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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Quantitative Characterization of Biological Tissues by NMR Relaxation in the Rotating Frame

Spear, John Thomas 18 March 2016 (has links)
Measurements of the spin-lattice relaxation rate in the rotating frame, R1rho, using spin-locking techniques have long been exploited to investigate relatively slow molecular motions and, more recently, to analyze chemical exchange. The variation of R1rho with spin-lock amplitude, or R1rho dispersion, provides the means to examine dynamic processes occurring on the time scale of the applied effective field, but corresponding techniques have been somewhat overlooked by the MRI community. Chemical exchange contributions to R1rho of protons in tissues are shown to dominate conventional dipole-dipole interactions at high fields, and R1rho dispersion depends on the exchange rate and chemical shift of the labile species. In addition, proton diffusion in the presence of intrinsic susceptibility gradients also contributes significantly to R1rho dispersion at low spin-lock amplitudes. Simulations and experiments performed in this work reveal these effects to largely be the dominant mechanisms influencing spin-locked relaxation at high static magnetic fields, and demonstrate the potential for using R1rho to characterize tissues across a variety of pathologies. Exchange-based R1rho methods are used to quantify exchange rates in solutions containing one or two solute pools and to produce images in which the contrast emphasizes the presence of metabolites exchanging at specific rates rather than with specific chemical shifts. A novel theory is derived that quantifies diffusion-based R1rho dispersion, which is subsequently applied to create parametric maps that reflect average sub-voxel microstructure and to calculate intrinsic gradient strengths in model systems of polystyrene microspheres and Red Blood Cells (RBCâs). This approach may further be used to estimate cell sizes and to emphasize vasculature of specific sizes in fMRI studies. Exchange and diffusion effects are also verified to be independent processes that may be analyzed simultaneously in biologically relevant applications. Collectively, R1rho dispersion methods provide a powerful alternative to traditional MRI methods and produce novel complementary information for quantitative tissue characterize.

Characterization of  Ultra High Molecular Weight Polyethylene Nano Composites with Mg0.15Ni0.15Zn0.70Fe2O3

Azam, Asad Muhammad January 2016 (has links)
Ultra high molecular weight polyethylene has been commonly used as a biomaterial for total joint replacements. This thesis concerns with the characterization of nano composites of ultra high molecular weight polyethylene (UHMWPE) with Mg0.15Ni0.15Zn0.70Fe2O3 using various analytic techniques such as fourier transform-infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). An accelerating aging of three different samples, two commercial and one laboratory grade UHMWPE purchased from Sigma Aldrich was done to study  the thermal stability of UHMWPE, and the results were checked with FTIR spectroscopy. The FTIR data revealed that UHWMPE purchased from Sigma Aldrich had the highest thermal stability. Therefore, UHMWPE purchased from Sigma Aldrich was used for further studies and preparation of nano composites with 1wt% and 2wt% Mg0.15Ni0.15Zn0.70Fe2O3 using the ball milling method. FTIR data show significant alterations as far as material degradation and crosslinking is concerned. The absorbance in the region 1650-1850 cm-1 and 3000-3700 cm-1 significantly increases due to the enhance of CH2 bending to stretching ratio with the incorporation of Mg0.15Ni0.15Zn0.70Fe2O3. As far as thermal stability is concerned, composites with 1 % of Mg0.15Ni0.15Zn0.70Fe2O3 contents were less stable compared to pure UHMWPE and UHMWPE composites with 2wt% of nano scale Mg0.15Ni0.15Zn0.70Fe2O3. The degree of crystallinity obtained from DSC data was 41%, 40%, and 43% for UHMWPE, UHMWPE+1% of Mg0.15Ni0.15Zn0.70Fe2O3, and UHMWPE+2% of Mg0.15Ni0.15Zn0.70Fe2O3, respectively. The results of current study are useful while considering the nano composites of UHMWPE with Mg0.15Ni0.15Zn0.70Fe2O3 in order to enhance the mechanical strength of UHWMPE for industrial as well as medical applications such as orthopedic implants and bullet proof jackets etc.

Astrophysical Laboratories and Advanced Imaging Techniques for Testing Stellar Models: Eclipsing Binaries, High Contrast Imaging, and Optical Interferometry

