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Unstable crack motion is predictable

Description: Yoffe's linear theory of dynamic brittle fracture suggests that crack motion will be unstable beyond {approx}70% of the Rayleigh speed, a prediction that is not supported by experiment. We show by atomistic simulations that hyperelasticity, the elasticity of large strains, plays a governing role in the instability dynamics of brittle fracture. A simple scaling model based on an effective elastic modulus, coupled with Yoffe's solution, gives successful predictions for the onset speed of the crack instability.
Date: August 22, 2004
Creator: Abraham, F
Partner: UNT Libraries Government Documents Department

Fluid Effects on Shear for Seismic Waves in Finely Layered Porous Media

Description: Although there are five effective shear moduli for any layered VTI medium, one and only one effective shear modulus of the layered system (namely the uniaxial shear) contains all the dependence of pore fluids on the elastic or poroelastic constants that can be observed in vertically polarized shear waves. Pore fluids can increase the magnitude the shear energy stored in this modulus by an amount that ranges from the smallest to the largest effective shear moduli of the VTI system. But, since there are five shear moduli in play, the overall increase in shear energy due to fluids is reduced by a factor of about 5 in general. We can therefore give definite bounds on the maximum increase of overall shear modulus, being about 20% of the allowed range as liquid is fully substituted for gas. An attendant increase of density (depending on porosity and fluid density) by approximately 5 to 10% decreases the shear wave speed and, thereby, partially offsets the effect of this shear modulus increase. The final result is an increase of shear wave speed on the order of 5 to 10%. This increase is shown to be possible under most favorable circumstances - i.e. when the shear modulus fluctuations are large (resulting in strong anisotropy) and the medium behaves in an undrained fashion due to fluid trapping. At frequencies higher than seismic (such as sonic and ultrasonic waves for well-logging or laboratory experiments), resulting short response times also produce the requisite undrained behavior and, therefore, fluids also affect shear waves at high frequencies by increasing rigidity.
Date: July 22, 2004
Creator: Berryman, J G
Partner: UNT Libraries Government Documents Department

Growth of nanocrystalline MoO3 on Au(111) studied by in-situ STM

Description: The growth of nanocrystalline MoO{sub 3} islands on Au(111) using physical vapor deposition of Mo has been studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The growth conditions affect the shape and distribution of the MoO{sub 3} nanostructures, providing a means of preparing materials with different percentages of edge sites that may have different chemical and physical properties than atoms in the interior of the nanostructures. MoO{sub 3} islands were prepared by physical vapor deposition of Mo and subsequent oxidation by NO{sub 2}exposure at temperatures between 450 K and 600 K. They exhibit a crystalline structure with a c(4x2) periodicity relative to unreconstructed Au(111). While the atomic-scale structure is identical to that of MoO{sub 3} islands prepared by chemical vapor deposition, we demonstrate that the distribution of MoO{sub 3} islands on the Au(111) surface reflects the distribution of Mo clusters prior to oxidation although the growth of MoO{sub 3} involves long-range mass transport via volatile MoO{sub 3} precursor species. The island morphology is kinetically controlled at 450 K, whereas an equilibrium shape is approached at higher preparation temperatures or after prolonged annealing at the elevated temperature. Mo deposition at or above 525 K leads to the formation of a Mo-Au surface alloy as indicated by the observation of embedded MoO{sub 3} islands after oxidation by NO{sub 2}. Au vacancy islands, formed when Mo and Au dealloy to produce vacancies, are observed for these growth conditions.
Date: April 22, 2004
Creator: Biener, M M; Biener, J; Schalek, R & Friend, C M
Partner: UNT Libraries Government Documents Department

Little Supersymmetry and the Supersymmetric Little Hierarchy Problem

Description: The current experimental lower bound on the Higgs mass significantly restricts the allowed parameter space in most realistic supersymmetric models, with the consequence that these models exhibit significant fine-tuning. We propose a solution to this `supersymmetric little hierarchy problem'. We consider scenarios where the stop masses are relatively heavy - in the 500 GeV to a TeV range. Radiative stability of the Higgs soft mass against quantum corrections from the top quark Yukawa coupling is achieved by imposing a global SU(3) symmetry on this interaction. This global symmetry is only approximate - it is not respected by the gauge interactions. A subgroup of the global symmetry is gauged by the familiar SU(2) of the Standard Model. The physical Higgs is significantly lighter than the other scalars because it is the pseudo-Goldstone boson associated with the breaking of this symmetry. Radiative corrections to the Higgs potential naturally lead to the right pattern of gauge and global symmetry breaking. We show that both the gauge and global symmetries can be embedded into a single SU(6) grand unifying group, thereby maintaining the prediction of gauge coupling unification. Among the firm predictions of this class of models are new states with the quantum numbers of 10 and $\bar{10}$ under SU(5) close to the TeV scale. The Higgs mass is expected to bebelow 130 GeV, just as in the MSSM.
Date: April 22, 2004
Creator: Birkedal, Andreas; Chacko, Z. & Gaillard, Mary K.
Partner: UNT Libraries Government Documents Department

