2,836 research outputs found
Survival of Fecal Contamination Indicator Organisms in Soil
Soils amended with human or animal waste may result in pathogen contamination of ground and surface water. Because temperature has been shown to affect pathogen survival, two laboratory studies were conducted to evaluate the impact of extremes in temperature on bacterial and viral pathogen indicator die-off in soil. A Captina silt loam was amended with broiler litter (0.1 g/g dry soil), septic tank effluent, or Escherichia coli (ATCC 13706) culture (both at 0.04 and 0.1 mL/g dry soil in the two respective studies), incubated at 5 and 35°C, and analyzed over time to determine the number of fecal coliform, E. coli, and coliphage remaining. Pathogen indicator die-off rate constants (k) for all indicator- temperature-treatment combinations were determined by first-order kinetics. For all three pathogen indicators, die-off was significantly more rapid at 35°C than at 5°C. In both studies, fecal coliform die-off rates were not different from E. coli die-off rates across each temperature-treatment combination. Levels of these bacterial indicators appeared in a ratio of 1:0.94 with 95% confidence intervals at 0.89 and 0.99 in the E. coli- and litter-amended soils. Die-off of the viral indicator was significantly slower than the die-off of the bacterial indicators at 5°C in litter-amended soil. Die-off of the bacterial indicator, E. coli, in soil amended with E. coli culture was not significantly different than die-off in soil amended with broiler litter at 5 or 35°C in the two studies. Because the higher incubation temperature increased die-off rates for all three indicators, it is expected that the potential for contamination of ground and surface water decreases with increasing temperature
Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-Doped Ba(Fe_{1-x}Co_x)_2As_2 Single Crystals using Scanning Tunneling Spectroscopy
Scanning tunneling spectroscopic studies of (x =
0.06, 0.12) single crystals reveal direct evidence for predominantly two-gap
superconductivity. These gaps decrease with increasing temperature and vanish
above the superconducting transition . The two-gap nature and the slightly
doping- and energy-dependent quasiparticle scattering interferences near the
wave-vectors and are consistent with
sign-changing -wave superconductivity. The excess zero-bias conductance and
the large gap-to- ratios suggest dominant unitary impurity scattering.Comment: 4 pages, 4 figures. Paper accepted for publication in Physical Review
Letters. Contact author: Nai-Chang Yeh ([email protected]
Evidence for Strain-Induced Local Conductance Modulations in Single-Layer Graphene on SiO_2
Graphene has emerged as an electronic material that is promising for device applications and for studying two-dimensional electron gases with relativistic dispersion near two Dirac points. Nonetheless, deviations from Dirac-like spectroscopy have been widely reported with varying interpretations. Here we show evidence for strain-induced spatial modulations in the local conductance of single-layer graphene on SiO_2 substrates from scanning tunneling microscopic (STM) studies. We find that strained graphene exhibits parabolic, U-shaped conductance vs bias voltage spectra rather than the V-shaped spectra expected for Dirac fermions, whereas V-shaped spectra are recovered in regions of relaxed graphene. Strain maps derived from the STM studies further reveal direct correlation with the local tunneling conductance. These results are attributed to a strain-induced frequency increase in the out-of-plane phonon mode that mediates the low-energy inelastic charge tunneling into graphene
Scanning Tunneling Spectroscopic Studies of the Low-Energy Quasiparticle Excitations in Cuprate Superconductors
We report scanning tunneling spectroscopic (STS) studies of the low-energy quasiparticle excitations of cuprate superconductors as a function of magnetic field and doping level. Our studies suggest that the origin of the pseudogap (PG) is associated with competing orders (COs), and that the occurrence (absence) of PG above the superconducting (SC) transition T_c is associated with a CO energy Δ_(CO) larger (smaller) than the SC gap Δ_(SC). Moreover, the spatial homogeneity of Δ_(SC) and Δ_(CO) depends on the type of disorder in different cuprates: For optimally and under-doped YBa_2Cu_3O_(7−δ) (Y-123), we find that Δ_(SC) < Δ_(CO) and that both Δ_(SC) and Δ(CO) exhibit long-range spatial homogeneity, in contrast to the highly inhomogeneous STS in Bi_2Sr_2CaCu_2O_(8+x) (Bi-2212). We attribute this contrast to the stoichiometric cations and ordered apical oxygen in Y-123, which differs from the non-stoichiometric Bi-to-Sr ratio in Bi-2212 with disordered Sr and apical oxygen in the SrO planes. For Ca-doped Y-123, the substitution of Y by Ca contributes to excess holes and disorder in the CuO_2 planes, giving rise to increasing inhomogeneity, decreasing Δ_(SC) and Δ_(CO), and a suppressed vortex-solid phase. For electron-type cuprate Sr_(0.9)La_(0.1)CuO_2 (La-112), the homogeneous Δ_(SC) and Δ_(CO) distributions may be attributed to stoichiometric cations and the absence of apical oxygen, with Δ_(CO) < Δ_(SC) revealed only inside the vortex cores. Finally, the vortex-core radius (ξ_(halo)) in electron-type cuprates is comparable to the SC coherence length ξ_(SC), whereas ξ_(halo) ∼ 10ξ_(SC) in hole-type cuprates, suggesting that ξ_(halo) may be correlated with the CO strength. The vortex-state irreversibility line in the magnetic field versus temperature phase diagram also reveals doping dependence, indicating the relevance of competing orders to vortex pinning
