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 Department: Department of Physics
 Collection: UNT Theses and Dissertations
Criticality in Cooperative Systems

Criticality in Cooperative Systems

Date: May 2012
Creator: Vanni, Fabio
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 collapses. In this study, I used cooperative systems based on self-propelled particle models (the flock models) which have been proved to be virtually equivalent to sociological network models mimicking the decision making processes (the decision making model). The critical region is an intermediate condition between a highly disordered state and a strong ordered one. At criticality the waiting times distribution density between two consecutive collapses shows an inverse power law form with an anomalous statistical behavior. The scientific evidences are based on measures of information theory, correlation in time and space, and fluctuation statistical analysis. In order to prove the benefit for a system to live at criticality, I made a flock system interact with another similar ...
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Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates

Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates

Date: May 2011
Creator: Poudel, Prakash Raj
Description: The systematic study of the formation of β-SiC formed by low energy carbon ion (C-)implantation into Si followed by high temperature annealing is presented. The research is performed to explore the optimal annealing conditions. The formation of crystalline β-SiC is clearly observed in the sample annealed at 1100 °C for a period of 1 hr. Quantitative analysis is performed in the formation of β-SiC by the process of implantation of different carbon ion fluences of 1×1017, 2×1017, 5×1017, and 8×1017 atoms /cm2 at an ion energy of 65 keV into Si. It is observed that the average size of β-SiC crystals decreased and the amount of β-SiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100°C for 1 hr. However, it is observed that the amount of β-SiC linearly increased with the implanted fluences up to 5×1017 atoms /cm2. Above this fluence the amount of β-SiC appears to saturate. The stability of graphitic C-C bonds at 1100°C limits the growth of SiC precipitates in the sample implanted at a fluence of 8×1017 atoms /cm2 which results in the saturation behavior of SiC formation in the present study. Secondly, the carbon cluster formation process ...
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Thorium and Uranium M-shell X-ray Production Cross Sections for 0.4 – 4.0 MeV Protons, 0.4 - 6.0 MeV Helium Ions, 4.5 – 11.3 MeV Carbon Ions, and 4.5 – 13.5 MeV Oxygen Ions.

Thorium and Uranium M-shell X-ray Production Cross Sections for 0.4 – 4.0 MeV Protons, 0.4 - 6.0 MeV Helium Ions, 4.5 – 11.3 MeV Carbon Ions, and 4.5 – 13.5 MeV Oxygen Ions.

Date: May 2011
Creator: Phinney, Lucas C.
Description: The M-shell x-ray production cross section for thorium and uranium have been determined for protons of energy 0.4 - 4.0 MeV, helium ions of energy 0.4 - 6.0 MeV, carbon ions of energy 4.5 - 11.3 MeV and oxygen ions of energy 4.5 - 13.5 MeV. The total cross sections and the cross sections for individual x-ray peaks in the spectrum, consisting of the following transitions Mz (M4-N2, M5-N3, M4-N3), Ma (M5-N6,7), Mb (M4-N6, M5-O3, M4- O2), and Mg (M4-O3, M5-P3, M3-N4, M3-N5), were compared to the theoretical values determined from the PWBA + OBKN and ECUSAR. The theoretical values for the carbon and oxygen ions were also modified to take into account the effects of multiple ionizations of the target atom by the heavier ions. It is shown that the results of the ECUSAR theory tend to provide better agreement with the experimental data.
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Polymer Gels: Kinetics, Dynamics Studies and Their Applications as Biomaterials

Polymer Gels: Kinetics, Dynamics Studies and Their Applications as Biomaterials

Date: December 2003
Creator: Wang, Changjie
Description: The polymer gels especially hydrogels have a very special structure and useful features such as unusual volume phase transition, compatibility with biological systems, and sensitivity to environmental stimuli (temperature, pH value, electric field, light and more), which lead to many potential applications in physical and biochemical fields. This research includes: (1) the theoretical and experimental studies of polymer gels on swelling kinetics, spinodal decomposition, and solution convection in gel matrix; (2) applications of polymer gels in wound dressing, tissue-simulating optical phantom and gel display. The kinetics of gel swelling has been theoretically analyzed by considering coupled motions of both solvent and polymer network. Analytical solutions of the solvent and the network movement are derived from collective diffusion equations for a long cylindrical and a large disk gel. Kinetics of spinodal decomposition of N-isopropylacrylamide (NIPA) polymer gel is investigated using turbidity and ultrasonic techniques. By probing movement of domains, a possible time-dependent gel structure in the spinodal decomposition region is presented. Theoretical studies of solution convection in gel matrix have been done and more analysis on dimensionless parameters is provided. To enhance the drug uptake and release capacity of silicone rubber (SR), NIPA hydrogel particles have been incorporated into a SR ...
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Oligonucleotide guanosine conjugated to gallium nitride nano-structures for photonics.

