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Equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations

Description: Article on the equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations. In this work, the authors compare the dipole correction and Coulomb cutoff methods under the same conditions in the framework of plane-wave based density-functional theory.
Date: June 3, 2008
Creator: Yu, Liping; Ranjan, Vivek; Lu, W.; Bernholc, Jerry & Buongiorno Nardelli, Marco
Partner: UNT College of Arts and Sciences

Catastrophic failure of contaminated fused silica optics at 355 nm

Description: For years, contamination has been known to degrade the performance of optics and to sometimes initiate laser-induced damage to initiate. This study has W to quantify these effects for fused silica windows used at 355 mm Contamination particles (Al, Cu, TiO{sub 2} and ZrO{sub 2}) were artificially deposited onto the surface and damage tests were conducted with a 3 ns NdYAG laser. The damage morphology was characterized by Nomarski optical microscopy. The results showed that the damage morphology for input and output surface contamination is different. For input surface contamination, both input and output surfaces can damage. In particular, the particle can induce pitting or drilling of the surface where the beam exits. Such damage usually grows catastrophically. Output surface contamination is usually ablated away on the shot but can also induce catastrophic damage. Plasmas are observed during illumination and seem to play an important role in the damage mechanism. The relationship between fluence and contamination size for which catastrophic damage occurred was plotted for different contamination materials. The results show that particles even as small as 10 {micro}m can substantially decrease the damage threshold of the window and that metallic particles on the input surface have a more negative effect than oxide particles.
Date: December 3, 1996
Creator: Genin, F. Y., LLNL
Partner: UNT Libraries Government Documents Department

Stabilization of insertion electrodes for lithium batteries.

Description: This paper discusses the techniques that are being employed to stabilize LiMn{sub 2}O{sub 4} spinel and composite Li{sub x}MnO{sub 2} positive electrodes. The critical role that spinel domains play in stabilizing these electrodes for operation at both 4 V and 3 V is highlighted. The concept of using an intermetallic electrode MM{prime} where M is an active alloying element and M{prime} is an inactive element (or elements) is proposed as an alternative negative electrode (to carbon) for lithium-ion cells. An analogy to metal oxide insertion electrodes, such as MnO{sub 2}, in which Mn is the electrochemically active ion and O is the inactive ion, is made. Performance data are given for the copper-tin electrode system, which includes the intermetallic phases eta-Cu{sub 6}Sn{sub 5} and Li{sub 2}CuSn.
Date: September 3, 1998
Creator: Thackeray, M. M.
Partner: UNT Libraries Government Documents Department

Weak matrix elements on the lattice - Circa 1995

Description: Status of weak matrix elements is reviewed. In particular, e{prime}/e, B {yields} K*{gamma}, B{sub B} and B{sub B}, are discussed and the overall situation with respect to the lattice effort and some of its phenomenological implications are summarised. For e{prime}/e the need for the relevant matrix elements is stressed in view of the forthcoming improved experiments. For some of the operators, (e.g. O{sub 6}), even bound on their matrix elements would be very helpful. On B {yields} K{degrees}{gamma}, a constant behavior of T{sub 2} appears disfavored although dependence of T{sub 2} could, of course, be milder than a simple pole. Improved data is badly needed to settle this important issue firmly, especially in view of its ramification for extractions of V{sub td} from B {yields} {rho}{gamma}. On B{sub {kappa}}, the preliminary result from JLQCD appears to contradict Sharpe et al. JLQCD data seems to fit very well to linear {alpha} dependence and leads to an appreciably lower value of B{sub {kappa}}. Four studies of B{sub {kappa}} in the {open_quotes}full{close_quotes} (n{sub f} = 2) theory indicate very little quenching effects on B{sub {kappa}}; the full theory value seems to be just a little less than the quenched result. Based on expectations from HQET, analysis of B-parameter (B{sub h}{ell}) for the heavy-light mesons via B{sub h}{ell}) = constant + constants{prime}/m{sub h}{ell} is suggested. A summary of an illustrative sample of hadron matrix elements is given and constraints on CKM parameters (e.g. V{sub td}/V{sub ts}, on the unitarity triangle and on x{sub s}/x{sub d}, emerging from the lattice calculations along with experimental results are briefly discussed. In quite a few cases, for the first time, some indication of quenching errors on weak matrix elements are now becoming available.
Date: October 3, 1995
Creator: Soni, A.
Partner: UNT Libraries Government Documents Department

