109,632 research outputs found
Discrete Redox Signaling Pathways Regulate Photosynthetic Light-Harvesting and Chloroplast Gene Transcription
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Resolving the discrepancy between X-ray and gravitational lensing mass measurements for clusters of galaxies
We present a detailed comparison of mass measurements for clusters of
galaxies using ASCA and ROSAT X-ray data and constraints from strong and weak
gravitational lensing. Our results for a sample of 13 clusters provide a
consistent description of the distribution of gravitating matter in these
systems. For the 6 cooling-flow clusters in the sample, which are the more
dynamically-relaxed systems, the X-ray and strong gravitational lensing mass
measurements show excellent agreement. The core radii for the mass
distributions are small, with a mean value of ~ 50 kpc.
For the non-cooling flow clusters, the masses determined from the strong
lensing data exceed the X-ray values by factors of . However, significant
offsets between the X-ray and lensing centres are observed, indicating that the
X-ray and strong-lensing data are probing different lines of sight through the
clusters. These offsets, and the generally complex dynamical states of the
clusters inferred from their X-ray morphologies, lensing data and galaxy
distributions, suggest that the gravitational potentials in the central regions
of the non-cooling flow systems are evolving rapidly, and that the assumption
of hydrostatic equilibrium involved in the X-ray mass measurements is likely to
have broken down. The discrepancies between the X-ray and strong lensing mass
measurements may be reconciled if the dynamical activity has caused the X-ray
analyses to overestimate the core radii of the dominant mass clumps in these
clusters. On larger spatial scales, comparisons of the X-ray mass results with
measurements from weak gravitational lensing show excellent agreement for both
cooling-flow and non-cooling flow clusters. (ABRIDGED)Comment: MNRAS in press. 18 pages including 4 figures in MNRAS LaTex styl
Weakly nonlinear waves in magnetized plasma with a slightly non-Maxwellian electron distribution. Part 1, Stability of solitary waves
Weakly nonlinear waves in strongly magnetized plasma with slightly non-isothermal electrons are governed by a modified Zakharov–Kuznetsov (ZK) equation, containing both quadratic and half-order nonlinear terms, which we refer to as the Schamel–Korteweg–de Vries–Zakharov–Kuznetsov (SKdVZK) equation. We present a method to obtain an approximation for the growth rate, γ, of sinusoidal perpendicular perturbations of wavenumber, k, to SKdVZK solitary waves over the entire range of instability. Unlike for (modified) ZK equations with one nonlinear term, in this method there is no analytical expression for kc, the cut-off wavenumber (at which the growth rate is zero) or its corresponding eigenfunction. We therefore obtain approximate expressions for these using an expansion parameter, a, related to the ratio of the nonlinear terms. The expressions are then used to find γ for k near kc as a function of a. The approximant derived from combining these analytical results with the ones for small k agrees very well with the values of γ obtained numerically. It is found that both kc and the maximum growth rate decrease as the electron distribution becomes progressively less peaked than the Maxwellian. We also present new algebraic and rarefactive solitary wave solutions to the equation
Recommended from our members
Domestic violence, sexual assault and stalking: findings from the British Crime Survey
Inter-personal violence comprises crimes of domestic violence, sexual assault and stalking. These are important forms of crime and the government is engaged in a major series of policy initiatives in order to deal with them. However, only a small fraction of these cases are reported to the police and recorded by them, and even interview based surveys have difficulty in getting people to disclose such events. This report presents the findings of an innovative computerised self-completion questionnaire included in the British Crime Survey (BCS) which encourages wider reporting of experiences than the main face-to-face part of the BCS. It builds on previous use of this methodology in the BCS, and provides the most reliable findings to date on the extent and nature of inter-personal violence in England and Wales
- …