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2,939 Matching Results
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Development and Characterization of a Single Line of Sight Framing Camera
We present initial characterization data from a new single line of sight (SLOS) x-ray framing camera. The instrument uses an image dissecting structure inside an electron optic tube to produce up to four simultaneous DC images from a single image incident on the cathode and a microchannel plate based device to provide the temporal gating of those images. A series of gated images have been obtained using a short pulse UV laser source, and the spatial resolution of those images is compared to those obtained using a more traditional MCP based system.
Date:
June 13, 2000
Creator:
Bradley, D K; Bell, P M; Dymoke-Bradshaw, A K L; Hares, J D; Bahr, R E & Smalyuk, V A
Object Type:
Article
System:
The UNT Digital Library
Cloud-Resolving Model Intercomparison with the ARM Summer 1997 IOP Data
The Atmospheric Radiation Measurement (ARM) Program's Single Column Model (SCM) working group conducted its intercomparison study of midlatitude summertime continental convection using the July 1995 Intensive Operational Period (IOP) data set (Ghan et al. 2000). Only one cloud-resolving model (CRM) participated in the study. On the other hand, several CRMs participated in the GEWEX (Global Energy and Water-cycle Experiment) Cloud System Study (GCSS) Working Group 4's intercomparison study of tropical deep convection (Krueger and Lazarus 1998; Redelsperger et al. 2000). Both groups decided to have a joint intercomparison project to maximize the resources and advance our understanding of midlatitude continental convection. This joint project compares the cloud-resolving and single-column simulations of summertime continental cumulus convection observed at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site during the ARM Summer 1997 IOP. This paper reports the findings and results of cloud-resolving simulations, while Cederwall et al. (2000) reports the SCM part of the project. Seven CRMs are participating in this project.
Date:
March 13, 2000
Creator:
Xu, K. M.; Johnson, D. E.; Tao, W. K.; Krueger, S. K.; Khairoutdinov, M.; Randall, D. A. et al.
Object Type:
Article
System:
The UNT Digital Library
Beam Energy Scaling of Ion-Induced Electron Yield From K+ Ions Impact on Stainless Steel Surfaces
None
Date:
May 13, 2005
Creator:
Covo, M K; Molvik, A; Friedman, A; Westenskow, G; Barnard, J J; Cohen, R et al.
Object Type:
Article
System:
The UNT Digital Library
FFAG-BASED HIGH-INTENSITY PROTON DRIVERS.
This paper is the summary of a feasibility study of a Fixed-Field Alternating-Gradient (FFAG) Accelerator for Protons in the one-to-few GeV energy range, and average beam power of several MWatt. The example they have adopted here is a beam energy of 1 GeV and an average power of 10 MWatt, but of course the same design approach can be used with other beam parameters. The design principles, merits and limitations of the FFAG accelerators have been described previously. In particular, more advanced techniques to minimize magnet dimension and field strength have been recently proposed. The design makes use of a novel concept by which it is possible to cancel chromatic effects, thus making betatron tunes and functions independent of the particle momentum, with an Adjusted Field Profile. The example given here assumes a pulsed mode of operation at the repetition rate of 1.0 kHz.
Date:
October 13, 2004
Creator:
RUGGIERO, A. G.
Object Type:
Article
System:
The UNT Digital Library
Calibration Tools for Measurement of Highly Enriched Uranium in Oxide and Mixed Uranium-Plutonium Oxide with a Passive-Active Neutron Drum Shuffler
Lawrence Livermore National Laboratory (LLNL) has completed an extensive effort to calibrate the LLNL passive-active neutron drum (PAN) shuffler (Canberra Model JCC-92) for accountability measurement of highly enriched uranium (HEU) oxide and HEU in mixed uranium-plutonium (U-Pu) oxide. Earlier papers described the PAN shuffler calibration over a range of item properties by standards measurements and an extensive series of detailed simulation calculations. With a single normalization factor, the simulations agree with the HEU oxide standards measurements to within {+-}1.2% at one standard deviation. Measurement errors on mixed U-Pu oxide samples are in the {+-}2% to {+-}10% range, or {+-}20 g for the smaller items. The purpose of this paper is to facilitate transfer of the LLNL procedure and calibration algorithms to external users who possess an identical, or equivalent, PAN shuffler. Steps include (1) measurement of HEU standards or working reference materials (WRMs); (2) MCNP simulation calculations for the standards or WRMs and a range of possible masses in the same containers; (3) a normalization of the calibration algorithms using the standard or WRM measurements to account for differences in the {sup 252}Cf source strength, the delayed-neutron nuclear data, effects of the irradiation protocol, and detector efficiency; and (4) a …
Date:
June 13, 2003
Creator:
Mount, M.; O'Connell, W.; Cochran, C. & Rinard, P.
