11. Fluctuating excitability : a mechanism for selfsustained information flow in excitable arraysMatjaž Perc, 2007, izvirni znanstveni članek Opis: We show that the fluctuating excitability of FitzHughNagumo neurons, constituting a diffusively coupled excitable array, can induce phase slips that lead to a symmetry break yielding a preferred spreading direction of excitatory events, thus enabling persistent selfsustained and selforganized information flow in a periodic array long after a localized stimulus perturbation has sized. Possible oscillation frequencies of the informationcarrying signal are expressed analytically, and necessary conditions for the phenomenon are derived. Our results suggest that cellular diversity in neural tissue is crucial for maintaining selfsustained and organized activity in the brain even in the absence of immediate stimuli, thus facilitating continuous evolution of its mechanisms for information retrieval and storage. Ključne besede: physics, complex systems, dynamical systems, flexibility, chaos, chaotic systems, oscillations, perturbation Objavljeno: 07.06.2012; Ogledov: 1143; Prenosov: 59 Povezava na celotno besedilo 
12. Annihilation of defects in liquid crystalsMilan Svetec, Milan Ambrožič, Samo Kralj, 2007, objavljeni znanstveni prispevek na konferenci Opis: The annihilation of defect is studied theoretically in liquid crystals (LCs). We consider the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase, respectively. We stres s qualitative similarities in these processes. The whole annihilation regime is taken into account, consisting of the precollision, collision, and postcollision stage. Ključne besede: physics, liquid crystals, annihilation, defects, point defects, point disclinations, edge dislocations Objavljeno: 07.06.2012; Ogledov: 771; Prenosov: 60 Povezava na celotno besedilo 
13. Confined liquid crystaline 5CB in 2D thermodynamic space : preliminary dielectric relaxation studySebastian Pawlus, Jana Osinska, Sylwester J. Rzoska, Samo Kralj, George Cordoyiannis, 2007, objavljeni znanstveni prispevek na konferenci Opis: Results of preliminary broadband dielectric spectroscopy studies in a wide range of temperatures and pressures range for a mixture of rodlike liquid crystalline 4cyano4pentylalkylbiphenyl (5CB) and hydrophilic silica spheres (Aerosil 300) are shown. Pretransitional anomaly, observed previously in the bulk 5CB, has been found. Temperature dynamics of the mixture was investigated with via the DC conductivity ?, coupled to the reorientational relaxation. The derivative based analysis of electric conductivity showed a clear nonArrhenius dynamics and indicated the anomalous increase of the fragility strength coefficient on approaching the isotropicnematic transition. Pressure investigations of the solidification from the nematic phase showed the increase of the transition temperature on pressuring but with unusual increasing of dTNS/dP coefficient. Ključne besede: physics, liquid crystals, complex dynamics, random constraints, high pressures Objavljeno: 07.06.2012; Ogledov: 658; Prenosov: 49 Povezava na celotno besedilo 
14. Introducing nonlinear time series analysis in undergraduate coursesMatjaž Perc, 2006, strokovni članek Opis: This article is written for undergraduate students and teachers who would like to get familiar with basic nonlinear time series analysis methods. We present a stepbystep study of a simple example and provide userfriendly programs that allow an easy reproduction of presented results. In particular, we study an artificial time series generated by the Lorenz system. The mutual information and false nearest neighbour method are explained in detail, and used to obtain the best possible attractor reconstruction. Subsequently, the times series is tested for stationarity and determinism, which are both important properties that assure correct interpretation of invariant quantities that can be extracted from the data set. Finally, as the most prominent invariant quantity that allows distinguishing between regular and chaotic behaviour, we calculate the maximal Lyapunov exponent. By following the above steps, we are able to convincingly determine that the Lorenz system is chaotic directly from the generated time series, without the need to use the differential equations. Throughout the paper, emphasis on clearcut guidance and a handson approach is given in order to make the reproduction of presented results possible also for undergraduates, and thus encourage them to get familiar with the presented theory. Ključne besede: nonlinear systems, nonlinear time series analyses, physics education Objavljeno: 07.06.2012; Ogledov: 782; Prenosov: 18 Povezava na celotno besedilo 
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16. Collective behavior and evolutionary gamesMatjaž Perc, Paolo Grigolini, 2013, izvirni znanstveni članek Ključne besede: kolektivni pojavi, evolucijske igre, fazni prehodi, kompleksne mreže, statistična fizika socioloških sistemov, collective phenomena, evolutionary games, phase transitions, complex networks, evolutionary statistical physics of social systems Objavljeno: 10.07.2015; Ogledov: 619; Prenosov: 19 Povezava na celotno besedilo 
17. The conceptual learning of physics in Slovenian secondary schoolsSimon Ülen, Ivan Gerlič, 2012, izvirni znanstveni članek Opis: In the last decade, educational researchers have been intensively searching for new, innovative teaching approaches. Information and Communication Technology (ICT) has a great didactic potential and project COLOS (Conceptual Learning of Science) encourages the use of ICT in the contemporary educational process. In this paper we present the conceptual learning of Physics. With experimental research we investigated the effectiveness of such learning in Slovenian secondary school. Two groups of thirdyear students who were enrolled in an introductory Physics course participated in the study. In the experimental group students were taught through the conceptual learning and in the control group a traditional expository instruction was used. We examined the knowledge of students after carrying out lessons specifically on the topic of Electricity. Five thinking processes were assessed  Knowledge (Recall), Analysis, Comparison, Inference and Evaluation. We found that the conceptual learning was more effective than the traditional instruction. Ključne besede: traditional instruction, conceptual learning, physics, ICT, simulations, physlets Objavljeno: 10.07.2015; Ogledov: 557; Prenosov: 193 Celotno besedilo (991,17 KB) Gradivo ima več datotek! Več...

