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1,575 Matching Results
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The Absence of Plasma in"Spark Plasma Sintering"
Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.
Date:
April 10, 2008
Creator:
Hulbert, Dustin M.; Anders, Andre; Dudina, Dina V.; Andersson, Joakim; Jiang, Dongtao; Unuvar, Cosan et al.
Object Type:
Article
System:
The UNT Digital Library
PREDICTION OF CHARACTERISTIC LENGTH AND FRACTURE TOUGHNESS IN DUCTILE-BRITTLE TRANSITION
Finite element method was used to analyze the three-point bend experimental data of A533B-1 pressure vessel steel obtained by Sherry, Lidbury, and Beardsmore [1] from -160 to -45 C within the ductile-brittle transition regime. As many researchers have shown, the failure stress ({sigma}{sub f}) of the material could be approximated as a constant. The characteristic length, or the critical distance (r{sub c}) from the crack tip, at which {sigma}{sub f} is reached, is shown to be temperature dependent based on the crack tip stress field calculated by the finite element method. With the J-A{sub 2} two-parameter constraint theory in fracture mechanics, the fracture toughness (J{sub C} or K{sub JC}) can be expressed as a function of the constraint level (A{sub 2}) and the critical distance r{sub c}. This relationship is used to predict the fracture toughness of A533B-1 in the ductile-brittle transition regime with a constant {sigma}{sub f} and a set of temperature-dependent r{sub c}. It can be shown that the prediction agrees well with the test data for wide range of constraint levels from shallow cracks (a/W= 0.075) to deep cracks (a/W= 0.5), where a is the crack length and W is the specimen width.
Date:
April 15, 2008
Creator:
Lam, P
Object Type:
Article
System:
The UNT Digital Library
Emittance Reduction between EBIS LINAC and Booster by Electron Beam Cooling; Is Single Pass Cooling Possible?
Electron beam cooling is examined as an option to reduce momentum of gold ions exiting the EBIS LINAC before injection into the booster. Electron beam parameters are based on experimental data (obtained at BNL) of electron beams extracted from a plasma cathode. Preliminary calculations indicate that single pass cooling is feasible; momentum spread can be reduced by more than an order of magnitude in less than one meter.
Date:
April 1, 2008
Creator:
Hershcovitch,A.
Object Type:
Report
System:
The UNT Digital Library
Carbon Dioxide Selective Supported Ionic Liquid Membranes: The Effect of Contaminants
The integrated gasification combined cycle (IGCC) is widely viewed as a promising technology for the large scale production of energy in a carbon constrained world. These cycles, which include gasification, contaminant removal, water-gas shift, CO2 capture and compression, and combustion of the reduced-carbon fuel gas in a turbine, often have significant efficiency advantages over conventional combustion technologies. A CO2 selective membrane capable of maintaining performance at conditions approaching those of low temperature water-gas shift (260oC) could facilitate the production of carbon-neutral energy by simultaneously driving the shift reaction to completion and concentrating CO2 for sequestration. Supported ionic liquid membranes (SILMs) have been previously evaluated for this application and determined to be physically and chemically stable to temperatures in excess of 300oC. These membranes were based on ionic liquids which interacted physically with CO2 and diminished considerably in selectivity at higher temperatures. To alleviate this problem, the original ionic liquids were replaced with ionic liquids able to form chemical complexes with CO2. These complexing ionic liquid membranes have a local maximum in selectivity which is observed at increasing temperatures for more stable complexes. Efforts are currently underway to develop ionic liquids with selectivity maxima at temperatures greater than 75oC, the best …
Date:
April 1, 2008
Creator:
Luebke, D. R.; Ilconich, J. B.; Myers, C. R. & Pennline, H. W.
Object Type:
Article
System:
The UNT Digital Library
MSTD 2007 Publications and Patents
The Materials Science and Technology Division (MSTD) supports the central scientific and technological missions of the Laboratory, and at the same time, executes world-class, fundamental research and novel technological development over a wide range of disciplines. Our organization is driven by the institutional needs in nuclear weapons stockpile science, high-energy-density science, nuclear reactor science, and energy and environment science and technology. We maintain expertise and capabilities in many diverse areas, including actinide science, electron microscopy, laser-materials interactions, materials theory, simulation and modeling, materials synthesis and processing, materials science under extreme conditions, ultrafast materials science, metallurgy, nanoscience and technology, nuclear fuels and energy security, optical materials science, and surface science. MSTD scientists play leadership roles in the scientific community in these key and emerging areas.
