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Articles 31921 - 31950 of 36559

Full-Text Articles in Physical Sciences and Mathematics

Strong X-Ray Emission From High-Temperature Plasmas Produced By Intense Irradiation Of Clusters, T. Ditmire, Thomas D. Donnelly, R. W. Falcone, M. D. Perry Oct 1995

Strong X-Ray Emission From High-Temperature Plasmas Produced By Intense Irradiation Of Clusters, T. Ditmire, Thomas D. Donnelly, R. W. Falcone, M. D. Perry

All HMC Faculty Publications and Research

The interaction of an intense laser pulse with large (∼100Å) clusters present in pulsed gas jets is shown to produce novel plasmas with electron temperatures far in excess of that predicted by above-threshold ionization theory. The enhanced absorption of the laser light by the dense clusters results in the production of high ion charge states via collisional ionization resulting in strong x-ray emission from the hot plasma.

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Doubled Co2 Experiments With The Global Change Research Center Two-Dimensional Statistical Dynamical Climate Model, R. M. Mackay, M. A. K. Khalil Oct 1995

Doubled Co2 Experiments With The Global Change Research Center Two-Dimensional Statistical Dynamical Climate Model, R. M. Mackay, M. A. K. Khalil

Physics Faculty Publications and Presentations

The zonally averaged response of the Global Change Research Center two-dimensional statistical dynamical climate model (GCRC 2-D SDCM) to a doubling of atmospheric carbon dioxide (350 parts per million by volume (ppmv) to 700 ppmv) is reported. The model solves the two-dimensional primitive equations in finite difference form (mass continuity, Newton's second law, and the first law of thermodynamics) for the prognostic variables: zonal mean density, zonal mean zonal velocity, zonal mean meridional velocity, and zonal mean temperature on a grid that has 18 nodes in latitude and 9 vertical nodes (plus the surface). The equation of state, p=rhoRT, and …

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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.

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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 larger scale gravity wave. …

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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 registered …

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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) the detection of significantly higher amounts of wave structure …

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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.

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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 vary considerably with altitude, often …

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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 parameters were …

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Review Of Environmental Physics By Egbert Boeker And Rienk Van Grondelle, David W. Hafemeister Oct 1995

Review Of Environmental Physics By Egbert Boeker And Rienk Van Grondelle, David W. Hafemeister

Physics

No abstract provided.

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Interaction Of An Expanding Plasma Cloud With A Simple Antenna: Application To Anomalous Voltage Signals Observed By Voyager 1, Voyager 2, Ice, And Vega Spacecraft, D. P. Sheehan, C. A. Casey, L. T. Volz Oct 1995

Interaction Of An Expanding Plasma Cloud With A Simple Antenna: Application To Anomalous Voltage Signals Observed By Voyager 1, Voyager 2, Ice, And Vega Spacecraft, D. P. Sheehan, C. A. Casey, L. T. Volz

Physics and Biophysics: Faculty Scholarship

High‐velocity impacts of interplanetary dust grains with spacecraft can give rise to transient plasma clouds from the spacecraft bodies. It is believed these plasma clouds can affect spacecraft instruments. Laboratory results are presented demonstrating the interaction of small expanding plasma clouds with a simple antenna. Results corroborate the hypothesized origin of anomalous impulsive voltage signals recorded by Voyager 1 and 2 spacecraft during flybys of Saturn, Uranus, and Neptune, the International Cometary Explorer (ICE) during its flyby of comet Giacobini‐Zinner, and Vega during its flyby of comet Halley. Results suggest that preflight calibration of antenna‐plasma interactions may extend the range …

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A Relativistic Model For Heavy Mesons, Jialin Zeng Oct 1995

A Relativistic Model For Heavy Mesons, Jialin Zeng

Physics Theses & Dissertations

Motivated by the present interest in the heavy quark effective theory, we construct a model for heavy mesons based on a relativistic bound state wave equation, the Gross equation. The kernel we use is based on scalar confining and vector Coulomb potentials. Wave functions are treated to leading order and energies to order 1/MQ in the heavy-light systems, and to order 1/M2Q in heavy-heavy systems. Our results are in good agreement with experimental measurements. This model may be used to study weak decay properties in the framework of the heavy quark effective theory and ultimately to …

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Heavy-Ion Interaction Models For Radiation Transport, Rajendra R. Dubey Oct 1995

Heavy-Ion Interaction Models For Radiation Transport, Rajendra R. Dubey

Physics Theses & Dissertations

This dissertation is concerned with finding the values for the nuclear cross sections used in the Boltzmann equation for space radiation transport and dose estimates. An extraordinary number of cross sections are required because of the large number of ion types and their extensive energy range, The Lippmann-Schwinger equation is numerically solved in momentum space for a first order optical potential (free space case) and calculations are made for the total and absorption cross sections for nudeus-nucleus scattering. Absorption cross sections are also calculated using a medium modified firstorder optical potential in the Lippmann-Schwinger equation and are compared with experimental …

