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Effects of the Electron Energy Distribution Function on Modeled X-ray Spectra (open access)

Effects of the Electron Energy Distribution Function on Modeled X-ray Spectra

This paper presents the results of a broad investigation into the effects of the electron energy distribution function on the predictions of non-LTE collisional-radiative atomic kinetics models. The effects of non-Maxwellian and suprathermal (''hot'') electron distributions on collisional rates (including three-body recombination) are studied. It is shown that most collisional rates are fairly insensitive to the functional form and characteristic energy of the electron distribution function as long as the characteristic energy is larger than the threshold energy for the collisional process. Collisional excitation and ionization rates, however, are highly sensitive to the fraction of hot electrons. This permits the development of robust spectroscopic diagnostics that can be used to characterize the electron density, bulk electron temperature, and hot electron fraction of plasmas with non-equilibrium electron distribution functions (EDFs). Hot electrons are shown to increase and spread out plasma charge state distributions, amplify the intensities of emission lines fed by direct collisional excitation and radiative cascades, and alter the structure of satellite features in both K- and L-shell spectra. The characteristic energy, functional form, and spatial properties of hot electron distributions in plasmas are open to characterization through their effects on high-energy continuum and line emission and on the polarization …
Date: February 19, 2004
Creator: Shlyaptseva, A S & Hansen, S B
System: The UNT Digital Library
Physical and Chemical Analytical Analysis: A key component of Bioforensics (open access)

Physical and Chemical Analytical Analysis: A key component of Bioforensics

The anthrax letters event of 2001 has raised our awareness of the potential importance of non-biological measurements on samples of biological agents used in a terrorism incident. Such measurements include a variety of mass spectral, spectroscopic, and other instrumental techniques that are part of the current armamentarium of the modern materials analysis or analytical chemistry laboratory. They can provide morphological, trace element, isotopic, and other molecular ''fingerprints'' of the agent that may be key pieces of evidence, supplementing that obtained from genetic analysis or other biological properties. The generation and interpretation of such data represents a new domain of forensic science, closely aligned with other areas of ''microbial forensics''. This paper describes some major elements of the R&D agenda that will define this sub-field in the immediate future and provide the foundations for a coherent national capability. Data from chemical and physical analysis of BW materials can be useful to an investigation of a bio-terror event in two ways. First, it can be used to compare evidence samples collected at different locations where such incidents have occurred (e.g. between the powders in the New York and Washington letters in the Amerithrax investigation) or between the attack samples and those seized …
Date: February 15, 2005
Creator: Velsko, S P
System: The UNT Digital Library
On the Possibility of the Sheath-Driven, Finite-Beta Modes Localized Near the Divertor Plate (open access)

On the Possibility of the Sheath-Driven, Finite-Beta Modes Localized Near the Divertor Plate

It is shown that, in a finite beta plasma, there may exist sheath driven modes whose amplitude decreases exponentially with the distance from the divertor plate. The modes are sensitive to the radial tilt of the divertor plate. The short-wavelength branch of the instability, with the cross-field wavelength Dof order of a few ion gyroradii, is present in the case of a ''positive'' tilt of the divertor plate, whereas the long-wavelength branch, with D of order of 10 or so gyroradii is unstable for the opposite sign of the tilt. The parallel e-folding length becomes less than the distance from the plate to the X point (thereby making the mode insensitive to the processes near the X-point and the upper scrape-off layer) at the plasma betas exceeding (2-3) {center_dot} 10{sup -4}. A detailed analysis of the dispersion relations is provided. The features of the modes that can be used for their experimental identification are discussed. It is pointed out that the analog of these modes may also exist in linear plasma devices with shaped end electrodes.
Date: February 10, 2005
Creator: Cohen, R & Ryutov, D
System: The UNT Digital Library
Out-of-Core Compression and Decompression of Large n-Dimensional Scalar Fields (open access)

