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Full-Text Articles in Physics

Nanoscale Oxide Patterns On Si (100) Surfaces, T. -C. Shen, C. Wang, J. W. Lyding, J. R. Tucker Dec 1995

Nanoscale Oxide Patterns On Si (100) Surfaces, T. -C. Shen, C. Wang, J. W. Lyding, J. R. Tucker

T. -C. Shen

Ultrathin oxide patterns of a linewidth of 50 Å have been created on Si(100)‐2×1 surfaces by a scanning tunneling microscope operating in ultrahigh vacuum. The oxide thickness is estimated to be 4–10 Å. The morphology and spectroscopy of the oxide region are obtained. Hydrogen passivation is used as an oxidation mask. The defects caused by oxidation in the passivated region before and after the hydrogen desorption are compared and discussed. The multistep silicon processings by an ultrahigh vacuum scanning tunneling micropscope is thus demonstrated.


Transitions Between Convective Patterns In Chemical Fronts, Y. Wu, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder Dec 1995

Transitions Between Convective Patterns In Chemical Fronts, Y. Wu, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

We present a theory for the transition from nonaxisymmetric to axisymmetric convection in iodate-arsenous acid reaction fronts propagating in a vertical slab. The transition takes place away from the onset of convection, where a convectionless flat front becomes unstable to a nonaxisymmetric convective front. The transition is studied by numerically solving a reaction-diffusion equation coupled with nonlinear hydrodynamics in a two-dimensional slab.


Evidence For Crystal-Field Splitting In Surface-Atom Photoemission From Potassium, G. K. Wertheim, D. Mark Riffe Nov 1995

Evidence For Crystal-Field Splitting In Surface-Atom Photoemission From Potassium, G. K. Wertheim, D. Mark Riffe

All Physics Faculty Publications

Photoemission spectra from the shallow 3p3/2 core levels of the surface atoms of metallic potassium exhibit the effects of a small but measurable crystal-field splitting of ∼38 meV. It manifests itself mainly as an apparent angle-dependent modulation of the spin-orbit splitting. This phenomenon may, in general, interfere with accurate determinations of surface-atom core-level shifts.


All-Sky Measurements Of Short Period Waves Imaged In The Oi (557.7 Nm), Na(589.2 Nm) And Near Infrared Oh And O2(0,1) Nightglow Emissions During The Aloha-93 Campaign, Michael J. Taylor, M. B. Bishop, V. Taylor Oct 1995

All-Sky Measurements Of Short Period Waves Imaged In The Oi (557.7 Nm), Na(589.2 Nm) And Near Infrared Oh And O2(0,1) Nightglow Emissions During The Aloha-93 Campaign, Michael J. Taylor, M. B. Bishop, V. Taylor

All Physics Faculty Publications

As part of the ALOHA‐93 campaign a high performance all‐sky CCD imaging system was operated at Haleakala Crater, Maui, to obtain novel information on the properties and sources of short period gravity waves over an extended height range ∼80–100 km. Sequential observations of the near infrared OH and O2(0,1) bands and the visible wavelength OI(557.7 nm) and Na(589.2 nm) line emissions have enabled a unique comparison of the morphology and dynamics of the wave motions and their occurrence frequency at each emission altitude to be made. Two major findings are: (a ...


Maximum Penetration Of Atmospheric Gravity Waves Observed During Aloha-93, G. R. Swenson, C. S. Gardner, Michael J. Taylor Oct 1995

Maximum Penetration Of Atmospheric Gravity Waves Observed During Aloha-93, G. R. Swenson, C. S. Gardner, Michael J. Taylor

All Physics Faculty Publications

Atmospheric Gravity Waves (AGWs) are subject to altitude propagation limits which are governed by the diffusion processes. Diffusion times and scales which exceed the wave period and wavelength define the limiting domain for AGWs. An expression is presented which defines the upper altitude limit to which AGWs can propagate given vertical diffusion constraints of the atmosphere. Airglow, lidar, and radar measurements are combined to characterize the intrinsic AGW parameters in the 80–105 km altitude region. A subset of AGWs (17) observed by airglow imagers during the ALOHA‐93 were made when simultaneous wind measurements were available and intrinsic wave ...


