3,621 research outputs found

    Survival of Fecal Contamination Indicator Organisms in Soil

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    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

    Development of a QA plan for a 3.0T Cannon Galan MR-SIM

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    Purpose: To develop and incorporate a QA (quality assurance) program for a Canon Galan 3 tesla MR Simulator for applications in radiation therapy. Methods and materials: The QA program was centered around tests performed with three separate levels of frequency. The daily QA procedure consisted of scanning a vendor provided daily QA cube phantom that measures basic performance parameters. Additionally, a series of basic safety check were performed. The monthly QA procedure consisted of several tests, including scanning the ACR MRI large accreditation phantom and manually performing its corresponding image quality tests. Scanning the MagPhan RT for its detailed geometric distortion analysis capabilities. Scanning the CaliberMR diffusion phantom for DWI QA. Performing a series of basic mechanical checks on the positional accuracy of the patient couch and external LAP laser positioning system. And outsourcing coil QA to a vendor service engineer who utilized a vendor analysis method. The annual QA tests consisted of an abbreviated version of the ACR image quality tests, along with an ACR table position accuracy test that was also performed on the ACR MRI large accreditation phantom. Further tests include a magnetic field homogeneity test, an evaluation of the complete clinical stock of RF coils, and a retroactive analysis of center frequency using results from the daily QA cube phantom. Additionally, the external laser offset from the isocenter was also verified using the AQUARIUS MRI phantom, monitor QC was performed based on the set of ACR advised SMPTE tests, and the ACR MRI accreditation visual checklist was filled out. Scanner manual and automatic transmit gain calculations were compared using the method outlined in AAPM report 100. All acquired images were examined for the presence of artifacts. Lastly, a qualified medical physicist performed a review of the facility’s MR safety program. Results: Daily QA has enabled long term tracking of basic performance parameters. Percent SNR experienced an initial drop during December 2021 before stabilizing for the remainder of project. Other basic performance parameters such RF level, helium level, and receiver gain maintained consistency with minor fluctuations occurring day to day. Center frequency remained at 123.196MHz for most of the project duration. Monthly QA and annual QA test protocols were successfully adopted and incorporated into the ongoing quality assurance effort. Conclusions: This project has established a foundational quality assurance program that can be adjusted to meet the evolving needs of VCU’s department of radiation oncology. Keywords: Quality Assurance (QA), Magnetic Resonance Simulator (MR-SIM), Phanto

    A REVIEW OF CONTRIBUTIONS TO THE WESTERN JOURNAL OF AGRICULTURAL ECONOMICS: 1977-81

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    In this study a complete survey of all WJAE articles was conducted. The 158 titles that have appeared in the WJAE as of December 1981 are categorized by institutional category, authorship affiliation, and subject category. These results are compared to similar studies concerning the SJAE and AJAE. Our findings indicate that the WJAE has a broad range of contributors and is not dominated by any one institution, author, or group of authors. We feel that these and other interesting results are of general interest to all WJAE readers.Teaching/Communication/Extension/Profession,

    Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of electron-doped cuprate superconductor Sr0.9La0.1CuO2Sr_{0.9}La_{0.1}CuO_2

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    We present the first demonstration of vortices in an electron-type cuprate superconductor, the highest TcT_c (= 43 K) electron-type cuprate Sr0.9La0.1CuO2Sr_{0.9}La_{0.1}CuO_2. Our spatially resolved quasiparticle tunneling spectra reveal a hidden low-energy pseudogap inside the vortex core and unconventional spectral evolution with temperature and magnetic field. These results cannot be easily explained by the scenario of pure superconductivity in the ground state of high-TcT_c superconductivity.Comment: 6 pages, 4 figures. Two new graphs have been added into Figure 2. Accepted for publication in Europhysics Letters. Corresponding author: Nai-Chang Yeh (E-mail: [email protected]

    On the methanol emission detection in the TW Hya disc: the role of grain surface chemistry and non-LTE excitation

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    The recent detection of gas-phase methanol (CH3_3OH) lines in the disc of TW Hya by Walsh et al. provided the first observational constraints on the complex O-bearing organic content in protoplanetary discs. The emission has a ring-like morphology, with a peak at 3050\sim 30-50 au and an inferred column density of 36×1012\sim 3-6\times10^{12} cm2^{-2}. A low CH3_3OH fractional abundance of 0.34×1011\sim 0.3-4\times 10^{-11} (with respect to H2_2) is derived, depending on the assumed vertical location of the CH3_3OH molecular layer. In this study, we use a thermo-chemical model of the TW Hya disc, coupled with the ALCHEMIC gas-grain chemical model, assuming laboratory-motivated, fast diffusivities of the surface molecules to interpret the CH3_3OH detection. Based on this disc model, we performed radiative transfer calculations with the LIME code and simulations of the observations with the CASA simulator. We found that our model allows to reproduce the observations well. The CH3_3OH emission in our model appears as a ring with radius of 60\sim60 au. Synthetic and observed line flux densities are equal within the rms noise level of observations. The synthetic CH3_3OH spectra calculated assuming local thermodynamic equilibrium (LTE) can differ by up to a factor of 3.5 from the non-LTE spectra. For the strongest lines, the differences between LTE and non-LTE flux densities are very small and practically negligible. Variations in the diffusivity of the surface molecules can lead to variations of the CH3_3OH abundance and, therefore, line flux densities by an order of magnitude.Comment: Accepted for publication in MNRAS, 8 pages, 8 figure

    Scanning Tunneling Spectroscopic Studies of the Effects of Dielectrics and Metallic Substrates on the Local Electronic Characteristics of Graphene

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    Atomically resolved imaging and spectroscopic characteristics of graphene grown by chemical vapor deposition (CVD) on copper foils are investigated and compared with those of mechanical exfoliated graphene on SiO_2. For exfoliated graphene, the local spectral deviations from ideal behavior may be attributed to strain induced by the SiO_2 substrate. For CVD grown graphene, the lattice structure appears strongly distorted by the underlying copper, with regions in direct contact with copper showing nearly square lattices whereas suspended regions from thermal relaxation exhibiting nearly honeycomb or hexagonal lattice structures. The electronic density of states (DOS) correlates closely with the atomic arrangements of carbon, showing excess zero-bias tunneling conductance and nearly energy-independent DOS for strongly distorted graphene, in contrast to the linearly dispersive DOS for suspended graphene. These results suggest that graphene can interact strongly with both metallic and dielectric materials in close proximity, leading to non-negligible modifications to the electronic properties
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