initial temperature of 1573 K can be fit with u_s = 4.102 (0.015) km/s + 1.610(0.014) u_p with \u03c1_o = 7.413\u00b10.012 Mg/m^3 We obtain for \u03b3-iron's bulk modulus and pressure derivative the values: 124.7\u00b11.1 GPa and 5.44\u00b10.06, respectively.\nWe present new data for sound velocities in the \u03b3- and liquid-phases. In the \u03b3-phase, to a first approximation, the longitudinal sound velocity is linear with respect to density: V_p = \u22123.13 (0.72) + 1.119(0.084) p(units for V_p and p are km/s and Mg/m^3, respectively). Melting was observed in the highest pressure (about 70\u201373 GPa) experiments at a calculated shock temperature of 2775\u00b1160 K. This result is consistent with a previously calculated melting curve (for \u03b5-iron) which is close to those measured by Boehler [1] and Saxena et al. [2]. The liquid iron sound velocity data yields a Gr\u00fcneisen parameter value of 1.63\u00b10.28 at 9.37\u00b10.02 Mg/m^3 at 71.6 GPa. The quantity \u03b3_\u03c1 is 15.2\u00b12.6 Mg/m^3, which agrees with the uncertainty bounds of Brown and McQueen [3] (13.3\u201319.6 Mg/m^3). Based on upward pressure and temperature extrapolation of the melting curve of \u03b3-iron, the estimated inner core-outer core boundary temperature is 5500\u00b1400 K, the temperature at the core-mantle boundary on the outer core side is 3930\u00b1630 K.", "doi": "10.1557/PROC-499-41", "isbn": "1-55899-404-1", "publisher": "Materials Research Society", "place_of_publication": "Warrendale, PA", "publication_date": "1997", "pages": "41-61" }, { "id": "authors:n0jk0-8rg13", "collection": "authors", "collection_id": "n0jk0-8rg13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-134418460", "type": "book_section", "title": "Application of shock compression science to Earth and planetary physics", "book_title": "Shock compression of condensed matter 1995", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Tao", "given_name": "W. C.", "clpid": "Tao-W-C" } ], "abstract": "After the development of shock compression methods for obtaining pressure-density Hugoniot curves, it became clear that these could be applied to both determining the equations-of-state and investigation of polymorphic phase changes in silicate minerals of planetary mantles and crusts, as well as, the iron alloys of the metallic cores of terrestrial planets. These data, when taken with seismological models of the Earth, yield constraints on the composition of the Earth's mantle and core. Shock data for molten silicates provide a basis for understanding the initial layering of a cooling terrestrial magma ocean. Application of shock-wave data is critical to delineating the energy partitioning upon hypervelocity impact on planetary surfaces, and permits calculation of the mass of melt and vapor produced by impactors as a function of impact velocity, as well as, providing a quantitative basis for determining the degree of erosion or accretion upon planetary impact as a function of impact and planetary escape velocity.", "doi": "10.1063/1.50667", "isbn": "1-56396-566-6", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1996", "pages": "3-8" }, { "id": "authors:w732g-cdh66", "collection": "authors", "collection_id": "w732g-cdh66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-134912422", "type": "book_section", "title": "Stress wave attenuation in shock damaged rock", "book_title": "Shock compression of condensed matter 1995", "author": [ { "family_name": "Luo", "given_name": "Cangli", "clpid": "Luo-C" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Tao", "given_name": "W. C.", "clpid": "Tao-W-C" } ], "abstract": "The attenuation of ultrasonic stress waves in samples of gabbroic rock subjected to shock loading in the 11 Gpa range were studied. We determined the damage deficits, D_p, and attenuation coefficients, \u03b1_p, for the samples with different damage deficits under dynamic strains of 2\u00d710^(\u22127) and at frequencies around 2 MHz using ultrasonic pulse-echo method. A fit to the data yields the P-wave spatial attenuation coefficient versus damage deficit: \u03b1_p=40.9D_p\u221230.5D^2_p\u2009(db/cm). Basing on the O'Connell-Budiansky theory, the relation between attenuation coefficient and crack density is given. The predictions of \u03b1_p from Walsh's theory agrees well with the experiment results for the samples with different damage deficits.", "doi": "10.1063/1.50816", "isbn": "1-56396-566-6", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1996", "pages": "589-592" }, { "id": "authors:1s854-12095", "collection": "authors", "collection_id": "1s854-12095", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160411-084949104", "type": "book_section", "title": "Geophysical and Material Science Implications of the Post-Stishovite Phase", "book_title": "Advanced materials '96: new trends in high pressure research", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Akaishi", "given_name": "M.", "clpid": "Akaishi-M" } ], "abstract": "Recent shock data for TiO_2 and SiO_2, when taken with static results for RuO_2 and HfO_2\nsuggest that this group of oxides transforms from the 6-fold coordinated rutile structure to the 8-fold\ncoordinated fluorite structure which is 7-8 % denser than rutile. In the case of SiO_2, the transition\nto a fluorite structure may be representative of the lower mantle silicate transitions which could\noccur in the D\" zone. There may be technological interest in the fluorite-structured oxides because\nthese are predicted to be as hard or harder than cubic boron nitride. In the case of fluorite-structured\nSiO_2 and HfO_2 hardnesses, comparable or greater than diamond are predicted.", "isbn": "4944122012", "publisher": "National Institute for Research in Inorganic Materials", "place_of_publication": "Tsukuba, Japan", "publication_date": "1996", "pages": "1-4" }, { "id": "authors:45tge-hzg13", "collection": "authors", "collection_id": "45tge-hzg13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-133451718", "type": "book_section", "title": "Characteristic of dynamic tensile fracture in augite-peridotite", "book_title": "Shock compression of condensed matter 1995", "author": [ { "family_name": "He", "given_name": "Hongliang", "clpid": "He-H" }, { "family_name": "Jin", "given_name": "Xiaogang", "clpid": "Jin-X" }, { "family_name": "Jing", "given_name": "Fuqian", "clpid": "Jing-F" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Tao", "given_name": "W. C.", "clpid": "Tao-W-C" } ], "abstract": "Planar impact experiments were carried out to induce controlled dynamic tensile fracture in augite-peridotite. Samples, backed with PMMA buffer and windows, were impacted with PMMA impactor at velocities of 30 to 160 m/s. This resulted in maximum tensile stresses were in the range of \u223c50 to 290 MPa. Spall strength was determined to be \u223c58.1\u2009MPa from a particle velocity profile measurement. The spall strength/HEL ratios for augite-peridotite and several other rocks were discussed based on the Griffith's yield criterion and the experimental measurements.", "doi": "10.1063/1.50630", "isbn": "1-56396-566-6", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1996", "pages": "593-596" }, { "id": "authors:wewcg-pn595", "collection": "authors", "collection_id": "wewcg-pn595", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-113638028", "type": "book_section", "title": "Theory of shock magnetization of asteroids Gaspra and Ida", "book_title": "Shock Compression of Condensed Matter, 1995", "author": [ { "family_name": "Chen", "given_name": "George Q.", "clpid": "Chen-G-Q" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Hide", "given_name": "Raymond", "clpid": "Hide-R" } ], "contributor": [ { "family_name": "Schmidt", "given_name": "S. C.", "clpid": "Schmidt-S-C" }, { "family_name": "Tao", "given_name": "W. C.", "clpid": "Tao-W-C" } ], "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, \u03b5 (hcp), phase. The magnetization was acquired upon rarefaction and reentry into the ferromagnetic, \u03b1, structure. The degree of re-magnetization depends on the strength of the ambient field, which may have been associated with a solar-system-wide magnetic field. A transient field induced by the impact event itself may have resulted in a significant, or possibly, even a dominant contribution, as well. The scaling law 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 Ida was magnetized when a large impact fractured a 125\u00b122\u2009km -radius proto-asteroid to form the Koronis family. Similarly, we calculate that Gaspra could be a magnetized fragment of a 45\u00b115\u2009km -radius proto-asteroid.", "doi": "10.1063/1.50597", "isbn": "1-56396-566-6", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1996", "pages": "929-932" }, { "id": "authors:787qg-9tc16", "collection": "authors", "collection_id": "787qg-9tc16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180516-161739057", "type": "book_section", "title": "Shock Wave Data for Rocks", "book_title": "A Handbook of Physical Constants", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Johnson", "given_name": "Mary L.", "clpid": "Johnson-M-L" } ], "contributor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "[no abstract]", "doi": "10.1029/RF003p0035", "isbn": "9780875908533", "publisher": "American Geophysical Union", "place_of_publication": "Washington, DC", "publication_date": "1995-01-01", "pages": "35-44" }, { "id": "authors:jehs4-n7047", "collection": "authors", "collection_id": "jehs4-n7047", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131438464", "type": "book_section", "title": "Shock wave data for minerals", "book_title": "Mineral Physics & Crystallography: A Handbook of Physical Constants", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Johnson", "given_name": "Mary L.", "clpid": "Johnson-M-L" } ], "contributor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "Introduction\n\nShock wave equation of state\n\nShock\u2010Induced Dynamic Yielding and Phase Transitions\n\nShock Temperatures", "doi": "10.1029/rf002p0143", "isbn": "0875908527", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1995", "pages": "143-184" }, { "id": "authors:pwxg6-8wd59", "collection": "authors", "collection_id": "pwxg6-8wd59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130618-133600167", "type": "book_section", "title": "Preface", "book_title": "Global earth physics: a handbook of physical constants", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "The purpose of this Handbook is to provide, in highly accessible form, selected\ncritical data for professional and student solid Earth and planetary geophysicists.\nCoverage of topics and authors were carefully chosen to fulfill these objectives.", "doi": "10.1002/9781118668078.fmatter", "isbn": "9780875908519", "publisher": "American Geophysical Union", "place_of_publication": "Washington, DC", "publication_date": "1995", "pages": "vii-vii" }, { "id": "authors:z7emd-chd52", "collection": "authors", "collection_id": "z7emd-chd52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-135113329", "type": "book_section", "title": "Oblique impact jetting of geological materials", "book_title": "High-pressure science and technology, 1993", "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\u20132 km/s and impacted inclined gabbro (5\u201310 mm thick), novaculite (10 mm thick) and porous sandstone (12 mm thick) targets at angles of 30\u00b0\u201360\u00b0. The ejecta were collected using a catcher box filled with styrofoam and the particles were extracted using chloroform. The mass of the ejected particles per unit area (\u223c50 mg/cm^2) remains almost independent of impact velocity, inclination angle, thickness of the target and sample mineralogy and density. Based on this result, we predict that a 500 m diameter asteroid will produce only \u223c10^7 gm tektite material. This is negligible comparing to an estimated 2\u00d710^(13) gm in the Ivory Coast tektite strewn field. The recovered ejecta, unlike most tektites, contains both target and impactor materials. Both of the above results suggest that the tektites are not produced by jetting.", "doi": "10.1063/1.46229", "isbn": "1-56396-219-5", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1994", "pages": "835-838" }, { "id": "authors:y32xg-dpx41", "collection": "authors", "collection_id": "y32xg-dpx41", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-133357464", "type": "book_section", "title": "Shock Temperature of Stainless Steel and a High Pressure - High Temperature Constraint on Thermal Diffusivity of Al_2O_3", "book_title": "High-pressure science and technology, 1993", "author": [ { "family_name": "Gallagher", "given_name": "Kathleen G.", "clpid": "Gallagher-Kathleen-G" }, { "family_name": "Bass", "given_name": "Jay D.", "clpid": "Bass-J-D" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Fitzner", "given_name": "M.", "clpid": "Fitzner-M" }, { "family_name": "Abelson", "given_name": "J. R.", "clpid": "Abelson-J-R" } ], "abstract": "Time dependent shock temperatures were measured for stainless steel (SS) films in contact with transparent anvils. The anvil/window material was the same as the driver material so that there would be symmetric heat flow from the sample. Inferred Hugoniot temperatures, T_h , of 5800\u20137500 K at 232\u2013321 GPa are consistent with previous measurements in SS. Temperatures at the film\u2010anvil interface (T_i ), which are more directly measured than T_h , indicate that T_i did not decrease measurably during the approximately 250 ns that the shock wave was in Al_2O_3 or LiF anvils. Thus an upper bound is obtained for the thermal diffusivity of Al_2O_3 at the metal/anvil interface at 230 GPa and 6000K of \u03ba\u22640.00096 cm_2/s. This is a factor of 17 lower than previously calculated values, resulting in a decrease of the inferred T_h by 730 k. The observed shock temperatures are combined with