1. Periodic calcium waves in coupled cells induced by internal noiseMatjaž Perc, Marko Gosak, Marko Marhl, 2007, izvirni znanstveni članek Opis: We show that internal stochasticity, originating from finite cell sizes and related small numbers of reactant ions participating in the dynamics, is able to extract a characteristic spatial frequency of calcium waves in the medium of diffusively coupled cells. Internal noise is thereby the only agent acting on the system. As the spatial periodicity is best pronounced at an intermediate level of stochasticity the reported phenomenon is thus a novel observation of internal noise spatial coherence resonance in biochemical tissuelike media. In addition, results shed light on the stochastic versus deterministic nature of dynamics at the cellular and tissue level. Ključne besede: noise, spatiotemporal noise, intensity, spatial resonance, chemical media, stochastic systems Objavljeno: 07.06.2012; Ogledov: 1186; Prenosov: 65 Povezava na celotno besedilo 
2. Transition from Gaussian to Levy distributions of stochastic payoff variations in the spatial prisoner's dilemma gameMatjaž Perc, 2007, izvirni znanstveni članek Opis: We study the impact of stochastic payoff variations with different distributions on the evolution of cooperation in the spatial prisoner's dilemma game. We find that Gaussiandistributed payoff variations are most successful in promoting cooperation irrespective of the temptation to defect. In particular, the facilitative effect of noise on the evolution of cooperation decreases steadily as the frequency of rare events increases. Findings are explained via an analysis of local payoff ranking violations. The relevance of results for economics and sociology is discussed. Ključne besede: stochastic systems, spatial resonance, stochastic payoff variations, nonlinear systems, noise, spatial dynamics, mathematical models, prisoner's dilemma Objavljeno: 07.06.2012; Ogledov: 1432; Prenosov: 72 Povezava na celotno besedilo 
3. Stochastic resonance in soft matter systems : combined effects of static and dynamic disorderMatjaž Perc, Marko Gosak, Samo Kralj, 2008, izvirni znanstveni članek Opis: We study the impact of static and dynamic disorder on the phenomenon of stochastic resonance (SR) in a representative soft matter system. Due to their extreme susceptibility to weak perturbations, soft matter systems appear to be excellent candidates for the observation of SR. Indeed, we derive generic SR equations from a polymerstabilized ferroelectric liquid crystal (LC) cell, which is a typical soft matter representative constituting one of the basic components in several electrooptic applications. We generalize these equations further in order to study an even broader class of qualitatively different systems, especially disclosing the influence of different types of static disorder and interaction ranges amongst LC molecules on the SR response. We determine the required conditions for the observation of SR in the examined system, and moreover, reveal that a random field type static disorder yields qualitatively different responses with respect to random dilution, random bond and spin glass universality classes. In particular, while the latter three decrease the level of dynamic disorder (Gaussian noise) warranting the optimal response, the former evokes exactly the opposite effect, hence increasing the optimal noise level that is needed to resonantly finetune the system's response in accordance with the weak deterministic electric field. These observations are shown to be independent of the system size and range of interactions, thus implying their general validity and potentially wide applicability also within other similar settings. We argue that soft matter systems might be particularly adequate as a base for different SRbased sensitive detectors and thus potent candidates for additional theoretical as well as experimental research in the presently outlined direction. Ključne besede: dynamic systems, stochastic processes, stochastic resonance, nonlinear dynamical systems, softmatter systems, static disorder, dynamic disorder Objavljeno: 07.06.2012; Ogledov: 1321; Prenosov: 66 Povezava na celotno besedilo 
4. Topologically determined optimal stochastic resonance responses of spatially embedded networksMarko Gosak, Dean Korošak, Marko Marhl, 2011, izvirni znanstveni članek Opis: We have analyzed the stochastic resonance phenomenon on spatial networks of bistable and excitable oscillators, which are connected according to their location and the amplitude of external forcing. By smoothly altering the network topology from a scalefree (SF) network with dominating longrange connections to a network where principally only adjacent oscillators are connected, we reveal that besides an optimal noise intensity, there is also a most favorable interaction topology at which the best correlation between the response of the network and the imposed weak external forcing is achieved. For various distributions of the amplitudes of external forcing, the optimal topology is always found in the intermediate regime between the highly heterogeneous SF network and the strong geometric regime. Our findings thus indicate that a suitable number of hubs and with that an optimal ratio between short and longrange connections is necessary in order to obtain the best global response of a spatial network. Furthermore, we link the existence of the optimal interaction topology to a critical point indicating the transition from a longrange interactionsdominated network to a more latticelike network structure. Ključne besede: physics, stochastic resonance, complex networks Objavljeno: 07.06.2012; Ogledov: 1251; Prenosov: 338 Celotno besedilo (2,08 MB) Gradivo ima več datotek! Več...

5. Stochastic resonance on excitable smallworld networks via a pacemakerMatjaž Perc, 2007, izvirni znanstveni članek Opis: We show that the correlation between the frequency of subthreshold pacemaker activity and the response of an excitable array is resonantly dependent on the intensity of additive spatiotemporal noise. Thereby, the effect of the underlying network, defining the interactions among excitable units, largely depends on the coupling strength. Only for intermediate coupling strengths is the small world property able to enhance the stochastic resonance, whereas for smaller and larger couplings the impact of the transition from diffusive to random networks is less profound. Thus, the optimal interplay between a localized source of weak rhythmic activity and the response of the whole array demands a delicate balance between the strength of excitation transfer and the effectiveness of the network structure to support it. Ključne besede: stochastic resonance, smallworld networks, cardiology, neurophysiology, nonlinear dynamical systems, spatiotemporal phenomena Objavljeno: 31.05.2012; Ogledov: 1373; Prenosov: 76 Povezava na celotno besedilo 