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Does strong heterogeneity promote cooperation by group interactions?
Matjaž Perc, 2011, izvirni znanstveni članek

Opis: Previous research has highlighted the importance of strong heterogeneity for the successful evolution of cooperation in games governed by pairwise interactions. Here we determine to what extent this is true for games governed by group interactions. We therefore study the evolution of cooperation in the public goods game on the square lattice, the triangular lattice, and the random regular graph, whereby the payoffs are distributed either uniformly or exponentially amongst the players by assigning to them individual scaling factors that determine the share of the public good they will receive. We find that uniformly distributed public goods are more successful in maintaining high levels of cooperation than exponentially distributed public goods. This is not in agreement with previous results on games governed by pairwise interactions, indicating that group interactions may be less susceptible to the promotion of cooperation by means of strong heterogeneity than originally assumed, and that the role of strongly heterogeneous states should be reexamined for other types of games.
Ključne besede: social dilemmas, cooperation, public goods, inequality, social diversity
Objavljeno: 30.06.2017; Ogledov: 79; Prenosov: 0
.pdf Polno besedilo (862,29 KB)

Costly hide and seek pays
Attila Szolnoki, Matjaž Perc, 2014, izvirni znanstveni članek

Opis: Deliberate deceptiveness intended to gain an advantage is commonplace in human and animal societies. In a social dilemma, an individual may only pretend to be a cooperator to elicit cooperation from others, while in reality he is a defector. With this as motivation, we study a simple variant of the evolutionary prisonerʼs dilemma game entailing deceitful defectors and conditional cooperators that lifts the veil on the impact of such two-faced behavior. Defectors are able to hide their true intentions at a personal cost, while conditional cooperators are probabilistically successful at identifying defectors and act accordingly. By focusing on the evolutionary outcomes in structured populations, we observe a number of unexpected and counterintuitive phenomena. We show that deceitful behavior may fare better if it is costly, and that a higher success rate of identifying defectors does not necessarily favor cooperative behavior. These results are rooted in the spontaneous emergence of cycling dominance and spatial patterns that give rise to fascinating phase transitions, which in turn reveal the hidden complexity behind the evolution of deception.
Ključne besede: social dynamics, deceit, evolutionary games, public goods, econophysics, cooperation
Objavljeno: 30.06.2017; Ogledov: 38; Prenosov: 0
.pdf Polno besedilo (580,42 KB)

Competition of tolerant strategies in the spatial public goods game
Attila Szolnoki, Matjaž Perc, 2016, izvirni znanstveni članek

Opis: Tolerance implies enduring trying circumstances with a fair and objective attitude. To determine whether evolutionary advantages might be stemming from diverse levels of tolerance in a population, we study a spatial public goods game, where in addition to cooperators, defectors, and loners, tolerant players are also present. Depending on the number of defectors within a group, a tolerant player can either cooperate in or abstain from a particular instance of the game.Weshow that the diversity of tolerance can give rise to synergistic effects, wherein players with a different threshold in terms of the tolerated number of defectors in a group compete most effectively against defection and default abstinence. Such synergistic associations can stabilise states of full cooperation where otherwise defection would dominate.Weobserve complex pattern formation that gives rise to an intricate phase diagram, where invisible yet stable strategy alliances require outmost care lest they are overlooked. Our results highlight the delicate importance of diversity and tolerance for the provisioning of public goods, and they reveal fascinating subtleties of the spatiotemporal dynamics that is due to the competition of subsystem solutions in structured populations.
Ključne besede: evolutionary game theory, public goods game, human cooperation
Objavljeno: 30.06.2017; Ogledov: 40; Prenosov: 0
.pdf Polno besedilo (1,84 MB)

Coevolution of teaching activity promotes cooperation
Attila Szolnoki, Matjaž Perc, 2008, izvirni znanstveni članek

