Physical Sciences and Mathematics Commons^™

N, L Distributions For Electron-Capture From H(1s) By C⁶⁺And O8+, Ronald E. Olson, D. R. Schultz

Physics Faculty Research & Creative Works

Total cross sections for electron-capture from the ground state of hydrogen by C⁶⁺(40, 50, 60, 80, 100 and 120 keV/u) and O⁸⁺(40, 50, 60, 80, 100, 120 and 140keV/u) have been calculated using the classical-trajectory Monte Carlo (CTMC) technique. We tabulate these cross sections as a function of projectile energy for (i) capture to all product states, (ii) capture to product n-levels, and (iii) capture to product n, l-levels. The results of these calculations agree with and extend previous CTMC n, ldistribution results. © 1989 IOP Publishing Ltd.

Pressure Dependence Of Ozone Interference In The Laser Fluorescence Measurement Of Oh In The Atmosphere [Comment], Thomas M. Hard, C. Y. Chan, A. A. Mehrabzadeh, Robert J. O'Brien

Chemistry Faculty Publications and Presentations

The authors comment on the paper by Shirinzadeh et al. (Applied Optics, vol. 26, p. 2102, 1987). They point out three errors which caused the overprediction of spurious HO data.

Nanosecond Optical Quenching Of Photoconductivity In A Bulk Gaas Switch, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, S. T. Ko

Electrical & Computer Engineering Faculty Publications

Persistent photoconductivity in copper-compensated, silicon-doped semi-insulating gallium arsenide with a time constant as large as 30 µs has been excited by sub-band-gap laser radiation of photon energy greater than 1 eV. This photoconductivity has been quenched on a nanosecond time scale by laser radiation of photon energy less than 1 eV. The proven ability to turn the switch conductance on and off on command, and to scale the switch to high power could make this semiconductor material the basis of an optically controlled pulsed-power closing and opening switch.

A Search For The Rare Decay Kaon(L) Going To Muon/Electron, John Fred Ginkel

Dissertations, Theses, and Masters Projects

A sensitive search has been carried out for the rare decay $\rm K\sb{L}\to\mu e$. This decay violates conservation of separate lepton-number and thus is forbidden in the Standard Model of electro-weak interactions. Many new models have been proposed which could permit this process. The data were collected in the B5 beamline of the Alternating Gradient Synchrotron facility at the Brookhaven National Laboratory during the Spring, 1988 slow-extracted beam running period. The experiment was sensitive to approximately fifty million $\rm K\sb{L}\to\pi\pi$ decays. No $\rm K\sb{L}\to\mu e$ candidate events were detected. The 90% confidence level upper limit for the branching ratio is …

Local Density Approximation Study Of Transition Andf-Electron Materials, Zhi Wei Lu

Dissertations, Theses, and Masters Projects

The local density approximation (LDA) has been proved to be a powerful starting point for calculating electronic and structural properties for many real materials. We have studied the effects of particular forms of exchange-correlation potentials (the X{dollar}\alpha{dollar} and Hedin-Lundqvist form) upon the structural properties for the 3d Ti and 4d Zr using a highly accurate linearized augmented plane wave (LAPW) method. The calculated equilibrium volumes differ by 6-8% for these two forms (with X{dollar}\alpha{dollar} results in better agreement with experiment) with proportional differences in other structural properties, which we take to be an indication of the intrinsic reliability of the …

A Measurement Of The Decay Rate For The Process Kaon(L) Going To Positive Muon Negative Muon, Christopher John Kenney

Dissertations, Theses, and Masters Projects

A sample of 87 events of the GIM suppressed decay K$\sb{\rm L} \to \mu\sp+\mu\sp-$ were observed in an experiment performed in 1988 at the Brookhaven National Laboratory. Concurrently, 8,887 examples of the CP-violating decay K$\sb{\rm L} \to \pi\sp+\pi\sp-$ were also seen. The apparatus consisted of a double-magnet spectrometer as well as electromagnetic and muon detector systems. From the previously measured branching ratio for K$\sb{\rm L} \to \pi\sp+\pi\sp-$ and the different instrumental acceptances of the detector for the two decays, the data sample was normalized to the effective number of K$\sb{\rm L}$ decays observed. A value for the ratio (K$\sb{\rm L} …

