An MS-DOS-based program for analyzing plutonium gamma-ray spectra (open access)

An MS-DOS-based program for analyzing plutonium gamma-ray spectra

A plutonium gamma-ray analysis system that operates on MS-DOS-based computers has been developed for the International Atomic Energy Agency (IAEA) to perform in-field analysis of plutonium gamma-ray spectra for plutonium isotopics. The user interacts with the system by means of menus and screens that allow the user to select various applications and to enter information pertinent to a measurement. This information, along with the plutonium weight-percent-abundance results from the data analysis, is stored in dBASE III files. The spectral-data-analysis program, IAEAPU, determines the relative plutonium isotopic abundances from gamma-ray peaks in the 110- to 390-keV region of the spectral data. The program is compact so that it may be used on a portable, battery-operated, laptop, personal computer (PC) that uses a 3-1/2-in. floppy diskette. This is intended to be the final report on this work. We describe in detail the data-analysis methodology, the software, and the operation of the plutonium gamma-ray analysis system. 10 refs., 1 fig., 2 tabs.
Date: September 7, 1989
Creator: Ruhter, W. D. & Buckley, W. M.
Object Type: Report
System: The UNT Digital Library
An MS-DOS-based program for analyzing plutonium gamma-ray spectra (open access)

An MS-DOS-based program for analyzing plutonium gamma-ray spectra

A plutonium gamma-ray analysis system that operates on MS-DOS-based computers has been developed for the International Atomic Energy Agency (IAEA) to perform in-field analysis of plutonium gamma-ray spectra for plutonium isotopics. The program titled IAEAPU consists of three separate applications: a data-transfer application for transferring spectral data from a CICERO multichannel analyzer to a binary data file, a data-analysis application to analyze plutonium gamma-ray spectra, for plutonium isotopic ratios and weight percents of total plutonium, and a data-quality assurance application to check spectral data for proper data-acquisition setup and performance. Volume 3 contains the software listings for these applications.
Date: September 7, 1989
Creator: Ruhter, W. D. & Buckley, W. M.
Object Type: Report
System: The UNT Digital Library
An MS-DOS-based program for analyzing plutonium gamma-ray spectra (open access)

An MS-DOS-based program for analyzing plutonium gamma-ray spectra

A plutonium gamma-ray analysis system that operates on MS-DOS-based computers has been developed for the International Atomic Energy Agency (IAEA) to perform in-field analysis of plutonium gamma-ray spectra for plutonium isotopics. The program titled IAEAPU consists of three separate applications: (1) a data-transfer application for transferring spectral data from a CICERO multichannel analyzer to a binary data file, (2) a data-analysis application to analyze plutonium gamma-ray spectra for plutonium isotopic ratios and weight percents of total plutonium, (3) and a data-quality assurance application to check spectral data for proper data-acquisition setup and performance. Volume 2 describes the operations of these applications and the installation and maintenance of the software.
Date: September 7, 1989
Creator: Ruhter, W. D. & Buckley, W. M.
Object Type: Report
System: The UNT Digital Library
Reel support for wind the magnet of the Mirror Fusion Test Facility (open access)

Reel support for wind the magnet of the Mirror Fusion Test Facility

The reel support has three main functions. It must support the reel, which is 134 in. in diameter, 40 in. wide, and stores up to 8,600 ft of superconductor weighing 8,600 lb. It also must serve as a tensioning device for the superconductor, exerting a force of up to 600 lb. Further, the support must move the reel vertically and laterally to facilitate the winding of the magnets. The support has been designed and is now being fabricated. This paper describes the performance requirements of this device and the evolution of design from concept to completion.
Date: September 7, 1977
Creator: Ling, R.C.; Chang, Y. & Hunt, L.D.
Object Type: Article
System: The UNT Digital Library
Numerical modeling of self-limiting and self-enhancing caprock alteration induced by CO2 storage in a depleted gas reservoir (open access)

Numerical modeling of self-limiting and self-enhancing caprock alteration induced by CO2 storage in a depleted gas reservoir

