Core dissolution and the dynamics of massive stars in young stellar clusters

We investigate the dynamical effects of rapid gas expulsion from the core of a young stellar cluster. The aims of this study are to determine 1) whether a mass-segregated core survives the gas expulsion and 2) the probable location of any massive stars that have escaped from the core. Feedback from massive stars is expected to remove the gas from the core of the cluster first, as that is where most massive stars are located. We find that gas expulsion has little effect on the core for a core star formation efficiency, of greater than 50%. For lower values of star formation efficiency down to 20%, a reduced core survives containing the majority of the massive stars while some of them are dispersed into the rest of the cluster. In fact we find that ejected stars migrate from radial to tangential orbits due to stellar encounters once they leave the core. Thus, the location of massive stars outside of the core does not exclude their forming in the dense cluster core. Few massive stars are expected to remain in the core for a star formation efficiency lower than 20%.Comment: 8 pages, 7 figures, accepted for publication in MNRA

Declining Volatility in the U.S. Automobile Industry

This paper documents the dramatic changes in volatility that occurred in the U.S. auto industry in the early 1980s. Namely, output volatility declined significantly, the covariance of inventory investment and sales became much more negative, and adjustments to output, which in earlier decades stemmed primarily from plants hiring and laying off workers, were more often accomplished with changes in average hours per worker after the mid 1980s. Building on the work of Blanchard (1983), we show how all of these changes could have stemmed from one underlying factor%u2014a decline in the persistence of motor vehicle sales. We use both industry-level data as well as micro data on production schedules from 103 assembly plants in the United States and Canada to document the developments in the early 1980s. We then use the original Holt, Modigliani, Muth and Simon (1960) linear quadratic inventory model to show how a decline in the persistence of sales leads to all of the changes noted above, including the propensity to use intensive margins of adjustment over extensive labor margins, even in the absence of technological change.

Why Do Real and Nominal Inventory-Sales Ratios Have Different Trends

This note explains the diverging trends between real and nominal aggregate inventory-sales ratios. The combined effect of two features of the data explains the divergence. First, while aggregate sales include both goods and services, inventories include only goods. Second, there has been a strong secular decrease in the relative price of goods. The combination of these two factors causes the real and nominal aggregate inventory-sales ratios to have different trends.

Tracking the Source of the Decline in GDP Volatility: An Analysis of the Automobile Industry

Recent papers by Kim and Nelson (1999) and McConnell and Perez-Quiros (2000) uncover a dramatic decline in the volatility of U.S. GDP growth beginning in 1984. Determining whether the source is good luck, good policy or better inventory management has since developed into an active area of research. This paper seeks to shed light on the source of the decline in volatility by studying the behavior of the U.S. automobile industry, where the changes in volatility have mirrored those of the aggregate data. We find that changes in the relative volatility of sales and output, which have been interpreted by some as evidence of improved inventory management, are in fact the result of changes in the process driving automobile sales. We first show that the autocorrelation of sales dropped during the 1980s, and that the behavior of interest rates may be the force behind the change in sales persistence. A simulation of the assembly plants' cost function illustrates that the persistence of sales is a key determinant of output volatility. A comparison of the ways in which assembly plants scheduled production in the 1990s relative to the 1970s supports the intuition of the simulation.

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

Alien Registration- Vine, Charles A. (Drew Plantation, Aroostook County)

https://digitalmaine.com/alien_docs/32443/thumbnail.jp

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

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