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Articles 991 - 1017 of 1017

Full-Text Articles in Physics

Einstein's Equations In Vacuum Spacetimes With Two Spacelinke Killing Vectors Using Affine Projection Tensor Geometry, Miles D. Lawrence Jan 1994

Einstein's Equations In Vacuum Spacetimes With Two Spacelinke Killing Vectors Using Affine Projection Tensor Geometry, Miles D. Lawrence

Theses and Dissertations

Einstein's equations in vacuum spacetimes with two spacelike killing vectors are explored using affine projection tensor geometry. By doing a semi-conformal transformation on the metric, a new "fiducial" geometry is constructed using a projection tensor fields. This fiducial geometry provides coordinate independent information about the underlying structure of the spacetime without the use of an explicit form of the metric tensor.

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Handwritten Word Recognition Based On Fourier Coefficients, Gary F. Shartle Dec 1993

Handwritten Word Recognition Based On Fourier Coefficients, Gary F. Shartle

Theses and Dissertations

A machine which can read unconstrained words remains an unsolved problem. For example, automatic entry o handwritten documents into a computer is yet to be accomplished. Most systems attempt to segment letters o a word and read words one character at a time. Segmenting a handwritten word is very difficult and often, the confidence of the results is low. Another method which avoids segmentation altogether is to treat each word as a whole. This research investigates the use of Fourier Transform coefficients, computed from the whole word, for the recognition of handwritten words. To test this concept, the particular pattern …

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Vibrational Energy Transfer Within The B3Π(0+U) State Of 79Br2 Upon Collision With N2, O2, No, And Sf6, Gregory S. Williams Dec 1993

Vibrational Energy Transfer Within The B3Π(0+U) State Of 79Br2 Upon Collision With N2, O2, No, And Sf6, Gregory S. Williams

Theses and Dissertations

Vibrational transfer and electronic quenching in the lower vibrational levels of the 79Br2(B; v'≤3) were investigated using spectrally resolved, temporally resolved pulsed laser induced fluorescence techniques. Spectrally resolved emissions from collisionally populated Br2(B) vibrational levels were observed for N2, O2, NO, and SF6collision partners. The vibrational transfer was efficient in the nonpredissociative vibrational levels and is adequately described by the Montroll-Shuler model. An average fundamental vibrational transfer rate coefficient of kv(l,0)=3.4(±0.6) x 10-11 cm3/molec-sec predicts the vibrational transfer rates for the 0≤v'≤3 collisions with …

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Experimental Verification Of Tomographic Reconstruction Of Turbulent Air Flow Structure Using Optical Wavefront Measurements, Bryon L. Pedersen Dec 1993

Experimental Verification Of Tomographic Reconstruction Of Turbulent Air Flow Structure Using Optical Wavefront Measurements, Bryon L. Pedersen

Theses and Dissertations

The performance of an aircraft based optical system is degraded by aero-optic turbulence. The varying index of refraction within the turbulent field causes phase perturbation in an optical wave. In order to compensate for aero-optic turbulence effects, the nature of the turbulence must be understood. Large scale, organized structure within the turbulence has been found to contribute significantly to the overall phase perturbation caused by a turbulent field. A unique approach was devised to determine the turbulence structure using tomographic reconstruction techniques. Tomography provides an excellent means to determine the underlying structure within a turbulent field. The tomographic reconstruction produces …

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Performance Comparison Of Shearing Interferometer And Hartmann Wave Front Sensors, Timothy L. Pennington Dec 1993

Performance Comparison Of Shearing Interferometer And Hartmann Wave Front Sensors, Timothy L. Pennington

Theses and Dissertations

The resolution of optical imaging systems is severely degraded from the diffraction limit by the random effects of the atmosphere. Techniques exist to compensate for the atmospheric turbulence, one of which is adaptive optics. A critical component in the adaptive optics system is the wavefront sensor. Presently, two types of sensors are being used-the Hartmann-Shack Wavefront Sensor and the Shearing Interferometer. Previous studies have compared these two sensors and found them to perform identically for a point source. However, to date, no comparison has been performed for an extended source and subaperture spacing larger than the correlation length of the …

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Improved Quality Of Reconstructed Images Through Sifting Of Data In Statistical Image Reconstruction, Craig A. Stoudt Dec 1993

Improved Quality Of Reconstructed Images Through Sifting Of Data In Statistical Image Reconstruction, Craig A. Stoudt

