Time filter

Source Type

Santos F.P.,University of Lisbon | Santos F.P.,Institute Investigacao Interdisciplinar | Santos F.C.,University of Lisbon | Santos F.C.,Institute Investigacao Interdisciplinar | And 3 more authors.
Journal of Theoretical Biology | Year: 2015

The emergence and impact of fairness is commonly studied in the context of 2-person games, notably the Ultimatum Game. Often, however, humans face problems of collective action involving more than two individuals where fairness is known to play a very important role, and whose dynamics cannot be inferred from what is known from 2-person games. Here, we propose a generalization of the Ultimatum Game for an arbitrary number of players - the Multiplayer Ultimatum Game. Proposals are made to a group of responders who must individually reject or accept the proposal. If the total number of individual acceptances stands below a given threshold, the offer will be rejected; otherwise, the offer will be accepted, and equally shared by all responders. We investigate the evolution of fairness in populations of individuals by means of evolutionary game theory, providing both analytical insights and results from numerical simulations. We show how imposing stringent consensuses significantly increases the value of the proposals, leading to fairer outcomes and more tolerant players. Furthermore, we show how stochastic effects - such as imitation errors and/or errors when assessing the fitness of others - may further enhance the overall success in reaching fair collective action. © 2015 Elsevier Ltd.


Moreira J.A.,Institute Investigacao Interdisciplinar | Pinheiro F.L.,Institute Investigacao Interdisciplinar | Nunes A.,Institute Investigacao Interdisciplinar | Nunes A.,University of Lisbon | And 2 more authors.
Journal of Theoretical Biology | Year: 2012

Many actions take some time to have an impact - their effects only appear at some point in the future. Such time lags turn out to be ubiquitous among living organisms. Here we study the impact of time lags in the evolutionary dynamics of cooperative collective action. We consider a population in which individuals interact via a N-Person Stag Hunt dilemma and must opt to cooperate or defect. In the absence of any delay, the replicator dynamics reveals the existence of regimes in which two internal fixed points appear simultaneously. We show that the presence of time delay in the fitness of individuals leads to a delayed replicator equation exhibiting new evolutionary profiles, each profile being separated by critical values of the delay that we determine explicitly. When we break the symmetry in the time lags, we show that, generally, defectors take more advantage from delay than cooperators. Finally, when we take into consideration, approximately, effects associated with the finite population size, we find that counter-intuitive evolutionary outcomes may occur, resulting from the interplay between delay and the basins of attraction in the neighborhood of the internal fixed-points, and which may lead to full cooperation in conditions under which the outcome would be Full Defection in infinite populations. © 2012 Elsevier Ltd.


Vukov J.,Institute Investigacao Interdisciplinar | Santos F.C.,Institute Investigacao Interdisciplinar | Santos F.C.,University of Lisbon | Pacheco J.M.,Institute Investigacao Interdisciplinar | Pacheco J.M.,University of Minho
New Journal of Physics | Year: 2012

Understanding the emergence and maintenance of cooperation is one of the most challenging topics of our time. Evolutionary game theory offers a very flexible framework within which to address this challenge. Here we use the prisoner's dilemma game to investigate the performance of individuals who are capable of adopting reactive strategies in communities structurally organized by means of Barabási-Albert scale-free networks. We find that basic cognitive abilities, such as the capability to distinguish their partners and act according to their previous actions, enable cooperation to thrive. This result is particularly significant whenever fear is the leading social tension, as this fosters retaliation, thus enforcing and sustaining cooperation. Being able to simultaneously reward fellow cooperators and punish defectors proves instrumental in achieving cooperation and the welfare of the community. As a result, central individuals can successfully lead the community and turn defective players into cooperative ones. Finally, even when participation costs-known to be detrimental to cooperation in scale-free networks-are explicitly included, we find that basic cognitive abilities have enough potential to help cooperation to prevail. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Mendes R.V.,Institute Investigacao Interdisciplinar | Mendes R.V.,University of Lisbon
Chaos | Year: 2011

Using a cocycle formulation, old and new ergodic parameters beyond the Lyapunov exponent are rigorously characterized. Dynamical Renyi entropies and fluctuations of the local expansion rate are related by a generalization of the Pesin formula. How the ergodic parameters may be used to chracterize the complexity of dynamical systems is illustrated by some examples: clustering and synchronization, self-organized criticality and the topological structure of networks. © 2011 American Institute of Physics.


Han T.A.,Vrije Universiteit Brussel | Han T.A.,Free University of Colombia | Pereira L.M.,New University of Lisbon | Santos F.C.,University of Lisbon | And 3 more authors.
IJCAI International Joint Conference on Artificial Intelligence | Year: 2013

When making a mistake, individuals can apologize to secure further cooperation, even if the apology is costly. Similarly, individuals arrange commitments to guarantee that an action such as a cooperative one is in the others' best interest, and thus will be carried out to avoid eventual penalties for commitment failure. Hence, both apology and commitment should go side by side in behavioral evolution. Here we provide a computational model showing that apologizing acts are rare in non-committed interactions, especially whenever cooperation is very costly, and that arranging prior commitments can considerably increase the frequency of such behavior. In addition, we show that in both cases, with or without commitments, apology works only if it is sincere, i.e. costly enough. Most interestingly, our model predicts that individuals tend to use much costlier apology in committed relationships than otherwise, because it helps better identify free-riders such as fake committers: 'commitments bring about sincerity'. Furthermore, we show that this strategy of apology supported by commitments outperforms the famous existent strategies of the iterated Prisoner's Dilemma.


Cortez A.F.V.,University of Coimbra | Garcia A.N.C.,University of Coimbra | Neves P.N.B.,Institute Investigacao Interdisciplinar | Santos F.P.,University of Coimbra | And 4 more authors.
Journal of Instrumentation | Year: 2013

In this paper we present the experimental results for the mobility of ions in argon-ethane gaseous mixtures (Ar-C2H6) for pressures ranging from 6 to 10 Torr and for reduced electric fields in the 10 Td to 25 Td range, at room temperature. For Ar concentrations below 80% two peaks were observed in the time of arrival spectra which were attributed to ion species with 3-carbons (C3H7 +, C3H 8 + and C3H9 +) and with 4-carbons (which includes C4H7 +, C 4H9 +, C4H10 + and C4H12 + ions). For Ar concentrations above 80% a third peak appears, which may belong to C5H11 +. The time of arrival spectra for Ar concentrations of 80%, 85%, 90% and 95% are displayed in the present paper as well as the reduced mobilities determined from the peaks observed for a typical reduced electric field used in gaseous detectors (E/N = 15 Td).© 2013 IOP Publishing Ltd and Sissa Medialab srl.


Cortez A.F.V.,University of Coimbra | Garcia A.N.C.,University of Coimbra | Neves P.N.B.,Institute Investigacao Interdisciplinar | Santos F.P.,University of Coimbra | And 4 more authors.
Journal of Instrumentation | Year: 2013

A recent experimental technique was used for measuring the mobility of positive ions originated from ethane in their parent gas. In this particular experiment, measurements were made in pure ethane (C2H6) for pressures ranging from 6 to 10 Torr and for reduced electric fields varying from 6 to 42 Td. The time of arrival spectra revealed two peaks and their reduced mobilities were determined. Extrapolation to zero field led to the values of 1.58 cm2V-1s-1 and 1.47 cm 2V-1s-1, which are likely to belong to a 3-carbon ions group which includes C3H5 +, C3H7 +, C3H8 + and C3H9 + and to a 4-carbon ions group which includes C4H9 + and C4H 10 + ions. For typical reduced electric fields used in gaseous detectors (E/N > 15 Td), the mobilities were 15% smaller than the Langevin limit [1]. © 2013 IOP Publishing Ltd and Sissa Medialab srl.


Trindade A.M.F.,University of Coimbra | Cortez A.F.V.,University of Coimbra | Neves P.N.B.,Institute Investigacao Interdisciplinar | Garcia A.N.C.,University of Coimbra | And 6 more authors.
Journal of Instrumentation | Year: 2014

In this paper we present the results of the ion mobility measurements made in gaseous mixtures of argon (Ar) and methane (CH4) for pressures ranging from 5 to 8 Torr and for low reduced electric fields (in the 17 Td to 43 Td range), at room temperature. The time of arrival spectra of the several mixture ratios studied revealed that the relative abundance of the ions formed depend on the mixture ratios. For CH4 concentrations in the 2.5-10% range three well defined peaks were observed which were attributed to single-carbon ions (CH5 +), 2-carbon ions (C 2H4 + and C2H5 +), and 3-carbon ions (C3H4 +, C 3H5 +, C3H6 + and C3H7 +). The time of arrival spectra for CH4 concentrations of 2.5% (P-2.5), 5% (P-5), 10% (P-10) and the reduced mobilities of the ions obtained from the peaks observed are presented in this paper. The ion mobility study was performed for typical reduced electric fields used in gaseous detectors (E/N > 15 Td). © 2014 IOP Publishing Ltd and Sissa Medialab srl.


Garcia A.N.C.,University of Coimbra | Neves P.N.B.,Institute Investigacao Interdisciplinar | Trindade A.M.F.,University of Coimbra | Cortez A.F.V.,University of Coimbra | And 2 more authors.
Journal of Instrumentation | Year: 2014

In this paper we present the results for the ion mobility measurements made in gaseous mixtures of xenon (Xe) and nitrogen (N2) for low reduced electric fields (in the 15 Td to 30 Td range), at room temperature. The choice of reduced electric fields was guided by typical gaseous detector's demands. In the 0-100% range of Xe concentrations in the mixture, only one peak was observed which was attributed to Xe2+; in fact its mobility was found to follow Blanc's law. A typical time-of-arrival spectrum for 90% Xe and 10% N2 is shown. The reduced mobilities, obtained from the peaks, are calculated and presented in this paper. © 2014 IOP Publishing Ltd and Sissa Medialab srl.


PubMed | Institute Investigacao Interdisciplinar
Type: | Journal: Journal of theoretical biology | Year: 2012

Many actions take some time to have an impact - their effects only appear at some point in the future. Such time lags turn out to be ubiquitous among living organisms. Here we study the impact of time lags in the evolutionary dynamics of cooperative collective action. We consider a population in which individuals interact via a N-Person Stag Hunt dilemma and must opt to cooperate or defect. In the absence of any delay, the replicator dynamics reveals the existence of regimes in which two internal fixed points appear simultaneously. We show that the presence of time delay in the fitness of individuals leads to a delayed replicator equation exhibiting new evolutionary profiles, each profile being separated by critical values of the delay that we determine explicitly. When we break the symmetry in the time lags, we show that, generally, defectors take more advantage from delay than cooperators. Finally, when we take into consideration, approximately, effects associated with the finite population size, we find that counter-intuitive evolutionary outcomes may occur, resulting from the interplay between delay and the basins of attraction in the neighborhood of the internal fixed-points, and which may lead to full cooperation in conditions under which the outcome would be Full Defection in infinite populations.

Loading Institute Investigacao Interdisciplinar collaborators
Loading Institute Investigacao Interdisciplinar collaborators