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Articles 35641 - 35670 of 36524
Full-Text Articles in Physical Sciences and Mathematics
The 6300Å Predawn Enhancement: Excitation By Protoelectrons From The Magnetic Conjugate Point, Vincent B. Wickwar
The 6300Å Predawn Enhancement: Excitation By Protoelectrons From The Magnetic Conjugate Point, Vincent B. Wickwar
All Physics Faculty Publications
Incoherent scatter and tilting filter photometer data from Arecibo Observatory were combined to search for a contribution to the 6300 Å predawn enhancement due to impact excitation by photoelectrons from the magnetic conjugate point. Prior to about 105° conjugate solar zenith angle, calculations of the 6300 Å intensities due to dissociative recombination gave good agreement with the observed intensities. Then, with the arrival of conjugate photoelectrons (confirmed by plasma line enhancements), the observed intensities rose above the calculated, the difference increasing until a plateau was achieved at a conjugate solar zenith angle of about 95°. The difference or residual intensity …
Diffusion-Controlled Reaction Kinetics, David Peak, J W. Corbett
Diffusion-Controlled Reaction Kinetics, David Peak, J W. Corbett
All Physics Faculty Publications
The theory of diffusion-controlled correlated reaction kinetics is developed for the radiation boundary condition (RBC) at the reaction surface. Limited only by the assumptions of purely radial spatial dependence, of a spherical reaction surface, and of continuum diffusion, these results comprise a complete solution for these kinetics. The limiting solutions are obtained for the case of the Smoluchowski boundary condition (SBC) at the reaction surface; numerical solutions are presented, as are the analytic forms of certain limiting cases. The initial recovery for the RBC is linear in time, whereas for the SBC it is well known to be proportional to …
Diffusiophoretic Forces Between Juxtaposed Atmospheric Particles, Allen L. Williams
Diffusiophoretic Forces Between Juxtaposed Atmospheric Particles, Allen L. Williams
Doctoral Dissertations
"The role of diffusiophoretics and Stefan flow in droplet growth by accretion and in-cloud scavenging is examined. A calculation is made for the diffusive forces between two juxtaposed spheres one or both of which are undergoing diffusional growth and the influence of the diffusive force on the trajectories of two spheres, assumed to obey the creeping flow equations is found. The results are: a) the diffusiophoretic force between two water droplets is zero. b) the diffusiophoretic force between a spherical ice particle and a water droplet, although non-zero, is too small to appreciably influence the fall trajectories. c) the diffusiophoretic …
The Eikonal Distorted Wave Born Approximation For The Excitation Of Hydrogen By Impact With Hydrogen And Helium In The Intermediate Energy Range, Richard Homer Shields
The Eikonal Distorted Wave Born Approximation For The Excitation Of Hydrogen By Impact With Hydrogen And Helium In The Intermediate Energy Range, Richard Homer Shields
Doctoral Dissertations
"An eikonal approximation is applied to atom-atom scattering in the intermediate energy range. The theory and the form of the eikonal approximation are reviewed. Also a brief survey of previous theoretical methods for all energy ranges is included.
In particular, the differential and total cross sections for the excitation of hydrogen to the 2s and 2p states by impact on hydrogen and helium atoms have been calculated using the eikonal distorted wave Born approximation (DWBA) for the incident energy range of 2.25-100 keV. The eikonal DWBA differential cross sections are compared to the differential cross sections given by the first …
An Inexpensive Electrical Vacuum Feedthrough, D. R. Kastelein, Richard A. Anderson, Kaare J. Nygaard
An Inexpensive Electrical Vacuum Feedthrough, D. R. Kastelein, Richard A. Anderson, Kaare J. Nygaard
Physics Faculty Research & Creative Works
No abstract provided.
