Physics Commons^™

Gain Of A Single Gas Electron Multiplier, Mythra Varun Nemallapudi

Graduate Theses and Dissertations

Gas Electron Multiplier (GEM) is a gaseous detector used in particle detection and is known for its high rate capability. Ever since its invention in 1997, GEM was applied in many areas and recently has been proposed to be installed in the CMS high η regions for upgrade at LHC, CERN. A complete understanding of the working and gain behaviour does not exist. GEM gain is influenced by charging up and this has been variedly interpreted in literature lacking consensus. I have attempted in this work through simulations and measurements to achieve a better understanding of single GEM gain and …

Phase Control In Atomic Coherence, Utsab Khadka

Graduate Theses and Dissertations

In this thesis, atomic coherence is used to enhance nonlinear optical processes in multi-level atoms. The multi-photon transitions are driven resonantly, and at the same time without absorptive losses, by using electromagnetically induced transparency (EIT), thereby allowing the study of χ⁽³⁾ and χ⁽⁵⁾ nonlinearities using weak driving fields. The coherently modified probe beam(s) and the atom-radiated signal fields arising from four- and six- wave- mixing (FWM and SWM) processes are measured in the spectral, temporal and spatial domains.

In a three-level ladder-type atomic system, multiple peaks having spectral asymmetries are observed in the EIT window as well as …

Event Shapes In Proton-Proton Collisions At Center Of Mass Energy = 1.96 Tev, Scott Atkins

Doctoral Dissertations

This dissertation presents the analysis of nine different event shapes measured in high energy pp¯ collisions. An event shape can be defined as an event-based quantity that measures how the final energies are distributed in the final event. This analysis will test strong interactions as described by Quantum Chromodynamics (QCD), through their implementation in different Monte Carlo-based models. Each of the event shapes provides information about the flow of energy in QCD events and about the hadronic final states that occur in pp¯ particle collisions, thus allowing the study of the dynamics of QCD multijet events. Any deviation of an …

Investigation Of Negative Differential Resistance Phenomena In Quantum Well Heterostructures, Nazariy Andrushchak

Graduate Theses and Dissertations

Increasing interest in entirely new possibilities for quantum mechanical description of carriers transport is becoming more evident with the developing advancements in epitaxial growth technique. Consequently, molecular beam epitaxy (MBE) technique is considered to be the most precise technique that allows the growth of ultra-thin layers of different compositions.

Those structures can be designed to investigate the wave-nature of carriers, which broadens the possibilities in device design and fabrication for a specific area. In this thesis the fundamental study of the real space charge transfer (RST) mechanism that took place in quantum well heterostructures and led to the negative differential …

Mott Transition And Electronic Structure In Complex Oxide Heterostructures, Jian Liu

Graduate Theses and Dissertations

Strongly correlated electron systems, particularly transition metal oxides, have been a focus of condensed matter physics for more than two decades since the discovery of high-temperature superconducting cuprates. Diverse competing phases emerge, spanning from exotic magnetism to unconventional superconductivity, in proximity to the localized-itinerant transition of Mott insulators. While studies were concentrated on bulk crystals, the recent rapid advance in synthesis has enabled fabrication of high-quality oxide heterostructures, offering a new route to create novel artificial quantum materials.

This dissertation details the investigation on ultrathin films and heterostructures of 3d⁷(t_2g⁶e_g¹) systems with …

Use Of Ultra High Vacuum Plasma Enhanced Chemical Vapor Deposition For Graphene Fabrication, Shannen Adcock

Graduate Theses and Dissertations

Graphene, what some are terming the "new silicon", has the possibility of revolutionizing technology through nanoscale design processes. Fabrication of graphene for device processing is limited largely by the temperatures used in conventional deposition. High temperatures are detrimental to device design where many different materials may be present. For this reason, graphene synthesis at low temperatures using plasma-enhanced chemical vapor deposition is the subject of much research. In this thesis, a tool for ultra-high vacuum plasma-enhanced chemical vapor deposition (UHV-PECVD) and accompanying subsystems, such as control systems and alarms, are designed and implemented to be used in future graphene growths. …

Spectroscopic Methods Of Process Monitoring For Safeguards Of Used Nuclear Fuel Separations, Jamie Lee Warburton

UNLV Theses, Dissertations, Professional Papers, and Capstones

To support the demonstration of a more proliferation-resistant nuclear fuel processing plant, techniques and instrumentation to allow the real-time, online determination of special nuclear material concentrations in-process must be developed. An ideal materials accountability technique for proliferation resistance should provide nondestructive, realtime, on-line information of metal and ligand concentrations in separations streams without perturbing the process. UV-Visible spectroscopy can be adapted for this precise purpose in solvent extraction-based separations.

