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Power Corrections in Charmless Nonleptonic B Decays: Annihilationis Factorizable and Real

Description: We classify {Lambda}{sub QCD}/m{sub b} power corrections to nonleptonic B {yields} M{sub 1}M{sub 2} decays, where M{sub 1,2} are charmless non-isosinglet mesons. Using recent developments in soft-collinear effective theory, we prove that the leading contributions to annihilation amplitudes of order {alpha}{sub s}(m{sub b}) {Lambda}{sub QCD}/m{sub b} are real. The leading annihilation amplitudes depend on twist-2 and the twist-3 three parton distributions. A complex nonperturbative parameter from annihilation first appears at {Omega}[{alpha}{sub s}{sup 2}({radical}{Lambda}m{sub b}){Lambda}{sub QCD}/m{sub b}]. 'Chirally enhanced' contributions are also factorizable and real at lowest order. Thus, incalculable strong phases are suppressed in annihilation amplitudes, unless the {alpha}{sub s}({radical}{Lambda}m{sub b}) expansion breaks down. Modeling the distribution functions, we find that (11 {+-} 9)% and (15 {+-} 11)% of the absolute values of the measured {bar B}{sup 0} {yields} K{sup -}{pi}{sup +} and B{sup -} {yields} K{sup -}K{sup 0} penguin amplitudes come from annihilation. This is consistent with the expected size of power corrections.
Date: October 10, 2006
Creator: Arnesen, Christian M.; Ligeti, Zoltan; Rothstein, Ira Z. & Stewart, Iain W.
Partner: UNT Libraries Government Documents Department

Beam matching and halo control

Description: We present an overview of the status of ongoing work on physics models describing beam matching and halo control for particle accelerators, particularly high power ion linacs. We consider moments and various new variables that more naturally describe beam halo evolution. We compute matched beams and ``mode invariants`` (analogs of moment invariants) using primarily symbolic techniques.
Date: September 1, 1997
Creator: Lysenko, W. & Parsa, Z.
Partner: UNT Libraries Government Documents Department

The Hamiltonian Mechanics of Stochastic Acceleration

Description: We show how to nd the physical Langevin equation describing the trajectories of particles un- dergoing collisionless stochastic acceleration. These stochastic di erential equations retain not only one-, but two-particle statistics, and inherit the Hamiltonian nature of the underlying microscopic equations. This opens the door to using stochastic variational integrators to perform simulations of stochastic interactions such as Fermi acceleration. We illustrate the theory by applying it to two example problems.
Date: July 17, 2013
Creator: Burby, J. W.
Partner: UNT Libraries Government Documents Department

Cumalative Distribution Functions for the Relative Humidity Thresholds for the Onset of Carbon Steel Corrosion

Description: The purpose of this calculation is to process the cumulative distribution functions (CDFs) characterizing the relative humidity (RH) thresholds for the onset of carbon steel corrosion provided by expert elicitation and minimize the set of values to 200 points for use in WAPDEG.
Date: May 13, 1998
Creator: Mon, K.G.
Partner: UNT Libraries Government Documents Department


Description: The purpose of this calculation is to process the cumulative distribution functions (CDFs) characterizing the temperature threshold for the onset of corrosion provided by expert elicitation and minimize the set of values to 200 points for use in WAPDEG.
Date: May 15, 1998
Creator: Mon, K.G.
Partner: UNT Libraries Government Documents Department

Finite Size Effects on the Real-Space Pair Distribution Function of Nanoparticles

Description: The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.
Date: October 1, 2008
Creator: Gilbert, Benjamin
Partner: UNT Libraries Government Documents Department

A comparison between Gauss-Newton and Markov chain Monte Carlo basedmethods for inverting spectral induced polarization data for Cole-Coleparameters