Nmr On Single Crystals Of Potassium Cyanogen Bromide (A Measurement Of The Orientational Probability Distribution Function Of The Negatively Charged Cyanogen Ion), Jeffrey Howard Walton

Dissertations, Theses, and Masters Projects

Single crystals of K(CN)$\sb{\rm x}$/(Br)$\sb{\rm 1-x}$ enriched in $\sp{15}$N have been studied by $\sp{15}$N NMR. Because of the anisotropic chemical shift, the NMR frequency spectrum of the orientational glass state reflects the distribution of cyanide orientations. By studying the spectrum at many orientations of each crystal, the orientational probability distribution function P($\Omega$) has been determined for x = 0.50 and for x = 0.20. The probability function is largest along the (100) directions, intermediate in the (110) directions, and nearly 0 along the (111) directions. The NMR determined P($\Omega$) is presented graphically and in terms of the Kubic Harmonic functions. …

Gaas Photoconductive Closing Switches With High Dark Resistance And Microsecond Conductivity Decay, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, R. Germer, G. M. Loubriel, F. J. Zutavern

Electrical & Computer Engineering Faculty Publications

Silicon-doped n-type gallium arsenide crystals, compensated with diffused copper, were studied with respect to their application as photoconductive, high-power closing switches. The attractive features of GaAs:Cu switches are their high dark resistivity, their efficient activation with Nd:YAG laser radiation, and their microsecond conductivity decay time constant. In the authors' experiment, electric fields are high as 19 kV/cm were switched, and current densities of up to 10 kA/cm² were conducted through a closely compensated crystal. At field strengths greater than approximately 10 kV/cm, a voltage `lock-on' effect was observed.

The Adiabatic Propagator, Br Holstein

Barry R Holstein

The Feynman propagator is expanded in the adiabatic limit, wherein the time scale over which the potential varies is long compared to typical quantum mechanical oscillation times in the problem. Comparison with known exact results is made for two simple models.

Rigidity Percolation, Anthony Day, M. Thorpe, W. Xia

Anthony Roy Day

No abstract provided.

The Adiabatic Theorem And Berry's Phase, Br Holstein

Barry R Holstein

A study is presented of Berry's observation that when a quantum-mechanical system is transported on a closed adiabatic journey, a topological phase arises in addition to the usual dynamical phase expected from the adiabatic theorem. Consequences are explored in the case of a simple magnetic moment-magnetic field interaction and are shown to lead, among other things, to Dirac's famous relation between electric and magnetic charges.

Random Elastic Networks, Anthony Day, M. Thorpe, W. Xia

Anthony Roy Day

Proceedings of the International Workshop on Condensed Matter Theories, 1988.

Hydrodynamic Forces And Band Formation In Swimming Magnetotactic Bacteria, D. C. Guell, H. Brenners, Richard B. Frankel, H. Hartman

Physics

Dense suspensions of magnetotactic bacteria form long, thin, stable bands perpendicular to the common, net direction of motion of the cells in a magnetic field. A mechanism for this phenomenon is proposed in which the hydrodynamic coupling between two swimming cells is described in terms of an approximate, far-field solution for the flow around one swimming cell. The calculated hydrodynamic interaction force and torque based upon this analysis are of the correct orders of magnitude and in the right directions to provide a reasonable explanation for band formation and stability.

Effects Of Surfaces On Dynamic Percolation, H. K. Janssen, B. Schaub, Beate Schmittmann

Beate Schmittmann

The general epidemic process, which is a stochastic multiparticle process belonging to the universality class of dynamic percolation, is studied in a semi-infinite geometry. Critical exponents characterizing the fractal properties are calculated to O(ε) (ε=6-d, where d is the spatial dimension) with use of renormalization-group techniques.

