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Heterogeneous aspirations promote cooperation in the prisoner's dilemma game
Matjaž Perc, Zhen Wang, 2010, izvirni znanstveni članek

Opis: To be the fittest is central to proliferation in evolutionary games. Individuals thus adopt the strategies of better performing players in the hopeof successful reproduction. In structured populations the array of those that are eligible to act as strategy sources is bounded to the immediate neighbors of each individual. But which one of these strategy sources should potentially be copied? Previous research dealt with this question either by selecting the fittest or by selecting one player uniformly at random. Here we introduce a parameter that interpolates between these two extreme options. Setting equal to zero returns the random selection of the opponent, while positive favor the fitter players. In addition, we divide the population intotwo groups. Players from group select their opponents as dictated by the parameter , while players from group do so randomly irrespective of . We denote the fraction of players contained in groups and by and , respectively. The two parameters and allow us to analyze in detail how aspirations in the context of the prisoner's dilemma game influence the evolution of cooperation. We find that for sufficiently positive values of there exist a robust intermediate for which cooperation thrives best. The robustness of this observation is tested against different levels of uncertainty in the strategy adoption process and for different interaction networks. We also provide complete phase diagrams depicting the dependence of the impact of and for different values of , and contrast the validity of ourconclusions by means of an alternative model where individual aspiration levels are subject to evolution as well. Our study indicates that heterogeneity in aspirations may be key for the sustainability of cooperation in structured populations.
Ključne besede: evolutionary game theory, prisoner's dilemma, spatial games, aspirations, social systems, physics and society
Objavljeno: 19.06.2017; Ogledov: 441; Prenosov: 166
.pdf Celotno besedilo (822,95 KB)
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Domen Bukovec, 2012, diplomsko delo

Opis: V diplomskem delu predstavimo računalniške igre, temelječe na zakonih fizike. Raziskali smo razvoj iger skozi čas z upoštevanjem fizikalnih zakonitosti. Pri implementaciji lastne simulacije, ki vsebuje osnovne fizikalne zakonitosti, smo uporabili orodja Visual Studio, XNA ter fizikalni pogon Farseer Physics Engine.
Ključne besede: Računalniške igre, Farseer Physics Engine, fizikalni pogon
Objavljeno: 02.07.2012; Ogledov: 1122; Prenosov: 79
.pdf Celotno besedilo (1,25 MB)

Influence of internal disorder on the superconducting state in the organic layered superconductor [kappa]-(BEDT-TTF)[sub]2Cu[N(CN)[sub]2]Br
Marko Pinterić, Silvija Tomić, Mladen Prester, Đuro Drobac, Kazumi Maki, 2002, izvirni znanstveni članek

Opis: We report high-sensitivity AC susceptibility measurements of the penetration depth in the Meissner state of the layered organic superconductor ▫$kappa$▫-(BEDT-TTF)▫$_2$▫Cu[N(CN)▫$_2$▫]Br. We have studied nominally pure single crystals from the two different syntheses and employed controlled cooling procedures in order to minimize intrinsic remnant disorder at low temperatures associated with the glass transition, caused by ordering of the ethylene moieties in BEDT-TTF molecule at ▫$T_{text{G}}$▫ = 75°K. We find that the optimal cooling procedures (slow cooling of -0.2°K/h or annealing for 3 days in the region of ▫$T_{text{G}}$▫) needed to establish the ground state, depend critically on the sample origin indicating different relaxationtimes of terminal ethylene groups. We show that, in the ground state, the behavior observed for nominally pure single crystals from both syntheses is consistent with unconventional $d$-wave order parameter. The in-plane penetration depth ▫$lambda_{text{in}}(T)$▫ is strongly linear, whereas the out-of-plane component ▫$lambda_{text{out}}(T)$▫ varies as ▫$T^2$▫. In contrast, the behavior of single crystals with long relaxation times observed after slow (-0.2°K/h) cooling is as expected for a $d$-wave superconductor with impurities (textit{i.e.} ▫$lambda_{text{in}}(T) proptolambda_{text{out}}(T) propto T^2$▫) or might be also reasonably welldescribed by the ▫$s$▫-wave model. Our results might reconcile the contradictory findings previously reported by different authors.
Ključne besede: solid state physics, organic superconductors, magnetic measurements
Objavljeno: 01.06.2012; Ogledov: 822; Prenosov: 18
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Influence of vacuum energy on scattering
Milan Marčič, 1997, izvirni znanstveni članek

Opis: We deal with photon-electron scattering which occurs between two uncharged conducting parallel plates moving away from each other at a constant velocity. The electromagnetic vacuum field between the two plates is defined by the configuration of space and also interacts with the electrons. We show the relevant operators for both the photon and the electron fields and the computation of the corresponding Feynman propagator, S-matrix and scattering cross section, taking into account the influence of the changeable vacuum field. Correction terms in the computed S-matrix and scattering cross section manifest the influence of the changeable vacuum field. We analyze an example for low-energy scattering of the influence of the changeable vacuum field uponthe scattering cross section.
Ključne besede: physics, quantum electrodynamics, statistical thermodynamics
Objavljeno: 01.06.2012; Ogledov: 1087; Prenosov: 45
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Topologically determined optimal stochastic resonance responses of spatially embedded networks
Marko 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 scale-free (SF) network with dominating long-range 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 long-range 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 long-range interactions-dominated network to a more lattice-like network structure.
Ključne besede: physics, stochastic resonance, complex networks
Objavljeno: 07.06.2012; Ogledov: 1003; Prenosov: 157
.pdf Celotno besedilo (2,08 MB)
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Finite-size effects on order reconstruction around nematic defects
Samo Kralj, Riccardo Rosso, Epifanio G. Virga, 2010, izvirni znanstveni članek