temperatures calculated from measured Hugoniots and are used to calculate thermal conductivities of Al_2O_3. Also we note that since there was no measurable intensity decrease during the time when the shock wave propagated through the window, we infer from this that Al_2O_3 remained transparent while in the shocked state. Thus sapphire is a good window material to at least 250 GPa for shock temperature measurements for metals.", "doi": "10.1063/1.46195", "isbn": "1-56396-219-5", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1994", "pages": "963-966" }, { "id": "authors:h0wsn-cmz76", "collection": "authors", "collection_id": "h0wsn-cmz76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-141525607", "type": "book_section", "title": "Shock compression and release of polycrystalline magnesium oxide", "book_title": "High-pressure science and technology, 1993", "author": [ { "family_name": "Duffy", "given_name": "Thomas S.", "clpid": "Duffy-T-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "Release wave profile and Hugoniot equation of state data for low\u2010porosity polycrystalline MgO are reported to 36 and 133 GPa, respectively. At low pressure, the Hugoniot lies above single\u2010crystal data, reflecting material strength of 3.1\u00b10.8 GPa. Unloading wave velocities to 27 GPa are consistent with extrapolated compressional sound velocities. The unloading profiles can be fit using a viscoplastic model, but there are significant differences between waveforms for different experimental geometries.", "doi": "10.1063/1.46299", "isbn": "1-56396-219-5", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1994", "pages": "1107-1110" }, { "id": "authors:f1vrm-vvx71", "collection": "authors", "collection_id": "f1vrm-vvx71", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-140509684", "type": "book_section", "title": "Free surface velocity profiles in molybdenum shock compressed at 1400\u2009\u00b0C", "book_title": "High-pressure science and technology, 1993", "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 equation of state, constitutive properties and unloading wave velocities of molybdenum have been determined from free surface velocity profiles on samples shock compressed from a 1400\u2009\u00b0C initial state. The equation of state of 1400\u2009\u00b0C molybdenum agrees with previous streak camera measurements and the combined equation of state between 12 and 96 GPa is: U_S =4.78 (0.02)+1.42 (0.02)u_p . Unloading wave velocities measured between 12 and 81 GPa range from 6.30 to 7.91 km/s and are 4\u20138% below extrapolated 25\u2009\u00b0C compressional velocities. The yield strength, Y, was found to be 0.79\u20130.94 GPa, compared with values of 1.3\u20131.6 GPa from ambient\u2010temperature experiments.", "doi": "10.1063/1.46292", "isbn": "1-56396-219-5", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "1994", "pages": "1079-1082" }, { "id": "authors:p2bpz-sba35", "collection": "authors", "collection_id": "p2bpz-sba35", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150225-131530915", "type": "book_section", "title": "Hypervelocity impact: Ejecta velocity, angle, and composition", "book_title": "Large Meteorite Impacts and Planetary Evolution", "author": [ { "family_name": "Evans", "given_name": "Noreen Joyce", "clpid": "Evans-Noreen-J" }, { "family_name": "Shahinpoor", "given_name": "M.", "clpid": "Shahinpoor-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Dressier", "given_name": "Burkhard O.", "clpid": "Dressier-B-O" }, { "family_name": "Grieve", "given_name": "Richard A. F.", "clpid": "Grieve-R-A-F" }, { "family_name": "Sharpton", "given_name": "Virgil L.", "clpid": "Sharpton-V-L" } ], "abstract": "The low projectile component in tektites in contrast to the high projectile component in the Cretaceous-Tertiary (K-T) boundary clay has prompted a study of hypervelocity target-projectile mixing processes. Results from a 6.4-km/sec impact of a Fe-Ni-PGE alloy projectile (90% Fe) into a Mo target indicate that high-angle (55\u00b0 to 75\u00b0), high-velocity (< 6 km/sec) melted ejecta is relatively projectile-rich, whereas low-angle (10\u00b0 to 40\u00b0), low-velocity ejecta (< 1 km/sec) contains less projectile material and is more enriched in the target component. These results support theoretical predictions. Not predicted by theoretical calculation, but observed here, is a break in the compositional trend such that at angles of ejection between 50\u00b0 and 70\u00b0, the projectile/target ratio in the melted ejecta decreases suddenly with increasing angle, only to rise to very high values at higher angles. It appears that for large-body terrestrial impacts, the composition of the high-angle, high-speed ejecta which reaches stratospheric heights will be critical to sudden changes in global climate and the induced environmental stresses. Application of these results to large impacts such as the K-T boundary event, are expected to provide new data pertinent to physical theories of extinction mechanisms.", "doi": "10.1130/SPE293-p93", "isbn": "9780813722931", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "1994", "pages": "93-101" }, { "id": "authors:yksr6-rn135", "collection": "authors", "collection_id": "yksr6-rn135", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-103902477", "type": "book_section", "title": "Free-Surface light emission from shocked Teflon", "author": [ { "family_name": "Gallagher", "given_name": "Kathleen G.", "clpid": "Gallagher-Kathleen-G" }, { "family_name": "Yang", "given_name": "Wenbo", "clpid": "Yang-Wenbo" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "Shock initiated light emission experiments were performed on Teflon shock loaded to pressures up to \u223c17 GPa. Radiances up to 600\u00d710^6W\u22c5m^(\u22122)/(ster \u22c5nm), were measured over a range of 390 to 820 nm. We have measured the spectra of light emitted upon reflection of the shock at the free surface and observed it to be distinctly non\u2010thermal in nature. The lights appears to result from bond destruction such as observed in shock recovery experiments on Teflon and in quasistatic experiments conducted on other polymers.", "doi": "10.1063/1.46380", "publisher": "American Institute of Physics", "publication_date": "1994" }, { "id": "authors:vh6ja-z4d30", "collection": "authors", "collection_id": "vh6ja-z4d30", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141022-085218891", "type": "book_section", "title": "Shock compression and isentropic release of rhyolite", "book_title": "High-pressure science and technology, 1993", "author": [ { "family_name": "Yang", "given_name": "W.", "clpid": "Yang-W" }, { "family_name": "Chen", "given_name": "G.", "clpid": "Chen-G-Q" }, { "family_name": "Anderson", "given_name": "W. W.", "clpid": "Anderson-W-W" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "A series of shock compression experiments have been conducted on rhyolite at pressure ranging from 6 to 33 GPa. A velocity interferometer (VISAR) was employed to monitor the particle velocity of an aluminum reflector with a diffused surface bonded to the rhyolite sample. In the forward ballistic experiments, a slow rise shock wave front is observed at 6 GPa. While in the forward experiments their release waves are smeared, in a reverse ballistic experiment, the particle velocity variation at the shock wave plateau and the isentropic release wave arrival have been clearly observed. Using Swegle's mixed phase model, we simulated the experimental results with WONDY code. Like quartz and granite, the rhyolite data could be fit to a frozen release model which has some hysteric behavior. The Eulerian sound velocity at shock pressure 8.7 GPa has been determined to be 5.6 km/s.", "doi": "10.1063/1.46484", "isbn": "1-56396-219-5", "publisher": "American Institute of Physics", "place_of_publication": "New York, NY", "publication_date": "1994", "pages": "1115-1118" }, { "id": "authors:wd8kv-5jw23", "collection": "authors", "collection_id": "wd8kv-5jw23", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150225-132357523", "type": "book_section", "title": "Impact-induced melting of planetary surfaces", "book_title": "Large Meteorite Impacts and Planetary Evolution", "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" } ], "contributor": [ { "family_name": "Dressier", "given_name": "Burkhard O.", "clpid": "Dressier-B-O" }, { "family_name": "Grieve", "given_name": "Richard A. F.", "clpid": "Grieve-R-A-F" }, { "family_name": "Sharpton", "given_name": "Virgil L.", "clpid": "Sharpton-V-L" } ], "abstract": "The objective of this paper is to determine the thickness of the melt layer relative to the crater diameter for simple and complex craters. A numerical code was employed to calculate the amount of melting and the crater geometry. We used the code results and the scaling formalism of Holsapple and Schmidt (1987) to determine the scaling laws for the relative melt layer thickness.\nSimple crater dimensions are dominated by impact parameters and the planet's strength, whereas complex crater dimensions are dominated by planetary gravity, strength, and the impact parameters.\nThe volume of melt is proportional to impact energy for impact velocities and melt enthalpies of interest to planetary science. Crater geometry and dimensions scale with an exponent, \u03bc, which is intermediate between momentum (\u03bc = 1/3) and energy (\u03bc = 2/3) scaling. For simple craters, the melt layer thickness/crater diameter, T/D, for a given planetary surface (constant melt enthalpy and mean impact velocity), is independent of the crater size. For complex craters, T/D, for a given planetary surface (constant melt enthalpy, impact velocity, and gravitational acceleration), increases with the size of the crater. For simple craters, at a fixed size, the relative melt layer thickness, T/D, increases slowly with increasing impact velocity, U, according to \u221d U^(0.1)), whereas, for complex craters (\u221d U^(0.22)).", "doi": "10.1130/SPE293-p103", "isbn": "9780813722931", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "1994", "pages": "103-109" }, { "id": "authors:wfj9z-nzj60", "collection": "authors", "collection_id": "wfj9z-nzj60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131438260", "type": "book_section", "title": "Lateral Variations in Lower Mantle Seismic Velocity", "book_title": "High\u2010Pressure Research: Application to Earth and Planetary Sciences", "author": [ { "family_name": "Duffy", "given_name": "Thomas S.", "clpid": "Duffy-T-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Syono", "given_name": "Yasuhiko", "clpid": "Syono-Yasuhiko" }, { "family_name": "Manghnani", "given_name": "Murli H.", "clpid": "Manghnani-M-H" } ], "abstract": "An important finding of recent tomographic studies is that the lower mantle, at a constant radius, has RMS variations of P\u2010and S\u2010wave velocity of \u223c0.1\u20130.2% and \u223c0.2\u20130.4% from average Earth models and these lateral variations correlate spatially. Both tomographic and free oscillation studies suggest that the magnitude of relative shear velocity variations is at least twice as large as the magnitude of relative compressional velocity variations. This result can be expressed as: v = (\u2202lnV_S /\u2202lnV_p)_P > 2. In contrast, laboratory studies near ambient pressure have consistently found that the ratio of relative shear velocity variations to relative compressional velocity variations is near unity for metals and minerals generally, and mantle minerals, in particular. Laboratory studies further suggest, although not yet conclusively, that v is not strongly pressure or temperature sensitive. In this paper, we seek to determine whether high observed values of vcan be explained by the presence of 0.1\u20132.0% volatile\u2010rich partial melt heterogeneously distributed in the lower mantle. the H_2O budget of the lower mantle is estimated to be 0.1\u20130.3 wt.