Scanning Tunnelling Spectroscopic Studies of Dirac Fermions in Graphene and Topological Insulators
We report novel properties derived from scanning tunnelling spectroscopic (STS) studies of Dirac fermions in graphene and the surface state (SS) of a strong topological insulator (STI), Bi_2Se_3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD), strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by the alternating anti-localization and localization spectra associated with the zero-mode of two sublattices while global time-reversal symmetry is preserved under the presence of pseudo-magnetic fields. For Bi_2Se_3 epitaxial films grown on Si(111) by molecular beam epitaxy (MBE), spatially localized unitary impurity resonances with sensitive dependence on the energy difference between the Fermi level and the Dirac point are observed for samples thicker than 6 quintuple layers (QL). These findings are characteristic of the SS of a STI and are direct manifestation of strong topological protection against impurities. For samples thinner than 6-QL, STS studies reveal the openup of an energy gap in the SS due to overlaps of wave functions between the surface and interface layers. Additionally, spin-preserving quasiparticle interference wave-vectors are observed, which are consistent with the Rashba-like spin-orbit splitting
Emission-Line Galaxy Surveys as Probes of the Spatial Distribution of Dwarf Galaxies. I. The University of Michigan Survey
Objective-prism surveys which select galaxies on the basis of line-emission
are extremely effective at detecting low-luminosity galaxies and constitute
some of the deepest available samples of dwarfs. In this study, we confirm that
emission-line galaxies (ELGs) in the University of Michigan (UM)
objective-prism survey (MacAlpine et al. 1977-1981) are reliable tracers of
large-scale structure, and utilize the depth of the samples to examine the
spatial distribution of low-luminosity (M -18.0) dwarfs relative to
higher luminosity giant galaxies (M -18.0) in the Updated Zwicky
Catalogue (Falco et al. 1999). New spectroscopic data are presented for 26 UM
survey objects. We analyze the relative clustering properties of the overall
starbursting ELG and normal galaxy populations, using nearest neighbor and
correlation function statistics. This allows us to determine whether the
activity in ELGs is primarily caused by gravitational interactions. We conclude
that galaxy-galaxy encounters are not the sole cause of activity in ELGs since
ELGs tend to be more isolated and are more often found in the voids when
compared to their normal galaxy counterparts. Furthermore, statistical analyses
performed on low-luminosity dwarf ELGs show that the dwarfs are less clustered
when compared to their non-active giant neighbors. The UM dwarf samples have
greater percentages of nearest neighbor separations at large values and lower
correlation function amplitudes relative to the UZC giant galaxy samples. These
results are consistent with the expectations of galaxy biasing.Comment: 17 pages, 4 tables, 10 figures. Accepted for publication in the Ap
Pricing and Conservation of Irrigation Water in Texas and New Mexico
Two possible policy alternatives for management of limited water supplies in arid portions of Texas and New Mexico were analyzed for economic feasibility. Detailed studies of the potential impact of a water accumulation policy for each of two irrigation districts (El Paso County Water Improvement District No. 1 in Texas, and the Elephant Butte Irrigation District in New Mexico) were undertaken using temporal linear programming techniques. Current cropping practices, soils, groundwater conditions, historical surface water allocations for Elephant Butte Reservoir and evaporation rates were incorporated within the analysis. Estimates of the benefits of accumulation of surplus portions of irrigation district member's annual surface water allocations, with subsequent use of the unevaporated portion in later years, were deemed insufficient to cover anticipated administrative costs of implementing the proposed policy. This suggests current allocations approximate a temporal optimum. Sensitivity analyses showed greater potential benefits, however, if current groundwater conditions worsen.
