Digital Commons Network^™

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.

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 InAs_1-xSb_x 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, …

Combination Effects Of Irradiation And Chemical Doping On High Temperature Superconductors, Russell J. Fedewa

Honors Theses

The goal of this project is to investigate some methods that improve the critical transport current in high temperature superconductors. A superconductor is a material which can allow an electrical current to flow through it with no resistance. This makes them ideal for a wide variety of applications. Most of the present use is in science or medicine, and show promise in computer circuitry materials and electromagnetic trains. This experiment explores a means of increasing the critical current, the maximum amount of electric current that can pass, and which at present is too low to permit the use of superconductors …

Broadband Dynamic, Holographically Self-Recorded, And Static Hexagonal Scattering Patterns In Photorefractive Knbo3:Fe, Nickolai Kukhtarev, Tatiana V. Kukhtareva, John Caulfield, Partha P. Banerjee, Hsueh-Ling Yu, Lambertus Hesselink

Electrical and Computer Engineering Faculty Publications

We have observed and explained three types of hexagon pattern formation in photo refractive crystal KNb03:Fe. These are:

• Dynamic (laser induced)
• Semipermanent (holographically stored)
• Permanent (induced by a static domain grid) over a wide wavelength range

College Physics Students' Conceptual Understanding Of Area And Volume, And Relationships Between These Concepts And Students' Understanding Of Physics Concepts, Jiang Yu

Dissertations

Concepts such as area and volume are foundational ideas for many concepts introduced in introductory science courses. At the college level, most instructors typically assume that incoming students have already developed an understanding of these underpinning ideas. However, doubt has surfaced in recent years about students' depth of understanding and mastery of these fundamental concepts. Because deficiencies in understanding basic concepts may relate to the learning of subsequent concepts, instructors have expressed concerns about students' understanding of fundamental ideas and if the failure to understand these ideas hinders students' subsequent progress.

This study was designed to (a) investigate the nature …

Transient Wave Mixing And Recording Kinetics In Photorefractive Barium Titanate: A Nonlinear Coupled Mode Approach, Partha P. Banerjee, John M. Jarem

Electrical and Computer Engineering Faculty Publications

By using rigorous coupled-wave diffraction theory along with a time-dependent nonlinear formulation, we analyze two- and multiplewave coupling and the grating kinetics in BaTi03 with different boundary interfaces. Efffects of electrostatic and optical anisotropy have been included in the analysis. Significant mode conversion to higher orders is observed only when the boundary interfaces are highly mismatched.

Comparison Of Time-Domain Reflectometry Performance Factors For Several Dielectric Geometries: Theory And Experiments, S. V. Maheshwarla, R. Venkatasubramanian, Robert F. Boehm

Electrical & Computer Engineering Faculty Research

We propose three nontraditional dielectric geometries and present an experimental and theoretical analysis and comparison of time domain reflectometry (TDR) performances for them. The traditional geometry (the probes inserted in material of essentially infinite extent) is compared to three nontraditional geometries where the probes are affixed outside of a core sample, inside of a bore, or flat on the surface of a semi-infinite solid. Our derivation relates the velocity of electromagnetic wave propagation to the complex permittivities and permeabilities of the media and the geometry for the three nontraditional configurations. Experimental results for air, styrofoam, dry sand, wet sand of …

Guest Editorial: Special Section On Photorefractive Nonlinear Optics, Partha P. Banerjee

Electrical and Computer Engineering Faculty Publications

Hand in hand with experimental work in photorefractives, there is a lot of activity in modeling photorefractive materials and experimental observations in the open literature. This special section contains a paper by Banerjee and Jarem, who use a rigorous coupled wave theory to analyze two- and multiple-wave mixing photorefractive barium titanate, modeled through the Kukhtarev equations.

