253 research outputs found
Phase transition in the modified fiber bundle model
We extend the standard fiber bundle model (FBM) with the local load sharing
in such a way that the conservation of the total load is relaxed when an
isolated fiber is broken. In this modified FBM in one dimension (1D), it is
revealed that the model exhibits a well-defined phase transition at a finite
nonzero value of the load, which is in contrast to the standard 1D FBM. The
modified FBM defined in the Watts-Strogatz network is also investigated, and
found is the existences of two distinct transitions: one discontinuous and the
other continuous. The effects of the long-range shortcuts are also discussed.Comment: 7 pages, to appear in Europhys. Let
Critical fluctuations and anomalous transport in soft Yukawa-Langevin systems
Simulation of a Langevin-dynamics model demonstrates emergence of critical
fluctuations and anomalous grain transport which have been observed in
experiments on "soft" quasi-two-dimensional dusty plasma clusters. It has been
suggested that these anomalies derive from particular non-equilibrium physics,
but our model does not contain such physics: the grains are confined by an
external potential, interact via static Yukawa forces, and are subject to
stochastic heating and dissipation from neutrals. One remarkable feature is
emergence of leptokurtic probability distributions of grain displacements
on time-scales , where is the
time at which the standard deviation
approaches the mean inter-grain distance . Others are development of
humps in the distributions on multiples of , anomalous Hurst exponents,
and transitions from leptokurtic towards Gaussian displacement distributions on
time scales . The latter is a signature of intermittency,
here interpreted as a transition from bursty transport associated with hopping
on intermediate time scales to vortical flows on longer time scales.Comment: 12 pages, 9 figure
Convective dispersion without molecular diffusion
A method-of-moments scheme is invoked to compute the asymptotic, long-time
mean (or composite) velocity and dispersivity (effective diffusivity) of a
two-state particle undergoing one-dimensional convective-diffusive motion
accompanied by a reversible linear transition (``chemical reaction'' or
``change in phase'') between these states. The instantaneous state-specific
particle velocity is assumed to depend only upon the instantaneous state of the
particle, and the transition between states is assumed to be governed by
spatially-independent, first-order kinetics. Remarkably, even in the absence of
molecular diffusion, the average transport of the ``composite'' particle
exhibits gaussian diffusive behavior in the long-time limit, owing to the
effectively stochastic nature of the overall transport phenomena induced by the
interstate transition. The asymptotic results obtained are compared with
numerical computations.Comment: to appear in Physica
Replica symmetry breaking in the `small world' spin glass
We apply the cavity method to a spin glass model on a `small world' lattice,
a random bond graph super-imposed upon a 1-dimensional ferromagnetic ring. We
show the correspondence with a replicated transfer matrix approach, up to the
level of one step replica symmetry breaking (1RSB). Using the scheme developed
by M\'ezard & Parisi for the Bethe lattice, we evaluate observables for a model
with fixed connectivity and long range bonds. Our results agree with
numerical simulations significantly better than the replica symmetric (RS)
theory.Comment: 21 pages, 3 figure
Phase ordering on small-world networks with nearest-neighbor edges
We investigate global phase coherence in a system of coupled oscillators on a
small-world networks constructed from a ring with nearest-neighbor edges. The
effects of both thermal noise and quenched randomness on phase ordering are
examined and compared with the global coherence in the corresponding \xy model
without quenched randomness. It is found that in the appropriate regime phase
ordering emerges at finite temperatures, even for a tiny fraction of shortcuts.
