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

Adjustment of interaural-time-difference analysis to sound level

To localize low-frequency sound sources in azimuth, the binaural system compares the timing of sound waves at the two ears with microsecond precision. A similarly high precision is also seen in the binaural processing of the envelopes of high-frequency complex sounds. Both for low- and high-frequency sounds, interaural time difference (ITD) acuity is to a large extent independent of sound level. The mechanisms underlying this level-invariant extraction of ITDs by the binaural system are, however, only poorly understood. We use high-frequency pip trains with asymmetric and dichotic pip envelopes in a combined psychophysical, electrophysiological, and modeling approach. Although the dichotic envelopes cannot be physically matched in terms of ITD, the match produced perceptually by humans is very reliable, and it depends systematically on the overall sound level. These data are reflected in neural responses from the gerbil lateral superior olive and lateral lemniscus. The results are predicted in an existing temporal-integration model extended with a level-dependent threshold criterion. These data provide a very sensitive quantification of how the peripheral temporal code is conditioned for binaural analysis

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

Development of technology for fluid-structure interaction modelling of a 1/8-scale dynamic model of the shuttle External Tank (ET). Volume 2: Supporting data appendixes A through C

For abstract, see N75-21359

Analytical and experimental investigation of a 1/8-scale dynamic model of the shuttle orbiter. Volume 3A: Supporting data

For abstract, see N75-15681

Analytical and experimental investigation of a 1/8-scale dynamic model of the shuttle orbiter. Volume 1: Summary report

A 1/8-scale structural dynamics model of the space shuttle orbiter was analyzed using the NASA Structural Analysis System (NASTRAN). Comparison of the calculated eigenvalues with preliminary test data for the unrestrained condition indicate that the analytical model was consistently stiffer, being about 20% higher in the first mode. The eigenvectors show reasonably good agreement with test data. A series of analytical and experimental investigations undertaken to resolve the discrepancy are described. Modifications in the NASTRAN model based upon these investigations resulted in close agreement for both eigenvalues and eigenvectors

Unstable Hadrons in Hot Hadron Gas in Laboratory and in the Early Universe

We study kinetic master equations for chemical reactions involving the formation and the natural decay of unstable particles in a thermal bath. We consider the decay channel of one into two particles, and the inverse process, fusion of two thermal particles into one. We present the master equations the evolution of the density of the unstable particles in the early Universe. We obtain the thermal invariant reaction rate using as an input the free space (vacuum) decay time and show the medium quantum effects on $\pi+\pi \leftrightarrow \rho$ reaction relaxation time. As another laboratory example we describe the $K+K \leftrightarrow \phi$ process in thermal hadronic gas in heavy-ion collisions. A particularly interesting application of our formalism is the $\pi^{0}\leftrightarrow \gamma +\gamma$ process in the early Universe. We also explore the physics of $\pi^{\pm}$ and $\mu^{\pm}$ freeze-out in the Universe.Comment: 13 pages, 9 figures, published in Physical Review

Modular exponentiation via the explicit Chinese remainder theorem

In this paper we consider the problem of computing xe mod m for large integers x, e, and m. This is the bottleneck in Rabin’s algorithm for testing primality, the Diffie-Hellman algorithm for exchanging cryptographic keys, and many other common algorithms