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2,644 Matching Results
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Insulator-to-metal transition induced by mid-IR vibrational excitation in a magnetoresistive manganite
Selective vibrational excitation of insulating Pr0.7Ca0.3MnO3 at 17 ?m triggers a transition to a metallic state. A four order of magnitude drop of the sample resistivity and ultrafast, nanosecond-lived reflectivity changes are observed
Date:
August 7, 2006
Creator:
Schoenlein, Robert William; Rini, Matteo; Itatani, Jiro; Tomioka, Yasuhide; Tokura, Yoshinori; Schoenlein, Robert W. et al.
Object Type:
Article
System:
The UNT Digital Library
A Core-Particle Model for Periodically Focused Ion Beams with Intense Space-Charge
A core-particle model is derived to analyze transverse orbits of test particles evolving in the presence of a core ion beam described by the KV distribution. The core beam has uniform density within an elliptical cross-section and can be applied to model both quadrupole and solenoidal focused beams in periodic or aperiodic lattices. Efficient analytical descriptions of electrostatic space-charge fields external to the beam core are derived to simplify model equations. Image charge effects are analyzed for an elliptical beam centered in a round, conducting pipe to estimate model corrections resulting from image charge nonlinearities. Transformations are employed to remove coherent utter motion associated with oscillations of the ion beam core due to rapidly varying, linear applied focusing forces. Diagnostics for particle trajectories, Poincare phase-space projections, and single-particle emittances based on these transformations better illustrate the effects of nonlinear forces acting on particles evolving outside the core. A numerical code has been written based on this model. Example applications illustrate model characteristics. The core-particle model described has recently been applied to identify physical processes leading to space-charge transport limits for an rms matched beam in a periodic quadrupole focusing channel [Lund and Chawla, Nuc. Instr. and Meth. A 561, 203 …
Date:
August 2, 2006
Creator:
Lund, S M; Barnard, J J; Bukh, B; Chawla, S R & Chilton, S H
Object Type:
Article
System:
The UNT Digital Library
Evaluation of Cavitation-Erosion Resistance of 316LN Stainless Steel in Mercury Containing Metallic Solutes
Room temperature cavitation tests of vacuum annealed type 316LN stainless steel were performed in pure Hg and in Hg with various amounts of metallic solute to evaluate potential mitigation of erosion/wastage. Tests were performed using an ultrasonic vibratory horn with specimens attached at the tip. All of the solutes examined, which included 5 wt% In, 10 wt% In, 4.4 wt% Cd, 2 wt% Ga, and a mixture that included 1 wt% each of Pb, Sn, and Zn, were found to increase cavitation-erosion as measured by increased weight loss and/or surface profile development compared to exposures for the same conditions in pure Hg. Qualitatively, each solute appeared to increase the post-test wetting tenacity of the Hg solutions and render the Hg mixture susceptible to manipulation of droplet shape.
Date:
August 1, 2006
Creator:
Pawel, Steven J & Mansur, Louis K
Object Type:
Report
System:
The UNT Digital Library
Effect of Lithium PFC Coatings on NSTX Density Control
Lithium coatings on the graphite plasma facing components (PFCs) in NSTX are being investigated as a tool for density profile control and reducing the recycling of hydrogen isotopes. Repeated lithium pellet injection into Center Stack Limited and Lower Single Null Ohmic Helium Discharges were used to coat graphite surfaces that had been pre-conditioned with Ohmic Helium Discharges of the same shape to reduce their contribution to hydrogen isotope recycling. The following deuterium NBI reference discharges exhibited a reduction in density by a factor of about 3 for limited and 2 for diverted plasmas respectively, and peaked density profiles. Recently, a lithium evaporator has been used to apply thin coatings on conditioned and unconditioned PFCs. Effects on the plasma density and the impurities were obtained by pre-conditioning the PFCs with ohmic helium discharges, and performing the first deuterium NBI discharge as soon as possible after applying the lithium coating.
Date:
August 21, 2006
Creator:
Kugel, H W; Bell, M G; Bush, C; Gates, D; Gray, T; Kaita, R et al.