Determination Of Horizontal And Vertical Structure Of A Novel Pattern Of Short Period Gravity Waves Imaged During Aloha-93, Michael J. Taylor, D. C. Fritts, J. R. Isler Oct 1995

Determination Of Horizontal And Vertical Structure Of A Novel Pattern Of Short Period Gravity Waves Imaged During Aloha-93, Michael J. Taylor, D. C. Fritts, J. R. Isler

All Physics Faculty Publications

An all‐sky CCD imager has been used to measure the properties of short period gravity waves present over the Hawaiian Islands during the ALOHA‐93 campaign. Observations of emissions from four different altitudes provided a capability to describe the vertical as well as the horizontal structure of the wave field. On several occasions during this campaign an unusual morphology wave pattern was detected that consisted of a group of small‐scale waves oriented in the same direction. These were most noticeable in the OI (557.7 nm) emission, altitude ∼96 km, and were usually observed in association with a ...


Height Measurements Of Oi (557.7 Nm) Gravity Wave Structure Over The Hawaiian Islands During Aloha-93, Michael J. Taylor, G. R. Swenson, V. Taylor Oct 1995

Height Measurements Of Oi (557.7 Nm) Gravity Wave Structure Over The Hawaiian Islands During Aloha-93, Michael J. Taylor, G. R. Swenson, V. Taylor

All Physics Faculty Publications

During the ALOHA‐93 campaign simultaneous observations of gravity wave structure in the OI(557.7 nm) nightglow emission were made using two all‐sky CCD imagers; one located near the summit of Haleakala Crater, Maui and the other at Mauna Loa Observatory, Hawaii. On 19 October a set of bright, planar, monochromatic waves was imaged by both systems as it progressed rapidly over the Hawaiian Islands. Triangulation on these wave forms indicates a mean altitude of 95±2 km in good agreement with previous rocket soundings at mid‐latitudes. Two methods of triangulation were employed, both achieving similar results.


Aloha-93 Measurements Of Intrinsic Agw Characteristics Using The Airborne Airglow Imager And Groundbased Na Wind/Temperature Lidar, G. R. Swenson, Michael J. Taylor, P. Espy, C. S. Gardner, X. Tao Oct 1995

Aloha-93 Measurements Of Intrinsic Agw Characteristics Using The Airborne Airglow Imager And Groundbased Na Wind/Temperature Lidar, G. R. Swenson, Michael J. Taylor, P. Espy, C. S. Gardner, X. Tao

All Physics Faculty Publications

Monochromatic Acoustic Gravity Waves (AGWs) with periods < 1 hour are a prevalent feature in the mesospheric airglow layers. These waves are important dynamically and energetically to the region where their temporal and spatial morphology are not well established. The purpose of this study is establish the intrinsic AGW characteristics over an extended region (as flown by the NCAR Electra aircraft) and to present the data in terms of the predicted spectral domain defined by the Brunt‐Vaisala frequency and the diffusive filtering limit proposed by Gardner [1994]. On October 21, 1993, observations were made from the NCAR Electra aircraft during a 6 hour flight in a large triangle N and W of Maui, for a integral distance of ∼3000 km. The entire area observed [∼1 M km²] had a monochromatic AGW propagating toward the NW and the western half had a SW propagating wave superimposed. These waves were also observed with the Michelson interferometer on the aircraft and an airglow imager at the Haleakala location during this time. Intrinsic phase velocities were computed where the Na Wind/Temperature (W/T) lidar at Haleakala provided a measure of the mean wind to compensate phase velocities observed with the imager. The data were tabulated and plotted in an AGW spectral reference frame and compared to cutoff conditions predicted by diffusive filtering theory.


An Investigation Of Intrinsic Gravity Wave Signatures Using Coordinated Lidar And Nightglow Image Measurements, Michael J. Taylor, Y. Y. Gu, X. Tao, C. S. Gardner, M. B. Bishop Oct 1995

An Investigation Of Intrinsic Gravity Wave Signatures Using Coordinated Lidar And Nightglow Image Measurements, Michael J. Taylor, Y. Y. Gu, X. Tao, C. S. Gardner, M. B. Bishop

All Physics Faculty Publications

Simultaneous observations of gravity waves using an Na wind/temperature lidar and a multi‐wavelength all‐sky nightglow imager were obtained, for the first time, during the ALOHA‐93 campaign. A novel investigation of intrinsic wave parameters has been made by combining measurements of the horizontal wave components imaged in four nightglow emissions (height range ∼80–100 km) with Na lidar soundings of the horizontal wind field and temperature profiles over the same height interval. On October 19 both instruments registered marked monochromatic wave motions. The intrinsic periods of several of these waves have been determined and were found to ...


