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Articles 31771 - 31800 of 36568

Full-Text Articles in Physical Sciences and Mathematics

High Density Qcd With Static Quarks, James E. Hetrick, T. Blum, D. Toussaint Feb 1996

High Density Qcd With Static Quarks, James E. Hetrick, T. Blum, D. Toussaint

All Faculty Articles - School of Engineering and Computer Science

We study lattice QCD in the limit that the quark mass and chemical potential are simultaneously made large, resulting in a controllable density of quarks which do not move. This is similar in spirit to the quenched approximation for zero density QCD. In this approximation we find that the deconfinement transition seen at zero density becomes a smooth crossover at very small density (possibly for any nonzero density), and that at low enough temperature chiral symmetry remains broken at all densities.

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Investigation Of Potential Oxygen Defect Mechanism Of Persistent Photoconductivity And Photoinduced Superconductivity In Yba2cu3ox, Denise Catherine Chew Jan 1996

Investigation Of Potential Oxygen Defect Mechanism Of Persistent Photoconductivity And Photoinduced Superconductivity In Yba2cu3ox, Denise Catherine Chew

Theses

In this thesis work, we conclude that oxygen vacancy defects play a fundamental role in the PPC/PISC mechanism and identify the oxygen defects as F centers (an oxygen vacancy which traps two electrons) or F+ centers. Also, the correlation between the peaks observed in the luminescence spectra and those observed in the wavelength dependence of PPC suggest that the photogeneration of charges and their annihilation via luminescent recombination occur in the same level (Cu-O chains) of the YBa2Cu3Ox crystal. Previous models had assigned the peaks in the PPC excitation spectrum to charge transfer in …

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The Genetic Algorithm And Maximum Entropy Dice, Laura Suzanne Fellman Jan 1996

The Genetic Algorithm And Maximum Entropy Dice, Laura Suzanne Fellman

Dissertations and Theses

The Brandeis dice problem, originally introduced in 1962 by Jaynes as an illustration of the principle of maximum entropy, was solved using the genetic algorithm, and the resulting solution was compared with that obtained analytically. The effect of varying the genetic algorithm parameters was observed, and the optimum values for population size, mutation rate, and mutation interval were determined for this problem. The optimum genetic algorithm program was then compared to a completely random method of search and optimization. Finally, the genetic algorithm approach was extended to several variations of the original problem for which an analytical approach would be …

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The Vacuum In Light Cone Field Theory, David G. Robertson Jan 1996

The Vacuum In Light Cone Field Theory, David G. Robertson

Physics Faculty Scholarship

This is an overview of the problem of the vacuum in light-cone field theory, stressing its close connection to other puzzles regarding light-cone quantization. I explain the sense in which the light-cone vacuum is ``trivial,'' and describe a way of setting up a quantum field theory on null planes so that it is equivalent to the usual equal-time formulation. This construction is quite helpful in resolving the puzzling aspects of the light-cone formalism. It furthermore allows the extraction of effective Hamiltonians that incorporate vacuum physics, but that act in a Hilbert space in which the vacuum state is simple. The …

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Polarization Of Astronomical Maser Radiation. Iii. Arbitrary Zeeman Splitting And Anisotropic Pumping, Moshe Elitzur Jan 1996

Polarization Of Astronomical Maser Radiation. Iii. Arbitrary Zeeman Splitting And Anisotropic Pumping, Moshe Elitzur

Physics and Astronomy Faculty Publications

General solutions of the maser polarization problem are presented for arbitrary absorption coefficients. The results are used to calculate polarization for masers permeated by magnetic fields with arbitrary values of χB, the ratio of Zeeman splitting to Doppler linewidth, and for anisotropic (m-dependent) pumping. In the case of magnetic fields, one solution describes the polarization for overlapping Zeeman components, χB < 1. The χB → 0 limit of this solution reproduces the linear polarization derived in previous studies, which were always conducted at this unphysical limit. Terms of higher order in χB have a negligible effect on …

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Ray Scattering By An Arbitrarily Oriented Spheroid .Ii. Transmission And Cross-Polarization Effects, James A. Lock Jan 1996

Ray Scattering By An Arbitrarily Oriented Spheroid .Ii. Transmission And Cross-Polarization Effects, James A. Lock

Physics Faculty Publications

Transmission of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit is considered in the context of ray theory. The transmitted electric field is added to the diffracted plus reflected ray-theory electric field that was previously derived to obtain an approximation to the far-zone scattered intensity in the forward hemisphere. Two different types of cross-polarization effects are found. These are (a) a rotation of the polarization state of the transmitted rays from when they are referenced with respect to their entrance into the spheroid to when they are referenced with respect to their exit from …

