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Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Ashkenazi Et Al. Reply, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb

Physics Articles and Papers

Ashkenazi et al. reply to Original Article: J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, and S. R. Chubb, Ground state of trans-polyacetylene and the Peierls mechanism, Physical Review Letters 62, 2016 (1989).

Ground State Of Trans-Polyacetylene And The Peierls Mechanism - Errata, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb

Physics Articles and Papers

Errata to Original Article: J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, and S. R. Chubb, Ground state of trans-polyacetylene and the Peierls mechanism, Physical Review Letters, 62, 2016 (1989).

Ground State Of Trans-Polyacetylene And The Peierls Mechanism, J. Ashkenazi, W. E. Pickett, H. Krakauer, C. S. Wang, B. M. Klein, S. R. Chubb

Physics Articles and Papers

It is shown formally that the Peierls expression is inadequate for studying the instabilities of a physically realizable one-dimensional chain of atoms, due to the long-range nature of the Coulomb interaction. Detailed total-energy studies of trans-polyacetylene, for both suggested crystal structures (P2₁/n,P2₁/a) and for the one-dimensional chain, establish that no appreciable total-energy minimum occurs for nonzero dimerization amplitude within the local-density approximation. The measured dimerization is discussed within the context of recent models of electron correlation.

Excitations In A Nearly Half-Filled Hubbard Model With U=∞, S. E. Barnes

Physics Articles and Papers

It is shown that, even near half filling, the elementary excitations of the large-U Hubbard model form wide bands of width ∼t, the intersite hopping integral, and that the slave-boson-based mean-field approximation is qualitatively wrong in the relevant limit. This large-U limit has no Kondo-type divergences.

Track “Core” Effects In Heavy Ion Radiolysis, Robert Katz, Guo-Rong Huang

Robert Katz Publications

By assuming that HO₂^● radical production in water and H₂ production in benzene are 2 hit processes, and applying the concepts of track physics, we are able to obtain a parametric fit to the yields of these reactions by heavy ion radiolysis from knowledge of the radial dose distribution about a heavy ion’s path. We make no use of the concept of a track core, for no clearly definable track core appears in our calculations of the radial dose distribution. Instead we calculate an action cross section σ from the assumed 2 hit response to γ-rays. The …

Magnetospheric Plasma Pressures In The Midnight Meridian: Observations From 2.5 To 35 Re, Harlan E. Spence, M. G. Kivelson, R. J. Walker, D. J. Mccomas

Physics & Astronomy

Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) were statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12–35 RE) magnetotail plasma sheet. The observed plasma pressure, assumed isotropic, was mapped along model magnetic field flux tubes (obtained from the Tsyganenko and Usmanov [1982] model) to the magnetic equator, sorted according to magnetic activity, and binned according to the mapped equatorial location. In regions (L ≳ 12 RE) where the bulk of the plasma pressure was contributed by particles in the energy range of the FPE (70 …

Inverse Ac Josephson Effect At Terahertz Frequencies, W C. Danchi, William Golightly, E C. Sutton

Physics and Astronomy

The inverse ac Josephson effect occurs when a Josephson junction driven by a microwave source of frequency  f  produces constant‐voltage steps at integer multiples of h f/2e. For low‐leakage current hysteretic junctions driven at microwave frequencies below about 100 GHz, some of these steps can cross the zero dc bias current axis. These zero‐crossing steps allow modern series array voltage standards to operate without individually biasing the junctions in the array. We reexamine the theory behind these steps and show that they can exist at frequencies much higher than thought previously. The Riedel singularity in the supercurrent …

Modeled F Region Response To Auroral Dynamics Based Upon Dynamics Explorer Auroral Observations, Jan Josef Sojka, Robert W. Schunk, J. D. Cravens, L. A. Frank, J. Sharber, J. D. Winningham

All Physics Faculty Publications

Auroral images from the Dynamics Explorer 1 (DE 1) scanning auroral imager have been combined with in situ auroral precipitation data from the DE 2 low altitude plasma instrument to form a time-dependent global auroral energy flux model. This model has both good time (12 min) and spatial (100 km) resolution compared to that currently available for global scale ionospheric and thermospheric modeling. The development and comparison of this model with others are discussed. Data from an aurorally active period, November 25, 1981, are presented and used as a case study for this model. Using a global ionospheric model, the …

Preliminary Results In Working With Molecular Modeling Software, Chris Hansen, Ray Hefferlin

Capstone Research Projects

In order to help facilitate the growing need for an understanding of periodic trends in molecules, an attempt was made to use a molecular modeling software package (ChemCad) to make a series of ab initio calculations of various properties of diaton1ic molecules. limitations of the package precluded calculations for strictly diatomic molecules, as well as precluding consecutive substitution of a large series of atoms into a larger molecule. This attempt does have significance in that it has allowed the physics department at Southern College to more effectively communicate with molecular modeling software developers and users.

