275 research outputs found
Constraints on the magnetic field in the inter-cluster bridge A399-A401
Galaxy cluster mergers are natural consequences of the structure formation in
the Universe. Such events involve a large amount of energy ( erg)
dissipated during the process. Part of this energy can be channelled in
particle acceleration and magnetic field amplification, enhancing non-thermal
emission of the intra- and inter-cluster environment. Recently, low-frequency
observations have detected a bridge of diffuse synchrotron emission connecting
two merging galaxy clusters, Abell 399 and Abell 401. Such a result provides
clear observational evidence of relativistic particles and magnetic fields
in-between clusters. In this work, we have used LOw Frequency ARray (LOFAR)
observations at 144 MHz to study for the first time the polarized emission in
the A399-A401 bridge region. No polarized emission was detected from the bridge
region. Assuming a model where polarization is generated by multiple shocks,
depolarization can be due to Faraday dispersion in the foreground medium with
respect to the shocks. We constrained its Faraday dispersion to be greater than
0.10 rad m at 95% confidence level, which corresponds to an average
magnetic field of the bridge region greater than 0.46 nG (or 0.41 nG if we
include regions of the Faraday spectrum that are contaminated by Galactic
emission). This result is largely consistent with the predictions from
numerical simulations for Mpc regions where the gas density is times
larger than the mean gas density.Comment: 12 pages, 13 figures; accepted in A&
A radio bubble shredded by gas sloshing?
We report on the detection of diffuse radio emission with peculiar morphology
in the central region of the galaxy cluster Abell 2657. The most striking
feature identified in our 144 MHz LOFAR image is a bifurcated radio arc that
extends for a projected size of 150-200 kpc. From the analysis of XMM-Newton
data, we find clear evidence of gas sloshing in the cluster and a possible dip
in X-ray surface brightness between the two radio arcs which deserves
confirmation. Interestingly, the synchrotron emission of the bifurcated radio
arc is stretched along the sloshing spiral. We compare our observational
results with numerical simulations of non-thermal components interacting with
gas motions. We suggest that the detected emission may trace a radio bubble
shredded by gas sloshing, where relativistic electrons and magnetic fields are
expected to be stretched and stirred as a consequence of tangential flows
induced by the spiralling gas motion. Lastly, we report on the presence of two
thin (6-7 kpc in width) and parallel strands of radio emission embedded in the
outer arc that are morphologically similar to the emerging population of
non-thermal filaments observed in galaxy clusters, radio galaxies, and the
Galactic centre. While this work further demonstrates the complex interplay
between thermal and non-thermal components in the intracluster medium,
follow-up observations in radio and X-rays are required to firmly determine the
origin of the features observed in Abell 2657.Comment: 12 pages, 9 figures, 1 table. Accepted for publication in MNRA
Complete Exact Solution of Diffusion-Limited Coalescence, A + A -> A
Some models of diffusion-limited reaction processes in one dimension lend
themselves to exact analysis. The known approaches yield exact expressions for
a limited number of quantities of interest, such as the particle concentration,
or the distribution of distances between nearest particles. However, a full
characterization of a particle system is only provided by the infinite
hierarchy of multiple-point density correlation functions. We derive an exact
description of the full hierarchy of correlation functions for the
diffusion-limited irreversible coalescence process A + A -> A.Comment: 4 pages, 2 figures (postscript). Typeset with Revte
Halogenated triazinediones behave as antagonists of PKR1: in vitro and in vivo pharmacological characterization
Different prokineticin receptor antagonists, based on the triazinedione scaffold, were synthesized by a new efficient method. Here we demonstrated that 5-benzyltriazinedionessubstituted in position para of the benzyl group with halogens provide compounds endowed with interesting selectivity for the Prokineticin receptor 1 (PKR1). BRET technology indicates that such substitutionresults in increased affinity for thePKR1.The affinity for PKR2, always in M range, was never significantly affected by the para-halogen-benzyl pharmacophores. The analog bearing a para-bromobenzyl pharmacophore (PC-25) displayed the highest affinity for PKR1 (~18 times higher than the reference PC-1 that bears apara-ethyl benzyl group) and the highest selectivity (~300 times). The other halogen substitutedanalogs (PC-7, PC-18 and PC-35), showed selectivity for PKR1 more than 100 times higher than for PKR2. Using transgenic mice lacking one of the two PKRs we demonstrated that all these compounds were able to abolish the Bv8-induced hyperalgesia in mice still expressing the PKR1 at doses lower than those necessary to abolish hyperalgesia in mice expressing only the PKR2. The dose ratio reflected the in- vitro evaluated receptor selectivity
A Method of Intervals for the Study of Diffusion-Limited Annihilation, A + A --> 0
We introduce a method of intervals for the analysis of diffusion-limited
annihilation, A+A -> 0, on the line. The method leads to manageable diffusion
equations whose interpretation is intuitively clear. As an example, we treat
the following cases: (a) annihilation in the infinite line and in infinite
(discrete) chains; (b) annihilation with input of single particles, adjacent
particle pairs, and particle pairs separated by a given distance; (c)
annihilation, A+A -> 0, along with the birth reaction A -> 3A, on finite rings,
with and without diffusion.Comment: RevTeX, 13 pages, 4 figures, 1 table. References Added, and some
other minor changes, to conform with final for
Correlation Functions for Diffusion-Limited Annihilation, A + A -> 0
The full hierarchy of multiple-point correlation functions for
diffusion-limited annihilation, A + A -> 0, is obtained analytically and
explicitly, following the method of intervals. In the long time asymptotic
limit, the correlation functions of annihilation are identical to those of
coalescence, A + A -> A, despite differences between the two models in other
statistical measures, such as the interparticle distribution function
Novel non-equilibrium critical behavior in unidirectionally coupled stochastic processes
Phase transitions from an active into an absorbing, inactive state are
generically described by the critical exponents of directed percolation (DP),
with upper critical dimension d_c = 4. In the framework of single-species
reaction-diffusion systems, this universality class is realized by the combined
processes A -> A + A, A + A -> A, and A -> \emptyset. We study a hierarchy of
such DP processes for particle species A, B,..., unidirectionally coupled via
the reactions A -> B, ... (with rates \mu_{AB}, ...). When the DP critical
points at all levels coincide, multicritical behavior emerges, with density
exponents \beta_i which are markedly reduced at each hierarchy level i >= 2.