Out-of-Core Compression and Decompression of Large n-Dimensional Scalar Fields

We present a simple method for compressing very large and regularly sampled scalar fields. Our method is particularly attractive when the entire data set does not fit in memory and when the sampling rate is high relative to the feature size of the scalar field in all dimensions. Although we report results for R{sup 3} and R{sup 4} data sets, the proposed approach may be applied to higher dimensions. The method is based on the new Lorenzo predictor, introduced here, which estimates the value of the scalar field at each sample from the values at processed neighbors. The predicted values are exact when the n-dimensional scalar field is an implicit polynomial of degree n-1. Surprisingly, when the residuals (differences between the actual and predicted values) are encoded using arithmetic coding, the proposed method often outperforms wavelet compression in an L{infinity} sense. The proposed approach may be used both for lossy and lossless compression and is well suited for out-of-core compression and decompression, because a trivial implementation, which sweeps through the data set reading it once, requires maintaining only a small buffer in core memory, whose size barely exceeds a single n-1 dimensional slice of the data.
Date: February 3, 2003
Creator: Ibarria, L.; Lindstrom, P.; Rossignac, J. & Szymczak, A.
System: The UNT Digital Library
Immobilization of uranium and plutonium into borobasalt, pyroxene and andradite mineral-like compositions (open access)

Immobilization of uranium and plutonium into borobasalt, pyroxene and andradite mineral-like compositions

The immobilization of plutonium-containing wastes into stable solid compositions is one of the problems to be solved in the disposal of radioactive wastes. Research efforts on the selection, preparation with the use of the cold crucible induction melter (CCIM) technology, and investigation of materials that are most suitable for immobilizing plutonium-containing wastes of different origin have been carried out at the All-Russian Scientific Research Institute of Inorganic Materials (VNIINM) and the Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences within the framework of agreements with Lawrence Livermore National Laboratory (LLNL, USA) regarding material and technical support. This paper presents the data on the synthesis of cerium-, uranium-, and plutonium-containing materials based on borobasalt, pyroxene, and andradite compositions in the muffle furnace and by the CCIM method. Compositions containing up to 15-18 wt% cerium oxide, 8-11 wt% uranium oxide, and 4.6-5.7 wt% plutonium oxide were obtained in laboratory facilities installed in glove boxes. Comparison studies of the materials synthesized in the muffle furnace and CCIM demonstrate the advantages of using the CCIM method. The distribution of components in the materials.
Date: February 5, 2001
Creator: Matyunin, Y I; Jardine, L J & Yudintsev, S V
System: The UNT Digital Library
Enhanced Adhesion of EVA Laminates to Primed Glass Substrates Subjected to Damp-Heat Exposure (open access)

Enhanced Adhesion of EVA Laminates to Primed Glass Substrates Subjected to Damp-Heat Exposure

We investigated the effectiveness of glass-surface priming to promote enhanced adhesion of EVA laminates during damp-heat exposure at 85 C and 85% relative humidity. The primary objective was to develop advanced encapsulant formulations by incorporation of various primer formulations that exhibit improved adhesion during damp-heat exposure. Several primer formulations were identified that greatly enhanced the EVA adhesion strength, including to the extent that peeling could not be initiated, even for the laminates of the glass substrate/fast-cure EVA15295P/TPE backsheet (a Tedlar/polyester/EVA tri-laminate) that were exposed in a damp-heat test chamber for more than 750 h. The results show that a synergistic increase in the interfacial hydrophobicity, siloxane density, and cross-linking density are the key attributes to the improvement in the EVA adhesion strength.
Date: February 1, 2005
Creator: Pern, F. J. & Jorgensen, G. J.
System: The UNT Digital Library
Nature's Greatest Puzzles (open access)

Nature's Greatest Puzzles

It is a pleasure to be part of the SLAC Summer Institute again, not simply because it is one of the great traditions in our field, but because this is a moment of great promise for particle physics. I look forward to exploring many opportunities with you over the course of our two weeks together. My first task in talking about Nature's Greatest Puzzles, the title of this year's Summer Institute, is to deconstruct the premise a little bit.
Date: February 1, 2005
Creator: Quigg, Chris
System: The UNT Digital Library
Uranus in 2003: Zonal Winds, Banded Structure, and Discrete Features (open access)

Uranus in 2003: Zonal Winds, Banded Structure, and Discrete Features

None
Date: February 2, 2005
Creator: Hammel, H B; de Pater, I; Gibbard, S G; Lockwood, G W & Rages, K
System: The UNT Digital Library
Stopping and Baryon Transport in Heavy Ion Reactions. (open access)

Stopping and Baryon Transport in Heavy Ion Reactions.