Calculations Of Scattered Light From Rigid Polymers By Shifrin And Rayleigh-Debye Approximations, M. F. Bishop

Physics Publications

ABSTRACT

We show that the commonly used Rayleigh-Debye method for calculating light scattering can lead to significant errors when used for describing scattering from dilute solutions of long rigid polymers, errors that can be overcome by use of the easily applied Shifrin approximation. In order to show the extent of the discrepancies between the two methods, we have performed calculations at normal incidence both for polarized and unpolarized incident light with the scattering intensity determined as a function of polarization angle and of scattering angle, assuming that the incident light is in a spectral region where the absorption of hemoglobin …

Theoretical Study Of Lattice Instabilities In Yba2Cu3O7, D. P. Billesbach, John R. Hardy, P. J. Edwardson

John R. Hardy Papers

We have performed a molecular dynamics simulation of the YBa₂Cu₃O₇ structure under the constraints of the rigid-ion model. These simulations used a variety of charge states for the Cu ions and the O ions, and except for one case, the interionic potentials were obtained in an ab initio fashion. The results of these simulations showed that a lattice instability involving the Cu-O chains existed. This instability was further investigated and it was shown that simple electronic screening is probably insufficient to stabilize the lattice. An instability of this nature provides a simple explanation of some …

Continuum Model Of Thin-Film Deposition And Growth, Andrew J. Bernoff, Seth Lichter

All HMC Faculty Publications and Research

A continuum theory for the deposition and growth of solid films is presented. The theory is developed in a coordinate-independent manner and so incorporates the fully nonlinear physics. The evolution of the film is modeled in three steps. First, the adsorption of atoms in the incident beam is modeled as a ballistic process. Second, the random motion of the adatoms is treated as a diffusive process. Finally, sticking of adatoms to the film occurs as a Poisson process. The resulting system of differential equations is examined in several parameter limits. The diffusively dominated limit appears similar to zone 1 of …

Global Scale, Physical Models Of The F Region Ionosphere, Jan Josef Sojka

All Physics Faculty Publications

During the last decade, ionospheric F region modeling has reached an accurate climatological level. We now have global computer models of the F region which simulate the interactions between physical processes in the ionosphere. Because of their complexity, these climatological models are confined to modern day supercomputers. This review focuses on the development and verification of these physical ionospheric models. Such models are distinct from local models, steady state models, and empirical models of the ionosphere, which are, by their conception, unable to represent physically the range of F region variability or storm dynamics. This review examines the limitations of …

A Three-Dimensional Time-Dependent Model Of The Polar Wind, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

A time-dependent global model of the polar wind was used to study transient polar wind perturbations during changing magnetospheric conditions. The model calculates three-dimensional distributions for the NO⁺, O₂⁺, N₂⁺, N⁺ and O⁺ densities and the ion and electron temperatures from diffusion and heat conduction equations at altitudes between 120 and 800 km. At altitudes above 500 km, the time-dependent nonlinear hydrodynamic equations for O⁺ and H⁺ are solved self-consistently with the ionospheric equations. The model takes account of supersonic ion outflow, shock formation, and ion energization during …

Crystallochemical Characterization Of Magnetic Spinels Prepared From Aqueous Solution, Stephen Mann, Nicholas H.C. Sparks, Suzanne B. Couling, Miranda C. Larcombe, Richard B. Frankel

Physics

The crystallochemical characterization of magnetic spinels prepared from aqueous solution has been studied primarily by electron microscopy and ⁵⁷Fe Mossbauer spectroscopy. Two synthetic routes have been investigated : method 1 ; partial oxidation of Fe" solutions in the presence of NO; at 100 C , and method 2; reaction of hydrated Ferrr oxide (ferrihydrite) with Fe" ions at room temperature, pH = 7, 8 and 9. Both routes gave small (10-60 nm) irregular magnetite (Fe,O,) particles that were readily oxidised to maghemite (y-Fe,O,). The reaction proceeded via a green-rust intermediate and anions such as inorganic phosphate (Pi) and SO,,- …

Thermospheric Dynamics During September 18-19, 1984, 2, Validation Of The Ncar Thermospheric General Circulation Model, G Crowley, B A. Emery, R G. Roble, H C. Carlson Jr., J E. Salah, Vincent B. Wickwar, K L. Miller, W L. Oliver, R G. Burnside, F A. Marcos

All Physics Faculty Publications

The validation of complex nonlinear numerical models such as the National Center for Atmospheric Research thermospheric general circulation model (NCAR TGCM) requires a detailed comparison of model predictions with data. The Equinox Transition Study (ETS) of September 17-24, 1984, provided a unique opportunity to address the verification of the NCAR TGCM, since unusually large quantities of high-quality thermospheric and ionospheric data were obtained during an intensive observation interval. In a companion paper (paper 1) by Crowley et al. (this issue) a simulation of the September 18-19 ETS interval was described. Using a novel approach to modeling, the TGCM inputs were …

