Publications

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The objectives of this project were to develop a new scientific tool for studies of chemical processes at the single molecule level, and to provide enhanced capabilities for multiplexed, ultrasensitive separations and immunoassays. We have combined microfluidic separation techniques with our newly developed technology for spectrally and temporally resolved detection of single molecules. The detection of individual molecules can reveal fluctuations in molecular conformations, which are obscured in ensemble measurements, and allows detailed studies of reaction kinetics such as ligand or antibody binding. Detection near the single molecule level also enables the use of correlation techniques to extract information, such as diffusion rates, from the fluorescence signal. The micro-fluidic technology offers unprecedented control of the chemical environment and flow conditions, and affords the unique opportunity to study biomolecules without immobilization. For analytical separations, the fluorescence lifetime and spectral resolution of the detection makes it possible to use multiple parameters for identification of separation products to improve the certainty of identification. We have successfully developed a system that can measure fluorescence spectra, lifetimes and diffusion constants of the components of mixtures separated in a microfluidic electrophoresis chip.

Veloce is a medium-voltage, high-current, compact pulsed power generator developed for isentropic and shock compression experiments. Because of its increased availability and ease of operation, Veloce is well suited for studying isentropic compression experiments (ICE) in much greater detail than previously allowed with larger pulsed power machines such as the Z accelerator. Since the compact pulsed power technology used for dynamic material experiments has not been previously used, it is necessary to examine several key issues to ensure that accurate results are obtained. In the present experiments, issues such as panel and sample preparation, uniformity of loading, and edge effects were extensively examined. In addition, magnetohydrodynamic (MHD) simulations using the ALEGRA code were performed to interpret the experimental results and to design improved sample/panel configurations. Examples of recent ICE studies on aluminum are presented.

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This document is considered a mechanical design best-practice guide to new and experienced designers alike. The contents consist of topics related to using Computer Aided Design (CAD) software, performing basic analyses, and using configuration management. The details specific to a particular topic have been leveraged against existing Product Realization Standard (PRS) and Technical Business Practice (TBP) requirements while maintaining alignment with sound engineering and design practices. This document is to be considered dynamic in that subsequent updates will be reflected in the main title, and each update will be published on an annual basis.

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Results from recent experimental studies suggest that the N vacancy (V{sub N}) may compensate Mg acceptors in GaN in addition to the compensation arising from H introduced during growth. To investigate this possibility further, density-functional-theory calculations were performed to determine the interactions of V{sub N} with H, Mg, and the MgH center in GaN, and modeling was performed to determine the state populations at elevated temperatures. The results indicate that V{sub N}H and MgV{sub N}H complexes with H inside the vacancy are highly stable in p-type GaN and act to compensate or passivate Mg acceptors. Furthermore, barriers for formation of these complexes were investigated and the results indicate that they can readily form at temperatures > 400 C, which is well below temperatures typically used for GaN growth. Overall, the results indicate that the V{sub N} compensation behavior suggested by experiments arises not from isolated V{sub N}, but rather from V{sub N}H and MgV{sub N}H complexes with H located inside the vacancy.

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