% based on the present ^3He flux, equation of state data for hydrous minerals, and shock devolatilization experiments which define a maximum radius of the Earth's primitive accretion core. the effect of hydrous melts on v is calculated using theories for the elastic properties of a two phase aggregate. Results indicate that, depending on aspect ratio and geometry, 0.1\u20132% partial melting in conjunction with \u223c100 K thermal anomalies can explain the seismic result so long as the compressibility of the melt differs by less than about 20% from the surrounding solid. On this basis, we conclude that small amounts of water\u2010rich partial melt are a possible explanation for the large values of (\u2202lnV_S /\u2202lnV_P)_P observed for the lower mantle.", "doi": "10.1029/gm067p0197", "isbn": "9781118663929", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1992", "pages": "197-205" }, { "id": "authors:n9w66-b5g11", "collection": "authors", "collection_id": "n9w66-b5g11", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131438374", "type": "book_section", "title": "Hugoniot Sound Velocities in Metals with Applications to the Earth's Inner Core", "book_title": "High\u2010Pressure Research: Application to Earth and Planetary Sciences", "author": [ { "family_name": "Duffy", "given_name": "Thomas S.", "clpid": "Duffy-T-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Syono", "given_name": "Yasuhiko", "clpid": "Syono-Yasuhiko" }, { "family_name": "Manghnani", "given_name": "Murli H.", "clpid": "Manghnani-M-H" } ], "abstract": "Hugoniot sound velocities in metals can be used to study the elastic properties of materials at high pressure. Both compressional and bulk sound velocities along the Hugoniot satisfy Birch's Law over the density range 2\u201327 g/cm^3. That is, velocities are linear in density with slopes proportional to atomic weight. This result provides empirical support for the validity of Birch's Law over the entire range of density distributions in the Earth's interior. Measured Hugoniot velocities are generally consistent with finite strain extrapolations of low pressure data. Differences between measured and extrapolated data can be attributed to thermal effects. Bulk sound velocities allow the volume dependence of the Gruneisen parameter, \u03b3, to be constrained. In agreement with previous results for porous metals, the sound speed data for both solid and liquid metals are consistent with q = \u2202ln\u03b3/\u2202lnV = 1, where V is the volume. Shear velocity, V_S , can be constrained to \u223c4% along the Hugoniot in the best cases but more generally uncertainties exceed 10%. At compressions above V_0/V \u2248\ufe01 1.43, 3d\u2010and 4d\u2010series transition metals are characterized by negative dV_S/dP slopes ranging between \u22120.01 and \u22120.001 km/s/GPa. the low shear velocities result in values of Poisson's ratio above 0.4 for these materials, significantly greater than zero pressure values of 0.3\u20130.35. This suggests that the shear properties of the inner core are not anomalous but rather are characteristic of the type of behavior observed in 3d\u2010and 4d\u2010series metals at high pressure and temperature.", "doi": "10.1029/gm067p0353", "isbn": "9781118663929", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1992", "pages": "353-361" }, { "id": "authors:f5k7y-5g815", "collection": "authors", "collection_id": "f5k7y-5g815", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150114-095339550", "type": "book_section", "title": "Earth Accretion", "book_title": "Origin of the Earth", "author": [ { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Newsom", "given_name": "Horton E.", "clpid": "Newsom-H-E" }, { "family_name": "Jones", "given_name": "John H.", "clpid": "Jones-J-H" } ], "abstract": "Accretion of the Earth is described in terms of the infall of volatile-, silicate-, sulfide-, and iron-bearing planetesimals. The shock pressures induced in the constituents of the planetesimals upon impact with the Earth determine their fate and the oxidation state associated with reaction of the coaccreting protoatmosphere. For planetesimal infall velocities of <0.9 km/sec, the accreting Earth has a radius of \u227e1400 km, and the impacting planetesimals retain their full complement of volatiles, e.g., H_2O, CO_2, SO_2 , NH_3, CH_4, and noble gases. This portion of the initially accreted Earth is the present source of the mantle-derived ^3He. The present rate of ^3He flux from the Earth's mantle is fully consistent with the existence of a planetesimal-derived primitive undifferentiated reservoir of an equivalent mass as a sphere of 1400 to 2000 km radius. Upon the onset of impact vaporization, at shock pressures of ~19 GPa, the water driven from the planetesimals by impact is able to react with metallic iron. This oxidation results in an increase in the iron silicate budget of the Earth. The composition of the mantle indicates that a maximum of 0.12 to 0.22 of the Earth's mantle accreted under oxidizing conditions. As more water is released by impact, the protoatmosphere inhibited infrared radiative cooling of the surface. As a consequence, impact energy is trapped under the protoatmosphere and the surface temperature rises to the melting point of wet silicates (~1400 K); surface temperature then becomes buffered by the melting reaction. Composition of the protoatmosphere is controlled by temperature and partial solubility in molten silicate. Iron silicates are reduced to metallic iron. Iron, both thermally and shock heated, and iron sulfide form the Earth's core. As accretion continues, the largest planetesimals impacting the Earth increase in diameter from several kilometers to several hundred kilometers and possibly to thousands of kilometers. We examine the constraints on impact-induced loss of the entire protoatmosphere as a result of giant impact of large planetesimals. A ~2000-km-diameter, 10^(37)-erg impactor is found to be sufficient to completely eject into space the protoatmosphere of the Earth. Impact of a larger 3000-km-diameter object is calculated to expel the protoatmosphere to speeds of >15 km/sec.", "isbn": "0-19-506619-7", "publisher": "Oxford University Press", "place_of_publication": "New York, NY", "publication_date": "1990", "pages": "211-227" }, { "id": "authors:kvdn0-23y57", "collection": "authors", "collection_id": "kvdn0-23y57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131438178", "type": "book_section", "title": "The temperature of shock compressed iron", "book_title": "Elastic Properties and Equations of State", "author": [ { "family_name": "Bass", "given_name": "Jay D.", "clpid": "Bass-J-D" }, { "family_name": "Svendsen", "given_name": "Bob", "clpid": "Svendsen-B" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Shankland", "given_name": "Thomas J.", "clpid": "Shankland-T-J" }, { "family_name": "Bass", "given_name": "Jay D.", "clpid": "Bass-J-D" } ], "abstract": "Measurements of the temperature of Fe under shock compression were performed to Hugoniot pressures of 300 GPa. The samples consisted of thin Fe films, 0.5 to 9.5\u03bcm in thickness, or Fe foils in contact with a transparent anvil of either single\u2010crystal Al_2O_3 or LiF. Temperatures at the sample/anvil interface were obtained by measuring the spectral radiance of the interface for the duration of the shock transit through the anvil, using a four\u2010color optical radiometer. Results indicate that the Al_2O_3 anvil remains at least partially transparent to pressures of 230 GPa and to temperatures of over 9000 K. The experimental data that yield the lowest temperature at any given pressure define a narrow pressure\u2010temperature trajectory which we infer to be the best estimate of the Hugoniot temperatures of Fe. Although these results must strictly be considered as an upper bound on the Hugoniot temperatures of crystal\u2010density Fe, we have obtained a melting temperature for Fe along the Hugoniot of 6700\u00b1400 K at 243 GPa. Taken together with recent measurements of the melting temperature to static pressures of 100 GPa (WILLIAMS et al., 1987), our results imply a melting temperature for Fe of 7800\u00b1500 K at the pressure of the inner core\u2010outer core boundary.", "doi": "10.1029/sp026p0532", "isbn": "0875902405", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1988", "pages": "532-541" }, { "id": "authors:xnn5j-e5a19", "collection": "authors", "collection_id": "xnn5j-e5a19", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131438044", "type": "book_section", "title": "Equations of state of iron sulfide and constraints on the sulfur content of the Earth", "book_title": "Elastic Properties and Equations of State", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Shankland", "given_name": "Thomas J.", "clpid": "Shankland-T-J" }, { "family_name": "Bass", "given_name": "Jay D.", "clpid": "Bass-J-D" } ], "abstract": "Introduction and Background\n\nExperimental Procedures for Shock Experiments on Pyrrhotite Single Crystals\n\nExperimental results for Pyrrhotite\n\nShock Wave Data and Conditions in the Earth\n\nReduction of Pyrite Shock Data\n\nReductions to Principal Isentropes\n\nOther Sulfides\n\nIsothermal Equations of State\n\nConstraints on the Sulfur Content of the Core\n\nDiscussion", "doi": "10.1029/sp026p0427", "isbn": "0875902405", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1988", "pages": "427-440" }, { "id": "authors:7b90v-yq571", "collection": "authors", "collection_id": "7b90v-yq571", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131437956", "type": "book_section", "title": "Optical radiation from shock-compressed materials and interfaces", "book_title": "High\u2010Pressure Research in Mineral Physics: A Volume in Honor of Syun\u2010iti Akimoto", "author": [ { "family_name": "Svendsen", "given_name": "Bob", "clpid": "Svendsen-B" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Bass", "given_name": "Jay D.", "clpid": "Bass-J-D" } ], "contributor": [ { "family_name": "Manghnani", "given_name": "Murli H.", "clpid": "Manghnani-M-H" }, { "family_name": "Syono", "given_name": "Yasuhiko", "clpid": "Syono-Yasuhiko" } ], "abstract": "Recent observations of shock\u2010induced 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, metal film or foil layer, and transparent window. We investigate the relationships between the temperature inferred from the observed radiation and the temperature of the shock\u2010compressed film or foil and/or window. Changes of the temperature field in each target component away from that of their respective shock\u2010compressed states occur because of: 1) shock\u2010impedance 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 window interface on the time scale of the experiments, and so control the intensity and history of the dominant thermal radiation sources in the target. Comparing this model to experiments on Fe\u2010Fe\u2010Al_2O_3 and Fe-Fe\u2010LiF targets, we note that: \n\n1) Fe at Fe\u2010Al_2O_3 interfaces releases from shock\u2010compressed states between 245 and 300 GPa to interface states between 190 and 230 GPa, respectively, with temperatures \u2248200\u20132000 K above model calculations for Fe experiencing no reshock at smooth Fe\u2010Al_2O_3 interfaces. This is so for both Fe foils and films. Below 190 GPa, reshock heating does not apparently affect the temperature of Fe\u2010Al_2O_3 interfaces. In contrast, from the same range of shock states, Fe at Fe\u2010LiF interfaces releases to states between 130 and 160 GPa (because it has a lower shock impedance than Al_2O_3); the data and model imply that Fe experiences little or no reshock at Fe\u2010LiF interfaces up to 140 GPa (where the data end). Both the Fe\u2010Al_2O_3 data and the model suggest that the degree of reshock is strongly pressure dependent above the solid Fe\u2010liquid Fe phase boundary. LiF appears to be a more ideal window than Al_2O_3 also because it is a poorer thermal\u2010inertia match to Fe than is Al_2O_3. \n\n2) In the absence of energy sources and significant energy flux from other parts of the target, the rate of change of the film/foil\u2010window interface temperature, (dT_(INT)/dt), is proportional to\u2010\u03bcexp(\u2212\u03bc2), where $$\\mu \\equiv \\delta _{{\\rm FW}} /2\\sqrt {\\kappa _{\\rm F} t} ,\\,\\delta _{{\\rm FW}}$$ is the thickness of the reshocked zone in the film/foil layer at the film/foil\u2010window interface, \u03ba_F is the thermal diffusivity of the film/foil material, and 0\u2264t\u2264t exp (t exp is the time scale of the experiment). On this basis, the temperature of a thin $$(\\delta _{{\\rm FW}} \\ll 2\\sqrt {\\kappa _{\\rm F} t_{\\exp } } )$$ reshockled layer relaxems much faster than that of a thick $$(\\delta _{{\\rm FW}} \\gg 2\\sqrt {\\kappa _{\\rm F} t_{\\exp } } )$$ layer. We estimate $$\\sqrt {\\kappa _{\\rm F} t_{\\exp } } \\sim 10\\,\\mu {\\rm m}$$ for Fe under the conditions of Fe\u2010Al2O3 and Fe\u2010LiF interfaces at high pressure. In this case, a 100\u2010\u03bcm\u2010thick reshocked Fe layer would relax very little, remaining near T_(INT)(0) on the time scale of the experiment, while a 1\u2010\u03bcm\u2010thick reshocked Fe layer would relax almost instantaneously (i.e., on a time scale much less than t_(exp)) to a temperature just above T_(INT)(\u221e). \n\n3) Greybody fits to an Fe\u2010Fe film\u2010Al_2O_3 experiment produce a gradually increasing effective greybody emissivity, $$\\hat \\varepsilon _{{\\rm gb}} (t)$$, and a gradually decreasing greybody temperature, T_(gb)(t). This behavior is characteristic of most Fe\u2010Fe\u2010Al_2O_3 experiments. The decrease of T_(gb)(t) can be explained in terms of the model for the film/foil\u2010window interface temperature, T_(INT)(t). For this experiment, the model implies that the thickness of the reshocked film layer, \u03b4_(FW), is approximately equal to the conduction length scale in the film, $$\\sqrt {\\kappa _{\\rm F} t_{\\exp } } ( \\sim 10\\,\\mu {\\rm m for}\\,{\\rm Fe})$$. Further, assuming T gb(t)=T INT(t), the greybody fit constrains the amount of reshock, \u0394T_(FW), to \u22722000 K with \u03c3_(WF), the film/foil\u2010window thermal mismatch, \u223c0.1, and $$\\delta _{{\\rm FW}} \\le 2\\sqrt {\\kappa _{\\rm F} t_{\\exp } }$$. A slight decrease of the Al2O3 absorption coefficient upon shock compression can explain the slight increase of $$\\hat \\varepsilon _{{\\rm gb}} (t)$$ with time; this may be consistent with the observation that the refractive index of Al_2O_3 seems to decrease with pressure. \n\n4) In contrast to the Fe\u2010Fe\u2010Al_2O_3 results, greybody fits to data from an Fe\u2010Fe foil\u2010LiF target show a relatively constant greybody temperature and a decreasing greybody emissivity. The constant greybody temperature implies a constant interface temperature, as expected for an interface experiencing minimal reshock, while the decaying $$\\hat \\varepsilon _{{\\rm gb}} (t)$$ is consistent with a shock\u2010induced increase in the absorption coefficient of LiF. Setting T_(INT)(0)=T_(gb)(0), we fit a simplified version of the full radiation model to these data and obtain an estimate of the absorption coefficient (\u223c100 m^(\u22121)) of LiF shock\u2010compressed to 122 GPa.", "doi": "10.1029/gm039p0403", "isbn": "0875900666", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1987", "pages": "403-423" }, { "id": "authors:7h0d8-9pj70", "collection": "authors", "collection_id": "7h0d8-9pj70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181130-131437836", "type": "book_section", "title": "The temperature of shock compressed iron", "book_title": "High\u2010Pressure Research in Mineral Physics: A Volume in Honor of Syun\u2010iti Akimoto", "author": [ { "family_name": "Bass", "given_name": "Jay D.", "clpid": "Bass-J-D" }, { "family_name": "Svendsen", "given_name": "Bob", "clpid": "Svendsen-B" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Manghnani", "given_name": "Murli