Description: We develop a Bayesian model to invert spectral induced polarization (SIP) data for Cole-Cole parameters using Markov chain Monte Carlo (MCMC) sampling methods. We compare the performance of the MCMC based stochastic method with an iterative Gauss-Newton based deterministic method for Cole-Cole parameter estimation through inversion of synthetic and laboratory SIP data. The Gauss-Newton based method can provide an optimal solution for given objective functions under constraints, but the obtained optimal solution generally depends on the choice of initial values and the estimated uncertainty information is often inaccurate or insufficient. In contrast, the MCMC based inversion method provides extensive global information on unknown parameters, such as the marginal probability distribution functions, from which we can obtain better estimates and tighter uncertainty bounds of the parameters than with the deterministic method. Additionally, the results obtained with the MCMC method are independent of the choice of initial values. Because the MCMC based method does not explicitly offer single optimal solution for given objective functions, the deterministic and stochastic methods can complement each other. For example, the stochastic method can first be used to obtain the means of the unknown parameters by starting from an arbitrary set of initial values and the deterministic method can then be initiated using the means as starting values to obtain the optimal estimates of the Cole-Cole parameters.
Date: May 15, 2008
Creator: Chen, Jinsong; Kemna, Andreas & Hubbard, Susan S.
Partner: UNT Libraries Government Documents Department

Study of the uncertainty of the gluon distribution

Description: The uncertainty in the calculation of many important new processes at the Tevatron and LHC is dominated by that concerning the gluon distribution function. We investigate the uncertainty in the gluon distribution of the proton by systematically varying the gluon parameters in the global QCD analysis of parton distributions. The results depend critically on the parton momentum fraction x and the QCD scale Q{sup 2}. The uncertainties are presented for integrated gluon-gluon and gluon-quark luminosities for both the Tevatron and LHC as a function of {radical}{tau}={radical}x{sub 1}x{sub 2}={radical}{cflx s}/s, the most relevant quantity for new particle production. The uncertainties are reasonably small, except for large x.
Date: July 1, 1998
Creator: Huston, J., FERMI
Partner: UNT Libraries Government Documents Department

Magnetic field effects on plasma ionization balance

Description: Magnetic fields give rise to several phenomena that can significantly affect ionization balance in a plasma. Theoretical models commonly used to determine the charge state distribution (viz., <Z>) of ions in non-magnetized plasmas are reviewed first, for both equilibrium and non-equilibrium situations. Then, after a brief survey of laboratory and cosmic plasmas with strong fields, B > 10{sup 6} Gauss, some of the ways such magnetic fields influence <Z> are highlighted. Most key problems have yet to be tackled.
Date: December 31, 1995
Creator: Weisheit, J.C.
Partner: UNT Libraries Government Documents Department

Local Atomic Structure of Semiconductor Alloys Using Pair Distribution Function Analysis

Description: We have been taking advantage of recent experimental developments, which involve utilizing diffraction data from x-rays or neutrons out to very large wave-vectors, to obtain a detailed structural characterization of semiconductor alloys. This approach allows an accurate Pair Distribution Function (PDF) to be obtained to 20A and beyond and reveals the local structure of the alloy directly. These data can be modeled explicitly to learn about local correlations and short-range order in materials. We are combining theory, modeling and experiments to study a range of materials from semiconductors to thermoelectrics and proton conductors.
Date: June 24, 2002
Creator: Billinge, S.J.L. & Thorpe, M.F.
Partner: UNT Libraries Government Documents Department

Numerical Calculation of Neoclassical Distribution Functions and Current Profiles in Low Collisionality, Axisymmetric Plasmas

