34 Matching Results

Results open in a new window/tab.

Cosmological moduli problem in a supersymmetric model with direct gauge mediation (open access)

Cosmological moduli problem in a supersymmetric model with direct gauge mediation

Recently, an interesting class of the direct gauge mediation supersymmetry (SUSY) breaking models are proposed, in which the minimum of the potential of the SUSY breaking field is determined by the inverted hierarchy mechanism. We consider their cosmological implications. In this class of models, SUSY breaking field has a very flat potential, which may have a cosmological importance. Assuming the initial amplitude of the SUSY breaking field to be of the order of the Planck scale, it can be a source of a large entropy production. A special attention is paid to the cosmological moduli problem, and we will see the cosmological mass density of the moduli field can be significantly reduced.
Date: July 7, 1998
Creator: Moroi, Takeo
System: The UNT Digital Library
Mongolia wind resource assessment project (open access)

Mongolia wind resource assessment project

The development of detailed, regional wind-resource distributions and other pertinent wind resource characteristics (e.g., assessment maps and reliable estimates of seasonal, diurnal, and directional) is an important step in planning and accelerating the deployment of wind energy systems. This paper summarizes the approach and methods being used to conduct a wind energy resource assessment of Mongolia. The primary goals of this project are to develop a comprehensive wind energy resource atlas of Mongolia and to establish a wind measurement program in specific regions of Mongolia to identify prospective sites for wind energy projects and to help validate some of the wind resource estimates. The Mongolian wind resource atlas will include detailed, computerized wind power maps and other valuable wind resource characteristic information for the different regions of Mongolia.
Date: September 7, 1998
Creator: Elliott, D.; Chadraa, B. & Natsagdorj, L.
System: The UNT Digital Library
Transuranic separation using organophophorus extractants adsorbed onto superparamagnetic carriers. (open access)

Transuranic separation using organophophorus extractants adsorbed onto superparamagnetic carriers.

Polymeric coated ferromagnetic carriers with an absorbed layer of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) diluted by tributyl phosphate (TBP) are being evaluated for application in the separation and the recovery of low concentrations of americium, plutonium, and uranium from nuclear waste solutions. Due to their chemical nature, these extractants selectively complex americium and plutonium contaminants onto the particles and the complexed particles can be recovered from the solution using a magnet. Physical and chemical characterization of the extractant-absorbed particles were performed by gamma and liquid scintillation counting, scanning electron microscopic (SEM) micrograph, and other physical measurements. Plutonium, americium, and uranium separations have been performed at various HNO{sub 3} and HCl concentrations. Parameters were studied to determine the limitations and capacity of the process. The status of the chemistry and application of the process to Department of Energy (DOE) remediation efforts for actinide decontamination are discussed.
Date: October 7, 1998
Creator: Nunez, L.
System: The UNT Digital Library
Imprinted spiral structures as neutron polarizers. (open access)

Imprinted spiral structures as neutron polarizers.

Neutron diffraction from magnetic spiral structures is governed by strong selection rules for the polarization of the outgoing beam. When the sample is entirely of one chirality--for instance a right handed spiral--the neutrons diffracted by some Bragg reflections are fully polarized. While the scattering theory has been formulated long ago, attempts to controllably modify the population of left handed and right handed spiral domains in natural magnetic structures (which for instance occur in some rare earth metals) have been largely unsuccessful. In contrast, we have been able to imprint helical magnetic structures in La/Fe multilayers (each layer approximately 30 {angstrom} thick) simply by rotating the growing sample in a weak external field (30e). A first estimate is given of the efficiency of these multilayers as polarizers of neutron beams.
Date: October 7, 1998
Creator: Lohstroh, W.
System: The UNT Digital Library
Development of corrosion models for high-level waste containers (open access)

Development of corrosion models for high-level waste containers

None
Date: January 7, 1998
Creator: Farmer, J.C.
System: The UNT Digital Library
Recent developments pertinent to processing of ENDF/B-6 type resonance cross section data. (open access)

Recent developments pertinent to processing of ENDF/B-6 type resonance cross section data.

