Digital Commons Network^™

Experimental Test Of Higher-Order Electron-Capture Processes In Collisions Of Fast Protons With Atomic Hydrogen, Hans G. Vogt, Reinhold S. Schuch, Edson L B Justiniano, Michael Schulz, W. Schwab

Physics Faculty Research & Creative Works

We present measurements of the angular distribution of fast hydrogen atoms formed by electron capture of 2.8- and 5.0-MeV protons in atomic hydrogen. In the angular region of the Thomas peak (0.47 mrad) the experimental results obtained with this pure three-body collision system are in reasonable agreement with a strong-potential Born calculation and the impulse approximation, but not with other higher-order theories.

Thin-Film Beam Splitter That Reflects Light As A Half-Wave Retarder And Transmits It Without Change Of Polarization: Application To A Michelson Interferometer, R. M.A. Azzam

Electrical Engineering Faculty Publications

The refractive index n₁ of a transparent layer of quarter-wave optical thickness coating a transparent substrate of refractive index n₂ can be chosen to produce half-wave retardation (HWR) in reflection and no change of polarization in refraction at any angle of incidence ø. The function n₁(ø, n₂), and the associated polarization-independent reflectance of the film-substrate system R(ø, n₂) are determined. Such a coated surface can be used as a beam splitter with excellent characteristics (e.g., split fractions that do not depend on source polarization, a split beam whose polarization is identical …

Equilibrium Properties Of Short Field-Reversed Configurations, Ross L. Spencer, M. Tuszewski

Faculty Publications

Some features of short field-reversed configuration (FRC) equilibria relevant to transport and stability are studied numerically and analytically. It is shown that magnetic field curvature effects significantly increase the FRC magnetization for plasma elongations epsilon is less than or equal to 4.

First-Principles Theoretical Explanation Of Incommensurate Behavior In Rbznc4, V. Katkanant, P. J. Edwardson, John R. Hardy, L. L. Boyer

John R. Hardy Papers

We have carried out an ab initio theoretical study of the potential energy and molecular dynamics of Rb₂ZnCl₄. These calculations demonstrate that the incommensurate transition in this compound is caused by the relaxation of imperfect-hexagonal spirals of highly unstable ZnCl₄^2- ions. This leads to angstrom-size displacements with essentially zero energy change. We argue that such "latent" (or imperfect) symmetry could be the general cause of incommensurate transitions in insulators.

Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager's relations.

Multicritical Points In An Ising Random-Field Model, Miron Kaufman, Philip E. Klunzinger, A. Khurana

Physics Faculty Publications

The phase diagram of the mean-field Ising model in a random field obeying a symmetric three-peak distribution is determined. This distribution is relevant to diluted antiferromagnets in a uniform magnetic field. The phase diagram includes a fourth-order point, tricritical points, ordered critical points, critical end points, and a double critical end point. An ordered phase persists for arbitrarily large random fields at low temperatures.

Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li

Physics Faculty Publications

Bulk, liquid-encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ~1 Ω cm) to semi-insulating (ρ~10⁷ Ω cm) by slow or fast cooling, respectively, following a 5 h, 950°C soak in an evacuated quartz ampoule. This effect has been studied by temperature-dependent Han-effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3 X 10¹⁴ cm^-3. Donor and acceptor concentrations, on the other hand, are in the mid 10¹⁵ cm^-3 range, which means …

Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li

Physics Faculty Publications

Bulk, liquid‐encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ∼1 Ω cm) to semi‐insulating (ρ∼10⁷ Ω cm) by slow or fast cooling, respectively, following a 5 h, 950 °C soak in an evacuated quartz ampoule. This effect has been studied by temperature‐dependent Hall‐effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3×10¹⁴ cm⁻³. Donor and acceptor concentrations, on the other hand, are in the mid 10¹⁵ cm⁻³ range, which means that …

Measurement Of The Lifetime Of The Metastable 5d3/226d3/2, J=0 Autoionizing State Of Barium, Linn D. Van Woerkom, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

We report a measurement of the lifetime of the metastable 5d_3/226d_3/2, J=0 autoionizing state of barium. We have determined the lifetime to be 190(10) ns.

