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Scaling Behaviors and Mechanical Properties of Polymer Gels

Description: Polymer gels undergo a volume phase transition in solvent in response to an infinitesimal environmental change. This remarkable phenomenon has resulted in many potential applications of polymer gels. The understanding of its mechanical properties has both scientific and technological importance. For this purpose, we have developed a novel method for measuring Poisson's ratio, which is one of the most important parameters determining the mechanical property of gels. Using this method, Poisson's … more
Date: May 1994
Creator: Li, Chʻun-fang
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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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
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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
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A Study of Quantum Electron Dynamics in Periodic Superlattices under Electric Fields

Description: This thesis examines the quantum dynamics of electrons in periodic semiconductor superlattices in the presence of electric fields, especially uniform static fields. Chapter 1 is an introduction to this vast and active field of research, with an analysis and suggested solutions to the fundamental theoretical difficulties. Chapter 2 is a detailed historical review of relevant theories, and Chapter 3 is a historical review of experiments. Chapter 4 is devoted to the time-independent quantum mechan… more
Date: May 1996
Creator: Yuan, Daiqing
Item Type: Refine your search to only Thesis or Dissertation
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L-Shell X-Ray Production Cross Sections for ₂₀Ca, ₂₆Fe, ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Hydrogen, Helium, and Lithium Ions

Description: L-shell x-ray production cross sections are presented for Fe, Ni, Cu, Zn, Ga, and Ge by 0.5- to 5.0-MeV protons and by 0.5- to 8.0-MeV helium ions and Ca, Fe, Ni, Cu, and Ge by 0.75- to 4.5-MeV lithium ions. These measurements are compared to the first Born theory and the perturbed-stationary- state theory with energy-loss, Coulomb deflection, and relativistic corrections (ECPSSR). The results are also compared to previous experimental investigations. The high precision x-ray measurements were … more
Date: May 1992
Creator: McNeir, Michael Ridge
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Electron Density and Collision Frequency Studies Using a Resonant Microwave Cavity as a Probe

Description: Electron densities and collision frequencies were obtained on a number of gases in a dc discharge at low pressures (0.70-2mm of Hg). These measurements were performed by microwave probing of a filament of the dc discharge placed coaxially in a resonant cavity operating in a TM₀₁₀ mode. The equipment and techniques for making the microwave measurements employing the resonant cavity are described. One of the main features of this investigation is the technique of differentiating the resonance sig… more
Date: May 1973
Creator: Freeman, Ronald Harold
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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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
Partner: UNT Libraries
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Zinc Oxide Nanoparticles for Nonlinear Bioimaging, Cell Detection and Selective Cell Destruction

Description: Light matter interactions have led to a great part of our current understanding of the universe. When light interacts with matter it affects the properties of both the light and the matter. Visible light, being in the region that the human eye can "see," was one of the first natural phenomenon we used to learn about our universe. The application of fundamental physics research has spilled over into other fields that were traditionally separated from physics, being considered two different scien… more
Date: May 2013
Creator: Urban, Ben E.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Criticality in Cooperative Systems

Description: Cooperative behavior arises from the interactions of single units that globally produce a complex dynamics in which the system acts as a whole. As an archetype I refer to a flock of birds. As a result of cooperation the whole flock gets special abilities that the single individuals would not have if they were alone. This research work led to the discovery that the function of a flock, and more in general, that of cooperative systems, surprisingly rests on the occurrence of organizational collap… more
Date: May 2012
Creator: Vanni, Fabio
Item Type: Refine your search to only Thesis or Dissertation
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A New Approach for Transition Metal Free Magnetic Sic: Defect Induced Magnetism After Self-ion Implantation

Description: SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3C-SiC, 4H-SiC and 6H-SiC are the most common polytypes used for research purpo… more
Date: May 2013
Creator: Kummari, Venkata Chandra Sekhar
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Monte Carlo simulation and experimental studies of the production of neutron-rich medical isotopes using a particle accelerator.

