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Azimuthal anisotropy in Au+Au collisions at {radical}s{sub NN} = 200 GeV (open access)

Azimuthal anisotropy in Au+Au collisions at {radical}s{sub NN} = 200 GeV

The results from the STAR Collaboration on directed flow (v{sub 1}), elliptic flow (v{sub 2}), and the fourth harmonic (v{sub 4}) in the anisotropic azimuthal distribution of particles from Au+Au collisions at {radical}s{sub NN} = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a Blast Wave model. For v{sub 2}, scaling with the number of constituent quarks and parton coalescence is discussed. For v{sub 4}, scaling with v{sub 22} and quark coalescence predictions for higher harmonic flow is discussed. The different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v{sub 2}, scaling with the number of constituent quarks and parton coalescence are discussed. For v{sub 2}{sup 2} and quark coalescence are discussed.
Date: September 29, 2004
Creator: Adams, J.; Aggarwal, M. M.; Ahammed, Z.; Amonett, J.; Anderson, B. D.; Akhipkin, D. et al.
System: The UNT Digital Library
Hexavalent uranium diffusion into soils from concentrated acidic and alkaline solutions (open access)

Hexavalent uranium diffusion into soils from concentrated acidic and alkaline solutions

Uranium contamination of soils and sediments often originates from acidic or alkaline waste sources, with diffusion being a major transport mechanism. Measurements of U(VI) diffusion from initially pH 2 and pH 11 solutions into a slightly alkaline Altamont soil and a neutral Oak Ridge soil were obtained through monitoring uptake from boundary reservoirs and from U concentration profiles within soil columns. The soils provided pH buffering, resulting in diffusion at nearly constant pH. Micro x-ray absorption near edge structure spectra confirmed that U remained in U(VI) forms in all soils. Time trends of U(VI) depletion from reservoirs, and U(VI) concentration profiles within soil columns yielded K{sub d} values consistent with those determined in batch tests at similar concentrations ({approx} 1 mM), and much lower than values for sorption at much lower concentrations (nM to {mu}M). These results show that U(VI) transport at high concentrations can be relatively fast at non-neutral pH, with negligible surface diffusion, because of weak sorption.
Date: March 29, 2004
Creator: Tokunaga, Tetsu K.; Wan, Jiamin; Pena, Jasquelin; Sutton, Stephen R. & Newville, Matthew
System: The UNT Digital Library
Specification and implementation of IFC based performance metrics to support building life cycle assessment of hybrid energy systems (open access)

Specification and implementation of IFC based performance metrics to support building life cycle assessment of hybrid energy systems

Minimizing building life cycle energy consumption is becoming of paramount importance. Performance metrics tracking offers a clear and concise manner of relating design intent in a quantitative form. A methodology is discussed for storage and utilization of these performance metrics through an Industry Foundation Classes (IFC) instantiated Building Information Model (BIM). The paper focuses on storage of three sets of performance data from three distinct sources. An example of a performance metrics programming hierarchy is displayed for a heat pump and a solar array. Utilizing the sets of performance data, two discrete performance effectiveness ratios may be computed, thus offering an accurate method of quantitatively assessing building performance.
Date: March 29, 2004
Creator: Morrissey, Elmer; O'Donnell, James; Keane, Marcus & Bazjanac, Vladimir
System: The UNT Digital Library
17th Annual ALS Users' Association Meeting (open access)

17th Annual ALS Users' Association Meeting

It's not exactly Russian roulette, but scheduling October events outdoors is not risk-free, even in usually sunny California. An overflow crowd of more than 400 registered users, ALS staff, and vendors enjoyed a full indoor program featuring science highlights and workshops spread over two and a half days from October 18 to October 20. However, a major storm, heralding the onset of the San Francisco Bay Area rainy season, posed a few weather challenges for the events on the ALS patio.
Date: November 29, 2004
Creator: Robinson, Art & Tamura, Lori
System: The UNT Digital Library
Multi-Pulse Effects in the Damage to the LCLS Reflective Optics (open access)

