New cluster members and halo stars of the Galactic globular cluster NGC 1851

NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar evolutionary sequences, light and heavy element abundance variations and indications of a surrounding stellar halo. We present the first results of a spectroscopic study of red giant stars within and outside of the tidal radius of this cluster. Our results identify nine probable new cluster members (inside the tidal radius) with heliocentric radial velocities consistent with that of NGC 1851. We also identify, based on their radial velocities, four probable extratidal cluster halo stars at distances up to ~3.1 times the tidal radius, which are supportive of previous findings that NGC 1851 is surrounded by an extended stellar halo. Proper motions were available for 12 of these 13 stars and all are consistent with that of NGC 1851. Apart from the cluster members and cluster halo stars, our observed radial velocity distribution agrees with the expected distribution from a Besancon disk/N-body stellar halo Milky Way model generated by the Galaxia code, suggesting that no other structures at different radial velocities are present in our field. The metallicities of these stars are estimated using equivalent width measurements of the near infrared calcium triplet absorption lines and are found, within the limitations of this method, to be consistent with that of NGC 1851. In addition we recover 110 red giant cluster members from previous studies based on their radial velocities and identify three stars with unusually high radial velocities.Comment: 10 pages, 8 figures. Accepted for publication in MNRA

New halo stars of the Galactic globular clusters M3 and M13 in the LAMOST DR1 Catalog

M3 and M13 are Galactic globular clusters with previous reports of surrounding stellar halos. We present the results of a search for members and extratidal cluster halo stars within and outside of the tidal radius of these clusters in the LAMOST Data Release 1. We find seven candidate cluster members (inside the tidal radius) of both M3 and M13 respectively. In M3 we also identify eight candidate extratidal cluster halo stars at distances up to ~9.8 times the tidal radius, and in M13 we identify 12 candidate extratidal cluster halo stars at distances up to ~13.8 times the tidal radius. These results support previous indications that both M3 and M13 are surrounded by extended stellar halos, and we find that the GC destruction rates corresponding to the observed mass loss are generally significantly higher than theoretical studies predict.Comment: 21 pages, 10 figures. Accepted for publication in Ap

The application of integral performance criteria to the analysis of discrete maneuvers in a driving simulator

The influence of vehicle transient response characteristics on driver-vehicle performance in discrete maneuvers as measured by integral performance criteria was investigated. A group of eight ordinary drivers was presented with a series of eight vehicle transfer function configurations in a driving simulator. Performance in two discrete maneuvers was analyzed by means of integral performance criteria. Results are presented

Quantitative chemical tagging, stellar ages and the chemo-dynamical evolution of the Galactic disc

The early science results from the new generation of high-resolution stellar spectroscopic surveys, such as GALAH and the Gaia-ESO survey, will represent major milestones in the quest to chemically tag the Galaxy. Yet this technique to reconstruct dispersed coeval stellar groups has remained largely untested until recently. We build on previous work that developed an empirical chemical tagging probability function, which describes the likelihood that two field stars are conatal, that is, they were formed in the same cluster environment. In this work we perform the first ever blind chemical tagging experiment, i.e., tagging stars with no known or otherwise discernable associations, on a sample of 714 disc field stars with a number of high quality high resolution homogeneous metal abundance measurements. We present evidence that chemical tagging of field stars does identify coeval groups of stars, yet these groups may not represent distinct formation sites, e.g. as in dissolved open clusters, as previously thought. Our results point to several important conclusions, among them that group finding will be limited strictly to chemical abundance space, e.g. stellar ages, kinematics, colors, temperature and surface gravity do not enhance the detectability of groups. We also demonstrate that in addition to its role in probing the chemical enrichment and kinematic history of the Galactic disc, chemical tagging represents a powerful new stellar age determination technique.Comment: 12 pages, 9 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS

Intellectual Capital and the Birth of U.S. Biotechnology Enterprises

We examine the relationship between the intellectual capital of scientists making frontier discoveries, the presence of great university bioscience programs, the presence of venture capital firms, other economic variables, and the founding of U.S. biotechnology enterprises during 1976-1989. Using a linked cross-section/time- series panel data set, we find that the timing and location of the birth of biotech enterprises is determined primarily by intellectual capital measures, particularly the local number of highly productive 'star' scientists actively publishing genetic sequence discoveries. Great universities are likely to grow and recruit star scientists, but their effect is separable from the universities. When the intellectual capital measures are included in our poisson regressions, the number of venture capital firms in an area reduces the probability of foundings. At least early in the process, star scientists appear to be the scarce, immobile factors of production. Our focus on intellectual capital is related to knowledge spillovers, but in this case 'natural excludability' permits capture of supranormal returns by scientists. Given this reward structure technology transfer was vigorous without any special intermediating structures. We believe biotechnology may be prototypical of the birth patterns in other innovative industries.

It is time to improve the quality of medical information distributed to students across social media

The ubiquitous nature of social media has meant that its effects on fields outside of social communication have begun to be felt. The generation undergoing medical education are of the generation referred to as “digital natives”, and as such routinely incorporate social media into their education. Social media’s incorporation into medical education includes its use as a platform to distribute information to the public (“distributive education”) and as a platform to provide information to a specific audience (“push education”). These functions have proved beneficial in many regards, such as enabling constant access to the subject matter, other learners, and educators. However, the usefulness of using social media as part of medical education is limited by the vast quantities of poor quality information and the time required to find information of sufficient quality and relevance, a problem confounded by many student’s preoccupation with “efficient” learning. In this Perspective, the authors discuss whether social media has proved useful as a tool for medical education. The current growth in the use of social media as a tool for medical education seems to be principally supported by students’ desire for efficient learning rather than by the efficacy of social media as a resource for medical education. Therefore, improvements in the quality of information required to maximize the impact of social media as a tool for medical education are required. Suggested improvements include an increase in the amount of educational content distributed on social media produced by academic institutions, such as universities and journals

Supersymmetric Brane World Scenarios from Off-Shell Supergravity

Using N=2 off-shell supergravity in five dimensions, we supersymmetrize the brane world scenario of Randall and Sundrum. We extend their construction to include supersymmetric matter at the fixpoints.Comment: 15 pages, no figures, late

The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy

We report on the abundance analysis of two red giants in the faint Hercules dwarf spheroidal (dSph) galaxy. These stars show a remarkable deficiency in the neutron-capture elements, while the hydrostatic alpha-elements (O, Mg) are strongly enhanced. Our data indicate [Ba/Fe] and [Mg/Fe] abundance ratios of <-2 dex and ~+0.8 dex, respectively, with essentially no detection of other n-capture elements. In contrast to the only other dSph star with similar abundance patterns, Dra 119, which has a very low metallicity at [Fe/H]=-2.95 dex, our objects, at [Fe/H]~-2.0 dex, are only moderately metal poor. The measured ratio of hydrostatic/explosive alpha-elements indicates that high-mass (~35 M_sun) Type II supernovae progenitors are the main, if not only, contributors to the enrichment of this galaxy. This suggests that star formation and chemical enrichment in the ultrafaint dSphs proceeds stochastically and inhomogeneously on small scales, or that the IMF was strongly skewed to high mass stars. The neutron capture deficiencies and the [Co/Fe] and [Cr/Fe] abundance ratios in our stars are similar to those in the extremely low metallicity Galactic halo. This suggests that either our stars are composed mainly of the ejecta from the first, massive, population III stars (but at moderately high [Fe/H]), or that SN ejecta in the Hercules galaxy were diluted with ~30 times less hydrogen than typical for extreme metal-poor stars.Comment: 5 pages, 3 figures, accepted by Astrophysical Journal Letter

Social Networks, Learning, and Flexibility: Sourcing Scientific Knowledge in New Biotechnology Firms

We examine how two highly successful new biotechnology firms (NBFs) source their most critical input -- scientific knowledge. We find that scientists at the two NBFs enter into large numbers of collaborative research efforts with scientists at other organizations, especially universities. Formal market contracts are rarely used to govern these exchanges of scientific knowledge. Our findings suggest that the use of boundary-spanning social networks by the two NBFs increases both their learning and their flexibility in ways that would not be possible within a self-contained hierarchical organization.