Phase Transition in strongly-correlated VO2: Time-domainAssignment of Cause and Effect

Description: We establish time-domain hierarchy between structural andelectronic effects in the strongly correlated system VO2. Theinsulator-to-metal transition is driven directly by structural changerather than by electron-electron correlations.
Date: July 22, 2004
Creator: Cavalleri, A.; Dekorsy, Th.; Chong, H. H.; Kieffer, J. C. & Schoenlein, R. W.
Partner: UNT Libraries Government Documents Department

Supersonic propagation of ionization waves in an under-dense, laser-produced plasma

Description: We observe a laser-driven supersonic ionization wave heating a mm-scale plasma of sub-critical density up to 2-3 keV electron temperatures. Propagation velocities initially 10 times the sound speed were measured by means of time-resolved x-ray imaging diagnostics. The measured ionization wave trajectory is modeled analytically and by a 2D radiation-hydrodynamics code. The comparison to the modeling suggests that nonlocal heat transport effects may contribute to the attenuation of the heat wave propagation.
Date: October 22, 2004
Creator: Constantin, C; Back, C A; Fournier, K B; Gregori, G; Landen, O L; Glenzer, S H et al.
Partner: UNT Libraries Government Documents Department

D-meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution

Description: When nonlinear effects on the gluon evolution are included with constraints from HERA, the gluon distribution in the free proton is enhanced at low momentum fractions, x {approx}< 0.01, and low scales, Q{sup 2} {approx}< 10 GeV{sup 2}, relative to standard, DGLAP-evolved, gluon distributions. Consequently, such gluon distributions can enhance charm production in pp collisions at center of mass energy 14 TeV by up to a factor of five at midrapidity, y {approx} 0, and transverse momentum p{sub T} {yields} 0 in the most optimistic case. We show that most of this enhancement survives hadronization into D mesons. Assuming the same enhancement at leading and next-to-leading order, we show that the D enhancement may be measured by D{sup 0} reconstruction in the K{sup -}{pi}{sup +} decay channel with the ALICE detector.
Date: August 22, 2004
Creator: Dainese, A.; Vogt, R.; Bondila, M.; Eskola, K.J. & Kolhinen, V.J.
Partner: UNT Libraries Government Documents Department

Crevice Corrosion Susceptibility of Alloy 22 in Fluoride and Chloride Containing Solutions

Description: Alloy 22 (N06022) is highly resistant to crevice corrosion in pure chloride (Cl{sup -}) solutions. Little research has been conducted to explore the resistance of this alloy to other halides such as fluoride (F{sup -}) and bromide (Br{sup -}). Even less information is available exploring the behavior of localized corrosion for Alloy 22 in mixtures of the halide ions. Standard electrochemical tests such as polarization resistance and cyclic potentiodynamic polarization (CPP), were conducted to explore the resistance to corrosion of Alloy 22 in deaerated aqueous solutions of 1 M NaCl, 1 M NaF and 0.5 M NaCl + 0.5 M NaF solutions at 60 C and 90 C. Results show that the general corrosion rate was the lowest in the mixed halide solution and the highest in the pure chloride solution. Alloy 22 was not susceptible to localized corrosion in the pure fluoride solution. In 1 M NaCl solution, Alloy 22 was susceptible to crevice corrosion at 90 C. In the mixed halide solution Alloy 22 was susceptible to crevice corrosion both at 60 C and 90 C.
Date: November 22, 2004
Creator: Day, S D & Rebak, R B
Partner: UNT Libraries Government Documents Department

Lawrence Livermore National Laboratory Experience Using 30-Gallon Drum Neutron Multiplicity Counter for Measuring Plutonium-Bearing Salts

