Cryogenic magnetometer development Final report, 1 Jul. 1964 - 7 Mar. 1967

Magnetometers for measuring stable magnetic fields produced by low field superconducting shield

The Detection of Temporal Changes in the Physiological Characteristics of the Activated Sludge in an Industrial Wastewater Treatment System using a Modified Biolog Identification System

The purpose of the study was to determine if the Biolog identification system could be adapted to detect physiological changes in the composite microbial community of activated sludge in an industrial wastewater treatment system. The detected temporal changes were correlated with other microbial characterization methods. Composite community samples were tested over time using Biolog titre plates. The results of the communities were compared with each other to 1) obtain an index of similarity with regard to their ability and inability to utilize the 95 substrates that are a part of the Biolog profile, and 2) ascertain shifts in the overall physiological capabilities of the community for the strict utilization of the 95 substrates. The results suggest that the Biolog identification system can be used to detect changes in the activated sludge microbial community. Other indices of community structure support the Biolog indications of community change.Master of Science in Public Healt

Mission Design and Optimal Asteroid Deflection for Planetary Defense

Planetary defense is a topic of increasing interest for many reasons, which has been mentioned in "Vision and Voyages for Planetary Science in the Decade 2013-2022''. However, perhaps one of the most significant rationales for asteroid studies is the number of close approaches that have been documented recently. A space mission with a planetary defense objective aims to deflect the threatening body as far as possible from Earth. The design of a mission that optimally deflects an asteroid has different challenges: speed, precision, and system trade-off. This work addresses such issues and develops a fast transcription of the problem that can be implemented into an optimization tool, which allows for a broader trade study of different mission concepts with a medium fidelity. Such work is suitable for a mission?s preliminary study. It is shown, using the fictitious asteroid impact scenario 2017 PDC, that the complete tool is able to account for the orbit sensitivity to small perturbations and quickly optimize a deflection trajectory. The speed in which the tool operates allows for a trade study between the available hardware. As a result, key deflection dates and mission strategies are identified for the 2017 PDC

Solid molecular hydrogen: The Broken Symmetry Phase

By performing constant-pressure variable-cell ab initio molecular dynamics simulations we find a quadrupolar orthorhombic structure, of $Pca2_1$ symmetry, for the broken symmetry phase (phase II) of solid H2 at T=0 and P =110 - 150 GPa. We present results for the equation of state, lattice parameters and vibronic frequencies, in very good agreement with experimental observations. Anharmonic quantum corrections to the vibrational frequencies are estimated using available data on H2 and D2. We assign the observed modes to specific symmetry representations.Comment: 5 pages (twocolumn), 4 Postscript figures. To appear in Phys. Rev. Let

Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study

The effect of stress-triaxiality on growth of a void in a three dimensional single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular dynamics (MD) simulations using an embedded-atom (EAM) potential for copper have been performed at room temperature and using strain controlling with high strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these magnitudes can be studied experimentally, e.g. using shock waves induced by laser ablation. Void growth has been simulated in three different conditions, namely uniaxial, biaxial, and triaxial expansion. The response of the system in the three cases have been compared in terms of the void growth rate, the detailed void shape evolution, and the stress-strain behavior including the development of plastic strain. Also macroscopic observables as plastic work and porosity have been computed from the atomistic level. The stress thresholds for void growth are found to be comparable with spall strength values determined by dynamic fracture experiments. The conventional macroscopic assumption that the mean plastic strain results from the growth of the void is validated. The evolution of the system in the uniaxial case is found to exhibit four different regimes: elastic expansion; plastic yielding, when the mean stress is nearly constant, but the stress-triaxiality increases rapidly together with exponential growth of the void; saturation of the stress-triaxiality; and finally the failure.Comment: 35 figures, which are small (and blurry) due to the space limitations; submitted (with original figures) to Physical Review B. Final versio

Theory and Applications of X-ray Standing Waves in Real Crystals

Theoretical aspects of x-ray standing wave method for investigation of the real structure of crystals are considered in this review paper. Starting from the general approach of the secondary radiation yield from deformed crystals this theory is applied to different concreat cases. Various models of deformed crystals like: bicrystal model, multilayer model, crystals with extended deformation field are considered in detailes. Peculiarities of x-ray standing wave behavior in different scattering geometries (Bragg, Laue) are analysed in detailes. New possibilities to solve the phase problem with x-ray standing wave method are discussed in the review. General theoretical approaches are illustrated with a big number of experimental results.Comment: 101 pages, 43 figures, 3 table

Multilayer Thin Film Thermoelectrics Produced by Sputtering

In this work we explore the possibility of achieving bulk electrical properties in single layer sputter deposited films grown epitaxially on (111) oriented BaF{sub 2} substrates. There are a number of sputter deposition parameters that can be varied in order to optimize the film quality. It is important to understand the effect of varying the deposition temperature, Ar sputtering gas pressure, and the substrate bias. We will consider only Bi and Bi{sub 0.86}Sb{sub 0.14} films in this paper. These materials were chosen since they have the same simple structure, two different band gaps and do not change significantly either in physical or electrical properties with small amounts of cross contamination. We will also present our work on multilayer thermoelectrics made of Bi and Bi{sub 0.86}Sb{sub 0.14} layers. There has been considerable interest in this multilayer structure in the literature. Theoretical calculations of the band structure and interface states of these multilayer structures have been made by Mustafaev and Agassi et al. respectively [6,7]. Experimentally Yoshida et al. have examined similar multilayer structures grown by MBE as well as Bi/Sb multilayer samples in which report an anomalous thermoelectric power [8]

Multilayer Thermoelectric Films: A Strategy for the Enhancement of Zt

The relative efficiency of a thermoelectric material is measured in terms of a dimensionless figure of merit, ZT. Although all known thermoelectric materials are believed to have ZT {le} 1, recent theoretical results predict that thermoelectric devices fabricated as two-dimensional quantum wells (2D QWs) could have ZT {ge} 3. Multilayers with the dimensions of 2D QWs have been synthesized by alternately sputtering Bi{sub 0.9}Sb{sub 0.1} and PbTe{sub 0.8}Se{sub 0.2} onto a moving substrate from a pair of magnetron sources. These materials have been synthesized to test the thermoelectric quantum-well concept and gain insight into relevant transport mechanisms. This work focuses primarily on the scientific issues involved in producing the materials necessary to examine the possibility of enhancing ZT using quantum confinement. The techniques needed to measure the relevant electrical parameters of thermoelectric thin films are developed in this paper. Ultimately, if a quantum well enhancement of thermoelectrics is experimentally observed, devices based on this technology could be used to greatly expand the role of thermoelectrics in power generation and refrigeration