The Interplay of Cluster and Galaxy Evolution

We review here the interplay of cluster and galaxy evolution. As a case study, we consider the Butcher-Oemler effect and propose that it is the result of the changing rate of cluster merger events in a hierarchical universe. This case study highlights the need for new catalogs of clusters and groups that possess quantified morphologies. We present such a sample here, namely the Sloan Digital Sky Survey (SDSS) C4 Catalog, which has been objectively-selected from the SDSS spectroscopic galaxy sample. We outline here the C4 algorithm and present first results based on the SDSS Early Data Release, including an X-ray luminosity-velocity dispersion (L_x-sigma) scaling relationship (as a function of cluster morphology), and the density-SFR relation of galaxies within C4 clusters (Gomez et al. 2003). We also discuss the merger of Coma and the NGC4839 group, and its effect on the galaxy populations in these systems. We finish with a brief discussion of a new sample of Hdelta-selected galaxies (i.e., k+a, post--starburst galaxies) obtained from the SDSS spectroscopic survey.Comment: Invited review at the JENAM 2002 Workshop on "Galaxy Evolution in Groups and Clusters", Porto, Sep 5-7 2002, eds. Lobo, Serote-Roos and Biviano, Kluwer in pres

Polarized Parton Densities

In this talk we summarize main results of a recent determination of the polarized deeply inelastic parton distributions to NLO from the world data. In the analysis the LO and NLO parton densities and their $1\sigma$ statistical errors were derived and parameterized. The strong coupling constant $\alpha_s(M_Z^2)$ is determined $\alpha_s(M_Z^2) = 0.113 \pm 0.004 {\rm (stat.)} \pm~0.004 {\rm (fac.)} +0.008/-0.005 {\rm (ren.)}$ Comparisons of the low moments of the parton densities with recent lattice results are given. A detailed error-analysis of the gluon density is performed.Comment: 3 pages LATEX, 1 style file, 1 eps file, to appear in the Proceedings of PANIC '02, Osaka, Ocrober 200

Numerical Regularization of Electromagnetic Quantum Fluctuations in Inhomogeneous Dielectric Media

Electromagnetic Casimir stresses are of relevance to many technologies based on mesoscopic devices such as MEMS embedded in dielectric media, Casimir induced friction in nano-machinery, micro-fluidics and molecular electronics. Computation of such stresses based on cavity QED generally require numerical analysis based on a regularization process. A new scheme is described that has the potential for wide applicability to systems involving realistic inhomogeneous media. From a knowledge of the spectrum of the stationary modes of the electromagnetic field the scheme is illustrated by estimating numerically the Casimir stress on opposite faces of a pair of perfectly conducting planes separated by a vacuum and the change in this result when the region between the plates is filled with an incompressible inhomogeneous non-dispersive dielectric.Comment: 5 pages, 2 figures, submitted to PR

The buckling of thin-walled circular cylinders under axial compression and bending

Bucking of thin-walled electroplated copper and Mylar circular cylinders under axial compression and bendin

Selection and photometric properties of K+A galaxies

Two different simple measurements of galaxy star formation rate with different timescales are compared empirically on $156,395$ fiber spectra of galaxies with $r<17.77$ mag taken from the Sloan Digital Sky Survey in the redshift range $0.05<z<0.20$: a ratio \Aamp / \Kamp found by fitting a linear sum of an average old stellar poplulation spectrum (\Kamp) and average A-star spectrum (\Aamp) to the galaxy spectrum, and the equivalent width (EW) of the \Halpha emission line. The two measures are strongly correlated, but there is a small clearly separated population of outliers from the median correlation that display excess \Aamp /\Kamp relative to \Halpha EW. These ``K+A'' (or ``E+A'') galaxies must have dramatically decreased their star-formation rates over the last $\sim 1$ Gyr. The K+A luminosity distribution is very similar to that of the total galaxy population. The K+A population appears to be bulge-dominated, but bluer and higher surface-brightness than normal bulge-dominated galaxies; it appears that K+A galaxies will fade with time into normal bulge-dominated galaxies. The inferred rate density for K+A galaxy formation is $\sim 10^{-4} h^3 Mpc^{-3} Gyr^{-1}$ at redshift $z\sim 0.1$. These events are taking place in the field; K+A galaxies don't primarily lie in the high-density environments or clusters typical of bulge-dominated populations.Comment: submitted to Ap

Chemical Analysis of a Diffuse Cloud along a Line of Sight Toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate

Absorption lines from the molecules OH+, H2O+, and H3+ have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH+ and H2O+ are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray ionization rate of atomic hydrogen. H3+ is used to infer the cosmic-ray ionization rate of H2 in the molecular interior of the cloud, which we find to be zeta_2=(4.8+-3.4)x10^-16 per second. Combining the results from all three species we find an efficiency factor---defined as the ratio of the formation rate of OH+ to the cosmic-ray ionization rate of H---of epsilon=0.07+-0.04, much lower than predicted by chemical models. This is an important step in the future use of OH+ and H2O+ on their own as tracers of the cosmic-ray ionization rate.Comment: 21 pages, 1 figure, 4 table