Engineering topics
Publications and source records attributed to Sanders, G. D..
(a) Cross-sectional TEM micrograph of 14 period InAs/GaSb SL, demonstrating abrupt interfaces; and (b) Shubnikov-de Haas oscillations testifying high mobility.
This report summarizes the activities and major accomplishments of the Variable Precision Computing Strategic Initiative project. The overarching goal of this project was to initiate and promote a new paradigm in High Performance Computing (HPC) that would fundamentally change how we represent and make use of representations of real numbers in finite precision and that would establish Lawrence Livermore National Laboratory (LLNL) as a leader in precision-related research for HPC. We pursued three integrated and concurrent research thrusts: new, more dynamic data representations to address data motion and capacity limitations; improved mixed precision algorithms to accelerate computation and to leverage new hardware; and new tools to help developers reason about precision and to automate code transformations. Within these thrust areas, we made significant advances in the use of compressed array data types in numerical calculations, in the theoretical justification, in improved performance, and in the prospects of hardware implementation; in the development of metrics to significantly reduce the storage needs of molecular dynamics simulations; in the development and analysis of efficient mixed-precision algorithms for time-dependent partial differential equations and for orthogonal factorization; and in the capability of tools that can analyze sensitivity of computed results to choices in precision and that can make automated code transformations based on such analysis. We established that there are definite opportunities to realize significant improvements in HPC above and beyond the 2x limits of traditional mixed precision using the technologies we have developed. The project produced numerous papers, presentations, and posters in important venues as well as open-source software contributions to the community, and many of the new capabilities have initiated or are being leveraged in ongoing projects.
Least squares Maxwellian fits have been made to data from the Apollo 15 suprathermal ion detector experiment (SIDE) during the moon's passage through the dusk magnetosheath. It is found that the data are best fit by superimposing two co-moving proton populations whose temperatures differ radically: kT roughly 10 eV and kT roughly 100 eV. This two-temperature distribution cannot be explained by alpha particles. The higher temperature population is typical of that expected for the fully shocked magnetosheath at lunar distances. The colder distribution could arise from cold plasma from within the magnetosphere brought up to magnetosheath flow speeds, but it is more probably due to unshocked solar wind.
The paper presents observational evidence from the Apollo suprathermal ion detector experiments that the injection of magnetosheath particles at the low-latitude magnetopause operates at lunar distances as well. An interface between the magnetosheath and the plasma sheet, termed the plasma sheet boundary layer (PSBL), is identified and believed to be the extension of the magnetospheric boundary layer (also called the plasma boundary layer) observed on the dayside. Using measurements of the PSBL's thickness, magnetic field, and plasma velocity the average electric potential drop across the PSBL is estimated at 4.2 kV and compared with the potential drop which is needed to insure that the magnetopause is an equipotential for a closed magnetosphere. It was concluded though that the magnetosphere is open since this drop is much larger than 4.2 kV.