@article{VolkovUllnerZaikinetal.2003, author = {Volkov, E. I. and Ullner, Ekkehard and Zaikin, Alexei A. and Kurths, J{\"u}rgen}, title = {Frequency-dependent stochastic resonance in inhibitory coupled excitable systems}, issn = {1063-651X}, year = {2003}, abstract = {We study frequency selectivity in noise-induced subthreshold signal processing in a system with many noise- supported stochastic attractors which are created due to slow variable diffusion between identical excitable elements. Such a coupling provides coexisting of several average periods distinct from that of an isolated oscillator and several phase relations between elements. We show that the response of the coupled elements under different noise levels can be significantly enhanced or reduced by forcing some elements in resonance with these new frequencies which correspond to appropriate phase relations}, language = {en} } @article{VianaGrebogiPintoetal.2003, author = {Viana, R. L. and Grebogi, Celso and Pinto, Seds and Lopes, S. R. and Batista, A. M. and Kurths, J{\"u}rgen}, title = {Validity of numerical trajectories in the synchronization transition of complex systems}, issn = {1063-651X}, year = {2003}, abstract = {We investigate the relationship between the loss of synchronization and the onset of shadowing breakdown via unstable dimension variability in complex systems. In the neighborhood of the critical transition to strongly nonhyperbolic behavior, the system undergoes on-off intermittency with respect to the synchronization state. There are potentially severe consequences of these facts on the validity of the computer-generated trajectories obtained from dynamical systems whose synchronization manifolds share the same nonhyperbolic properties}, language = {en} } @article{SteuerKurthsFiehnetal.2003, author = {Steuer, Ralf and Kurths, J{\"u}rgen and Fiehn, Oliver and Weckwerth, Wolfram}, title = {Interpreting correlations in metabolomic networks}, issn = {0300-5127}, year = {2003}, abstract = {Correlations, as observed between the concentrations of metabolites in a biological sample, may be used to gain additional information about the physiological state of a given tissue. in this mini-review, we discuss the integration of these observed correlations into metabolomic networks and their relationships with the underlying biochemical pathways}, language = {en} } @article{PetrovKurthsGeorgiev2003, author = {Petrov, Valko and Kurths, J{\"u}rgen and Georgiev, Nikola}, title = {Reconstructing differential equation from a time series}, issn = {0218-1274}, year = {2003}, abstract = {This paper treats a problem of reconstructing ordinary differential equation from a single analytic time series with observational noise. We suppose that the noise is Gaussian (white). The investigation is presented in terms of classical theory of dynamical systems and modern time series analysis. We restrict our considerations on time series obtained as a numerical analytic solution of autonomous ordinary differential equation, solved with respect to the highest derivative and with polynomial right-hand side. In case of an approximate numerical solution with a rather small error, we propose a geometrical basis and a mathematical algorithm to reconstruct a low-order and low-power polynomial differential equation. To reduce the noise the given time series is smoothed at every point by moving polynomial averages using the least-squares method. Then a specific form of the least-squares method is applied to reconstruct the polynomial right-hand side of the unknown equation. We demonstrate for monotonous, periodic and chaotic solutions that this technique is very efficient}, language = {en} } @article{WesselMalberg2003, author = {Wessel, Niels and Malberg, A.}, title = {Heart rate turbulence : an independent risk factor?}, issn = {1045-3873}, year = {2003}, language = {en} } @article{KuhlbrodtMonahan2003, author = {Kuhlbrodt, Till and Monahan, A. H.}, title = {Stochastic stability of open-ocean deep convection}, issn = {0022-3670}, year = {2003}, abstract = {Open-ocean deep convection is a highly variable and strongly nonlinear process that plays an essential role in the global ocean circulation. A new view of its stability is presented here, in which variability, as parameterized by stochastic forcing, is central. The use of an idealized deep convection box model allows analytical solutions and straightforward conceptual understanding while retaining the main features of deep convection dynamics. In contrast to the generally abrupt stability changes in deterministic systems, measures of stochastic stability change smoothly in response to varying forcing parameters. These stochastic stability measures depend chiefly on the residence times of the system in different regions of phase space, which need not contain a stable steady state in the deterministic sense. Deep convection can occur frequently even for parameter ranges in which it is deterministically unstable; this effect is denoted wandering unimodality. The stochastic stability concepts are readily applied to other components of the climate system. The results highlight the need to take climate variability into account when analyzing the stability of a climate state}, language = {en} } @article{SteuerZhouKurths2003, author = {Steuer, Ralf and Zhou, Changsong and Kurths, J{\"u}rgen}, title = {Constructive effects of fluctuations in genetic and biochemical regulatory systems}, issn = {0303-2647}, year = {2003}, abstract = {Biochemical and genetic regulatory systems that involve low concentrations of molecules are inherently noisy. This intrinsic stochasticity, has received considerable interest recently, leading to new insights about the sources and consequences of noise in complex systems of genetic regulation. However, most prior work was devoted to the reduction of fluctuation and the robustness of cellular function with respect to intrinsic noise. Here, we focus on several scenarios in which the inherent molecular fluctuations are not merely a nuisance, but act constructively and bring about qualitative changes in the dynamics of the system. It will be demonstrated that in many typical situations biochemical and genetic regulatory systems may utilize intrinsic noise to their advantage. (C) 2002 Elsevier Ireland Ltd. All rights reserved}, language = {en} } @article{GinelliAhlersLivietal.2003, author = {Ginelli, F. and Ahlers, Volker and Livi, R. and Mukamel, D. and Pikovskij, Arkadij and Politi, Antonio and Torcini, A.}, title = {From multiplicative noise to directed percolation in wetting transitions}, issn = {1063-651X}, year = {2003}, abstract = {A simple one-dimensional microscopic model of the depinning transition of an interface from an attractive hard wall is introduced and investigated. Upon varying a control parameter, the critical behavior observed along the transition line changes from a directed-percolation type to a multiplicative-noise type. Numerical simulations allow for a quantitative study of the multicritical point separating the two regions. Mean-field arguments and the mapping on yet a simpler model provide some further insight on the overall scenario}, language = {en} } @article{BurghardtNestWorth2003, author = {Burghardt, I. and Nest, Mathias and Worth, G. A.}, title = {Multiconfigurational system-bath dynamics using Gaussian wave packets : Energy relaxation and decoherence induced by a finite-dimensional bath}, issn = {0021-9606}, year = {2003}, language = {en} } @article{AnishchenkoVadivasovaKopeikinetal.2003, author = {Anishchenko, Vadim S. and Vadivasova, T. E. and Kopeikin, A. S. and Strelkova, G. I. and Kurths, J{\"u}rgen}, title = {Spectral and correlation analysis of spiral chaos}, issn = {0219-4775}, year = {2003}, abstract = {We study numerically the behavior of the autocorrelation function (ACF) and the power spectrum of spiral attractors without and in the presence of noise. It is shown that the ACF decays exponentially and has two different time scales. The rate of the ACF decrease is defined by the amplitude fluctuations on small time intervals, i.e., when tau < tau(cor), and by the effective diffusion coefficient of the instantantaneous phase on large time intervals. it is also demonstrated that the ACF in the Poincare map also decreases according to the exponential law exp(-lambda(+)k), where lambda(+) is the positive Lyapunov exponent. The obtained results are compared with the theory of fluctuations for the Van der Pol oscillator}, language = {en} }