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Articles 35101 - 35130 of 36531

Full-Text Articles in Physical Sciences and Mathematics

Calculations Of Ion‐Ion Recombination Rates At High Pressures, J. M. Wadehra, J. N. Bardsley Jan 1978

Calculations Of Ion‐Ion Recombination Rates At High Pressures, J. M. Wadehra, J. N. Bardsley

Physics and Astronomy Faculty Research Publications

The classical theory of ion‐ion recombination in gases of high density is extended to allow for arbitrary ratios of the masses of the three species involved. Calculations are performed for the recombination of Ar+, Ar+ 2, Kr+, and Kr+ 2 ions with F− and of Hg+ and Ar+ with Cl− in an argon gas. The effective two‐body rates peak between 2×10−6 and 3×10−6 cm3 sec−1 at pressures above 1 atm.

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Direct Observation Of Pulsed Third Sound Mass Displacement Waves In Unsaturated Superfluid 4he Films, Robert Hallock, J. S. Brooks, F. M. Ellis Jan 1978

Direct Observation Of Pulsed Third Sound Mass Displacement Waves In Unsaturated Superfluid 4he Films, Robert Hallock, J. S. Brooks, F. M. Ellis

Robert Hallock

We report direct observation of pulsed third-sound film thickness oscillations in unsaturated superfluid 4He films using a capacitance technique. Simultaneous measurements of accompanying temperature oscillations allow the first study of the relative amplitudes of these oscillations and the results are in reasonable agreement with the theory of Bergman although some discrepancies are noted.

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Interpretation Emphasis In Exploration Geophysics, Paul J. Wolfe, Benjamin H. Richard Jan 1978

Interpretation Emphasis In Exploration Geophysics, Paul J. Wolfe, Benjamin H. Richard

Physics Faculty Publications

No abstract provided.

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Note On The Constant Coupling Approximation, M. Jursich, Harry A. Brown Jan 1978

Note On The Constant Coupling Approximation, M. Jursich, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Design And Construction Of An Inexpensive Anechoic Chamber, Charles E. Hughes Jr. Jan 1978

Design And Construction Of An Inexpensive Anechoic Chamber, Charles E. Hughes Jr.

Journal of the Arkansas Academy of Science

No abstract provided.

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Two-Step Photoionization Of Potassium Atoms, Kaare J. Nygaard, Robert J. Corbin, James A. Jones Jan 1978

Two-Step Photoionization Of Potassium Atoms, Kaare J. Nygaard, Robert J. Corbin, James A. Jones

Physics Faculty Research & Creative Works

The cross section for photoionization of potassium atoms in the 4P2 states has been measured in a triple-crossed-beam experiment. © 1978 The American Physical Society.

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Production Of Cl⁻·Hcl Cluster Ions In Hcl-N2 Mixtures, R. J. Corbin, Kaare J. Nygaard, William R. Snow, Laird D. Schearer Jan 1978

Production Of Cl⁻·Hcl Cluster Ions In Hcl-N2 Mixtures, R. J. Corbin, Kaare J. Nygaard, William R. Snow, Laird D. Schearer

Physics Faculty Research & Creative Works

A drift-tube-mass-spectrometer apparatus has been used to study the production of Cl-·HCl cluster molecules in HCl-N2 mixtures. The concentration of HCl was 730 ppm and the total pressure ranged from 0.1-5 Torr. The primary ion Cl- is produced mainly by dissociative attachment of HCl and is converted to a cluster ion in a three-body collision. The rate of formation of the cluster ion is k2≃ 10-25 cm6/sec at E/N=12 Td. © 1978 American Institute of Physics.

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Absolute Doubly Differential Cross Sections For Ejection Of Secondary Electrons From Gases By Electron Impact. Ii. 100-500-Ev Electrons On Neon, Argon, Molecular Hydrogen, And Molecular Nitrogen, R. D. Dubois, M. Eugene Rudd Jan 1978

Absolute Doubly Differential Cross Sections For Ejection Of Secondary Electrons From Gases By Electron Impact. Ii. 100-500-Ev Electrons On Neon, Argon, Molecular Hydrogen, And Molecular Nitrogen, R. D. Dubois, M. Eugene Rudd

M. Eugene Rudd Publications

Absolute doubly differential cross sections for secondary electron production by electron impact have been measured for static gas targets of neon, argon, hydrogen, and nitrogen. Electron impact energies were from 100 to 500 eV. An electrostatic analyzer was used to analyze secondary electrons with energies between 4 eV and the primary electron energy minus the first ionization potential of the target. Angles of emission were 10° to 150°. The present data agree well with the data of Opal, Beaty, and Peterson at 90° but, as was observed previously for helium, the agreement becomes increasingly poorer for larger and smaller angles. …

