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 Degree Discipline: Physics
 Collection: UNT Theses and Dissertations
Absolute Beta Counting Using Thick Sources

Absolute Beta Counting Using Thick Sources

Date: 1950
Creator: Anderson, Miles E., 1926-
Description: The problem with which we shall concern ourselves in this paper is the self-scattering and self-absorption of beta particles by the source.
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L- and M-Shell X-Ray Production Cross Sections of Neodymium Gadolinium, Holmium, Ytterbium, Gold and Lead by 25-MeV Carbon and 32-MeV Oxygen Ions

L- and M-Shell X-Ray Production Cross Sections of Neodymium Gadolinium, Holmium, Ytterbium, Gold and Lead by 25-MeV Carbon and 32-MeV Oxygen Ions

Date: August 1987
Creator: Andrews, Mike C., 1949-
Description: L- and M-shell x-ray production cross sections have been measured for thin solid targets of neodymium, gadolinium, holmium, ytterbium, gold, and lead by 25 MeV 12/6C^q+ (q=4,5,6) and by 32 MeV 16/8O^q+ (q=5,7,8). The cross sections were determined from measurements made with thin targets (< 2.5 μg/cm2). For projectiles with one or two K-shell vacancies, the target x-ray production cross sections were found to be enhanced over those for projectiles without a K-shell vacancy. The sum of direct ionization to the continuum (DI) plus electron capture (EC) to the L, M, N... shells and EC to the K-shell of the projectile have been extracted from the data. The results are compared to the predictions of first Born theories, i.e., plane wave Born approximation for DI and Oppenheimer-Brinkman-Kramers formula of Nikolaev for EC and to the ECPSSR approach that accounts for Energy loss and Coulomb deflection of the projectile as well as for Relativistic and Perturbed Stationary States of inner shell electrons.
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Non-Poissonian statistics, aging and "blinking'" quantum dots.

Non-Poissonian statistics, aging and "blinking'" quantum dots.

Date: August 2004
Creator: Aquino, Gerardo
Description: This dissertation addresses the delicate problem of aging in complex systems characterized by non-Poissonian statistics. With reference to a generic two-states system interacting with a bath it is shown that to properly describe the evolution of such a system within the formalism of the continuous time random walk (CTRW), it has to be taken into account that, if the system is prepared at time t=0 and the observation of the system starts at a later time ta>0, the distribution of the first sojourn times in each of the two states depends on ta, the age of the system. It is shown that this aging property in the fractional derivative formalism forces to introduce a fractional index depending on time. It is shown also that, when a stationary condition exists, the Onsager regression principle is fulfilled only if the system is aged and consequently if an infinitely aged distribution for the first sojourn times is adopted in the CTRW formalism used to describe the system itself. This dissertation, as final result, shows how to extend to the non-Poisson case the Kubo Anderson (KA) lineshape theory, so as to turn it into a theoretical tool adequate to describe the time evolution of ...
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Z1 Dependence of Ion-Induced Electron Emission

Z1 Dependence of Ion-Induced Electron Emission

Date: December 1993
Creator: Arrale, Abdikarim M. (Abdikarim Mohamed)
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 a normal direction on sputter-cleaned carbon foils. Yields measured in this work plotted as a function of the ion's atomic number reveal an oscillatory behavior with pronounced maxima and minima. This nonmonotonic dependence of the yield on Zx will be discussed in the light of existing theories.
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EEG, Alpha Waves and Coherence

EEG, Alpha Waves and Coherence

Date: May 2010
Creator: Ascolani, Gianluca
Description: This thesis addresses some theoretical issues generated by the results of recent analysis of EEG time series proving the brain dynamics are driven by abrupt changes making them depart from the ordinary Poisson condition. These changes are renewal, unpredictable and non-ergodic. We refer to them as crucial events. How is it possible that this form of randomness be compatible with the generation of waves, for instance alpha waves, whose observation seems to suggest the opposite view the brain is characterized by surprisingly extended coherence? To shed light into this apparently irretrievable contradiction we propose a model based on a generalized form of Langevin equation under the influence of a periodic stimulus. We assume that there exist two different forms of time, a subjective form compatible with Poisson statistical physical and an objective form that is accessible to experimental observation. The transition from the former to the latter form is determined by the brain dynamics interpreted as emerging from the cooperative interaction among many units that, in the absence of cooperation would generate Poisson fluctuations. We call natural time the brain internal time and we make the assumption that in the natural time representation the time evolution of the EEG variable ...
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Charge State Dependence of L-Shell X-Ray Production Cross Sections of ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Energetic Oxygen Ions