Hamiltonian Formulation Of Induced Gravity In Two Dimensions, Charles G. Torre

All Physics Faculty Publications

A Hamiltonian formulation of the theory of induced gravity in two dimensions is constructed. This formulation differs from previous efforts in that the formalism is covariant under all relevant transformation groups. In particular, spatial diffeomorphism covariance and/or invariance is manifest throughout; the phase space carries a representation of the Lie algebra of the spacetime diffeomorphism group; the group of conformal isometries is projectively represented on the phase space as a symmetry group. The key ingredient that allows covariance with respect to the above groups is the enlargement of the gravitational phase space by the inclusion of the cotangent bundle over …

Ion Beam Mixing In Ag-Pd Alloys, J L. Klatt, R S. Averback, David Peak

All Physics Faculty Publications

Ion beam mixing during 750 keV Kr⁺ irradiation at 80 K was measured on a series of Ag‐Pd alloys using Au marker atoms. The mixing in pure Ag was the greatest and it decreased monotonically with increasing Pd content, being a factor of 10 higher in pure Ag than in pure Pd. This large difference in mixing cannot be explained by the difference in cohesion energy between Ag and Pd in the thermodynamic model of ion beam mixing proposed by Johnson et al. [W. L. Johnson, Y. T. Cheng, M. Van Rossum, and M‐A. Nicolet, Nucl. …

Optical And Electrochemical Studies Of Passive Film Formation In Amorphous Ni‐Cr‐P‐C Alloys, D. B. Hagan, B. W. Sloope, V. A. Niculescu

Physics Publications

The investigation of passivation of an amorphous Ni‐l4Cr‐17P‐0.5C alloy in lN H₂ SO₄ through anodic polarization and near‐normal optical reflectance is reported. It was found that the alloy passivates with a current density of 10^{− 1} A/m² extending to 1.0 V with current density dependent upon surface morphology. In the transpassive region under constant current density conditions the reflectance of the film exhibits strong interference phenomena and overall exponential decay in intensity. The behavior of the system in this region is described with a single thin‐film optical model consistent with the formation of a chromium …

The Exchange Potential In Path Integral Studies: Analytical Justification, Randall W. Hall

Collected Faculty Scholarship

We present analytical justification for our previously described exchange pseudopotential. We show how the fermi quantum partition function can be constructed from the Boltzmann (distinguishable particle) wave functions if the states that correspond to like‐spin electrons occupying the same quantum state are excluded. A class of weighting functions that satisfy this constraint approximately is discussed. Our previous pseudopotential falls under this class. Essentially, our pseudopotential forces the unwanted states to have high energy and, hence, to make negligible contribution to the partition function. Exchange potentials of the form discussed in this article should be useful for studying systems where the …

World Sheet Diffeomorphisms And The Canonical String, Charles G. Torre

All Physics Faculty Publications

The degree to which the phase space of a closed bosonic string carries a representation of the two‐dimensional diffeomorphism group Diff(M) is investigated. In particular, homomorphic mappings from the associated Lie algebra diff(M) into the Poisson algebra of functions on three natural phase spaces associated with the string are constructed. Two of these spaces are extended phase spaces based on the conformal and harmonic gauges, respectively. The third space is essentially the original phase space; the homomorphism in this case relies on the validity of the light‐cone gauge. Homomorphisms from diff(M) into the extended phase spaces of the Batalin–Fradkin–Vilkovisky formalism …

Theoretical Study Of The Seasonal Behavior Of The Global Ionosphere At Solar Maximum, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

A time-dependent, three-dimensional, multi-ion numerical model of the global ionosphere was used to study the asymmetry in large-scale ionospheric features between the northern and southern hemispheres. The comparisons were done for June and December solstice conditions at solar maximum for quiet geomagnetic activity. Simple conditions and diurnally reproducible ionospheric features were established in order to elucidate the intrinsic hemispherical differences that are associated with the different displacements between the geomagnetic and geographic poles and the different atmospheric conditions. In comparing the ionospheric densities in the northern and southern hemispheres for a given season, we found the following: (1) The winter …

Infrared Monitoring Of Nuclear Power In Space, David W. Hafemeister

Physics

This paper assesses the level of confidence for monitoring a ban on nuclear power in earth orbit using unclassified information from astronomical observatories based on Maui, Hawaii, and from the Kuiper Airborne Observatory. It is concluded that existing military and astronomical observatories can detect and identify operating nuclear reactor sources, such as the Soviet RORSAT and US SP-100, on satellites with a very high level of confidence out to distances beyond geosynchronous orbit. The smaller radioisotope thermal sources, RTG and DIPS, could be detected with a medium level of confidence under certain conditions.

