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COMPUTER SIMULATION OP FRANK LOOP CONTRAST IN FIELD IONIMAGES

Description: A computer model for simulation of the image contrast caused by Frank dislocation loops in field ion tips of fcc materials is presented. The model is based on the shell model for ion image simulation, whereas the displacement field of Frank loops is computed from the exact displacement equation for a closed dislocation loop in an isotropically elastic continuum. A method for taking surface effects into account by superposition of the displacement field of an image loop is introduced. The result… more
Date: September 1, 1973
Creator: Stolt, Kaj Gunnar
Partner: UNT Libraries Government Documents Department
open access

Developments and Applications of Electrophoresis and Small Molecule Laser Desorption Ionization Mass Spectrometry

Description: Ultra-sensitive native fluorescence detection of proteins with miniaturized one- and two-dimensional polyacrylamide gel electrophoresis was achieved with laser side-entry excitation, which provides both high excitation power and low background level. The detection limit for R-phycoerythrin protein spots in 1-D SDS-PAGE was as low as 15 fg, which corresponds to 40 thousand molecules only. The average detection limit of six standard native proteins was 5 pg per band and the dynamic range spanned … more
Date: December 1, 2007
Creator: Zhang, Hui
Partner: UNT Libraries Government Documents Department
open access

A transient, quadratic nodal method for triangular-Z geometry

Description: Many systematically-derived nodal methods have been developed for Cartesian geometry due to the extensive interest in Light Water Reactors. These methods typically model the transverse-integrated flux as either an analytic or low order polynomial function of position within the node. Recently, quadratic nodal methods have been developed for R-Z and hexagonal geometry. A static and transient quadratic nodal method is developed for triangular-Z geometry. This development is particularly challengi… more
Date: June 1, 1993
Creator: DeLorey, T. F.
Partner: UNT Libraries Government Documents Department
open access

A High Current, Short Pulse Electron Source for Wakefield Accelerators

Description: Design studies for the generation of a high current, short pulse electron source for the Argonne Wakefield Accelerator are presented. An L-band laser photocathode rf gun cavity is designed using the computer code URMEL to maximize the electric field on the cathode surface for fixed frequency and rf input power. A new technique using a curved incoming laser wavefront to minimize the space charge effect near the photocathode is studied. A preaccelerator with large iris to minimize wakefield effec… more
Date: 1992
Creator: Ho, Ching-Hung
Partner: UNT Libraries Government Documents Department
open access

NMR studies of molecules in liquid crystals and graphite

Description: NMR experiments to measure proton dipole couplings were performed on a series of n-alkanes (n-hexane through n-decane) dissolved in nematic liquid crystals. Computer modeling of the experimental NMR-spectra was done using several different models for intermolecular interactions in these systems. The model of Photinos et al. was found to be best in describing the intermolecular interactions in these systems and can provide a statistical picture of the conformation and orientation of the alkane m… more
Date: June 1, 1992
Creator: Rosen, M. E.
Partner: UNT Libraries Government Documents Department
open access

Calculations of Bottom Quark Production at Hadron Colliders

Description: This thesis studies Monte Carlo simulations of QCD heavy flavor production processes (p{bar p} {yields} Q({anti Q})X) at hadron colliders. ISAJET bottom quark cross-sections are compared to the O({alpha} {sub s}{sup 3}) perturbative calculation of Nason, Dawson, and Ellis. These Monte Carlo cross-sections are computed from data samples which use different parton distribution functions and physics parameters. Distributions are presented in the heavy quark`s transverse momentum and rapidity. Corr… more
Date: June 29, 1991
Creator: Kuebel, D.
Partner: UNT Libraries Government Documents Department
open access

Nonlinear self-focus of pulsed-wave beams in Kerr media

Description: A modified finite-difference time-domain method for solving Maxwell`s equations in nonlinear media is presented. This method allows for a finite response time to be incorporated in the medium, physically creating dispersion and absorption mechanisms. The technique models electromagnetic fields in two space dimensions and time and encompasses both the TE{sub z} and TM{sub z} set of decoupled field equations. Aspects of an ultra-short pulsed Gaussian beam are studied in a variety of linear and no… more
Date: December 31, 1992
Creator: Judkins, J. B.
Partner: UNT Libraries Government Documents Department
open access

An investigation of the vortex method

Description: The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of t… more
Date: May 1, 1994
Creator: Pryor, D. W. Jr.
Partner: UNT Libraries Government Documents Department
open access

