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Articles 121 - 134 of 134
Full-Text Articles in Physics
Comparison Of Simultaneous Chatanika And Millstone Hill Temperature Measurements With Ionospheric Model Predictions, C. E. Rasmussen, Jan Josef Sojka, Robert W. Schunk, Vincent B. Wickwar, O. De La Beaujariere, J. Foster, J. Holt
Comparison Of Simultaneous Chatanika And Millstone Hill Temperature Measurements With Ionospheric Model Predictions, C. E. Rasmussen, Jan Josef Sojka, Robert W. Schunk, Vincent B. Wickwar, O. De La Beaujariere, J. Foster, J. Holt
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. The temperature data obtained during these days were compared with predictions made by a high-latitude ionospheric model. The comparison of the temperature measurements and the results of the ionospheric model depend on the assumptions made both in reducing the data and on the inputs that are needed by the model. The deduction of electron temperature from radar measurements depends upon a knowledge of the mean ion mass as a function of altitude. The …
A Model Study Of How Electric Field Structures Affect The Polar Cap F Region, Jan Josef Sojka, Robert W. Schunk
A Model Study Of How Electric Field Structures Affect The Polar Cap F Region, Jan Josef Sojka, Robert W. Schunk
All Physics Faculty Publications
A three-dimensional time-dependent ionospheric model was used to study how electric field structures affect the polar F region. The electric field structures are represented by elongated Volland two-cell models whose dimensions range from tens to 1000 km. These model structures are intended to represent the polar cap electric field for IMF Bz northward conditions. A statistical method is used to generate a set of these structures. Their electric field strength and polarity are varied in order to study the F region’s dependence on this magnetospheric input. For electric field structures whose size and electric field strengths are consistent with …
Low-Temperature Ion Beam Mixing In Metals, S J. Kim, M A. Nicolet, R S. Averback, David Peak
Low-Temperature Ion Beam Mixing In Metals, S J. Kim, M A. Nicolet, R S. Averback, David Peak
All Physics Faculty Publications
A systematic study of ion-beam mixing of tracer impurities in thin metal films at low temperatures has been conducted. We have investigated the dependence of ion mixing on two matrix properties: atomic mass and cohesive energy. We have also studied the dependence of ion mixing on tracer impurity properties: its heat of mixing with the matrix and its thermal diffusivity in the matrix. The matrices investigated were thin films of C, Al, Ti, Fe, Ni, Cu, Mo, Ru, Ag, Hf, Ta, W, Pt, and Au. The tracer impurities, Al, Ti, Cr, Mn, Fe, Ni, Cu, Y, Nb, Mo, Ru, Ag, …
A Photochemical Equilibrium Model For Ionospheric Conductivity, C. E. Rasmussen, Robert W. Schunk, Vincent B. Wickwar
A Photochemical Equilibrium Model For Ionospheric Conductivity, C. E. Rasmussen, Robert W. Schunk, Vincent B. Wickwar
All Physics Faculty Publications
A photochemical equilibrium model of the high-latitude ionosphere has been developed. This model provides densities of the ionospheric constituents, N2 +, O2 +, O+, and NO+, from 85 km to approximately 220 km. These densities are then used to calculate Pedersen and Hall conductivities. A comparison of the model results with Arecibo and Chatanika radar observations was made, covering periods of solar minimum and solar maximum. The comparison showed the model to predict ionospheric densities to within 50% and conductivities to within 40% in the illuminated portion of the ionosphere. In regions …
Observations Of Auroral E Region Plasma Waves And Electron Heating Witheiscat And A Vhf Radar Interferometer, J. Providakes, D. T. Farley, B. G. Fejer, J. Sahr, W. E. Swartz, I. Haggstrom, A. Hedberg, J. A. Nordling
Observations Of Auroral E Region Plasma Waves And Electron Heating Witheiscat And A Vhf Radar Interferometer, J. Providakes, D. T. Farley, B. G. Fejer, J. Sahr, W. E. Swartz, I. Haggstrom, A. Hedberg, J. A. Nordling
All Physics Faculty Publications
Two radars were used simultaneously to study naturally occurring electron heating events in the auroral E-region ionosphere. During a joint campaign in March 1986 the Cornell University Portable Radar Interferometer (CUPRI) was positioned to look perpendicular to the magnetic field to observe unstable plasma waves over Tromsø, Norway, while EISCAT measured the ambient conditions in the unstable region. On two nights EISCAT detected intense but short lived (< 1 min) electron heating events during which the temperature suddenly increased by a factor of 2–4 at altitudes near 108 km and the electron densities were less than 7 × 104 cm−3. On the second of these nights CUPRI was operating and detected strong plasma waves with very large phase velocities at precisely the altitudes and times at which the heating was observed. The altitudes, as well as one component of the irregularity drift velocity, were determined by interferometric techniques. From the observations and our analysis, we conclude that the electron temperature increases were caused by plasma wave heating and not by either Joule heating or particle precipitation.
Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy James Gay, Jimmie Garwin Edwards, Edward Boyd Hale, M. L. Mckenzie, Ronald E. Olson
Projectile-Charge Dependence Of Ejected-Electron Spectra, V. D. Irby, Timothy James Gay, Jimmie Garwin Edwards, Edward Boyd Hale, M. L. Mckenzie, Ronald E. Olson
Physics Faculty Research & Creative Works
We have studied H++He and He++3+He ionizing collisions at intermediate energies (60 to 120 keV/amu) and have observed a significant shift in the velocity position of the maxima in forward-ejected electron spectra when changing projectiles from protons to particles. In ionizing collisions, a large portion of the ejected electrons are stranded near the transitory equiforce, or saddle point, position between the target ion and receding projectile. The shift in the electron spectra maxima to smaller velocities, due to changing projectiles from protons to particles, is consistent with the shift in the saddle-point velocity when the projectile …
Dynamics Of Antimatter-Atom Collisions, Ronald E. Olson, Timothy James Gay
Dynamics Of Antimatter-Atom Collisions, Ronald E. Olson, Timothy James Gay
Physics Faculty Research & Creative Works
Classical-trajectory Monte Carlo calculations have been used to study ionizing collisions between charged particles (p,p»,e+,e-) and He atoms at an incident velocity of 2.83 a.u. While differences in the total single-ionization cross sections for these projectiles are small, our calculations reveal large effects at all angles in the ionized electron spectra and provide qualitative evidence for a Barkas effect in p and p» collisions. Experimental data agree well with our fully classical calculations, including cross sections involving ejected electrons of long wavelength. © 1988 The American Physical Society.
Nonlocal Symmetries And Backlund Transformations For The Self-Dual Yang-Mills System, C. J. Papachristou, Kent B. Harrison
Nonlocal Symmetries And Backlund Transformations For The Self-Dual Yang-Mills System, C. J. Papachristou, Kent B. Harrison
Faculty Publications
The observation is made that generalized evolutionary isovectors of the self-dual Yang–Mills equation, obtained by "verticalization'' of the geometrical isovectors derived in a previous paper [J. Math. Phys. 28, 1261 (1987)], generate Bäcklund transformations for the self-dual system. In particular, new Bäcklund transformations are obtained by "verticalizing'' the generators of point transformations on the solution manifold. A geometric ansatz for the derivation of such (generally nonlocal) symmetries is proposed.
Generation Of Moire Contours With Acousto-Optic Cells, Joel H. Blatt, Huey-Chin Chang Ho, Eddie H. Young
Generation Of Moire Contours With Acousto-Optic Cells, Joel H. Blatt, Huey-Chin Chang Ho, Eddie H. Young
Aerospace, Physics, and Space Science Faculty Publications
Moire contours are seen on a curved surface viewed through a grating when the surface is illuminated with a matched grating. We have been able to replace both the projection and viewing physical gratings with gratings of variable spacing generated in acousto-optic cells, and have been able to observe and record Moire contours. The gratings are generated by amplitude modulating 70 MHz AO cells with a 1 to 10 MHz square wave. The gratings become visible on the curved object by strobing the illuminating laser beam with 50 nsec pulses by means of an AO modulator. Data is given showing …
Charge- And Angle-Correlated Inelasticities In Collisions Of Bare Fast Carbon Ions With Neon, R. Schuch, H. Schöne, P. D. Miller, H. F. Krause, P. F. Dittner, S. Datz, Ronald E. Olson
Charge- And Angle-Correlated Inelasticities In Collisions Of Bare Fast Carbon Ions With Neon, R. Schuch, H. Schöne, P. D. Miller, H. F. Krause, P. F. Dittner, S. Datz, Ronald E. Olson
Physics Faculty Research & Creative Works
We have studied the detailed energy balance in collisions of 10-MeV C6+ ions with Ne. In these collisions, the Ne is multiply ionized and the C ion may emerge as either C6+ or C5+. Projectile energy loss and scattering angle for a given carbon-ion charge state were determined in a high-resolution magnetic spectrograph and were measured in coincidence with the formation of a given Ne recoil-ion charge state. The amount of energy transferred to the continuum electrons exceeds, by far, the sum of the values of the ionization potentials. © 1988 The American Physical Society.