Description: The developments of nuclear medicine lead to an increasing demand for the production of radioisotopes with suitable nuclear and chemical properties. Furthermore, from the literature it is evident that the production of radioisotopes using charged-particle accelerators instead of nuclear reactors is gaining increasing popularity. The main advantages of producing medical isotopes with accelerators are carrier free radionuclides of short lived isotopes, improved handling, reduction of the radioact… more
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Date: May 2002
Creator: Rosencranz, Daniela Necsoiu
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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The Effect of Average Grain Size on Polycrystalline Diamond Films

Description: The work function of hydrogen-terminated, polycrystalline diamond was studied using ultraviolet photoelectron spectroscopy. Polycrystalline diamond films were deposited onto molybdenum substrates by electrophoresis for grain sizes ranging from 0.3 to 108 microns. The work function and electron affinity were measured using 21.2 eV photons from a helium plasma source. The films were characterized by x-ray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fractio… more
Date: May 2002
Creator: Abbott, Patrick Roland
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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The Effects of Cesium Deposition and Gas Exposure on the Field Emission Properties of Single Wall and Multiwall Carbon Nanotubes

Description: The effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotube (SWNT) bundles were studied. In addition, a comparative study was made on the effects of O2, Ar and H2 gases on the field emission properties of SWNT bundles and multiwall carbon nanotubes (MWNTs). We observed that Cs deposition decreases the turn-on field for FE by a factor of 2.1 - 2.9 and increases the FE current by 6 orders of magnitude. After Cs deposition, the FE current versus voltage (… more
Date: May 2002
Creator: Wadhawan, Atul
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Complexity as Aging Non-Poisson Renewal Processes

Description: The search for a satisfactory model for complexity, meant as an intermediate condition between total order and total disorder, is still subject of debate in the scientific community. In this dissertation the emergence of non-Poisson renewal processes in several complex systems is investigated. After reviewing the basics of renewal theory, another popular approach to complexity, called modulation, is introduced. I show how these two different approaches, given a suitable choice of the parameter … more
Date: May 2007
Creator: Bianco, Simone
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Partner: UNT Libraries
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Optical Nonlinearities in Semiconductors for Limiting

Description: I have conducted detailed experimental and theoretical studies of the nonlinear optical properties of semiconductor materials useful for optical limiting. I have constructed optical limiters utilizing two-photon absorption along with photogenerated carrier defocusing as well as the bound electronic nonlinearity using the semiconducting material ZnSe. I have optimized the focusing geometry to achieve a large dynamic range while maintaining a low limiting energy for the device. The ZnSe monolithi… more
Date: May 1990
Creator: Wu, Yuan-Yen
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Microwave Spectra of ¹³C Isotopic Species of Methyl Cyanide in the Ground, v₈=1 and v₈=2 Vibrational States

Description: The problem of the quadrupole interaction occurring in a vibrating-rotating C₃v symmetric top molecule has been studied in detail. The quadrupole interaction has been treated as another perturbation term to a general frequency expression accounting for the vibrating-rotating interaction of the molecule so that a complete frequency formula is obtained for both interactions, and from which hyperfine spectral components are predicted and measured. The hyperfine transitions in the ground, and v₈=1 … more
Date: May 1988
Creator: Tam, Hungsze
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Photon Exchange Between a Pair of Nonidentical Atoms with Two Forms of Interactions

Description: A pair of nonidentical two-level atoms, separated by a fixed distance R, interact through photon exchange. The system is described by a state vector which is assumed to be a superposition of four "essential states": (1) the first atom is excited, the second one is in the ground state, and no photon is present, (2) the first atom is in its ground state, the second one is excited, and no photon is present, (3) both atoms are in their ground states and a photon is present, and (4) both atoms are e… more
Date: May 1987
Creator: Golshan, Shahram Mohammad-Mehdi
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Measurement of the Rate Coefficients for the Bimolecular and Termolecular Charge Transfer Reactions of He₂⁺ with Ne, Ar, N₂, CO, CO₂, and CH₄

Description: The problem with which this investigation is concerned is that of measuring the rate coefficients for termolecular charge transfer reactions of He2+ in atmospheric pressure afterglows with the minority reacting species. Of particular interest was the discovery that the presence of a third body can change an improbable charge transfer reaction involving He+2 into a very probable one, as in the case of the reaction with argon. For example, in Tables II and II it was shown that less than a 300 tor… more
Date: May 1977
Creator: Lee, Francis Wha-Pyo
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Picosecond Measurement of Nonlinear Diffusion and Recombination Processes in Germanium

