The hierarchical formation of a stellar cluster

Recent surveys of star forming regions have shown that most stars, and probably all massive stars, are born in dense stellar clusters. The mechanism by which a molecular cloud fragments to form several hundred to thousands of individual stars has remained elusive. Here, we use a numerical simulation to follow the fragmentation of a turbulent molecular cloud and the subsequent formation and early evolution of a stellar cluster containing more than 400 stars. We show that the stellar cluster forms through the hierarchical fragmentation of a turbulent molecular cloud. This leads to the formation of many small subclusters which interact and merge to form the final stellar cluster. The hierarchical nature of the cluster formation has serious implications in terms of the properties of the new-born stars. The higher number-density of stars in subclusters, compared to a more uniform distribution arising from a monolithic formation, results in closer and more frequent dynamical interactions. Such close interactions can truncate circumstellar discs, harden existing binaries, and potentially liberate a population of planets. We estimate that at least one-third of all stars, and most massive stars, suffer such disruptive interactions.Comment: 6 pages, 4 figures, accepted for publication in MNRAS. Version including hi-res colour postscript figure available at http://star-www.st-and.ac.uk/~sgv/ps/clufhier.ps.g

Electronic magnification for astronomical camera tubes

Definitions, test schemes, and analyses used to provide variable magnification in the image section of the television sensor for large space telescopes are outlined. Experimental results show a definite form of magnetic field distribution is necessary to achieve magnification in the range 3X to 4X. Coil systems to establish the required field shapes were built, and both image intensifiers and camera tubes were operated at high magnification. The experiments confirm that such operation is practical and can provide satisfactory image quality. The main problem with such a system was identified as heating of the photocathode due to concentration of coil power dissipation in that vicinity. Suggestions for overcoming this disadvantage are included

From Rural to Urban: Critical Differentiations in Ministry Contexts within Rural and Urban Environments

This article seeks to delineate three critical dimensions of ministry that impact ministry strategies in predominantly rural and in predominantly urban contexts for AFM Front Line Workers (FLWs). First, the community contexts within rural and urban environments. Second, the ministry strategy considerations for FLWs in rural and urban environments. Third, personal factors impacting FLWs in rural and in urban environments. The article provides in summary form the three key critical dimensions of ministry that are shared with AFM FLWs during initial training and that are utilized post-launch by AFM FLWs with their supervisors when prayerfully demonstrating urban ministry strategies within their unique urban contexts. The article will not provide an exhaustive analysis of each of these critical dimensions of ministry, but will provide a conceptual framework that FLWs can and do utilize when prayerfully reflecting on mission strategies on the ground

Search for long lived charged massive particles in pp collisions at s-hat = 1.8TeV

We report a search for the production of long-lived charged massive particles in a data sample of 90   pb-1 of √s=1.8   TeV pp̅ collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton

Fluorides, orthodontics and demineralization: a systematic review

Objectives: To evaluate the effectiveness of fluoride in preventing white spot lesion (WSL) demineralization during orthodontic treatment and compare all modes of fluoride delivery. Data sources: The search strategy for the review was carried out according to the standard Cochrane systematic review methodology. The following databases were searched for RCTs or CCTs: Cochrane Clinical Trials Register, Cochrane Oral Health Group Specialized Trials Register, MEDLINE and EMBASE. Inclusion and exclusion criteria were applied when considering studies to be included. Authors of trials were contacted for further data. Data selection: The primary outcome of the review was the presence or absence of WSL by patient at the end of treatment. Secondary outcomes included any quantitative assessment of enamel mineral loss or lesion depth. Data extraction: Six reviewers independently, in duplicate, extracted data, including an assessment of the methodological quality of each trial. Data synthesis: Fifteen trials provided data for this review, although none fulfilled all the methodological quality assessment criteria. One study found that a daily NaF mouthrinse reduced the severity of demineralization surrounding an orthodontic appliance (lesion depth difference –70.0 µm; 95% CI –118.2 to –21.8 µm). One study found that use of a glass ionomer cement (GIC) for bracket bonding reduced the prevalence of WSL (Peto OR 0.35; 95% CI 0.15–0.84) compared with a composite resin. None of the studies fulfilled all of the methodological quality assessment criteria. Conclusions: There is some evidence that the use of a daily NaF mouthrinse or a GIC for bonding brackets might reduce the occurrence and severity of WSL during orthodontic treatment. More high quality, clinical research is required into the different modes of delivering fluoride to the orthodontic patient

The influence of anxiety on visual attentional control in basketball free throw shooting.

addresses: School of Sport and Health Sciences, University of Exeter, St. Luke's Campus, Exeter, U.K.types: Journal Article© 2009 Human Kinetics, IncThe aim of this study was to test the predictions of attentional control theory using the quiet eye period as an objective measure of attentional control. Ten basketball players took free throws in two counterbalanced experimental conditions designed to manipulate the anxiety they experienced. Point of gaze was measured using an ASL Mobile Eye tracker and fixations including the quiet eye were determined using frame-by-frame analysis. The manipulation of anxiety resulted in significant reductions in the duration of the quiet eye period and free throw success rate, thus supporting the predictions of attentional control theory. Anxiety impaired goal-directed attentional control (quiet eye period) at the expense of stimulus-driven control (more fixations of shorter duration to various targets). The findings suggest that attentional control theory may be a useful theoretical framework for examining the relationship between anxiety and performance in visuomotor sport skills

Anxiety, Attentional Control, and Performance Impairment in Penalty Kicks

© 2009 Human Kinetics, IncThe current study sought to test the predictions of attentional control theory (ACT) in a sporting environment. Fourteen experienced footballers took penalty kicks under low- and high-threat counterbalanced conditions while wearing a gaze registration system. Fixations to target locations (goalkeeper and goal area) were determined using frame-by-frame analysis. When anxious, footballers made faster first fixations and fixated for significantly longer toward the goalkeeper. This disruption in gaze behavior brought about significant reductions in shooting accuracy, with shots becoming significantly centralized and within the goalkeeper’s reach. These findings support the predictions of ACT, as anxious participants were more likely to focus on the “threatening” goalkeeper, owing to an increased influence of the stimulus-driven attentional control system