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Physics Faculty Publications

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Articles 2101 - 2130 of 2156

Full-Text Articles in Physical Sciences and Mathematics

Optical Pulse Compression In A Cholesteric Liquid Crystal, D. N. Ghosh Roy, D.V.G.L.N. Rao, H. Bronk Sep 1981

Optical Pulse Compression In A Cholesteric Liquid Crystal, D. N. Ghosh Roy, D.V.G.L.N. Rao, H. Bronk

Physics Faculty Publications

A 20‐ns laser pulse is compressed to nearly 2.5 ns in a 10‐cm‐long sample of liquid‐crystal cholesteryl oleate in the isotropic phase. Pulse compression in a length as short as only 5 cm has been observed. A semiquantitative explanation is given in terms of stimulated Brillouin scattering.

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Negative Acceleration Components For A Relativistic Particle, James A. Lock Jul 1981

Negative Acceleration Components For A Relativistic Particle, James A. Lock

Physics Faculty Publications

Newtonian acceleration is considered in the light of special relativity theory with the result that the component of acceleration in the direction of an arbitrary applied force is always positive.(AIP)

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Observation Of The Transition From Semiconductor To High-Tc Superconductor In (Snxeu1-X)Ymo6s8 Under High Pressure, D. W. Harrison, K. C. Lim, J. D. Thompson, C. Y. Huang, Paul D. Hambourger, H. L. Luo Jan 1981

Observation Of The Transition From Semiconductor To High-Tc Superconductor In (Snxeu1-X)Ymo6s8 Under High Pressure, D. W. Harrison, K. C. Lim, J. D. Thompson, C. Y. Huang, Paul D. Hambourger, H. L. Luo

Physics Faculty Publications

Pressure-induced high-temperature superconductivity is observed in semiconducting (SnxEu1-x)yMo6S8, where 0<~x<~0.1 and y=1.0 and 1.2, having a carrier concentration ≃1019/cm3 at 4.2 K as determined from Hall-effect measurements. Above a threshold pressure ≃7 kbar, superconductivity appears with dTc/dP≃2 K/kbar. The maximum superconducting temperature (Tc∼10 K), reached at ∼ 12 kbar, represents the highest pressure-induced Tc in any semiconductor. For P>~13 kbar, the temperature-dependent resistance appears metallic.

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Hall Effect At High Pressure In (Snxeu1-X)1.2mo6s8, Paul D. Hambourger, C. Y. Huang, H. L. Luo Jan 1981

Hall Effect At High Pressure In (Snxeu1-X)1.2mo6s8, Paul D. Hambourger, C. Y. Huang, H. L. Luo

Physics Faculty Publications

No abstract provided.

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O++ In The Venusian Ionosphere, Jane L. Fox, G. A. Victor Jan 1981

O++ In The Venusian Ionosphere, Jane L. Fox, G. A. Victor

Physics Faculty Publications

It is shown that the revised photochemical theory for O++ in the earth's ionopshere, where double photoionization of O is the dominant source, is consistent with recent O++ measurements on Venus. A rate coefficient of 1.5 × 10−10 cm³ s−1 for O++ + O is obtained, and the possible importance of O++ chemistry on minor atomic ions and airglow emissions is explored.

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An Experiment In Discovery, Daniel J. Steck Dec 1980

An Experiment In Discovery, Daniel J. Steck

Physics Faculty Publications

No abstract provided.

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Automation Of A Popular Monochromator, David C. Look, J. W. Farmer, R. N. Ely Jul 1980

Automation Of A Popular Monochromator, David C. Look, J. W. Farmer, R. N. Ely

Physics Faculty Publications

A wavelength‐scan and intensity‐control system for a widely‐used, high‐intensity monochromator is described. The wavelength scan is bidirectional and variable speed, and may be controlled manually or by TTL logic from a computer. The intensity control is effected by use of a programmable dc power supply and D–A converter. Various filters are described which allow an intensity of up to 2×1014 photons/cm2 s to be achieved in a 1 cm×3 cm area over a wavelength range 0.76–2.50 μm, at 0.07 μm bandwidth, with a single grating. (A lesser intensity is available to 3.4 μm.) This wide range is made …

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Electron Irradiation Defects In N-Type Gaas, J. W. Farmer, David C. Look Apr 1980

Electron Irradiation Defects In N-Type Gaas, J. W. Farmer, David C. Look

Physics Faculty Publications

We have studied the production and annealing of defects produced by 1-MeV electron irradiation of n-type GaAs. Two of these defects lie at 0.15 and 0.31 eV from the conduction band, respectively; in addition, there is at least one acceptor much closer to the valence band. The carrier-removal rate depends upon sample purity but is independent of the irradiation flux. The removal rate is also highly dependent upon the position of the the Fermi level, an effect which is considered in some detail. At about 200°C, the defects recover in two stages, with the respective recovery rates given by λ …

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Hall-Coefficient And Resistivity At High Pressure In 1t-Tas2, Paul D. Hambourger, F. J. Disalvo Jan 1980

Hall-Coefficient And Resistivity At High Pressure In 1t-Tas2, Paul D. Hambourger, F. J. Disalvo

Physics Faculty Publications

No abstract provided.