Theses and Dissertations

The U.S. Air Force employs adaptive optics systems to produce images of exo-atmospheric objects. Typically, a large set of short exposure images are collected, re-centered to compensate for random image motion, averaged together to improve the signal to noise ratio, and then processed to form a reconstructed image. It is known that some short exposure images will be better than others, so some researchers have suggested that image quality can be improved by selecting a subset of the short exposure images according to some quality criterion, and then processing the average of this subset to form a single, high quality …

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Objective Image Quality Metrics: Applications For Partially Compensated Images Of Space Objects, David J. Lee Dec 1993

Objective Image Quality Metrics: Applications For Partially Compensated Images Of Space Objects, David J. Lee

Theses and Dissertations

Digital image reconstruction tasks currently require human intervention for a subjective evaluation of image quality. A method for unsupervised measurement of digital image quality is desired. This research investigated various parameters metrics that can be automatically extracted from a digital image and tested how well they correlated with image quality. Specifically, images of orbiting satellites captured by a partially compensated adaptive optics telescope were dealt with. Two different types of quantities were investigated 1) Fourier spectral parameters, based on the spatial- frequency sensitivities of the HVS; and 2) Histogram shape parameters i.e image statistical moments giving quantitative insight into the …

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Hyperspectral Analysis Of Space Objects: Signal To Noise Evaluation, Daniel Hrovat Dec 1993

Hyperspectral Analysis Of Space Objects: Signal To Noise Evaluation, Daniel Hrovat

Theses and Dissertations

Hyperspectral analysis of space objects is being considered as a means of enhancing Space Object Identification. SOI capabilities. This study develops a mathematical simulation based on fundamental radiometry principles to evaluate the feasibility of hyperspectral analysis of space objects. The study uses Signal to Noise Ratio SNR as the basis for the feasibility evaluation, and addresses the question Is there enough target signal in narrow wavelength bandwidths to conduct hyperspectral measurements of space objects The analysis characterizes the target signal and noise sources using fundamental radiometry, and develops a flexible radiometry model which calculates the target signal count rate, and …

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Performance Impacts For Actuator Misalignments And Failures In Large- Aperture Adaptive-Optic Telescopes, Timothy D. Hogan Dec 1993

Performance Impacts For Actuator Misalignments And Failures In Large- Aperture Adaptive-Optic Telescopes, Timothy D. Hogan

Theses and Dissertations

Large-aperture telescopes require adaptive optics in order to compensate for atmospheric turbulence which would otherwise negate the resolution advantages of using large apertures. This investigation analyzes the impacts of misalignments and failures, in the deformable mirror actuators, upon the performance of such systems. A numerical simulation of a standard adaptive optics system is used to generate characteristic optical transfer function OTF and signal-to-noise ratio SNR performance metrics. The performance impacts of the misalignments are shown to be dependent upon the Fried parameter effective telescope diameter, the source object brightness, and the control system time delay. The degree of performance degradation …

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A Non-Homogeneous, Spatio-Temporal, Wavelet Multiresolution Analysis And Its Application To The Analysis Of Motion, Thomas J. Burns Dec 1993

A Non-Homogeneous, Spatio-Temporal, Wavelet Multiresolution Analysis And Its Application To The Analysis Of Motion, Thomas J. Burns

Theses and Dissertations

This research presents a multiresolution wavelet analysis tool for analyzing motion in time sequential imagery. A theoretical framework is developed for constructing an L2R wavelet multiresolution analysis from three non-identical spatial and temporal L2R wavelet multiresolution analyses. This framework provides the flexibility to tailor the spatio-temporal frequency characteristics of the three dimensional wavelet filter to match the frequency behavior of the analyzed signal. An unconventional, discrete multiresolution wavelet decomposition algorithm is developed which yields a rich set of independent spatio-temporally oriented frequency channels for analyzing, the size and speed characteristics of moving objects. Unlike conventional wavelet decomposition methods, this algorithm …

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Spectroscopic And Vibrational Energy Transfer Studies In Molecular Bromine, Courtney D. Holmberg Dec 1993

Spectroscopic And Vibrational Energy Transfer Studies In Molecular Bromine, Courtney D. Holmberg

Theses and Dissertations

Vibrational transfer and electronic quenching in the lower vibrational levels (v' < 3) of the B3π(0u+) state of 79Br2 were investigated using spectrally resolved, temporally resolved laser induced fluorescence techniques. Spectrally resolved emissions from collisionally populated Br2(B) vibrational levels were observed for Br2 and rare gas collision partners. Vibrational transfer was efficient in the non-predissociative vibrational levels and was adequately described by the Montroll-Shuler model for harmonic oscillators. A single fundamental rate coefficient for vibrational transfer from v' = 1 to v' = 0, kv(1,0), characterizes vibrational relaxation. For Br2, the …

