Models for the Magnitude-Distribution of Brightest Cluster Galaxies

The brightest, or first-ranked, galaxies (BCGs) in rich clusters show a very small dispersion in luminosity, making them excellent standard candles. This small dispersion has raised questions about the nature of BCGs. Are they simply the extremes of normal galaxies formed via a stochastic process, or do they belong to a special class of atypical objects? Arguments have been proposed on both sides of the debate. Bhavsar (1989) suggested that the distribution in magnitudes can only be explained by a two-population model. Thus, a new controversy has arisen. Do first-ranked galaxies consist of one or two populations of objects? We examine an older and newer data set and present our results. Two-population models do better than do one-population models. A simple model where a random boost in the magnitude of a fraction of bright normal galaxies forms a class of atypical galaxies best describes the observed distribution of BCG magnitudes. Moreover, the parameters that describe the model and the parameters of the boost have a strong physical basis.Comment: Abstract submitted to AAS. Paper (6 pages, 4 figs.) to be published in the MNRAS; uses mn.st

The Extrema-effect in Total Elastic Molecular Beam Scattering Cross Sections for Characterization of the Potential Well

Extrema effect in total elastic molecular beam scattering cross sections for characterization of potential wel

Development of technology for modeling of a 1/8-scale dynamic model of the shuttle Solid Rocket Booster (SRB)

A NASTRAN analysis of the solid rocket booster (SRB) substructure of the space shuttle 1/8-scale structural dynamics model. The NASTRAN finite element modeling capability was first used to formulate a model of a cylinder 10 in. radius by a 200 in. length to investigate the accuracy and adequacy of the proposed grid point spacing. Results were compared with a shell analysis and demonstrated relatively accurate results for NASTRAN for the lower modes, which were of primary interest. A finite element model of the full SRB was then formed using CQUAD2 plate elements containing membrane and bending stiffness and CBAR offset bar elements to represent the longerons and frames. Three layers of three-dimensional CHEXAI elements were used to model the propellant. This model, consisting of 4000 degrees of freedom (DOF) initially, was reduced to 176 DOF using Guyan reduction. The model was then submitted for complex Eigenvalue analysis. After experiencing considerable difficulty with attempts to run the complete model, it was split into two substructres. These were run separately and combined into a single 116 degree of freedom A set which was successfully run. Results are reported