Physical Sciences and Mathematics Commons^™

Immobilization Diffusion In R2Fe17 Nitrides, Ralph Skomski, S. Wirth

Ralph Skomski Publications

The diffusion of nitrogen in R₂Fe₁₇ intermetallics is investigated by an approach which reconciles the solid-solution and immobilization theories of nitrogen diffusion. It turns out that two-sublattice diffusions may yield sharp concentration profiles but leave the phase structure of the nitride unchanged. Beside the reaction time and a local relaxation time there exists a global relaxation time which governs the smoothing of concentration gradients. Due to the large number of unknown energy parameters involved it is difficult to make quantitative predictions, but in general the diffusion behavior depends on factors such as the use of N_{2 …}

Finite-Temperature Behavior Of Anisotropic Two-Sublattice Magnets, Ralph Skomski

Ralph Skomski Publications

The finite-temperature magnetism of rare-earth transition-metal intermetallics is investigated by extending the n-component vector spin model to two-sublattice magnets. Mean-field analysis shows that the influence of the rare-earth anisotropy on the mean-field Curie temperature is much smaller than expected from the low-temperature rare-earth anisotropy. The use of ultraspherical polynomials yields a generalization of the famous m (m+1)/2 power-law exponent to m (m+n-2)/( n-1).

Micromagnetic Localization, Ralph Skomski

Ralph Skomski Publications

The localization of nucleation modes in inhomogeneous ferromagnets and its influence on the coercivity are investigated. From the formal analogy between quantum mechanics and micromagnetics follows that anisotropy inhomogeneities may cause localization. The nucleation modes of one-dimensional arrays, such as multilayers composed of hard and soft magnetic materials, are localized even if the superlattice exhibits a nearly ideal periodicity. Gaussian distributions of the layer thicknesses lead to Urbach tails and very low coercivities, but a maximum thickness l_m of the soft layers suppresses the Urbach tails. The related problem of magnetic viscosity leads to a supersymmetric Fokker–Planck description where …

Phase Formation And Magnetic Properties Of Co-Rare Earth Magnetic Films, Yi Liu, Richard A. Thomas, S.S. Malhotra, Z.S. Shan, Sy_Hwang Liou, David J. Sellmyer

Sy-Hwang Liou Publications

Co–Sm and Co–Pr films were deposited by dc magnetron sputtering. Transmission electron microscopy and magnetic measurement were used to study the microstructure and magnetic property relationship. The nanostructure of the as-deposited Co 19 at. % Sm films consists of two phases: the amorphous phase and the crystallite phase. Upon annealing at 600 °C, the Co₅Sm phase with the Cu₅Ca structure, having grain size of about 20 nm, is obtained along with high coercivity (45 kOe). The as-deposited Co 22 at. % Sm films also have nanostructure similar to the Co 19 at. % films except the …

Nanostructured Ndfeb Films Processed By Rapid Thermal Annealing, M. Yu, Yi Liu, Sy_Hwang Liou, David J. Sellmyer

Sy-Hwang Liou Publications

Nanostructured NdFeB films were prepared by magnetron sputtering followed by rapid thermal annealing at a ramp rate of 200 °C/s. Isotropically oriented Nd₂Fe₁₄B crystallites were formed in the films and coercivities up to 20 kOe and remanence ratios up to 0.8 were obtained. Transmission electron microscopy analysis shows that the majority phase of the magnetic layer in the high coercivity films consists of Nd₂Fe₁₄B nanocrystallites with an average size of about 50 nm. These nanocrystallites are believed to be single-domain particles, which are responsible for the high coercivities. MFM measurements show that …

Postimpact Deformation Associated With The Late Eocene Chesapeake Bay Impact Structure In Southeastern Virginia, Gerald H. Johnson, Sarah E. Kruse, Allison W. Vaughn, John K. Lucey, C. Hobbs, David S. Powars