Additional analysis of possible price-induced water conservation for the areas within the two states currently mining groundwater from the exhaustible Ogallala aquifer was also undertaken. The High Plains of Texas served as the representative region of study, with results assumed to be analogous for the portions of Eastern New Mexico relying on the Ogallala. Both static and temporal effects of a per unit tax on water pumpage and net returns were examined using a recursive linear programming model. Results indicated that imposition of a $20 per acre-foot tax on water pumped induced very little change in water use over a 40 year period, while reducing the present value of producer net returns from 9% to 27% depending upon initial groundwater conditions and the irrigation technology in use. These results imply that a price induced water conservation policy for the Ogallala is not economically justified
Possible Competing Order-Induced Fermi Arcs in Cuprate Superconductors
We investigate the scenario of competing order (CO) induced Fermi arcs and
pseudogap in cuprate superconductors. For hole-type cuprates, both phenomena as
a function of temperature and doping level can be accounted for if the CO
vanishes at above the superconducting transition and the CO
wave-vector Q is parallel to the antinodal direction. In contrast, the absence
of these phenomena and the non-monotonic d-wave gap in electron-type cuprates
may be attributed to and a CO wave-vector Q parallel to the
nodal direction.Comment: 6 pages and 5 figures, with one figure added in the updated version.
Accepted for publication in Solid State Communications, Fast Communications.
Corresponding author: Nai-Chang Yeh ([email protected]
Annotating Whole Genome Sequencing in COSMIC (The Catalogue of Somatic Mutations in Cancer)
"COSMIC, the Catalogue Of Somatic Mutations In Cancer":http://www.sanger.ac.uk/cosmic is designed to store and display somatic mutation information relating to human cancers, combining detailed information on publications, samples and mutation types. The information is curated both from the primary literature and the laboratories at the Cancer Genome Project, Sanger Institute, UK, and then semi-automatically entered into the COSMIC database. The v47 release (May 2010) contained the curation of 9202 papers describing 116,977 mutations across 466,851 samples. In order to provide consistent annotation of the data, COSMIC has developed a classification system for cancer histology and tissue ontology, and adapted HGVS mutation nomenclature recommendations to describe the multiple mutation types involved in cancer. 

Cancer genetics is moving from systematic screens of candidate gene sets to whole genome sequencing analyses, and COSMIC displays and navigates this new data; we have recently included systematic gene screens and whole genome sequencing studies. COSMIC will annotate and display somatic mutation data that will be emerging from the "International Cancer Genome Consortium (ICGC)":http://www.icgc.org/ and "The Cancer Genome Atlas (TCGA)":http://cancergenome.nih.gov/ projects. New tools are being developed to interpret this genomic data with coding mutation annotations. In addition COSMIC will be expanded to curate and display data from mouse insertional mutagenesis screening and mouse cancer model exome/genome sequencing in the future. The data within COSMIC is freely available without restriction via a website, in datasheets on the "FTP site":ftp://ftp.sanger.ac.uk/pub/CGP/cosmic and through the "COSMIC Biomart":http://www.sanger.ac.uk/genetics/CGP/cosmic/biomart/martview/, available from the "COSMIC homepage":http://www.sanger.ac.uk/cosmic 

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