9,554 research outputs found
Comment on: Kinetic Roughening in Slow Combustion of Paper
We comment on a recent Letter by Maunuksela et al. [Phys. Rev. Lett. 79, 1515
(1997)].Comment: 1 page, 1 figure, http://polymer.bu.edu/~hmakse/Home.htm
Ising Model on Edge-Dual of Random Networks
We consider Ising model on edge-dual of uncorrelated random networks with
arbitrary degree distribution. These networks have a finite clustering in the
thermodynamic limit. High and low temperature expansions of Ising model on the
edge-dual of random networks are derived. A detailed comparison of the critical
behavior of Ising model on scale free random networks and their edge-dual is
presented.Comment: 23 pages, 4 figures, 1 tabl
Canonical Transformations in a Higher-Derivative Field Theory
It has been suggested that the chiral symmetry can be implemented only in
classical Lagrangians containing higher covariant derivatives of odd order.
Contrary to this belief, it is shown that one can construct an exactly soluble
two-dimensional higher-derivative fermionic quantum field theory containing
only derivatives of even order whose classical Lagrangian exhibits chiral-gauge
invariance. The original field solution is expressed in terms of usual Dirac
spinors through a canonical transformation, whose generating function allows
the determination of the new Hamiltonian. It is emphasized that the original
and transformed Hamiltonians are different because the mapping from the old to
the new canonical variables depends explicitly on time. The violation of
cluster decomposition is discussed and the general Wightman functions
satisfying the positive-definiteness condition are obtained.Comment: 12 pages, LaTe
Directed Surfaces in Disordered Media
The critical exponents for a class of one-dimensional models of interface
depinning in disordered media can be calculated through a mapping onto directed
percolation (DP). In higher dimensions these models give rise to directed
surfaces, which do not belong to the directed percolation universality class.
We formulate a scaling theory of directed surfaces, and calculate critical
exponents numerically, using a cellular automaton that locates the directed
surfaces without making reference to the dynamics of the underlying interface
growth models.Comment: 4 pages, REVTEX, 2 Postscript figures avaliable from [email protected]
Higher-Derivative Two-Dimensional Massive Fermion Theories
We consider the canonical quantization of a generalized two-dimensional
massive fermion theory containing higher odd-order derivatives. The
requirements of Lorentz invariance, hermiticity of the Hamiltonian and absence
of tachyon excitations suffice to fix the mass term, which contains a
derivative coupling. We show that the basic quantum excitations of a
higher-derivative theory of order 2N+1 consist of a physical usual massive
fermion, quantized with positive metric, plus 2N unphysical massless fermions,
quantized with opposite metrics. The positive metric Hilbert subspace, which is
isomorphic to the space of states of a massive free fermion theory, is selected
by a subsidiary-like condition. Employing the standard bosonization scheme, the
equivalent boson theory is derived. The results obtained are used as a
guideline to discuss the solution of a theory including a current-current
interaction.Comment: 23 pages, Late
Driven interfaces in disordered media: determination of universality classes from experimental data
While there have been important theoretical advances in understanding the
universality classes of interfaces moving in porous media, the developed tools
cannot be directly applied to experiments. Here we introduce a method that can
identify the universality class from snapshots of the interface profile. We
test the method on discrete models whose universality class is well known, and
use it to identify the universality class of interfaces obtained in experiments
on fluid flow in porous media.Comment: 4 pages, 5 figure
Emergence of Complex Dynamics in a Simple Model of Signaling Networks
A variety of physical, social and biological systems generate complex
fluctuations with correlations across multiple time scales. In physiologic
systems, these long-range correlations are altered with disease and aging. Such
correlated fluctuations in living systems have been attributed to the
interaction of multiple control systems; however, the mechanisms underlying
this behavior remain unknown. Here, we show that a number of distinct classes
of dynamical behaviors, including correlated fluctuations characterized by
-scaling of their power spectra, can emerge in networks of simple
signaling units. We find that under general conditions, complex dynamics can be
generated by systems fulfilling two requirements: i) a ``small-world'' topology
and ii) the presence of noise. Our findings support two notable conclusions:
first, complex physiologic-like signals can be modeled with a minimal set of
components; and second, systems fulfilling conditions (i) and (ii) are robust
to some degree of degradation, i.e., they will still be able to generate
-dynamics
- …