UNT Libraries - 353 Matching Results

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open access

The Physics of Gaseous Exposures on Active Field Emission Microcathode Arrays

Description: The interaction of active molybdenum field emission microcathode arrays with oxygen, water, carbon dioxide, methane, hydrogen and helium gases was studied. Experiments were setup to measure the emission characteristics as a function of gas exposures. The resulting changes in the surface work function of the tips were determined from the Fowler-Nordheim plots. The kinetics of the FEA-gas interaction were studied by observing the ion species originating from the array during and after gas exposur… more
Date: September 1996
Creator: Chalamala, Babu Reddy
Item Type: Refine your search to only Thesis or Dissertation
open access

Picosecond Dynamics of Free-Carrier Populations, Space-Charge Fields, and Photorefractive Nonlinearities in Zincblende Semiconductors

Description: Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and… more
Date: August 1999
Creator: Stark, Thomas S.
Item Type: Refine your search to only Thesis or Dissertation
open access

Placing High-Redshift Quasars in Perspective: Unifying Distant Quasars with Their Lower Redshift Counterparts through Near-Infrared Spectroscopy

Description: I present spectroscopic measurements for 260 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample of Sloan Digital Sky Survey (SDSS) quasars at 1.5 < z < 3.5. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C IV λ1549, Mg II λλ2798, 2803, Hβ λ4861, and [O III] λλ4959, 5007 emission lines, in each source. The spectral… more
Date: May 2023
Creator: Matthews, Brandon M.
Item Type: Refine your search to only Thesis or Dissertation
open access

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

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 … more
Date: December 2003
Creator: Wang, Changjie
Item Type: Refine your search to only Thesis or Dissertation
open access

A Positive Ion Source

Description: This paper describes the construction of a positive ion source of the electrodeless discharge type and may be divided into two main topis; (1) the radio frequency oscillator and power amplifier and associated power supply and (2) the ionization chamber.
Date: 1948
Creator: Hannah, Kenneth W.
Item Type: Refine your search to only Thesis or Dissertation
open access

A Precise Few-nucleon Size Difference by Isotope Shift Measurements of Helium

Description: We perform high precision measurements of an isotope shift between the two stable isotopes of helium. We use laser excitation of the 2^3 S_1-2^3 P_0 transition at 1083 nm in a metastable beam of 3He and 4He atoms. A newly developed tunable laser frequency selector along with our previous electro-optic frequency modulation technique provides extremely reliable, adaptable, and precise frequency and intensity control. The intensity control contributes negligibly to overall experimental uncertai… more
Date: August 2015
Creator: Hassan Rezaeian, Nima
Item Type: Refine your search to only Thesis or Dissertation
open access

A Precision Angular Correlation Table and Calculation of Geometrical Correction Factors

Description: In recent years y-y angular correlations have been very useful in confirming the spins of excited nuclear states. Angular correlation techniques have also been employed to study the electric and magnetic character of excited nuclear states. With these things in mind, it was decided to design, construct, and test a precision angular correlation table.
Date: January 1970
Creator: Rowton, Larry James
Item Type: Refine your search to only Thesis or Dissertation
open access

Pressure Dependence of Line Widths of Microwave Spectra of Sulphur Dioxide

Description: Measurements of line width parameters for eleven rotational transitions of type (J -- J + 1) of SO2 were made and are reported herein. The line width quantum number (J) trend was obtained. The microwave spectrograph used for these measurements of line width is described. Operational methods to operate the spectrograph are presented and discussed, with particular attention given to how to measure the line width. Suggestions for future avenues of probing this molecule to ascertain the non-uniform… more
Date: December 1972
Creator: Yang, Wei Han
Item Type: Refine your search to only Thesis or Dissertation
open access

Proton-Induced L-shell X-Rays of Pr, Sm, Eu, Gd, and Dy

Description: Characteristic L-shell x rays of the five rare earths Pr, Sm, Eu, Gd, and Dy were studied in this work. The x rays were produced by ionization from 0.3 to 2.0 MeV protons from the 2.0 MV Van de Graaff at North Texas State University. Total L-shell ionization and x-ray production cross sections were measured for Sm and compared to the BEA, CBEA and PWBA theories. Total L-shell ionization cross sections were measured for Pr, Eu, Gd, and Dy and compared to the BEA, CBEA, and PWBA. The CBEA and PW… more
Date: August 1974
Creator: Abrath, Frederick G.
Item Type: Refine your search to only Thesis or Dissertation
open access

Proton Nuclear Magnetic Resonance in Mica

Description: The experiments to be described here were undertaken for the purpose of determining, if possible, by NMR techniques whether or not the hydroxyl protons in mica are bound in a regular crystalline array, and, if so, whether or not the hydroxyl protons occur in reasonably isolated pairs as in waters of hydration.
Date: May 1962
Creator: Townsend, Don H.
Item Type: Refine your search to only Thesis or Dissertation
open access

