Big Bang Nucleosynthesis with Independent Neutrino Distribution Functions

We have performed new Big Bang Nucleosynthesis calculations which employ arbitrarily-specified, time-dependent neutrino and antineutrino distribution functions for each of up to four neutrino flavors. We self-consistently couple these distributions to the thermodynamics, the expansion rate and scale factor-time/temperature relationship, as well as to all relevant weak, electromagnetic, and strong nuclear reaction processes in the early universe. With this approach, we can treat any scenario in which neutrino or antineutrino spectral distortion might arise. These scenarios might include, for example, decaying particles, active-sterile neutrino oscillations, and active-active neutrino oscillations in the presence of significant lepton numbers. Our calculations allow lepton numbers and sterile neutrinos to be constrained with observationally-determined primordial helium and deuterium abundances. We have modified a standard BBN code to perform these calculations and have made it available to the community.Comment: 9 pages, 5 figure

Targeting foreclosure interventions: an analysis of neighborhood characteristics associated with high foreclosure rates in two Minnesota counties

This study examines the statistical association of foreclosure sales with social, economic and housing variables measured at the Census tract level for two purposes of interest to foreclosure mitigation practitioners —- to assess whether it is feasible to identify in advance neighborhoods likely to have high rates of foreclosure, and to explore the socioeconomic traits of high-foreclosure neighborhoods so as to design appropriate mitigation programs. We collected data on foreclosure sales in 2002 from the sheriff’s departments of Hennepin and Ramsey counties, the two core counties that comprise the Minneapolis-St. Paul MSA. We find that several factors commonly associated with high foreclosure sale rates could have correctly identified, in advance, most neighborhoods with high rates of mortgage foreclosure. To guide the design of foreclosure mitigation programs, we also present evidence that foreclosure risks in our two counties were highest in neighborhoods with elevated credit risk indicators and a high proportion of homeowners who are recent minority buyers or young. We show that an accurate credit risk variable is among the best predictors of foreclosure and also critically affects our multivariate analysis of factors associated with foreclosure. To limit social losses associated with foreclosures, we conclude that consideration should be given to enhancing public access to data on mortgages, foreclosures, and foreclosure risk factors, especially the neighborhood distribution of credit scores.

A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening

Accurate maps of Galactic reddening are important for a number of applications, such as mapping the peculiar velocity field in the nearby Universe. Of particular concern are systematic errors which vary slowly as a function of position on the sky, as these would induce spurious bulk flow. We have compared the reddenings of Burstein & Heiles (BH) and those of Schlegel, Finkbeiner & Davis (SFD) to independent estimates of the reddening, for Galactic latitudes |b| > 10. Our primary source of Galactic reddening estimates comes from comparing the difference between the observed B-V colors of early-type galaxies, and the predicted B-V color determined from the B-V--Mg_2 relation. We have fitted a dipole to the residuals in order to look for large-scale systematic deviations. There is marginal evidence for a dipolar residual in the comparison between the SFD maps and the observed early-type galaxy reddenings. If this is due to an error in the SFD maps, then it can be corrected with a small (13%) multiplicative dipole term. We argue, however, that this difference is more likely to be due to a small (0.01 mag.) systematic error in the measured B-V colors of the early-type galaxies. This interpretation is supported by a smaller, independent data set (globular cluster and RR Lyrae stars), which yields a result inconsistent with the early-type galaxy residual dipole. BH reddenings are found to have no significant systematic residuals, apart from the known problem in the region 230 < l < 310, -20 < b < 20.Comment: 8 pages, PASP, in press (Jan 1999

Topological structure of the SU(3) vacuum and exceptional eigenmodes of the improved Wilson-Dirac operator

We present a study of the instanton size and spatial distributions in pure SU(3) gauge theory using under-relaxed cooling. We also investigate the low-lying eigenmodes of the (improved) Wilson-Dirac operator, in particular, the appearance of zero-modes and their space-time localisation with respect to instantons in the underlying gauge field.Comment: Contribution to Lattice97 proceedings: 3 pages, LaTeX2e, 4 postscript figures, uses espcrc2.st

Alginate hydrogel has a negative impact on in vitro collagen 1 deposition by fibroblasts

Hydrogels have been widely investigated as 3D culture substrates because of their reported structural similarity to the extracellular matrix (ECM). Limited ECM deposition, however, occurs within these materials, so the resulting “tissues” bear little resemblance to those found in the body. Here matrix deposition by fibroblasts encapsulated within a calcium alginate (Ca-alg) hydrogel was investigated. Although the cells transcribed mRNA for coll Iα over a period of 3 weeks, very little collagen protein deposition was observed within the gel by histology or immunohistochemistry (IHC). Although molecular diffusion demonstrated charge dependency, this did not prevent the flux of both positively and negative charged amino acids through the gel, suggesting that the absence of ECM could not be attributed to substrate limitation. The flux of protein, however, was charge-dependent as proteins with a net negative charge passed quickly through the Ca-alg into the medium. The minimal collagen deposition within the Ca-alg was attributed to a combination of rapid movement of negatively charged procollagen through the gel and steric hindrance of fibril formation