Physical Sciences and Mathematics Commons^™

Harmonic Detection Of Resonance In Micro- And Nano- Cantilevers, Jay Gaillard

All Dissertations

Over the past decade there has been an explosion in the study of cantilevered beams on the micron and submicron dimension. The applications and research that involve these structures include state-of-the-art electronic components, sensors, and more recently, studies aimed at elucidating the mechanical properties of cantilevered carbon nanotubes and semiconducting nanowires. In nanoelectro-mechanical systems (NEMS), it is desirable to develop a capacitive readout method involving only two electrodes that are fully compliant with standard CMOS technology. However, the main drawback with this method is the ability to detect resonance in the presence of parasitic capacitance, which is due to the …

Assembly And Modification Of A Hyperthermal And Low Energy Ion Beamline For Detecting Electron-Hole Pair Production In Schottky Diodes, Matthew Ray

All Theses

A hyperthermal and low energy ion beamline to measure electron-hole pair production due to ion bombardment of Schottky diodes has been modified and assembled.
A brief overview of the instrument is given and the reason for operating the ion beamline in the hyperthermal and low energy regime is discussed. The capabilities of the ion beamline are unique and provide the means to measure quantities that offer insight into various energy exchange mechanisms that occur at surfaces. Combined with the ability to accept Schottky diode samples, the beamline is capable of measuring both charge transfer and electron-hole pair production caused by …

The X-Ray Variability Of Seyfert Galaxies, Kevin Marshall

Physics and Astronomy Dissertations

Strong and variable X-ray emission has long been known to be a universal property of active galaxies. However, despite years of study, the exact nature of the variability remains relatively unknown. We present here results of a multi-year monitoring campaign of a sample of Seyfert galaxies (3C 120, Mkn 509, 3C 390.3, and Akn 120), carried out using the Rossi X-ray Timing Explorer (RXTE). For Mkn 509, we also present results of optical monitoring. Mkn 509 shows a strong correlation between X-ray and optical variations, with the optical leading the X-ray by 25 days. We also investigate the rms-flux relationship …

Threshold Extension Of Gallium Arsenide/Aluminum Gallium Arsenide Terahertz Detectors And Switching In Heterostructures, Mohamed Buhary Rinzan

Physics and Astronomy Dissertations

In this work, homojunction interfacial workfunction internal photoemission (HIWIP) detectors based on GaAs, and heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors based mainly on the Gallium Arsenide/Aluminum Gallium Arsenide material system are presented. Design principles of HIWIP and HEIWIP detectors, such as free carrier absorption, photocarrier generation, photoemission, and responsivity, are discussed in detail. Results of p-type HIWIPs based on GaAs material are presented. Homojunction detectors based on p-type GaAs were found to limit their operating wavelength range. This is mainly due to band depletion arising through carrier transitions from the heavy/light hole bands to the split off band. Designing …

The Effects Of Fast Secondary Electrons On Low Voltage Electron Beam Lithography, Mehdi Bolorizadeh

Doctoral Dissertations

In 1981 Prof. Sir Alec Broers suggested that the spatial limit of direct writing electron beam lithography (DWEBL) would be limited to ~10 nm by the laterally scattered fast secondary electrons (FSE) even in atomically thin resist. Experiments and simulations have been carried out to quantify the contribution of FSE to the energy deposition that results in exposure of the resist over high beam energies. One possible solution to this restriction would be to use low energy electrons.

To examine Broers' hypothesis in low voltage electron beam lithography (EBL), studies in the low energy range on the effects of FSE …

Linear And Nonlinear Chiroptical Effects, Watheq Ahmad Al-Basheer

Doctoral Dissertations

Chiroptical effects of linear and nonlinear nature are investigated by employing a variety of spectroscopic methods, such as linear and nonlinear circular dichroism, optical rotation, vibrational Raman scattering, infrared absorption and Vibrational Circular Dichroism. (2+1) Resonance Enhanced Multiphoton Ionization Circular Dichroism (REMPICD) is a direct demonstration of the nonlinear chiroptical effects of a sample of R-(+)-3-methylcyclopentanone. Solvent effects on circular dichroism is studied for 35 common solvents, which is significantly attributed to the solute- solvent electrostatic and Van der waals interactions for CD and ORD of R3MCP. Hartree-Fock and Density Function Theoretical calculations of R3MCP CD and …

