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PAOFLOW-Aided Computational Materials Design

Description: Functional materials are essential to human welfare and to provide foundations for emerging industries. As an alternative route to experimental materials discovery, computational materials designs are playing an increasingly significant role in the whole discovery process. In this work, we use an in-house developed python utility: PAOFLOW, which generates finite basis Hamiltonians from the projection of first principles plane-wave pseudopotential wavefunctions on pseudo atomic orbitals(PAO) for… more
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Date: December 2019
Creator: Wang, Haihang
open access

Physical Boundary as a Source of Anomalies in Transport Processes in Acoustics and Electrodynamics

Description: Various anomalous effects that emerge when the interfaces between media are involved in sound-matter or light-matter interactions are studied. The three specific systems examined are a fluid channel between elastic metal plates, a linear chain of metallic perforated cylindrical shells in air, and a metal-dielectric slab with the interfaces treated as finite regions of smoothly changing material properties. The scattering of acoustic signals on the first two is predicted to be accompanied by the… more
Date: December 2018
Creator: Bozhko, Andrii
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
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
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-
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
open access

A Search for Periodic and Quasi-Periodic Patterns in Select Proxy Data with a Goal to Understanding Temperature Variation

Description: In this work over 200 temperature proxy data sets have been analyzed to determine if periodic and or quasi-periodic patterns exist in the data sets. References to the journal articles where data are recorded are provided. Chapter 1 serves an introduction to the problem of temperature determination in providing information on how various proxy data sources are derived. Examples are given of the techniques followed in producing proxy data that predict temperature for each method used. In chapte… more
Date: May 2016
Creator: Otto, James (James Robert)
open access

Sputtering of Bi and Preferential Sputtering of an Inhomogeneous Alloy

Description: Angular distributions and total yields of atoms sputtered from bismuth targets by normally incident 10 keV -50 keV Ne+ and Ar+ ions have been measured both experimentally and by computer simulation. Polycrystalline Bi targets were used for experimental measurements. The sputtered atoms were collected on high purity aluminum foils under ultra-high vacuum conditions, and were subsequently analyzed using Rutherford backscattering spectroscopy. The Monte-Carlo based SRIM code was employed to simula… more
Date: December 2014
Creator: Deoli, Naresh T.
open access

Studies of Charged Particle Dynamics for Antihydrogen Synthesis

Description: Synthesis and capture of antihydrogen in controlled laboratory conditions will enable precise studies of neutral antimatter. The work presented deals with some of the physics pertinent to manipulating charged antiparticles in order to create neutral antimatter, and may be applicable to other scenarios of plasma confinement and charged particle interaction. The topics covered include the electrostatic confinement of a reflecting ion beam and the transverse confinement of an ion beam in a purely … more
Date: December 2014
Creator: Correa, Jose Ricardo
open access

Synthesis and Characterization of Ion Beam Assisted Silver Nanosystems in Silicon Based Materials for Enhanced Photocurrent Collection Efficiency

Description: In recent years a great deal of interest has been focused on the synthesis of transitional metal (e.g. Ag, Cu, Fe, Au) nanosystems at the surface to sub-surface regions of Si and SiO2 matrices for fundamental understanding of their structures as well as for development of technological applications with enhanced electronic and optical properties. The applications of the metal nanoparticle or nanocluster (NC) systems range from plasmonics, photovoltaic devices, medical, and biosensors. In all o… more
Date: May 2015
Creator: Dhoubhadel, Mangal S.
open access

Synthesis, Characterization, Structural, and Optical Properties of Zinc Oxide Nanostructures Embedded in Silicon Based Substrates

Description: Structural and optical properties of ZnO nanostructures synthesized by low energy ion implantation technique were examined. ZnO molecular ions were implanted into Si/SiO2 substrates at room temperature and then furnace annealed under different temperatures and environments. In all as-implanted samples only Zn nanostructures with varying diameters distributed into the Si/SiO2 matrices were observed. No trace of ZnO was found. The distributions of Zn nanostructures in Si/SiO2 closely matched resu… more
Date: May 2014
Creator: Pandey, Bimal
open access

Synthesis Strategies and a Study of Properties of Narrow and Wide Band Gap Nanowires

Description: Various techniques to synthesize nanowires and nanotubes as a function of growth temperature and time were investigated. These include growth of nanowires by a chemical vapor deposition (CVD) system using vapor-liquid-solid (VLS) growth mechanism and electro-chemical synthesis of nanowires and nanotubes. Narrow band gap InSb Eg = 0.17 eV at room temp) nanowires were successively synthesized. Using a phase diagram, the transition of the nanowire from metallic- semiconducting- semi-metallic phase… more
Date: May 2014
Creator: Sapkota, Gopal
open access

Temporal Complexity and Stochastic Central Limit Theorem

Description: Complex processes whose evolution in time rests on the occurrence of a large and random number of intermittent events are the systems under study. The mean time distance between two consecutive events is infinite, thereby violating the ergodic condition and activating at the same time a stochastic central limit theorem that explains why the Mittag-Leffler function is a universal property of nature. The time evolution of these complex systems is properly generated by means of fractional differen… more
Date: August 2014
Creator: Pramukkul, Pensri
open access