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Disorder And Synchronization In A Josephson Junction Plaquette, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld Sep 1995

Disorder And Synchronization In A Josephson Junction Plaquette, Adam S. Landsberg, Yuri Braiman, Kurt Wiesenfeld

WM Keck Science Faculty Papers

We describe the effects of disorder on the coherence properties of a 2 x 2 array of Josephson junctions (a "plaquette"). The disorder is introduced through variations in the junction characteristics. We show that the array will remain one-to-one frequency locked despite large amounts of the disorder, and determine analytically the maximum disorder that can be tolerated before a transition to a desynchronized state occurs. Connections with larger N x M arrays are also drawn.

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The Phase Diagram Of Crystalline Surfaces, Simon Catterall, Konstantinos N. Anagnostopoulos, Mark Bowick, Marco Falcioni, G. Thorleifsson Sep 1995

The Phase Diagram Of Crystalline Surfaces, Simon Catterall, Konstantinos N. Anagnostopoulos, Mark Bowick, Marco Falcioni, G. Thorleifsson

Physics - All Scholarship

We report the status of a high-statistics Monte Carlo simulation of non-self-avoiding crystalline surfaces with extrinsic curvature on lattices of size up to 128^2 nodes. We impose free boundary conditions. The free energy is a gaussian spring tethering potential together with a normal-normal bending energy. Particular emphasis is given to the behavior of the model in the cold phase where we measure the decay of the normal-normal correlation function.

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Magnetic-Field-Induced Griffiths Phase Versus Random-Field Criticality And Domain Wall Susceptibility Of Fe0.47zn0.53f2, Christian Binek, S. Kuttler, Wolfgang Kleemann Sep 1995

Magnetic-Field-Induced Griffiths Phase Versus Random-Field Criticality And Domain Wall Susceptibility Of Fe0.47zn0.53f2, Christian Binek, S. Kuttler, Wolfgang Kleemann

Christian Binek Publications

The well-known peak of the parallel ac susceptibility arising below TN in Fe0.47Zn0.53F2 splits into a narrow critical peak at Tc (H) and a broad field-induced Griffiths phase shoulder peaking at Tp>Tc(H) in magnetic fields H≳1.6 MA /m. Random-field (RF) criticality with α̃≈0 and subsequent rounding due to RF trapping of thermal fluctuations are observed upon zero-field cooling as T→Tc-(H). The frozen domain state obtained after rapid field cooling reveals excess susceptibility Δχw′∝H2.6, owing to rough walls with thermally activated stiffness.

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Control Of Bright Picosecond X-Ray Emission From Intense Subpicosecond Laser-Plasma Interactions, J. Workman, Anatoly Maksimchuk, X. Liu, U. Ellenberger, J.S. Coe, C.-Y. Chien, Donald P. Umstadter Sep 1995

Control Of Bright Picosecond X-Ray Emission From Intense Subpicosecond Laser-Plasma Interactions, J. Workman, Anatoly Maksimchuk, X. Liu, U. Ellenberger, J.S. Coe, C.-Y. Chien, Donald P. Umstadter

Donald Umstadter Publications

Using temporally and spectrally resolved diagnostics, we show that the pulse duration of laser-produced soft x rays emitted from solid targets can be controlled, permitting a reduction to as short as a few picoseconds. To enable this control, only a single parameter must be adjusted, namely, the intensity of the high-contrast ultrashort laser pulse (400 fs). These results are found to be in qualitative agreement with a simple model of radiation from a collisionally dominated atomic system.

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Temperature Fluctuations In Photoionized Nebulae, J. B. Kingdon, Gary J. Ferland Sep 1995

Temperature Fluctuations In Photoionized Nebulae, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

Recombination lines in gaseous nebulae frequently yield parent-ion abundances that are several times larger than abundances derived from forbidden lines. One possible explanation for this discrepancy is the presence of temperature fluctuations. We examine temperature fluctuations in model nebulae by utilizing Peimbert's t2 parameter. We have run large grids of models, varying the stellar temperature and the total hydrogen density. We consider two abundance sets: The first uses "typical" planetary nebulae abundances, while the second examines the effect of increasing the metals and grains by a factor of 3. We also consider both a constant density distribution and one …

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Remanence Measurements On Individual Magnetotactic Bacteria Using A Pulsed Magnetic Field, Ietje Penninga, Hendrik De Waard, Bruce M. Moskowitz, Dennis A. Bazylinski, Richard B. Frankel Sep 1995

