http://hdl.handle.net/2374.OX/3386 2013-05-22T19:32:49Z http://hdl.handle.net/2374.OX/103799 Defining and Measuring Robustness in Wireless Sensor Communication for Telemedicine Bhattarai, Sudha Wireless sensor network is useful in a wide range of applications. Motes are used as a media for communication in wireless networks. A robust network is a stable network that can endure various noise factors present in the system. Dropped packets during mote communication are an important parameter to determine the robustness of the system. This can be further explained as properties that are insensitive to small fluctuation from the actual assumption on which they depend. We propose mote technology as a potential source for wireless communication of medical signals in body area networks. In order to determine if the proposed system is useful, a robustness metric is developed specifically for a biosensor shirt application. The objective is to provide a tool to evaluate whether the mote hardware will deliver acceptable performance given perturbations in a wireless environment. 2009-04-09T21:33:21Z http://hdl.handle.net/2374.OX/103798 Tracking Storms through Time: Event Deposition and Biologic Response in Storr…#8482;s Lake, San Salvador Island, Bahamas Sipahioglu, Sara M. Because of its position within the southwestern Atlantic Ocean, San Salvador Island, Bahamas has been the site of many hurricane strikes throughout its history. As such, it remains an effective setting in which to examine hurricane intensity in the Late Holocene. The lakes along the island…#8482;s margin provide a depositional archive recording the paleotempestites from these storm events. Storrs Lake is a shallow (66µS) lake located along the eastern side of the island and is separated from the ocean by Holocene dunes. It, like other lakes on San Salvador, is constantly recording climatic changes, vegetation shifts and the history of colonization. This study addresses the following questions: 1) What is the depositional history of Storrs Lake through the last 3,000 years and 2) Can we see large storm events in the sediment record and determine the biologic response to these events? Cores were recovered from Storrs Lake that varied in length from 5 to 200 cm, including transects across the Fortune Hill basin. The cores from Fortune Hill basin were analyzed for organic and carbonate content, dry bulk density, grain size, chemical composition, sediment fabric, trace elements, spectralphotometry, ostracode and mollusk faunal composition. Large storms can be identified through time by a distinct increase in grain size and a change in dry bulk density. The adjacent dunes have been mapped and sediment analyzed. The allochthonous sand found within the basin matches the sand found on the dune faces and identified as storm wash-over deposits. Biologic patterns suggest that species richness and abundance change after these large storm events, possibly due to the freshening that occurs from the storm and a change in the basin substrate. Cyanobacterial mats, or stromatolites, that are prevalent throughout many of the lakes on San Salvador also have a documented response to these freshening events by a community shift and increase in productivity. These cores record a major climatic shift occurring approximately 700 ybp and which is contemporaneous with colonization of the island. There is also evidence of multiple hurricane strikes, and a hurricane ‘hyperactivity period…#8482; from 1000 …ldquo; 3000 ybp that has been identified in other records along the Gulf Coast of North America. Caribbean hurricanes are directly related to the position and strength of the Bermuda High and North Atlantic Oscillation. The ability to identify paleohurricane strikes in the Bahamas may be useful in climatic reconstructions as well generating a recurrence interval and predicting the frequency of CAT 5 hurricanes through this area and the ecological response to these disturbances. 