This paper presents numerical simulations of reactive transport which may be induced in the caprock of an on-shore depleted gas reservoir by the geological sequestration of carbon dioxide. The objective is to verify that CO{sub 2} geological disposal activities currently being planned for the study area are safe and do not induce any undesired environmental impact. In our model, fluid flow and mineral alteration are induced in the caprock by penetration of high CO{sub 2} concentrations from the underlying reservoir, where it was assumed that large amounts of CO{sub 2} have already been injected at depth. The main focus is on the potential effect of precipitation and dissolution processes on the sealing efficiency of caprock formations. Concerns that some leakage may occur in the investigated system arise because the seal is made up of potentially highly-reactive rocks, consisting of carbonate-rich shales (calcite+dolomite averaging up to more than 30% of solid volume fraction). Batch simulations and multi-dimensional 1D and 2D modeling have been used to investigate multicomponent geochemical processes. Numerical simulations account for fracture-matrix interactions, gas phase participation in multiphase fluid flow and geochemical reactions, and kinetics of fluid-rock interactions. The geochemical processes and parameters to which the occurrence of high …
Date: September 7, 2007
Creator: Xu, Tianfu; Gherardi, Fabrizio; Xu, Tianfu & Pruess, Karsten
Object Type: Article
System: The UNT Digital Library
Thermodynamic Modeling of Hanford Waste Tank 241-AN-107 (open access)

Thermodynamic Modeling of Hanford Waste Tank 241-AN-107

The high level waste storage double-shell tanks at the Hanford site are highly basic. The high basicity is a key factor in controlling the chemical behavior of different components of the waste and in influencing the corrosion rate of the carbon steel primary tanks. However, the introduction of atmospheric CO2 can act to reduce the pH of the tank wastes over time and possibly alter the corrosion rate of the carbon steel tanks. In order to at least partially address this issue for waste tank 241-AN-107, thermodynamic modeling calculations were performed to predict the changes in pH and carbonate concentration that could occur as CO2 is absorbed from the atmosphere. The calculations extended to complete equilibrium with the partial pressure of CO2 in the atmosphere (i.e. pCO2 = 10-3.5 atm). Simulations were performed for both the “upper” segments of tank 241-AN-107, which have been influenced by the introduction of high concentrations of NaOH to the supernatant, and for the “lower” segments where the salt cake/interstitial liquid have not been substantially altered by the introduction of base concentration.
Date: September 7, 2005
Creator: Felmy, Andrew R.
Object Type: Report
System: The UNT Digital Library
Reactions of Monomeric [1,2,4-(Me3C)3C5H2]2CeH and CO with orwithout H2:An Experimental and Computational Study (open access)

Reactions of Monomeric [1,2,4-(Me3C)3C5H2]2CeH and CO with orwithout H2:An Experimental and Computational Study

Addition of CO to [1,2,4-(Me3C)3C5H2]2CeH, Cp'2CeH, intoluene yields the cis (Cp'2Ce)2(mu-OCHCHO), in which the cis enediolategroup bridges the two metallocene fragments. The cis enediolatequantitatively isomerizes intramolecularly to the trans-enediolate inC6D6 at 100oC over seven months. When the solvent is pentane,Cp'2Ce(OCH2)CeCp'2 forms, in which the oxomethylene group or theformaldehyde dianion bridges the two metallocene fragments. The cisenediolate is suggested to form by insertion of CO into the Ce-C bond ofCp'2Ce(OCH2)CeCp'2 generating Cp'2CeOCH2COCeCp'2. The stereochemistry ofthe cis-enediolate is determined by a 1,2-hydrogen shift in the OCH2COfragment that has the OC(H2) bond anti periplanar relative to the carbenelone pair. The bridging oxomethylene complex reacts with H2, but not withCH4, to give Cp'2CeOMe, which is also the product of the reaction betweenCp'2CeH and a mixture of CO and H2. The oxomethylene complex reacts withCO to give the cis enediolate complex. DFT calculations on C5H5 modelmetallocenes show that the reaction of Cp2CeH with CO and H2 to giveCp2CeOMe is exoergic by 50 kcal mol-1. The net reaction proceeds by aseries of elementary reactions that occur after the formyl complex,Cp2Ce(eta-2 CHO), is formed by further reaction with H2. The key pointthat emerges from the calculated potential energy surface is thebifunctional nature of the metal formyl in …
Date: September 7, 2006
Creator: Werkema, Evan L.; Maron, Laurent; Eisenstein, Odile & Andersen, Richard A.
Object Type: Article
System: The UNT Digital Library
A Automated Tool for Supporting FMEAs of Digital Systems (open access)