Description: Lawrence Livermore National Laboratory (LLNL) has been performing accountability measurements of plutonium (Pu) -bearing items with the 30-gallon drum neutron multiplicity counter (NMC) since August 1998. A previous paper focused on the LLNL experience with Pu-bearing oxide and metal items. This paper expands on the LLNL experience with Pu-bearing salts containing low masses of Pu. All Pu-bearing salts used in this study were measured using calorimetry and gamma isotopic analyses (Cal/Iso) as well as the 30-gallon drum NMC. The Cal/Iso values were treated as being the true measure of Pu content because of the inherent high accuracy of the Cal/Iso technique, even at low masses of Pu, when measured over a sufficient period of time. Unfortunately, the long time period required to achieve high accuracy from Cal/Iso can impact other required accountability measurements. The 30-gallon drum NMC is a much quicker system for making accountability measurements of a Pu-bearing salt and might be a desirable tradeoff. The accuracy of 30-gallon drum NMC measurements of Pu-bearing salts, relative to that of Cal/Iso, is presented in relation to the mass range and alpha associated with each item. Conclusions drawn from the use of the 30-gallon drum NMC for accountability measurements of salts are also included.
Date: June 22, 2004
Creator: Dearborn, D M & Keeton, S C
Partner: UNT Libraries Government Documents Department

Resolving the Nature of the LMC Microlensing Event LMC-5

Description: The authors present the results from an analysis of Hubble Space Telescope High Resolution Camera data for the Large Magellanic Cloud microlensing event MACHO-LMC-5. By determining the parallax and proper motion of this object they find that the lens is an M dwarf star at a distance of 578{sub -53}{sup +65}pc with a proper motion of 21.39 {+-} 0.04 mas/yr. Based on the kinematics and location of this star is it more likely to be part of the Galactic thick disk than thin disk population. They confirm that the microlensing event LMC-5 is a jerk-parallax microlensing event.
Date: April 22, 2004
Creator: Drake, A J; Cook, K H & Keller, S C
Partner: UNT Libraries Government Documents Department

A prediction for |U{sub e3}| from patterns in the charged lepton spectra

Description: It is shown that empirical relations between the charged lepton spectra and the quark spectra together with a bimaximal or near bimaximal neutrino mixing matrix necessarily imply that there is a contribution to |U{sub e3}| given by {theta}{sub C}/ 3{radical}2 {approx} {radical}(m{sub e}/2m{sub {mu}}) {approx} 0.052, where {theta}{sub C}is the Cabibbo angle. This prediction could be tested in the near future reactor experiments. The charged lepton mixing also generates a less robust prediction for the angle {theta}{sub 23} and a small contribution to the phase {delta}.
Date: September 22, 2004
Creator: Ferrandis, Javier & Pakvasa, Sandip
Partner: UNT Libraries Government Documents Department

The evaluated gamma-ray activation file (EGAF)

Description: The Evaluated Gamma-ray Activation File (EGAF), a new database of prompt and delayed neutron capture g-ray cross sections, has been prepared as part of an International Atomic Energy Agency (IAEA) Coordinated Research Project to develop a ''Database of Prompt Gamma-rays from Slow Neutron Capture for Elemental Analysis.'' Recent elemental g-ray cross-section measurements performed with the guided neutron beam at the Budapest Reactor have been combined with data from the literature to produce the EGAF database. EGAF contains thermal cross sections for {approx} 35,000 prompt and delayed g-rays from 262 isotopes. New precise total thermal radiative cross sections have been derived for many isotopes from the primary and secondary gamma-ray cross sections and additional level scheme data. An IAEA TECDOC describing the EGAF evaluation and tabulating the most prominent g-rays will be published in 2004. The TECDOC will include a CD-ROM containing the EGAF database in both ENSDF and tabular formats with an interactive viewer for searching and displaying the data. The Isotopes Project, Lawrence Berkeley National Laboratory continues to maintain and update the EGAF file. These data are available on the Internet from both the IAEA and Isotopes Project websites.
Date: September 22, 2004
Creator: Firestone, R.B.; Molnar, G.L.; Revay, Zs.; Belgya, T.; McNabb, D.P. & Sleaford, B.W.
Partner: UNT Libraries Government Documents Department

Development of a Multiview Time Domain Imaging Algorithm (MTDI) with a Fermat Correction

Description: An imaging algorithm is presented based on the standard assumption that the total scattered field can be separated into an elastic component with monopole like dependence and an inertial component with a dipole like dependence. The resulting inversion generates two separate image maps corresponding to the monopole and dipole terms of the forward model. The complexity of imaging flaws and defects in layered elastic media is further compounded by the existence of high contrast gradients in either sound speed and/or density from layer to layer. To compensate for these gradients, we have incorporated Fermat's method of least time into our forward model to determine the appropriate delays between individual source-receiver pairs. Preliminary numerical and experimental results are in good agreement with each other.
Date: September 22, 2004
Creator: Fisher, K A; Lehman, S K & Chambers, D H
Partner: UNT Libraries Government Documents Department

STATUS OF HIGH TEMPERATURE SUPERCONDUCTOR MAGNET R AND D AT BNL.