Date:
April 1, 2008
Creator:
King, W. E.
Object Type:
Book
System:
The UNT Digital Library
Plug-In Hybrid Electric Vehicle Value Proposition Study: Phase 1, Task 2: Select Value Propositions/Business Model for Further Study
The Plug-In Hybrid Electric Vehicle (PHEV) Value Propositions Workshop held in Washington, D.C. in December 2007 served as the Task 1 Milestone for this study. Feedback from all five Workshop breakout sessions has been documented in a Workshop Summary Report, which can be found at www.sentech.org/phev. In this report, the project team compiled and presented a comprehensive list of potential value propositions that would later serve as a 'grab bag' of business model components in Task 2. After convening with the Guidance and Evaluation Committee and other PHEV stakeholders during the Workshop, several improvements to the technical approach were identified and incorporated into the project plan to present a more realistic and accurate case study and evaluation. The assumptions and modifications that will have the greatest impact on the case study selection process in Task 2 are described in more detail in this deliverable. The objective of Task 2 is to identify the combination of value propositions that is believed to be achievable by 2030 and collectively hold promise for a sustainable PHEV market by 2030. This deliverable outlines what the project team (with input from the Committee) has defined as its primary scenario to be tested in depth for …
Date:
April 1, 2008
Creator:
Sikes, Karen R; Markel, Lawrence C; Hadley, Stanton W & Hinds, Shaun
Object Type:
Report
System:
The UNT Digital Library
EE&RE; Session: CIGS
This project supports the Solar America Initiative by carrying out work on target topics identified for Photovoltaic Systems: (1) Improving cell and module efficiency of thin film Cu(In,Ga)Se2 materials; (2) Implementing the Science and Technology Facility (S&TF) and the Process Development and Integration Laboratory (PDIL) to facilitate laboratory/industry interaction in developing PV manufacturing technologies; (3) Addressing industrial issues in materials and manufacturing processes with the objective to lower the cost of PV power; (4) Providing technology transfer efforts to accelerate transition of thin film PV technology to market and deployment; (5) Assisting R&D efforts to asses and improve reliability and stability of thin film PV products; and (6) Assist the SAI TPPs in technical matters related to CIGS PV technology.
Date:
April 1, 2008
Creator:
Contreras, M.
Object Type:
Presentation
System:
The UNT Digital Library
Calculation of Reactive-evaporation Rates of Chromia
A methodology is developed to calculate Cr-evaporation rates from Cr2O3 with a flat planar geometry. Variables include temperature, total pressure, gas velocity, and gas composition. The methodology was applied to solid-oxide, fuel cell conditions for metallic interconnects and to advanced-steam turbines conditions. The high velocities and pressures of the advanced steam turbine led to evaporation predictions as high as 5.18 9 10-8 kg/m2/s of CrO2(OH)2(g) at 760 °C and 34.5 MPa. This is equivalent to 0.080 mm per year of solid Cr loss. Chromium evaporation is expected to be an important oxidation mechanism with the types of nickel-base alloys proposed for use above 650 °C in advanced-steam boilers and turbines. It is shown that laboratory experiments, with much lower steam velocities and usually much lower total pressure than found in advanced steam turbines, would best reproduce chromium-evaporation behavior with atmospheres that approach either O2 + H2O or air + H2O with 57% H2O.
Date:
April 1, 2008
Creator:
Holcomb, G. R.
Object Type:
Article
System:
The UNT Digital Library
Regional Consumer Hydrogen Demand and Optimal Hydrogen Refueling Station Siting
Using a GIS approach to spatially analyze key attributes affecting hydrogen market transformation, this study proposes hypothetical hydrogen refueling station locations in select subregions to demonstrate a method for determining station locations based on geographic criteria.
Date:
April 1, 2008
Creator:
Melendez, M. & Milbrandt, A.
Object Type:
Report
System:
The UNT Digital Library
Search for Heavy, Long-Lived Neutralinos that Decay to Photons at CDF II Using Photon Timing
The authors present the results of the first hadron collider search for heavy, long-lived neutralinos that decay via {tilde {chi}}{sub 1}{sup 0} {yields} {gamma}{tilde G} in gauge-mediated supersymmetry breaking models. Using an integrated luminosity of 570 {+-} 34 pb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV, they select {gamma}+jet+missing transverse energy candidate events based on the arrival time of a high-energy photon at the electromagnetic calorimeter as measured with a timing system that was recently installed on the CDF II detector. They find 2 events, consistent with the background estimate of 1.3 {+-} 0.7 events. While the search strategy does not rely on model-specific dynamics, they set cross section limits and place the world-best 95% C.L. lower limit on the {tilde {chi}}{sub 1}{sup 0} mass of 101 GeV/c{sup 2} at {tau}{sub {tilde {chi}}{sub 1}{sup 0}} = 5 ns.