Oligonucleotide guanosine conjugated to gallium nitride nano-structures for photonics.

Date: August 2008
Creator: Li, Jianyou
Description: In this work, I studied the hybrid system based on self-assembled guanosine crystal (SAGC) conjugated to wide-bandgap semiconductor gallium nitride (GaN). Guanosine is one of the four bases of DNA and has the lowest oxidation energy, which favors carrier transport. It also has large dipole moment. Guanosine molecules self-assemble to ribbon-like structure in confined space. GaN surface can have positive or negative polarity depending on whether the surface is Ga- or N-terminated. I studied SAGC in confined space between two electrodes. The current-voltage characteristics can be explained very well with the theory of metal-semiconductor-metal (MSM) structure. I-V curves also show strong rectification effect, which can be explained by the intrinsic polarization along the axis of ribbon-like structure of SAGC. GaN substrate property influences the properties of SAGC. So SAGC has semiconductor properties within the confined space up to 458nm. When the gap distance gets up to 484nm, the structure with guanosine shows resistance characteristics. The photocurrent measurements show that the bandgap of SAGC is about 3.3-3.4eV and affected by substrate properties. The MSM structure based on SAGC can be used as photodetector in UV region. Then I show that the periodic structure based on GaN and SAGC can have photonic ...
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Energy Losses of Protons Projected through a Plasma Due to Collisions with Electrons of the Plasma for a Variety of Non-Maxwellian Electron Velocity Distributions

Energy Losses of Protons Projected through a Plasma Due to Collisions with Electrons of the Plasma for a Variety of Non-Maxwellian Electron Velocity Distributions

Date: August 1961
Creator: Kregel, Mark Douglas
Description: The purpose of this thesis is to study energy losses suffered by protons in traversing a plasma through collision with the electrons of the plasma. For these electrons a variety of non-Maxwellian velocity distributions are assumed.
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A Computer Analysis of Complex Gamma-Ray Spectra

A Computer Analysis of Complex Gamma-Ray Spectra

Date: August 1965
Creator: Cunningham, William K.
Description: The purpose of this investigation was to provide a method for determining the relative intensities of all gamma rays in a particular spectrum, and thereby determine the relative transition probabilities.
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Galvanomagnetic Phenomena in Arsenic at Liquid Helium Temperatures

Galvanomagnetic Phenomena in Arsenic at Liquid Helium Temperatures

Date: June 1966
Creator: Yarbrough, Jack Lee
Description: The purpose of this investigation was to study some of the transport effects in a single crystal of arsenic at liquid helium temperatures in a magnetic field up to twenty-four kilogauss. The experimental coefficients determined were the isothermal magnetoresistivity and the isothermal Hall resistivity.
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Thermomagnetic Effects in Antimony at 4.2 [degrees]K

Thermomagnetic Effects in Antimony at 4.2 [degrees]K

Date: August 1965
Creator: Taaffe, Thomas J.
Description: The purpose of this investigation was to study the thermoelectric effects in a single crystal of antimony at liquid-helium temperatures.
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A Calculation of the Kaon-Neutron Scattering Cross Section

A Calculation of the Kaon-Neutron Scattering Cross Section

Date: June 1966
Creator: Hooper, Robert Gibson
Description: The purpose of this investigation was to study the scattering processes of K+ mesons with neutrons. In order to do such a study one must first make certain basic assumptions about the type of interaction involved and then proceed to calculate physically meaningful qualities which describe the processes. Thus, the problem is this: assuming the validity of Feynman's rules for these strongly interacting particles, calculate the differential and total scattering cross sections for the interaction of scalar K+ mesons and neutrons.
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Analyzing Magnet System for the Electrostatic Accelerator

Analyzing Magnet System for the Electrostatic Accelerator

Date: August 1954
Creator: Young, Thomas E.
Description: This thesis describes the design and construction of a linear accelerator, specifically, a positive-ion source, a high voltage supply, an accelerating column, and the necessary associated vacuum system.
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Stochastic Mechanical Systems