Description: We report the status and test results of the High Temperature Superconductor (HTS) cable and magnet R&D at Brookhaven National Laboratory (BNL). If successful, this will enhance the performance and reduce the cost of operation of magnets that must absorb a large amount of energy. The need for developing this technology has been seen in a number of high field magnet applications for high energy colliders, and a medium field application in the proposed Rare Isotope Accelerator (RIA). The likelihood of the future use of HTS is improving because of the availability of longer and more uniform length tapes and cables and because of the ongoing construction and test experience at BNL and elsewhere. The design of a super-ferric quadrupole, that must survive the very high radiation environment of RIA, and operate at 20-40 K, is also presented.
Date: January 22, 2004
Creator: GUPTA,R.; ANERELLA,M.; COZZOLINO,J.; ESCALLIER,J.; GANETIS,G.; GHOSH,A. et al.
Partner: UNT Libraries Government Documents Department

Cable Design for Fast Ramped Superconducting Magnets (Cos-θ Design).

Description: The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 300 T-m and 100 T-m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of ac loss and magnetic field distortion. The development of the low loss Rutherford cable that can be used is described, together with a novel insulation scheme designed to promote efficient cooling. Measurements of contact resistance in the cable are presented and the results of these measurements are used to predict the ac losses, in the magnets during fast ramp operation. For the high energy ring, a lm model dipole magnet was built, based on the RHIC dipole design. This magnet was tested under boiling liquid helium in a vertical cryostat. The quench current showed very little dependence on ramp rate. The ac losses, measured by an electrical method, were fitted to straight line plots of loss/cycle versus ramp rate, thereby separating the eddy current and hysteresis components. These results were compared with calculated values, using parameters which had previously been measured on short samples of cable. Reasonably good agreement between theory and experiment was found, although the measured hysteresis loss is higher than expected in ramps to the highest field levels.
Date: March 22, 2004
Creator: Ghosh, A.
Partner: UNT Libraries Government Documents Department

Error Estimation for Reduced Order Models of Dynamical Systems

Description: The use of reduced order models to describe a dynamical system is pervasive in science and engineering. Often these models are used without an estimate of their error or range of validity. In this paper we consider dynamical systems and reduced models built using proper orthogonal decomposition. We show how to compute estimates and bounds for these errors, by a combination of small sample statistical condition estimation and error estimation using the adjoint method. Most importantly, the proposed approach allows the assessment of regions of validity for reduced models, i.e., ranges of perturbations in the original system over which the reduced model is still appropriate. Numerical examples validate our approach: the error norm estimates approximate well the forward error while the derived bounds are within an order of magnitude.
Date: January 22, 2004
Creator: Homescu, C.; Petzold, L. & Serban, R.
Partner: UNT Libraries Government Documents Department

Simultaneous Analyses and Applications of Multiple Fluorobenzoate and Halide Tracers in Hydrologic Studies

Description: An analytical method that employs ion chromatography has been developed to more fully exploit the use of fluorobenzoic acids (FBAs) and halides as hydrologic tracers. In a single run, this reliable, sensitive, and robust method can simultaneously separate and quantify halides (fluoride, chloride, bromide, and iodide) and up to seven FBAs from other common groundwater constituents (e.g., nitrate and sulfate). The usefulness of this ion chromatographic (IC) analytical method is demonstrated in both field and laboratory tracer experiments. Field experiments in unsaturated tuff featuring fractures or a fault show that this efficient and cost-effective method helps achieve the objectives of tracer studies that use multiple FBAs and/or diffusivity tracers (simultaneous use of one or more FBA and halide). The field study examines the hydrologic response of fractures and the matrix to different flow rates and the contribution of matrix diffusion in chemical transport. Laboratory tracer experiments with eight geologic media from across the United States--mostly from Department of Energy facilities where groundwater contamination is prevalent and where subsurface characterization employing tracers has been ongoing or is in need--reveal several insights about tracer transport behavior: (1) Bromide and FBAs are not always transported conservatively. (2) The delayed transport of these anionic tracers is likely related to geologic media characteristics, such as organic matter, pH, iron oxide content, and clay mineralogy. (3) Any use of iodine as a hydrologic tracer should take into account the different sorption behaviors of iodide and iodate and the possible conversion of iodine's initial chemical form. (4) The transport behavior of potential FBA and halide tracers under relevant geochemical conditions should be evaluated before beginning ambitious, large-scale field tracer experiments.
Date: January 22, 2004
Creator: Hu, Q & Moran, J E
Partner: UNT Libraries Government Documents Department

