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Articles 1 - 18 of 18
Full-Text 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 …
Extension Of The Metal Light Pipe Infrared Spectroscopy Technique: Applications To Surface Adsorption And High Tc Superconductors, Torsten Will
All Graduate Theses and Dissertations, Spring 1920 to Summer 2023
The development of an infrared instrument for the study of surface adsorption and high Tc superconductors is presented and its applicability is discussed. The use of and theoretical background for the metal light pipe multiple-reflection technique are discussed in comparison to other infrared devices. Measurements are carried out to determine its limitations with powdered substrates as well as its sensitivity limitation for thin films. The results of the two test measurements, adsorption of CO on MgO and investigation of the energy gap of high Tc superconductors, are presented. Comparisons of the spectra with the experimental and theoretical literature …
A Loading Device For Fracture Testing Of Compact Tension Specimens In The Scanning Electron Microscope, Jügen Rödel, James F. Kelly, Mark R. Stoudt, Stephen J. Bennison
A Loading Device For Fracture Testing Of Compact Tension Specimens In The Scanning Electron Microscope, Jügen Rödel, James F. Kelly, Mark R. Stoudt, Stephen J. Bennison
Scanning Microscopy
A loading device for performing fracture experiments on compact tension specimens in the SEM has been designed. Its key elements are a piezoelectric translator for applying controlled displacements to the loading points on the specimen and a load cell to measure applied loads. The effective transmission of displacement from the piezoelectric driver to the specimen was found to be the major mechanical design problem. The peripheral equipment includes a function generator and a high voltage amplifier that drives the piezoelectric translator as well as a video overlay and standard video equipment to record the image continuously during the course of …
Chemical And Reconstruction Induced Surface Core-Level Shifts: H On Low-Index W Surfaces, D. Mark Riffe, G. K. Wertheim, P. H. Citrin
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
Mars And Beyond: The Solar System Beckons, Frank J. Redd
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
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
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.
Lowand Mid-Latitude Ionospheric Electric Fields During The January 1984 Gismos Campaign, Bela G. Fejer, M. C. Kelley, C. Senior, O. De La Beaujardiere, J. A. Holt, C. A. Tepley, R. Burnside, M. A. Abdu, J. H.A. Sobral, R. F. Woodman, Y. Kamide, R. Lepping
Lowand Mid-Latitude Ionospheric Electric Fields During The January 1984 Gismos Campaign, Bela G. Fejer, M. C. Kelley, C. Senior, O. De La Beaujardiere, J. A. Holt, C. A. Tepley, R. Burnside, M. A. Abdu, J. H.A. Sobral, R. F. Woodman, Y. Kamide, R. Lepping
Bela G. Fejer
This paper examines in detail the electrical coupling between the high-, middle-, and low-latitude ionospheres during January 17–19, 1984, using interplanetary and high-latitude magnetic field data together with F region plasma drift measurements from the EISCAT, Sondre Stromfjord, Millstone Hill, Saint-Santin, Arecibo, and Jicamarca incoherent scatter radars. We study the penetration of both the zonal and meridional electric field components of high-latitude origin into the low-latitude and the equatorial ionospheres. In the dusk sector, a large perturbation of the zonal equatorial electric field was observed in the absence of similar changes at low and middle latitudes in the same longitudinal …
Hydrogen Adsorption On The Β N-Covered W(100) Surface: An Infrared Study Of The W–Hstretch, D. Mark Riffe, A. J. Sievers
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*/ε∞≥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 surface characterized …
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, John R. Dennison
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, John R. 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
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 recent …
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 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 Schrödinger …
Seasonal Variations In Theequatorial Thermospheric Wind Measured At Arequipa, Peru, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalez
Seasonal Variations In Theequatorial Thermospheric Wind Measured At Arequipa, Peru, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalez
Bela G. Fejer
Studies have been carried out at Arequipa, Peru, of the seasonal variations in the thermospheric winds at moderate solar flux levels and low geomagnetic activity. Fabry-Perot interferometer measurements of the Doppler shifts in the 630.0 nm nightglow emission line from March to August 1983 and from April to October 1988 have yielded monthly-average meridional winds that are nearly zero (<50 m/s) and possibly fluctuating in direction through much of the night but develop a southward flow at 50–100 m/s in the early and the late night from May onward. The average zonal winds are eastward throughout the night, reaching peak velocities before local midnight and then decreasing. The peak velocities increase to a maximum around the June solstice. The winds are generally stronger in 1988 than in 1983, even though the solar EUV fluxes are comparable for both years. Comparison of the present results with earlier satellite measurements, as embodied in the Horizontal Wind Model of Hedin et al., reveals generally satisfactory agreement at the equinox and June solstice, except for the June 1988 period. Killeen et al.'s vector spherical harmonic form of the NCAR Thermospheric General Circulation Model, calculated for similar solar flux levels, yields meridional and zonal wind variations which exhibit the same temporal behaviors but generally smaller values than the present measurements. The present wind patterns are also compared with those measured during the same years at Arecibo, Puerto Rico; one finds oppositely directed meridional flows and similar, eastward zonal flows at the two locations, as expected from a consideration of solar EUV heating as the principal driving force.
On The Linearization Stability Of The Conformally (Anti-) Self-Dual Einstein Equations, Charles G. Torre
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 linearization instability occurs whenever the unperturbed geometry possesses …
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 grating …
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 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 constant. …
The Longitude Dependence Of The Dayside F Region Trough: A Detailed Model-Observation Comparison, Jan Josef Sojka, Robert W. Schunk, J. A. Whalen
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
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 and thermosphere. The near infra‐red …