Stochastic Mechanical Systems

Date: August 1960
Creator: Bost, Robert Berton
Description: To understand the phenomena associated with such stochastic processes and to predict, at least qualitatively, the behavior of mechanical systems within environments which are completely random in time, new mechanical tools are necessary. Fortunately, the derivation of these tools does not necessitate a complete departure from existing theories. In fact, they may be considered as an extension of the well-defined theory of the integral transform, in particular, the exponential Fourier integral transform.
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Dynamical Friction Coefficients for Plasmas Exhibiting Non-Spherical Electron Velocity Distributions

Dynamical Friction Coefficients for Plasmas Exhibiting Non-Spherical Electron Velocity Distributions

Date: August 1961
Creator: Williams, G. Bruce
Description: This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a non-spherical velocity distribution.
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D-D and D-T Neutron Excitation of Energy Levels in Cs133

D-D and D-T Neutron Excitation of Energy Levels in Cs133

Date: January 1961
Creator: Dawson, Horace Ray
Description: The purpose of this experiment was to make positive assignment of the Cs133 energy levels excited by the inelastic scattering of neutrons.
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A Study of Emitter Drift in Transistors

A Study of Emitter Drift in Transistors

Date: August 1961
Creator: Malone, Farris Douglas
Description: The purpose of this investigation was to determine the parameters of emitter drift and to suggest a mechanism for this phenomenon.
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Temperature Dependence of the Magnetic Susceptibility of the Organic Free Radical Galvinoxyl

Temperature Dependence of the Magnetic Susceptibility of the Organic Free Radical Galvinoxyl

Date: August 1965
Creator: Morphew, Sam W.
Description: This thesis examines temperature dependence of magnetic susceptibility of the organic free radical galvinoxyl.
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Design and Testing of a Corona Column and a Closed Gas Distribution System for a Tandem Van de Graaff Voltage Generator

Design and Testing of a Corona Column and a Closed Gas Distribution System for a Tandem Van de Graaff Voltage Generator

Date: June 1962
Creator: Gray, Thomas Jack
Description: The purpose of this study had been to design and test a corona column and an insulating gas distribution system for a small tandem Van de Graaff. The intent of this paper is to describe the gas handling system and to compare experimentally the effects of corona electrode shape on the corona current carried between adjacent sections of the column.
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A Microwave Spectrometer for Narrow-line Electron Spin Resonance Studies

A Microwave Spectrometer for Narrow-line Electron Spin Resonance Studies

Date: January 1966
Creator: Neie, Van ElRoy
Description: This thesis explores the basic theory, design and construction of electron spin resonance spectrometer.
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A Vacuum Tube for an Electrostatic Generator

A Vacuum Tube for an Electrostatic Generator

Date: August 1966
Creator: Pool, John Reginald
Description: The purpose of this study has been to construct two accelerating tubes with small beam apertures for the Van de Graaff, modifying the prototype tube designed and tested by Wiley (20), to design and construct a vacuum system for evacuating the tubes, and to determine the characteristics of the tube under operating conditions while installed in the generator.
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The Diurnal Variation of Cosmic Radiation

The Diurnal Variation of Cosmic Radiation

Date: August 1965
Creator: Fowler, Brooks C.
Description: The primary purpose of this investigation was to study the diurnal variation of cosmic-ray intensity.
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Nuclear Magnetic Resonance in a Crystalline Stable Free Radical--Wurster's Blue Perchlorate

Nuclear Magnetic Resonance in a Crystalline Stable Free Radical--Wurster's Blue Perchlorate

Date: August 1965
Creator: McCann, Thomas E.
Description: This thesis investigates the nuclear magnetic resonance in a crystalline stable free radical.
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Design and Testing of a Positive Ion Accelerator and Necessary Vacuum System

Design and Testing of a Positive Ion Accelerator and Necessary Vacuum System

Date: August 1953
Creator: McKay, Vern A.
Description: This thesis is a study of the design and testing of a positive ion accelerator and necessary vacuum system.
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Antiferromagnetic Ordering in Picryl-Amino-Carbazyl

Antiferromagnetic Ordering in Picryl-Amino-Carbazyl

Date: August 1964
Creator: Porter, Wilbur A.
Description: The purpose of the experiment was to investigate other paramagnetic salts to determine whether the W. B. perchlorate type peak was more common than previously suspected. An organic salt, picryl-n-amino-carbazyl, was chosen.
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The Optimum Design of a Broad-band Helix for Use in Electron Spin Resonance

The Optimum Design of a Broad-band Helix for Use in Electron Spin Resonance

Date: June 1967
Creator: Garlow, John R.
Description: This thesis examines optimum designs for broad-band helix to be used in electron spin resonance.
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