A Correction To Classical Homogeneous Nucleation Theory For Polar Molecules Exhibiting An Electric Double Layer At The Liquid Surface, Daniel R. White, James L. Kassner
A Correction To Classical Homogeneous Nucleation Theory For Polar Molecules Exhibiting An Electric Double Layer At The Liquid Surface, Daniel R. White, James L. Kassner
Physics Faculty Research & Creative Works
An oriented dipole surface layer is added to the classical liquid drop model of nucleation to account for the surface behavior of substances having polar nonsymmetrical molecules. The preliminary treatment of the change in free energy as given by Abraham is modified to include Fletcher's exponential decay of the degree of orientation. An additional correction for the excess binding energy due to the presence of a foreign molecule in the prenucleation cluster is included to account for the inflections observed in the experimental results of Allen and Kassner. The resulting free energy of formation is combined with the kinetic treatment …
Collisional Excitation Of N+ At 50 Kev, D. H. Crandall, G. York, V. Pol, John T. Park
Collisional Excitation Of N+ At 50 Kev, D. H. Crandall, G. York, V. Pol, John T. Park
Physics Faculty Research & Creative Works
The excitation spectrum of N+ has been observed by examining the energy lost by a 50- keV N+ beam passing through a He target. The spectrum exhibits dramatic features with large cross sections. Determination of the approximate ratio of metastable to ground-state ions in the primary ion beam has permitted measurement of excitation cross sections from both ground-state and metastable N+ ions colliding with He target atoms. © 1972 The American Physical Society.
Some Bonding Aspects Of Cobalt Ions In Phosphate Glasses, Tewfik Boutros Absi
Some Bonding Aspects Of Cobalt Ions In Phosphate Glasses, Tewfik Boutros Absi
Archived Theses and Dissertations
No abstract provided.
Gamma Decay Of States Excited By 300 And 600 Mev Protons On Targets Of Boron, Carbon, Nitrogen, Oxygen, Magnesium, And Calcium, Max David Holt
Gamma Decay Of States Excited By 300 And 600 Mev Protons On Targets Of Boron, Carbon, Nitrogen, Oxygen, Magnesium, And Calcium, Max David Holt
Dissertations, Theses, and Masters Projects
No abstract provided.
Nuclear-Spin Relaxation In Low-Density Molecular Hydrogen At Room Temperature, Peter A. Beckmann, E. Elliott Burnell, Krovvidi Lalita, Robin L. Armstrong, Kenneth E. Kisman, F. R. Mccourt
Nuclear-Spin Relaxation In Low-Density Molecular Hydrogen At Room Temperature, Peter A. Beckmann, E. Elliott Burnell, Krovvidi Lalita, Robin L. Armstrong, Kenneth E. Kisman, F. R. Mccourt
Physics Faculty Research and Scholarship
No abstract provided.
Observation Of The Influence Of Centrifugal Distortion Of The Methane Molecule On Nuclear Spin Relaxation In The Gas., Peter A. Beckmann, M. Bloom, E. E. Burnell
Observation Of The Influence Of Centrifugal Distortion Of The Methane Molecule On Nuclear Spin Relaxation In The Gas., Peter A. Beckmann, M. Bloom, E. E. Burnell
Physics Faculty Research and Scholarship
The spin–lattice relaxation time T1 was measured in gaseous CH4 as a function of density at room temperature between 0.006 and 7.0 amagats. T1 was found to pass through a minimum near 0.04 amagats in agreement with previous, less precise measurements. The spin–rotation interaction is the dominant relaxation mechanism in gaseous CH4. Since the spin–rotation constants are accurately known for CH4, the relaxation experiments provide a check on the theory of spin–lattice relaxation for spherical top molecules. In the conventional theory, it is assumed that the correlation function of the spin–rotation interaction is …
Observation Of The Influence Of Centrifugal Distortion Of The Methane Molecule On Nuclear Spin Relaxation In The Gas., Peter A. Beckmann, M. Bloom, E. E. Burnell
Observation Of The Influence Of Centrifugal Distortion Of The Methane Molecule On Nuclear Spin Relaxation In The Gas., Peter A. Beckmann, M. Bloom, E. E. Burnell
Physics Faculty Research and Scholarship
The spin–lattice relaxation time T1 was measured in gaseous CH4 as a function of density at room temperature between 0.006 and 7.0 amagats. T1 was found to pass through a minimum near 0.04 amagats in agreement with previous, less precise measurements. The spin–rotation interaction is the dominant relaxation mechanism in gaseous CH4. Since the spin–rotation constants are accurately known for CH4, the relaxation experiments provide a check on the theory of spin–lattice relaxation for spherical top molecules. In the conventional theory, it is assumed that the correlation function of the spin–rotation interaction is …
