Resource Type

Month

10 Matching Results

Results open in a new window/tab.

SNAP Satellite Focal Plane Development (open access)

SNAP Satellite Focal Plane Development

The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square degree field in the visible and near-infrared wavelength regime. The requirements for the instrument suite and the present configuration of the focal plane concept are presented. A two year R&D phase, largely supported by the Department of Energy, is just beginning. We describe the development activities that are taking place to advance our preparedness for mission proposal in the areas of detectors and electronics.
Date: July 7, 2003
Creator: Bebek, C.; Akerlof, C.; Aldering, G.; Amanullah, R.; Astier, P.; Baltay, C. et al.
System: The UNT Digital Library
High resolution angle-resolved photoemission study of hightemperature superconductors: charge-ordering, bilayer splitting andelectron-phonon coupling (open access)

High resolution angle-resolved photoemission study of hightemperature superconductors: charge-ordering, bilayer splitting andelectron-phonon coupling

The latest development of angle-resolved photoemission spectroscopy (ARPES) technique has seen extremely high energy resolution and momentum resolution, as well as multiple angle detection. These advancements have led to new findings through efficient Fermi surface mapping, fine electronic structure resolving, and direct determination of electron self-energy. In this paper, we will highlight some recent high resolution ARPES work on high temperature superconductors. These include: (1) charge-ordering and evolution of electronic structure with doping; (2) bilayer splitting and Fermi surface topology of Bi2212; and (3) strong electron phonon coupling and electron electron interaction in high temperature superconductors.
Date: July 7, 2003
Creator: Zhou, Xingjiang; Hussain, Zahid & Shen, Zhi-xun
System: The UNT Digital Library
Prediction of water seepage into a geologic repository for high-level radioactive waste (open access)

Prediction of water seepage into a geologic repository for high-level radioactive waste

Predicting the amount of water that may seep into waste emplacement drifts is important for assessing the performance of the proposed geologic repository for high-level radioactive waste at Yucca Mountain, Nevada. The repository would be located in thick, partially saturated fractured tuff that will be heated to above-boiling temperatures as a result of heat generation from the decay of nuclear waste. Since infiltrating water will be subject to vigorous boiling for a significant time period, the superheated rock zone (i.e., rock temperature above the boiling point of water) can form an effective vaporization barrier that reduces the possibility of water arrival at emplacement drifts. In this paper, we analyze the behavior of episodic preferential flow events that penetrate the hot fractured rock, evaluate the impact of such flow behavior on the effectiveness of the vaporization barrier, and discuss the implications for the performance assessment of the repository. A semi-analytical solution is utilized to determine the complex flow processes in the hot rock environment. The solution is applied at several discrete times after emplacement, covering the time period of strongly elevated temperatures at Yucca Mountain.
Date: July 7, 2003
Creator: Birkholzer, Jens; Mukhophadhyay, Sumit & Tsang, Yvonne
System: The UNT Digital Library
Performance evaluation of cleanroom environmental systems (open access)

Performance evaluation of cleanroom environmental systems

This paper presents in-situ measurement results for energy and environmental performance of thirteen cleanroom systems located in the USA, including key metrics for evaluating cleanroom air system performance and overall electric power intensity. Comparisons with the IEST Recommended Practice (IEST-RP-CC012.1) are made to examine the performance of cleanroom air systems. Based upon the results, the paper discusses likely opportunities for improving cleanroom energy efficiency while maintaining effective contamination control. The paper concludes that there are wide variations in energy performance of cleanroom environmental systems, and that performance benchmarking can serve as a vehicle to identify energy efficient cleanroom design practices and to highlight important issues in cleanroom operation and maintenance.
Date: July 7, 2003
Creator: Xu, Tengfang
System: The UNT Digital Library
Exhaustive Search for Fuzzy Gene Networks from Microarray Data (open access)

Exhaustive Search for Fuzzy Gene Networks from Microarray Data

Recent technological advances in high-throughput data collection allow for the study of increasingly complex systems on the scale of the whole cellular genome and proteome. Gene network models are required to interpret large and complex data sets. Rationally designed system perturbations (e.g. gene knock-outs, metabolite removal, etc) can be used to iteratively refine hypothetical models, leading to a modeling-experiment cycle for high-throughput biological system analysis. We use fuzzy logic gene network models because they have greater resolution than Boolean logic models and do not require the precise parameter measurement needed for chemical kinetics-based modeling. The fuzzy gene network approach is tested by exhaustive search for network models describing cyclin gene interactions in yeast cell cycle microarray data, with preliminary success in recovering interactions predicted by previous biological knowledge and other analysis techniques. Our goal is to further develop this method in combination with experiments we are performing on bacterial regulatory networks.
Date: July 7, 2003
Creator: Sokhansanj, B. A.; Fitch, J. P.; Quong, J. N. & Quong, A. A.
System: The UNT Digital Library
Domain Decomposition and Load Balancing in the Amtran Neutron Transport Code (open access)