Opis: Evolutionary games are studied where the teaching activity of players can evolve in time. Initially all players following either the cooperative or defecting strategy are distributed on a square lattice. The rate of strategy adoption is determined by the payoff difference and a teaching activity characterizing the donor's capability to enforce its strategy on the opponent. Each successful strategy adoption process is accompanied by an increase in the donor's teaching activity. By applying an optimum value of the increment, this simple mechanism spontaneously creates relevant inhomogeneities in the teaching activities that support the maintenance of cooperation for both the prisoner's dilemma and the snowdrift game.
Ključne besede: evolutionary game theory, prisoner's dilemma, spatial games, snowdrift game, coevolution
Objavljeno: 30.06.2017; Ogledov: 57; Prenosov: 0
.pdf Polno besedilo (521,01 KB)

Smectic A herringbone patterns
Samo Kralj, Emmanuelle Lacaze, George Cordoyiannis, Zdravko Kutnjak, 2014, objavljeni znanstveni prispevek na konferenci

Opis: Two qualitatively different SmA structures exhibiting herringbone-type layer patterns, to which we refer as the Defectless Smectic Herringbone (DSH) and the Dislocation Decorated Smectic Herringbone (DDSH) pattern are studied by a Landau-de Gennes-Ginzburg mesoscopic approach. Liquid crystal structures are described in terms of a nematic director field and a smectic complex order parameter. It is demonstrated that, in the proximity of the N-SmA phase transition, a melting of smectic layers could be realised even for relatively weakly-tilted smectic layers in DSH patterns (i.e. θt ≈ 100) for type I Sm4 phase. The width of melted region could be relatively large with respect to bulk values of the smectic characteristic lengths. In addition, a critical value of θt is determined at which a DDSH pattern is expected to appear.
Ključne besede: liquid crystals, patterns, structural transitions
Objavljeno: 30.06.2017; Ogledov: 34; Prenosov: 0
.pdf Polno besedilo (1005,99 KB)

Wisdom of groups promotes cooperation in evolutionary social dilemmas
Attila Szolnoki, Zhen Wang, Matjaž Perc, 2012, izvirni znanstveni članek

Opis: Whether or not to change strategy depends not only on the personal success of each individual, but also on the success of others. Using this as motivation, we study the evolution of cooperation in games that describe social dilemmas, where the propensity to adopt a different strategy depends both on individual fitness as well as on the strategies of neighbors. Regardless of whether the evolutionary process is governed by pairwise or group interactions, we show that plugging into the wisdom of groups strongly promotes cooperative behavior. The more the wider knowledge is taken into account the more the evolution of defectors is impaired. We explain this by revealing a dynamically decelerated invasion process, by means of which interfaces separating different domains remain smooth and defectors therefore become unable to efficiently invade cooperators. This in turn invigorates spatial reciprocity and establishes decentralized decision making as very beneficial for resolving social dilemmas.
Ključne besede: cooperation, public goods, wisdom of crowds, phase transitions, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 129; Prenosov: 2
.pdf Polno besedilo (646,99 KB)

Triggered dynamics in a model of different fault creep regimes
Srđan Kostić, Igor Franović, Matjaž Perc, Nebojša Vasović, Kristina Todorović, 2014, izvirni znanstveni članek

Opis: The study is focused on the effect of transient external force induced by a passing seismic wave on fault motion in different creep regimes. Displacement along the fault is represented by the movement of a spring-block model, whereby the uniform and oscillatory motion correspond to the fault dynamics in post-seismic and inter-seismic creep regime, respectively. The effect of the external force is introduced as a change of block acceleration in the form of a sine wave scaled by an exponential pulse. Model dynamics is examined for variable parameters of the induced acceleration changes in reference to periodic oscillations of the unperturbed system above the supercritical Hopf bifurcation curve. The analysis indicates the occurrence of weak irregular oscillations if external force acts in the post-seismic creep regime. When fault motion is exposed to external force in the inter-seismic creep regime, one finds the transition to quasiperiodic- or chaos-like motion, which we attribute to the precursory creep regime and seismic motion, respectively. If the triggered acceleration changes are of longer duration, a reverse transition from inter-seismic to post-seismic creep regime is detected on a larger time scale.
Ključne besede: geophysics, nonlinear dynamics, chaos, earthquake
Objavljeno: 23.06.2017; Ogledov: 96; Prenosov: 0
.pdf Polno besedilo (669,71 KB)