VIMS Articles

Upper Cenozoic strata covering the Chesapeake Bay impact structure in southeastern Virginia record intermittent differential movement around its buried rim. Miocene strata in a graben detected by seismic surveys on the York River exhibit variable thickness and are deformed above the crater rim. Fan-like interformational and intraformational angular unconformities within Pliocene–Pleistocene strata, which strike parallel to the crater rim and dip2°–3° away from the crater center, indicate that deformation and deposition were synchronous.Concentric, large-scale crossbedded, bioclastic sand bodies of Pliocene age within ~20 km of the buried crater rim formed on offshore shoals, presumably as subsiding listric slump blocks rotated …

A Study Of The Knowledge Structure Of Expert, Intermediate, And Novice Subjects In The Domain Of Physics, Jennifer L. Discenna

Dissertations

The objective of this research was to investigate the knowledge structure in physics by describing the knowledge of experts, intermediates, and novices. A review of the literature on expertise, physics knowledge, and conceptual structure provided two competing representations of physics knowledge: one defined as a hierarchy of models arranged from general to specific models, the second defined by theories which link knowledge together.

In order to investigate the two representations described above, a reiterative categorization task was employed. This task resulted in a hierarchical sort with larger piles at the top of the hierarchy and smaller piles at the bottom …

Computational Geometry Column 33, Joseph O'Rourke

Computer Science: Faculty Publications

Several recent SIGGRAPH papers on surface simplification are described.

General Formulation Of The Semirelativistic Approach To Atomic Sum Rules, P.T. Leung, Scott M. Cohen

Physics Faculty Publications and Presentations

A general scheme is presented for obtaining systematic relativistic corrections to quantum-mechanical sum rules for various calculations in atomic physics. The single-particle picture and the Foldy-Wouthuysen transformation [Phys. Rev. 78, 29 (1950)] are adopted to derive such corrections. Results are obtained for the ldquogeneralized Bethe sums,rdquo which include all higher moments of the energy transfer, and explicit results are given to the lowest order of relativistic corrections.

Avoiding Conflicts Dynamically In Direct Mapped Caches With Minimal Hardware Support, Peter N. Desantis

Dartmouth College Undergraduate Theses

The memory system is often the weakest link in the performance of today's computers. Cache design has received increasing attention in recent years as increases in CPU performance continues to outpace decreases in memory latency. Bershad et al. proposed a hardware modification called the Cache Miss Lookaside buffer which attempts to dynamically identify data which is conflicting in the cache and remap pages to avoid future conflicts. In a follow-up paper, Bershad et al. tried to modify this idea to work with standard hardware but had less success than with their dedicated hardware. In this thesis, we focus on a …

Trigonometric Transforms For Image Reconstruction, Thomas M. Foltz

Theses and Dissertations

This dissertation demonstrates how the symmetric convolution-multiplication property of discrete trigonometric transforms can be applied to traditional problems in image reconstruction with slightly better performance than Fourier techniques and increased savings in computational complexity for symmetric point spread functions. The fact that the discrete Fourier transform a circulant matrix provides an alternate way to derive the symmetric convolution-multiplication property for discrete trigonometric transforms. Derived in this manner, the symmetric convolution-multiplication property extends easily to multiple dimensions and generalizes to multidimensional asymmetric sequences. The symmetric convolution-multiplication property allows for linear filtering of degraded images via point-by-point multiplication in the transform domain …

The Effect Of Convection On A Propagating Front With A Liquid Product: Comparison Of Theory And Experiments, B. Mccaughey, John A. Pojman, C. Simmons, V.A. Volpert

Faculty Publications

This work is devoted to the investigation of propagating polymerization fronts converting a liquid monomer into a liquid polymer. We consider a simplified mathematical model which consists of the heat equation and equation for the depth of conversion for one-step chemical reaction and of the Navier-Stokes equations under the Boussinesq approximation. We fulfill the linear stability analysis of the stationary propagating front and find conditions of convective and thermal instabilities. We show that convection can occur not only for ascending fronts but also for descending fronts. Though in the latter case the exothermic chemical reaction heats the cold monomer from …