Description: A new code, the Neoclassical Ion-Electron Solver (NIES), has been written to solve for stationary, axisymmetric distribution functions (f ) in the conventional banana regime for both ions and elec trons using a set of drift-kinetic equations (DKEs) with linearized Fokker-Planck-Landau collision operators. Solvability conditions on the DKEs determine the relevant non-adiabatic pieces of f (called h ). We work in a 4D phase space in which Ψ defines a flux surface, θ is the poloidal angle, v is the total velocity referenced to the mean flow velocity, and λ is the dimensionless magnetic moment parameter. We expand h in finite elements in both v and λ#21; . The Rosenbluth potentials, φ#8; and ψ, which define the integral part of the collision operator, are expanded in Legendre series in cos χ , where #31;χ is the pitch angle, Fourier series in cos #18;θ , and finite elements in v . At each ψ , we solve a block tridiagonal system for hi (independent of fe ), then solve another block tridiagonal system for he (dependent on fi ). We demonstrate that such a formulation can be accurately and efficiently solved. NIES is coupled to the MHD equilibrium code JSOLVER [J. DeLucia, et al., J. Comput. Phys. 37 , pp 183-204 (1980).] allowing us to work with realistic magnetic geometries. The bootstrap current is calculated as a simple moment of the distribution function. Results are benchmarked against the Sauter analytic formulas and can be used as a kinetic closure for an MHD code (e.g., M3D-C1 [S.C. Jardin, et al ., Computational Science &amp; Discovery, 4 (2012).]).
Date: June 28, 2012
Creator: B.C. Lyons, S.C. Jardin, and J.J. Ramos
Partner: UNT Libraries Government Documents Department

Ion acceleration and cooling in gasless self-sputtering

Description: Copper plasma with hyperthermal directed velocity (8.8 eV) but very low temperature (0.6 eV) has been obtained using self-sputtering far above the runaway threshold. Ion energy distribution functions (IEDFs) were simultaneously measured at 34 locations. The IEDFs show the tail of the Thompson distribution near the magnetron target. They transform to shifted Maxwellians with the ions being accelerated and cooled. We deduce the existence of a highly asymmetric, pressure-driven potential hump which acts as a controlling&quot;watershed&quot; between the ion return flux and the expanding plasma.
Date: October 31, 2010
Creator: Horwat, David & Anders, Andre
Partner: UNT Libraries Government Documents Department

Naive time-reversal odd phenomena in semi-inclusive deep-inelastic scattering from light-cone constituent quark models

Description: We present results for leading-twist azimuthal asymmetries in semi-inclusive lepton-nucleon deep-inelastic scattering due to naively time-reversal odd transverse-momentum dependent parton distribution functions from the light-cone constituent quark model. We carefully discuss the range of applicability of the model, especially with regard to positivity constraints and evolution effects. We find good agreement with available experimental data from COMPASS and HERMES, and present predictions to be tested in forthcoming experiments at Jefferson Lab.
Date: June 1, 2011
Creator: Barbara Pasquini, Peter Schweitzer
Partner: UNT Libraries Government Documents Department

Production of a sterile species: Quantum kinetics

Description: Production of a sterile species is studied within an effective model of active-sterile neutrino mixing in a medium in thermal equilibrium. The quantum kinetic equations for the distribution functions and coherences are obtained from two independent methods: the effective action and the quantum master equation. The decoherence time scale for active-sterile oscillations is tau(dec)=2/Gamma(aa), but the evolution of the distribution functions is determined by the two different time scales associated with the damping rates of the quasiparticle modes in the medium: Gamma(1)=Gamma(aa)cos^2theta(m); Gamma(2)=Gamma(aa)sin^2theta(m) where Gamma(aa) is the interaction rate of the active species in the absence of mixing and theta(m) the mixing angle in the medium. These two time scales are widely different away from Mikheyev-Smirnov-Wolfenstein resonances and preclude the kinetic description of active-sterile production in terms of a simple rate equation. We give the complete set of quantum kinetic equations for the active and sterile populations and coherences and discuss in detail the various approximations. A generalization of the active-sterile transition probability in a medium is provided via the quantum master equation. We derive explicitly the usual quantum kinetic equations in terms of the&quot;polarization vector&quot; and show their equivalence to those obtained from the quantum master equation and effective action.
Date: April 23, 2007
Creator: Ho, Chiu Man; Boyanovsky, D. & Ho, C.M.
Partner: UNT Libraries Government Documents Department

A sampling-based Bayesian model for gas saturation estimationusing seismic AVA and marine CSEM data

