Digital Commons Network^™

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(²P_1/2) and Br(²P_3/2). Side fluorescence intensity from Br(²P_1/2) 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.

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

Ionic Charge Dependence Of The Zero Degree Binary Encounter Peak For Partially Stripped Heavy Ions, W. Wolff, H. E. Wolff, J. L. Shinpaugh, Jee-Ching Wang, Ronald E. Olson, D. Fainstein, S. Lencinas, U. Bechthold, R. Herrmann, H. Schmidt-Bocking

Chemical and Biochemical Engineering Faculty Research & Creative Works

We report on the measurements of double differential cross sections, at zero degree, for the production of secondary electrons from the collision of 0, 6 MeV amu^-1 Cu⁵⁺, I⁷⁺, Au¹¹⁺, U¹³⁺, Cu¹⁹⁺, t²³⁺ and Au²⁹⁺ projectiles with H₂ and He. The shapes and positions of the observed binary encounter electron peaks are compared with continuum distorted wave-eikonal initial state (CDW-EIS), impulse approximation and classical trajectory Monte Carlo calculations, as well as with predictions from an adiabatic resonant tunnelling model recently proposed by Fainstein and co-workers. The …

Critical Slowing Down Of Cluster Algorithms For Ising Models Coupled To 2-D Gravity, Mark Bowick, Marco Falcioni, Geoffrey Harris, Enzo Marinari

Physics - All Scholarship

We simulate single and multiple Ising models coupled to 2-d gravity using both the Swendsen-Wang and Wolff algorithms to update the spins. We study the integrated autocorrelation time and find that there is considerable critical slowing down, particularly in the magnetization. We argue that this is primarily due to the local nature of the dynamical triangulation algorithm and to the generation of a distribution of baby universes which inhibits cluster growth.

Microphysical Approach To Nonequilibrium Dynamics Of Quantum Fields, Marcelo Gleiser, Rudnei O. Ramos

Dartmouth Scholarship

We examine the nonequilibrium dynamics of a self-interacting λφ4 scalar field theory. Using a real time formulation of finite temperature field theory we derive, up to two loops and O(λ2), the effective equation of motion describing the approach to equilibrium. We present a detailed analysis of the approxi- mations used in order to obtain a Langevin-like equation of motion, in which the noise and dissipation terms associated with quantum fluctuations obey a fluctuation-dissipation relation. We show that, in general, the noise is colored (time-dependent) and multiplicative (couples nonlinearly to the field), even though it is still Gaussian distributed. The noise …

Radial Excited States For Heavy Quark Systems In Nrqcd, Simon Catterall, F. R. Devlin, I. T. Drummond, R. R. Hogan

Physics - All Scholarship

Following the Non-Relativistic QCD approach we use a gauge invariant smearing method with factorization to measure the excitation energies for a heavy Q\bar{Q} system on a 24^3\times 48 lattice at \beta=6.2. The results come from averaging over an ensemble of 60 QCD configurations. In order to enhance the signal from each configuration we use wall sources for quark propagators. The quark Hamiltonian contains only the simplest non-relativistic kinetic energy term. The results are listed for a range of bare quark masses. The mass splittings are insensitive to this variable though there are a slight trends with increasing quark mass. For …

Simulation Of Bulk Silicon Crystals And Si(111) Surfaces With Application To A Study Of Fluorine Coverage Of The Surfaces, Chen K. Lutrus, T. Oshiro, Donald E. Hagen, Sung-Ho Suck Salk

Physics Faculty Research & Creative Works

Computational efficiency for the simulation of bulk crystals and surfaces is highly desirable. In an effort to study semiconductor crystals, we present a self-consistent treatment for the simulation of silicon crystals and surfaces based on the combination of a siligen model and a semiempirical Hamiltonian method. An artificial atom called siligen is introduced for the application of the semiempirical method to finite-size silicon clusters. The calculated average bond energies for the saturated silicon clusters are between 2.045 and 2.568 eV, compared to the measured value of 2.31 eV. A simulated bulk silicon surface using siligens is introduced in order to …

Cation Distribution In Natural Ferrites, H. A. Maia, F. F. T. De Araújo, M. A. B. De Araújo, J. Danon, Richard B. Frankel

Physics

Mössbauer spectra of jacobsite have been recorded at temperatures of 4.2, 125, 180, 240 and 300 K and with an external magnetic field of 60 kOe applied parallel to the incident radiation at 4.2 K. The results show the presence of two different magnetic hyperfine interactions associated with the iron nuclei. Spectra of samples in external magnetic fields indicate the same sign for the magnetic hyperfine interactions, implying that both iron ions occupy only the octahedral sublattice. These results are compared with data from synthetic stoichiometry manganese ferrite, and a model of cation distribution, assuming the existence of vacancies, is …

