522 research outputs found

    Deep Photometry in a Remote M31 Major Axis Field Near G1

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    We present photometry from Hubble Space Telescope (HST)/Wide Field Planetary Camera 2 parallel imagery of a remote M31 field at a projected distance of about 34 kpc from the nucleus near the SW major axis. This field is near the globular cluster G1, and near one of the candidate tidal plumes identified by Ferguson et al. (2002). The F606W (V) and F814W (I) images were obtained in parallel with Space Telescope Imaging Spectrograph spectroscopy of G1 (GO-9099) and total 7.11 hours of integration time -- the deepest HST field in the outer disk of M31 to date, reaching to V ~ 28. The color-magnitude diagram of the field shows a clearly-defined red clump at V = 25.25 and a red giant branch consistent with [Fe/H] ~ -0.7. The lack of a blue horizontal branch contrasts with other M31 halo fields, the Andromeda dwarf spheroidals, and with the nearby globular cluster G1. Comparing the observed luminosity function to the Padova models, we find that at least some of the stellar population must be younger than 6 - 8 Gyr. The outermost detected neutral hydrogen gas disk of M31 lies only 2 kpc in projection from our field. The finding that some giants in the field have radial velocities close to that of the neutral hydrogen gas (Reitzel, Guhathakurta, & Rich 2003) leads us to conclude that our field samples the old, low-surface-brightness disk rather than the true Population II spheroid.Comment: 15 pages, 3 figures. accepted for publication in the A

    Kinematics and Metallicity of M31 Red Giants: The Giant Southern Stream and Discovery of a Second Cold Component at R = 20 kpc

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    We present spectroscopic observations of red giant branch (RGB) stars in the Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck II 10-m telescope. The three fields targeted in this study are in the M31 spheroid, outer disk, and giant southern stream. In this paper, we focus on the kinematics and chemical composition of RGB stars in the stream field located at a projected distance of R = 20 kpc from M31's center. A mix of stellar populations is found in this field. M31 RGB stars are isolated from Milky Way dwarf star contaminants using a variety of spectral and photometric diagnostics. The radial velocity distribution of RGB stars displays a clear bimodality -- a primary peak centered at v = -513 km/s and a secondary one at v = -417 km/s -- along with an underlying broad component that is presumably representative of the smooth spheroid of M31. Both peaks are found to be dynamically cold with intrinsic velocity dispersions of sigma(v) = 16 km/s. The mean metallicity and metallicity dispersion of stars in the two peaks is also found to be similar: [Fe/H] = -0.45 and sigma([Fe/H]) = 0.2. The observed velocity of the primary peak is consistent with that predicted by dynamical models for the stream, but there is no obvious explanation for the secondary peak. The nature of the secondary cold population is unclear: it may represent: (1) tidal debris from a satellite merger event that is superimposed on, but unrelated to, the giant southern stream; (2) a wrapped around component of the giant southern stream; (3) a warp or overdensity in M31's disk at R > 50 kpc (this component is well above the outward extrapolation of the smooth exponential disk brightness profile).Comment: 32 pages, 13 figures, 1 table. Accepted for publication in Ap

    Potential Drug Interactions with Coumadin (Warfarin) and Prozac (Fluoxetine): A Brief Report and Review of the Literature

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    We were asked to see a woman with recurrent depression and a history of deep vein thrombosis. (Consultation and Liaison Service). She had been started initially on Prozac (fluoxetine) and was secondarily started on Coumadin (warfarin). The patient presented with severe bruising of both lower extremities. We were asked to investigate the case to determine if a drug interaction with Prozac had produced the problem. A review of the world\u27s literature failed to produce a report of a drug interaction between Prozac and Coumadin producing a bleeding disorder. Scrutiny of this case could not produce evidence that this occurred. A retrospective analysis of 4 additional cases was performed. None of these patients required adjustment of their Coumadin while on Prozac

    The status of beavers in the delta area of the San Joaquin River, San Joaquin County, California, 1950-1951

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    The term “delta area” refers to a region roughly 40 miles long and 15 miles wide situated 65 miles east of San Francisco Bay where the San Joaquin and Sacramento Rivers join and enter Suisun Bay. The waterways in this area are fresh water from these rivers, but they are affected by the ocean tides and to some extent by the salinity of the ocean water. The rgeion ecompasses about 507,000 acres, most of which has been reclaimed for agricultural purposes by the construction of levees to contain the tides and high waters. The word “islands” is used locally to designate this area. The part played by beavers in the exploration and colonization of this nation was a very important one. The fur trappers in their quest for new areas in which to trap, vigorously explored unknown regions. Knowledge concerning the geography of the new land was passed on the colonists who were eagerly seeking new and suitable sites for home and farms. Thus did the beaver and other fur-bearing animals indirectly speed the development of the nation

