The Tycho-Gaia astrometric solution. How to get 2.5 million parallaxes with less than one year of Gaia data

Context. The first release of astrometric data from Gaia will contain the mean stellar positions and magnitudes from the first year of observations, and proper motions from the combination of Gaia data with Hipparcos prior information (HTPM). Aims. We study the potential of using the positions from the Tycho-2 Catalogue as additional information for a joint solution with early Gaia data. We call this the Tycho-Gaia astrometric solution (TGAS). Methods. We adapt Gaia's Astrometric Global Iterative Solution (AGIS) to incorporate Tycho information, and use simulated Gaia observations to demonstrate the feasibility of TGAS and to estimate its performance. Results. Using six to twelve months of Gaia data, TGAS could deliver positions, parallaxes and annual proper motions for the 2.5 million Tycho-2 stars, with sub-milliarcsecond accuracy. TGAS overcomes some of the limitations of the HTPM project and allows its execution half a year earlier. Furthermore, if the parallaxes from Hipparcos are not incorporated in the solution, they can be used as a consistency check of the TGAS/HTPM solution.Comment: Accepted for publication in A&A, 24 Dec 201

Gaia astrometry for stars with too few observations - a Bayesian approach

Gaia's astrometric solution aims to determine at least five parameters for each star, together with appropriate estimates of their uncertainties and correlations. This requires at least five distinct observations per star. In the early data reductions the number of observations may be insufficient for a five-parameter solution, and even after the full mission many stars will remain under-observed, including faint stars at the detection limit and transient objects. In such cases it is reasonable to determine only the two position parameters. Their formal uncertainties would however grossly underestimate the actual errors, due to the neglected parallax and proper motion. We aim to develop a recipe to calculate sensible formal uncertainties that can be used in all cases of under-observed stars. Prior information about the typical ranges of stellar parallaxes and proper motions is incorporated in the astrometric solution by means of Bayes' rule. Numerical simulations based on the Gaia Universe Model Snapshot (GUMS) are used to investigate how the prior influences the actual errors and formal uncertainties when different amounts of Gaia observations are available. We develop a criterion for the optimum choice of priors, apply it to a wide range of cases, and derive a global approximation of the optimum prior as a function of magnitude and galactic coordinates. The feasibility of the Bayesian approach is demonstrated through global astrometric solutions of simulated Gaia observations. With an appropriate prior it is possible to derive sensible positions with realistic error estimates for any number of available observations. Even though this recipe works also for well-observed stars it should not be used where a good five-parameter astrometric solution can be obtained without a prior. Parallaxes and proper motions from a solution using priors are always biased and should not be used.Comment: Revised version, accepted 21st of August 2015 for publication in A&

Beta-hydroxybutyrate concentration influences timing of pregnancy in young beef cows

Timing of conception can influence productivity within the cow herd and can be negatively influenced by metabolic dysfunctions. Selection for maternal traits like milk production in beef cattle may decrease reproductive efficiency due to metabolic dysfunctions caused by an increased metabolic load of lactation. Therefore, our objective was to analyze the association of milk production, serum metabolites as an indicator of nutrient status, cow BW and BW change, and calf performance with timing of pregnancy in 183 spring-calving beef cows. Cows were classified by timing of pregnancy as cows that were diagnosed pregnant by timed artificial insemination (TAI; n=118) or natural breeding (NAT; n=65). In addition, cows were grouped by age to represent young (3-to 4-yr-old), mature (5- to 6-yr-old), and old (7- to 9-yrold) cows. Starting approximately d 30 postpartum, cow BW and BCS were recorded and blood samples were collected weekly through the end of breeding. Weekly serum samples were composited by cow within production periods: (1) pre-breeding; (2) timed- artificial insemination to end of natural breeding. Cow BW and BCS did not influence (P \u3e 0.40) timing of pregnancy during the entire study. Calf, BW at birth and weaning were not different (P \u3e 0.30) between timing of pregnancy groups. However, calf BW at weaning and value the subsequent year of the study were greater (P \u3c 0.001) for TAI than NAT cows. An age group × treatment interaction (P \u3c 0.01) occurred for serum β-hydroxybutyrate (BHB). Serum BHB concentrations for mature and old cows were similar regardless of timing of pregnancy. However, serum BHB concentrations for young NAT cows were greater than young TAI cows. In addition, serum NEFA exhibited (P = 0.04) a timing of pregnancy × sampling period interaction. Pre-breeding serum NEFA concentrations were greater for NAT cows than TAI cows. Contrarily, serum NEFA concentrations during the natural breeding season were similar regardless of timing of pregnancy. Results from this study indicate that only the young, postpartum beef cows during early lactation were susceptible to measured metabolic dysfunctions of elevated blood BHB concentrations, which may have caused a delay in timing of pregnancy

