Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Physics

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 30781 - 30810 of 36659

Full-Text Articles in Physical Sciences and Mathematics

Saturation In “Nonmagnetic” Stainless Steel, Christopher P. Weber, J. Fajans Oct 1998

Saturation In “Nonmagnetic” Stainless Steel, Christopher P. Weber, J. Fajans

Physics

Scientific equipment often uses “nonmagnetic” stainless steel, relying on the steel’s nonmagnetic behavior to leave external magnetic fields unaltered. However, stainless steel’s permeability can rise significantly when it is welded or machined, possibly perturbing an external field. Such perturbations will diminish well above the stainless steel’s saturation point. The authors measured the permeability of both welded and machined 304 stainless steel as a function of an external magnetic field, and found that both saturate at fields of approximately 0.25 T.

Go to article

Cusp Energetic Ions: A Bow Shock Source, S. W. Chang, J. D. Scudder, S. A. Fuselier, J. F. Fennell, K. J. Trattner, J. S. Pickett, Harlan E. Spence, J. D. Menietti, W. K. Peterson, R. P. Lepping, R. Friedel Oct 1998

Cusp Energetic Ions: A Bow Shock Source, S. W. Chang, J. D. Scudder, S. A. Fuselier, J. F. Fennell, K. J. Trattner, J. S. Pickett, Harlan E. Spence, J. D. Menietti, W. K. Peterson, R. P. Lepping, R. Friedel

Physics & Astronomy

Recent interpretations of cusp energetic ions observed by the POLAR spacecraft have suggested a new energization process in the cusp [Chen et al., 1997; 1998]. Simultaneous enhancement of H+, He+2, and O>+2 fluxes indicates that they are of solar wind origin. In the present study, we examine H+ and He+2 energy spectra from 20 eV to several 100 keV measured by the Hydra, Toroidal Imaging Mass-Angle Spectrograph (TIMAS), and Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) on POLAR. The combined spectrum for each species is shown to be continuous with a …

Go to article

Cross Sections Fall 1998, Department Of Physics And Astronomy Oct 1998

Cross Sections Fall 1998, Department Of Physics And Astronomy

Cross Sections

No abstract provided.

Go to article

Evidence Of Initial-State Two-Center Effects For (E, 2e) Reactions, Sindu P. Jones, Don H. Madison Oct 1998

Evidence Of Initial-State Two-Center Effects For (E, 2e) Reactions, Sindu P. Jones, Don H. Madison

Physics Faculty Research & Creative Works

Coincidence, or (e, 2e), measurements of electron-impact ionization of atoms have established that the largest values of triply differential cross sections are obtained in collisions involving small momentum transfer to the target. Absolute measurements for these reactions are now available for hydrogen at 54.4-eV impact energy, and relative data have recently been reported at 27.2 eV. Previous theoretical works have concentrated on employing asymptotically correct two-center wave functions for the final state, leaving the initial state described by the Born approximation. Here we report results for which asymptotically correct two-center wave functions are used for both the initial and final …

Go to article

A Note On The Green Dyadic Calculation Of The Decay Rates For Admolecules At Multiple Planar Interfaces, P.T. Leung, R. L. Hartman, Scott M. Cohen Oct 1998

A Note On The Green Dyadic Calculation Of The Decay Rates For Admolecules At Multiple Planar Interfaces, P.T. Leung, R. L. Hartman, Scott M. Cohen

Physics Faculty Publications and Presentations

The Green dyadic formulation for calculating classical decay rates of admolecules at multiple planar interfaces first published by Chance, Prock and Silbey is reexamined. It is pointed out that, for the case of fluorescing molecules sandwiched between a system of super- and substrate interfaces, the original formalism requires significant modifications in order to lead to results consistent with those obtained from the Sommerfeld radiation theory.

