Pathway confirmation and flux analysis of central metabolicpathways in Desulfovibrio vulgaris Hildenborough using gaschromatography-mass spectrometry and fourier transform-ion cyclotronresonance mass spectrometry (open access)

Pathway confirmation and flux analysis of central metabolicpathways in Desulfovibrio vulgaris Hildenborough using gaschromatography-mass spectrometry and fourier transform-ion cyclotronresonance mass spectrometry

It has been proposed that during growth under anaerobic oroxygen-limited conditions Shewanella oneidensis MR-1 uses theserine-isocitrate lyase pathway common to many methylotrophic anaerobes,in which formaldehyde produced from pyruvate is condensed with glycine toform serine. The serine is then transformed through hydroxypyruvate andglycerate to enter central metabolism at phosphoglycerate. To examine itsuse of the serine-isocitrate lyase pathway under anaerobic conditions, wegrew S. oneidensis MR-1 on [1-13C]lactate as the sole carbon source witheither trimethylamine N-oxide (TMAO) or fumarate as an electron acceptor.Analysis of cellular metabolites indicates that a large percentage(>75 percent) of lactate was partially oxidized to either acetate orpyruvate. The 13C isotope distributions in amino acids and other keymetabolites indicate that, under anaerobic conditions, a complete serinepathway is not present, and lactate is oxidized via a highly reversibleserine degradation pathway. The labeling data also suggest significantactivity in the anaplerotic (malic enzyme and phosphoenolpyruvatecarboxylase) and glyoxylate shunt (isocitrate lyase and malate synthase)reactions. Although the tricarboxylic acid (TCA) cycle is often observedto be incomplete in many other anaerobes (absence of 2-oxoglutaratedehydrogenase activity), isotopic labeling supports the existence of acomplete TCA cycle in S. oneidensis MR-1 under TMAO reductioncondition.
Date: July 11, 2006
Creator: Tang, Yinjie; Pingitore, Francesco; Mukhopadhyay, Aindrila; Phan,Richard; Hazen, Terry C. & Keasling, Jay D.
Object Type: Article
System: The UNT Digital Library
FRAMES Software System: Linking to the Statistical Package R (open access)

FRAMES Software System: Linking to the Statistical Package R

This document provides requirements, design, data-file specifications, test plan, and Quality Assurance/Quality Control protocol for the linkage between the statistical package R and the Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES) Versions 1.x and 2.0. The requirements identify the attributes of the system. The design describes how the system will be structured to meet those requirements. The specification presents the specific modifications to FRAMES to meet the requirements and design. The test plan confirms that the basic functionality listed in the requirements (black box testing) actually functions as designed, and QA/QC confirms that the software meets the client’s needs.
Date: December 11, 2006
Creator: Castleton, Karl J.; Whelan, Gene & Hoopes, Bonnie L.
Object Type: Report
System: The UNT Digital Library
Material Evaluation Test Series 07, 08A, and 09A (open access)

Material Evaluation Test Series 07, 08A, and 09A

This research effort examines the post-detonation environmental, safety, health and operational aspects of experimental explosive tests with mercury. Specific experimental information is necessary for the evaluation of post-detonation by-products in comparison with those potentially resulting from mercury-bearing material accumulation in biomass accumulation areas, such as landfills, from batteries, electrical switches, thermometers, and fluorescent lights (Lindberg et al 2001). This will assist in determining appropriate abatement techniques for cleaning the work environment and environmental mitigation to determine waste stream components and risk assessment protocol. Determination of the by-products for personal protection equipment and personal exposure monitoring parameters are also part of this experimental work.
Date: April 11, 2006
Creator: Zalk, D.; Ingram, C.; Simmons, L.; Arganbright, R.; Koester, C. & Lyle, J.
Object Type: Report
System: The UNT Digital Library
Metals Analysis Results for the Structural Qualification Test Series (SQTS) 01 - 05. (open access)

Metals Analysis Results for the Structural Qualification Test Series (SQTS) 01 - 05.

