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Opacity of stellar matter

Description: New efforts to calculate opacity have produced significant improvements in the quality of stellar models. The most dramatic effect has been large opacity enhancements for stars subject to large amplitude pulsations. Significant improvement in helioseismic modeling has also been obtained. A description and comparisons of the new opacity efforts are give
Date: September 17, 1998
Creator: Rogers, F J
Partner: UNT Libraries Government Documents Department

Alpha Dithering to Correct Low-Opacity 8 Bit Compositing Errors

Description: This paper describes and analyzes a dithering technique for accurately specifying small values of opacity ({alpha}) that would normally not be possible because of the limited number of bits available in the alpha channel of graphics hardware. This dithering technique addresses problems related to compositing numerous low-opacity semitransparent polygons to create volumetric effects with graphics hardware. The paper also describes the causes and a possible solution to artifacts that arise from parallel or distributed volume rendering using bricking on multiple GPU's.
Date: March 31, 2003
Creator: Williams, P L; Frank, R J & LaMar, E C
Partner: UNT Libraries Government Documents Department

ProTec Tear-Offs: A Preliminary Assessment

Description: The Savannah River National Laboratory (SRNL) has conducted a series of ''scoping'' tests (referred to as Phase 1) to assess the potential use of a Mylar{reg_sign} tear-off system as a primary or secondary protective barrier to minimize acid etching (''frosting''), accidental scratching, and/or radiation damage for shielded cells windows. Conceptually, thin, multi-layered sheets of Mylar (referred to as a ''tear-off'' system) could be directly applied to the Lexan{reg_sign} sheet or glovebox/hood sash window to serve as a secondary (or primary) barrier. Upon degradation of visual clarity due to accidental scratching, spills/splatters, and/or radiation damage, the outer layer (or sheet) of Mylar could be removed ''refreshing'' or restoring the view. Due to the multi-layer aspect, the remaining Mylar layers would provide continued protection for the window from potential reoccurrences (which could be immediate or after some extended time period). Although the concept of using a tear-off system as a protective barrier was conceptually enticing, potential technical issues were identified and addressed as part of this Phase 1 feasibility study. These included resistance to: (1) acid(s) (concentrated (28.9 M) HF, concentrated (15.9M) HNO{sub 3}, 6M HCl, and 0.6M H{sub 3}BO{sub 3}), (2) base (a simulated sludge with pH of 12.9), (3) gamma radiation (cumulative dose of {approx}200,000 rad), and (4) scratch resistance (simulating accidental scratching with the manipulators). Not only can these four factors play a significant role in determining the visual clarity of the integrated system, they can also contribute to the mechanical integrity issues which could dictate the ability to remove the outer layer when visual clarity has degraded. The results of the Phase 1 study clearly indicate that the Mylar tear-off concept (as a primary or secondary protective barrier) is a potential technical solution to prevent or retard excessive damage that would result from acid etching, base damage (as ...
Date: September 1, 2005
Creator: Peeler, D
Partner: UNT Libraries Government Documents Department

Smoothed Emission for IMC

Description: Here is a review of the current way we handle source photons in Implicit Monte Carlo (IMC). A source photon is created with a randomly sampled position x{sub p} in the zone, a direction {Omega}{sub p}, a frequency v{sub p} sampled from the appropriate distribution, and a time t{sub p} uniformly sampled from [t{sup n}, t{sup n+1}]. The source photons each have an energy E{sub p}. The sum of E{sub p} over all of the photons equals the energy of the source for that time step. In the case of thermal emission in a zone with Volume V, they would have {Sigma}{sub p=1}{sup N} E{sub p} = {sigma} {sub p}acT{sup 4}V{Delta}t, where N is the number of thermal source photons for that time step, and {sigma}{sub p} is the Planck mean opacity. Census photons do not differ from source photons in any way, except that they all start the time step with t{sub p} = t{sup n}. Then they advance each photon until it reaches the end of the time step. When they are done with all of the photons, they update the matter temperature using the difference between the emitted and absorbed energy, and proceed to the next time step.
Date: January 24, 2011
Creator: Gentile, N A
Partner: UNT Libraries Government Documents Department

New computational method for non-LTE, the linear response matrix

Description: We investigate non-local thermodynamic equilibrium atomic kinetics using nonequilibrium thermodynamics and linear response theory. This approach gives a rigorous general framework for exploiting results from non-LTE kinetic calculations and offers a practical data-tabulation scheme suitable for use in plasma simulation codes. We describe how this method has been implemented to supply a fast and accurate non-LTE option in Lasnex.
Date: October 1, 1998
Creator: Fournier, K. B.; Graziani, F. R.; Harte, J. A.; Libby, S. B.; More, R. M.; Rathkopf, J. et al.
Partner: UNT Libraries Government Documents Department

