High statistics, (> 4 x 10{sup 8} counts), room temperature measurements of the electron-positron momentum density of La{sub 2-x}Sr{sub x}CuO{sub 4} have been performed for samples with Sr concentrations of x - 0.0, 0.1, 0.13 and 0.2. These spectra have been analyzed in conjunction with theoretical calculations of the electron-positron momentum density. The metallic samples show features consistent with the presence of a Fermi surface, but its evolution with increasing Sr concentration does not follow the predictions of band theory. These results may indicate the effects of electron-electron correlation on the electron momentum distribution in the Cu-O plane.

Ultra-shallow, box-like impurity profiles are produced using Gas Immersion Laser Doping (GILD) and then analyzed by spreading resistance profilometry (SRP) and secondary ion mass spectrometry (SIMS) to determine the impurity distribution. At high concentrations, the profiles obtained by SRP exhibit the expected box-like shape over the entire range of junction depths: The measured concentration within the junction region is uniform while the dopant gradient at the junction exceeds 0.5 decades/nm. In comparison, the same profiles analyzed by SIMS show a broader transition at the metallurgical junction. Caused by knock-ons and ion mixing during the sputtering process, this inaccuracy is reduced, but not eliminated by lowering the acceleration energy of the primary Cs{sup +} ion beam. At lower concentrations (< 10{sup 19}/cm{sup 3}), profiles analyzed by SRP exhibit shallower junctions than expected. Electrical measurements of diodes and Hall structures show that high-quality, ultra-shallow n{sup +}p, np and pn are fabricated with good dose control using GILD. For complete characterization of GILD, accurate measurement of both chemical and electrically-active dopant profiles are required. At present, neither SIMS nor SRP provides an entirely accurate impurity profile.

CIRCE is an efficient beam dynamics code developed to facilitate the design and analysis of heavy-ion accelerators. The code combines an envelope description of the beam transverse dynamics with a fluid-like treatment of longitudinal dynamics, and terms are included to account for the effects of space charge, emittance, and image forces. CIRCE is currently being adapted to model the Induction Linac Systems Experiments (ILSE) facility, a proposed heavy-ion accelerator designed to test aspects of an inertial-fusion driver. The numerical model in the code is discussed, and changes needed for modeling ILSE are outlined. Preliminary work is presented on beam matching along the ILSE lattice and on transport around the ILSE achromatic bend.

A 1200 channel Si(Li) detector system has been developed for transvenous coronary angiography experiments using synchrotron radiation. It is part of the synchrotron medical imaging facility at the National Synchrotron Light Source. The detector is made from a single crystal of lithium-drifted silicon with an active area 150 mm long {times} 11 mm high {times} 5 mm thick. The elements are arranged in two parallel rows of 600 elements with a center-to-center spacing of 0.25 mm. All 1200 elements are read out simultaneously every 4 ms. A Intel 80486 based computer with a high speed digital signal processing interface is used to control the beamline hardware and to acquire a series of images. The signal-to-noise, linearity and resolution of the system have been measured. Human images have been taken with this system.

A Texas Instruments (TI) TMS320C30-based S-Bus digital signal processing (DSP) module was used to accelerate a wavelet-based compression and decompression algorithm applied to high-resolution fingerprint images. The law enforcement community, together with the National Institute of Standards and Technology (NISI), is adopting a standard based on the wavelet transform for the compression, transmission, and decompression of scanned fingerprint images. A two-dimensional wavelet transform of the input image is computed. Then spatial/frequency regions are automatically analyzed for information content and quantized for subsequent Huffman encoding. Compression ratios range from 10:1 to 30:1 while maintaining the level of image quality necessary for identification. Several prototype systems were developed using SUN SPARCstation 2 with a 1280 {times} 1024 8-bit display, 64-Mbyte random access memory (RAM), Tiber distributed data interface (FDDI), and Spirit-30 S-Bus DSP-accelerators from Sonitech. The final implementation of the DSP-accelerated algorithm performed the compression or decompression operation in 3.5 s per print. Further increases in system throughput were obtained by adding several DSP accelerators operating in parallel.

In general, the diffraction efficiency of gratings is limited by the constraints imposed by the type of geometry used to scan the photon energy. In the simplest example, the spherical grating monochromator (SGM), the deviation angle, the grating groove width and depth and the groove density are all constrained by considerations of the maximum photon energy and the tuning range for individual gratings. We have examined the case in which these parameters are unconstrained, resulting in predictions of the ultimate performance of lamellar type gratings for groove densities from 300 to 2400 1/mm for gold and nickel coatings. The differential method of Neviere et al was used for modeling the behavior of the gratings and justification is presented for this by rigorous comparison with measurements. The implications of these results for future monochromators based on a variable included angle geometry are discussed.

This report discusses the scientific and economic feasibility of fusion energy, especially in regards to the tokamak reactor.