2009-04-09T21:33:02Z http://hdl.handle.net/2374.OX/103795 Theoretical Modeling of the Nanostructure Formation in Soft Condensed Matter Using Atomic Force Microscopy Paramonov, Pavel B. A novel nanolithography technique is developed for nanoscale patterning of polymers: atomic force microscope assisted electrostatic nanolithography (AFMEN). In AFMEN, nanostructures are generated by mass transport of polymeric material within an initially uniform, planar film. The combination of localized softening of attolitres of polymer, a strongly non-uniform electric field to polarize and manipulate the soften dielectric, and single-step process methodology using conventional atomic force microscopy (AFM), establishes a new paradigm for polymer nanolithography. We develop a basic theoretical understanding of the processes associated with AFMEN and present modeling of the relevant phenomena. The analysis of polymer heating indicates that the AFMEN resolution is not directly limited by the radius of the AFM tip, which is distinctly different from alternative AFM–based lithographic techniques. Instead, the feature size depends critically on the thermal characteristics of the polymer, such as its thermal conductivity. The dielectric properties of the polymer play a secondary role, affecting the magnitude of the electric field but do not directly impact the feature size. The nanostructure shape is determined by the competition between the ponderomotive forces acting on the dielectric material in non–uniform electric field, and the polymer surface tension. An exact analytical solution, as well as numerical solutions, are determined for the electric field distribution in the tip–sample junction, which allow prediction of the nanostructure geometry. The response of the AFM tip during the nanolithography process is investigated. An analysis of the free energy of the system, comprising AFM tip, sample surface and water meniscus, shows that the tip is spontaneously lifted away from the polymer surface. The mechanical work required to lift the tip is drawn from the energy of electric field. In addition, water condensation in the proximity of nanoscale asperities such as an AFM tip is studied. A general framework based on the density functional theory (DFT) is developed and applied to describe the liquid meniscus condensation, providing the first (to the best of our knowledge) molecular–level theory of water condensation on the nanoscale in the presence of external electric fields. 2009-04-09T21:32:49Z http://hdl.handle.net/2374.OX/103794 Anionic Synthesis of Well-defined Functionalized and Star-branched Polymers Ocampo, Manuela Novel methods for the synthesis of chain-end and in-chain functionalized polymers, as well as star polymers, were developed using anionic polymerization techniques. A new mechanism for the reaction of polymeric organolithium compounds with thiiranes has been found. The reaction of poly(styryl)lithium and poly(butadienyl)lithium with propylene sulfide and ethylene sulfide was investigated in hydrocarbon solution for the preparation of thiol-functional polymers. It was found by MALDI-TOF mass spectral analysis of the reaction products that the reaction proceeded by attack of the anion on the methylene carbon atom of the thiirane ring followed by ring opening to form the thiol-functionalized polymer. The reaction of poly(styryl)lithium with trimethylene sulfide did not produce the corresponding thiol-functionalized polymer; the resulting methyl-terminated polymer was formed by attack of the anion on the sulfur atom followed by ring opening to form a primary carbanion. A new method for synthesis of alkoxysilyl-functionalized polymers was developed. Using a general functionalization methodology based on the hydrosilation of vinyltrimethoxysilane with w-silyl hydride-functionalized polystyrene, alkoxysilyl-functionalized polystyrene was obtained in high yield (83 %). The main side product was vinylsilane-functionalized polymer. A small amount of dimer (approximately 2 %) was formed from the hydrosilation reaction of silyl hydride-functionalized polymer and vinylsilane-functionalized polymer. Star polymers with an average number of 6.8 arms were obtained by reacting poly(styryl)lithium with 6.6 equivalents of vinyldimethylchlorosilane in benzene at 30 C. It was found that, in benzene at 30 C, vinyldimethylchlorosilane is an efficient linking agent for the preparation of well-defined star-branched polymers. In contrast, the reaction of poly(styryl)lithium with 5 equivalents of vinyldimethylchlorosilane in THF at -78 C produced vinylsilane-functionalized polymer in high yield (> 93 %). Poly(styryl)lithium was reacted with 2.5 equivalents of vinyldimethylethoxysilane; reaction occurred exclusively by the addition of the living anion to the vinyl group. In-chain, dihydroxyl-functionalized polystyrene was prepared by reaction of poly(styryl)lithium and 1,3-butadiene diepoxide. The hydroxyl functionalities were activated with potassium naphthalenide. Addition of ethylene oxide monomer yielded the corresponding heteroarm polystyrene/poly(ethylene oxide) stars. Two commercially available triepoxides, N,N-diglycidyl-4-glycidyloxyaniline and Tactix 742, were used to prepare the corresponding 3-armed stars in high yield. 2009-04-09T21:32:37Z