Exciton dynamicsstudied via internal THz transitions (open access)

Exciton dynamicsstudied via internal THz transitions

We employ a novel, ultrafast terahertz probe to investigatethe dynamical interplay of optically-induced excitons and unboundelectron-hole pairs in GaAs quantum wells. Resonant creation ofheavy-hole excitons induces a new low-energy oscillator linked totransitions between the internal exciton degrees of freedom. The timeresolved terahertz optical conductivity is found to be a probe wellsuited for studies of fundamental processes such as formation, relaxationand ionization of excitons.
Date: February 26, 2003
Creator: Kaindl, R. A.; Hagele, D.; Carnahan, M. A.; Lovenich, R. & Chemla, D. S.
Object Type: Article
System: The UNT Digital Library
Frequency Control Concerns in the North American Electric Power System (open access)

Frequency Control Concerns in the North American Electric Power System

This paper examines the relationship between system frequency, reliability and markets. It was prompted by the frequency deviations recently experienced at 2200 hours daily but is more generally concerned with the question of what frequency control is necessary. The paper does not provide new information or document new research. Nor is it intended to educate readers concerning power system engineering. Instead, the purpose is to reexamine well known truths concerning the power system and to freshly explore the basic relationship between frequency, reliability and markets: stepping back, if you will, to see if we are collectively missing something. The concern of this paper is with frequency and reliability. Off-nominal frequency can impact reliability and markets efficiency (as we are using the term here) in four ways. It could damage equipment (generation, transmission, or load). It could degrade the quality of the product being delivered to end users (too low and lights would flicker unacceptably, for example). It could result in the collapse of the power system itself (by triggering protective system actions, for example). Or it could result in overloading transmission lines as various generators try to restore system frequency impacting markets efficiency. Often these causes operate in concert. Generator …
Date: March 26, 2003
Creator: Kirby, B.J.
Object Type: Report
System: The UNT Digital Library
Energy effects of heat-island reduction strategies in Toronto,Canada (open access)

Energy effects of heat-island reduction strategies in Toronto,Canada

The effect of heat-island reduction (HIR) strategies on annual energy savings and peak-power avoidance of the building sector of the Greater Toronto Area is calculated, using an hourly building energy simulation model. Results show that ratepayers could realize potential annual energy savings of over $11M from the effects of HIR strategies. The residential sector accounts for over half (59%) of the total savings, offices 13% and retail stores 28%. Savings from cool roofs are about 20%, shade trees 30%, wind shielding of trees 37%, and ambient cooling by trees and reflective surfaces 12%. These results are preliminary and highly sensitive to the relative price of gas and electricity. Potential annual electricity savings are estimated at about 150GWh and potential peak-power avoidance at 250MW.
Date: August 26, 2003
Creator: Akbari, Hashem & Konopacki, Steven
Object Type: Article
System: The UNT Digital Library
Delamination Failure Investigation for Out-Of-Plane Loading in Laminates (open access)

Delamination Failure Investigation for Out-Of-Plane Loading in Laminates

In contrast to failure approaches at the lamina level or the micromechanics level the present work concerns failure characterization at the laminate level. Specifically, attention is given to the ultimate failure characterization for quasi-isotropic laminates. This is in further contrast to the commonly used approaches for initial damage or progressive damage. It is shown that the analytical failure forms decompose into two modes, one for out of plane, delamination type failure and one for in plane, fiber controlled type failure. The work here is mainly given over to the delamination mode of failure. Experimental results are presented for laminates in this mode of failure. These results are then integrated with the analytical forms to give a simple criterion for delamination failure.
Date: March 26, 2003
Creator: Christensen, R M & DeTeresa, S J
Object Type: Article
System: The UNT Digital Library
Proposed Specification of EUVL Mask Substrate Roughness (open access)