Object Type:
Article
System:
The UNT Digital Library
Low energy spread 100 MeV-1 GeV electron bunches from laserwakefiel d acceleration at LOASIS
Experiments at the LOASIS laboratory of LBNL recentlydemonstrated production of 100 MeV electron beams with low energy spreadand low divergence from laser wakefield acceleration. The radiationpressure of a 10 TW laser pulse guided over 10 diffraction ranges by aplasma density channel was used to drive an intense plasma wave(wakefield), producing acceleration gradients on the order of 100 GV/m ina mm-scale channel. Beam energy has now been increased from 100 to 1000MeV by using a cm-scale guiding channel at lower density, driven by a 40TW laser, demonstrating the anticipated scaling to higher beam energies.Particle simulations indicate that the low energy spread beams wereproduced from self trapped electrons through the interplay of trapping,loading, and dephasing. Other experiments and simulations are alsounderway to control injection of particles into the wake, and henceimprove beam quality and stability further.
Date:
August 1, 2006
Creator:
Geddes, C. G. R.; Esarey, E.; Michel, P.; Nagler, B.; Nakamura, K.; Plateau, G. R. et al.
Object Type:
Article
System:
The UNT Digital Library
Neutral Kaon Interferometry in Au+Au collisions at sqrt(s_NN) =200 GeV
We present the first statistically meaningful results fromtwo-K0s interferometry in heavy-ion collisions. A model that takes theeffect of the strong interaction into account has been used to fit themeasured correlation function. The effects of single and coupled channelwere explored. At the mean transverse mass m_T = 1.07 GeV, we obtain thevalues R = 4.09 +- 0.46 (stat.) +- 0.31 (sys) fm and lambda = 0.92 +-0.23 (stat) +- 0.13 (sys), where R and lambda are the invariant radiusand chaoticity parameters respectively. The results are qualitativelyconsistent with m_T systematics established with pions in a scenariocharacterized by a strong collective flow.
Date:
August 5, 2006
Creator:
Abelev, B. I.; Adams, J.; Aggarwal, M. M.; Ahammed, Z.; Amonett, J.; Anderson, B. D. et al.
Object Type:
Article
System:
The UNT Digital Library
Remaining Sites Verification Package for the 100-F-31, 144-F Sanitary Sewer System, Waste Site Reclassification Form 2006-033
The 100-F-31 waste site is a former septic system that supported the inhalation laboratories, also referred to as the 144-F Particle Exposure Laboratory (132-F-2 waste site), which housed animals exposed to particulate material. The 100-F-31 waste site has been remediated to achieve the remedial action objectives specified in the Remaining Sites ROD. The results of 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:
August 24, 2006
Creator:
Dittmer, L. M.
Object Type:
Report
System:
The UNT Digital Library
Dual-Environment Effects on the Oxidation of Metallic Interconnects
Metallic interconnects in solid oxide fuel cells are exposed to a dual environment: fuel on one side (i.e., H2 gas) and oxidizer on the other side (i.e., air). It has been observed that the oxidation behavior of thin stainless steel sheet in air is changed by the presence of H2 on the other side of the sheet. The resulting dual-environment scales are flaky and more friable than the single-environment scales. The H2 disrupts the scale on the air side. A model to explain some of the effects of a dual environment is presented where hydrogen diffusing through the stainless steel sheet reacts with oxygen diffusing through the scale to form water vapor, which has sufficient vapor pressure to mechanically disrupt the scale. Experiments on preoxidized 316L stainless steel tubing exposed to air-air, H2-air, and H2-Ar environments are reported in support of the model.
Date:
2006-08~
Creator:
Holcomb, Gordon R.; Ziomek-Moroz, Malgorzata; Cramer, Stephen D.; Covino, Bernard S., Jr. & Bullard, Sohpie J.
