26,624 research outputs found

    Implicit Large-Eddy Simulations of Hot and Cold Supersonic Jets in Loci-CHEM

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    This paper introduces a 4th-order accurate low-dissipation flux scheme for use on un- structured CFD codes, and compares this flux scheme with two others for LES calculations of hot and cold supersonic jets. The flux schemes are compared with experimental profiles of jet centerline Mach number, total temperature and total pressure, with jet spreading rate data, and with near- field acoustic measurements. The influence of grid resolution on these solution accuracy is also evaluated. The new low-dissipation flux scheme is shown to be stable on a high-speed compressible turbulent ow problem, and to be significantly more accurate than the existing baseline flux approach

    Adaptive Optics Near-Infrared Spectroscopy of the Sgr A* Cluster

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    We present K-band λ/Δλ\lambda/\Delta\lambda ~ 2600 spectroscopy of five stars (K ~ 14 - 16 mag) within 0.''5 of Sgr A*, the radio source associated with the compact massive object suspected to be a 2.6 x 106^{6} \msun black hole at the center of our Galaxy. High spatial resolution of ~ 0.''09, and good strehl ratios of ~ 0.2 achieved with adaptive optics on the 10-meter Keck telescope make it possible to measure moderate-resolution spectra of these stars individually for the first time. Two stars (S0-17 and S0-18) are identified as late-type stars by the detection of CO bandhead absorption in their spectra. Their absolute K magnitudes and CO bandhead absorption strengths are consistent with early K giants. Three stars (S0-1, S0-2, and S0-16), with rproj_{proj} << 0.0075 pc (~ 0.''2) from Sgr A*, lack CO bandhead absorption, confirming the results of earlier lower spectral and lower spatial resolution observations that the majority of the stars in the Sgr A* Cluster are early-type stars. The absolute K magnitudes of the early-type stars suggest that they are late O - early B main sequence stars of ages << 20 Myr. The presence of young stars in the Sgr A* Cluster, so close to the central supermassive black hole, poses the intriguing problem of how these stars could have formed, or could have been brought, within its strong tidal field.Comment: 19 pages, 8 figures, 2 tables. Accepted for publication in Ap

    QSO hosts and environments at z=0.9 to 4.2: JHK images with adaptive optics

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    We have observed nine QSOs with redshifts 0.85 to 4.16 at near-IR wavelengths with the adaptive optics bonnette of the Canada-France-Hawaii telescope. Exposure times ranged from 1500 to 24000s (mostly near 7000s) in J, H, or K bands, with pixels 0.035 arcsec on the sky. The FWHM of the co-added images at the location of the quasars are typically 0.16 arcsec. Including another QSO published previously, we find associated QSO structure in at least eight of ten objects, including the QSO at z = 4.16. The structures seen in all cases include long faint features which appear to be tidal tails. In four cases we have also resolved the QSO host galaxy, but find them to be smooth and symmetrical: future PSF removal may expand this result. Including one object previously reported, of the nine objects with more extended structure, five are radio-loud, and all but one of these appear to be in a dense small group of compact galaxy companions. The radio-quiet objects do not occupy the same dense environments, as seen in the NIR. In this small sample we do not find any apparent trends of these properties with redshift, over the range 0.8 < z < 2.4. The colors of the host galaxies and companions are consistent with young stellar populations at the QSO redshift. Our observations suggest that adaptive optic observations in the visible region will exhibit luminous signatures of the substantial star-formation activity that must be occurring.Comment: 22 pages including 10 tables, plus 11 figures. To appear in A

    Can analyses of electronic patient records be independently and externally validated? The effect of statins on the mortality of patients with ischaemic heart disease: a cohort study with nested case-control analysis

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    Objective To conduct a fully independent and external validation of a research study based on one electronic health record database, using a different electronic database sampling the same population. Design Using the Clinical Practice Research Datalink (CPRD), we replicated a published investigation into the effects of statins in patients with ischaemic heart disease (IHD) by a different research team using QResearch. We replicated the original methods and analysed all-cause mortality using: (1) a cohort analysis and (2) a case-control analysis nested within the full cohort. Setting Electronic health record databases containing longitudinal patient consultation data from large numbers of general practices distributed throughout the UK. Participants CPRD data for 34 925 patients with IHD from 224 general practices, compared to previously published results from QResearch for 13 029 patients from 89 general practices. The study period was from January 1996 to December 2003. Results We successfully replicated the methods of the original study very closely. In a cohort analysis, risk of death was lower by 55% for patients on statins, compared with 53% for QResearch (adjusted HR 0.45, 95% CI 0.40 to 0.50; vs 0.47, 95% CI 0.41 to 0.53). In case-control analyses, patients on statins had a 31% lower odds of death, compared with 39% for QResearch (adjusted OR 0.69, 95% CI 0.63 to 0.75; vs OR 0.61, 95% CI 0.52 to 0.72). Results were also close for individual statins. Conclusions Database differences in population characteristics and in data definitions, recording, quality and completeness had a minimal impact on key statistical outputs. The results uphold the validity of research using CPRD and QResearch by providing independent evidence that both datasets produce very similar estimates of treatment effect, leading to the same clinical and policy decisions. Together with other non-independent replication studies, there is a nascent body of evidence for wider validity