Sustainable institutionalized punishment requires elimination of second-order free-riders
Matjaž Perc, 2012, izvirni znanstveni članek

Opis: Although empirical and theoretical studies affirm that punishment can elevate collaborative efforts, its emergence and stability remain elusive. By peer-punishment the sanctioning is something an individual elects to do depending on the strategies in its neighborhood. The consequences of unsustainable efforts are therefore local. By pool-punishment, on the other hand, where resources for sanctioning are committed in advance and at large, the notion of sustainability has greater significance. In a population with free-riders, punishers must be strong in numbers to keep the "punishment pool" from emptying. Failure to do so renders the concept of institutionalized sanctioning futile. We show that pool-punishment in structured populations is sustainable, but only if second-order free-riders are sanctioned as well, and to a such degree that they cannot prevail. A discontinuous phase transition leads to an outbreak of sustainability when punishers subvert second-order free-riders in the competition against defectors.
Ključne besede: cooperation, public goods, punishment, institutions, phase transitions, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 108; Prenosov: 1
.pdf Polno besedilo (469,23 KB)

Stability of cooperation under image scoring in group interactions
Matjaž Perc, Attila Szolnoki, Heinrich H. Nax, Dirk Helbing, 2015, izvirni znanstveni članek

Opis: Image scoring sustains cooperation in the repeated two-player prisoner's dilemma through indirect reciprocity, even though defection is the uniquely dominant selfish behaviour in the one-shot game. Many real-world dilemma situations, however, firstly, take place in groups and, secondly, lack the necessary transparency to inform subjects reliably of others' individual past actions. Instead, there is revelation of information regarding groups, which allows for "group scoring" but not for image scoring. Here, we study how sensitive the positive results related to image scoring are to information based on group scoring. We combine analytic results and computer simulations to specify the conditions for the emergence of cooperation. We show that under pure group scoring, that is, under the complete absence of image-scoring information, cooperation is unsustainable. Away from this extreme case, however, the necessary degree of image scoring relative to group scoring depends on the population size and is generally very small. We thus conclude that the positive results based on image scoring apply to a much broader range of informational settings that are relevant in the real world than previously assumed.
Ključne besede: public goods, group interactions, phase transition, social dilemma, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 102; Prenosov: 0
.pdf Polno besedilo (329,32 KB)

Spreading of cooperative behaviour across interdependent groups
Luo-Luo Jiang, Matjaž Perc, 2013, izvirni znanstveni članek

Opis: Recent empirical research has shown that links between groups reinforce individuals within groups to adopt cooperative behaviour. Moreover, links between networks may induce cascading failures, competitive percolation, or contribute to efficient transportation. Here we show that there in fact exists an intermediate fraction of links between groups that is optimal for the evolution of cooperation in the prisoners dilemma game. We consider individual groups with regular, random, and scale-free topology, and study their different combinations to reveal that an intermediate interdependence optimally facilitates the spreading of cooperative behaviour between groups. Excessive between-group links simply unify the two groups and make them act as one, while too rare between-group links preclude a useful information flow between the two groups. Interestingly, we find that between-group links are more likely to connect two cooperators than in-group links, thus supporting the conclusion that they are of paramount importance.
Ključne besede: social dilemma, cooperation, public goods, biased utility, interdependent networks, statistical physics of social systems
Objavljeno: 23.06.2017; Ogledov: 157; Prenosov: 0
.pdf Polno besedilo (665,03 KB)

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