The evolution of galaxy groups and of galaxies therein

Properties of groups of galaxies depend sensitively on the algorithm for group selection, and even the most recent catalogs of groups built from redshift-space selection should suffer from projections and infalling galaxies. The cosmo-dynamical evolution of groups from initial Hubble expansion to collapse and virialization leads to a fundamental track (FT) in virial-theorem-M/L vs crossing time. The increased rates of mergers, both direct and after dynamical friction, in groups relative to clusters, explain the higher fraction of elliptical galaxies at given local number density in X-ray selected groups, relative to clusters, even when the hierarchical evolution of groups is considered. Galaxies falling into groups and clusters should later travel outwards to typically 2 virial radii, which is somewhat less than the outermost radius where observed galaxy star formation efficiencies are enhanced relative to field galaxies of same morphological type. An ongoing analysis of the internal kinematics of X-ray selected groups suggests that the radial profiles of line of sight velocity dispersion are consistent with isotropic NFW distributions for the total mass density, with higher (lower) concentrations than LambdaCDM predictions in groups of high (low) mass. The critical mass, at M200 ~ 10^13 M_sun is consistent with possible breaks in the X-ray luminosity-temperature and Fundamental Plane relations. The internal kinematics of groups indicate that the M-T relation of groups should agree with that extrapolated from clusters with no break at the group scale. The analyses of observed velocity dispersion profiles and of the FT both suggest that low velocity dispersion groups (compact and loose, X-ray emitting or undetected) are quite contaminated by chance projections.Comment: Invited review, ESO workshop "Groups of Galaxies in the Nearby Universe", held in Santiago, Chile, 5-9 December 2005, ed. I. Saviane, V. Ivanov & J. Borissova, 16 page

Social networks and political participation in a Sicilian community context

AbstractThis study shows the linkage between political and social participation, underlining the relevance of the motivational sphere. The aim is to evaluate politically relevant social capital by adopting a relational perspective and ego-network measures, so that we can understand the interdependence between cognitive maps, motivational factors and relational dimension, both in qualitative and quantitative dimensions

Evolution of mitral regurgitation in patients with heart failure referred to a tertiary heart failure clinic

Aims: Significant mitral regurgitation (MR) is an important predictor for all-cause mortality and heart failure (HF) hospitalizations independent of left ventricular ejection fraction (LVEF). The aims of this study were to investigate (i) in how many patients referred to a tertiary outpatient HF clinic HF therapy could be optimized, (ii) the effect of optimized treatment on MR severity, and (iii) whether a reduction in MR resulted in improvement of symptoms. Methods and results: Forty-seven referred patients with therapy-resistant symptomatic chronic HF with an LVEF <40% and at least moderate MR were analysed on admission and after optimization of HF treatment after 6–18 months. The patients were classified as a volume responder when LV end-systolic volume (LVESV) decreased ≥15%, as LVEF responder when LVEF increased by ≥5% points, as clinical responder when New York Heart Association (NYHA) class improved at least one category, and as MR responder when MR severity improved at least one category to maximally moderate. After 14 ± 4 months of treatment optimization, optimal doses of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker were seen in 18 (38%) patients compared with three (6%) at baseline (P < 0.001), and optimal doses of beta-blockers were seen in 14 (30%) patients compared with four (9%) at baseline (P < 0.001). In total, 68% of the patients were clinical responders, 57% MR responders, 34% volumetric responders, and 49% LVEF responders. NYHA class improved from 2.9 ± 0.6 to 2.0 ± 0.9 (P < 0.001), MR class from 5.2 ± 0.8 to 3.6 ± 1.5 (P < 0.001), LVEF from 24% ± 9% to 31% ± 12% (P < 0.01), and LVESV non-significantly improved. The positive predictive value of MR response to NYHA response was 88%; the negative predictive value was 53%, agreement 69%, and kappa 0.39. The positive predictive value of LVEF response to NYHA response was 76%; the negative predictive value was 44%, agreement 60%, and kappa 0.21. The positive predictive value of LVESV volume response to NYHA response was 75%; the negative predictive value was 39%, agreement 51%, and kappa 0.12. Conclusions: Although this study was limited by a small number of patients, initiation and up-titration of recommended HF therapy in patients referred to our tertiary HF outpatient clinic resulted in significant MR reduction in over half of the patients, emphasizing the importance of optimal medical treatment in these very sick cardiac patients with otherwise grave prognosis. MR reduction was best correlated to NYHA improvement

Recent Advances in Understanding Particle Acceleration Processes in Solar Flares

We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Biased competition through variations in amplitude of γ-oscillations

Experiments in visual cortex have shown that the firing rate of a neuron in response to the simultaneous presentation of a preferred and non-preferred stimulus within the receptive field is intermediate between that for the two stimuli alone (stimulus competition). Attention directed to one of the stimuli drives the response towards the response induced by the attended stimulus alone (selective attention). This study shows that a simple feedforward model with fixed synaptic conductance values can reproduce these two phenomena using synchronization in the gamma-frequency range to increase the effective synaptic gain for the responses to the attended stimulus. The performance of the model is robust to changes in the parameter values. The model predicts that the phase locking between presynaptic input and output spikes increases with attention