Ionization Mechanisms In Cesium, Yu Bong Hahn
Ionization Mechanisms In Cesium, Yu Bong Hahn
Doctoral Dissertations
"Autoionizing states in Cs between 12 and 20 eV have been studied by electron impact. The retarding-potential-difference(RPD) method was used to obtain an electron beam with energy spread of about 0.1 eV. To determine the threshold energies, inelastically scattered electrons were analyzed by the trapped-electron method. We have been able to identify about 20 levels, and the agreement with spectroscopic data is excellent. A peak appearing at 12.80 eV is probably due to the quartet states observed by Feldman and Novick"--Abstract, page 2. "The structure in the electron impact ionization cross section in cesium can be partially accounted for by …
Gas-To-Particle Conversions Of So₂-No₂-H₂O-Air Gas Mixtures Under Specific Uv Irradiation, James Leonard Fowler
Gas-To-Particle Conversions Of So₂-No₂-H₂O-Air Gas Mixtures Under Specific Uv Irradiation, James Leonard Fowler
Masters Theses
"In these series of experiments, mixtures of sulfur dioxide and nitrogen dioxide were irradiated in an absorption cell with monochromatic radiation found in the tropospheric region of the atmosphere. The irradiated mixtures were then introduced into a Wilson type cloud chamber to investigate the effects of these specific wavelength induced gas to particle conversions on nucleation. Results showed that sulfur dioxide could not be the sole agent for the formation of condensation nuclei. A mixture of sulfur dioxide and nitrogen dioxide irradiated at 3660 angstroms produced copious droplet formation identifying nitrogen dioxide as an integral reactant in nuclei production"--Abstract, page …
Nmr Studies Of Ammonium Dihydrogen Arsenate And High Temperature Transitions In The Potassium Dihydrogen Phosphate Group, John Young Nicholson
Nmr Studies Of Ammonium Dihydrogen Arsenate And High Temperature Transitions In The Potassium Dihydrogen Phosphate Group, John Young Nicholson
Dissertations, Theses, and Masters Projects
No abstract provided.
Low Energy Studies Of The Experimental Elastic Differential Cross-Sections For The Systems Proton-Helium, Proton-Neon And Signly Ionized Helium-Helium, William Guy Rich
Low Energy Studies Of The Experimental Elastic Differential Cross-Sections For The Systems Proton-Helium, Proton-Neon And Signly Ionized Helium-Helium, William Guy Rich
Dissertations, Theses, and Masters Projects
No abstract provided.
Time Resolved Measurements Of Droplet Growth In A Wilson Cloud Chamber, Michael Anthony Vietti
Time Resolved Measurements Of Droplet Growth In A Wilson Cloud Chamber, Michael Anthony Vietti
Doctoral Dissertations
"The growth rates of water drops in a Wilson expansion cloud chamber are measured with air, argon and helium as the carrier gas, in the size range of .5 to 10 microns. The drops growing in the supersaturated chamber exhibit oscillations in the scattered intensity as predicted by Mie theory. Scattered intensity is measured at 30 degrees to the He-Ne laser beam. Supersaturation ratios during growth range from S =1.2 to S = 3.5 for all three gases. The initial temperature is measured and the pressure is monitored continuously so that droplet growth theory can be compared with experiment. Three …
Radiative And Predissociative Lifetimes Of The A²Σ⁺ State Of Oh, Robert Allen Sutherland
Radiative And Predissociative Lifetimes Of The A²Σ⁺ State Of Oh, Robert Allen Sutherland
Doctoral Dissertations
"Lifetime measurements have been made on the A²Σ⁺ state of OH by the delayed coincidence technique in conjunction with an interrupted rf discharge through water vapor. Lifetimes are reported for rotational states up to K = 29 and K = 20 in the v = 0 and v = 1 vibrational levels respectively and on the unresolved levels of v =2. A predissociation, previously predicted from relative intensity measurements, resulting from a curve crossing by the repulsive 4 Σˉ state, was observed for the rotational states above K = 23 of v = 0, for those above K = 14 …
An Investigation Of One And Two State Molecular Systems Based On The Results Of Elastic Differential Scattering Experiments, Stephen Michael Bobbio
An Investigation Of One And Two State Molecular Systems Based On The Results Of Elastic Differential Scattering Experiments, Stephen Michael Bobbio
Dissertations, Theses, and Masters Projects
No abstract provided.
