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.
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.
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
System: The UNT Digital Library
Observation of amplification of a 1ps pulse by SRS of a 1 ns pulse in a plasma with conditions relevant to pulse compression (open access)

Observation of amplification of a 1ps pulse by SRS of a 1 ns pulse in a plasma with conditions relevant to pulse compression

The compression of a laser pulse by amplification of an ultra short pulse beam which seeds the stimulated Raman scatter of the first beam has been long been discussed in the context of solid and gas media. We investigate the possibility of using intersecting beams in a plasma to compress nanosecond pulses to picosecond duration by scattering from driven electron waves. Recent theoretical studies have shown the possibility of efficient compression with large amplitude, non-linear Langmuir waves driven either by SRS [1] or non-resonantly [2].
Date: October 28, 2005
Creator: Kirkwood, R K; Dewald, E; Wilks, S C; Meezan, N; Niemann, C; Divol, L et al.
System: The UNT Digital Library
Looking Ahead - Biofuels, H2, & Vehicles: 21st Industry Growth Forum (open access)

Looking Ahead - Biofuels, H2, & Vehicles: 21st Industry Growth Forum

This presentation on the future of biofuels, hydrogen, and hybrid vehicles was presented at NREL's 21st Industry Growth Forum in Denver, Colorado, on October 28, 2008.
Date: October 28, 2008
Creator: Gardner, D.
System: The UNT Digital Library
Beta-Phosphinoethylboranes as Ambiphilic Ligands in Nickel-Methyl Complexes (open access)

Beta-Phosphinoethylboranes as Ambiphilic Ligands in Nickel-Methyl Complexes

The ambiphilic {beta}-phosphinoethylboranes Ph{sub 2}PCH{sub 2}CH{sub 2}BR{sub 2} (BR{sub 2} = BCy{sub 2} (1a), BBN (1b)), which feature a ethano spacer CH{sub 2}CH{sub 2} between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a and 1b were fully characterized by elemental analysis, and by NMR and IR spectroscopy. X-ray crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through P{hor_ellipsis}B donor-acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe{sub 2}. Zwitterionic complexes (dmpe)NiMe(Ph{sub 2}PCH{sub 2}CH{sub 2}BCy{sub 2}Me) (2a) and (dmpe)NiMe(Ph{sub 2}PCH{sub 2}CH{sub 2}[BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C{sub 6}F{sub 5}){sub 3} abstracts the methyl group of a coordinated borate ligand to generate a free, 3-coordinate borane center in [(dmpe)NiMe(1a)]{sup +}[MeB(C{sub 6}F{sub 5}){sub 3}]{sup -} (3).
Date: October 28, 2007
Creator: Fischbach, Andreas; Bazinet, Patrick R.; Waterman, Rory & Tilley, T. Don
System: The UNT Digital Library
Scanning Josephson Tunneling Microscopy of Single Crystal Bi2Sr2CaCu2O8+delta with a Conventional Superconducting Tip (open access)

Scanning Josephson Tunneling Microscopy of Single Crystal Bi2Sr2CaCu2O8+delta with a Conventional Superconducting Tip

We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi2Sr2CaCu2O8+ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson ICRN product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local ICRN product and the local energy gap.
Date: October 28, 2009
Creator: Kimura, H.; Barber Jr., R. P.; Ono, S.; Ando, Yoichi & Dynes, Robert C.
System: The UNT Digital Library
Energy and system size dependence of phi meson production in Cu+Cu and Au+Au collisions (open access)

Energy and system size dependence of phi meson production in Cu+Cu and Au+Au collisions

We study the beam-energy and system-size dependence of {phi} meson production (using the hadronic decay mode {phi} {yields} K{sup +}K{sup -}) by comparing the new results from Cu + Cu collisions and previously reported Au + Au collisions at {radical}s{sub NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from midrapidity (|y| < 0.5) for 0.4 < p{sub T} < 5 GeV/c. At a given beam energy, the transverse momentum distributions for {phi} mesons are observed to be similar in yield and shape for Cu + Cu and Au + Au colliding systems with similar average numbers of participating nucleons. The {phi} meson yields in nucleus-nucleus collisions, normalized by the average number of participating nucleons, are found to be enhanced relative to those from p + p collisions with a different trend compared to strange baryons. The enhancement for {phi} mesons is observed to be higher at {radical}s{sub NN} = 200 GeV compared to 62.4 GeV. These observations for the produced {phi}(s{bar s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions …
Date: October 28, 2008
Creator: STAR Collaboration
System: The UNT Digital Library
Laser-Induced Damage in DKDP Crystals under Simultaneous Exposure to Laser Harmonics (open access)

Laser-Induced Damage in DKDP Crystals under Simultaneous Exposure to Laser Harmonics

