Digital Commons Network^™

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 …

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 …

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 (*) …

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 …

Considerations Of Temperature Stability In A Cylindrical Plasma, S. Neil Rasband, Yao-Hui Xu

Faculty Publications

A variational formulation is used to consider thermal equilibrium and stability for a cylindrical plasma modeled by dissipative magnetohydrodynamics. The parameter dependence of equilibrium solutions and their stability is followed using homotopy techniques. Solution branches and their connections are studied in relation to the applied fields.

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 …

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.

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.

Comment On "Universality Of The Kosterlitz-Thouless Transition In 4he Films As A Function Of Thickness", Rolfe G. Petschek

Faculty Scholarship

[No abstract available]

Surface-Reconstruction-Induced Changes In Free-Carrier Scattering From The W(100) Surface: Aninfrared Surface-Electromagnetic-Wave Study, D. Mark Riffe, L. M. Hanssen, A. J. Sievers

All Physics Faculty Publications

Using the infrared-absorption technique of surface-electromagnetic-wave spectroscopy (SEWS) we have studied the effects of H₂ and D₂ chemisorption on the SEW attenuation coefficient α in the 10-μm region between 165 and 350 K. The change in α at room temperature has also been measured for N₂, O₂, and CO adsorption. The coverage (CTHETA) dependence of α for N₂, O₂, and CO is fairly simple [either a monotonic increase (N₂) or a peak at some intermediate coverage (O₂, CO)] and points to changes in free-carrier (FC) surface …

Observation Of Resonant Tunneling In Silicon Inversion Layers, A. B. Fowler, G. L. Timp, J. J. Wainer, Richard A. Webb

Faculty Publications

Measurements of the temperature and carrier-density dependence of the strongly localized conductance of short silicon inversion layers are reported. At the lowest temperatures we observe well-isolated, large conductance peaks whose width and temperature dependence are only consistent with resonant tunneling and are inconsistent with Mott hopping. Several new features are observed which we believe may be the result of Coulomb interactions.

The Average Magnetic Field Draping And Consistent Plasma Properties Of The Venus Magnetotail, David J. Mccomas, Harlan E. Spence, C. T. Russell, M. A. Saunders

Physics & Astronomy

A new technique has been developed to determine the average structure of the Venus magnetotail (in the range from −8 R_v to −12 R_v) from the Pioneer Venus magnetometer observations. The spacecraft position with respect to the cross-tail current sheet is determined from an observed relationship between the field-draping angle and the magnitude of the field referenced to its value in the nearby magnetosheath. This allows us statistically to remove the effects of tail flapping and variability of draping for the first time and thus to map the average field configuration in the Venus tail. From this …

Comment On ‘‘Valence-Bond Theory And The Evaluation Of Electronic Energy Matrix Elements Between Nonorthogonal Slater Determinants’’, Gordon A. Gallup

Gordon Gallup Publications

In a recent article [Phys. Rev. A 31, 2107 (1985)] Leasure and Balint-Kurti claim to give a more efficient algorithm than any previously available for determining matrix elements of the Hamiltonian in valence-bond calculations. Actually, an algorithm of no significant difference and the same efficiency has been available since 1972 and has been applied to valence-bond calculations.

Relationship Between The P And S Fresnel Reflection Coefficients Of An Interface Independent Of Angle Of Incidence, R. M.A. Azzam

Electrical Engineering Faculty Publications

The Fresnel reflection coefficients r_p and r_s of p- and s-polarized light at the planar interface between two linear isotropic media are found to be interrelated by (r_s - r_p)/(1 - r_sr_p) = cos 2β, independent of the angle of incidence ø, where tan²β = ∊ and ∊ is the (generally complex) ratio of dielectric constants of the media of refraction and incidence. This complements another relation (found earlier), (r²_s - r_p)/(r_s - r_sr_p) = …

The Cal Poly House Doctor Lab, David W. Hafemeister

Physics

No abstract provided.

