Electrical Characterization of Crystalline UO\u3csub\u3e2\u3c/sub\u3e, ThO\u3csub\u3e2\u3c/sub\u3e AND U\u3csub\u3e0.71\u3c/sub\u3eTh\u3csub\u3e0.29\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e

Uranium dioxide (UO2), thorium dioxide (ThO2), and UxTh1-xO2 alloys are characterized for suitability in uranium-based neutron detectors. ThO2 was studied for an envisioned UO2/ThO2 heterojunction. A U0.71Th0.29O2 alloy was studied because of its resistance to oxidation and potential use in surface passivation. The U0.71Th0.29O2 effective Debye temperature of 217± 24 K was measured using temperature-dependent x-ray photoemission spectroscopy (XPS). The specific heat capacity for the U0.71Th0.29O2 alloy was calculated from the Debye temperature and compared to the heat capacity obtained from modulated-temperature differential scanning calorimetry (MDSC). The XPS derived Debye temperature specific heat capacity was lower than with MDSC due to effects of a vacuum reduced crystal surface. Angle resolved XPS provides depth profiling of a UO2 surface. The U 4f7/2 peaks are evident of U4+ and U6+ oxidation states with an increase in the U4+ oxidation state further from the surface. The presence of U 5f peaks in the valence band spectra provided evidence of U4+ but does not preclude the presence of U6+, while the electronic band-gap energy remained at 2.2 eV, confirming the presence of UO2. These surface characteristics indicated a vacuum reduced UO2 surface and excess oxygen incorporated into the lattice forming a UO2+x selvedge region

Cathodoluminescence and Photoemission of Doped Lithium Tetraborate

Lithium tetraborate (Li2B4O7) crystals are being developed for possible use in solid state neutron detectors. The 6Li(n,α)3H and 10B(n,α)7Li reactions are the basis for neutron detection, and a Li2B4O7 crystal enriched with Mn should show improved efficiency for neutron detection. There is a lack of fundamental characterization information regarding this useful material, particularly with regard to its electronic configuration. Photoemission spectroscopy was used to determine the energy level structure of the Mn doped Li2B4O7 crystals. Measurements were made using ultraviolet photoemission spectroscopy (UPS) using synchrotron radiation on two different beamlines. The first was the 3 m toroidal grating monochromator (TGM) beam line confirming the presence of Mn. Secondly, the normal incident monochromator (NIM) beamline studied the band gap states. Measurements were made at elevated sample temperatures to reduce charging effects. Photoemission studies provided evidence of Mn in the bulk crystal at 47.2 eV. Valence band analysis provided the presence of surface states but no acceptor sites. Cathodoluminescence studies were performed on undoped and Mn doped at beam energies from 5 to 10 KeV and at room temperature. Self trapped exciton emission states are evident in the undoped and Mn doped Li2B4O7 sample ranging in energies from 3.1 to 4.1 eV

Aerial Radiation Detection Identification and Measurement System Detector Material Comparison Study

The 20th Chemical Biological Radiological Nuclear and Explosives Command (CBRNE) currently utilizes an airborne sodium iodide gamma and beta detection system to map radiation fields over large areas of interest. The 20th CBRNE explored emergent detector technologies utilizing two detection materials; thallium-activated cesium iodide and high purity germanium (HPGe). These detectors were simulated at various altitudes and compared to background measurements. The sodium iodide detector failed to provide isotopic discrimination at distance. The thallium-activated cesium iodide CsI(Tl) detector provided sufficient absolute efficiency and energy resolution to identify isotopics at distance. The HPGe detector provided the best energy resolution. However, current crystal growth technology limits the size of HPGe detectors. New CsI(TI) detectors would enable source identification by the Aerial Radiation Detection Identification and Measurement System (ARDIMS)

Infrared-active Phonon Modes in Single-crystal Thorium Dioxide and Uranium Dioxide