Description: We develop a sampling-based Bayesian model to jointly invertseismic amplitude versus angles (AVA) and marine controlled-sourceelectromagnetic (CSEM) data for layered reservoir models. The porosityand fluid saturation in each layer of the reservoir, the seismic P- andS-wave velocity and density in the layers below and above the reservoir,and the electrical conductivity of the overburden are considered asrandom variables. Pre-stack seismic AVA data in a selected time windowand real and quadrature components of the recorded electrical field areconsidered as data. We use Markov chain Monte Carlo (MCMC) samplingmethods to obtain a large number of samples from the joint posteriordistribution function. Using those samples, we obtain not only estimatesof each unknown variable, but also its uncertainty information. Thedeveloped method is applied to both synthetic and field data to explorethe combined use of seismic AVA and EM data for gas saturationestimation. Results show that the developed method is effective for jointinversion, and the incorporation of CSEM data reduces uncertainty influid saturation estimation, when compared to results from inversion ofAVA data only.
Date: April 4, 2006
Creator: Chen, Jinsong; Hoversten, Michael; Vasco, Don; Rubin, Yoram & Hou,Zhangshuan
Partner: UNT Libraries Government Documents Department

Obtaining the Bidirectional Transfer Distribution Function ofIsotropically Scattering Materials Using an Integrating Sphere

Description: This paper demonstrates a method to determine thebidirectional transfer distribution function (BTDF) using an integratingsphere. Information about the sample's angle dependent scattering isobtained by making transmittance measurements with the sample atdifferent distances from the integrating sphere. Knowledge about theilluminated area of the sample and the geometry of the sphere port incombination with the measured data combines to an system of equationsthat includes the angle dependent transmittance. The resulting system ofequations is an ill-posed problem which rarely gives a physical solution.A solvable system is obtained by using Tikhonov regularization on theill-posed problem. The solution to this system can then be used to obtainthe BTDF. Four bulk-scattering samples were characterised using both twogoniophotometers and the described method to verify the validity of thenew method. The agreement shown is great for the more diffuse samples.The solution to the low-scattering samples contains unphysicaloscillations, butstill gives the correct shape of the solution. Theorigin of the oscillations and why they are more prominent inlow-scattering samples are discussed.
Date: October 19, 2006
Creator: Jonsson, Jacob C. & Branden, Henrik
Partner: UNT Libraries Government Documents Department

Dilepton Production from Collisions of Polarized Spin 1/2 Hadrons. 2. Parton-model predictions

Description: Parton-model predictions for lepton-pair production from polarized spin-1/2 particles are considered within the context of a formalism explained in a companion paper. The polarization effects in the quantum-chromodynamic 2 {yields} 2 subprocesses which contribute to lepton-pair production are found to be quite simple. Following the work of Ralston and Soper, polarized distribution functions are defined for gluons as well as quarks. Finally, a detailed discussion of polarization and the hard-scattering formalism is presented for the two cases of intrinsic parton transverse momentum allowed or forbidden.
Date: June 1, 1980
Creator: Donohue, J.T.; U., /Argonne /Bordeaux; Gottlieb, Steven A. & /Argonne
Partner: UNT Libraries Government Documents Department

Purgatorio calculations of Zbar at melt

Description: Purgatorio calculates self-consistent bound and continuum electron densities {rho}{sub bound}(r) and {rho}{sub continuum}(r) in a neutral ion sphere with radius R{sub ion} by populating relativistic wave functions P(r) and Q(r) according to their statistical weights and the Fermi distribution function f({var_epsilon},{mu}) = (1+e{sup {var_epsilon}-{mu}/{tau}}){sup -1}.
Date: August 31, 2007
Creator: Hansen, S B
Partner: UNT Libraries Government Documents Department

The Application of Reliability-Based Design Factors In Stress Corrosion Cracking Evaluations