Using A Performance-Based Assessment to Measure the Rate at Which Severely Retarded Subjects Learn to Communicate With Signs and Pictures

Severely/profoundly mentally retarded children and adults comprise approximately one tenth of one percent of the general population (Goldstein, 1978). This population of individuals functions at a general developmental level of half or less than the level which would be expected on the basis of chronological age (Justen, 1976)

Improving distances to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia

Starting in 2013, Gaia will deliver highly accurate astrometric data, which eventually will supersede most other stellar catalogues in accuracy and completeness. It is, however, lim- ited to observations from magnitude 6 to 20 and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall Japanese astrometry satellite, will observe these bright stars, but with much lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the main source of accurate distances to bright nearby stars. We are investigating how this might be improved by optimally combining data from all three missions in a joint astrometric solu- tion. This would take advantage of the unique features of each mission: the historic bright-star measurements of Hipparcos, the updated bright-star observations of Nano-JASMINE, and the very accurate reference frame of Gaia. The long temporal baseline between the missions pro- vides additional benefits for the determination of proper motions and binary detection, which indirectly improve the parallax determination further. We present a quantitative analysis of the expected gains based on simulated data for all three missions.Comment: Final draft for the proceedings of the IAU Symposium 289: Advancing the physics of cosmic distances, held in Beijing, China, August 2012, eds. Richard de Grijs and Giuseppe Bono, Cambridge Univ. Pres

Human Capital Indicators and Academic Success in Executive MBA Programs: A multi-program study

This paper investigates various human capital indicators as predictors of academic success for students in Executive MBA programs. Previous literature has focused on student performance in traditional full-time MBA programs and typically only for a single school. Data was examined from two different universities, with over 130 Executive MBA students. Undergraduate GPA had a statistically significant, positive relation to academic success in the Executive MBA program, while other factors, including GMAT scores and age, were not found to be as important in predicting academic success in the Executive MBA programs

Radial migration and vertical action in N-body simulations

We study the radial migration of stars as a function of orbital action as well as the structural properties of a large suite of N-body simulations of isolated disc galaxies. Our goal is to establish a relationship between the radial migration efficiency of stars and their vertical action. We aim to describe how that relationship depends on the relative gravitational dominance between the disc and the dark matter halo. By changing the mass ratio of our disc and dark matter halo we find a relationship between disc dominance, number and strength of spiral arms, and the ensuing radial migration as a function of the vertical action. We conclude that the importance of migration at large vertical action depends on the strength of the spiral arms and therefore the dominance of the disc. Populations with more radial action undergo less radial migration, independently of disc dominance. Our results are important for the future of analytical modelling of radial migration in galaxies and furthers the understanding of radial migration which is a key component of the restructuring of galaxies, including the Milky Way.Comment: 13 pages, 12 figures, accepted for publication in MNRA

PATHOGENIC ROLE OF PHOSPHODIESTERASE TYPE 5 UPREGULATION IN CARDIAC ISCHEMIA/REPERFUSION INJURY

Phosphodiesterase Type 5 (PDE5) inhibitors are cardioprotective against ischemia/reperfusion (I/R) injury. However, it remains uncertain if I/R affects PDE5. We hypothesized that generation of reactive oxygen species (ROS) during I/R leads to upregulation of PDE5, which contributes to pathological changes following acute myocardial infarction (AMI). Adult male ICR mice were subjected to 30 minutes of in vivo or ex vivo I/R. To examine the role of ROS, a subset of hearts were perfused with 100 µM hydrogen peroxide (H2O2). Expression and activity of PDE5, pPDE5, and cGMP-dependent protein kinase (PKG) were measured by Western blots and spectrophotometric assay. The results show that ischemia and I/R significantly increased expression of PDE5. H2O2 had no effect on PDE5 expression and activity but significantly increased PKG activity. We conclude that acute cardiac ischemia or I/R upregulate PDE5 independent of oxidant stress in the heart