Go to article

Magnetic Control Of Convection In Nonconducting Diamagnetic Fluids, J. Huang, D. D. Gray, Boyd F. Edwards Oct 1998

Magnetic Control Of Convection In Nonconducting Diamagnetic Fluids, J. Huang, D. D. Gray, Boyd F. Edwards

All Physics Faculty Publications

Inhomogeneous magnetic fields exert a body force on electrically nonconducting, diamagnetic fluids. This force can be used to compensate for gravity and to control convection. The field effect on convection is represented by a dimensionless vector parameter Rm=(μ0αχ0d3ΔT/ρ0νDT)(H⋅∇H)r=0ext, which measures the relative strength of the induced magnetic buoyancy force due to the applied field gradient. The vertical component of this parameter competes with the gravitational buoyancy effect and a critical relationship between this component and the Rayleigh number is identified for the onset of convection. …

Go to article

The Development And Characterisation Of A Red-Sensitised Photopolymer Holographic Recording Material, Clodagh Feely Oct 1998

The Development And Characterisation Of A Red-Sensitised Photopolymer Holographic Recording Material, Clodagh Feely

Doctoral

The development and characterisation of a photopolymerisable photopolymer holographic recording material, for red sensitisation is described. The material comprises dye (methylene blue), an electron donor (triethanolamine) and monomer (acrylamide and methylene-bis-acrylamide). A binder is also included (poly(vinylalcohol) to allow recording in dry layer format. One of the main advantages of the material is its ability to self-develop, which makes it highly suitable for a range of applications which includes the fabrication of Holographic Optical Elements (HOEs). The optimisation of the material formula for red-sensitisation using holographic techniques is described. Diffraction efficiencies of over 70% were obtained in 25 seconds with …

Go to article

Qed On A Circle, James E. Hetrick, Y. Hosotani Oct 1998

Qed On A Circle, James E. Hetrick, Y. Hosotani

All Faculty Articles - School of Engineering and Computer Science

QED with massless fermions on a circle is exactly solved. The nonintegrable phase [see file], which is a dynamical degree of freedom on a circle, couples through the anomaly to the zero mode of the fermion-antifermion bound states, leading to the θ vacuum.

Go to article

Auger Resonance Decay Process In Ar 2p Shell Excitation And Ionization, Y. Lu, Wayne C. Stolte, J.A. R. Samson Oct 1998

Auger Resonance Decay Process In Ar 2p Shell Excitation And Ionization, Y. Lu, Wayne C. Stolte, J.A. R. Samson

Chemistry and Biochemistry Faculty Research

The production and subsequent autoionization of the Ar+ (1D2)6d1 satellite state that is formed either by shake-up or recapture during the Auger decay of a 2p vacancy in Ar has been studied by photoelectron spectroscopy in the energy region from 243 to 256 eV. The creation of near zero energy electrons below and immediately above the Ar 2p ionization threshold is discussed. Some ambiguous points in previous studies are clarified.

Go to article

Computer Simulations Of Electromigration Based On A Molecular Dynamics Approach, John Stephen Peake Oct 1998

Computer Simulations Of Electromigration Based On A Molecular Dynamics Approach, John Stephen Peake

Electrical & Computer Engineering Theses & Dissertations

Most research on electromigration has centered around macroscopic simulations of electromigration where a value for the diffusion coefficient was assumed to be spatially uniform throughout the material. The research in this thesis goes a step further and, through microscopic molecular dynamics computer simulations, calculates and updates the atomic drift velocity and atomic position as a function of time to analyze how various defects within the conductor affect these quantities. The simulations are carried out with defects in the form of dislocation half-planes placed in different locations within the simulation space. The atomic drift velocity and position changes derived from these …

Go to article

Spectral Features Of The Stimulated Raman Backscattering Of Modulated Laser Pulses In A Plasma, Nikolai E. Andreev, Serguei Y. Kalmykov Sep 1998

Spectral Features Of The Stimulated Raman Backscattering Of Modulated Laser Pulses In A Plasma, Nikolai E. Andreev, Serguei Y. Kalmykov

