9,877 research outputs found
Sznajd Complex Networks
The Sznajd cellular automata corresponds to one of the simplest and yet most
interesting models of complex systems. While the traditional two-dimensional
Sznajd model tends to a consensus state (pro or cons), the assignment of the
contrary to the dominant opinion to some of its cells during the system
evolution is known to provide stabilizing feedback implying the overall system
state to oscillate around null magnetization. The current article presents a
novel type of geographic complex network model whose connections follow an
associated feedbacked Sznajd model, i.e. the Sznajd dynamics is run over the
network edges. Only connections not exceeding a maximum Euclidean distance
are considered, and any two nodes within such a distance are randomly selected
and, in case they are connected, all network nodes which are no further than
are connected to them. In case they are not connected, all nodes within
that distance are disconnected from them. Pairs of nodes are then randomly
selected and assigned to the contrary of the dominant connectivity. The
topology of the complex networks obtained by such a simple growth scheme, which
are typically characterized by patches of connected communities, is analyzed
both at global and individual levels in terms of a set of hierarchical
measurements introduced recently. A series of interesting properties are
identified and discussed comparatively to random and scale-free models with the
same number of nodes and similar connectivity.Comment: 10 pages, 4 figure
Garigliano nuclear power plant: seismic evaluation of the turbine building
The Italian Garigliano Nuclear Power Plant (NPP) started its energy production in 1963. At present it is in the decommissioning stage. In order to get a proper management of the radioactive waste that will be produced during the dismantling operations it has been considered convenient to convert the turbine building of the plant into a temporary waste repository. This decision posed a remarkable seismic safety assessment issue. As a matter of fact, the challenge was to extend, in satisfactory safety conditions, the use of an important facility that has reached the end of its designed lifetime and to have this extended use approved by nuclear safety agencies. In this context many tasks have been accomplished, of which the most important are:
(a) a new appraisal of site seismic hazard;
(b) the execution of many investigations and testing on the
construction materials;
(c) the set up of a detailed 3D finite element model including the explicit representation of foundation piles and soil;
(d) consideration of soil structure kinematic and dynamic nteraction effects.
This paper describes the adopted seismic safety assessment criteria which are based on a performance objectives design approach. While performance based design is the approach currently recommended by European Regulations to manage seismic risk and it is fully incorporated in the Italian code for conventional buildings, bridges and plants, NPP are not explicitly considered. Therefore it was necessary to delineate a consistent interpretation of prescribed rules in order to properly select the maximum and operating design earthquakes on one side and corresponding acceptable limit states on the other side. The paper further provides an outline of the numerical analyses carried out, of the main results obtained and of the principal retrofitting actions that will be realized
The rich-club phenomenon across complex network hierarchies
The so-called rich-club phenomenon in a complex network is characterized when
nodes of higher degree (hubs) are better connected among themselves than are
nodes with smaller degree. The presence of the rich-club phenomenon may be an
indicator of several interesting high-level network properties, such as
tolerance to hub failures. Here we investigate the existence of the rich-club
phenomenon across the hierarchical degrees of a number of real-world networks.