Time-Dependent Ionization Equilibrium And Line Radiation Under Flarelike Conditions, Menas Kafatos, W. H. Tucker
Time-Dependent Ionization Equilibrium And Line Radiation Under Flarelike Conditions, Menas Kafatos, W. H. Tucker
Mathematics, Physics, and Computer Science Faculty Articles and Research
The results of calculations for time-dependent ionization equilibrium and line emission are presented and compared with the values obtained under the assumption that steady-state conditions prevail. In the models considered, it is assumed that the electron density is constant (=10^3 cm^-3) and that the temperature increases by a factor of 10 from 3 x 10^6 K on timescales ranging from 100 to 300 s and decays back to 3 x 10^6 K on a timescale ranging from 600 to 1400 s. Ions of oxygen and silicon are considered, and it is found that the spectrum is softer during the rise …
Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach
Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach
David Sellmyer Publications
Magnetic breakdown in the basal plane of Be was investigated in fields up to 150 kG. Geometrical aspects of the open orbits caused by breakdown are discussed. An estimate of 30 kG for the characteristic breakdown field is obtained by applying the theory of Falicov et al. Shubnikov-de Haas frequency measurements are reported for the central-cigar cross section. These measurements are relevant to a recent conjecture that the Onsager-Lifshitz quantization scheme may be violated in the presence of magnetic breakdown.
A Study Of Isospin Mixing In 16O Near 18 Mev Exitation Energy, Li-Yun Kuo
A Study Of Isospin Mixing In 16O Near 18 Mev Exitation Energy, Li-Yun Kuo
Masters Theses
No abstract provided.
Average Solid Angle For Detection Of Photon Pair Positron Annihilations, Albert S. Ferrari
Average Solid Angle For Detection Of Photon Pair Positron Annihilations, Albert S. Ferrari
Masters Theses
No abstract provided.
Even-Parity Lattice Resonances And Anharmonicity In Ki: Ag+, Roger D. Kirby
Even-Parity Lattice Resonances And Anharmonicity In Ki: Ag+, Roger D. Kirby
Roger Kirby Publications
We report here the observation of four impurity-induced lattice resonances in KI:Ag+. In addition to the well-known T1u symmetry resonant mode at 17.3 cm-1, we have observed two even-parity resonant modes of A1g and Eg symmetries at 25 and 16.35 cm-1, respectively, and a T1u symmetry gap mode at 86.2 cm-1. The two even-parity modes were detected using far-infrared spectroscopic techniques with the sample in an external electric field. The field induces a strong mixing of the modes of opposite parity and results in large field-induced shifts. The Eg symmetry resonance has also been seen in the Raman spectrum of …
Mössbauer-Effect Studies Of The Phase Transitions In Antiferroelectric Pbzro₃ And Ferroelectric Pbti₀.₀₂Zr₀.₈O₃, James P. Canner, C. M. Yagnik, Robert Gerson, William Joseph James
Mössbauer-Effect Studies Of The Phase Transitions In Antiferroelectric Pbzro₃ And Ferroelectric Pbti₀.₀₂Zr₀.₈O₃, James P. Canner, C. M. Yagnik, Robert Gerson, William Joseph James
Physics Faculty Research & Creative Works
The Mössbauer spectra were studied for the antiferroelectric compound PbZrO3 and for the closely related ferroelectric PbTi0.2Zr0.8O3. In both cases, a substitution of 5-mol% BiFeO3 was made to permit the Mössbauer measurements. Little difference was found in the isomer shift in these compounds, whether they were in the ferroelectric, antiferroelectric, or cubic state, indicating that the bonding character is not affected by the transitions among the states. There was a pronounced and approximately equivalent dip in the recoil-free fraction at the Curie points of both the antiferroelectric and ferroelectric materials, associated with …
Thermionic Space Charge Oscillations, William Carl
Thermionic Space Charge Oscillations, William Carl
Masters Theses & Specialist Projects