Multi-Pulse Effects in the Damage to the LCLS Reflective Optics

A number of experiments to be performed on the planned Linac Coherent Light Source (LCLS) will have to use various types of reflective optics (see, e.g., [1]). On the other hand, LCLS will operate at a rate of 120 x-ray pulses per second. Therefore, when considering effects leading to the damage to its optics, one has to be concerned not only with a possible damage within one pulse, but also with effects accumulating during many pulses. We identify and analyze two of such effects: a thermal fatigue, and the intensity-dependent radiation damage. The first effect is associated with thermal stresses and deformations that occur in every pulse. The heating of the surface layers of the optics leads to a peculiar distribution of stresses, with a strong concentration near the surface. The quasistatic analysis of this problem was presented in [2]. In the present study, we show that transients in both transverse and longitudinal acoustic perturbations play a significant role and generally worsen the situation. If the maximum stresses approach the yield strength, the thermal fatigue causes degradation of the surface within a few thousands pulses. The second effect is related to formation of clusters of ionized atoms which lead to …
Date: July 29, 2004
Creator: Ryutov, D
System: The UNT Digital Library
Shock Compressing Diamond to a Conducting Fluid (open access)

Shock Compressing Diamond to a Conducting Fluid

Laser generated shock reflectance data show that diamond undergoes a continuous transition from optically absorbing to reflecting between Hugoniot pressures 600<P{sub H}<1000 GPa. The data are consistent with diamond having a thermal population of carriers at P{sub H}{approx}600 GPa, undergoing band overlap metallization at P{sub H}{approx}1000 GPa and melting at 800<P{sub H}<1000 GPa. The results agree well with an equation of state model that predicts that elemental carbon remains solid throughout the interior of Neptune.
Date: July 29, 2004
Creator: Bradley, D K; Eggert, J H; Hicks, D G; Celliers, P M; Moon, S J; Cauble, R C et al.
System: The UNT Digital Library
Parallel Implementation and Scaling of an Adaptive Mesh Discrete Ordinates Algorithm for Transport (open access)

Parallel Implementation and Scaling of an Adaptive Mesh Discrete Ordinates Algorithm for Transport

Block-structured adaptive mesh refinement (AMR) uses a mesh structure built up out of locally-uniform rectangular grids. In the BoxLib parallel framework used by the Raptor code, each processor operates on one or more of these grids at each refinement level. The decomposition of the mesh into grids and the distribution of these grids among processors may change every few timesteps as a calculation proceeds. Finer grids use smaller timesteps than coarser grids, requiring additional work to keep the system synchronized and ensure conservation between different refinement levels. In a paper for NECDC 2002 I presented preliminary results on implementation of parallel transport sweeps on the AMR mesh, conjugate gradient acceleration, accuracy of the AMR solution, and scalar speedup of the AMR algorithm compared to a uniform fully-refined mesh. This paper continues with a more in-depth examination of the parallel scaling properties of the scheme, both in single-level and multi-level calculations. Both sweeping and setup costs are considered. The algorithm scales with acceptable performance to several hundred processors. Trends suggest, however, that this is the limit for efficient calculations with traditional transport sweeps, and that modifications to the sweep algorithm will be increasingly needed as job sizes in the thousands of …
Date: November 29, 2004
Creator: Howell, L H
System: The UNT Digital Library
Is the Short Distance Scale a Result of a Problem with the LMC Photometric Zero Point? (open access)

Is the Short Distance Scale a Result of a Problem with the LMC Photometric Zero Point?

I present a promising route to harmonize distance measurements based on clump giants and RR Lyrae stars. This is achieved by comparing the brightness of these distance indicators in three environments: the solar neighborhood, Galactic bulge and Large Magellanic Cloud (LMC). As a result of harmonizing the distance scales in the solar neighborhood and Baade's Window, I derive the new absolute magnitude of RR Lyrae stars, M{sub v}(RR) at [Fe/H] = -1.6 (0.59 {+-} 0.05, 0.70 {+-} 0.05). Being somewhat brighter than the statistical parallax solution, but fainter than typical results of the main sequence fitting to Hipparcos data, these values of M{sub V}(RR) favor intermediate or old ages of globular clusters. Harmonizing the distance scales in the LMC and Baade's Window, I show that the most likely distance modulus to the LMC, {mu}{sub LMC} is in the range 18.24 - 18.44. The Hubble constant of about 70 km/s/Mpc reported by the HST Key Project is based on the assumption that the distance modulus to the LMC equals 18.50. The results presented here indicate that the Hubble Constant may be up to 12% higher. This in turn would call for a younger Universe and could result in some tension between …
Date: March 29, 2004
Creator: Popowski, P
System: The UNT Digital Library
Subextensive Scaling in the Athermal, Quasistatic Limit of Amorphous Matter in Plastic Shear Flow (open access)