Combined Study Of Reactor And Terrestrial Antineutrinos With Kamland, Mikhail Batygov

Doctoral Dissertations

This dissertation presents a combined study of antineutrinos of terrestrial and reactor origin detected by Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND). Of special physical interest are neutrino oscillation parameters and the terrestrial antineutrino flux, the former being of a profound importance for new physics beyond the Standard Model, and the latter having significant implications for geophysics. The analysis described here uses a comprehensive likelihood model to naturally combine terrestrial and reactor antineutrino studies within a single framework. The use of this likelihood model and better event reconstruction tools allowed to obtain narrower limits for the oscillation parameters and the terrestrial …

Interference Effects Among J = 3/2+ Resonances In 19Ne System & Searching For Resonances In The Unbound 6Be Nucleus, Kyung Yuk Chae

Doctoral Dissertations

The ¹⁸F(p,α)¹⁵O reaction plays a crucial role in understanding γ-ray emission from novae. Because of the importance of understanding the ¹⁸F + p reactions, a number of studies of the A=19 isobars have been made using stable and exotic beams. The interference effects among J ^π = 3/2⁺ resonances in the ¹⁸F + p system, however, have never been measured, but they can change the S-factor by a factor of 20 at nova energies. R-matrix calculations indicate that the cross sections above the Ec.m. = 665 keV resonance are sensitive …

Single-Molecule Detection With Active Transport, David Allan Ball

Doctoral Dissertations

A glass capillary is used near the focal region of a custom-built confocal microscope to investigate the use of active transport for single-molecule detection in solution, with both one and two-photon laser excitation. The capillary tip has a diameter of several microns and is carefully aligned nearby to the sub-micron laser beam waist, collinear to the optical axis, so that a negative pressure-difference causes molecules to be drawn into the capillary, along the laser beam axis. The flow of solution, which is characterized by fluorescence correlation spectroscopy (FCS), can increase the single-molecule detection rate for slowly diffusing proteins by over …

Regularization Of The Particle-Particle Interaction In The Nuclear Density Functional Theory, Piotr Jerzy Borycki

Doctoral Dissertations

In this work we show how to regularize the ultraviolet divergences appearing in the local pairing term of the energy density functional. Our approach, entirely rooted in the framework of the Density Functional Theory, is based on the regularization of local densities and currents and can be applied to various classes of energy density functionals. We demonstrated, that for the particular choice of the pairing term of energy density functional, our procedure gives the same regularization scheme to the one obtained earlier by the means of the pairing gap regularization.

We also investigated the non-unitarity of the Bogoliubov tranformation due …

Measurement Of The 32S(P,D)31S Reaction And Its Astrophysical Implications, Zhanwen Ma

Doctoral Dissertations

The ³⁰P(p,γ)³¹S reaction plays a crucial role in the synthesis of heavier nuclear species, from Si to Ca, in nova outbursts on ONe White Dwarfs [26, 28, 35]. However, its rate is very uncertain as a result of the lack of spectroscopic information on the levels above proton threshold in ³¹S. The currently adopted rate of this reaction, based on statistical Hauser-Feshbach calculations [36], could have an uncertainty as much as a factor of 100 higher or lower under nova conditions [26].