Quantum Coherence Effects Coupled via Plasmons

Description: This thesis is an attempt at studying quantum coherence effects coupled via plasmons. After introducing the quantum coherence in atomic systems in Chapter 1, we utilize it in Chapter 2 to demonstrate a new technique of detection of motion of single atoms or irons inside an optical cavity. By taking into account the interaction of coherences with surface plasmonic waves excited in metal nanoparticles, we provide a theoretical model along with experimental data in Chapter 3 to describe the modifi… more
Date: December 2018
Creator: Moazzezi, Mojtaba
Item Type: Refine your search to only Thesis or Dissertation
open access

Quantum Coherent Control and Propagation in Lambda System

Description: Strong coherence in quasi-resonant laser driven system interferes with effective relaxations, resulting in behaviors like, coherent population trapping and Electromagnetically induced transparency. The Raman system can optimize this utilizing excited coherence in the lambda system when exposed to counter- intuitive pump-stokes pulses. The phenomenon can result in complete population transfer between vibrational levels called Stimulated Raman adiabatic passage(STIRAP). STIRAP and CHIRAP have bee… more
Date: May 2016
Creator: Singh, Pooja, 1983-
Item Type: Refine your search to only Thesis or Dissertation
open access

Quantum-Confined CdS Nanoparticles on DNA Templates

Description: As electronic devices became smaller, interest in quantum-confined semiconductor nanostructures increased. Self-assembled mesoscale semiconductor structures of II-VI nanocrystals are an especially exciting subject because of their controllable band gap and unique photophysical properties. Several preparative methods to synthesize and control the sizes of the individual nanocrystallites and the electronic and optical properties have been intensively studied. Fabrication of patterned nanostructur… more
Date: May 1998
Creator: Rho, Young Gyu
Item Type: Refine your search to only Thesis or Dissertation
open access

Quaternion Representation of Crystal Point Groups

Description: The physical behavior of crystalline solids is very closely related to the internal symmetry of the crystal structure. For this reason it is desirable to represent mathematically this symmetry in such a way that the actual physical problems can be handled as they arise. In the case of this thesis the research has been guided by a list of desired properties for such a representation. No claim is made that the list is complete.
Date: August 1959
Creator: West, Richard Harrison
Item Type: Refine your search to only Thesis or Dissertation

Random growth of interfaces: Statistical analysis of single columns and detection of critical events.

Description: The dynamics of growth and formation of surfaces and interfaces is becoming very important for the understanding of the origin and the behavior of a wide range of natural and industrial dynamical processes. The first part of the paper is focused on the interesting field of the random growth of surfaces and interfaces, which finds application in physics, geology, biology, economics, and engineering among others. In this part it is studied the random growth of surfaces from within the perspecti… more
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Date: August 2004
Creator: Failla, Roberto
Item Type: Refine your search to only Thesis or Dissertation
open access

Relaxation Time Approximations in PAOFLOW 2.0

Description: Electronic transport properties have been used to classify and characterize materials and describe their functionality. Recent surge in computational power has enabled computational modelling and accelerated theoretical studies to complement and accelerate experimental discovery of novel materials. This work looks at methods for theoretical calculations of electronic transport properties and addresses the limitations of a common approximation in the calculation of these properties, namely, the … more
Date: May 2022
Creator: Jayaraj, Anooja
Item Type: Refine your search to only Thesis or Dissertation
open access

Relaxation Time Measurements for Collision Processes in the Surface Layers of Conductors and Semiconductors Near 10 Ghz

Description: This thesis represents one phase of a joint effort of research on the properties of liquids and solids. This work is concerned primarily with the microwave properties of solids. In this investigation the properties exhibited by conductor and semiconductor materials when they are subjected to electromagnetic radiation of microwave frequency are studied. The method utilized in this experiment is the perturbation of a resonant cavity produced by introduction of a cylindrically shaped sample into i… more
Date: December 1973
Creator: Childress, Larry Wayne
Item Type: Refine your search to only Thesis or Dissertation
open access

Renewal and Memory Approaches to Study Biological and Physiological Processes

Description: In nature we find many instances of complex behavior for example the dynamics of stock markets, power grids, internet networks, highway traffic, social networks, heartbeat dynamics, neural dynamics, dynamics of living organisms, etc. The study of these complex systems involves the use of tools of non-linear dynamics and non-equilibrium statistical physics. This dissertation is devoted to understanding two different sources of complex behavior – non-poissonian renewal events also called crucial… more
Date: May 2019
Creator: Tuladhar, Rohisha
Item Type: Refine your search to only Thesis or Dissertation
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