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Articles 31981 - 32010 of 34204

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Problems With Deducing Ionospheric Plasma Convection Patterns, Jan Josef Sojka, Robert W. Schunk Jan 1986

Problems With Deducing Ionospheric Plasma Convection Patterns, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

It is well-known that convection electric fields have an important effect on the ionosphere-thermosphere system at high latitudes and that a quantitative understanding of their effect requires a knowledge of the plasma convection pattern. Consequently, convection electric fields have been measured by a variety of techniques, including satellite, rocket, and balloon-borne probes, optical tracking of ionized barium clouds, incoherent scatter observations of drifting F region plasma, and coherent scatter observations of drifting E region irregularities. Since all of these measurement techniques provide information on only a limited spatial region at any time, the construction of the overall convection pattern requires …

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Crossover From Contact Propagation To Chemical Propagation In First-Passage Percolation, A. R. Kerstein, Boyd F. Edwards Jan 1986

Crossover From Contact Propagation To Chemical Propagation In First-Passage Percolation, A. R. Kerstein, Boyd F. Edwards

All Physics Faculty Publications

On lattices whose bonds are assigned time delays from a bimodal distribution with modes at b and a≫b whose relative weights are p and 1-p, the dependence of the first-passage velocity v on p is investigated by means of scaling arguments and computations. As p increases, v exhibits a sharp rise near the percolation threshold due to a crossover from the contact-propagation regime, in which slow-bond crossings are rate limiting, to the chemical-propagation regime, in which the tortuosity of the shortest path through the fast-bond network is rate limiting. Previous analyses of criticality in the limit a/b→∞ are extended by …

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A Theoretical Study Of The Production And Decay Of Localized Electron Density Enhancements In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk Jan 1986

A Theoretical Study Of The Production And Decay Of Localized Electron Density Enhancements In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

The origins, transport, and decay of large-scale (≳ 10 km) F region density irregularities were theoretically studied using a high-latitude time dependent ionospheric model. Such density irregularities (blobs) have been found both in the polar cap and the auroral zone. The model study, which focuses on blobs being produced by auroral precipitation, shows that the observed energy fluxes can readily account for the blob densities if a plasma flux tube is exposed to the precipitation for 5-10 min. Once the flux tube is transported away from the source, the F region density profile recovers its shape on a time scale …

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Comparison Of Simultaneous Chatanika And Millstone Hill Observations With Ionospheric Model Predictions, C. E. Rasmussen, Robert W. Schunk, Jan Josef Sojka, Vincent B. Wickwar, O. De La Beaujardiere, J. Foster, J. Holt, D. S. Evans, E. Nielsen Jan 1986

Comparison Of Simultaneous Chatanika And Millstone Hill Observations With Ionospheric Model Predictions, C. E. Rasmussen, Robert W. Schunk, Jan Josef Sojka, Vincent B. Wickwar, O. De La Beaujardiere, J. Foster, J. Holt, D. S. Evans, E. Nielsen

All Physics Faculty Publications

As part of the MITHRAS program, the Chatanika and Millstone Hill incoherent-scatter radars made coordinated observations of the polar ionosphere on June 27 and 28, 1981. We compare these data with predictions made by a high-latitude ionospheric model. Qualitatively, the same features are evident in both the model and the radar data: fairly constant densities on the dayside with a mid-latitude trough forming poleward of 65 degrees around 1900 MLT (magnetic local time). This trough is seen to extend equatorward with increasing MLT, such that the minimum densities occurring in the trough appear just after midnight around 60 degrees dipole …

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Theoretical Study Of The Electron Temperature In The High-Latitude Ionosphere For Solar Maximum And Winter Conditions, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline Jan 1986

Theoretical Study Of The Electron Temperature In The High-Latitude Ionosphere For Solar Maximum And Winter Conditions, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline

All Physics Faculty Publications

The electron temperature (Te) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, Te hot spots develop, and …

