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Full-Text Articles in Physics

String Induced Space Compactification, P. G. Freund, P. Oh, James Thomas Wheeler Nov 1984

String Induced Space Compactification, P. G. Freund, P. Oh, James Thomas Wheeler

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Motivated by the possibility of a finite theory of gravity provided by superstrings in ten space-time dimensions, we analyze the problem of space compactification in the context of string dynamics. Such an analysis is hampered by conceptual and technical problems, stemming from the existence of the quantum string's own graviton mode on the one hand, and from Witten's observation of anomalies in a not specially chosen curves space-time on the other hand. Still, in the context of a classical local field presentation of string theory à la Nambu and Hosotani, supplemented by gravitational and Kalb-Ramond interactions, we are ...


The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, Jr Dennison, R. Jones Nov 1984

The Spectral Momentum Density Of Amorphous Carbon From (E, 2e) Spectroscopy, A. L. Ritter, Jr Dennison, R. Jones

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The spectral momentum density of the valence band of an amorphous carbon film has been measured by (e, 2e) spectroscopy. Two "bands," energy as a function of momentum, are resolved. One extends from 23 eV below the Fermi energy to about 10 eV below EF. The other, ∼ 9 eV below EF, does not disperse significantly. Although the existence of diamond bonding in the film cannot be ruled out, the bands are more suggestive of the graphite band structure.


Onset Of Oscillations In Rayleigh-Benard Convection: Horizontally Unbounded Slab, Boyd F. Edwards, A. L. Fetter Jul 1984

Onset Of Oscillations In Rayleigh-Benard Convection: Horizontally Unbounded Slab, Boyd F. Edwards, A. L. Fetter

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Rayleigh–Bénard convection in a laterally unbounded classical fluid layer with low Prandtl number P (ratio of kinematic viscosity to thermal diffusivity) is reexamined. An amplitude expansion with only a few normal modes yields lateral oscillations of the convective rolls, which are therefore only weakly nonlinear. For free boundary conditions, additional modes (absent for rigid boundaries) lead to long wavelength (‘‘hydrodynamic’’) oscillations, with explicit nonlinear distortions in the velocity and temperature fields. For oscillations with rigid boundaries, the finite critical wavenumbers are approximately independent of P for small P, and the calculated Rayleigh number, frequency, and wavenumber at onset agree ...


An Spectrometer For Investigating The Spectral Momentum Density Of Thin Films, A. L. Ritter, Jr Dennison, J. Dunn Apr 1984

An Spectrometer For Investigating The Spectral Momentum Density Of Thin Films, A. L. Ritter, Jr Dennison, J. Dunn

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An (e, 2e) spectrometer has been constructed for detecting scattered and recoiling electrons from a thin solid film. The cross section for observing the two electrons in coincidence is proportional to the spectral momentum density of the target. In this spectrometer the energy of the incident electron beam is 25 keV and the beam current is approximately 40 μA. The energy resolution (FWHM) is ≤4 eV. The momentum resolution (FWHM) can be varied from 0.2 to 1.0 Å1. Preliminary coincidence data from an amorphous carbon film are presented.


Ionospheric Currents And F-Region Plasma Boundaries Near The Dayside Cusp, S Vennerstrom, E Friis-Christensen, T S. Jorgensen, C E. Rasmussen, C R. Clauer, Vincent B. Wickwar Jan 1984

Ionospheric Currents And F-Region Plasma Boundaries Near The Dayside Cusp, S Vennerstrom, E Friis-Christensen, T S. Jorgensen, C E. Rasmussen, C R. Clauer, Vincent B. Wickwar

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Observational evidence of the location of a dayside high‐latitude ionospheric current (DPY current) with respect to the different regimes of the high‐latitude magnetosphere is obtained by analyzing data from the magnetometer chain along the west coast of Greenland in conjunction with simultaneous measurements from the newly established incoherent‐scatter radar facility at Sondre Stromfjord. The latitudinal location of the DPY current is compared with the location of the maximum F‐region electron temperature and with the location of the plasma convection reversal from sunward to antisunward. The maximum in the F‐region electron temperature roughly coincides with the ...