While KDP and DKDP crystals remain the only viable solution for frequency conversion in large aperture laser systems in the foreseeable future, our understanding of damage behavior in the presence of multiple colors is very limited. Such conditions exist during normal operation where, for third harmonic generation, 1{omega}, 2{omega} and 3{omega} components are present with different energy ratios as they propagate inside the crystal. The objective of this work is to shed light into the damage behavior of frequency conversion crystals during operational conditions as well as probe the fundamental mechanisms of damage initiation. We have performed a series of experiments to quantify the damage performance of pristine (unconditioned) DKDP material under simultaneous exposure to 2{omega} and 3{omega} laser pulses from a 3-ns Nd:YAG laser system as a function of the laser influences at each frequency. Results show that simultaneous dual wavelength exposure leads to a much larger damage density as compared to the total damage resulting from separate exposure at each wavelength. Furthermore, under such excitation conditions, the damage performance is directly related to and can be predicted from the damage behavior of the crystal at each wavelength separately while the mechanism and type of defects responsible for damage …
Date: October 28, 2005
Creator: Negres, R A; DeMange, P; Radousky, H B & Demos, S G
System: The UNT Digital Library
In-Situ Observations of Phase Transformations During Welding of 1045 Steel using Spatially Resolved and Time Resolved X-Ray Diffraction (open access)

In-Situ Observations of Phase Transformations During Welding of 1045 Steel using Spatially Resolved and Time Resolved X-Ray Diffraction

Synchrotron-based methods have been developed at Lawrence Livermore National Laboratory (LLNL) for the direct observation of microstructure evolution during welding. These techniques, known as spatially resolved (SRXRD) and time resolved (TRXRD) x-ray diffraction, allow in-situ experiments to be performed during welding and provide direct observations of high temperature phases that form under the intense thermal cycles that occur. This paper presents observations of microstructural evolution that occur during the welding of a medium carbon AISI 1045 steel, using SRXRD to map the phases that are present during welding, and TRXRD to dynamically observe transformations during rapid heating and cooling. SRXRD was further used to determine the influence of welding heat input on the size of the high temperature austenite region, and the time required to completely homogenize this region during welding. These data can be used to determine the kinetics of phase transformations under the steep thermal gradients of welds, as well as benchmark and verify phase transformation models.
Date: October 28, 2005
Creator: Elmer, J.; Palmer, T. & DebRoy, T.
System: The UNT Digital Library
Optical pump-probe processes in Nd 3+ doped KPb2Br5, RbPb2Br5, and KPb2CI5 (open access)

Optical pump-probe processes in Nd 3+ doped KPb2Br5, RbPb2Br5, and KPb2CI5

Recently, laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2}+{sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. In this paper we present cw pump-probe spectra in order to discuss excited state absorption, reabsorption processes due to the long lived lower laser levels as well as possible depopulation mechanisms feasible for more efficient laser operation in these crystals. The bromides will be compared with potassium lead chloride (Nd{sup 3+}:KPb{sub 2}Cl{sub 5}).
Date: October 28, 2004
Creator: Rademaker, K; Huber, G; Payne, S A; Osiac, E & Isaenko, L I
System: The UNT Digital Library
Design and simulations of indirect drive ignition targets for NIF (open access)

Design and simulations of indirect drive ignition targets for NIF

None
Date: October 28, 2004
Creator: Haan, S. W.; Amendt, P. A.; Dittrich, T. R.; Hammel, B. A.; Hatchett, S. P.; Herrmann, M. C. et al.
System: The UNT Digital Library
WMAPping out Neutrino Masses (open access)

WMAPping out Neutrino Masses

Recent data from the Wilkinson Microwave Anisotropy Probe (WMAP) place important bounds on the neutrino sector. The precise determination of the baryon number in the universe puts a strong constraint on the number of relativistic species during Big-Bang Nucleosynthesis. WMAP data, when combined with the 2dF Galaxy Redshift Survey (2dFGRS), also directly constrain the absolute mass scale of neutrinos. These results impinge upon a neutrino oscillation interpretation of the result from the Liquid Scintillator Neutrino Detector (LSND).We also note that the Heidelberg-Moscow evidence for neutrinoless double beta decay is only consistent with the WMAP+2dFGRS data for the largest values of the nuclear matrix element.
Date: October 28, 2003
Creator: Pierce, Aaron & Murayama, Hitoshi
System: The UNT Digital Library
Azimuthal anisotropy at RHIC: The first and fourth harmonics (open access)

Azimuthal anisotropy at RHIC: The first and fourth harmonics

No abstract prepared.
Date: October 28, 2003
Creator: Adams, J.; Adler, C.; Aggarwal, M. M.; Ahammed, Z.; Amonett, J.; Anderson, B. D. et al.
System: The UNT Digital Library
Workshop Summary: Workshop on Assessing Human Germ Cell Mutagenesis in the Post-Genome Era (open access)