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Formation Kinetics Of Thermal Donors In Silicon, J T. Borenstein, J W. Corbett, David Peak Jan 1986

Formation Kinetics Of Thermal Donors In Silicon, J T. Borenstein, J W. Corbett, David Peak

All Physics Faculty Publications

The kinetics of thermal donor formation in Czochralski-silicon at ca. 450° C are explained by a simple model based on the work of Suezawa and Sumino which derives forward and reverse reaction rates for each electrically active species from the general features of the infrared electronic absorption spectra. The model, which is independent of the chemical nature of the thermal donor core, assumes that all thermal donors beyond the first donor species are chemically stable at the donor formation temperature, and approximates the reactions for species smaller than the first thermal donor as being in chemical equilibrium. The model is …

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Effects Of Different Convection Models Upon The High-Latitude Ionosphere, C. E. Rasmussen, Robert W. Schunk, Jan Josef Sojka Jan 1986

Effects Of Different Convection Models Upon The High-Latitude Ionosphere, C. E. Rasmussen, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

It is well known that convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of plasma convection over the entire high-latitude region. Two empirical models of plasma convection that have been proposed for use in studying the ionosphere are the Volland and Heelis models. Both of these models provide a similar description of two-celled ionospheric convection, but they differ in several ways, in particular, in the manner in which plasma flows over the central polar cap and near the polar cap boundary. In order to …

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A Simple Conceptual-Model For 2-Photon Absorption, Frank Moscatelli Jan 1986

A Simple Conceptual-Model For 2-Photon Absorption, Frank Moscatelli

Physics & Astronomy Faculty Works

The process of two‐photon excitation of atoms is explained by a simple conceptual model which takes into account virtual states of the atom as well as photon statistics. In addition to predicting the correct dependence of the two‐photon excitation probability on the intensity of incident light, the model also provides an explanation for a number of experimentally observed effects.

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An Interplanetary Magnetic Field Dependent Model Of The Ionospheric Convection Electric Field, Jan Josef Sojka, C. E. Rasmussen, Robert W. Schunk Jan 1986

An Interplanetary Magnetic Field Dependent Model Of The Ionospheric Convection Electric Field, Jan Josef Sojka, C. E. Rasmussen, Robert W. Schunk

All Physics Faculty Publications

A mathematical model of the magnetospheric electric field imposed upon the ionosphere is presented. The model provides an interplanetary magnetic field (IMF) dependent description of the magnetospheric electric field at ionospheric altitudes for global ionospheric and thermospheric modelers. Although many theoretical and empirical ionospheric convection models have been published, none give both a quantitative and a general Kp, IMF (Bx , By , Bz) dependent description. The need for such a model is particularly pressing with the success of the Dynamic Explorer (DE) mission. As a result of this mission, extensive data sets of …

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On The Existence Of Periodic And Eventually Periodic Solutions Of A Fluid Dynamic Forced Harmonic Oscillator, Charlie H. Cooke Jan 1986

On The Existence Of Periodic And Eventually Periodic Solutions Of A Fluid Dynamic Forced Harmonic Oscillator, Charlie H. Cooke

Mathematics & Statistics Faculty Publications

For certain flow regimes, the nonlinear differential equation Y¨=F(Y)−G, Y≥0, G>0 and constant, models qualitatively the behaviour of a forced, fluid dynamic, harmonic oscillator which has been a popular department store attraction. The device consists of a ball oscillating suspended in the vertical jet from a household fan. From the postulated form of the model, we determine sets of attraction and exploit symmetry properties of the system to show that all solutions are either initially periodic, with the ball never striking the fan, or else eventually approach a periodic limit cycle, after a sufficient number of bounces away from …

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Nuclear Magnetic Resonance Spectroscopy And Relaxation In Molecular Solids Containing Isopropyl Groups. Part 2—The Large Two-Phase Temperature Region In 1,4-Di-Isopropylbenzene, Peter A. Beckmann Jan 1986