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Studies Of The Temporary Anion States Of Unsaturated Hydrocarbons By Electron Transmission Spectroscopy, Kenneth D. Jordan, Paul Burrow Jan 1978

Studies Of The Temporary Anion States Of Unsaturated Hydrocarbons By Electron Transmission Spectroscopy, Kenneth D. Jordan, Paul Burrow

Paul Burrow Publications

The concept of occupied and unoccupied orbitals has provided a useful means for visualizing many of the most important properties of molecular systems. Yet, there is a curious imbalance in our experimental knowledge of the energies of occupied and unoccupied orbitals. Whereas photoelectron spectroscopy has provided a wealth of data on positive ion states and has established that they can be associated, within the context of Koopmans’ theorem, with the occupied orbitals of the neutral molecule, the corresponding information for the negative ion states, associated with the normally unoccupied orbitals, is sparse. In part this reflects the experimental difficulties connected …

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Evolved Contact Systems Of Spectral Type A: Au Puppis, V535 Arae, And V1073 Cygni, Kam-Ching Leung, Donald P. Schneider Jan 1978

Evolved Contact Systems Of Spectral Type A: Au Puppis, V535 Arae, And V1073 Cygni, Kam-Ching Leung, Donald P. Schneider

Department of Physics and Astronomy: Faculty Publications

The photoelectric observations of AU Pup, V535 Ara, and V1073 Cyg were reanalyzed with Wilson and Devinney's approach. All three systems are found to be contact configurations. AU Pup has an unusually large degree of overcontact, 72%. V1073 Cyg is found to be an evolved contact system since the radius of the primary is twice that of a zero-age main-sequence star of corresponding mass. All three systems are found to be evolved according to their locations in the period-spectral-type diagram. Improved photometric parameters are reported for all three systems.

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On The Classical‐Spin Model Of Amorphous Ferromagnets, Harry A. Brown Jan 1978

On The Classical‐Spin Model Of Amorphous Ferromagnets, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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The Bethe‐Peierls‐Weiss Approximation For Amorphous Magnets, Harry A. Brown Jan 1978

The Bethe‐Peierls‐Weiss Approximation For Amorphous Magnets, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Time Resolved Fluorescence Of The A ²∑+ State Of Gef, R. (Richard) A. Anderson, L. Hanko, S. J. Davis Jan 1978

Time Resolved Fluorescence Of The A ²∑+ State Of Gef, R. (Richard) A. Anderson, L. Hanko, S. J. Davis

Physics Faculty Research & Creative Works

The radiative lifetime and quenching rates for the A 2∑ + state of GeF have been measured in the flame of GeH 4+F2 by pulsed laser induced fluorescence. In addition, the radiative lifetime of the ν′=0 level of the A 2∑ + state of SiF has been measured in the flame of SiH 4+F2. Quenching rates for He, N2, and SF 6 on GeF A 2∑ and He on SiF A 2∑ have also been determined. The average zero pressure lifetime of ν′=0, 1, and 2 levels of A 2∑ GeF is 990±100 nsec. The zero-pressure lifetime of the A …

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A Xenon Ion Pumped Blue Dye Laser, D. W. Fahey, Laird D. Schearer Jan 1978

A Xenon Ion Pumped Blue Dye Laser, D. W. Fahey, Laird D. Schearer

Physics Faculty Research & Creative Works

A pulsed xenon ion laser with an output power of 5 kW at 364.5 nm has been used as a pump source for several blue dyes. Broadband conversion efficiencies exceed 20 percent. The use of a birefringent filter provides tunable output in the blue region of the spectrum with a bandwidth of 0.08 nm and a pulse width of 120 ns. © 1978 IEEE

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Plasma Lines In The Auroral E Layer, Vincent B. Wickwar Jan 1978

Plasma Lines In The Auroral E Layer, Vincent B. Wickwar

All Physics Faculty Publications

The first successful measurements of plasma lines in the auroral E layer were made in January 1976 using the Chatanika incoherent scatter radar. Although they are considerably weaker than the signal from the ion component, the plasma line signals are readily detectable. Typical signal-to-noise ratios were about 4%. In this series of experiments, plasma lines were observed in the interval between 3.8 and 6.0 MHz, which corresponds to phase energies between 0.55 and 1.4 eV. They were found between 98 and 134 km; the derived plasma wave intensities varied between 0.06 and 1.0 eV, and the enhancements between 4 and …

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Photoelectron Flux Build-Up In The Plasmasphere, G P. Mantas, Herbert C. Carlson, Vincent B. Wickwar Jan 1978

