RPI Theses Online (Complete)

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This collection consists of Ph.D. dissertations and Master's theses completed at Rensselaer Polytechnic Institute, Troy campus. Ph.D. dissertations since December 2006 and Master's theses since December 2007 are available. In addition, some older theses and dissertations have been added. Theses in this collection have either a Standard Rensselaer License or a Creative Commons License. Original paper copies of all dissertations and theses (including those not available online) are available in the Rensselaer Libraries.

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Now showing 1 - 5 of 3765
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    An investigation of the pampean flat slab and its role in andean tectonics through the analysis of enhanced earthquake catalogues
    (Rensselaer Polytechnic Institute, Troy, NY, 2023-05) Maharaj, Ariane; Roecker, Steve
    The Andean margin of South America is an archetypal example of a convergent tectonic environment that has played a fundamental role in the creation, evolution, and consumption of both continental and oceanic lithosphere. An enigmatic aspect of this margin is the existence of several regions of flat slab subduction, the causes and consequences of which remain poorly understood despite years of intensive investigation. The research discussed in this dissertation focuses on the Pampean flat slab beneath central Chile and Argentina, partly in response to the discovery of an unusual pattern of P wave arrival times from earthquakes beneath Argentina recorded in Chile, but also because recently developed techniques in automated phase onset estimation allow us to take significantly greater advantage of a substantial archive of seismic data that has been collected in this region over the past several decades. After constructing enhanced catalogues of seismic activity and analyzing them with various techniques of seismic tomography, the improved images of the elastic wavespeed structure of this region allow insights into the state of the subducted Nazca plate, the effects of subducting anomalous bathymetry such as ridges and seamounts shortening on the interaction between the Nazca plate and the overriding South American plate, and the consequences of lithospheric shortening of the South American plate on the geometry of the Nazca plate. We find that dense clusters of seismicity associated with the Pampean flat slab are most likely a consequence of the subduction of ridges and seamounts, and that the extensive alteration and devolatilization of the oceanic lithosphere by these features leads both to an increased buoyancy and to the release of volatiles that hydrate the South American mantle and fracture the lower crust. The existence of these features far from the trench lends support to the contention that subduction erosion is more episodic than continuous. We also find 2 low velocity anomalies, particularly in Vp, within and below the subducting slab. The western low velocity anomaly correlates with the Juan Fernandez Ridge and is postulated to be due to an increase in silica content or the presence of supercritical fluids. The eastern low velocity anomaly seems to be a result of rising hot asthenosphere. Furthermore, it appears that the gradient in wavespeeds that generated the pattern of anomalous P wave residuals that originally motivated this research may be due more to the low wavespeeds in overthickened crust beneath the high Andes grading into the higher wavespeeds of the Nazca plate, rather than a pronounced lithospheric root beneath a normal crustal root. At the same time, much of the original signal remains, which suggests that the ultimate cause of the higher apparent wavespeeds may be due as much to anisotropy as opposed to lateral heterogeneity.
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    MoveOn and E-motion : the paradox of cyberactivism in consumer society
    (Rensselaer Polytechnic Institute, Troy, NY, 2006-08) Dincki, Sandrine; Nadel, Alan, 1947-
    The relationship between media and democracy has always been characterized by a tension between public and private interests with a tendency for the latter to prevail. Mediated politics and consumption in a democratic society paradoxically enable “lifestyle politics” and degrade the “public sphere.” The political and the commercial realms are not necessarily exclusive as MoveOn illustrates. MoveOn is an online activist group with a conventional mass media approach to politics. The production, representation, and consumption dimensions of the “circuit of culture” are used to investigate MoveOn. It has strong ties with the conventional media industry and the Silicon Valley culture and heavily relies on marketing techniques, standardization and pseudo-individualization. MoveOn members are a crucial site of production that shows the tension between empowerment and control. MoveOn produces the conditions for action while members materialize action and become both producer and consumer. MoveOn also exemplifies the confluence of political and symbolic representations in that its members are both subjects of the former and objects of the latter. Its representation practices include pseudo-events and pseudo-heroes. These practices are mediated by the rules of the “public screen.” “Astroturfing” practices problematize the dichotomy artificial vs. real/grassroots. MoveOn follows two axes of representation: “voice” and “numbers.” MoveOn communicates via the “discourse of images” and e-motion, a process through which emotions are filtered, repackaged, and electronically mediated in order to set people in vicarious motion. E-motion encapsulates the convergence of mass media and the internet, and the confluence of activism and consumerism. MoveOn also complies with the “info-tainment” conventions via silent sound bites and the participation of celebrities in its campaigns. Consumption is viewed from the perspective of “consumer culture” that views consumption as mediation between the individual and the social. Consumer activism is one aspect of the convergence of activism and consumerism. “Activist consumerism,” in the form of repetitive participation in campaigns and as exemplified by MoveOn, is another aspect. MoveOn membership consists in “window shoppers,” “immobile activists,” and grassroots activists. Consumption practices can also be a form of dissent or resistance.
