The authors describe a theoretical model to study the transmission of relativistic H{sup {minus}} ions through thin carbon foils. The approach is based on a Monte Carlo solution of the Langevin equation describing electronic excitations of the atoms during the transport through the foil. Calculations for the subshell populations of outgoing hydrogen atoms are found to be in good agreement with recent experimental data on an absolute scale and show that there exists a propensity for populating extreme Stark states.

We describe a general strategy we have found effective for parallelizing solid mechanics simula- tions. Such simulations often have several computationally intensive parts, including finite element integration, detection of material contacts, and particle interaction if smoothed particle hydrody- namics is used to model highly deforming materials. The need to balance all of these computations simultaneously is a difficult challenge that has kept many commercial and government codes from being used effectively on parallel supercomputers with hundreds or thousands of processors. Our strategy is to load-balance each of the significant computations independently with whatever bal- ancing technique is most appropriate. The chief benefit is that each computation can be scalably paraIlelized. The drawback is the data exchange between processors and extra coding that must be written to maintain multiple decompositions in a single code. We discuss these trade-offs and give performance results showing this strategy has led to a parallel implementation of a widely-used solid mechanics code that can now be run efficiently on thousands of processors of the Pentium-based Sandia/Intel TFLOPS machine. We illustrate with several examples the kinds of high-resolution, million-element models that can now be simulated routinely. We also look to the future and dis- cuss what possibilities …

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