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Ray Scattering By An Arbitrarily Oriented Spheroid .I. Diffraction And Specular Reflection, James A. Lock Jan 1996

Ray Scattering By An Arbitrarily Oriented Spheroid .I. Diffraction And Specular Reflection, James A. Lock

Physics Faculty Publications

Diffraction and reflection of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit are considered in the context of ray theory. A closed-form solution for both diffraction and reflection is obtained, and the polarization character of the diffracted plus reflected electric field is obtained. It is found that the magnitude of the reflected electric field is multivalued for forward scattering. This is interpreted in terms of the variation of the spheroid's Gaussian curvature at the points where grazing ray incidence occurs.

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Error In The Calculation Of Synchronized Spontaneous Otoacoustic Emission Frequencies Measured With The Ilo88 System, Jacek Smurzynski, Rudolf Probst Jan 1996

Error In The Calculation Of Synchronized Spontaneous Otoacoustic Emission Frequencies Measured With The Ilo88 System, Jacek Smurzynski, Rudolf Probst

Jacek Smurzynski

No abstract provided.

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Fabrication Of Boron-Carbide Boron Heterojunction Devices, Seong-Don Hwang, Dongjin Byun, N.J. Ianno, Peter A. Dowben, H.R. Kim Jan 1996

Fabrication Of Boron-Carbide Boron Heterojunction Devices, Seong-Don Hwang, Dongjin Byun, N.J. Ianno, Peter A. Dowben, H.R. Kim

Peter Dowben Publications

We have succeeded in the fabrication of a boron–carbide/boron diode on an aluminum substrate, and a boron–carbide/boron junction field effect transistor. Our results suggest that with respect to the approximately 2 eV band gap pure boron material, 0.9 eV band gap boron–carbide (B5C) acts as a p-type material. Both boron and boron–carbide (B5C) thin films were fabricated from single source borane cage molecules using plasma enhanced chemical vapor deposition (PECVD). Epitaxial growth does not appear to be a requirement. ©1996 American Institute of Physics.

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The Possibility Of Flux Flow Spectroscopy, S. E. Barnes, J. L. Cohn, F. Zuo Jan 1996

The Possibility Of Flux Flow Spectroscopy, S. E. Barnes, J. L. Cohn, F. Zuo

Physics Articles and Papers

A novel spectroscopic technique applicable to the study of spin excitations in magnetic materials is described. The probe frequency and wave vector are determined by the moving Abrikosov flux lattice of a type II superconductor in the mixed state. The feasibility of employing oxide superconductors and relevant material parameters are discussed.

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Theoretical Hei Line Intensities In Gaseous Nebulae: Ngc 1976, 6572 And Ic 4997, J. B. Kingdon, Gary J. Ferland Jan 1996

Theoretical Hei Line Intensities In Gaseous Nebulae: Ngc 1976, 6572 And Ic 4997, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Smits has recently calculated theoretical He I intensities for a large number of lines for conditions appropriate to gaseous nebulae. These are likely to remain the definitive calculations for some time to come. A comparison of these line ratios with observed values in three nebulae reveals some discrepancies. We show that these discrepancies are reduced when collisional effects from the metastable 23S level are included, and that it is not necessary to invoke an unknown depopulation mechanism for the He I23S level.

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Tribological Properties Of Fullerenes C60 And C70 Microparticles, Wei Zao, Jinke Tang, Ashok Puri, Ray L. Sweany, Yuxin Li, Liquan Chen Jan 1996

Tribological Properties Of Fullerenes C60 And C70 Microparticles, Wei Zao, Jinke Tang, Ashok Puri, Ray L. Sweany, Yuxin Li, Liquan Chen

Physics Faculty Publications

The frictional behaviors of fullerenes C60 and C70 were studied because they were speculated to be solid lubricants. For the sublimated pure C60 films on Si(001), a high friction coefficient (0.55–0.8) was observed under different loads and pin materials. For the C70 film, the friction coefficient showed a pin dependence, which changed from 0.5 with an Al2O3 pin to about 0.9 with a 440 stainless steel pin. The relatively high friction coefficients of C60 and C70 films were due to the tendency of the C60 and C70 particles to …

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Oblique Electron Transport In The Presence Of Collinear And Noncollinear Magnetizations, Horacio E. Camblong Jan 1996

Oblique Electron Transport In The Presence Of Collinear And Noncollinear Magnetizations, Horacio E. Camblong