A Study Of Vapor Phase Self-Initiated Thermal Polymerization Of Styrene With An Expansion Chamber, John L. Schmitt
A Study Of Vapor Phase Self-Initiated Thermal Polymerization Of Styrene With An Expansion Chamber, John L. Schmitt
Physics Faculty Research & Creative Works
Studies of the self-initiated polymerization of styrene have been performed in the uniform environment of an expansion cloud chamber, using nucleation of liquid monomer drops for detection. These studies are the first of this kind in an expansion chamber and, although preliminary and designed to explore feasibility, have yielded many interesting results. The occurrence of the self-initiated nonterminated gas phase processes, previously observed in a diffusion cloud chamber, has now been confirmed in an expansion chamber. At 15 °C the initiation rate is measured to be 2 to 6 radicals cm-3 s-1 and the propagation constant is approximately 6X10-21 cm3 …
An Optically Controlled Closing And Opening Semiconductor Switch, K. H. Schoenbach, V. K. Lakdawala, R. Germer, S. T. Ko
An Optically Controlled Closing And Opening Semiconductor Switch, K. H. Schoenbach, V. K. Lakdawala, R. Germer, S. T. Ko
Electrical & Computer Engineering Faculty Publications
A concept for a bulk semiconductor switch is presented, where the conductivity is increased and reduced, respectively, through illumination with light of different wavelengths. The increase in conductivity is accomplished by electron ionization from deep centers and generation of bound holes. The reduction of conductivity is obtained by hole ionization from the excited centers and subsequent recombination of free electrons and holes. The transient behavior of electron and hole density in a high power semiconductor (GaAs:Cu) switch is computed by means of a rate equation model. Changes in conductivity by five orders of magnitude can be obtained.
Quantum Electrodynamics Based On Self-Fields, Without Second Quantization: A Nonrelativisitc Calculation Of G – 2, A. O. Barut, Jonathan P. Dowling, Jean F. Van Huele
Quantum Electrodynamics Based On Self-Fields, Without Second Quantization: A Nonrelativisitc Calculation Of G – 2, A. O. Barut, Jonathan P. Dowling, Jean F. Van Huele
Faculty Publications
Using a formulation of quantum electrodynamics that is not second quantized, but rather based on self-fields, we compute the anomalous magnetic moment of the electron to first order in the fine structure constant α. In the nonrelativistic (NR) case and in the dipole approximation, our result is ae≡(g—2)/2=(4Λ/3m)(α/2π), where Λ is a positive photon energy cutoff and m the electron mass. A reasonable choice of cutoff, Λ/m=¾, yields the correct sign and magnitude for g—2 namely, ae=+α/2π. . In our formulation the sign of a3 is correctly positive, …
Comparison Of Effective Medium Procedures For Optical Modeling Of Laminar Structures, David D. Allred, Robert F. Edgerton
Comparison Of Effective Medium Procedures For Optical Modeling Of Laminar Structures, David D. Allred, Robert F. Edgerton
Faculty Publications
This study addresses the question, "How can the optical properties of matter in ultrathin amorphous nonmetallic films in multilayers best be determined from reflectance (R) and transmission (T) measurements?" A blue shift in the band gap of plasma CVD a-Si:H/a-SiNx:H multilayers was reported several years ago. It was suggested that the shift in the band gap, Eg, Relative to bulk a-Si:H as given by the Tauç plot was due to quantum confinement effects. The purpose of this study is to evaluate the usefulness of various effective media theories (EMT) for determining the optical constants of materials in a multilayer and …