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

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

Inferring the dark matter power spectrum from the Lyman-alpha forest in high-resolution QSO absorption spectra

We use the LUQAS sample (Kim et al. 2004), a set of 27 high-resolution and high signal-to-noise QSO absorption spectra at a median redshift of z=2.25, and the data from Croft et al. (2002) at a median redshift of z=2.72, together with a large suite of high-resolution large box-size hydro-dynamical simulations, to estimate the linear dark matter power spectrum on scales 0.003 s/km < k <0.03 s/km. Our re-analysis of the Croft et al. data agrees well with their results if we assume the same mean optical depth and gas temperature-density relation. The inferred linear dark matter power spectrum at z=2.72 also agrees with that inferred from LUQAS at lower redshift if we assume that the increase of the amplitude is due to gravitational growth between these redshifts. We further argue that the smaller mean optical depth measured from high-resolution spectra is more accurate than the larger value obtained from low-resolution spectra by Press et al. (1993) which Croft et al. used. For the smaller optical depth we obtain a ~ 20% higher value for the rms fluctuation amplitude of the matter density. By combining the amplitude of the matter power spectrum inferred from the Lyman-alpha forest with the amplitude on large scales inferred from measurements of the CMB we obtain constraints on the primordial spectral index n and the normalisation sigma_8. For values of the mean optical depth favoured by high-resolution spectra, the inferred linear power spectrum is consistent with a LambdaCDM model with a scale-free (n=1) primordial power spectrum.Comment: 13 pages, 9 figures, 6 tables. Very minor changes to match the accepted version. MNRAS in pres

Predictive learning, prediction errors, and attention: evidence from event-related potentials and eye tracking

Prediction error (‘‘surprise’’) affects the rate of learning: We learn more rapidly about cues for which we initially make incorrect predictions than cues for which our initial predictions are correct. The current studies employ electrophysiological measures to reveal early attentional differentiation of events that differ in their previous involvement in errors of predictive judgment. Error-related events attract more attention, as evidenced by features of event-related scalp potentials previously implicated in selective visual attention (selection negativity, augmented anterior N1). The earliest differences detected occurred around 120 msec after stimulus onset, and distributed source localization (LORETA) indicated that the inferior temporal regions were one source of the earliest differences. In addition, stimuli associated with the production of prediction errors show higher dwell times in an eyetracking procedure. Our data support the view that early attentional processes play a role in human associative learning

Stereodynamical Control of a Quantum Scattering Resonance in Cold Molecular Collisions

Cold collisions of light molecules are often dominated by a single partial wave resonance. For the rotational quenching of HD (v=1, j=2) by collisions with ground state para-H2, the process is dominated by a single L=2 partial wave resonance centered around 0.1 K. Here, we show that this resonance can be switched on or off simply by appropriate alignment of the HD rotational angular momentum relative to the initial velocity vector, thereby enabling complete control of the collision outcome

Constraints on the Primordial Power Spectrum from High Resolution Lyman-alpha Forest Spectra and WMAP

The combined analysis of the cosmic microwave background on large scales and Lyman-alpha forest on small scales provides a sufficiently long lever arm to obtain strong constraints on the slope and curvature of the power spectrum of primordial density fluctuations. We present results from the combination of the first year WMAP data and the dark matter power spectrum inferred by Viel et al. (2004) for two different sets of high resolution and high signal-to-noise quasar absorption spectra: the Croft et al. (2002) sample with a median redshift z=2.72 and the LUQAS sample (Kim et al. 2004) with a median redshift z=2.125. The best fit value for the {\it rms} fluctuation amplitude of matter fluctuations is sigma_8 =0.94 +- 0.08 and n=0.99 +- 0.03, if we do not include running of the spectral index. The best fit model with a running spectral index has parameters n=0.959 +- 0.036 and n_run=-0.033 +- 0.025. The data is thus consistent with a scale-free primordial power spectrum with no running of the spectral index. We further include tensor modes and constrain the slow-roll parameters of inflation.Comment: 6 pages, 4 Figures, 1 Table. One figure added and second order extension of the standard slow-roll approximation included. Main results unchanged. MNRAS in pres

