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**Partner:**UNT Libraries

**Degree Discipline:**Physics

**Collection:**UNT Theses and Dissertations

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc277827/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc279387/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc2657/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc4235/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc130453/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc163933/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc278620/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc107940/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc278232/

### Maxwell's Equations from Electrostatics and Einstein's Gravitational Field Equation from Newton's Universal Law of Gravitation Using Tensors

**Date:**May 2004

**Creator:**Burns, Michael E.

**Description:**Maxwell's equations are obtained from Coulomb's Law using special relativity. For the derivation, tensor analysis is used, charge is assumed to be a conserved scalar, the Lorentz force is assumed to be a pure force, and the principle of superposition is assumed to hold. Einstein's gravitational field equation is obtained from Newton's universal law of gravitation. In order to proceed, the principle of least action for gravity is shown to be equivalent to the maximization of proper time along a geodesic. The conservation of energy and momentum is assumed, which, through the use of the Bianchi identity, results in Einstein's field equation.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc4532/