In this report I will give an experimental overview on nuclear stopping in hadron collisions, and relate observations to understanding of baryon transport. Baryon number transport is not only evidenced via net-proton distributions but also by the enhancement of strange baryons near mid-rapidity. Although the focus is on high-energy data obtained from pp and heavy ions from RHIC, relevant data from SPS and ISR will be considered. A discussion how the available data at higher energy relates and gives information on baryon junction, quark-diquark breaking will be made.
Date: February 5, 2005
Creator: Videbaek, F.
System: The UNT Digital Library
Study of Z gamma events and limits on anomalous Z Z gamma and Z gamma gamma couplings in p anti-p collisions at s**(1/2) = 1.96-TeV (open access)

Study of Z gamma events and limits on anomalous Z Z gamma and Z gamma gamma couplings in p anti-p collisions at s**(1/2) = 1.96-TeV

The authors present a measurement of the Z{gamma} production cross section and limits on anomalous ZZ{gamma} and Z{gamma}{gamma} couplings for form-factor scales of {Lambda} = 750 and 1000 GeV. The measurement is based on 138 (152) candidate events in the ee{gamma} ({mu}{mu}{gamma}) final state using 320 (290) pb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h{sub 10,30}{sup Z}| < 0.23, |h{sub 20,40}{sup Z}| < 0.020, |h{sub 10,30}{gamma}| < 0.23, and |h{sub 20,40}{gamma}| < 0.019 for {Lambda} = 1000 GeV.
Date: February 1, 2005
Creator: Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al.
System: The UNT Digital Library
Recent results of high p(T) physics at the CDF II (open access)

Recent results of high p(T) physics at the CDF II

The Tevatron Run II program has been in progress since 2001. The CDF experiment has accumulated roughly five times as much data as did Run I, with much improved detectors. Preliminary results from the CDF experiment are presented. The authors focus on recent high p{sub T} physics results in the Tevatron Run II program.
Date: February 1, 2005
Creator: Tsuno, Soushi & U., /Okayama
System: The UNT Digital Library
Charge-state distribution and Doppler effect in an expanding photoionized plasma (open access)

Charge-state distribution and Doppler effect in an expanding photoionized plasma

None
Date: February 23, 2004
Creator: Foord, M E; Heeter, R F; Thoe, R S; Chung, H; Liedahl, D A; Goldstein, W H et al.
System: The UNT Digital Library
Optimal Segmentation Strategy for Compact Representation of Hyperspectral Image Cubes (open access)

Optimal Segmentation Strategy for Compact Representation of Hyperspectral Image Cubes

By producing compact representations of hyperspectral image cubes (hypercubes), image storage requirements and the amount of time it takes to extract essential elements of information can both be dramatically reduced. However, these compact representations must preserve the important spectral features within hypercube pixels and the spatial structure associated with background and objects or phenomena of interest. This paper describes a novel approach for automatically and efficiently generating a particular type of compact hypercube representation, referred to as a supercube. The hypercube is segmented into regions that contain pixels with similar spectral shapes that are spatially connected, and the pixel connectivity constraint can be relaxed. Thresholds of similarity in spectral shape between pairs of pixels are derived directly from the hypercube data. One superpixel is generated for each region as some linear combination of pixels belonging to that region. The superpixels are optimal in the sense that the linear combination coefficients are computed so as to minimize the level of noise. Each hypercube pixel is represented in the supercube by applying a gain and bias to the superpixel assigned to the region containing that pixel. Examples are provided.
Date: February 8, 2000
Creator: Paglieroni, D & Roberts, R
System: The UNT Digital Library
Control of Moisture Ingress into Photovoltaic Modules (open access)