A Automated Tool for Supporting FMEAs of Digital Systems

Although designs of digital systems can be very different from each other, they typically use many of the same types of generic digital components. Determining the impacts of the failure modes of these generic components on a digital system can be used to support development of a reliability model of the system. A novel approach was proposed for such a purpose by decomposing the system into a level of the generic digital components and propagating failure modes to the system level, which generally is time-consuming and difficult to implement. To overcome the associated issues of implementing the proposed FMEA approach, an automated tool for a digital feedwater control system (DFWCS) has been developed in this study. The automated FMEA tool is in nature a simulation platform developed by using or recreating the original source code of the different module software interfaced by input and output variables that represent physical signals exchanged between modules, the system, and the controlled process. For any given failure mode, its impacts on associated signals are determined first and the variables that correspond to these signals are modified accordingly by the simulation. Criteria are also developed, as part of the simulation platform, to determine whether the …
Date: September 7, 2008
Creator: Yue, M.; Chu, T. L.; Martinez-Guridi, G. & Lehner, J.
Object Type: Article
System: The UNT Digital Library
Technical Safety Requirements for the B695 Segment of the Decontamination and Waste Treatment Facility (open access)

Technical Safety Requirements for the B695 Segment of the Decontamination and Waste Treatment Facility

This document contains Technical Safety Requirements (TSRs) for the Radioactive and Hazardous Waste Management (RHWM) Division's B695 Segment of the Decontamination and Waste Treatment Facility (DWTF) at Lawrence Livermore National Laboratory (LLNL). The TSRs constitute requirements regarding the safe operation of the B695 Segment of the DWTF. The TSRs are derived from the Documented Safety Analysis (DSA) for the B695 Segment of the DWTF (LLNL 2004). The analysis presented there determined that the B695 Segment of the DWTF is a low-chemical hazard, Hazard Category 3, nonreactor nuclear facility. The TSRs consist primarily of inventory limits as well as controls to preserve the underlying assumptions in the hazard analyses. Furthermore, appropriate commitments to safety programs are presented in the administrative controls section of the TSRs. The B695 Segment of the DWTF (B695 and the west portion of B696) is a waste treatment and storage facility located in the northeast quadrant of the LLNL main site. The approximate area and boundary of the B695 Segment of the DWTF are shown in the B695 Segment of the DWTF DSA. Activities typically conducted in the B695 Segment of the DWTF include container storage, lab-packing, repacking, overpacking, bulking, sampling, waste transfer, and waste treatment. B695 …
Date: September 7, 2007
Creator: Larson, H L
Object Type: Report
System: The UNT Digital Library
Strongly Interacting Matter at High Energy Density (open access)

Strongly Interacting Matter at High Energy Density

This lecture concerns the properties of strongly interacting matter (which is described by Quantum Chromodynamics) at very high energy density. I review the properties of matter at high temperature, discussing the deconfinement phase transition. At high baryon density and low temperature, large N{sub c} arguments are developed which suggest that high baryonic density matter is a third form of matter, Quarkyonic Matter, that is distinct from confined hadronic matter and deconfined matter. I finally discuss the Color Glass Condensate which controls the high energy limit of QCD, and forms the low x part of a hadron wavefunction. The Glasma is introduced as matter formed by the Color Glass Condensate which eventually thermalizes into a Quark Gluon Plasma.
Date: September 7, 2008
Creator: McLerran, L.
Object Type: Article
System: The UNT Digital Library
Ab-Initio Study on Plutonium Compounds Pu3M (M=Al, Ga, In), PuNp and Elemental Neptunium (open access)