H.", "clpid": "Manghnani-M-H" }, { "family_name": "Syono", "given_name": "Yasuhiko", "clpid": "Syono-Yasuhiko" } ], "abstract": "Measurements of the temperature of Fe under shock compression were performed to Hugoniot pressures of 300 GPa. The samples consisted of thin Fe films, 0.5 to 9.5 \u03bcm in thickness, or Fe foils in contact with a transparent anvil of either single\u2010crystal Al_2O_3 or LiF. Temperatures at the sample/ anvil interface were obtained by measuring the spectral radiance of the interface for the duration of the shock transit through the anvil, using a four\u2010color optical radiometer. Results indicate that the Al_2O_3 anvil remains at least partially transparent to pressures of 230 GPa and to temperatures of over 9000 K. The experimental data that yield the lowest temperature at any given pressure define a narrow pressure temperature trajectory which we infer to be the best estimate of the Hugoniot temperatures of Fe. Although these results must strictly be considered as an upper bound on the Hugoniot temperatures of crystal\u2010density Fe, we have obtained a melting temperature for Fe along the Hugoniot of 6700\u00b1400 K at 243 GPa. Taken together with recent measurements of the melting temperature to static pressures of 100 GPa (Williams et al., 1987), our results imply a melting temperature for Fe of 7800\u00b1500 K at the pressure of the inner core\u2010outer core boundary.", "doi": "10.1029/gm039p0393", "isbn": "0875900666", "publisher": "American Geophysical Union", "place_of_publication": "Washington, D. C.", "publication_date": "1987", "pages": "393-402" }, { "id": "authors:jk6hz-c2310", "collection": "authors", "collection_id": "jk6hz-c2310", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150217-090705062", "type": "book_section", "title": "Holographic Measurement Of Elastic Moduli", "author": [ { "family_name": "Schmitt", "given_name": "D. R.", "clpid": "Schmitt-D-R" }, { "family_name": "Smither", "given_name": "C. L.", "clpid": "Smither-C-L" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" }, { "family_name": "Jensen", "given_name": "B. L.", "clpid": "Jensen-B-L" } ], "abstract": "The in situ elastic moduli of rock are measured holographically by a borehole instrument in marble and oil shale. A point force induced displacement field is recorded with double exposure holography. Data consists of a fringe pattern on the viewed hologram. The elastic moduli are determined by modeling of the fringe pattern. Only Young's modulus is fairly constrained by the present data reduction. For an applied force of 520 \u00b1 50 Newtons, a marble was found to have a Young's modulus of 56 \u00b1 8 GPa, near an ultrasonically determined value of 48 \u00b1 6 GPa. In an oil shale, an applied force of 295 \u00b1 10 Newtons indicates a Young's modulus of 25 \u00b1 1GPa.", "publisher": "American Rock Mechanics Association", "publication_date": "1986" }, { "id": "authors:b6ykj-jag51", "collection": "authors", "collection_id": "b6ykj-jag51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150206-140613553", "type": "book_section", "title": "Shock Consolidation of Ni-Ti 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" } ], "contributor": [ { "family_name": "Bailey", "given_name": "G. W.", "clpid": "Bailey-G-W" } ], "abstract": "A spherically-shaped, microcrystalline Ni-Ti alloy powder having fairly nonhomogeneous particle size distribution and chemical composition was consolidated\nwith shock input energy of 316 kJ/kg. In the process of consolidation,\nshock energy is preferentially input at particle surfaces, resulting in melting\nof near-surface material and interparticle welding. The Ni-Ti powder\nparticles were 2-60 \u00b5m diameter (Fig. 1). About 30-40% of the powder particles\nwere Ni-65wt% and balance were Ni-45wt%Ti (estimated by EMPA).", "publisher": "San Francisco Press", "publication_date": "1986" }, { "id": "authors:gctnx-3tp62", "collection": "authors", "collection_id": "gctnx-3tp62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150304-110114335", "type": "book_section", "title": "The Effect of Shock Duration on the Dynamic Consolidation of Powders", "book_title": "Shock waves in condensed matter 1983", "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": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Asay", "given_name": "J. R.", "clpid": "Asay-J-R" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" }, { "family_name": "Straub", "given_name": "G. K.", "clpid": "Straub-G-K" } ], "abstract": "A recently advanced model for the shock consolidation of powders predicts, for a powder of given distension, the regimes of shock pressure and shock duration expected to yield fully densified compacts of near optimum strength. The model is evaluated in terms of UTS measurements in compacts of rapidly solidified powders of AISI 9310 alloy, shocked to initial shock pressures between 3.6 and 17.9 GPa and to shock durations between 0.23 and 2.1 \u03bcs. We find that in powders of distention 1.7, shock durations > 1 \u03bcs are required at 10 GPa to properly solidify the melt.", "doi": "10.1016/B978-0-444-86904-3.50098-1", "isbn": "9780444869043", "publisher": "Elsevier", "place_of_publication": "Amsterdam", "publication_date": "1984", "pages": "435-438" }, { "id": "authors:hr1m4-my173", "collection": "authors", "collection_id": "hr1m4-my173", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150206-142948518", "type": "book_section", "title": "Shock Consolidation of Powders \u2013 Theory and Experiment", "book_title": "Rapidly Solidified Metastable Materials", "author": [ { "family_name": "Vreeland", "given_name": "T., Jr.", "clpid": "Vreeland-T-Jr" }, { "family_name": "Kasiraj", "given_name": "P.", "clpid": "Kasiraj-P" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Schwarz", "given_name": "R. B.", "clpid": "Schwarz-R-B" } ], "contributor": [ { "family_name": "Kear", "given_name": "B. H.", "clpid": "Kear-B-H" }, { "family_name": "Giessen", "given_name": "B. C.", "clpid": "Giessen-B-C" } ], "abstract": "A recently proposed model of shock consolidation of powders quantitatively predicts regimes of input energy and shock duration required to produce well-bonded compacts. A growing data base from shock experiments in which the shock wave and powder parameters of importance are controlled allows evaluation of the model.\n\nRapidly solidified crystalline AISI 9310, and microcrystalline Markomet 3.11, as well as amorphous Markomet 1064 and crystalline Mo powders, have been consolidated by shocks up to 2 \u03bcsec duration. The formation of amorphous layers on Marko 3.11 particle surfaces indicates that surface melting and rapid solidification occurred. Decreasing amounts of amorphous structure are retained in Marko 3.11 and 1064 powder compacts with increasing shock energies. Significant improvement in Mo particle bonding is achieved by reducing surface oxides prior to shock consolidation.", "doi": "10.1557/PROC-28-139", "isbn": "9780444009357", "publisher": "Materials Research Society", "place_of_publication": "Warrendale, PA", "publication_date": "1983-11", "pages": "139-143" }, { "id": "authors:m168e-v2a09", "collection": "authors", "collection_id": "m168e-v2a09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181127-143909221", "type": "book_section", "title": "Impact of an asteroid or comet in the ocean and extinction of terrestrial life", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "O'Keefe", "given_name": "John D.", "clpid": "O'Keefe-J-D" } ], "contributor": [ { "family_name": "Boynton", "given_name": "William V.", "clpid": "Boynton-W-V" } ], "abstract": "Finite difference calculations describing the impact mechanics associated with a 10 to 30 km diameter silicate or water object impacting a 5 km deep ocean overlying a silicate solid planet at 30 km/sec demonstrate that from 12 to 15% of the bolide energy resides in the water. In the gravity field of the earth some 10 to 30 times the impactor mass of water is launched on trajectories which would take it to altitudes of 10 km or higher. This ejecta launched on trajectories which can achieve stratospheric heights is 10^1 to 10^2 projectile masses, similar to that resulting from impact of objects on an ocean\u2010free silicate half\u2010space (continent). As in the case of impact directly onto a continent, only the ejecta composed of impactor material, launched on trajectories which would carry it to stratospheric heights, matches the fraction (10^(\u22122) to 10^(\u22121)) of bolide (extraterrestrial) material found in the platinum\u2010metal\u2010rich Cretaceous\u2010Tertiary and Eocene\u2010Oligocene boundary layers. Oceanic impact results in impulsivelike giant tsunamis initially having amplitudes of \u223c4 km, representing the solitary waterwave stability limit in the deep ocean, and containing 10^(\u22122) to 10^(\u22121) of the energy of the impact. Using the constraint of no observed turbidites in marine sediments in the Cretaceous\u2010Tertiary and Eocene\u2010Oligocene boundary materials (calculated maximum water\u2010sediment interface particle velocity \u223c10\u00b0 m/sec) implies a maximum impactor energy of \u223c10^(28) to \u223c10^(29) erg corresponding to a maximum diameter for a silicate impactor of \u223c2 km (at 11 km/sec). Minimal global tsunami run\u2010up heights on the continents corresponding to impacts of this energy are 300\u2013400 m. We speculate that such waves would inundate all low altitude continental areas and strip and silt over virtually all vegetation. As a result, the terrestrial animal food chain would be seriously perturbed. This, in turn, could have caused extinction of large terrestrial animals including the archosaurs.", "doi": "10.1029/2003JE002184", "publisher": "American Geophysical Union", "publication_date": "1983-02-10" }, { "id": "authors:zterm-djh50", "collection": "authors", "collection_id": "zterm-djh50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150123-091514139", "type": "book_section", "title": "Shock Compaction of Molybdenum Powder", "book_title": "Shock waves in condensed matter", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Kostka", "given_name": "D.", "clpid": "Kostka-D" }, { "family_name": "Vreeland", "given_name": "T., Jr.", "clpid": "Vreeland-T-Jr" }, { "family_name": "Schwarz", "given_name": "R. B.", "clpid": "Schwarz-R-B" }, { "family_name": "Kasiraj", "given_name": "P.", "clpid": "Kasiraj-P" } ], "contributor": [ { "family_name": "Asay", "given_name": "J. R.", "clpid": "Asay-J-R" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" }, { "family_name": "Straub", "given_name": "G. K.", "clpid": "Straub-G-K" } ], "abstract": "Incident shocks varying from 9 to 12 GPa and 2 \u00b5s duration, impinging on porous pure Mo\n(100 \u00b5m) powder of distension 1.4, are found to produce compacts of at least 99.4% of\ncrystal density. Although recovered samples are consolidated and exhibit diamond\npyramid hardness of ~330 to 400, the particles do not appear to be well bonded. Among\nseveral possible models for producing a melt layer on particles vie propose a dynamic\nfrictional model. The shock pressures required to produce a ~1 \u00b5m film of molten\nmaterial as a result of dynamic friction varies from 11 to 108 GPa for grain sizes of\n100 to 10 \u00b5m.", "doi": "10.1016/B978-0-444-86904-3.50100-7", "isbn": "9780444869043", "publisher": "Elsevier", "place_of_publication": "Amsterdam", "publication_date": "1983", "pages": "443-446" }, { "id": "authors:k0sxr-cxs47", "collection": "authors", "collection_id": "k0sxr-cxs47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150126-145543632", "type": "book_section", "title": "Mechanical Properties of a Shock Consolidated Steel Powder", "book_title": "Shock Waves in Condensed Matter", "author": [ { "family_name": "Kasiraj", "given_name": "Prakash", "clpid": "Kasiraj-P" }, { "family_name": "Vreeland", "given_name": "Thad, Jr.", "clpid": "Vreeland-T-Jr" }, { "family_name": "Schwarz", "given_name": "Ricardo B.", "clpid": "Schwarz-R-B" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Asay", "given_name": "J. R.", "clpid": "Asay-J-R" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" }, { "family_name": "Straub", "given_name": "G. K.", "clpid": "Straub-G-K" } ], "abstract": "The microhardness, ultimate tensile strength, and elastic modulus of 44-74 \u00b5m AISI\n9310 rapidly solidified powder, consolidated by shock waves with energies varying\nfrom 94 to 770 kJ/kg and a shock duration of 2-3 \u00b5s, are presented. The compacts produced\nhave a variation in diamond pyramid hardness from 390 to 510, in strength from\n0 to 1.4 GPa, and in elastic modulus from 66 to 181 GPa. The hardness and strength\nreach a maximum at 500 kJ/kg shock energy. The strength and elastic modulus results\nimply that 800 kJ /kg shock energy produces complete interparticle bonding.", "doi": "10.1016/B978-0-444-86904-3.50099-3", "isbn": "9780444600172", "publisher": "Elsevier", "publication_date": "1983", "pages": "439-442" }, { "id": "authors:wray2-szx85", "collection": "authors", "collection_id": "wray2-szx85", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-100030825", "type": "book_section", "title": "A method of determining points on the principal isentropes of molecular liquids", "book_title": "Shock Waves in Condensed Matter - 1981", "author": [ { "family_name": "Boslough", "given_name": "M. B.", "clpid": "Boslough-M-B" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Nellis", "given_name": "W. J.", "clpid": "Nellis-W-J" }, { "family_name": "Seaman", "given_name": "L.", "clpid": "Seaman-L" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" } ], "abstract": "We have examined the feasibility of using a large\u2010diameter, projectile\u2010target impact to carry out one\u2010dimensional, isentropic compression experiments on molecular fluids. By employing a three\u2010layered