2,832 research outputs found

    Discovery of Photospheric Calcium Line Strength Variations in the DAZd White Dwarf G29-38

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    Metals in the photospheres of white dwarfs with Teff between 12,000 and 25,000 K should gravitationally settle out of these atmospheres in 1-2 weeks. Temporal variations in the line strengths of these metals could provide a direct measurement of episodic metal accretion. Using archival VLT and Keck spectroscopy, we find evidence that the DAZd white dwarf G29-38 shows significant changes in its Ca II K line strength. At the two best-observed epochs, we find that the Ca line equivalent width (EW) = 165 +- 4 mA (in 1996.885) and 280 +- 8 mA (in 1999.653), which is an increase of 70%. We consider the effect that pulsation has on the Ca EWs for this known variable star, and find that it adds an error of < 1 mA to these measurements. Calcium line strengths at other observational epochs support variations with timescales as short as two weeks. These Ca EW variations indicate that the metal accretion process in G29-38, presumably from its debris disk, is episodic on timescales of a few weeks or less, and thus the accretion is not dominated by Poynting-Robertson drag from an optically thin, continuous disk, which has a timescale of ~1 year.Comment: 15 pages, 4 figures, ApJ accepte

    A new species of the spittlebug genus \u3ci\u3eClastoptera\u3c/i\u3e Germar (Hemiptera: Cercopoidea: Clastopteridae) on Florida oaks

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    Over the past decade, a previously unrecorded spittlebug of the genus Clastoptera Germar (Hemip­tera: Cercopoidea: Clastopteridae) has been observed in abundance on oaks (Quercus L. spp., Fagaceae) in several Florida counties. We describe this spittlebug as a new species, Clastoptera querci Thompson, Halbert and Rothschild, new species, provide information on its life history, host plants and distribution, and place it in the context of other members of the genus. Clastoptera spp. can transmit Xylella fastidiosa Wells et al., a bacterial pathogen that causes bacterial leaf scorch associated with oak decline. Thus C. querci should be monitored as a possible vector of X. fastidiosa in oaks

    Geographic risk modeling of childhood cancer relative to county-level crops, hazardous air pollutants and population density characteristics in Texas

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    <p>Abstract</p> <p>Background</p> <p>Childhood cancer has been linked to a variety of environmental factors, including agricultural activities, industrial pollutants and population mixing, but etiologic studies have often been inconclusive or inconsistent when considering specific cancer types. More specific exposure assessments are needed. It would be helpful to optimize future studies to incorporate knowledge of high-risk locations or geographic risk patterns. The objective of this study was to evaluate potential geographic risk patterns in Texas accounting for the possibility that multiple cancers may have similar geographic risks patterns.</p> <p>Methods</p> <p>A spatio-temporal risk modeling approach was used, whereby 19 childhood cancer types were modeled as potentially correlated within county-years. The standard morbidity ratios were modeled as functions of intensive crop production, intensive release of hazardous air pollutants, population density, and rapid population growth.</p> <p>Results</p> <p>There was supportive evidence for elevated risks for germ cell tumors and "other" gliomas in areas of intense cropping and for hepatic tumors in areas of intense release of hazardous air pollutants. The risk for Hodgkin lymphoma appeared to be reduced in areas of rapidly growing population. Elevated spatial risks included four cancer histotypes, "other" leukemias, Central Nervous System (CNS) embryonal tumors, CNS other gliomas and hepatic tumors with greater than 95% likelihood of elevated risks in at least one county.</p> <p>Conclusion</p> <p>The Bayesian implementation of the Multivariate Conditional Autoregressive model provided a flexible approach to the spatial modeling of multiple childhood cancer histotypes. The current study identified geographic factors supporting more focused studies of germ cell tumors and "other" gliomas in areas of intense cropping, hepatic cancer near Hazardous Air Pollutant (HAP) release facilities and specific locations with increased risks for CNS embryonal tumors and for "other" leukemias. Further study should be performed to evaluate potentially lower risk for Hodgkin lymphoma and malignant bone tumors in counties with rapidly growing population.</p

    Pulsational Mapping of Calcium Across the Surface of a White Dwarf

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    We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a model for polar accretion of calcium and rules out equatorial accretion

    A Concept Paper for a VCU Social Sciences Initiative

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    This project proposes the development of a Social Sciences Initiative at the undergraduate and graduate levels that will provide educational, research and service opportunities for faculty and students. These opportunities are envisioned as interdisciplinary, with a focus on community issues and priorities, and with the potential to create new links among existing educational/research units within the University. The development of a Social Sciences Initiative provides a direct link to the Mission of VCU through several of the Mission’s intents: “activities that increase knowledge and understanding of the world and inspire and enrich teaching” The Social Sciences Initiative will expand current activities and promote innovative teaching in an interdisciplinary manner. “diverse educational programs” The Social Sciences Initiative increases the diversity of educational program offerings. “development of innovative approaches to meet the changing needs of our society” The Social Sciences Initiative will directly address the changing societal needs through support of interdisciplinary education, research, and service. Further, this initiative is consistent with the VCU Vision in that it will “advance a climate of scholarly inquiry…serve as a model of diversity in higher education…addressing urban issues in the nation and the world…build upon its substantial foundations in the…applied social sciences.” (VCU Strategic Plan for the Future of Virginia Commonwealth University, Phase II, 1998)
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