Collisional Grooming Models of the Kuiper Belt Dust Cloud

We modeled the 3-D structure of the Kuiper Belt dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of ~10^-4 primarily show an azimuthally-symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical Kuiper Belt. For models with lower optical depths (10^-6 and 10^-7), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of of Neptune; this feature is caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's Kuiper Belt dust, and probably other aspects of the Solar System dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly-trapped small grains ("transport dominated") to being dominated by the birth ring ("collision dominated") when the optical depth reaches a critical value of tau ~ v/c, where v is the local Keplerian speed.Comment: 31 pages, including 9 figure

Acoustic Oscillations in the Early Universe and Today

During its first ~100,000 years, the universe was a fully ionized plasma with a tight coupling by Thompson scattering between the photons and matter. The trade--off between gravitational collapse and photon pressure causes acoustic oscillations in this primordial fluid. These oscillations will leave predictable imprints in the spectra of the cosmic microwave background and the present day matter-density distribution. Recently, the BOOMERANG and MAXIMA teams announced the detection of these acoustic oscillations in the cosmic microwave background (observed at redshift ~1000). Here, we compare these CMB detections with the corresponding acoustic oscillations in the matter-density power spectrum (observed at redshift ~0.1). These consistent results, from two different cosmological epochs, provide further support for our standard Hot Big Bang model of the universe.Comment: To appear in the journal Science. 6 pages, 1 color figur

A comparison of design and model selection methods for supersaturated experiments

Various design and model selection methods are available for supersatu-rated designs having more factors than runs but little research is available ontheir comparison and evaluation. In this paper, simulated experiments areused to evaluate the use of E(s2)-optimal and Bayesian D-optimal designs,and to compare three analysis strategies representing regression, shrinkageand a novel model-averaging procedure. Suggestions are made for choosingthe values of the tuning constants for each approach. Findings include that(i) the preferred analysis is via shrinkage; (ii) designs with similar numbersof runs and factors can be effective for a considerable number of active effectsof only moderate size; and (iii) unbalanced designs can perform well. Somecomments are made on the performance of the design and analysis methodswhen effect sparsity does not hol

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

Approaching Evaluation in Youth Community Informatics

In the Youth Community Informatics project, young people from disadvantaged communities use audio and video recording and editing tools, GPS/GIS, presentation software, graphics, and other digital technologies as the means for addressing community needs. They build community asset maps, document community history, develop exhibits in collaboration with libraries and museums, present cultural heritage, organize political action, operate community radio, create and maintain community technology centers, and express themselves through multiple media. These activities typically involve multiple partners and develop in unpredictable ways in response to community life. In order to understand what they mean in the lives of the youth and the community we need richer evaluation approaches.published or submitted for publicationis peer reviewe