target geometry, with a thin foam driver layer and a thick, high\u2010impedance anvil layer, liquid H_2O can be compressed to a state within 0.1% of its principal isentrope at pressures up to about 30 GPa. The pressure and density of the state achieved can be determined from electromagnetic particle velocity gauges imbedded on the interfaces bounding the sample.", "doi": "10.1063/1.33366", "isbn": "0-88318-177-0", "publisher": "American Institute of Physics", "place_of_publication": "New York, NY", "publication_date": "1982-04-01", "pages": "236-240" }, { "id": "authors:demd1-8tj85", "collection": "authors", "collection_id": "demd1-8tj85", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-094118553", "type": "book_section", "title": "One-dimensional isentropic compression", "book_title": "Shock waves in condensed matter--1981", "author": [ { "family_name": "Lyzenga", "given_name": "Gregory A.", "clpid": "Lyzenga-G-A" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Nellis", "given_name": "W. J.", "clpid": "Nellis-W-J" }, { "family_name": "Seaman", "given_name": "L.", "clpid": "Seaman-L" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" } ], "abstract": "The generation of nearly isentropic pressure\u2010density states in a molecular fluid sample, e.g. H_2O is examined by a series of one\u2010dimensional finite difference calculations. We employ a series of buffer materials of increasing shock impedance (Lexan, Al, Fe, W) behind the sample and impact it with a composite flyer plate of the same series of materials. In the case of H_2O impacted at 2.5 km/sec, three\u2010fold nearly isentropic compression to a pressure of 70 GPa is achieved in 10 \u03bcsec with a 3 cm thick composite impactor.", "doi": "10.1063/1.33365", "isbn": "0-88318-177-0", "publisher": "American Institute of Physics", "place_of_publication": "New York, NY", "publication_date": "1982-04-01", "pages": "231-235" }, { "id": "authors:khrj0-erv29", "collection": "authors", "collection_id": "khrj0-erv29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-084124664", "type": "book_section", "title": "Electrical and optical measurements on fused quartz under shock compression", "book_title": "Shock Waves in Condensed Matter-1981", "author": [ { "family_name": "Kondo", "given_name": "K.", "clpid": "Kondo-K" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" }, { "family_name": "Sawaoka", "given_name": "A.", "clpid": "Sawaoka-A" } ], "contributor": [ { "family_name": "Nellis", "given_name": "W. J.", "clpid": "Nellis-W-J" }, { "family_name": "Seaman", "given_name": "L.", "clpid": "Seaman-L" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" } ], "abstract": "The resistivities of specimens of SiO_2 (fused quartz) singly and doubly shocked in the 10 to 45 and 27 to 90 GPa range, respectively, demonstrate a marked decrease from values of \u223c10\u03a9\u22c5m to \u223c0.1\u03a9\u22c5m at single shock pressure of \u223c40 and double shock pressure of \u223c74 GPa. The shock\u2010induced polarizatio profiles also show a sudden change of electrical properties of the material at those pressures. The rapid decrease in resistivity suggests a further transformation to an unknown phase or production of an electron bound level.", "doi": "10.1063/1.33328", "isbn": "0-88318-177-0", "publisher": "American Institute of Physics", "place_of_publication": "New York, NY", "publication_date": "1982-04-01", "pages": "299-303" }, { "id": "authors:113kp-06d87", "collection": "authors", "collection_id": "113kp-06d87", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141031-080712710", "type": "book_section", "title": "Shock wave apparatus for studying minerals at high pressure and impact phenomena on planetary surfaces", "book_title": "Shock Waves in Condensed Matter-1981", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Boslough", "given_name": "Mark B.", "clpid": "Boslough-M-B" }, { "family_name": "Ginn", "given_name": "Warren G.", "clpid": "Ginn-W-G" }, { "family_name": "Vassiliou", "given_name": "Mario S.", "clpid": "Vassiliou-M-S" }, { "family_name": "Lange", "given_name": "Manfred A.", "clpid": "Lange-M-A" }, { "family_name": "Watt", "given_name": "J. Peter", "clpid": "Watt-J-P" }, { "family_name": "Kondo", "given_name": "Kenichi", "clpid": "Kondo-Kenichi" }, { "family_name": "Svendsen", "given_name": "Robert F.", "clpid": "Svendsen-R-F" }, { "family_name": "Rigden", "given_name": "Sally M.", "clpid": "Rigden-S-M" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "contributor": [ { "family_name": "Nellis", "given_name": "W. J.", "clpid": "Nellis-W-J" }, { "family_name": "Seaman", "given_name": "L.", "clpid": "Seaman-L" }, { "family_name": "Graham", "given_name": "R. A.", "clpid": "Graham-R-A" } ], "abstract": "Shock wave and experimental impact phenomena research on geological and planetary materials is being carried out using two propellant (18 and 40 mm) guns (up to 2.5 km/sec) and a two\u2010stage light gas gun (up to 7 km/sec). Equation of state measurements on samples initially at room temperature and at low and high temperatures are being conducted using the 40 mm propellant apparatus in conjunction with Helmholtz coils, and radiative detectors and, in the case of the light gas gun, with streak cameras. The 18 mm propellant gun is used for recovery experiments on minerals, impact on cryogenic targets, and radiative post\u2010shock temperature measurements.", "doi": "10.1063/1.33290", "isbn": "0-88318-177-0", "publisher": "American Institute of Physics", "place_of_publication": "New York, NY", "publication_date": "1982-04-01", "pages": "631-633" }, { "id": "authors:ep4np-d7t46", "collection": "authors", "collection_id": "ep4np-d7t46", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150327-103946761", "type": "book_section", "title": "The interaction of the Cretaceous/Tertiary Extinction Bolide with the atmosphere, ocean, and solid 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" } ], "contributor": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Schultz", "given_name": "Peter H.", "clpid": "Schultz-P-H" } ], "abstract": "The mechanics of large-scale (~10-km diameter) asteroidal, cometary, and meteoroid swarm impact onto a silicate Earth covered by water and a gas layer (atmosphere) demonstrate that only ~ 15% to ~ 5% of the energy of 15 to 45 km/s bolides is taken up directly during the passage through the ocean and atmosphere, respectively. Upon impact with the Earth, ~ 10 to 10^2 times the bolide mass of water or rock can be ejected to the stratosphere: however, only ~0.1 bolide masses is in < 1 \u03bcm particles. The vaporized, melted, and (< 1 mm) solid ejecta transfer up to ~40% of their energy to the atmosphere and possibly oceanic surface water, giving rise to a short, possibly lethal (to large animals) heating pulse. The initial high-speed ejecta that lofted to and above the stratosphere early in the cratering flow is enriched in bolide material and has concentrations of extraterrestrial material in the range of those measured (0.01 to 0.2) in the Cretaceous/Tertiary (C/T) boundary layer. We suggest that the origin of the C/T boundary layer is this ejecta, which is heavily shocked and in the < l-\u03bcm range and, hence, once entrained in the stratosphere may be spread worldwide. Penetration of the atmosphere by the bolide creates a temporary hole in the atmosphere surrounded by strongly shocked air. The resultant inward and upward flow of the shocked atmosphere backward along the bolide trajectory lofts the vapor, fine-melted and solid ejecta to heights greater than 10 km. The larger, millimeter- to centimetersize, melt droplets that are lofted by this mechanism reenter the atmosphere and may represent microtektites and tektites. Sufficient impact-induced vapor, melted and comminuted silicate is ejected to stratospheric heights to markedly reduce the light levels at the Earth's surface. The short-term effects of heating, followed by dust and possibly water-cloud deck induced worldwide cooling, provide several mechanisms to cause severe environmental stress to biota and possibly give rise to the varied and massive extinctions that occurred at the C/T boundary.", "doi": "10.1130/SPE190-p103", "publisher": "Geological Society of America", "publication_date": "1982" }, { "id": "authors:t0jth-5ns68", "collection": "authors", "collection_id": "t0jth-5ns68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150218-080657874", "type": "book_section", "title": "Temperatures Induced by Shock Waves in Minerals: Applications to Geophysics", "book_title": "High-pressure research in geophysics", "author": [ { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" }, { "family_name": "Lyzenga", "given_name": "G. A.", "clpid": "Lyzenga-G-A" }, { "family_name": "Mitchell", "given_name": "A. C.", "clpid": "Mitchell-A-C" } ], "contributor": [ { "family_name": "Akimoto", "given_name": "S.", "clpid": "Akimoto-S" }, { "family_name": "Manghnani", "given_name": "M. H.", "clpid": "Manghnani-M-H" } ], "abstract": "The temperatures of initially transparent minerals of geophysical interest are measured\nusing a six-channel optical pyrometry system operating over the range 450 to 790 nm. The\nradiative temperatures and emissivity of minerals are measured by recording spectral\nradiances versus time during the time interval that an intense shock wave is driven through\nthe sample. The shock wave is induced by the impact of a projectile accelerated by a two-stage light-gas gun. Taken together with the pressure-density Hugoniot data, complete\npressure-density-temperature equations of state may be constructed over the entire pressure\nrange present within the earth. Shock temperature and shock pressure data for NaCl\nextending to 1,040 kbar (104 GPa) demonstrate that a transition from the B1 to B2 phase\noccurs below 300 kbar (with a phase transition energy of ~0.2 MJ/kg) and melting of the B2\nphase occurs above 550 kbar. Shock temperatures for the high-pressure phase assemblage\nof Mg_2SiO_4, believed to be MgO (periclase) and MgSiO_3 (perovskite), are closely matched\nby theoretical calculations that assume a phase transition energy from olivine to this\nassemblage of ~1.5 MJ/kg. Shock temperature data for \u03b1\n-quartz and fused quartz\nshocked into the stishovite regime display dramatic decreases in shock temperatures at\n~700 and ~1,050 kbar, which are interpreted as representing shock-induced melting of\nstishovite. The observed data can be fit theoretically by assuming that stishovite is driven\ninto the super-heated regime ~1,000 K above the melting point and melts suddenly to a\ntemperature of 4,400 K (at 700 kbar) with a latent heat of melting of 3.5 MJ/kg. Assuming\nthat SiO_2 stishovite is a component in a ternary MgO-SiO_2-FeO mantle and taking into\naccount the expected decrease in the solidus of this system relative to the oxides, the\nminimum melting point obtained implies a maximum lower mantle temperature of\n3,500 K. The slight increase in the melting point of stishovite may be used in conjunction\nwith a Weertman-type relation between homologous temperature and creep viscosity to\nestimate the effect of pressure on viscosity. Such an analysis for SiO_2 suggests an activation\nvolume for the lower mantle of the earth of ~1 to 4 cm^3 /mole for Mg_2SiO_4. This value is a\nfactor of 2 to 4 less than inferred from measurements of the activation volume of an upper\nmantle mineral such as olivine. This small activation volume implies a maximum increase\nof viscosity with depth in the lower mantle of a factor of between ~1 to ~10^4 depending on\nthe assumed rheological model, activation energy, and the temperature. Whereas a slight\nincrease with depth of viscosity in the earth's lower mantle as compared with the upper\nmantle supports theories of convection throughout the mantle, an increase in viscosity by a\nfactor of 10^4 probably precludes single-cell, mantle-wide convection.", "isbn": "978-90-277-1439-8", "publisher": "Kluwer", "place_of_publication": "Boston, MA", "publication_date": "1982", "pages": "579-594" }, { "id": "authors:2an84-cca29", "collection": "authors", "collection_id": "2an84-cca29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150128-083525276", "type": "book_section", "title": "Structural study of Cactus Crater", "book_title": "Proceedings of the Lunar and Planetary Science Conference", "author": [ { "family_name": "Vizgirda", "given_name": "Joana", "clpid": "Vizgirda-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "The detailed structure of Cactus Crater, a 105 m diameter nuclear explosion crater formed in water-saturated carbonate rock of Eniwetok Atoll, is delineated using the high to low Mg calcite diagenetic transition as a stratigraphic tracer. Outside Cactus, this transition is observed as a discontinuous horizon which appears to be depressed, possibly as a result of the cratering event,\nnear the crater. Beneath the crater, this transition occurs gradually over a 4.5 \u00b1 0.5 m interval, leading to the following conclusions: material inside Cactus Crater underwent primarily in situ brecciation and mixing, the maximum depth of the excavation cavity is 20 m below sea level, and a fallback breccia lens, if it exists, has a maximum thickness of l m. A central uplift of 4.5 \u00b1 0.5 m is inferred from the observation that the transition interval occurs at a 4 to 5 m greater depth at 1/2 crater radius than in the center. The excavation process, deduced from the Mg calcite transition as well as gamma well log data, involves high velocity injection of strongly shocked material to form the excavation cavity lining. The in situ brecciation and mixing appears to be a turbulent process, probably facilitated by fluidization of the carbonate rock. Based on the Mg calcite transition patterns beneath\nthe crater floor, dynamic rebound is inferred as the modification mechanism for Cactus Crater. Using the Melosh Bingham