Serge Youri Kalmykov

The characteristic features of the stimulated Raman backscattering of short modulated (multi-frequency) laser pulses in an underdense plasma are investigated. A laser pulse consisting of a given pair of spectral components with the frequency difference close to the double plasma frequency is studied in the weak mode coupling approximation. The scattering of the component with the higher frequency is shown to be a five-wave resonant process, and the conditions under which this process is totally suppressed are found. The scattering of the component with the lower frequency is an ordinary three-wave decay process without any suppression. When the difference between …

Go to article

Improved Treatment Of Loop Diagrams In Su(3) Baryon Chiral Perturbation Theory, Jf Donoghue, Br Holstein Sep 1998

Improved Treatment Of Loop Diagrams In Su(3) Baryon Chiral Perturbation Theory, Jf Donoghue, Br Holstein

Barry R Holstein

Baryon chiral perturbation theory as conventionally applied has a well-known problem with the SU(3) chiral expansion in that loop diagrams generate very large SU(3) breaking corrections and greatly upset the subsequent phenomenology. We argue that the problem comes from the portions of loop integrals corresponding to propagation at such short distances that the effective theory is not valid. One can reformulate the theory equally rigorously by regulating the loop integrals using a momentum-space cutoff which removes the spurious short-distance physics. We show that this reformulation improves the phenomenology for reasonable values of the cutoff.

Go to article

A Zero Point And Accidental Errors For Published Values Of [Fe/H] For Cool Giants, B. J. Taylor Sep 1998

A Zero Point And Accidental Errors For Published Values Of [Fe/H] For Cool Giants, B. J. Taylor

Faculty Publications

This paper is one of a series based on published values of [Fe/H] for late-type evolved stars. Only values of [Fe/H] from high-dispersion spectroscopy or related techniques are used. The narrative in this paper begins at a point where mean values of [Fe/H] have been derived for xiVir, alphaBoo, betaGem, and the Hyades giants. By using these stars as standard stars when necessary, a zero-point data base is assembled. This data base is then expanded into its final version by correcting and adding additional data in a step-by-step process. As that process proceeds, data comparisons are used to establish rms …

Go to article

An Analysis Of Temperature Dependent Photoluminescence Line Shapes In Ingan, John S. Colton, K. L. Teo, P. Y. Yu, E. R. Weber, M. F. Li, W. Lui, K. Uchida, H. Tokunaga, N. Akutsu, K. Matsumoto Sep 1998

An Analysis Of Temperature Dependent Photoluminescence Line Shapes In Ingan, John S. Colton, K. L. Teo, P. Y. Yu, E. R. Weber, M. F. Li, W. Lui, K. Uchida, H. Tokunaga, N. Akutsu, K. Matsumoto

Faculty Publications

Photoluminescence (PL) line shapes in InGaN multiple quantum well structures have been studied experimentally and theoretically between 10 and 300 K. The higher temperature PL spectra can be fitted qualitatively with a thermalized carrier distribution and a broadened joint-density-of-states. The low temperature PL line shapes suggest that carriers are not thermalized, as a result of localization by band-gap fluctuations. We deduce a localization energy of ~7 meV as compared with an activation energy of ~63 meV from thermal quenching of the PL intensity. We thus conclude that this activation energy and the band-gap fluctuation most likely have different origins.

Go to article

Monte Carlo Renormalization Of 2d Simplicial Quantum Gravity Coupled To Gaussian Matter, Simon Catterall, Eric B. Gregory, G. Thorleifsson Sep 1998

Monte Carlo Renormalization Of 2d Simplicial Quantum Gravity Coupled To Gaussian Matter, Simon Catterall, Eric B. Gregory, G. Thorleifsson

Physics - All Scholarship

We extend a recently proposed real-space renormalization group scheme for dynamical triangulations to situations where the lattice is coupled to continuous scalar fields. Using Monte Carlo simulations in combination with a linear, stochastic blocking scheme for the scalar fields we are able to determine the leading eigenvalues of the stability matrix with good accuracy both for c = 1 and c = 10 theories.