Spectrometric And Imaging Measurements Of A Spectacular Gravity Wave Event Observed During The Aloha-93 Campaign, Michael J. Taylor, D. N. Turnbull, R. P. Lowe Oct 1995

Spectrometric And Imaging Measurements Of A Spectacular Gravity Wave Event Observed During The Aloha-93 Campaign, Michael J. Taylor, D. N. Turnbull, R. P. Lowe

All Physics Faculty Publications

During the ALOHA‐93 campaign coincident imaging and interferometric measurements of the near infrared and visible wavelength nightglow emissions were made from Haleakala Crater, Maui. On 10 October, 1993 a most unusual wave event was observed. This disturbance appeared as a sharp “front” followed by several conspicuous wave crests which progressed rapidly through the imager's field of view (180°). As the front passed overhead the interferometer detected a sudden jump in both the OH intensity (>50%) and its rotational temperature (∼20 K) with the temperature increase leading the intensity by almost 15 min. At the same time the imager ...


A Two-Dimensional Spectral Analysis Of Short Period Gravity Waves Imaged In The Oi (557.7 Nm) And Near Infrared Oh Nightglow Emissions Over Arecibo, Puerto Rico, Michael J. Taylor, F. J. Garcia Sep 1995

A Two-Dimensional Spectral Analysis Of Short Period Gravity Waves Imaged In The Oi (557.7 Nm) And Near Infrared Oh Nightglow Emissions Over Arecibo, Puerto Rico, Michael J. Taylor, F. J. Garcia

All Physics Faculty Publications

In January 1993 an extensive set of radar and optical data was gathered from various key sites around the world during a coordinated “10 Day Run” designed to investigate the coupled dynamic behavior of the upper atmosphere on a large, medium and small scale. As part of this campaign an all‐sky CCD imaging system was operated at Arecibo Observatory, Puerto Rico, to help quantify the response of the low latitude mesosphere‐thermosphere system to short period (<1 hour) gravity waves. Measurements of the OI(557.7 nm) and near infrared OH nightglow emissions were made in conjunction with photometric and ISR radar soundings and revealed an abundance of small‐scale structure in the 80–100 km range. In this letter we apply two‐dimensional spectral analysis techniques to aid in the interpretation of a complex set of image data that consisted of two intersecting quasi‐monochromatic gravity wave patterns progressing on approximately orthogonal headings. An investigation of the spectral content and temporal evolution of these wave motions at each emission altitude is presented.


Structure And Interaction Energies Of Kr Atoms Adsorbed On Graphitic Amorphous Carbon, Sang -Joon Lee Aug 1995

Structure And Interaction Energies Of Kr Atoms Adsorbed On Graphitic Amorphous Carbon, Sang -Joon Lee

All Graduate Theses and Dissertations

The physisorption of Kr on graphitic amorphous carbon (g-C) has been investigated using a statistical approach. The interaction energy calculation process (i) established a structural model of g-C and (ii) determined the adsorbate-adsorbate and the adsorbate-substrate interaction potentials on g-C.

The structural model of g-C was divided into three regions. For the interaction potential between a Kr atom and a carbon atom the short and medium range order of g-C was described with a discrete medium model based on three ring clusters using ring statistics from Beeman's continuous random network C1120 model of g-C. For the intermediate distance region ...


Simultaneous Determination Of Fe 3p Spin-Orbit And Exchange Splittings In Photoemission, D. J. Huang, D. Mark Riffe, J. L. Erskine Jun 1995

Simultaneous Determination Of Fe 3p Spin-Orbit And Exchange Splittings In Photoemission, D. J. Huang, D. Mark Riffe, J. L. Erskine

All Physics Faculty Publications

Spin-resolved core-level photoemission data from the 3p level of ultrathin Fe films [1.4–5.1 monolayers (ML)] epitaxially grown on W(110) have been obtained. A nonlinear least-squares analysis, based on a one-particle Hamiltonian that simultaneously includes core-valence exchange and core-hole spin-orbit interactions, is developed. It is first tested on Fe 2p magnetic circular dichroism (MCD) photoemission spectra and shown to successfully describe the MCD asymmetry data. The model is then used to analyze our thin-film 3p data. With increasing film thickness the spin-orbit splitting (0.67±0.02 eV) remains constant (as expected), the exchange splitting increases from ...


Finite Thermal Diffusivity At Onset Of Convection In Autocatalytic Systems: Discontinuous Fluid Density, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder Jun 1995

Finite Thermal Diffusivity At Onset Of Convection In Autocatalytic Systems: Discontinuous Fluid Density, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

A linear convective stability analysis for propagating autocatalytic reaction fronts includes density differences due to both thermal and chemical gradients. Critical parameters for the onset of convection are calculated for an unbounded geometry, a vertical slab, and a vertical cylinder. Thermal effects are important at unstable wavelengths well above the critical wavelength for the onset of convection.