Enclosed is the report summarizing the metals analysis results at the Contained Firing Facility (CFF), during SQTS 01 - 05. This metals analysis includes evaluation of a bulk dust and surface swipe sampling protocol during the testing series that obtained samples at 3 primary locations in the CFF chamber area. The sampling protocol for each of the bulk dust samples involves an assessment of the concentration for 20 different metals, the oxidation state of selected metals, a particle size selective analysis, and morphological information. In addition, surface swipes were taken during SQTS 05 on the equipment and personnel door frames to indicate the characteristics of airborne metals due to leakage past the gasket seals. The bulk dust metals analysis indicates a nearly complete conversion of the aluminum casing to an oxide form with an even split between spherical and non-spherical morphology. Size selective analysis shows 83% of the particulates are in the inhalable size range of less than 100 microns and 46% are in the respirable range of less than 10 microns. Combining metals analysis and leakage results indicate the potential for a problematic personal exposure to metals external to the chamber unless modifications are made. Please feel free to …
Date: April 11, 2006
Creator: Zalk, D
Object Type: Report
System: The UNT Digital Library
U.S. Aims for Zero-Energy: Support for PV on New Homes (open access)

U.S. Aims for Zero-Energy: Support for PV on New Homes

As a market segment for solar photovoltaic (PV) adoption, new homes have a number of attractive attributes. Homebuyers can easily roll the cost of the PV system into their mortgage and, with rebates or other financial incentives, potentially realize an immediate net positive cash flow from the investment. PV system performance can be optimized by taking roof orientation, shading, and other structural factors into account in the design of new homes. Building-integrated photovoltaics (BIPV), which are subject to fewer aesthetic concerns than traditional, rack-mounted systems, are well-suited to new construction applications. In large new residential developments, costs can be reduced through bulk purchases and scale economies in system design and installation. Finally, the ability to install PV as a standard feature in new developments - like common household appliances - creates an opportunity to circumvent the high transaction costs and other barriers typically confronted when each individual homeowner must make a distinct PV purchase decision.
Date: May 11, 2006
Creator: Barbose, Galen; Wiser, Ryan & Bolinger, Mark
Object Type: Article
System: The UNT Digital Library
On the electronic configuration in Pu: spectroscopy and theory (open access)

On the electronic configuration in Pu: spectroscopy and theory

Photoelectron spectroscopy, synchrotron-radiation-based x-ray absorption, electron energy-loss spectroscopy, and density-functional calculations within the mixed-level and magnetic models, together with canonical band theory have been used to study the electron configuration in Pu. These methods suggest a 5f{sup n} configuration for Pu of 5 {le} n < 6, with n {ne} 6, contrary to what has recently been suggested in several publications. We show that the n = 6 picture is inconsistent with the usual interpretation of photoemission and x-ray absorption spectra. Instead, these spectra support the traditional conjecture of a 5f{sup 5} configuration in Pu as is obtained by density-functional theory. We further argue, based on 5f-band filling, that an n = 6 hypothesis is incompatible with the position of Pu in the actinide series and its monoclinic ground-state phase.
Date: October 11, 2006
Creator: Tobin, J G; Soderlind, P; Landa, A; Moore, K T; Schwartz, A J; Chung, B W et al.
Object Type: Article
System: The UNT Digital Library
Accurate Method for Forward and Reverse Bias Curve Fitting of TPV I-V Data (open access)

Accurate Method for Forward and Reverse Bias Curve Fitting of TPV I-V Data

None
Date: May 11, 2006
Creator: Danielson, L. & Depoy, D.
Object Type: Report
System: The UNT Digital Library
Study of Bunch Instabilities By the Nonlinear Vlasov-Fokker-Planck Equation (open access)

