23 research outputs found
Structure of characteristic Lyapunov vectors in spatiotemporal chaos
We study Lyapunov vectors (LVs) corresponding to the largest Lyapunov
exponents in systems with spatiotemporal chaos. We focus on characteristic LVs
and compare the results with backward LVs obtained via successive Gram-Schmidt
orthonormalizations. Systems of a very different nature such as coupled-map
lattices and the (continuous-time) Lorenz `96 model exhibit the same features
in quantitative and qualitative terms. Additionally we propose a minimal
stochastic model that reproduces the results for chaotic systems. Our work
supports the claims about universality of our earlier results [I. G. Szendro et
al., Phys. Rev. E 76, 025202(R) (2007)] for a specific coupled-map lattice.Comment: 9 page
Van Kampen's expansion approach in an opinion formation model
We analyze a simple opinion formation model consisting of two parties, A and
B, and a group I, of undecided agents. We assume that the supporters of parties
A and B do not interact among them, but only interact through the group I, and
that there is a nonzero probability of a spontaneous change of opinion (A->I,
B->I). From the master equation, and via van Kampen's Omega-expansion approach,
we have obtained the "macroscopic" evolution equation, as well as the
Fokker-Planck equation governing the fluctuations around the deterministic
behavior. Within the same approach, we have also obtained information about the
typical relaxation behavior of small perturbations.Comment: 17 pages, 6 figures, submited to Europ.Phys.J.
Theory and computation of covariant Lyapunov vectors
Lyapunov exponents are well-known characteristic numbers that describe growth
rates of perturbations applied to a trajectory of a dynamical system in
different state space directions. Covariant (or characteristic) Lyapunov
vectors indicate these directions. Though the concept of these vectors has been
known for a long time, they became practically computable only recently due to
algorithms suggested by Ginelli et al. [Phys. Rev. Lett. 99, 2007, 130601] and
by Wolfe and Samelson [Tellus 59A, 2007, 355]. In view of the great interest in
covariant Lyapunov vectors and their wide range of potential applications, in
this article we summarize the available information related to Lyapunov vectors
and provide a detailed explanation of both the theoretical basics and numerical
algorithms. We introduce the notion of adjoint covariant Lyapunov vectors. The
angles between these vectors and the original covariant vectors are
norm-independent and can be considered as characteristic numbers. Moreover, we
present and study in detail an improved approach for computing covariant
Lyapunov vectors. Also we describe, how one can test for hyperbolicity of
chaotic dynamics without explicitly computing covariant vectors.Comment: 21 pages, 5 figure
Antibiotic resistance: a physicist鈥檚 view
The problem of antibiotic resistance poses challenges across many
disciplines. One such challenge is to understand the fundamental science of how
antibiotics work, and how resistance to them can emerge. This is an area where
physicists can make important contributions. Here, we highlight cases where
this is already happening, and suggest directions for further physics
involvement in antimicrobial research.Comment: 7 pages, 1 figur
Scaling properties of spatially extended chaotic systems
We investigate the scaling properties of Lyapunov eigenvectors and
exponents in coupled-map lattices exhibiting space-time chaos. A
deep interrelation between spatiotemporal chaos and kinetic
roughening of surfaces is postulated. We show that the logarithm
of unstable eigenvectors exhibits scale-invariance with roughness
exponents that can be predicted by a simple scaling conjecture. We
argue that these scaling properties should be generic in spatially
homogeneous extended systems with local diffusive-like couplings
Spatial correlations of synchronization errors in extended chaotic systems
We discuss the temporal evolution of correlations of synchronization errors in spatially extended chaotic systems near (and below) the synchronization transition. We exploit the fact that, by construction, synchronization errors are finite perturbations of the coupled system in order to analyze the dynamics of the error and how their properties are determined by the nearby phase transition. We introduce a novel diagram plot that allows us to identify the transition universality class in a very intuitive and computationally inexpensive way
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Dynamic scaling of bred vectors in spatially extended chaotic systems
We unfold a profound relationship between the dynamics of finite-size perturbations in spatially extended chaotic systems and the universality class of Kardar-Parisi-Zhang (KPZ). We show how this relationship can be exploited to obtain a complete theoretical description of the bred vectors dynamics. The existence of characteristic length/time scales, the spatial extent of spatial correlations and how to time it, and the role of the breeding amplitude are all analyzed in the light of our theory. Implications to weather forecasting based on ensembles of initial conditions are also discussed