In view of our increasing dependence on computations rather than construction and operation of more costly experimental facilities, the rigor and accuracy achievable by calculational methods certainly deserve more attention. This is particularly so for the Monte Carlo methods which are generally regarded as the ultimate computational standard for the entire nuclear community around the globe. One obvious question that one may raise is whether the numerical algorithms deployed to process cross sections accurately reflect the rigor of the state-of-the-art nuclear data. The case in point is particularly essential in the resolved and the unresolved resonance regions, which constitute the most demanding task in all processing codes for reactor applications. For the resolved energy region, the point-wise cross sections are highly fluctuating functions of energy and temperature. In light of the availability of a large body of resonance data spanning over the much expanded energy ranges for most of major nuclides, critical examinations and improvement where appropriate, of the existing methods are apparently in order. For the unresolved energy region, improvement of traditional methods based on statistical approaches for treating the self-shielding effects is also desirable. From the perspective of the Monte Carlo approach, an alternative means for generating the …
Date: July 7, 1998
Creator: Hwang, R. N.
System: The UNT Digital Library
What causes Psi suppression in Pb + Pb Collisions? (open access)

What causes Psi suppression in Pb + Pb Collisions?

A reexamination of hadronic comover scattering indicates that this mechanism cannot explain the observed {psi} suppression in Pb+Pb interactions. The possibility of quark-gluon plasma formation is therefore considered. Implications for RHIC and LHC are also discussed. The agreement of the NA50 Pb+Pb data with naive comover models is reassessed. Previous work is reanalyzed and expanded to include feeding of the {psi}' and {chi}{sub c} states to the {psi}. The effect of color screening is also investigated. Only the {psi}/Drell-Yan (DY) ratios are discussed here.
Date: January 7, 1998
Creator: Vogt, R.
System: The UNT Digital Library
Performance and Modeling of Amorphous Silicon Photovoltaics for Building-Integrated Applications (Preprint prepared for Solar 99) (open access)

Performance and Modeling of Amorphous Silicon Photovoltaics for Building-Integrated Applications (Preprint prepared for Solar 99)

Amorphous silicon photovoltaic (PV) modules offer several advantages for building-integrated applications. The material can be deposited on glass or flexible substrates, which allows for products like roofing shingles and integrated PV/building glass. The material also has a uniform surface, which is ideal for many architectural applications. Amorphous silicon modules perform well in warm weather and have a small temperature coefficient for power. Depending on the building load, this may be beneficial when compared to crystalline systems. At the National Renewable Energy Laboratory, we are monitoring the performance of a triple-junction a-Si system. The system consists of 72 roofing shingles mounted directly to simulated roofing structures. This paper examines the performance of the building-integrated amorphous silicon PV system and applicability for covering residential loads. A simple model of system performance is also developed and is presented.
Date: June 7, 1998
Creator: Kroposki, B. & Hansen, R.
System: The UNT Digital Library
Cosmic Closure: Relating the Ultimate Fate of Massive Stars and the Ultimate Fate of the Universe (open access)

Cosmic Closure: Relating the Ultimate Fate of Massive Stars and the Ultimate Fate of the Universe

We give a brief overview of the status of core collapse supernova modeling, particularly as it pertains to predictions of neutrino signatures for the next galactic or near extragalactic supernova. We also consider the implications of neutrino mass for both the supernova mechanism and neutrino signature predictions.
Date: September 7, 1998
Creator: Bruenn, S.W. & Mezzacappa, A.
System: The UNT Digital Library
Parameter identification and on-line estimation for reduced kinetic model (open access)

Parameter identification and on-line estimation for reduced kinetic model

The base hydrolysis process for the destruction of energetic or explosive materials results is a high pH hydrolysate solution with reaction products that include a series of carboxylic acid salts, glycolates, amines, and nitrates. The hydrolysate solutions obtained from this process contain from two to ten wt% of organic carbon and nitrogen compounds that must be further treated before disposal. Hydrothermal oxidation at elevated temperatures (450 C) and pressure (14,000 psi) was selected as the treatment process for the hydrolysate solutions obtained from hydrolysis of the high explosive PBX 9404 at the Department of Energy Pantex facility in Amarillo, Texas. In this work, the authors describe the use of receding horizon identification and estimation techniques to determine the model parameters for a reduced kinetic model describing the oxidation-reduction reactions in a hydrothermal oxidation reactor. This model is used in a model predictive controller that minimizes the total aqueous nitrogen in the hydrothermal oxidation reactor effluent.
Date: August 7, 1998
Creator: Littel, J. D.; Muske, K. R.; Del`Orco, P. C.; Le, L. A. & Flesner, R. L.
System: The UNT Digital Library
Vitrification of Simulated Fernald K-65 Silo Waste at Low Temperature (open access)