Workshop Summary: Workshop on Assessing Human Germ Cell Mutagenesis in the Post-Genome Era

The workshop summary inlcudes the keynote address by Liane B. Russell, a summary of each ot the nine sessions, and highlights of two open discussions.
Date: October 28, 2004
Creator: Sander, Miriam
System: The UNT Digital Library
Magnetism in heterogeneous thin film systems: Resonant x-ray scattering studies (open access)

Magnetism in heterogeneous thin film systems: Resonant x-ray scattering studies

Magnetic and chemical heterogeneity are common in a broad range of magnetic thin film systems. Emerging resonant soft x-ray scattering techniques are well suited to resolve such heterogeneity at relevant length scales. Resonant x-ray magneto-optical Kerr effect measurements laterally average over heterogeneity but can provide depth resolution in different ways, as illustrated in measurements resolving reversible and irreversible changes in different layers of exchange-spring heterostructures. Resonant small-angle scattering measures in-plane heterogeneity and can resolve magnetic and chemical scattering sources in different ways, as illustrated in measurements of granular alloy recording media.
Date: October 28, 2002
Creator: Kortright, J. B.; Jiang, J. S.; Bader, S. D.; Hellwig, O.; Marguiles, D. T. & Fullerton, E. E.
System: The UNT Digital Library
An evaluation of enhanced cooling techniques for high-heat load absorbers. (open access)

An evaluation of enhanced cooling techniques for high-heat load absorbers.

Many components of the storage ring and front ends in the third generation of light sources are subjected to high heat loads from intense x-rays. Temperature rises and thermal stresses in these components must be kept within acceptable limits of critical heat flux and low-cycle fatigue failure. One of the design solutions is to improve heat transfer to the cooling water either by increasing water velocity in the cooling channels or by using inserts, such as porous media, twisted tapes and wire springs. In this paper we present experimental and analytical results to compare various enhanced cooling techniques for conditions specific to heating from an x-ray fan.
Date: October 28, 2002
Creator: Sharma, S.; Doose, C.; Rotela, E. & Barickowski, A.
System: The UNT Digital Library
Mechanical Behavior Analysis of a Test Coil for MICE Coupling Solenoid during Quench (open access)

Mechanical Behavior Analysis of a Test Coil for MICE Coupling Solenoid during Quench

The coupling magnet for the Muon Ionization Cooling Experiment has a self-inductance of 592 H and the magnet stored energy of 13 MJ at a full current of 210 A for the worst operation case of the MICE channel. The high level of stored energy in the magnet can cause high peak temperature during a quench and induce considerable impact of stresses. One test coil was built in order to validate the design method and to practice the stress and strain situation to occur in the coupling coil. In this study, the analysis on stress redistribution during a quench with sub-divided winding was performed. The stress variation may bring about failure of impregnating material such as epoxy resin, which is the curse of a new normal zone arising. Spring models for impregnating epoxy and fiber-glass cloth in the coil were used to evaluate the mechanical disturbance by impregnated materials failure. This paper presents the detailed dynamic stress and stability analysis to assess the stress distribution during the quench process and to check whether the transient loads are acceptable for the magnet.
Date: October 28, 2009
Creator: Pan, Heng; Wang, Li; Guo, Xinglong; Wu, Hong & Green, M.A.
System: The UNT Digital Library
STOMP: A Software Architecture for the Design and Simulation UAV-Based Sensor Networks (open access)

STOMP: A Software Architecture for the Design and Simulation UAV-Based Sensor Networks

This paper presents the Simulation, Tactical Operations and Mission Planning (STOMP) software architecture and framework for simulating, controlling and communicating with unmanned air vehicles (UAVs) servicing large distributed sensor networks. STOMP provides hardware-in-the-loop capability enabling real UAVs and sensors to feedback state information, route data and receive command and control requests while interacting with other real or virtual objects thereby enhancing support for simulation of dynamic and complex events.
Date: October 28, 2002
Creator: Jones, E. D.; Roberts, R. S. & Hsia, T. C. S.
System: The UNT Digital Library
ROBUST TECHNIQUES FOR BACKGROUND SUBTRACTION IN URBAN TRAFFIC VIDEO (open access)

ROBUST TECHNIQUES FOR BACKGROUND SUBTRACTION IN URBAN TRAFFIC VIDEO

Identifying moving objects from a video sequence is a fundamental and critical task in many computer-vision applications. A common approach is to perform background subtraction, which identifies moving objects from the portion of a video frame that differs significantly from a background model. There are many challenges in developing a good background subtraction algorithm. First, it must be robust against changes in illumination. Second, it should avoid detecting non-stationary background objects such as swinging leaves, rain, snow, and shadow cast by moving objects. Finally, its internal background model should react quickly to changes in background such as starting and stopping of vehicles. In this paper, we compare various background subtraction algorithms for detecting moving vehicles and pedestrians in urban traffic video sequences. We consider approaches varying from simple techniques such as frame differencing and adaptive median filtering, to more sophisticated probabilistic modeling techniques. While complicated techniques often produce superior performance, our experiments show that simple techniques such as adaptive median filtering can produce good results with much lower computational complexity.
Date: October 28, 2003
Creator: Kamath, C & Cheung, S S
System: The UNT Digital Library
RF Power and HOM Coupler Tutorial (open access)