Opacity measurements: extending the range and filling in the gaps

Description: A series of experiments to explore Ge opacity at temperatures where the M-shell is almost filled will be discussed. Data are obtained at lower temperatures than previously explored and allow us to investigate the role of atomic structure calculations and their impact on opacity scalings. The experiment uses the Nova laser to irradiate a gold hohlraum within which a CH-tamped Ge sample is radiatively heated. A Nd backlight probes the sample 2 ns later to produce Ge spectral absorption features in the 1.2-1.5 keV energy range. Temperature is monitored by the use of an Al dopant and density is monitored by measuring the edge-on expansion of the sample. Temporal resolution of about 200 ps is obtained by using a short pulse backlight. Calculations in this photon energy region show significant changes in the spectral features.
Date: March 17, 1997
Creator: Back, C.A.; Perry, T.S.; Bach, D.R.; Wilson, G.; Iglesias, G.A.; Laden, O.L. et al.
Partner: UNT Libraries Government Documents Department

Evaluation of Aerogel Materials for High-Temperature Batteries

Description: Siiica aerogels have 1/3 the thermal conductivity of the best commercial composite insulations, or ~13 mW/m-K at 25°C. However, aerogels are transparent in the near IR region of 4-7 µm, which is where the radiation peak from a thermal-battery stack occurs. Titania and carbon- black powders were examined as thermal opacifiers, to reduce radiation at temperatures between 300°C and 600°C, which spans the range of operating temperature for most thermal batteries. The effectiveness of the various opacifiers depended on the loading, with the best overall results being obtained using aerogels filled with carbon black. Fabrication and strength issues still remain, however.
Date: May 4, 1999
Creator: Ashley, Carol S.; Guidotti, Ronald A.; Reed, Scott T. & Reinhardt, Frederick W.
Partner: UNT Libraries Government Documents Department


Description: The radiation transport and linearized thermal energy equations have been analyzed to find the temporal dependence of the component modes in a radiation/thermal front. The fully resolved spectral variation of the opacity as a function of energy, as well as the exact time and angular dependence, is treated in this work. As we are able to study arbitrarily complicated opacity spectra, we stress the importance of the new results as a check on the effect of using opacity averages.
Date: December 1, 2000
Creator: AUER, L. & LOWRIE, R.
Partner: UNT Libraries Government Documents Department

The Effects of Color Concentrate in Polyolefins.

Description: Throughout history consumer products were generally manufactured from wood and metal. They either had to hold their natural color or become subject to painting. When plastics entered the industry, it was recognized for its ease of shaping, re-usability, physical properties and its low cost. One of plastics' greatest benefits is its ability to hold a given color from within allowing it to avoid use of paint. This paper will give a brief overview on the effects of pigments when incorporated in a polyolefin. It will provide a classification of the main types of pigments and how each effect the properties of the product through: crystallization, weatherability, opacity, coloristic values and of course viscosity.
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Date: December 2001
Creator: Flora, Paul
Partner: UNT Libraries

Laboratory astrophysics

Description: We propose an experiment to test opacity models for stellar atmospheres. Particularly important is to perform experiments at very low density and temperature where line shape treatments give large differences in Rosseland mean opacities for astrophysical mixtures, and to test the range of validity for the unresolved transition array treatments. Experimental requirements are ultra high spectral resolution combined with large homogenous plasma sources lasting tens of nanoseconds, and with Planckian radiation fields. These requirements dovetail nicely with emerging pulsed power capabilities. We propose a high resolution measurement of the frequency dependent opacity, for ultra low density iron plasmas in radiatively driven equilibrium plasmas.
Date: May 1, 1995
Creator: Springer, P.T.; Goldstein, W.H.; Iglesias, C.A.; Wilson, B.G.; Rogers, F.J. & Stewart, R.E.
Partner: UNT Libraries Government Documents Department

Possible origin of RHIC R{sub out}/R{sub sid} HBT results

Description: The effects of opacity of the nuclei together with a blackbody type of emission along the system history are considered as a means to explain the ratio R{sub out}=R{sub sid} observed by STAR and PHENIX collaborations at RHIC. Within our model, no flow is required to explain the data trend of this ratio for large surface emissivities.
Date: September 30, 2002
Creator: Padula, Sandra S.
Partner: UNT Libraries Government Documents Department