Nuclear Magnetic Resonance Spectroscopy And Relaxation In Molecular Solids Containing Isopropyl Groups. Part 2—The Large Two-Phase Temperature Region In 1,4-Di-Isopropylbenzene, Peter A. Beckmann

Physics Faculty Research and Scholarship

We report a proton n.m.r. study of the large, long-lived two-phase temperature region in 1,4-di-isopropylbenzene (DIB). The proton spectra are characterized by a narrow line superimposed on a 42 kHz broad line. The narrow line shows the chemical shift structure of DIB. When the sample is in the solid state the narrow lines are sharp (<30 Hz) near the melting point of 256 K and they broaden to ca.1.5 kHz at ca. 170 K where they disappear. A variety of selective and non-selective Zeeman relaxation experiments as well as a Goldman–Shen exchange experiment were performed. It is concluded that the two sets of spins do not communicate on any timescale shorter …

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Ar+ In The Terrestrial Ionosphere, Jane L. Fox Jan 1986

Ar+ In The Terrestrial Ionosphere, Jane L. Fox

Physics Faculty Publications

The Ar+ densities in the terrestrial ionosphere are computed for both low and high solar activity models. The reaction N2+(υ > 0) + Ar → N2+ Ar+ is found to be a significant source of Ar+, nearly equal to photoionization and electron impact ionization in the high solar activity model. Peak densities of Ar+ of 11 cm−3 near 190 km and 22 cm−3 near 220 km are predicted for the low and high solar activity models. It is suggested that a simultaneous measurement of Ar+ and Ar densities …

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Deuteron Zeeman Relaxation Of Cd4 In The Isotropic Liquid, The Liquid Crystalline, And The Solid State Of Several Substances, Peter A. Beckmann, Myer Bloom, E. Elliott Burnell Jan 1986

Deuteron Zeeman Relaxation Of Cd4 In The Isotropic Liquid, The Liquid Crystalline, And The Solid State Of Several Substances, Peter A. Beckmann, Myer Bloom, E. Elliott Burnell

Physics Faculty Research and Scholarship

Measurement of deuteron Zeeman relaxation rates of CD4 dissolved in benzene, hexane, and the liquid crystals MBBA, EBBA, and Merck ZLI‐1132 and in pure CD4 gas as a function of temperature at 30.7 and 61.4 MHz shows that the CD4 is uniformly dispersed in the liquid solvents but resides in gas pockets when the solvents are in the solid state. Effects of centrifugal distortion were observed in the gas phase. The relaxation rate was found to be nearly independent of solvent, temperature, and pressure for the methane–liquid mixtures. This result is explained in terms of the extended …

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Static And Dynamic Properties Of Polystyrene In Good Solvents: Ethylbenzene And Tetrahydrofuran, K. Venkataswamy, Alexander M. Jamieson, Rolfe G. Petschek Jan 1986

Static And Dynamic Properties Of Polystyrene In Good Solvents: Ethylbenzene And Tetrahydrofuran, K. Venkataswamy, Alexander M. Jamieson, Rolfe G. Petschek

Faculty Scholarship

We report static and dynamic light scattering studies of polystyrenes of narrow molecular weight distribution in ethylbenzene (EtPh) and tetrahydrofuran (THF) as solvents. These experiments generate values for z-average radius of gyration, (Rg)₂, weight-average second osmotic virial coefficient, A₂, z-average translational diffusion coefficients, (Dt)z, and hence the diffusion virial coefficients, kD, and the z-average of the inverse frictional radius, 〈Rf-1〉z. The results show that while for a specific molecular weight the 〈Rg〉z values in THF are similar to our experimental values in ethylbenzene and to literature values in benzene or toluene, the A2 values, as well as hydrodynamic radii, are …

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An Approximate Variational Method For Improved Thermodynamics Of Molecular Fluids, M. S. Shaw, J. D. Johnson, John D. Ramshaw Jan 1986