Garcia, Eugenio Victor 12 April 2016 (has links)
In chapter 1, we determine the masses, radii and temperatures of the eclipsing binary V578 Mon, a detached system of two early B-type stars in the Rosette Nebula, to better than 5% accuracy. We compare these measurements to the stellar models of the Geneva, Utrecht and Granada group. We find all three sets of models marginally reproduce the absolute dimensions of both stars. However - there are some apparent discrepancies, and the Utrecht models worked best. We also compute the combined internal structure constants for V578 Mon. We find that the predicted internal structure constants of the Granada models fully agrees with our observations. In chapter 2, we present the results of a Hubble Space Telescope survey of the lowest mass brown dwarfs in the Pleiades. These objects represent the predecessors to T-dwarfs in the field. Using a new PSF-fitting technique, we are able to probe to 30 milliarcseconds, better than 2Ã the HST diffraction limit. We did not find any companions to our targets. Our survey is the first to attain the high angular resolution needed to resolve brown dwarf binaries in the Pleiades at separations that are most common in the field population. We constrain the binary frequency to be <26% at 2? . This binary frequency is consistent with both younger and older brown dwarfs in this mass range and with brown dwarf formation models. Visible-light long baseline interferometry holds the promise of advancing a number of important applications in fundamental astronomy, including the direct measurement of the angular diameters and oblateness of stars, and the orbits of binary and multiple star systems. To advance, the field requires instruments capable of combining light from 6 telescopes simultaneously. In chapter 3, we present the Visible Imaging System for Interferometric Observations at NPOI (VISION) is a new visible light beam combiner for the Navy Precision Optical Interferometer (NPOI) that coherently combines light from up to six telescopes simultaneously. We detail the commissioning of VISION with laboratory and on-sky tests. We provide a new set of corrections for the power spectrum and bispectrum when using EMCCDs.

Search for Long-Duration Transient Gravitational Waves Associated with Magnetar Bursts during LIGO's Sixth Science Run

Quitzow-James, Ryan 14 April 2016 (has links)
<p> Soft gamma repeaters (SGRs) and anomalous X-ray pulsars are thought to be neutron stars with strong magnetic fields, called magnetars, which emit intermittent bursts of hard X-rays and soft gamma rays. Three highly energetic bursts, known as giant flares, have been observed originating from three different SGRs, the latest and most energetic of which occurred on December 27, 2004, from the SGR with the largest estimated magnetic field, SGR 1806-20. Modulations in the X-ray tails of giant flares may be caused by global seismic oscillations. Non-radial oscillations of the dense neutron star matter could emit gravitational waves powered by the magnetar's magnetic energy reservoir. This analysis searched for long-duration transient gravitational waves associated with three magnetar bursts that occurred during LIGO's sixth science run, from July 7, 2009 to October 20, 2010. The search results were consistent with the calculated background, and 90% confidence upper limits on the possible undetected gravitational wave energy were found.</p>

Search for dark matter and supersymmetry via vector boson fusion at the Large Hadron Collider

Delannoy Sotomayor, Andres Guillermo 28 March 2016 (has links)
A first search for pair production of dark matter candidates through vector boson fusion, in proton-proton collisions at sqrt(s) = 8 TeV, is performed with the CMS detector. The vector boson fusion topology enhances missing transverse momentum, providing a way to probe supersymmetry also in the case of compressed mass spectrum. The observed dijet mass spectrum is compatible with the background prediction. Upper limits are set on the production cross section of dark matter particles using an effective field theory. Production of a bottom squark with mass below 315 GeV is excluded at 95% confidence limit, assuming a 5 GeV mass difference with the lightest neutralino.

Probing Planetary Formation and Evolution: Transiting Planets and Occulting Disks

Rodriguez, Joseph Enrique 29 March 2016 (has links)
The circumstellar environments of young stellar objects (YSOs) involve complex dynamical interactions between dust and gas that directly influence the formation of planets. However, our understanding of the evolution from the material in the circumstellar disk to the thousands of planetary systems discovered to date, is limited. One means to better constrain the size, mass, and composition of this planet-forming material is to observe a YSO being eclipsed by its circumstellar disk. Through this dissertation project, we are discovering and characterizing both disk eclipsing systems and exoplanets using the Kilodegree Extremely Little Telescope (KELT) project. KELT is a photometric survey for transiting planets orbiting bright stars (8 < V < 11); such bright planet host targets are well-suited for atmospheric characterization of the planets. KELT has discovered 15 planets transiting stars brighter than V ~11 to date. I will present some of the recently discovered planets from the survey and discuss their potential to advance our understanding of planetary atmospheres. In addition, KELT provides photometric monitoring of ~3 million stars, presenting the opportunity to perform multi-year studies of stellar variability generally and rare disk occultations specifically. Using time-series photometry from KELT we are conducting the Disk Eclipse Search with KELT (DESK) survey to look for disk eclipsing events, specifically in young stellar associations. To date, the survey has discovered and analyzed four previously unknown large dimming events around the stars RW Aurigae, V409 Tau, AA Tau, and TYC 2505-672-1, the latter now representing the longest-period eclipsing object known (period ~ 69 years). The results from this project on planet atmosphere characterization and protoplanetary disk structure and composition, will provide a framework to search for these kinds of systems in future surveys such as LSST.

