Physics Commons^™

Auxiliary Field In Conformal Gauge Theory, James Thomas Wheeler

All Physics Faculty Publications

When the full conformal algebra is gauged there arises a gauge field for inverse translations in addition to the usual translational gauge field. By considering every scale-invariant action constructible from the curvatures of the conformal group and the metric, we show that when the gauge field of the usual translations is identified as the vierbein, the gauge field of inverse translations may always be eliminated by its own field equation. After this elimination, every torsion-free, scale-invariant action reduces to a linear combination of the square of the conformal curvature tensor C_αβμν and the square of the Weyl field strength …

Equatorial Thermospheric Wind Changes During The Solar Cycle: Measurements At Arequipa,Peru From 1983 To 1990, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalesz, D. C. Hallenbeck

Bela G. Fejer

Fabry-Perot interferometer measurements of Doppler shifts in the nightglow 630-nm emission line have been used to determine near-equatorial thermospheric wind velocities at Arequipa, Peru, over ∼2/3 of a solar cycle. Monthly-average nocturnal variations in the meridional and zonal wind components were calculated from the nightly data to remove short term (day-to-day) variability, facilitating display of seasonal changes in the wind patterns, as well as any additional changes introduced by the progression of the solar cycle. The measured seasonal variations in the wind patterns are more pronounced than the solar cycle variations and are more readily understandable in terms of the …

Average Vertical And Zonal F-Region Plasma Drifts Over Jicamarca, Bela G. Fejer, E. R. De Paula, S. Gonzalez, R. F. Woodman

Bela G. Fejer

The seasonal averages of the equatorial F region vertical and zonal plasma drifts are determined using extensive incoherent scatter radar observations from Jicamarca during 1968–1988. The late afternoon and nighttime vertical and zonal drifts are strongly dependent on the 10.7-cm solar flux. We show that the evening prereversal enhancement of vertical drifts increases linearly with solar flux during equinox but tends to saturate for large fluxes during southern hemisphere winter. We examine in detail, for the first time, the seasonal variation of the zonal plasma drifts and their dependence on solar flux and magnetic activity. The seasonal effects on the …

Enhanced Vibrational Broadening Of Core-Level Photoemission From The Surface Of Na(110), D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

High-resolution temperature-dependent photoemission data from Na 2p core levels reveal substantially larger phonon broadening in the first atomic layer of Na(110) than in the bulk. We show that the enhanced width is due primarily to the excitation of relatively soft phonon modes perpendicular to the surface. Soft surface-phonon modes also account for previously reported but uninterpreted broadening of transition-metal surface-atom core levels.

Crystal Field Splitting And Charge Flow In The Buckled-Dimer Reconstruction Of Si(100)—2× 1, G. K. Wertheim, D. Mark Riffe, J. E. Rowe, P. H. Citrin

All Physics Faculty Publications

The effect of the 2×1 reconstruction on the core-electron binding energies of the outermost Si(100) layers has been determined using high-resolution photoemission data. A previously unobserved 190-meV crystal-field splitting is resolved for the up-atoms of the asymmetric surface dimers, whose average core-level shift is -400 meV. The signal from the down-atoms is clearly identified and has a shift of +220 meV. These new findings indicate a charge flow of ∼0.05e from the subsurface to the surface layers, with a substantially larger difference of ∼0.34e between the up-atoms and down-atoms in the dimer.

Near-Infrared Imaging Of Hydroxyl Wave Structure Over An Ocean Site At Low Latitudes, Michael J. Taylor, M. J. Hill

All Physics Faculty Publications

Coordinated observations of wave structure in the near infrared hydroxyl (OH) nightglow emission have been made from Maui, Hawaii using a suite of narrow angle and all‐sky TV cameras. Two sets of data were obtained, the first in conjunction with the ALOHA‐90 campaign and the second during the subsequent new moon period. Well formed, short period (<20 min) wave patterns of comparable morphology, dynamics and abundance to those regularly imaged from mid‐latitude mountain sites were detected on several occasions. Although the Hawaiian islands comprise several high volcanic peaks, the patterns were not consistent with gravity waves generated by the interaction of strong winds with the local island topography. This suggests that other mid‐latitude wave patterns may also not be of mountain origin. The wave patterns imaged during ALOHA‐90 were of significantly lower contrast than those detected later. This effect may be related to changes in the characteristics of the middle atmosphere that occur shortly after the spring equinox.