An Approximate Variational Method For Improved Thermodynamics Of Molecular Fluids, M. S. Shaw, J. D. Johnson, John D. Ramshaw

Physics Faculty Publications and Presentations

For a certain class of thermodynamic perturbation theories, a generalization of the Gibbs-Bogoliubov inequality holds through second order of perturbation theory and for a subset of terms the inequality is true to infinite order. Using this approximate variational principle, a perturbation theory is chosen for which the Helmholtz free energy of the reference system is minimized under the constraint that the first order term is identically zero. We apply these ideas to the determination of effective spherical potentials that accurately reproduce the thermodynamics of nonspherical molecular potentials. For a diatomic-Lennard-Jones (DLJ) potential with l ∕σ = 0.793, the resulting spherical …

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The Homodyne Interferometer And Its Use In Finding The Optical Properties Of Graphite, Steven Randle Frey Jan 1986

The Homodyne Interferometer And Its Use In Finding The Optical Properties Of Graphite, Steven Randle Frey

Masters Theses

"An interferometer based on the principle of homodyning can be used to measure the reflectance of solid samples at microwave frequencies. These measurements provide the low frequency values needed for a Kramers-Kronig analysis. This analysis yields the complex dielectric function, e1+ ie2, and complex index of refraction, n + ik, of the solid. 2 This interferometer was tested on a pressed pellet sample of powdered Dixon 200-10 graphite and yielded satisfactory results. Also investigated were two different methods of signal modulation: mechanical chopping and a rotating wire grid polarizer" Abstract, p. ii

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Magnetite And Magnetotaxis In Bacteria And Algae, Richard B. Frankel Jan 1986

Magnetite And Magnetotaxis In Bacteria And Algae, Richard B. Frankel

Physics

We are using Mössbauer spectroscopy and magnetic measurements in conjunction with electrochemical, pH and optical spectroscopic measurements to study the mechanisms of iron containing core of these proteins.

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Biological Effects Of Static Magnetic Fields, Richard B. Frankel Jan 1986

Biological Effects Of Static Magnetic Fields, Richard B. Frankel

Physics

No abstract provided.

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Lna: A New Cw Nd Laser Tunable Around 1.05 And 1.08 Μm, Laird D. Schearer, Michele Leduc, Daniel Vivien, Anne Marie Lejus, Jeanine Thery Jan 1986

Lna: A New Cw Nd Laser Tunable Around 1.05 And 1.08 Μm, Laird D. Schearer, Michele Leduc, Daniel Vivien, Anne Marie Lejus, Jeanine Thery

Physics Faculty Research & Creative Works

We have investigated the CW laser properties of the lanthamide hexa-aluminate La0.9Nd0.1MgAl11O19 at room temperature. When a I cm long crystal is pumped by an Ar+ laser (514 nm) or a Kr+ laser (752 nm), CW emission is obtained with slope efficiencies of 10 and 26 percent, respectively. A four-plate Lyot filter in the cavity forces the LNA crystal to oscillate in either of the two major bands centered at 10 820 A (tuning range 80 A) and 10 545 A (tuning range 35 Å). Copyright © 1986 by The Institute of Electrical and Electronics Engineers, Inc.

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Electron Transitions In Multiply-Charged Ion-Helium Collisions, M. Lou Mckenzie Jan 1986

Electron Transitions In Multiply-Charged Ion-Helium Collisions, M. Lou Mckenzie

Masters Theses

"A classical model for He using the Classical Trajectory Monte Carlo method is developed to study multiply charged ions colliding with He at intermediate energies. Reactions studied are single and double electron capture and ionization and electron capture-ionization for projectile charge states q = +1 to +50. The dominant collision process is single ionization. Charge exchange is found to be a two-electron process, where one electron is ionized and one is captured by the projectile. We find our calculations to be in good agreement with available experimental data, supporting our interpretations of the collision mechanisms"-- Abstract, p. iii