Plasma Characteristics Of Polar Cap F-Layer Arcs, H C. Carlson Jr., Vincent B. Wickwar, E J. Weber, J Buchau, J G. Moore, W Whiting Jan 1984

Plasma Characteristics Of Polar Cap F-Layer Arcs, H C. Carlson Jr., Vincent B. Wickwar, E J. Weber, J Buchau, J G. Moore, W Whiting

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First results are reported of a comprehensive campaign to measure ionospheric structure and dynamics of nighttime polar cap F‐layer or F‐region arcs. Airborne optical and digital ionosonde data were collected simultaneously with ground based incoherent scatter radar data, continuously over many hours in time and 500 to 1000 km in space. Polar cap F‐region sub‐visual auroral arcs, which are commonly observed during quiet magnetic conditions, are found to represent boundaries (or shears) in the polar cap plasma circulation pattern. F‐region electron concentration enhancements are found in these features and can be of significance to polar ...


Observations Of Interplanetary Magnetic Field And Of Ionospheric Plasma Convection In The Vicinity Of The Dayside Polar Cleft, C R. Clauer, P M. Banks, A Q. Smith, T S. Jorgensen, E Friis-Christensen, S Vennerstrom, Vincent B. Wickwar Jan 1984

Observations Of Interplanetary Magnetic Field And Of Ionospheric Plasma Convection In The Vicinity Of The Dayside Polar Cleft, C R. Clauer, P M. Banks, A Q. Smith, T S. Jorgensen, E Friis-Christensen, S Vennerstrom, Vincent B. Wickwar

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Dayside ionospheric convection at high latitudes has been examined during a series of experiments using the Sondrestrom radar together with ancillary observations of the interplanetary magnetic field (IMF) by the IMP‐8 spacecraft. The radar experiments obtained a latitude coverage of 67.6° Λ to 81.30° Λ and a temporal resolution of between 14 to 25 minutes. A total of 17 rotations through the dayside cleft region during April, June and July, 1983 have been examined. The observations show two convection cells with sunward flow at lower latitudes and antisunward flow at higher latitudes. The flow commonly rotates through ...


Mithras: A Brief Description, O De La Beaujardiere, Vincent B. Wickwar, M J. Baron, J Holt, R M. Wand, W L. Oliver, P Bauer, M Blanc, C Senior, D Alcayde, G Caudal, J Foster, E Nielsen, R Heelis Jan 1984

Mithras: A Brief Description, O De La Beaujardiere, Vincent B. Wickwar, M J. Baron, J Holt, R M. Wand, W L. Oliver, P Bauer, M Blanc, C Senior, D Alcayde, G Caudal, J Foster, E Nielsen, R Heelis

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Between May 1981 and June 1982 an intensive campaign of 33 coordinated observations was carried out using the three incoherent-scatter radars capable of probing the auroral zone. During this period the groups operating the Dynamic Explorer satellites and the STARE radar made special efforts to acquire data coincident with the radar observations. The objective of these MITHRAS experiments and subsequent analysis is to further our understanding of the interactions of the magnetosphere, the ionosphere, and the thermosphere, with special emphasis on local time/universal time variations. Three experimental modes with different time resolution and spatial coverage were used to examine ...


On The Reversal From “Sunward” To “Antisunward” Plasma Convection In The Dayside High Latitude Ionosphere, T S. Jorgensen, E Friis-Christensen, Vincent B. Wickwar, J D. Kelly, C R. Clauer, P M. Banks Jan 1984

On The Reversal From “Sunward” To “Antisunward” Plasma Convection In The Dayside High Latitude Ionosphere, T S. Jorgensen, E Friis-Christensen, Vincent B. Wickwar, J D. Kelly, C R. Clauer, P M. Banks

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Preliminary observations of dayside high latitude ionospheric plasma convection with the Sondrestrom incoherent‐scatter radar indicate that plasma can be observed to enter the polar cap region through rotational reversals at most local times between dawn and dusk and not just in a narrow region around noon. Assuming that rotational reversals are signatures of a solar wind‐magnetosphere interaction which drives magnetospheric convection, the observations indicate that this interaction occurs over a longitudinally wide area of the dayside magnetosphere. The observations also show that the distribution of F‐region plasma in the polar cap is dependent on ionization sources anywhere ...