Date:
April 1, 2008
Creator:
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Alvarez Gonzalez, B.; Amerio, S. et al.
Object Type:
Article
System:
The UNT Digital Library
Electronic structure effects in liquid water studied by photoelectron spectroscopy and density functional theory
We present valence photoelectron emission spectra of liquid water in comparison with gas-phase water, ice close to the melting point, low temperature amorphous and crystalline ice. All aggregation states have major electronic structure changes relative to the free molecule, with rehybridization and development of bonding and anti-bonding states accompanying the hydrogen bond formation. Sensitivity to the local structural order, most prominent in the shape and splitting of the occupied 3a{sub 1} orbital, is understood from the electronic structure averaging over various geometrical structures, and reflects the local nature of the orbital interaction.
Date:
April 29, 2008
Creator:
Nordlund, Dennis; Odelius, Michael; Bluhm, Hendrik; Ogasawara, Hirohito; Pettersson, Lars G.M. & Nilsson, Anders
Object Type:
Article
System:
The UNT Digital Library
PV Conversion Technologies; Session: OPV, Sensitized, Seed Funds
None
Date:
April 1, 2008
Creator:
Olson, D. C. & Ginley, D.
Object Type:
Presentation
System:
The UNT Digital Library
Search for CPT Violation in B0-B0bar Oscillations with BABAR
None
Date:
April 11, 2008
Creator:
Stoker, D. P. & /UC, Irvine
Object Type:
Article
System:
The UNT Digital Library
Technical Basis for Assessing Uranium Bioremediation Performance
In situ bioremediation of uranium holds significant promise for effective stabilization of U(VI) from groundwater at reduced cost compared to conventional pump and treat. This promise is unlikely to be realized unless researchers and practitioners successfully predict and demonstrate the long-term effectiveness of uranium bioremediation protocols. Field research to date has focused on both proof of principle and a mechanistic level of understanding. Current practice typically involves an engineering approach using proprietary amendments that focuses mainly on monitoring U(VI) concentration for a limited time period. Given the complexity of uranium biogeochemistry and uranium secondary minerals, and the lack of documented case studies, a systematic monitoring approach using multiple performance indicators is needed. This document provides an overview of uranium bioremediation, summarizes design considerations, and identifies and prioritizes field performance indicators for the application of uranium bioremediation. The performance indicators provided as part of this document are based on current biogeochemical understanding of uranium and will enable practitioners to monitor the performance of their system and make a strong case to clients, regulators, and the public that the future performance of the system can be assured and changes in performance addressed as needed. The performance indicators established by this document and …
Date:
April 1, 2008
Creator:
Long, P. E.; Yabusaki, S. B.; Meyer, P. D.; Murray, C. J. & N’Guessan, A. L.
Object Type:
Report
System:
The UNT Digital Library
Dissipative Cryogenic Filters with Zero DC Resistance
The authors designed, implemented and tested cryogenic RF filters with zero DC resistance, based on wires with a superconducting core inside a resistive sheath. The superconducting core allows low frequency currents to pass with negligible dissipation. Signals above the cutoff frequency are dissipated in the resistive part due to their small skin depth. The filters consist of twisted wire pairs shielded with copper tape. Above approximately 1 GHz, the attenuation is exponential in {radical}{omega}, as typical for skin depth based RF filters. By using additional capacitors of 10 nF per line, an attenuation of at least 45 dB above 10 MHz can be obtained. Thus, one single filter stage kept at mixing chamber temperature in a dilution refrigerator is sufficient to attenuate room temperature black body radiation to levels corresponding to 10 mK above about 10 MHz.