Triply Differential (E,2e) Cross Sections For He From Threshold To 50 Ev Above, C. Pan, Anthony F. Starace

Anthony F. Starace Publications

Distorted wave calculations of the triply differential cross sections for electron-impact ionization of He are presented for electrons sharing ≤ 50 eV excess energy (E_x) and having the coplanar, θ₁₂ = π geometry. The results are in good agreement with absolute experimental measurements of T. Rösel et al. [Phys. Rev. A 46 (1992) 2539-2552] and of A. J. Murray, M. B. Woolf, and F. H. Read [J. Phys. B 25 (1992) 3021-3036]. For final state electrons sharing 2 eV excess energy equally, many-body perturbation theory corrections to the authors' first order (e,2e) triply differential cross …

Differential Cross Sections For Single And Double Ionization Of Helium By Protons And Antiprotons, L. Meng, Ronald E. Olson, R. Dömer, J. Ullrich, H. Schmidt-Bocking

Physics Faculty Research & Creative Works

Theoretical and experimental cross sections are presented for single and double ionization of He differential in the projectile scattering angle and the transverse energy of the outgoing recoil ion. A dynamical four-body classical trajectory Monte Carlo method that includes radial electron correlation is utilized to calculate total and differential cross sections for 300 and 500 keV protons and antiprotons in impact collisions with He. The azimuthal emission characteristics of electrons, recoil ion and projectile relative to each other are analyzed to provide detailed information on the dynamical differences between single and double ionization and between proton and antiproton impact. © …

Driven Diffusion Of Particles, First-Passage Front, And Interface Growth, R. Bidaux, Ras B. Pandey

Faculty Publications

We study a computer-simulation model for driven particles on a discrete lattice where a fraction p of the lattice sites is randomly occupied by frozen impurities (barriers), and an imposed bias governs the particles’ hopping through the lattice. These particles (the carriers) are initially released from a source of wetting fluid from one end of the lattice in order to wet and the dry lattice on their trails. We study the transport of particles, frontier of their trail, and the growth of the interface between the wet and dry regions as a function of the biased field and the number …

Simulation Of Vertical Tail Buffet In Internal Vortex Breakdown Flows, Mark William Flanagan

Mechanical & Aerospace Engineering Theses & Dissertations

Computational simulation of vertical tail buffet in an internal vortex breakdown flow is considered. The fiuid-flow problem is formulated using the full, compressible, unsteady Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite volume scheme. The fluid-flow problem is solved in a configured circular duct using quasi-axisymmetric assumptions to simplify the flow equations. A plate is placed transverse to the incoming flow. Solution of the flow in the duct is performed with and without a rigid plate, and with and without an elastic plate. The elastic response of the plate is calculated assuming that it is a cantilever …

Resonant And Non-Resonant Pieces Of The D\Rightarrow \Bar{K}Π Semileptonic Transition Amplitude, Joseph Schechter, A. Subbaraman, S. Surya

Physics - All Scholarship

We compare the resonant and non-resonant contributions in various regions of phase space for the D\rightarrow \bar{K}\p semileptonic transition amplitude, computed in a chiral model which incorporates the heavy quark symmetry. Remarks on the significance for experiment and for chiral perturbation theory are made. hep-ph/yymmnnn

Long-Range Interactions And The Pair-Correlation Function In Dipolar Main-Chain Nematic Polymers, Eugene M. Terentjev, Rolfe G. Petschek

Faculty Scholarship

A thermotropic nematic phase of dipole mesogenic polymers with long-range interactions is considered. Using a graphical representation of the corresponding path integrals for the grand canonical ensemble, we derive a Dyson-type equation for the pair-correlation function. We calculate this correlation function in the random-phase approximation, accounting for anisotropic steric repulsion, dispersion, and dipole-dipole interactions between monomers. As an implication of the model, we calculate the (anisotropic) dielectric susceptibiity of a dipolar nematic polymer, which shows a divergent behavior at some critical temperature.

