J. Stahlman

The stability of biogenic uraninite with respect to oxidation is seminal to the success of in situ bioreduction strategies for remediation of subsurface U(VI) contamination. The properties and hence stability of uraninite are dependent on its size, structure, and composition. In this study, the local-, intermediate-, and long-range molecular-scale structure of nanoscale uraninite produced by Shewanella oneidensis strain MR-1 was investigated using EXAFS, SR-based powder diffraction and TEM. The uraninite products were found to be structurally homologous with stoichiometric U02 under all conditions considered. Significantly, there was no evidence for lattice strain of the biogenic uraninite nanoparticles. The fresh nanoparticles were found to exhibit a well-ordered interior core of diameter ca. 1.3 nm and an outer region of thickness ca approximately 0.6 nm in which the structure is locally distorted. The lack of nanoparticle strain and structural homology with stoichiometric U02 suggests that established thermodynamic parameters for the latter material are an appropriate starting point to model the behavior of nanobiogenic uraninite. The detailed structural analysis in this study provides an essential foundation for subsequent investigations of environmental samples.

5-Fluoroanthranilic acid (FAA)-resistant mutants were selected in homothallic diploids of three Saccharomyces species, taking care to isolate mutants of independent origin. Mutations were assigned to complementation groups by interspecific complementation with S. cerevisiae tester strains. In all three species, trp3, trp4 and trp5 mutants were recovered. trp1 mutants were also recovered if the selection was imposed on a haploid strain. Thus, FAA selection may be more generally applicable than was previously described.

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three sub-systems of the ATLAS Inner Detector at the Large Hadron Collider at CERN. It consists of close to 300000 thin-wall drift tubes (straws) providing ∼30 measurements with position resolution of about 120 μm for charged particle tracks with |η| < 2 and pT > 0.5 GeV. Along with continuous tracking, it provides particle identification capability through the detection of transition radiation, X-ray photons generated by high momentum particles in the many polymer fibers or films that fill the spaces between the straws. Custom-built analog and digital electronic read-out are optimized to operate at the LHC design luminosity. In this article, a review of the commissioning and first operational experience of the TRT detector will be presented. Emphasis will be given to performance studies based on the reconstruction and analysis of proton-proton collision data collected at the LHC. In addition, the response of the TRT detector to the extremely high track density conditions encountered during the first heavy ion LHC collisons will be presented.

The discovery of a new scalar particle in the search for the Higgs boson at the Large Hadron Collider (LHC) was a great success for the ATLAS and CMS collaborations. Additional measurements of this new particle present opportunities to both test the Standard Model (SM) predictions for the Higgs boson and to search for non-SM properties of this new particle. This thesis presents measurements of the mass, signal strength, and production cross sections of the Higgs boson in the H -&gt; ZZ* -&gt; lll'l' (l,l'=e,μ) decay channel. The cross section measurements are performed using 20.3 fb^-1 of pp collisions at center of mass energy sqrt(s) = 8 TeV collected by the ATLAS detector and the mass and signal strength measurements are performed using an additional 4.5 fb^-1 of pp collisions at sqrt(s) = 7 TeV. From the data in the H -&gt; 4l channel, the best estimate of the mass is 124.51 ± 0.52 (stat) ± 0.06 (syst) GeV. The signal strength (the ratio of observed signal events to expected events from a Standard Model Higgs boson) is measured to be 1.64 ± 0.38 (stat) ± 0.18 (syst). An inclusive cross section time branching ratio measurement is performed within a fiducial volume and found to be 2.11+0.53- 0.47 (stat) + 0.08- 0.08(syst) fb. Differential cross section measurements are performed for six observables which are sensitive to properties of the Higgs boson production and decay. An unfolding procedure is used to correct for detector effects in the differential measurements and comparisons are made to several theoretical calculations. No significant deviations from the SM predictions are observed.