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Characterization Of An Lcd For Use As A Programmable Phase Shifter To Produce A Single-Lobed Far-Field Pattern In A Phased Array, Gregory S. Kenyon Dec 1993

Characterization Of An Lcd For Use As A Programmable Phase Shifter To Produce A Single-Lobed Far-Field Pattern In A Phased Array, Gregory S. Kenyon

Theses and Dissertations

The liquid crystal display LCD from an inexpensive pocket television was converted to a spatial light modulator SLM for the purpose of altering the phase front of a ten element diode laser array to produce a single lobe far field pattern. Characterization of the SLM determined the amount of phase shift, amplitude modulation and polarization rotation properties. Nonuniformities within the phase shifter and insufficient phase shift prevented the formation of a single lobe. However, a very limited phase grating was created and analyzed. LCDs from inexpensive commercial pocket televisions were found unsuitable for use as phase shifting spatial light modulators.

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High Resolution Fourier Transform Absorption Spectrum Of 79Br2 B3Π(0U+) ← X1ΣG+, Robert E. Franklin Dec 1993

High Resolution Fourier Transform Absorption Spectrum Of 79Br2 B3Π(0U+) ← X1ΣG+, Robert E. Franklin

Theses and Dissertations

High Resolution Fourier Transform Spectroscopy has been conducted for the 79Br2 B3π(0u+) ← X1Σg+ system of 79Br2. A total of 64 vibrational levels, including v"= 0-3 and v' = 10-33, have been observed and assigned. Rotational levels as high as J=76 were observed. A global fitting routine has been developed to fit the rotational spectra to the Dunham Expansion. Using Bv and Dv for both the X and B state, rotational transitions were calculated to within 0. 02 cm-1. The expansions of …

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Characterization Of Nonlinear Effects In Optically Pumped Vertical Cavity Surface Emitting Lasers, Scott L. Brown Dec 1993

Characterization Of Nonlinear Effects In Optically Pumped Vertical Cavity Surface Emitting Lasers, Scott L. Brown

Theses and Dissertations

The nonlinear characteristics of optically pumped Vertical Cavity Surface Emitting Lasers VCSELs are identified, isolated, and quantified. Three different VCSELs are evaluated including two with gain regions of bulk GaAs operating at 875nm and one multi-quantum well MQW InGaAs VCSEL operating at 950nm. The nonlinearities evaluated include those due to cavity temperature, carrier injection, and internal lasing field. The VCSELs are pumped by a picosecondfemtosecond TiSapphire laser which is configured to operate in CW, gated CW minimum gate width was 200ns, picosecond, and gated picosecond modes. A linear relationship is shown between wavelength and substrate temperature, cavity temperature, and injected …

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Predicting Nonlinear Time Series, James C. Gainey Jr. Dec 1993

Predicting Nonlinear Time Series, James C. Gainey Jr.

Theses and Dissertations

Predicting future values of a time series has many practical uses in real-time signal processing and understanding. This thesis implements an Adaptive Time Delay Neural Network ATNN capable of user-defined degeneration to the more common Time Delay Neural Network TDNN. Time delays along axons or at the synapses, which vary in biological systems, motivate this research. The ATNNTDNN test results and time series prediction capabilities are compared to those of the Real-Time Recurrent Learning RTRL algorithm. To show the advantages and disadvantages of using TDNN and ATNN for prediction versus the RTRL, the networks were applied to two problems incommensurate …

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Optical Wavelet Transform For Fingerprint Identification, Robert P. Macdonald Dec 1993

Optical Wavelet Transform For Fingerprint Identification, Robert P. Macdonald

Theses and Dissertations

The Federal Bureau of Investigation FBI has recently sanctioned a wavelet fingerprint image compression algorithm developed for reducing storage requirements of digitized fingerprints. This research implements an optical wavelet transform of a fingerprint image, as the first step in an optical fingerprint identification process. Wavelet filters are created from computer generated holograms of biorthogonal wavelets, the same wavelets implemented in the FBI algorithm. Using a detour phase holographic technique, a complex binary filter mask is created with both symmetry and linear phase. The wavelet transform is implemented with continuous shift using an optical correlation between binarized fingerprints written on a …

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Color Image Segmentation, Kimberley A. Mccrae Dec 1993