Very High Electron Temperatures In The Daytime F-Region At Sondrestrom, W Kofman, Vincent B. Wickwar Jan 1984

Very High Electron Temperatures In The Daytime F-Region At Sondrestrom, W Kofman, Vincent B. Wickwar

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Sondrestrom observations show that a characteristic F‐region signature of the interaction between the magnetosphere and ionosphere is a narrow band of elevated electron temperatures. Its location is associated with the ion convection reversal in the morning and evening convection cells. Typically, near 500 km altitude, the temperature is 3500 to 4000 K. However, on 24 April 1983, a geomagnetically very active day with Kp values of 6‐ during the period of interest, the electron temperature reached 6000 K in the afternoon convection reversal. The ion velocities were between 1 and 2 km/s on both sides of the reversal ...


Nighttime Thermospheric Winds Over Sondre Stromfjord, Greenland, J W. Meriwether Jr., P Shih, T L. Killeen, Vincent B. Wickwar, R G. Roble Jan 1984

Nighttime Thermospheric Winds Over Sondre Stromfjord, Greenland, J W. Meriwether Jr., P Shih, T L. Killeen, Vincent B. Wickwar, R G. Roble

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Observations of nighttime thermospheric neutral winds made at Sondre Stromfjord, Greenland, with optical and radar instrumentation, showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells. This abatement appeared primarily in the poleward observations. In contrast, however, the characteristic midnight “surge” was usually seen in the equatorward set of observations. The apparent acceleration of about 250 m/s or greater within 4.6° latitude we attribute, in part, to a merging of neutral jet streams generated by polar cap ion drag adjacent to the ...


Initial Millstone Hill, Sondrestrom, And Hilat Observations Of Thermospheric Temperatures And Frictional Heating, W L. Oliver, J C. Foster, J M. Holt, G B. Loriot, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, P F. Bythrow, D I. Meng, F J. Rich, R E. Huffman Jan 1984

Initial Millstone Hill, Sondrestrom, And Hilat Observations Of Thermospheric Temperatures And Frictional Heating, W L. Oliver, J C. Foster, J M. Holt, G B. Loriot, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, P F. Bythrow, D I. Meng, F J. Rich, R E. Huffman

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Elevation scan observations made by the Millstone Hill and Sondrestrom incoherent scatter radars are combined to provide extended latitudinal coverage of thermospheric measurements. Maps of the latitudinal and temporal structure of the exospheric temperature are presented for two 24‐hour periods over the latitude range 45 to 72 degrees north. On the magnetically quiet June day the Millstone and Sondrestrom data formed a consistent picture of thermospheric structure. On the disturbed July day the two radars observed very different behavior, with Millstone Hill observing strong, long‐lived ion frictional heating events but Sondrestrom observing more quiescent behavior. Comparison with HILAT ...


Thermospheric Neutral Wind At –39° Azimuth During The Daytime Sector At Sondrestrom, Vincent B. Wickwar Jan 1984

Thermospheric Neutral Wind At –39° Azimuth During The Daytime Sector At Sondrestrom, Vincent B. Wickwar

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Measurements with the Sondrestrom radar have been used to examine the daytime thermospheric neutral wind and to relate that wind to other geophysical parameters. Ion drag is found to be particularly important for determining the wind pattern. However, evidence is presented that the wind pattern is significantly influenced by soft particle precipitation and, possibly, by Joule heating.


