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Precision Atomic Spectroscopy with an Integrated Electro- Optic Modulator and DBR Diode Laser at 1083nm

Description: We have explored the use of recently developed high speed integrated electro optic modulators and DBR diode lasers as a tool for precision laser studies of atoms. In particular, we have developed a technique using a high speed modulator as a key element and applied it to the study of the fine structure of the 23P state of atomic helium. This state has been of long standing interest in atomic physics and its study has been the aim of several recent experiments using various precision techniques.… more
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Date: December 1999
Creator: Castillega, Jaime
Item Type: Refine your search to only Thesis or Dissertation
open access

Photoelectric Emission Measurements for CVD Grown Polycrystalline Diamond Films

Description: We examined CVD grown polycrystalline diamond films having different methane concentrations to detect defects and study the possible correlation between the methane concentration used during the growth process and the defect density. SEM and Raman results show that the amorphous and sp2 carbon content of the films increases with methane concentration. Furthermore, photoelectric emission from diamond is confirmed to be a two-photon process, hence the electrons are emitted from normally unoccupie… more
Date: August 1999
Creator: Hassan, Tarek
Item Type: Refine your search to only Thesis or Dissertation
open access

Picosecond Dynamics of Free-Carrier Populations, Space-Charge Fields, and Photorefractive Nonlinearities in Zincblende Semiconductors

Description: Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and… more
Date: August 1999
Creator: Stark, Thomas S.
Item Type: Refine your search to only Thesis or Dissertation
open access

Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous Fowler-Nordheim I-V Plots with Field Emission Energy Distributions

Description: The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography… more
Date: August 1999
Creator: Bernhard, John Michael
Item Type: Refine your search to only Thesis or Dissertation
open access

Evolution of Vacancy Supersaturations in MeV Si Implanted Silicon

Description: High-energy Si implantation into silicon creates a net defect distribution that is characterized by an excess of interstitials near the projected range and a simultaneous excess of vacancies closer to the surface. This defect distribution is due to the spatial separation between the distributions of interstitials and vacancies created by the forward momentum transferred from the implanted ion to the lattice atom. This dissertation investigates the evolution of the near-surface vacancy excess in… more
Date: May 1999
Creator: Venezia, Vincent C.
Item Type: Refine your search to only Thesis or Dissertation
open access

Fluorine Adsorption and Diffusion in Polycrystalline Silica

Description: The measurement of fluorine penetration into archeological flint artifacts using Nuclear Reaction Analysis (NRA) has been reported to be a potential dating method. However, the mechanism of how fluorine is incorporated into the flint surface, and finally transported into the bulk is not well understood. This research focuses on the study of the fluorine uptake phenomenon of flint mineral in aqueous fluoride solutions. Both theoretical and experimental approaches have been carried out. In a theo… more
Date: December 1998
Creator: Jin, Jian-Yue
Item Type: Refine your search to only Thesis or Dissertation
open access

Two-Fold Role of Randomness: A Source of Both Long-Range Correlations and Ordinary Statistical Mechanics

Description: The role of randomness as a generator of long range correlations and ordinary statistical mechanics is investigated in this Dissertation. The difficulties about the derivation of thermodynamics from mechanics are pointed out and the connection between the ordinary fluctuation-dissipation process and possible anomalous properties of statistical systems is highlighted.
Date: December 1998
Creator: Rocco, A. (Andrea)
Item Type: Refine your search to only Thesis or Dissertation
open access

On Chaos and Anomalous Diffusion in Classical and Quantum Mechanical Systems

Description: The phenomenon of dynamically induced anomalous diffusion is both the classical and quantum kicked rotor is investigated in this dissertation. We discuss the capability of the quantum mechanical version of the system to reproduce for extended periods the corresponding classical chaotic behavior.
Date: August 1998
Creator: Stefancich, Marco
Item Type: Refine your search to only Thesis or Dissertation
open access

Structural and Photoelectron Emission Properties of Chemical Vapor Deposition Grown Diamond Films