Low-temperature fabrication of transparent silicon nitride

Description: Feasibility of producing nano-phase Si{sub 3}N{sub 4} with improved properties, and ultrafine-grained nano-phase transparent Si{sub 3}N{sub 4} by working with amorphous nano-size powders without the use of sintering aids was investigated. The approach uses cryogenic compaction of nano-size particles under liquid nitrogen followed by pressureless sintering.
Date: May 31, 1994
Creator: Chen, Wei; Malghan, S. G.; Danforth, S. C. & Pechenik, A.
Partner: UNT Libraries Government Documents Department

Measurement of the absolute hohlraum wall albedo under ignition foot drive conditions

Description: We present the first measurements of the absolute albedos of hohlraums made from gold or from high-Z mixtures. The measurements are performed over the range of radiation temperatures (70-100 eV) expected during the foot of an indirect-drive temporally-shaped ignition laser pulse, where accurate knowledge of the wall albedo (i.e. soft x-ray wall re-emission) is most critical for determining capsule radiation symmetry. We find that the gold albedo agrees well with calculations using the super transition array opacity model, potentially providing additional margin for ICF ignition.
Date: November 25, 2003
Creator: Suter, L J; Wallace, R J; Hammel, B A; Weber, F A; Landen, O L; Campbell, K M et al.
Partner: UNT Libraries Government Documents Department

Interactions of Ionic Liquids with Uranium and its Bioreduction

Description: We investigated the influence of ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM]{sup +}[PF{sub 6}]{sup -}, N-ethylpyridinium trifluoroacetate [EtPy]{sup +}[CF{sub 3}COO]{sup -} and N-ethylpyridinium tetrafluoroborate [Et-Py]{sup +}[BF{sub 4}]{sup -} on uranium reduction by Clostridium sp. under anaerobic conditions. Potentiometric titration, UV-vis spectrophotometry, LC-MS and EXAFS analyses showed monodentate complexation between uranyl and BF{sub 4}{sup -} PF{sub 6}{sup -}; and bidentate complexation with CF{sub 3}COO{sup -}. Ionic liquids affected the growth of Clostridium sp. as evidenced by decrease in optical density, changes in pH, gas production, and the extent of U(VI) reduction and precipitation of U(IV) from solution. Reduction of U(VI) to U(IV) was observed in the presence of [EtPy][BF{sub 4}] and [BMIM][PF{sub 6}] but not with [EtPy][CF{sub 3}COO].
Date: September 18, 2012
Creator: Zhang, C. & Francis, A.
Partner: UNT Libraries Government Documents Department

Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b

Description: Using the integral field spectrograph OSIRIS, on the Keck II telescope, broad near-infrared H and K-band spectra of the young exoplanet HR8799b have been obtained. In addition, six new narrow-band photometric measurements have been taken across the H and K bands. These data are combined with previously published photometry for an analysis of the planet's atmospheric properties. Thick photospheric dust cloud opacity is invoked to explain the planet's red near-IR colors and relatively smooth near-IR spectrum. Strong water absorption is detected, indicating a Hydrogen-rich atmosphere. Only weak CH{sub 4} absorption is detected at K band, indicating efficient vertical mixing and a disequilibrium CO/CH{sub 4} ratio at photospheric depths. The H-band spectrum has a distinct triangular shape consistent with low surface gravity. New giant planet atmosphere models are compared to these data with best fitting bulk parameters, T{sub eff} = 1100K {+-} 100 and log(g) = 3.5 {+-} 0.5 (for solar composition). Given the observed luminosity (log L{sub obs}/L{sub {circle_dot}} {approx} -5.1), these values correspond to a radius of 0.75 R{sub Jup{sub 0.12}{sup +0.17}} and mass {approx} 0.72 M{sub Jup{sub -0.6}{sup +2.6}} - strikingly inconsistent with interior/evolution models. Enhanced metallicity (up to {approx} 10 x that of the Sun) along with thick clouds and non-equilibrium chemistry are likely required to reproduce the complete ensemble of spectroscopic and photometric data and the low effective temperatures (< 1000K) required by the evolution models.
Date: March 21, 2011
Creator: Barman, T. S.; Macintosh, B. A.; Konopacky, Q. M. & Marois, C.
Partner: UNT Libraries Government Documents Department

