UNT Theses and Dissertations - 50 Matching Results

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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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Anomalous Behavior in the Rotational Spectra of the v₈=2 and the v₈=3 Vibrations for the ¹³C and ¹⁵N Tagged Isotopes of the CH₃CN Molecule in the Frequency Range 17-95 GHz

Description: The rotational microwave spectra of the three isotopes (^13CH_3^12C^15N, ^12CH_3^13C^15N, and ^13CH_3^13C^15N) of the methyl cyanide molecule in the v_8=3, v_8=2, v_7=1 and v_4=1 vibrational energy levels for the rotational components 1£J£5 (for a range of frequency 17-95 GHz.) were experimentally and theoretically examined. Rotational components in each vibration were measured to determine the mutual interactions in each vibration between any of the vibrational levels investigated. The method … more
Date: December 1990
Creator: Al-Share, Mohammad A. (Mohammad Abdel)
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Magneto-Optical and Chaotic Electrical Properties of n-InSb

Description: This thesis investigation concerns the optical and nonlinear electrical properties of n-InSb. Two specific areas have been studied. First is the magneto-optical study of magneto-donors, and second is the nonlinear dynamic study of nonlinear and chaotic oscillations in InSb. The magneto-optical study of InSb provides a physical picture of the magneto-donor levels, which has an important impact on the physical model of nonlinear and chaotic oscillations. Thus, the subjects discussed in this thesi… more
Date: December 1991
Creator: Song, Xiang-Ning
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Ultrasensitive Technique for Measurement of Two-Photon Absorption

Description: Intensive demands have arisen to characterize nonlinear optical properties of materials for applications involving optical limiters, waveguide switches and bistable light switches. The technique of Pulse Delay Modulation is described which can monitor nonlinear changes in transmission with shot noise limited signal-to-noise ratios even in the presence of large background signals. The theoretical foundations of the experiment are presented followed by actual measurements of beam depletion due to… more
Date: December 1991
Creator: Miller, Steven A. (Steven Alan)
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Expulsion of Carriers from the Double-Barrier Quantum Well and Investigation of Its Spectral and Transport Consequences

Description: In this work I investigate the expulsion of carriers from nanostructures using the double-barrier quantum well (DBQW) as an example and discuss manifestations of this effect in the spectrum of the DBQW in absence of bias, and in the tunneling current in presence of bias. Assuming equality of the Fermi energy in all regions of the considered system, I compute the relative density of carriers localized in the DBQW and conclude that a fraction of carriers is expelled from this nanostructure.
Date: March 1992
Creator: Chyla, Wojciech Tadeusz
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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
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Nonlinear Optical Properties of GaAs at 1.06 micron, picosecond Pulse Investigation and Applications

Description: The author explores absorptive and refractive optical nonlinearities at 1.06 [mu]m in bulk, semi-insulating, undoped GaAs with a particular emphasis on the influence of the native deep-level defect known as EL2. Picosecond pump-probe experimental technique is used to study the speed, magnitude, and origin of the absorptive and refractive optical nonlinearities and to characterize the dynamics of the optical excitation of EL2 in three distinctly different undoped, semi-insulating GaAs samples. I… more
Date: August 1992
Creator: Cui, A.G. (Aiguo G.)
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Studies of Classically Chaotic Quantum Systems within the Pseudo-Probablilty Formalism

Description: The evolution of classically chaotic quantum systems is analyzed within the formalism of Quantum Pseudo-Probability Distributions. Due to the deep connections that a quantum system shows with its classical correspondent in this representation, the Pseudo-Probability formalism appears to be a useful method of investigation in the field of "Quantum Chaos." In the first part of the thesis we generalize this formalism to quantum systems containing spin operators. It is shown that a classical-like e… more
Date: August 1992
Creator: Roncaglia, Roberto
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Nonlinear Optical Absorption and Refraction Study of Metallophthalocyanine Dyes

Description: This dissertation deals with the characterization of the nonlinear absorption and refraction of two representative metallophthalocyanine dyes: chloro aluminum phthalocyanine dissolved in methanol, referred to as CAP, and a silicon naphthalocyanine derivative dissolved in toluene, referred to as SiNc. Using the Z-scan technique, the experiments are performed on both the picosecond and nanosecond timescales at a wavelength of 0.532 μm.
Date: December 1992
Creator: Wei, Tai-Huei
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An Experimental Study of Collision Broadening of some Excited Rotational States of the Bending Vibration of Methyl Cyanide

Description: A double modulation microwave spectrometer is used to evaluate the linewidth parameters for some excited rotational components in the bending vibration v_8 of 13CH3 13C 15N and 13CH3C15N isotopomers of methyl cyanide. The linewidth parameters for self-broadening of the ΔJ=2←1 rotational components for the ground v_8 , 1v_8, and the 2v_8 vibrations were determined over a pressure range of 1 to 13 mtorr and at a temperature of 300 K. The double modulation technique is used to explore the high eig… more
Date: May 1993
Creator: Hajsaleh, Jamal Y. (Jamal Yousef)
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Deterministic Brownian Motion