Off-training-set error for the Gibbs and the Bayes optimal generalizers

Description: In this paper we analyze the average off-training-set behavior of the Bayes-optimal and Gibbs learning algorithms. We do this by exploiting the concept of refinement, which concerns the relationship between probability distributions. For non-uniform sampling distributions the expected off training-set error for both learning algorithms can rise with, training set size. However we show in this paper that for uniform sampling and either algorithm, the expected error is a non-increasing function of training set size. For uniform sampling distributions, we also characterize the priors for which the expected error of the Bayes-optimal algorithm stays constant. In addition we show that when the target function is fixed, expected off-training-set error can increase with training set size if and only if the expected error averaged over all targets decreases with training set size. Our results hold for arbitrary noise and arbitrary loss functions.
Date: January 3, 1995
Creator: Grossman, T.; Knill, E. & Wolpert, D.
Partner: UNT Libraries Government Documents Department

Fabrication of high-density cantilever arrays and through-wafer interconnects

Description: Processes to fabricate dense, dry released microstructures with electrical connections on the opposite side of the wafer are described. A 10 x 10 array of silicon and polysilicon cantilevers with high packing density (5 tips/mm<sup>2</sup>) and high uniformity (<10 µm length variation across the wafer) are demonstrated. The cantilever release process uses a deep SF<sub>6</sub>/C<sub>4</sub>F<sub>8</sub>, plasma etch followed by a HBr plasma etch to accurately release cantilevers. A process for fabricating electrical contacts through the backside of the wafer is also described. Electrodeposited resist, conformal CVD metal deposition and deep SF<sub>6</sub>/C<sub>4</sub>F<sub>8</sub> plasma etching are used to make 30 µm/side square vias each of which has a resistance of 50 m(omega).
Date: November 3, 1998
Creator: A. Harley, J.; Abdollahi-Alibeik, S.; Chow, E. M.; Kenney, T. W.; McCarthy, A. M.; McVittie, J. P. et al.
Partner: UNT Libraries Government Documents Department

Hard x-ray production from high intensity laser solid interactions

Description: Intense laser (> 10{sup 21} W/cm{sup 2}) driven hard x-ray sources offer a new alternative to conventional electron accelerator bremsstrahlung sources. These laser driven sources offer considerable simplicity in design and cost advantage for multiple axis views and have the potential for much higher spatial and temporal resolution than is achievable with accelerator sources We have begun a series of experiments using the Petawatt Laser system at LLNL to determine the potential of these sources for radiography applications Absolutely calibrated spectra extending to 20 MeV and high resolution radiographs through a {rho}r{>=}150 gm/cm{sup 2} have been obtained The physics of these sources and the scaling relationships and laser technology required to provide the dose levels necessary for radiography applications will be discussed Diagnostics of the laser produced electrons and photons will be addressed
Date: June 3, 1998
Creator: Sefcik, J. A.
Partner: UNT Libraries Government Documents Department

Bulk band gaps in divalent hexaborides: A soft x-ray emission study

Description: Boron K-edge soft x-ray emission and absorption are used to address the fundamental question of whether divalent hexaborides are intrinsic semimetals or defect-doped bandgap insulators. These bulk sensitive measurements, complementary and consistent with surface-sensitive angle-resolved photoemission experiments, confirm the existence of a bulk band gap and the location of the chemical potential at the bottom of the conduction band.
Date: October 3, 2001
Creator: Denlinger, Jonathan D.; Gweon, Gey-Hong; Allen, James W.; Bianchi, Andrea D. & Fisk, Zachary
Partner: UNT Libraries Government Documents Department

Progress report on VENUS

Description: The construction of VENUS, a next generation superconducting Electron Cyclotron Resonance ion source designed to operate at 28 GHz, is complete. The cryostat including the superconducting magnet assembly was delivered in September 2001. During acceptance tests, the superconducting magnets produced an axial magnetic field strength of 4T at injection, 3T at extraction, and a radial field strength of 2T at the plasma chamber wall without any quenches. These fields are sufficient for optimum operation at 28 GHz. The cryogenic system for VENUS has been designed to operate at 4.2 K with two cryocoolers each providing up to 45 W of cooling at 50 K and 1.5 W at 4 K in a closed loop mode without further helium transfers. However, during the acceptance tests an excessive heat leak of about 3W was measured. In addition, the liquid helium heat exchanger did not work properly and had to be redesigned. The cryogenic system modifications will be described. In addition, an update on the installation of the ion source and its beam line components will be given.
Date: September 3, 2002
Creator: Leitner, Matthaeus A.; Leitner, Daniela; Abbott, Steve R.; Taylor, Clyde E. & Lyneis, Claude
Partner: UNT Libraries Government Documents Department

