5,844 research outputs found

    Discovery of a New Dusty B[e] Star in the Small Magellanic Cloud

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    We present new optical spectroscopic and archival Spitzer IRAC photometric observations of a B-type star in the SMC cluster NGC 346, NGC 346:KWBBe 200. We detect numerous Fe II, [O I], and [Fe II] lines, as well as strong P-Cygni profile H I emission lines in its optical spectrum. The star's near-IR color and optical to IR SED clearly indicate the presence of an infrared excess, consistent with the presence of gas and warm, T ~800 K, circumstellar dust. Based on a crude estimate of the star's luminosity and the observed spectroscopic line profile morphologies, we find that the star is likely to be a B-type supergiant. We suggest that NGC 346:KWBBe 200 is a newly discovered B[e] supergiant star, and represents the fifth such object to be identified in the SMC.Comment: 12 pages, accepted by Ap

    HFE and transferrin directly compete for transferrin receptor in solution and at the cell surface

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    Transferrin receptor (TfR) is a dimeric cell surface protein that binds both the serum iron transport protein transferrin (Fe-Tf) and HFE, the protein mutated in patients with the iron overload disorder hereditary hemochromatosis. HFE and Fe-Tf can bind simultaneously to TfR to form a ternary complex, but HFE binding to TfR lowers the apparent affinity of the Fe-Tf/TfR interaction. This apparent affinity reduction could result from direct competition between HFE and Fe-Tf for their overlapping binding sites on each TfR polypeptide chain, from negative cooperativity, or from a combination of both. To explore the mechanism of the affinity reduction, we constructed a heterodimeric TfR that contains mutations such that one TfR chain binds only HFE and the other binds only Fe-Tf. Binding studies using a heterodimeric form of soluble TfR demonstrate that TfR does not exhibit cooperativity in heterotropic ligand binding, suggesting that some or all of the effects of HFE on iron homeostasis result from competition with Fe-Tf for TfR binding. Experiments using transfected cell lines demonstrate a physiological role for this competition in altering HFE trafficking patterns

    Advanced mission analysis programs

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    Computer programs provide preliminary trajectory and guidance information required for feasibility studies in space mission analysis. The advanced mission analysis computer programs include programs for approximate solutions, programs for targeting and output, and programs for Monte Carlo and linear guidance analysis

    Power to the people : evidence from a randomized field experiment of a community-based monitoring project in Uganda

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    This paper analyzes the importance of strengthening the relationship of accountability between health service providers and citizens for improving access to and quality of health care. How this is to be achieved, and whether it works, however, remain open questions. The paper presents a randomized field experiment on increasing community-based monitoring. As communities began to more extensively monitor the provider, both the quality and quantity of health service provision improved. One year into the program, there are large increases in utilization, significant weight-for-age z-score gains of infants, and markedly lower deaths among children. The findings on staff behavior suggest that the improvements in quality and quantity of health service delivery resulted from an increased effort by the staff to serve the community. Overall, the results suggest that community monitoring can play an important role in improving service delivery when traditional top-down supervision is ineffective.Health Monitoring&Evaluation,Housing&Human Habitats,Health Economics&Finance,Disease Control&Prevention,Health Systems Development&Reform

    Few and Far Between: How HIV May Be Evading Antibody Avidity

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