105 research outputs found

    Review of \u3cem\u3eFreefall: America, Markets and the Sinking of the World Economy.\u3c/em\u3e Joseph E. Stiglitz. Reviewed by Helen Lachs Ginsburg.

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    Book review of Joseph E. Stiglitz, Freefall: America, Markets and the Sinking of the World Economy. New York, N.Y.: W. W. Norton, 2010. $27.95 hardcover

    Review of \u3cem\u3eSocial Security Works! Why Social Security Isn\u27t Going Broke & How Expanding It Will Help Us All\u3c/em\u3e. Nancy J. Altman & Eric R. Kingson. 135 Reviewed by Helen Lachs Ginsburg

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    Nancy J. Altman & Eric R. Kingson, Social Security Works! Why Social Security Isn\u27t Going Broke & How Expanding It Will Help Us All. New Press (2015), 320 pages, $16.95 (paperback)

    The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt

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    We present an overview of the first data release (DR1) and first-look science from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green Bank Telescope to map all Gould Belt star-forming regions with AV7A_V \gtrsim 7 mag visible from the northern hemisphere in emission from NH3_3 and other key molecular tracers. This first release includes the data for four regions in Gould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and Orion A North in Orion. We compare the NH3_3 emission to dust continuum emission from Herschel, and find that the two tracers correspond closely. NH3_3 is present in over 60\% of lines-of-sight with AV7A_V \gtrsim 7 mag in three of the four DR1 regions, in agreement with expectations from previous observations. The sole exception is B18, where NH3_3 is detected toward ~ 40\% of lines-of-sight with AV7A_V \gtrsim 7 mag. Moreover, we find that the NH3_3 emission is generally extended beyond the typical 0.1 pc length scales of dense cores. We produce maps of the gas kinematics, temperature, and NH3_3 column densities through forward modeling of the hyperfine structure of the NH3_3 (1,1) and (2,2) lines. We show that the NH3_3 velocity dispersion, σv{\sigma}_v, and gas kinetic temperature, TKT_K, vary systematically between the regions included in this release, with an increase in both the mean value and spread of σv{\sigma}_v and TKT_K with increasing star formation activity. The data presented in this paper are publicly available.Comment: 33 pages, 27 figures, accepted to ApJS. Datasets are publicly available: https://dataverse.harvard.edu/dataverse/GAS_DR

    Droplets I: Pressure-Dominated Sub-0.1 pc Coherent Structures in L1688 and B18

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    We present the observation and analysis of newly discovered coherent structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using data from the Green Bank Ammonia Survey (GAS), we identify regions of high density and near-constant, almost-thermal, velocity dispersion. Eighteen coherent structures are revealed, twelve in L1688 and six in B18, each of which shows a sharp "transition to coherence" in velocity dispersion around its periphery. The identification of these structures provides a chance to study the coherent structures in molecular clouds statistically. The identified coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4 Msun, generally smaller than previously known coherent cores identified by Goodman et al. (1998), Caselli et al. (2002), and Pineda et al. (2010). We call these structures "droplets." We find that unlike previously known coherent cores, these structures are not virially bound by self-gravity and are instead predominantly confined by ambient pressure. The droplets have density profiles shallower than a critical Bonnor-Ebert sphere, and they have a velocity (VLSR) distribution consistent with the dense gas motions traced by NH3 emission. These results point to a potential formation mechanism through pressure compression and turbulent processes in the dense gas. We present a comparison with a magnetohydrodynamic simulation of a star-forming region, and we speculate on the relationship of droplets with larger, gravitationally bound coherent cores, as well as on the role that droplets and other coherent structures play in the star formation process.Comment: Accepted by ApJ in April, 201

    Ubiquitous NH3\rm NH_3 supersonic component in L1688 coherent cores

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    Context : Star formation takes place in cold dense cores in molecular clouds. Earlier observations have found that dense cores exhibit subsonic non-thermal velocity dispersions. In contrast, CO observations show that the ambient large-scale cloud is warmer and has supersonic velocity dispersions. Aims : We aim to study the ammonia (NH3\rm NH_3) molecular line profiles with exquisite sensitivity towards the coherent cores in L1688 in order to study their kinematical properties in unprecedented detail. Methods : We used NH3\rm NH_3 (1,1) and (2,2) data from the first data release (DR1) in the Green Bank Ammonia Survey (GAS). We first smoothed the data to a larger beam of 1' to obtain substantially more extended maps of velocity dispersion and kinetic temperature, compared to the DR1 maps. We then identified the coherent cores in the cloud and analysed the averaged line profiles towards the cores. Results : For the first time, we detected a faint (mean NH3\rm NH_3(1,1) peak brightness <<0.25 K in TMBT_{MB}), supersonic component towards all the coherent cores in L1688. We fitted two components, one broad and one narrow, and derived the kinetic temperature and velocity dispersion of each component. The broad components towards all cores have supersonic linewidths (MS1\mathcal{M}_S \ge 1). This component biases the estimate of the narrow dense core component's velocity dispersion by \approx28% and the kinetic temperature by \approx10%, on average, as compared to the results from single-component fits. Conclusions : Neglecting this ubiquitous presence of a broad component towards all coherent cores causes the typical single-component fit to overestimate the temperature and velocity dispersion. This affects the derived detailed physical structure and stability of the cores estimated from NH3\rm NH_3 observations.Comment: Accepted for publication in Astronomy & Astrophysics on 06/07/2020. 15 pages, 16 figures, 1 table. Language edits from previous versio

    The Roles of Youth in Society: A Reconceptualization

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    The 1980s have been characterized as a decade of platforms for educational change. In 19S3 alone, five reports were released by national task forces and commissions, all expressing serious concern for the future of youth and society, and all proposing recommendations for ways in which educational policies and practices might be altered, to address such concerns

    Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA

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    Inclusive photoproduction of D*+- mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of 37 pb^-1. Total and differential cross sections as functions of the D* transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured results in a kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure
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