    Blunt traumatic celiac artery avulsion managed with celiac artery ligation and open aorto-celiac bypass.

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    Traumatic celiac artery injuries are rare and highly lethal with reported mortality rates of 38-62%. The vast majority are caused by penetrating trauma with only 11 reported cases due to blunt trauma (Graham et al., 1978; Asensio et al., 2000, 2002). Only 3 of these cases were complete celiac artery avulsions. Management options described depend upon the type of injury and have included medical therapy with anti-platelet agents or anti-coagulants, endovascular stenting, and open ligation. We report a case of a survivor of complete celiac artery avulsion from blunt trauma managed by open bypass

    Gauged Dimension Bubbles

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    Some of the peculiar electrodynamical effects associated with gauged ``dimension bubbles'' are presented. Such bubbles, which effectively enclose a region of 5d spacetime, can arise from a 5d theory with a compact extra dimension. Bubbles with thin domain walls can be stabilized against total collapse by the entrapment of light charged scalar bosons inside the bubble, extending the idea of a neutral dimension bubble to accommodate the case of a gauged U(1) symmetry. Using a dielectric approach to the 4d dilaton-Maxwell theory, it is seen that the bubble wall is almost totally opaque to photons, leading to a new stabilization mechanism due to trapped photons. Photon dominated bubbles very slowly shrink, resulting in a temperature increase inside the bubble. At some critical temperature, however, these bubbles explode, with a release of radiation.Comment: 14 pages, no figures; to appear in Phys.Rev.

    Individual Nurse Productivity in Preparing Patients for Discharge Is Associated with Patient Likelihood of 30-Day Return to Hospital

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    Objective: Applied to value-based health care, the economic term “individual productivity” refers to the quality of an outcome attributable through a care process to an individual clinician. This study aimed to (1) estimate and describe the discharge preparation productivities of individual acute care nurses and (2) examine the association between the discharge preparation productivity of the discharging nurse and the patient’s likelihood of a 30-day return to hospital [readmission and emergency department (ED) visits]. Research Design: Secondary analysis of patient-nurse data from a cluster-randomized multisite study of patient discharge readiness and readmission. Patients reported discharge readiness scores; postdischarge outcomes and other variables were extracted from electronic health records. Using the structure-process-outcomes model, we viewed patient readiness for hospital discharge as a proximal outcome of the discharge preparation process and used it to measure nurse productivity in discharge preparation. We viewed hospital return as a distal outcome sensitive to discharge preparation care. Multilevel regression analyses used a split-sample approach and adjusted for patient characteristics. Subjects: A total 522 nurses and 29,986 adult (18+ y) patients discharged to home from 31 geographically diverse medical-surgical units between June 15, 2015 and November 30, 2016. Measures: Patient discharge readiness was measured using the 8-item short form of Readiness for Hospital Discharge Scale (RHDS). A 30-day hospital return was a categorical variable for an inpatient readmission or an ED visit, versus no hospital return. Results: Variability in individual nurse productivity explained 9.07% of variance in patient discharge readiness scores. Nurse productivity was negatively associated with the likelihood of a readmission (−0.48 absolute percentage points, P\u3c0.001) and an ED visit (−0.29 absolute percentage points, P=0.042). Conclusions: Variability in individual clinician productivity can have implications for acute care quality patient outcomes

    Book Reviews

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    Reviews of the following books: Lewiston: A Textile City in Transition by James S. Leamon; Massachusetts: A Bibliography of its History edited by John D. Haskell; Bibliography of Maine, 1960-1975 compiled by Eric S. Flower; Maine in the Revolution: A Reader\u27s Guide compiled by Edwin A. Churchill and James Leamon; Maine Communities and War for Independence: A Guide for Study of Local Maine History as Related to the American Revolution compiled by Edwin A Churchill
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