Subextensive Scaling in the Athermal, Quasistatic Limit of Amorphous Matter in Plastic Shear Flow

We present the results of numerical simulations of an atomistic system undergoing plastic shear flow in the athermal, quasistatic limit. The system is shown to undergo cascades of local re-arrangements, associated with quadrupolar energy fluctuations, which induce system-spanning events organized into lines of slip oriented along the Bravais axes of the simulation cell. A finite size scaling analysis reveals subextensive scaling of the energy drops and participation numbers, linear in the length of the simulation cell, in good agreement with the real-space structure of plastic events
Date: January 29, 2004
Creator: Maloney, C & Lemaitre, A
System: The UNT Digital Library
High Gradient Induction Cell (open access)

High Gradient Induction Cell

A concept being developed for high current electron beams may have application to HEDP and is described here. It involves the use of planar Blumlein stacks placed inside an induction cell. The output end of the Blumlein stack is applied across a high gradient insulator (HGI). These insulators have been used successfully in the presence of kilo Ampere-level electron beam currents for tens of nanoseconds at gradients of 20 MV/meter.
Date: November 29, 2004
Creator: Caporaso, G J
System: The UNT Digital Library
A Generalized Mass Lumping Technique for Vector Finite Element Solutions of the Time Dependent Maxwell Equations (open access)

A Generalized Mass Lumping Technique for Vector Finite Element Solutions of the Time Dependent Maxwell Equations

None
Date: July 29, 2004
Creator: Fisher, A; Rieben, R; Rodrigue, G & White, D
System: The UNT Digital Library
ParaDiS on BlueGene/L: scalable line dynamics (open access)

ParaDiS on BlueGene/L: scalable line dynamics

We describe an innovative highly parallel application program, ParaDiS, which computes the plastic strength of materials by tracing the evolution of dislocation lines over time. We discuss the issues of scaling the code to tens of thousands of processors, and present early scaling results of the code run on a prototype of the BlueGene/L supercomputer being developed by IBM in partnership with the US DOE's ASC program.
Date: April 29, 2004
Creator: Bulatov, V.; Cai, W.; Fier, J.; Hiratani, M.; Pierce, T.; Tang, M. et al.
System: The UNT Digital Library
PortVis: A Tool for Port-Based Detection of Security Events (open access)

PortVis: A Tool for Port-Based Detection of Security Events

Most visualizations of security-related network data require large amounts of finely detailed, high-dimensional data. However, in some cases, the data available can only be coarsely detailed because of security concerns or other limitations. How can interesting security events still be discovered in data that lacks important details, such as IP addresses, network security alarms, and labels? In this paper, we discuss a system we have designed that takes very coarsely detailed data-basic, summarized information of the activity on each TCP port during each given hour-and uses visualization to help uncover interesting security events.
Date: June 29, 2004
Creator: McPherson, J; Ma, K; Krystosk, P; Bartoletti, T & Christensen, M
System: The UNT Digital Library
High Resolution Transmission Grating Spectrometer for Edge Toroidal Rotation Measurements of Tokamak Plasmas (open access)

High Resolution Transmission Grating Spectrometer for Edge Toroidal Rotation Measurements of Tokamak Plasmas

We present a high throughput (f/3) visible (3500 - 7000 Angstrom) Doppler spectrometer for toroidal rotation velocity measurements of the Alcator C-Mod tokamak plasma. The spectrometer has a temporal response of 1 ms and a rotation velocity sensitivity of {approx}10{sup 5} cm/s. This diagnostic will have a tangential view and map out the plasma rotation at several locations along the outer half of the minor radius (r/a > 0.5). The plasma rotation will be determined from the Doppler shifted wavelengths of D{sub alpha} and magnetic and electric dipole transitions of highly ionized impurities in the plasma. The fast time resolution and high spectral resolving power are possible due to a 6' diameter circular transmission grating that is capable of {lambda}/{Delta}{lambda} {approx} 15500 at 5769 Angstrom in conjunction with a 50 {micro}m slit.
Date: April 29, 2004
Creator: Graf, A.; May, M.; Beiersdorfer, P.; Magee, E.; Lawrence, M.; Terry, J. et al.
System: The UNT Digital Library
Mono and Multivalency In Tethered Protein-Carbohydrate Bonds (open access)