Passive Corrosion Behavior of Alloy 22 in Multi-Ionic Aqueous Environments

Description: In current waste packaging design, Alloy 22 (Ni-22Cr-13Mo-3W-3Fe) has been chosen as the candidate materials to fabricate a 2 cm outer layer of the high-level nuclear waste containers, as part of proposed geological repository at Yucca Mountain, Nevada. During the repository period, the container materials will be subject to the corrosion due to its exposure to the multi-ionic aqueous environments. Although Alloy 22 has demonstrated excellent corrosion resistance, but accumulation of small yearly corrosion rate for 10,000 or more years can be significant enough. The goal of this research is to seek alternative techniques to obtain a reasonably confident corrosion rate determination, since the conventional weight loss technique requires many years to achieve a detectable weight loss in Alloy 22 samples. This paper will discuss the latest experiment results in using potentiostatic technique to determine passive dissolution rates.
Date: June 3, 2002
Creator: Lian, T.; Estill, J.C.; Hust, G.A.; Fix, D.V. & Rebak, R.B.
Partner: UNT Libraries Government Documents Department


Description: The Spallation Neutron Source (SNS) extraction kicker system brings the proton beam from the accumulator ring through a beam transfer line into the target area. The 14 kicker magnets are located in one straight section. The kicker magnets are energized by 14 Blumlein type Pulse Forming Networks (BPFN). The first article of the SNS extraction kicker BPFN was assembled and tested at this laboratory. This paper describes the kicker BPFN system arrangement and parameters. The first article BPFN design and its main components used are explained. High voltage BPFN test results and the load current waveform are illustrated in this paper. Temperature measurements of the kicker ferrite blocks at full power showed only small or no heating. This paper discusses the modifications to the BPFN design, such as a saturating inductor and 25 Q termination, to minimize the transverse coupling impedance.
Date: June 3, 2002
Creator: Mi, J.; Pai, C.; Davino, D.; Hahn, H.; Lambiase, R.; Lee, Y. Y. et al.
Partner: UNT Libraries Government Documents Department


Description: We study the influence of space charge on the crossing of the second-order resonance and the associated space-charge limit in high-intensity rings. Two-dimensional simulation studies are compared and found to agree with the envelope models in the finding of an increased intensity limit due to the coherent frequency shift. We also discuss application of this effect to bunched beams and multi-turn injection painting, and the effect of high-order resonances and issues of the envelope instability.
Date: June 3, 2002
Partner: UNT Libraries Government Documents Department

The magnification of SN 1997ff, the farthest known supernova

Description: With a redshift of z {approx} 1.7, SN 1997ff is the most distant type Ia supernova discovered so far. This SN is close to several bright, z = 0.6-0.9 galaxies, and we consider the effects of lensing by those objects on the magnitude of SN 1997ff. We estimate their velocity dispersions using the Tully-Fisher and Faber-Jackson relations corrected for evolution effects, and calculate, applying the multiple-plane lensing formalism, that SN 1997ff is magnified by 0.34{+-}0.12 mag. Due to the spatial configuration of the foreground galaxies, the shear from individual lenses partially cancels out,and the total distortion induced on the host galaxy is considerably smaller than that produced by a single lens having the same magnification. After correction for lensing, the revised distance to SN 1997ff is m-M = 45.49 {+-} 0.34 mag, which improves the agreement with the {Omega}{sub M} = 0.35, {Omega}{Lambda} = 0.65 cosmology expected from lower-redshift SNe Ia, and is inconsistent at the {approx} 3 sigma confidence level with a uniform gray dust model or a simple evolution model.
Date: September 3, 2002
Creator: Benitez, Narciso; Riess, Adam; Nugent, Peter; Dickinson, Mark; Chornock, Ryan & Filippenko, Alexei V.
Partner: UNT Libraries Government Documents Department

Estimation of environmental noise impacts within architectural spaces.

