12,578 research outputs found
Collective synchronization induced by epidemic dynamics on complex networks with communities
Much recent empirical evidence shows that \textit{community structure} is
ubiquitous in the real-world networks. In this Letter, we propose a growth
model to create scale-free networks with the tunable strength (noted by ) of
community structure and investigate the influence of community strength upon
the collective synchronization induced by SIRS epidemiological process. Global
and local synchronizability of the system is studied by means of an order
parameter and the relevant finite-size scaling analysis is provided. The
numerical results show that, a phase transition occurs at from
global synchronization to desynchronization and the local synchronization is
weakened in a range of intermediately large . Moreover, we study the impact
of mean degree upon synchronization on scale-free networks.Comment: 5 pages, 4 figures. to appeared in Phys. Rev. E 75 (2007
Pulsating magneto-dipole radiation of a quaking neutron star powered by energy of Alfven seismic vibrations
We compute the characteristic parameters of magnetic dipole radiation of a
neutron star undergoing torsional seismic vibrations under the action of
Lorentz restoring force about axis of a dipolar magnetic field experiencing
decay. After brief outline of general theoretical background of the model of
vibration powered neutron star, we present numerical estimates of basic
vibration and radiation characteristics, such as the oscillation frequency,
lifetime, luminosity of radiation, and investigate their time dependence upon
magnetic field decay. The presented analysis suggests that gradual decrease in
frequencies of pulsating high-energy emission detected from a handful of
currently monitored AXP/SGR-like X-ray sources can be explained as being
produced by vibration powered magneto-dipole radiation of quaking magnetars.
\keywords{neutron stars, torsion Alfv\'en vibrations, vibration powered
radiation, magnetic field decay, magnetars}Comment: Preprint of article accepted for publication in "Research in
Astronomy and Astrophysics" [RAA-Vol.11-No9-(2011)-p.1074
Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO
Following the discovery of superconductivity in an iron-based arsenide
LaO1-xFxFeAs with a superconducting transition temperature (Tc) of 26 K[1], Tc
was pushed up surprisingly to above 40 K by either applying pressure[2] or
replacing La with Sm[3], Ce[4], Nd[5] and Pr[6]. The maximum Tc has climbed to
55 K, observed in SmO1-xFxFeAs[7, 8] and SmFeAsO1-x[9]. The value of Tc was
found to increase with decreasing lattice parameters in LnFeAsO1-xFx (Ln stands
for the lanthanide elements) at an apparently optimal doping level. However,
the F- doping in GdFeAsO is particularly difficult[10,11] due to the lattice
mismatch between the Gd2O2 layers and Fe2As2 layers. Here we report observation
of superconductivity with Tc as high as 56 K by the Th4+ substitution for Gd3+
in GdFeAsO. The incorporation of relatively large Th4+ ions relaxes the lattice
mismatch, hence induces the high temperature superconductivity.Comment: 4 pages, 3 figure
A new parametric equation of state and quark stars
It is still a matter of debate to understand the equation of state of cold
supra-nuclear matter in compact stars because of unknown on-perturbative strong
interaction between quarks. Nevertheless, it is speculated from an
astrophysical view point that quark clusters could form in cold quark matter
due to strong coupling at realistic baryon densities. Although it is hard to
calculate this conjectured matter from first principles, one can expect the
inter-cluster interaction to share some general features to nucleon-nucleon
interaction. We adopt a two-Gaussian component soft-core potential with these
general features and show that quark clusters can form stable simple cubic
crystal structure if we assume Gaussian form wave function. With this
parameterizing, Tolman-Oppenheimer-Volkoff equation is solved with reasonable
constrained parameter space to give mass-radius relation of crystalline solid
quark star. With baryon densities truncated at 2 times nuclear density at
surface and range of interaction fixed at 2fm we can reproduce similar
mass-radius relation to that obtained with bag model equations of state. The
maximum mass ranges from about 0.5 to 3 solar mass. Observed maximum pulsar
mass (about 2 solar mass) is then used to constrain parameters of this simple
interaction potential.Comment: 5 pages, 2 figure
Memory-Based Snowdrift Game on Networks
We present a memory-based snowdrift game (MBSG) taking place on networks. We
found that, when a lattice is taken to be the underlying structure, the
transition of spatial patterns at some critical values of the payoff parameter
is observable for both 4 and 8-neighbor lattices. The transition points as well
as the styles of spatial patterns can be explained by local stability analysis.