Single-Layer-Coated Surfaces With Linearized Reflectance Versus Angle Of Incidence: Application To Passive And Active Silicon Rotation Sensors, R. M.A. Azzam, M. M. K. Howlader, T. Y. Georgiou

Electrical Engineering Faculty Publications

A transparent or absorbing substrate can be coated with a transparent thin film to produce a linear reflectanceversus- angle-of-incidence response over a certain range of angles. Linearization at and near normal incidence is a special case that leads to a maximally flat response for p-polarized, s-polarized, or unpolarized light. For midrange and high-range linearization with moderate and high slopes, respectively, the best results are obtained when the incident light is s polarized. Application to a Si substrate that is coated with a SiO₂ film leads to novel passive and active reflection rotation sensors. Experimental results and an error analysis …

All‐Optical Light Modulation In Bacteriorhodopsin Films, F. J. Aranda, R. Garimella, N. F. Mccarthy, D. Narayana Rao, D.V.G.L.N. Rao, Z. Chen, J. A. Akkar, D. L. Kaplan

Physics Faculty Publications

We report a convenient method to obtain all‐optical light modulation in bacteriorhodopsin films using a degenerate four‐wave mixing geometry. Chemically stabilized films of bacteriorhodopsin in a polymer matrix for which the lifetime of the excited M state is tens of seconds were used to demonstrate all‐optical light intensity modulation. The films are observed to be stable over a period of 4 years. Due to the sensitivity of the films, small intensities of order microwatt/ cm² are required in the modulation experiments. Furthermore the fast photochemical transition from M to B permit reasonably fast modulation speeds independent of the slow …

37th Rocky Mountain Conference On Analytical Chemistry

Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 37th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, July 23-27, 1995.

Kolmogorov-Smirnov Test Distinguishes Attractors With Similar Dimensions, Alfonso M. Albano, P. E. Rapp, A. Passamante

Physics Faculty Research and Scholarship

Recent advances in nonlinear dynamics have led to more informative characterizations of complex signals making it possible to probe correlations in data to which traditional linear statistical and spectral analyses were not sensitive. Many of these new tools require detailed knowledge of small scale structures of the attractor; knowledge that can be acquired only from relatively large amounts of precise data that are not contaminated by noise-not the kind of data one usually obtains from experiments. There is a need for tools that can take advantage of ''coarse-grained'' information, but which nevertheless remain sensitive to higher-order correlations in the data. …

Studies Of Mixing Processes In Gases And Effects On Combustion And Stability, Frank Paul Kozusko Jr.

Mathematics & Statistics Theses & Dissertations

Three physical models of laminar mixing of initially separated gases are studied. Two models study the effects of the mixing dynamics on the chemical reactions between the gases. The third model studies the structure and stability of a laminar mixing layer in a binary gas. The three models are:

1. Two ideal and incompressible gases representing fuel and oxidizer are initially at rest and separated across an infinite linear interface in a two dimensional system. Combustion, expected as the gases mix, will lead to a rapid rise in temperature in a localized area, i.e. ignition. The mixing of the gases …

Ohmic Contact To Ion Implanted Gallium Arsenide Antimonide For Application To Indium Aluminum Arsenide-Gallium Arsenide Antimonide Heterostructure Insulated-Gate Field Effect Transistors, Kenneth G. Merkel Ii

Theses and Dissertations

The p-channel In_0.52Al_0.48As-GaAs_1-xSb_x heterostructure insulated-gate field effect transistor (p-HIGFET) is a candidate for complementary integrated circuits due to superior cutoff characteristics and low gate leakage current. Advancement of the In_0.52Al_0.48As-GaAs_1-xSb_x p-HIGFET requires improved source-drain design. Five main tasks were accomplished to achieve this goal. First, thermal limits of the In_0.52Al_0.48As-GaAs_0.51Sb_0.49 HIGFET were investigated. Second, the temperature dependence of band gap and impurity energies were determined for beryllium doped In_0.52Al_0.48. Third, high acceptor concentrations were obtained …

Binary Nucleation Kinetics. I. Self-Consistent Size Distribution, Gerald Wilemski, Barbara Ellen Wyslouzil

Physics Faculty Research & Creative Works

Using the principle of detailed balance, we derive a new self-consistency requirement, termed the kinetic product rule, relating the evaporation coefficients and equilibrium cluster distribution for a binary system. We use this result to demonstrate and resolve an inconsistency for an idealized Kelvin model of nucleation in a simple binary mixture. We next examine several common forms for the equilibrium distribution of binary clusters based on the capillarity approximation and ideal vapor behavior. We point out fundamental deficiencies for each expression. We also show that each distribution yields evaporation coefficients that formally satisfy the new kinetic product rule but are …