Physics and Astronomy

The nonlocal real‐space Kubo approach to electron transport in magnetic multilayers is applied to a new geometry, ‘‘oblique transport,’’ whose complexity is traced back to a combination of the layering, of the nonlocal character of the linear response, and of the oblique direction transport in this new geometry. The problem is dealt with by applying a condition on the average current density vector or on the average electric‐field vector, depending upon the external driving conditions. Its solution exhibits a characteristic anisotropy and it yields the global oblique conductance and magnetoresistance as simple trigonometric expressions in terms of the in‐plane and …

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Equilibrium Structure And Bonding Of Small Iron-Carbon Clusters, Beth K. Nash, B. K. Rao, Puru Jena Jan 1996

Equilibrium Structure And Bonding Of Small Iron-Carbon Clusters, Beth K. Nash, B. K. Rao, Puru Jena

Physics Publications

The equilibrium geometries, binding energies, and electronic structure of neutral FeC n (n≤3) clusters have been calculated self‐consistently using ab initio molecular orbital theory. The exchange and correlation contributions to the total energy were computed using both the density functional method (with and without nonlocal correction) as well as the Hartree–Fock–Möller–Plesset theory. All levels of theory predict the equilibrium geometries to be cyclic. The binding energies, bond lengths, and the Mulliken charges obtained from both methods of calculations are also in agreement. The results are compared with recent mobility and photoelectron spectroscopy experiments.

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Track Structure And Radiation Transport Model For Space Radiobiology Studies, F. A. Cucinotta, J. W. Wilson, Robert Katz, W. Atwell, G. D. Badhwar, M. R. Shavers Jan 1996

Track Structure And Radiation Transport Model For Space Radiobiology Studies, F. A. Cucinotta, J. W. Wilson, Robert Katz, W. Atwell, G. D. Badhwar, M. R. Shavers

Robert Katz Publications

Radiobiology experiments performed in space are deemed necessary for validation of risk-assessment methods. The understanding of space radiobiology experiments must combine knowledge of the space radiation environment, radiation transport, and models of biological response. The heavy ion transport code HZETRN has recently been combined with improved models of the galactic cosmic rays (GCR) and extensive comparisons made to measurements on the space shuttle with a tissue equivalent, proportional counter. HZETRN was also coupled with track-structure models of biological damage from heavy ions. Track-structure calculations using improved models of the radial dose distribution around the path of heavy ions provide a …

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Scanning Force Microscopy For The Study Of Domain Structure In Ferroelectric Thin Films, Alexei Gruverman, O. Auciello, H. Tokumoto Jan 1996

Scanning Force Microscopy For The Study Of Domain Structure In Ferroelectric Thin Films, Alexei Gruverman, O. Auciello, H. Tokumoto

Alexei Gruverman Publications

A piezoresponse technique based on scanning force microscopy (SFM) has been used for studying domain structure in ferroelectric thin films. Studies were performed on Pb(Zrx,Ti1-x)O3(PZT) thin films produced by a sol–gel method. The piezoresponse images of the PZT films were taken before and after inducing polarization in the films by applying a direct current voltage between the bottom electrode and the SFM tip. Polarization induced patterns were written with 20 V pulses and subsequently imaged by the SFM piezoresponse technique. The effect of the film structure on the imaging resolution of domains is discussed.

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Nonlinear Deformed Su(2) Algebras Involving Two Deforming Function, Andrei Ludu Jan 1996

Nonlinear Deformed Su(2) Algebras Involving Two Deforming Function, Andrei Ludu

Andrei Ludu

No abstract provided.

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Gaussian Phase Approximation For Evaluating The Decay Of Nmr Spin Echoes, Charles Recchia, K Gorny, C Pennington Jan 1996

Gaussian Phase Approximation For Evaluating The Decay Of Nmr Spin Echoes, Charles Recchia, K Gorny, C Pennington

Charles H Recchia

No abstract provided.

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Effects Of Local Non-Equilibrium Solute Diffusion On Rapid Solidification Of Alloys, Sergey Sobolev Jan 1996

Effects Of Local Non-Equilibrium Solute Diffusion On Rapid Solidification Of Alloys, Sergey Sobolev

Sergey Sobolev

A conceptual foundation for the study of local non-equilibrium solute diffusion under rapid solidifica- tion conditions is proposed. The model takes into account the relaxation to local equilibrium of the solute flux and incorporates two diffusion speeds, VDb, the bulk liquid diffusion speed, and VDi, the interface diffusive speed, as the most important parameters governing the solute concentration in the liquid phase and solute partitioning. The analysis of the model predicts complete solute trapping and the transition to a purely thermally controlled solidification, which occur abruptly when the interface velocity V equals the bulk liquid diffusion speed VDb. The abrupt …

