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Synthesis and Characterization of Piezo-Magneto (PVDF-Fe3O4) CompositesMulamba, Oliver Kasongo 2011 May 1900 (has links)
This research entails the synthesis and characterization of a novel class of materials which incorporate both magnetic and piezoelectric characteristics. The composite is made up of the piezoelectric polymer PVDF and magnetic nanoparticles.
The testing samples are produced using a spin casting process. The characterizations of the samples were performed using X-ray diffraction, Atomic force microscopy, linear staging, Dynamic mechanical analysis, Differential scanning calorimetry, and Fourier transform Infra-Red. X-ray diffraction and Atomic force microscopy showed that the presence of the Fe3O4 particles have no effect on the crystallinity of the polymer matrix, therefore allowing for the incorporation of inclusions without directly affecting the piezoelectric property. Changes in the thermal characteristics of the polymer matrix, observed using Differential scanning calorimetry, indicated increases in the thermal conductivity of the composite. Decreases in the heat of melting and crystallization were also observed and further solidified the conclusion that the presence of the Fe3O4 nanoparticles changes the thermal behavior of the polymer. It was observed from the DMA results caused an increase in the storage modulus of the polymer matrix which is related to an increase in the material's ability to store energy. Linear staging results showed that the presence of the nanoparticles had an effect on the mechanical properties of the composites and altered the time dependent voltage output readings. These results were used to calculate the energy capabilities of the composite material and it was found that the composites showed greater energy outputs with increasing amounts of nanoparticles. Interaction was observed between the embedded particles and an external magnetic field, which was found to decrease the energy outputs of the composites.
This research showed enhancements in the composite material's energy outputs in comparison to the pure PVDF samples. This research also showed that the embedded nanoparticles interacted with an exteriorly applied magnetic field. This observation introduces a new dimension of possible activation processes for piezoelectric devices which have been largely based on physical forms of activation. PVDF which is widely used in research and applications for its superior output capabilities has been enhanced in this research and shown to have capabilities to exhibit higher energy outputs.
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Array combination for parallel imaging in Magnetic Resonance ImagingSpence, Dan Kenrick 17 September 2007 (has links)
In Magnetic Resonance Imaging, the time required to generate an image is
proportional to the number of steps used to encode the spatial information. In rapid
imaging, an array of coil elements and receivers are used to reduce the number of
encoding steps required to generate an image. This is done using knowledge of the
spatial sensitivity of the array and receiver channels. Recently, these arrays have begun
to include a large number of coil elements. Ideally, each coil element would have its
own receiver channel to acquire the image data. In practice, this is not always possible
due to economic or other constraints. In this dissertation, methods are explored to
combine a large array to a limited number of receivers so as to optimize the performance
for parallel imaging; this dissertation focuses on SENSE in particular. Simple
combinations that represent larger coils that might be constructed are discussed. More
complex solutions form current sheets. One solution uses Roemer'ÃÂÃÂs method to optimize
image SNR at a set of points. In this dissertation, Roemer's solution is generalized to
give the weighting coefficients that optimize SNR over regions. Also, solutions fitted to
ideal profiles that minimize noise amplification are shown. These fitted profiles can
allow the SENSE algorithm to function at optimal reduction factors. Finally, a
description of how to build the combiner in hardware is discussed.
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Electric field effect and transport mechanism research on Co-doped ZnO filmsLin, Cheng-Pang 26 August 2008 (has links)
The mechanism for the room temperature magnetic coupling and electric conduction in oxide diluted magnetic semiconductors (DMS) has been studied simultaneously on the Co:ZnO thin film by utilization of the electric field effect. We find that the carriers are bound on a defect in a radius much larger than the bounded magnetic polaron (BMP) radius, and can move by the variable range hopping (VRH) over a relative small distance. Therefore, a concentric bounded model consisting of a concentric localization configuration with a limited carrier VRH capability was proposed. In this model, the carriers localized around defects couples strongly with the doped magnetic ions forming a BMP in the inner sphere and can only itinerate with no spin coherence in the outer shell. Carriers can hop either by spin-polarized or by spin-independent VRH directly between or not directly between adjacent inner spheres, respectively. This model can explain both the electric and magnetic properties of the oxide DMS, and depicts an evolution of electric and magnetic properties associated with defect concentration.
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Calculating depths to shallow magnetic sources using aeromagnetic data from the Tucson BasinCasto, Daniel W. January 2001 (has links)
Thesis (M.S.)--University of Arizona, 2001. / Added thesis t.p. Title from HTML title screen (viewed Apr. 25, 2002). Includes bibliographical references.
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Mobile magnetic resonance imaging system and its applicationYeung, Sze-man. January 2001 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 89-90).
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Force detection of nuclear magnetic resonance using double-torsional micro-oscillatorsChabot, Michelle Diane. January 2001 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.
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Experimental investigations of magnetic and magneto-rheological materials and their rigidification properties /Glaser, Radek, January 2009 (has links)
Thesis (M.S.) in Mechanical Engineering--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 214-219).
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Ultrafast coherent transients & excited state dynamics in gases and solidsBromberg, J. Philip, McConnell, Harden M. January 1959 (has links)
Thesis (Masters)--California Institute of Technology, 1959. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/09/10. Includes bibliographical references.
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Advanced analysis and design of some field generating devices in magnetic resonance imaging /Snape-Jenkinson, Christopher John. January 2001 (has links) (PDF)
Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.
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Studies on magnetic recordingWestmijze, Willem Klaas, January 1953 (has links)
Proefschrift--Leiden. / eContent provider-neutral record in process. Description based on print version record. Bibliography: p. 91.
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