Object Type:
Article
System:
The UNT Digital Library
Nucleation of GaN/AlN quantum dots
We study the nucleation of GaN islands grown by plasma-assisted molecular-beam epitaxy on AlN in a Stranski-Krastanov mode. In particular, we assess the variation of their height and density as a function of GaN coverage. We show that the GaN growth passes four stages: initially, the growth is layer-by-layer; subsequently, bidimensional precursor islands form, which transform into genuine three-dimensional islands. During the latter stage, the height and the density of the islands increase with GaN coverage until the density saturates. During further GaN growth, the density remains constant and a bimodal height distribution appears. The variation of island height and density as a function of substrate temperature is discussed in the framework of an equilibrium model for Stranski-Krastanov growth [R. E. Rudd et al., Phys. Rev. Lett. 90, 146101 (2003)].
Date:
October 13, 2003
Creator:
Adelmann, C.; Daudin, B.; Oliver, R. A.; Briggs, G. A. D. & Rudd, R. E.
Object Type:
Article
System:
The UNT Digital Library
Energy End-Use Technologies for the 21st Century
The World Energy Council's recent study examined the potential of energy end-use technologies and of research, development, and demonstration (RD&D) into these technologies on a global scale. Surprises are likely, but nevertheless, current research and development offer a picture of what might happen in the future as new technologies face the competition of the marketplace. Given the breadth of energy end-use technologies and the differences between regions and economic conditions, the study focused on technologies that appear most important from today's vantage point. Globally, robust research and development followed by demonstrations of new end-use technologies can potentially save at least 110 EJ/year by 2020 and over 300 EJ/year by 2050. If achieved, this translates to worldwide energy savings of as much as 25% by 2020 and over 40% by 2050, over what may be required without these technologies. It is almost certain that no single technology, or even a small set of technologies, will dominate in meeting the needs of the globe in any foreseeable timeframe. Absent a significant joint government-industry effort on end-use technology RD&D, the technologies needed will not be ready for the marketplace in the timeframes required with even the most pessimistic scenarios. Based on previous detailed …
Date:
April 13, 2005
Creator:
Gehl, Stephen; Haegermark, Harald; Larsen, Hans; Morishita, Masao; Nakicenovic, Nebojsa; Schock, Robert N. et al.
Object Type:
Article
System:
The UNT Digital Library
Validation of Two CFD Urban Dispersion Models using High Resolution Wind Tunnel Data
Numerical modeling of air flow and pollutant dispersion around buildings in the urban environment is a challenging task due to the geometrical variations of buildings and the extremely complex flow created by such surface-mounted obstacles. Building-scale air flows inevitably involve flow impingement, stagnation, separation, a multiple vortex system, and jetting effects in street canyons. Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL) have developed two complementary, robust computational fluid dynamics (CFD) models, FEM3MP by LLNL and HIGRAD by LANL, for such purposes. Our primary goal is to support emergency response planning, vulnerability analysis, and development of mitigation strategies for chem-bio agents released in the urban environment. Model validation is vitally important in establishing the credibility of CFD models. We have, in the past, performed model validation studies involving simpler geometries, such as flow and dispersion past a cubical building [1] and flow around a 2-D building array [2]. In this study, wind tunnel data for a 7 x 11 array of cubical buildings [3] are used to further validate our models.
