634 research outputs found

    Dye Tracing Through Thick Unsaturated Zones

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    Using the fluorescent dye Rhodamine WT, a field fluorometer, and direct samples of water collected from springs, wells, cave drips, and pools we have conducted two successful dye traces through thick unsaturated zones in karst regions. The first dye trace was of a proposed expansion site for a landfill in Winona County, southeastern Minnesota. The site sits on top of a narrow ridge about 150 meters above the adjacent valleys. The second trace was at Jewel Cave National Monument in the southern Black Hills of South Dakota. This trace was initiated to evaluate the impact of tourist facilities on the underlying cave. A visitor center was constructed on the surface, 50 to 100 meters directly above the cave. In both traces, small, irregular pulses of dye began to appear (in springs and wells at the Winona Landfill site and in cave drips and pools at Jewel Cave) within days of the dye injection, and the pulses continued to emerge for months. The pulses were typically a day or less in duration and a very small (10s to 100s of parts per trillion, 10- 12 g/g). The pulses are more frequent after major precipitation/runoff events but appear to be moving through both unsaturated zones in a very irregular, stochastic fashion. The very low levels of dye detected in many of the pulses required so.me type of confirmation analysis. We have successfully used the large negative temperature coefficient of Rhodamine WT's fluorescence to discriminate between low levels of Rhodamine WT and fluorescence due to background materials.Winona County and the Legislative Commission on Minnesota Resources. The dye trace of Jewel Cave was supported by a grant (USDI-CX-1200-5-A047) from the National Park Service

    Making Learning Easier: Connecting New Knowledge to Things Students Already Know

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    This is the publisher's version, also found at http://sped.org

    A Pilot Study to Examine Maturation of Body Temperature Control in Preterm Infants

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    To test instrumentation and develop analytic models to use in a larger study to examine developmental trajectories of body temperature and peripheral perfusion from birth in extremely low birth weight (EBLW) infants

    Stealth Branes

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    We discuss the brane world model of Dvali, Gabadadze and Porrati in which branes evolve in an infinite bulk and the brane curvature term is added to the action. If Z_2 symmetry between the two sides of the brane is not imposed, we show that the model admits the existence of "stealth branes" which follow the standard 4D internal evolution and have no gravitational effect on the bulk space. Stealth branes can nucleate spontaneosly in a Minkowski bulk. This process is described by the standard 4D quantum cosmology formalism with tunneling boundary conditions for the brane world wave function. The notorious ambiguity in the choice of boundary conditions is fixed in this case due to the presence of the embedding spacetime. We also point to some problematic aspects of models admitting stealth brane solutions.Comment: 24 pages; Final version, to appear in Phys. Rev. D. The discussion of "embeddability obstruction" is removed (thanks to Takahiro Tanaka who convinced us that there is no such obstruction

    Complementary and alternative medical therapies for chronic low back pain: What treatments are patients willing to try?

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    BACKGROUND: Although back pain is the most common reason patients use complementary and alternative medical (CAM) therapies, little is known about the willingness of primary care back pain patients to try these therapies. As part of an effort to refine recruitment strategies for clinical trials, we sought to determine if back pain patients are willing to try acupuncture, chiropractic, massage, meditation, and t'ai chi and to learn about their knowledge of, experience with, and perceptions about each of these therapies. METHODS: We identified English-speaking patients with diagnoses consistent with chronic low back pain using automated visit data from one health care organization in Boston and another in Seattle. We were able to confirm the eligibility status (i.e., current low back pain that had lasted at least 3 months) of 70% of the patients with such diagnoses and all eligible respondents were interviewed. RESULTS: Except for chiropractic, knowledge about these therapies was low. Chiropractic and massage had been used by the largest fractions of respondents (54% and 38%, respectively), mostly for back pain (45% and 24%, respectively). Among prior users of specific CAM therapies for back pain, massage was rated most helpful. Users of chiropractic reported treatment-related "significant discomfort, pain or harm" more often (23%) than users of other therapies (5–16%). Respondents expected massage would be most helpful (median of 7 on a 0 to 10 scale) and meditation least helpful (median of 3) in relieving their current pain. Most respondents indicated they would be "very likely" to try acupuncture, massage, or chiropractic for their back pain if they did not have to pay out of pocket and their physician thought it was a reasonable treatment option. CONCLUSIONS: Most patients with chronic back pain in our sample were interested in trying therapeutic options that lie outside the conventional medical spectrum. This highlights the need for additional studies evaluating their effectiveness and suggests that researchers conducting clinical trials of these therapies may not have difficulties recruiting patients

