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  Partner: UNT Libraries
 Degree Discipline: Physics
 Collection: UNT Theses and Dissertations
An Experimental Study of Collision Broadening of some Excited Rotational States of the Bending Vibration of Methyl Cyanide

An Experimental Study of Collision Broadening of some Excited Rotational States of the Bending Vibration of Methyl Cyanide

Date: May 1993
Creator: Hajsaleh, Jamal Y. (Jamal Yousef)
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 eighth derivative of the line shape profile of the spectral line. This technique proved to give good signal-to-noise ratios and enabled the recovery of weak signals. An experimental method is developed to correct for source modulation broadening. The tests of the ratios of the two inner peak's separation of the eighth derivative of the line showed that they were up to 95% similar to those for a Lorentzian line shape function. The line shapes were assumed to be Lorentzian for the theoretical analysis of the derivative profiles and comparisons were made between experiment and theory on this basis. Dipole moments for vibrationally excited states were calculated from linewidth parameters and show systematic decrease with the increase of excitation. Impact parameters ...
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Experimental Synchronization of Chaotic Attractors Using Control

Experimental Synchronization of Chaotic Attractors Using Control

Date: December 1994
Creator: Newell, Timothy C. (Timothy Charles)
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 can be implemented in fast dynamical systems where timing is critical. Techniques developed in this work are of fundamental importance for future problems regarding high dimensional chaotic dynamical systems or arrays of mutually linked chaotically operating elements.
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Exploration of hierarchical leadership and connectivity in neural networks in vitro.

Exploration of hierarchical leadership and connectivity in neural networks in vitro.

Date: December 2008
Creator: Ham, Michael I.
Description: Living neural networks are capable of processing information much faster than a modern computer, despite running at significantly lower clock speeds. Therefore, understanding the mechanisms neural networks utilize is an issue of substantial importance. Neuronal interaction dynamics were studied using histiotypic networks growing on microelectrode arrays in vitro. Hierarchical relationships were explored using bursting (when many neurons fire in a short time frame) dynamics, pairwise neuronal activation, and information theoretic measures. Together, these methods reveal that global network activity results from ignition by a small group of burst leader neurons, which form a primary circuit that is responsible for initiating most network-wide burst events. Phase delays between leaders and followers reveal information about the nature of the connection between the two. Physical distance from a burst leader appears to be an important factor in follower response dynamics. Information theory reveals that mutual information between neuronal pairs is also a function of physical distance. Activation relationships in developing networks were studied and plating density was found to play an important role in network connectivity development. These measures provide unique views of network connectivity and hierarchical relationship in vitro which should be included in biologically meaningful models of neural networks.
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Expulsion of Carriers from the Double-Barrier Quantum Well and Investigation of Its Spectral and Transport Consequences

Expulsion of Carriers from the Double-Barrier Quantum Well and Investigation of Its Spectral and Transport Consequences

Date: March 1992
Creator: Chyla, Wojciech Tadeusz
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.
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Extinguishment of a Low-pressure Argon Discharge by a Magnetic Field

Extinguishment of a Low-pressure Argon Discharge by a Magnetic Field

Date: January 1964
Creator: Criswell, David Russell
Description: The experiment in this study involves the extinguishment of a low-pressure argon discharge by a magnetic field.
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Field Dependence of Optical Properties in Quantum Well Heterostructures Within the Wentzel, Kramers, and Brillouin Approximation

Field Dependence of Optical Properties in Quantum Well Heterostructures Within the Wentzel, Kramers, and Brillouin Approximation

Date: August 1989
Creator: Wallace, Andrew B.
Description: This dissertation is a theoretical treatment of the electric field dependence of optical properties such as Quantum Confined Stark (QCS) shifts, Photoluminescence Quenching (PLQ), and Excitonic Mixing in quantum well heterostructures. The reduced spatial dimensionality in heterostructures greatly enhances these optical properties, more than in three dimensional semiconductors. Charge presence in the quantum well from doping causes the potential to bend and deviate from the ideal square well potential. A potential bending that varies as the square of distance measured from the heterostructure interfaces is derived self-consistently. This potential is used to solve the time-independent Schrodinger equation for bound state energies and wave functions within the framework of the Wentzel, Kramers, and Brillouin (WKB) approximation. The theoretical results obtained from the WKB approximation are limited to wide gap semiconductors with large split off bands such as gallium arsenide-gallium aluminum arsenide and indium gallium arsenide—indium phosphide. Quantum wells with finite confinement heights give rise to an energy dependent WKB phase. External electric and magnetic fields are incorporated into the theory for two different geometries. For electric fields applied perpendicular to the heterostructure multilayers, QCS shifts and PLQ are found to be in excellent agreement with the WKB calculations. Orthogonality between electrons ...
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Fluorine Adsorption and Diffusion in Polycrystalline Silica

Fluorine Adsorption and Diffusion in Polycrystalline Silica

Date: December 1998
Creator: Jin, Jian-Yue
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 theoretical approach, a pipe-diffusion model was used to simulate the complicated fluorine transportation problem in flint, in which several diffusion mechanisms may be involved.
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Foil Depression Factors for Disc-shaped Detectors

Foil Depression Factors for Disc-shaped Detectors

Date: June 1954
Creator: Gallagher, Tom Lewis
Description: The generalized data which are presented in this thesis are the culmination of the determination of the foil depression factor using oblate spheroidal coordinates.
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The Fractal Stochastic Point Process Model of Molecular Evolution and the Multiplicative Evolution Statistical Hypothesis

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

Date: May 1997
Creator: Bickel, David R. (David Robert)
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 substitutions in mammalian genes. That analysis yields a power-law increase in the index of dispersion and an inverse power-law decrease in the coefficient of variation with the mean number of substitutions, as predicted by the FSPP model but not by the doubly stochastic Poisson model. This result is compatible with the selection theory of evolution and the nearly-neutral theory of evolution.
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Fractional Brownian motion and dynamic approach to complexity.

Fractional Brownian motion and dynamic approach to complexity.

Date: August 2007
Creator: Cakir, Rasit
Description: The dynamic approach to fractional Brownian motion (FBM) establishes a link between non-Poisson renewal process with abrupt jumps resetting to zero the system's memory and correlated dynamic processes, whose individual trajectories keep a non-vanishing memory of their past time evolution. It is well known that the recrossing times of the origin by an ordinary 1D diffusion trajectory generates a distribution of time distances between two consecutive origin recrossing times with an inverse power law with index m=1.5. However, with theoretical and numerical arguments, it is proved that this is the special case of a more general condition, insofar as the recrossing times produced by the dynamic FBM generates process with m=2-H. Later, the model of ballistic deposition is studied, which is as a simple way to establish cooperation among the columns of a growing surface, to show that cooperation generates memory properties and, at same time, non-Poisson renewal events. Finally, the connection between trajectory and density memory is discussed, showing that the trajectory memory does not necessarily yields density memory, and density memory might be compatible with the existence of abrupt jumps resetting to zero the system's memory.
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