University of Potsdam

About: University of Potsdam is a education organization based out in Potsdam, Germany. It is known for research contribution in the topics: Population & Computer science. The organization has 9629 authors who have published 26740 publications receiving 759745 citations. The organization is also known as: Universität Potsdam.

Coherence Resonance in a Noise-Driven Excitable System

Abstract: We study the dynamics of the excitable Fitz Hugh ‐ Nagumo system under external noisy driving. Noise activates the system producing a sequence of pulses. The coherence of these noise-induced oscillations is shown to be maximal for a certain noise amplitude. This new effect of coherence resonance is explained by different noise dependencies of the activation and the excursion times. A simple one-dimensional model based on the Langevin dynamics is proposed for the quantitative description of this phenomenon. [S0031-9007(97)02349-1] The response of dynamical systems to noise has attracted large attention recently. There are many examples demonstrating that noise can lead to more order in the dynamics. To be mentioned here are the effects of noiseinduced order in chaotic dynamics [1], synchronization by external noise [2], and stochastic resonance [3‐5]. Also, noise has been shown to play a stabilizing role in ensembles of coupled oscillators and maps [6]. Especially interesting is the phenomenon of stochastic resonance, which appears when a nonlinear system is simultaneously driven by noise and a periodic signal. At a certain noise amplitude the periodic response is maximal; this has been confirmed by numerous experimental studies (cf. [7,8]). In this paper we study the effect of noise on the autonomous excitable oscillator—the famous Fitz Hugh ‐ Nagumo system. We demonstrate that a characteristic correlation time of the noise-excited oscillations has a maximum for a certain noise amplitude, and present a theory of this effect. Contrary to the usual setup of stochastic resonance, no external periodic driving is assumed, so the coherence appears as a nonlinear response to purely noisy excitation. The phenomenon considered is also different from stochastic resonance without periodic force reported recently in Ref. [9], where the effect of noise on a limit cycle at a bifurcation point was studied. The Fitz Hugh‐Nagumo model is a simple but representative example of excitable systems that occur in different fields of application ranging from kinetics of chemical reactions and solid-state physics to biological processes [10]. Originally it was suggested for the description of nerve pulses [11]; it was also widely used for modeling of spiral waves in a two-dimensional excitable medium. Different aspects of the dynamics of this and similar excitable models in the presence of noise have been discussed in Refs. [12‐16]. The equations of motion are

Emotional experience in everyday life across the adult life span.

Abstract: Age differences in emotional experience over the adult life span were explored, focusing on the frequency, intensity, complexity, and consistency of emotional experience in everyday life. One hundred eighty-four people, age 18 to 94 years, participated in an experience-sampling procedure in which emotions were recorded across a 1-week period. Age was unrelated to frequency of positive emotional experience. A curvilinear relationship best characterized negative emotional experience. Negative emotions declined in frequency until approximately age 60, at which point the decline ceased. Individual factor analyses computed for each participant revealed that age was associated with more differentiated emotional experience. In addition, periods of highly positive emotional experience were more likely to endure among older people and periods of highly negative emotional experience were less stable. Findings are interpreted within the theoretical framework of socioemotional selectivity theory.

Multifractality in human heartbeat dynamics

Abstract: There is evidence that physiological signals under healthy conditions may have a fractal temporal structure. Here we investigate the possibility that time series generated by certain physiological control systems may be members of a special class of complex processes, termed multifractal, which require a large number of exponents to characterize their scaling properties. We report on evidence for multifractality in a biological dynamical system, the healthy human heartbeat, and show that the multifractal character and nonlinear properties of the healthy heart rate are encoded in the Fourier phases. We uncover a loss of multifractality for a life-threatening condition, congestive heart failure.

Anomalous diffusion models and their properties: non-stationarity, non-ergodicity, and ageing at the centenary of single particle tracking.

Abstract: Modern microscopic techniques following the stochastic motion of labelled tracer particles have uncovered significant deviations from the laws of Brownian motion in a variety of animate and inanimate systems. Such anomalous diffusion can have different physical origins, which can be identified from careful data analysis. In particular, single particle tracking provides the entire trajectory of the traced particle, which allows one to evaluate different observables to quantify the dynamics of the system under observation. We here provide an extensive overview over different popular anomalous diffusion models and their properties. We pay special attention to their ergodic properties, highlighting the fact that in several of these models the long time averaged mean squared displacement shows a distinct disparity to the regular, ensemble averaged mean squared displacement. In these cases, data obtained from time averages cannot be interpreted by the standard theoretical results for the ensemble averages. Here we therefore provide a comparison of the main properties of the time averaged mean squared displacement and its statistical behaviour in terms of the scatter of the amplitudes between the time averages obtained from different trajectories. We especially demonstrate how anomalous dynamics may be identified for systems, which, on first sight, appear to be Brownian. Moreover, we discuss the ergodicity breaking parameters for the different anomalous stochastic processes and showcase the physical origins for the various behaviours. This Perspective is intended as a guidebook for both experimentalists and theorists working on systems, which exhibit anomalous diffusion.

Detection of n:m Phase Locking from Noisy Data: Application to Magnetoencephalography

Abstract: We use the concept of phase synchronization for the analysis of noisy nonstationary bivariate data. Phase synchronization is understood in a statistical sense as an existence of preferred values of the phase difference, and two techniques are proposed for a reliable detection of synchronous epochs. These methods are applied to magnetoencephalograms and records of muscle activity of a Parkinsonian patient. We reveal that the temporal evolution of the peripheral tremor rhythms directly reflects the time course of the synchronization of abnormal activity between cortical motor areas.