Mono and Multivalency In Tethered Protein-Carbohydrate Bonds

Molecular recognition in biological systems typically involves large numbers of interactions simultaneously. By using a multivalent approach, weak interactions with fairly low specificity can become strong highly specific interactions. Additionally, this allows an organism to control the strength and specificity of an interaction simply by controlling the number of binding molecules (or binding sites), which in turn can be controlled through transcriptional regulation.
Date: January 29, 2004
Creator: Ratto, T V; Langry, K C; Rudd, R E; Balhorn, R L & McElfresh, M W
System: The UNT Digital Library
Accurate Position Sensing of Defocused Beams Using Simulated Beam Templates (open access)

Accurate Position Sensing of Defocused Beams Using Simulated Beam Templates

In position detection using matched filtering one is faced with the challenge of determining the best position in the presence of distortions such as defocus and diffraction noise. This work evaluates the performance of simulated defocused images as the template against the real defocused beam. It was found that an amplitude modulated phase-only filter is better equipped to deal with real defocused images that suffer from diffraction noise effects resulting in a textured spot intensity pattern. It is shown that the there is a tradeoff of performance dependent upon the type and size of the defocused image. A novel automated system was developed that can automatically select the right template type and size. Results of this automation for real defocused images are presented.
Date: September 29, 2004
Creator: Awwal, A.; Candy, J.; Haynam, C.; Widmayer, C.; Bliss, E. & Burkhart, S.
System: The UNT Digital Library
Design and Implementation of the Control System for a 2 kHz Rotary Fast Tool Servo (open access)

Design and Implementation of the Control System for a 2 kHz Rotary Fast Tool Servo

This paper presents a summary of the performance of our 2 kHz rotary fast tool servo and an overview of its control systems. We also discuss the loop shaping techniques used to design the power amplifier current control loop and the implementation of that controller in an op-amp circuit. The design and development of the control system involved a long list of items including: current compensation; tool position compensation; notch filter design and phase stabilizing with an additional pole for a plant with an undamped resonance; adding viscous damping to the fast tool servo; voltage budget for driving real and reactive loads; dealing with unwanted oscillators; ground loops; digital-to-analog converter glitches; electrical noise from the spindle motor switching power supply; and filtering the spindle encoder signal to generate smooth tool tip trajectories. Eventually, all of these topics will be discussed in detail in a Ph.D. thesis that will include this work. For the purposes of this paper, rather than present a diluted discussion that attempts to touch on all of these topics, we will focus on the first item with sufficient detail for providing insight into the design process.
Date: March 29, 2004
Creator: Montesanti, R C & Trumper, D L
System: The UNT Digital Library
Optical Pumping Experiments on Next Generation Light Sources (open access)

Optical Pumping Experiments on Next Generation Light Sources

Laser-based plasma spectroscopic techniques have been used with great success to determine the line shapes of atomic transitions in plasmas, study the population kinetics of atomic systems embedded in plasmas, and look at the redistribution of radiation. However, the possibilities for optical lasers end for plasmas with n{sub e}>10{sup 22}cm{sup -3} as light propagation is severely altered by the plasma. The construction of the Tesla Test Facility(TTF) at DESY(Deutsche Elektronen-Synchrotron), a short pulse tunable free electron laser in the vacuum-ultraviolet and soft X-ray regime (VUV FEL), based on the SASE(self amplified spontaneous emission) process, will provide a major advance in the capability for dense plasma-related research. This source will provide 10{sup 13} photons in a 200 fs duration pulse that is tunable from {approx} 6nm to 100nm. Since an VUV FEL will not have the limitation associated with optical lasers the entire field of high density plasmas kinetics in laser produced plasma will then be available to study with tunable source. Thus, one will be able to use this and other FEL x-ray sources to pump individual transitions creating enhanced population in the excited states that can easily be monitored. We show two case studies illuminating different aspects of plasma …
Date: July 29, 2004
Creator: Moon, S J; Fournier, K B; Scott, H; Chung, H K & Lee, R W
System: The UNT Digital Library
Turbulence Kinetic Energy Budgets and Dissipation Rates in Disturbed Stable Boundary Layers (open access)

Turbulence Kinetic Energy Budgets and Dissipation Rates in Disturbed Stable Boundary Layers

