Simulation of Stellar Objects in SDSS Color Space

We present a simulation of the spatial, luminosity and spectral distributions of four types of stellar objects. We simulate: (1) Galactic stars, based on a Galactic structure model, a stellar population synthesis model, stellar isochrones, and stellar spectral libraries; (2) white dwarfs, based on model atmospheres, the observed luminosity function, mass distribution, and Galactic distribution of white dwarfs; (3) quasars, based on their observed luminosity function and its evolution, and models of emission and absorption spectra of quasars; and (4) compact emission line galaxies, based on the observed distribution of their spectral properties and sizes. The results are presented in the color system of the Sloan Digital Sky Survey (SDSS), with realistic photometric error and Galactic extinction. The simulated colors of stars and quasars are compared with observations in the SDSS system and show good agreement. The stellar simulation can be used as a tool to analyze star counts and constrain models of Galactic structure, as well as to identify stars with unusual colors. The simulation can also be used to establish the quasar target selection algorithm for the SDSS.Comment: 52 pages, 22 figures, to appear in AJ; simulated catalogs available at http://www.astro.princeton.edu/~fan/sdss_simu.htm

Influence of crystallography on aspects of solid-solid nucleation theory

Expressions for the major variables in the general rate equation for solid-solid nucleation were developed on the basis of various models of the critical nucleus shape during homogeneous and heterogeneous nucleation. These models are based upon spheres, but in some a facet was incorporated at one boundary orientation to represent the presence of a partially or fully coherent structure. Gibbs\u27 relationship for the critical radius is applicable to all of the models. The other variables in the nucleation rate equation are affected by the model and by faceting. Reduction of AG* by faceting is concluded to be the primary cause for the presence of reproducible lattice orientation relationships and for the existence of transition phases during precipitation from solid solutions. © 1975 American Society for Metals, The Melallurgical Society of AIME

From sustainable community to Big Society: ten years learning with the Imagine approach

Community is a key word in the current UK political vocabulary. As part of Big Society or as a sustainable means to develop social coherence, community has been an area of focus which has attained UK political party interest since 2003. In 1999 the Imagine method was first hinted at in the Earthscan book: ‘Sustainability Indicators: measuring the immeasurable’. The approach allows citizens to learn about and self-evaluate their own sustainability by developing their own sustainability indicators in a manner which is participatory and evidence-based. Communities could make use of the approach, not in an attempt to arrive at some ‘absolute’ value of sustainability, but in striving to achieve a self-knowing sense of how sustainable they are, by their own measured indicators and to use this evaluation in discourse with other agencies such as local and national government. The tone of Imagine is to empower citizens to own their own sustainability and to plan for sustainable futures. The method, developed for spatial and temporal sustainability assessment, has been trialled by countries in the Mediterranean region within Coastal Area Management Programmes (CAMPs). Building off this engagement with geographically and culturally diverse communities, the method has been supported by the Homes and Communities Agency (HCA) in the UK and developed into a teaching module which has been subsequently tested at undergraduate, postgraduate, continuing professional development (CPD), Virtual Learning Environment (VLE) and working with practitioners, as a hands-on Masterclass . The resulting course: Creating Sustainable Communities (CSC) has now been introduced to 20 UK Universities and has seen use by 7. This paper tracks the development of the Imagine method, explores its major elements and sets out the learning impacts it has had to-date

Characterization of Vibrio cholerae O1 El Tor galU and galE Mutants: Influence on Lipopolysaccharide Structure, Colonization, and Biofilm Formation

Recently we described the isolation of spontaneous bacteriophage K139-resistant Vibrio cholerae O1 El Tor mutants. In this study, we identified phage-resistant isolates with intact O antigen but altered core oligosaccharide which were also affected in galactose catabolism; this strains have mutations in the galU gene. We inactivated another gal gene, galE, and the mutant was also found to be defective in the catabolism of exogenous galactose but synthesized an apparently normal lipopolysaccharide (LPS). Both gal mutants as well as a rough LPS (R-LPS) mutant were investigated for the ability to colonize the mouse small intestine. The galU and R-LPS mutants, but not the galE mutant, were defective in colonization, a phenotype also associated with O-antigen-negative mutants. By investigating several parameters in vitro, we could show that galU and R-LPS mutants were more sensitive to short-chain organic acids, cationic antimicrobial peptides, the complement system, and bile salts as well as other hydrophobic agents, indicating that their outer membrane no longer provides an effective barrier function. O-antigen-negative strains were found to be sensitive to complement and cationic peptides, but they displayed significant resistance to bile salts and short-chain organic acids. Furthermore, we found that galU and galE are essential for the formation of a biofilm in a spontaneous phage-resistant rugose variant, suggesting that the synthesis of UDP-galactose via UDP-glucose is necessary for biosynthesis of the exopolysaccharide. In addition, we provide evidence that the production of exopolysaccharide limits the access of phage K139 to its receptor, the O antigen. In conclusion, our results indicate involvement of galU in V. cholerae virulence, correlated with the observed change in LPS structure, and a role for galU and galE in environmental survival of V. cholerae