A Collision of Subclusters in Abell 754

We present direct evidence of a collision of subclusters in the galaxy cluster Abell 754. Our comparison of new optical data and archival ROSAT PSPC X-ray data reveal three collision signatures predicted by n-body/hydrodynamical simulations of hierarchical cluster evolution. First, there is strong evidence of a non-hydrostatic process; neither of the two major clumps in the galaxy distribution lies on the off-center peak of the X-ray emission from the intracluster gas. Second, the peak of the X-ray emission is elongated perpendicular to the collision axis defined by the centroids of the two galaxy clumps. Third, there is evidence of compression-heated gas; one of A754's two X-ray temperature components (Henry & Briel 1995) is among the hottest observed in any cluster and hotter than that inferred from the velocity dispersion of the associated galaxy clump. These signatures are consistent with the qualitative features of simulations (Evrard 1990a,b) in which two subclusters have collided in the plane of the sky during roughly the last Gyr. The detection of such collisions is crucial for understanding both the dynamics of individual clusters and the underlying cosmology. First, for systems like A754, estimating the cluster X-ray mass from assumptions of hydrostatic equilibrium and isothermality is incorrect and may produce the discrepancies sometimes found between X-ray masses and those derived from gravitational lens models (Babul & Miralda-Escude 1994). Second, the fraction of nearby clusters in which subclusters have collided in the last Gyr is especially sensitive to the mean mass density parameter Omega_0 (cf. Richstone et al. 1992; Evrard et al. 1993; Lacey & Cole 1993). With a large, well-defined cluster sample, it will be possible to place a new and powerful constraint on cosmological models.Comment: 4 pages + 1 color figure (Postscript). Accepted for Publication in ApJ Letter

Students’ Attitudes and Perceptions toward Interprofessional Education

Three scales were administered to measure attitudes of graduate students in health professions prior to their participation in an interprofessional education (IPE) pilot program. Overall, results indicated that students’ attitudes toward IPE were generally positive, but there is room for improvement. Additionally, medical students’ attitudes differed from the other disciplines

Determination of 2-methoxy-3-alkylpyrazines in wine by gas chromatography/mass spectrometry

2-Methoxy-3-alkylpyrazines have been isolated for the first time from a Sauvignon blanc wine by using a combination of distillation or headspace sampling and trapping by an ion-exchange resin. 2-Methoxy-3-isobutylpyrazine has been identified by gas chromatography/mass spectrometry as the major methoxypyrazine in a New Zealand Sauvignon blanc and, with the aid of 2-methoxy-d3-3-isobutylpyrazine as internal standard, its concentration has been determined as 35 ± 2 ppt. The method can be applied to small wine samples (< 60 ml) and detection limits are below the olfactory thresholds

Homeless population

The aim was to derive and analyze a model for numbers of homeless and non-homeless people in a borough, in particular to see how these figures might be affected by different policies regarding housing various categories of people. Most attention was focused on steady populations although the stability of these and possible timescales of dynamic problems were also discussed. The main outcome of this brief study is the identification of the key role played by the constant k_1 - the constant which fixes the speed at which the homeless are rehoused in permanent council property. Reducing this constant, i.e. making the system "fairer" with less priority to accommodating homeless families, appears to have little effect on the sizes of other categories on the waiting list but there is a marked increase in the number of households in temporary accommodation. The model, indicated by the size of its longest time-scale, should be modified to allow for births etc. It could be varied by allowing people to remove themselves from the register or by allowing the rates at which registered and unregistered people become homeless to differ, but these modifications are unlikely to substantially change the main result. The inclusion of movement from the homeless to the general population would have the effect of limiting the numbers in temporary accommodation. However, it is thought this effect is very small so a great reduction in k_1 would be needed for this flow to become significant

A Two-Phase Chemical Enrichment Model for the Milky Way Globular Cluster System

Many globular cluster systems have a distinct bimodal metallicity distribution function (MDF) which has strikingly similar features in many large galaxies of all types. By using the Milky Way cluster system as a typical example, we show that bimodal MDFs can be very well matched with a double ``accreting-box'' chemical enrichment model in which both the halo (metal-poor) and bulge (metal-rich) clusters form during an early phase of gas inflow simultaneously with star formation. However, differences in effective yield between the two phases are not enough by themselves to reproduce the observed MDF shape: gas infall is required for both phases, and either the initial gas or the infalling gas must have very different metallicities in the two separate phases.Comment: 12 pages, 2 figures, accepted for publication in A

Activation of the <i>gluteus maximus</i> during performance of the back squat, split squat and barbell hip thrust and the relationship with maximal sprinting

The purpose of this research was to compare muscle activation of the gluteus maximus and ground reaction force between the barbell hip thrust, back squat, and split squat and to determine the relationship between these outcomes and vertical and horizontal forces during maximal sprinting. Twelve male team sport athletes (age 25.0 ± 4.0 years, stature 184.1 ± 6.0 cm, body mass 82.2 ± 7.9 kg) performed separate movements of the three strength exercises at a load equivalent to their individual three repetition maximum. The ground reaction force was measured using force plates and the electromyography (EMG) activity of the upper and lower gluteus maximus was recorded in each leg and expressed as percentage of the maximum voluntary isometric contraction (MVIC). Participants then completed a single sprint on a non-motorized treadmill for the assessment of maximal velocity, horizontal and vertical forces. Although ground reaction force was lower, peak EMG activity in the gluteus maximus was higher in the hip thrust than the back squat (p = 0.024; 95%CI = 4 – 56%MVIC) and split squat (p = 0.016; 95%CI = 6 – 58%MVIC). Peak sprint velocity was correlated with both anterior-posterior horizontal force (r = 0.72) and peak ground reaction force during the barbell hip thrust (r = 0.69) but no other variables. The increased activation of gluteus maximus during the barbell hip thrust and the relationship with maximal running speed suggests that this movement may be optimal for training this muscle group in comparison to the back squat and split squat

Constraints on the mass and abundance of black holes in the Galactic halo: the high mass limit

We establish constraints on the mass and abundance of black holes in the Galactic halo by determining their impact on globular clusters which are conventionally considered to be little evolved. Using detailed Monte Carlo simulations and simple analytic estimates, we conclude that, at Galactocentric radius R~8 kpc, black holes with masses M_bh >~(1-3) x 10^6 M_sun can comprise no more than a fraction f_bh ~ 0.025-0.05 of the total halo density. This constraint significantly improves those based on disk heating and dynamical friction arguments as well as current lensing results. At smaller radius, the constraint on f_bh strengthens, while, at larger radius, an increased fraction of black holes is allowed.Comment: 13 pages, 10 figures, revised version, in press, Monthly Notice