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Characterization Of Phase Transitions In Vanadium Deuterides, R. L. Tober, Gust Bambakidis Jan 1980

Characterization Of Phase Transitions In Vanadium Deuterides, R. L. Tober, Gust Bambakidis

Physics Faculty Publications

No abstract provided.

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Continental Drift, Tectonics, And Joshua, Joel W. Block Jan 1980

Continental Drift, Tectonics, And Joshua, Joel W. Block

Physics Faculty Publications

The Bible has served as a source of spiritual inspiration for many centuries. It has been used as a text in the academic disciplines of history, geography, archeology, literature, law, language, and health, as well as in theology. Yet this multipurpose manuscript has been virtually ignored as an earth science reference It is this writer's intent to demonstrate the Bible's value as a geological resource.

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Model For Fe2+ Intracenter-Induced Photoconductivity In Inp: Fe, David C. Look Nov 1979

Model For Fe2+ Intracenter-Induced Photoconductivity In Inp: Fe, David C. Look

Physics Faculty Publications

We have observed a broad, room-temperature photoconductivity band, with a peak at 0.44 eV, in Fe-doped InP. This band is attributed to an Fe2+ intracenter optical excitation, followed by a thermal excitation to the conduction band. We derive a photoconductivity expression which takes into account optical and thermal transitions between impurity ground and excited states, within the band gap, and the conduction band. The parameters yielded by the model include a thermal excitation prefactor of 1×1011 sec-1, an electron capture cross section of 1×10-15 cm2, a spontaneous recombination coefficient of 1×106 sec …

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Physical Consequences Of Anomalies In Nonlocal Potential Problems, L. L. Foldy, James A. Lock Aug 1979

Physical Consequences Of Anomalies In Nonlocal Potential Problems, L. L. Foldy, James A. Lock

Physics Faculty Publications

An s-wave two-body separable potential may give rise to several phenomena which are absent for nonsingular local potentials. We examine the physical implications of a well known example of such phenomena, the continuum bound state, as well as of two lesser known anomalies, the so-called positive energy spurious state and negative energy bound states with improper long-range behavior. By examining these anomalies in light of Levinson's theorem, Wigner's phase shift inequality, and the effect of a perturbation on the anomalous states by their insertion in a three-body scattering situation, we find in agreement with previous studies that the continuum bound …

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Type Conversion In Electron‐Irradiated Gaas, J. W. Farmer, David C. Look Apr 1979

Type Conversion In Electron‐Irradiated Gaas, J. W. Farmer, David C. Look

Physics Faculty Publications

The unambiguous type conversion of GaAs by electron irradiation is reported here for the first time. Several high‐quality n‐type vapor‐phase epitaxial layers (ρ?3 Ω cm and μ?7000 cm2/V sec at 300 K) were converted by 1‐MeV electrons to high‐quality p‐type layers (ρ?30 Ω cm and μ?400 cm2/V sec). Temperature‐dependent Hall‐effect data show energy levels at 0.5, 0.3, and about 0.1 eV above the valence band. Evidence is presented to indicate that the failure of some of our samples (and, perhaps, other samples reported in the literature) to convert to low‐r …

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Electron Transport In Se-Doped Lt-Tas2, Paul D. Hambourger, F. J. Disalvo Jan 1979

Electron Transport In Se-Doped Lt-Tas2, Paul D. Hambourger, F. J. Disalvo

Physics Faculty Publications

No abstract provided.

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Ionization, Luminosity, And Heating Of The Upper Atmosphere Of Mars, Jane L. Fox, Alexander Dalgarno Jan 1979

Ionization, Luminosity, And Heating Of The Upper Atmosphere Of Mars, Jane L. Fox, Alexander Dalgarno

Physics Faculty Publications

A model based upon Viking data is constructed of the Martian atmosphere, and a comprehensive quantitative discussion is given of the measurements of the ultraviolet dayglow. A detailed assessment is made of the heating of the neutral and ionized components of the atmosphere arising from the absorption of ultraviolet solar radiation.

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Electronic Structure Calculation Of Icosahedral B-12, R. P. Wagner, Gust Bambakidis Jan 1979

Electronic Structure Calculation Of Icosahedral B-12, R. P. Wagner, Gust Bambakidis

Physics Faculty Publications

No abstract provided.

