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Browsing Duke Student Scholarship by Affiliation "Duke Science & Society"

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    ItemOpen Access
    A study of the aeroelastic behavior of flat plates and membranes with mixed boundary conditions in axial subsonic flow
    (2011) Bloomhardt, Elizabeth M.
    In support of the noise reduction targets for future generations of transport aircraft, as set forth by NASA, the fundamental aeroelastic behavior of trailing edge flap technology was explored. Using a plate structural model to approximate the structural configuration and linear potential flow theory to represent the aerodynamics, aeroelastic behavior was characterized for two structural configurations using two different sets of boundary conditions for each. The two structural configurations considered were a) all edges fixed and b) leading and side edges fixed, trailing edge free. In each configuration both simply supported and clamped boundary conditions were considered. Results are compared to calculations presented in the literature for the all edges simply supported configuration.
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    ItemOpen Access
    Barnacle cement: a polymerization model based on evolutionary concepts.
    (2009-11) Dickinson, Gary H.
    The tenacity by which barnacles adhere has sparked a long history of scientific investigation into their adhesive mechanisms. To adhere, barnacles utilize proteinaceous cement that rapidly polymerizes and forms adhesive bonds underwater, and is insoluble once polymerized. Although progress has been made towards understanding the chemical properties of cement proteins, the biochemical mechanisms of cement polymerization remain largely unknown. In this dissertation, I used evolutionary concepts to elucidate barnacle cement polymerization. Well-studied biological phenomena (blood coagulation in vertebrates and invertebrates) were used as models to generate hypotheses on proteins/biochemical mechanisms involved in cement polymerization. These model systems are under similar selective pressures to cement polymerization (life or death situations) and show similar chemical characteristics (soluble protein that quickly/efficiently coagulates). I describe a novel method for collection of unpolymerized cement. Multiple, independent techniques (AFM, FTIR, chemical staining for peroxidase and tandem mass spectroscopy) support the validity of the collection technique. Identification of a large number of proteins besides ‘barnacle cement proteins’ with mass spectrometry, andobservations of hemocytes in unpolymerized cement inspired the hypothesis that barnacle cement is hemolymph. A striking biochemical resemblance was shown between barnacle cement polymerization and vertebrate blood coagulation. Clotted fibrin and polymerized cement were shown to be structurally similar (mesh of fibrous protein) but biochemically distinct. Heparin, trypsin inhibitor and Ca2+ chelators impeded cement polymerization, suggesting trypsin and Ca2+ involvement in polymerization. The presence/activity of a cement trypsin-like serine protease was verified and shown homologous to bovine pancreatic trypsin. Protease activity may activate cement structural precursors, allowing loose assembly with other structural proteins and surface rearrangement. Tandem mass spectrometry and Western blotting revealed a homologous protein to human coagulation factor XIII (fibrin stabilizing factor: transglutaminase that covalently cross-links fibrin monomers). Transglutaminase activity was verified and may covalently cross-link assembled cement monomers. Similar to other protein coagulation systems, heritable defects occur during cement polymerization. High plasma protein concentration combined with sub-optimal enzyme, and/or cofactor concentrations and sub-optimal physical/muscular parameters (associated with hemolymph release) results in improperly cured cement in certain individuals when polymerization occurs in contact with low surface energy silicone and its associated leached molecules.
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    ItemOpen Access
    Deposition of silver nanoparticles in geochemically heterogeneous porous media: predicting affinity from surface composition analysis.
    (2011) Lin, Shihong
    The transport of uncoated silver nanoparticles (AgNPs) in a porous medium composed of silica glass beads modified with a partial coverage of iron oxide (hematite) was studied and compared to that in a porous medium composed of unmodified glass beads (GB). At a pH lower than the point of zero charge (PZC) of hematite, the affinity of AgNPs for a hematite-coated glass bead (FeO-GB) surface was significantly higher than that for an uncoated surface. There was a linear correlation between the average nanoparticle affinity for media composed of mixtures of FeO-GB and GB collectors and the relative composition of those media as quantified by the attachment efficiency over a range of mixing mass ratios of the two types of collectors, so that the average AgNPs affinity for these media is readily predicted from the mass (or surface) weighted average of affinities for each of the surface types. X-ray photoelectron spectroscopy (XPS) was used to quantify the composition of the collector surface as a basis for predicting the affinity between the nanoparticles for a heterogeneous collector surface. A correlation was also observed between the local abundances of AgNPs and FeO on the collector surface.