Vitrification of Simulated Fernald K-65 Silo Waste at Low Temperature

Vitrification is the technology that has been chosen to solidify approximately 18,000 tons of geologic mill tailings, designated as K-65 wastes, at the Fernald Environmental Management Project (FEMP) in Fernald, Ohio. The glass formula developed in this study for the FEMP wastes is a lithia substituted soda-lime-lithia-silica (SLLS) composition which melts at 1050 degrees Celsius. Low melting formulations minimize volatilization of hazardous species such as arsenic, selenium, chromium, and lead during vitrification. Formulation in the SLLS system avoids problematic phase separation known to occur in the MO-B2O3-SiO2 glass forming system (where MO = CaO, MgO, BaO, and PbO which are all constituents of the FEMP wastes). The SLLS glass passed the Environmental Protection Agency (EPA) Toxic Characteristic Leach Procedure (TCLP) for all the hazardous constituents of concern under the current regulations. The SLLS glass is as durable as the high melting soda-lime-silica glasses and is more durable than the borosilicate glasses previously developed for the K-65 wastes. Optimization of glass formulations in the SLLS glass forming system should provide glasses which will pass the newly promulgated Universal Treatment Standards which take effect of August 28, 1998.
Date: July 7, 1998
Creator: Jantzen, Carol M. & Pickett, J. B.
System: The UNT Digital Library
Parallel Strategies for Crash and Impact Simulations (open access)

Parallel Strategies for Crash and Impact Simulations

We describe a general strategy we have found effective for parallelizing solid mechanics simula- tions. Such simulations often have several computationally intensive parts, including finite element integration, detection of material contacts, and particle interaction if smoothed particle hydrody- namics is used to model highly deforming materials. The need to balance all of these computations simultaneously is a difficult challenge that has kept many commercial and government codes from being used effectively on parallel supercomputers with hundreds or thousands of processors. Our strategy is to load-balance each of the significant computations independently with whatever bal- ancing technique is most appropriate. The chief benefit is that each computation can be scalably paraIlelized. The drawback is the data exchange between processors and extra coding that must be written to maintain multiple decompositions in a single code. We discuss these trade-offs and give performance results showing this strategy has led to a parallel implementation of a widely-used solid mechanics code that can now be run efficiently on thousands of processors of the Pentium-based Sandia/Intel TFLOPS machine. We illustrate with several examples the kinds of high-resolution, million-element models that can now be simulated routinely. We also look to the future and dis- cuss what possibilities …
Date: December 7, 1998
Creator: Attaway, S.; Brown, K.; Hendrickson, B. & Plimpton, S.
System: The UNT Digital Library
Generation of Chloride Active Defects at the Aluminum Oxide Surface for the Study of Localized Corrosion Initiation (open access)

Generation of Chloride Active Defects at the Aluminum Oxide Surface for the Study of Localized Corrosion Initiation

The generation of surface defects on electron cyclotron resonance (ECR) plasma derived aluminum oxide films has been studied. We find that Cl active O vacancies can be generated using electron and ion irradiation yielding surface concentrations of 3 xl 013 to 1X1014 sites"cm-2. These values correspond to surface defect concentrations of 3 to 10% when compared to ordered, crystalline u-alumina. The vacancies appear to be responsible for increased surface O concentrations when immersed in water. Anodic polarization of irradiated films yields a decrease in the stable pitting potential which correlates with electron dose.
Date: December 7, 1998
Creator: Barbour, J.C.; Missert, N.; Son, K.-A; Wall, F.D. & Zavadil, K.R.
System: The UNT Digital Library
Novel transport-vehicle design for moving optic modules in the National Ignition Facility (open access)

Novel transport-vehicle design for moving optic modules in the National Ignition Facility

The National Ignition Facility, currently under design and construction at Lawrence Livermore National Laboratory, will be the world`s largest laser when complete. The NIF will use about 8,000 large optics of 26 different types to focus up to 192 laser beams on a dime-size target. Given the constraints of the NIF operating environment, the tasks associated with optics transport and handling require a novel, versatile transport system. The system will consist of a computer system containing guidance, traffic management and order entry functions, and four or more automated laser-guided vehicles. This transport system will transport optics enclosures that are essentially portable clean rooms and will lift, align, and position them as needed to contact and engage mating points on the laser support structure.
Date: May 7, 1998
Creator: Grasz, E. & Tiszauer, D.
System: The UNT Digital Library
Self-Irradiation Effects on 99Mo Reagents and Products (open access)