Proposed Specification of EUVL Mask Substrate Roughness

A revised specification of mask substrate roughness was proposed at the 1st International EUVL Symposium in Dallas in 2002 [1]. This document describes the reasoning behind the proposed revision in more detail. The specification of mask substrate roughness should be based on its effect on lithographic performance. The effects of mask roughness can be considered according to the spatial frequency. At high frequencies (f > M x NA/{lambda}) corresponding to spatial periods too small to be resolved, light is scattered outside the angular acceptance of the camera effectively reducing the reflectivity of the mask. At lower frequencies, f > M x NA/{lambda}, light is scattered within the acceptance angle of the camera and can degrade the aerial image quality. The loss in reflectivity due to high-spatial frequency roughness (HSFR) is given by R/R{sub 0} = exp(-(4{pi}{sigma}/{lambda}){sup 2}), (1) where R{sub 0} is the peak reflectivity of the coating on a smooth substrate, {sigma} is the HSFR after multilayer coating. The relationship between top surface roughness and substrate roughness depends on the multilayer deposition process and significant smoothing of substrate roughness has been demonstrated [2]. Ultimately the specification of HSFR may be best decided based on the multilayer deposition process. For …
Date: September 26, 2003
Creator: Gullikson, E.; Walton, C. C. & Taylor, J. S.
Object Type: Article
System: The UNT Digital Library
6th Workshop on Fast Ignition of Fusion Targets (open access)

6th Workshop on Fast Ignition of Fusion Targets

None
Date: March 26, 2003
Creator: Key, M H
Object Type: Report
System: The UNT Digital Library
A Reduced Model of Kinetic Effects Related to the Saturation of Stimulated Brillouin Scattering (open access)

A Reduced Model of Kinetic Effects Related to the Saturation of Stimulated Brillouin Scattering

We developed a reduced description of kinetic effects that is included in a fluid model of stimulated Brillouin backscattering (SBS) in low Z plasmas (e.g. He, Be). Following hybrid-PIC simulations, the modified ion distribution function is parametrized by the width {delta} of the plateau created by trapping around the phase velocity of the SBS-driven acoustic wave. An evolution equation is derived for {delta}, which affects SBS through a frequency shift and a reduced Landau damping. This model recovers the linear Landau damping value for small waves and the time-asymptotic nonlinear frequency shift calculated by Morales and O'Neil. Finally we compare our reduced model with Bzohar simulations of a Be plasma representative of experiments that have shown evidence of ion trapping.
Date: August 26, 2003
Creator: Divol, L.; Williams, E. A.; Cohen, B. I.; Langdon, A. B. & Lasinski, B. F.
Object Type: Article
System: The UNT Digital Library
Proteins as paradigms of complex systems. (open access)

Proteins as paradigms of complex systems.

The science of complexity has moved to center stage within the past few decades. Complex systems range from glasses to the immune system and the brain. Glasses are too simple to possess all aspects of complexity; brains are too complex to expose common concepts and laws of complexity. Proteins, however, are systems where many concepts and laws of complexity can be explored experimentally, theoretically, and computationally. Such studies have elucidated crucial aspects. The energy landscape has emerged as one central concept; it describes the free energy of a system as a function of temperature and the coordinates of all relevant atoms. A second concept is that of fluctuations. Without fluctuations, proteins would be dead and life impossible. A third concept is slaving. Proteins are not isolated systems; they are embedded in cells and membranes. Slaving arises when the fluctuations in the surroundings of a protein dominate many of the motions of the protein proper.
Date: March 26, 2003
Creator: Fenimore, Paul W.; Frauenfelder, Hans & Young, Robert D.
Object Type: Article
System: The UNT Digital Library
Lepton-flavor mixing and K --> pi nu nu bar decays (open access)

Lepton-flavor mixing and K --> pi nu nu bar decays

The impact of possible sources of lepton-flavor mixing on K {yields} {pi}{nu}{bar {nu}} decays is analyzed. At the one-loop level lepton-flavor mixing originated from non-diagonal lepton mass matrices cannot generate a CP-conserving K{sub L} {yields} {pi}{sup 0}{nu}{bar {nu}} amplitude. The rates of these modes are sensitive to leptonic flavor violation when there are at least two different leptonic mixing matrices. New interactions that violate both quark and lepton universalities could enhance the CP-conserving component of {Lambda}(K{sub L} {yields} {pi}{sup 0}{nu}{bar {nu}}) and have a substantial impact. Explicit examples of these effects in the context of supersymmetric models, with and without R-parity conservation, are discussed.
Date: November 26, 2003
Creator: Grossman, Yuval; Isidori, Gino & Murayama, Hitoshi
Object Type: Article
System: The UNT Digital Library
The Minimal Supersymmetric Fat Higgs Model (open access)