Object Type:
Article
System:
The UNT Digital Library
Clean Slate Environmental Remediation DSA for 10 CFR 830 Compliance
Clean Slate Sites II and III are scheduled for environmental remediation (ER) to remove elevated levels of radionuclides in soil. These sites are contaminated with legacy remains of non-nuclear yield nuclear weapons experiments at the Nevada Test Site, that involved high explosive, fissile, and related materials. The sites may also hold unexploded ordnance (UXO) from military training activities in the area over the intervening years. Regulation 10 CFR 830 (Ref. 1) identifies DOE-STD-1120-98 (Ref. 2) and 29 CFR 1910.120 (Ref. 3) as the safe harbor methodologies for performing these remediation operations. Of these methodologies, DOE-STD-1120-98 has been superseded by DOE-STD-1120-2005 (Ref. 4). The project adopted DOE-STD-1120-2005, which includes an approach for ER projects, in combination with 29 CFR 1910.120, as the basis documents for preparing the documented safety analysis (DSA). To securely implement the safe harbor methodologies, we applied DOE-STD-1027-92 (Ref. 5) and DOE-STD-3009-94 (Ref. 6), as needed, to develop a robust hazard classification and hazards analysis that addresses non-standard hazards such as radionuclides and UXO. The hazard analyses provided the basis for identifying Technical Safety Requirements (TSR) level controls. The DOE-STD-1186-2004 (Ref. 7) methodology showed that some controls warranted elevation to Specific Administrative Control (SAC) status. In addition to …
Date:
August 1, 2006
Creator:
James L. Traynor, Stephen L. Nicolosi, Michael L. Space, Louis F. Restrepo
Object Type:
Article
System:
The UNT Digital Library
Measurement of the relaxation time of hot electrons in laser-solid interaction at relativistic laser intensities
The authors have measured the relaxation time of hot electrons in short pulse laser-solid interactions using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. Employing laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, they find increased laser coupling to hot electrons as the laser intensity becomes relativistic and thermalization of hot electrons at timescales on the order of 10 ps at all laser intensities. They propose a simple model based on collisional coupling and plasma expansion to describe the rapid relaxation of hot electrons. The agreement between the resulting K{sub {alpha}} time-history from this model with the experiments is best at highest laser intensity and less satisfactory at the two lower laser intensities.
Date:
August 22, 2006
Creator:
Chen, H; Shepherd, R; Chung, H K; Dyer, G; Faenov, A; Fournier, K B et al.
Object Type:
Article
System:
The UNT Digital Library
High-luminosity primary vertex selection in top-quark studies using the Collider Detector at Fermilab
Improving our ability to identify the top quark pair (t{bar t}) primary vertex (PV) on an event-by-event basis is essential for many analyses in the lepton-plus-jets channel performed by the Collider Detector at Fermilab (CDF) Collaboration. We compare the algorithm currently used by CDF (A1) with another algorithm (A2) using Monte Carlo simulation at high instantaneous luminosities. We confirm that A1 is more efficient than A2 at selecting the t{bar t} PV at all PV multiplicities, both with efficiencies larger than 99%. Event selection rejects events with a distance larger than 5 cm along the proton beam between the t{bar t} PV and the charged lepton. We find flat distributions for the signal over background significance of this cut for all cut values larger than 1 cm, for all PV multiplicities and for both algorithms. We conclude that any cut value larger than 1 cm is acceptable for both algorithms under the Tevatron's expected instantaneous luminosity improvements.
Date:
August 1, 2006
Creator:
Buzatu, Adrian
Object Type:
Report
System:
The UNT Digital Library
DARHT-II Injector Transients and the Ferrite Damper
This report summarizes the transient response of the DARHT-II Injector and the design of the ferrite damper. Initial commissioning of the injector revealed a rise time excited 7.8 MHz oscillation on the diode voltage and stalk current leading to a 7.8 MHz modulation of the beam current, position, and energy. Commissioning also revealed that the use of the crowbar to decrease the voltage fall time excited a spectrum of radio frequency modes which caused concern that there might be significant transient RF electric field stresses imposed on the high voltage column insulators. Based on the experience of damping the induction cell RF modes with ferrite, the concept of a ferrite damper was developed to address the crowbar-excited oscillations as well as the rise-time-excited 7.8 MHz oscillations. After the Project decided to discontinue the use of the crowbar, further development of the concept focused exclusively on damping the oscillations excited by the rise time. The design was completed and the ferrite damper was installed in the DARHT-II Injector in February 2006. The organization of this report is as follows. The suite of injector diagnostics are described in Section 2. The data and modeling of the injector transients excited on the rise-time …
Date:
August 4, 2006
Creator:
Waldron, Will; Reginato, Lou; Chow, Ken; Houck, Tim; Henestroza, Enrique; Yu, Simon et al.