Color Image Segmentation, Kimberley A. Mccrae

Theses and Dissertations

The most difficult stage of automated target recognition ATR is segmentation. Current AFIT segmentation problems include faces and tactical targets previous efforts to segment these objects have used intensity and motion cues. This thesis develops a color preprocessing scheme to be used with the other segmentation techniques. A neural network is trained to identify the color of a desired object, eliminating all but that color from the scene. Gabor correlations and 2D wavelet transformations will be performed on stationary images and 3D wavelet transforms on multispectral data will incorporate color and motion detection into the machine visual system. The thesis …

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A Theoretical Investigation Of Electrically Tunable Birefringent Optical Filters As The Special Discriminator In Hyperspectral Imaging Systems, Duane A. Sauve Dec 1993

A Theoretical Investigation Of Electrically Tunable Birefringent Optical Filters As The Special Discriminator In Hyperspectral Imaging Systems, Duane A. Sauve

Theses and Dissertations

This study investigated electrically tunable birefringent optical filters for use as the spectral discriminator in hyperspectral imaging systems. Spectral discrimination requirements for hyperspectral systems were defined using specification from two state-of-the-art hyperspectral imaging systems. The spectral discrimination requirements led to the definition of the ideal tunable optical filter for spectral discrimination purposes. Analytical and computer an analysis was performed for known birefringent filters which showed promise of electrical tunability excluding acousto-optic filters. No perfect match was found to the ideal tunable optical filter for hyperspectral imaging defined in this thesis. Both Lyot and Solc based filters exhibited two drawbacks for …

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System Design Analysis Of A Lightweight Laser Satellite Terminal, Brian C. Page Dec 1993

System Design Analysis Of A Lightweight Laser Satellite Terminal, Brian C. Page

Theses and Dissertations

This study investigated the technological feasibility of a man- portable satellite laser communications system. Areas of interest were an end- to-end system analysis on the communications link evaluation of atmospheric effects and evaluation of semi-conductor lasers as the laser source. A literature search revealed that satellite laser communication research is primarily directed at inter-satellite links. There have been some proposed systems for space-to-ground laser communications systems, but they all utilize large fixed ground stations. The focus of this research effort is directed at a small man-portable ground station capitalizing on recent advances in semiconductor laser devices. Baseline satellite communication systems …

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Infrared Fluorescence Studies Of Electronic-To-Vibrational Energy Transfer In A Br2:No System, Michael R. Hawks Dec 1993

Infrared Fluorescence Studies Of Electronic-To-Vibrational Energy Transfer In A Br2:No System, Michael R. Hawks

Theses and Dissertations

Steady-state photolysis techniques were used to study electronic-to- vibrational energy transfer mechanisms from atomic bromine to nitric oxide. Molecular bromine was photodissociated by 488nm radiation to produce equal parts Br(2P1/2) and Br(2P3/2). Side fluorescence intensity from Br(2P1/2) at 2.7 µm and from NO (v=1 and 2) around 5.3 µm measured as a function of bromine pressure and nitric oxide pressure. The branching ratio collisional transfer into the first and second states of NO was determined, and previously reported rates for quenching of NO by molecular bromine were verified.

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The Effects Of Optical Feedback On Polarization Of Vertical Cavity Surface Emitting Lasers, Gregory J. Vansuch Dec 1993

The Effects Of Optical Feedback On Polarization Of Vertical Cavity Surface Emitting Lasers, Gregory J. Vansuch

Theses and Dissertations

Vertical Cavity Surface Emitting Lasers VCSELs are a type of semiconductor laser with a cavity oriented orthogonally to the planes of material growth. These lasers differ from conventional edge emitting lasers in several important ways. They have symmetric output beams and they are easily built into two dimensional arrays, making them very attractive as photonic components. The characteristic of interest in this thesis is polarization. While the asymmetric cavities of edge emitters exhibit a clear preference for light polarized in a particular direction, the cylindrically symmetric cavity of a VCSEL has no clear preference. Therefore, it should be relatively easy …

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Design And Performance Evaluation Of A Gas Chromatograph Micromachined In A Single Crystal Silicon Substrate, Rocky R. Reston Mar 1993

Design And Performance Evaluation Of A Gas Chromatograph Micromachined In A Single Crystal Silicon Substrate, Rocky R. Reston