Experimental Fine-Structure Branching Ratios For Na-Rare-Gas Optical Collisions, Mark D. Havey, F. T. Delahanty, Linda L. Vahala, Gary E. Copeland

Electrical & Computer Engineering Faculty Publications

Experimental ratios for branching into the fine-structure levels of the Na 3p multiplet, as a consequence of an optical collision with He, Ne, Ar, Kr, or Xe, are reported. The process studied is Na(3s²S_1/2)+R+nhNNa(3^p2P_j)+R+(n-1)_hN, where R represents a rare-gas atom and where the laser frequency N is tuned in the wings of the Na resonance transitions. The branching ratios are defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic Na D1 and D2 lines. The ratios are determined for detunings ranging from about 650 …

Effects Of Second Sound On Acoustic Trasmission At The Solid-Liquid 4He Interface, Matthew J. Moelter, M. B. Manning, C. Elbaum

Physics

We have calculated the reflection and transmission coefficients of acoustic waves propagating across a solid-liquid interface of ⁴He, using an extension of the treatment of Castaing and Nozières in which we include pressure changes associated with second sound. These calculations account well for the experimental results obtained over the temperature range 0.83 K≤ T ≤1.46 K and provide an alternative explanation to the one we offered previously for the lack of agreement between experiment and the theory of Castaing and Nozières.

Selection Rules For Vibrational Energy Loss By Resonant Electron Impact In Polyatomic Molecules, Gordon A. Gallup

Gordon Gallup Publications

Approximate expressions for inelastic elements of the S matrix are given in terms of integrals over vibrational functions and R-matrix electron states. The magnitude and symmetry of these integrals determine the vibrations that are excited by various resonances, and the present analysis successfully predicts the spectra measured for benzene, ethylene, and formaldehyde. The recently observed s-wave component in the rotational excitation of N₂ is also explained by the treatment. The theory shows how vibrational excitation can give information about the symmetries of resonant electronic states. This can be particularly useful when angular distribution measurements are unavailable.

Lung Cancer Risk At Low Doses Of Α Particles, Werner Hofmann, Robert Katz, Zhang Chunxiang

Robert Katz Publications

A survey of inhabitant exposures arising from the inhalation of ²²²Rn and ²²⁰Rn progeny, and lung cancer mortality has been carried out in two adjacent areas in Guangdong Province, People’s Republic of China, designated as the “high background” and the “control” area. Annual exposure rates are 0.38 working level months (WLM) per year in the high background, and 0.16 WLM/yr in the control area. In 14 yr of continuous study, from 1970 to 1983, age-adjusted mortality rates were found to be 2.7 per 10⁵ living persons of all ages in the high background area, and 2.9 per …

General Results On Glueball Masses In Qcd, I. J. Muzinich, V. Parameswaran Nair

Publications and Research

A number of authors have investigated mass inequalities for mesons and baryons in QCD. These provide rigorous nonperturbative constraints on the mass spectrum. Similar inequalities for glueballs are investigated. For nonzero spin J, in the large-N_c approximation, m_J ^- ⩾ m_J⁺ is found. (For J = 0, the existence of a gluon condensate can modify this statement.) There are also constraints on how fast m_J can grow with J. For example, for m_J = a + bJ^α, 0 ⩽ α ⩽ 1 is found, a result consistent with Regge behaviour.

Elastic Scattering Of Positrons And Electrons By Argon, Sultana N. Nahar, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Differential and integrated cross sections for the elastic scattering of low- and intermediate-energy (3–300 eV) positrons and electrons by argon atoms are calculated. Higher transport cross sections, representing moments of 1-(costheta)^n, for these systems are also obtained for n=1–4. Model potentials are used to represent the interactions between positrons or electrons and argon atoms. For each impact energy, the phase shifts of the lower partial waves are obtained exactly by numerical integration of the radial equation. The Born approximation is used to obtain the contribution of the higher partial waves to the scattering amplitude. The phase shifts of the seven …