Description: A variation of the excite-and-probe technique is used to measure the picosecond evolution of laser-induced transient gratings that are produced in germanium by the direct absorption of 40 psec optical pulses at 1.06-μm. Grating lifetimes are determined for free carrier densities between 10¹⁸ cm⁻³ and 10²¹ cm⁻³ . For carrier densities less than 10¹⁹ cm⁻³ , a linear diffusion-recombination model for the grating provides a good fit to the experimental data and allows the extraction of the diffusio… more
Date: May 1981
Creator: Moss, Steven Charles
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Electron-Ion Time-of-Flight Coincidence Measurements of K-K Electron Capture, Cross Sections for Nitrogen, Methane, Ethylene, Ethane, Carbon Dioxide and Argon (L-K) Targets

Description: Protons with energies ranging from 0.4 to 2.0 MeV were used to measure K-shell vacancy production cross sections (oVK) for N_2, CH_4, C_2H_4, C_2H_6, and CO_2 gas targets under single collision conditions. An electron-ion time-of-flight coincidence technique was used to determind the ration of the K-K electron capture cross section, OECK, to the K-vacancy production cross section, oVK. These ratios were then combined with the measured values of oVK to extract the K-K electron capture cross sect… more
Date: May 1986
Creator: Toten, Arvel D.
Item Type: Refine your search to only Thesis or Dissertation
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The Effect of Intervalence-Band Absorption, Auger Recombination, Surface Recombination, Diffusion and Carrier Cooling on the Picosecond Dynamics of Laser-Induced Plasmas in Germanium

Description: The picosecond optical response of germanium is investigated by performing excitation-probe experiments on a thin, intrinsic-germanium wafer maintained at 135 K. The results of three distinct experiments are reported: (1) the transmission of a single pulse is measured as a function of irradiance, (2) the probe transmission is measured at a fixed time after excitation as a function of the excitation energy, and (3) the transmission of a probe pulse is monitored as a function of time after excita… more
Date: May 1983
Creator: Lindle, James Ryan
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Photoconductivity Investigation of Two-Photon Magneto-Absorption, PACRH, and Deep Levels in n-InSb

Description: A high resolution photoconductivity investigation of two 13 -3 photon magneto-absorption (TPMA) in n-InSb (n - 9 x 10 cm ) has been performed. This is the first time that two-photon absorption in a semiconductor has been studied with cw lasers only. With a stable cw CC>2 laser and a highly sensitive sampling and magnetic field modulation technique, a minimum of 4 2 transitions in the TPMA photoconductivity spectra can be observed. Most of these transitions are a result of the usual spherical ap… more
Date: May 1982
Creator: Goodwin, Mike Watson
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Low-Velocity K-Shell Ionization Cross Sections for Protons, Deuterons and Alpha Particles Bombarding Thin Metal Targets

Description: The purpose of this work was to examine the effect of the use the assumption κω2K/ΕCM «1 in calculating K-shell ionization cross sections in the plane wave Born approximation (PWBA) where κω2K is the observed binding energy of the K-shell and ECM is the energy of the incident particle in the center of mass system. Avoiding this assumption produces a threshold for ionization at Ecm = κω2K. Calculations employing the assumption, which leads to the use of approximate limits of integration, do not … more
Date: May 1981
Creator: Rice, Roger Karl
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Partner: UNT Libraries
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Microwave Properties of Hyaluronate Solutions Using a Resonant Microwave Cavity as a Probe

Description: Physiological functions of a biomacromolecule seem to be closely related to its molecular conformations. The knowledge of any conformational changes due to changes in its environment may lead to a proper understanding of its functions. Hyaluronic acid, a biomacromolecule with unusually high molecular weight and some important biological functions is the subject of the present work. A temperature-dependent transition in hyaluronate solution of 120 mg/ml concentration was observed at physiologica… more
Date: May 1980
Creator: Jani, Shirish K.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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