STAR Vertex Detector Upgrade Development (open access)

STAR Vertex Detector Upgrade Development

We report on the development and prototyping efforts undertaken with the goal of producing a micro-vertex detector for the STAR experiment at the RHIC accelerator at BNL. We present the basic detector requirements and show a sensor development path, conceptual mechanical design candidates and readout architecture. Prototyping and beam test results with current generation MimoSTAR-2 sensors and a readout system featuring FPGA based on-the-fly hit finding and data sparsification are also presented.
Date: January 28, 2008
Creator: Greiner, Leo C.; Matis, Howard S.; Stezelberger, Thorsten; Vu,Chinh Q.; Wieman, Howard; Szelezniak, Michal et al.
Object Type: Article
System: The UNT Digital Library
RAD/COMM Cricket Test Report (open access)

RAD/COMM Cricket Test Report

The Environmental Effects Laboratory of the Engineering Science and Technology Division of Oak Ridge National Laboratory performed a series of tests to further evaluate and characterize the radiological response of a ''Cricket'' radiation detection system. The Cricket, manufactured by Rad/Comm Systems Corporation of Ontario, Canada, is designed to detect radioactive material that may be contained in scrap metal. The Cricket's detection unit is designed to be mounted to the base of a grappler, allowing it to monitor material while the material is being held by the grappler tines. The Cricket was tested for background stability, energy response, spherical response, surface uniformity, angular dependence, and alarm actuation. Some of these tests were repeated from a prior test of a Cricket at the Environmental Effects Laboratory as reported in ORNL/TM-2002/94. Routine environmental tests--normal temperature and relatively humidity--were also performed as part of this testing process. Overall, the Cricket performed well during the testing process. The design of the instrument and the inherent photon energy of the radionuclides had some affect on portions of the tests but do not detract from the value-added benefits of the Cricket's detection capabilities.
Date: August 28, 2003
Creator: Chiaro, PJ
Object Type: Report
System: The UNT Digital Library
Zambia: Long-Term Generation Expansion Study - Executive Summary. (open access)

Zambia: Long-Term Generation Expansion Study - Executive Summary.

The objective of this study is to analyze possible long-term development options of the Zambian electric power system in the period up to 2015. The analysis involved the hydro operations studies of the Zambezi river basin and the systems planning studies for the least-cost generation expansion planning. Two well-known and widely accepted computer models were used in the analysis: PC-VALORAGUA model for the hydro operations and optimization studies and the WASP-III Plus model for the optimization of long-term system development. The WASP-III Plus model is a part of the Argonne National Laboratory's Energy and Power Evaluation Model (ENPEP). The analysis was conducted in close collaboration with the Zambia Electricity Supply Corporation (ZESCO). On the initiative from The World Bank, the sponsor of the study, ZESCO formed a team of experts that participated in the analysis and were trained in the use of computer models. Both models were transferred to ZESCO free of charge and installed on several computers in the ZESCO corporate offices in Lusaka. In September-October 1995, two members of the ZESCO National Team participated in a 4-week training course at Argonne National Laboratory near Chicago, U.S.A., focusing on the long-term system expansion planning using the WASP and VALORAGUA …
Date: February 28, 2008
Creator: Conzelmann, G.; Koritarov, V.; Buehring, W.; Veselka, T. & Sciences, Decision and Information
Object Type: Report
System: The UNT Digital Library
Laser Drilling - Drilling with the Power of Light (open access)

Laser Drilling - Drilling with the Power of Light

Gas Technology Institute (GTI) has been the leading investigator in the field of high power laser applications research for well construction and completion applications. Since 1997, GTI (then as Gas Research Institute- GRI) has investigated several military and industrial laser systems and their ability to cut and drill into reservoir type rocks. In this report, GTI continues its investigation with a 5.34 kW ytterbium-doped multi-clad high power fiber laser (HPFL). When compared to its competitors; the HPFL represents a technology that is more cost effective to operate, capable of remote operations, and requires considerably less maintenance and repair. Work performed under this contract included design and implementation of laboratory experiments to investigate the effects of high power laser energy on a variety of rock types. All previous laser/rock interaction tests were performed on samples in the lab at atmospheric pressure. To determine the effect of downhole pressure conditions, a sophisticated tri-axial cell was designed and tested. For the first time, Berea sandstone, limestone and clad core samples were lased under various combinations of confining, axial and pore pressures. Composite core samples consisted of steel cemented to rock in an effort to represent material penetrated in a cased hole. The results …
Date: February 28, 2007
Creator: Salehi, Iraj A.; Gahan, Brian C. & Batarseh, Samih
Object Type: Report
System: The UNT Digital Library
Quantitive DNA Fiber Mapping (open access)