To reduce these uncertainties, we have measured differential cross sections for the ³²S(p,d) …

Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson

Theses and Dissertations

Electromagnetic scattering from a rough two dimensional homogeneous scatterer has been computationally modeled. The scatterer is intended to simulate reflection from a two interface multilayer. The rough scatterer was created from Gaussian random points centered about an ideal interface. The points were connected with a third order spline interpolant which accounts for correlation between neighboring surface atoms. The scalar electric field integral equation (EFIE) and magnetic field integral equation (MFIE) were solved using the Nystrom method to obtain the reflected intensity as a function of observation angle. Verification of the accuracy of the code was obtained by means of comparison …

Photochemical Route To The Production Of Fullerene Allotropes, Olga Ovchinnikova

Masters Theses

A photochemical route to the formation of two C₆₀ molecules which are bridged by one and up to eighteen carbon atoms to form bucky-dumbbell shaped molecules, i.e., C₆₀ > C < C₆₀ to C₆₀ > C = C = C = C = C = C = C = C = C = C < C₆₀, etc. is described. Irradiation of C60 in solutions of chloroform and iodine (magenta color) with pulsed laser light from the frequency tripled (355 nm) Nd:YAG laser produced a dark crimson color. Matrix assisted laser desorption ionization (MALDI) negative ion mass spectroscopy was used to …

Neutron Diffraction Study Of Heavy Water Intercalation In Superconducting Deuterated Sodium Cobaltate Na0.35Coo21.4d2O, Cinzia Metallo

Masters Theses

When Na-deficient Na_xCoO₂ is intercalated with water¹ or heavy water², it becomes a superconductor. The maximum critical temperature of 4.5 K is found for the composition Na_xCoO₂yD₂O (x= 0.3 and y=1.4). In spite of its low transition temperature, several similarities with high temperature superconducting cuprates have raised interest in this compound. Nevertheless, up to now, a clear understanding of the role of water has not been achieved.

Since superconductivity appears only when water is inserted in the parent compound, the goal of this research work was to understand …

Four-Dimensional Mvct Imaging And Spatial Translation Of Helical Tomotherapy Dose Distributions Using Sinogram Modification, Samuel Scott Outten

Masters Theses

Helical tomotherapy systems have the unique attribute of using sinograms as a machine input and a machine output. These sinograms have well understood properties that may allow for operational changes that simplify and/or improve radiation treatment.

In the first part of this work, the detector array output sinogram of an MVCT imaging study is used to produce images of an object at different locations along a pattern of motion and the multi-leaf collimator (MLC) control sinogram is used to translate dose distributions in space. A temporal re-binning algorithm was written that divided the MVCT sinogram projections into positional bins that …

A Measurement Of The Top Quark Mass With A Matrix Element Method, Adam Paul Gibson '96

Doctoral Dissertations

We present a measurement of the mass of the top quark. Our event sample is selected from proton-antiproton collisions, at 1.96 TeV center-of-mass energy, observed with the CDF detector at Fermilab's Tevatron. We consider a 318 pb^-1 dataset collected between March 2002 and August 2004. We select events that contain one energetic lepton, large missing transverse energy, exactly four energetic jets, and at least one displaced vertex b tag. Our analysis uses leading-order tt and background matrix elements along with parameterized parton showering to construct event-by-event likelihoods as a function of top quark mass. From the 63 events observed …

Fast Scene Based Nonuniformity Correction With Minimal Temporal Latency, Christopher A. Rice

Theses and Dissertations

The focus of this research was to derive a new algorithm for correction of gain nonuniformities in LIDAR focal plane arrays using as few frames as possible. Because of the current low production rate of LIDAR focal plane arrays there is a natural tendency for extreme nonuniformities to exist on a pixel by pixel basis as the manufacturing technique has not yet been perfected. Generally, nonuniformity correction techniques require a large number of frames and/or have obscure requirements on the translational shifts in the input image frames. This thesis presents a solution for finding multiplicative nonuniformities that exist in a …

A New Application Of The Channel Packet Method For Low Energy 1-D Elastic Scattering, Clint M. Zeringue

Theses and Dissertations

An algorithm is presented which uses the channel packet method (CPM) to simulate low-energy, wave-packet propagation and compute S-matrix elements. A four-by-four matrix containing the momentum, expansion coefficients of the reactants and products is introduced to account for initial and final states having both positive and negative momentum. The approach does not consider scattering from one side or the other, rather it considers both incoming and outgoing wave packets from the left and right simultaneously. Therefore, during one simulation all four S-matrix elements, and elements, S_+k,-K, S_{-k, +k}, S_{+k, +k} and S_-k,-k are computed. …

Feasibility Of Superconductivity In Semiconductor Superlatices, Kenneth P. Walsh

Dissertations

The objective of this thesis is to explore superconductivity in semiconductor superlattices of alternating hole and electron layers. The feasibility of superconductivity in semiconductor superlattices is based on a model formulated by Harshrnan and Mills. In this model, a semiconductor superlattice forms the layered electron and hole reservoirs of high transition temperature (high-Tc) superconductors.