Date:
July 13, 2001
Creator:
Chan, S; Stevens, D E & Smith, W. S.
Object Type:
Article
System:
The UNT Digital Library
A Fusion Reactor Design with a Liquid First Wall and Divertor
Within the magnetic fusion energy program in the US, a program called APEX is investigating the use of free flowing liquid surfaces to form the inner surface of the chamber around the plasma. As part of this work, the APEX Team has investigated several possible design implementations and developed a specific engineering concept for a fusion reactor with liquid walls. Our approach has been to utilize an already established design for a future fusion reactor, the ARIES-RS, for the basic chamber geometry and magnetic configuration and to replace the chamber technology in this design with liquid wall technology for a first wall and divertor and a blanket with adequate tritium breeding. This paper gives an overview of one design with a molten salt (a mixture of lithium, beryllium and sodium fluorides) forming the liquid surfaces and a ferritic steel for the structural material of the blanket. The design point is a reactor with 3840MW of fusion power of which 767MW is in the form of energetic particles (alpha power) and 3073MW is in the form of neutrons. The alpha plus auxiliary power total 909MW of which 430MW is radiated from the core mostly onto the first wall and the balance …
Date:
November 13, 2003
Creator:
Nygren, R E; Rognlien, T D; Rensink, M E; Smolentsev, S S; Youssef, M E; Sawan, M Z et al.
Object Type:
Article
System:
The UNT Digital Library
Radionuclide Mobility at the Nevada Test Site
Underground nuclear tests conducted at the Nevada Test Site (NTS) are characterized by abundant fission product and actinide source terms. Included are {sup 99}Tc and other soluble radionuclides ({sup 3}H, {sup 14}C, {sup 36}Cl, {sup 85}Kr, and {sup 129}I), which are presumably mobile in groundwater and potentially toxic to down-gradient receptors. NTS provides the Office of Civilian Radioactive Waste Management (OCRWM) with an analog of the release of these radionuclides from a nuclear waste repository in the absence of engineered barriers. The investigation described in this report synthesizes a substantial body of data collected on the identity and distribution of soluble radionuclides at field scales over distances of hundreds of meters, for durations up to 40 years, and under hydrogeologic conditions very similar to the proposed geological repository at Yucca Mountain. This body of data is complemented by laboratory transport studies and a synthesis of recent modeling investigations from the NTS, with an emphasis on the ongoing Yucca Mountain Program (YMP) efforts. Overall, understanding the controls of radionuclide mobility associated with these nuclear tests will provide insight into the repository's future performance as well as bounds and calibrations for the numerical predictions of long-term radionuclide releases and migration.
Date:
November 13, 2003
Creator:
Hu, Qinhong (Max); Smith, David K.; Rose, Timothy; Glascoe, Lee; Steefel, Carl & Zavarin, Mavrik
Object Type:
Report
System:
The UNT Digital Library
Oxidative Dna Damage Background Estimated by a System Model of Base Excision Repair
Human DNA can be damaged by natural metabolism through free radical production. It has been suggested that the equilibrium between innate damage and cellular DNA repair results in an oxidative DNA damage background that potentially contributes to disease and aging. Efforts to quantitatively characterize the human oxidative DNA damage background level based on measuring 8-oxoguanine lesions as a biomarker have led to estimates varying over 3-4 orders of magnitude, depending on the method of measurement. We applied a previously developed and validated quantitative pathway model of human DNA base excision repair, integrating experimentally determined endogenous damage rates and model parameters from multiple sources. Our estimates of at most 100 8-oxoguanine lesions per cell are consistent with the low end of data from biochemical and cell biology experiments, a result robust to model limitations and parameter variation. Our results show the power of quantitative system modeling to interpret composite experimental data and make biologically and physiologically relevant predictions for complex human DNA repair pathway mechanisms and capacity.
Date:
May 13, 2004
Creator:
Sokhansanj, B. A. & Wilson, D. M., III
Object Type:
Article
System:
The UNT Digital Library