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Fock-Tani Transformation And A First-Order Theory Of Charge Transfer, P. C. Ojha, M. D. Girardeau, J. D. Gilbert, Jack C. Straton Jan 1986

Fock-Tani Transformation And A First-Order Theory Of Charge Transfer, P. C. Ojha, M. D. Girardeau, J. D. Gilbert, Jack C. Straton

Physics Faculty Publications and Presentations

A unitary (Fock-Tani) transformation of the second-quantized Hamiltonian breaks the interaction into its component parts, e.g., elastic scattering, inelastic scattering, rearrangement interaction, etc. The interaction for a particular process is ‘‘weaker’’ than the overall interaction; this is reflected in certain orthogonality corrections which appear in a perturbation expansion of the T-matrix element. As a result, the internuclear potential makes a negligible contribution of order me/mp to the first-order amplitude for charge transfer. We find very good agreement with experimental and the best available theoretical results for the total cross section for the reaction p+H(1s)→H(1s)+p for …

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Conductivity And Photoconductivity Mechanisms Of Iron And Magnesium Doped Lithium Niobate, Joseph Francis Kirchhoff Jan 1986

Conductivity And Photoconductivity Mechanisms Of Iron And Magnesium Doped Lithium Niobate, Joseph Francis Kirchhoff

Masters Theses

Various compositions of lithium niobate crystals were observed to have an electrical conductivity given by 2.3 x 103 exp(-1.21/kT) Ω-1 m-1 between 200 and 3 15°C. This implies that in this temperature range, all such crystals exhibit comparable carrier concentration and mobility. A model based on intrinsic conductivity is presented which adequately agrees with experiment. In addition, a model is presented by which electronic photoconductivity can be predicted by evaluating the trapping cross-section associated with Fe3+ ions dependent upon their lattice sites"-- Abstract, p. ii

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The Spin‐1 Anisotropic Heisenberg Ferromagnet With Biquadratic Exchange, Harry A. Brown Jan 1986

The Spin‐1 Anisotropic Heisenberg Ferromagnet With Biquadratic Exchange, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Comments On The Raindrop Problem, I. Adawi Jan 1986

Comments On The Raindrop Problem, I. Adawi

Physics Faculty Research & Creative Works

No abstract provided.

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Resonant Transfer And Excitation: Dependence On Projectile Charge State And Target-Electron Momentum Distribution, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, J. R. Mowat, D. W. Mueller, A. Müller, M. P. Stockli, K. H. Berkner, P. Gohil, R. J. Mcdonald, A. S. Schlachter, J. W. Stearns Jan 1986

Resonant Transfer And Excitation: Dependence On Projectile Charge State And Target-Electron Momentum Distribution, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, J. R. Mowat, D. W. Mueller, A. Müller, M. P. Stockli, K. H. Berkner, P. Gohil, R. J. Mcdonald, A. S. Schlachter, J. W. Stearns

Physics Faculty Research & Creative Works

Resonant transfer and excitation (RTE) involving simultaneous electron capture and projectile K-shell excitation has been measured for calcium ions in charge states ranging from neon like to hydrogen like incident on molecular hydrogen over an energy range 100-370 MeV. The results establish a projectile charge-state dependence for RTE and provide a detailed test of theoretical calculations. The effect of the target-electron momentum distribution on the RTE process is demonstrated by comparing with previous results for calcium ions incident on helium. © 1986 The American Physical Society.

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Electron Capture And Loss For 2.5-200-Mev 16s13++He Collisions, M. W. Clark, E. M. Bernstein, J. A. Tanis, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron Jan 1986

Electron Capture And Loss For 2.5-200-Mev 16s13++He Collisions, M. W. Clark, E. M. Bernstein, J. A. Tanis, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron

Physics Faculty Research & Creative Works

Electron capture and loss cross sections have been measured for highly charged (q=13+) sulfur ions with energies 2.5-200 MeV colliding with helium. Electron capture varies by nearly six orders of magnitude over the energy range investigated, while electron loss varies by only about a factor of 2. The capture cross sections are in reasonable agreement with classical and empirical scaling rules, while the loss cross sections agree well with the plane-wave Born approximation. © 1986 The American Physical Society.