A GaAs-A1xGa1-xAs semiconductor structure is proposed which is predicted to superconduct at Tc = 2.0 K and may be analogous to the layered electronic structure of high-Tc superconductors. Formation of an alternating sequence of electron- and hole-populated quantum wells (an electron-hole superlattice) in a modulation-doped GaAs- …

Earthshine : Photometry, Modeling, And Spectral Observations, Jeffrey Patrick Hickey

Theses

The Earthshine group has been making sustained observations of the Earthshine from Big Bear Solar Observatory in California since late 1998. There have also been intermittent observations from 1994-5. High and low resolution Earthshine spectral observations have also been under taken at Palomar Observatory since 1999. The group has re-invigorated and modernized a nearly forgotten way of measuring the Earth's albedo, and hence its energy balance, previously studied by Danjon (and his followers) for about twenty-five years early in the last century, using their observations of the Earthshine from France. This is an overview paper covering observations, reductions, simulations, and …

Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter

Theses and Dissertations

Measurements in a reverberation chamber use spatially averaged squared pressure to calculate sound absorption, sound power, and other sound measurements. While a reverberation chamber provides an approximation of a diffuse sound field, variations in the measurements introduce uncertainty in measurement results. Room qualification procedures require a sufficient number of source-receiver locations to obtain suitable measurements. The total acoustic energy density provides greater spatial uniformity than squared pressure, which requires fewer source-receiver positions to produce similar or better accuracy in measurement results. This paper explores the possibility of using energy density in place of squared pressure, using methods outlined in current …

Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green

Theses and Dissertations

Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being. Previous research has successfully implemented feed-forward ANC, targeting specific narrow-band fan noise content related to the blade passage frequency (BPF) of the fan. The reference signal required for a feed-forward algorithm limits its ability to attenuate much of the …

Modeling The Power Evolution Of Classical Double Radio Galaxies Over Cosmological Scales, Paramita Barai

Physics and Astronomy Dissertations

During the quasar era (redshifts between 1 and 3) Radio Galaxies (RGs) have been claimed to have substantially influenced the growth and evolution of large scale structures in the universe. In this dissertation I test the robustness of these exciting claims. In order to probe the impacts in more detail, good theoretical models for such RG systems are required. With this motivation, I seek to develop an essentially analytical model for the evolution of Fanaroff-Riley Class II radio galaxies both as they age individually and as their numbers vary with cosmological epoch. To do so, I first compare three sophisticated …

Kinematics Of The Narrow-Line Regions In The Seyfert Galaxies Ngc 4151 And Ngc 1068, Varendra Das

Physics and Astronomy Dissertations

We present a study of high-resolution long-slit spectra of the Narrow-Line Regions (NLRs) of NGC 4151 (a Seyfert 1 galaxy) and NGC 1068 (a Seyfert 2 galaxy) obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). The spectra were retrieved from the Multimission Archive at Space Telescope (MAST) and were obtained from five and seven orbits of HST time resulting in five and seven parallel slit configurations at position angles of 52 degrees and 38 degrees for NGC 4151 and NGC 1068 respectively. The spectra have a spatial resolution of 0.2 arcsecond across and 0.1 …

Growth And Superconductivity Of Pb And Pb-Bi Alloys In The Quantum Regime, Mustafa Murat Ozer