Description: The effects of methane (CH4), diborone (B2H6) and nitrogen (N2) concentrations on the structure and photoelectron emission properties of chemical vapor deposition (CVD) polycrystalline diamond films were studied. The diamond films were grown on single-crystal Si substrates using the hot-tungsten filament CVD technique. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to characterize the different forms of carbon in the films, and the fraction of sp3 carbon to sp3 plus sp2… more
Date: August 1998
Creator: Akwani, Ikerionwu Asiegbu
Item Type: Refine your search to only Thesis or Dissertation
open access

Synthesis and Study of Engineered Heterogenous Polymer Gels

Description: This dissertation studies physical properties and technological applications of engineered heterogenous polymer gels. Such gels are synthesized based on modulation of gel chemical nature in space. The shape memory gels have been developed in this study by using the modulated gel technology. At room temperature, they form a straight line. As the temperature is increased, they spontaneously bend or curl into a predetermined shape such as a letter of the alphabet, a numerical number, a spiral, a s… more
Date: August 1998
Creator: Chen, Yuanye
Item Type: Refine your search to only Thesis or Dissertation
open access

On Delocalization Effects in Multidimensional Lattices

Description: A cubic lattice with random parameters is reduced to a linear chain by the means of the projection technique. The continued fraction expansion (c.f.e.) approach is herein applied to the density of states. Coefficients of the c.f.e. are obtained numerically by the recursion procedure. Properties of the non-stationary second moments (correlations and dispersions) of their distribution are studied in a connection with the other evidences of transport in a one-dimensional Mori chain. The second mom… more
Date: May 1998
Creator: Bystrik, Anna
Item Type: Refine your search to only Thesis or Dissertation
open access

Quantum-Confined CdS Nanoparticles on DNA Templates

Description: As electronic devices became smaller, interest in quantum-confined semiconductor nanostructures increased. Self-assembled mesoscale semiconductor structures of II-VI nanocrystals are an especially exciting subject because of their controllable band gap and unique photophysical properties. Several preparative methods to synthesize and control the sizes of the individual nanocrystallites and the electronic and optical properties have been intensively studied. Fabrication of patterned nanostructur… more
Date: May 1998
Creator: Rho, Young Gyu
Item Type: Refine your search to only Thesis or Dissertation
open access

Scanning Tunneling Microscopy of Epitaxial Diamond (110) and (111) Films and Field Emission Properties of Diamond Coated Molybdenum Microtips

Description: The growth mechanism of chemical vapor deposition (CVD) grown homo-epitaxial diamond (110) and (111) films was studied using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). In addition, the field emission properties of diamond coated molybdenum microtips were studied as a function of exposure to different gases.
Date: May 1998
Creator: Lim, Seong-Chu
Item Type: Refine your search to only Thesis or Dissertation
open access

The Fractal Stochastic Point Process Model of Molecular Evolution and the Multiplicative Evolution Statistical Hypothesis

Description: A fractal stochastic point process (FSPP) is used to model molecular evolution in agreement with the relationship between the variance and mean numbers of synonymous and nonsynonymous substitutions in mammals. Like other episodic models such as the doubly stochastic Poisson process, this model accounts for the large variances observed in amino acid substitution rates, but unlike other models, it also accounts for the results of Ohta's (1995) analysis of synonymous and nonsynonymous substitution… more
Date: May 1997
Creator: Bickel, David R. (David Robert)
Item Type: Refine your search to only Thesis or Dissertation
open access

Microstructural Studies of Dental Amalgams Using Analytical Transmission Electron Microscopy

Description: Dental amalgams have been used for centuries as major restorative materials for decaying teeth. Amalgams are prepared by mixing alloy particles which contain Ag, Sn, and Cu as the major constituent elements with liquid Hg. The study of microstructure is essential in understanding the setting reactions and improving the properties of amalgams. Until the work reported in this dissertation, optical microscopy (OM), scanning electron microscopy (SEM), and x-ray diffractometry (XRD) were used common… more
Date: May 1997
Creator: Hooghan, Tejpal Kaur
Item Type: Refine your search to only Thesis or Dissertation
open access

Model for Long-range Correlations in DNA Sequences

Description: We address the problem of the DNA sequences developing a "dynamical" method based on the assumption that the statistical properties of DNA paths are determined by the joint action of two processes, one deterministic, with long-range correlations, and the other random and delta correlated. The generator of the deterministic evolution is a nonlinear map, belonging to a class of maps recently tailored to mimic the processes of weak chaos responsible for the birth of anomalous diffusion. It is assu… more
Date: December 1996
Creator: Allegrini, Paolo
Item Type: Refine your search to only Thesis or Dissertation
open access

