Bridgman growth of semiconductors

The purpose of this study was to improve the understanding of the transport phenomena which occurs in the directional solidification of alloy semiconductors. In particular, emphasis was placed on the strong role of convection in the melt. Analytical solutions were not deemed possible for such an involved problem. Accordingly, a numerical model of the process was developed which simulated the transport. This translates into solving the partial differential equations of energy, mass, species, and momentum transfer subject to various boundary and initial conditions. A finite element method with simple elements was initially chosen. This simulation tool will enable the crystal grower to systematically identify and modify the important design factors within her control to produce better crystals

Flood Frequency Design in Sparse-data Regions

Project Completion Report OWRT Contract No. 14-31-0001-5217 Grant No. B-030-ALASThis report summarizes work conducted with funds received from the Office of Water Research and Technology (OWRT), Project B-030-ALAS, Flood Frequency in Sparse-Data Regions. The study was conducted from July 1, 1974, to June 30, 1976, plus a one-year extension to June 30, 1977. The technical results are given in a number of publications which are referenced and abstracted here along with a presentation of the overall philosophy of the project and a coherent summary of the work. Alaska may be characterized, as can most northern areas, by a very sparse data collection network of hydrologic variables. In combination with several physical characteristics of northern hydrology, the sparse data network leads to a very difficult design circumstance. The most well known physical aspect of northern hydrology is permafrost. Other factors of importance are large elevation differences, regional inhomogeneity, high latitude, low temperatures, and the very dynamic nature of the spring breakup. These factors, in combination with the short data base in northern regions, cause hydrologic design to have a large degree of uncertainty.The work upon which this completion report is based was supported by funds provided by the U. S. Department of the Interior, Office of Water Research and Technology, as authorized under the Water Resources Research Act of 1964, Public Law 88-379, as amended

Effective Widths and Effective Number of Phonons of Multiphonon Giant Resonances

We discuss the origin of the difference between the harmonic value of the width of the multiphonon giant resonances and the smaller observed value. Analytical expressions are derived for both the effective width and the average cross-section. The contribution of the Brink-Axel mechanism in resolving the discrepancy is pointed out.Comment: 9 pages, 4 figure

Development of an Operational Northern Aquatic Ecosystem Model: Completion Report

OWRR Contract No. 14-31-0001-5217 Grant No. C-6169The work upon which this completion report is based was supported by funds provided by the U. S. Department of the Interior, Office of Water Research and Technology as authorized under the Water Resources Research Act of 1964, Public Law 88-379, as amended

Modeling of convection phenomena in Bridgman-Stockbarger crystal growth

Thermal convection phenomena in a vertically oriented Bridgman-Stockbarger apparatus were modeled by computer simulations for different gravity conditions, ranging from earth conditions to extremely low gravity, approximate space conditions. The modeling results were obtained by the application of a state-of-the art, transient, multi-dimensional, completely densimetrically coupled, discrete-element computational model which was specifically developed for the simulation of flow, temperature, and species concentration conditions in two-phase (solid-liquid) systems. The computational model was applied to the simulation of the flow and the thermal conditions associated with the convection phenomena in a modified Germanium-Silicon charge enclosed in a stationary fused-silica ampoule. The results clearly indicated that the gravitational field strength influences the characteristics of the coherent vortical flow patterns, interface shape and position, maximum melt velocity, and interfacial normal temperature gradient

Neutrino scattering and flavor transformation in supernovae

We argue that the small fraction of neutrinos that undergo direction-changing scattering outside of the neutrinosphere could have significant influence on neutrino flavor transformation in core-collapse supernova environments. We show that the standard treatment for collective neutrino flavor transformation is adequate at late times, but could be inadequate in the crucial shock revival/explosion epoch of core-collapse supernovae, where the potentials that govern neutrino flavor evolution are affected by the scattered neutrinos. Taking account of this effect, and the way it couples to entropy and composition, will require a new paradigm in supernova modeling.Comment: 5 pages, 3 figure

Halo Modification of a Supernova Neutronization Neutrino Burst

We give the first self-consistent calculation of the effect of the scattered neutrino halo on flavor evolution in supernovae. Our example case is an O-Ne-Mg core collapse supernova neutronization neutrino burst. We find that the addition of the halo neutrinos produces qualitative and quantitative changes in the final flavor states of neutrinos. We also find that the halo neutrinos produce a novel distortion of the neutrino flavor swap. Our results provide strong motivation for tackling the full multidimensional and composition-dependent aspects of this problem in the future.Comment: 14 pages, 13 figures, 1 tabl

Stick-Slip Motion and Phase Transition in a Block-Spring System

We study numerically stick slip motions in a model of blocks and springs being pulled slowly. The sliding friction is assumed to change dynamically with a state variable. The transition from steady sliding to stick-slip is subcritical in a single block and spring system. However, we find that the transition is continuous in a long chain of blocks and springs. The size distribution of stick-slip motions exhibits a power law at the critical point.Comment: 8 figure