Quantitive DNA Fiber Mapping

Several hybridization-based methods used to delineate single copy or repeated DNA sequences in larger genomic intervals take advantage of the increased resolution and sensitivity of free chromatin, i.e., chromatin released from interphase cell nuclei. Quantitative DNA fiber mapping (QDFM) differs from the majority of these methods in that it applies FISH to purified, clonal DNA molecules which have been bound with at least one end to a solid substrate. The DNA molecules are then stretched by the action of a receding meniscus at the water-air interface resulting in DNA molecules stretched homogeneously to about 2.3 kb/{micro}m. When non-isotopically, multicolor-labeled probes are hybridized to these stretched DNA fibers, their respective binding sites are visualized in the fluorescence microscope, their relative distance can be measured and converted into kilobase pairs (kb). The QDFM technique has found useful applications ranging from the detection and delineation of deletions or overlap between linked clones to the construction of high-resolution physical maps to studies of stalled DNA replication and transcription.
Date: January 28, 2008
Creator: Lu, Chun-Mei; Wang, Mei; Greulich-Bode, Karin M.; Weier, Jingly F. & Weier, Heinz-Ulli G.
Object Type: Book
System: The UNT Digital Library
A discontinuous Galerkin front tracking method for two-phase flows with surface tension (open access)

A discontinuous Galerkin front tracking method for two-phase flows with surface tension

A Discontinuous Galerkin method for solving hyperbolic systems of conservation laws involving interfaces is presented. The interfaces are represented by a collection of element boundaries and their position is updated using an arbitrary Lagrangian-Eulerian method. The motion of the interfaces and the numerical fluxes are obtained by solving a Riemann problem. As the interface is propagated, a simple and effective remeshing technique based on distance functions regenerates the grid to preserve its quality. Compared to other interface capturing techniques, the proposed approach avoids smearing of the jumps across the interface which leads to an improvement in accuracy. Numerical results are presented for several typical two-dimensional interface problems, including flows with surface tension.
Date: December 28, 2008
Creator: Nguyen, V. T.; Peraire, J.; Cheong, K. B. & Persson, P. O.
Object Type: Article
System: The UNT Digital Library
Remaining Sites Verification Package for the 600-111, P-11 Critical Mass Laboratory Crib, and UPR-600-16, Fire and Contamination Spread Waste Sites, Waste Site Reclassification Form 2008-045 (open access)

Remaining Sites Verification Package for the 600-111, P-11 Critical Mass Laboratory Crib, and UPR-600-16, Fire and Contamination Spread Waste Sites, Waste Site Reclassification Form 2008-045

The UPR-600-16, Fire and Contamination Spread waste site is an unplanned release that occurred on December 4, 1951, when plutonium contamination was spread by a fire that ignited inside the 120 Experimental Building. The 120 Experimental Building was a laboratory building that was constructed in 1949 and used for plutonium criticality studies as part of the P-11 Project. In November 1951, a criticality occurred in the 120 Experimental Building that resulted in extensive plutonium contamination inside the building. The confirmatory evaluation supports a reclassification of this site to Interim Closed Out. The current site conditions achieve the remedial action objectives and the corresponding remedial action goals established in the Remaining Sites ROD. The results of the extensive radiological survey of the surface soil and the confirmatory and verification sampling show that residual contaminant concentrations do not preclude any future uses and allow for unrestricted use of shallow zone soils. The results also demonstrate that residual contaminant concentrations are protective of groundwater and the Columbia River.
Date: October 28, 2008
Creator: Capron, J. M.
Object Type: Report
System: The UNT Digital Library
Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene (open access)

Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene

Heats of formation of the lowest triplet state of ethylene and the ground triplet state of ethylidene have been predicted by high level electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T) energies extrapolated to the complete basis set limit using correlation consistent basis sets (CBS), plus additional corrections predict the following heats of formation in kcal/mol: Delta H0f(C2H4,3A1) = 80.1 at 0 K and 78.5 at 298 K, and Delta H0f(CH3CH,3A") = 86.8 at 0 K and 85.1 at 298 K, with an error of less than +-1.0 kcal/mol. The vertical and adiabatic singlet-triplet separation energies of ethylene were calculated as Delta ES-T,vert = 104.1 and Delta ES-T,adia = 65.8 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo (DMC) values of 103.5 +- 0.3 and 66.4 +- 0.3 kcal/mol. Both sets of computational values differ from the experimental estimate of 58 +- 3 kcal/mol for the adiabatic splitting. The computed singlet-triplet gap at 0 K for acetylene is Delta ES-T,adia(C2H2) = 90.5 kcal/mol, which is in notable disagreement with the experimental value of 82.6 kcal/mol. The heat of formation of the triplet is Delta H0f(C2H2,3B2) = 145.3 kcal/mol. There is a systematic underestimation of …
Date: June 28, 2007
Creator: Nguyen, M. T.; Matus, M. H.; Lester, W. A. Jr. & Dixon, David A.
Object Type: Article
System: The UNT Digital Library
SODIUM ALUMINOSILICATE FOULING AND CLEANING OF DECONTAMINATED SALT SOLUTION COALESCERS (open access)

SODIUM ALUMINOSILICATE FOULING AND CLEANING OF DECONTAMINATED SALT SOLUTION COALESCERS

During initial non-radioactive operations at the Modular Caustic Side Solvent Extraction Unit (MCU), the pressure drop across the decontaminated salt solution coalescer reached {approx}10 psi while processing {approx}1250 gallons of salt solution, indicating possible fouling or plugging of the coalescer. An analysis of the feed solution and the 'plugged coalescer' concluded that the plugging was due to sodium aluminosilicate solids. MCU personnel requested Savannah River National Laboratory (SRNL) to investigate the formation of the sodium aluminosilicate solids (NAS) and the impact of the solids on the decontaminated salt solution coalescer. Researchers performed developmental testing of the cleaning protocols with a bench-scale coalescer container 1-inch long segments of a new coalescer element fouled using simulant solution. In addition, the authors obtained a 'plugged' Decontaminated Salt Solution coalescer from non-radioactive testing in the MCU and cleaned it according to the proposed cleaning procedure. Conclusions from this testing include the following: (1) Testing with the bench-scale coalescer showed an increase in pressure drop from solid particles, but the increase was not as large as observed at MCU. (2) Cleaning the bench-scale coalescer with nitric acid reduced the pressure drop and removed a large amount of solid particles (11 g of bayerite if all …
Date: October 28, 2008
Creator: Poirier, M; Thomas Peters, T; Fernando Fondeur, F & Samuel Fink, S
Object Type: Report
System: The UNT Digital Library
SEQUESTRATION AND TREATMENT OF VADOSE ZONE SOLVENTS USING EDIBLE OILS (open access)

SEQUESTRATION AND TREATMENT OF VADOSE ZONE SOLVENTS USING EDIBLE OILS

Edible oils have emerged as an effective treatment amendment for a variety of contaminants. When applied to chlorinated volatile organic compounds (cVOCs) in the saturated zone, edible oils have been shown to enhance anaerobic bioremediation and sequester the contaminants. However, edible oils have not been applied to the vadose zone for contaminant treatment. Soybean oil was injected into the vadose zone in M-Area at the Department of Energy's (DOE) Savannah River Site (SRS) as a research study to evaluate the effectiveness of edible oils for solvent sequestration and the ability to change a vadose system from aerobic to anaerobic to initiate reductive dechlorination. The proposed use of this technique would be an enhanced attenuation/transition step after active remediation. The goals of the research were to evaluate oil emplacement methods and monitoring techniques to measure oil placement, partitioning and degradation. Gas sampling was the cornerstone for this evaluation. Analyses for cVOCs and biotransformation products were performed. Overall, the cVOC concentration/flux reduction was 75-85% in this vadose zone setting. Destruction of the cVOCs by biotic or abiotic process has not yet been verified at this site. No reductive dechlorination products have been measured. The deployment has resulted in a substantial generation of …
Date: March 28, 2008
Creator: Riha, B; Brian02 Looney, B & Richard Hall (NOEMAIL), R
Object Type: Article
System: The UNT Digital Library
Polarization Studies of CdZnTe Detectors Using Synchrotron X-Ray Radiation. (open access)

Polarization Studies of CdZnTe Detectors Using Synchrotron X-Ray Radiation.

