J. P. Van Dyke

Nuclear magnetic resonance measurements and the energy band structure of PtSn

Abstract Nuclear magnetic resonance measurements of the Knight shift and spin-lattice relaxation time for 195 Pt and 119 Sn in PtSn are reported. The energy band structure as determined by the relativistic orthogonalized plane wave method is also presented. The band model developed has holes in the Pt d -band but does not have a large density of states associated therewith.

Seismic imaging on the intel paragon

Abstract A key to reducing the risks and costs associated with oil and gas exploration is the fast, accurate imaging of complex geologies, such as salt domes in the Gulf of Mexico and overthrust regions in U.S. onshore regions. Prestack depth migration generally yields the most accurate images, and one approach to this is to solve the scalar-wave equation using finite differences. Current industry computational capabilities are insufficient for the application of finite-difference, 3-D, prestack, depth-migration algorithms. A 3-D seismic data can be several terabytes in size, and the multiple runs necessary to refine the velocity model may take many years. The oil companies and seismic contractors need to perform complete velocity field refinements in weeks and single iterations overnight. High-performance computers and state-of-the-art algorithms and software are required to meet this need. As part of an ongoing ACTI project funded by the U.S. Department of Energy, we have developed a finite-difference, 3-D prestack, depth-migration code for the Intel Paragon. The goal of this work is to demonstrate that massively parallel computers (thousands of processors) can be used efficiently for seismic imaging, and that sufficient computing power exists (or soon will exist) to make finite-difference, prestack, depth migration practical for oil and gas exploration.

High‐temperature series studies of Ising‐like Wilson models in three dimensions

We have studied the susceptibility of continuous‐spin Landau‐Wilson models on the FCC lattice using exact series expansions through 10‐th order in the inverse temperature. Both order‐disorder (double‐well) and displacive (single‐well) models have been considered. The exponent γ of the dominant singularity is found to be 1.25 for both types of model. The confluent singularity arising from corrections to scaling is found to have the universal value δ=0.5. We discuss in detail the crossover from Gaussian to Ising constant, and find a crossover exponent o/=1 in all dimensions.

Series studies of critical exponents in continuous dimensions

Using results we have previously derived for the high‐temperature susceptibility expansion of classical models as a closed‐form function of lattice dimension, we study the dimensional dependence of the critical exponent γ and critical temperature, as well as the correction‐to‐scaling exponent Δ1, for Ising‐like (n=1) models. The numerical results are obtained by extrapolation of 10‐th order series on loose‐packed hypercubical lattices, and 8‐th order series on close‐packed hypertriangular lattices. The critical exponent γ increases monotonically with decreasing dimension, d, for d<4, and apparently tends to infinity at d=1; while the critical temperature decreases monotonically and smoothly to zero at d=1. Detailed contact is made with the e‐expansion estimates for critical exponents obtained in the context of renormalization group theory.