Control of Moisture Ingress into Photovoltaic Modules

During long-term exposure of photovoltaic modules to environmental stress, the ingress of water into the module is correlated with decreased performance. By using diffusivity measurements for water through encapsulants such as ethylene vinyl acetate (EVA), we have modeled moisture ingress using a finite-element analysis with atmospheric data from various locations such as Miami, Florida. This analysis shows that because of the high diffusivity of EVA, even an impermeable glass back-sheet alone is incapable of preventing significant moisture ingress from the edges for a 20-year lifecycle. This result has led us to investigate ways to protect modules from moisture through the use of different encapsulating chemistries and materials.
Date: February 1, 2005
Creator: Kempe, M. D.
System: The UNT Digital Library
Unusual Capacitance Emission Transients in CIGS Caused by Large Defect Entropy Changes (open access)

Unusual Capacitance Emission Transients in CIGS Caused by Large Defect Entropy Changes

Capacitance transient data from bias-pulse experiments on CdS/CIGS solar cells show an unusual behavior at high temperatures. Above 350 K, a minority-carrier trap, with a larger activation energy than a majority-carrier trap, emits faster than the lower activation-energy minority trap. A simple enthalpy model for trap emission cannot explain this counterintuitive behavior; but the more complete Gibbs free-energy model that includes entropy can explain it. We show that entropy plays a major role in carrier emission from traps in CIGS.
Date: February 1, 2005
Creator: Young, D. L.; Ramanathan, K. & Crandall, R. S.
System: The UNT Digital Library
Creating Ensembles of Decision Trees Through Sampling (open access)

Creating Ensembles of Decision Trees Through Sampling

Recent work in classification indicates that significant improvements in accuracy can be obtained by growing an ensemble of classifiers and having them vote for the most popular class. This paper focuses on ensembles of decision trees that are created with a randomized procedure based on sampling. Randomization can be introduced by using random samples of the training data (as in bagging or arcing) and running a conventional tree-building algorithm, or by randomizing the induction algorithm itself. The objective of this paper is to describe our first experiences with a novel randomized tree induction method that uses a subset of samples at a node to determine the split. Our empirical results show that ensembles generated using this approach yield results that are competitive in accuracy and superior in computational cost.
Date: February 2, 2001
Creator: Kamath, C & Cantu-Paz, E
System: The UNT Digital Library
Defining Electron Backscatter Diffraction Resolution (open access)

Defining Electron Backscatter Diffraction Resolution

Automated electron backscatter diffraction (EBSD) mapping systems have existed for more than 10 years [1,2], and due to their versatility in characterizing multiple aspects of microstructure, they have become an important tool in microscale crystallographic studies. Their increasingly widespread use however raises questions about their accuracy in both determining crystallographic orientations, as well as ensuring that the orientation information is spatially correct. The issue of orientation accuracy (as defined by angular resolution) has been addressed previously [3-5]. While the resolution of EBSD systems is typically quoted to be on the order of 1{sup o}, it has been shown that by increasing the pattern quality via acquisition parameter adjustment, the angular resolution can be improved to sub-degree levels. Ultimately, the resolution is dependent on how it is identified. In some cases it can be identified as the orientation relative to a known absolute, in others as the misorientation between nearest neighbor points in a scan. Naturally, the resulting values can be significantly different. Therefore, a consistent and universal definition of resolution that can be applied to characterize any EBSD system is necessary, and is the focus of the current study. In this work, a Phillips (FEI) XL-40 FEGSEM coupled to a …
Date: February 7, 2005
Creator: El-Dasher, B S & Rollett, A D
System: The UNT Digital Library
Coalescence of Multiple Plasmoids as a Means of Efficient Spheromak Formation (open access)

