Morphological stability and fluid dynamics of vapor crystal growth

Research on morphological stability and fluid dynamics of crystal growth is discussed. Interfacial heat and mass transfer research is discussed. The finding of surface roughening is a precursor to a solid-solid phase transition was further quantified. Progress was obtained with the mass spectroscopic characterization of GeSe-Ge I sub 4

A proposed non-intrusive method for finding coefficients of slip and molecular reflectivity in microgravity

A proposed experimental program to look at a series of vapor transport properties measured along solid and liquid surfaces is described. The research objectives proposed are: (1) with accuracy otherwise unobtainable on ground, to determine the coefficient of slip measured between gases and the surfaces of liquids and solids; (2) for the first time, to classify and tabulate dominant surface effects found for a variety of solids, particularly those crystalized by vapor transport; and (3) to extend understanding of settling rates predicted for cosmic dust and condensed vapor falling through planetary atmospheres. The method used to obtain these objectives, has aided, to an order of magnitude, understanding of various liquid-gas interfaces such as oil and water. But to date, no similar characterization has proved successful for solids or liquids of uncertain densities. Likewise, no data exist in either ground-based research or as part of a microgravity program that, when collected with the high accuracy expected in low gravity, could definitely settle outstanding questions in kinetic theory, molecular dynamics, and cosmic physics

How One Georgia Performance Learning Center Helps Students Succeed

The purpose of this study has been to understand how one Georgia Performance Learning Center helps students succeed. Performance Learning Centers are nontraditional high schools created by Communities in Schools in partnership with local school boards to serve students at risk of dropping out of school. Although started in Georgia in only 2003, the Performance Learning Centers have already resulted in student improvement as evidenced by their growth from only seven centers in the first year to 29 centers by 2007 and by their student performance reports. The perceptions of the administrator, staff, teachers, and students at one Performance Learning Center that had opened in 2005 informed this researcher of successful practices at the center. Multiple observations of the participating centers operations and classroom interactions were conducted. Interviews were conducted with the Administrator, Vice-Principal, Service Coordinator, Counselor, all five teachers, and 12 students. The Performance Learning Center implemented the seven major school improvement strategies identified in the literature, including additional instruction and monitoring in core academic areas; future job skill training; instruction on study skills, test taking skills, and time management; modification to the learning environment; student counseling for academic and personal issues; participation in community service projects; and increased parental involvement. The research identified themes of student progress, flexibility, individual student attention, relationships, preparation for lifelong learning, and community as contributing to student success at the Performance Learning Center. The school improvement strategies employed at the Performance Learning Center can be implemented in other educational environments to address specific student needs. State policy makers and educators can look at the Performance Learning Centers as a successful program worthy of emulation

Asymptotic eigenfunctions for Schrödinger operators on a vector bundle

In the limit $\hbar\to 0$, we analyze a class of Schr\"odinger operators $H_\hbar = \hbar^2 L + \hbar W + V\cdot \mathrm{id}$ acting on sections of a vector bundle $\mathcal{Eh}$ over a Riemannian manifold $M$ where $L$ is a Laplace type operator, $W$ is an endomorphism field and the potential energy $V$ has a non-degenerate minimum at some point $p\in M$. We construct quasimodes of WKB-type near $p$ for eigenfunctions associated with the low lying eigenvalues of $H_\hbar$. These are obtained from eigenfunctions of the associated harmonic oscillator $H_{p, \hbar}$ at $p$, acting on smooth functions on the tangent space

X-ray transmission microscope development

We are developing a hard x-ray microscope for direct observation of solidification dynamics in metal alloys and metal matrix composites. The Fein-Focus Inc. x-ray source was delivered in September and found to perform better than expected. Confirmed resolution of better than 2 micrometers was obtained and magnifications up to 800X were measured. Nickel beads of 30 micrometer diameter were easily detected through 6mm of aluminum. X-ray metallography was performed on several specimens showing high resolution and clear definition of 3-dimensional structures. Prototype furnace installed and tested

X-ray transmission microscope development

This report covers the third 6 month period, from February 28, 1995 to August 31, 1995, under this contract. The main efforts during this period were the construction of the X-ray furnace, evaluation and selection of the CCD technology for the X-ray camera, solidification experiments with Al alloys and Al-zirconia composites in the prototype furnace, evaluation of specimens for the particle pushing flight experiment - PEPSI, measurements of emitted spectra from X-ray source, testing of the high resolution X-ray test targets, and the establishment of criteria for and selection of peripheral equipment. In addition to these tasks, two presentations were prepared in this period; one for the AIAA Microgravity Symposium and another for the Gordon Conference on Gravitational Effects in Pyisico-Chemical Systems

Mutations of fake weighted projective planes

In previous work by Coates, Galkin, and the authors, the notion of mutation between lattice polytopes was introduced. Such a mutation gives rise to a deformation between the corresponding toric varieties. In this paper we study one-step mutations that correspond to deformations between weighted projective planes, giving a complete characterisation of such mutations in terms of T-singularities. We show also that the weights involved satisfy Diophantine equations, generalising results of Hacking-Prokhorov

Analysis of the Results of Surface Free Energy Measurement of Ti6Al4V by Different Methods

AbstractSurface Free Energy (SFE) of solids should be calculated using theoretical models. The contact angle (CA) measurement on a surface is considered the most practical way to obtain the SFE. The results of five methods based in the models are compared: the method of Zisman (ZI), the geometric mean (GM), the harmonic mean (HM), the Lifshitz-van der Waals/ Acid-Base (LW/AB) and the equation of state (ES). The SFE calculated with GM, HM and LW/AB methods change with the amount and type of liquid used, however, when water, glycerol and dimethyl sulfoxide are used together the SFE and its dispersive and polar components are similar in value for the three methods. In the case of the ES model the values of SFE change with the liquid used; finally using the ZI method the SFE values are 20% lower than the values of SFE obtained with the other methods

Polynomial functions for direct calculation of the surface free energy developed from the Neumann Equation of State method

The Neumann Equation of State (EQS) allows obtaining the value of the surface free energy of a solid {\gamma}_{SV} from the contact angle ({\theta}) of a probe liquid with known surface tension {\gamma}_{LV}. The value of {\gamma}_{SV} is obtained by numerical methods solving the corresponding EQS. In this work, we analyzed the discrepancies between the values of {\gamma}_SV obtained using the three versions of the EQS reported in the literature. The condition number of the different EQS was used to analyze their sensitivity to the uncertainty in the {\theta} values. Polynomials fit to one of these versions of EQS are proposed to obtain values of {\gamma}_{SV} directly from contact angles ({\gamma}_SV ({\theta})) of particular probe liquids. Finally, a general adjusted polynomial is presented to obtain the values of {\gamma}_{SV} not restricted to a particular probe liquid ({\gamma}_{SV}({\theta},{\gamma}_{LV})). Results showed that the three versions of EQS present non-negligible discrepancies, especially at high values of {\theta}. The sensitivity of the EQS to the uncertainty in the values of {\theta} is very similar in the three versions and depends on the probe liquid used (greater sensitivity at higher {\gamma}_{LV}) and on the value of {\gamma}_{SV} of the solid (greater sensitivity at lower {\gamma}_{SV}). The discrepancy of the values obtained by numerical resolution of both the fifth-order fit polynomials and the general fit polynomial was low, no larger than {\pm}0.40 mJ/m^{2}. The polynomials obtained allow the analysis and propagation of the uncertainty of the input variables in the determination of {\gamma}_{SV} in a simple and fast way.Comment: 37 pages, 13 figure