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In the problems of detonation we are going to present here, the capture of shocks is crucial, since from its accuracy depends the very physical relevance of the whole solution. We already obtained some improvements in the capture of detonation fronts on underresolved grids in the one-dimensional case thanks to Harten’s artificial compression [1], [2], and we now turn to two-dimensional cartesian grids. In two space dimensions, the complexity of the discontinuity implies not only the location and speed of the front, but also its shape. These three aspects will be explored here, for the ZND detonation model, based on Euler’s system. We will use two-dimensional central schemes for main computations, namely the classical “Lax-Friedrichs” first order scheme and the second order “Jiang-Tadmor” scheme [3]. To each of these methods, we will add two different versions of ACM (Artificial Compression Method), one that uses space splitting, and the other based on directional differencing [4]. Finally, as ACM require a good knowledge of the regions of the solution potentially carrying discontinuities, it will be assisted by a DoD (Detector of Discontinuities) based on the entropy production rate. [ABSTRACT FROM AUTHOR]

Using ACE data, we selected a number of characteristic “energetic storm particle” (ESP) events, i.e., solar energetic particles events in which the CME-driven interplanetary shock passes the spacecraft, to compare observed local proton flux profiles with those obtained from hybrid simulations (kinetic ions, electron fluid). The events were selected for undisturbed solar wind and profiles indicating local shock acceleration. Interestingly, in the sub-MeV range, we find very little variation of peak proton fluxes with shock normal angle. This is in stark contrast to the Earth’s bow shock, which in both observations and simulations only shows weak reflected ion beams, but no significant turbulence or secondary ion acceleration for shock-normal angles of ∼45° or larger. We find that in sufficiently large simulations of oblique, planar shocks, even the dilute upstream ion beams suffice to generate upstream compressional waves, which change the local shock-normal angle upon impact on the shock. In a feed-back mechanism, this leads to more wave-particle interactions in now more parallel portions of the shock, and results in a shock undulation propagating along the surface, and in energetic proton fluxes that are enhanced by up to three orders of magnitude. [ABSTRACT FROM AUTHOR]

It has been known for some time that batches of the secondary explosive RDX from different manufacturers show significant variation in their shock sensitivity. No clear correlation between shock sensitivity and either chemical composition or morphology has been identified. As yet no comprehensive study has been reported covering RDX from different manufacturers, different production methods, and different particle sizes. In this work we use a range of techniques to study the morphology of RDX grains more closely and to assess which hotspot mechanisms might be dominant. Crystals were characterised using mercury porosimetry, environmental scanning electron microscopy (ESEM) and optical microscopy. This range of methods yields quantitative data on internal void size and number and surface porosity. Shock sensitivity is quantified using small-scale gap tests and these demonstrate clear differences in sensitivity between batches from different manufacturers. The samples used are from three manufacturers, produced by both the Woolwich and Bachmann processes, and of two different sizes, so a comprehensive study of how morphology might affect hotspot formation is possible. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Experimental study of shock reloading processes during the uniaxial strain loading of aluminum alloy targets reveals a dependence of reloading response of material on the particle velocity dispersion behavior. This response is found to be elastic-plastic in case the velocity dispersion at the plateau of compressive pulse equals zero. In the presence of the velocity dispersion the reloading response is pure plastic. This phenomenon is considered from the position of non-local hydrodynamic theory developed for description of high-nonequilibrium processes in heterogeneous media. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Pyrometry measurements on shock-heated metals are often performed through a transparent anvil. Sapphire is an interesting anvil, but is also known to emit light when shocked above its Hugoniot Elastic Limit (HEL). To study its optical response, we have carried out experiments in the 15–37 GPa pressure range on c-cut sapphire in contact with a metallic sample (tin or bismuth) or a lithium fluoride window. Even though a significant amount of light is emitted by sapphire, we notice that the signal rise is directly related to the volume of sapphire under shock-loading. Consequently, the window emission can be subtracted to infer the thermal radiation originating from the metal under study. A theoretical calculation of the expected pyrometer signals supports that point of view. These results give evidence that sapphire, despite its shock-induced optical emission above the HEL, can be used as a transparent anvil for quantitative pyrometry measurements at medium and high shock pressures. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The literature suggests that retention rates are lowest following the first year at an academic institution. Often referred to as "freshmen shock," the implication is that many first-year students have a difficult time transitioning into the academic rigors of post-secondary education. The concept of "freshmen shock" has also been applied to transfer students who enter during a period beyond their traditional freshmen year. We know little about the factors that contribute to the stresses and strains experienced among these populations causing them to drop out or experience lower academic success. As such, our study has four purposes. First, we investigated the similarities (or differences) between transfer and native students (those arriving as freshmen) who declared criminal justice as a major on two key measures: (1) academic success, and (2) retention. Second, we examined factors that influence academic success and retention across these two student populations. Third, we designed intervention strategies to improve upon factors which were associated with lower academic success and lower retention within the two populations. Finally, we conducted a post test to investigate the effects of the intervention strategies. ..PAT.-Unpublished Manuscript [ABSTRACT FROM AUTHOR]