Photoelectron Flux Build-Up In The Plasmasphere, G P. Mantas, Herbert C. Carlson, Vincent B. Wickwar

All Physics Faculty Publications

Processes which confine photoelectrons to the plasmasphere (e.g., collisional backscattering from the thermosphere and magnetic trapping due to pitch angle redistribution through Coulomb collisions in the plasmasphere) tend to increase the steady state photoelectron flux in the plasmasphere above the amplitude level that would otherwise have been attained. Theoretical calculations are presented of steady state photoelectron fluxes in the plasmasphere, for specified atmospheric and ionospheric conditions. (Observational plasma line intensity data for these conditions exist and will be compared elsewhere.) General features of the angular distribution are presented and compared with observations. The transparency of the plasmasphere and the backscattering …

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Time Lag In Diffusion-Controlled Nucleation, David Peak Jan 1978

Time Lag In Diffusion-Controlled Nucleation, David Peak

All Physics Faculty Publications

Nucleation occurring in the presence of a dense solvent is accompanied by spatial correlations among the reactant clusters and monomers which affect the aggregation rates. The classical theory of nucleation, which does not take such correlations into account, overestimates the observed nucleation rate and underestimates the time lag in condensed systems. An explicit expression for the time lag in diffusion‐controlled nucleation is derived. Values associated with miscibility gap experiments differ from the classical predictions by factors of 5 to 10.

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Radar Observations Of Two Dimensional Turbulencein The Equatorial Electrojet, 3. Nighttime Observations Of Type I Waves, D. T. Farley, Bela G. Fejer, B. B. Balsley Jan 1978

Radar Observations Of Two Dimensional Turbulencein The Equatorial Electrojet, 3. Nighttime Observations Of Type I Waves, D. T. Farley, Bela G. Fejer, B. B. Balsley

Bela G. Fejer

The large vertically directed 50-MHz radar at Jicamarca has sufficient sensitivity to study nighttime echoes from the equatorial electrojet in detail with good resolution. Here we concentrate on type 1 (‘two-stream’) echoes. We find that (1) these echoes sometimes dominate the spectrum (which is never the case in daytime for a vertically directed radar), (2) they are observed over a much wider range of altitudes than they are during daytime, (3) they show an asymmetry which reverses from day to night (downgoing waves are more common at night), (4) the magnitude of the mean Doppler shift appears to increase somewhat …

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Magnetoresistance Of 1t-Tase2, Paul D. Hambourger, F. J. Disalvo Jan 1978

Magnetoresistance Of 1t-Tase2, Paul D. Hambourger, F. J. Disalvo

Physics Faculty Publications

No abstract provided.

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The Coma/A1367 Supercluster And Its Environs, Stephen A. Gregory, Laird A. Thompson Jan 1978

The Coma/A1367 Supercluster And Its Environs, Stephen A. Gregory, Laird A. Thompson

Department of Physics and Astronomy: Faculty Publications

The three-dimensional galaxy distribution in the region of space surrounding the two rich clusters Coma and A1367 is analyzed by using a nearly complete redshift sample of 238 galaxies with mp < 15.0 in a 260 degree2 region of the sky; 44 of these redshifts are reported here for the first time. We find that the two clusters are enveloped in a common supercluster which also contains four groups and a population of isolated galaxies. The least dense portions of the Coma/A1367 supercluster have a density which is approximately 6 times that of the Local Supercluster in the regions of our own Galaxy. In …

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Spin Correlations In Actinide Materials: A Neutron Study Of Usb, G. H. Lander, S. K. Sinha, Don M. Sparlin, O. Vogt Jan 1978

Spin Correlations In Actinide Materials: A Neutron Study Of Usb, G. H. Lander, S. K. Sinha, Don M. Sparlin, O. Vogt

Physics Faculty Research & Creative Works

Measurements have been made of the short-range spin correlations in USb, a metallic compound that orders antiferromagnetically. The system has no transverse fluctuations, and the longitudinal spin correlations are anisotropic, showing stronger interactions within the ferromagnetic sheets than between them. The results of this and other experiments can be understood with simple concepts involving the bonding of 5f electrons. © 1978 The American Physical Society.