Modified Broyden’S Method For Accelerating Convergence In Self-Consistent Calculations, Duane D. Johnson

Duane D. Johnson

A modification to Broyden’s method for obtaining stable and computationally efficient convergence in self-consistent calculations is developed and discussed. The method incorporates the advantages of two schemes proposed by Srivastava and by Vanderbilt and Louie without any increase in complexity. Its improvement over their methods is discussed. The present method is compared with two other widely used convergence methods, simple mixing and Anderson’s method, for the case of the disordered binary alloy Ni0.35Fe0.65 on the verge of a magnetic instability and is shown to be much improved in stability and rate of convergence.

Microstructure Of Epitaxial Ybba2Cu3O7 Superconducting Films Grown By A New Liquid-Gas-Solidification Technique, C.H. Chen, H.S. Chen, Sy_Hwang Liou

Sy-Hwang Liou Publications

We have studied the microstructures of epitaxial YbBa₂Cu₃O₇ superconducting films grown on SrTiO₃ [100] and [110] substrates by a new liquid-gas-solidification processing technique. Films grown on SrTiO₃ [100] and [110] substrates are epitaxially oriented with [001] and [110] axes normal to the film surface. Twinned domains of ~200 Å in size are observed in the [001] oriented films. Most defects observed can be attributed to the presence of stacking faults along the c axis. The presence of Cu-O bilayer defects is also observed. Rapid oxygen diffusion in the liquid phase is found to …

On The Possibility Of Quasi-Static Convection In The Quiet Magnetotail, Margaret G. Kivelson, Harlan E. Spence

Physics & Astronomy

Abstract

The magnetotail is known to serve as a reservoir of energy transferred into the terrestrial magnetosphere from the solar wind. In principle, the stored energy can be dissipated impulsively, as in a substorm, or steadily through the process of steady adiabatic plasma convection. However, some theoretical arguments have suggested that quasi-static adiabatic convection cannot occur throughout the magnetotail because of the structure of the magnetic field. Here we reexamine the question. We show that in a magnetotail of finite width, downtail pressure gradients depend strongly on the ratio of the potential across half the tail to the ion temperature …

Spin-Polarized ³He Nuclear Targets And Metastable 4he Atoms By Optical Pumping With A Tunable, Nd:Yap Laser, C. L. Bohler, Laird D. Schearer, M. Leduc, P. J. Nacher, L. Zachorowski, R. G. Milner, R. D. Mckeown, C. E. Woodward

Physics Faculty Research & Creative Works

Several Nd:YAP lasers were constructed which could be broadly tuned in the 1083-nm region which includes the helium ²³S-²³P transition, using a Lyot filter and thin, uncoated etalons within the laser cavity. 1 W of power could be extracted at 1083 nm through a 1% transmitting output coupler. This laser beam was used to optically pump metastable ⁴He and ³He ²³S helium atoms in a weak discharge cell, spin polarizing the metastable ensemble. In a ³He cell the polarization is transferred to the nuclear spin system. A ³He target cell at 0.3 …

Quasidegenerate Variational Perturbation Theory And The Calculation Of First‐Order Properties From Variational Perturbation Theory Wave Functions, Robert J. Cave, Ernest R. Davidson

All HMC Faculty Publications and Research

In previous work on the treatment of correlation in molecular systems we have applied a multireference version of second‐order Hylleraas variational perturbation theory. The choice made for the partitioning of H treated the interactions between the correlating functions to infinite order and gave the corrections to the wave function to first order. The method was shown to be accurate in many cases, but became less so when near degeneracies occurred between the reference energy and other eigenvalues of H0. In this article we introduce an effective Hamiltonian method that is analogous to variational perturbation theory, but which is significantly more …

Tunneling Characteristics Of Internal Josephson Junctions In Yba2Cu3O7-Δ Thin Films, W.S. Brocklesby, Don Monroe, M. Hong, Sy_Hwang Liou, J. Kwo, G.J. Fisanick, P.M. Mankiewich, R.E. Howard

Sy-Hwang Liou Publications

We have measured detailed I-V characteristics of small areas of YBa₂Cu₃O_7-δ films, which exhibit structure associated with individual Josephson junctions within the film. Both hysteretic and nonhysteretic junctions are seen. A simple model relating the voltage steps to the junction properties is developed. The temperature dependence of l_c for the hysteretic junctions fits that predicted for quasiparticle tunneling junctions between conventional superconductors.

