811 research outputs found
"Soft power" as an instrument for external political influence of the South Korea
An alternative approach to exercising political influence through "soft power" by South Korea is viewed. Instruments used by Korean diplomacy in its pursuit of its goals are described
Replica Symmetry Breaking and the Renormalization Group Theory of the Weakly Disordered Ferromagnet
We study the critical properties of the weakly disordered -component
ferromagnet in terms of the renormalization group (RG) theory generalized to
take into account the replica symmetry breaking (RSB) effects coming from the
multiple local minima solutions of the mean-field equations. It is shown that
for the traditional RG flows at dimensions , which are
usually considered as describing the disorder-induced universal critical
behavior, are unstable with respect to the RSB potentials as found in spin
glasses. It is demonstrated that for a general type of the Parisi RSB
structures there exists no stable fixed points, and the RG flows lead to the
{\it strong coupling regime} at the finite scale , where
is the small parameter describing the disorder. The physical concequences
of the obtained RG solutions are discussed. In particular, we argue, that
discovered RSB strong coupling phenomena indicate on the onset of a new spin
glass type critical behaviour in the temperature interval near . Possible relevance of the considered RSB effects for
the Griffith phase is also discussed.Comment: 32 pages, Late
Entanglement entropy of highly degenerate states and fractal dimensions
We consider the bipartite entanglement entropy of ground states of extended
quantum systems with a large degeneracy. Often, as when there is a
spontaneously broken global Lie group symmetry, basis elements of the
lowest-energy space form a natural geometrical structure. For instance, the
spins of a spin-1/2 representation, pointing in various directions, form a
sphere. We show that for subsystems with a large number m of local degrees of
freedom, the entanglement entropy diverges as (d/2) log m, where d is the
fractal dimension of the subset of basis elements with nonzero coefficients. We
interpret this result by seeing d as the (not necessarily integer) number of
zero-energy Goldstone bosons describing the ground state. We suggest that this
result holds quite generally for largely degenerate ground states, with
potential applications to spin glasses and quenched disorder.Comment: 5 pages. v2: Small changes, published versio
Critical region of the random bond Ising model
We describe results of the cluster algorithm Special Purpose Processor
simulations of the 2D Ising model with impurity bonds. Use of large lattices,
with the number of spins up to , permitted to define critical region of
temperatures, where both finite size corrections and corrections to scaling are
small. High accuracy data unambiguously show increase of magnetization and
magnetic susceptibility effective exponents and , caused by
impurities. The and singularities became more sharp, while the
specific heat singularity is smoothed. The specific heat is found to be in a
good agreement with Dotsenko-Dotsenko theoretical predictions in the whole
critical range of temperatures.Comment: 11 pages, 16 figures (674 KB) by request to authors:
[email protected] or [email protected], LITP-94/CP-0
Cooperative behavior of qutrits with dipole-dipole interactions
We have identified a class of many body problems with analytic solution
beyond the mean-field approximation. This is the case where each body can be
considered as an element of an assembly of interacting particles that are
translationally frozen multi-level quantum systems and that do not change
significantly their initial quantum states during the evolution. In contrast,
the entangled collective state of the assembly experiences an appreciable
change. We apply this approach to interacting three-level systems.Comment: 5 pages, 3 figures. Minor correction
Current-mediated synchronization of a pair of beating non-identical flagella
The basic phenomenology of experimentally observed synchronization (i.e., a
stochastic phase locking) of identical, beating flagella of a biflagellate alga
is known to be captured well by a minimal model describing the dynamics of
coupled, limit-cycle, noisy oscillators (known as the noisy Kuramoto model). As
demonstrated experimentally, the amplitudes of the noise terms therein, which
stem from fluctuations of the rotary motors, depend on the flagella length.
Here we address the conceptually important question which kind of synchrony
occurs if the two flagella have different lengths such that the noises acting
on each of them have different amplitudes. On the basis of a minimal model,
too, we show that a different kind of synchrony emerges, and here it is
mediated by a current carrying, steady-state; it manifests itself via
correlated "drifts" of phases. We quantify such a synchronization mechanism in
terms of appropriate order parameters and - for an ensemble of
trajectories and for a single realization of noises of duration ,
respectively. Via numerical simulations we show that both approaches become
identical for long observation times . This reveals an ergodic
behavior and implies that a single-realization order parameter is
suitable for experimental analysis for which ensemble averaging is not always
possible.Comment: 10 pages, 2 figure
Effect of Random Impurities on Fluctuation-Driven First Order Transitions
We analyse the effect of quenched uncorrelated randomness coupling to the
local energy density of a model consisting of N coupled two-dimensional Ising
models. For N>2 the pure model exhibits a fluctuation-driven first order
transition, characterised by runaway renormalisation group behaviour. We show
that the addition of weak randomness acts to stabilise these flows, in such a
way that the trajectories ultimately flow back towards the pure decoupled Ising
fixed point, with the usual critical exponents alpha=0, nu=1, apart from
logarithmic corrections. We also show by examples that, in higher dimensions,
such transitions may either become continuous or remain first order in the
presence of randomness.Comment: 13 pp., LaTe
The One-dimensional KPZ Equation and the Airy Process
Our previous work on the one-dimensional KPZ equation with sharp wedge
initial data is extended to the case of the joint height statistics at n
spatial points for some common fixed time. Assuming a particular factorization,
we compute an n-point generating function and write it in terms of a Fredholm
determinant. For long times the generating function converges to a limit, which
is established to be equivalent to the standard expression of the n-point
distribution of the Airy process.Comment: 15 page
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