Observations Of Short Period Mesospheric Wave Patterns: In Situ Or Tropospheric Wave Generation, Michael J. Taylor, R. Edwards

All Physics Faculty Publications

Near infrared images showing wave structure in the hydroxyl (OH) nightglow emission have been obtained from Maui, Hawaii during the ALOHA‐90 campaign. Analysis of two nights during this campaign (25 and 31 March) indicate extensive, highly coherent, linear wave patterns of very short apparent period (∼5 and 10 min respectively). Both displays exhibited several features characteristic of the in situ breakdown of a large scale, long period, upper atmospheric wave disturbance. Data in support of this mechanism was found by other ALOHA instruments which detected concurrent long period (1–2 hour) mesospheric wave disturbances on both occasions. However, a tropospheric source …

Coincident Imaging And Spectrometric Observations Of Zenith Oh Nightglow Structure, Michael J. Taylor, D. N. Turnbull, R. P. Lowe

All Physics Faculty Publications

During the ALOHA‐90 campaign a novel comparative study was made between near infrared wave structure imaged in the zenith using a CCD camera and that detected at infrared wavelengths by a Fourier Transform Spectrometer. Coincident measurements were made briefly on several occasions and for an extended period on 31 March. The temporal variations imaged in the near infrared structure during this night almost completely matched those detected in the OH (3,1) band spectrometer data when similar viewing fields were compared. However, the image data also displayed small scale wave forms that were not resolved by the larger field instrument. These …

Onset Of Convection For Autocatalytic Reaction Fronts: Laterally Bounded Systems, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

Linear hydrodynamics yields the onset of convection for ascending autocatalytic reaction fronts in laterally bounded geometries. The system is studied in the limit of infinite and zero thermal diffusivity. For convection in a vertical slab of thickness a or a long vertical cylinder of radius a, the appropriate dimensionless driving parameter scrS=δga³/νD_c involves the fractional density difference δ between the unreacted and reacted fluids, the acceleration of gravity g, the kinematic viscosity ν, and the catalyst molecular diffusivity D_c. Calculated critical values scrS_c for onset of convection agree with recent experiments on iodate–arsenous acid …

Anisotropic, Time-Dependent Solutions In Maximally Gauss-Bonnet Extended Gravity, T. Kitaura, James Thomas Wheeler

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In an arbitrary number of dimensions, we find the full exact anisotropic, time-dependent, diagonal-metric solutions to maximally Gauss-Bonnet extended gravity theory. This class of theories, for which the lagrangian is an arbitrary linear combination of dimensionally extended Euler forms, is the most general gravitational theory in which the field equations contain no more than second derivatives of the metric.

We show that the space-time exponentially approaches an asymptotic state of constant, anisotropic curvature and prove three theorems concerning two generic types of singularities. The first theorem gives conditions for the existence of Kasner-like curvature singularities. For these the metric diverges …

Spacetime Dimension From A Variational Principle, D. Hochberg, James Thomas Wheeler

All Physics Faculty Publications

We consider spacetime as having an a priori arbitrary, possibly fractional dimension p>0 and propose a new variational principle for actions defined on p-dimensional spaces. Demanding that the action be stationary with respect to variations in p leads to a constraint equation whose solution yields an explicit determination of the dimension at the classical level. We illustrate these concepts by analyzing a model which reduces to free scalar field theory when p is any positive integer.

Phenomena Relating To Charge In Insulators: Macroscopic Effects And Microscopic Causes, Jacques Cazaux, Claude Le Gressus

Scanning Microscopy

Conservation of current under steady-state conditions makes it possible to determine the sign of charges trapped in an insulator subjected to ionizing radiation. The maximum value of the surface potential can thus be estimated.

On the basis of a given trapped charge distribution, the pattern of the electrical field and of the potential can thus be established, and the influence of the shape of the sample and its environment can be clearly shown. Change of trapped charges with time (at the start and after irradiation) is then examined. Finally, the microscopic causes of trapping of charge is suggested by analogy …

Ion Irradiation Effects On Graphite With Scanning Tunneling Microscope, T. -C. Shen, R. T. Brockenbrough, J. R. Tucker, J. W. Lyding

T. -C. Shen

Scanning tunneling microscope is used to create local surface modifications by means of ion impact damage. Graphite has been used as a test case to demonstrate this local surface sputtering. Using 0.1-µs voltage pulse of - 30 to - 140 V applied to the sample in a rough vacuum of 10-2 Torr, a confined area of damage (typically about 100 Å in diameter) is usually obtained. The damaged area consists of several layers of terraces. Defects of the size of a few atoms can also be found. Electronic perturbations caused by defects can form superlattices with a spacing three times …

A Deformation Theory Of Self-Dual Einstein Spaces, Charles G. Torre

All Physics Faculty Publications

The self-dual Einstein equations on a compact Riemannian 4-manifold can be expressed as a quadratic condition on the curvature of an $SU(2)$ (spin) connection which is a covariant generalization of the self-dual Yang-Mills equations. Local properties of the moduli space of self-dual Einstein connections are described in the context of an elliptic complex which arises in the linearization of the quadratic equations on the $SU(2)$ curvature. In particular, it is shown that the moduli space is discrete when the cosmological constant is positive; when the cosmological constant is negative the moduli space can be a manifold the dimension of which …

Harmonic Gauge In Canonical Gravity, K. V. Kuchal, Charles G. Torre

All Physics Faculty Publications

The Isham-Kuchař representation theory of the spacetime diffeomorphism group in canonical geometrodynamics is implemented in the context of harmonic coordinate conditions. The representation is carried by either an extended phase space, consisting of the cotangent bundle over the space of three-metrics, spacelike embeddings, and Lagrange multipliers which serve to enforce the harmonic gauge in the action, or by a reduced space in which the multipliers are eliminated. The approach used here is applicable to any generally covariant theory and to any coordinate conditions. The physical interpretation of the diffeomorphism Hamiltonians is discussed and compared with the analogous interpretation given by …