Ab-Initio Study on Plutonium Compounds Pu3M (M=Al, Ga, In), PuNp and Elemental Neptunium

Using spin-polarized relativistic density functional theory the electronic and magnetic structures for the plutonium compounds Pu{sub 3}M(M = Al; Ga; In) and PuNp have been investigated. For the first group of compounds the enhanced hybridization between Pu 5f and p-states of alloying element, as it has been found in spin-polarized calculations, is believed to be the main reason for the higher formation energies obtained in such kind of studies in comparison with the non-spin-polarized case. Also, comparative analysis of the actinides U, Np, Pu, Am, and Cm has been performed based on their electronic and magnetic structure. Some noticeable difference in the calculated magnetic structure was discovered between the actinide with local magnetic moments (Cm) and the actinides (Pu, Am) in which magnetic moments were found only in the calculations.
Date: September 7, 2005
Creator: Kutepov, A L
Object Type: Report
System: The UNT Digital Library
Analysis of Potential Benefits and Costs of Updating the Commercial Building Energy Code in Iowa (open access)

Analysis of Potential Benefits and Costs of Updating the Commercial Building Energy Code in Iowa

The state of Iowa is considering adpoting ASHRAE 90.1-1999 as its commercial building energy code. In an effort to evaluate whether or not this is an appropraite code for the state, the potential benefits and costs of adopting this standard are considered. Both qualitative and quantitative benefits are assessed. The energy simulation and economic results suggest that adopting ASHRAE 90.1-1999 would provide postitive net benefits to the state relative to the building and design requirements currently in place.
Date: September 7, 2002
Creator: Cort, Katherine A.; Belzer, David B.; Richman, Eric E. & Winiarski, David W.
Object Type: Report
System: The UNT Digital Library
BENCAP, LLC: CAPSULE VELOCITY TEST (open access)

BENCAP, LLC: CAPSULE VELOCITY TEST

Ben Cap, LLC, has a technology that utilizes bebtonite to plug wells. The bentonite is encapsulated in a cardboard capsule, droped down to the bottom of the well where it is allowed to hydrate, causing the bentonite to expand and plug the well. This method of plugging a well is accepted in some, but not all states. This technology can save a significant amount of money when compared to cementing methods currently used to plug and abandon wells. The test objective was to obtain the terminal velocity of the capsule delivery system as it drops through a column of water in a wellbore. Once the terminal velocity is known, the bentonite swelling action can be timed not to begin swelling until it reaches the bottom of the well bore. The results of the test showed that an average speed of 8.93 plus or minus 0.12 ft/sec was achieved by the capsule as it was falling through a column of water. Plotting the data revealed a very linear function with the capsules achieving terminal velocity shortly after being released. The interference of the capsule impacting the casing was not readily apparent in any of the runs, but a siginal sampling anomaly …
Date: September 7, 2005
Creator: Meidinger, Brian
Object Type: Report
System: The UNT Digital Library
Extension of the operating parameters of the two stage light gas gun to velocities below 2 km/sec (open access)

Extension of the operating parameters of the two stage light gas gun to velocities below 2 km/sec

None
Date: September 7, 2007
Creator: Thoe, R S
Object Type: Article
System: The UNT Digital Library
PLASMA WINDOW FOR VACUUM - ATMOSPHERE INTERFACE AND FOCUSING LENS OF SOURCES FOR NON-VACUUM MATERIAL MODIFICATION. (open access)

PLASMA WINDOW FOR VACUUM - ATMOSPHERE INTERFACE AND FOCUSING LENS OF SOURCES FOR NON-VACUUM MATERIAL MODIFICATION.