Doctoral Dissertations

Superconductivity is a collective quantum phenomenon that is inevitably suppressed in reduced dimensionality. Questions of how thin superconducting wires or films can be before they lose their superconducting properties have important technological ramifications and go to the heart of understanding formation, coherence, and robustness of the superconducting state in quantum confined geometries. Suppression of superconductivity in low dimensions is usually attributed to thermal or quantum fluctuations, or to pair-breaking Coulomb interactions in the presence of strong disorder. Control and quantification of a film’s disorder length scale remained a critical experimental obstacle, however. Here, we exploit quantum confinement of itinerant electrons …

Ab-Initio Calculations Of The Charge-Density Response In Complex Materials, Oscar Dario Restrepo Tovar

Doctoral Dissertations

Our main goal is to have a realistic description of the charge excitations in complex materials in the range of energies such as the coulomb energy U, which is in the eV range. Spectra of these charge excitations, for a large range of wave vector transfers, may provide signatures of the underlying electronic structures. The charge-density response function calculated within Time-dependent Density functional (TDDFT) is an ideal theoretical framework for the calculation of these excitations, since comparison with experimental data (in particular with non-resonant inelastic x-ray scattering experiments) can be done in absolute units (without the need of any adjustable …

Neutron Scat- Tering In The Novel Quantum Magnets: Livo2 And Dmacucl3, Wei Tian

Doctoral Dissertations

The behavior of magnetic systems in the extreme quantum limit is one of the most interesting forefront areas in condensed matter physics. This dissertation investigates two particularly interesting quantum magnets: LiVO₂ and DMACuCl₃. Systematic studies were performed on single crystal samples using different experimental techniques, especially inelastic neutron scattering. Detailed experimental results and corresponding model calculations are presented and discussed in this dissertation.

LiVO₂ is a good candidate to study the interplay between “magnetic frustration” and orbital ordering. V³⁺ ions in LiVO₂ form a triangular lattice involving threefold degenerate t_2g orbitals. LiVO2 undergoes …

Manifestations Of Broken Symmetry: The Surfaces Phases Of Ca2−XSrXRuo4, Robert G. Moore Ii

Doctoral Dissertations

The discovery of superconductivity in Sr₂RuO₄ has renewed vigor in the study of correlated electron systems. The evolution of a p-wave superconducting state from a para- magnetic 2-dimensional Fermi liquid shows the ruthenate superconductivity is anything but conventional. Sr₂RuO₄ is isostructural with La₂CuO₄, the parent compound for the high temperature superconducting family La2_−xSr_xRuO₄. The substitution of Ca²⁺ for Sr²⁺ generates a different structure involving a static rotation and tilt of the RuO₆ octahedral, however, the antiferromagnetic insulating ground state of Ca …

Surface Studies Of Selective Hydrogen Desorption From Silicon, Jason Kenneth Smith

Masters Theses

This thesis examines quantum confined quasi-one-dimensional structures on silicon surfaces. An in situ prepared and hydrogenated Si(100)-(2x1) is investigated, on which a quasi-dimensional nanostructure is fabricated via scanning tunneling microscopy. Also, the feasibility of STM-based nanolithography on an ex situ hydrogenated Si(111)-(1x1) surface is explored. Using methods such as those discussed herein it is possible to create quasi one-dimensional semiconducting metallic nanowires as well as contact pads, useful for four point probe measurements at the nanoscale. Using a STM, dimer wide strips of hydrogen are removed from the passivated layer to reveal bare silicon surface bonds forming a nanowire approximately …

Ultraviolet Image Analysis Of Spacecraft Exhaust Plumes, Karen L. Norton

Masters Theses

Data obtained during the April 26, 2000 MirEx experiment is used to infer the chemical mechanisms responsible for ultraviolet radiation observed to emanate from Russian spacecraft exhaust plumes in low Earth orbit. The principle objective of this experiment was to use the Mir Space Station instruments to study the plume collisional processes occurring in the rarified atmosphere of the far-field; at distances greater than one kilometer away from the spacecraft. This was accomplished by observing the automated Progress cargo ship as the auxiliary engines were being retrofired in a ram-burn configuration at 330 kilometers in altitude above Earth. The primary …