Sondrestrom Overview, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, C A. Leger, F Steenstrup, C H. Dawson Jan 1984

Sondrestrom Overview, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, C A. Leger, F Steenstrup, C H. Dawson

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This overview of the Sondrestrom radar provides background material to help understand the early scientific results discussed in the following series of papers. It describes the geophysical region probed by the radar, the data acquisition procedure, and the extensive set of physical parameters derived.


The Polar Ionosphere: Editorial, Vincent B. Wickwar, J W. Meriwether Jr. Jan 1984

The Polar Ionosphere: Editorial, Vincent B. Wickwar, J W. Meriwether Jr.

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Editorial


The Meridional Thermospheric Neutral Wind Measured By Radar And Optical Techniques In The Auroral Region, Vincent B. Wickwar, J W. Meriwether Jr., P B. Hays, A F. Nagy Jan 1984

The Meridional Thermospheric Neutral Wind Measured By Radar And Optical Techniques In The Auroral Region, Vincent B. Wickwar, J W. Meriwether Jr., P B. Hays, A F. Nagy

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Radar observations of ion velocities in the magnetic zenith over Chatanika, Alaska, were used to determine the geomagnetic meridional component of the thermospheric neutral wind. Corrections for molecular diffusion and molecular ion contamination of the pure O+ composition assumed for the ionosphere were included in the analysis. Comparison of the averaged diurnal variation of the meridional wind showed good agreement between the two measurement techniques. Good agreement was also found for several cases of simultaneous observations. The evidence suggested that differences were caused by gravity waves. The 7 years of radar meridional wind results were examined with respect to magnetic ...


A Theoretical F Region Study Of Ion Compositional And Temperature Variations In Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk Jan 1984

A Theoretical F Region Study Of Ion Compositional And Temperature Variations In Response To Magnetospheric Storm Inputs, Jan Josef Sojka, Robert W. Schunk

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The response of the polar ionosphere to magnetospheric storm inputs was modeled. During the “storm,” the spatial extent of the auroral oval, the intensity of the precipitating auroral electron energy flux, and the plasma convection pattern were varied with time. The convection pattern changed from a symmetric two-cell pattern with a 20-kV cross-tail potential to an asymmetric two-cell pattern with enhanced plasma flow in the dusk sector and a total cross-tail potential of 90 kV. During the storm there were significant changes in the ion temperature, ion composition, and molecular/atomic ion transition height. The storm time asymmetric convection pattern ...


Pitch Angle Properties Of Magnetospheric Thermal Protons And Satellite Sheath Interference In Their Observation, Jan Josef Sojka, G. L. Wrenn, J.F. E. Johnson Jan 1984

Pitch Angle Properties Of Magnetospheric Thermal Protons And Satellite Sheath Interference In Their Observation, Jan Josef Sojka, G. L. Wrenn, J.F. E. Johnson

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Cold proton observations from the geosynchronous GEOS 2 satellite are presented to show the pitch angle distribution of the refilling cold ion population found beyond the plasmapause. This refilling cold ion population flows into the depleted equatorial regions of the flux tubes from the topside ionosphere. This refilling is observed both day and night. The ions have energies between 0.5 and 3 eV. These energy characteristics are consistent with other recent observations. Although the observed angular distribution of these ions is highly complex, when allowance is made for the satellite sheath several conclusions can be made concerning the ion ...


Dayside Red Auroras At Very High Latitudes: The Importance Of Thermal Excitation, Vincent B. Wickwar, W Kofman Jan 1984

Dayside Red Auroras At Very High Latitudes: The Importance Of Thermal Excitation, Vincent B. Wickwar, W Kofman

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Extensive radar observations have been made from Sondrestrom of the F region in the daytime sector between 70 and 79° Λ. Regions of enhanced electron temperature and electron density are found in close association with the velocity reversal in the morning and afternoon convection cells. From the radar measurements, calculations are made of the contributions to the atomic oxygen emission at 6300A from dissociative recombination and thermal excitation. The latter mechanism, in particular, in the enhancement regions gives rise to intensities that are comparable to those observed at very high latitudes during the past decade.