Study of Bunch Instabilities By the Nonlinear Vlasov-Fokker-Planck Equation

Instabilities of the bunch form in storage rings may be induced through the wake field arising from corrugations in the vacuum chamber, or from the wake and precursor fields due to coherent synchrotron radiation (CSR). For over forty years the linearized Vlasov equation has been applied to calculate the threshold in current for an instability, and the initial growth rate. Increasing interest in nonlinear aspects of the motion has led to numerical solutions of the nonlinear Vlasov equation, augmented with Fokker-Planck terms to describe incoherent synchrotron radiation in the case of electron storage rings. This opens the door to much deeper studies of coherent instabilities, revealing a rich variety of nonlinear phenomena. Recent work on this topic by the author and collaborators is reviewed.
Date: July 11, 2006
Creator: Warnock, Robert L.
Object Type: Article
System: The UNT Digital Library
Transverse momentum and centrality dependence of high-ptnon-photonic electron suppression in Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV (open access)

Transverse momentum and centrality dependence of high-ptnon-photonic electron suppression in Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV

The STAR collaboration at RHIC reports measurements of theinclusive yield of non-photonic electrons, which arise dominantly fromsemi-leptonic decays of heavy flavor mesons, over a broad range oftransverse momenta (1.2<pt<10 gevc) in pp, dAu, and AuAucollisions at sqrt sNN = 200 GeV. The non-photonic electron yieldexhibits unexpectedly large suppression in central AuAu collisions athigh pt, suggesting substantial heavy quark energy loss at RHIC. Thecentrality and \pt dependences of the suppression provide constraints ontheoretical models of suppression.
Date: July 11, 2006
Creator: Abelev, B. I.; Adams, J.; Aggarwal, M. M.; Ahammed, Z.; Amonett, J.; Anderson, B. D. et al.
Object Type: Article
System: The UNT Digital Library
Supersymmetry with Small mu: Connections between Naturalness, DarkMatter, and (Possibly) Flavor (open access)

Supersymmetry with Small mu: Connections between Naturalness, DarkMatter, and (Possibly) Flavor

Weak scale supersymmetric theories often suffer from several naturalness problems: the problems of reproducing the correct scale for electroweak symmetry breaking, the correct abundance for dark matter, and small rates for flavor violating processes. We argue that the first two problems point to particular regions of parameter space in models with weak scale supersymmetry: those with a small {mu} term. This has an interesting implication on direct dark matter detection experiments. We find that, if the signs of the three gaugino mass parameters are all equal, we can obtain a solid lower bound on the spin-independent neutralino-nucleon cross section, {sigma}{sub SI}. In the case that the gaugino masses satisfy the unified mass relations, we obtain {sigma}{sub SI} {approx}&gt; 4 x 10{sup -46} cm{sup 2} (1 x 10{sup -46} cm{sup 2}) for fine-tuning in electroweak symmetry breaking no worse than 10% (5%). We also discuss a possibility that the three problems listed above are all connected to the hierarchy of fermion masses. This occurs if supersymmetry breaking and electroweak symmetry breaking (the Higgs fields) are coupled to matter fields with similar hierarchical structures. The discovery of {mu} {yields} e transition processes in near future experiments is predicted in such a framework.
Date: June 11, 2006
Creator: Kitano, Ryuichiro Kitano & Nomura, Yasunori
Object Type: Article
System: The UNT Digital Library
Zinc Single Crystal Deformation Experiments using a "6 Degrees of Freedom" Apparatus (open access)

Zinc Single Crystal Deformation Experiments using a "6 Degrees of Freedom" Apparatus

