Verification of the proteus two-dimensional Navier-Stokes code for flat plate and pipe flows

The Proteus Navier-Stokes Code is evaluated for 2-D/axisymmetric, viscous, incompressible, internal, and external flows. The particular cases to be discussed are laminar and turbulent flows over a flat plate, laminar and turbulent developing pipe flows, and turbulent pipe flow with swirl. Results are compared with exact solutions, empirical correlations, and experimental data. A detailed description of the code set-up, including boundary conditions, initial conditions, grid size, and grid packing is given for each case

Atomistic models of hydrogenated amorphous silicon nitride from first principles

We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principles molecular-dynamics within density-functional theory the models were generated by cooling from the liquid. Where both models have a short-range order resembling that of crystalline Si3N4 because of their different densities and hydrogen concentrations they show marked differences at longer length scales. The low-density nitride forms a percolating network of voids with the internal surfaces passivated by hydrogen. Although some voids are still present for the high-density nitride, this material has a much denser and uniform space filling. The structure factors reveal some tendency for the nonstoichiometric high-density nitride to phase separate into nitrogen rich and poor areas. For our slowest cooling rate (0.023 K/fs) we obtain models with a modest number of defect states, where the low (high) density nitride favors undercoordinated (overcoordinated) defects. Analysis of the structural defects and electronic density of states shows that there is no direct one-to-one correspondence between the structural defects and states in the gap. There are several structural defects that do not contribute to in-gap states and there are in-gap states that do only have little to no contributions from (atoms in) structural defects. Finally an estimation of the size and cooling rate effects on the amorphous network is reported.

Disaggregating the United States Military: An Analysis of the Current Organizational and Management Structure of U.S. National Security Policy as It Relates to Military Operations in Space

This thesis was written to provide the reader with a comprehensive assessment about the realities of the current organizational and management structure of United States national security policy as it relates to the conduct of military operations in space. To create an encompassing argument, this thesis considers the current organizational structure of United States space policy while acknowledging that space has, in fact, become a warfighting domain. A reorganization of this magnitude has the potential to generate a succinct chain of command for military space operations while condensing the space acquisitions process and ultimately providing military space operations with the attention and resources needed to keep America and its allies safe. However, this thesis examines if reconfiguring the current organizational and management structure of United States national security space components does, in fact, have the power to accomplish such objectives. This thesis relies heavily upon the testimonies and documentation derived from both the Department of Defense, as well as the United States Congress. In addition, it is acknowledged that U.S. policymakers have driven this issue into becoming one that is largely bureaucratic and inherently politicized. This thesis ultimately concludes that some degree of reconfiguration to the current organizational and management structure of United States policy as it relates to military operations in space has the potential to positively affect the national security space establishment

Effective Properties of Textile Composites: Application of the Mori-Tanaka Method

An efficient approach to the evaluation of effective elastic properties of carbon-carbon plain weave textile composites using the Mori-Tanaka method is presented. The method proves its potential even if applied to real material systems with various types of imperfections including the non-uniform waviness of the fiber-tow paths, both along its longitudinal direction and through the laminate thickness. Influence of the remaining geometrical parameters is accounted for by optimal calibration of the shape of the equivalent ellipsoidal inclusion. An application of the method to a particular sample of the carbon-carbon composite laminate demonstrates not only its applicability but also its efficiency particularly when compared to finite element simulations.Comment: 18 pages, 6 figure