The Correlation Function of Rich Clusters of Galaxies in CDM-like Models

We use ensembles of high-resolution CDM simulations to investigate the shape and amplitude of the two point correlation function of rich clusters. The standard scale-invariant CDM model with $\Omega=1$ provides a poor description of the clustering measured from the APM rich cluster redshift survey, which is better fitted by models with more power at large scales. The amplitudes of the rich cluster correlation functions measured from our models depend weakly on cluster richness. Analytic calculations of the clustering of peaks in a Gaussian density field overestimate the amplitude of the N-body cluster correlation functions, but reproduce qualitatively the weak trend with cluster richness. Our results suggest that the high amplitude measured for the correlation function of richness class $R \geq 2$ Abell clusters is either an artefact arising from incompleteness in the Abell catalogue, or an indication that the density perturbations in the early universe were very non-Gaussian.Comment: uuencoded compressed postscript ,MNRAS, in press, OUAST-93-1

Personal propulsion unit Patent

Lightweight propulsion unit for movement of personnel and equipment across lunar surfac

Noise Estimates for Measurements of Weak Lensing from the Lyman-alpha Forest

We have proposed a method for measuring weak lensing using the Lyman-alpha forest. Here we estimate the noise expected in weak lensing maps and power spectra for different sets of observational parameters. We find that surveys of the size and quality of the ones being done today and ones planned for the future will be able to measure the lensing power spectrum at a source redshift of z~2.5 with high precision and even be able to image the distribution of foreground matter with high fidelity on degree scales. For example, we predict that Lyman-alpha forest lensing measurement from the Dark Energy Spectroscopic Instrument survey should yield the mass fluctuation amplitude with statistical errors of 1.5%. By dividing the redshift range into multiple bins some tomographic lensing information should be accessible as well. This would allow for cosmological lensing measurements at higher redshift than are accessible with galaxy shear surveys and correspondingly better constraints on the evolution of dark energy at relatively early times.Comment: 8 pages, 8 figures, submitted to MNRA

Impacts of an active travel intervention with a cycling focus in a suburban context: One-year findings from an evaluation of London’s in-progress mini-Hollands programme

Background More evidence is needed on the impacts of building infrastructure for walking and cycling. A knowledge gap and an implementation gap have been mutually reinforcing. This paper reports on a longitudinal study examining the impacts of the still in progress ‘mini-Hollands programme’, which seeks to transform local environments for walking and cycling, in three Outer London boroughs. Compared to Inner London, Outer London has low levels of cycling and low levels of walking, and is relatively car dependent. Methods We conducted a longitudinal study of 1712 individuals sampled from households in mini-Holland boroughs (intervention sample) and from non mini-Holland Outer London boroughs (control sample). The intervention sample was further divided, a priori, into those living in “high-dose neighbourhoods”, where substantial changes to the local walking and cycling infrastructure had been implemented, versus “low-dose neighbourhoods” where such improvements had not (yet) been made. At both baseline (2016) and one-year follow-up (2017), we administered an online survey of travel behaviour and attitudes to transport and the local environment. Results One year’s worth of interventions was associated with an increase in active travel among those living in areas defined as ‘high-dose’ neighbourhoods. Specifically, those in high-dose areas were 24% more likely to have done any past-week cycling at follow-up, compared to those living in non mini-Holland areas (95% CI, 2% to 52%). The mid-point estimate for increase in active travel (walking plus cycling) time for the same group was an additional 41.0 min (95% CI 7.0, 75.0 min). Positive changes in views about local environments were recorded in intervention areas, driven by a perceived improvement in cycling-related items. Controversy related to the interventions is expressed in a growth in perceptions that ‘too much’ money is spent on cycling in intervention areas. However, intervention areas also saw a reduction in perceptions that ‘too little’ money is spent (the latter view being common both at baseline and Wave 1 in control areas). Conclusion Overall, the findings here suggest that programme interventions, while controversial, are having a measurable and early impact on active travel behaviour and perceptions of the local cycling environment

The Peculiar Velocity Function of Galaxy Clusters

The peculiar velocity function of clusters of galaxies is determined using an accurate sample of cluster velocities based on Tully-Fisher distances of Sc galaxies (Giovanelli et al 1995b). In contrast with previous results based on samples with considerably larger velocity uncertainties, the observed velocity function does not exhibit a tail of high velocity clusters. The results indicate a low probability of $\lesssim$\,5\% of finding clusters with one-dimensional velocities greater than $\sim$ 600 {\kms}. The root-mean-square one-dimensional cluster velocity is 293$\pm$28 {\kms}. The observed cluster velocity function is compared with expectations from different cosmological models. The absence of a high velocity tail in the observed function is most consistent with a low mass-density ($\Omega \sim$0.3) CDM model, and is inconsistent at $\gtrsim 3 \sigma$ level with $\Omega$= 1.0 CDM and HDM models. The root-mean-square one-dimensional cluster velocities in these models correspond, respectively, to 314, 516, and 632 {\kms} (when convolved with the observational uncertainties). Comparison with the observed RMS cluster velocity of 293$\pm$28 {\kms} further supports the low-density CDM model.Comment: revised version accepted for publication in ApJ Letters, 18 pages, uuencoded PostScript with 3 figures included; complete paper available through WWW at http://www.astro.princeton.edu/~library/prep.htm

Rainstorm Debris Floods: A Problem in Public Welfare

This item is part of the Agricultural Experiment Station archive. It was digitized from a physical copy provided by the University Libraries at the University of Arizona. For more information, please email CALS Publications at [email protected]