The infrared-active phonon modes, in single-crystal samples of thorium dioxide (ThO2) and uranium dioxide (UO2), were investigated using spectroscopic ellipsometry and compared with density functional theory. Both ThO2 and UO2 are found to have one infrared-active phonon mode pair [consisting of one transverse optic (TO) and one associated longitudinal optic (LO) mode], which is responsible for the dominant features in the ellipsometric data. At room temperature, our results for the mode pair’s resonant frequencies and broadening parameters are comparable with previous reflectance spectroscopy characterizations and density functional theory predictions. For ThO2, our ellipsometry and density function theory results both show that the LO mode broadening parameter is larger than the TO mode broadening. This signifies mode anharmonicity, which can be attributed to the intrinsic phonon–phonon interaction. In addition to the main mode pair, a broad low-amplitude impurity-like vibrational mode pair is detected within the reststrahlen band for both ThO2 and UO2. Elevated temperature measurements were performed for ThO2 in order to study the mechanisms by which the phonon parameters evolve with increased heat. The observed change in the TO resonant frequency is in excellent agreement with previous density functional calculations, which only consider volume expansion of the crystal lattice. This suggests that the temperature-dependent change in the TO frequency is primarily due to volume expansion. The change in the main mode pair’s broadening parameters is nearly linear within the temperature range of this study, which indicates the intrinsic anharmonic scattering (via cubic anharmonicities) as the main decay mechanism

Band-to-band Transitions and Critical Points in the Near-infrared to Vacuum Ultraviolet Dielectric Functions of Single Crystal Urania and Thoria

Band-to-band transition energy parameters for single-crystal actinide samples of uranium oxide and thorium oxide were determined and compared using spectroscopic ellipsometry and critical-point dielectric function analyses. Spectroscopic ellipsometry measurements from the near-infrared to the vacuum ultraviolet spectral region were used to determine the dielectric functions of uranium oxide and thorium oxide. The critical-point structure is similar between UO2 and ThO2 but strongly blue shifted for ThO2. We find bandgap energies of 2.1 eV and 5.4 eV for UO2 and ThO2, respectively

Electrical and material properties of hydrothermally grown single crystal (111) UO2

The semiconductor and optical properties of UO2 are investigated. The very long drift carrier lifetimes, obtained from current-voltage I(V) and capacitance-voltage C(V) measurements, along with the well-defined optical properties provide little evidence of an abundance of material defects away from the surface region. Schottky barrier formation may be possible, but very much dependent on the choice of contact and surface stoichiometry and we find that Ohmic contacts are in fact favored. Depth resolved photoemission provided evidence of a chemical shift at the surface. Density functional theory, with the Heyd-Scuseria-Ernzerhof (HSE) functional, indicates a band gap of a 2.19 eV and an anti-ferromagnetic ground state. Ellipsometry measurements indicates at UO2 is relatively isotropic with a band gap of approximately 2.0 eV band gap, consistent with theoretical expectations

A framework for human microbiome research

A variety of microbial communities and their genes (the microbiome) exist throughout the human body, with fundamental roles in human health and disease. The National Institutes of Health (NIH)-funded Human Microbiome Project Consortium has established a population-scale framework to develop metagenomic protocols, resulting in a broad range of quality-controlled resources and data including standardized methods for creating, processing and interpreting distinct types of high-throughput metagenomic data available to the scientific community. Here we present resources from a population of 242 healthy adults sampled at 15 or 18 body sites up to three times, which have generated 5,177 microbial taxonomic profiles from 16S ribosomal RNA genes and over 3.5 terabases of metagenomic sequence so far. In parallel, approximately 800 reference strains isolated from the human body have been sequenced. Collectively, these data represent the largest resource describing the abundance and variety of the human microbiome, while providing a framework for current and future studies

