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**Department:**Department of Physics

**Degree Discipline:**Physics

**Collection:**UNT Theses and Dissertations

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc3706/

### A Comprehensive Model for the Rotational Spectra of Propyne CH₃CCH in the Ground and V₁₀=1,2,3,4,5 Vibrational States

**Date:**December 1986

**Creator:**Rhee, Won Myung

**Description:**The energy states of C₃ᵥ symmetric top polyatomic molecules were studied. Both classical and quantum mechanical methods have been used to introduce the energy states of polyatomic molecules. Also, it is shown that the vibration-rotation spectra of polyatomic molecules in the ground and excited vibrational states can be predicted by group theory. A comprehensive model for predicting rotational frequency components in various v₁₀ vibrational levels of propyne was developed by using perturbation theory and those results were compared with other formulas for C₃ᵥ symmetric top molecules. The v₁₀=1,2,3 and ground rotational spectra of propyne in the frequency range 17-70 GHz have been reassigned by using the derived comprehensive model. The v₁₀=3 and v₁₀=4 rotational spectra of propyne have been investigated in the 70 GHz, and 17 to 52 GHz regions, respectively, and these spectral components assigned using the comprehensive model. Molecular constants for these vibrationally excited states have been determined from more than 100 observed rotational transitions. From these experimentally observed components and a model based upon first principles for C₃ᵥ symmetry molecules, rotational constants have been expressed in a form which enables one to predict rotational components for vibrational levels for propyne up to v₁₀=5. This comprehensive model also ...

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### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc130612/

### The Concept of Collision Strength and Its Applications

**Date:**May 2004

**Creator:**Chang, Yongbin

**Description:**Collision strength, the measure of strength for a binary collision, hasn't been defined clearly. In practice, many physical arguments have been employed for the purpose and taken for granted. A scattering angle has been widely and intensively used as a measure of collision strength in plasma physics for years. The result of this is complication and unnecessary approximation in deriving some of the basic kinetic equations and in calculating some of the basic physical terms. The Boltzmann equation has a five-fold integral collision term that is complicated. Chandrasekhar and Spitzer's approaches to the linear Fokker-Planck coefficients have several approximations. An effective variable-change technique has been developed in this dissertation as an alternative to scattering angle as the measure of collision strength. By introducing the square of the reduced impulse or its equivalencies as a collision strength variable, many plasma calculations have been simplified. The five-fold linear Boltzmann collision integral and linearized Boltzmann collision integral are simplified to three-fold integrals. The arbitrary order linear Fokker-Planck coefficients are calculated and expressed in a uniform expression. The new theory provides a simple and exact method for describing the equilibrium plasma collision rate, and a precise calculation of the equilibrium relaxation time. It generalizes ...

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc4530/

### A Continuously Sensitive Cloud Chamber

**Date:**1951

**Creator:**Hughes, James E.

**Description:**A continuous cloud chamber would be a valuable asset to laboratory work in nuclear and atomic physics. For this reason the construction and investigation of a continuously sensitive diffusion cloud chamber has been undertaken. It is the purpose of this paper to report the design and operating characteristics of such a chamber.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc97019/

### Cooperation-induced Criticality in Neural Networks

**Date:**August 2013

**Creator:**Zare, Marzieh

**Description:**The human brain is considered to be the most complex and powerful information-processing device in the known universe. The fundamental concepts behind the physics of complex systems motivate scientists to investigate the human brain as a collective property emerging from the interaction of thousand agents. In this dissertation, I investigate the emergence of cooperation-induced properties in a system of interacting units. I demonstrate that the neural network of my research generates a series of properties such as avalanche distribution in size and duration coinciding with the experimental results on neural networks both in vivo and in vitro. Focusing attention on temporal complexity and fractal index of the system, I discuss how to define an order parameter and phase transition. Criticality is assumed to correspond to the emergence of temporal complexity, interpreted as a manifestation of non-Poisson renewal dynamics. In addition, I study the transmission of information between two networks to confirm the criticality and discuss how the network topology changes over time in the light of Hebbian learning.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc283813/

### A Correction Factor for the First Born Approximation

**Date:**January 1965

**Creator:**Russell, Jerry Brent

**Description:**This thesis looks at a Schroedinger equation and the Born approximation.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc130574/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc271910/

### Cross-Section at 15.6 and 16.1 MeV

**Date:**May 1969

**Creator:**Pepper, George H.

**Description:**The intent of this investigation is the determination of the values of the Cs-133 (n,2n)Cs-132 cross-section at neutron energies of 15.6 and 16.1 MeV. Neutrons of this energy are produced with comparative ease by means of the D-T reaction, in which deuterons of energy 500 and 750 keV, respectively, are impingent upon a tritium target.