18. Progressive glucose stimulation of islet beta cells reveals a transition from segregated to integrated modular functional connectivity patternsRene Markovič, Andraž Stožer, Marko Gosak, Jurij Dolenšek, Marko Marhl, Marjan Rupnik, 2015, izvirni znanstveni članek Opis: Collective beta cell activity in islets of Langerhans is critical for the supply of insulin within an organism. Even though individual beta cells are intrinsically heterogeneous, the presence of intercellular coupling mechanisms ensures coordinated activity and a wellregulated exocytosis of insulin. In order to get a detailed insight into the functional organization of the syncytium, we applied advanced analytical tools from the realm of complex network theory to uncover the functional connectivity pattern among cells composing the intact islet. The procedure is based on the determination of correlations between long temporal traces obtained from confocal functional multicellular calcium imaging of beta cells stimulated in a stepwise manner with a range of physiological glucose concentrations. Our results revealed that the extracted connectivity networks are sparse for low glucose concentrations, whereas for higher stimulatory levels they become more densely connected. Most importantly, for all ranges of glucose concentration beta cells within the islets form locally clustered functional subcompartments, thereby indicating that their collective activity profiles exhibit a modular nature. Moreover, we show that the observed nonlinear functional relationship between different network metrics and glucose concentration represents a wellbalanced setup that parallels physiological insulin release. Ključne besede: endocrinology, computational biophysics, calcium signalling, biological physics Objavljeno: 23.06.2017; Ogledov: 478; Prenosov: 181 Celotno besedilo (957,14 KB) Gradivo ima več datotek! Več...

19. Adaptive and bounded investment returns promote cooperation in spatial public goods gamesXiaojie Chen, Yongkui Liu, Yonghui Zhou, Long Wang, Matjaž Perc, 2012, izvirni znanstveni članek Opis: The public goods game is one of the most famous models for studying the evolution of cooperation in sizable groups. The multiplication factor in this game can characterize the investment return from the public good, which may be variable depending on the interactive environment in realistic situations. Instead of using the same universal value, here we consider that the multiplication factor in each group is updated based on the differences between the local and global interactive environments in the spatial public goods game, but meanwhile limited to within a certain range. We find that the adaptive and bounded investment returns can significantly promote cooperation. In particular, full cooperation can be achieved for high feedback strength when appropriate limitation is set for the investment return. Also, we show that the fraction of cooperators in the whole population can become larger if the lower and upper limits of the multiplication factor are increased. Furthermore, in comparison to the traditionally spatial public goods game where the multiplication factor in each group is identical and fixed, we find that cooperation can be better promoted if the multiplication factor is constrained to adjust between one and the group size in our model. Our results highlight the importance of the locally adaptive and bounded investment returns for the emergence and dominance of cooperative behavior in structured populations. Ključne besede: cooperation, public goods, social dilemmas, physics of social systems Objavljeno: 19.06.2017; Ogledov: 334; Prenosov: 214 Celotno besedilo (590,51 KB) Gradivo ima več datotek! Več...

20. Directional learning and the provisioning of public goodsHeinrich H. Nax, Matjaž Perc, 2015, izvirni znanstveni članek Opis: We consider an environment where players are involved in a public goods game and must decide repeatedly whether to make an individual contribution or not. However, players lack strategically relevant information about the game and about the other players in the population. The resulting behavior of players is completely uncoupled from such information, and the individual strategy adjustment dynamics are driven only by reinforcement feedbacks from each player's own past. We show that the resulting "directional learning" is sufficient to explain cooperative deviations away from the Nash equilibrium. We introduce the concept of kstrong equilibria, which nest both the Nash equilibrium and the Aumannstrong equilibrium as two special cases, and we show that, together with the parameters of the learning model, the maximal kstrength of equilibrium determines the stationary distribution. The provisioning of public goods can be secured even under adverse conditions, as long as players are sufficiently responsive to the changes in their own payoffs and adjust their actions accordingly. Substantial levels of public cooperation can thus be explained without arguments involving selflessness or social preferences, solely on the basis of uncoordinated directional (mis)learning. Ključne besede: cooperation, public goods, directional learning, phase transitions, physics of social systems Objavljeno: 23.06.2017; Ogledov: 275; Prenosov: 187 Celotno besedilo (1,40 MB) Gradivo ima več datotek! Več...