The primary goal of this project is to understand fundamental URanium EXtraction (UREX) and Plutonium-URanium EXtraction (PUREX) reprocessing chemistry and corresponding UV-Visible spectroscopy for application in process monitoring for safeguards. By …

Symmetry-Based Techniques For Qualitative Understanding Of Rovibrational Effects In Spherical-Top Molecular Spectra And Dynamics, Justin Chadwick Mitchell

Graduate Theses and Dissertations

Using light to probe the structure of matter is as natural as opening our eyes. Modern physics and chemistry have turned this art into a rich science, measuring the delicate interactions possible at the molecular level.

Perhaps the most commonly used tool in computational spectroscopy is that of matrix diagonalization. While this is invaluable for calculating everything from molecular structure and energy levels to dipole moments and dynamics, the process of numerical diagonalization is an opaque one. This work applies symmetry and semi-classical techniques to elucidate numerical spectral analysis for high-symmetry molecules.

Semi-classical techniques, such as the Potential Energy Surfaces, …

Modeling Of Compositionally Graded Barium Strontium Titanate From First Principles, Laura Elizabeth Walizer

Graduate Theses and Dissertations

"Barium Strontium Titanate (BaxSr1-xTiO3 or BST) is a Perovskite alloy of interest for both technological and intellectual reasons. Its ferroelectric and piezoelectric properties make it useful in a variety of electric components such as transducers and actuators, and BST in particular is a material of interest for the development of a ferroelectric RAM for computers. The inclusion of SrTiO3, an incipient ferroelectric, and the fact that the properties of a BST system depend strongly on its relative composition of BaTiO3 and SrTiO3 (ST), make also this a material of high interest. Compositionally graded systems are of further interest , partly …

A Finite Difference Method For Studying Thermal Deformation In Three-Dimensional Thin Films Exposed To Ultrashort Pulsed Lasers, Suyang Zhang

Doctoral Dissertations

Thermal analysis related to ultrashort-pulsed lasers has been intensely studied in science and engineering communities in recent years, because the pulse duration of ultrashort-pulsed lasers is only the order of sub-picoseconds to femtoseconds, and the lasers have exclusive capabilities in limiting the undesirable spread of the thermal process zone in the heated sample. Studying the thermal deformation induced by ultrashort-pulsed lasers is essential for preventing thermal damage. For the ultrashort-pulsed laser, the thermal damage is different from that caused by the long pulsed lasers and cracks occur after heating.

This dissertation presents a new finite difference method for studying thermal …

Self-Organization In Cathode Boundary Layer Discharges, Nobuhiko Takano

Electrical & Computer Engineering Theses & Dissertations

Cathode boundary layer (CBL) discharge, which has been developed as a UV light source, operates in a direct current between a planar cathode and a ring-shape anode that are separated by a dielectric with an opening of the same diameter as the anode. The nonthermal CBL discharges operate in a medium pressure range down to 30 Torr, emitting excimer radiation when operated with noble gases. The radiant excimer emittance at 172 nm in xenon reaches 1.7 W/cm², and a maximum excimer efficiency of 6 % has been obtained. The high excimer radiant emittance, in addition to low cost …

Developing A B -Tagging Algorithm Using Soft Muons At Level-3 For The Dø Detector At Fermilab, Mayukh Das

Doctoral Dissertations

The current data-taking phase of the DØ detector at Fermilab, called Run II, is designed to aid the search for the Higgs Boson. The neutral Higgs is postulated to have a mass of 117 GeV. One of the channels promising the presence of this hypothetical particle is through the decay of b-quark into a muon. The process of identifying a b-quark in a jet using muon as a reference is b-tagging with a muon tag.

At the current data taking and analysis rate, it will take long to reach the process of identifying valid events. The triggering mechanism of the …

Molecular Dynamics Simulations Of Amphiphilic Molecules, Roger L. Mcmullen Jr.

Seton Hall University Dissertations and Theses (ETDs)

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Field Emission Based Sensors Using Carbon Nanotubes, Changkun Dong

Physics Theses & Dissertations

A number of sensitive applications would be greatly benefited by the development of better cold cathodes that employ the electron field emission process. Among the many kinds of field emitters that could be tried, carbon nanotubes (CNT) have a number of distinct advantages because of their unique geometrical structure, chemical inertness, mechanical stiffness, and high thermal and electrical conductivities. This dissertation describes research in which CNT cathodes were fabricated and their emission characteristics were measured.

Multi-walled carbon nanotubes (MWNT) were grown by chemical vapor deposition (CVD) on various substrates: Ni and Hastelloy gauze, 304 stainless steel (SS) plates, and Ni-coated …

Fluid Flow In Micro-Channels: A Stochastic Approach, Hilda Marino Black

Doctoral Dissertations

In this study free molecular flow in a micro-channel was modeled using a stochastic approach, namely the Kolmogorov forward equation in three dimensions. Model equations were discretized using Central Difference and Backward Difference methods and solved using the Jacobi method. Parameters were used that reflect the characteristic geometry of experimental work performed at the Louisiana Tech University Institute for Micromanufacturing.

The solution to the model equations provided the probability density function of the distance traveled by a particle in the micro-channel. From this distribution we obtained the distribution of the residence time of a particle in the micro-channel. Knowledge of …