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

Date: August 1996
Creator: Azordegan, Amir R. (Amir Reza)
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 Corporation tandem Pelletron accelerator. Different charge states, with and without K-vacancies, were produced using a post acceleration nitrogen striping gas cell or ¹²C stripping foils. L-shell x-rays from ultra-thin ₂₈Ni, ₂₉Cu,₃₀Zn,₃₁Ga, and ₃₂Ge targets were measured using a Si(Li) x-ray detector with a FWHM resolution of 135 eV at 5.9 keV. The scattered projectiles were detected simultaneously by means of silicon surface barrier detectors at angle of 45° and 169° with respect to the beam direction. The electron capture (EC) as well as direct ionization (DI) contributions were determined from the projectile charge state dependence of the target x-ray production cross sections under single collision conditions. The present work was undertaken to expand the measurements of L-shell x-ray production cross sections upon selected elements with low ...
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The Nonadditive Generalization of Klimontovich's S-Theorem for Open Systems and Boltzmann's Orthodes

The Nonadditive Generalization of Klimontovich's S-Theorem for Open Systems and Boltzmann's Orthodes

Date: August 2008
Creator: Bagci, Gokhan Baris
Description: We show that the nonadditive open systems can be studied in a consistent manner by using a generalized version of S-theorem. This new generalized S-theorem can further be considered as an indication of self-organization in nonadditive open systems as prescribed by Haken. The nonadditive S-theorem is then illustrated by using the modified Van der Pol oscillator. Finally, Tsallis entropy as an equilibrium entropy is studied by using Boltzmann's method of orthodes. This part of dissertation shows that Tsallis ensemble is on equal footing with the microcanonical, canonical and grand canonical ensembles. However, the associated entropy turns out to be Renyi entropy.
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Anderson Localization in Two-Channel Wires with Correlated Disorder: DNA as an Application

Anderson Localization in Two-Channel Wires with Correlated Disorder: DNA as an Application

Date: December 2007
Creator: Bagci, V. M. Kemal
Description: This research studied the Anderson localization of electrons in two-channel wires with correlated disorder and in DNA molecules. It involved an analytical calculation part where the formula for the inverse localization length for electron states in a two-channel wire is derived. It also involved a computational part where the localization length is calculated for some DNA molecules. Electron localization in two-channel wires with correlated disorder was studied using a single-electron tight-binding model. Calculations were within second-order Born-approximation to second-order in disorder parameters. An analytical expression for localization length as a functional of correlations in potentials was found. Anderson localization in DNA molecules were studied in single-channel wire and two-channel models for electron transport in DNA. In both of the models, some DNA sequences exhibited delocalized electron states in their energy spectrum. Studies with two-channel wire model for DNA yielded important link between electron localization properties and genetic information.
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Design and Testing of a Coincidence System

Design and Testing of a Coincidence System

Date: January 1961
Creator: Barnes, W. L., Jr.
Description: This paper is concerned with the design, testing and performance of a coincidence system, the proposed North Texas State College accelerator.
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The Interactions of Plasma with Low-k Dielectrics: Fundamental Damage and Protection Mechanisms

The Interactions of Plasma with Low-k Dielectrics: Fundamental Damage and Protection Mechanisms

Date: August 2011
Creator: Behera, Swayambhu Prasad
Description: Nanoporous low-k dielectrics are used for integrated circuit interconnects to reduce the propagation delays, and cross talk noise between metal wires as an alternative material for SiO2. These materials, typically organosilicate glass (OSG) films, are exposed to oxygen plasmas during photoresist stripping and related processes which substantially damage the film by abstracting carbon, incorporating O and OH, eventually leading to significantly increased k values. Systematic studies have been performed to understand the oxygen plasma-induced damage mechanisms on different low-k OSG films of various porosity and pore interconnectedness. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy are used to understand the damage kinetics of O radicals, ultraviolet photons and charged species, and possible ways to control the carbon loss from the film. FTIR results demonstrate that O radical present in the plasma is primarily responsible for carbon abstraction and this is governed by diffusion mechanism involving interconnected film nanopores. The loss of carbon from the film can be controlled by closing the pore interconnections, He plasma pretreatment is an effective way to control the damage at longer exposure by closing the connections between the pores.
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Fractional Calculus and Dynamic Approach to Complexity