Coalescence of Multiple Plasmoids as a Means of Efficient Spheromak Formation

We have produced single bursts of helicity from the source in the SSPX spheromak in order to study the efficiency of the simplest example of helicity injection. We find that the helicity injection rate can be written in terms of the injected current and an inductance, and that a simple circuit analogue demonstrates unambiguously the relationship of helicity to energy: helicity injection is the addition of inductive loops. While helicity balance points to the conservation of helicity, the electrical efficiency is around 15%. However, in the expulsion of the loop, electrical energy is converted to directional motion, which may be recoverable usefully as heat by collisions, thus the efficiency of the injection process is arguably quite high. Integral to this notion of helicity injection is the idea that reconnection is necessary: without disconnection from the source by a reconnection event, the spheromak fields are just proportional to the injected current. Sometimes the multiple bursts occur spontaneously and cause a step-wise increase in the field (and helicity). However, in all instances when the current remains above the ejection threshold for t > 50 {micro}s, the n=l mode initiates and builds field, although with much reduced efficiency, and to a level which …
Date: February 28, 2002
Creator: Woodruff, S; McLean, H S & Stallard, B W
System: The UNT Digital Library
Molecular dynamics simulation of cascade damage in gold (open access)

Molecular dynamics simulation of cascade damage in gold

High-energy cascades have been simulated in gold using molecular dynamics with a modified embedded atom method potential. The results show that both vacancy and interstitial clusters form with high probability as a result of intracascade processes. The formation of clusters has been interpreted in terms of the high pressures generated in the core of the cascade during the early stages. We provide evidence that correlation between interstitial and vacancy clustering exists.
Date: February 1, 2000
Creator: Alonso, E.; Caturla, M. J.; Tang, M.; Huang, H. & Diaz de la Rubia, T
System: The UNT Digital Library
Very Fine Aerosols from the World Trade Center Collapse Piles: Anaerobic Incineration (open access)

Very Fine Aerosols from the World Trade Center Collapse Piles: Anaerobic Incineration

By September 14, three days after the initial World Trade Center collapse, efforts at fire suppression and heavy rainfall had extinguished the immediate surface fires. From then until roughly mid-December, the collapse piles continuously emitted an acrid smoke and fume in the smoldering phase of the event. Knowledge of the sources, nature, and concentration of these aerosols is important for evaluation and alleviation of the health effects on workers and nearby residents. In this paper, we build on our earlier work to ascribe these aerosols to similar processes that occur in urban incinerators. The simultaneous presence of finely powdered (circa 5 {micro}m) and highly basic (pH 11 to 12) cement dust and high levels of very fine (< 0.25 {micro}m) sulfuric acid fumes helps explain observed health impacts. The unprecedented levels of several metals in the very fine mode can be tied to liberation of those metals that are both present in elevated concentrations in the debris and have depressed volatility temperatures caused by the presence of organic materials and chlorine.
Date: February 27, 2004
Creator: Cahill, Thomas A.; Cliff, Steven S.; Shackelford, James; Meier, Michael; Dunlap, Michael; Perry, Kevin D. et al.
System: The UNT Digital Library
Architecture and High-Resolution Structure of Bacillus thuringiensis and Bacillus cereus Spore Coat Surfaces (open access)

Architecture and High-Resolution Structure of Bacillus thuringiensis and Bacillus cereus Spore Coat Surfaces

We have utilized atomic force microscopy (AFM) to visualize the native surface topology and ultrastructure of Bacillus thuringiensis and Bacillus cereus spores in water and in air. AFM was able to resolve the nanostructure of the exosporium and three distinctive classes of appendages. Removal of the exosporium exposed either a hexagonal honeycomb layer (B. thuringiensis) or a rodlet outer spore coat layer (B. cereus). Removal of the rodlet structure from B. cereus spores revealed an underlying honeycomb layer similar to that observed with B. thuringiensis spores. The periodicity of the rodlet structure on the outer spore coat of B. cereus was {approx}8 nm, and the length of the rodlets was limited to the cross-patched domain structure of this layer to {approx}200 nm. The lattice constant of the honeycomb structures was {approx}9 nm for both B. cereus and B. thuringiensis spores. Both honeycomb structures were composed of multiple, disoriented domains with distinct boundaries. Our results demonstrate that variations in storage and preparation procedures result in architectural changes in individual spore surfaces, which establish AFM as a useful tool for evaluation of preparation and processing ''fingerprints'' of bacterial spores. These results establish that high-resolution AFM has the capacity to reveal species-specific assembly …
Date: February 18, 2005
Creator: Plomp, Marco; Leighton, Terrance J.; Wheeler, Katherine E. & Malkin, Alexander J.
System: The UNT Digital Library
Diamond-Like Carbon Coatings as Encapsulants for Photovoltaic Solar Cells (open access)