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    Exploring cavity effects on protein dynamic disorder with pressure perturbation
    (Rensselaer Polytechnic Institute, Troy, NY, 2022-08) Zhang, Siwen; Royer, Catherine Ann
    Given the central role of conformational dynamics in protein function, it is essential to characterize the timescales and structures associated with these transitions. High-pressure perturbation favors transitions to excited states because they typically occupy a smaller molar volume, thus high pressure facilitates the characterization of conformational dynamics. In this dissertation, we describe the use of a combination of NMR chemical exchange spectroscopy, small-angle X-ray scattering, and high hydrostatic pressure to better investigate conformational exchange during protein folding process. Repeat proteins, with their straightforward architecture, provide good models for probing the sequence dependence of protein conformational dynamics. We choose the leucine rich repeat (LRR) domain of the tumor suppressor pp32 as a model. Pp32 is composed of five LRRs with a capping motif on each of its termini. We show here that the introduction of a cavity in the N-terminal capping motif of pp32 leads to pressure-dependent conformational exchange detected on the 500 µs - 2 ms timescale by 15N CPMG relaxation dispersion analysis. Exchange amplitude and minimum chemical shifts decrease from the N- to the C-terminus, revealing a gradient of structural disruption across the protein. In contrast, introduction of a cavity in the central core of pp32 leads to pressure-induced exchange on a slower (> 2 ms) timescale detected by 15N-CEST analysis. Excited state 15N chemical shifts indicate that in the major excited state, the N-terminal region is mostly unfolded, while the core retains native-like structure. These high-pressure chemical state exchange measurements reveal that cavity position dictates distinct structural dynamics, highlighting the subtle, yet central role of sequence in determining protein conformational dynamics.
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    The impact of surface modification on magneto-functional iron oxide – polyethylene oxide nanocomposites
    (Rensselaer Polytechnic Institute, Troy, NY, 2022-08) Weiblen, Donovan George, III; Ozisik, Rahmi
    Remote triggering of smart materials such as shape memory polymers and nanocomposites for drug delivery are research areas of continued interest for magneto-functional nanocomposites. Magnetically susceptible nanoparticles (NPs) generate heat when exposed to an alternating magnetic field (AMF), making these NPs an ideal candidate for use in smart nanocomposites. While a wide range of nanoparticle chemistries have been studied as ferrofluids in various liquid carrier media, the behavior of these nanoparticles in solid state polymers is not widely understood. This research studies the dependence of heat generation mechanisms and interfacial interactions on nanocomposite structure and morphology, nanoparticle surface coating and nanoparticle concentration in iron oxide (Fe3O4) - poly(ethylene oxide), PEO, nanocomposites. Nanoparticles were coated with surfactants and polymers to improve dispersion and magnetic properties. In this work we first focused on the impact of surface coating of iron oxide (Fe3O4) NPs on magnetic volume reduction, structure, magnetic heating efficiency and mechanical properties of poly(ethylene oxide), PEO, nanocomposites. Uncoated, poly(ethylene glycol), PEG, coated and amine coated 10–nm–diameter Fe3O4 NPs were dispersed at concentrations less than 1% by weight in PEO. Although loaded at low concentration these nanocomposites displayed excellent values for intrinsic power loss especially at low concentrations. We found that dispersion of nanoparticles was strongly related to the character of the surface coating. Uncoated nanoparticles formed large aggregates which led to a significant decrease in the heat generation capabilities. The surface coatings also strongly impacted the magnetic phase reduction. Amine coated nanoparticles had the least magnetic phase reduction. All nanoparticles showed unexpectedly higher heating efficiencies in PEO than when dispersed in water due to decreased magnetic volume loss. Aggregation was determined to be the dominant factor for decreased heating efficiency. Calorimetry experiments explored the impact of the nanoparticles on crystallinity and nucleation rates. Nanoindentation was used to evaluate the mechanical properties via stress relaxation and creep experiments. Amine coated nanoparticles were found to improve the moduli of the nanocomposites. Low concentrations of nanoparticles led to increased relaxation and decreased creep compliance whereas high concentrations had no effect on relaxation and increased creep compliance. The relevance of five rheological models was evaluated. Stress relaxation was best modeled by a power law or logarithmic based model whereas the creep was best modeled by a Generalized Maxwell model. In the second part of this work, single core aminosilane coated 10–nm–diameter Fe3O4 NPs were dispersed at concentrations less than 2% by weight in PEO matrices with varying molecular weights. Altering the matrix molecular weight of the matrix polymer allows for consistent intermolecular interactions between the NP surface groups and the PEO in order to determine relative importance of Brownian and Neel relaxation processes. Increased matrix molecular weight above the polymer matrix entanglement molecular weight led to decreased heat generation efficiency that was consistent with decreases in the nanoparticle magnetic volume determined via vibrating sample magnetometry. Brownian and Neelian relaxation mechanisms were proven to be present despite the high viscosity of the matrix media. Dynamic polymer relaxation modes such as the Reptation or Rouse models were found to be inactive.
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    Cell free production of isobutanol
    (Rensselaer Polytechnic Institute, Troy, NY, 2022-08) Wong, Matthew; Belfort, Georges; Koffas, Mattheos A. G.
    With a need for greener fuels, research into production of biofuels is essential. Isobutanol out preforms ethanol in key metrics such as engine compatibility, energy density, and gasoline blending. Current biofuel strategies of fermentation are constrained by the inherent toxicity of alcohol on microbial cells. While work has been performed on engineering these strains for higher tolerance, cell-free production with enzymes offers a novel approach to bypass the toxicity limitations altogether. These enzymes can also be immobilized to retain enzyme activity and facilitate separations. Based on previous work in the Belfort laboratory, the ketoisovaleric acid pathway was chosen for production of the biofuel, isobutanol. High preforming and stable enzymes were selected from the literature, cloned, expressed, and purified and tested for activity, kinetics, and stability. They were utilized in a novel in vivo to in vitro system, resulting isobutanol titer of 1.78 g/L and yield of 93%. An epoxy immobilized reaction scheme resulted in a titer of 2 g/L and 43% yield. The pathway enzymes were then fused to dockerins, which bound to a cohesin scaffold on cellulose. The reaction utilizing this immobilization scheme resulted in a titer of 5.92 g/L and 78.4% yield. Further work can be done to optimize this reaction, as well as to expand the pathway or scaffold, and incorporate separation of the isobutanol for eventual scaleup.
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