Parallel Linear Congruential Generators With Prime Moduli, Michael Mascagni

Faculty Publications

Linear congruential generators (LCGs) remain the most popular method of pseudorandom number generation on digital computers. Ease of implementation has favored implementing LCGs with power-of-two moduli. However, prime modulus LCGs are superior in quality to power-of-two modulus LCGs, and the use of a Mersenne prime minimizes the computational cost of generation. When implemented for parallel computation, quality becomes an even more compelling issue. We use a full-period exponential sum as the measure of stream independence and present a method for producing provably independent streams of LCGs in parallel by utilizing an explicit parameterization of all of the primitive elements module …

Empirical Studies Of A Safe Regression Test Selection Technique, Gregg Rothermel, Mary Jean Harrold

School of Computing: Faculty Publications

Regression testing is an expensive testing procedure utilized to validate modified software. Regression test selection techniques attempt to reduce the cost of regression testing by selecting a subset of a program’s existing test suite. Safe regression test selection techniques select subsets that, under certain well-defined conditions, exclude no tests (from the original test suite) that if executed would reveal faults in the modified software. Many regression test selection techniques, including several safe techniques, have been proposed, but few have been subjected to empirical validation. This paper reports empirical studies on a particular safe regression test selection technique, in which the …

Semiclassical Formula For Oscillator Strengths Of Atomic Spectra In External Fields, V. Kondratovich, John B. Delos

Arts & Sciences Articles

In a previous Rapid Communication [Phys. Rev. A 56, R5 (1997)] we reported a semiclassical formula describing oscillator strengths for transitions to a high Rydberg state of a hydrogen atom in an electric field. The formula relates the oscillator strength for an atomic transition into a Rydberg state to the angular distribution of outgoing electron waves and to the density of classical tori. Here we give a derivation of that formula and we suggest some generalizations. We compare the formula with experimental measurements of the absorption spectrum of hydrogen in an electric field. This absorption spectrum consists of quasidiscrete resonances …

Optimized Preparation Of Quantum States By Conditional Measurements, G. Harel, G. Kurizki, Evangelos A. Coutsias, J. K. Mciver

Branch Mathematics and Statistics Faculty and Staff Publications

We introduce a general strategy for preparation of arbitrary quantum states via optimal control of repeated conditional measurements. The effectiveness of this strategy in generating finite Fock-state superpositions with a high level of confidence from experimentally accessible coherent states is demonstrated for the simple and well known Jaynes-Cummings model dynamics.

The Discovery Of Trapped Energetic Electrons In The Outer Cusp, R. B. Sheldon, Harlan E. Spence, J. D. Sullivan, T. A, Fritz, Jiasheng Chen

Physics & Astronomy

We report on the POLAR/CEPPAD discovery of a trapped, 60°<θ<120° pitch angle electron population in the outer cusp (7−9+ Re), whose energetic electron component extends from below 30 keV to ∼2 MeV. Because the time variability in the outer cusp precludes mapping with POLAR, we have carried out test particle simulations using the Tsyganenko 1996 model (T96) to demonstrate the trapping of these energy electrons in the outer cusp region and the resonant frequencies of its trapped motion. We discuss the boundaries and regions of the cusp trap and show that it is analogous to the dipole trap. We show that the phase space densities observed there are equal or greater than the phase space densities observed in the radiation belts at constant magnetic moment, thus allowing the possibility of diffusive filling of the radiation belts from the cusp

Possible Evidence Of Gravity Wave Coupling Into The Mid-Latitude F Region Ionosphere During The Seek Campaign, Michael J. Taylor, J. M. Jahn, S. Fukao, A. Saito

All Physics Faculty Publications

On five of eight observation nights during the 1996 SEEK (Sporadic E Experiment over Kyushu) campaign, Japan, unusual “wave‐like” structures were imaged in the 630 nm thermospheric nightglow emission. Four of these events were observed to travel towards the southwest, providing new evidence in support of recent theories describing the coupling of medium‐scale gravity waves into the mid‐latitude F region ionosphere. Available ionosonde data and the visual characteristics of the wave structures indicate no association with the occurrence of mid‐latitude spread F or F region upwellings. Instead, the data support the novel concept of feedback from the ionosphere into the …

Long Base-Line Measurements Of Short Period Mesospheric Gravity Waves During The Seek Campaign, Michael J. Taylor, S. H. Seo, T. Nakamura, T. Tsuda, H. Fukunishi, Y. Takahashi