Diamond-Like Carbon Coatings as Encapsulants for Photovoltaic Solar Cells

High-quality single-layer and bilayer diamond-like carbon (DLC) thin films are fabricated by two technologies, namely, ion-assisted plasma-enhanced deposition (IAPED) and electron cyclotron resonance (ECR) deposition. Deposition on various substrates, such as sapphires and solar cells, has been performed at low substrate temperatures (50 {approx} 80 C). The two deposition technologies allow good control over the growth conditions to produce DLC films with desired optical properties, thickness, and energy bandgap. The bilayer-structured DLC can be fabricated by using IAPED for the bottom layer followed by ECR for the top layer, or just by IAPED for both layers with different compositions. The DLC films have shown good spatial uniformity, density, microhardness, and adhesion strength. They exhibit excellent stability against attack by strong acids, prolonged damp-heat exposure at 85 C and 85% relative humidity, mechanical scratch, ultrasonication, and irradiation by ultraviolet (UV), protons, and electrons. When deposited on crystalline Si and GaAs solar cells in single-layer and/or bilayer structure, the DLC films not only serve as antireflection coating and protective encapsulant, but also improve the cell efficiencies.
Date: February 1, 2005
Creator: Pern, F. J.; Panosyan, Zh.; Gippius, A. A.; Kontsevoy, J. A.; Touryan, K.; Voskanyan, S. et al.
System: The UNT Digital Library
A Multiplex PCR-coupled Liquid Bead Array for the Simultaneous Detection of Four Biothreat Agents (open access)

A Multiplex PCR-coupled Liquid Bead Array for the Simultaneous Detection of Four Biothreat Agents

We have developed a 10-plexed PCR assay coupled to a 12-plexed liquid bead array to rapidly screen environmental samples for B. anthracis, Y. pestis, F. tularensis, and B. melitensis. Highly validated species -specific primer sets were used to simultaneously amplify multiple diagnostic regions unique to each individual pathogen. Resolution of the mix of amplified products was achieved by PCR product hybridization to corresponding probe sequences, attached to unique sets of fluorescent beads. The hybridized beads were processed through a flow cytometer, which detected presence and quantity of each PCR product. The assay was optimized to allow for maximum sensitivity in a multiplexed format. A high- throughput demonstration was performed where 384 simulated environmental samples were spiked with different amounts of B. thuringensis spores and pathogen DNA. The samples were robotically processed to extract DNA and arrayed for multiplexed PCR-liquid bead detection. The assay correctly identified the presence or absence of each pathogen and collected over 3,000 individual data points within a single 8-hour shift for approximately $1.20 per sample in a 10-plexed assay.
Date: February 4, 2004
Creator: Wilson, W. J.; Erler, A. M.; Nasarabadi, S. L.; Skowronski, E. W. & McCready, P. M.
System: The UNT Digital Library
XWRAPComposer: A Multi-Page Data Extraction Service for Bio-Computing Applications (open access)

XWRAPComposer: A Multi-Page Data Extraction Service for Bio-Computing Applications

This paper presents a service-oriented framework for the development of wrapper code generators, including the methodology of designing an effective wrapper program construction facility and a concrete implementation, called XWRAPComposer Three unique features distinguish XWRAPComposer from existing wrapper development approaches. First, XWRAPComposer is designed to enable multi-stage and multi-page data extraction. Second, XWRAPComposer is the only wrapper generation system that promotes the distinction of information extraction logic from query-answer control logic, allowing higher level of robustness against changes in the service provider's web site design or infrastructure. Third, XWRAPComposer provides a user-friendly plug-and-play interface, allowing seamless incorporation of external services and continuous changing service interfaces and data format.
Date: February 16, 2005
Creator: Liu, L.; Zhang, J.; Han, W.; Pu, C.; Caverlee, J.; Park, S. et al.
System: The UNT Digital Library