Semiclassical Approach To Quantum-Mechanical Problems With Broken Supersymmetry, Ranabir Dutt, Asim Gangopadhyaya, Avinash Khare, A. Pagnamenta, Uday P. Sukhatne

Physics: Faculty Publications and Other Works

The semiclassical WKB approximation method is reexamined in the context of nonrelativistic quantum-mechanical bound-state problems with broken supersymmetry (SUSY). This gives rise to an alternative quantization condition (denoted by BSWKB) which is different from the standard WKB formula and also different from the previously studied supersymmetric (SWKB) formula for unbroken SUSY. It is shown that to leading order in ħ, the BSWKB condition yields exact energy eigenvalues for shape-invariant potentials with broken SUSY (harmonic oscillator, Pöschl-Teller I and II) which are known to be analytically solvable. Further, we show explicitly that the higher-order corrections to these energy eigenvalues, up to …

Photoluminescence Spectroscopy Of Zinc Germanium Diphosphide (Zngep2), Jack E. Mccrae

Theses and Dissertations

Zinc germanium diphosphide (ZnGeP₂) is a chalcopyrite semiconductor with strong nonlinear optical properties and potential application to Air Force interests. The characteristics of this material have been studied using photoluminescence (PL) spectroscopy. The PL spectrum is dominated by transitions from the conduction band to a deep acceptor level, and features in the spectrum suggest that more than one transition is being observed. The PL is partially polarized, and the degree of polarization appears to differ for each feature in the spectrum. The relative PL intensity of these features are seen to depend upon the wavelength of the excitation …

Size Imperfections In One-Dimensional Periodic Optical Arrays, Yan Zhong

Masters Theses

The concepts of band theory for electrons can also be employed to describe the behavior of electromagnetic waves propagating in periodic dielectric structures. These periodic structures can produce photonic band gaps in which the propagation of electromagnetic waves is strictly prohibited. The introduction of impurities in such system gives rise to donor and acceptor gap modes in electron system and to energy gap modes in photonic system.

In my thesis, the impurity modes in one-dimensional, periodic, dielectric system will be studied. These modes are introduced in the 1-d dielectric structure by altering the thickness of one slab in an otherwise …

Observation Of Non-Isotropic Auger Angular Distribution In The C(1s) Shape Resonance Of Co, Oliver Hemmers, Franz Heiser, J. Eiben, R. Wehlitz, U. Becker

Environmental Studies Faculty Publications

Angle-resolved high-resolution C(KVV) Auger spectra of CO were taken in the vicinity of the C(1s) σ^* shape resonance. These spectra show clear evidence for the theoretically predicted anisotropic K-shell Auger emission in molecules. Complementary results from angle-resolved photoion spectroscopy show that the small size of the observed effect is, besides the varying intrinsic anisotropy of the Auger decay, also due to a smaller anisotropy in the primary absorption process than originally predicted but in good agreement with more recent calculations. Contrary to this, satellite Auger transitions show unexpectedly large anisotropies.

Electron-Beam Modification Of Gaas Surface-Potential - Measurement Of Richardson Constant, S. M. Lindsay, Joseph W. Hemsky, David C. Look

Physics Faculty Publications

The surface potential of GaAs is strongly modified in the presence of a high‐energy electron beam due to the creation of electron‐hole pairs in the depletion region and the subsequent drift of the holes to the surface where they neutralize surface states. This effect is modeled in terms of a parameter K=A∗T²/I_b(dE/dz)η, where I_b is the beam current density, A∗ is the effective Richardson constant, dE/dz is the beam energy loss per unit length, and η⁻¹ is the average energy required to …

Cellular Track Model For Study Of Heavy Ion Beams, Judy L. Shinn, Robert Katz, Francis A. Cucinotta, John W. Wilson, Duc M. Ngo

Robert Katz Publications

Track theory is combined with a realistic model of a heavy ion beam to study the effects of nuclear fragmentation on cell survival and biological effectiveness . The effects of secondary reaction products are studied as a function of depth in a water column. Good agreement is found with experimental results for the survival of human T-1 cells exposed to monoenergetic carbon, neon, and argon beams under aerobic and hypoxic conditions. The present calculation, which includes the effect of target fragmentation, is a significant improvement over an earlier calculation because of the use of a vastly improved beam model with …

Temperature And Supersaturation Dependent Nucleation Rates Of Heterogeneous Water By Molecular Cluster Model Calculation, Chen K. Lutrus, Donald E. Hagen, Sung-Ho Suck Salk

Physics Faculty Research & Creative Works

A statistical mechanical method to evaluate the energy of formation of water clusters attached to a foreign particle surface is described, with the binding energy being evaluated on a molecular level, using semiempirical modified neglect of diatomic overlap (MNDO) theory. The model is applied to water nucleation on a silicon oxide surface. The binding energy contribution, which represents the energy of formation at T=0 K, is found to slightly (but not negligibly in the thermal sense) increase with the number of hydrogen bonds between the water cluster and the condensation nucleus whose surface is made of silicon oxide. An analytic …