Analytically Reduced Form Of Multicenter Integrals From Gaussian Transforms, Jack C. Straton

Physics Faculty Publications and Presentations

In a previous paper the analytically reduced form was found for the general class of integrals containing multicenter products of ls hydrogenic orbitals, Coulomb or Yukawa potentials, and plane waves. The method consisted of combining all angular dependence within a single quadratic form by means of a three-dimensional Fourier transform and a one-dimensional Feynman transform for each term in the product and an additional integral transformation to move the resulting denominator into an exponential to be summed with the vector products in the plane waves. This quadratic form was then diagonalized with respect to the (introduced) momentum integrals and diagonalized …

A Search For Interstellar And Circumstellar C60, T P. Sno, C G. Seab

Physics Faculty Publications

It has recently been suggested that the diffuse interstellar bands may be formed by ionized polyhedral carbon molecules such as C60(+). While specific laboratory measurements of absorption bands of this molecular ion have not been made, a feature due to the neutral molecule C60 has been discovered at 3860A. Examination of spectra of several reddened stars, as well as one star known to have circumstellar carbonaceous dust, shows no sign of the feature, leading to upper limits of the order of 10 to the 14th/sq cm for the column density of C60. These limits are not yet sensitive enough to …

Exciton Diffusion At Finite Frequency: Luminescence Observables For Anisotropic Percolating Solids, Paul Ernest Parris

Physics Faculty Research & Creative Works

A study is made of the luminescence intensities associated with exciton diffusion and trapping on a three-dimensional anisotropic percolating lattice. The calculation is based upon a relationship that exists between the frequency dependent diffusion tensor at frequencies comparable to the inverse excitation lifetime, and luminescence observables such as the host and trap luminescence intensities for conditions of constant illumination. The present approach allows the study of crossover behavior in percolative systems that are of intermediate transport dimensionality 2 < d_t < 3. Our results suggest that curvature seen in luminescence observables near the transition need not always be a direct reflection of the critical indices associated with classical isotropic percolation. We have identified three possible sources of deviation from the classical behavior: (1) the radiative time scale of the luminescence measurements, (2) the functional dependence of the luminescence yields on the diffusion tensor, and (3) the demands of dimensional crossover in the critical region arising from the anisotropy of the medium.

Electron Removal From Molecular Hydrogen By Fully Stripped Ions At Intermediate Energies, L. Meng, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

A classical phase-space model of the hydrogen molecule is presented and applied to the study of the electron-capture and -ionization processes in collisions of fully stripped ions with H2 at intermediate impact energies and charge states from 1 to 10. The model is based on the independent-electron and the impact-parameter approximations. The electron impinging-ion and electron target-nuclei interactions are exactly taken into account. The interaction between the electrons is approximated by model potentials. The calculated total cross sections for production of free electrons and capture of one electron are in good agreement with different experimental data. The ratio between the …

Single- And Double-Ionization Cross Sections For Angular Scattering Of Fast Protons By Helium, R. (Ronald) E. Olson, J. Ullrich, R. Dörner, H. Schmidt-Böcking

Physics Faculty Research & Creative Works

The angular scattering of H⁺ by He has been investigated for single ionization at energies of 0.5, 1.0, and 3.0 MeV; and for double ionization at 1.0 MeV. The classical-trajectory Monte Carlo method has been used within one- and two-electron models to illustrate the collision dynamics. The angular differential single-ionization cross sections are in good agreement with experiment and display the combined effects of proton scattering from the He nucleus and its electrons. The relative fraction of double ionization, as a function of scattering angle, shows a maximum at 0.9 mrad that is in agreement with the experiments of …

A Study Of Oxygen Precipitation In Heavily Doped Silicon, Robert Kurt Graupner

Dissertations and Theses

Gettering of impurities with oxygen precipitates is widely used during the fabrication of semiconductors to improve the performance and yield of the devices. Since the effectiveness of the gettering process is largely dependent on the initial interstitial oxygen concentration, accurate measurements of this parameter are of considerable importance. Measurements of interstitial oxygen following thermal cycles are required for development of semiconductor fabrication processes and for research into the mechanisms of oxygen precipitate nucleation and growth. Efforts by industrial associations have led to the development of standard procedures for the measurement of interstitial oxygen in wafers. However practical oxygen measurements often …

High-Temperature Defect Structure Of Nb-Doped Lacro3, Chikung J. Yu, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Electrical conductivity and Seebeck measurements on LaCr_0.98Nb_0.02CrO₃ show that the defect structure of the material is mainly controlled by the extrinsic electrons formed by the Nb donors through the electronic compensation process. The experimental results also indicate that this material conducts electricity via a small polaron mechanism with an electron mobility around 0.004-0.01 cm2/V sec between 1100 and 1300°C. © 1989.