501 Matching Results

Search Results

Advanced search parameters have been applied.

Isomer Energy Differences for the C4H3 and C4H5 Isomers UsingDiffusion Monte Carlo

Description: A new diffusion Monte Carlo study is performed on the isomers of C{sub 4}H{sub 3} and C{sub 4}H{sub 5} emulating the methodology of a previous study [Int. J. Chem. Kinetics 33, 808 (2001)]. Using the same trial wave function form of the previous study, substantially different isomerization energies were found owing to the use of larger walker populations in the present work. The energy differences between the E and I isomers of C{sub 4}H{sub 3} were found to be 10.5 {+-} 0.5 kcal/mol and for C{sub 4}H{sub 5}, 9.7 {+-} 0.6 kcal/mol. These results are in reasonable accord with recent MRCI and CCSD(T) findings.
Date: December 1, 2007
Creator: Domin, D.; Lester Jr., W.A.; Whitesides, R. & Frenklach, M.
Partner: UNT Libraries Government Documents Department


Description: The ground-state wave function and energy of a finite system of interacting fermions are expanded in terms of multiple-particle excitations on an uncorrelated zero-order state. The resulting set of coupled equations constitutes a systematic variational generalization of Hartree-Fock theory. Comparison is made with many-body perturbation theory and it is shown that to any order the theory incorporates an infinite number of perturbation theory terms. Solutions of the equations for ground-state atomic systems are discussed and related to previous work using many-body perturbation theory. It is shown that the sums of perturbation terms necessary for convergence are automatically included in the equations for two-particle excitations. Application of the equations to open-shell atoms is described.
Date: July 1, 1963
Creator: Kelly, Hugh P. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Two-electron time-delay interference in atomic double ionization by attosecond pulses

Description: A two-color two-photon atomic double ionization experiment using subfemtosecond UV pulses can be designed such that the sequential two-color process dominates and one electron is ejected by each pulse. Nonetheless, ab initio calculations show that, for sufficiently short pulses, a prominent interference pattern in the joint energy distribution of the sequentially ejected electrons can be observed that is due to their indistinguishability and the exchange symmetry of the wave function.
Date: October 4, 2009
Creator: Rescigno, Thomas N
Partner: UNT Libraries Government Documents Department

Variational Wave Function for Sodium

Description: The practical method of applying the variation principle to the calculation of the energy of an atom demands a trial function which contains variable parameters. The previous work done using this approach was based on the use of some combination of hydrogenic wave functions containing parameters inserted in appropriate places. The present calculation of the energy of the eleven-electron atom has been brought about using this method.
Date: August 1953
Creator: Smith, Daniel Montague
Partner: UNT Libraries

Effects of stacking faults on the electronic structures of quantum rods

Description: Atomistic semiempirical pseudopotential method is used to study the effects of stacking faults in a wurtzite structure quantum rod. It is found that a single stacking fault can cause a 10-50 meV change in the conduction state eigen energy, and a localization in the electron wave function. However, the effects on the hole eigen energies and wave functions are very small.
Date: March 30, 2004
Creator: Wang, Lin-Wang
Partner: UNT Libraries Government Documents Department

Scalar wave diffraction from a circular aperture

Description: The scalar wave theory is used to evaluate the expected diffraction patterns from a circular aperture. The standard far-field Kirchhoff approximation is compared to the exact result expressed in terms of oblate spheroidal harmonics. Deviations from an expanding spherical wave are calculated for circular aperture radius and the incident beam wavelength using suggested values for a recently proposed point diffractin interferometer. The Kirchhoff approximation is increasingly reliable in the far-field limit as the aperture radius is increased, although significant errors in amplitude and phase persist.
Date: January 25, 1995
Creator: Cerjan, C.
Partner: UNT Libraries Government Documents Department

SAR Window Functions: A Review and Analysis of the Notched Spectrum Problem

Description: Imaging systems such as Synthetic Aperture Radar collect band-limited data from which an image of a target scene is rendered. The band-limited nature of the data generates sidelobes, or ''spilled energy'' most evident in the neighborhood of bright point-like objects. It is generally considered desirable to minimize these sidelobes, even at the expense of some generally small increase in system bandwidth. This is accomplished by shaping the spectrum with window functions prior to inversion or transformation into an image. A window function that minimizes sidelobe energy can be constructed based on prolate spheroidal wave functions. A parametric design procedure allows doing so even with constraints on allowable increases in system bandwidth. This approach is extended to accommodate spectral notches or holes, although the guaranteed minimum sidelobe energy can be quite high in this case. Interestingly, for a fixed bandwidth, the minimum-mean-squared-error image rendering of a target scene is achieved with no windowing at all (rectangular or boxcar window).
Date: September 1, 2002
Partner: UNT Libraries Government Documents Department

