Thermal shock and erosion resistant tantalum carbide ceramic material

Ceramic tantalum carbide artifacts with high thermal shock and mechanical erosion resistance are provided by incorporating tungsten-rhenium and carbon particles in a tantalum carbide matrix. The mix is sintered by hot pressing to form the ceramic article which has a high fracture strength relative to its elastic modulus and thus has an improved thermal shock and mechanical erosion resistance. The tantalum carbide is preferable less than minus 100 mesh, the carbon particles are preferable less than minus 100 mesh, and the tungsten-rhenium particles are preferable elongate, having a length to thickness ratio of at least 2/1. Tungsten-rhenium wire pieces are suitable as well as graphite particles

Thermal distortion analysis of a deployable parabolic reflector

A thermal distortion analysis of the ATS-6 Satellite parabolic reflector was performed using NASTRAN level 15.1. The same NASTRAN finite element method was used to conduct a one g static load analysis and a dynamic analysis of the reflector. In addition, a parametric study was made to determine which parameters had the greatest effect on the thermal distortions. The method used to model the construction of the reflector is described and the results of the analyses are presented

Development of high temperature materials for solid propellant rocket nozzle applications

Evaluation of tantalum carbide-tungsten fiber composites has been completed as far as weight percent carbon additions and weight percent additions of tungsten fiber. Extensive studies were undertaken concerning Young's Modulus and fracture strength of this material. Also, in-depth analysis of the embrittling effects of the extra carbon additions on the tungsten fibers has been completed. The complete fabrication procedure for the tantalum carbide-tungsten fiber composites with extra carbon additions is given. Microprobe and metallographic studies showed the effect of extra carbon on the tungsten fibers, and evaluation of the thermal shock parameter fracture strength/Young's Modulus is included

Abnormal diffusion of a single vortex in the two dimensional XY model

We study thermal diffusion dynamics of a single vortex in two dimensional XY model. By numerical simulations we find an abnormal diffusion such that the mobility decreases with time $t$ as $1/\ln t$. In addition we construct a one dimensional diffusion-like equation to model the dynamics and confirm that it conserves quantitative property of the abnormal diffusion. By analyzing the reduced model, we find that the radius of the collectively moving region with the vortex core grows as $R(t) \propto t^{1/2}$. This suggests that the mobility of the vortex is described by dynamical correlation length as $1/\ln R(t)$.Comment: 13 pages, 8 figure

Identification of Potential Seepage Locations Along the Herbert Hoover Dike, Lake Okeechobee FL., by Electromagnetic Geophysical Method. Prediction and Confirmation.

This case history demonstrates the use of electromagnetic (EM) induction methods to examine known seepage locations and then predict future ones along the Herbert Hoover Dike (HHD) in south central Florida. The HHD forms an embankment dam 20 to 30 feet high and 140 miles long surrounding Lake Okeechobee. Approximately 26 miles of embankment was surveyed with EM induction. The objective of the EM survey was to identify active and potential foundation seepage locations and conduits. Areas of greater conductivity were often associated with seepage locations observed during a record high water event in October, 1995. These problems included boils and piping of foundation and embankment materials. One great benefit of this investigation was that large areas of competent dike foundations could be separated from areas containing potential problems requiring additional examination

Restocking Northern Bobwhites in East Texas: A Genetic Assessment

Habitat on a 610-ha study area in the Pineywoods Ecological Region of eastern Texas was enhanced for northern bobwhites ( Coli nus virginianus). In February and March 1990, 1991, and 1992, bobwhites from south Texas (C. v. texanus) and disjunct areas of east Texas (C. v. mexicanus) were captured, radio tagged, and relocated to the study area which had a small ( \u3c25 birds) resident population. Blood samples were collected from the birds relocated in 1991. Samples were also collected from birds in the resident population during 1991 and 1992; these birds were assumed to be offspring of the previous years\u27 resident and relocated bobwhites. Restriction site variation of mitochondrial DNA (mtDNA) revealed geographic subdivision between the subspecies but not between resident and east Texas relocated birds. The observed frequency differences of mtDNA haplotypes were used to assess the relative reproductive success of the 2 subspecies. Among the birds examined for mtDNA variation, offspring produced on the study area during 1990 and 1991 were genetically more similar to the east Texas subspecies than to the south Texas subspecies. These results suggest that efforts to restock northern bobwhite should involve either local birds or birds from the same subspecies. Management implications of these findings are discussed

Quantum open systems and turbulence

We show that the problem of non conservation of energy found in the spontaneous localization model developed by Ghirardi, Rimini and Weber is very similar to the inconsistency between the stochastic models for turbulence and the Navier-Stokes equation. This sort of analogy may be useful in the development of both areas.Comment: to appear in Physical Review

Folding, Design and Determination of Interaction Potentials Using Off-Lattice Dynamics of Model Heteropolymers

We present the results of a self-consistent, unified molecular dynamics study of simple model heteropolymers in the continuum with emphasis on folding, sequence design and the determination of the interaction parameters of the effective potential between the amino acids from the knowledge of the native states of the designed sequences.Comment: 8 pages, 3 Postscript figures, uses RevTeX. Submitted to Physical Review Letter

Promoting Policy and Environmental Change in Faith-Based Organizations: Organizational Level Findings From a Mini Grants Program

Background: High rates of heart disease, cancer, and stroke exist in rural South Georgia, where Emory’s Cancer Prevention and Control Research Network provided mini-grants and technical assistance to six faith-based organizations to implement policy and environmental changes to promote healthy eating (HE), physical activity (PA), and tobacco use prevention (TUP). Drawing from a Social Ecological Framework, we hypothesized that church members would perceive an increase in messages, programs, and the availability of facilities to support HE, PA, and TUP over a 1-year period. Methods: Members (N=258) completed self-administered questionnaires that assessed perceptions of the existing church health promotion environment relative to HE, PA, and TUP policies, as well as their eating behavior and intention to use PA facilities at church at baseline and 1-year follow-up. Results:Members at three of the six churches perceived increases in delivery of HE messages via sermons, church bulletins, and food labels, and increased availability of programs that support HE (p Conclusions: Community mini-grants may be a viable mechanism for promoting environmental change supporting HE, PA, and TUP policies in church environments