UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Nature of Mesoscopic Aggregates in Solutions of Lysozyme
    (2018) NIKFARJAM, SHAKIBA; Woehl, Taylor J; Anisimov, Mikhail; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    An anomalous class of mesoscopic aggregates have previously been observed in solutions of lysozyme. These aggregates are thought to play an important role in nucleation of protein crystals and ordered protein aggregates, like amyloid fibers. Mesoscopic aggregates are currently thought to be in thermodynamic equilibrium with the protein solution, where transient oligomers of partially unfolded lysozyme monomers are thought to be the formation source of these aggregates. However, there is little experimental evidence to back up this proposed formation mechanism and thermodynamic behavior. Specifically, the effects of temperature on these aggregates and their thermodynamic reversibility have not been systematically tested. In this thesis, we investigate the equilibrium nature and the formation source of mesoscopic aggregates in solutions of model protein, lysozyme. We tested the effects of temperature on aggregate size and concentration and the aggregate reversibility after removal by systematic filtration. We used light and x-ray scattering and chromatography to experimentally characterize the aggregates during this study. Our findings indicate that mesoscopic aggregates are minimally sensitive to temperature changes and do not reform after removal by filtration. Together, these results indicate that mesoscopic aggregates are not in thermodynamic equilibrium with protein monomers or oligomers in solution. Overall, our experimental results contrast the current accepted formation mechanism of these mesoscopic aggregates and suggest they instead form due to contaminants present in solution or a sub-population of partially unfolded proteins.
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    Spin injection and detection in copper spin valve structures
    (2005-01-25) Garzon, Samir Y; Webb, Richard A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    We report measurements of spin injection and detection in a mesoscopic copper wire from which the electron spin relaxation time and the spin current polarization in copper can be found. Spin injection is realized by applying a voltage to drive a current from a ferromagnet into the normal metal, while spin detection is done using transport measurements. Precession of the spin of the injected electrons due to an external magnetic field is also studied. The existence of a previously unobserved spin signal which vanishes at low temperatures but increases nonlinearly above 100K is reported and a possible explanation for its origin, based on interfacial spin-flip scattering, is suggested. Multiple cross checks to test the possibility of artifacts as an origin of this signal are discussed. An alternative spin detection method using magnetic force microscopy (MFM) is also studied. This method measures the magnetic field produced by the injected spins directly, so the spin coherence length and the spin current polarization can be extracted directly without the need of a particular transport model, avoiding issues like contact resistance and interface scattering. The MFM method can also be useful for measuring the spin polarization of currents in semiconductors and semiconductor heterostructures, which is important for the development of spintronics.