Go to article

New Analytical Results On Anisotropic Membranes, Mark Bowick, Alex Travesset Sep 1998

New Analytical Results On Anisotropic Membranes, Mark Bowick, Alex Travesset

Physics - All Scholarship

We report on recent progress in understanding the tubular phase of self-avoiding anisotropic membranes. After an introduction to the problem, we sketch the renormalization group arguments and symmetry considerations that lead us to the most plausible fixed point structure of the model. We then employ an epsilon-expansion about the upper critical dimension to extrapolate to the physical interesting 3-dimensional case. The results are $\nu=0.62$ for the Flory exponent and $\zeta=0.80$ for the roughness exponent. Finally we comment on the importance that numerical tests may have to test these predictions.

Go to article

Dynamics Of The Conformal Mode And Simplicial Gravity, Simon Catterall, Emil Mottola, T. Bhattacharya Sep 1998

Dynamics Of The Conformal Mode And Simplicial Gravity, Simon Catterall, Emil Mottola, T. Bhattacharya

Physics - All Scholarship

We review the derivation of the Liouville action in 2DQG via the trace anomaly and emphasize how a similar approach can be used to derive an effective action describing the long wavelength dynamics of the conformal factor in 4D. In 2D we describe how to make an explicit connection between dynamical triangulations and this continuum theory, and present results which confirm the equivalance of the two approaches. By reconstructing a lattice conformal mode from DT simulations it should be possible to test this equivalence in 4D also.

Go to article

Anisotropic Membranes, Simon Catterall, Mark Bowick, Simeon Warner, Gudmar Thorleifsson, Marco Falcioni Sep 1998

Anisotropic Membranes, Simon Catterall, Mark Bowick, Simeon Warner, Gudmar Thorleifsson, Marco Falcioni

Physics - All Scholarship

We describe the statistical behavior of anisotropic crystalline membranes. In particular we give the phase diagram and critical exponents for phantom membranes and discuss the generalization to self-avoiding membranes.

Go to article

Wave-Vector-Dependent Exchange Splitting In A Local Moment System, C. Waldfried, T. Mcavoy, D. Welipitiya, Takashi Komesu, Peter A. Dowben, Elio Vescovo Sep 1998

Wave-Vector-Dependent Exchange Splitting In A Local Moment System, C. Waldfried, T. Mcavoy, D. Welipitiya, Takashi Komesu, Peter A. Dowben, Elio Vescovo

Peter Dowben Publications

Wave-vector-dependent exchange splitting in a local moment system The electronic structure of strained thin films of Gd has been studied with spin- and angle-resolved photoemission and spin-polarized inverse photoemission. The spin-dependent electronic structure is dominated by a very distinct k dependence of the exchange splitting. The surface magnetic structure is observed to be different from that of the bulk, as indicated by the different electronic structure and a much higher surface Curie temperature. The 4% strain within the Gd films results in an enhanced Curie temperature.

Go to article

Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher Sep 1998

Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher

Physics Faculty Publications

A critique of the instantaneous normal mode (INM) theory of diffusion by Gezelter, Rabani, and Berne (GRB) [J. Chem. Phys. 107, 4618 (1997)] is analyzed. GRB assert that imaginary-frequency INM are corrupted with modes unrelated to barrier crossing, that proposals for removing such nondiffusive (ND) modes are inadequate, and thus that INM cannot be used to predict the self-diffusion constant, D. In rebuttal it is argued that Lennard-Jones, the system studied by GRB, is anamolously rich in ND modes. INM in molecular liquids are shown to behave as excellent indicators of barrier crossing. Even in LJ ND-INM, while plentiful, do …

Go to article

Catalogs Of Temperatures And [Fe/H] Averages For Evolved G And K Stars, B. J. Taylor Sep 1998

Catalogs Of Temperatures And [Fe/H] Averages For Evolved G And K Stars, B. J. Taylor

Faculty Publications

A catalog of mean values of [Fe/H] for evolved G and K stars is described. The zero point for the catalog entries has been established by using differential analyses. Literature sources for those entries are included in the catalog. The mean values are given with rms errors and numbers of degrees of freedom, and a simple example of the use of these statistical data is given. For a number of the stars with entries in the catalog, temperatures have been determined. A separate catalog containing those data is briefly described.