Gaussian Reference Fluid And Interpretation Of Quantum Geometrodynamics, Karel Kucha, Charles G. Torre

All Physics Faculty Publications

The Wheeler-DeWitt equation of vacuum geometrodynamics is turned into a Schrödinger equation by imposing the normal Gaussian coordinate conditions with Lagrange multipliers and then restoring the coordinate invariance of the action by parametrization. This procedure corresponds to coupling the gravitational field to a reference fluid. The source appearing in the Einstein law of gravitation has the structure of a heat-conducting dust. When one imposes only the Gaussian time condition but not the Gaussian frame conditions, the heat flow vanishes and the dust becomes incoherent. The canonical description of the fluid uses the Gaussian coordinates and their conjugate momenta as the …

Field-Aligned Current Associated With A Distorted Two-Cell Convection Pattern During Northward Interplanetary Magnetic Field, Lie Zhu, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

A systematic study of the influence of the ionospheric conductance on the field-aligned current associated with a distorted two-cell convection pattern during northward interplanetary magnetic field (IMF) has been conducted. Our modeling results indicate that the NBZ current can be associated with the distorted two-cell convection for most of the ionospheric conductivity conditions. It is shown that the conductivity conditions related to the seasonal variation and the aurora activity can significantly influence the basic features of the field-aligned current associated with a distorted two-cell convection pattern. It is found that the increase of the field-aligned current in the polar cap …

Ionospheric Physics, Jan Josef Sojka

All Physics Faculty Publications

The author has taken a parochial view of the subject matter
under the title of ionospheric physics. Physics is used as the
key to separating this section of the aeronomy review from the
other aeronomy reports. Specifically, work categorized as
chemistry, optical emissions, and thermosphere will not be
reviewed in this section. However, coupling to the
thermosphere and more specifically to the magnetosphere is
considered. A brief section is also included on active
experiments which is a productive area in plasma physics and
also to some extent in ionospheric physics, but one that has
fallen on hard times with regard …

Revised Global Model Of Thermosphere Winds Using Satellite And Ground-Based Observations, A E. Hedin, M A. Biondi, R G. Burnside, G Hernandez, R M. Johnson, T L. Killeen, C Mazaudier, J W. Meriwether, J E. Salah, R W. Smith, N W. Spencer, Vincent B. Wickwar, T S. Virdi

All Physics Faculty Publications

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground-based incoherent scatter radar and Fabry-Perot optical interferometers to generate a revision (HWM90) of the HWM87 empirical model and extend its applicability to 100 km. Comparison of the various data sets with the aid of the model shows in general remarkable agreement, particularly at mid and low latitudes. The ground-based data allow modeling of seasonal/diurnal variations, which are most distinct at mid latitudes. While solar activity variations are now included, they are found …

Exact And Asymptotic Scaling Solutions For Fragmentation With Mass Loss, M. Cai, Boyd F. Edwards, H. Han

All Physics Faculty Publications

Exact and asymptotic solutions to a linear rate equation for fragmentation with mass loss are presented. Solutions for spatially discrete random bond annihilation illustrate the mutual exclusiveness of the fragmentation and recession terms in the rate equation. Exact solutions for deterministic equal fragment recession show that continuous mass loss between fragmentation events can be approximated by discrete mass loss during fragmentation events when this mass loss is small. Evidence that continuous and discrete mass loss preclude shattering mass loss, the loss of mass to zero-mass particles due to runaway fragmentation, is presented. General asymptotic scaling forms, general solutions reflecting arbitrary …

Onset Of Convection For Autocatalytic Reaction Fronts: Laterally Unbounded System, Boyd F. Edwards, J. W. Wilder, K. Showalter

All Physics Faculty Publications

The linear stability of exothermic autocatalytic reaction fronts that convert unreacted fluid into a lighter reacted fluid is considered using the viscous thermohydrodynamic equations. For upward front propagation and a thin front, the discontinuous jump in density at the front is reminiscent of the Rayleigh-Taylor problem of an interface between two immiscible fluids, whereas the vertical thermal gradient near the front is reminiscent of the Rayleigh-Bénard problem of a fluid layer heated from below. The problem is also similar to flame propagation, except that here the front propagation speed is limited by catalyst diffusion rather than by activation kinetics. For …

Silicon (2p) Surface Core-Level Line Shape Of Si(111)—B, J. E. Rowe, G. K. Wertheim, D. Mark Riffe

All Physics Faculty Publications

Several recent structural studies of the Si(111)–B ((3)^1/2×(3)^1/2) surface have established that the boron atoms occupy substitutional sites in the second full Si layer and have Si adatoms directly above them. High‐resolution (∼80–100 meV) Si(2p) core‐level photoemission was used to determine the B‐induced perturbation of the surface Si atoms. The samples were prepared by surface segregation from Si(111) wafers (∼1.5 at. % B) after thermally removing the thin protective oxide layer on the surface. Photoemission spectra for photon energies from 110 to 140 eV show three peaks, indicative of at least two well‐separated spin‐orbit …