Description: First-order reliability methodology (FORM) is used to develop reliability-based design factors for deterministic analyses of stress corrosion cracking. The basic elements of FORM as applied to structural reliability problems are reviewed and then employed specifically to stress corrosion cracking evaluations. Failure due to stress corrosion cracking is defined as crack initiation followed by crack growth to a critical depth. The stress corrosion cracking process is thus represented in terms of a crack initiation time model and a crack growth rate model, with the crack growth rate integrated from the initiation time to the time at which the crack grows to its critical depth. Both models are described by log-normal statistical distribution functions. A procedure is developed to evaluate design factors that are applied to the mean values of the crack initiation time and the crack growth rate for specified temperature and stress conditions. The design factors, which depend on the standard deviations of the statistical distributions, are related to a target reliability, which is inversely related to an acceptable probability of failure. The design factors are not fixed, but are evaluated on a case-to-case basis for each application. The use of these design factors in a deterministic analysis assures that the target reliability will be attained and the corresponding acceptable probability of failure will not be exceeded. An example problem illustrates use of this procedure.
Date: December 20, 2001
Creator: Friedman, E.
Partner: UNT Libraries Government Documents Department

Proof that stable monotonic equilibrium distributions in a continuous focusing channel are necessarily axisymmetric

Description: The transverse Vlasov equilibrium distribution function of an unbunched ion beam propagating in a continuous focusing channel is specified by a function f{perpendicular} (H{perpendicular}), where H{perpendicular} is the single-particle Hamiltonian. In standard treatments of continuous focusing equilibria in Vlasov-Poisson electrostatic models, it is assumed that a stable beam equilibrium specified by monotonic f{perpendicular}(H{perpendicular}) with {partial_derivative}f{perpendicular}(H{perpendicular})/{partial_derivative}H{perpendicular} {le} 0 is axisymmetric (no variation in azimuthal angle, i.e., with {partial_derivative}/{partial_derivative}{theta} = 0). In this paper a simple, but rigorous, proof is presented that only axisymmetric equilibrium solutions are possible in Vlasov-Poisson models for any physical choice of f{perpendicular}(H{perpendicular}) with {partial_derivative}f{perpendicular}(H{perpendicular})/{partial_derivative}H{perpendicular} {le} 0 if the confining boundary of the system (the beam pipe) is axisymmetric or if the geometry is radially unbounded.
Date: March 28, 2007
Creator: Lund, S M
Partner: UNT Libraries Government Documents Department

Generalized Kapchinskij-Vladimirskij Distribution and Envelope Equation for High-intensity Beams in a Coupled Transverse Focusing Lattice

Description: In an uncoupled lattice, the Kapchinskij-Vladimirskij (KV) distribution function first analyzed in 1959 is the only known exact solution of the nonlinear Vlasov-Maxwell equations for high- intensity beams including self-fields in a self-consistent manner. The KV solution is generalized here to high-intensity beams in a coupled transverse lattice using the recently developed generalized Courant-Snyder invariant for coupled transverse dynamics. This solution projects to a rotating, pulsating elliptical beam in transverse configuration space, determined by the generalized matrix envelope equation.
Date: November 20, 2009
Creator: Hong Qin, Moses Chung, and Ronald C. Davidson
Partner: UNT Libraries Government Documents Department

Statistical and systematic uncertainties in the event reconstruction and S(1000) determination by the Pierre Auger surface detector

Description: We discuss the statistical and systematic uncertainties in the event reconstruction (core location, and determination of S(1000) , i.e., the signal at a distance of 1000 m from the shower core) by the Pierre Auger surface detector for showers with zenith angle less than 60 degrees. The method is based on a maximum likelihood method where the reference lateral distribution function is obtained through the experimental data. We also discuss S(1000) as primary energy estimator.
Date: July 1, 2005
Creator: Ghia, Piera L. & Sasso, /Gran
Partner: UNT Libraries Government Documents Department

X-ray line polarization spectroscopy of Li-like satellite line spectra

Description: We apply the magnetic-sublevel atomic kinetics model POLAR to the calculation of polarization properties of satellite lines in Li-like Si driven by subpicosecond-duration laser pulses. We identify spectral lines whose polarization can serve as a marker of plasma anisotropy due to anisotropy in the electron distribution function. We also discuss the utility and limitations of ur current theoretical approach and point out possible future improvements and directions.
Date: January 1, 2008
Creator: Sherrill, Manolo Edgar; Abdallah, Joseph; Zhang, Honglin; Hakel, Peter & Mancini, Roberto C
Partner: UNT Libraries Government Documents Department