None
Date: March 29, 2004
Creator: Lundquist, J K; Piper, M D & Kosovic, B
System: The UNT Digital Library
Elastic Face, An Anatomy-Based Biometrics Beyond Visible Cue (open access)

Elastic Face, An Anatomy-Based Biometrics Beyond Visible Cue

This paper describes a face recognition method that is designed based on the consideration of anatomical and biomechanical characteristics of facial tissues. Elastic strain pattern inferred from face expression can reveal an individual's biometric signature associated with the underlying anatomical structure, and thus has the potential for face recognition. A method based on the continuum mechanics in finite element formulation is employed to compute the strain pattern. Experiments show very promising results. The proposed method is quite different from other face recognition methods and both its advantages and limitations, as well as future research for improvement are discussed.
Date: March 29, 2004
Creator: Tsap, L V; Zhang, Y; Kundu, S J; Goldgof, D B & Sarkar, S
System: The UNT Digital Library
Experimental Demonstration of Wavelength Tuning in High-Gain Harmonic Generation Free Electron Laser. (open access)

Experimental Demonstration of Wavelength Tuning in High-Gain Harmonic Generation Free Electron Laser.

Tunability is one of the key aspects of any laser system. In High-Gain Harmonic Generation Free Electron Laser (HGHG FEL) the seed laser determines the output wavelength. Conventional scheme of tunable HGHG FEL requires tunable seed laser. The alternative scheme [1] is based on compression of the electron bunch with energy-time correlation (chirped bunch) in the FEL dispersive section. The chirped energy modulation, induced by the seed laser with constant wavelength, compressed as the whole bunch undergoes compression. In this paper we discuss experimental verification of the proposed approach at the DUV FEL [2,3] and compare experimental results with analytical estimates.
Date: August 29, 2004
Creator: Shaftan, T.; Johnson, E.; Krinsky, S.; Loos, H.; Murphy, J. B.; Rakowsky, G. et al.
System: The UNT Digital Library
X-ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals (open access)

X-ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals

None
Date: November 29, 2004
Creator: Magid, K R; Lilleodden, E T; Tamura, N; Florando, J N; Lassila, D H; LeBlanc, M. M. et al.
System: The UNT Digital Library
Design of a Multi-Channel Ultra-High Resolution Superconducting Gamma-Ray Spectrometer (open access)

Design of a Multi-Channel Ultra-High Resolution Superconducting Gamma-Ray Spectrometer

Superconducting Gamma-ray microcalorimeters operated at temperatures around {approx}0.1 K offer an order of magnitude improvement in energy resolution over conventional high-purity Germanium spectrometers. The calorimeters consist of a {approx}1 mm{sup 3} superconducting or insulating absorber and a sensitive thermistor, which are weakly coupled to a cold bath. Gamma-ray capture increases the absorber temperature in proportion to the Gamma-ray energy, this is measured by the thermistor, and both subsequently cool back down to the base temperature through the weak link. We are developing ultra-high-resolution Gamma-ray spectrometers based on Sn absorbers and superconducting Mo/Cu multilayer thermistors for nuclear non-proliferation applications. They have achieved an energy resolution between 60 and 90 eV for Gamma-rays up to 100 keV. We also build two-stage adiabatic demagnetization refrigerators for user-friendly detector operation at 0.1 K. We present recent results on the performance of single pixel Gamma-ray spectrometers, and discuss the design of a large detector array for increased sensitivity.
Date: November 29, 2004
Creator: Friedrich, S.; Terracol, S. F.; Miyazaki, T.; Drury, O. B.; Ali, Z. A.; Cunningham, M. F. et al.
System: The UNT Digital Library
Preliminary Measurments of the High-Gain FEL Radiation Properties Along the Radiator. (open access)

Preliminary Measurments of the High-Gain FEL Radiation Properties Along the Radiator.

We present preliminary experimental results on evolution of properties of the DUV FEL [1,2] radiation along the radiator. Intercepting the electron beam at the different locations inside the undulator we recorded and analyzed transverse profiles, spectra and intensity of the FEL output. Shot-to-shot fluctuations of the FEL radiation may significantly affect the accuracy of measurement. In the paper we present and discuss a single-shot measurement technique, based on a special imaging system.
Date: August 29, 2004
Creator: Shaftan, T.; Loos, H.; Sheehy, B. & Yu, L. H.
System: The UNT Digital Library