Acceleration of electrons using an inverse free electron laser auto- accelerator

Description: We present data from our study of a device known as the inverse free electron laser. First, numerical simulations were performed to optimize the design parameters for an experiment that accelerates electrons in the presence of an undulator by stimulated absorption of radiation. The Columbia free electron laser (FEL) was configured as an auto-accelerator (IFELA) system; high power (MW`s) FEL radiation at {approximately}1.65 mm is developed along the first section of an undulator inside a quasi-o… more
Date: July 1, 1992
Creator: Wernick, I. K. & Marshall, T. C.
Partner: UNT Libraries Government Documents Department
open access

Structural studies in limestone sulfidation

Description: This study investigates the sulfidation of limestone at high temperatures (700--900{degree}C) as the first step in the design of a High-Temperature Coal-Gas Clean-Up system using millimeter-size limestone particles. Several workers have found that the rate of this reaction significantly decreases after an initial 10 to 15% conversion of CaCO{sub 3} to CaS. The present work attempts to explain this feature. It is first established that millimeter-size limestone particles do not sinter at tempera… more
Date: May 1, 1993
Creator: Fenouil, L. A. & Lynn, S.
Partner: UNT Libraries Government Documents Department
open access

Rare event simulation in radiation transport

Description: This dissertation studies methods for estimating extremely small probabilities by Monte Carlo simulation. Problems in radiation transport typically involve estimating very rare events or the expected value of a random variable which is with overwhelming probability equal to zero. These problems often have high dimensional state spaces and irregular geometries so that analytic solutions are not possible. Monte Carlo simulation must be used to estimate the radiation dosage being transported to a … more
Date: October 1, 1993
Creator: Kollman, C.
Partner: UNT Libraries Government Documents Department
open access

Scanning tunneling microscopy of charge density wave structure in 1T- TaS{sub 2}

Description: I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two othe… more
Date: November 1, 1991
Creator: Thomson, R. E.
Partner: UNT Libraries Government Documents Department
open access

Studies of transition states and radicals by negative ion photodetachment

Description: Negative ion photodetachment is a versatile tool for the production and study of transient neutral species such as reaction intermediates and free radicals. Photodetachment of the stable XHY{sup {minus}} anion provides a direct spectroscopic probe of the transition state region of the potential energy surface for the neutral hydrogen transfer reaction X + HY {yields} XH + Y, where X and Y are halogen atoms. The technique is especially sensitive to resonances, which occur at a specific energy, b… more
Date: December 1, 1991
Creator: Metz, R. B.
Partner: UNT Libraries Government Documents Department
open access

Evaluating Radionuclide Air Emission Stack Sampling Systems

Description: The Pacific Northwest National Laboratory (PNNL) operates a number of research and development (R&D) facilities for the U.S. Department of Energy at the Hanford Site, Washington. These facilities are subject to Clean Air Act regulations that require sampling of radionuclide air emissions from some of these facilities. A revision to an American National Standards Institute (ANSI) standard on sampling radioactive air emissions has recently been incorporated into federal and state regulations and … more
Date: December 16, 2002
Creator: Ballinger, Marcel Y.
Partner: UNT Libraries Government Documents Department
open access

A High-Brightness Thermionic Microwave Electron Gun

Description: In a collaborative effort by SSRL, AET Associates, and Varian Associates, a high-brightness microwave electron gun using a thermionic cathode has been designed, built, tested, and installed for use with the SSRL 150 MeV linear accelerator. This thesis discusses the physics behind the design and operation of the gun and associated systems, presenting predictions and experimental tests of the gun`s performance. The microwave gun concept is of increasing interest due to its promise of providing hi… more
Date: February 1991
Creator: Borland, Michael
Partner: UNT Libraries Government Documents Department
open access

The effect of simplifying the building description on the numerical modeling of its thermal performance

Description: A thermal building simulation program is a numerical model that calculates the response of the building envelopes to weather and human activity, simulates dynamic heating and cooling loads, and heating and cooling distribution systems, and models building equipment operation. The scope of the research is to supply the users of such programs with information about the dangers and benefits of simplifying the input to their models. The Introduction describes the advantages of modeling the heat tra… more
Date: July 1, 1993
Creator: Stetiu, C.
Partner: UNT Libraries Government Documents Department
open access

MagRad: A code to optimize the operation of superconducting magnets in a radiation environment