Go to article

Chemical Signals From Submarine Fluid Advection Onto The Continental Shelf, W. S. Moore, Timothy J. Shaw Sep 1998

Chemical Signals From Submarine Fluid Advection Onto The Continental Shelf, W. S. Moore, Timothy J. Shaw

Faculty Publications

No abstract provided.

Go to article

Optical Implementation Of The Wavelet Transform By Using A Bacteriorhodopsin Film As An Optically Addressed Spatial Light Modulator, Joby Joseph, F. J. Aranda, D.V.G.L.N. Rao, B. S. Decristofano, B. R. Kimball, M. Nakashima Sep 1998

Optical Implementation Of The Wavelet Transform By Using A Bacteriorhodopsin Film As An Optically Addressed Spatial Light Modulator, Joby Joseph, F. J. Aranda, D.V.G.L.N. Rao, B. S. Decristofano, B. R. Kimball, M. Nakashima

Physics Faculty Publications

An optical system utilizing the photoinduced dichroism in a bacteriorhodopsin film has been demonstrated for the optical implementation of wavelet transforms. The dichroism, induced by the image of a wavelet filter on a bacteriorhodopsin film leads to polarization rotation of the Fourier components of an image. The polarization-rotated Fourier components of an input scene are analyzed with a polarizer to give the wavelet transform components. The dichroism is induced with beams whose profiles are determined by wavelet filters in order to perform the optical wavelet transform.

Go to article

The Global Response Of Relativistic Radiation Belt Electrons To The January 1997 Magnetic Cloud, G. D. Reeves, D. N. Baker, R. D. Belian, J. B. Blake, T. E. Cayton, J. F. Fennell, R. H.W. Friedel, M. M. Meier, R. S. Selesnick, Harlan E. Spence Sep 1998

The Global Response Of Relativistic Radiation Belt Electrons To The January 1997 Magnetic Cloud, G. D. Reeves, D. N. Baker, R. D. Belian, J. B. Blake, T. E. Cayton, J. F. Fennell, R. H.W. Friedel, M. M. Meier, R. S. Selesnick, Harlan E. Spence

Physics & Astronomy

In January 1997 a large fleet of NASA and US military satellites provided the most complete observations to date of the changes in >2 MeV electrons during a geomagnetic storm. Observations at geosynchronous orbit revealed a somewhat unusual two-peaked enhancement in relativistic electron fluxes [ Reeves et al., 1998]. In the heart of the radiation belts at L ≈ 4, however, there was a single enhancement followed by a gradual decay. Radial profiles from the POLAR and GPS satellites revealed three distinct phases. (1) In the acceleration phase electron fluxes increased simultaneously at L ≈ 4–6. (2) During the …

Go to article

Polarization Of Astronomical Maser Radiation. Iv. Circular Polarization Profiles, Moshe Elitzur Sep 1998

Polarization Of Astronomical Maser Radiation. Iv. Circular Polarization Profiles, Moshe Elitzur

Physics and Astronomy Faculty Publications

Profile comparison of the Stokes parameters V and I is a powerful tool for maser data analysis, which provides the first direct methods for unambiguous determination of (1) the maser saturation stage, (2) the amplification optical depth and intrinsic Doppler width of unsaturated masers, and (3) the comparative magnitudes of Zeeman splitting and Doppler line width. Circular polarization recently detected in OH 1720 MHz emission from the Galactic center appears to provide the first direct evidence for maser saturation.

Go to article

Radial Distribution Of Electron Spectra From High-Energy Ions, Francis A. Cucinotta, Robert Katz, John W. Wilson Sep 1998

Radial Distribution Of Electron Spectra From High-Energy Ions, Francis A. Cucinotta, Robert Katz, John W. Wilson

Robert Katz Publications

The average track model describes the response of physical and biological systems using radial dose distribution as the key physical descriptor. We report on an extension of this model to describe the average distribution of electron spectra as a function of radial distance from an ion. We present calculations of these spectra for ions of identical linear energy transfer (LET), but dissimilar charge and velocity to evaluate the differences in electron spectra from these ions. To illustrate the usefulness of the radial electron spectra for describing effects that are not described by electron dose, we consider the evaluation of the …