Pulling Through: A Biomechanical Analysis of Normal and Aberrant Embryogenesis in Drosophila

McCleery, Winston Tyler 06 April 2016 (has links)
Biomechanical analysis of the developing Drosophila embryo has historically focused on the role of individual cells. Cells translate genetic information into protein machinery that is capable of generating forces. With this perspective, the field has tried to identify which cells are responsible for the morphological changes that occur during embryogenesis. Taking a different perspective, this work considers the cumulative effect of all cells in a coherent epithelium. This reveals a mechanical trade-off between cell-type dependent tensions and embryo-imposed constraints on cells. To investigate this further, a 2.5-D cellular finite element model is built and used to analyze the mechanics of one stage of development, germband retraction. This analysis finds that germband retraction is robust to cell-type dependent tensions, but contingent on the initial cell geometry. Experiments then test the embryoâs mechanical robustness to environmental perturbation. A non-specific heat shock stress to the embryo results in delayed development and the formation of holes in the epithelium. These holes disrupt the mechanical integrity of the tissue preventing development beyond germband retraction. The model is expanded to explain how germband retraction fails, thus providing a mechanical explanation for failure due to holes in heat-shocked embryos. This dissertation finds that embryogenesis is a mechanically robust process that is not dependent on any single group of differentiated cells, but rather is contingent on coherent and contiguous epithelial tissues that maintain developmental information through cell morphology.

A search for supersymmetric top quarks in CMS 8TeV data in the b/tau + jets + met + muon final state

Melo, Andrew Malone 05 April 2016 (has links)
This dissertation examines data recorded in 2012 by the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) to search for supersymmetric top quark decay. In order to reduce the substantial backgrounds and properly calibrate simulation with data, the Simultaneous Heavy Flavor and Tag (SHyFT) method is employed. SHyFT divides events into bins based on their event content to produce signal and background-enriched regions. Then, a global fit is performed over all the bins simultaneously, which not only extracts the estimated signal contribution, but also constrains the contributions of the backgrounds and estimates the values of several systematic uncertainties. Using currently available data, this dissertation sets limits on the cross-section of particular supersymmetric models.

Measurements of the Double-Spin Asymmetry A<sub>1</sub> on Helium-3: Toward a Precise Measurement of the Neutron A<sub>1</sub>

Parno, Diana Marwick Seymour 01 April 2011 (has links)
The spin structure of protons and neutrons has been an open question for nearly twenty-five years, after surprising experimental results disproved the simple model in which valence quarks were responsible for nearly 100% of the nucleon spin. Diverse theoretical approaches have been brought to bear on the problem, but a shortage of precise data – especially on neutron spin structure – has prevented a thorough understanding. Experiment E06-014, conducted in Hall A of Jefferson Laboratory in 2009, presented an opportunity to add to the world data set for the neutron in the poorly covered valence-quark region. Jefferson Laboratory’s highly polarized electron beam, combined with Hall A’s facilities for a high-density, highly polarized 3He target, allowed a high-luminosity double-polarized experiment, while the large acceptance of the BigBite spectrometer gave coverage over a wide kinematic range: 0.15 < x < 0.95. In this work, we present the analysis of a portion of the E06-014 data, measured with an incident beam energy of 4.74 GeV and spanning 1.5 < Q2 < 5.5 (GeV/c)2 . From these data, we extract the longitudinal asymmetry in virtual photon-nucleon scattering, A1, on the 3He nucleus. Combined with the remaining E06-014 data, this will form the basis of a measurement of the neutron asymmetry An 1 that will extend the kinematic range of the data available to test models of spin-dependent parton distributions in the nucleon.

Study of quantum games

Razavi, Ahmad Kafaee 01 July 2015 (has links)
Game theory is the study of strategic competition used in many branches of science. In general, a game is a match between two or more players and each wants to maximize his or her score. In a game, the player’s score depends on their strategies. The goal is to find the optimized decision, with regard to the payoff, in conformity with the rules of the game. This thesis considers the games with two players who know both their own and their rival’s payoff. However, they do not know the strategy chosen by the opponent. In a classical game, the options of players are referred to as cooperation and defect. Quantum game theory is a generalization of classical game theory. In quantum games a linear combination of two options specify the strategy based on qubit. The quantum domain is characterized by entanglement. The quantum entanglement coefficient (y) varies from 0 to . The game is in the classical regime when y is smaller than a threshold. Quantum entanglement is intrinsically non-local. In an iterated game tournament, 63 different strategies contest with four known strategies. Depending on the result, they are divided to a number of groups. The competition specifies which group of strategies can obtain a higher score. Other types of games are discussed in the thesis. They are known as incomplete information games. In these games one player has two payoff matrixes, and the rival does not know which of them is used. We discuss the advantage of using quantum strategy over the classical game, particular in avoiding the dilemma in classical games.

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