In sharp contrast to previously reported results, cooperation is promoted by
the spatial structure in the MBSG. Interestingly, we found that the frequency
of cooperation of the MBSG on a scale-free network peaks at a specific value of
the payoff parameter. This phenomenon indicates that properly encouraging
selfish behaviors can optimally enhance the cooperation. The memory effects of
individuals are discussed in detail and some non-monotonous phenomena are
observed on both lattices and scale-free networks. Our work may shed some new
light on the study of evolutionary games over networks.Comment: 6 pages, 6 figures, to be published in Phys. Rev.
Time-dependent Ginzburg-Landau equations for mixed d- and s-wave superconductors
A set of coupled time-dependent Ginzburg-Landau equations (TDGL) for
superconductors of mixed d- and s-wave symmetry are derived microscopically
from the Gor'kov equations by using the analytical continuation technique. The
scattering effects due to impurities with both nonmagnetic and magnetic
interactions are considered. We find that the d- and s-wave components of the
order parameter can have very different relaxation times in the presence of
nonmagnetic impurities. This result is contrary to a set of phenomenologically
proposed TDGL equations and thus may lead to new physics in the dynamics of
flux motion.Comment: 22 pages, 6 figures are available upon request, to appear in Phys.
Rev.
The Current Flows in Pulsar Magnetospheres
The global structure of the current flows in pulsar magnetospheres is
investigated, with rough calculations of the elements in the magnetospheric
circuit. It is emphasized that the potential of critical field lines is the
same as that of interstellar medium, and that the pulsars whose rotation axes
and magnetic dipole axes are parallel should be positively charged, in order to
close the pulsar's current flows. The statistical relation between the radio
luminosity and pulsar's electric charge (or the spindown power) may hint that
the millisecond pulsars could be low-mass bare strange stars.Comment: 10 pages, 4 figure
Noise bridges dynamical correlation and topology in coupled oscillator networks
We study the relationship between dynamical properties and interaction
patterns in complex oscillator networks in the presence of noise. A striking
finding is that noise leads to a general, one-to-one correspondence between the
dynamical correlation and the connections among oscillators for a variety of
node dynamics and network structures. The universal finding enables an accurate
prediction of the full network topology based solely on measuring the dynamical
correlation. The power of the method for network inference is demonstrated by
the high success rate in identifying links for distinct dynamics on both model
and real-life networks. The method can have potential applications in various
fields due to its generality, high accuracy and efficiency.Comment: 2 figures, 2 tables. Accepted by Physical Review Letter
Magnetars: fact or fiction?
Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are
enigmatic pulsar-like objects. The energy budget is the fundamental problem in
their studies. In the magnetar model, they are supposed to be powered by the
extremely strong magnetic fields (>~ 10^14 G) of neutron stars. Observations
for and against the magnetar model are both summarized. Considering the
difficulties encountered by the magnetar model to comfortably understand more
and more observations, one may doubt that AXPs and SGRs are really magnetars.
If they are not magnetar candidates (including magnetar-based models), then
they must be "quark star/fallback disk" systems.Comment: 10 pages, 1 figure; talk at SMFN201
Particle Emission-dependent Timing Noise of Pulsars?
Though pulsars spin regularly, the differences between the observed and
predicted ToA (time of arrival), known as "timing noise", can still reach a few
milliseconds or more. We try to understand the noise in this paper. As proposed
by Xu & Qiao in 2001, both dipole radiation and particle emission would result
in pulsar braking. Accordingly, possible fluctuation of particle current flow
is suggested here to contribute significant ToA variation of pulsars. We find
that the particle emission fluctuation could lead to timing noise which can't
be eliminated in timing process, and that a longer period fluctuation would
arouse a stronger noise. The simulated timing noise profile and amplitude are
in accord with the observed timing behaviors on the timescale of years.Comment: 6 pages, 2 figures. (Accepted by Chin. Phys. Lett.
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