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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    On the Dynamics of Binary Asteroids Applied to DART Mission Target (65803) Didymos
    (2022) Agrusa, Harrison Fitzgerald; Richardson, Derek C; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    NASA’s Double Asteroid Redirection Test (DART) mission will be the first full-scale demonstration of a kinetic impactor for planetary defense. On September 26, 2022, the DART spacecraft is expected to impact Dimorphos, the secondary component of the Didymos binary asteroid system. The DART impact will reduce Dimorphos’s relative orbital velocity, shrinking both its semimajor axis and orbit period. The mutual orbit period will then be measured us- ing ground- and space-based observations in order to deduce the momentum transfer efficiency, which is an important parameter in planetary defense that has never been measured experimentally at a realistic scale. This thesis comprises a set of studies on the spin and orbital dynamics of the Didymos system conducted in support of the DART mission. Owing to the close proximity of Didymos and Dimorphos and their irregular shapes, the mutual dynamics are non-Keplerian and exhibit a high degree of spin-orbit coupling, which often requires the use of specialized numerical methods to model the system. First, we conducted a benchmarking and sensitivity study to identify the best simulation codes for future DART-supported studies and to understand how small perturbations in the initial conditions can affect the resulting dynamical evolution of the system. Then, we demonstrated that Dimorphos can enter a wide range of post-impact spin states, including possible chaotic non-principal axis rotation, depending on its shape and the amount of momentum transferred by the DART impact. We then explored the implications of an excited spin state, including the possibility of ongoing granular motion on Dimorphos’s surface resulting from the orbital perturbation induced by the DART impact. This thesis is focused predominantly on the dynamics of the Didymos binary. However, there are many other binary systems among the near-Earth asteroid population with similar physical and dynamical properties, making the results presented here relevant to the NEA binary population in general.
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    SYNTHESIS OF MAIN GROUP ELEMENT CLUSTERS OF GROUPS 13 AND 15 FROM DISPROPORTIONATION PATHWAYS AND ZINTL POLYANIONS
    (2019) Stevens, Lauren Marie; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis details the synthesis and characterization of main group element clusters of Groups 13 (aluminum) and 15 (phosphorus, arsenic). Aluminum clusters were synthesized from metastable Al(I)X (X = Cl, Br) solutions, which have proven adept at fostering the growth of metalloid clusters of the form AlnRm (where n > m). Group 15 – transition metal coordination complexes and ligand-free binary anions are synthesized through the use of Zintl ion precursors, originating from phases K3Pn7 (Pn = P, As, Sb). The novel cluster [(Bu2O)3Li][Li4Al5Ph12] has been synthesized and characterized, reported here in seven different crystallographic modifications. In addition to being the first low-valent phenyl aluminum cluster, this anion exhibits an unusual metastability in both the solid-state and solution, as indicated through ESI-MS, LDI-MS, and solid-state NMR analyses. The Zintl-derived coordination complexes [(η4-As7)Co(η3-As3)]3-, [(η4-As7)Rh(COD)]2-, and [(η4-As7)Ir(COD)]2- are reported as the first As / Group 9 clusters, and are isoelectronic to known coordination species of Zintl anions and transition metal carbonyl fragments. Additionally, the product [(η4-As7)Co(η3-As3)]3-is the first known carbon-free binary anion of As / Co. These complexes have been characterized via LDI-MS, NMR, single crystal XRD, and quantum chemical calculations. The doubly substituted coordination complex [(en)(CO)3Mo(η4-P7)Mo(CO)3]3- completes a series of previously reported Group 6 polyphosphide complexes, and is compared to its W congener, [(en)(CO)3W(η4-P7)W(CO)3]3-. Unlike coordination complexes, which retain the nuclearity of the seven-atom precursors [Pn7]3-, binary intermetalloids [Mo2P16]4- and [Rh3As16]3- show extensive reorganization of the original polypnictide cages. These anions feature cyclo-[P10]2- and cyclo-[As5]1- subunits, which are the first to be isolated and described in products of Zintl anions. Additionally, these are the first binary systems to be reported for Mo/P and Rh/As, and could potentially be used for the formation of binary phases (i.e. RhAs2) upon oxidation