Object Type:
Report
System:
The UNT Digital Library
SQUID-Detected Magnetic Resonance Imaging in MicroteslaFields
Magnetic resonance imaging (MRI) has developed into a powerful clinical tool for imaging the human body (1). This technique is based on nuclear magnetic resonance (NMR) of protons (2, 3) in a static magnetic field B{sub 0}. An applied radiofrequency pulse causes the protons to precess about B{sub 0} at their Larmor frequency {nu}{sub 0} = ({gamma}/2{pi})B{sub 0}, where {gamma} is the gyromagnetic ratio; {gamma}/2{pi} = 42.58 MHz/tesla. The precessing protons generate an oscillating magnetic field and hence a voltage in a nearby coil that is amplified and recorded. The application of three-dimensional magnetic field gradients specifies a unique magnetic field and thus an NMR frequency in each voxel of the subject, so that with appropriate encoding of the signals one can acquire a complete image (4). Most clinical MRI systems involve magnetic fields generated by superconducting magnets, and the current trend is to higher magnetic fields than the widely used 1.5-T systems (5). Nonetheless, there is ongoing interest in the development of less expensive imagers operating at lower fields. Commercially available 0.2-T systems based on permanent magnets offer both lower cost and a more open access than their higher-field counterparts, at the expense of signal-to-noise-ratio (SNR) and spatial resolution. …
Date:
August 14, 2006
Creator:
Moessle, Michael; Hatridge, Michael & Clarke, John
Object Type:
Article
System:
The UNT Digital Library
Lawrence Livermore National Laboratory Workshop Characterization of Pathogenicity, Virulence and Host-Pathogen Interactions
The threats of bio-terrorism and newly emerging infectious diseases pose serious challenges to the national security infrastructure. Rapid detection and diagnosis of infectious disease in human populations, as well as characterizing pathogen biology, are critical for reducing the morbidity and mortality associated with such threats. One of the key challenges in managing an infectious disease outbreak, whether through natural causes or acts of overt terrorism, is detection early enough to initiate effective countermeasures. Much recent attention has been directed towards the utility of biomarkers or molecular signatures that result from the interaction of the pathogen with the host for improving our ability to diagnose and mitigate the impact of a developing infection during the time window when effective countermeasures can be instituted. Host responses may provide early signals in blood even from localized infections. Multiple innate and adaptive immune molecules, in combination with other biochemical markers, may provide disease-specific information and new targets for countermeasures. The presence of pathogen specific markers and an understanding of the molecular capabilities and adaptations of the pathogen when it interacts with its host may likewise assist in early detection and provide opportunities for targeting countermeasures. An important question that needs to be addressed is …
Date:
August 30, 2006
Creator:
Krishnan, A.
Object Type:
Article
System:
The UNT Digital Library
1,2-HOIQO--A highly versatile 1,2-HOPO analog
A cyclic, bidentate hydroxamic acid binding unit based on an isoquinoline scaffold has been utilized for the synthesis of a hexadentate tripodal ligand based on the TREN backbone. This prototype for a new class of multidentate chelators forms mononuclear iron(III) complexes and one-dimensional coordination polymers with lanthanide(III) cations. The latter has been determined by single crystal X-ray analysis of the cerium species. The solid state structure in the monoclinic space group P2{sub 1}/c (C{sub 36}H{sub 34}CeN{sub 7}O{sub 11}, a = 12.341(2){angstrom}, b = 26.649(4){angstrom}, c = 10.621(2){angstrom}, {alpha} = {gamma} = 90{sup o}, {beta} = 96.753(3){sup o}, V = 3468.6(9) {angstrom}{sup 3}, Z = 4) exhibits a trigonal-dodecahedral environment around the cerium cation. The proof of concept for the versatility of the new scaffold has been shown by the modification of the crucial precursor 3-carboxyiso-coumarin through electrophilic aromatic substitutions to yield the corresponding chlorosulfonated and nitrated analogs.
Date:
August 7, 2006
Creator:
Seitz, Michael; Pluth, Michael D. & Raymond, Kenneth N.