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Electrical Resistivity Studies Of Order-Disorder Phenomena In V2h And V2d, Gust Bambakidis, M. W. Pershing, R. C. Bowman Jan 1979

Electrical Resistivity Studies Of Order-Disorder Phenomena In V2h And V2d, Gust Bambakidis, M. W. Pershing, R. C. Bowman

Physics Faculty Publications

No abstract provided.

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Role Of Low-Energy Two-Body Virtual States In Three-Particle Scattering Situations, James A. Lock Dec 1978

Role Of Low-Energy Two-Body Virtual States In Three-Particle Scattering Situations, James A. Lock

Physics Faculty Publications

A model three-particle scattering situation consisting of a projectile incident on a target bound to a residual core was considered under the assumptions that there was a low-energy virtual state in the projectile-target channel, that the projectile and core did not interact, and that the projectile-target and target-core interactions were s-wave separable interactions. When the appropriate Faddeev equations were solved by inversion, an enhancement was found in the three-body elastic cross section for virtual state energies less than or comparable to the target-core binding energy. This enhancement was determined to be kinematical in origin.

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Infrared Spectral Detectivity Of Cr‐Doped Gaas, David C. Look Jun 1978

Infrared Spectral Detectivity Of Cr‐Doped Gaas, David C. Look

Physics Faculty Publications

The room‐temperature spectral detectivity of Cr‐doped GaAs has been examined in the impurity excitation region out to 1.7 μ, a range which includes the wavelengths of several important lasers as well as low‐loss optical fibers. The results include values of D∗ greater than 1011 cm Hz1/2/W in the photoconductive mode, and 1010 cm Hz1/2/W in the photomagnetoelectric mode. Small carrier lifetimes, ∼10−8 sec, offer the potential of high‐speed operation; however, the measured response times are much larger, ∼10−3–10−2 sec, because of very high input impedances. Formulas are presented to …

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Isospin Forbidden And Allowed Reactions 16O(Α,Α0)160 And 160(Α,Γ)20Ne, Daniel J. Steck Mar 1978

Isospin Forbidden And Allowed Reactions 16O(Α,Α0)160 And 160(Α,Γ)20Ne, Daniel J. Steck

Physics Faculty Publications

Six 20Ne levels have been investigated in detail via the 16O+α channel between 6.9≤Eα≤10.2 MeV. Level parameters for states at Ex(20Ne)=10.264±0.008, 11.077±0.008, 11.259±0.008, 11.552±0.008,12.237±0.008, and 12.390±0.008 MeV have been extracted from γ decay properties and phase shift analysis of the elastic scattering. With the exception of the 11.552 and 12.39 MeV states, these levels display primarily TT=0 states, several other weak γ decaying resonances were observed at 11.97 ± 0.04, 12.05 ± 0.04, and 12.49 ± 0.02 MeV but were not studied in detail. Charge dependent matrix elements (4-120 …

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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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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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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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Astronomy And The Bible: Joshua's Long Day, Joel W. Block Nov 1977

Astronomy And The Bible: Joshua's Long Day, Joel W. Block

Physics Faculty Publications

The Bible has served as a multipurpose text for thousands of years. However, the Bible has been ignored in the area of astronomy. Several teaching points can be demonstrated using the Bible stories and modern astronomical principles.

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Fermi-Surface Topology Of 2h-Tase2 At 4.2k, Paul D. Hambourger Feb 1977

Fermi-Surface Topology Of 2h-Tase2 At 4.2k, Paul D. Hambourger

Physics Faculty Publications

The magnetoresistance of single-crystal 2H-TaSe2 in the commensurate charge-density-wave state has been measured at 4.2 K in magnetic fields up to 48 kG. The results indicate that the Fermi surface supports open orbits parallel to the [0001] direction for all orientations of magnetic field in the (0001) plane. No evidence of open orbits in other directions was observed.

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Search For Volume Anomaly In Paramagnetic Zrzn2, Paul D. Hambourger Jan 1977

Search For Volume Anomaly In Paramagnetic Zrzn2, Paul D. Hambourger

Physics Faculty Publications

No abstract provided.

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Positron Annihilation In Copper, K. White, W. H. Rickles, Thomas Listerman Jan 1977

Positron Annihilation In Copper, K. White, W. H. Rickles, Thomas Listerman

Physics Faculty Publications

No abstract provided.

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A Geomagnetic Survey Of Greene County, Ohio, V. E. D. Obot, Paul J. Wolfe Jan 1977

A Geomagnetic Survey Of Greene County, Ohio, V. E. D. Obot, Paul J. Wolfe

Physics Faculty Publications

No abstract provided.

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