Structure in a Loitering Universe

We study the formation of structure for a universe that undergoes a recent loitering phase. We compare the nonlinear mass distribution to that in a standard, matter dominated cosmology. The statistical aspects of the clustered matter are found to be robust to changes in the expansion law, an exception being that the peculiar velocities are lower by a factor of $\sim 3$ in the loitering model. Further, in the loitering scenario, nonlinear growth of perturbation occurs more recently ($z\sim 3-5$) than in the matter dominated case. Differences in the high redshift appearances of the two models will result but observable consequences depend critically on the chosen form, onset and duration of the loitering phase.Comment: 8 pages, (uses revtex.sty), 5 figures not included, available on request, UM AC 92-

Mass Estimates of X-Ray Clusters

We use cosmological gas dynamic simulations to investigate the accuracy of galaxy cluster mass estimates based on X-ray observations. The experiments follow the formation of clusters in different cosmological models and include the effects of gravity, pressure gradients, and hydrodynamical shocks. A subset of our ensemble also allows for feedback of mass and energy from galactic winds into the intracluster medium. We find that mass estimates based on the hydrostatic, isothermal beta-model are remarkably accurate when evaluated at radii where the cluster mean density is between 500-2500 times the critical density. Applied to 174 artificial ROSAT images constructed from the simulations, the distribution of the estimated-to-true mass ratio is nearly unbiased and has a standard deviation of 14-29%. The scatter can be considerably reduced (to 8-15%) by using an alternative mass estimator that exploits the tightness of the mass-temperature relation found in the simulations. The improvement over beta-model estimates is due to the elimination of the variance contributed by the gas outer slope parameter. We discuss these findings and their implications for recent measurements of cluster baryon fractions.Comment: TeX, 24p; 11 Postscript figs. Submitted to the Astrophysical Journa

Treatment of Obesity in Mentally Retarded Persons: The Rehabilitator\u27s Role

Obesity is a common problem for the mentally retarded and nonretarded populations. Prevalence estimates ranging from 40 to 80 million obese Americans have been reported. The relationship between obesity and cardiovascular disease, diabetes mellitus, and other health related problems is strong. Also, the greater the degree of obesity, the higher the risk of medical problems. In addition to the health problems associated with obesity, the obese mentally retarded person is likely to be the object of increased social prejudice and nonacceptance as a result of being mentally retarded and obese. Fortunately, this solution does not need to be an intractable one. Van Itallie cited studies reporting a positive influence for weight reduction on health. Another treatment goal has been enhanced self-esteem. Given these promising outcomes for weight reduction, the field of obesity has witnessed an explosion of diet programs and exercise regimes to promote weight loss. These programs have varied in their initial success but nearly all have failed to produce long-term maintenance of weight loss. The application of behavioral procedures to the problem of obesity has produced more promising results. This approach has also been successfully extended to the mentally retarded population. This article describes the treatment rationale and procedures for a behavioral self-control package that has been developed for the obese retarded population. Implications of this approach for professionals concerned with rehabilitation efforts for mentally retarded persons will be delineated

Dynamics of early planetary gear trains

A method to analyze the static and dynamic loads in a planetary gear train was developed. A variable-variable mesh stiffness (VVMS) model was used to simulate the external and internal spur gear mesh behavior, and an equivalent conventional gear train concept was adapted for the dynamic studies. The analysis can be applied either involute or noninvolute spur gearing. By utilizing the equivalent gear train concept, the developed method may be extended for use for all types of epicyclic gearing. The method is incorporated into a computer program so that the static and dynamic behavior of individual components can be examined. Items considered in the analysis are: (1) static and dynamic load sharing among the planets; (2) floating or fixed Sun gear; (3) actual tooth geometry, including errors and modifications; (4) positioning errors of the planet gears; (5) torque variations due to noninvolute gear action. A mathematical model comprised of power source, load, and planetary transmission is used to determine the instantaneous loads to which the components are subjected. It considers fluctuating output torque, elastic behavior in the system, and loss of contact between gear teeth. The dynamic model has nine degrees of freedom resulting in a set of simultaneous second order differential equations with time varying coefficients, which are solved numerically. The computer program was used to determine the effect of manufacturing errors, damping and component stiffness, and transmitted load on dynamic behavior. It is indicated that this methodology offers the designer/analyst a comprehensive tool with which planetary drives may be quickly and effectively evaluated