Material modifications by ion implantation, dry etching, and micro-fabrication are widely used technologies, all of which are performed in vacuum, since ion beams at energies used in these applications are completely attenuated by foils or by long differentially pumped sections, which ate currently used to interface between vacuum and atmosphere. A novel plasma window, which utilizes a short arc for vacuum-atmosphere interface has been developed. This window provides for sufficient vacuum atmosphere separation, as well as for ion beam propagation through it, thus facilitating non-vacuum ion material modification.
Date: September 7, 1997
Creator: Hershcovitch, A.
Object Type: Article
System: The UNT Digital Library
High Pressure Structure of Half-Metallic CrO2 (open access)

High Pressure Structure of Half-Metallic CrO2

Evidence for a structural phase transition from rutile {alpha}-CrO{sub 2} phase I (P4{sub 2}/mnm) to orthorhombic {beta}-CrO{sub 2} phase II (CaCl{sub 2}-like, Pnnm) is presented using angle-resolved synchrotron x-ray diffraction and high sensitivity confocal Raman spectroscopy. The transition to the CaCl{sub 2} structure, which appears to be second-order, occurs at 12 {+-} 3 GPa without any measurable discontinuity in volume, but is accompanied by an apparent increase in compressibility. Raman data are also presented to show further evidence for a second-order structural phase transition as well to demonstrate soft-mode behavior of the B{sub 1g} phonon mode.
Date: September 7, 2005
Creator: Maddox, B.; Yoo, C. S.; Kasinathan, D.; Pickett, W. E. & Scalettar, R. T.
Object Type: Article
System: The UNT Digital Library
Targets for the National Ignition Campaign (open access)

Targets for the National Ignition Campaign

The National Ignition Facility (NIF) is a 192 beam Nd-glass laser facility presently under construction at Lawrence Livermore National Laboratory (LLNL) for performing inertial confinement fusion (ICF) and experiments studying high energy density (HED) science. When completed in 2009, NIF will be able to produce 1.8 MJ, 500 TW of ultraviolet light for target experiments that will create conditions of extreme temperatures (>10{sup 8} K), pressures (10 GBar) and matter densities (>100 g/cm{sup 3}). A detailed program called the National Ignition Campaign (NIC) has been developed to enable ignition experiments in 2010, with the goal of producing fusion ignition and burn of a deuterium-tritium (DT) fuel mixture in millimeter-scale target capsules. The first of the target experiments leading up to these ignition shots will begin in 2008. The targets for the NIC are both complex and precise, and are extraordinarily demanding in materials fabrication, machining, assembly, cryogenics and characterization. The DT fuel is contained in a 2-millimeter diameter graded copper/beryllium or CH shell. The 75mm thick cryogenic ice DT fuel layer is formed to sub-micron uniformity at a temperature of approximately 18 Kelvin. The capsule and its fuel layer sit at the center of a gold/depleted uranium 'cocktail' hohlraum. Researchers …
Date: September 7, 2007
Creator: Atherton, L J
Object Type: Article
System: The UNT Digital Library
Theoretical Study on the Compounds NpM2, PuM2, AmM2 (M = Mn, Fe, Ni,Co) and on the System Pu-U (open access)

Theoretical Study on the Compounds NpM2, PuM2, AmM2 (M = Mn, Fe, Ni,Co) and on the System Pu-U

The relativistic spin-polarized density functional theory has been used for the study of electronic and magnetic structure of the compounds NpM{sub 2}, PuM{sub 2} and AmM{sub 2} (M = Mn; Fe;Co;Ni). It has been shown that the peculiarities in their magnetic properties come mainly from the hybridization between 5f-electrons of actinides and 3d-electrons of transition metals. It is interesting, that existence of the local magnetic moments appears to be possible on the atoms, despite the fact that Hill's condition is not satisfied for these compounds of actinides. Besides, the electronic and magnetic structures of PuU have been studied and the comparative analysis of them with another compounds of plutonium and its neighbors in Periodic System: PuNp and PuAm has been performed. It has been found that in all the cases the electronic structure formation is a result of a superposition of spin-orbit and exchange band splitting with some increasing of the role of exchange as we are going to americium. Atoms of plutonium appear to be near the point of equal importance of both interactions.
Date: September 7, 2005
Creator: Kutepov, A L
Object Type: Report
System: The UNT Digital Library
Technical Safety Requirements for the Waste Storage Facilities (open access)