Date:
April 22, 2008
Creator:
Bluhm, Hendrik; Moler, Kathryn A. & /Stanford U., Appl. Phys. Dept
Object Type:
Article
System:
The UNT Digital Library
Ambient-temperature Conditioning as a Probe of Double-C Transformation Mechanisms in Pu-2.0 at. % Ga
The gallium-stabilized Pu-2.0 at. % Ga alloy undergoes a partial or incomplete low-temperature martensitic transformation from the metastable {delta} phase to the gallium-containing, monoclinic {alpha}{prime} phase near -100 C. This transformation has been shown to occur isothermally and it displays anomalous double-C kinetics in a time-temperature-transformation (TTT) diagram, where two nose temperatures anchoring an upper- and lower-C describe minima in the time for the initiation of transformation. The underlying mechanisms responsible for the double-C behavior are currently unresolved, although recent experiments suggest that a conditioning treatment--wherein, following an anneal at 375 C, the sample is held at a sub-anneal temperature for a period of time--significantly influences the upper-C of the TTT diagram. As such, elucidating the effects of the conditioning treatment upon the {delta} {yields} {alpha}{prime} transformation can provide valuable insights into the fundamental mechanisms governing the double-C kinetics of the transition. Following a high-temperature anneal, a differential scanning calorimeter (DSC) was used to establish an optimal conditioning curve that depicts the amount of {alpha}{prime} formed during the transformation as a function of conditioning temperature for a specified time. With the optimal conditioning curve as a baseline, the DSC was used to explore the circumstances under which the effects of …
Date:
April 2, 2008
Creator:
Jeffries, J R; Blobaum, K M; Wall, M A & Schwartz, A J
Object Type:
Article
System:
The UNT Digital Library
Supercomputers: Super-polluters?
Thanks to imperatives for limiting waste heat, maximizing performance, and controlling operating cost, energy efficiency has been a driving force in the evolution of supercomputers. The challenge going forward will be to extend these gains to offset the steeply rising demands for computing services and performance.
Date:
April 8, 2008
Creator:
Mills, Evan; Mills, Evan; Tschudi, William; Shalf, John & Simon, Horst
Object Type:
Article
System:
The UNT Digital Library
Modeling and Analysis Session: Market, Value, and Policy Analysis
The Primary objectives: to provide a broad range of analytical support to the Solar Program; and to anticipate and respond to the rapidly evolving analytical needs of the Solar Program. Three broad types of analysis are being carried out under this project including: (1) Market analysis: Developing a PV market penetration model--the SolarDS model--and other tools, in order to gain insight into the factors influencing market penetration of PV technology in U.S. markets. (2) Value analysis: Providing inputs to, support for, and review of the annual GPRA benefits analysis. Also developing methods and tools for improving the quantification of the benefits and cost of solar technologies. (3) Policy analysis: Defining and carrying out analysis that meets the needs of the Solar Energy Technologies Program in a timely fashion, for example evaluating the potential role of solar in the energy economy in the long-term.
Date:
April 1, 2008
Creator:
Margolis, R. M.
Object Type:
Presentation
System:
The UNT Digital Library
Worldlines as Wilson Lines
Gravitational theories do not admit gauge invariant local operators. We study the limits under which there exists a quasi-local description for a class of non-local gravitational observables where a sum over worldlines plays the role of the Wilson line for gauge theory observables. We study non-local corrections to the local description and circumstances where these corrections become large. We find that these operators are quasi-local in at space and AdS, but fail to be quasi-local in de Sitter space.
Date:
April 29, 2008
Creator:
Green, Daniel & /SLAC /Stanford U., Dept. Phys.
Object Type:
Article
System:
The UNT Digital Library
Multi-year search for a diffuse flxu of muon neutrinos with AMANDA-II
A search for TeV-PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent livetime of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with non-thermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of E{sup 2}{Phi}{sub 90%C.L.} < 7.4 x 10{sup -8} GeV cm{sup -2} s{sup -1} sr{sup -1} is placed on the diffuse flux of muon neutrinos with a {Phi} {proportional_to} E{sup -2} spectrum in the energy range 16 TeV to 2.5 PeV. This is currently the most sensitive {Phi} {proportional_to} E{sup -2} diffuse astrophysical neutrino limit. We also set upper limits for astrophysical and prompt neutrino models, all of which have spectra different than {Phi} {proportional_to} E{sup -2}.