This scenario can be understood on the basis of the mean-field rate equations,
which yield \beta_i = 1/2^{i-1} at the multicritical point. We then include
fluctuations by using field-theoretic renormalization group techniques in d =
4-\epsilon dimensions. In the active phase, we calculate the fluctuation
correction to the density exponent for the second hierarchy level, \beta_2 =
1/2 - \epsilon/8 + O(\epsilon^2). Monte Carlo simulations are then employed to
determine the values for the new scaling exponents in dimensions d<= 3,
including the critical initial slip exponent. Our theory is connected to
certain classes of growth processes and to certain cellular automata, as well
as to unidirectionally coupled pair annihilation processes. We also discuss
some technical and conceptual problems of the loop expansion and their possible
interpretation.Comment: 29 pages, 19 figures, revtex, 2 columns, revised Jan 1995: minor
changes and additions; accepted for publication in Phys. Rev.
CHEX-MATE: Constraining the origin of the scatter in galaxy cluster radial X-ray surface brightness profiles
We investigate the statistical properties and the origin of the scatter within the spatially resolved surface brightness profiles of the CHEXâ MATE sample, formed by 118 galaxy clusters selected via the SZ effect. These objects have been drawn from the Planck SZ catalogue and cover a wide range of masses, M500â =â [2â â â 15]à - 1014â Mâ , and redshift, zâ =â [0.05,â 0.6]. We derived the surface brightness and emission measure profiles and determined the statistical properties of the full sample and sub-samples according to their morphology, mass, and redshift. We found that there is a critical scale, Râ â ¼â 0.4R500, within which morphologically relaxed and disturbed object profiles diverge. The median of each sub-sample differs by a factor of â ¼10 at 0.05R500. There are no significant differences between mass- and redshift-selected sub-samples once proper scaling is applied. We compare CHEXâ MATE with a sample of 115 clusters drawn from the THE THREE HUNDRED suite of cosmological simulations. We found that simulated emission measure profiles are systematically steeper than those of observations. For the first time, the simulations were used to break down the components causing the scatter between the profiles. We investigated the behaviour of the scatter due to object-by-object variation. We found that the high scatter, approximately 110%, at R
Applications of Field-Theoretic Renormalization Group Methods to Reaction-Diffusion Problems
We review the application of field-theoretic renormalization group (RG)
methods to the study of fluctuations in reaction-diffusion problems. We first
investigate the physical origin of universality in these systems, before
comparing RG methods to other available analytic techniques, including exact
solutions and Smoluchowski-type approximations. Starting from the microscopic
reaction-diffusion master equation, we then pedagogically detail the mapping to
a field theory for the single-species reaction k A -> l A (l < k). We employ
this particularly simple but non-trivial system to introduce the
field-theoretic RG tools, including the diagrammatic perturbation expansion,
renormalization, and Callan-Symanzik RG flow equation. We demonstrate how these
techniques permit the calculation of universal quantities such as density decay
exponents and amplitudes via perturbative eps = d_c - d expansions with respect
to the upper critical dimension d_c. With these basics established, we then
provide an overview of more sophisticated applications to multiple species
reactions, disorder effects, L'evy flights, persistence problems, and the
influence of spatial boundaries. We also analyze field-theoretic approaches to
nonequilibrium phase transitions separating active from absorbing states. We
focus particularly on the generic directed percolation universality class, as
well as on the most prominent exception to this class: even-offspring branching
and annihilating random walks. Finally, we summarize the state of the field and
present our perspective on outstanding problems for the future.Comment: 10 figures include
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