Domain Decomposition and Load Balancing in the Amtran Neutron Transport Code

Effective spatial domain decomposition for discrete ordinate (Sn) neutron transport calculations has been critical for exploiting massively parallel architectures typified by the ASCI White computer at Lawrence Livermore National Laboratory. A combination of geometrical and computational constraints has posed a unique challenge as problems have been scaled up to several thousand processors. Carefully scripted decomposition and corresponding execution algorithms have been developed to handle a range of geometrical and hardware configurations.
Date: July 7, 2003
Creator: Compton, J & Clouse, C
System: The UNT Digital Library
Progress in the SSPX Spheromak (open access)

Progress in the SSPX Spheromak

The spheromak, with its simply connected geometry, holds promise as a less expensive fusion reactor. It has reasonably good plasma beta and can be formed and sustained in steady state with a magnetized coaxial plasma gun. The Sustained Spheromak Physics Experiment (SSPX) shown in Fig. 1 was constructed to investigate the key issues of magnetic field generation and energy confinement. In addition to the coaxial gun, nine magnetic field coils are utilized to shape the vacuum magnetic flux. This flexibility allows operation in many different regimes producing very different plasma characteristics. Pulse length is extended and magnetic field strength is increased. Improved surface conditioning produces plasmas with low impurity content, and higher electron temperature, T{sub e}. Electron heat transport within the separatrix is reduced by a factor of 4. The results strongly suggest the existence of closed flux surfaces even though the plasma is connected to the coaxial source. The CORSICA Grad-Shafranov 2-d equilibrium code with data from edge magnetic probes along with T {sub e} and electron density ne from Thomson scattering is used to calculate internal profiles: normalized current {gamma} = {mu}{sub 0}J/B, safety factor = q, ohmic heating, thermal energy density, and thermal diffusivity = {xi}{sub e}. …
Date: July 7, 2003
Creator: McLean, H. S.; Woodruff, S.; Hill, D. N.; Bulmer, R. H.; Cohen, B. I.; Hooper, E. B. et al.
System: The UNT Digital Library
Fabrication of Meter-Scale Laser Resistant Mirrors for the National Ignition Facility, a Fusion Laser (open access)

Fabrication of Meter-Scale Laser Resistant Mirrors for the National Ignition Facility, a Fusion Laser

Large-aperture laser-resistant mirrors are required for the construction of the National Ignition Facility, a 1.8 MJ laser. In order to fabricate the 1408 mirrors, a development program was started in 1994 to improve coating quality, manufacturing rate, and lower unit cost. New technologies and metrology tools were scaled to meter size for facilitization in 1999 at Spectra-Physics and the Laboratory of Laser Energetics at the University of Rochester. Pilot production, to fabricate 5-10% of each component, commenced in 2001 and full production rates were achieved in 2002. Coating production will be completed in 2008 with the coating of 460 m{sup 2} of high-damage-threshold precision coatings on 100 tons of BK7 glass with yields exceeding 90%.
Date: July 7, 2003
Creator: Stolz, C J; Weinzapfel, C L; Rigatti, A L; Oliver, J B; Taniguchi, J; Bevis, R P et al.
System: The UNT Digital Library
The Formation of First Generation Stars and Globular Clusters in Protogalactic Clouds (open access)

The Formation of First Generation Stars and Globular Clusters in Protogalactic Clouds

Within collapsing protogalaxies, thermal instability leads to the formation of a population of cool fragments which are confined by the pressure of a residual hot background medium. The critical mass required for the cold clouds to become gravitationally unstable and to form stars is determined by both their internal temperature and external pressure. Massive first generation stars form in primordial clouds with sufficient column density to shield themselves from external UV photons emitted by nearby massive stars or AGNs. Less massive photoionized clouds gain mass due to ram pressure stripping by the residual halo gas. Collisions may also trigger thermal instability and fragmentation into cloudlets. While most cloudlets have substellar masses, the largest become self-gravitating and collapse to form protostellar cores without further fragmentation. The initial stellar mass function is established as these cores capture additional residual cloudlets. Energy dissipation from the mergers ensures that the cluster remains bound in the limit of low star formation efficiency. Dissipation also promotes the formation and retention of the most massive stars in the cluster center. On the scale of the protogalactic clouds, the formation of massive stars generates intense UV radiation which photoionizes gas and quenches star formation in nearby regions. As …
Date: July 7, 2003
Creator: Murray, S.
System: The UNT Digital Library
Effect of Profiles and Space on Ideal Stability of Advanced Tokamak Equilibria (open access)

Effect of Profiles and Space on Ideal Stability of Advanced Tokamak Equilibria

The pressure profile and plasma shape, parameterized by elongation ({kappa}), triangularity ({delta}), and squareness ({zeta}), strongly influence stability. In this study, ideal stability of single null and symmetric, double-null, advanced tokamak (AT) configurations is examined. All the various shapes are bounded by a common envelope and can be realized in the DIII-D tokamak. The calculated AT equilibria are characterized by P{sub 0}/{l_angle}P{r_brace} {approx} 2.0-4.5, weak negative central shear, high q{sub min} (>2.0), high bootstrap fraction, an H-mode pedestal, and varying shape parameters. The pressure profile is modeled by various polynomials together with a hyperbolic tangent pedestal, consistent with experimental observations. Stability is calculated with the DCON code and the resulting stability boundary is corroborated by GATO runs.
Date: July 7, 2003
Creator: Makowski, M A; Casper, T A; Ferron, J R; Taylor, T S & Turnbull, A D
System: The UNT Digital Library