Description: A powerful computational tool, called MagRad, has been developed which optimizes magnet design for operation in radiation fields. Specifically, MagRad has been used for the analysis and design modification of the cable-in-conduit conductors of the TF magnet systems in fusion reactor designs. Since the TF magnets must operate in a radiation environment which damages the material components of the conductor and degrades their performance, the optimization of conductor design must account not only… more
Date: December 31, 1995
Creator: Yeaw, Christopher T.
Partner: UNT Libraries Government Documents Department
open access

Considering value of information when using CFD in design

Description: This thesis presents an approach to find lower resolution CFD models that can accurately lead a designer to a correct decision at a lower computational cost. High-fidelity CFD models often contain too much information and come at a higher computational cost, limiting the designs a designer can test and how much optimization can be performed on the design. Lower model resolution is commonly used to reduce computational time. However there are no clear guidelines on how much model accuracy is req… more
Date: December 19, 2009
Creator: Misra, John Satprim
Partner: UNT Libraries Government Documents Department
open access

Time-varying Reeb Graphs: A Topological Framework Supporting the Analysis of Continuous Time-varying Data

Description: I present time-varying Reeb graphs as a topological framework to support the analysis of continuous time-varying data. Such data is captured in many studies, including computational fluid dynamics, oceanography, medical imaging, and climate modeling, by measuring physical processes over time, or by modeling and simulating them on a computer. Analysis tools are applied to these data sets by scientists and engineers who seek to understand the underlying physical processes. A popular tool for anal… more
Date: November 28, 2006
Creator: Mascarenhas, A
Partner: UNT Libraries Government Documents Department
open access

Development of Modeling and Simulation for Magnetic Particle Inspection Using Finite Elements

Description: Magnetic particle inspection (MPI) is a widely used nondestructive inspection method for aerospace applications essentially limited to experiment-based approaches. The analysis of MPI characteristics that affect sensitivity and reliability contributes not only reductions in inspection design cost and time but also improvement of analysis of experimental data. Magnetic particles are easily attracted toward a high magnetic field gradient. Selection of a magnetic field source, which produces a mag… more
Date: May 31, 2003
Creator: Lee, Jun-Youl
Partner: UNT Libraries Government Documents Department
open access

Compact D-D/D-T neutron generators and their applications

Description: Neutron generators based on the {sup 2}H(d,n){sup 3}He and {sup 3}H(d,n){sup 4}He fusion reactions are the most commonly available neutron sources. The applications of current commercial neutron generators are often limited by their low neutron yield and their short operational lifetime. A new generation of D-D/D-T fusion-based neutron generators has been designed at Lawrence Berkeley National Laboratory (LBNL) by using high current ion beams hitting on a self-loading target that has a large su… more
Date: May 1, 2003
Creator: Lou, Tak Pui
Partner: UNT Libraries Government Documents Department
open access

Potential Release Site Sediment Concentrations Correlated to Storm Water Station Runoff through GIS Modeling

Description: This research examined the relationship between sediment sample data taken at Potential Release Sites (PRSs) and storm water samples taken at selected sites in and around Los Alamos National Laboratory (LANL). The PRSs had been evaluated for erosion potential and a matrix scoring system implemented. It was assumed that there would be a stronger relationship between the high erosion PRSs and the storm water samples. To establish the relationship, the research was broken into two areas. The first… more
Date: June 1, 2005
Creator: McLean, C.T.
Partner: UNT Libraries Government Documents Department
open access

The dynamics of variable-density turbulence

Description: The dynamics of variable-density turbulent fluids are studied by direct numerical simulation. The flow is incompressible so that acoustic waves are decoupled from the problem, and implying that density is not a thermodynamic variable. Changes in density occur due to molecular mixing. The velocity field is, in general, divergent. A pseudo-spectral numerical technique is used to solve the equations of motion. Three-dimensional simulations are performed using a grid size of 128{sup 3} grid points.… more
Date: November 1, 1995
Creator: Sandoval, D.L.
Partner: UNT Libraries Government Documents Department
open access

Computer simulation of martensitic transformations

Description: The characteristics of martensitic transformations in solids are largely determined by the elastic strain that develops as martensite particles grow and interact. To study the development of microstructure, a finite-element computer simulation model was constructed to mimic the transformation process. The transformation is athermal and simulated at each incremental step by transforming the cell which maximizes the decrease in the free energy. To determine the free energy change, the elastic ene… more
Date: November 1, 1993
Creator: Xu, Ping
Partner: UNT Libraries Government Documents Department
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