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The Local-Nonequilibrium Temperature Field Around The Melting And Crystallization Front Induced By Picosecond Pulsed Laser Irradiation, Sergey Sobolev Jan 1996

The Local-Nonequilibrium Temperature Field Around The Melting And Crystallization Front Induced By Picosecond Pulsed Laser Irradiation, Sergey Sobolev

Sergey Sobolev

The local-nonequilibrium model for heat transport around melting and crystallization zone induced by ultrafast laser irradiation is considered. The model predicts strong overheating during melting of the material near the interface. Moreover, the local-nonequilibrium effects lead to an interface temperature gradient steeper than expected from the classical heat flow calculations. Possible modification of the kinetics of melting to include the relaxation effects is also discussed.

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Applications Of Extended Thermodynamics ...Part Iii., Sergey Sobolev Jan 1996

Applications Of Extended Thermodynamics ...Part Iii., Sergey Sobolev

Sergey Sobolev

No abstract provided.

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Synthesis And Characterization Of A New Class Of Μ3-Oh-Bridged Trimers That Contain Octahedrally Coordinated Divalent Metal Ions Bridged By Three Acetate Ligands And A Unique Catecholate Ligand. Solid State Molecular Structures Of The [(Py)5mii3(Oac)3(Μ3-Oh)((Cat)] Complexes (M = Mn(Ii), Fe(Ii), Co(Ii), Ni(Ii)), R.A. Reynolds, Edward Yu, W.R. Dunham, D. Coucouvanis Jan 1996

Synthesis And Characterization Of A New Class Of Μ3-Oh-Bridged Trimers That Contain Octahedrally Coordinated Divalent Metal Ions Bridged By Three Acetate Ligands And A Unique Catecholate Ligand. Solid State Molecular Structures Of The [(Py)5mii3(Oac)3(Μ3-Oh)((Cat)] Complexes (M = Mn(Ii), Fe(Ii), Co(Ii), Ni(Ii)), R.A. Reynolds, Edward Yu, W.R. Dunham, D. Coucouvanis

Edward Yu

The synthesis and structural characterization of a new class of “basic” trinuclear acetate clusters with solely divalent metal ions and a central μ3-OH ligand are reported. These molecules with the [(py)5MII3(OAc)3(μ3-OH)(cat)] stoichiometry (M = Mn, Fe, Co, Ni) are X-ray isomorphous and isostructural and contain octahedrally coordinated metal ions. The core consists of an antiferromagnetically coupled M3 unit with the metals arranged in the corners of an isosceles triangle. Two of the M−M distances vary between 2.98 and 3.16 Å, and the longer M−M distance is observed between 3.65 and 3.76 Å. As expected from the relative ionic radius lengths, …

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Formation Energies And Energy Levels Of Deep Defects In Narrow-Gap Semiconductors, James D. Patterson, Weigang Li Jan 1996

Formation Energies And Energy Levels Of Deep Defects In Narrow-Gap Semiconductors, James D. Patterson, Weigang Li

Aerospace, Physics, and Space Science Faculty Publications

We use a Green's function technique for deep defect energy level calculations in mercury cadmium telluride, mercury zinc telluride, and mercury zinc selenide. The formation energy is calculated from the difference between the total binding energy with an impurity cluster and with a perfect cluster. These alloys are among those that have been experimentally grown in microgravity aboard the Space Shuttle. To evaluate the quality of these crystals, it is necessary to characterize them, and one important aspect of this characterization is the study of deep defects which can limit carrier lifetime. Relaxation effects are calculated with molecular dynamics. The …

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A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1996

A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

Presents a train model that shows the long-range spatial correlations of fluctuations in nonequilibrium fluid systems. Illustration of model through analysis of flat-car trains running on parallel tracks; Simulation of train model in computers; Theoretical analysis for fluctuations in the train model; Relationship between train model and the fluctuating hydrodynamic theory of fluids.

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Logic And The Second Law Of Thermodynamics, David Van Den Einde Jan 1996

Logic And The Second Law Of Thermodynamics, David Van Den Einde

Journal of the Minnesota Academy of Science

This paper presents a 2T thermodynamic cycle operating around the critical locus of ethylene. The cycle converts heat energy to work at a rate greater than the Carnot cycle. This energy conversion rate challenges the use of Carnot's thermodynamic efficiency as a foundation for the second Jaw of thermodynamics. The paper discusses the historical development of classical theory and the second law's foundation in logic.

