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Articles 1  14 of 14
FullText Articles in Physics
Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams
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 CoreLevel Shifts: H On LowIndex W Surfaces, D. Mark Riffe, G. K. Wertheim, P. H. Citrin
Chemical And Reconstruction Induced Surface CoreLevel Shifts: H On LowIndex W Surfaces, D. Mark Riffe, G. K. Wertheim, P. H. Citrin
All Physics Faculty Publications
The Hinduced shift of the surfaceatom corelevel 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 selfconsistent interpretation of previously reported shifts from Hcovered W(111) and W(100) surfaces.
Mars And Beyond: The Solar System Beckons, Frank J. Redd
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.
PairCorrelation Kinetics And The Reversible DiffusionControlled Reaction, David Peak, D C. Greenlaw, L A. Schick
PairCorrelation Kinetics And The Reversible DiffusionControlled 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 paircorrelation function for reactant pairs. The classical analysis of such reactions has led to a kind of standard rule: The association rate constant for a diffusioncontrolled 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
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 twophase heterogeneous solids. For a massdependent fragmentation rate x^{α} and a continuousmassloss rate εx^{γ},σ=γα1<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 NCovered W(100) Surface: An Infrared Study Of The W–Hstretch, D. Mark Riffe, A. J. Sievers
Hydrogen Adsorption On The Β NCovered 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) βNcovered W(100) surface has been studied with infrared and thermaldesorption spectroscopies. A new dipoleactive vibrational absorption due to chemisorbed hydrogen has been discovered. Its center frequency (1738 cm^{1} for minimal H_{2} adsorption), isotopic dependence (1252 cm^{1} for D_{2} adsorption and the existence of both lines for HD adsorption), absorption strength versus βN coverage, and effective dynamic charge e^{*}/ε_{∞}≥0.12e lead to the assignment of the WH stretch associated with a topbonded H species. The vibration has been studied in detail on the highly ordered ...
Corrugation In The NitrogenGraphite Potential Probed By Inelastic Neutron Scattering, F. Y. Hansen, L. W. Bruch, H. Taub, V. L. Frank, H. J. Lauter, Jr Dennison
Corrugation In The NitrogenGraphite 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 polycrystallineaveraged onephonon coherent neutron cross section. The observed zonecenter energy gap of ∼0.4 THz in the acousticphonon branches is a factor of 2 larger than calculated from central atomatom 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
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 alkalimetalcharge donation, these findings fully support ...
Quantum Measurement And Geometry, James Thomas Wheeler
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 Weylconjugate gaugedependent 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) SelfDual Einstein Equations, Charles G. Torre
On The Linearization Stability Of The Conformally (Anti) SelfDual 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
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 ModelObservation Comparison, Jan Josef Sojka, Robert W. Schunk, J. A. Whalen
The Longitude Dependence Of The Dayside F Region Trough: A Detailed ModelObservation 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 ƒ_{o}F_{2} observations. In this study we show that the longitude effect is the same as that contained in the Utah State University timedependent 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 MidLatitude: First Results Using An Imaging FabryPerot Interferometer, D Rees, A Aruliah, T J. FullerRowell, Vincent B. Wickwar, R J. Sica
Winds In The Upper Mesosphere At MidLatitude: First Results Using An Imaging FabryPerot Interferometer, D Rees, A Aruliah, T J. FullerRowell, 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
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 finiteaction solutions of the Euclidean Einstein equations (with a nonzero cosmological constant) possessing an antiselfdual Weyl curvature tensor. It is shown that, with an appropriate "onshell" 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 gaugeinequivalent perturbations. Using this elliptic complex we prove that there are no nontrivial solutions to the linearized instanton equation on conformally antiselfdual Einstein spaces with a positive cosmological ...