Go to article

Higher-Order And Next-Nearest-Neighbor Néel Anisotropies , Y.T. Millev, Ralph Skomski, J. Kirschner Sep 1998

Higher-Order And Next-Nearest-Neighbor Néel Anisotropies , Y.T. Millev, Ralph Skomski, J. Kirschner

Ralph Skomski Publications

The problem of higher-order Néel anisotropies is solved by exploiting the addition theorem for spherical functions. A key advantage of the present approach is the orthonormal character of the expansion of the magnetic energy that simplifies the formalism and makes possible the treatment of nonideal morphologies as well. Explicit expressions for second-, fourth-, and sixth-order anisotropies are obtained for ideal bulk of fcc and bcc symmetry as well as for (001), (110), and (111) surfaces with nearest-neighbor (NN) Néel interactions. The systematic examination of the pair model involves partition by species of inequivalent sites, interaction spheres, and orders in the …

Go to article

Can Photoemission Accurately Probe The Bulk Electronic Structure Of The Complex Oxides?, Jaewu Choi, C. Waldfried, Sy_Hwang Liou, Peter A. Dowben Sep 1998

Can Photoemission Accurately Probe The Bulk Electronic Structure Of The Complex Oxides?, Jaewu Choi, C. Waldfried, Sy_Hwang Liou, Peter A. Dowben

Peter Dowben Publications

The surface of the complex oxides, in particular the manganese perovskites, is dominated by a different free enthalpy at the surface. This can be demonstrated by surface segregation after annealing the samples. By comparing relative x-ray photoelectron spectroscopy intensities of the manganese perovskite La1-xCaxMnO3 (x=0.1, 0.35) for different emission angles, the profile of elemental concentration was determined. Analysis shows evidence for pronounced surface segregation of calcium. Our results suggest that there are strong differences between surface and bulk enthalpies without segregation or surface relaxation. This is consistent with the previously observed surface resonance …

Go to article

Can Photoemission Accurately Probe The Bulk Electronic Structure Of The Complex Oxides?, Jaewu Choi, C. Waldfried, Sy-Hwang Liou, Peter A. Dowben Sep 1998

Can Photoemission Accurately Probe The Bulk Electronic Structure Of The Complex Oxides?, Jaewu Choi, C. Waldfried, Sy-Hwang Liou, Peter A. Dowben

Peter Dowben Publications

The surface of the complex oxides, in particular the manganese perovskites, is dominated by a different free enthalpy at the surface. This can be demonstrated by surface segregation after annealing the samples. By comparing relative x-ray photoelectron spectroscopy intensities of the manganese perovskite La1-xCaxMnO3 (x=0.1, 0.35) for different emission angles, the profile of elemental concentration was determined. Analysis shows evidence for pronounced surface segregation of calcium. Our results suggest that there are strong differences between surface and bulk enthalpies without segregation or surface relaxation. This is consistent with the previously observed surface resonance in the …

Go to article

Track Structure Model For Radial Distributions Of Electron Spectra And Event Spectra From High-Energy Ions, F. A. Cucinotta, Robert Katz, J. W. Wilson Sep 1998

Track Structure Model For Radial Distributions Of Electron Spectra And Event Spectra From High-Energy Ions, F. A. Cucinotta, Robert Katz, J. W. Wilson

Robert Katz Publications

An analytic method is described for evaluating the average radial electron spectrum and the radial and total frequency-event spectrum for high-energy ions. For high-energy ions, indirect events make important contributions to frequency-event spectra. The method used for evaluating indirect events is to fold the radial electron spectrum with measured frequency-event spectrum for photons or electrons. The contribution from direct events is treated using a spatially restricted linear energy transfer (LET). We find that high-energy heavy ions have a significantly reduced frequency-averaged lineal energy (YF) compared to LET, while relativistic protons have a significantly increased YF and dose-averaged lineal energy (YD) …

Go to article

First Prev Next Last