Conduction-Electron Screening In The Bulk And At Low-Index Surfaces Of Ta Metal, D. Mark Riffe, W. Hale, B. Kim, J. L. Erskine Apr 1995

Conduction-Electron Screening In The Bulk And At Low-Index Surfaces Of Ta Metal, D. Mark Riffe, W. Hale, B. Kim, J. L. Erskine

All Physics Faculty Publications

High-resolution core-level photoemission spectra from Ta(100) have been measured. The well-resolved peak from the first atomic layer allows a separate assessment of bulk and surface-layer screening responses: singularity indices αB=0.10±0.01 and α100=0.205±0.025, respectively, are obtained. The measured surface-atom lifetime broadening of 70±20 meV (compared to 37±5 meV in the bulk) is consistent with published Auger–photoemission coincidence measurements. The result for the bulk singularity index has been applied in the analysis of previous data in order to extract the screening response in the first atomic layer of ...


Time Dependent Response Of Equatorial Ionospheric Electric Fieldsto Magnetospheric Disturbances, Bela G. Fejer, L. Scherliess Apr 1995

Time Dependent Response Of Equatorial Ionospheric Electric Fieldsto Magnetospheric Disturbances, Bela G. Fejer, L. Scherliess

Bela G. Fejer

We use extensive radar measurements of F region vertical plasma drifts and auroral electrojet indices to determine the storm time dependence of equatorial zonal electric fields. These disturbance drifts result from the prompt penetration of high latitude electric fields and from the dynamo action of storm time winds which produce largest perturbations a few hours after the onset of magnetic activity. The signatures of the equatorial disturbance electric fields change significantly depending on the relative contributions of these two components. The prompt electric field responses, with lifetimes of about one hour, are in excellent agreement with results from global convection ...


Mass Distribution On Clusters At The Percolation Threshold, M. F. Gyure, M. V. Ferer, Boyd F. Edwards, G. Huber Mar 1995

Mass Distribution On Clusters At The Percolation Threshold, M. F. Gyure, M. V. Ferer, Boyd F. Edwards, G. Huber

All Physics Faculty Publications

Monte Carlo simulations and a scaling hypothesis are used to study the distribution of blob masses on two-dimensional finite-mass clusters at the percolation threshold. The exponents associated with this distribution function are a combination of backbone and percolation exponents. This work offers insights into the structure and fragmentation properties of percolation clusters in particular, and provides methods applicable to other fractal distribution problems in general.


Convective Chemical-Wave Propagation In The Belousov- Zhabotinsky Reaction, Y. Wu, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder Feb 1995

Convective Chemical-Wave Propagation In The Belousov- Zhabotinsky Reaction, Y. Wu, D. A. Vasquez, Boyd F. Edwards, J. W. Wilder

All Physics Faculty Publications

We investigate the onset of convection for chemical-wave propagation in the Belousov-Zhabotinsky reaction based on the two-variable Oregonator model coupled with the fluid dynamic equations. For chemical waves in a vertical slab, two-dimensional convection occurs only for slab widths greater than a critical threshold width. The convective threshold is different for ascending and descending waves. Convectionless waves are flat and propagate with constant speed. Above the onset of convection, the wave velocity increases and the flat wave deforms due to two counterrotating steady rolls. For a horizontal slab, convection is always present and the wave velocity increases with increasing slab ...


Global Equatorial Ionosphericvertical Plasma Drifts Measured By The Ae-E Satellite, Bela G. Fejer, E. R. De Paula, R. A. Heelis, W. B. Hanson Jan 1995

Global Equatorial Ionosphericvertical Plasma Drifts Measured By The Ae-E Satellite, Bela G. Fejer, E. R. De Paula, R. A. Heelis, W. B. Hanson

Bela G. Fejer

Ion drift meter observations from the Atmosphere Explorer E satellite during the period of January 1977 to December 1979 are used to study the dependence of equatorial (dip latitudes ≤ 7.5°) F region vertical plasma drifts (east-west electric fields) on solar activity, season, and longitude. The satellite-observed ion drifts show large day-to-day and seasonal variations. Solar cycle effects are most pronounced near the dusk sector with a large increase of the prereversal velocity enhancement from solar minimum to maximum. The diurnal, seasonal, and solar cycle dependence of the longitudinally averaged drifts are consistent with results from the Jicamarca radar except ...