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### Cross Section for the 165/Ho (n, 2n) 164/Ho Reaction at 15.6 MeV

**Date:**August 1969

**Creator:**Lear, Richard D.

**Description:**It was the purpose of this investigation to bring together the ideas and procedures involved in the measurement of (n, 2n) reaction cross sections. Some of the inherent properties of the material under investigation (Holium) are involved in determining these relationships.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc131148/

### Cross Section Measurements in Praseodymium-141 as a Function of Neutron Bombarding Energy

**Date:**May 1971

**Creator:**Marsh, Stephen Addison

**Description:**Using the parallel disk method of activation analysis, the (n,2n) reaction cross section in 141-Pr was measured as a function of neutron energy in the range 15.4 to 18.4 MeV. The bombarding neutrons were produced from the 3-T(d,n)4-He reaction, where the deuterons were accelerated by the 3-MV Van de Graff generator of the North Texas Regional Physics Laboratory in Denton, Texas.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc131376/

### Crystalline Polymorphism of Nitrates

**Date:**1951

**Creator:**Shepherd, Jimmie G.

**Description:**The purpose of this study was to investigate the polymorphism of a group of related compounds. Special emphasis was placed upon the temperature at which transitions occurred and a possible correlation of these temperatures with other properties of the compounds.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc97053/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc130455/

### A Decay Scheme for 164 Ho

**Date:**December 1972

**Creator:**Guertin, James

**Description:**The present investigation was prompted by several considerations. In previous studies there was considerable variance with regard to the reported values for the half-lives of the isomeric and ground states in 164 Ho. There was also considerable variance with regard to the values reported for the branching ratios and the relative intensities of the transitions. Thus a further study of the problem was needed.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc131582/

### Decoherence, Master Equation for Open Quantum Systems, and the Subordination Theory

**Date:**August 2005

**Creator:**Giraldi, Filippo

**Description:**This thesis addresses the problem of a form of anomalous decoherence that sheds light into the spectroscopy of blinking quantum dots. The system studied is a two-state system, interacting with an external environment that has the effect of establishing an interaction between the two states, via a coherence generating coupling, called inphasing. The collisions with the environment produce also decoherence, named dephasing. Decoherence is interpreted as the entanglement of the coherent superposition of these two states with the environment. The joint action of inphasing and dephasing generates a Markov master equation statistically equivalent to a random walker jumping from one state to the other. This model can be used to describe intermittent fluorescence, as a sequence of "light on" and "light off" states. The experiments on blinking quantum dots indicate that the sojourn times are distributed with an inverse power law. Thus, a proposal to turn the model for Poisson fluorescence intermittency into a model for non-Poisson fluorescence intermittency is made. The collision-like interaction of the two-state system with the environment is assumed to takes place at random times rather than at regular times. The time distance between one collision and the next is given by a distribution, called the ...

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc4812/

### Design and Construction of a Positive Radio-Frequency Ion Source for the Production of Negative Ions

**Date:**August 1958

**Creator:**Thompson, B. Cecil

**Description:**It is the purpose of this paper to present a detailed account of the design and construction of this positive-ion source and associated equipment.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc108015/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc108113/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc163849/

### 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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc163830/

### Detection of the Resonant Vibration of the Cellular Membrane Using Femtosecond Laser Pulses

**Date:**December 1989

**Creator:**Jamasbi, Nooshin

**Description:**An optical detection technique is developed to detect and measure the resonant vibration of the cellular membrane. Biological membranes are active components of living cells and play a complex and dynamic role in life processes. They are believed to have oscillation modes of frequencies in the range of 1 to 1000 GHz. To measure such a high-frequency vibration, a linear laser cavity is designed to produce a train of femtosecond pulses of adjustable repetition rate. The method is then directly applied to liposomes, "artificial membrane", stained with a liphophilic potential sensitive dye. The spectral behavior of a selection of potential sensitive dyes in the membrane is also studied.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc331235/

### A Determination of the Bothe Depression Factor for Discs in Water

**Date:**August 1950

**Creator:**Patton, Bob

**Description:**The purpose of this work is to determine experimentally the depression of the neutron density by a detecting foil. The depression factor is known as the "self-shading" of the foil.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc130255/

### A Determination of the Fine Structure Constant Using Precision Measurements of Helium Fine Structure

**Date:**August 2010

**Creator:**Smiciklas, Marc

**Description:**Spectroscopic measurements of the helium atom are performed to high precision using an atomic beam apparatus and electro-optic laser techniques. These measurements, in addition to serving as a test of helium theory, also provide a new determination of the fine structure constant α. An apparatus was designed and built to overcome limitations encountered in a previous experiment. Not only did this allow an improved level of precision but also enabled new consistency checks, including an extremely useful measurement in 3He. I discuss the details of the experimental setup along with the major changes and improvements. A new value for the J = 0 to 2 fine structure interval in the 23P state of 4He is measured to be 31 908 131.25(30) kHz. The 300 Hz precision of this result represents an improvement over previous results by more than a factor of three. Combined with the latest theoretical calculations, this yields a new determination of α with better than 5 ppb uncertainty, α-1 = 137.035 999 55(64).

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc31547/

### Deterministic Brownian Motion

**Date:**August 1993

**Creator:**Trefán, György

**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 that particle with its environment. We show that standard diffusion which is the basis of the Fokker-Planck equation rests on the Central Limit Theorem, and, consequently, on the possibility of deriving it from a deterministic process with a quickly decaying correlation function. The sensitive dependence on initial conditions, one of the defining properties of chaos insures this rapid decay. We carefully address the problem of deriving dissipation from the interaction of a particle with a fully deterministic nonlinear bath, that we term the booster. We show that the solution of this problem essentially rests on the linear response of a booster to an external perturbation. This raises a long-standing problem concerned with Kubo's Linear Response Theory and the strong criticism against it by van ...

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc279262/

### A Deuterium-Deuterium Type Neutron Source

**Date:**1951

**Creator:**Windham, Pat M.

**Description:**In view of the advantages of its type, the decision to construct a neutron source of the particle accelerator type was made. The purpose of this thesis is to survey the problems encountered in the construction of the source.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc96980/