Theses and Dissertations

This investigation designed and developed a miniature gas chromatograph (GC) using silicon micromachining techniques. The GC is composed of a miniature sample injector (10 µl sample loop); a 0.9 m long, rectangular-shaped (300 µm width and 10 micrometers height) capillary column coated with a 0.2 µm thick copper phthalocyanine (CuPc) stationary phase; and a dual-detector scheme incorporating a CuPc-coated chemiresistor and a 125 µm diameter thermal conductivity detector bead. Micromachining was employed to fabricate the sample injector interface, the GC column, and the dual-detector cavity. A novel processing technique was developed to sublime the CuPc stationary phase coating on the …

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Increasing The Corrected Field Of View Of An Adaptive Optical Telescope, Dustin C. Johnston Dec 1992

Increasing The Corrected Field Of View Of An Adaptive Optical Telescope, Dustin C. Johnston

Theses and Dissertations

Current adaptive optical telescope designs use a single deformable mirror (DM) to compensate for atmospheric distortion. The corrected field of view (FOV) of an adaptive optics system could be increased through the use of multiple DMs optically conjugated to corresponding planes which sample the turbulence region in altitude. Often, the atmospheric turbulence responsible for the degradation of telescope images is concentrated in several layers. Each DM would correct for the component of the total wavefront in the pupil contributed by one or more layers. If the atmosphere does not possess a layered structure, the best fit of the turbulence profile …

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Collisional Detachment Of Anions Using Fourier Transform Mass Spectrometry, Kevin B. Riehl Dec 1992

Collisional Detachment Of Anions Using Fourier Transform Mass Spectrometry, Kevin B. Riehl

Theses and Dissertations

Fourier Transform Mass Spectrometry (FTMS) is used to make energy resolved ion-neutral reaction measurements at high translational energies (up to several hundred eV). The technique is demonstrated for collisional detachment of anions, and should be easily applied to other inelastic reactions. Collisional detachment cross sections of iodine anions onto gas phase targets of neon, xenon, and trifluoromethyl iodide are measured for 1-300 eV (lab frame). Peak detachment cross sections are roughly 2, 8.5, and 7 Å2, respectively. Ion kinetic measurements show the iodine anion is unreactive in trifluoromethyl iodide at thermal energies. Positive ion chemistry is consistent with …

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Lasing Conditions Of Elemental Sulfur In A Gas Discharge, David E. Egbert Sep 1972

Lasing Conditions Of Elemental Sulfur In A Gas Discharge, David E. Egbert

Theses and Dissertations

The partial pressures from heated sulfur crystals and helium, and sulfur and nitrogen required for ionic sulfur laser action in a gas discharge were determined. Previous work with sulfur lasers is reviewed and population inversion mechanisms are presented for the ionic sulfur laser lines. Possible excitation mechanisms are presented for both electron and ion or atomic collision excitation. Transition diagrams for all the known ionic sulfur laser transitions and an approximate potential energy curve for the diatomic sulfur molecule are presented. Laser action was achieved only when a spark gap pulser was used with a laser tube especially designed to …

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Mechanical Effects Of Acoustic Transients On Tobacco Mosaic Virus, Philip Edward Hamrick Jan 1968

Mechanical Effects Of Acoustic Transients On Tobacco Mosaic Virus, Philip Edward Hamrick

Theses and Dissertations

The mechanical breakage of tobacco mosaic virus (TMV) due to the action of acoustic transients has been investigated. The acoustic transients were produced by transient heating of a Prussian blue dye solution (attenuation coefficient of 1000 per cm) when a ruby laser light (20 x 106 watts) was incident on the dye surface. A quartz piezoelectric transducer was used to determine the amplitude and form of the acoustic wave. The production of acoustic waves by transient heating is discussed, and the theoretical form of the acoustic wave determined for various boundary and initial conditions are compared to the experimentally …

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Investigation Of The Platinum-Rich Portion Of The Platinum-Tantalum Phase Diagram, Bob Dean Browning Aug 1961

Investigation Of The Platinum-Rich Portion Of The Platinum-Tantalum Phase Diagram, Bob Dean Browning

Theses and Dissertations

The Pt-Ta binary system was investigated at two isotherms;1000°C and 1500°C, and at eleven alloy compositions in the range of 50 to 100 atomic percent platinum. The alloys were examined by x-ray diffraction and metallography. Three intermetallic compounds, Pt2Ta, Pt3Ta, and Pt4Ta were found to exist in this composition range. The Pt4Ta intermetallic appeared only at the 1500°C isotherm. Platinum dissolved tantalum substitutionally to 90 atomic percent at 1500 °C and to approximately 80 atomic percent at 1000 °C.

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