Theses and Dissertations from UMD

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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 give thesis/dissertation in DRUM

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

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    Sparse Signal Representation in Digital and Biological Systems
    (2016) Guay, Matthew; Czaja, Wojciech; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Theories of sparse signal representation, wherein a signal is decomposed as the sum of a small number of constituent elements, play increasing roles in both mathematical signal processing and neuroscience. This happens despite the differences between signal models in the two domains. After reviewing preliminary material on sparse signal models, I use work on compressed sensing for the electron tomography of biological structures as a target for exploring the efficacy of sparse signal reconstruction in a challenging application domain. My research in this area addresses a topic of keen interest to the biological microscopy community, and has resulted in the development of tomographic reconstruction software which is competitive with the state of the art in its field. Moving from the linear signal domain into the nonlinear dynamics of neural encoding, I explain the sparse coding hypothesis in neuroscience and its relationship with olfaction in locusts. I implement a numerical ODE model of the activity of neural populations responsible for sparse odor coding in locusts as part of a project involving offset spiking in the Kenyon cells. I also explain the validation procedures we have devised to help assess the model's similarity to the biology. The thesis concludes with the development of a new, simplified model of locust olfactory network activity, which seeks with some success to explain statistical properties of the sparse coding processes carried out in the network.
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    SCAFFOLDING-MEDIATED VIRUS ASSEMBLY: VISUALIZATION AND CHARACTERIZATION OF BACTERIOPHAGE T7 SCAFFOLDING PROTEIN
    (2009) Smith, Charles Stewart; Beckett, Dorothy; Steven, Alasdair C; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In bacteriophage T7 as well as many other dsDNA phages and some animal viruses, scaffolding protein is essential for the accurate formation of the metastable precursor particle (prohead) and thus it is a vital aspect of the viral infection cycle. When purified by anion exchange and gel filtration chromatography, the T7 scaffolding protein (gp9) exists as an extended monomer in solution. These monomers of gp9 associate with other scaffolding monomers to form the extended filaments in T7 procapsids visualized by electron tomography. These filaments interact with the negatively charged inner surface of the procapsid at unique sites, probably via the extended positively charged C-terminus of gp9. Scaffolding protein, via these interactions, facilitates isometric capsid assembly by helping to define the proper curvature of the viral capsid. Consequently, scaffolding-mediated viral assembly does not require a rigid structural network, nor does it require a stoichiometric amount of gp9 to be present in each procapsid. The observed flexibility of the scaffolding network, association of scaffolding filaments with the core connector complex, as well as the variable copy number of gp9 per particle suggests an assembly mechanism where capsid formation is nucleated around the core/connector complex. In such a mechanism there is more than one path to a single end - production of the correctly formed prohead particles that are required for T7 phage maturation.