Nd:Lna Laser Optical Pumping Of ⁴He: Application To Space Magnetometers, R. E. Slocum, Laird D. Schearer, P. Tin, R. Marquedant

Physics Faculty Research & Creative Works

We have observed Hanle signals and n=0, p=1 parametric resonances of ₂₃S¹ metastable helium atoms in a discharge cell by optically pumping the helium atoms with a tunable Nd:LNA laser. These resonances were used to construct a sensitive magnetometer for the measurement of very small magnetic fields. Since magnetometer sensitivity is proportional to the slope of the parametric resonance signal (signal amplitude divided by linewidth), the slopes for single-line laser pumping were compared with similar quantities obtained from conventional helium lamp pumping. Laser pumping yielded 45 times greater slopes with comparable power requirements, thus establishing the potential for …

Cooperative Effects Among Partial Waves In Mie Scattering, James A. Lock

Physics Faculty Publications

Observations of an illuminated water droplet at a close distance are described mathematically by the Fourier transform of the Mie-scattering amplitude convolved with the aperture function of the observer’s eye. Most of the sharp enhancements found in the Fourier transform correspond to geometrical rays associated with the various terms in the Debye-series expansion of the Mie amplitude. However, there are some enhancements that cannot be ascribed to any individual Debye-series term. Instead, they arise from a constructive interference cooperation of the phase of a scattering resonance in a single partial wave with the region of the stationary phase corresponding to …

Nuclear-Spin Relaxation In Molecular Solids With Reorienting Methyl And T-Butyl Groups: The Spectral Density And The State Of The Solid, Peter A. Beckmann, Audrey I. Hill, Ellen B. Kohler, Hong Yu

Physics Faculty Research and Scholarship

There are two solid phases which either have a large hysteresis of at least 90 K, or are both stable below 200 K. The sample melts at 262 K. We interpret the high-temperature phase R-versus-T-1 data with three models. First, we adopt a one-correlation-time model using a Davidson-Cole spectral density which suggests that there is a distribution of correlation times, or, equivalently, a distribution of activation energies for t-butyl and methyl group reorientation. In this case, the methyl and t-butyl reorientation is characterized by a cutoff activation energy of 17±1 kJ/mol which is to be compared with 18±1 kJ/mol in …

Superconducting Tl-Ba-Ca-Cu-O Films By Sputtering, M. Hong, Sy_Hwang Liou, D.D. Bacon, G.S. Grader, J. Kwo, A.R. Kortan, B.A. Davidson

Sy-Hwang Liou Publications

Superconducting Tl-Ba-Ca-Cu-O thin films 0.2–1.0 µm thick have been prepared on MgO(100) and SrTiO₃ (100) substrates by dc diode sputtering using a single oxide target. Films containing primarily the Tl₂Ba₂Ca₁Cu₂O₈ phase were obtained with a T_c (R =0) at 102 K and a transport J_c of 10⁴ A/cm² at 90 K. For the nearly pure phase Tl₂Ba₂Ca₂Cu₃O₁₀ films, the T_c's (R =0) are higher at 116 K and the transport J_c's …

A Current Algebra For Some Gauge Theory Amplitudes, V. Parameswaran Nair

Publications and Research

The classical amplitude for scattering of two positive helicity and n-2 negative helicity (or the other way) gauge bosons is shown to be generated by a Wess-Zumino-Witten (WZW) model for N= 4 supersymmetric gauge theory; i.e. the current algebra of the WZW model (with central charge k= 1 ) gives a Kac-Moody algebra as the symmetry behind these amplitudes.