Self-Irradiation Effects on 99Mo Reagents and Products

produced in 1996 and shipped to pharmaceutical houses for evaluation of compatibility with oxime solution used to precipitate `?vfo as the oxime complex is both air and light-sensitive, and containing a black precipitate that forms during shipment, presumably as a result of self- irradiation. Addition of sodium hypochlorite to the product solution prior to shipment prevents precipitate formation, indicating the precipitate is a reduced form of `%lo. to remove any precipitate. Duplicate aliquots of the filtered samples were titrated to a phenolphthalein irradiation and afler standing at room temperature for 86.4 hours. Precipitates were washed to a FTIR analysis of the white precipitate showed it to be alpha benzoin oxime. Since the basic After 86.4 hours, no precipitate had formed in bottles containing sodium hypochlorite. Black precipitate had formed in all bottles that did not contain sodium hypochlorite after 14.4 hours. The precipitate appeared to initially form on the surface of the HDPE sample bottles and Black precipitate was first noticed in sample set 1 after 28.8 hrs' irradiation. No visible sample containing precipitate was kept at room temperature in the original bottle. Precipitate in sample sets 2 and 3. Since no precipitate formed in these bottles, this was equivalent …
Date: October 7, 1998
Creator: Carson, S. D.; Garcia, M. J.; McDonald, M. J.; Simpson, R. L. & Tallant, D. R.
System: The UNT Digital Library
Electronic excitation in transmission of relativistic H{sup {minus}} ions through thin foils (open access)

Electronic excitation in transmission of relativistic H{sup {minus}} ions through thin foils

The authors describe a theoretical model to study the transmission of relativistic H{sup {minus}} ions through thin carbon foils. The approach is based on a Monte Carlo solution of the Langevin equation describing electronic excitations of the atoms during the transport through the foil. Calculations for the subshell populations of outgoing hydrogen atoms are found to be in good agreement with recent experimental data on an absolute scale and show that there exists a propensity for populating extreme Stark states.
Date: May 7, 1998
Creator: Reinhold, C.O.; Kuerpick, P.; Burgdoerfer, J.; Yoshida, S. & Gervais, B.
System: The UNT Digital Library
Dissipative Chaos and Symmetry Breaking in AC-Driven Nanostructures (open access)

Dissipative Chaos and Symmetry Breaking in AC-Driven Nanostructures

None
Date: December 7, 1998
Creator: Campbell, D. K.; Alekseev, K. N.; Berman, G. P. & Cannon, E. H.
System: The UNT Digital Library
Modeling A.C. Electronic Transport through a Two-Dimensional Quantum Point Contact (open access)

Modeling A.C. Electronic Transport through a Two-Dimensional Quantum Point Contact

We present the results on the a.c. transport of electrons moving through a two-dimensional (2D) semiconductor quantum point contact (QPC). We concentrate our attention on the characteristic properties of the high frequency admittance ({omega}{approximately}0 - 50 GHz), and on the oscillations of the admittance in the vicinity of the separatrix (when a channel opens or closes), in presence of the relaxation effects. The experimental verification of such oscillations in the admittance would be a strong confirmation of the semi-classical approach to the a.c. transport in a QPC, in the separatrix region.
Date: December 7, 1998
Creator: Aronov, I. E.; Beletskii, N. N.; Berman, G. P.; Campbell, D. K.; Doolen, G. D. & Dudiy, S. V.
System: The UNT Digital Library
Electron-Nuclear Spin Dynamics in a Mesoscopic Solid-State Quantum Computer (open access)

Electron-Nuclear Spin Dynamics in a Mesoscopic Solid-State Quantum Computer

We numerically simulate the process of nuclear spin measurement in Kane's quantum computer. For this purpose, we model the quantum dynamics of two coupled nuclear spins located on {sup 31}P donors implanted in Si. We estimate the minimum time of measurement necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic one and the probability of error for typical values of external noise.
Date: December 7, 1998
Creator: Berman, G. P.; Campbell, D. K.; Doolen, G. D. & Nagaev, K. E.
System: The UNT Digital Library
Low Temperature Anomaly of LO Phonons in La{sub 1.85}Cu{sub 3}O{sub 7} (open access)

Low Temperature Anomaly of LO Phonons in La{sub 1.85}Cu{sub 3}O{sub 7}

None
Date: January 7, 1998
Creator: Egami, T.; McQueeney, R.J.; Peetrov, Y.; Vethiraj, M.; Shirane, G. & Endoh, Y.
System: The UNT Digital Library
High-Damage-Threshold Pinhole for Glass Fusion Laser Applications (open access)

High-Damage-Threshold Pinhole for Glass Fusion Laser Applications

We are investigating methods to fabricate high-damage-threshold spatial-filter pinholes that might not be susceptible to plasma closure for relatively high energies and long pulses. These are based on the observation that grazing-incidence reflection from glass can withstand in excess of 5 kJ/cm{sup 2} (normal to the beam) without plasma formation. The high damage threshold results from both the cos q spreading of the energy across the surface and the reflection of a large fraction of the energy from the surface, thereby greatly reducing the field strength within the medium.
Date: June 7, 1998
Creator: Kumit, N. A.; Letzring, S. A. & Johnson, R. P.
System: The UNT Digital Library
Multiscale Modeling of Recrystallization (open access)

Multiscale Modeling of Recrystallization

We propose a multi length scale approach to modeling recrystallization which links a dislocation model, a cell growth model and a macroscopic model. Although this methodology and linking framework will be applied to recrystallization, it is also applicable to other types of phase transformations in bulk and layered materials. Critical processes such as the dislocation structure evolution, nucleation, the evolution of crystal orientations into a preferred texture, and grain size evolution all operate at different length scales. In this paper we focus on incorporating experimental measurements of dislocation substructures, rnisorientation measurements of dislocation boundaries, and dislocation simulations into a mesoscopic model of cell growth. In particular, we show how feeding information from the dislocation model into the cell growth model can create realistic initial microstructure.
Date: December 7, 1998
Creator: Godfrey, A. W.; Holm, E. A.; Hughes, D. A.; Lesar, R. & Miodownik, M. A.
System: The UNT Digital Library
National Laboratories and Internatioanl Partnering (open access)

National Laboratories and Internatioanl Partnering

For nearly fifty years the US held a dominant position in research and development in the free world. The situation has changed dramatically in the last decade. Countries around the world realize that to foster sustainable economic growth, they must build and maintain a foundation in science and technology. The time in which a country could base its gross national product solely on extraction of raw materials or on people-intensive manufacturing is drawing to a close. The funding for research and development has been growing in the rest of the world, while US expenditures have not kept pace. In 1961, the United States funded 71 `?40 of the world's R&D. It is estimated that the US contribution to research and development fimding today has reached the 3 3o/0 level, and will drop to 26o/0 of the world's total by 2003.1 In 1981 US government spending per capita on non-defense research and development was nearly fifty percent above our major competitors; by 2002 it is projected to be f@ percent below them.2 This trend has a profound impact on how research and development institutions in the United States plan for their future technical growth. Sandia National Laboratories, as one of the …
Date: December 7, 1998
Creator: Eagan, R. J.; Gauster, W. B.; Hartley, D. L. & Jones, G. J.
System: The UNT Digital Library
Identification of mine collapses, explosions and earthquakes using INSAR: a preliminary investigation (open access)

Identification of mine collapses, explosions and earthquakes using INSAR: a preliminary investigation

Interferograms constmcted from satellite-borne synthetic aperture radar images have the capability of mapping sub-cm ground surface deformation over areas on the order of 100 x 100 km with a spatial resolution on the order of 10 meters. We investigate the utility of synthetic aperture radar interferomehy (InSAR) used in conjunction with regional seismic methods in detecting and discriminating different types of seismic events in the context of special event analysis for the CTBT. For this initial study, we carried out elastic dislocation modeling of underground explosions, mine collapses and small (M<5.5) shallow earthquakes to produce synthetic interferograms and then analyzed satellite radar data for a large mine collapse. The synthetic modeling shows that, for a given magnitude each type of event produces a distinctive pattern of ground deformation that can be recognized in, and recovered from, the corresponding interferogram. These diagnostic characteristics include not only differences in the polarities of surface displacements but also differences in displacement amplitudes from the different sources. The technique is especially sensitive to source depth, a parameter that is crucial in discriminating earthquakes from the other event types but is often very poorly constrained by regional seismic data alone. The ERS radar data analyzed is …
Date: July 7, 1998
Creator: Foxall, B.; Sweeney, J. J. & Walter, W. R.
System: The UNT Digital Library