The Minimal Supersymmetric Fat Higgs Model

We present a calculable supersymmetric theory of a composite"fat'" Higgs boson. Electroweak symmetry is broken dynamically through a new gauge interaction that becomes strong at an intermediate scale. The Higgs mass can easily be 200-450 GeV along with the superpartner masses, solving the supersymmetric little hierarchy problem. We explicitly verify that the model is consistent with precision electroweak data without fine-tuning. Gauge coupling unification can be maintained despite the inherently strong dynamics involved in electroweak symmetry breaking. Supersymmetrizing the Standard Model therefore does not imply a light Higgs mass, contrary to the lore in the literature. The Higgs sector of the minimal Fat Higgs model has a mass spectrum that is distinctly different from the Minimal Supersymmetric Standard Model.
Date: November 26, 2003
Creator: Harnik, Roni; Kribs, Graham D.; Larson, Daniel T. & Murayama, Hitoshi
Object Type: Article
System: The UNT Digital Library
Adventures in Coulomb Gauge (open access)

Adventures in Coulomb Gauge

We study the phase structure of SU(2) gauge theories at zero and high temperature, with and without scalar matter fields, in terms of the symmetric/broken realization of the remnant gauge symmetry which exists after fixing to Coulomb gauge. The symmetric realization is associated with a linearly rising color Coulomb potential (which we compute numerically), and is a necessary but not sufficient condition for confinement.
Date: September 26, 2003
Creator: Greensite, J. & Olejnik, S.
Object Type: Article
System: The UNT Digital Library
On the speed of gravity and the nu/c corrections to the Shapirotime delay (open access)

On the speed of gravity and the nu/c corrections to the Shapirotime delay

I compute the v/c correction to the gravitational time delayfor light passing by a massive object moving with speed v, and I finddisagreement with previously published results. It is also argued thatthe speed of gravity formula that was recently used in the conjunction ofJupiter and quasar J0842+1845 is frame dependent.
Date: March 26, 2003
Creator: Samuel, Stuart
Object Type: Article
System: The UNT Digital Library
Fundamentals of Delayed Coking Joint Industry Project (open access)

Fundamentals of Delayed Coking Joint Industry Project

Delayed coking evolved steadily over the early to mid 1900s to enable refiners to convert high boiling, residual petroleum fractions to light products such as gasoline. Pound for pound, coking is the most energy intensive of any operation in a modern refinery. Large amounts of energy are required to heat the thick, poor-quality petroleum residuum to the 900 to 950 degrees F required to crack the heavy hydrocarbon molecules into lighter, more valuable products. One common misconception of delayed coking is that the product coke is a disadvantage. Although coke is a low valued (near zero economic value) byproduct, compared to transportation fuels, there is a significant worldwide trade and demand for coke as it is an economical fuel. Coke production has increased steadily over the last ten years, with further increases forecast for the foreseeable future. Current domestic production is near 111,000 tons per day. A major driving force behind this increase is the steady decline in crude quality available to refiners. Crude slates are expected to grow heavier with higher sulfur contents while environmental restrictions are expected to significantly reduce the demand for high-sulfur residual fuel oil. Light sweet crudes will continue to be available and in even …
Date: September 26, 2003
Creator: Volk, Michael & Wisecarver, Keith
Object Type: Report
System: The UNT Digital Library
Beneficial Reuse of San Ardo Produced Water (open access)

