521 research outputs found
Comment on "Ising model on a small world network"
In the recent study of the Ising model on a small-world network by A.
P\c{e}kalski [Phys. Rev. E {\bf 64}, 057104 (2001)], a surprisingly small value
of the critical exponent has been obtained for the
temperature dependence of the magnetization. We perform extensive Monte Carlo
simulations of the same model and conclude, via the standard finite-size
scaling of various quantities,that the phase transition in the model is of the
mean-field nature, in contrast to the work by A. P\c{e}kalski but in accord
with other existing studies.Comment: to be published in PR
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Studying Wildlife at Local and Landscape Scales: Bachman's Sparrow at the Savannah River Site
Mutual interests between land managers at SRS and scientists resulted in a landscape ecology study of Bachman's sparrow. The species is declining throughout it's range. The distribution of suitable habitats across the landscape may provide an explanation. The species occupies early successional and late successional savanna habitat. Modeling was closely linked to field observations to demonstrate how the species demographics change with the distribution and dynamics of habitats
Stability of shortest paths in complex networks with random edge weights
We study shortest paths and spanning trees of complex networks with random
edge weights. Edges which do not belong to the spanning tree are inactive in a
transport process within the network. The introduction of quenched disorder
modifies the spanning tree such that some edges are activated and the network
diameter is increased. With analytic random-walk mappings and numerical
analysis, we find that the spanning tree is unstable to the introduction of
disorder and displays a phase-transition-like behavior at zero disorder
strength . In the infinite network-size limit (), we
obtain a continuous transition with the density of activated edges
growing like and with the diameter-expansion coefficient
growing like in the regular network, and
first-order transitions with discontinuous jumps in and at
for the small-world (SW) network and the Barab\'asi-Albert
scale-free (SF) network. The asymptotic scaling behavior sets in when , where the crossover size scales as for the
regular network, for the SW network, and
for the SF network. In a
transient regime with , there is an infinite-order transition with
for the SW network
and for the SF network. It
shows that the transport pattern is practically most stable in the SF network.Comment: 9 pages, 7 figur
The ultraviolet Behaviour of Integrable Quantum Field Theories, Affine Toda Field Theory
We investigate the thermodynamic Bethe ansatz (TBA) equations for a system of
particles which dynamically interacts via the scattering matrix of affine Toda
field theory and whose statistical interaction is of a general Haldane type. Up
to the first leading order, we provide general approximated analytical
expressions for the solutions of these equations from which we derive general
formulae for the ultraviolet scaling functions for theories in which the
underlying Lie algebra is simply laced. For several explicit models we compare
the quality of the approximated analytical solutions against the numerical
solutions. We address the question of existence and uniqueness of the solutions
of the TBA-equations, derive precise error estimates and determine the rate of
convergence for the applied numerical procedure. A general expression for the
Fourier transformed kernels of the TBA-equations allows to derive the related
Y-systems and a reformulation of the equations into a universal form.Comment: 37 pp Latex, 5 figure
Gravitational waves from rapidly rotating neutron stars
Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed
as an interesting source of gravitational waves. In this chapter we present
estimates of the gravitational wave emission for various scenarios, given the
(electromagnetically) observed characteristics of these systems. First of all
we focus on the r-mode instability and show that a 'minimal' neutron star model
(which does not incorporate exotica in the core, dynamically important magnetic
fields or superfluid degrees of freedom), is not consistent with observations.
We then present estimates of both thermally induced and magnetically sustained
mountains in the crust. In general magnetic mountains are likely to be
detectable only if the buried magnetic field of the star is of the order of
G. In the thermal mountain case we find that gravitational
wave emission from persistent systems may be detected by ground based
interferometers. Finally we re-asses the idea that gravitational wave emission
may be balancing the accretion torque in these systems, and show that in most
cases the disc/magnetosphere interaction can account for the observed spin
periods.Comment: To appear in 'Gravitational Waves Astrophysics: 3rd Session of the
Sant Cugat Forum on Astrophysics, 2014', Editor: Carlos F. Sopuert
An effective local routing strategy on the BA network
In this paper, We propose a effective routing strategy on the basis of the
so-called nearest neighbor search strategy by introducing a preferential
delivering exponent alpha. we assume that the handling capacity of one vertex
is proportional to its degree when the degree is smaller than a cut-off value
, and is infinite otherwise. It is found that by tuning the parameter alpha,
the scale-free network capacity measured by the order parameter is considerably
enhanced compared to the normal nearest-neighbor strategy. Traffic dynamics
both near and far away from the critical generating rate R_c are discussed. We
also investigate R_c as functions of m (connectivity density), K (cutoff
value). Due to the low cost of acquiring nearest-neighbor information and the
strongly improved network capacity, our strategy may be useful and reasonable
for the protocol designing of modern communication networks.Comment: 9 pages, 5 figure
Self-avoiding walks and connective constants in small-world networks
Long-distance characteristics of small-world networks have been studied by
means of self-avoiding walks (SAW's). We consider networks generated by
rewiring links in one- and two-dimensional regular lattices. The number of
SAW's was obtained from numerical simulations as a function of the number
of steps on the considered networks. The so-called connective constant,
, which characterizes the long-distance
behavior of the walks, increases continuously with disorder strength (or
rewiring probability, ). For small , one has a linear relation , and being constants dependent on the underlying
lattice. Close to one finds the behavior expected for random graphs. An
analytical approach is given to account for the results derived from numerical
simulations. Both methods yield results agreeing with each other for small ,
and differ for close to 1, because of the different connectivity
distributions resulting in both cases.Comment: 7 pages, 5 figure
Modelling of Incident Sound Wave Propagation around Sound Barriers Using Cellular Automata
Effect of Quantum Fluctuations in an Ising System on Small-World Networks
We study quantum Ising spins placed on small-world networks. A simple model
is considered in which the coupling between any given pair of spins is a
nonzero constant if they are linked in the small-world network and zero
otherwise. By applying a transverse magnetic field, we have investigated the
effect of quantum fluctuations. Our numerical analysis shows that the quantum
fluctuations do not alter the universality class at the ferromagnetic phase
transition, which is of the mean-field type. The transition temperature is
reduced by the quantum fluctuations and eventually vanishes at the critical
transverse field . With increasing rewiring probability,
is shown to be enhanced.Comment: 5 pages, 5 figure
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
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