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This work presents the first electrochemical observation of single polystyrene microbead collisions with an electrode within a microchannel. We have observed that detecting single microbead collisions is facile with this system. Additionally, we have shown that by increasing flow within the channel, one can increase both the frequency and magnitude of collision signals. This technique may provide a means of signal amplification in future sensing work. / text

The present study combines modern jet reconstruction algorithms and particle identification (PID) techniques in order to study the enhancement of proton/pion ratio at mid transverse momentum ([mathematical symbols] 1.5 - 4.0 GeV/c) observed in central Au + Au collisions at [mathematical symbols] = 200 GeV. The ratio enhancement is thought to be caused by recombination processes and/or parton fragmentation modification of jets in relativistic heavy ion collisions. The fragmentation modification hypothesis is tested in this analysis by reconstructing and selecting energetic jets presumably biased to fragment outside of the medium created in Au + Au collisions and comparing their particle composition to the recoiling (medium-traversing) jets. The bias assumption is confirmed by comparing jets in central collisions, where the effect of proton/pion enhancement is present, with peripheral ones where no medium effects are expected. The selected jets are reconstructed by using the anti-k[subscript T] algorithm from the modern FASTJET package. The PID in the p[subscript T] region of interest is possible by combining measurements of the particles' energy deposition and velocity from the Time Projection Chamber and the recently installed (2009-2010) Time of Flight detectors at STAR. The acceptance of these detectors, [eta] < 1.0 and full azimuth, make them extraordinary tools for correlation studies. These features allow for the measurement of relative azimuth ([phi] [subscript jet] - [phi] [subscript pion,proton]) distributions by using the selected jet axis in order to disentangle the uncorrelated background present in the high multiplicity heavy ion collisions. The proton/pion ratios in two different centrality bins and p[subscript T] = 1.2 - 3.0 GeV/c are presented for biased (vacuum fragmenting) jets and their recoiling counterparts / text

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Understanding the radiolysis of impure water and resulting reactions is crucial to many fields. Reactions driven by low energy electrons (LEE) are of special interest, as high-energy radiation generates large quantities of these electrons, which then provide the energy for most subsequent reactions. Interfacially located reactions are also of particular interest, both as models for heterogeneously distributed reactions occurring during radiolysis, and in their own right, as radiation-driven reactions at interfaces are responsible for key processes such as corrosion and DNA damage. To study LEE-driven reactions at interfaces, thin-layered films of amorphous solid water (ASW) and methanol were grown under ultra-high vacuum conditions using molecular beam techniques. The films were exposed to a beam of low-energy (100eV or less) electrons, and studied using electron-stimulated desorption (ESD) and temperature programmed desorption (TPD). ESD studies indicated that methanol moves through a water film during deposition at 80 K but not at 50 K. This transport was not seen during thermal annealing, but radiation-induced mixing was observed at all temperatures. Major and minor LEE radiation products of pure methanol films were identified and found to be consistent with previous results. Products of LEE irradiated layered methanol/water films were determined for the first time using ESD and TPD spectra, and found to be limited to H₂, O, O₂, CH₂O, C₂H₆, CO, CO₂, CH₃OCH₃, and CH₃CH₂OH. The effect of adding methanol to an ASW film on the production in ASW of H₂ and O₂ was also examined. The interface created by the addition of CH₃OH to ASW was found to generate H₂ in previously non-reactive regions of the water film by increasing water-water and water-methanol reactions. Radiative mixing of CH₃OH and ASW enhanced this effect, presumably by increasing the region of disrupted H-bonding in the ASW. In contrast, the addition of CH₃OH at low coverages suppressed O₂ production in both unprocessed and preprocessed ASW layers. Modeling indicates that methanol scavenging of the O₂ precursor OH and of the reaction-driving electrons is responsible for this reduction in O₂ signal.

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published_or_final_version / Geography and Geology / Master / Master of Philosophy

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No description available.