Beneficial Reuse of San Ardo Produced Water

This report summarizes the work performed from 1 April 2003 to 30 September 2003 and recommends the tasks to be performed during Phase II (Pilot Evaluation). During this period discussions were held with various water agencies regarding use of the treated produced water either directly or indirectly through a water trading arrangement. In particular, several discussions were held with Monterey County Water Resources Agency, that has been charged with the long-term management and preservation of water resources in Monterey County. The Agency is very supportive of the program. However, they would like to see water quality/cost estimate data for the treated produced water from the pilot study prior to evaluating water use/water trade options. The agency sent a letter encouraging the project team to perform the pilot study to evaluate feasibility of the project. In addition, the regulations related to use of the treated water for various applications were updated during this period. Finally, the work plan, health and safety plan and sample analyses plan for performing pilot study to treat the oilfield produced water were developed during this period.
Date: September 26, 2003
Creator: Liske, Robert A.
Object Type: Report
System: The UNT Digital Library
Local Structure and Vibrational Properties of α'-Pu Martensitein Ga-Stabilized δ-Pu (open access)

Local Structure and Vibrational Properties of α'-Pu Martensitein Ga-Stabilized δ-Pu

Extended x-ray absorption fine structure spectroscopy (EXAFS) is used to investigate the local atomic environment and vibrational properties of plutonium and gallium atoms in the {alpha}{prime} and {delta} phases of a mixed phase Pu-Ga alloy. EXAFS results measured at low temperature compare the structure of the mixed phase sample with a single-phase {delta}-Pu sample. EXAFS spectral components attributed to both {alpha}{prime}-Pu and {delta}-Pu were observed in the mixed phase sample. Ga K-edge EXAFS spectra indicate local atomic environments similar to the Pu LIII-edge EXAFS results, which suggests that Ga is substitutional for Pu atoms in both the monoclinic {alpha}{prime}-Pu and the fcc {delta}-Pu structures. In {delta}-Pu, we measure a Ga-Pu bond length contraction of 0.11 Angstroms with respect to the Pu-Pu bond length. The corresponding bond-length contraction around Ga in {alpha}{prime}-Pu is only 0.03 Angstroms. Results from temperature-dependent Pu LIII-edge EXAFS measurements are fit to a correlated Debye model, and a large difference in the Pu-Pu bond Debye temperature is observed for the {alpha}{prime} and {delta} phases: {theta}{sub cD}({alpha}{prime})=159{+-}13 K versus {theta}{sub cD}({delta})=120{+-}3 K. The corresponding analysis for the Ga K EXAFS determines a Ga-Pu bond Debye temperature of {theta}{sub cD}({delta})=188{+-}12 K in the {delta}-Pu phase. These results are related …
Date: February 26, 2003
Creator: Nelson, E. J.; Blobaum, K. J. M.; Wall, M. A.; Allen, P. G.; Schwartz, A. J. & Booth, C. H.
Object Type: Article
System: The UNT Digital Library
Economic Feasibility of Carbon Sequestration with Enhanced Gas Recovery (CSEGR) (open access)

Economic Feasibility of Carbon Sequestration with Enhanced Gas Recovery (CSEGR)

Prior reservoir simulation and laboratory studies have suggested that injecting carbon dioxide into mature natural gas reservoirs for carbon sequestration with enhanced gas recovery (CSEGR) is technically feasible. Reservoir simulations show that the high density of carbon dioxide can be exploited to favor displacement of methane with limited gas mixing by injecting carbon dioxide in low regions of a reservoir while producing from higher regions in the reservoir. Economic sensitivity analysis of a prototypical CSEGR application at a large depleting gas field in California shows that the largest expense will be for carbon dioxide capture, purification, compression, and transport to the field. Other incremental costs for CSEGR include: (1) new or reconditioned wells for carbon dioxide injection, methane production, and monitoring; (2) carbon dioxide distribution within the field; and, (3) separation facilities to handle eventual carbon dioxide contamination of the methane. Economic feasibility is most sensitive to wellhead methane price, carbon dioxide supply costs, and the ratio of carbon dioxide injected to incremental methane produced. Our analysis suggests that CSEGR may be economically feasible at carbon dioxide supply costs of up to $4 to $12/t ($0.20 to $0.63/Mcf). Although this analysis is based on a particular gas field, the approach …
Date: February 26, 2003
Creator: Oldenburg, C. M.; Stevens, S. H. & Benson, S. M.
Object Type: Article
System: The UNT Digital Library
St. Louis FUSRAP Lessons Learned (open access)