Measurement of double polarized asymmetries in quasi-elastic processes ${}^3\vec{He}(\vec{e},e' d)$ and ${}^3\vec{He}(\vec{e},e' p)$

Description: This thesis is dedicated to a study of a spin-isospin structure of the polarized {sup 3}He. First, an introduction to the spin structure of {sup 3}He is given, followed by a brief overview of past experiments. The main focus of the thesis is the E05-102 experiment at Jefferson Lab, in which the reactions {sup 3}{ovr He} ({rvec e}, e'd) and {sup 3}{ovr He} ({rvec e}, e'p) in the quasi-elastic region were studied. The purpose of this experiment was to better understand the effects of the S'- and D-state contributions to the {sup 3}He ground-state wave-functions by a precise measurement of beam-target asymmetries A{sub x} and A{sub z} in the range of recoil momenta from 0 to about 300 MeV/c. The experimental equipment utilized in these measurements is described, with special attention devoted to the calibration of the hadron spectrometer, BigBite. Results on the measured asymmetries are presented, together with first attempts at their comparison to the state-of-the art Faddeev calculations. The remaining open problems and challenges for future work are also discussed.
Date: August 1, 2012
Creator: Mihovilovic, Miha
Partner: UNT Libraries Government Documents Department

How well do we know the neutron structure function?

Description: We present a detailed analysis of the uncertainty in the neutron F{sub 2}n structure function extracted from inclusive deuteron and proton deep-inelastic scattering data. The analysis includes experimental uncertainties as well as uncertainties associated with the deuteron wave function, nuclear smearing, and nucleon off-shell corrections. Consistently accounting for the Q{sup 2} dependence of the data and calculations, and restricting the nuclear corrections to microscopic models of the deuteron, we find significantly smaller uncertainty in the extracted F{sub 2}n/F{sub 2}p ratio than in previous analyses. In addition to yielding an improved extraction of the neutron structure function, this analysis also provides an important baseline that will allow future, model-independent extractions of neutron structure to be used to examine nuclear medium effects in the the deuteron.
Date: June 1, 2012
Creator: J. Arrington, J. G. Rubin, W. Melnitchouk
Partner: UNT Libraries Government Documents Department

Covariant nucleon wave function with S, D, and P-state components

Description: Expressions for the nucleon wave functions in the covariant spectator theory (CST) are derived. The nucleon is described as a system with a off-mass-shell constituent quark, free to interact with an external probe, and two spectator constituent quarks on their mass shell. Integrating over the internal momentum of the on-mass-shell quark pair allows us to derive an effective nucleon wave function that can be written only in terms of the quark and diquark (quark-pair) variables. The derived nucleon wave function includes contributions from S, P and D-waves.
Date: May 1, 2012
Creator: Franz Gross, G. Ramalho, M. T. Pena
Partner: UNT Libraries Government Documents Department


Description: Angle-resolved photoemission energy distributions (PED's) were obtained from valence bands of MnF{sub 2} single crystals using AlK{alpha} radiation. A pronounced variation in the PED's was observed as the electron take-off angle was varied relative to the crystalline axes, for the (111) crystal face. The observed variation is attributed to the t{sub 2g} and e{sub g} symmetry properties of the manganese 3d initial state wave functions and is well described by an angle-dependent transition-matrix model. The results are in good agreement with the multi-configurational Hartree-Fock calculations of Viinikka and Bagus.
Date: September 1, 1977
Creator: Sherwood, P.M.A.; McFeely, F.R.; Kowalczyk, S.P. & Shirley, D.A.
Partner: UNT Libraries Government Documents Department

Two-photon double ionization of H2 at 30 eV using Exterior Complex Scaling

Description: Calculations of fully differential cross sections for two-photon double ionization of the hydrogen molecule with photons of 30 eV are reported. The results have been obtained by using the method of exterior complex scaling, which allows one to construct essentially exact wave functions that describe thedouble continuum on a large, but finite, volume. The calculated cross sections are compared with those previously obtained by Colgan et al., and discrepancies are found for specific molecular orientations and electron ejection directions.
Date: January 20, 2009
Creator: Morales, Felipe; Martin, Fernando; Horner, Daniel; Rescigno, Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene

Description: This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).
Date: May 30, 2008
Creator: Domin, D.; Braida, Benoit & Lester Jr., William A.
Partner: UNT Libraries Government Documents Department

The Color Glass Condensate and the Glasma: Two Lectures.