Fractional Calculus and Dynamic Approach to Complexity

Date: December 2015
Creator: Beig, Mirza Tanweer Ahmad
Description: Fractional calculus enables the possibility of using real number powers or complex number powers of the differentiation operator. The fundamental connection between fractional calculus and subordination processes is explored and affords a physical interpretation for a fractional trajectory, that being an average over an ensemble of stochastic trajectories. With an ensemble average perspective, the explanation of the behavior of fractional chaotic systems changes dramatically. Before now what has been interpreted as intrinsic friction is actually a form of non-Markovian dissipation that automatically arises from adopting the fractional calculus, is shown to be a manifestation of decorrelations between trajectories. Nonlinear Langevin equation describes the mean field of a finite size complex network at criticality. Critical phenomena and temporal complexity are two very important issues of modern nonlinear dynamics and the link between them found by the author can significantly improve the understanding behavior of dynamical systems at criticality. The subject of temporal complexity addresses the challenging and especially helpful in addressing fundamental physical science issues beyond the limits of reductionism.
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Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous Fowler-Nordheim I-V Plots with Field Emission Energy Distributions

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

Date: August 1999
Creator: Bernhard, John Michael
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. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated. Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous ...
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Carbon K-Shell X-Ray and Auger-Electron Cross Sections and Fluorescence Yields for Selected Molecular Gases by 0.6 To 2 .0 MeV Proton Impact

Carbon K-Shell X-Ray and Auger-Electron Cross Sections and Fluorescence Yields for Selected Molecular Gases by 0.6 To 2 .0 MeV Proton Impact

Date: August 1986
Creator: Bhalla, Raj P. (Raj Pal), 1948
Description: Absolute K-shell x-ray cross sections and Auger-electron cross sections are measured for carbon for 0.6 to 2.0 MeV proton incident on CH₄, n-C₄H₁₀ (n-Butane), i-C₄H₁₀ (isobutane), C₆H₆ (Benzene), C₂H₂ (Acetylene), CO and CO₂. Carbon K-shell fluorescence yields are calculated from the measurements of x-ray and Auger-electron cross sections. X-ray cross sections are measured using a variable geometry end window proportional counter. An alternate method is described for the measurement of the transmission of the proportional counter window. Auger electrons are detected by using a constant transmission energy Π/4 parallel pi ate electrostatic analyzer. Absolute carbon K-shell x-ray cross sections for CH₄ are compared to the known results of Khan et al. (1965). Auger-electron cross sections for proton impact on CH₄ are compared to the known experimental values of RΦdbro et al. (1979), and to the theoretical predictions of the first Born and ECPSSR. The data is in good agreement with both the first Born and ECPSSR, and within our experimental uncertainties with the measurements of RΦdbro et al. The x-ray cross sections, Auger-electron cross sections and fluorescence yields are plotted as a function of the Pauling charge, and show significant variations. These changes in the x-ray cross sections are compared ...
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Complexity as Aging Non-Poisson Renewal Processes

Complexity as Aging Non-Poisson Renewal Processes

Date: May 2007
Creator: Bianco, Simone
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 involved, can generate the same macroscopic outcome, namely an inverse power law distribution density of events occurrence. To solve this ambiguity, a numerical instrument, based on the theoretical analysis of the aging properties of renewal systems, is introduced. The application of this method, called renewal aging experiment, allows us to distinguish if a time series has been generated by a renewal or a modulation process. This method of analysis is then applied to several physical systems, from blinking quantum dots, to the human brain activity, to seismic fluctuations. Theoretical conclusions about the underlying nature of the considered complex systems are drawn.
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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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The Stopping Power of Amorphous and Channelled Silicon at All Energies as Computed with the Binary Encounter Approximation

The Stopping Power of Amorphous and Channelled Silicon at All Energies as Computed with the Binary Encounter Approximation

Date: December 1994
Creator: Bickel, David, 1970-
Description: This thesis utilizes the binary encounter approximation to calculate the stopping power of protons penetrating silicon. The main goal of the research was to make predictions of the stopping power of silicon for low-energy and medium-energy channelled protons, in the hope that this will motivate experiments to test the theory developed below. In attaining this goal, different stopping power theories were compared and the binary encounter approach was applied to random (non-channelled) and high-energy channelled protons in silicon, and these results were compared with experimental data.
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Energy Distribution of Sputtered Neutral Atoms from a Multilayer Target

