4,399 research outputs found

    The Principal Axis of the Virgo Cluster

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    Using accurate distances to individual Virgo cluster galaxies obtained by the method of Surface Brightness Fluctuations, we show that Virgo's brightest ellipticals have a remarkably collinear arrangement in three dimensions. This axis, which is inclined by 10 to 15 degrees from the line of sight, can be traced to even larger scales where it appears to join a filamentary bridge of galaxies connecting Virgo to the rich cluster Abell 1367. The orientations of individual Virgo ellipticals also show some tendency to be aligned with the cluster axis, as does the jet of the supergiant elliptical M87. These results suggest that the formation of the Virgo cluster, and its brightest member galaxies, have been driven by infall of material along the Virgo-A1367 filament.Comment: 8 pages, 4 figures, accepted for publication in ApJ Letter

    TeV scale resonant leptogenesis from supersymmetry breaking

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    We propose a model of TeV-scale resonant leptogenesis based upon recent models of the generation of light neutrino masses from supersymmetry-breaking effects with TeV-scale right-handed (rhd) neutrinos, NiN_i. The model leads to naturally large cosmological lepton asymmetries via the resonant behaviour of the one-loop self-energy contribution to NiN_i decay. Our model addresses the primary problems of previous phenomenological studies of low-energy leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa couplings so that the out-of equilibrium condition for NiN_i decay is satisfied; the origin of the tiny, but non-zero mass splitting required between at least two NiN_i masses; and the necessary non-trivial breaking of flavour symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos and their superpartners, and the TeV-scale AA-terms automatically contained within the model offer opportunities for partial direct experimental tests of this leptogenesis mechanism at future colliders.Comment: 10 Pages latex, version for JHE

    Northern Bobwhite Survival, Nest Success, and Habitat Use in Kentucky During the Breeding Season

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    Northern bobwhite (Colinus virginianus) populations have experienced protracted declines over much of their range. There has been an annual decrease of 2.61% since the 1960s in Kentucky, an area representative of the Mid-South where there is a lack of data on basic population parameters. Much of the decline is attributed to prevailing land-use practices and associated habitat loss. We monitored northern bobwhite on a 515-ha farm in Oldham County, Kentucky to assess survival rates, nest success rates, and habitat use in the Mid- South. The farm consisted of row crops, cool-season pastures and hay (primarily tall fescue), fallow native warm-season grass fields, and woods. We captured birds using baited funnel traps and fitted them with harness radio transmitters and monitored them daily during April–August, 2009 and 2010. We radiomarked 88 birds (40 females, 48 males) and monitored 24 nests, 9 (37.5%) of which were successful, over the 2 years. Survival rates were 25.3 and 27.9% for 2009 and 2010, respectively, based on estimates from Program MARK. Home range size (54.0, range 1⁄4 38.0–55.9 ha) did not differ by sex, age, or year (P .0.05). Quail favored food plots in both years and avoided developed areas

    Defect tolerance in as-deposited selenium-alloyed cadmium telluride solar cells

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    The efficiency of cadmium telluride (CdTe) solar cells is limited primarily by voltage, which is known to depend on the carrier concentration and carrier lifetimes within the absorber layer of the cell. Here, cathodoluminescence measurements are made on an as-deposited CdSeTe/CdTe solar cell that show that selenium alloyed CdTe material luminesces much more strongly than non-alloyed CdTe. This reduction in non-radiative recombination in the CdSeTe suggests that the selenium gives it a certain defect tolerance. This has implications for carrier lifetimes and voltages in cadmium telluride solar cells

    A New Sample of Cool Subdwarfs from SDSS: Properties and Kinematics

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    We present a new sample of M subdwarfs compiled from the 7th data release of the Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample significantly increases the number of spectroscopically confirmed low-mass subdwarfs. This catalog also includes 905 extreme and 534 ultra sudwarfs. We present the entire catalog including observed and derived quantities, and template spectra created from co-added subdwarf spectra. We show color-color and reduced proper motion diagrams of the three metallicity classes, which are shown to separate from the disk dwarf population. The extreme and ultra subdwarfs are seen at larger values of reduced proper motion as expected for more dynamically heated populations. We determine 3D kinematics for all of the stars with proper motions. The color-magnitude diagrams show a clear separation of the three metallicity classes with the ultra and extreme subdwarfs being significantly closer to the main sequence than the ordinary subdwarfs. All subdwarfs lie below (fainter) and to the left (bluer) of the main sequence. Based on the average (U,V,W)(U,V,W) velocities and their dispersions, the extreme and ultra subdwarfs likely belong to the Galactic halo, while the ordinary subdwarfs are likely part of the old Galactic (or thick) disk. An extensive activity analysis of subdwarfs is performed using Hα\alpha emission and 208 active subdwarfs are found. We show that while the activity fraction of subdwarfs rises with spectral class and levels off at the latest spectral classes, consistent with the behavior of M dwarfs, the extreme and ultra subdwarfs are basically flat.Comment: 66 pages, 23 figures, accepted in Ap

    A Computational Fluid Dynamics Study of Swirling Flow Reduction by using Anti-vortex Baffle

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    An anti-vortex baffle is a liquid propellant management device placed adjacent to an outlet of the propellant tank. Its purpose is to substantially reduce or eliminate the formation of free surface dip and vortex, as well as prevent vapor ingestion into the outlet, as the liquid drains out through the flight. To design an effective anti-vortex baffle, Computational Fluid Dynamic (CFD) simulations were undertaken for the NASA Ares I vehicle LOX tank subjected to the simulated flight loads with and without the anti-vortex baffle. The Six Degree-Of-Freedom (6- DOF) dynamics experienced by the Crew Launch Vehicle (CLV) during ascent were modeled by modifying the momentum equations in a CFD code to accommodate the extra body forces from the maneuvering in a non-inertial frame. The present analysis found that due to large moments, the CLV maneuvering has significant impact on the vortical flow generation inside the tank. Roll maneuvering and side loading due to pitch and yaw are shown to induce swirling flow. The vortical flow due to roll is symmetrical with respect to the tank centerline, while those induced by pitch and yaw maneuverings showed two vortices side by side. The study found that without the anti-vortex baffle, the swirling flow caused surface dip during the late stage of drainage and hence early vapor ingestion. The flow can also be non-uniform in the drainage pipe as the secondary swirling flow velocity component can be as high as 10% of the draining velocity. An analysis of the vortex dynamics shows that the swirling flow in the drainage pipe during the Upper Stage burn is mainly the result of residual vortices inside the tank due to conservation of angular momentum. The study demonstrated that the swirling flow in the drainage pipe can be effectively suppressed by employing the anti-vortex baffle

    A backward glance of who and what marketing scholars have been researching 1977-2002

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    Despite the diversity of all those involved within the marketing discipline, all have a stake in maximizing the advancement of marketing knowledge. Without a specific analysis it is difficult to reflect on where a field has been or where it might be heading. The purpose of this chapter is to examine who and what marketing scholars have been researching over the period 1977&ndash;2002 using content analysis. This chapter provides longitudinal benchmarking of the &lsquo;&lsquo;inputs&rsquo;&rsquo; (authors and institutions) and &lsquo;&lsquo;outputs&rsquo;&rsquo; (articles) examining the marketing literature in the four major marketing journals: the Journal of Marketing, the Journal of Marketing Research, the Journal of Consumer Research, and the Journal of the Academy of Marketing Science.<br /
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