None
Date: October 28, 2007
Creator: Camarda, G. S.; Bolotnikov, A. E.; Cui, Y.; Hossain, A. & James, R. B.
Object Type: Article
System: The UNT Digital Library
3C454.3 Revelas the Structure and Physics of its 'Blazar Zone' (open access)

3C454.3 Revelas the Structure and Physics of its 'Blazar Zone'

Recent multi-wavelength observations of 3C454.3, in particular during its giant outburst in 2005, put severe constraints on the location of the 'blazar zone', its dissipative nature, and high energy radiation mechanisms. As the optical, X-ray, and millimeter light-curves indicate, significant fraction of the jet energy must be released in the vicinity of the millimeter-photosphere, i.e. at distances where, due to the lateral expansion, the jet becomes transparent at millimeter wavelengths. We conclude that this region is located at {approx} 10 parsecs, the distance coinciding with the location of the hot dust region. This location is consistent with the high amplitude variations observed on {approx} 10 day time scale, provided the Lorentz factor of a jet is {Gamma}{sub j} {approx} 20. We argue that dissipation is driven by reconfinement shock and demonstrate that X-rays and {gamma}-rays are likely to be produced via inverse Compton scattering of near/mid IR photons emitted by the hot dust. We also infer that the largest gamma-to-synchrotron luminosity ratio ever recorded in this object - having taken place during its lowest luminosity states - can be simply due to weaker magnetic fields carried by a less powerful jet.
Date: November 28, 2007
Creator: Sikora, M.; Moderski, R. & Madejski, G.M.
Object Type: Article
System: The UNT Digital Library
Tradeoff Analysis for Combat Service Support Wireless Communications Alternatives (open access)

Tradeoff Analysis for Combat Service Support Wireless Communications Alternatives

As the Army moves toward more mobile and agile forces and continued sustainment of numerous high-cost legacy logistics management systems, the requirement for wireless connectivity and a wireless network to supporting organizations has become ever more critical. There are currently several Army communications initiatives underway to resolve this wireless connectivity issue. However, to fully appreciate and understand the value of these initiatives, a Tradeoff Analysis is needed. The present study seeks to identify and assess solutions. The analysis identified issues that impede Interim Brigade Combat Team (IBCT) communication system integration and outlined core requirements for sharing of logistics data between the field and Army battle command systems. Then, the analysis examined wireless communication alternatives as possible solutions for IBCT logistics communications problems. The current baseline system was compared with possible alternatives involving tactical radio systems, wireless/near term digital radio, cellular satellite, and third-generation (3G) wireless technologies. Cellular satellite and 3G wireless technologies offer clear advantages and should be considered for later IBCTs.
Date: February 28, 2002
Creator: Burnette, John R.; Thibodeau, Christopher C. & Greitzer, Frank L.
Object Type: Report
System: The UNT Digital Library
Supervisory Control Strategy Development (open access)

Supervisory Control Strategy Development

Task 4 of this collaborative effort between ORNL, Brazil, and Westinghouse for the International Nuclear Energy Research Initiative entitled “Development of Advanced Instrumentation and Control for an Integrated Primary System Reactor” focused on the design of the hierarchical supervisory control for multiple-module units. The state of the IRIS plant design – specifically, the lack of a detailed secondary system design – made developing a detailed hierarchical control difficult at this time. However, other simultaneous and ongoing efforts have contributed to providing the needed information. This report summarizes the results achieved under Task 4 of this Financial Assistance Award. Section 1.2 describes the scope of this effort. Section 2 discusses the IRIS control functions. Next, it briefly reviews the current control concepts, and then reviews the maneuvering requirements for the IRIS plant. It closes by noting the benefits that automated sequences have in reducing operator workload. Section 3 examines reactor loading in the frequency domain to establish some guidelines for module operation, paying particular attention to strategies for using process steam for desalination and/or district heating. The final subsection discusses the implications for reactor control, and argues that using the envisioned percentage (up to 10%) of the NSSS thermal output for …
Date: February 28, 2007
Creator: Storrick, Gary D. & Petrovic, Bojan
Object Type: Report
System: The UNT Digital Library
Comparison of AEO 2009 Natural Gas Price Forecast to NYMEX Futures Prices (open access)