Energy Distribution of Sputtered Neutral Atoms from a Multilayer Target

Date: August 2000
Creator: Bigelow, Alan W.
Description: Energy distribution measurements of sputtered neutral particles contribute to the general knowledge of sputtering, a common technique for surface analysis. In this work emphasis was placed on the measurement of energy distribution of sputtered neutral atoms from different depths. The liquid Ga-In eutectic alloy as a sample target for this study was ideal due to an extreme concentration ratio gradient between the top two monolayers. In pursuing this study, the method of sputter-initiated resonance ionization spectroscopy (SIRIS) was utilized. SIRIS employs a pulsed ion beam to initiate sputtering and tunable dye lasers for resonance ionization. Observation of the energy distribution was achieved with a position-sensitive detector. The principle behind the detector's energy resolution is time of flight (TOF) spectroscopy. For this specific detector, programmed time intervals between the sputtering pulse at the target and the ionizing laser pulse provided information leading to the energy distribution of the secondary neutral particles. This experiment contributes data for energy distributions of sputtered neutral particles to the experimental database, required by theoretical models and computer simulations for the sputtering phenomenon.
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The Dynamic Foundation of Fractal Operators.

The Dynamic Foundation of Fractal Operators.

Date: May 2003
Creator: Bologna, Mauro
Description: The fractal operators discussed in this dissertation are introduced in the form originally proposed in an earlier book of the candidate, which proves to be very convenient for physicists, due to its heuristic and intuitive nature. This dissertation proves that these fractal operators are the most convenient tools to address a number of problems in condensed matter, in accordance with the point of view of many other authors, and with the earlier book of the candidate. The microscopic foundation of the fractal calculus on the basis of either classical or quantum mechanics is still unknown, and the second part of this dissertation aims at this important task. This dissertation proves that the adoption of a master equation approach, and so of probabilistic as well as dynamical argument yields a satisfactory solution of the problem, as shown in a work by the candidate already published. At the same time, this dissertation shows that the foundation of Levy statistics is compatible with ordinary statistical mechanics and thermodynamics. The problem of the connection with the Kolmogorov-Sinai entropy is a delicate problem that, however, can be successfully solved. The derivation from a microscopic Liouville-like approach based on densities, however, is shown to be impossible. ...
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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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Gamma Ray Distribution from Neutron Excitation in Cesium

Gamma Ray Distribution from Neutron Excitation in Cesium

Date: January 1969
Creator: Bowers, Richard Morgan
Description: The purpose of this investigation was to analyze the gamma rays resulting from excitation of Cs133 by the inelastic scattering of 14 MeV neutrons and to determine the relative intensity of each gamma ray.
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Distribution of Nighttime F-region Molecular Ion Concentrations and 6300 Å Nightglow Morphology

Distribution of Nighttime F-region Molecular Ion Concentrations and 6300 Å Nightglow Morphology

Date: December 1970
Creator: Brasher, William Ernest, 1939-
Description: The purpose of this study is two-fold. The first is to determine the dependence of the molecular ion profiles on the various ionospheric and atmospheric parameters that affect their distributions. The second is to demonstrate the correlation of specific ionospheric parameters with 6300 Å nightglow intensity during periods of magnetically quiet and disturbed conditions.
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Radar Scattering Cross-section of Triangular Corner Reflectors

Radar Scattering Cross-section of Triangular Corner Reflectors

Date: 1957
Creator: Budwine, Robert E.
Description: The series of experimental studies to be described has been carried out in order to determine the feasibility of using corner reflectors as laboratory standards for model cross-section measurements.
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Steady-state and Dynamic Probe Characteristics in a Low-density Plasma

Steady-state and Dynamic Probe Characteristics in a Low-density Plasma

Date: December 1970
Creator: Bunting, William David
Description: The problem with which this investigation is concerned is that of determining the steady-state and dynamic characteristics of the admittance of a metallic probe immersed in a laboratory plasma which has the low electron densities and low electron temperatures characteristic of the ionospheric plasma. The problem is separated into three related topics: the design and production of the laboratory plasma, the measurement of the steady-state properties of dc and very low frequency probe admittance, and the study of transient ion sheath effects on radio frequency probe admittance.
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On Delocalization Effects in Multidimensional Lattices

On Delocalization Effects in Multidimensional Lattices

Date: May 1998
Creator: Bystrik, Anna
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 moments and the spectral density are computed for the various degrees of disorder in the prototype lattice. The possible directions of the further development are outlined. The physical problem that is addressed in the dissertation is the possibility of the existence of a non-Anderson disorder of a specific type. More precisely, this type of a disorder in the one-dimensional case would result in a positive localization threshold. A specific type of such non-Anderson disorder was obtained by adopting a transformation procedure which assigns to the matrix expressing the physics of the multidimensional crystal a tridiagonal Hamiltonian. This Hamiltonian is then assigned to an equivalent one-dimensional tight-binding model. One of the benefits of this approach is that we are guaranteed to obtain a linear crystal with a ...
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