Description: The goal of this thesis is to contribute to the ambitious program of the foundation of developing statistical physics using chaos. We build a deterministic model of Brownian motion and provide a microscpoic derivation of the Fokker-Planck equation. Since the Brownian motion of a particle is the result of the competing processes of diffusion and dissipation, we create a model where both diffusion and dissipation originate from the same deterministic mechanism - the deterministic interaction of t… more
Date: August 1993
Creator: Trefán, György
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Synchronous Chaos, Chaotic Walks, and Characterization of Chaotic States by Lyapunov Spectra

Description: Four aspects of the dynamics of continuous-time dynamical systems are studied in this work. The relationship between the Lyapunov exponents of the original system and the Lyapunov exponents of induced Poincare maps is examined. The behavior of these Poincare maps as discriminators of chaos from noise is explored, and the possible Poissonian statistics generated at rarely visited surfaces are studied.
Date: August 1993
Creator: Albert, Gerald (Gerald Lachian)
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Z1 Dependence of Ion-Induced Electron Emission

Description: Knowledge of the atomic number (Zt) dependence of ion-induced electron emission yields (Y) can be the basis for a general understanding of ion-atom interaction phenomena and, in particular, for the design of Zrsensitive detectors that could be useful, for example, in the separation of isobars in accelerator mass spectrometry. The Zx dependence of ion-induced electron emission yields has been investigated using heavy ions of identical velocity (v = 2 v0, with v0 as the Bohr velocity) incident in… more
Date: December 1993
Creator: Arrale, Abdikarim M. (Abdikarim Mohamed)
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Diffusion Kinetics and Microstructure of Eutectic and Composite Solder/Copper Joints

Description: Sn/Pb solders are widely used by the electronics industry to provide both mechanical and electrical interconnections between electronic components and printed circuit boards. Solders with enhanced mechanical properties are required for high reliability for Surface Mount Technology (SMT) applications. One approach to improve the mechanical properties of solder is to add metallic or intermetallic particles to eutectic 63Sn/37Pb solder to form composite solders. Cu6Sn5 and Cu3Sn form and grow at t… more
Date: May 1994
Creator: Wu, Yujing
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Nonlinear Dynamics of Semiconductor Device Circuits and Characterization of Deep Energy Levels in HgCdTe by Using Magneto-Optical Spectroscopy

Description: The nonlinear dynamics of three physical systems has been investigated. Diode resonator systems are experimentally shown to display a period doubling route to chaos, quasiperiodic states, periodic locking states, and Hopf bifurcation to chaos. Particularly, the transition from quasiperiodic states to chaos in line-coupled systems agrees well with the Curry-Yorke model. The SPICE program has been modified to give realistic models for the diode resonator systems.
Date: May 1994
Creator: Yü, Chi
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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
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Transport Processes in Synchrotrons

Description: This thesis examines the evolution of beams in synchrotrons. Following an introduction to accelerator physics in Chapter 1, in Chapter 2 I describe the Fermilab E778 'diffusion' experiment. Families of sextupoles were powered to drive the 2/5 resonance, and a beam was then kicked to populate a nonlinear region of the transverse phase space. The beam was then observed over periods of approximately 30 minutes for a variety of kick amplitudes and physical apertures. In Chapter 3 comments about the… more
Date: May 1994
Creator: Cole, Benjamin H. (Benjamin Holland)
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Charge State Dependence of M-Shell X-Ray Production in 67Ho by 2-12 MeV Carbon Ions

Description: The charge state dependence of M-shell x-ray production cross sections of 67HO bombarded by 2-12 MeV carbon ions with and without K-vacancies are reported. The experiment was performed using an NEC 9SDH-2 tandem accelerator at the Ion Beam Modification and Analysis Laboratory of the University of North Texas. The high charge state carbon ions were produced by a post-accelerator stripping gas cell. Ultra-clean holmium targets were used in ion-atom collision to generate M-shell x rays at energies… more
Date: August 1994
Creator: Sun, Hsueh-Li
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Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 335 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode

Description: The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute te… more
Date: August 1994
Creator: Wang, Henry F. S. (Henry Fu-Sen)
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Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions

Description: The existence of singly, doubly, and triply charged diatomic molecular ions was observed by using an Accelerator Mass Spectrometry (AMS) technique. The mean lifetimes of 3 MeV boron diatomic molecular ions were measured. No isotopic effects on the mean lifetimes of boron diatomic molecules were observed for charge state 3+. Also, the mean lifetime of SiF^3+ was measured.
Date: December 1994
Creator: Kim, Yong-Dal
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Experimental Synchronization of Chaotic Attractors Using Control

Description: The focus of this thesis is to theoretically and experimentally investigate two new schemes of synchronizing chaotic attractors using chaotically operating diode resonators. The first method, called synchronization using control, is shown for the first time to experimentally synchronize dynamical systems. This method is an economical scheme which can be viably applied to low dimensional dynamical systems. The other, unidirectional coupling, is a straightforward means of synchronization which ca… more
Date: December 1994
Creator: Newell, Timothy C. (Timothy Charles)
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