Thermionic electrons emitted into a potential well will produce radiation, the frequency of which is determined by the transit time of the electrons. This paper investigates the case where radiation is produced by a vacuum tube in which two Pierce guns face each other, one acting as the emitter, the other acting as a reflector. Symmetry and the focusing of the electron beam by the Pierce guns make it possible to make an accurate determination of the electron transit time. Measurements showed that the period of the oscillation was 1.5 times the period required for an electron to traverse the …
Cellular Inactivation By Heavy Ions, Neutrons, And Pions, Robert Katz, S. C. Sharma, M. Hamayoonfar
Cellular Inactivation By Heavy Ions, Neutrons, And Pions, Robert Katz, S. C. Sharma, M. Hamayoonfar
Robert Katz Publications
The delta-ray theory of the inactivation of cells by energetic heavy ions describes cellular survival after heavy ion bombardment through a two-component survival model, in which 4 operational parameters (E0,m0, σ0, and κ) describe the response of a particular cellular variety in a particular ambient condition, for an arbitrary radiation environment. The quantities m and E0 are the extrapolation number and extrapolated D-37 dose of the survival curve after gamma-ray irradiation. The quantities σ0 and κ are found from the initial slope of survival curves after irradiation with ions of different LET, …
Nuclear-Magnetic-Resonance Studies Of The Semiconductor-To-Metal Transition In Chlorine-Doped Cadmium Sulfide, Frank D. Adams, David C. Look, Carlton L. Brown, Donald R. Locker
Nuclear-Magnetic-Resonance Studies Of The Semiconductor-To-Metal Transition In Chlorine-Doped Cadmium Sulfide, Frank D. Adams, David C. Look, Carlton L. Brown, Donald R. Locker
Physics Faculty Publications
Spin-lattice relaxation times (T1) and Knight shifts were measured for Cd113 nuclei in 12 CdS crystals doped with various amounts of chlorine. Hall coefficients were measured in order to estimate conduction-electron concentrations. Data were obtained for all samples at 300 °K and for some highly doped samples at 77, 4.2, and 2.13 °K. Metallic properties were observed in all samples having electron concentrations n>2×1018 cm-3. At 300 °K, we find 1/T1∝n for nonmetallic samples and 1/T1∝n2/3 when samples are metallic. The latter proportionality continues to hold at lower …
Comment On Electron Scattering In The Image Potential Well, Pavel Smejtek, M. Silver
Comment On Electron Scattering In The Image Potential Well, Pavel Smejtek, M. Silver
Physics Faculty Publications and Presentations
Comments are made on the model of electron injection into SiO₂ proposed by Berglund and Powell. Their assumptions on electron scattering, disregarding the change of the escape cone with the distance from the emitter, lead to serious underestimation of the injected current. Two alternative models of electron injection, based solely on elastic scattering are discussed and do not predict the experimental results. We suggest that observed field dependence of the injected current into SiO₂ indicates that energy relaxation associated with the injected electrons is responsible for the voltage dependence of the current.
Measurement Of Currents In Lake Mead With The Deep Water Isotopic Current Analyzer (Dwica), J. J. Sartoris, D. A. Hoffman, Bureau Of Reclamation
Measurement Of Currents In Lake Mead With The Deep Water Isotopic Current Analyzer (Dwica), J. J. Sartoris, D. A. Hoffman, Bureau Of Reclamation
Publications (WR)
In Nov 1967, a Deep Water Isotopic Current Analyzer (DWICA) was used to study current patterns in the Boulder Basin of Lake Mead to determine if low-quality water from Las Vegas Bay might enter the Southern Nevada Water Project intake on Saddle Island. Secondary objectives were to study the general current patterns in Boulder Basin and the effect of power discharges at Hoover Dam on these currents. Results of current measurements at 3 stations in Boulder Basin are given. Observations indicate a definite possibility that low-quality water from Las Vegas Bay might enter the water intake on Saddle Island. Current …