A new experimental technique to study crystallographic slip system activity in metallic single crystals deformed under a condition of uniaxial stress is applied to study the behavior of Zn single crystals. The experimental apparatus allows essentially unconstrained shape change of inherently anisotropic materials under a condition of uniaxial stress by allowing 3 translational and 3 rotational degrees of freedom during compression; hence we have named the experiment 6 degrees of freedom (6DOF). The experiments also utilize a 3-D digital image correlation system to measure full-field displacement fields, which are used to calculate strain and make direct observations of slip system activity. We show that the experimental results associated with a pristine zinc single crystal are precisely consistent with the theoretical predicted shape change (sample distortion) assuming that the most favored slip system on the basal plane is the only one that is active. Another experiment was performed on a processed and annealed Zn single crystal to investigate slip that is inconsistent with the critical resolved shear stress (CRSS) theory. These experiments on zinc illustrate the ability of the 6DOF experiment, together with image correlation (IC) data, to measure slip system activity with a high degree of fidelity.
Date: May 11, 2006
Creator: Lassila, D. H.; LeBlanc, M. M. & Florando, J. N.
Object Type: Article
System: The UNT Digital Library
Half-life of 14O (open access)

Half-life of 14O

We have measured the half-life of 14O, a superallowed (0+\rightarrow 0+) \beta decay isotope. The 14O was produced by the12C(3He,n)14O reaction using a carbon aerogel target. A low-energy ionbeam of 14O was mass separated and implanted in a thin beryllium foil.The beta particles were counted with plastic scintillator detectors. Wefind \tau 1/2 = 70.696 +- 0.037\sigma. This result is 2.0\sigma higherthan an average value from six earlier experiments, but agrees moreclosely with the most recent previous measurment.
Date: January 11, 2006
Creator: Burke, Jason T.; Vetter, Paul A.; Freedman, Stuart J.; Fujikawa,Brian K. & Winter, Wesley T.
Object Type: Article
System: The UNT Digital Library
Real-Time Quadrupole Mass Spectrometer Analysis of Gas in Borehole Fluid Samples Acquired Using the U-Tube Sampling Methodology (open access)

Real-Time Quadrupole Mass Spectrometer Analysis of Gas in Borehole Fluid Samples Acquired Using the U-Tube Sampling Methodology

Sampling of fluids in deep boreholes is challenging becauseof the necessity to minimize external contamination and maintain sampleintegrity during recovery. The U-tube sampling methodology was developedto collect large volume, multiphase samples at in situ pressures. As apermanent or semi-permanent installation, the U-tube can be used forrapidly acquiring multiple samples or it may be installed for long-termmonitoring applications. The U-tube was first deployed in Liberty County,TX to monitor crosswell CO2 injection as part of the Frio CO2sequestration experiment. Analysis of gases (dissolved or separate phase)was performed in the field using a quadrupole mass spectrometer, whichserved as the basis for determining the arrival of the CO2 plume. Thepresence of oxygen and argon in elevated concentrations, along withreduced methane concentration, indicate sample alteration caused by theintroduction of surface fluids during borehole completion. Despiteproducing the well to eliminate non-native fluids, measurementsdemonstrate that contamination persists until the immiscible CO2injection swept formation fluid into the observationwellbore.
Date: January 11, 2006
Creator: Freifeld, Barry M. & Trautz, Robert C.
Object Type: Article
System: The UNT Digital Library
Rhamm-/- mice are defective in skin wound repair due to aberrantERK1,2 signaling in fibroblast migration (open access)

Rhamm-/- mice are defective in skin wound repair due to aberrantERK1,2 signaling in fibroblast migration

None
Date: September 11, 2006
Creator: Tolg, Cornelia; Hamilton, Sara R.; Nakrieko, Kari-Anne; Walton, Paul; McCarthy, James B.; Bissell, Mina J. et al.
Object Type: Article
System: The UNT Digital Library
IFE Final Optics and Chamber Dynamics Modeling and Experiments Final Technical Report (open access)

IFE Final Optics and Chamber Dynamics Modeling and Experiments Final Technical Report