model for dynamic rebound, a maximum strength of ~1 bar is inferred for the cratered carbonate medium. This strength value is representative of clays, such as those in which Snowball, a chemical explosion crater having dimensions and features similar to Cactus', was formed. Comparisons between Cactus and meteorite impact craters are also presented.", "isbn": "0080280749", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1982", "pages": "1623-1639" }, { "id": "authors:c3c9d-kcb38", "collection": "authors", "collection_id": "c3c9d-kcb38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150213-092357505", "type": "book_section", "title": "Fragmentation of ice by low velocity impact", "book_title": "Proceedings of the Lunar and Planetary Science Conference", "author": [ { "family_name": "Lange", "given_name": "Manfred A.", "clpid": "Lange-M-A" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "Low velocity impact experiments (0.14 to l km/s) carried out in polycrystalline water ice targets at 257 and 81 K resulted in interactions which can be assigned to four fragmentation classes, cratering, erosion, disruption, and total fragmentation. Specific kinetic energies for the transitions between these classes range from l x 10^5 to 7 x 10^5 ergs/g for 81 K ice and from 3 x 10^5 to ~ 2 x 10^6 ergs/g for 257 K ice. These values are about one to two orders of magnitude below those for silicate rocks. The mass vs. cumulative number distribution of fragments in our experiments can be described by a simple power law, similar to that observed in fragmented rocks in both the laboratory\nand in nature. The logarithmic slopes of cumulative number vs. fragment weight vary between - 0.9 and - 1.8 decreasing with increasing projectile energy and are approximately independent of target temperature. The shapes of fragments resulting from erosion and disruption of ice targets are\nsignificantly less spherical for 257 K targets than for 81 K targets. Fragment sphericity increases with increasing projectile energy at 257 K, but no similar trend is observed for 81 K ice. Our results support the hypothesis that the specific projectile energy is a measure for target\ncomminution for a relatively wide range of projectile energies and target masses. We apply our results to the collisional interaction of icy planetary bodies and find that the complete destruction of a target body with radii between 50 m and 100 km\u00b7 range from 10^(17) to 10^(27) ergs. Energies corresponding to basaltic bodies of the same size range from 10^(18) to 10^(28) ergs. Our experiments suggest that regolith components on icy planets resemble those on rocky planetary bodies in size and shape. We\npredict that the initial shapes of icy particles in the Saturnian ring system were roughly spherical. The initial mass distribution of ring particles should follow a power law with a slope of ~ - 1.5.", "isbn": "0080280749", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1981-03", "pages": "1667-1687" }, { "id": "authors:rt1qn-2m387", "collection": "authors", "collection_id": "rt1qn-2m387", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130717-131458838", "type": "book_section", "title": "Absorption spectroscopy in solids under shock compression", "book_title": "High-Pressure Science and Technology: Sixth AIRAPT Conference", "author": [ { "family_name": "Goto", "given_name": "T.", "clpid": "Goto-T" }, { "family_name": "Rossman", "given_name": "G. R.", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "abstract": "Experimental techniques that allow measurement of the optical\nabsorption spectra of solids during the short time interval that\nthey can be compressed dynamically offer the opportunity to supplement\nthe more familiar equation of state data, which are usually\nreported in the form of a Hugoniot curve [1], with knowledge of the\ntransition element (cation) coordination environment, charge transfer\nenergy spectrum, and population of electronic states at high\n(dynamic) pressures. In principle, shock pressures in excess of\n100 GPa (1 Mbar) can be obtained; moreover, the absolute pressures\nare known for any given experiment to ~ 1%. The spectral range,\nhowever, is limited to about 350 to 700 nm by the response of photographic\nfilm. Thus spectroscopy under dynamic compression offers\nboth advantages and disadvantages with respect to the gathering of\nspectral data in static high-pressure equipment [2,3]. In addition\nto the application of spectroscopic data in obtaining a fundamental\nunderstanding of the solid-state physics and chemistry of solids,\nhigh-pressure optical data have two important applications to the\nphysics of the earth's interior, particularly with regard to the\nenvironment of the lower mantle of the earth. In the pressure\nregime above ~30 GPa, a major objective of both contemporary\nstatic [4,5] and dynamic [6,7] experimentation is the discovery\nand characterization of the crystal structures appropriate for the\nsilicates and oxides of the earth's lower mantle. Because transition\nelement absorption spectra are highly sensitive to the coordination\nnumber and geometry of the cation sites in oxides and\nsilicates, the present techniques appear promising with regard to\ndistinguishing among the different possible high-pressure phases\n[8]. The second geophysical application of spectral data for candidate mantle minerals and their crystal-chemical analogs is the\ndetermination of the dependence of photon opacity and index of refraction\non wavelength, pressure, and temperature. The opacity and,\nto a lesser extent, the index of refraction (a subject not addressed\nby the present paper) control the radiative transport of heat in\nthe temperature regime of the earth's lower mantle (> 3000 K) [9-12].\nThe above considerations have motivated both earlier exploratory\nstudies of the optical properties of oxides under shock [13] and the\ndevelopment of the present refined apparatus for measuring mineral\nspectra under shock conditions. In this report, our apparatus is\ndescribed in detail together with its application to the measurement\nof optical absorption spectra of Cr^(3+)-doped Al_2O_3 (ruby) under shock\ncompression.", "isbn": "9780306400698", "publisher": "Plenum Press", "place_of_publication": "New York", "publication_date": "1979", "pages": "895-900" }, { "id": "authors:vkved-6j609", "collection": "authors", "collection_id": "vkved-6j609", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150903-074125515", "type": "book_section", "title": "The equation of state of a lunar anorthosite: 60025", "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, equation-of-state measurements of lunar anorthosite 60025 (-18% initial porosity) and single crystal anorthite in the 40 to 120 GPa (0.4-1.2 Mbar) pressure range are presented and compared, along with previous results on nonporous anorthosite and lunar samples.\nThe porous lunar anorthosite exhibits a lower shock impedance than nonporous anorthosite which, in turn, has a lower impedance than either nonporous gabbroic anorthosite (15418) or high-titanium, mare basalt (70215). This suggests that crater statistics (and, hence, apparent cratering ages) for different lunar terranes are biased by the properties of the different target rocks: for a given set of impacts, systematically smaller craters will tend to be formed in (nonporous) high-Ti mare basalt, gabbroic anorthosite and anorthosite, respectively. The effect of initial porosity in anorthosite 60025 is significant: for a given impact, peak stresses are distinctly lower in the porous anorthosite (typically by about 20% in the 40-100 GPa range) than in the nonporous equivalent, whereas both shock and post-shock temperatures are considerably higher. For example, shock temperatures (at a given pressure) differ by about 10^3 to 4 X 10^3 Kover the range 40-100 GPa. Thus, maturing of a planetary surface by repeated impact (resulting in even mild brecciation and, hence, porosity) strongly enhances the thermal energy partitioning into the planet during meteoritic bombardment. The coupling of kinetic energy on impact is, however, decreased leading to a decrease in cratering efficiency due to increased porosity. These results imply that, as a result of successive impact events, the dynamic properties of a given rock unit as well as the entire planetary surface will evolve such that the efficiency in the trapping of thermal energy associated with impact will tend to increase with time.", "publisher": "Pergamon Press", "publication_date": "1978-03" }, { "id": "authors:hvcyw-bf561", "collection": "authors", "collection_id": "hvcyw-bf561", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150902-153359119", "type": "book_section", "title": "Energy and mass distributions of impact ejecta blankets on the moon and Mercury", "book_title": "9th Lunar and Planetary Science Conference", "author": [ { "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": "The distribution of the mass and energy of the ejecta from the impact of gabbroic anorthosite objects at 7 .5, 15, and 30 km/sec. on a half-space of similar material is described for planetary objects having the mass and radius of the moon and Mercury. For impact flows for which the peak stresses have decayed to a few kilobars, both the resulting mass and total energy distribution per unit area, S, decrease with radius, R, more slowly than the - 3 power of the radius, and the formula of the form: /n_(10)S = A + B /n_(10)R + C(/n^(10)R)^2 always displays a negative sign for the constant, C. The value of C is more negative for ejecta distributions on Mercury versus the moon. A newly recognized feature of the ejecta cloud is the near constancy with range of the ratio of internal energy to kinetic energy of ~1.1 to ~3 for material launched within a few shock transit times of the meteorite, whereas at times corresponding to many shock transit times in the meteorite this ratio exceeds ~10 when R \u2265 l0^4 cm. Calculated \"stratigraphic\" sections indicate characteristics such that\nsuch units might be recognized in Apollo drill core on the basis of shock metamorphic zoning. The initial fast ejecta which arrives at great distances from the impact zone is lightly shocked, and largely represents target material which was near or at the free surface. Where resolved, this layer is overlain by a 5 to 10 times thicker, more heavily shocked ejecta layer. The latter is again overlain by a layer of lightly shocked material. The latter thickens rapidly toward the crater.", "isbn": "0080229662", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1978-03", "pages": "3787-3802" }, { "id": "authors:tttjm-gjj61", "collection": "authors", "collection_id": "tttjm-gjj61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150903-075903383", "type": "book_section", "title": "Shock compression and adiabatic release of a titaniferous mare basalt", "book_title": "8th Lunar Science Conference", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Jackson", "given_name": "Ian", "clpid": "Jackson-I" }, { "family_name": "Jeanloz", "given_name": "Raymond", "clpid": "Jeanloz-R" } ], "abstract": "Hugoniot and release adiabat data for a high-titanium basalt (70215) of initial density 3.4 g/cm^3, are reported to shock stresses of 120 GPa, at which point a density of 5.7 g/cm^3 is achieved along the Hugoniot. Although only three Hugoniot states were measured in the relatively lowpressure regime (7-16 GPa), this limited data set, which includes some release adiabat measurements, indicates that nearly reversible compression takes place to stress levels of ~14 GPa, above which the post-shock zero-pressure density becomes greater than 3.4 g/cm^3. At shock stresses between ~14GPa and \u227350 GPa an assemblage of low- and high-pressure phases is inferred to exist along the Hugoniot curve, but has not been studied here. Release adiabat states at ~90 GPa, centered at Hugoniot states of 120 GPa, suggest the formation of a shock-induced high-pressure mineral assemblage with a zero-pressure density of ~5.2 g/cm^3. Substantial (~4 GPa) elastic precursors observed in the shock compression of the terrestrial Vacaville basalt and lunar gabbroic anorthosite\nare absent from the present study of 70215. Our results indicate that the Hugoniot elastic limit for 70215 is \u22640.4 GPa. The large compressions associated with the major phase changes in the principal minerals (Fe-rich pyroxene, calcic plagioclase, and ilmenite) imply that larger craters will be\nexcavated by a given influx spectrum of meteoroid masses and velocities, on mare terranes than on the less compressible, anorthositic highland terranes. Qualitatively, the present results imply either that previous mare cratering ages may have been overestimated relative to mare basin ejecta and highland units or, more probably, that the integrated meteoroid fluxes could have suffered an even sharper decline with time during the first 1.5 G.y. of lunar history than previously inferred.", "isbn": "0080220525", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1977-03", "pages": "3437-3455" }, { "id": "authors:gspka-xaa68", "collection": "authors", "collection_id": "gspka-xaa68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151118-131142403", "type": "book_section", "title": "Pyroxenes and olivines; structural implications of shock-wave data for high pressure phases", "book_title": "High-Pressure research: applications in geophysics", "author": [ { "family_name": "Jeanloz", "given_name": "R.", "clpid": "Jeanloz-R" }, { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Manghnani", "given_name": "M. H.", "clpid": "Manghnani-M-H" }, { "family_name": "Akimoto", "given_name": "Shun\u02bcichi", "clpid": "Akimoto-S" } ], "abstract": "A reexamination of Hugoniot equation of state data and three\nnew release adiabat points indicates that results for enstatite-bronzite composition pyroxene are compatible with its transforming\nto a perovskite phase at high pressure (For En_(90):\n\u03c1_0 = 4.20 g/cm^3, K_0 ~ 2.6 \u00b1 0.35 Mbar, K'_0 ~ 3.5 \u00b1 .65). The\nrelease adiabat data, as well as results from porous samples,\nimply that the shock-wave data do not define an equilibrium,\nhigh-pressure phase Hugoniot below about 1.00 Mbar. These also\nsuggest a further transformation to a phase (or assemblage) with\ndensity about 5% (or more) greater than that of or thorhombic\nperovskite. The data would allow such a transformation to occur\nat pressures as low as 0.60 Mbar under shock, representing an\nupper bound for the equilibrium transition pressure.