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Full-Text Articles in Physics

Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams Dec 1990

Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams

Senior Theses and Projects

The purpose of this lab is to help the student become more familiar with, or get a better feel for what is actually occurring, when observing the effects of double slit diffraction patterns. In most sophomore labs dealing with double slit diffraction, the student simply determines the diffraction angle, and slit spacing, from marking the positions of the maxima on the screen. No attempt is made to measure the relative intensity of the interference pattern, and see how the experimental data compare with the theory of interference and diffraction. In an attempt to further clarify this phenomena, we will attempt ...


Chemical And Reconstruction Induced Surface Core-Level Shifts: H On Low-Index W Surfaces, D. Mark Riffe, G. K. Wertheim, P. H. Citrin Jul 1990

Chemical And Reconstruction Induced Surface Core-Level Shifts: H On Low-Index W Surfaces, D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

The H-induced shift of the surface-atom core-level binding energy in W(110) is shown to arise from two distinct effects, one chemical in nature and the other structural. The structural shift supports a recently proposed (1p×1) reconstruction that turns on at ∼0.5 monolayer coverage. These new findings are used to provide a self-consistent interpretation of previously reported shifts from H-covered W(111) and W(100) surfaces.


Mars And Beyond: The Solar System Beckons, Frank J. Redd May 1990

Mars And Beyond: The Solar System Beckons, Frank J. Redd

USU Faculty Honor Lectures

To space zealots, 1989 was the year the drought ended. The space shuttle was operational again; Voyager's grand reconnaissance of the Solar System climaxed with the glorious encounter with the planet Neptune and its startling moon, Triton; the launches of the Magellan spacecraft to Venus and the Gallileo to Jupiter broke a decade long hiatus in the launch of U.S. planetary missions; and, for the first time in over twenty years, a U.S. president announced a daring new initiative in human exploration with the goal of first returning humans to the Moon, then going on to Mars.


Pair-Correlation Kinetics And The Reversible Diffusion-Controlled Reaction, David Peak, D C. Greenlaw, L A. Schick May 1990

Pair-Correlation Kinetics And The Reversible Diffusion-Controlled Reaction, David Peak, D C. Greenlaw, L A. Schick

All Physics Faculty Publications

It has long been known that the time course of a bimolecular reaction occurring in a condensed host depends on the behavior of the nonequilibrium pair-correlation function for reactant pairs. The classical analysis of such reactions has led to a kind of standard rule: The association rate constant for a diffusion-controlled reaction is 4πDR and this rate constant produces the fastest possible kinetics. This result is only (approximately) true for the case of an irreversible reaction, however. Here, we reexamine this old problem, looking closely at the reversible case. We report a result that challenges the standard wisdom: When the ...


Rate Equation And Scaling For Fragmentation With Mass Loss, Boyd F. Edwards, M. Cai, H. Han May 1990

Rate Equation And Scaling For Fragmentation With Mass Loss, Boyd F. Edwards, M. Cai, H. Han

All Physics Faculty Publications

A linear rate equation describes fragmentation with continuous and discrete mass loss typified by consumption of porous reactive solids and two-phase heterogeneous solids. For a mass-dependent fragmentation rate xα and a continuous-mass-loss rate εxγ,σ=γ-α-1<0 yields a>‘‘recession regime’’ where small particles lose mass continuously without breaking, σ>0 yields a ‘‘fragmentation regime’’ where all particles break, and σ=0 yields scaling for α>0. Shattering for α<0 and>σ≥0 is runaway fragmentation producing an infinte number of particles in a finite time, Exact and asymptotic solutions, exponent relations, and connections with static percolation are found.


Hydrogen Adsorption On The Β N-Covered W(100) Surface: An Infrared Study Of The W–Hstretch, D. Mark Riffe, A. J. Sievers Feb 1990

Hydrogen Adsorption On The Β N-Covered W(100) Surface: An Infrared Study Of The W–Hstretch, D. Mark Riffe, A. J. Sievers

All Physics Faculty Publications

The adsorption of hydrogen on the c(2×2) β-N-covered W(100) surface has been studied with infrared and thermal-desorption spectroscopies. A new dipole-active vibrational absorption due to chemisorbed hydrogen has been discovered. Its center frequency (1738 cm-1 for minimal H2 adsorption), isotopic dependence (1252 cm-1 for D2 adsorption and the existence of both lines for HD adsorption), absorption strength versus β-N coverage, and effective dynamic charge e*≥0.12e lead to the assignment of the W-H stretch associated with a top-bonded H species. The vibration has been studied in detail on the highly ordered ...


Corrugation In The Nitrogen-Graphite Potential Probed By Inelastic Neutron Scattering, F. Y. Hansen, L. W. Bruch, H. Taub, V. L. Frank, H. J. Lauter, Jr Dennison Feb 1990

Corrugation In The Nitrogen-Graphite Potential Probed By Inelastic Neutron Scattering, F. Y. Hansen, L. W. Bruch, H. Taub, V. L. Frank, H. J. Lauter, Jr Dennison

All Physics Faculty Publications

Inelastic neutron spectra of the commensurate √3 ×3 herringbone monolayer phase of nitrogen physisorbed on the graphite (002) surface at low temperature have been compared with lattice dynamics calculations of the polycrystalline-averaged one-phonon coherent neutron cross section. The observed zone-center energy gap of ∼0.4 THz in the acoustic-phonon branches is a factor of 2 larger than calculated from central atom-atom potentials. We conclude that current models of the corrugation in the adatom substrate potential greatly underestimate the lateral restoring forces in this relatively simple molecular film.