    Relation Between Stellar Mass and Star Formation Activity in Galaxies

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    For a mass-selected sample of 66544 galaxies with photometric redshifts from the Cosmic Evolution Survey (COSMOS), we examine the evolution of star formation activity as a function of stellar mass in galaxies. We estimate the cosmic star formation rates (SFR) over the range 0.2 < z < 1.2, using the rest-frame 2800 A flux (corrected for extinction). We find the mean SFR to be a strong function of the galactic stellar mass at any given redshift, with massive systems (log (M/M(Sun)) > 10.5) contributing less (by a factor of ~ 5) to the total star formation rate density (SFRD). Combining data from the COSMOS and Gemini Deep Deep Survey (GDDS), we extend the SFRD-z relation as a function of stellar mass to z~2. For massive galaxies, we find a steep increase in the SFRD-z relation to z~2; for the less massive systems, the SFRD which also increases from z=0 to 1, levels off at z~1. This implies that the massive systems have had their major star formation activity at earlier epochs (z > 2) than the lower mass galaxies. We study changes in the SFRDs as a function of both redshift and stellar mass for galaxies of different spectral types. We find that the slope of the SFRD-z relation for different spectral type of galaxies is a strong function of their stellar mass. For low and intermediate mass systems, the main contribution to the cosmic SFRD comes from the star-forming galaxies while, for more massive systems, the evolved galaxies are the most dominant population.Comment: 34 pages; 8 figures; Accepted for publication in Ap

    Resolution of the type material of the Asian elephant, Elephas maximus Linnaeus, 1758 (Proboscidea, Elephantidae)

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    The understanding of Earth’s biodiversity depends critically on the accurate identification and nomenclature of species. Many species were described centuries ago, and in a surprising number of cases their nomenclature or type material remain unclear or inconsistent. A prime example is provided by Elephas maximus, one of the most iconic and well-known mammalian species, described and named by Linnaeus (1758) and today designating the Asian elephant. We used morphological, ancient DNA (aDNA), and high-throughput ancient proteomic analyses to demonstrate that a widely discussed syntype specimen of E. maximus, a complete foetus preserved in ethanol, is actually an African elephant, genus Loxodonta. We further discovered that an additional E. maximus syntype, mentioned in a description by John Ray (1693) cited by Linnaeus, has been preserved as an almost complete skeleton at the Natural History Museum of the University of Florence. Having confirmed its identity as an Asian elephant through both morphological and ancient DNA analyses, we designate this specimen as the lectotype of E. maximus

    A Radio Survey of Seven Southern X-ray Luminous Clusters of Galaxies

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    The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38 GHz to survey seven southern Abell clusters of galaxies with high X-ray luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters have also been surveyed at 0.843 GHz with the Molonglo Observatory Synthesis Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio sources within the Abell circles centred on their X-ray centroids. We compare their identification fractions, emitted 1.38-GHz and optical powers, radio spectral indices and radial variation in projected source density with those of the radio-selected samples of Slee et al. (1998). We compare our fractional radio luminosity function with that of the radio-selected samples of Ledlow and Owen (1996) and Slee et al. (1998). Three significant differences are noted between X-ray and radio-selected samples of clusters; (1) the X-ray sample has an excess of flat-spectrum radio sources; (2) the fractional radio luminosity function for the FR I sources in the X-ray selected sample is much steeper, implying that fewer of their cluster galaxies become hosts for the stronger FR I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray selected sample. The average excess projected density of radio sources near our cluster centres is approx. 5 times the background source density.Comment: 24 pages, 8 figures, plus 6 figures to be published online only; accepted to appear in MNRA

    Accounting for Institutional Variation in Expected Returns to Higher Education

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    This study leverages human capital theory to identify the correlates of expected returns on investment in higher education at the level of institutions. We leverage estimates of average ROI in post-secondary education among more than 400 baccalaureate degree conferring colleges and universities to understand the correlates of a relatively new metric of institutional ROI. Results indicate that a diverse undergraduate student body, high graduation rate, and public university status are strong, positive, and robustly associated with institutional ROI. The model accounts for more than 70% of inter-university variation in ROI, suggesting that the factors we have identified are among the most important correlates of institutional ROI. We discuss the policy implications of these findings for institutions of higher education in the context of institutional rankings and a rapidly evolving education landscape, giving special attention to student body characteristics colleges and universities

    Nuclear Weapons After the Cold War:Change and Continuity in Public Discourses

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    This dissertation assesses the rhetorical dynamics of American public argumentation about the appropriate role of nuclear weapons since the end of the Cold War. Four case studies are examined, including the controversy created by "fallen priests" like General George Lee Butler, the U.S. Senate's deliberations on ratification of the Comprehensive Test Ban Treaty, the George W. Bush administration's campaign to implement its 2001 Nuclear Posture Review, and the public debate about the development and deployment of "mini" nuclear weapons. Collectively, the case studies reveal that a potent combination of institutional interests, restricted access to official deliberative spaces, the deployment of threat discourses, the presumption that nuclear deterrence was effective during the Cold War, and the utilization of technical discursive practices narrowed the scope of public debate about the role of nuclear weapons and allowed advocates of robust nuclear deterrence to construct rhetorical and policy bridges between the Cold War and post-Cold War eras. "Security" and "risk management" frames dominated public discussions about nuclear weapons, and advocates of nuclear abolition were largely unsuccessful in their efforts to reconfigure public argumentation on nuclear weapons policy

    Capabilities and Skill Configurations of Information Security Incident Responders

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    This paper identifies skill sets that contribute to effective InfoSec incident response. Even though many organizations have staff dedicated to InfoSec incident response teams, there is a lack of consensus as to the skill set each team member needs to effectively perform his/her job, and general and specialized skills that need to be represented in incident response teams (but usually not all held by each team member). Previous guidance was offered based on non-empirical methods. In this study, we used the Repertory Grid (RepGrid) method to elicit lists of incident response skills from industry experts. Skill archetypes were then identified by clustering incident responders who share similar characteristics. The findings extend the Theory of Resource Complements and provide managers with practical guidance regarding the skill sets most critical to the incident response role
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