A Correlative Comparison Of The Ring Current And Auroral Electrojets Using Geomagnetic Indices, W. B. Cade Iii, Jan Josef Sojka, Lie Zhu Jan 1995

A Correlative Comparison Of The Ring Current And Auroral Electrojets Using Geomagnetic Indices, W. B. Cade Iii, Jan Josef Sojka, Lie Zhu

All Physics Faculty Publications

From a study of the 21 largest geomagnetic storms during solar cycle 21, a strong correlation is established between the ring current index Dst and the time-weighted accumulation of the 1-hour auroral electrojet indices, AE and AL. The time-weighted accumulation corresponds to convolution of the auroral electrojet indices with an exponential weighting function with an e-folding time of 9.4 hours. The weighted indices AEw and ALw have correlation coefficients against Dst ranging between 0.8 and 0.95 for 20 of the 21 storms. Correlation over the entire solar cycle 21 database is also strong but ...


Vibrational Dynamics And Structure Of Amorphous Carbon Modeled Using The Embedded Ring Approach, T. E. Doyle, Jr Dennison Jan 1995

Vibrational Dynamics And Structure Of Amorphous Carbon Modeled Using The Embedded Ring Approach, T. E. Doyle, Jr Dennison

All Physics Faculty Publications

The Raman spectrum of graphitic amorphous carbon (g-C) is modeled with simple classical methods, using rings as medium-range structural units. g-C provides a simple [nearly two dimensional (2D) with a single type of atom and one dominant bond type] prototypic example of a large class of continuous random network (CRN) solids where ring or cluster vibrations cannot be decoupled from the network in which they are embedded. We determined the in-plane vibrational modes of n=4, 5, 6, 7, and 8-membered symmetric, planar carbon rings using bond-stretching and bond-angle bending force constants; an additional force constant couples each ring node ...


Parameterized Ionospheric Model: A Global Ionospheric Parameterization Based On First Principles Models, R. E. Daniell Jr., L. D. Brown, D. N. Anderson, M. W. Fox, P. H. Doherty, D. T. Decker, Jan Josef Sojka, Robert W. Schunk Jan 1995

Parameterized Ionospheric Model: A Global Ionospheric Parameterization Based On First Principles Models, R. E. Daniell Jr., L. D. Brown, D. N. Anderson, M. W. Fox, P. H. Doherty, D. T. Decker, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

We describe a parameterized ionospheric model (PIM), a global model of theoretical ionospheric climatology based on diurnally reproducible runs of four physics based numerical models of the ionosphere. The four numerical models, taken together, cover the E and F layers for all latitudes, longitudes, and local times. PIM consists of a semianalytic representation of diurnally reproducible runs of these models for low, moderate, and high levels of both solar and geomagnetic activity and for June and December solstice and March equinox conditions. PIM produces output in several user selectable formats including global or regional latitude/longitude grids (in either geographic ...


What Is The Source Of Observed Annual Variations In Plasmaspheric Density?, S. M. Guiter, C. E. Rasmussen, T. I. Gombosi, Jan Josef Sojka, Robert W. Schunk Jan 1995

What Is The Source Of Observed Annual Variations In Plasmaspheric Density?, S. M. Guiter, C. E. Rasmussen, T. I. Gombosi, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

Plasmaspheric densities have been observed previously to be higher in December than in June, with the ratio varying between 1.5 and 3.0 and with larger variations at lower L shells. In order to search for the cause of the observed annual variations, we have modeled plasmaspheric density, using a time-dependent hydrodynamic model. On an L = 2 field line with geomagnetic longitude equal to 300°, the modeled plasmaspheric densities were a factor of 1.5 times higher in December than in June. The modeled December to June density ratio was found to increase slightly with L shell, in contrast ...


Some Remarks On Gravitational Analogs Of Magnetic Charge, Charles G. Torre Jan 1995

Some Remarks On Gravitational Analogs Of Magnetic Charge, Charles G. Torre

All Physics Faculty Publications

Existing mathematical results are applied to the problem of classifying closed p-forms which are locally constructed from Lorentzian metrics on an n-dimensional orientable manifold M(0


Natural Symmetries Of The Yang-Mills Equations, Charles G. Torre Jan 1995

Natural Symmetries Of The Yang-Mills Equations, Charles G. Torre

All Physics Faculty Publications

A natural generalized symmetry of the Yang–Mills equations is defined as an infinitesimal transformation of the Yang–Mills field, built in a local, gauge invariant, and Poincaré invariant fashion from the Yang–Mills field strength and its derivatives to any order, which maps solutions of the field equations to other solutions. On the jet bundle of Yang–Mills connections a spinorial coordinate system is introduced that is adapted to the solution subspace defined by the Yang–Mills equations. In terms of this coordinate system the complete classification of natural symmetries is carried out in a straightforward manner. It is ...