All Physics Faculty Publications

Simultaneous observations of short‐period (<1 hour) mesospheric gravity waves were made over an extended base‐line (∼660 km) from two sites in Japan (at Shigaraki and Yamagawa) during the SEEK (Sporadic‐E Experiment over Kyushu) campaign, 9–23 August, 1996. Coincident image data obtained on four nights provided a rare opportunity to investigate the horizontal spatial extent and propagation characteristics of the waves in detail. Surprisingly, out of a total of 12 events observed from Shigaraki and 10 from Yamagawa at most only three exhibited similar propagation characteristics at each site. The majority of the wave displays (∼70–75%) had quite dissimilar characteristics suggesting a preponderance for localized wave motions of limited lifetimes and geographical extent. A marked preference for wave progression towards the N‐NE indicates that the gravity waves imaged in the near infrared OH and OI (557.7 nm) nightglow emissions were probably not directly associated with the observed E‐region irregularities.

Utilization Of The Meteorological Data In The Prediction Of The Potential Of The Renewable Energy Resources In The United Arab Emirates, Nasser A.N. Albaloushi

Theses

There has been an increasing world interest in clean renewable energies ( mainly radiation and wind energies ) due to the minimal environmental problems resulting from their use. The continuous depletion of conventional energy resources and the growing world concern about the environment have lead to extensive research and development efforts in order to improve the energy conversion efficiencies and economics of devices utilizing solar energy. However, it is important to identify first the potential of available energy resources in the site where renewable energy is to be utilized.

Meteorological information are critical to the assessment of the energy resources …

Estimate Of Bottom And Surface Stress During A Spring-Neap Tide Cycle By Dynamical Assimilation Of Tide Gauge Observatons In The Chesapeake Bay, Y. H. Spitz, J. M. Klinck

CCPO Publications

Dynamical assimilation of surface elevation from tide gauges is investigated to estimate the bottom drag coefficient and surface stress as a first step in improving modeled tidal and wind-driven circulation in the Chesapeake Bay. A two-dimensional shallow water model and an adjoint variational method with a limited memory quasi-Newton optimization algorithm are used to achieve this goal. Assimilation of tide gauge observations from 10 permanent stations in the Bay and use of a two-dimensional model adequately estimate the bottom drag coefficient, wind stress, and surface elevation at the Bay mouth. Subsequent use of these estimates in the circulation model considerably …

Inventory Of Sensitive Species And Ecosystems In Utah, Endemic And Rare Plants Of Utah: An Overview Of Their Distribution And Status, Utah Division Of Wildlife Resources

All U.S. Government Documents (Utah Regional Depository)

The Utah Division of Wildlife Resources (UDWR), under an agreement with the U.S. Department of the Interior, began work in March 1994 to develop a study plan for a statewide inventory of sensitive species and ecosystems. Activities enumerated in the plan include (1) completing a literature review for vertebrate, invertebrate, and plant species, (2) conducting field studies on sensitive species identified in the plan, and (3) using information obtained from the literature review and field studies to enhance UDWR's central database. UDWR's study plan was approved by the Utah Reclamation Mitigation and Conservation Commission (Mitigation Commission) in February 1995, and …

A Management-Oriented Classification Of Pinyon-Juniper Woodlands Of The Great Basin, Neil E. West, Robin J. Tausch, Paul T. Tueller, United States Department Of Agriculture, Forest Service, Rocky Mountain Research Station

All U.S. Government Documents (Utah Regional Depository)

Pinyon-juniper woodlands occupy about 18 percent (7.1 million ha, 17.6 million acres) of the land area of the Great Basin (Tueller and others 1979). The associated tree species are found over a wide range of environmental conditions extending from communities representative of the upper fringes of the Mohave Desert to communities found at the lower fringes of high mountain forests. Over this spatial and elevational range, communities associated with pinyon-juniper woodlands are highly variable, with complex distribution and compositional patterns. This variability is due to climatic changes occurring over the last 10,000 years and to variation in current environmental conditions …

Units In Integral Group Rings For Direct Products, Richard M. Low

Dissertations

Given a finite group G and the ring of integers, one can form the integral group ring ZG . A natural problem to investigate is to find a description of the group of units for this ring ZG. Since the unit problem for integral group rings arises in the contexts of algebraic topology, number theory, and algebra, it is an important question to try to answer. For this reason, it has drawn the attention of researchers from diverse areas of mathematics.

