A Detailed Study of Giants and Horizontal Branch Stars in M68: Atmospheric Parameters and Chemical Abundances

In this paper, we present a detailed high-resolution spectroscopic study of post main sequence stars in the Globular Cluster M68. Our sample, which covers a range of 4000 K in $T_{eff}$, and 3.5 dex in $log(g)$, is comprised of members from the red giant, red horizontal, and blue horizontal branch, making this the first high-resolution globular cluster study covering such a large evolutionary and parameter space. Initially, atmospheric parameters were determined using photometric as well as spectroscopic methods, both of which resulted in unphysical and unexpected $T_{eff}$, $log(g)$, $\xi_{t}$, and [Fe/H] combinations. We therefore developed a hybrid approach that addresses most of these problems, and yields atmospheric parameters that agree well with other measurements in the literature. Furthermore, our derived stellar metallicities are consistent across all evolutionary stages, with $\langle$[Fe/H]$\rangle$ = $-$2.42 ($\sigma$ = 0.14) from 25 stars. Chemical abundances obtained using our methodology also agree with previous studies and bear all the hallmarks of globular clusters, such as a Na-O anti-correlation, constant Ca abundances, and mild $r$-process enrichment.Comment: Accepted to the Astronomical Journa

The Structure of Koolau Volcano from Seismic Refraction Studies

Volume: 19Start Page: 306End Page: 31

The Abundances Of Neutron-Capture Species In The Very Metal-Poor Globular Cluster M15: A Uniform Analysis Of Red Giant Branch And Red Horizontal Branch Stars

The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Delta(RHB-RGB) approximate to 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.National Science Foundation AST 07-07447, AST 09-08978Astronom

Migrating learning management systems: A case of a large public university

In the past 20 years, institutions of higher education have made major investments in Learning Management Systems (LMSs). As institutions have integrated the LMS into campus culture, the potential of migrating to not only an upgraded version of the LMS, but also an entirely different LMS, has become a reality. This qualitative research study examines the perspectives of five stakeholders involved with the migration of an LMS at a major research institution in the southeastern United States. Using Lewin’s (1947) Change Management Model and Enterprise Resource Planning (ERP) Model as analogies, this research seeks to understand the role and responsibilities of the various stakeholders, their decision-making, and the implications of the decisions on the migration process. Using Glaser and Strauss’s (1967) constant comparative method and Charmaz’s (2006) work related to grounded theory, four major categories emerged from our data: time as a catalyst for change, power of communication, compatibility of technologies, and faith in the system. The categories contribute to a preliminary model that may assist other institutions as they consider whether to migrate LMSs

Flight Calibration of four airspeed systems on a swept-wing airplane at Mach numbers up to 1.04 by the NACA radar-phototheodolite method

The calibrations of four airspeed systems installed in a North American F-86A airplane have been determined in flight at Mach numbers up to 1.04 by the NACA radar-phototheodolite method. The variation of the static-pressure error per unit indicated impact pressure is presented for three systems typical of those currently in use in flight research, a nose boom and two different wing-tip booms, and for the standard service system installed in the airplane. A limited amount of information on the effect of airplane normal-force coefficient on the static-pressure error is included. The results are compared with available theory and with results from wind-tunnel tests of the airspeed heads alone. Of the systems investigated, a nose-boom installation was found to be most suitable for research use at transonic and low supersonic speeds because it provided the greatest sensitivity of the indicated Mach number to a unit change in true Mach number at very high subsonic speeds, and because it was least sensitive to changes in airplane normal-force coefficient. The static-pressure error of the nose-boom system was small and constant above a Mach number of 1.03 after passage of the fuselage bow shock wave over the airspeed head

Undergraduate medical students’ readiness for online learning at a South African university: Implications for decentralised training

Background. Decentralised teaching has the potential to transform medical education but requires greater use of online learning to address some of the challenges of decentralised teaching in low- and middle-income countries. Given the digital divide that exists in South Africa (SA), it is necessary to establish the extent of student readiness for the broader implementation of online learning. Objectives. To determine medical students’ device ownership, usage and attitudes towards online learning at the University of the Witwatersrand, Johannesburg. Methods. A cross-sectional survey of first-, third- and sixth-year students was conducted in 2017. The questionnaire included open- and closed-ended questions. Quantitative data were analysed using frequency and custom tables and Kruskal-Wallis one-way analysis of variance (ANOVA) tests. Open-ended responses were analysed using content analysis. Results. The survey response rate was 48.5% (448/924). No significant differences in device usage and attitudes towards online learning were observed across the 3 years of study. Most respondents (99%) owned internet-capable devices, and >90% wanted some degree of online learning. The perceived barriers included poor internet connectivity on university campuses and the high cost of data in SA. Conclusion. The majority of respondents owned internet-capable devices and requested more online learning, but the socioeconomic disparities in the country raise concerns about students’ readiness. Wider online learning requires policy decisions to ensure not only access to devices and data but also the implementation of online learning in ways that avoid further disadvantaging already disadvantaged students. Institutional barriers must be addressed before an expanded online learning environment can be considered

Chern-Simons Theory on S^1-Bundles: Abelianisation and q-deformed Yang-Mills Theory

We study Chern-Simons theory on 3-manifolds $M$ that are circle-bundles over 2-dimensional surfaces $\Sigma$ and show that the method of Abelianisation, previously employed for trivial bundles $\Sigma \times S^1$, can be adapted to this case. This reduces the non-Abelian theory on $M$ to a 2-dimensional Abelian theory on $\Sigma$ which we identify with q-deformed Yang-Mills theory, as anticipated by Vafa et al. We compare and contrast our results with those obtained by Beasley and Witten using the method of non-Abelian localisation, and determine the surgery and framing presecription implicit in this path integral evaluation. We also comment on the extension of these methods to BF theory and other generalisations.Comment: 37 pages; v2: references adde