Comparison of AEO 2009 Natural Gas Price Forecast to NYMEX Futures Prices

On December 17, 2008, the reference-case projections from Annual Energy Outlook 2009 (AEO 2009) were posted on the Energy Information Administration's (EIA) web site. We at LBNL have, in the past, compared the EIA's reference-case long-term natural gas price forecasts from the AEO series to contemporaneous natural gas prices that can be locked in through the forward market, with the goal of better understanding fuel price risk and the role that renewables can play in mitigating such risk. As such, we were curious to see how the latest AEO reference-case gas price forecast compares to the NYMEX natural gas futures strip. This brief memo presents our findings. Note that this memo pertains only to natural gas fuel price risk (i.e., the risk that natural gas prices might differ over the life of a gas-fired generation asset from what was expected when the decision to build the gas-fired unit was made). We do not take into consideration any of the other distinct attributes of gas-fired and renewable generation, such as dispatchability (or lack thereof), differences in capital costs and O&M expenses, or environmental externalities. A comprehensive comparison of different resource types--which is well beyond the scope of this memo--would need to …
Date: January 28, 2009
Creator: Bolinger, Mark & Wiser, Ryan
Object Type: Report
System: The UNT Digital Library
Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging (open access)

Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging

Neutron imaging systems measure the spatial distribution of neutron emission from burning inertial confinement fusion (ICF) targets. These systems use a traditional pinhole geometry to project an image of the source onto a two-dimensional scintillator array, and a CCD records the resulting scintillation image. The recent history of ICF neutron images has produced images with qualities that have improved as the fusion neutron yields have increased to nearly 10{sup 14} neutrons. Anticipated future neutron yields in excess of 10{sup 16} at the National Ignition Facility and LMJ have raised the prospect of neuron imaging diagnostics which simultaneously probe several different characteristics of burning fusion targets. The new measurements rely on gated-image recording to select images corresponding to specific bands of neutron energies. Gated images of downscattered neutrons with energies from 5 to 8 MeV can emphasize regions of the target which contain DT fuel which is not burning. At the same time, gated images which select different portions of the 14-MeV spectral peak can produce spatial temperature maps of a burning target. Since the neutron production depends on the DT fuel density and temperature, simultaneous images of temperature and neutron emission can be combined to infer the an image of …
Date: September 28, 2005
Creator: Moran, M. J.; Koch, J.; Landen, O. L.; Haan, S. W.; Barrera, C. A. & Morse, E. C.
Object Type: Article
System: The UNT Digital Library
Enhanced Functionality for Materials Analysis in the DTEM (open access)

Enhanced Functionality for Materials Analysis in the DTEM

The recent explosion in the use of pump–probe studies on the picosecond timescale to investigate structural and electronic phase transitions and the dynamics of chemical reactions has been based largely on laser–induced reactions coupled with laser interrogation techniques, or on laser induced reactions coupled with synchrotron radiation interrogation techniques. Much less attention has been given to approaches based on laser–induced (or electron–beam–induced) reactions coupled with electron interrogation methods, despite the fact that electron sources are brighter, and their interactions with matter stronger (thereby giving higher signal levels). The use of electrons as probes has great potential to study complex transient events not only because of the possible high temporal resolution using ultrafast electron diffraction (UED) but also the potential for high spatial resolution using dynamic transmission electron microscopy (DTEM). Taking this potential of electron interrogation methods and turning it into a routine nanoscale characterization technique requires several key aspects of the instrumentation used for electron microscopy/diffraction to be optimized. In this proposal, several approaches to instrument optimization for DTEM and UED (to be performed in the same instrument) will be addressed. The new instrumentation developments will be used to study the dynamics of strongly driven materials, aging and corrosion in …
Date: April 28, 2008
Creator: Browning, Nigel D.
Object Type: Report
System: The UNT Digital Library
Enhancement of T1 and T2 relaxation by paramagnetic silica-coated nanocrystals (open access)