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    ItemOpen Access
    Expert assessments of retrofitting coal-fired power plants with carbon dioxide capture technologies
    (2009) Chung, Timothy S.
    Carbon dioxide capture and storage is an emerging set of technologies that can contribute to significant reductions in CO2 emissions. However, a substantial amount of uncertainty belies the technical and economic feasibility of capturing CO2 at commercial scale. This study explores the uncertainties associated with carbon dioxide capture technologies, with a specific focus on retrofitting existing coal-fired power plants. 13 respondents with expertise in post-combustion and oxy-fuel combustion capture systems responded to an extensive questionnaire and provided their opinions on present status and future expected performance and costs for amine-based systems, chilled ammonia process, and oxy-combustion. Expert elicitation, a formal protocol for obtaining probabilistic judgments on a subject with insufficient data, was the primary method used to establish best estimates and 95% confidence limits of the energy penalties associated with the technologies under focus. Additionally, this paper presents observations based on the aggregated responses for technology maturity, ideal plant characteristics for early adopters, and the extent to which R&D and deployment incentives will impact costs. The results show a general consensus that amine-based systems are closer to commercial application, but potential for improving performance and lowering costs is limited; chilled ammonia and oxy-combustion contain greater potential for cost reductions, but not without greater uncertainty in regard to scale and technical feasibility. A cost model using expert estimates of expected energy penalties was developed to establish 2030 projections of CO2 capturecosts for amine-based systems. Results from the model indicate that under the reference case(current trends in RD&D), the energy penalty reduction equates to an 11% decrease in annual energycosts. In the best case scenario(best results under an enhanced RD&D policy), the annual energy savings are 29% and the CO2capturecost decreases 16% from $55(in the reference case)to $46per ton of CO2(2006 dollars).
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    ItemOpen Access
    Functional neuroimaging of autobiographical memory.
    (2010) St. Jacques, Peggy L.
    Autobiographical memory (AM) refers to memory for events from our own personal past. Functional neuroimaging studies of AM are important because they can investigate the neural correlates of processes that are difficult to study using laboratory stimuli, including: complex constructive processes, subjective qualities of memory retrieval, and remote memory. Three functional magnetic resonance imaging (fMRI) studies are presented to examine these important contributions of AM. The first study investigates the neural correlates of temporal-order memory for autobiographical events using a novel photo paradigm. Participants took photographs at many campus locations over a period of several hours, and the following day they were scanned while making temporal-order judgments to pairs of photographs from different locations. It was found that temporal-order decisions associated with recollection recruited left prefrontal (PFC) and left posterior parahippocampal cortex, whereas temporal-order decisions relying on familiarity recruited greater activity in the right PFC. The second study examines self-projection, the capacity to re-experience the personal past and to mentally infer another person’s perspective. A novel camera technology was used to examine self-projection by prospectively generating dynamic visuospatial images taken from a first-person perspective. Participants were literally asked to self-project into the personal past or into the life of another person. Self-projection of one’s own past self recruited greater ventral medial PFC (mPFC), and self-projection of another individual recruited dorsal mPFC. Activity in ventral vs. dorsal mPFC was also sensitive to the ability to relive or understand the perspective taken on each trial. Further, task-related functional connectivity analysis revealed that ventral mPFC contributed to the medial temporal lobe network linked to memory processes, whereas dorsal mPFC contributed to the frontoparietal network linked to controlled processes. The third study focuses on the neural correlates underlying age-related differences in the recall of episodically rich AMs. Age-related attenuation in the episodic richness of AM was linked to reductions in activity elicited during elaboration. Age effects on AM were more pronounced during elaboration than search, with older adults showing less sustained recruitment of the hippocampus and ventrolateral PFC for less episodically rich AMs. Further, there was an age-related reduction in the top-down modulation of the PFC on the hippocampus by episodic richness, possibly reflecting fewer controlled processes operating on the recovery of information in the hippocampus. Ultimately, the goal of all memory research is to understand how memory operates in the real-world; the present research highlights the important contribution of functional neuroimaging studies of AM in attaining this goal.