Our OFES-sponsored research on IFE technology originally focused on studies of grazing-incidence metal mirrors (GIMM's). After the addition of GIMM research to the High Average Power Laser (HAPL) program, our OFES-sponsored research evolved to include laser propagation studies, surface material evolution in IFE wetted-wall chambers, and magnetic intervention. In 2003, the OFES IFE Technology program was terminated. We continued to expend resources on a no-cost extension in order to complete student research projects in an orderly way and to help us explore new research directions. Those explorations led to funding in the field of extreme ultraviolet lithography, which shares many issues in common with inertial fusion chambers, and the field of radiative properties of laser-produced plasma.
Date: January 11, 2006
Creator: Najmabadi, F. & Tillack, M. S.
Object Type: Report
System: The UNT Digital Library
High-Performance Corrosion-Resistant Iron-Based Amorphous Metals: The Effects of Composition, Structure and Environment on Corrosion Resistance (open access)

High-Performance Corrosion-Resistant Iron-Based Amorphous Metals: The Effects of Composition, Structure and Environment on Corrosion Resistance

New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative thermal phase stability, microstructure, mechanical properties, damage tolerance, and corrosion resistance. Some alloy additions are known to promote glass formation and to lower the critical cooling rate [F. Guo, S. J. Poon, Applied Physics Letters, 83 (13) 2575-2577, 2003]. Other elements are known to enhance the corrosion resistance of conventional stainless steels and nickel-based alloys [A. I. Asphahani, Materials Performance, Vol. 19, No. 12, pp. 33-43, 1980] and have been found to provide similar benefits to iron-based amorphous metals. Many of these materials can be cast as relatively thick ingots, or applied as coatings with advanced thermal spray technology. A wide variety of thermal spray processes have been developed by industry, and can be used to apply these new materials as coatings. Any of these can be used for the deposition of the formulations discussed here, with varying degrees of residual porosity and crystalline structure. Thick protective coatings have now been made that are fully dense and completely amorphous in the as-sprayed condition. An overview of the High-Performance Corrosion Resistant Materials (HPCRM) Project will be given, with particular …
Date: April 11, 2006
Creator: Farmer, J; Choi, J S; Haslam, J; Lian, T; Day, S; Yang, N et al.
Object Type: Article
System: The UNT Digital Library
2006 U.S. Department of Energy Strategic Plan: Discovering the Solutions to Power and Secure America’s Future (open access)

2006 U.S. Department of Energy Strategic Plan: Discovering the Solutions to Power and Secure America’s Future

The Department of Energy Organization Act, which created DOE, was enacted in 1977 and DOE officially came into existence in October of that year. That law brought together for the first time, not only most of the government’s energy programs, but also science and technology programs and defense responsibilities that included the design, construction, and testing of nuclear weapons. Over its history, DOE has shifted its emphasis and focus as the energy and security needs of the Nation have changed. Today, DOE stands at the forefront of helping the Nation meet our energy, scientific, environmental, and national security goals. These include developing and deploying new energy technologies, reducing our dependence on foreign energy sources, protecting our nuclear weapons stockpile, and ensuring that America remains competitive in the global marketplace. To help achieve these goals, President Bush has launched two key initiatives: the American Competitiveness Initiative (ACI) and the Advanced Energy Initiative (AEI). The President launched these initiatives recognizing that science, technology, and engineering hold the answers to many of the critical challenges our world faces. These new initiatives to spur scientific innovation and technology development expand DOE’s continuing support for the competitive energy markets, both domestically and internationally, and of …
Date: October 11, 2006
Creator: unknown
Object Type: Text
System: The UNT Digital Library
Dark Energy in the Dark Ages (open access)

Dark Energy in the Dark Ages

Non-negligible dark energy density at high redshifts would indicate dark energy physics distinct from a cosmological constant or&quot;reasonable'&quot; canonical scalar fields. Such dark energy can be constrained tightly through investigation of the growth of structure, with limits of&lt;~;;2percent of total energy density at z&gt;&gt; 1 for many models. Intermediate dark energy can have effects distinct from its energy density; the dark ages acceleration can be constrained to last less than 5percent of a Hubble e-fold time, exacerbating the coincidence problem. Both the total linear growth, or equivalently sigma 8, and the shape and evolution of the nonlinear mass power spectrum for z&lt;2 (using the Linder-White nonlinear mapping prescription) provide important windows. Probes of growth, such as weak gravitational lensing, can interact with supernovae and CMB distance measurements to scan dark energy behavior over the entire range z=0-1100.
Date: April 11, 2006
Creator: Linder, Eric V.
Object Type: Article
System: The UNT Digital Library
Development of a Quantum-Limited Microwave Amplifier using a dc Superconducting Quantum Interference Device (dc-SQUID) (open access)