Binary Nucleation Kinetics. Ii. Numerical Solution Of The Birth-Death Equations, Barbara Ellen Wyslouzil, Gerald Wilemski

Physics Faculty Research & Creative Works

We numerically solve the complete set of coupled differential equations describing transient binary nucleation kinetics for vapor-to-liquid phase transitions. We investigate binary systems displaying both positive and negative deviations from ideality in the liquid phase and obtain numerical solutions over a wide range of relative rates of monomer impingement. We emphasize systems and conditions that either have been or can be investigated experimentally. In almost every case, we find behavior consistent with Stauffer's idea that the major particle flux passes through the saddle point with an orientation angle that depends on the rates of monomer impingement. When this is true, …

The Kelvin Equation And Self-Consistent Nucleation Theory, Gerald Wilemski

Physics Faculty Research & Creative Works

Issues of self-consistency are reviewed for several unary equilibrium size distributions based on the capillarity approximation. Some apparent difficulties of interpretation are resolved. In terms of the kinetic approach to nucleation theory, the influence of self-consistency on the nucleation rate is shown to arise entirely from differences in the dimer evaporation rates for nearly all versions of classical theory. The nucleation rate behavior of the Kelvin model is explored. In this model, the Kelvin equation is used to prescribe all cluster evaporation rates. Nucleation rates predicted by the Kelvin model are quantitatively similar to those of the self-consistent classical (SCC) …

Intersubband Lasing Lifetimes Of Sige/Si And Gaas/Algaas Multiple Quantum Well Structures, Greg Sun, L. Friedman, Richard A. Soref

Physics Faculty Publications

The feasibility of population inversion is studied for the SiGe/Si system and compared with that of GaAs/AlGaAs. Because of the absence of strong polar optical phonon scattering in SiGe/Si, the lifetime difference of the upper and lower lasing levels, to which the population inversion and laser gain are proportional, is consistently an order of magnitude larger than that of GaAs/AlGaAs; nor does it show the sudden drop to zero or negative values when the lasing energy exceeds the optical phonon energy. Both systems studied are superlattices, each period of which consists of three coupled quantum wells and barriers.

Optimal Wavefront Reconstruction For A Coherent Diffracted Field, William W. Arrasmith

Theses and Dissertations

In sheared coherent beam interferometric imaging, an estimate of the average reflectivity profile of the object can be computed from measurements of point to point phase differences in the far field interference pattern and a suitable phase reconstruction technique. The phase difference information is encoded in the irradiance of three identical, shifted and superimposed speckled laser beam patterns. A minimum variance phase reconstruction technique is presented to estimate the phase of the field in the measurement plane from the phase differences and evaluate its performance. Prior knowledge of the phase covariance is used in the minimum variance reconstructor. Analytic calculations …

A High-Bandwidth Frequency-Domain Photon Migration Instrument For Clinical Use, Steen J. Madsen, Eric R. Anderson, Richard C. Haskell, Bruce J. Tromberg

All HMC Faculty Publications and Research

We have developed a high-bandwidth frequency-domain photon migration (FDPM) instrument which is capable of noninvasively determining the optical properties of biological tissues in near-real-time. This portable, inexpensive, diode-based instrument is unique in the sense that we employ direct diode laser modulation and avalanche photodiode detection. Diffusion models were used to extract the optical properties (absorption and transport scattering coefficients)of tissue-simulating solutions.from the 300 kHz to I GHz photon density wave data.

Nanoscale Visualization And Control Of Ferroelectric Domains By Atomic Force Microscopy, Oleg Kolosov, Alexei Gruverman, Jun Hatano, Koichiro Takahashi, Hiroshi Tokumoto

Alexei Gruverman Publications

The nanoscale visualization and control of domain structure with atomic force microscopy (AFM) in the ferroelectric crystal guanidinium aluminum sulfate hexahydrate is reported. The origin of the domain contrast in the topographic of AFM images is explained by the piezoelectric deformation of the crystal surface in the internal electric field. The domain structure was modified by applying a voltage to the conductive AFM tip. The dynamics of domain growth has been directly observed for the first time with a resolution of 10 nm.

Bandwidth And Additive Bandwidth Of Graphs, Maria Kujawski

Honors Capstone Projects and Theses

No abstract provided.