Enhancement of T1 and T2 relaxation by paramagnetic silica-coated nanocrystals

We present the first comprehensive investigation on water-soluble nanoparticles embedded into a paramagnetic shell and their properties as an MRI contrast agent. The nanoprobes are constructed with an inorganic core embedded into an ultra-thin silica shell covalently linked to chelated Gd{sup 3+} paramagnetic ions that act as an MRI contrast agent. The chelator contains the molecule DOTA and the inorganic core contains a fluorescent CdSe/ZnS qdots in Au nanoparticles. Optical properties of the cores (fluorescence emission or plasmon position) are not affected by the neither the silica shell nor the presence of the chelated paramagnetic ions. The resulting complex is a MRI/fluorescence probe with a diameter of 8 to 15 nm. This probe is highly soluble in high ionic strength buffers at pH ranging from {approx}4 to 11. In MRI experiments at clinical field strengths of 60 MHz, the QDs probes posses spin-lattice (T{sub 1}) and a spin-spin (T{sub 2}) relaxivities of 1018.6 +/- 19.4 mM{sup -1} s{sup -1} and 2438.1 +/- 46.3 mM{sup -1} s{sup -1} respectively for probes having {approx}8 nm. This increase in relaxivity has been correlated to the number of paramagnetic ions covalently linked to the silica shell, ranging from approximately 45 to over 320. We …
Date: August 28, 2006
Creator: Gerion, D; Herberg, J; Gjersing, E; Ramon, E; Maxwell, R; Gray, J W et al.
Object Type: Article
System: The UNT Digital Library
Plasma and Ion Assistance in Physical Vapor Deposition: AHistorical Perspective (open access)

Plasma and Ion Assistance in Physical Vapor Deposition: AHistorical Perspective

Deposition of films using plasma or plasma-assist can betraced back surprisingly far, namely to the 18th century for arcs and tothe 19th century for sputtering. However, only since the 1960s thecoatings community considered other processes than evaporation for largescale commercial use. Ion Plating was perhaps the first importantprocess, introducing vapor ionization and substrate bias to generate abeam of ions arriving on the surface of the growing film. Ratherindependently, cathodic arc deposition was established as an energeticcondensation process, first in the former Soviet Union in the 1970s, andin the 1980s in the Western Hemisphere. About a dozen various ion-basedcoating technologies evolved in the last decades, all characterized byspecific plasma or ion generation processes. Gridded and gridless ionsources were taken from space propulsion and applied to thin filmdeposition. Modeling and simulation have helped to make plasma and ionseffects to be reasonably well understood. Yet--due to the complex, oftennon-linear and non-equilibrium nature of plasma and surfaceinteractions--there is still a place for the experience plasma"sourcerer."
Date: February 28, 2007
Creator: Anders, Andre
Object Type: Article
System: The UNT Digital Library
Evaluation of Open Geospatial Consortium Standards fur Use In LLNL Geographic Information Systems (GIS) (open access)

Evaluation of Open Geospatial Consortium Standards fur Use In LLNL Geographic Information Systems (GIS)

The objective of this project is to evaluate existing and emerging Open Geospatial Consortium (OGC) standards for use in LLNL programs that rely heavily on geographic data. OGC standards are intended to facilitate interoperability between geospatial processing systems to avoid duplication of effort, lower development costs, and encourage competition based on improved capability and performance rather than vendor lock-in. Some of these standards appear to be gaining traction in the geospatial data community, the Federal government, DOE and DHS. A serious evaluation of this technology is appropriate at this time due to increasing interest and mandated compliance in the Federal government in some situations. A subset of OGC standards is identified and reviewed with a focus on applications to LLNL programs. Each standard or recommendation reviewed was evaluated in general terms. In addition, for specific programs such as Gen&SIS and NARAC, a specific evaluation was made of several of the standards and how they could be used most effectively. It is also important to evaluate the acceptance of these standards in the commercial arena. The implementation of OGC standards by the largest GIS vendor (ESRI) was reviewed. At present, OGC standards are primary useful in specific situations. More generally, many …
Date: September 28, 2005
Creator: Walker, H; Chou, R; Chubb, K & Schek, J
Object Type: Report
System: The UNT Digital Library
Metal-induced assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si (open access)

Metal-induced assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si

We report the two-dimensional alignment of semiconductor islands using rudimentary metal patterning to control nucleation and growth. In the Ge on Si system, a square array of sub-micron Au dots on the Si (001) surface induces the assembly of deposited Ge adatoms into an extensive island lattice. Remarkably, these highly ordered Ge islands form between the patterned Au dots and are characterized by a unique truncated pyramidal shape. A model based on patterned diffusion barriers explains the observed ordering and establishes general criteria for the broader applicability of such a directed assembly process to quantum dot ordering.
Date: August 28, 2005
Creator: Robinson, J. T.; Liddle, J. A.; Minor, A.; Radmilovic, V.; Yi, D. O.; Greaney, P. A. et al.
Object Type: Article
System: The UNT Digital Library
An Iterative Phase-Space Explicit Discontinuous Galerkin Method for Stellar Radiative Transfer in Extended Atmospheres (open access)