Description: These two lectures concern the Color Glass Condensate and the Glasma. These are forms of matter which might be studied in high energy hadronic collisions. The Color Glass Condensate is high energy density gluonic matter. It constitutes the part of a hadron wave function important for high energy processes. The Glasma is matter produced from the Color Glass Condensate in the first instants after a collision of two high energy hadrons. Both types of matter are associated with coherent fields. The Color Glass Condensate is static and related to a hadron wavefunction, where the Glasma is transient and evolves quickly after a collision. I present the properties of such matter, and some aspects of what is known of their properties.
Date: August 29, 2007
Creator: McLerran,L.
Partner: UNT Libraries Government Documents Department

First Principles Study of Double Photoionization of H2 UsingExterior Complex Scaling

Description: Exterior complex scaling provides a practical path forfirst-principles studies of atomic and molecular ionizationproblemssince it avoids explicit enforcement of asymptotic boundary conditionsfor 3-body Coulomb breakup. We have used the method of exterior complexscaling, implemented with both the discrete variable representation andB-splines, to obtain the first-order wave function for molecular hydrogencorresponding to a single photon having been absorbed by a correlatedinitial state. These wave functions are used to construct convergedtriple differential cross sections for double photoionization of alignedH2 molecules.
Date: July 21, 2006
Creator: Rescigno, Thomas N.; Vanroose, Wim; Horner, Daniel A.; Martin,Fernando & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

Hard probes of short-range nucleon-nucleon correlations

Description: The strong interaction of nucleons at short distances leads to a high-momentum component to the nuclear wave function, associated with short-range correlations between nucleons. These short-range, high-momentum structures in nuclei are one of the least well understood aspects of nuclear matter, relating to strength outside of the typical mean-field approaches to calculating the structure of nuclei. While it is difficult to study these short-range components, significant progress has been made over the last decade in determining how to cleanly isolate short-range correlations in nuclei. We have moved from asking if such structures exist, to mapping out their strength in nuclei and studying their microscopic structure. A combination of several different measurements, made possible by high-luminosity and high-energy accelerators, coupled with an improved understanding of the reaction mechanism issues involved in studying these structures, has led to significant progress, and provided significant new information on the nature of these small, highly-excited structures in nuclei. We review the general issues related to short-range correlations, survey recent experiments aimed at probing these short-range structures, and lay out future possibilities to further these studies.
Date: October 1, 2012
Creator: J. Arrington, D. W. Higinbotham, G. Rosner, M. Sargsian
Partner: UNT Libraries Government Documents Department

Perturbative Gluon Exchange in a Covariant Quark Model of the Pion

Description: A covariant pion wave function, which reproduces the low energy data, is used to calculate the perturbative gluon exchange contributions to the pion charge form factor. It is found that the perturbative process dominates at q > 3.5 GeV/c. The dependence on the quark mass and the asymptotic behavior of the form factor are explicitly displayed.
Date: September 1, 1990
Creator: Gross, Franz & Ito, Hiroshi
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

Orbital HP-Clouds for Solving Schr?dinger Equation inQuantum Mechanics

Description: Solving Schroedinger equation in quantum mechanics presents a challenging task in numerical methods due to the high order behavior and high dimension characteristics in the wave functions, in addition to the highly coupled nature between wave functions. This work introduces orbital and polynomial enrichment functions to the partition of unity for solution of Schroedinger equation under the framework of HP-Clouds. An intrinsic enrichment of orbital function and extrinsic enrichment of monomial functions are proposed. Due to the employment of higher order basis functions, a higher order stabilized conforming nodal integration is developed. The proposed methods are implemented using the density functional theory for solution of Schroedinger equation. Analysis of several single and multi-electron/nucleus structures demonstrates the effectiveness of the proposed method.
Date: October 19, 2006
Creator: Chen, J; Hu, W & Puso, M
Partner: UNT Libraries Government Documents Department

Observation of Two-source Interference in the Photoproduction Reaction AuAu --> AuAu rho 0

Description: In ultra-peripheral relativistic heavy-ion collisions, a photon from the electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair and scatter from the other nucleus, emerging as a {rho}{sup 0}. The {rho}{sup 0} production occurs in two well-separated (median impact parameters of 20 and 40 fermi for the cases considered here) nuclei, so the system forms a 2-source interferometer. At low transverse momenta, the two amplitudes interfere destructively, suppressing {rho}{sup 0} production. Since the {rho}{sup 0} decays before the production amplitudes from the two sources can overlap, the two-pion system can only be described with an entangled non-local wave function, and is thus an example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in 200 GeV per nucleon-pair gold-gold collisions. The interference is 87% {+-} 5%(stat.) {+-} 8% (syst.) of the expected level. This translates into a limit on decoherence due to wave function collapse or other factors, of 23% at the 90% confidence level.
Date: March 2, 2009
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Semileptonic Weak Interactions in Nuclei: a Relativistic Analysis

Description: We use a consistent relativistic formalism, with relativistic Hartree wave-functions and a covariant effective current operator with all the properties of the Standard Model, to study semileptonic weak processes in nuclei.Results are obtained for Beta - decay, mu-capture, charge-changing nu-reactions and neutral nu-scattering involving the isodoublet systems ^17F - ^17O and ^3H - ^3He.
Date: January 1, 1987
Creator: Kim, E.
Partner: UNT Libraries Government Documents Department