Our simulations reveal that the phenomenon may appear in some hierarchies but
not in others and, moreover, that it may appear and disappear as we move across
hierarchies. This reveals the interesting possibility of non-monotonic behavior
of the phenomenon; the possible implications of our findings are discussed.Comment: 4 page
Nonadiabatic high-Tc superconductivity in hole-doped fullerenes
In this paper we address the possibility of high-T-c superconductivity (T(c)similar to100 K) in hypothetical hole doped C-60 within the context of the nonadiabatic theory of superconductivity. Our analysis shows that electron doped fullerenes, represented by the A(3)C(60) family, are characterized by relatively small values of the electron-phonon coupling constant lambda, which can thus be further increased by hole doping before lattice instabilities occur. In particular we show that T-c larger than 100 K are compatible in the nonadiabatic context with microscopic parameters lambda(h)similar or equal to0.5-1.0, mu(*)similar or equal to0.3-0.5 and phonon frequencies omega(ph)similar or equal to1500-2000 K. These results provide a stimulus for material engineering and optimization along the lines indicated
Neutron-star Radius from a Population of Binary Neutron Star Mergers
We show how gravitational-wave observations with advanced detectors of tens
to several tens of neutron-star binaries can measure the neutron-star radius
with an accuracy of several to a few percent, for mass and spatial
distributions that are realistic, and with none of the sources located within
100 Mpc. We achieve such an accuracy by combining measurements of the total
mass from the inspiral phase with those of the compactness from the postmerger
oscillation frequencies. For estimating the measurement errors of these
frequencies we utilize analytical fits to postmerger numerical-relativity
waveforms in the time domain, obtained here for the first time, for four
nuclear-physics equations of state and a couple of values for the mass. We
further exploit quasi-universal relations to derive errors in compactness from
those frequencies. Measuring the average radius to well within 10% is possible
for a sample of 100 binaries distributed uniformly in volume between 100 and
300 Mpc, so long as the equation of state is not too soft or the binaries are
not too heavy.Comment: 9 pages and 7 figure
A Kolmogorov-Smirnov test for the molecular clock on Bayesian ensembles of phylogenies
Divergence date estimates are central to understand evolutionary processes
and depend, in the case of molecular phylogenies, on tests of molecular clocks.
Here we propose two non-parametric tests of strict and relaxed molecular clocks
built upon a framework that uses the empirical cumulative distribution (ECD) of
branch lengths obtained from an ensemble of Bayesian trees and well known
non-parametric (one-sample and two-sample) Kolmogorov-Smirnov (KS)
goodness-of-fit test. In the strict clock case, the method consists in using
the one-sample Kolmogorov-Smirnov (KS) test to directly test if the phylogeny
is clock-like, in other words, if it follows a Poisson law. The ECD is computed
from the discretized branch lengths and the parameter of the expected
Poisson distribution is calculated as the average branch length over the
ensemble of trees. To compensate for the auto-correlation in the ensemble of
trees and pseudo-replication we take advantage of thinning and effective sample
size, two features provided by Bayesian inference MCMC samplers. Finally, it is
observed that tree topologies with very long or very short branches lead to
Poisson mixtures and in this case we propose the use of the two-sample KS test
with samples from two continuous branch length distributions, one obtained from
an ensemble of clock-constrained trees and the other from an ensemble of
unconstrained trees. Moreover, in this second form the test can also be applied
to test for relaxed clock models. The use of a statistically equivalent
ensemble of phylogenies to obtain the branch lengths ECD, instead of one
consensus tree, yields considerable reduction of the effects of small sample
size and provides again of power.Comment: 14 pages, 9 figures, 8 tables. Minor revision, additin of a new
example and new title. Software:
https://github.com/FernandoMarcon/PKS_Test.gi
Host redshifts from gravitational-wave observations of binary neutron star mergers
Inspiralling compact binaries as standard sirens will soon become an
invaluable tool for cosmology when advanced interferometric gravitational-wave
detectors begin their observations in the coming years. However, a degeneracy
in the information carried by gravitational waves between the total rest-frame
mass and the redshift of the source implies that neither can be
directly extracted from the signal, but only the combination , the
redshifted mass. Recent work has shown that for binary neutron star systems, a
tidal correction to the gravitational-wave phase in the late-inspiral signal
that depends on the rest-frame source mass could be used to break the
mass-redshift degeneracy. We propose here to use the signature encoded in the
post-merger signal to deduce the redshift to the source. This will allow an
accurate extraction of the intrinsic rest-frame mass of the source, in turn
permitting the determination of source redshift and luminosity distance solely
from gravitational-wave observations. This will herald a new era in precision
cosmography and astrophysics. Using numerical simulations of binary neutron
star mergers of very slightly different mass, we model gravitational-wave
signals at different redshifts and use Bayesian parameter estimation to
determine the accuracy with which the redshift can be extracted for a source of
known mass. We find that the Einstein Telescope can determine the source
redshift to -- at redshifts of .Comment: 10 pages, 4 figures; same as the version before except for
acknowledgment
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