Development of a Quantum-Limited Microwave Amplifier using a dc Superconducting Quantum Interference Device (dc-SQUID)

This report summarizes the research performed on the LDRD project 02-ERD-071 to develop a quantum-limited microwave amplifier based on a dc Superconducting Quantum Interference Device (dc-SQUID). This project began in June 2002 and concluded in May 2005. This project produced the lowest noise temperature amplifiers ever produced, both in absolute terms and in relation to the Standard Quantum Limit. Being an order of magnitude lower in noise than the best HFET devices available, they are of great interest to a number of groups. Potential applications are numerous, from dark-matter searches to national security applications in Quantum Information Processing. Collaborations started during this project are continuing with the goal of single-spin detection using the rf-SET. Publications are forthcoming covering both the experimental results and the theoretical modeling. The most important publication with the noise temperature results will appear after the low frequency follow-up experiment. The other publications in production cover the input impedance measurements and the resulting transmission line models.
Date: December 11, 2006
Creator: Kinion, D.
Object Type: Report
System: The UNT Digital Library
FINAL REPORT - Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments (open access)

FINAL REPORT - Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments

A magnetically coupled microbalance system has been used to measure adsorption and desorption isotherms and rates of desorption for carbon tetrachloride on dry prepared porous silica particles with narrow pore size distributions in the mesoporous range. Pore size distributions estimated from the carbon tetrachloride isotherms were found to be in close agreement with those determined using standard low temperature nitrogen adsorption. Three different types of particles were studied, with average pore diameters of 2.7 nm, 4.6 nm, and 5.9 nm. Prior to desorption rate studies, evacuated particulate samples were charged with volatile organic vapor at pressures sufficient to fill all mesopores with condensed fluid. Desorption rates into dry flowing helium were determined at 25 °C and atmospheric pressure, using the microbalance system combined with chromatographic analysis of the exit helium stream. Initial rates were found to decrease significantly, as mass adsorbed decreased. This residual mass was desorbing at such a low rate, that it can be considered a migration resistant fraction of the original mass adsorbed. Attempts to remove this residual mass at higher temperatures were partially successful; however, differences between the microbalance and gas chromatograph responses leave open uncertainty about whether the residual mass was pure carbon tetrachloride. To …
Date: December 11, 2006
Creator: Miller, Reid C. & Peyton, Brent M.
Object Type: Report
System: The UNT Digital Library
SULFATE RETENTION IN HIGH LEVEL WASTE SLUDGE BATCH 4 GLASSES: A PRELIMINARY ASSESSMENT (open access)

SULFATE RETENTION IN HIGH LEVEL WASTE SLUDGE BATCH 4 GLASSES: A PRELIMINARY ASSESSMENT

Early projections of the Sludge Batch 4 (SB4) composition predicted relatively high concentrations of alumina (Al{sub 2}O{sub 3}, 23.5 wt%) and sulfate (SO{sub 4}{sup 2-}, 1.2 wt%) in the sludge. A high concentration of Al{sub 2}O{sub 3} in the sludge, combined with Na{sub 2}O additions in the frit, raises the potential for nepheline crystallization in the glass. However, strategic frit development efforts at the Savannah River National Laboratory (SRNL) have shown that frits containing a relatively high concentration of B{sub 2}O{sub 3} can both suppress nepheline crystallization and improve melt rates. A high sulfate concentration is a concern to the DWPF as it can lead to the formation of sulfate inclusions in the glass and/or the formation of a molten, sulfate-rich phase atop the melt pool. To avoid these issues, a sulfate concentration limit of 0.4 wt% SO{sub 4}{sup 2-} in glass was originally set in the Product Composition Control System (PCCS) used at DWPF. It was later shown that this limit could be increased to 0.6 wt% SO{sub 4}{sup 2-} in glass for the Frit 418, Sludge Batch 3 (SB3) system.
Date: December 11, 2006
Creator: Fox, K; Tommy Edwards, T & David Peeler, D
Object Type: Report
System: The UNT Digital Library
The Self Attenuation Correction for Holdup Measurements, a Historical Perspective (open access)