Temporal Properties Of Dynamic Processes On Complex Networks

Description: Many social, biological and technological systems can be viewed as complex networks with a large number of interacting components. However despite recent advancements in network theory, a satisfactory description of dynamic processes arising in such cooperative systems is a subject of ongoing research. In this dissertation the emergence of dynamical complexity in networks of interacting stochastic oscillators is investigated. In particular I demonstrate that networks of two and three state stoc… more
Date: December 2011
Creator: Turalska, Malgorzata A.
open access

Theoretical and Experimental Investigations Concerning Microgels of Varied Spherical Geometries

Description: Polymer gels have been studied extensively due to their ability to simulate biological tissues and to swell or collapse reversibly in response to external stimuli. This work presents a variety of studies using poly-N-isopropylacrylamide (PNIPA) hydrogels. The projects have been carried out both in the lab of Dr. Zhibing Hu and in collaboration with others outside of UNT: (1) an analysis of the swelling kinetics of microgel spherical shells prepared using a novel design of microfluidic devices; … more
Date: August 2012
Creator: Wahrmund, Joshua Joseph
open access

Theoretical and Experimental Investigations of Peg Based Thermo Sensitive Hydro Microgel

Description: Poly ethylene glycol (PEG) based microgels were synthesized and investigated. The PEG microgel has the same phase transition as the traditional poly N-isopropylacrylamide (PNIPAM). As a good substitute of PNIPAM, PEG microgel exhibits many advantages: it is easier to control the lower critical solution temperature (LCST) of the microgel by changing the component of copolymers; it has a more solid spherical core-shell structure to have a double thermo sensitivity; it is straightforward to add ot… more
Date: December 2012
Creator: Chi, Chenglin
open access

Thorium and Uranium M-shell X-ray Production Cross Sections for 0.4 – 4.0 MeV Protons, 0.4 - 6.0 MeV Helium Ions, 4.5 – 11.3 MeV Carbon Ions, and 4.5 – 13.5 MeV Oxygen Ions.

Description: The M-shell x-ray production cross section for thorium and uranium have been determined for protons of energy 0.4 - 4.0 MeV, helium ions of energy 0.4 - 6.0 MeV, carbon ions of energy 4.5 - 11.3 MeV and oxygen ions of energy 4.5 - 13.5 MeV. The total cross sections and the cross sections for individual x-ray peaks in the spectrum, consisting of the following transitions Mz (M4-N2, M5-N3, M4-N3), Ma (M5-N6,7), Mb (M4-N6, M5-O3, M4- O2), and Mg (M4-O3, M5-P3, M3-N4, M3-N5), were compared to the t… more
Date: May 2011
Creator: Phinney, Lucas C.
open access

Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells

Description: Group III nitrides are efficient light emitters. The modification of internal optoelectronic properties of these materials due to strain, external or internal electric field are an area of interest. Insertion of metal nanoparticles (MNPs) (Ag, Au etc) inside the V-shaped inverted hexagonal pits (IHP) of InGaN/GaN quantum wells (QWs) offers the potential of improving the light emission efficiencies. We have observed redshift and blueshift due to the Au MNPs and Ag MNPs respectively. This sh… more
Date: August 2012
Creator: Mahat, Meg Bahadur

UV Magnetic Plasmons in Cobalt Nanoparticles

Description: The main goals of this research were to fabricate magnetic cobalt nanoparticles and study their structural, crystal structure, optical, and magnetic properties. Cobalt nanoparticles with average particle size 8.7 nm were fabricated by the method of high temperature reduction of cobalt salt utilizing trioctylphosphine as a surfactant, oleic acid as a stabilizer, and lithium triethylborohydride as a reducing reagent. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the formation of c… more
Access: Restricted to UNT Community Members. Login required if off-campus.
Date: May 2019
Creator: Bhatta, Hari Lal
open access

Variational Calculations of Positronium Scattering with Hydrogen

Description: Positronium-hydrogen (Ps-H) scattering is of interest, as it is a fundamental four-body Coulomb problem. We have investigated low-energy Ps-H scattering below the Ps(n=2) excitation threshold using the Kohn variational method and variants of the method with a trial wavefunction that includes highly correlated Hylleraas-type short-range terms. We give an elegant formalism that combines all Kohn-type variational methods into a single form. Along with this, we have also developed a general formali… more
Date: December 2015
Creator: Woods, Denton
open access

Zinc Oxide Nanoparticles for Nonlinear Bioimaging, Cell Detection and Selective Cell Destruction

Description: Light matter interactions have led to a great part of our current understanding of the universe. When light interacts with matter it affects the properties of both the light and the matter. Visible light, being in the region that the human eye can "see," was one of the first natural phenomenon we used to learn about our universe. The application of fundamental physics research has spilled over into other fields that were traditionally separated from physics, being considered two different scien… more
Date: May 2013
Creator: Urban, Ben E.
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