Technical Safety Requirements for the Waste Storage Facilities

This document contains Technical Safety Requirements (TSR) for the Radioactive and Hazardous Waste Management (RHWM) WASTE STORAGE FACILITIES, which include Area 612 (A612) and the Decontamination and Waste Treatment Facility (DWTF) Storage Area at Lawrence Livermore National Laboratory (LLNL). The TSRs constitute requirements regarding the safe operation of the WASTE STORAGE FACILITIES. These TSRs are derived from the Documented Safety Analysis for the Waste Storage Facilities (DSA) (LLNL 2006). The analysis presented therein determined that the WASTE STORAGE FACILITIES are low-chemical hazard, Hazard Category 2 non-reactor nuclear facilities. The TSRs consist primarily of inventory limits and controls to preserve the underlying assumptions in the hazard and accident analyses. Further, appropriate commitments to safety programs are presented in the administrative controls sections of the TSRs. The WASTE STORAGE FACILITIES are used by RHWM to handle and store hazardous waste, TRANSURANIC (TRU) WASTE, LOW-LEVEL WASTE (LLW), mixed waste, California combined waste, nonhazardous industrial waste, and conditionally accepted waste generated at LLNL as well as small amounts from other U.S. Department of Energy (DOE) facilities, as described in the DSA. In addition, several minor treatments (e.g., drum crushing, size reduction, and decontamination) are carried out in these facilities. The WASTE STORAGE FACILITIES are …
Date: September 7, 2007
Creator: Larson, H L
Object Type: Report
System: The UNT Digital Library
Numerical modeling of injection and mineral trapping of CO2 withH2S and SO2 in a Sandstone Formation (open access)

Numerical modeling of injection and mineral trapping of CO2 withH2S and SO2 in a Sandstone Formation

Carbon dioxide (CO{sub 2}) injection into deep geologic formations could decrease the atmospheric accumulation of this gas from anthropogenic sources. Furthermore, by co-injecting H{sub 2}S or SO{sub 2}, the products respectively of coal gasification or combustion, with captured CO{sub 2}, problems associated with surface disposal would be mitigated. We developed models that simulate the co-injection of H{sub 2}S or SO{sub 2} with CO{sub 2} into an arkose formation at a depth of about 2 km and 75 C. The hydrogeology and mineralogy of the injected formation are typical of those encountered in Gulf Coast aquifers of the United States. Six numerical simulations of a simplified 1-D radial region surrounding the injection well were performed. The injection of CO{sub 2} alone or co-injection with SO{sub 2} or H{sub 2}S results in a concentrically zoned distribution of secondary minerals surrounding a leached and acidified region adjacent to the injection well. Co-injection of SO{sub 2} with CO{sub 2} results in a larger and more strongly acidified zone, and alteration differs substantially from that caused by the co-injection of H{sub 2}S or injection of CO{sub 2} alone. Precipitation of carbonates occurs within a higher pH (pH > 5) peripheral zone. Significant quantities of CO{sub …
Date: September 7, 2004
Creator: Xu, Tianfu; Apps, John A.; Pruess, Karsten & Yamamoto, Hajime
Object Type: Article
System: The UNT Digital Library
Calculational Study on the Compounds Np3M, Am3M, and on the System Pu-Am (open access)

Calculational Study on the Compounds Np3M, Am3M, and on the System Pu-Am

Spin-polarized relativistic density functional theory has been employed for the study of the electronic and magnetic structures for the compounds Np{sub 3}M and Am{sub 3}M (M = Al; Ga; In) and their comparison with plutonium's alloys Pu{sub 3}M has been made. It has been found that of the three actinides (Np, Pu, Am) only plutonium has its FCC structure essentially more stable after alloying with aforementioned elements. Apart from that, the electronic and magnetic structures for the system Pu-Am presented by three different compounds: Pu{sub 3}Am, PuAm, and PuAm{sub 3} have been investigated. Their magnetic structures have been found to be too robust in comparison with the experimental fact that magnetism in Pu-Am system depends strongly on the percentage of the americium in the alloy. One possible explanation consists in the overestimation of the spin splitting and in the disregarding of orbital dependence of the exchange-correlation potential.
Date: September 7, 2005
Creator: Kutepov, A L
Object Type: Report
System: The UNT Digital Library
NON-DESTRUCTIVE RADIOCARBON DATING: NATURALLY MUMMIFIED INFANT BUNDLE FROM SW TEXAS (open access)

