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**Department:**Department of Physics

**Degree Discipline:**Physics

**Collection:**UNT Theses and Dissertations

### 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 ...

**Contributing Partner:**UNT Libraries

**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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**Permallink:**digital.library.unt.edu/ark:/67531/metadc131110/

### 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/