2,051 research outputs found
Development of improved amorphous materials for laser systems
Crystallization calculations were performed in order to determine the possibility of forming a particular type of laser glass with the avoidance of devitrification in an outer space laboratory. It was demonstrated that under the homogenuous nucleating conditions obtainable in a zero gravity laboratory this laser glass may be easily quenched to a virtually crystal-free product. Experimental evidence is provided that use of this material as a host in a neodymium glass laser would result in more than a 10 percent increase in efficiency when compared to laser glass rods of a similar composition currently commercially available. Differential thermal analysis, thermal gradient oven, X-ray diffraction, and liquidus determination experiments were carried out to determine the basics of the crystallization behavior of the glass, and small-angle X-ray scattering and splat-cooling experiments were performed in order to provide additional evidence for the feasibility of producing this laser glass material, crystal free, in an outer space environment
The nature and extent of trace element contamination associated with fly-ash disposal sites in the Chisman Creek Watershed
This study was conducted by the Virginia Institute of Marine Science (VIMS) and the Virginia Associated Research Campus (VARC), both branches of the College of William and Mary, to document the nature, extent, and severity of environmental contamination by trace elements from the landfill disposal of fly-ash within the Chisman Creek watershed. Previous work in the area demonstrated that some metals were apparently mobile in the groundwater, and that two nearby household wells were contaminated (Va. SWCB, 1981). These short term studies were limited to the testing of only a few selected contaminants in wells near the fly-ash pits. The goal of our study was to provide a more comprehensive sampling of the basin to delineate the geographical extent of trace element contamination, and to assess whether the levels found there pose a hazard to man or to the terrestrial and aquatic ecosystem. An important aspect of the program is the use of an analytical technique which provides simultaneous measurement of a large number of elements, thereby obviating the need to speculate which elements would be found before the field work was begun. Proton Induced X-ray Emission (PIXE) is such a technique and provided data on 70 elements from each sample collected during this study
Large Exploding Wires—Correlation to Small Wires and Pause Time Versus Length Dependency
The results of small exploding-wire studies were found to be capable of direct extrapolation to larger wires (an increase in cross-sectional area of 1500 to 1500 from the small wires). Copper wires up to 40 mils in diameter and iron wires to 62 mils in diameter were studied for use as fuses. in lengths up to 18 in. A dependency between pause time (the time between system current cut-off and current restrike) and wire length is described for several sizes of copper wires exploded with 16.5- and 49.5-kilojoule sources. The role of wire confinement is discussed in connection with establishment of the pause. (auth
Pseudo-random operators of the circular ensembles
We demonstrate quantum algorithms to implement pseudo-random operators that
closely reproduce statistical properties of random matrices from the three
universal classes: unitary, symmetric, and symplectic. Modified versions of the
algorithms are introduced for the less experimentally challenging quantum
cellular automata. For implementing pseudo-random symplectic operators we
provide gate sequences for the unitary part of the time-reversal operator.Comment: 5 pages, 4 figures, to be published PR
Measurement of interfacial tension of immiscible liquid pairs in microgravity
A discussion is given of a containerless microgravity experiment aimed at measuring the interfacial tension of immiscible liquid pairs using a compound drop rotation method. The reasons for the failure to execute such experiments in microgravity are described. Also, the results of post-flight analyses used to confirm our arguments are presented
Comparative Modelling of the Spectra of Cool Giants
Our ability to extract information from the spectra of stars depends on
reliable models of stellar atmospheres and appropriate techniques for spectral
synthesis. Various model codes and strategies for the analysis of stellar
spectra are available today. We aim to compare the results of deriving stellar
parameters using different atmosphere models and different analysis strategies.
The focus is set on high-resolution spectroscopy of cool giant stars. Spectra
representing four cool giant stars were made available to various groups and
individuals working in the area of spectral synthesis, asking them to derive
stellar parameters from the data provided. The results were discussed at a
workshop in Vienna in 2010. Most of the major codes currently used in the
astronomical community for analyses of stellar spectra were included in this
experiment. We present the results from the different groups, as well as an
additional experiment comparing the synthetic spectra produced by various codes
for a given set of stellar parameters. Similarities and differences of the
results are discussed. Several valid approaches to analyze a given spectrum of
a star result in quite a wide range of solutions. The main causes for the
differences in parameters derived by different groups seem to lie in the
physical input data and in the details of the analysis method. This clearly
shows how far from a definitive abundance analysis we still are.Comment: accepted for publication in A&A. This version includes also the
online tables. Reference spectra will later be available via the CD
Dynamic correlations in symmetric electron-electron and electron-hole bilayers
The ground-state behavior of the symmetric electron-electron and
electron-hole bilayers is studied by including dynamic correlation effects
within the quantum version of Singwi, Tosi, Land, and Sjolander (qSTLS) theory.
The static pair-correlation functions, the local-field correction factors, and
the ground-state energy are calculated over a wide range of carrier density and
layer spacing. The possibility of a phase transition into a density-modulated
ground state is also investigated. Results for both the electron-electron and
electron-hole bilayers are compared with those of recent diffusion Monte Carlo
(DMC) simulation studies. We find that the qSTLS results differ markedly from
those of the conventional STLS approach and compare in the overall more
favorably with the DMC predictions. An important result is that the qSTLS
theory signals a phase transition from the liquid to the coupled Wigner crystal
ground state, in both the electron-electron and electron-hole bilayers, below a
critical density and in the close proximity of layers (d <~ r_sa_0^*), in
qualitative agreement with the findings of the DMC simulations.Comment: 13 pages, 11 figures, 2 table
Characterization of the Hamamatsu S8664 Avalanche Photodiode for X-Ray and VUV-light detection
We present the first operation of the Avalanche Photodiode (APD) from
Hamamatsu to xenon scintillation light and to direct X-rays of 22.1 keV and 5.9
keV. A large non-linear response was observed for the direct X-ray detection.
At 415 V APD bias voltage it was of about 30 % for 22.1 keV and about 45 % for
5.9 keV. The quantum efficiency for 172 nm photons has been measured to be 69
+/- 15 %.Comment: 11 pages, 3 figures, submitted to Elsevie
Ternary Quarter Wavelength Coatings for Gravitational Wave Detector Mirrors: Design Optimization via Exhaustive Search
Multimaterial optical coatings are a promising viable option to meet the
challenging requirements (in terms of transmittance, absorbance and thermal
noise) of next generation gravitational wave detector mirrors. In this paper we
focus on ternary coatings consisting of quarter-wavelength thick layers, where
a third material (H') is added to the two presently in use, namely Silica (L)
and Titania-doped Tantala (H), featuring higher dielectric contrast (against
Silica), and lower thermal noise (compared to Titania-doped Tantala), but
higher optical losses. We seek the optimal material sequences, featuring
minimal thermal (Brownian) noise under prescribed transmittance and absorbance
constraints, by exhaustive simulation over all possible configurations, for
different values (in a meaningful range) of the optical density and extinction
coefficient of the third material. In all cases studied, the optimal designs
consist of a stack of (H'|L) doublets topped by a stack of (H|L) doublets,
confirming previous heuristic assumptions, and the achievable coating noise
power spectral density reduction factor is \sim 0.5. The robustness of the
found optimal designs against layer thickness deposition errors and
uncertainties and/or fluctuations in the optical losses of the third material
is also investigated. Possible margins for further thermal noise reduction by
layer thickness optimization, and strategies to implement it, are discussed.Comment: (twocolum style) 13 pages, 8 figures, 4 table (updated version 5)
Appearing on Physical Review Researc
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