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Proton Spin-Lattice Relaxation And Methyl Group Rotation, Peter A. Beckmann, C. I. Ratcliffe, B. A. Dunell Jan 1978

Proton Spin-Lattice Relaxation And Methyl Group Rotation, Peter A. Beckmann, C. I. Ratcliffe, B. A. Dunell

Physics Faculty Research and Scholarship

Proton spin-lattice relaxation times have been measured at 16, 31, and 59 MHz in 4-methyl-2,6-ditertiarybutyl phenol between 80 K and its melting point, 340 K. The variation of T1 with temperature shows too distinct minima. The lower-temperature minimum has been analyzed in terms of relaxation by reorientation of four of the six t-butyl methyl groups with an average apparent activation energy of about 2.4 kcal mole−1 (104 meV molecule−1). The higher-temperature minimum has been analyzed in terms of relaxation by reorientation of the t-butyl groups about their C3 axes with four of the six t-butyl methyl groups reorienting …

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Electron Spin Relaxation And Tunnelling Methyl Groups, Peter A. Beckmann, S. Clough Jan 1978

Electron Spin Relaxation And Tunnelling Methyl Groups, Peter A. Beckmann, S. Clough

Physics Faculty Research and Scholarship

The energy transfer has been studied between free radicals and nearby tunnelling methyl groups near the resonant condition that the electron Larmor frequency and the methyl tunnelling frequency are equal. The measurements were made in a gamma -irradiated single crystal of 4-methyl-2,6-ditertiarybutylphenol (MDBP) at 4.2K and consisted of saturating the ESR signal and observing its return to equilibrium. This has been done at eleven ESR frequencies in the range 8.97< nu s<0.63 GHz and for saturation times of 5, 50 and 200 s. A theoretical model has been developed for the non-exponential recovery which assumes that all the 4-methyl groups of the molecules surrounding a free radical have the same tunnelling rotation frequency nu t and that the only coupling between the electrons and the methyl groups is the intermolecular dipole-dipole interaction.

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Electrically-Induced Shifts Of The Gallium Arsenide Nuclear Spin Levels, Katherine Ann. Dumas Jan 1978

Electrically-Induced Shifts Of The Gallium Arsenide Nuclear Spin Levels, Katherine Ann. Dumas

Dissertations, Theses, and Masters Projects

No abstract provided.

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Semiclassical Calculation Of Vibrational Energy Levels Of Nonseparable Systems, Randall T. Swimm Jan 1978

Semiclassical Calculation Of Vibrational Energy Levels Of Nonseparable Systems, Randall T. Swimm

Dissertations, Theses, and Masters Projects

No abstract provided.

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Theory Of Solid State Muonsr Experiments: Positive Muon Hyperfine Fields And Trap-Limited Spin Depolarization, Ram Lal Munjal Jan 1978

Theory Of Solid State Muonsr Experiments: Positive Muon Hyperfine Fields And Trap-Limited Spin Depolarization, Ram Lal Munjal

Dissertations, Theses, and Masters Projects

No abstract provided.

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Gamma Ray Radiation Studies Of Undoped Gaas, William P. Winfree Jan 1978

Gamma Ray Radiation Studies Of Undoped Gaas, William P. Winfree

Dissertations, Theses, and Masters Projects

No abstract provided.

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Studies Of Negative Ion-Atom Scattering At Low Collision Energies, Barry T. Smith Jan 1978

Studies Of Negative Ion-Atom Scattering At Low Collision Energies, Barry T. Smith

Dissertations, Theses, and Masters Projects

No abstract provided.

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Impurity Photomagnetoelectric Effect: Application To Semi-Insulating Gaas, David C. Look Dec 1977

Impurity Photomagnetoelectric Effect: Application To Semi-Insulating Gaas, David C. Look

Physics Faculty Publications

The theories of the photomagnetoelectric (PME) and photoconductivity (PC) effects in semiconductors are extended to include unequal excitation rates of holes and electrons, as might be expected from impurity photo-excitation. The results are applied to two semi-insulating Cr-doped GaAs crystals, which exhibit mixed conductivity. It is seen that the PC and PME effects give complementary information on the holes and electrons. In the impurity excitation region the PME current responds strongly to changes in the absorption coefficient, and provides a convenient way to study this quantity.

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The Electrical Characterization Of Semi‐Insulating Gaas: A Correlation With Mass‐Spectrographic Analysis, David C. Look Dec 1977

The Electrical Characterization Of Semi‐Insulating Gaas: A Correlation With Mass‐Spectrographic Analysis, David C. Look

Physics Faculty Publications

The room‐temperature electrical properties of 28 semi‐insulating GaAs crystals have been determined by using a mixed‐conductivity analysis. It is shown that for most of these samples, such an analysis gives good accuracy for the electron mobility μn and electron concentration n, but poorer accuracy for the hole mobility μp, hole concentration p, and intrinsic concentration ni. The intrinsic concentration is determined at 296 °K to be ni ≈ (1.7±0.4) ×106 cm−3, which compares favorably with the theoretical value deduced from the band gap and the effective masses. From a …

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