Broadband THz response of a resonantly excited high-densityexciton gas

Description: The density-driven crossover of electron-hole pairs frominsulating to conducting states is observed via the internal 1s-2pexciton resonance. Decreasing interparticle distance induces strongshifts and broadening, and ultimately the disappearance of the excitonicresonance.
Date: November 22, 2004
Creator: Huber, Rupert; Kaindl, Robert A.; Schmid, Benjamin A. & Chemla,Daniel S.
Partner: UNT Libraries Government Documents Department

Effect of Colorspace Transformation, the Illuminance Component, and Color Modeling on Skin Detection

Description: Skin detection is an important preliminary process in human motion analysis. It is commonly performed in three steps: transforming the pixel color to a non-RGB colorspace, dropping the illumination component of skin color, and classifying by modeling the skin color distribution. In this paper, we evaluate the effect of these three steps on the skin detection performance. The importance of this study is a new comprehensive colorspace and color modeling testing methodology that would allow for making the best choices for skin detection. Combinations of nine colorspaces, the presence of the absence of the illuminance component, and the two color modeling approaches are compared. The performance is measured by using a receiver operating characteristic (ROC) curve on a large dataset of 805 images with manual ground truth. The results reveal that (1) the absence of the illuminance component decreases performance, (2) skin color modeling has a greater impact than colorspace transformation, and (3) colorspace transformations can improve performance in certain instances. We found that the best performance was obtained by transforming the pixel color to the SCT, HSI, or CIELAB colorspaces, keeping the illuminance component, and modeling the color with the histogram approach.
Date: March 22, 2004
Creator: Jayaram, S; Schmugge, S; Shin, M C & Tsap, L V
Partner: UNT Libraries Government Documents Department

Precision short-pulse damage test station utilizing optical parametric chirped-pulse amplification

Description: The next generation of high-energy petawatt (HEPW)-class lasers will utilize multilayer dielectric diffraction gratings for pulse compression, due to their high efficiency and high damage threshold for picosecond pulses. The peak power of HEPW lasers will be determined by the aperture and damage threshold of the final dielectric grating in the pulse compressor and final focusing optics. We have developed a short-pulse damage test station for accurate determination of the damage threshold of the optics used on future HEPW lasers. Our damage test station is based on a highly stable, high-beam-quality optical parametric chirped-pulse amplifier (OPCPA) operating at 1053 nm at a repetition rate of 10 Hz. We present the design of our OPCPA system pumped by a commercial Q-switched pump laser and the results of the full system characterization. Initial short-pulse damage experiments in the far field using our system have been performed.
Date: March 22, 2004
Creator: Jovanovic, I; Brown, C; Wattellier, B; Nielsen, N; Molander, W; Stuart, B et al.
Partner: UNT Libraries Government Documents Department

Utilizing Strong Tight Intermodal Waste Packaging to Meet Accelerated Cleanup Goals at The Savannah River Site

Description: In support of the accelerated cleanup challenge, personnel at the Savannah River Site have been working diligently to identify and acquire cost-effective waste containers that can be used to package a voluminous amount of low level radioactive waste that needs to be disposed. In so doing, personnel have transformed their paradigm in packaging low level radioactive waste in traditional 45-cubic-foot and 90-cubic-foot containers and utilizing refurbished intermodal containers instead. The transition has increased efficiencies in the processing, packaging, transportation, storage, and disposal of low level radioactive waste, while providing decreased procurement costs. Since large items do not have to be size-reduced to fit into the large containers, additional cost savings are being realized by minimizing void space, labor, time, equipment, and risks if size reduction techniques were performed. Cost savings for fiscal year 2003 exceeded one million dollars. Additional savings are estimated to be between 3 million dollars and 4 million dollars through fiscal year 2006.
Date: January 22, 2004
Creator: Kinney, JosephC.
Partner: UNT Libraries Government Documents Department