We present a multiscale strength model in which strength depends on pressure, strain rate, temperature, and evolving dislocation density. Model construction employs an information passing paradigm to span from the atomistic level to the continuum level. Simulation methods in the overall hierarchy include density functional theory, molecular statics, molecular dynamics, dislocation dynamics, and continuum based approaches. Given the nature of the subcontinuum simulations upon which the strength model is based, the model is particularly appropriate to strain rates in excess of 104 s−1. Strength model parameters are obtained entirely from the hierarchy of simulation methods to obtain a full strength model in a range of loading conditions that so far has been inaccessible to direct measurement of material strength. Model predictions compare favorably with relevant high energy density physics (HEDP) experiments that have bearing on material strength. The model is used to provide insight into HEDP experimental observations and to make predictions of what might be observable using dynamic x-ray diffraction based experimental methods.

The Rayleigh-Taylor (RT) instability occurs at an interface between two fluids of differing density during an acceleration. These instabilities can occur in very diverse settings, from inertial confinement fusion (ICF) implosions over spatial scales of [Formula: see text] cm (10-1,000 μm) to supernova explosions at spatial scales of [Formula: see text] cm and larger. We describe experiments and techniques for reducing ("stabilizing") RT growth in high-energy density (HED) settings on the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. Three unique regimes of stabilization are described: () at an ablation front, () behind a radiative shock, and () due to material strength. For comparison, we also show results from nonstabilized "classical" RT instability evolution in HED regimes on the NIF. Examples from experiments on the NIF in each regime are given. These phenomena also occur in several astrophysical scenarios and planetary science [Drake R (2005) 47:B419-B440; Dahl TW, Stevenson DJ (2010) 295:177-186].

Observational evidence suggests that many of the variations of the surface abundances of light to intermediate mass elements (A < 28) in globular cluster red-giant-branch (RGB) stars can be attributed to non-canonical mixing between the surface and the deep stellar interior during the RGB phase. As a first step to studying this mixing in more detail, we have combined a large nuclear reaction network with four detailed stellar evolutionary sequences of different metallicities in order to follow the production and destruction of the C, N, O, Ne, Na, Mg, and Al isotopes around the hydrogen-burning shell (H shell) of globular cluster RGB stars. The abundance distributions determined by this method allow for the variation in the temperature and density around the H shell as well as for the dependence on both the stellar luminosity and cluster metallicity. Because our nuclear reaction network operates separately from the stellar evolution code, we are able to more readily to explore the effects of the uncertainties in the reaction rates on the calculated abundances.We discuss implications of our results for mixing in the context of the observational data. Our results are qualitatively consistent with the observed C vs. N, O vs. N, Na vs. O, and Al vs. O anticorrelations and their variations -2with both luminosity and metallicity. We see evidence for variations in Na without requiring changes in O, independent of metallicity, as observed by Norris &Da Costa (1995a) andBriley et al. (1997). Also, we derive 12 C/ 13 C ratios near the observed equilibrium value of 4 for all sequences, and predict the temperature-dependent 16 O/ 17 O equilibrium ratio based on new data for the 17 O(p, α) 14 N reaction rate. Additionally, we discuss the Mg isotopic abundances in light of the recent observations of M13 (Shetrone 1996b) and NGC 6752 (Shetrone 1997).

We study the production of Na and Al around the hydrogen shell of two red-giant sequences of different metallicity in order to explain the abundance variations seen in globular cluster stars in a mixing scenario. Using detailed stellar models together with an extensive nuclear reaction network, we have calculated the distribution of the various isotopic abundances around the hydrogen shell at numerous points along the red-giant branch. These calculations allow for the variation in both temperature and density in the shell region as well as the timescale of the nuclear processing, as governed by the outward movement of the hydrogen shell. The reaction network uses updated rates over those of Caughlin & Fowler (1988). We find evidence for the production of Na and Al occurring in the NeNa and MgAl cycles. In particular, Na is significantly enhanced throughout the region above the hydrogen shell. The use of the newer reaction rates causes a substantial increase in the production of 27 Al above the hydrogen shell through heavy leakage from the NeNa cycle and should have an important effect on the predicted surface abundances. We also find that the nuclear processing is considerably more extensive at lower metallicities.

We analyze high resolution, high signal-to-noise spectra of six red-giant-branch (RGB) stars in the globular cluster M 3 (NGC 5272) and three in M 13 (NGC 6205) that were obtained with the Mayall 4-meter telescope and echelle spectrometer on Kitt Peak. The spectra include lines of O, Na, Mg, Al, Si, Ca, Ti, V, Mn, Fe and Ni. We also analyze the [Al/Fe] values of 96 RGB stars in M 13 covering the brightest 3.5 magnitudes, which include 66 measurements that were derived from moderate resolution, low signal-to-noise spectra obtained with the WIYN 3.5-meter telescope and Hydra multi-object spectrograph, also on Kitt Peak. In addition, we compile from the literature and inspect the [Na/Fe] values of 119 RGB stars in M 13. We test for bimodality in the [Al/Fe] and [Na/Fe] distributions using the KMM algorithm and find that the [Al/Fe] values in M 13 are distributed bimodally at all points along the RGB that were observed, while the [Na/Fe] values are bimodal only over the brightest two magnitudes. The ratios of Alenhanced to Al-normal and Na-enhanced to Na-normal giants increase towards the tip of the RGB in M 13, which is suggestive of deep mixing in this cluster. The limited M 3 data exhibit a bimodal distribution of [Al/Fe] values and are suggestive of no deep mixing; however, they are too few to be conclusive. We further test for a relationship between deep mixing on the RGB and a second parameter that can create the extended blue tail seen along the horizontal-branches of some clusters by using an "instantaneous" mixing algorithm, which we develop here. We