Description: Public Law 91-596, ''Occupational Safety and Health Act of 1970,'' Dec. 29, 1970, stimulated interest in modeling the impacts of interior noise on employees, as well as the intelligibility of interior public-address and other speech intra-communication systems. The classical literature on this topic has primarily featured a statistical uniform diffuse-field model. This was pioneered by Leo L. Beranek in the 1950s, based on energy-density formulations at the former Bell Telephone (AT and T) Laboratories in the years from 1930 to 1950. This paper compares the classical prediction approach to the most recent statistical methods. Such models were developed in the late 1970s and included innovations such as consideration of irregularly shaped (e.g., L-shaped) interior room spaces and coupled spaces.
Date: May 3, 2002
Creator: Chang, Y. S.; Liebich, R. E. & Chun, K. C.
Partner: UNT Libraries Government Documents Department


Description: The Spallation Neutron Source (SNS) is a second generation pulsed neutron source and is presently in the fourth year of a seven-year construction cycle at Oak Ridge National Laboratory. A collaboration of six national laboratories (ANL, BNL, LANL, LBNL, ORNL, TJNAF) is responsible for the design and construction of the various subsystems. The operation of the facility will begin in 2006 and deliver a 1.0 GeV, 1.4 MW proton beam with pulse length of 650 nanosecond at a repetition rate of 60 Hz, on a liquid mercury target. It consists of an RF volume H{sup -} source of 50 mA peak current at 6% duty; an all electrostatic Low-Energy Beam Transport (LEBT) which also serves as a first stage beam chopper with {+-} 25 ns rise/fall time; a 402.5 MHz, 4-vane Radio-Frequency Quadrupole (RFQ) for acceleration up to 2.5 MeV; a Medium Energy Beam Transport (MEBT) housing a second stage chopper (&lt;{+-} 10ns rise/fall), an adjustable beam halo scraper, and diagnostics devices; a 6-tank Drift Tube Linac (DTL) with permanent magnet quadrupoles up to 87 MeV; an 805 MHz, 4-module, Side Coupled Cavity Linac (CCL) up to 186 MeV; an 805 MHz, superconducting RF (SRF) linac with eleven medium beta ({beta} = 0.61) cryo-modules and twelve high beta ({beta} = 0.81) cryo-modules accelerating the beam to the full energy; a High Energy Beam transport (HEBT) for diagnostics, transverse and longitudinal collimation, energy correction, painting and matching; an accumulator ring compressing the 1 GeV, 1 ms pulse to 650 ns for delivery onto the target through a Ring to Target Beam Transport (RTBT) with transverse collimators.
Date: February 3, 2003
Creator: RAPARIA,D.
Partner: UNT Libraries Government Documents Department


Description: 1.7 x 10{sup 8} x-ray photons per 3.5 ps pulse have been produced in Thomson scattering by focusing CO{sub 2} laser pulse on counter-propagating relativistic electron beam. We explore a possibility of further enhancement of process efficiency by propagating both beams in a plasma capillary. Conventional synchrotron light sources based on using giga-electron-volt electron synchrotron accelerators and magnetic wigglers generate x-ray radiation for versatile application in multi-disciplinary research. An intense laser beam causes relativistic electron oscillations similar to a wiggler. However, because the laser wavelength is thousand times shorter than a wiggler period, very moderate electron energy is needed to produce hard x-rays via Thomson scattering. This allows using relatively compact mega-electron-volt linear accelerators instead of giga-electron-volt synchrotrons. Another important advantage of Thomson sources is a possibility to generate femtosecond x-ray pulses whereas conventional synchrotron sources have typically {approx}300 ps pulse duration. This promises to revolutionize x-ray research in chemistry, physics, and biology expanding it to ultra-fast processes. Thomson sources do not compete in repetition rate and average intensity with conventional light sources that operate at the megahertz frequency. However, Thomson sources have a potential to produce much higher photon numbers per pulse. This may allow developing a single shot exposure important for structural analysis of live biological objects. The BNL Thomson source is a user's experiment conducted at the Accelerator Test Facility since 1998 by an international collaboration in High Energy Physics. Since inception, the ATF source produces the record peak x-ray yield, intensity and brightness among other similar proof-of-principle demonstrations attempted elsewhere. Note that this result is achieved with a moderate laser power of 15 GW. A key to this achievement is in choosing right apparatus and efficient interaction geometry. We use a CO{sub 2} laser that delivers 10 times more photons per unit energy than the 1-{micro}m ...
Date: December 3, 2001
Partner: UNT Libraries Government Documents Department


Description: During the RHIC Au-run in 2001 the 200 MHz storage cavity system was used for the first time. The rebucketing procedure caused significant beam debunching in addition to amplifying debunching due to other mechanisms. At the end of a four hour store, debunched beam could account for approximately 30%-40% of the total beam intensity. Some of it will be in the abort gap. In order to minimize the risk of magnet quenching due to uncontrolled beam losses at the time of a beam dump, a combination of a fast transverse kicker and copper collimators were used to clean the abort gap. This report gives an overview of the gap cleaning procedure and the achieved performance.
Date: June 3, 2002
Partner: UNT Libraries Government Documents Department

Spectral measurements of the second harmonic of the SASE FEL radiation at APS.