Alkali Metal Adsorbates On W(110): Ionic, Covalent, Or Metallic?, D. Mark Riffe, G. K. Wertheim, P. H. Citrin Jan 1990

Alkali Metal Adsorbates On W(110): Ionic, Covalent, Or Metallic?, D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

The photoemission signal from the first atomic layer of W(110) is used to assess the nature of the interaction between the surface atoms of the metal substrate and the adsorbates Na, K, and Cs for coverages up to 1 atomic layer. Our results indicate that there is little or no charge transfer from the alkali metal to the W surface, even in the limit of low coverage. The satellite structure of the photoemission lines of the outermost p shell of the alkali metals confirms this conclusion. While contrary to the conventional picture of alkali-metal-charge donation, these findings fully support ...


Quantum Measurement And Geometry, James Thomas Wheeler Jan 1990

Quantum Measurement And Geometry, James Thomas Wheeler

All Physics Faculty Publications

A model for the interpretation of spacetime as a Weyl geometry is proposed, based on the hypothesis that a system moves on any given path with a probability which is inversely proportional to the resulting change in length of the system. The results of physical measurements are calculated as the product of Weyl-conjugate gauge-dependent probabilities for the detection of conjugate objects. Each probability, expressed as a Wiener integral, is the Green's function for a diffusion equation. If the line integral of the Weyl field equals the action functional divided by ℏ this equation provides the stochastic equivalent of the ...


On The Linearization Stability Of The Conformally (Anti-) Self-Dual Einstein Equations, Charles G. Torre Jan 1990

On The Linearization Stability Of The Conformally (Anti-) Self-Dual Einstein Equations, Charles G. Torre

All Physics Faculty Publications

The Einstein equations with a cosmological constant, when restricted to Euclidean space‐times with anti‐self‐dual Weyl tensor, can be replaced by a quadratic condition on the curvature of an SU(2) (spin) connection. As has been shown elsewhere, when the cosmological constant is positive and the space‐time is compact, the moduli space of gauge‐inequivalent solutions to this equation is discrete, i.e., zero dimensional; when the cosmological constant is negative, the dimension of the moduli space is essentially controlled by the Atiyah–Singer index theorem provided the field equations are linearization stable. It is shown that ...


Improved Resolution Of A 6m Torodial Grating Monochromator, G. K. Wertheim, J. E. Rowe, D. Mark Riffe, N. V. Smith Jan 1990

Improved Resolution Of A 6m Torodial Grating Monochromator, G. K. Wertheim, J. E. Rowe, D. Mark Riffe, N. V. Smith

All Physics Faculty Publications

We report a modification of the AT&T Bell Laboratories 6m toroidal grating monochromator at the National Synchrotron Light Source at Brookhaven National Laboratory which provides greatly improved resolution at midrange without the use of a movable exit slit. This modification is based on detailed ray tracing calculation, using the precedures developed by Haber, Howells, and McKinney and Howells, modified to include the holographic correction terms to the focusing equations. To maintain the optimum resolution requires an exit slit assembly movable over a distance of ∼20 cm. However, we show that an additional fixed slit 16.8 cm closer to ...


The Longitude Dependence Of The Dayside F Region Trough: A Detailed Model-Observation Comparison, Jan Josef Sojka, Robert W. Schunk, J. A. Whalen Jan 1990

The Longitude Dependence Of The Dayside F Region Trough: A Detailed Model-Observation Comparison, Jan Josef Sojka, Robert W. Schunk, J. A. Whalen

All Physics Faculty Publications

The nighttime main F region trough extends into the sunlit afternoon sector. This trough feature exhibits both a strong magnetic activity dependence and a longitude (UT) dependence. Whalen (1987), using International Geophysical Year (IGY) ionosonde data, showed that both of these effects are readily extracted from ƒoF2 observations. In this study we show that the longitude effect is the same as that contained in the Utah State University time-dependent ionospheric model. It arises from the offset of the geomagnetic axis from the geographic axis. The magnetic activity dependency is associated with the westward convection in the afternoon ...


Winds In The Upper Mesosphere At Mid-Latitude: First Results Using An Imaging Fabry-Perot Interferometer, D Rees, A Aruliah, T J. Fuller-Rowell, Vincent B. Wickwar, R J. Sica Jan 1990

Winds In The Upper Mesosphere At Mid-Latitude: First Results Using An Imaging Fabry-Perot Interferometer, D Rees, A Aruliah, T J. Fuller-Rowell, Vincent B. Wickwar, R J. Sica

All Physics Faculty Publications

The first stage of a new midlatitude facility at the Hardware Ranch Observatory near Bear Lake (41.93°N, 111.42°W, 1970 M elevation), for studies of the aeronomy of the middle and upper atmosphere, was completed during early September 1989. An Imaging Fabry‐Perot interferometer (IFPI) (Rees et al., 1982; Rees et al., 1990), was commissioned with a special Imaging Photon Detector (IPD) (McWhirter et al., 1982), equipped with a Gallium Arsenide (GaAs) photocathode. Wind and temperature structure can be deduced from observations of the Doppler shift and Doppler broadening of airglow and auroral emissions from the mesosphere ...


Perturbations Of Gravitational Instantons, Charles G. Torre Jan 1990

Perturbations Of Gravitational Instantons, Charles G. Torre

All Physics Faculty Publications

Ashtekar's spinorial formulation of general relativity is used to study perturbations of gravitational instantons corresponding to finite-action solutions of the Euclidean Einstein equations (with a nonzero cosmological constant) possessing an anti-self-dual Weyl curvature tensor. It is shown that, with an appropriate "on-shell" form of infinitesimal gauge transformations, the space of solutions to the linearized instanton equation can be described in terms of an elliptic complex; the cohomology of the complex defines gauge-inequivalent perturbations. Using this elliptic complex we prove that there are no nontrivial solutions to the linearized instanton equation on conformally anti-self-dual Einstein spaces with a positive cosmological ...