\nHugoniot data on magnesian olivines also appear to represent\nstates of thermodynamic disequilibrium or a mixed-phase region\nbelow about 0.80-1.00 Mbar. However, Hugoniot points for Mgpyroxene\nand Mg-olivine coincide at pressures above 0.70 Mbar,\nsuggesting that these minerals transform to high-pressure phases\n(or phase assemblages) of comparable density. Since MgO (presumably\nas periclase or in a closely related structure) attains\nrelatively low densities at these pressures, the shock- wave data\nare in strong disagreement with the disproportionation of Mg_2SiO_4\nto a MgSiO_3 (perovskite) + MgO assemblage above 0.80-1.00 Mbar.\nConversely, the shock- wave data do not preclude a transformation\nof the type Mg_2Si_2O_6 \u2192 Mg_2SiO_4 (\"post- perovskite\" phase) + SiO_2\n(rutile or fluorite structure). Again, these results would imply\npolymorphism to very dense \"post- perovskite\" phases. Based on\nthe arguments made for pyroxene, such a transformation could\noccur at pressures as low as 0.60 Mbar under equilibrium conditions.\n\nWe note that the combined results of high-pressure experiments\nallow Mg-pyroxene compositions to be as likely candidates\nfor the lower mantle as olivine.", "isbn": "9780124687509", "publisher": "Academic Press", "place_of_publication": "New York, NY", "publication_date": "1977", "pages": "439-461" }, { "id": "authors:r2eqc-wm665", "collection": "authors", "collection_id": "r2eqc-wm665", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151120-143740179", "type": "book_section", "title": "Equations of state and impact-induced shock-wave attenuation on the moon", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "O'Keefe", "given_name": "John D.", "clpid": "O'Keefe-J-D" } ], "contributor": [ { "family_name": "Roddy", "given_name": "David John", "clpid": "Roddy-D-J" }, { "family_name": "Pepin", "given_name": "R. O.", "clpid": "Pepin-R-O" }, { "family_name": "Merrill", "given_name": "R. B.", "clpid": "Merrill-R-B" } ], "abstract": "Current equation-of-state formulations, used for finite-difference cratering flow calculations, are cast into a framework permitting comparison of peak pressures attained upon impact of a sphere, with a half-space, along the impact symmetry axis, to one-dimensional impedance match solutions. On the basis of this formulation and application of thermochemical data, the regimes of melting and vaporization are examined. For the purpose of identifying material which will, upon isentropic release from the impact-induced shock state, result in a solid just brought to its melting point, i.e., incipiently melted (IM), completely melted (CM), just brought to its boiling point, i.e., incipiently vaporized (IV), and completely vaporized (CV) state, the pressures at which the critical isentropes intersect the Hugoniots of iron and gabbroic anorthosite (GA) are examined in detail. The latter rock type is assumed to be representative of the lunar highlands. The Hugoniot pressures, for which IM, CM, IV, and CV will occur upon isentropic expansion, are calculated to range from 2.2 to\n16.8 Mbar, respectively for iron. For the high-pressure phase (hpp) assemblage of GA, modelled as a mixture of plagioclase in the hollandite structure and pyroxene in the perovskite structure, IM, CM, IV, and CV are calculated to occur upon isentropic expansion from Hugoniot states ranging from 0.43 to 5.9 Mbar, respectively. The spatial attenuation of shock pressure along the impact axis is\nfound to be clearly represented by two regimes, if the peak pressure, P, and radius normalized to that of the projectile, r, are fitted to expressions of the form P \u221d r^\u03b1. At distances from 2.2 to 5.6 projectile radii into a GA target, the constant, a, is on the order of -0.2. This low-attenuation rate, near-field regime, extends further into the target at the slower impact velocities and arises because of\nthe slightly divergent flow associated with the penetration of a spherical projectile. For the near-field impact regime, an impact at 5 km/sec of an iron object with a GA surface will induce CM for GA but\nthe iron will remain solid. At 15 km/sec, partial vaporization (PV) occurs for both GA and iron, whereas at 45 km/sec, CV occurs in both materials. Similar calculations are summarized for a GA meteoroid striking a GA surface at velocities ranging from 5 to 45 km/sec. At greater radii, in thefar-field regime, the exponent, a, varies systematically from -1.45 to -2.15 for impacts of GA onto GA as the impact velocity is increased from 5 to 45 km/sec. For an iron projectile impacting at speeds of 5-45 km/sec, the exponent, a, varies from -1.67 to -2.95. By comparison, the equivalent value of a, reported for both contained and surface explosions in various rocks is ~ -2. It is suggested that, given field data on shock attenuation (based on identification of various shock metamorphic features versus distance), overall crater size, and some chemical data as to the type of meteoroid which produced a crater, quantitative bounds on the impact velocity of the meteorite may be obtained.", "publisher": "Pergamon Press", "publication_date": "1977" }, { "id": "authors:ne6pe-k3q52", "collection": "authors", "collection_id": "ne6pe-k3q52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150902-072955353", "type": "book_section", "title": "Impact-induced energy partitioning, melting, and vaporization on terrestrial planets", "book_title": "8th Lunar Science Conference", "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": "Hypervelocity flows produced by impact of iron and gabbroic anorthosite objects onto a half-space of gabbroic anorthosite at speeds of 5-45 km/ sec are considered in detail in terms of the following processes, or regimes: penetration, cavitation, and excavation. The flows are computed using Eulerian finite-difference methods which take into account the major phase changes and thermodynamic properties of silicates and iron at high pressure, and rheological properties at the stress levels at which dynamic yielding occurs. For iron (Fe) and gabbroic anorthosite (An) impactors most of the kinetic energy of the meteoroid is converted into internal energy residing in\nthe planetary surf ace material. The fraction of meteoroid kinetic energy transformed into internal energy ranges from 0.70 at 5 km/sec to 0.85 at 30 km/sec for an An \u2192 An impact, and 0.74-0.91 at these same speeds for an Fe \u2192 An impact. At low velocities (for both cases) much of the internal energy (approximately 0.5 at 5 km/sec) is produced by the plastic work resulting from a finite yield strength of the rock whereas the balance of the internal energy results largely from shock heating. The relative fraction of the impact energy residing in the kinetic energy of the planetary surface ranges from 0.1 to 0.07 for the An \u2192 An impacts and 0.09-0.07 for the Fe \u2192 An impacts. Most of this\nenergy resides in the ejecta. Our results imply that the energy consumed by plastic work in strong rocks is available for conversion to kinetic energy in weak rocks and thus can increase the amount of ejecta for impact into weak rocks and unconsolidated regoliths. The degree of melting and vaporization produced by impact was calculated by constructing the isentropes, passing through the energy and volume states at 1 atm pressure, that correspond to\nincipient and complete melting and vaporization. The amount of melt for an An \u2192 An impact ranged from approximately 1.5 times the meteoroid volume at 7.5 km/sec to 102 times the meteoroid volume at 45 km/sec; for an Fe \u2192 An impact the volume ranged from approximately 5 times the meteoroid\nvolume at 7.5 km/sec to over 250 times the meteoroid volume at 45 km/sec. The use of a similarity variable (which is related to the physical properties of both the projectile and target) allows the relative volumes of melt and the condensed volumes of vaporized materials to be plotted on a single curve. For high impact velocities the relative masses of melted and vaporized material are found to\nbe proportional to impactor kinetic energy and the mass of impact melt exceeds the mass of vaporized material by a factor of 6. From the observed dependence of crater diameter, D, on impact energy and planetary surface gravity we infer the volume of melt relative to the volume of the crater would increase with crater diameter at least as rapidly as D^(0.55). This predicted relative increase in\nmelting with crater diameter is observed in terrestrial and inferred to occur in lunar craters. The results also predict that the amount of melt for a given crater diameter is greater for planets that have higher values of surface gravity. This implies that more melt will be observed in large terrestrial craters than similar-sized lunar craters.", "isbn": "0080220525", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1977", "pages": "3357-3374" }, { "id": "authors:vpgqy-pfc20", "collection": "authors", "collection_id": "vpgqy-pfc20", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150902-094720006", "type": "book_section", "title": "Impact ejecta on the moon", "book_title": "7th Lunar Science Conference", "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 partitioning of energy and the distribution of the resultant ejecta on the moon is numerically modeled using a Eulerian finite-difference grid. The impact of an iron meteoroid at 15 km/sec on a gabbroic anorthosite lunar crust is examined in detail. The high-speed impact-induced\nflow is described over the entire hydrodynamic regime from a time where the peak pressures are 6 Mbar until the stresses everywhere in the flow are linearly elastic, and less than 5 kbar. For 5 cm radius projectile the latter condition is achieved some ~0.5 msec after impact. The effect of taking into account the shock-induced polymorphic phase changes, in the plagioclase and pyroxene structure (in\ngabbro) to the hollandite and perovskite structures, respectively, and the subsequent reversion to low-pressure phases is demonstrated to enhance shock-wave attenuation. A rate-dependent equation of state, is used for describing the hysteretic effect of the phase change. The ballistic equations for spherical planet taking into account the decrease of gravity with height, are systematically applied to material with net velocity away from the moon. The mass of material escaping the moon corresponds to some 28% of the mass of meteorite, less than previous estimates, and most of the material lost, is lunar crust. Only 0.2% of the meteoroid escapes the moon, all in the vapor phase. In the case of accreting planets, a relatively sharp decrease in energy and mass lost from such impacts occurs when\nthe escape velocities begin to exceed ~ 1 km/sec. This implies that since the fraction of kinetic energy lost is less than 5%, impact heating of lunar-sized planets in the latter stages of accretion is efficient. Most of the impact energy remains on the lunar crust (86.1%), however the bulk of the impact energy (66.8%) resides in crustal impact ejecta which is distributed with a surface density (mass/area) which decays as R^(-2715), where R, is the radius from the impact. At large distances from the impact, the ratio of lunar to meteorite ejecta is \u2a9e10^2, implying that the higher concentrations of meteorite components\nobserved in the Apollo 17 breccias, resulted from mostly local impacts.", "isbn": "0080217710", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1976-04", "pages": "3007-3025" }, { "id": "authors:h3cfg-bf813", "collection": "authors", "collection_id": "h3cfg-bf813", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150709-070308864", "type": "book_section", "title": "Shock effects from a large impact on the moon", "book_title": "Lunar Science Conference", "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" } ], "contributor": [ { "family_name": "Merrill", "given_name": "R. B.", "clpid": "Merrill-R-B" }, { "family_name": "Hubbard", "given_name": "N. J.", "clpid": "Hubbard-N-J" }, { "family_name": "Mendell", "given_name": "W. W.", "clpid": "Mendel-W-W" }, { "family_name": "Williams", "given_name": "R. J.", "clpid": "Williams-R-J" } ], "abstract": "The shock and shear deformation induced internal energy distribution is calculated for a major basin-forming hypervelocity meteorite impact on the moon. Using the Hageman and Walsh formulation of the axisymmetric two-dimensional conservation equations in finite difference form, the flow field induced upon impact of an iron meteorite traveling at 15 km/sec with a gabbroic anorthosite\nlunar crust is calculated for sequential time steps over a grid of hoop-shaped zones fixed in space. A grid of massless tracer particles follows the outline in detail of the deformed meteorite and lunar surf ace in the cratering region. Assuming an energy of 5 x 10^(32) ergs for the projectile energy required to excavate a basin of Imbrium size yields a flow field some 210 km in radius, ~19 sec after impact. At this point the maximum stress level has decayed to pressures less than 200 kbar and left a zone of\nshock-melted rock immediately surrounding the meteorite at stresses below 100 kbar. However, portions of the meteorite are still moving downward at speeds of 2 km/sec. At this time