28,941 research outputs found
Clear detection of dusty torus signatures in a Weak-Line Radio Galaxy: the case of PKS 0043-42
We report the clearest detection to date of dusty torus signatures in a
Weak-Line Radio Galaxy (WLRG). The deep Spitzer InfraRed Spectrograph (IRS)
rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 0043-42 (z=0.116) shows
a clear spectral turnover at wavelengths longer than ~20 micron suggestive of
warm dust, as well as a 9.7 micron silicate absorption feature. In addition,
the hard X-ray results, based on Chandra data, strongly support a picture in
which PKS 0043-42 has a torus and accretion disc more typical of Strong-Line
Radio Galaxies (SLRGs). The MIR and X-ray spectra are markedly different from
those of other WLRGs at similar redshifts, and here we show that the former can
be successfully fitted with clumpy torus models with parameters characteristic
of Type-2 AGN tori: close to edge-on (i=74 deg) and relatively broad (torus
angular width=60 deg), with an outer radius of 2 pc, hydrogen column density
~1.6x10^(23) cm^(-2), and AGN bolometric luminosity ~1.6x10^(44) erg s^(-1).
The presence of a compact torus in PKS 0043-42 provides evidence that this WLRG
is fuelled by cold, rather than hot, gas accretion. We suggest that WLRGs are a
diverse population, and PKS 0043-42 may represent a type of radio galaxy in
which the AGN activity has been recently re-triggered as a consequence of
intermittent gas supply, or in which the covering factor of the Narrow-Line
Region (NLR) clouds is relatively low.Comment: 7 pages, 6 figures, 1 table. Accepted by MNRA
A geometric technique to generate lower estimates for the constants in the Bohnenblust--Hille inequalities
The Bohnenblust--Hille (polynomial and multilinear) inequalities were proved
in 1931 in order to solve Bohr's absolute convergence problem on Dirichlet
series. Since then these inequalities have found applications in various fields
of analysis and analytic number theory. The control of the constants involved
is crucial for applications, as it became evident in a recent outstanding paper
of Defant, Frerick, Ortega-Cerd\'{a}, Ouna\"{\i}es and Seip published in 2011.
The present work is devoted to obtain lower estimates for the constants
appearing in the Bohnenblust--Hille polynomial inequality and some of its
variants. The technique that we introduce for this task is a combination of the
Krein--Milman Theorem with a description of the geometry of the unit ball of
polynomial spaces on .Comment: This preprint does no longer exist as a single manuscript. It is now
part of the preprint entitled "The optimal asymptotic hypercontractivity
constant of the real polynomial Bohnenblust-Hille inequality is 2" (arXiv
reference 1209.4632
Hamming distance and mobility behavior in generalized rock-paper-scissors models
This work reports on two related investigations of stochastic simulations
which are widely used to study biodiversity and other related issues. We first
deal with the behavior of the Hamming distance under the increase of the number
of species and the size of the lattice, and then investigate how the mobility
of the species contributes to jeopardize biodiversity. The investigations are
based on the standard rules of reproduction, mobility and predation or
competition, which are described by specific rules, guided by generalization of
the rock-paper-scissors game, valid in the case of three species. The results
on the Hamming distance indicate that it engenders universal behavior,
independently of the number of species and the size of the square lattice. The
results on the mobility confirm the prediction that it may destroy diversity,
if it is increased to higher and higher values.Comment: 7 pages, 9 figures. To appear in EP
Boundary versus bulk behavior of time-dependent correlation functions in one-dimensional quantum systems
We study the influence of reflective boundaries on time-dependent responses
of one-dimensional quantum fluids at zero temperature beyond the low-energy
approximation. Our analysis is based on an extension of effective mobile
impurity models for nonlinear Luttinger liquids to the case of open boundary
conditions. For integrable models, we show that boundary autocorrelations
oscillate as a function of time with the same frequency as the corresponding
bulk autocorrelations. This frequency can be identified as the band edge of
elementary excitations. The amplitude of the oscillations decays as a power law
with distinct exponents at the boundary and in the bulk, but boundary and bulk
exponents are determined by the same coupling constant in the mobile impurity
model. For nonintegrable models, we argue that the power-law decay of the
oscillations is generic for autocorrelations in the bulk, but turns into an
exponential decay at the boundary. Moreover, there is in general a nonuniversal
shift of the boundary frequency in comparison with the band edge of bulk
excitations. The predictions of our effective field theory are compared with
numerical results obtained by time-dependent density matrix renormalization
group (tDMRG) for both integrable and nonintegrable critical spin- chains
with , and .Comment: 20 pages, 12 figure
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