Object Type:
Article
System:
The UNT Digital Library
Accurate iterative analytic solution of theKapchinskij-Vladimirskij equations for the case of a matched beam
The well-known Kapchinskij-Vladimirskij (KV) equations are difficult to solve in general, but the problem is simplified for the matched-beam case with sufficient symmetry. They show that the interdependence of the two KV equations is eliminated, so that only one needs to be solved--a great simplification. They present an iterative method of solution which can potentially yield any desired level of accuracy. The lowest level, the well-known smooth approximation, yields simple, explicit results with good accuracy for weak or moderate focusing fields. The next level improves the accuracy for high fields; they previously showed how to maintain a simple explicit format for the results. That paper used expansion in a small parameter to obtain the second level. The present paper, using straightforward iteration, obtains equations of first, second, and third levels of accuracy. For a periodic lattice with beam matched to lattice, they use the lattice and beam parameters as input and solve for phase advances and envelope waveforms. They find excellent agreement with numerical solutions over a wide range of beam emittances and intensities.
Date:
August 6, 2006
Creator:
Anderson, Oscar A.
Object Type:
Report
System:
The UNT Digital Library
Holographic optical elements for the extreme-ultravioletregime
As the development of extreme ultraviolet (EUV) lithography progresses, interest grows in the extension of traditional optical components to the EUV regime. The strong absorption of EUV by most materials and its extremely short wavelength, however, makes it very difficult to implement many components that are commonplace in the longer wavelength regimes. One such component is the diffractive optical element used, for example, in illumination systems to efficiently generate modified pupil fills. Here we demonstrate the fabrication and characterization of EUV binary phase-only computer-generated holograms allowing arbitrary far-field diffraction patterns to be generated.
Date:
August 14, 2006
Creator:
Naulleau, Patrick P.; Salmassi, Farhad; Gullikson, Eric M. & Anderson, Erik H.
Object Type:
Article
System:
The UNT Digital Library
LC Computing Systems Summary
None
Date:
August 8, 2006
Creator:
East, D
Object Type:
Report
System:
The UNT Digital Library
Deployment Notes for Sodars at the Stevens Institute of Technology during the March 2005 Urban Dispersion Program Field Campaign (MSG05)
This report documents the deployment of two sodars at the Stevens Institute of Technology (SIT) in Hoboken, New Jersey, during the March 2005 Madison Square Garden Urban Dispersion Field Campaign (MSG05) conducted in the vicinity of Madison Square Garden in Midtown Manhattan. One sodar was a Scintec MFAS sodar that was operated on a dock along the Hudson River. This sodar was only operated during Intensive Observation Periods (IOPs). The other sodar was an AeroVironment (AV) Model 3000 MiniSodar that was located on top of the Howe Center at SIT. This sodar was operated continually, but there were data quality issues in the lowest three and upper seven range gates during non-IOP periods. The IOP data from the AeroVironment was reprocessed so that only data from the lowest three and highest seven range gates was removed. Measurements from both sodars were compared to measurements made using a propeller and vane anemometer that was also located on top of the Howe Center. This report also describes the quality control methods applied to data from each sodar and the structure of the data files available. The agreement between the sodars is generally good, and we recommend using either the AV data or …
Date:
August 1, 2006
Creator:
Berg, Larry K. & Allwine, K Jerry
Object Type:
Report
System:
The UNT Digital Library
STROBOSCOPIC IMAGE CAPTURE: REDUCING THE DOSE PER FRAME BY AFACTOR OF 30 DOES NOT PREVENT BEAM-INDUCED SPECIMEN MOVEMENT INPARAFFIN
Beam-induced specimen movement may be the major factor that limits the quality of high-resolution images of organic specimens. One of the possible measures to improve the situation that was proposed by Henderson and Glaeser (Henderson and Glaeser, 1985), which we refer to here as 'stroboscopic image capture', is to divide the normal exposure into many successive frames, thus reducing the amount of electron exposure--and possibly the amount of beam-induced movement--per frame. The frames would then be aligned and summed. We have performed preliminary experiments on stroboscopic imaging using a 200-kV electron microscope that was equipped with a high dynamic range CCD camera for image recording and a liquid N{sub 2}-cooled cryoholder. Single-layer paraffin crystals on carbon film were used as a test specimen. The ratio F(g)/F(0) of paraffin reflections, calculated from the images, serves as our criterion for the image quality. In the series that were evaluated, no significant improvement of the F{sub image}(g)/F{sub image}(0) ratio was found, even though the electron exposure per frame was reduced by a factor of 30. A frame-to-frame analysis of image distortions showed that considerable beam-induced movement had still occurred during each frame. In addition, the paraffin crystal lattice was observed to move relative …
Date:
August 1, 2006
Creator:
Typke, Dieter; Gilpin, Christopher J.; Downing, Kenneth H. & Glaeser, Robert M.