Saturation Of Beat-Excited Plasma Waves By Electrostatic Mode Coupling, C. Darrow, Donald P. Umstadter, T. Katsouleas, W.B. Mori, C.E. Clayton, C. Joshi

Donald Umstadter Publications

The nature of plasma waves which are resonantly excited when two laser beams beat in a rippled-density plasma is explored both theoretically and experimentally. A theoretical model is presented which, for commonly encountered experimental parameters, predicts rapid saturation of the high—phase-velocity beat wave at an amplitude below that expected for relativistic detuning. Results of experimental studies of this process are presented.

Structure-Induced Electronic States For Hg Overlayers On Ag(100), M. Onellion, J.L. Erskine, Y.J. Kime, Shikha Varma, Peter A. Dowben

Peter Dowben Publications

Angle-resolved photoemission was used to observe the electronic band structure of one and two monolayers of Hg on Ag(100). Evidence for new Hg electronic states and band structure arising from the hybridization of the atomic 5d_5/2 orbitals is presented. Low-energy electron diffraction results indicate that the Hg overlayers assume the face-centered-cubic (fcc) structure of the Ag(100) substrate, which is not the natural (rhombohedral) structure of bulk Hg. The new electronic states are induced as a result of the bonding of Hg atoms with adjacent metal atoms.

Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki

Faculty Publications

We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory.

Origin Of Nonuniversality In Micellar Solutions: Comment, R. G. Caflisch, Miron Kaufman, J. R. Banavar

Physics Faculty Publications

No abstract provided.

Radiation Pressure And Emission Clouds Around Active Galactic Nuclei, Moshe Elitzur, Gary J. Ferland

Physics and Astronomy Faculty Publications

Detailed calculations of the contribution of the trapped line photons to the overall pressure in line-emitting regions around active galactic nuclei are presented. They lead to the conclusion that radiation pressure is a significant factor in determining the stability of these clouds.

Experimental Measurements Of Phase Space, Roger Mcwilliams, D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

Direct measurements of integrated phase-space densities, e.g., f(x,vy,t), have been made in an experiment. Using spectroscopically active ions, measurements in a plasma show the ion response, fi(x,v,t), to linear and nonlinear waves and phase-space particle bunching. Time-resolved measurements show coherent and incoherent phase-space density changes in the presence of waves, indicating that transitions to turbulence and chaos may be studied. The time, space, and velocity-space resolution may allow experimental tests of predictions from the Boltzmann equation.

Application Of A Scaled Homogeneous Nucleation-Rate Formalism To Experimental Data At T≪TC, Barbara N. Hale

Physics Faculty Research & Creative Works

It is pointed out that for temperatures T<0.5T_c, where T_c is the critical temperature, the classical steady-state nucleation-rate formalism of Becker and Doring predicts an approximate critical supersaturation ratio S_cr (for the onset of nucleation) given by lnS_cr/Ω^3/2~0.53(T_c/T-1)^3/2. Ω is a material-dependent quantity approximately equal to the excess surface entropy per molecule. For most substances Ω ~ 2.0 and for associated liquids Ω ~ 1.5.The experimental data (for nucleation from vapor to liquid) from diffusion chamber and nozzle beam studies are found to be consistent with the above …

Symmetric Solutions To The Gauss-Bonnet Extended Einstein Equations, James Thomas Wheeler

All Physics Faculty Publications

Low-energy limits of string theories suggest that gravity lagrangians should include quadratic and higheorder curvature terms, in the form of dimensionally continued Gauss-Bonnet densities. In an arbitrary number of dimensions, we consider the static, spherically symmetric solutions to the lowest order Gauss-Bonnet extended Einstein equations. We also find isotropic, homogeneous cosmological solutions with an ideal fluid source.

Solar- Terrestrial Physics: A Space Age Birth, R. W. Schunk

Faculty Honor Lectures

Solar- Terrestrial Physics, in its broadest sense, is concerned with the transport of energy, particles, and fields from the sun to the earth and their consequent effect on the terrestrial environment. Most of the solar energy eventually deposited in our atmosphere, at a rate of approximately a trillion megawatts, arrives in the form of visible light. The study of how this energy affects our environment falls within the purview of meteorology, a discipline that has experienced an independent development and that has sufficiently different problems from solar-terrestrial physics that it can be regarded as a separate but neighboring discipline. In …