Extreme scattering events and Galactic dark matter

Extreme Scattering Events (ESEs) are attributed to radio-wave refraction by a cloud of free-electrons crossing the line-of-sight. We present a new model in which these electrons form the photo-ionized 'skin' of an underlying cool, self-gravitating cloud in the Galactic halo. In this way we avoid the severe over-pressure problem which afflicts other models. The UV flux in the Galactic halo naturally generates electron densities of the right order. We demonstrate, for the first time, a good reproduction of the prototypical ESE in the quasar 0954+658. The neutral clouds are a few AU in radius and have masses less than about 10^{-3} solar. The observed rate of ESEs implies that a large fraction of the mass of the Galaxy is in this form.Comment: 5 pp incl 3 figs, LaTeX, uses aas2pp4.sty. Minor revisions. ApJ Letters in pres

\u3ci\u3eEnallagma Anna,\u3c/i\u3e A Damselfly New to the Great Lakes Region (Odonata: Coenagrionidae)

Enallagma anna, a predominantly western North America damselfly, is now recorded from southwestern Michigan and southwestern Ontario for the first time

Walk or wait?: An empirical analysis of street crossing decisions

We examine the behaviour of pedestrians wishing to cross a stream of trasffic at signalized intersections. We model each padestrian as making a desccrete crossing choice by comparing the gaps between vehicles in traffic to an individual-specific "critical gap" that characterizes the individual's minimal acceptable gap. We propose both parametric and nonparametric approaches to estimate the distribution of critical gaps in the population of pedestrians. To estimate the model, we gather field data on crossing decisions and vehicle flows at three intersections in New Delhi. The estimates provide information about heterogeneity in critical gaps across pedestrians and intersections and permits simulation of the effect of changes in traffic light sequence (flows)on pedestran crossing behavior and waiting times.