A Study of Nonlinear Dynamics in an Internal Water Wave Field in a Deep Ocean

Description: The Hamiltonian of a stably stratified incompressible fluid in an internal water wave in a deep ocean is constructed. Studying the ocean internal wave field with its full dynamics is formidable (or unsolvable) so we consider a test-wave Hamiltonian to study the dynamical and statistical properties of the internal water wave field in a deep ocean. Chaos is present in the internal test-wave dynamics using actual coupling coefficients. Moreover, there exists a certain separatrix net that fills the… more
Date: December 1996
Creator: Kim, Won-Gyu, 1962-
Item Type: Refine your search to only Thesis or Dissertation
open access

A Study of Some Biological Effects of Non-Ionizing Electromagnetic Radiation

Description: The experimental studies of this work were done using a microwave cavity spectrometer, Escherichia coli (E-coli) bacteria, and other peripheral equipment. The experiment consists of two steps. First, a general survey of frequencies from 8 GHz to 12 GHz was made. Second, a detailed experiment for specific frequencies selected from the first survey were further studied. Interesting frequency dependent results, such as unusually higher growing or killing rates of E-coli at some frequencies, were f… more
Date: December 1996
Creator: Park, Young C. (Young Chul), 1960-
Item Type: Refine your search to only Thesis or Dissertation
open access

The Physics of Gaseous Exposures on Active Field Emission Microcathode Arrays

Description: The interaction of active molybdenum field emission microcathode arrays with oxygen, water, carbon dioxide, methane, hydrogen and helium gases was studied. Experiments were setup to measure the emission characteristics as a function of gas exposures. The resulting changes in the surface work function of the tips were determined from the Fowler-Nordheim plots. The kinetics of the FEA-gas interaction were studied by observing the ion species originating from the array during and after gas exposur… more
Date: September 1996
Creator: Chalamala, Babu Reddy
Item Type: Refine your search to only Thesis or Dissertation
open access

Charge State Dependence of L-Shell X-Ray Production Cross Sections of ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Energetic Oxygen Ions

Description: Charge state dependence of L-shell x-ray production cross sections have been measured for 4-14 MeV ¹⁶O^q (q=3⁺-8⁺) ions incident on ultra-clean, ultra-thin copper, and for 12 MeV ¹⁶O^q (q=3⁺-8⁺) on nickel, zinc, gallium and germanium solid foils. L-shell x-ray production cross section were measured using target foils of thickness ≤0.6 μg/cm² evaporated onto 5 μg/cm² carbon backings. Oxygen ions at MeV energies and charge state q were produced using a 3MV 9SDH-2 National Electrostatics Corporati… more
Date: August 1996
Creator: Azordegan, Amir R. (Amir Reza)
Item Type: Refine your search to only Thesis or Dissertation
open access

Temperature Dependency of Some of the Thermodynamical Properties of Aqueous Binary-Mixture Systems

Description: The temperature dependence of the refractive index and the density of aqueous binary mixtures of water and ethyl alcohol (C₂H₅OH) were measured by using a modified Michelson interferometer and a narrow glass capillary tube over the temperature range of 278≤T≤353 K for solutions of 100, 75,65, 50, 25, 10 and 0 volume percent ethyl alcohol. The temperature was cycled over both increasing and decreasing directions to explore hysteresis in the cycling. The data are discussed and compared with the L… more
Date: August 1996
Creator: Zheng, Yueming
Item Type: Refine your search to only Thesis or Dissertation
open access

Spatiotemporal Properties of Coupled Nonlinear Oscillators

Description: Spatiotemporal properties of classical coupled nonlinear oscillators are investigated in this thesis. Chapter 1 gives an introduction to nonlinear lattices and to the concept of breathers, that are spatially localized and temporally periodic excitation in nonlinear lattices. The concept of anti-continuous limit that provides the basic methodology in probing spatiotemporal breather properties is discussed. In Chapter 2, the general approach for finding exact breather solutions from the anti-cont… more
Date: July 1996
Creator: Chen, Ding
Item Type: Refine your search to only Thesis or Dissertation
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