Intense ion beams as a tool for opacity measurements in warm dense matter

Description: Opacity measurements in warm dense matter (WDM) provide a valuable benchmark for the diverging theoretical models in this regime. Heating of thin foils with intense heavy-ion beams allows one to create isolated samples of warm dense matter suitable for experimental determination of frequency-dependent opacities. A prerequisite for the measurements is the isothermal expansion of the heated foil. Hydrodynamic simulations predict that this condition is fulfilled. The analysis shows that existing ion-beam accelerators are capable to contribute to this field of research.
Date: January 1, 2009
Creator: Abdallah, Joseph; Tauschwiz, An; Jacoby, J; Maruhn, J A; Novikov, V G; Tauschwitz, A et al.
Partner: UNT Libraries Government Documents Department

Physiomics Array: A Platform for Genome Research and Cultivation of Difficult-to-Cultivate Microorganisms Final Technical Report

Description: A scalable array technology for parametric control of high-throughput cell cultivations is demonstrated. The technology makes use of commercial printed circuit board (PCB) technology, integrated circuit sensors, and an electrochemical gas generation system. We present results for an array of eight 250 μl microbioreactors. Each bioreactor contains an independently addressable suite that provides closed-loop temperature control, generates feed gas electrochemically, and continuously monitors optical density. The PCB technology allows for the assembly of additional off-the-shelf components into the microbioreactor array; we demonstrate the use of a commercial ISFET chip to continuously monitor culture pH. The electrochemical dosing system provides a powerful paradigm for reproducible gas delivery to high-density arrays of microreactors. We have scaled the technology to a standard 96-well format and have constructed a system that could be easily assembled.
Date: July 10, 2006
Creator: Keasling, Jay D.
Partner: UNT Libraries Government Documents Department

Formaldehyde Absorption toward W51

Description: We have measured formaldehyde (H{sub 2}CO) absorption toward the HII region complex W51A (G49.5-0.4) in the 6 cm and 2 cm wavelength rotational transitions with angular resolution of approximately 4 inch. The continuum HII region shows a large, previously undetected shell structure 5.5 pc along the major axis. We observe no H{sub 2}CO emission in regions of low continuum intensity. The absorption, converted to optical depth, shows a higher degree of clumping than previous maps at lower resolution. The good S/N of the maps allows accurate estimation of the complicated line profiles, showing some of the absorbing clouds to be quite patchy. We list the properties of the opacity spectra for a number of positions both in the clumps and in the more diffuse regions of the absorbing clouds, and derive column densities for the 1{sub 11} and 2{sub 12} rotational levels of ortho-formaldehyde.
Date: April 1, 1988
Creator: Kogut, A.; Smoot, G.F.; Bennett, C.L. & Petuchowski, S.J.
Partner: UNT Libraries Government Documents Department

A collisional-radiative average atom model for hot plasmas

Description: A collisional-radiative `average atom` (AA) model is presented for the calculation of opacities of hot plasmas not in the condition of local thermodynamic equilibrium (LTE). The electron impact and radiative rate constants are calculated using the dipole oscillator strengths of the average atom. A key element of the model is the photon escape probability which at present is calculated for a semi infinite slab. The Fermi statistics renders the rate equation for the AA level occupancies nonlinear, which requires iterations until the steady state. AA level occupancies are found. Detailed electronic configurations are built into the model after the self-consistent non-LTE AA state is found. The model shows a continuous transition from the non-LTE to the LTE state depending on the optical thickness of the plasma. 22 refs., 13 figs., 1 tab.
Date: October 17, 1996
Creator: Rozsnyai, B. F.
Partner: UNT Libraries Government Documents Department

Linear pulsations of strange modes in LBVs

Description: Outbursts of the luminous blue variables have been studied for a long time, but a detailed understanding of the mechanism has eluded astronomers. In the last few years it has been recognized that the dramatic increase in outburst brightness is due almost entirely to the luminosity being shifted into the visual band, rather than a true luminosity increase. Some ideas about how these very massive and very luminous stars might display their dramatic increase of visual brightness have been given by many. A sampling is given here. The strange modes we consider in this paper have been studied by the G{umlt o}ttingen group under Fricke and Glatzel. We are interested in strange modes because some are very rapidly growing when conditions are right, and amplitudes reach large radial velocity (200 km/s) and luminosity (0.1 mag). Then the radiative luminosity in deep layers can surpass the Eddington limit during each pulsation cycle, and outbursts occur.
Date: December 31, 1996
Creator: Cox, A.N.; Guzik, J.A. & Soukup, M.S.
Partner: UNT Libraries Government Documents Department