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Type-Ii Interface Exciton In Znse/(Zn,Mn)Se Heterostructures, V V. Rossin, Thomas Böttger, F Henneberger Jan 1996

Type-Ii Interface Exciton In Znse/(Zn,Mn)Se Heterostructures, V V. Rossin, Thomas Böttger, F Henneberger

Physics and Astronomy

Two emission bands are observed in the photoluminescence spectrum of ZnSe/~Zn,Mn!Se heterostructures. These bands emerge in a magnetic field and are associated with interface excitons formed as a result of a magnetic-field-induced type-I–type-II transition of the band alignment. Time-resolved measurements yield lifetimes in the ns range signifying a relatively large spatial separation of electrons and holes and hence low optical oscillator strength. These features are confirmed by a theoretical analysis of the interface exciton state revealing a reduced importance of the electron-hole Coulomb interaction in comparison with type-II excitons in quantum wells.

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Effects Of In Profile On Material And Device Properties Of Algaas/Ingaas/Gaas High Electron Mobility Transistors, David C. Look, B. Jogai, R. Kaspi, J. L. Ebel, K. R. Evans, R. L. Jones, K. Nakano, R. E. Sherriff, C. E. Stutz, G. C. Desalvo, C. Ito Jan 1996

Effects Of In Profile On Material And Device Properties Of Algaas/Ingaas/Gaas High Electron Mobility Transistors, David C. Look, B. Jogai, R. Kaspi, J. L. Ebel, K. R. Evans, R. L. Jones, K. Nakano, R. E. Sherriff, C. E. Stutz, G. C. Desalvo, C. Ito

Physics Faculty Publications

The molecular‐beam‐epitaxial growth of InxGa1−xAs on GaAs or AlyGa1−yAs leads to a variation of In content with depth, due to In segregation. However, by predepositing In at the beginning of InxGa1−xAs growth, and also thermally removing the excess In at the end, we can produce a layer with the ideal ‘‘square’’ In profile. We find that the performance of AlyGa1−yAs/InxGa1−xAs/GaAs high electron mobility transistors is most enhanced by the predeposition step alone.

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Magnetophotoluminescence Study Of Excited States Associated With Donor Bound Excitons In High-Purity Gaas, D. C. Reynolds, David C. Look, B. Jogai, G. L. Mccoy, K. K. Bajaj Jan 1996

Magnetophotoluminescence Study Of Excited States Associated With Donor Bound Excitons In High-Purity Gaas, D. C. Reynolds, David C. Look, B. Jogai, G. L. Mccoy, K. K. Bajaj

Physics Faculty Publications

Detailed magnetic-field splitting of the two rotator states designated as (Γ6+Γ8, J=5/2) and (Γ7, J=1/2) associated with donor bound excitons in high-purity epitaxial GaAs is observed in magnetophotoluminescence spectra. These two states are associated with the light-hole mass and are split by the spin-orbit interaction. The ordering in energy of these two states agrees with that predicted by theory. Also observed are the rotator states in which, after the radiative collapse of the exciton, the donor is left in the excited states. A good agreement between the energies of the excited states of the …

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A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1996

A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour

Alejandro Garcia

Presents a train model that shows the long-range spatial correlations of fluctuations in nonequilibrium fluid systems. Illustration of model through analysis of flat-car trains running on parallel tracks; Simulation of train model in computers; Theoretical analysis for fluctuations in the train model; Relationship between train model and the fluctuating hydrodynamic theory of fluids.

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Double Ionization Of Helium And Neon For Fast Heavy-Ion Impact: Correlated Motion Of Electrons From Bound To Continuum States, R. Moshammer, J. Ullrich, H. Kollmus, W. Schmitt, M. Unverzagt, O. Jagutzki, V. Mergel, H. Schmidt-Böcking, R. Mann, C. J. Woods, Ronald E. Olson Jan 1996

Double Ionization Of Helium And Neon For Fast Heavy-Ion Impact: Correlated Motion Of Electrons From Bound To Continuum States, R. Moshammer, J. Ullrich, H. Kollmus, W. Schmitt, M. Unverzagt, O. Jagutzki, V. Mergel, H. Schmidt-Böcking, R. Mann, C. J. Woods, Ronald E. Olson

Physics Faculty Research & Creative Works

Double ionization of He and Ne by charged particle impact was explored in kinematically complete experiments measuring the final momenta of the two emerging electrons(Pfe1, Pfe2) and of the recoiling target ion PRf. The momentum transfer from the 3.6 MeV/u Se28+projectile to the electrons is found to be negligibly small. Thus distinct patterns observed in the Pfe1- versus - Pfe2spectra sensitively reflect the details of the electrons' correlated motion. Classical calculations reasonably describe the data only when the (e-e)interaction during the ionization reaction is included. © 1996 The American Physical Society.

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