Symmetric Solutions To The Maximally Gauss-Bonnet Extended Einsteinequations, James Thomas Wheeler

All Physics Faculty Publications

The most general gravitational lagrangian which can be constructed from the curvature two-form, the vielbein one-form, and tensors invariant in the tangent space is a linear combination of dimensionally extended Euler characteristics. Several recent studies indicate that superstring lagrangians include such terms. In an arbitrary number of dimensions, with arbitrary torsion, we show that in the most general such extended theory the only static, spherically symmetric, massive solutions to the variational equations of motion contain gravitational singularities. The existence of an event horizon is proved for certain cases, and a bound on the location of singularities is found. A certain …

Phase-Transition Behavior In A Random-Anisotropy System , David J. Sellmyer, S. Nafis

David Sellmyer Publications

The character of the magnetic transition is studied for a magnetic glass with strong random-anisotropy and ferromagnetic interactions. Field-dependent ac susceptibility measurements are presented near the ordering temperature of Tb₆₄Fe₂₀Ga₁₆. The data are analyzed with a scaling theory for the singular susceptibility. An excellent collapse of the H, T data is obtained for reduced temperatures in the range 0.002-0.13. These results, which are compared with recent theoretical work, provide strong evidence for a true phase transition in a random-anisotropy system.

Modeling The Evolution Of A Dendritic Structure, Alexander Umantsev

Chemistry and Physics Faculty Working Papers

The authors give the results of mathematical modeling of the evolution of a dendritic structure with the aid of the model proposed in Ref. I. They show that, as also in experiment, on the side surface of the model dendrite secondary branches form and develop into the side structure. They make a detailed investigation of its evolution in the process of growth. They show that as time passes the side structure becomes coarser. They study the changes in the dendritic structure in relation to the supercooling. With increasing supercooling the structure becomes denser, then changes to a cellular form, and …

Resource Letter Cpe-1: Computers In Physics Education, Robert Fuller

Robert G. Fuller Publications

This resource letter provides a source of information for physics teachers who wish to use computers in physics education. The letter "E” after a reference indicates a relatively elementary item useful for people just beginning to develop an interest in using computers; the letter "I" denotes intermediate level references for people who have already mastered the specialized vocabulary of computer uses; and the letter "A" denotes advanced material for people who have experience using computers in physics teaching. This letter code does not refer to the level of the physics concepts discussed in any of the articles. An asterisk (*) …

Equilibrium Polymerization Of Chains And Rings: A Bicritical Phenomenon, Rolfe G. Petschek

Faculty Scholarship

The equilibrium polymerization of chains and rings together is a (n=1) critical phenomenon with aspects of bicriticality, governed by exponents not found in any symmetric O(n) model. The bicritical nature of the critical point is the result of a competition between a transition to form long-chain polymers and a transition to form an infinite-rings condensate. As a result the fraction of monomers incorporated in chains and in rings varies with temperature according to a different power law than that for the total fraction of polymerized material and is governed by an exponent that depends on the crossover exponent φfor …

28th Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and abstracts from the 28th annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, August 3-7, 1986.

New Insights Into Mott-Scattering Electron Polarimetry, G. D. Fletcher, Timothy J. Gay, M. S. Lubell

Timothy J. Gay Publications

In order to understand some of the systematic effects associated with conventional Mottscattering electron polarization measurements, we analyzed asymmetry data obtained with 94-keV polarized electrons scattered at 120° from gold-foil targets ranging in thickness from 27 to 62 μg/cm2. Based upon an examination of the influence of multiple and plural scattering, we conclude that the precision of such Mott measurements is fundamentally limited by an experimental uncertainty of greater than ±2.5% and an absolute uncertainty of approximately ±5%, considerably worse than is customarily assumed. We believe that similar conclusions can be drawn for measurements made with “compact” cylindrical and spherical …

On The Kinetics Of Thermal Donor Formation In Silicon, J T. Borenstein, J W. Corbett, David Peak