    The Chandra Source Catalog

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    The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual X-ray sources, and is designed to satisfy the needs of a broad-based group of scientists, including those who may be less familiar with astronomical data analysis in the X-ray regime. The first release of the CSC includes information about 94,676 distinct X-ray sources detected in a subset of public ACIS imaging observations from roughly the first eight years of the Chandra mission. This release of the catalog includes point and compact sources with observed spatial extents <~ 30''. The catalog (1) provides access to the best estimates of the X-ray source properties for detected sources, with good scientific fidelity, and directly supports scientific analysis using the individual source data; (2) facilitates analysis of a wide range of statistical properties for classes of X-ray sources; and (3) provides efficient access to calibrated observational data and ancillary data products for individual X-ray sources, so that users can perform detailed further analysis using existing tools. The catalog includes real X-ray sources detected with flux estimates that are at least 3 times their estimated 1 sigma uncertainties in at least one energy band, while maintaining the number of spurious sources at a level of <~ 1 false source per field for a 100 ks observation. For each detected source, the CSC provides commonly tabulated quantities, including source position, extent, multi-band fluxes, hardness ratios, and variability statistics, derived from the observations in which the source is detected. In addition to these traditional catalog elements, for each X-ray source the CSC includes an extensive set of file-based data products that can be manipulated interactively.Comment: To appear in The Astrophysical Journal Supplement Series, 53 pages, 27 figure

    Statistical Characterization of the Chandra Source Catalog

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    The first release of the Chandra Source Catalog (CSC) contains ~95,000 X-ray sources in a total area of ~0.75% of the entire sky, using data from ~3,900 separate ACIS observations of a multitude of different types of X-ray sources. In order to maximize the scientific benefit of such a large, heterogeneous data-set, careful characterization of the statistical properties of the catalog, i.e., completeness, sensitivity, false source rate, and accuracy of source properties, is required. Characterization efforts of other, large Chandra catalogs, such as the ChaMP Point Source Catalog (Kim et al. 2007) or the 2 Mega-second Deep Field Surveys (Alexander et al. 2003), while informative, cannot serve this purpose, since the CSC analysis procedures are significantly different and the range of allowable data is much less restrictive. We describe here the characterization process for the CSC. This process includes both a comparison of real CSC results with those of other, deeper Chandra catalogs of the same targets and extensive simulations of blank-sky and point source populations.Comment: To be published in the Astrophysical Journal Supplement Series (Fig. 52 replaced with a version which astro-ph can convert to PDF without issues.

    Niche as a determinant of word fate in online groups

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    Patterns of word use both reflect and influence a myriad of human activities and interactions. Like other entities that are reproduced and evolve, words rise or decline depending upon a complex interplay between {their intrinsic properties and the environments in which they function}. Using Internet discussion communities as model systems, we define the concept of a word niche as the relationship between the word and the characteristic features of the environments in which it is used. We develop a method to quantify two important aspects of the size of the word niche: the range of individuals using the word and the range of topics it is used to discuss. Controlling for word frequency, we show that these aspects of the word niche are strong determinants of changes in word frequency. Previous studies have already indicated that word frequency itself is a correlate of word success at historical time scales. Our analysis of changes in word frequencies over time reveals that the relative sizes of word niches are far more important than word frequencies in the dynamics of the entire vocabulary at shorter time scales, as the language adapts to new concepts and social groupings. We also distinguish endogenous versus exogenous factors as additional contributors to the fates of words, and demonstrate the force of this distinction in the rise of novel words. Our results indicate that short-term nonstationarity in word statistics is strongly driven by individual proclivities, including inclinations to provide novel information and to project a distinctive social identity.Comment: Supporting Information is available here: http://www.plosone.org/article/fetchSingleRepresentation.action?uri=info:doi/10.1371/journal.pone.0019009.s00
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