RF Power and HOM Coupler Tutorial

Radio frequency (RF) couplers are used on superconducting cavities to deliver RF power for creating accelerating fields and to remove unwanted higher-order mode power for reducing emittance growth and cryogenic load. RF couplers in superconducting applications present a number of interdisciplinary design challenges that need to be addressed, since poor performance in these devices can profoundly impact accelerator operations and the overall success of a major facility. This paper will focus on critical design issues for fundamental and higher order mode (HOM) power couplers, highlight a sampling of reliability-related problems observed in couplers, and discuss some design strategies for improving performance.
Date: October 28, 2003
Creator: Rusnak, B
System: The UNT Digital Library
New 100 mm Gun Assembly Installation at Lawrence Livermore National Laboratory High Explosives Applications Facility (open access)

New 100 mm Gun Assembly Installation at Lawrence Livermore National Laboratory High Explosives Applications Facility

A new 100mm gun assembly was recently installed and tested at Lawrence Livermore National Laboratories located in the High Explosives Applications Facility (HEAF). Thiot Ingenierie performed the design of the replacement barrel, based on improvements to the initial design. This design incorporated barrel and breech sections forged from CLARM series high-strength alloys obtained from Tecphy Corporation and machined by Manufacture de Forage. Part of the improvement of the design was implementing a laser alignment system for quick and accurate barrel alignment checks. This laser is also used to align the target assembly. This paper will detail the design changes incorporated into the installation, the testing process, and future direction of research for the new gun.
Date: October 28, 2003
Creator: Vandersall, K S; Lee, R A; Chiao, P I; Garcia, F; Travis, J O & Forbes, J W
System: The UNT Digital Library
Pre-bomb {Delta}{sup 14}C variability and the Suess Effect in Cariaco Basin Surface Waters as Recorded in Hermatypic Corals (open access)

Pre-bomb {Delta}{sup 14}C variability and the Suess Effect in Cariaco Basin Surface Waters as Recorded in Hermatypic Corals

The {Delta}{sup 14}C content of surface waters in and around the Cariaco Basin were reconstructed from {sup 14}C measurements on sub-annually sampled coral skeletal material. During the late 1930s - early 1940s surface waters within and outside of the Cariaco Basin are similar. Within the Cariaco Basin at Islas Tortugas coral {Delta}{sup 14}C averages -51.9 {+-}3.3 {per_thousand}. Corals collected outside of the basin at Boca de Medio and Los Testigos have {Delta}{sup 14}C values of -53.4 {+-} 3.3 {per_thousand} and -54.3 {+-} 2.6 respectively. Additional {sup 14}C analyses on the Isla Tortugas coral document an {approx} 11 {per_thousand} decrease between {approx}1905 (-40.9 {+-}4.5 {per_thousand}) and {approx}1940. The implied Suess Effect trend (-3 {per_thousand}/decade) is nearly as large as that observed in the atmosphere over the same time period. If we assume that there is little to no fossil fuel {sup 14}CO{sub 2} signature in Cariaco surface waters in {approx}1905, the waters have an equivalent reservoir age of {approx}312 years.
Date: October 28, 2004
Creator: Guilderson, T; Cole, J & Southon, J
System: The UNT Digital Library
HADES, A Code for Simulating a Variety of Radiographic Techniques (open access)

HADES, A Code for Simulating a Variety of Radiographic Techniques

It is often useful to simulate radiographic images in order to optimize imaging trade-offs and to test tomographic techniques. HADES is a code that simulates radiography using ray tracing techniques. Although originally developed to simulate X-Ray transmission radiography, HADES has grown to simulate neutron radiography over a wide range of energy, proton radiography in the 1 MeV to 100 GeV range, and recently phase contrast radiography using X-Rays in the keV energy range. HADES can simulate parallel-ray or cone-beam radiography through a variety of mesh types, as well as through collections of geometric objects. HADES was originally developed for nondestructive evaluation (NDE) applications, but could be a useful tool for simulation of portal imaging, proton therapy imaging, and synchrotron studies of tissue. In this paper we describe HADES' current capabilities and discuss plans for a major revision of the code.
Date: October 28, 2004
Creator: Aufderheide, Maurice B.; Henderson, Gary; Schach von Wittenau, Alexis E.; Slone, Dale M.; Barty, Anton & Martz, Harry E., Jr.
System: The UNT Digital Library