All Physics Faculty Publications

A model for the kinetic growth of oxygen-related thermal donors in Czochralski silicon at about 450°C is presented. The model, which is based on the work of Suezawa and Sumino, derives forward reaction rates for the electrically active species by comparing analytic expressions for the early-time annealing kinetics with the infrared electronic absorption data. The analytic expressions, which are independent of the chemical structure of each species, result from three assumptions: (1) the donor defects beyond the first donor species (TD-1) are chemically stable at the donor formation temperature, (2) the reactions for the TD-1 and those electrically inactive clusters …

Further Studies On Purification Of A Mannitol Binding Protein: Use Of Ph Gradients For Elution From Cation Exchange Resin, Kristyne Ann Baumgarten

Masters Theses

Studies on the purification of a mannitol binding protein (MBP) from Pseudomonas aeruginosa PAO were performed. Utilizing the alkaline isoelectric point (pi 8.3) of MBP, pH gradients were used to elute MBP from carboxymethylcellulose cation exchange resins. Purification of MBP was monitored by sodium dodecyl sulfate-polyacrylam ide gel electrophoresis (SDS-PAGE). Only one protein band was seen on SDS-PAGE from MBP fractions elutedat pH 7-8 and 8 .2. Although pH gradients appear to give good purification from cation exchange resins, these procedures lead to loss of MBP activity.

Rewarding Scientists Who Pursue And Discuss Physics In The Public Interest, David W. Hafemeister, Barbara Levi

Physics

No abstract provided.

A Study Of Classical Elastic Scattering For Heavy-Ion Nuclear Reactions, John C. Orrison

Masters Theses

Numerical computer programs were developed to calculate the classical elastic scattering orbits, deflection functions and differential scattering cross-sections for a heavy-ion nuclear reaction model.

Critical points of the deflection functions and differential scattering cross-sections were examined.

Semiclassical modifications were developed for future study to account for the phase relation between independent orbits that lead to the same scattering direction.

Universality Classes For The Isotropic-To-Nematic Transition In Systems Of Interacting, Semiflexible Polymers, Rolfe G. Petschek

Faculty Scholarship

This paper discusses the behavior of simple models of interacting, semiflexible, nonchiral polymers. The Ursell-Mayer expansion is used to systemize calculation of the properties of such systems and avoid problems encountered with the strong, bonding interactions in a direct analysis of this problem. The formation of a nematic phase is discussed within a field theory which is equivalent, order by order in perturbation theory, to the Ursell-Mayer expansion. Symmetry analysis allows two universality classes; one has the usual, tensor order parameter, the other has a vectorlike order parameter. The vectorlike order parameter has no direct physical interpretation (distinguishing the transition …

Experiment Module For Microprocessor Based Data Acquisition And Speech Processing, Namazi Bin Azhari

Masters Theses

This project involves microprocessor applications to the acquisition of physical data. The experiment module developed here will help the physics teacher and the scientist demonstrate the uses and advantages of digital techniques to students. Specific examples of data acquisition and processing are illustrated using speech and repetitive waveforms. The project centers on a module that is programmed to perform a number of types of data recordings and processings.

Science And Society Test Ix: Technical Means Of Verification, David W. Hafemeister

Physics

Technical means of monitoring are used to verify compliance to arms control treaties. Numerical estimates are developed in order to quantify some aspects of (1) nuclear testing (signatures, optical double pulse calibration, decoupling in cavities, and high-frequency components in seismic signals), (2) optical reconnaissance (films versus CCDs, air turbulence, adaptive optics, and digital image processing), (3) infrared (resolution and detection sensitivity), and (4) radar (synthetic aperture and missile coefficient).

Magnetite And Magnetotaxis In Algae, F. F. Torres De Araujo, M. A. Pires, Richard B. Frankel, C. E. M. Bicudo

Physics

Magnetotactic algae of the genus Anisonema (Euglenophyceae) have been isolated from a coastal mangrove swamp in northeastern Brazil. The magnetotactic response is based on a permanent magnetic dipole moment per cell ~7 10^-10 emu. Each cell contains many magnetite (Fe₃O₄) particles organized in chains.