Object Type:
Article
System:
The UNT Digital Library
Temperature sensitivity of Cu K(alpha) imaging efficiency using a spherical Bragg reflecting crystal
The Vulcan laser facility at the Rutherford Appleton Laboratory was used to study the interaction of a 75 J 10 ps, high intensity laser beam with low-mass solid, Cu targets. Two instruments were fielded as diagnostics of the Cu K-shell emission from the targets: A single photon counting CCD spectrometer provided the absolute K{sub {alpha}} yield and a spherically bent Bragg crystal recorded 2D monochromatic images with a spatial resolution of 10 {micro}m. Due to the shifting and broadening of the K{sub {alpha}} spectral lines with increasing temperature, there is a temperature dependence of the crystal collection efficiency. This provides a temperature diagnostic when cross calibrated against a single hit CCD spectrometer, and it affects measurements of the spatial pattern of electron transport. The experimental data showing changing collection efficiency are presented. The results are discussed in light of modeling of the temperature-dependent spectrum of Cu K-shell emission.
Date:
August 7, 2006
Creator:
Akli, K. U.; Key, M. H.; Chung, H. K.; Hansen, S. B.; Freeman, R. R.; Chen, M. H. et al.
Object Type:
Article
System:
The UNT Digital Library
H(curl) Auxiliary Mesh Preconditioning
This paper analyzes a two-level preconditioning scheme for H(curl) bilinear forms. The scheme utilizes an auxiliary problem on a related mesh that is more amenable for constructing optimal order multigrid methods. More specifically, we analyze the case when the auxiliary mesh only approximately covers the original domain. The latter assumption is important since it allows for easy construction of nested multilevel spaces on regular auxiliary meshes. Numerical experiments in both two and three space dimensions illustrate the optimal performance of the method.
Date:
August 31, 2006
Creator:
Kolev, T V; Pasciak, J E & Vassilevski, P S
Object Type:
Article
System:
The UNT Digital Library
The structure of a-C: What NEXAFS and EXAFS see
Mechanically hard ha-C and soft sa-C amorphous carbon films of 2.9 and 2.2 g cm-3 approximate densities were prepared by filtered cathodic arc deposition and analyzed by near-edge x-ray absorption spectroscopy NEXAFS and extended x-ray absorption spectroscopy EXAFS to determine their structure. The analysis observed an insignificant level of pi bond conjugation in both kind of films. EXAFS distinguished two types of atomic environments in them: one semiordered with well defined bond lengths, and the other with so strong bond disorder that its contribution to EXAFS was undetectable. The proportion of atoms in the semiordered atomic environments was of less than 40percent in both films. Their bond lengths were similar to those of diamond in the ha-C films and to graphite in the sa-C. NEXAFS spectra analysis was based on the linear relation between sigma* energy and bond length. It served to quantify the proportion of sp3 bonded atoms in a-C, to deduce the average bond length of the atoms undetected by EXAFS, and to determine the level of bond conjugation in the films. The sp3 concentration estimated with the proposed method was of 44percent in the ha-C films and 10percent in the sa-C films. These values were consistent with …
Date:
August 1, 2006
Creator:
Hussain, Zahid; Diaz, J.; Monteiro, O.R. & Hussain, Z.
Object Type:
Article
System:
The UNT Digital Library
Summary of research output from DOE grant DE-FG02-92ER45471 during the period 1992-2006: publications, invited talks, conference organization, and PhD students graduated.
In this report I summarize some of the main results obtained during the present grant period. They are: (1) Orientation selection in dendritic evolution; (2) Globubar-dendritic transition; and (3) Physics and prediction of grain boundary mobility.
Date:
August 1, 2006
Creator:
Karma, Alain, PhD.
Object Type:
Article
System:
The UNT Digital Library