some 7.2 and 4.2 meteorite masses of lunar surf ace material has been partially or completely melted or vaporized, respectively. Using recent estimates of ejecta volume for Imbrium-sized craters and the present results implies that the ejecta from a single such event will contain only 0.03-8% melt depending upon the scaling relation used. This implies that for impacts in the present velocity range, multiple events are required to produce the (larger) mass fractions of glass seen in the lunar breccias and soils. Comparison with predictions of the Gault and Heitowit formulation indicates that this earlier model is\napproximately valid. It predicts too rapid a decay of shock pressure with distance and hence, energy densities which are too high in the mass of surf ace material immediately surrounding the impacting meteorite.", "isbn": "9780080205663", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1976", "pages": "2831-2844" }, { "id": "authors:df4hx-f5229", "collection": "authors", "collection_id": "df4hx-f5229", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150902-080955905", "type": "book_section", "title": "Shock-induced fine-grained recrystallization of olivine: Evidence against subsolidus reduction of Fe^(2+)", "book_title": "7th Lunar Science Conference", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Tsay", "given_name": "Fun-Dow", "clpid": "Tsay-Fun-Dow" }, { "family_name": "Live", "given_name": "David H.", "clpid": "Live-D-H" } ], "abstract": "Electron spin resonance (ESR) studies have been carried out on three single grains of terrestrial olivine (F0_(90)) shock loaded along [010] to peak pressures of 280, 330, and 440 kbar. The results indicate that neither metallic Fe similar to that observed in returned lunar soils nor paramagnetic Fe^(3+) caused by oxidation of Fe^(2+) has been produced in these shock experiments. Trace amounts of Mn^(2+) have been detected in both shocked and unshocked olivine. The ESR signals of Mn^(2+) show spectral features which are found to correlate with the degree of shock-induced recrystallization observed petrographically. The increasing mass fraction of recrystallized olivine correlates with increasing shock pressures. This phenomenon is modelled assuming it results from the progressive effect of the shock-induced transformation of the olivine to, a yet unknown high-pressure phase, and its subsequent reversion to the low-pressure, olivine phase. The mass fraction of recrystallized material is predicted to be nearly linear with shock pressure.", "isbn": "0080217710", "publisher": "Pergamon Press", "place_of_publication": "New york, NY", "publication_date": "1976", "pages": "1143-1156" }, { "id": "authors:2qw74-dex40", "collection": "authors", "collection_id": "2qw74-dex40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150902-091954040", "type": "book_section", "title": "Alkali mobility in shocked basalt", "book_title": "7th Lunar Science Conference", "author": [ { "family_name": "Jeanloz", "given_name": "Raymond", "clpid": "Jeanloz-R" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "abstract": "Plagioclase (An_(45)-An_(55)) in unshocked and experimentally shocked samples of Vacaville basalt was analyzed by electron microprobe. Sodium X-ray intensity measurements were found to be unstable for the diaplectic and shock-fused plagioclases, and for synthetic plagioclase glasses with An \u227e 80. Unstable microprobe analyses have also been reported for shocked chondritic meteorites. That\nis, sodium is mobilized and volatilized under the electron beam, probably by a thermal mechanism. Crystalline plagioclase, even when shocked to just below the transition pressure to diaplectic glass, gives stable analyses as does synthetic plagioclase glass with An > 80, and shocked calcic plagioclase in Apollo 16 sample 68415. In this study, we conclude that: (i) there is no evidence for selective sodium loss due to the shock process; (ii) sodium mobilization under the electron beam reflects increasingly severe lattice damage for increasing shock pressures; (iii) sodium mobilization is, in any case, not significant for\ncalcic plagioclase. Thus we find no evidence supporting shock-related alkali loss as an important lunar process for impacts generating maximum pressures below about 1 Mbar, corresponding to projectile velocities ~4 km/sec for metallic objects and \u2a9d6 km/sec for silicate objects.", "isbn": "0080217710", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1976", "pages": "1623-1632" }, { "id": "authors:2gvdx-19h64", "collection": "authors", "collection_id": "2gvdx-19h64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150709-075513625", "type": "book_section", "title": "Shock-induced deformation features in terrestrial peridot and lunar dunite", "book_title": "Proceedings of the Sixth Lunar Science Conference", "author": [ { "family_name": "Snee", "given_name": "Lawrence W.", "clpid": "Snee-L-W" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Merrill", "given_name": "R. B.", "clpid": "Merrill-R-B" }, { "family_name": "Hubbard", "given_name": "N. J.", "clpid": "Hubbard-N-J" }, { "family_name": "Mendell", "given_name": "W. W.", "clpid": "Mendell-W-W" }, { "family_name": "Williams", "given_name": "R. J.", "clpid": "Williams-R-J" } ], "abstract": "Single crystals of terrestrial olivine (Fo90) were experimentally shock-loaded along [010] to peak pressures 280, 330, and 440 kbar and the resulting deformation features were compared to those present in olivine from lunar dunite 72415. Recovered fragments were examined on the Universal stage to determine the orientation of the planar fractures. With increasing pressure the percentage of\npinacoids ({100}, {010}, and {001}) and prisms ({hkO}, {hOl}, and {Okl}), decreases (~40 to ~25%), whereas the percentage of bi pyramids {hkl} increases (~20-50% ). The complexity of the distribution of bipyramids also increases with increasing pressure. Other shock-induced deformation features, including varying degrees of recrystallization, are found to depend on pressure as observed by others.\nLunar dunite 72415 was examined and found to contain olivine with well-developed shock deformation features. The relative proportion of pinacoid, prism, and bipyramid planar fractures measured for olivine from 72415 indicates that this rock appears to have undergone shock pressure in\nthe range 330-440 kbar. It displays a preponderance of bipyramid fractures along (2 h = k) planes which have not previously been reported in laboratory or naturally shocked samples. If this dunite was brought to the surface of the moon as a result of excavation of an Imbrium event-sized impact crater, the shock-pressure range experienced by the sample and the results of cratering calculations suggest that it could have originated no deeper than 50-150 km.", "isbn": "9780080205663", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1975", "pages": "833-842" }, { "id": "authors:fsrph-6xv88", "collection": "authors", "collection_id": "fsrph-6xv88", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150709-102912012", "type": "book_section", "title": "Shock compression and adiabatic release of lunar fines from Apollo 17", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Cole", "given_name": "David M.", "clpid": "Cole-D-M" } ], "contributor": [ { "family_name": "Dorman", "given_name": "J.", "clpid": "Dorman-J" }, { "family_name": "Duennebier", "given_name": "F.", "clpid": "Duennebier-F-K" }, { "family_name": "McKay", "given_name": "D. S.", "clpid": "McKay-D-S" }, { "family_name": "Nyquist", "given_name": "L. E.", "clpid": "Nyquist-L-E" } ], "abstract": "Shock compression and adiabatic release data on lunar fines (sample, 70051), with an initial density of 1.80 g/cm^3, are obtained in the 20-125 kbar range. The sample contains approximately 60% pyroxenes, 30% plagioclase and 10% brown glass and opaques, and has an estimated intrinsic density\nof 3 .10 \u00b1 0.10 g/cm^3. Irreversible compaction, and presumably, induration to a post-shock, zero-pressure density of 3.06 \u00b1 0.01 g/cm^3 occurs upon shock compression to 20 kbar (or lower) and subsequent adiabatic release. Above this pressure level the Hugoniot data are closely predicted, at a given volume, by adding the thermal pressure calculated from the Mie-Gruneisen equation\n(Gruneisen's ratio 0.8) to the pressure along the theoretical Hugoniot for intrinsic crystal density material. For shock compression to pressures of between 20 and 125 kbar, the calculated post shock temperature varies from 215\u00b115 to 770\u00b1155\u00b0C. When taken with the determined post-shock density variation from 3.1 to 2.6 g/cm^3, this result implies that increasing quantities of glassy material is produced via solid-state reaction and possibly melting over this pressure range. The onset of post-shock thermal melting is calculated to occur upon impact of iron or stony meteoroids traveling at a minimum of 2.5 and 3 km/sec, respectively. This implies that appreciable solid-state transformation of plagioclase, and melting of previously lightly shocked surficial rubble will result only from primary impacts. However, the pressures required for irreversible compaction imply that agglutinates will form in the regolith upon impact of secondary objects (ejecta) at speeds on the order of only 1 km/sec.", "publisher": "Pergamon Press", "publication_date": "1974" }, { "id": "authors:x2ssd-9mr40", "collection": "authors", "collection_id": "x2ssd-9mr40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150709-112806665", "type": "book_section", "title": "Shock compression of a recrystallized anorthositic rock from Apollo 15", "author": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "O'Keefe", "given_name": "John D.", "clpid": "O'Keefe-J-D" }, { "family_name": "Gibbons", "given_name": "Rex V.", "clpid": "Gibbons-R-V" } ], "contributor": [ { "family_name": "Brett", "given_name": "R.", "clpid": "Brett-R" }, { "family_name": "Phinney", "given_name": "W. C.", "clpid": "Phinney-W-C" }, { "family_name": "Strangway", "given_name": "D. W.", "clpid": "Strangway-D-E" } ], "abstract": "Hugoniot measurements on 15,418, a recrystallized and brecciated gabbroic anorthosite, yield a value of the Hugoniot elastic limit (HEL) varying from - 45 to 70 kbar as the final shock pressure is varied from 70 to 280 kbar. Above the HEL and to 150 kbar the pressure-density Hugoniot\nis closely described by a hydrostatic equation of state constructed from ultrasonic data for single-crystal\nplagioclase and pyroxene. Above - 150 kbar, the Hugoniot states indicate that a series of one or more shock-induced phase changes are occurring in the plagioclase and pyroxene. From Hugoniot data for both the single-crystal minerals and the Frederick diabase, we infer that the shock-induced high-pressure phases in 15,418 probably consist of a 3.71 g/cm^3 density, high-pressure structure for\nplagioclase (An_(93)) and a 4.70 g/cm^3 perovskite-type structure (En_(64)) for pyroxene. Using the Kelly Truesdell\nmixture theory we separately calculated the entropy production in each phase, and predict incipient and complete melting in the plagioclase occurs upon release from ~ 500 and ~ 600 kbar. For the pyroxene component, incipient and complete melting occurs upon release from 700 and 850 kbar. The onset of shock-induced vaporization will occur upon release from ~ 1300 kbar and would require\nthe impact of an iron meteoroid traveling at a velocity of ~8 km/sec.", "publisher": "Pergamon Press", "publication_date": "1973-03" }, { "id": "authors:fnc12-3hb17", "collection": "authors", "collection_id": "fnc12-3hb17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151110-071238386", "type": "book_section", "title": "Shock-wave Equations of State of Minerals", "author": [ { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" } ], "contributor": [ { "family_name": "Corso", "given_name": "L.", "clpid": "Corso-L" }, { "family_name": "Coulomb", "given_name": "J.", "clpid": "Coulomb-J" }, { "family_name": "Caputo", "given_name": "M.", "clpid": "Caputo-M" } ], "abstract": "Shock-wave data play a unique role in the study of the interior of the Earth in that at pressures of 500 kbar to 3700 kbar, or at equivalent depths in the Earth of 1200 km and 6400 km (center), dynamic techniques provide the only means of studying mineral properties in the laboratory. The relation betwaen shock pressure (p), shock-induced density (Q), and internal energy (e), along a curve called the Hugoniot, is the form of an equation of state for solids\nor fluids which is usually obtained with shock-wave techniques.", "publisher": "Academic Press", "publication_date": "1971" }, { "id": "authors:xr7n8-yv053", "collection": "authors", "collection_id": "xr7n8-yv053", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151209-070904823", "type": "book_section", "title": "Shock wave data and the study of the Earth", "book_title": "The application of modern physics to the earth and planetary interiors", "author": [ { "family_name": "Ahrens", "given_name": "T. J.", "clpid": "Ahrens-T-J" }, { "family_name": "Petersen", "given_name": "C. F.", "clpid": "Petersen-C-F" } ], "contributor": [ { "family_name": "Runcorn", "given_name": "S. K.", "clpid": "Runcorn-S-K" } ], "abstract": "Basic concepts underlying equation of state measurements on earth materials using shock wave techniques are discussed, and results of experiments on Twin Sisters olivine and experiments of others are examined. Results provide direct evidence for 'breakdown of olivine to a yet unknown structure having the density of the oxides; this presumably occurs in the Earth at depths of about 650 km. It appears that this type of reaction can occur in the submicrosecond time scale of a shock experiment.", "isbn": "978-0471745051", "publisher": "John Wiley & Sons Ltd", "place_of_publication": "New York, NY", "publication_date": "1969-01-01", "pages": "449-461" } ]