Remanence Measurements On Individual Magnetotactic Bacteria Using A Pulsed Magnetic Field, Ietje Penninga, Hendrik De Waard, Bruce M. Moskowitz, Dennis A. Bazylinski, Richard B. Frankel

Physics

We describe pulsed-magnetic-field remanence measurements of individual, killed, undisrupted cells of three different types of magnetotactic bacteria. The measurement technique involved the observation of aligned, individual magnetotactic bacteria with a light microscope as they were subjected to magnetic pulses of increasing amplitude. We show that for MM cells, the hysteresis loop is square, with the coercive field variable from cell to cell. This is consistent with just two magnetization states for the single chain of magnetite particles. For MR and MMP cells, the hysteresis loops are not square, indicating that there are several different magnetization states, and that individual cells …

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Controlled Biomineralization Of Magnetite (Fe3O4) And Greigite (Fe3S4) In A Magnetotactic Bacterium, Dennis A. Bazylinski, Richard B. Frankel, Brigid R. Heywood, Stephen Mann, John W. King, Percy L. Donaghay, Alfred K. Hanson Sep 1995

Controlled Biomineralization Of Magnetite (Fe3O4) And Greigite (Fe3S4) In A Magnetotactic Bacterium, Dennis A. Bazylinski, Richard B. Frankel, Brigid R. Heywood, Stephen Mann, John W. King, Percy L. Donaghay, Alfred K. Hanson

Physics

A slowly moving, rod-shaped magnetotactic bacterium was found in relatively large numbers at and below the oxic-anoxic transition zone of a semianaerobic estuarine basin. Unlike all magnetotactic bacteria described to date, cells of this organism produce single-magnetic-domain particles of an iron oxide, magnetite (Fe3O4), and an iron sulfide, greigite (Fe3O4), within their magnetosomes. The crystals had different morphologies, being arrowhead or tooth shaped for the magnetite particles and roughly rectangular for the greigite particles, and were coorganized within the same chain(s) in the same cell with their long axes along the chain …

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Thindown In Biological 1-Hit Detectors: E. Coli B/R And Bs-1*, Zhang Chunxiang, Robert Katz Sep 1995

Thindown In Biological 1-Hit Detectors: E. Coli B/R And Bs-1*, Zhang Chunxiang, Robert Katz

Robert Katz Publications

According to the theory of Butts and Katz and the new radial dose distribution of Zhang et al., we have calculated inactivation cross sections for the heavy ion bombardment of E. Coli B/r and Bs-1 which w& in agreement with the measurements of Scliafer et made with ions from O to U at energies from 1.5 to 19.5 MeV/u. The data display "thindown", and the decrease in cross section with an increase in stopping power is accompanied by a decrease in energy of a bombarding ion. Following an earlier analysis of heavy ion bombardments of these E. Coli mutants with …

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A Novel Design For A Small Retractable Cylindrical Mirror Analyzer, D.N. Mcilroy, Peter A. Dowben, A. Knop, E. Ruhl Sep 1995

A Novel Design For A Small Retractable Cylindrical Mirror Analyzer, D.N. Mcilroy, Peter A. Dowben, A. Knop, E. Ruhl

Peter Dowben Publications

In this paper we will review the performance of a “miniature” single pass cylindrical mirror analyzer (CMA) which we have used successfully in a variety of experiments. The underlying premise behind this CMA design was to minimize spatial requirements while maintaining an acceptable level of instrumental resolution. While we are presenting the results of a single pass cylindrical mirror analyzer, improvements on the present design, such as going to a double pass design, will undoubtedly improve the instrumental resolution.

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A Novel Design For A Small Retractable Cylindrical Mirror Analyzer, D.N. Mcilroy, Peter A. Dowben, A. Knop, E. Ruhl Sep 1995

A Novel Design For A Small Retractable Cylindrical Mirror Analyzer, D.N. Mcilroy, Peter A. Dowben, A. Knop, E. Ruhl

Peter Dowben Publications

In this paper we will review the performance of a “miniature” single pass cylindrical mirror analyzer (CMA) which we have used successfully in a variety of experiments. The underlying premise behind this CMA design was to minimize spatial requirements while maintaining an acceptable level of instrumental resolution. While we are presenting the results of a single pass cylindrical mirror analyzer, improvements on the present design, such as going to a double pass design, will undoubtedly improve the instrumental resolution.