Date:
April 13, 2008
Creator:
Collaboration, IceCube; Klein, Spencer; Achterberg, A. & Collaboration, IceCube
Object Type:
Article
System:
The UNT Digital Library
LUsim: A Framework for Simulation-Based Performance Modelingand Prediction of Parallel Sparse LU Factorization
Sparse parallel factorization is among the most complicated and irregular algorithms to analyze and optimize. Performance depends both on system characteristics such as the floating point rate, the memory hierarchy, and the interconnect performance, as well as input matrix characteristics such as such as the number and location of nonzeros. We present LUsim, a simulation framework for modeling the performance of sparse LU factorization. Our framework uses micro-benchmarks to calibrate the parameters of machine characteristics and additional tools to facilitate real-time performance modeling. We are using LUsim to analyze an existing parallel sparse LU factorization code, and to explore a latency tolerant variant. We developed and validated a model of the factorization in SuperLU_DIST, then we modeled and implemented a new variant of slud, replacing a blocking collective communication phase with a non-blocking asynchronous point-to-point one. Our strategy realized a mean improvement of 11percent over a suite of test matrices.
Date:
April 15, 2008
Creator:
Univ. of California, San Diego
Object Type:
Article
System:
The UNT Digital Library
On the Suitability of Lanthanides as Actinide Analogs
With the current level of actinide materials used in civilian power generation and the need for safe and efficient methods for the chemical separation of these species from their daughter products and for long-term storage requirements, a detailed understanding of actinide chemistry is of great importance. Due to the unique bonding properties of the f-elements, the lanthanides are commonly used as structural and chemical models for the actinides, but differences in the bonding between these 4f and 5f elements has become a question of immediate applicability to separations technology. This brief overview of actinide coordination chemistry in the Raymond group at UC Berkeley/LBNL examines the validity of using lanthanide analogs as structural models for the actinides, with particular attention paid to single crystal X-ray diffraction structures. Although lanthanides are commonly accepted as reasonable analogs for the actinides, these comparisons suggest the careful study of actinide materials independent of their lanthanide analogs to be of utmost importance to present and future efforts in nuclear industries.
Date:
April 11, 2008
Creator:
Szigethy, Geza & Raymond, Kenneth N.
Object Type:
Article
System:
The UNT Digital Library
Corrective Action Investigation Plan for Corrective Action Unit 370: T-4 Atmospheric Test Site, Nevada Test Site, Nevada with ROTC-1, Revision 0
Corrective Action Unit (CAU) 370 is located in Area 4 of the Nevada Test Site, which is approximately 65 miles northwest of Las Vegas, Nevada. Corrective Action Unit 370 is comprised of Corrective Action Site (CAS) 04-23-01, Atmospheric Test Site T-4. This site is being investigated because existing information on the nature and extent of potential contamination is insufficient to evaluate and/or implement a corrective action. Additional information will be obtained by conducting a corrective action investigation (CAI) before evaluating corrective action alternatives and selecting the appropriate corrective action for this CAS. The results of the field investigation will support a defensible evaluation of viable corrective action alternatives that will be presented in the Corrective Action Decision Document. The investigation results may also be used to evaluate improvements in the Soils Project strategy to be implemented. The site will be investigated based on the data quality objectives (DQOs) developed on December 10, 2007, by representatives of the Nevada Division of Environmental Protection; U.S. Department of Energy (DOE), National Nuclear Security Administration Nevada Site Office; Desert Research Institute; Stoller-Navarro Joint Venture; and National Security Technologies, LLC. The DQO process was used to identify and define the type, amount, and quality of …
Date:
April 1, 2008
Creator:
Matthews, Pat
Object Type:
Report
System:
The UNT Digital Library
Information Resources in High-Energy Physics: Surveying the Present Landscape and Charting the Future Course
Access to previous results is of paramount importance in the scientific process. Recent progress in information management focuses on building e-infrastructures for the optimization of the research workflow, through both policy-driven and user-pulled dynamics. For decades, High-Energy Physics (HEP) has pioneered innovative solutions in the field of information management and dissemination. In light of a transforming information environment, it is important to assess the current usage of information resources by researchers and HEP provides a unique test-bed for this assessment. A survey of about 10% of practitioners in the field reveals usage trends and information needs. Community-based services, such as the pioneering arXiv and SPIRES systems, largely answer the need of the scientists, with a limited but increasing fraction of younger users relying on Google. Commercial services offered by publishers or database vendors are essentially unused in the field. The survey offers an insight into the most important features that users require to optimize their research workflow. These results inform the future evolution of information management in HEP and, as these researchers are traditionally 'early adopters' of innovation in scholarly communication, can inspire developments of disciplinary repositories serving other communities.
Date:
April 22, 2008
Creator:
Gentil-Beccot, Anne; Mele, Salvatore; Holtkamp, Annette; O'Connell, Heath B. & Brooks, Travis C.
Object Type:
Article
System:
The UNT Digital Library