An Iterative Phase-Space Explicit Discontinuous Galerkin Method for Stellar Radiative Transfer in Extended Atmospheres

A phase-space discontinuous Galerkin (PSDG) method is presented for the solution of stellar radiative transfer problems. It allows for greater adaptivity than competing methods without sacrificing generality. The method is extensively tested on a spherically symmetric, static, inverse-power-law scattering atmosphere. Results for different sizes of atmospheres and intensities of scattering agreed with asymptotic values. The exponentially decaying behavior of the radiative field in the diffusive-transparent transition region and the forward peaking behavior at the surface of extended atmospheres were accurately captured. The integrodifferential equation of radiation transfer is solved iteratively by alternating between the radiative pressure equation and the original equation with the integral term treated as an energy density source term. In each iteration, the equations are solved via an explicit, flux-conserving, discontinuous Galerkin method. Finite elements are ordered in wave fronts perpendicularly to the characteristic curves so that elemental linear algebraic systems are solved quickly by sweeping the phase space element by element. Two implementations of a diffusive boundary condition at the origin are demonstrated wherein the finite discontinuity in the radiative intensity is accurately captured by the proposed method. This allows for a consistent mechanism to preserve photon luminosity. The method was proved to be robust and …
Date: January 28, 2004
Creator: de Almeida, V.F.
Object Type: Report
System: The UNT Digital Library
An Evaluation of Three Commercially Available Technologies For Real-Time Measurement of Rates of Outdoor Airflow Into HVAC Systems (open access)

An Evaluation of Three Commercially Available Technologies For Real-Time Measurement of Rates of Outdoor Airflow Into HVAC Systems

During the last few years, new technologies have been introduced for real-time continuous measurement of the flow rates of outdoor air (OA) into HVAC systems; however, an evaluation of these measurements technologies has not previously been published. This document describes a test system and protocols developed for a controlled evaluation of these measurement technologies. The results of tests of three commercially available measurement technologies are also summarized. The test system and protocol were judged practical and very useful. The three commercially available measurement technologies should provide reasonably, e.g., 20%, accurate measurements of OA flow rates as long as air velocities are maintained high enough to produce accurately measurable pressure signals. In HVAC systems with economizer controls, to maintain the required air velocities the OA intake will need to be divided into two sections in parallel, each with a separate OA damper. All of the measurement devices had pressure drops that are likely to be judged acceptable. The influence of wind on the accuracy of these measurement technologies still needs to be evaluated.
Date: October 28, 2004
Creator: Fisk, William J.; Faulkner, David & Sullivan, Douglas P.
Object Type: Article
System: The UNT Digital Library
Mitigation of Laser Damage Growth in Fused Silica with a Galvanometer Scanned CO2 Laser (open access)

Mitigation of Laser Damage Growth in Fused Silica with a Galvanometer Scanned CO2 Laser

At the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL), mitigation of laser surface damage growth on fused silica using single and multiple CO{sub 2} laser pulses has been consistently successful for damage sites whose lateral dimensions are less than 100 {micro}m, but has not been for larger sites. Cracks would often radiate outward from the damage when a CO{sub 2} pulse was applied to the larger sites. An investigation was conducted to mitigate large surface damage sites using galvanometer scanning of a tightly focused CO{sub 2} laser spot over an area encompassing the laser damage. It was thought that by initially scanning the CO{sub 2} spot outside the damage site, radiating crack propagation would be inhibited. Scan patterns were typically inward moving spirals starting at radii somewhat larger than that of the damage site. The duration of the mitigation spiral pattern was {approx}110 ms during which a total of {approx}1.3 J of energy was delivered to the sample. The CO{sub 2} laser spot had a 1/e{sup 2}-diameter of {approx}200 {micro}m. Thus, there was general heating of a large area around the damage site while rapid evaporation occurred locally at the laser spot position in the spiral. …
Date: October 28, 2005
Creator: Bass, I L; Guss, G M & Hackel, R P
Object Type: Article
System: The UNT Digital Library