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Stress Evolution During The Growth Of Ultrathin Layers Of Iron And Iron Silicide On Si(111), D. Sander, Axel Enders, J. Kirschner Sep 1995

Stress Evolution During The Growth Of Ultrathin Layers Of Iron And Iron Silicide On Si(111), D. Sander, Axel Enders, J. Kirschner

Axel Enders Publications

Using a simple optical deflection technique, we measured continuously the mechanical stress during the growth of Fe films of 0.1–1.5 nm thickness on Si(111) in ultrahigh vacuum (UHV). The stress versus coverage dependence is discussed in view of the different growth modes during the various stages of Fe deposition. The deposition of up to 0.3 nm Fe induces a compressive stress of -1 N/m. We assign this stress to the formation of a reactive Fe–Si interface layer with a silicide-like structure. Subsequent Fe deposition at 300 K leads to a small tensile stress of 0.7 N/m, whereas the deposition at …

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Collisional Dynamics Of The Rubidium 52P Levels, Matthew D. Rotondaro Sep 1995

Collisional Dynamics Of The Rubidium 52P Levels, Matthew D. Rotondaro

Theses and Dissertations

The collisional dynamics of the 52P levels in rubidium has been examined using steady-state laser absorption and spectrally-resolved laser induced fluorescence techniques. State-to-state cross-sections for energy transfer between Zeeman split levels ranged from 16-248 °A2 for collisions with nitrogen and rare gases. These energy transfer cross-sections exhibit a significant dependence on (J,mj) state and certain symmetry relationships are demonstrated. A sub-Doppler spectrum of the Zeeman split levels indicating the isotopic shift in the D1 line of 106 ± 35 was obtained using laser saturation spectroscopy.

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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.

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Comparison Of Branching Ratio And Sum-Rule Analyses Of Magnetic Circular Dichroism In X-Ray-Absorption Spectroscopy, James G. Tobin, George Daniel Waddill, Alan F. Jankowski, Philip A. Sterne, David P. Pappas Sep 1995

Comparison Of Branching Ratio And Sum-Rule Analyses Of Magnetic Circular Dichroism In X-Ray-Absorption Spectroscopy, James G. Tobin, George Daniel Waddill, Alan F. Jankowski, Philip A. Sterne, David P. Pappas

Physics Faculty Research & Creative Works

Two localized picture methods of analyzing the magnetic circular dichroism in x-ray absorption will be applied to experimental results: the branching ratio (BR) and sum rule (SR) approaches. A derivation of the BR formulas and detailed comparison to the SR expressions will be made, including error estimations. The BR approach will be seen to be a limiting case form of the SR spin-moment expression and provide a simple picture of the underlying physics in magnetic x-ray circular dichroism absorption in 3d magnetic materials.

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Optical Characterization Of Indium Arsenide Antimonide Semiconductors Grown By Molecular Beam Epitaxy, Michael A. Marciniak Sep 1995

Optical Characterization Of Indium Arsenide Antimonide Semiconductors Grown By Molecular Beam Epitaxy, Michael A. Marciniak

Theses and Dissertations

The material parameters and crystalline quality of undoped, MBE-grown InAs1-xSbx nearly lattice-matched to (100) GaSb (-0.617% ≤ Δ a-a ≤ +0.708%) similar to material used for mid-infrared semiconductor lasers were determined by optical characterization. Absorption measurements at temperatures between 6-295 K determined the energy gap and wavelength-dependent absorption coefficient for each sample. The compositional dependence of the energy gap was anomalous when compared to previously reported data, suggesting phase separation existed in the material. The samples were also studied by temperature- and excitation-dependent photoluminescence (PL), which, for the majority of cases, showed only a single band-edge peak, …

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Non-Imaging Infrared Spectral Target Detection, Matthew R. Whiteley Sep 1995

Non-Imaging Infrared Spectral Target Detection, Matthew R. Whiteley

Theses and Dissertations

Automatic detection of time-critical mobile targets using spectral-only infrared radiance data is explored. A quantification of the probability of detection, false alarm rate, and total error rate associated with this detection process is provided. A set of classification features is developed for the spectral data, and these features are utilized in a Bayesian classifier singly and in combination to provide target detection. The results of this processing are presented and sensitivity of the class separability to target set, target configuration, diurnal variations, mean contrast, and ambient temperature estimation errors is explored. This work introduces the concept of atmospheric normalization of …

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Floquet Description Of Multiphoton Processes In Li, D. I. Duncan, J. Greg Story, Thomas F. Gallagher Sep 1995

Floquet Description Of Multiphoton Processes In Li, D. I. Duncan, J. Greg Story, Thomas F. Gallagher

Physics Faculty Research & Creative Works

We have made several different types of measurements of the three-photon ionization of Li produced by 3-ps laser pulses and describe the results using a Floquet picture. Over the photon frequency range 15 000 to 15 800 cm-1, Li represents a strongly coupled three-state system with the 2s ground state coupled to the 2p and 3d states by one and two photons, respectively. Energy analysis of the photoelectrons allows the measurement of the intensity dependent shift of the 2s Floquet state during the laser pulse. The shift shows a strong frequency dependence that is not predicted by first-order …

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