Description: We present the z-dependent spectral measurement results for the second harmonic of the SASE FEL radiation before and after saturation. The measurements were performed at the Advanced Photon Source FEL with the fundamental wavelength of 530 nm. The spectral properties of the second harmonic are compared with those of the fundamental and with the theoretical expectations.
Date: October 3, 2002
Creator: Sajaev, V. & Huang, Z.
Partner: UNT Libraries Government Documents Department

Fault tolerant issues in the BTeV trigger

Description: The BTeV trigger performs sophisticated computations using large ensembles of FPGAs, DSPs, and conventional microprocessors. This system will have between 5,000 and 10,000 computing elements and many networks and data switches. While much attention has been devoted to developing efficient algorithms, the need for fault-tolerant, fault-adaptive, and flexible techniques and software to manage this huge computing platform has been identified as one of the most challenging aspects of this project. They describe the problem and offer an approach to solving it based on a distributed, hierarchical fault management system.
Date: December 3, 2002
Creator: al., Jeffrey A. Appel et
Partner: UNT Libraries Government Documents Department

Production of an Accelerated Oxygen-14 Beam

Description: BEARS is an ongoing project to provide a light-ion radioactive-beam capability at the 88-Inch Cyclotron at LBNL. Light radioactive isotopes are produced at a 10 MeV proton medical cyclotron, transported 350 m via a high-speed gas transport capillary, cryogenically separated, and injected into the 88-Inch Cyclotron's ion source. The first radioactive beam successfully accelerated was Carbon-11 and beams of intensity more than 108 ions/sec have been utilized for experiments. Development of Oxygen-14 as the second BEARS beam presented considerable technical challenges, both due to its short half-life of 71 seconds and the radiation chemistry of oxygen in the target. The usual techniques developed for medical uses of Oxygen-15 involve the addition of significant amounts of carrier oxygen, something that would overload the ion source. As a solution, Oxygen-14 is produced as water in a carrier-free form, and is chemically converted in two steps to carbon dioxide, a form readily usable by the BEARS. This system has been built and is operational, and initial tests of accelerating an Oxygen-14 beam have been performed.
Date: May 3, 2002
Creator: Powell, James; O'Neil, James P. & Cerny, Joseph
Partner: UNT Libraries Government Documents Department


Description: Brookhaven National Laboratory has developed a Power Supply Interface (PSI) as part of the construction of the accumulator ring and transfer lines of the Spallation Neutron Source (SNS) that will be located in Oak Ridge, Tennessee. These units have now been constructed in production quantities. This paper will be in two parts. The first part reports the results of performance testing for it's application to the SNS. But the PSI can also be used for other applications, and is currently being used for another application at BNL, the Booster Application Facility (BAF). The second part of this paper will describe how the versatile PSI can be configured for other machines, and it's performance in ramping applications.
Date: June 3, 2002
Partner: UNT Libraries Government Documents Department


Description: No abstract prepared.
Date: June 3, 2002
Partner: UNT Libraries Government Documents Department

Atmospheric Transport of Radionuclides

Description: The purpose of atmospheric transport and diffusion calculations is to provide estimates of concentration and surface deposition from routine and accidental releases of pollutants to the atmosphere. This paper discusses this topic.
Date: March 3, 2003
Creator: Crawford, T.V.
Partner: UNT Libraries Government Documents Department

Particle Diffusion Due to Coulomb Scattering

Description: Conventionally, the multiple and single particle scattering in a storage ring are considered to be independent. Such an approach is simple and often yields sufficiently accurate results. Nevertheless, there is a class of problems where such an approach is not adequate and the single and multiple scattering need to be considered together. This can be achieved by solving an integro-differential equation for the particle distribution function, which correctly treats particle Coulomb scattering in the presence of betatron motion. A derivation of the equation is presented in the article. A numerical solution for one practical case is also considered.
Date: June 3, 2002
Creator: Nagaitsev, V. Lebedev and S.
Partner: UNT Libraries Government Documents Department