Opis: By use of the Landau-de Gennes phenomenological theory, we study the texture of a nematic liquid crystal confined within a hybrid cell. Precisely, we consider cylindrically symmetric solutions containing topological defects dictated by appropriate boundary conditions. We focus our attention on cells whose dimensions are comparable with the biaxial correlation length ▫$xi_b$▫. For such severe confinements the order reconstruction (OR) configuration could be stable. Its structural details reflect the balance among boundary-enforced frustration, elastic penalties, and finite-size effects. In particular, we analyze the interplay between finite-size effects and topological defects. We show that defects are always pinned to the negatively (planar) uniaxial sheet of the OR structure. The presence of a ring defect can dramatically increase the critical threshold below which the OR structure is stable.
Ključne besede: physics, liquid crystals, nematic crystals, nematic defects, structural transitions
Objavljeno: 07.06.2012; Ogledov: 926; Prenosov: 50
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Fingered core structure of nematic boojums
Samo Kralj, Riccardo Rosso, Epifanio G. Virga, 2008, izvirni znanstveni članek

Opis: Using the Landau-de Gennes phenomenological approach, we study the fine biaxial core structure of a boojum residing on the surface of a nematic liquid crystal phase. The core is formed by a negatively uniaxial finger, surrounded by a shell with maximal biaxiality. The characteristic finger's length and the shell's width are comparable to the biaxial correlation length. The finger tip is melted for topological reasons. Upon decreasing the surface anchoring strength below a critical value, the finger gradually leaves the bulk and it is expelled through the surface.
Ključne besede: physics, liquid crystals, nematic crystals, line defects, surface phenomena
Objavljeno: 07.06.2012; Ogledov: 773; Prenosov: 51
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Effects of small-world connectivity on noise-induced temporal and spatial order in neural media
Matjaž Perc, 2006, izvirni znanstveni članek

Opis: We present an overview of possible effects of small-world connectivity on noise-induced temporal and spatial order in a two-dimensional network of excitable neural media with FitzHugh-Nagumo local dynamics. Small-world networks are characterized by a given fraction of so-called long-range couplings or shortcut links that connect distant units of the system, while all other units are coupled in a diffusive-like manner. Interestingly, already a small fraction of these long-range couplings can have wide-ranging effects on the temporal as well as spatial noise-induced dynamics of the system. Here we present two main effects. First, we show that the temporal order, characterized by the autocorrelation of a firing-rate function, can be greatly enhanced by the introduction of small-world connectivity, whereby the effect increases with the increasing fraction of introduced shortcut links. Second, we show that the introduction of long-range couplings induces disorderof otherwise ordered, spiral-wave-like, noise-induced patterns that can be observed by exclusive diffusive connectivity of spatial units. Thereby, already a small fraction of shortcut links is sufficient to destroy coherent pattern formation in the media. Although the two results seem contradictive, we provide an explanation considering the inherent scale-free nature of small-world networks, which on one hand, facilitates signal transduction and thus temporal order in the system, whilst on the other hand, disrupts the internal spatial scale of the media thereby hindering the existence of coherent wave-like patterns. Additionally, the importance of spatially versus temporally ordered neural network functioning is discussed.
Ključne besede: physics, complex systems, dynamical systems, noise, chaos, chaotic systems, chaos control, resonance
Objavljeno: 07.06.2012; Ogledov: 1038; Prenosov: 46
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Spatial coherence resonance in neuronal media with discrete local dynamics
Matjaž Perc, 2006, izvirni znanstveni članek

Opis: We study effects of spatiotemporal additive noise on the spatial dynamics of excitable neuronal media that is locally modelled by a two-dimensional map. We focus on the ability of noise to enhance a particular spatial frequency of the media in a resonant manner. We show that there exists an optimal noise intensity for which the inherent spatial periodicity of the media is resonantly pronounced, thus marking the existence of spatial coherence resonance in the studied system. Additionally, results are discussed in view of their possible biological importance.
Ključne besede: physics, complex systems, dynamical systems, noise, spatial dynamics, chaos, chaotic systems, chaos control, resonance
Objavljeno: 07.06.2012; Ogledov: 1243; Prenosov: 58
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Role of cascades in converting oscillatory signals into stationary step-like responses
Marko Marhl, Vladimir Grubelnik, 2007, izvirni znanstveni članek

Opis: In biological signal transduction pathways intermediates are often oscillatory and need to be converted into smooth output signals at the end. We show by mathematical modelling that protein kinase cascades enable converting oscillatory signals into sharp stationary step-like outputs. The importance of this result is demonstrated for the switch-like protein activation by calcium oscillations, which is of biological importance for regulating different cellular processes. In addition, we found that protein kinase cascades cause memory effects in the protein activation, which might be of a physiological advantage since a smaller amount of calcium transported in the cell is required for an effective activation of cellular processes.
Ključne besede: physics, calcium oscillations, mathematical modelling, calcium, calcium oscillations, sygnalling cascade, protein kinase cascades, signal transduction, ultrasensitivity, biochemical switch, cellular dynamics
Objavljeno: 07.06.2012; Ogledov: 986; Prenosov: 24
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