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Structure In The Energy Dependence Of High-Energy Electron-Capture Cross Sections, W. G. Graham, E. M. Bernstein, M. W. Clark, J. A. Tanis, K. H. Berkner, P. Gohil, R. J. Mcdonald, A. S. Schlachter, J. W. Stearns, Robert H. Mcfarland, T. J. Morgan, A. M̈Ller Jan 1986

Structure In The Energy Dependence Of High-Energy Electron-Capture Cross Sections, W. G. Graham, E. M. Bernstein, M. W. Clark, J. A. Tanis, K. H. Berkner, P. Gohil, R. J. Mcdonald, A. S. Schlachter, J. W. Stearns, Robert H. Mcfarland, T. J. Morgan, A. M̈Ller

Physics Faculty Research & Creative Works

Previous experimental and theoretical work has found electron capture to be a monotonically decreasing function of energy in fast ion-atom collisions. We report here the experimental observation of nonmonotonic behavior of the electron-capture cross sections in fast collisions of calcium ions, in charge states 16+ to 19+, with molecular hydrogen, in the energy range 97368 MeV. The structure observed in the measured cross sections is attributed to the contribution of resonant transfer and excitation to electron capture. © 1986 The American Physical Society.

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V/2 Electrons In H++H Ionizing Collisions, Ronald E. Olson Jan 1986

V/2 Electrons In H++H Ionizing Collisions, Ronald E. Olson

Physics Faculty Research & Creative Works

Classical-trajectory Monte Carlo calculations are used to determine the velocity and angular dependence of the electron ionized in the H++HH++H++e- collision. The energy range studied is 40200 keV. At energies E60 keV, ionized electrons with velocities that are near one-half (v/2) the relative velocity v of the collision dominate the electron spectra. At higher energies the maximum position of the ionized electrons shifts and is found centered about the target nucleus. © 1986 The American Physical Society.

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Resonant Charge Transfer In Symmetric Alkali-Ion Alkali-Atom Collisions, F. K. Men, M. Kimura, Ronald E. Olson Jan 1986

Resonant Charge Transfer In Symmetric Alkali-Ion Alkali-Atom Collisions, F. K. Men, M. Kimura, Ronald E. Olson

Physics Faculty Research & Creative Works

Resonant charge transfer in alkali-ion alkali-atom collisions is investigated by using the molecular-orbital expansion method incorporating the use of electron translation factors. Molecular wave functions and eigen energies are obtained by the pseudopotential method. Molecular properties, Re, De, and e, obtained in the present calculation are in good accord with other recent theoretical results, as well as spectroscopic measurements. Three-state close-coupling calculations reproduce the positions of the maxima and minima in the oscillatory structure seen experimentally in the resonant-charge-transfer cross sections for the Li2 + and Cs2 + systems. The magnitude of the total cross sections and their velocity dependence …

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Energy Transfer Collisions Between Vibrationally Excited Molecular Nitrogen And Atoms, Laird D. Schearer Jan 1986

Energy Transfer Collisions Between Vibrationally Excited Molecular Nitrogen And Atoms, Laird D. Schearer

Physics Faculty Research & Creative Works

Chemiluminescent reactions between metastable states of molecular nitrogen and atoms are used to determine the vibrational temperatures of these Non radiating molecular systems. The excitation rates of Na, Mg, Cd, and Zn are used to obtain the vibrational temperature of N2(X 1Σ) and N2(A 3Σ) states in a fast-flowing nitrogen afterglow. The exponential dependence of the intensities of the emission from atoms excited by the energy transfer collisions on the energy of the level yields vibrational temperatures on the order of 3100 K. We also report the presence of apparent strong selection rules on the total spin of the system …

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