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Non-Debye Enhancements In The Mie Scattering Of Light From A Single Water Droplet, James A. Lock, Judith R. Woodruff

Physics Faculty Publications

The glare spots usually seen on a single water droplet which has been illuminated by a plane wave are produced by geometrical rays which correspond to the different terms of the Debye series expansion of the Mie scattered field. Recently other glare spot enhancements have been predicted which correspond to scattering resonances coupling to the orbiting rays associated with high-order geometrical rainbows. We observed the non-Debye enhancement of the eleventh-order rainbow glare spot at an observation angle of 90° on a 3.5-mm water droplet illuminated by polarized He-Ne laser light.

A New Technique For Whole-Wafer Etch-Pit Density Mapping In Gaas, David C. Look, D. C. Walters, J. S. Sewell, S. C. Dudley, M. G. Mier, J. S. Sizelove

Physics Faculty Publications

The pits formed on an etched GaAs surface, due to the anisotropic etching around dislocations, are efficient light scatterers, and thus reduce transmission. We have derived a quantitative relationship between the fractional transmission and the etch‐pit density (EPD) and have shown that the same absorption apparatus which is commonly used to obtain a whole‐wafer [EL2] map can also be used to generate an EPD map. The technique is verified by comparing the fractional transmission with the actual EPD count at 166 points on a three‐inch, low‐pressure, liquid‐encapsulated Czochralski wafer. Also, [EL2] and EPD maps, with more than 3500 points each, …

Elastic Angular Differential Cross Sections For Quasi-Oneelectron Collision Systems At Intermediate Energies: (Na+, Li+)+H And (Mg+, Be+)+He, J. L. Peacher, E. Redd, D. G. Seely, Timothy J. Gay, D. M. Blakenship, J. T. Park

Timothy J. Gay Publications

Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies. Data are presented for Na⁺+H collisions at laboratory energies of 35.94, 51.75, 63.89, and 143.75 keV, for Li⁺+H collisions at energies of 19.44 and 43.75 keV, for Mg⁺+He collisions at energies of 30, 66.7, and 150 keV, and for Be⁺+He collisions at an energy of 56.25 keV. The highest energy in each case corresponds to a projectile velocity of (1/2 a.u. Born and Eikonal calculations, in which we model the projectile ion as …

Measured Spectra Of The Hygroscopic Fraction Of Atmospheric Aerosol Particles, Darryl J. Alofs, Donald E. Hagen, Max B. Trueblood

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The relation between dry diameter (X₀) and critical supersaturation (S_c) for atmospheric submicron aerosol particles is investigated using a long term air sampling program at Rolla, Missouri. The particles are passed through an electrostatic aerosol size classifier, and then through an isothermal haze chamber. Results are reported in terms of an apparent volume fraction of soluble material, ε_v defined such that for particles composed only of ammonium sulfate and water insoluble compounds, ε_v is the actual volume fraction of soluble material. The probability distribution of ε_v is found to be approximately Gaussian in …

Elastic Angular Differential Cross Sections For Quasi-One-Electron Collision Systems At Intermediate Energies: (Na⁺, Li⁺)+H And (Mg⁺, Be⁺)+He, Jerry Peacher, E. Redd, Denver G. Seely, Timothy Gay, D. M. Blankenship, John T. Park

Physics Faculty Research & Creative Works

Measurements of elastic angular differential cross sections have been carried out for four quasi-one-electron collision systems at intermediate energies. Data are presented for Na⁺+H collisions at laboratory energies of 35.94, 51.75, 63.89, and 143.75 keV, for Li⁺+H collisions at energies of 19.44 and 43.75 keV, for Mg⁺+He collisions at energies of 30, 66.7, and 150 keV, and for Be⁺+He collisions at an energy of 56.25 keV. The highest energy in each case corresponds to a projectile velocity of (1/2 a.u. Born and Eikonal calculations, in which we model the projectile ion as …

The 157 Nm Photodissociation Of Ocs, C. E. Strauss, George C. Mcbane, P. L. Houston, I. Burak, J. W. Hepburn

Peer Reviewed Articles

The photodissociation of OCS at 157 nm has been investigated by using tunable vacuum ultraviolet radiation to probe the CO and S photoproducts. Sulfur is produced almost entirely in the ¹S state, while CO is produced in its ground electronic state and in vibrational levels from v=0-3 in the appropriate ratio (v=0):(v=1):(v=2):(v=3) = (1.0):(1.0):(0.5):(0.3). The rotational distribution for each vibrational level is found to be near Boltzmann, with temperatures that decrease from 1350 K for v=0 to 780 K for v=3. Measurements of the CO Doppler profiles demonstrate that the dissociation takes place from …

Low-Energy Features Of The E--H(N=2) System Exhibited In Fast H- Detachment Collisions, Chih-Ray Liu, Anthony F. Starace

Anthony F. Starace Publications

Quantitative predictions for the doubly differential detachment collisions, 0.5-MeV H^-+He→H(n=2)+He*+e^-, are provided by use of hyperspherical wave functions for the H-e^- system. Individual H-e^- hyperspherical channels are identified as producing distinct "cusp," "shape resonance," and/or "shoulder" features in the laboratory-frame cross sections. Moreover, the first quantitative predictions of the expected Gailitis-Damburg dipole-field-induced oscillations in the cross sections above the H(n=2) threshold are presented and distinguished from ¹P∘ shape resonance effects.

Application Of The Linear Muffin-Tin-Orbital Band-Structure Method To Calculate Optical Properties Of Solids, R. Zemach, J. Ashkenazi, E. Ehrenfreund

Physics Articles and Papers

Optical matrix elements have been derived for crystals by applying the theory of optical transitions within the formalism of the linear muffin-tin-orbital band-structure method and using Racah algebra. A Brillouin-zone integration by the tetrahedron method allows straightforward numerical computation of the optical function ε₂(ω) [or σ(ω)]. Other optical functions may be derived by using a Kramers-Kronig analysis.

Calculation Of Optical Properties Of Trans-Polyacetylene By The Linear Muffin-Tin-Orbital Method, R. Zemach, J. Ashkenazi, E. Ehrenfreund

Physics Articles and Papers

The basic optical properties of trans-(CH)_x in the P2₁/n and the P2₁/a space groups are derived from first principles. The relevant optical matrix elements are calculated within the self-consistent linear muffin-tin-orbital band-structure method. The derived optical response functions are compared with the results from a variety of optical as well as electron-energy-loss experimental studies. It is shown that the measured optical constants are consistent with the P2₁/n structure.

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 …