Structure, function and diversity of the healthy human microbiome

Author Posting. © The Authors, 2012. This article is posted here by permission of Nature Publishing Group. The definitive version was published in Nature 486 (2012): 207-214, doi:10.1038/nature11234.Studies of the human microbiome have revealed that even healthy individuals differ remarkably in the microbes that occupy habitats such as the gut, skin and vagina. Much of this diversity remains unexplained, although diet, environment, host genetics and early microbial exposure have all been implicated. Accordingly, to characterize the ecology of human-associated microbial communities, the Human Microbiome Project has analysed the largest cohort and set of distinct, clinically relevant body habitats so far. We found the diversity and abundance of each habitat’s signature microbes to vary widely even among healthy subjects, with strong niche specialization both within and among individuals. The project encountered an estimated 81–99% of the genera, enzyme families and community configurations occupied by the healthy Western microbiome. Metagenomic carriage of metabolic pathways was stable among individuals despite variation in community structure, and ethnic/racial background proved to be one of the strongest associations of both pathways and microbes with clinical metadata. These results thus delineate the range of structural and functional configurations normal in the microbial communities of a healthy population, enabling future characterization of the epidemiology, ecology and translational applications of the human microbiome.This research was supported in part by National Institutes of Health grants U54HG004969 to B.W.B.; U54HG003273 to R.A.G.; U54HG004973 to R.A.G., S.K.H. and J.F.P.; U54HG003067 to E.S.Lander; U54AI084844 to K.E.N.; N01AI30071 to R.L.Strausberg; U54HG004968 to G.M.W.; U01HG004866 to O.R.W.; U54HG003079 to R.K.W.; R01HG005969 to C.H.; R01HG004872 to R.K.; R01HG004885 to M.P.; R01HG005975 to P.D.S.; R01HG004908 to Y.Y.; R01HG004900 to M.K.Cho and P. Sankar; R01HG005171 to D.E.H.; R01HG004853 to A.L.M.; R01HG004856 to R.R.; R01HG004877 to R.R.S. and R.F.; R01HG005172 to P. Spicer.; R01HG004857 to M.P.; R01HG004906 to T.M.S.; R21HG005811 to E.A.V.; M.J.B. was supported by UH2AR057506; G.A.B. was supported by UH2AI083263 and UH3AI083263 (G.A.B., C. N. Cornelissen, L. K. Eaves and J. F. Strauss); S.M.H. was supported by UH3DK083993 (V. B. Young, E. B. Chang, F. Meyer, T. M. S., M. L. Sogin, J. M. Tiedje); K.P.R. was supported by UH2DK083990 (J. V.); J.A.S. and H.H.K. were supported by UH2AR057504 and UH3AR057504 (J.A.S.); DP2OD001500 to K.M.A.; N01HG62088 to the Coriell Institute for Medical Research; U01DE016937 to F.E.D.; S.K.H. was supported by RC1DE0202098 and R01DE021574 (S.K.H. and H. Li); J.I. was supported by R21CA139193 (J.I. and D. S. Michaud); K.P.L. was supported by P30DE020751 (D. J. Smith); Army Research Office grant W911NF-11-1-0473 to C.H.; National Science Foundation grants NSF DBI-1053486 to C.H. and NSF IIS-0812111 to M.P.; The Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231 for P.S. C.; LANL Laboratory-Directed Research and Development grant 20100034DR and the US Defense Threat Reduction Agency grants B104153I and B084531I to P.S.C.; Research Foundation - Flanders (FWO) grant to K.F. and J.Raes; R.K. is an HHMI Early Career Scientist; Gordon&BettyMoore Foundation funding and institutional funding fromthe J. David Gladstone Institutes to K.S.P.; A.M.S. was supported by fellowships provided by the Rackham Graduate School and the NIH Molecular Mechanisms in Microbial Pathogenesis Training Grant T32AI007528; a Crohn’s and Colitis Foundation of Canada Grant in Aid of Research to E.A.V.; 2010 IBM Faculty Award to K.C.W.; analysis of the HMPdata was performed using National Energy Research Scientific Computing resources, the BluBioU Computational Resource at Rice University

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead