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41.
Self-organization of progress across the century of physics
Matjaž Perc, 2013, izvirni znanstveni članek

Opis: We make use of information provided in the titles and abstracts of over half a million publications that were published by the American Physical Society during the past 119 years. By identifying all unique words and phrases and determining their monthly usage patterns, we obtain quantifiable insights into the trends of physics discovery from the end of the 19th century to today. We show that the magnitudes of upward and downward trends yield heavy-tailed distributions, and that their emergence is due to the Matthew effect. This indicates that both the rise and fall of scientific paradigms is driven by robust principles of self-organization. Data also confirm that periods of war decelerate scientific progress, and that the later is very much subject to globalisation.
Ključne besede: self-organization, preferential attachment, evolution of progress, history of physics, statistical physics of social systems
Objavljeno: 23.06.2017; Ogledov: 387; Prenosov: 163
.pdf Celotno besedilo (865,74 KB)
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42.
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: 686; Prenosov: 214
.pdf Celotno besedilo (665,03 KB)
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43.
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: 499; Prenosov: 204
.pdf Celotno besedilo (469,23 KB)
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44.
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: 484; Prenosov: 186
.pdf Celotno besedilo (646,99 KB)
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45.
Isospin violating decays of positive parity Bs mesons in HMχPT
Svjetlana Fajfer, Anita Prapotnik Brdnik, 2016, izvirni znanstveni članek

Opis: Recent lattice QCD results suggest that the masses of the first two positive parity Bs mesons lie below the BK threshold, similar to the case of D∗s0(2317)+ and Ds1(2460)+ mesons. The mass spectrum of Bs mesons seems to follow the pattern of a Ds mass spectrum. As in the case of charmed mesons, the structure of positive parity Bs mesons is very intriguing. To shed more light on this issue, we investigate the strong isospin violating decays B∗0s0→B0sπ0, B0s1→B∗0sπ0, and B0s1→B0sππ within heavy meson chiral perturbation theory. The two-body decay amplitude arises at tree level and we show that the loop corrections give significant contributions. On the other hand, in the case of three-body decay B0s1→B0sππ the amplitude occurs only at loop level. We find that the decay widths for these decays are Γ(B0s1→B0sππ)∼10−3 keV, and Γ(B∗0s0→B0sπ0)≤55 keV, Γ(B0s1→B∗0sπ0)≤50 keV. More precise knowledge of the coupling constant describing the interaction of positive and negative parity heavy mesons with light pseudo-scalar mesons would help to increase the accuracy of our calculation.
Ključne besede: physics, elementary particles, B mesons, decays
Objavljeno: 26.06.2017; Ogledov: 295; Prenosov: 30
.pdf Celotno besedilo (743,71 KB)
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46.
47.
Measurement of time-dependent CP violation in B 0 → η′K 0 decays
Luka Šantelj, Marko Bračko, Boštjan Golob, Samo Korpar, Peter Križan, Tara Nanut, Rok Pestotnik, Marko Petrič, Eva Ribežl, Marko Starič, Anže Zupanc, 2014, izvirni znanstveni članek

Opis: We present a measurement of the time-dependent CP violation parameters in B0 → η′K0 decays. The measurement is based on the full data sample containing 772 × 10^6 BB pairs collected at the Υ(4S) resonance using the Belle detector at the KEKB asymmetric-energy e+e− collider. The measured values of the mixing-induced and direct CP violation parameters are: sin⁡ 2ϕ1eff=+0.68±0.07±0.03, Aη′K0=+0.03±0.05±0.04, where the first uncertainty is statistical and the second is systematic. The values obtained are the most accurate to date. Furthermore, these results are consistent with our previous measurements and with the world-average value of sin 2ϕ1 measured in B0 → J/ψK0 decays.
Ključne besede: CP violation, CKM angle beta, e+-e- Experiments, B physics
Objavljeno: 27.06.2017; Ogledov: 394; Prenosov: 213
.pdf Celotno besedilo (448,79 KB)
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48.
Search for B decays to final states with the η c meson
A. Vinokurova, Marko Bračko, Boštjan Golob, Samo Korpar, Peter Križan, Rok Pestotnik, Marko Petrič, Eva Ribežl, Samo Stanič, Marko Starič, Luka Šantelj, Anže Zupanc, 2015, izvirni znanstveni članek

Opis: We report a search for B decays to selected final states with the ηc meson: B± → K±ηcπ+π−, B± → K±ηcω, B± → K±ηcη and B± → K±ηcπ0. The analysis is based on 772 × 10^6 B¯B pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We set 90% confidence level upper limits on the branching fractions of the studied B decay modes, independent of intermediate resonances, in the range (0.6–5.3)×10^−4. We also search for molecular-state candidates in the D^0 ¯D^∗0 − ¯D^0D^∗0, D^0 ¯D^0 + ¯D^0D^0 and D^∗0¯D^∗0 + ¯D^∗0D^∗0 combinations, neutral partners of the Z(3900)± and Z(4020)±, and a poorly understood state X(3915) as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range (0.6–6.9)×10^−5.
Ključne besede: exotics, quarkonium, e+-e- experiments, B physics, particle and resonance production
Objavljeno: 27.06.2017; Ogledov: 413; Prenosov: 242
.pdf Celotno besedilo (129,32 KB)
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49.
Evolutionary advantages of adaptive rewarding
Attila Szolnoki, Matjaž Perc, 2012, izvirni znanstveni članek

Opis: Our well-being depends on both our personal success and the success of our society. The realization of this fact makes cooperation an essential trait. Experiments have shown that rewards can elevate our readiness to cooperate, but since giving a reward inevitably entails paying a cost for it, the emergence and stability of such behavior remains elusive. Here we show that allowing for the act of rewarding to self-organize in dependence on the success of cooperation creates several evolutionary advantages that instill new ways through which collaborative efforts are promoted. Ranging from indirect territorial battle to the spontaneous emergence and destruction of coexistence, phase diagrams and the underlying spatial patterns reveal fascinatingly rich social dynamics that explain why this costly behavior has evolved and persevered. Comparisons with adaptive punishment, however, uncover an Achilles heel of adaptive rewarding, coming from over-aggression, which in turn hinders optimal utilization of network reciprocity. This may explain why, despite its success, rewarding is not as firmly embedded into our societal organization as punishment.
Ključne besede: cooperation, public goods, reward, punishment, phase transitions, physics of social systems
Objavljeno: 30.06.2017; Ogledov: 622; Prenosov: 224
.pdf Celotno besedilo (2,15 MB)
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50.
Information sharing promotes prosocial behaviour
Attila Szolnoki, Matjaž Perc, 2013, izvirni znanstveni članek

Opis: More often than not, bad decisions are bad regardless of where and when they are made. Information sharing might thus be utilized to mitigate them. Here we show that sharing information about strategy choice between players residing on two different networks reinforces the evolution of cooperation. In evolutionary games, the strategy reflects the action of each individual that warrants the highest utility in a competitive setting. We therefore assume that identical strategies on the two networks reinforce themselves by lessening their propensity to change. Besides network reciprocity working in favour of cooperation on each individual network, we observe the spontaneous emergence of correlated behaviour between the two networks, which further deters defection. If information is shared not just between individuals but also between groups, the positive effect is even stronger, and this despite the fact that information sharing is implemented without any assumptions with regard to content.
Ključne besede: cooperation, information, social dilemma, public goods, interdependent networks, statistical physics of social systems
Objavljeno: 03.07.2017; Ogledov: 355; Prenosov: 209
.pdf Celotno besedilo (756,59 KB)
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