5,628 research outputs found

    Recombinant Charmonium in strongly coupled Quark-Gluon Plasma

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    We update our previous work of a Langevin-with-interaction model for charmonium in heavy-ion collisions, by considering the effect due to recombination. We determine the contribution to J/psi yields from charm-anticharm pairs whose constituent quarks originate from two different hard processes. Like the surviving J/psi states, the recombinant J/psi also undergo both a stochastic interaction, determined by a hydrodynamical simulation of the heavy-ion collision, and an interaction determined by the heavy quark-antiquark potentials measured on the lattice for appropriate temperatures. From the results of these simulations, we determine both the direct and the recombinant contribution to the J/psi yields for RHIC conditions, and find that for central collisions, between 30% and 50% of the J/psi yield is due to recombinant production. We compare our results with other models and look for how the recombinant contribution differs from the surviving contribution in the differential p_t yields. Including the recombinant contribution improves the agreement with the latest analysis of charmonium at RHIC, which shows an absence of anomalous suppression except in the most central collisions.Comment: 5 pages, 4 figure

    Uniform Silicon Isotope Ratios Across the Milky Way Galaxy

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    We report the relative abundances of the three stable isotopes of silicon, 28^{28}Si, 29^{29}Si and 30^{30}Si, across the Galaxy using the v=0,J=10v = 0, J = 1 \to 0 transition of silicon monoxide. The chosen sources represent a range in Galactocentric radii (RGCR_{\rm GC}) from 0 to 9.8 kpc. The high spectral resolution and sensitivity afforded by the GBT permit isotope ratios to be corrected for optical depths. The optical-depth-corrected data indicate that the secondary-to-primary silicon isotope ratios 29Si/28Si^{29}{\rm Si}/^{28}{\rm Si} and 30Si/28Si^{30}{\rm Si}/^{28}{\rm Si} vary much less than predicted on the basis of other stable isotope ratio gradients across the Galaxy. Indeed, there is no detectable variation in Si isotope ratios with RGCR_{\rm GC}. This lack of an isotope ratio gradient stands in stark contrast to the monotonically decreasing trend with RGCR_{\rm GC} exhibited by published secondary-to-primary oxygen isotope ratios. These results, when considered in the context of the expectations for chemical evolution, suggest that the reported oxygen isotope ratio trends, and perhaps that for carbon as well, require further investigation. The methods developed in this study for SiO isotopologue ratio measurements are equally applicable to Galactic oxygen, carbon and nitrogen isotope ratio measurements, and should prove useful for future observations of these isotope systems.Comment: 18 pages, 12 figures, 2 tables. Published in The Astrophysical Journal, Volume 839, Issue

    A Hidden Broad-Line Region in the Weak Seyfert 2 Galaxy NGC 788

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    We have detected a broad H alpha emission line in the polarized flux spectrum of the Seyfert 2 galaxy NGC 788, indicating that it contains an obscured Seyfert 1 nucleus. While such features have been observed in ~15 other Seyfert 2s, this example is unusual because it has a higher fraction of galaxy starlight in its spectrum, a lower average measured polarization, and a significantly lower radio luminosity than other hidden Seyfert 1s discovered to date. This demonstrates that polarized broad-line regions can be detected in relatively weak classical Seyfert 2s, and illustrates why well-defined, reasonably complete spectropolarimetric surveys at H alpha are necessary in order to assess whether or not all Seyfert 2s are obscured Seyfert 1s.Comment: 10 pages using (AASTEX) aaspp4.sty and 4 postscript figures. Publications of the Astronomical Society of the Pacific, Research Notes, in pres

    Transitory Eye Shapes and the Vertical Distribution of Two Midwater Squids

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    In two cranchiid squids, Sandalops melancholicus and Taonius pavo, the shapes of the eyes change with growth. Compressed eyes with ocular appendages occur in the larvae living in the upper few hundred meters of the ocean. Tubular eyes occur in juveniles that live within a depth zone between about 400 and 700 m. Nearly hemispherical eyes are found in adults living at depths greater than 700 m. The shapes of the compressed and tubular eyes offer strong countershading advantages to squids living at depths where downwelling light is important in prey-predator relationships

    To Change the World: The Irony, Tragedy, and Possibility of Christianity in the Late Modern World (Book Review)

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    Reviewed Title: Hunter, James Davison. To Change the World: The Irony, Tragedy, and Possibility of Christianity in the Late Modern World. Oxford: Oxford University Press, 2010. 358 pages. ISBN: 978-0-19-973080-3