Graham Higman (circa 1940) made substantial contributions to the solution of this problem, in the case where G was …

The John Muir Newsletter, Summer 1998, The John Muir Center For Regional Studies

Muir Center Newsletters (1981-2015)

John Muir On Mount Ritter: A New Wilderness Aesthetic by Philip G. Terrie (Editor's note: Philip G. Terrie is Professor of English and f American Studies at Bowling Green State University, and author •f Forever Wild: Environmental Aesthetics and the Adirondack wporest Preserve (1985). This article first appeared in The Pacific Historian (1987), and is reproduced here by permission.) hile John Muir has been the subject of considerable scholarly scrutiny in recent years, we have yet to arrive at a complete understanding of his response to nature.1 One on is that we are often too eager to portray him as …

Path Integral For The Quantum Harmonic Oscillator Using Elementary Methods, Scott M. Cohen

Physics Faculty Publications and Presentations

We present a purely analytical method to calculate the propagator for the quantum harmonic oscillator using Feynman’s path integral. Though the details of the calculation are involved, the general approach uses only matrix diagonalization and well-known integrals, techniques which an advanced undergraduate should understand. The full propagator, including both the prefactor and the classical action, is obtained from a single calculation which involves the exact diagonalization of the discretized action for the system.

Ichnology Of Holocene Carbonate Eolianites On San Salvador Island, Bahamas: Diversity And Significance, H. Allen Curran, Brian White

Geosciences: Faculty Publications

Reprinted from: H. Allen Curran and John E. Mylroie (eds.), Proceedings of the 9th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Bahamian Field Station

Observation Of Oscillations Between Degenerate Bound-State Configurations In Rapidly Autoionizing Two-Electron Atoms, M. B. Campbell, Thomas J. Bensky, Robert R. Jones

Physics

The oscillation between bound-state configurations in a rapidly autoionizing three-body Coulomb system has been directly observed. Using a 500-fsec laser pulse, calcium atoms are excited to the pure 4p_3/215d two-electron configuration at an energy greater than 3 eV above the ionization limit. As a result of configuration interaction, the electrons scatter coherently into multiple bound and continuum configurations. The oscillation between the degenerate 4p_1/2n′d and 4p_3/2nd modes as well as autoionization into 4s_1/2εl, 3d_3/2εl, and 3d_5/2εl …

Translational Diffusion Of Small And Large Mesoscopic Probes In Hydroxypropylcellulose-Water In The Solutionlike Regime, Kiril A. Streletzky, George D.J. Phillies

Physics Faculty Publications

Quasi-elastic light scattering spectroscopy was used to study the translational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypropylcellulose (HPC) at 25 °C. Probe diameters d spanned 14–455 nm; HPC concentrations were 0⩽c⩽7g/L. Light scattering spectroscopy consistently found spectra having the form g(1)(t)=(1−Af)exp(−θtβ)+Af exp(−θftβf). Here θf and βf refer to the “fast” mode; θ and β describe the “slow” mode. We examine the dependence of θ, β, θf, βf, and Af on d, c, scattering vector q, and viscosity η. β=1 for large probes; elsewise, β and βf are ∈(0,1). The slow mode, with short-lived memory function, is diffusive; for …

Ranking And Explaining The Scholarly Impact Of Law Schools, Theodore Eisenberg, Martin T. Wells

Cornell Law Faculty Publications

This article measures 32 law schools' academic reputations by citations to their faculties' works. Yale, Chicago, Harvard, and Stanford rank alone at the top. Seven or eight schools compose the next group. We also explore the relation between scholarly impact and entry-level or lateral hire status, gender, minority status, subjects taught, and years in teaching. Lateral hires systematically outperform entry-level hires. We find no substantial evidence of male-female differences. We find some evidence of lower citations for minority females, but this difference is largely attributable to those in teaching fewer than 8 years. For faculty members in teaching more than …