In the standard Richtmyer-Meshkov instability, perturbations at a shocked interface grow after the passage of a shock. Freeze-out refers to the phenomenon whereby the perturbations do not grow, i.e., freeze-out, after the passage of a shock. This is fairly straightforward, at least theoretically (no experiments have been done so far) in a doubly shocked system. The first shock induces a growth which can be completely neutralized by a second shock, provided that the direction and the strength and timing of the second shock are properly chosen. This type of double-shock freeze-out occurs in compressible as well as incompressible fluids, and is easy to understand. Somewhat more subtle is single-shock freeze-out; in the pursuit of this phenomenon, the author found that in certain cases Richtmyer`s prescription fails to give the correct growth rate.

So far the only experimental evidence for CP violation is the 1964 discovery of K{sub L}{yields}2{pi} where the two mass eigenstates produced by neutral meson mixing both decay into the same CP eigenstate. This result is described by two parameters {epsilon} and {epsilon}{prime}. Today {epsilon} {approx} its 1964 value, {epsilon}{prime} data are still inconclusive and there is no new evidence for CP violation. One might expect to observe similar phenomena in other systems and also direct CP violation as charge asymmetries between decays of charge conjugate hadrons H{sup {+-}} {yields} f{sup {+-}}. Why is it so hard to find CP violation? How can B Physics help? Does CP lead beyond the standard model? The author presents a pedestrian symmetry approach which exhibits the difficulties and future possibilities of these two types of CP-violation experiments, neutral meson mixing and direct charge asymmetry: what may work, what doesn`t work and why.

Low rank coals (lignite and subbituminous) contain exchangeable cations. A sample of {minus}20+200 mesh Argonne Premium Wyodak coal was washed with nitric acid in a burette fitted with a coarse glass frit at the base of the graduations to remove the exchangeable cations from the system. The eluent was passed to a flow-through pH electrode and a titration curve was obtained on a computer file. A series of electrodes (pH, calcium, sodium and potassium) were used in separate experiments to follow the elution from the coal. Some implications for coal structure are also indicated.

The serious environmental problems of the South Urals Region of Russia have been broadly described in a report coauthored by Russian weapons scientists. The importance of taking the first steps to prevent further environmental damage and adverse public health effects has been recognized by the international scientific community. Scientists at the Lawrence Livermore National Laboratory have initiated a project to assist the Russians in their pollution prevention efforts. The specific objectives of this project are to: (1) conduct a pragmatic survey of the industrial and governmental pollution sources in a limited geographic region of the South Urals and (2) identify the priorities for pollution prevention and for food and water supply improvements at distribution points. The emphasis is on preventing adverse impacts to human health and improving industrial productivity. This project focuses on immediate pollution problems resulting from current operations and their solutions, not on long-term research related to the large-scale cleanup of legacy wastes. The project emphasizes near-term cost effective solutions to prevent pollution while longer term research aimed at contamination from past practices is pursued by other scientists. The project is being conducted in collaboration with environmental and physical scientists from institutes associated with the Ural Branch of …

Has any progress been made on understanding and predicting the 13 parameters which describe the observed masses and mixing angles of the quarks and leptons? Arguments are given in favor of pursuing schemes in which grand unified and family symmetries provide many relations among these 13 parameters. A sequence of simple assumptions leads to a supersymmetric SO(10) theory with 8 predictions: tan {beta}, M{sub t}, V{sub cb}, M{sub s},M{sub s}/M{sub d}, M{sub u}/M{sub d}, V{sub ub} and the amount of CP violation J. These predictions are presented, together with experiments which will test them.

This paper presents a new approach for the automatic definition and treatment of mechanical contact in explicit nonlinear finite element analysis. Automatic contact offers the benefits of significantly reduced model construction time and fewer opportunities for user error, but faces significant challenges in reliability and computational costs. Key aspects of the proposed new method include automatic identification of adjacent and opposite surfaces in the global search phase, and the use of a well-defined surface normal which allows a consistent treatment of shell intersection and corner contact conditions without a ad-hoc rules. The paper concludes with three examples which illustrate the performance of the newly proposed algorithm in the public DYNA3D code.

Sisal is a general-purpose functional language that hides the complexity of parallel processing, expedites parallel program development, and guarantees determinacy. Parallelism and management of concurrent tasks are realized automatically by the compiler and runtime system. Spatial domain decomposition is a widely-used method that focuses computational resources on the most active, or important, areas of a domain. Many complex programming issues are introduced in paralleling this method including: dynamic spatial refinement, dynamic grid partitioning and fusion, task distribution, data distribution, and load balancing. In this paper, we describe a spatial domain decomposition algorithm programmed in Sisal. We explain the compilation process, and present the execution performance of the resultant code on two different multiprocessor systems: a multiprocessor vector supercomputer, and cache-coherent scalar multiprocessor.

Article on a discharge-flow/chemiluminescence study of the reaction O + Si2H6 at room temperature.