Nature of the phase transition is also discussed.Comment: 5 pages, 4 figures, Phys. Rev. E (in press
Only connect: unifying the social in social work and social media
This paper utilises ‘Only Connect’, the epigraph from Forster’s novel ‘Howards End’ as the starting point for exploring the challenges and opportunities of integrating social networking with relationship based social work practice. The paper discusses the more deleterious implications of social networking, whilst assuming a deliberately optimistic stance to uncover ways in which the opportunities afforded by online space can be utilised effectively within social work education and practice. Whilst recognising that social networking platforms are transforming constantly, the paper adopts Kaplan’s definition of social media as a ‘group of internet based applications that build on the ideological and technological foundations of Web 2.0’. Whilst much of the discussion within the paper relates to Twitter and Facebook, two of the most endemic international social networking platforms, it is also applicable to myriad forms of social networking. The paper begins with a discussion of UK professional conduct cases and explores these both within Klein’s concept of splitting and historical attitudes to new technologies. Drawing from emerging research data and other examples, the positive relational practices educed by social media within social work education and practice are emphasised and discussed. The paper concludes by highlighting Forster’s plea for connection and recommending that social work embraces the renewed opportunities provided by online networking
Ising model in small-world networks
The Ising model in small-world networks generated from two- and
three-dimensional regular lattices has been studied. Monte Carlo simulations
were carried out to characterize the ferromagnetic transition appearing in
these systems. In the thermodynamic limit, the phase transition has a
mean-field character for any finite value of the rewiring probability p, which
measures the disorder strength of a given network. For small values of p, both
the transition temperature and critical energy change with p as a power law. In
the limit p -> 0, the heat capacity at the transition temperature diverges
logarithmically in two-dimensional (2D) networks and as a power law in 3D.Comment: 6 pages, 7 figure
Mobility and stochastic resonance in spatially inhomogeneous system
The mobility of an overdamped particle, in a periodic potential tilted by a
constant external field and moving in a medium with periodic friction
coefficient is examined. When the potential and the friction coefficient have
the same periodicity but have a phase difference, the mobility shows many
interesting features as a function of the applied force, the temperature, etc.
The mobility shows stochastic resonance even for constant applied force, an
issue of much recent interest. The mobility also exhibits a resonance like
phenomenon as a function of the field strength and noise induced slowing down
of the particle in an appropriate parameter regime.Comment: 14 pages, 12 figures. Submitted to Phys. Rev.
Diffusion Processes on Small-World Networks with Distance-Dependent Random-Links
We considered diffusion-driven processes on small-world networks with
distance-dependent random links. The study of diffusion on such networks is
motivated by transport on randomly folded polymer chains, synchronization
problems in task-completion networks, and gradient driven transport on
networks. Changing the parameters of the distance-dependence, we found a rich
phase diagram, with different transient and recurrent phases in the context of
random walks on networks. We performed the calculations in two limiting cases:
in the annealed case, where the rearrangement of the random links is fast, and
in the quenched case, where the link rearrangement is slow compared to the
motion of the random walker or the surface. It has been well-established that
in a large class of interacting systems, adding an arbitrarily small density
of, possibly long-range, quenched random links to a regular lattice interaction
topology, will give rise to mean-field (or annealed) like behavior. In some
cases, however, mean-field scaling breaks down, such as in diffusion or in the
Edwards-Wilkinson process in "low-dimensional" small-world networks. This
break-down can be understood by treating the random links perturbatively, where
the mean-field (or annealed) prediction appears as the lowest-order term of a
naive perturbation expansion. The asymptotic analytic results are also
confirmed numerically by employing exact numerical diagonalization of the
network Laplacian. Further, we construct a finite-size scaling framework for
the relevant observables, capturing the cross-over behaviors in finite
networks. This work provides a detailed account of the
self-consistent-perturbative and renormalization approaches briefly introduced
in two earlier short reports.Comment: 36 pages, 27 figures. Minor revisions in response to the referee's
comments. Furthermore, some typos were fixed and new references were adde
Child Health Research Funding and Policy: Imperatives and Investments for a Healthier World
Although pediatric research enjoyed significant benefits during the National Institutes of Health (NIH) doubling era, the proportion of the NIH budget devoted to the pediatric-research portfolio has declined overall. In light of this declining support for pediatric biomedical research, the Federation of Pediatric Organizations held a topic symposium at the 2009 Pediatric Academic Societies annual meeting as a forum for discussion of the past and future states of funding, the rationale for directing public funds toward the understanding of child health and disease, and new programs and paradigms for promoting child health research. This report of the symposium is intended to disseminate more broadly the information presented and conclusions discussed to encourage those in the child health research community to exert influence with policy makers to increase the allocation of national funding for this underfunded area
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