The Self Attenuation Correction for Holdup Measurements, a Historical Perspective

Self attenuation has historically caused both conceptual as well as measurement problems. The purpose of this paper is to eliminate some of the historical confusion by reviewing the mathematical basis and by comparing several methods of correcting for self attenuation focusing on transmission as a central concept.
Date: July 11, 2006
Creator: Oberer, R. B.; Gunn, C. A. & Chiang, L. G.
Object Type: Report
System: The UNT Digital Library
From Question Answering to Visual Exploration (open access)

From Question Answering to Visual Exploration

Research in Question Answering has focused on the quality of information retrieval or extraction using the metrics of precision and recall to judge success; these metrics drive toward finding the specific best answer(s) and are best supportive of a lookup type of search. These do not address the opportunity that users? natural language questions present for exploratory interactions. In this paper, we present an integrated Question Answering environment that combines a visual analytics tool for unstructured text and a state-of-the-art query expansion tool designed to compliment the cognitive processes associated with an information analysts work flow. Analysts are seldom looking for factoid answers to simple questions; their information needs are much more complex in that they may be interested in patterns of answers over time, conflicting information, and even related non-answer data may be critical to learning about a problem or reaching prudent conclusions. In our visual analytics tool, questions result in a comprehensive answer space that allows users to explore the variety within the answers and spot related information in the rest of the data. The exploratory nature of the dialog between the user and this system requires tailored evaluation methods that better address the evolving user goals and …
Date: August 11, 2006
Creator: McColgin, Dave W.; Gregory, Michelle L.; Hetzler, Elizabeth G. & Turner, Alan E.
Object Type: Article
System: The UNT Digital Library
The Dark Matter Halos of Massive, Relaxed Galaxy Clusters Observed With Chandra (open access)

The Dark Matter Halos of Massive, Relaxed Galaxy Clusters Observed With Chandra

We use the Chandra X-ray Observatory to study the dark matter halos of 34 massive, dynamically relaxed galaxy clusters, spanning the redshift range 0.06 &lt; z &lt; 0.7. The observed dark matter and total mass (dark-plus-luminous matter) profiles can be approximated by the Navarro Frenk & White (hereafter NFW) model for cold dark matter (CDM) halos; for {approx} 80 percent of the clusters, the NFW model provides a statistically acceptable fit. In contrast, the singular isothermal sphere model can, in almost every case, be completely ruled out. We observe a well-defined mass-concentration relation for the clusters with a normalization and intrinsic scatter in good agreement with the predictions from simulations. The slope of the mass-concentration relation, c {infinity} M{sub vir}{sup a}/(1 + z){sup b} with a = -0.41 {+-} 0.11 at 95 percent confidence, is steeper than the value a {approx} -0.1 predicted by CDM simulations for lower mass halos. With the slope a included as a free fit parameter, the redshift evolution of the concentration parameter, b = 0.54 {+-} 0.47 at 95 percent confidence, is also slower than, but marginally consistent with, the same simulations (b {approx} 1). Fixing a {approx} -0.1 leads to an apparent evolution that …
Date: October 11, 2006
Creator: Schmidt, Robert W.; /Heidelberg, Astron. Rechen Inst.; Allen, S.W. & /KIPAC, Menlo Park
Object Type: Article
System: The UNT Digital Library