NON-DESTRUCTIVE RADIOCARBON DATING: NATURALLY MUMMIFIED INFANT BUNDLE FROM SW TEXAS

Plasma oxidation was used to obtain radiocarbon dates on six different materials from a naturally mummified baby bundle from the Lower Pecos River region of southwest Texas. This bundle was selected because it was thought to represent a single event and would illustrate the accuracy and precision of the plasma oxidation method. Five of the materials were clearly components of the original bundle with 13 dates combined to yield a weighted average of 2135 {+-} 11 B.P. Six dates from a wooden stick of Desert Ash averaged 939 {+-} 14 B.P., indicating that this artifact was not part of the original burial. Plasma oxidation is shown to be a virtually non-destructive alternative to combustion. Because only sub-milligram amounts of material are removed from an artifact over its exposed surface, no visible change in fragile materials has been observed, even under magnification. The method is best applied when natural organic contamination is unlikely and serious consideration of this issue is needed in all cases. If organic contamination is present, it will have to be removed before plasma oxidation to obtain accurate radiocarbon dates.
Date: September 7, 2004
Creator: Steelman, K L; Rowe, M W; Turpin, S A; Guilderson, T P & Nightengale, L
Object Type: Article
System: The UNT Digital Library
Modeling Water Management in Polymer-Electrolyte Fuel Cells (open access)

Modeling Water Management in Polymer-Electrolyte Fuel Cells

Fuel cells may become the energy-delivery devices of the 21st century with realization of a carbon-neutral energy economy. Although there are many types of fuel cells, polymerelectrolyte fuel cells (PEFCs) are receiving the most attention for automotive and small stationary applications. In a PEFC, hydrogen and oxygen are combined electrochemically to produce water, electricity, and waste heat. During the operation of a PEFC, many interrelated and complex phenomena occur. These processes include mass and heat transfer, electrochemical reactions, and ionic and electronic transport. Most of these processes occur in the through-plane direction in what we term the PEFC sandwich as shown in Figure 1. This sandwich comprises multiple layers including diffusion media that can be composite structures containing a macroporous gas-diffusion layer (GDL) and microporous layer (MPL), catalyst layers (CLs), flow fields or bipolar plates, and a membrane. During operation fuel is fed into the anode flow field, moves through the diffusion medium, and reacts electrochemically at the anode CL to form hydrogen ions and electrons. The oxidant, usually oxygen in air, is fed into the cathode flow field, moves through the diffusion medium, and is electrochemically reduced at the cathode CL by combination with the generated protons and electrons. …
Date: September 7, 2007
Creator: Department of Chemical Engineering, University of California, Berkeley; Weber, Adam; Weber, Adam Z.; Balliet, Ryan; Gunterman, Haluna P. & Newman, John
Object Type: Book
System: The UNT Digital Library
Probing the nonlocal approximation to resonant collisions ofelectrons with diatomic molecules (open access)

Probing the nonlocal approximation to resonant collisions ofelectrons with diatomic molecules

A numerically solvable two-dimensional model introduced bythe authors [Phys. Rev. A 73, 032721 (2006)]is used to investigate thevalidity of the nonlocal approximation to the dynamics of resonantcollisions of electrons with diatomic molecules. The nonlocalapproximation to this model is derived in detail, all underlyingassumptions are specified and explicit expressions for the resonant andnon-resonant (background) T matrix for the studied processes are given.Different choices of the so-called discrete state, which fully determinesthe nonlocal approximation, are discussedand it is shown that a physicalchoice of this state can in general give poorer results than otherchoices that minimize the non-adiabatic effects and/or the backgroundterms of the T matrix. The background contributions to the crosssections, which are usually not considered in the resonant theory ofelectron-molecule collisions, can be significant not only for elasticscattering but also for the inelastic process of vibrationalexcitation.
Date: September 7, 2007
Creator: Houfek, Karel; Rescigno, Thomas N. & McCurdy, C. William
Object Type: Article
System: The UNT Digital Library