B2 1144+35B, a giant low power radio galaxy with superluminal motion. Orientation and evidence for recurrent activity

The goal of this work is a detailed study of the nearby, low power radio galaxy B2 1144+35B. For this purpose, we performed new Very Long Baseline Array (VLBA) and Very Large Array (VLA) observations. This source has several properties (bright, nearby, large range of spatial structures, visible counterjet, etc.) that make it an excellent astrophysical laboratory for the study of the evolution of radio jets. Here we report the detection of motion in the counterjet at 0.23 $\pm$ 0.07 c, which allows us to estimate the orientation of the parsec-scale jet at 33$^\circ \pm 7^\circ$ from the line of sight, with an intrinsic velocity of (0.94$^{+0.06}_{-0.11}$)c. We also report on a brightening of the core at high frequencies which we suggest could be the result of a new component emerging from the core. High dynamic range VLBA observations at 5 GHz reveal, for the first time, extended emission connecting the core with the bright complex of emission that dominates the flux density of the parsec scale structure at frequencies below 20 GHz. The evolution of this bright complex is considered and its slow decline in flux density is interpreted as the result of an interaction with the interstellar medium of the host galaxy.Comment: 7 pages, 6 b&w figures. A&A in pres

The Allen Telescope Array Twenty-centimeter Survey -- A 700-Square-Degree, Multi-Epoch Radio Dataset -- II: Individual Epoch Transient Statistics

We present our second paper on the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch, ~700 sq. deg. radio image and catalog at 1.4 GHz. The survey is designed to detect rare, bright transients as well as to commission the ATA's wide-field survey capabilities. ATATS explores the challenges of multi-epoch transient and variable source surveys in the domain of dynamic range limits and changing (u,v) coverage. Here we present images made using data from the individual epochs, as well as a revised image combining data from all ATATS epochs. The combined image has RMS noise 3.96 mJy / beam, with a circular beam of 150 arcsec FWHM. The catalog, generated using a false detection rate algorithm, contains 4984 sources, and is >90% complete to 37.9 mJy. The catalogs generated from snapshot images of the individual epochs contain between 1170 and 2019 sources over the 564 sq. deg. area in common to all epochs. The 90% completeness limits of the single epoch catalogs range from 98.6 to 232 mJy. We compare the catalog generated from the combined image to those from individual epochs, and from the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency. We are able to place new constraints on the transient population: fewer than 6e-4 transients / sq. deg., for transients brighter than 350 mJy with characteristic timescales of minutes to days. This strongly rules out an astronomical origin for the ~1 Jy sources reported by Matsumura et al. (2009), based on their stated rate of 3.1e-3 / sq. deg.Comment: 28 pages, 12 figures, ApJ accepte

Defining and mapping the person with osteoarthritis for population studies and public health

OBJECTIVE: To determine population-based estimates for the prevalence of the person with OA, predicted to be the single greatest cause of disability in the general population by 2030, in order to inform the planning and commissioning of health, social care and prevention services. METHODS: A postal survey to all adults ≥50 years of age registered with eight general practices in the UK. Self-reported data on chronic joint pain in four body regions (hand, hip, knee, foot) and the disabling nature of the pain was collected to determine gender and age-group specific prevalence estimates of clinical OA in the joint region and in the person. Multiple imputation and weighted logistic regression was used to allow for missing data. RESULTS: A total of 26 705 mailed surveys resulted in 18 474 responses (adjusted response = 71.8%). Approximately half of the mailed population had OA in at least one of the four regions (53.23%, 95% CI 52.3, 54.1) and less than half of these had disabling OA (21.87%, 95% CI 21.2, 22.5). The more joint regions involved, the more likely that the OA was disabling. OA prevalence was higher in females and increased with age. Applied to the population of England, this yielded an estimated 3.5 million persons with disabling OA, including 1.45 million people between 50 and 65 years of age and 370 000 ≥85 years of age. CONCLUSIONS: A simple approach to defining the person with OA can contribute to population comparisons, public health projections and health care needs assessments