558 research outputs found

    Archie's saturation exponent for natural gas hydrate in coarseā€grained reservoirs

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    Author Posting. Ā© American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 2069-2089, doi:10.1002/2017JB015138.Accurately quantifying the amount of naturally occurring gas hydrate in marine and permafrost environments is important for assessing its resource potential and understanding the role of gas hydrate in the global carbon cycle. Electrical resistivity well logs are often used to calculate gas hydrate saturations, Sh, using Archie's equation. Archie's equation, in turn, relies on an empirical saturation parameter, n. Though n = 1.9 has been measured for iceā€bearing sands and is widely used within the hydrate community, it is highly questionable if this n value is appropriate for hydrateā€bearing sands. In this work, we calibrate n for hydrateā€bearing sands from the Canadian permafrost gas hydrate research well, Mallik 5Lā€38, by establishing an independent downhole Sh profile based on compressionalā€wave velocity log data. Using the independently determined Sh profile and colocated electrical resistivity and bulk density logs, Archie's saturation equation is solved for n, and uncertainty is tracked throughout the iterative process. In addition to the Mallik 5Lā€38 well, we also apply this method to two marine, coarseā€grained reservoirs from the northern Gulf of Mexico Gas Hydrate Joint Industry Project: Walker Ridge 313ā€H and Green Canyon 955ā€H. All locations yield similar results, each suggesting n ā‰ˆ 2.5 Ā± 0.5. Thus, for the coarseā€grained hydrate bearing (Sh > 0.4) of greatest interest as potential energy resources, we suggest that n = 2.5 Ā± 0.5 should be applied in Archie's equation for either marine or permafrost gas hydrate settings if independent estimates of n are not available.DOE Grant Number: DEā€FE0023919; Gas Hydrate Project of the U.S. Geological Survey's Coastal and Marine Geology Program2018-08-1

    The Journal of the Center for Interdisciplinary Teaching and Learning

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    IMPACT: The Journal of the Center for Interdisciplinary Teaching & Learning is a peer-reviewed, biannual online journal that publishes scholarly and creative non-fiction essays about the theory, practice and assessment of interdisciplinary education. Impact is produced by the Center for Interdisciplinary Teaching & Learning at the College of General Studies, Boston University (www.bu.edu/cgs/citl).How do our students learn what it means to be a human being, with all the attendant responsibilities and joys? How do we learn to teach in a truly interdisciplinary manner? These are some of the questions that preoccupy this issueā€™s contributors

    Dating submarine landslides using the transient response of gas hydrate stability

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    Submarine landslides are prevalent on the modern-day seafloor, yet an elusive problem is constraining the timing of past slope failure. We present a novel age-dating technique based on perturbations to underlying gas hydrate stability caused by slide-impacted seafloor changes. Using three-dimensional (3-D) seismic data, we mapped an irregular bottom simulating reflection (BSR) underneath a submarine landslide in the Orca Basin, Gulf of Mexico. The irregular BSR mimics the pre-slide seafloor geometry rather than the modern bathymetry. Therefore, we suggest that the gas hydrate stability zone (GHSZ) is still adjusting to the post-slide sediment temperature. We applied transient conductive heat-flow modeling to constrain the response of the GHSZ to the slope failure, which yielded a most likely age of ca. 8 ka, demonstrating that gas hydrate can respond to landslides even on multimillennial time scales. We further provide a generalized analytical solution that can be used to remotely date submarine slides in the absence of traditional dating technique

    A nematode demographics assay in transgenic roots reveals no significant impacts of the Rhg1 locus LRR-Kinase on soybean cyst nematode resistance

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    <p>Abstract</p> <p>Background</p> <p>Soybean cyst nematode (<it>Heterodera glycines</it>, SCN) is the most economically damaging pathogen of soybean (<it>Glycine max</it>) in the U.S. The <it>Rhg1 </it>locus is repeatedly observed as the quantitative trait locus with the greatest impact on SCN resistance. The Glyma18g02680.1 gene at the <it>Rhg1 </it>locus that encodes an apparent leucine-rich repeat transmembrane receptor-kinase (LRR-kinase) has been proposed to be the SCN resistance gene, but its function has not been confirmed. Generation of fertile transgenic soybean lines is difficult but methods have been published that test SCN resistance in transgenic roots generated with <it>Agrobacterium rhizogenes</it>.</p> <p>Results</p> <p>We report use of artificial microRNA (amiRNA) for gene silencing in soybean, refinements to transgenic root SCN resistance assays, and functional tests of the <it>Rhg1 </it>locus LRR-kinase gene. A nematode demographics assay monitored infecting nematode populations for their progress through developmental stages two weeks after inoculation, as a metric for SCN resistance. Significant differences were observed between resistant and susceptible control genotypes. Introduction of the <it>Rhg1 </it>locus LRR-kinase gene (genomic promoter/coding region/terminator; Peking/PI 437654-derived SCN-resistant source), into <it>rhg1</it><sup>- </sup>SCN-susceptible plant lines carrying the resistant-source <it>Rhg4</it><sup><it>+ </it></sup>locus, provided no significant increases in SCN resistance. Use of amiRNA to reduce expression of the LRR-kinase gene from the <it>Rhg1 </it>locus of Fayette (PI 88788 source of <it>Rhg1</it>) also did not detectably alter resistance to SCN. However, silencing of the LRR-kinase gene did have impacts on root development.</p> <p>Conclusion</p> <p>The nematode demographics assay can expedite testing of transgenic roots for SCN resistance. amiRNAs and the pSM103 vector that drives interchangeable amiRNA constructs through a soybean polyubiqutin promoter (Gmubi), with an intron-GFP marker for detection of transgenic roots, may have widespread use in legume biology. Studies in which expression of the <it>Rhg1 </it>locus LRR-kinase gene from different resistance sources was either reduced or complemented did not reveal significant impacts on SCN resistance.</p

    Mapping Review of Fieldwork Education Literature

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    Fieldwork is an integral phase of occupational therapy education, bolstered by a small but growing evidence base. A broad understanding of the state of that evidence base is necessary to inform the directions for future growth. The purpose of this work was to establish the current state of occupational therapy fieldwork literature, map that literature to recognized criteria for educational research, and identify gaps in the existing literature. Authors followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to conduct a mapping review of articles with a primary focus on fieldwork education of occupational therapy (OT) or occupational therapy assistant (OTA) students in United States (Accreditation for Occupational Therapy Education)-based programs. Mapping criteria included level of education [OT, OTA], level of fieldwork [Level I, Level II], and categories of the AOTA Education Research Agenda - Revised (2018). Sources included four databases (Academic Search Premier, CINAHL, ERIC, PubMed) and one additional journal (Journal of Occupational Therapy Education). A total of 1,619 articles were identified, with 67 articles meeting inclusion criteria. The 67 included articles disproportionately focused on Level II OT fieldwork (53%, n=36), with sparse representation of Level I OTA fieldwork (1.5%, n=1), and addressed only two categories of the Education Research Agenda (2018; 80%, n=54). Level I fieldwork, occupational therapy assistant programs, and large swaths of the associationā€™s Education Research Agenda (2018) were dramatically (or completely) underrepresented in fieldwork education research, suggesting important priorities for the immediate future of occupational therapy fieldwork education
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