St. Louis FUSRAP Lessons Learned

The purpose of this paper is to present lessons learned from fours years' experience conducting Remedial Investigation and Remedial Action activities at the St. Louis Downtown Site (SLDS) under the Formerly Utilized Sites Remedial Action Program (FUSRAP). Many FUSRAP sites are experiencing challenges conducting Remedial Actions within forecasted volume and budget estimates. The St. Louis FUSRAP lessons learned provide insight to options for cost effective remediation at FUSRAP sites. The lessons learned are focused on project planning (budget and schedule), investigation, design, and construction.
Date: February 26, 2003
Creator: Eberlin, J.; Williams, D. & Mueller, D.
Object Type: Article
System: The UNT Digital Library
Waste Management Policy Framework to Mitigate Terrorist Intrusion Activities (open access)

Waste Management Policy Framework to Mitigate Terrorist Intrusion Activities

A policy-directed framework is developed to support US Department of Energy (DOE) counterterrorism efforts, specifically terrorist intrusion activities that affect of Environmental Management (EM) programs. The framework is called the Security Effectiveness and Resource Allocation Definition Forecasting and Control System (SERAD-FACS). Use of SERAD-FACS allows trade-offs between resources, technologies, risk, and Research and Development (R&D) efforts to mitigate such intrusion attempts. Core to SERAD-FACS is (1) the understanding the perspectives and time horizons of key decisionmakers and organizations, (2) a determination of site vulnerabilities and accessibilities, and (3) quantifying the measures that describe the risk associated with a compromise of EM assets. The innovative utility of SERAD-FACS is illustrated for three integrated waste management and security strategies. EM program risks, time delays, and security for effectiveness are examined to demonstrate the significant cost and schedule impact terrorist activities can have on cleanup efforts in the DOE complex.
Date: February 26, 2003
Creator: Redus, Kenneth, S.
Object Type: Article
System: The UNT Digital Library
Risk Communication Within the EM Program (open access)

Risk Communication Within the EM Program

The U.S. Department of Energy Environmental Management program (EM) conducts the most extensive environmental remediation effort in the world. The annual EM budgets have exceeded $6,000,000,000 for approximately ten years and EM has assumed responsibility for the cleanup of the largest DOE reservations (i.e., at Hanford, Washington, Aiken, South Carolina, and Idaho Falls, Idaho) as well as the facilities at Rocky Flats, Colorado and in Ohio. Each of these sites has areas of extensive radioactive and chemical contamination, numerous surplus facilities that require decontamination and removal, while some have special nuclear material that requires secure storage. The EM program has been criticized for being ineffective (1) and has been repeatedly reorganized to address perceived shortcomings. The most recent reorganization was announced in 2001 to become effective at the beginning of the 2003 Federal Fiscal Year (i.e., October 2002). It was preceded by a ''top to bottom'' review (TTBR) of the program (2) that identified several deficiencies that were to be corrected as a result of the reorganization. One prominent outcome of the TTBR was the identification of ''risk reduction'' as an organizing principle to prioritize the activities of the new EM program. The new program also sought to accelerate progress …
Date: February 26, 2003
Creator: Edelson, M.
Object Type: Article
System: The UNT Digital Library
Managing Decommissioning Projects Using D&D Trak (open access)

Managing Decommissioning Projects Using D&D Trak

Numerous buildings throughout the DOE complex are being decommissioned. The decommissioning process typically includes dismantling equipment and utility systems for disposal, decontaminating remaining surfaces to meet regulatory limits, demolishing the building structure, and remediating the surrounding environment to address any historical releases. Typically, a large amount of information and radiation survey data needs to be processed and evaluated. Rapid assessment of project information is required to effectively manage unanticipated conditions that are frequently encountered as building components are dismantled. Parsons has developed a relational database called D&D TRAK to estimate, plan, manage, and track decommissioning projects. D&D TRAK has been successfully used at DOE and other federal facilities to terminate radioactive licenses thus allowing the unrestricted free-release of these buildings to public and private sectors.
Date: February 26, 2003
Creator: Stegen, R.; Wilkinson, R.; Frink, P. & Karas, T.
Object Type: Article
System: The UNT Digital Library
Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III-nitride alloys (open access)

Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III-nitride alloys

None
Date: August 26, 2003
Creator: Li, S. X.; Wu, J.; Haller, E. E.; Walukiewicz, W.; Shan, W.; Lu, Hai et al.
Object Type: Article
System: The UNT Digital Library
Substantial Variability Exists in Utilities' Nuclear Decommissioning Funding Adequacy: Baseline Trends (1997-2001); and Scenario and Sensitivity Analyses (Year 2001) (open access)

Substantial Variability Exists in Utilities' Nuclear Decommissioning Funding Adequacy: Baseline Trends (1997-2001); and Scenario and Sensitivity Analyses (Year 2001)

This paper explores the trends over 1997-2001 in my baseline simulation analysis of the sufficiency of electric utilities' funds to eventually decommission the nation's nuclear power plants. Further, for 2001, I describe the utilities' funding adequacy results obtained using scenario and sensitivity analyses, respectively. In this paper, I focus more on the wide variability observed in these adequacy measures among utilities than on the results for the ''average'' utility in the nuclear industry. Only individual utilities, not average utilities -- often used by the nuclear industry to represent its funding adequacy -- will decommission their nuclear plants. Industry-wide results tend to mask the varied results for individual utilities. This paper shows that over 1997-2001, the variability of my baseline decommissioning funding adequacy measures (in percentages) for both utility fund balances and current contributions has remained very large, reflected in the sizable ranges and frequency distributions of these percentages. The relevance of this variability for nuclear decommissioning funding adequacy is, of course, focused more on those utilities that show below ideal balances and contribution levels. Looking backward, 42 of 67 utility fund (available) balances, in 2001, were above (and 25 below) their ideal baseline levels; in 1997, 42 of 76 were …
Date: February 26, 2003
Creator: Williams, D. G.
Object Type: Article
System: The UNT Digital Library
Technology Roadmapping for Waste Management (open access)

Technology Roadmapping for Waste Management

Technology roadmapping can be an effective strategic technology planning tool. This paper describes a process for customizing a generic technology roadmapping process. Starting with a generic process reduces the learning curve and speeds up the roadmap development. Similarly, starting with a generic domain model provides leverage across multiple applications or situations within the domain. A process that combines these two approaches facilitates identifying technology gaps and determining common core technologies that can be reused for multiple applications or situations within the domain. This paper describes both of these processes and how they can be integrated. A core team and a number of technology working groups develop the technology roadmap, which includes critical system requirements and targets, technology areas and metrics for each area, and identifies and evaluates possible technology alternatives to recommend the most appropriate ones to pursue. A generalized waste management model, generated by considering multiple situations or applications in terms of a generic waste management model, provides the domain requirements for the technology roadmapping process. Finally, the paper discusses lessons learns from a number of roadmapping projects.
Date: February 26, 2003
Creator: Bray, O.
Object Type: Article
System: The UNT Digital Library
Time-Temperature-Transformation Study of Simulated Hanford Tank Waste (AZ-101) and Optimization of Glass Formulation for Processing Such Waste (open access)

Time-Temperature-Transformation Study of Simulated Hanford Tank Waste (AZ-101) and Optimization of Glass Formulation for Processing Such Waste

This paper presents the current results of a study for the optimization of the quality of the wasteform to be produced by vitrification of Hanford High Level Waste (HLW). A simulant of the content of Hanford Tank AZ-101 has been used for the experiments. A first phase of the research focused on the wasteform composition and showed that a high quality and chemical-resistant wasteform can be formed incorporating 60 weight % of dried waste into a borosilicate glass enriched with zinc oxide and boric acid and provided some indication about the heat treatment of the melt. A second phase of the study, still in progress, refines these findings. A detailed crystallinity survey of the waste form after various heat treatments has been performed, culminating in the development of a time-temperature-transformation (TTT) diagram. The results of the first phase of research and preliminary results from the second phase are described.
Date: February 26, 2003
Creator: Ramsey, W. G.; Kauffman, B. M.; Bricka, M.; Meaker, T. F.; Giordana, A.; Smith, J. D. et al.
Object Type: Article
System: The UNT Digital Library