A Fractal Analysis Of Diffusion Limited Aggregation, Cliff Myers

Dissertations and Theses

A modified Witten-Sander algorithm was devised for the diffusion-limited aggregation process. The simulation and analysis were performed on a personal computer. The fractal dimension was determined by using various forms of a two-point density correlation function and by the radius of gyration. The results of computing the correlation function with square and circular windows were analyzed. The correlation function was further modified to include the edge from analysis and those results were compared to the fractal dimensions obtained from the whole aggregate. The fractal dimensions of 1.67 ± .01 and 1.75 ± .08 agree with the accepted values. Animation of …

Magnetic And Structural Properties Of Melt-Spun Rare-Earth Transition-Metal Intermetallics With Thmn12 Structure, E.W. Singleton, J. Strzeszewski, George C. Hadjipanayis, David J. Sellmyer

David Sellmyer Publications

The magnetic and structural properties of melt-spun R₈Fe₈₄Ti₈ with R=Nd, Sm, Dy, Gd and R₈ (Fe,Co) ₇₆ [V(Mo)] ₁₆ with R=Nd, Sm have been studied with x-ray diffraction, transmission electron microscopy, and magnetic measurements. The tetragonal ThMn₁₂-type structure was found in all alloys after annealing at about 700 °C. The Curie temperature (T_c) of the as-spun amorphous samples was in the range of 40–100 °C. Crystallized Nd₈ (Fe_1-xCo_x)₈₄Ti₈ samples with the 1:12 structure have a T_c around 250 °C for …

Structure And Magnetic Properties Of Nanostructured Dy/Transition-Metal Multilayered Films, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

We report the results of magnetic and microstructural studies for T/Dy (T=Fe, Co, Ni) compositionally modulated films prepared in a multiple-gun sputtering system. The perpendicular anisotropy and magnetization were measured systematically for X-Å Fe/Y-Å Dy and X-Å Co/Y-Å Dy films. The layer-thickness dependence of the magnetization for Co/Dy and Fe/Dy was interpreted in terms of the antiparallel coupling between transition-metal and Dy magnetic moments. For Co/Dy films the ranges of X and Y required for perpendicular anisotropy were determined. A comparision of the structural and magnetic properties of Ni/Dy, Co/Dy, and Fe/Dy is given and the origin of the perpendicular …

Magnetic And Structural Properties Of Nd2Fe14B Permanent-Magnet Films And Multilayers With Fe And Ag, K.D. Aylesworth, Z.R. Zhao, David J. Sellmyer, George C. Hadjipanayis

David Sellmyer Publications

The effects of sputtering conditions on the structure and magnetic properties of Nd₂ (Fe_0.9Co_0.1)₁₄B films and multilayers are reported. The samples were sputtered onto temperature-controlled mica and Ta substrates, at temperatures between 20 and 620 °C. X-ray diffraction results indicate that films deposited directly onto 500–600 °C substrates with Fe buffer layers are nearly single-phase materials with the c axis of the grains largely perpendicular to the film plane. Room-temperature magnetization measurements to 17.4 kOe indicate that these films have strong perpendicular anisotropy with coercivities in excess of 10 kOe and magnetizations greater …

Electronic Structure And Surface Reactivity Of Nd2Fe14B And Related Compounds, Sitaram Jaswal, Marjorie Langell, Y.G. Ren, M.A. Engelhardt, David J. Sellmyer

David Sellmyer Publications

Studies of electronic and magnetic structure and surface reactivity are reported for R₂T₁₄B compounds where R=Y, Nd, Gd, and T=Fe, Co. The calculations employed the self-consistent, spin-polarized linear-muffin-tin orbital method. Experiments included ultraviolet, x-ray, and Auger electron spectroscopy. Comparisons are made between the calculated and measured electronic densities of states, and the reactions of the surfaces with O₂, H₂, and CO gases are studied. The effects of heat treatment on surface segregation are also reported. Journal of Applied Physics is copyrighted by The American Institute of Physics.