摘要:

Dynamic loading experiments are described using nanosecond scale laser pulses of 2 to 1000 GW/cm2over a region 5 mm in diameter. The laser irradiance was tailored to generate shocks or quasi‐isentropic compression. The experiments include novel diagnostic techniques with high temporal resolution: transient x‐ray diffraction (TXD) and polarization‐dependent reflectivity (ellipsometry). TXD uses a laser‐produced plasma to form an x‐ray source. These x rays are collimated by a pinhole to form a Bragg scattering source, which allowed powder lines to be detected from polycrystalline samples such as beryllium foils. Ellipsometry has been demonstrated with 50 ps resolution using the reflectance of a pulsed 660 nm laser from silicon and tin samples through lithium fluoride windows. Ellipsometry can indicate phase changes and potentially yields estimates of surface temperature via the dielectric conductivity. The combination of TXD and ellipsometry with VISAR measurements provides precision characterization of dynamic material properties at high pressures. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780503

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

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 1027J 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 × 1032J Moon‐forming impact we calculate that ∼50&percent; of the Earth’s atmosphere is accelerated to escape. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780504

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper presents experimental results and computational simulations of spherical wave propagation in Danby marble. The experiment consisted of a 2‐cm‐diameter explosive charge detonated in the center of a cylindrical rock sample. Radial particle velocity histories were recorded at several concentric locations in the sample. An extensively damaged region near the charge cavity and two networks of cracks were evident in the specimen after the test. The first network consists of radial cracks emanating form the cavity and extending about halfway through the specimen. The second network consists of circumferential cracks occurring in a relatively narrow band that extends from the outer boundary of the radially cracked region toward the free surface. The experiment was simulated using the GEODYN code and a multi‐directional damage model. The model is developed within the framework of a properly invariant nonlinear thermomechanical theory with damage represented by a second order tensor that admits load‐induced anisotropy such as was observed in the experiment. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780505

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Some shock wave researchers have long contended that phase transitions of minerals under shock compression occur more rapidly than under comparable static compression conditions. Other researchers argue that phase transition behavior under shock compression does not differ from observations of static high pressure behavior. Many meteorites contain high‐pressure phases that are ascribed to impact. These high‐pressure phases are found within or adjacent to so‐called melt veins, sheets of material that was once molten and was quenched via conduction to surrounding material. Possible mechanisms for melt vein formation on impact include adiabatic shear and jetting. Thermal analysis of melt vein solidification and cooling, together with knowledge of phase stability fields and conditions for metastable survival of high‐pressure phases, constrains the shock conditions and provides evidence that the observed reconstructive phase transitions occurred via the same nucleation and growth mechanisms observed in static high pressure studies. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780506

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Pressure waves have the potential to cause injury to cells and tissue or enable novel therapeutic modalities, such as fragmentation of kidney stones and drug delivery. Research on the biological effects of pressure waves have shown that the biological response on depends the pressure‐wave characteristics. One of the most prominent effects induced by pressure waves is the permeabilization of a number of barrier structures (cell plasma membrane, skin and microbial biofilms) and facilitate the delivery of macromolecules. The permeabilization of the barrier structure is transient and the barrier function recovers. Thus, pressure waves can induce delivery of molecular species that would not normally cross the barrier structure. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780507

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A two‐phase equilibrium equation of state (EOS) for periclase (MgO) was constructed using ab initio quantum mechanics, including a rigorous calculation of quasiharmonic phonon modes. Much of the shock wave data reported for periclase is on porous material. We compared the theoretical EOS with porous data using a simple ‘snowplough’ treatment and also a model using finite equilibration rates suitable for continuum mechanics simulations. (This model has been applied previously to various heterogeneous explosives as well as other porous materials.) The results were consistent and matched the data well at pressures above the regime affected by strength — and ramp‐wave formation — during compaction. Ab initio predictions of the response of porous material have been cited recently as a novel and advanced capability; we feel that this is a fairly routine extension to established ab initio techniques. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780508

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The effect of charge size and geometry has been investigated. A series of experiments have been performed with explosive masses up to 2 lbs. in which the effect of internal blast performance in a rectangular structure was measured. Performance was based upon pressure measurements at multiple locations within the structure. Confidence in the measurements was achieved with the use of multiple gauges at the same location. The explosives tested contained both ideal and non‐ideal compositions. A correlation was determined that allows for research size samples (< 100g) to be compared with greater sized charges. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780509

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

13 shots of shock compression data were measured for enstatite (Mg0.92, Fe0.08)SiO3with initial density of 3.06g/cm3up to 140 GPa, using impedance‐match method and electrical probe technique. The relationship between shock wave velocityDand particle velocityucan been described linearly by:D= 3.76 +1.48u(km/s), and no evidence of phase transition was shown in the experimental shock pressure range. Our experimental Hugoniot is about 7&percent; denser than the model Hugoniot of (Mg0.92, Fe0.08)O (Mw.) plus SiO2(St.) calculated by additive principle. This excluded the possibility that chemical decomposition of enstatite with perovskite structure to oxides would happen during shock compression up to 140GPa. The Gru¨neisen parameter &ggr;obtained by fitted our experimental data to: &ggr;=&ggr;0(&rgr;0/&rgr;)q, yields &ggr;0=1.84,q=1.69, with &rgr;0=4.19g/cm3. By using the third‐order Birch‐Murnaghan finite strain equation of state (EOS), Our shock experimental data yield a zero‐pressure bulk modulusK0s=260.09GPa and pressure derivativeK0s=4.17, given our new value of &ggr;, with &rgr;0=4.19g/cm3. From density constraint only, the purely perovskite model of (Mg1−x, Fex)SiO3(x=0∼0.1) can explain that of PREM well. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780510

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The response of proteins to fast shock compression is poorly understood at the molecular level. Proteins are complex molecular systems and traditional physical chemistry models do not successfully explain protein dynamics and protein structural dynamics. Energy landscape models are frequently used to understand structural relaxation of viscous liquids, supercooled liquids, and polymers. A rugged potential energy topography, or energy landscape with many potential minima is helpful in understanding many unique properties of such systems. We have developed an energy landscape model to understand shock compression of proteins. Shock compression changes the shape of the energy landscape and causes dynamic motions along the energy landscape. The energy landscape model provides a molecular‐level interpretation of viscoelastic shock compression. The first observation of viscoelastic shock compression in proteins was made using the laser‐driven nanoshock technique. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780511

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A series of plate impact experiments was performed on granite from the Stone Mountain in Atlanta, Georgia. Longitudinal stresses were measured by means of embedded manganin gauges and the Hugoniot was established up toca.10 GPa. The results are then compared and contrasted to data for other geologic materials. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780512

出版商:AIP    

年代:1904

数据来源: AIP