In social networks humans are generally benefited by maintaining friendships and community affiliation in which factors like homophily play key roles. These networks are far from being static, rather they are continually transforming or... more
In social networks humans are generally benefited by maintaining friendships and community affiliation in which factors like homophily play key roles. These networks are far from being static, rather they are continually transforming or evolving as people from time to time decide to make new friendships and dissociate themselves from old ones. There is an element of risk in dissociations from friendships or group affiliations, especially when the decision to dissociate is done with limited information. In an experiment in the form of a cooperative game with human players we investigate the formation of groups and measure the perception of risk. In the game, the players set initially to a small world network and having limited information of its structure, coordinate their movements to form the groups. We also study the local coordination between players using a data-driven model of agents based on probability matching. Our results show that the pace of group formation is mainly depe...
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It is well known that simple reaction–diffusion systems can display very rich pattern formation behaviour. Here we have studied two examples of such systems in three dimensions. First we investigate the morphology and stability of a... more
It is well known that simple reaction–diffusion systems can display very rich pattern formation behaviour. Here we have studied two examples of such systems in three dimensions. First we investigate the morphology and stability of a generic Turing system in three dimensions and then the well-known Gray–Scott model. In the latter case, we added a small number of morphogen sources in the system in order to study its robustness and the formation of connections between the sources. Our results raise the question of whether Turing patterning can produce an inductive signalling mechanism for neuronal growth.
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As scientists we like to think that modern societies and their members base their views, opinions and behaviour on scientific facts. This is not necessarily the case, even though we are all (over-) exposed to information flow through... more
As scientists we like to think that modern societies and their members base their views, opinions and behaviour on scientific facts. This is not necessarily the case, even though we are all (over-) exposed to information flow through various channels of media, i.e. newspapers, television, radio, internet, and web. It is thought that this is mainly due to the conflicting information on the mass media and to the individual attitude (formed by cultural, educational and environmental factors), that is, one external factor and another personal factor. In this paper we will investigate the dynamical development of opinion in a small population of agents by means of a computational model of opinion formation in a co-evolving network of socially linked agents. The personal and external factors are taken into account by assigning an individual attitude parameter to each agent, and by subjecting all to an external but homogeneous field to simulate the effect of the media. We then adjust the f...
In this study we present a dynamical agent-based model to investigate the interplay between the socio-economy of and SEIRS-type epidemic spreading over a geographical area, divided to smaller area districts and further to smallest area... more
In this study we present a dynamical agent-based model to investigate the interplay between the socio-economy of and SEIRS-type epidemic spreading over a geographical area, divided to smaller area districts and further to smallest area cells. The model treats the populations of cells and authorities of districts as agents, such that the former can reduce their economic activity and the latter can recommend economic activity reduction both with the overall goal to slow down the epidemic spreading. The agents make decisions with the aim of attaining as high social positions as possible relative to other agents. They evaluate their social positions based on the local and regional infection rates, compliance to the authorities’ regulations, regional drops in economic activity, and the efforts they make to mitigate the spread of epidemic. We find that the willingness of populations to comply with authorities’ recommendations has the most drastic effect to the spreading of epidemic: perio...
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Oscillator networks found in social and biological systems are characterized by the presence of wide ranges of coupling strengths and complex organization. Yet robustness and synchronization of oscillations are found to emerge on... more
Oscillator networks found in social and biological systems are characterized by the presence of wide ranges of coupling strengths and complex organization. Yet robustness and synchronization of oscillations are found to emerge on macro-scales that eventually become key to the functioning of these systems. In order to model this kind of dynamics observed, for example, in systems of circadian oscillators, we study networks of Van der Pol oscillators that are connected with hierarchical couplings. For each isolated oscillator we assume the same fundamental frequency. Using numerical simulations, we show that the coupled system goes to a phase-locked state, with both phase and frequency being the same for every oscillator at each level of the hierarchy. The observed frequency at each level of the hierarchy changes, reaching an asymptotic lowest value at the uppermost level. Notably, the asymptotic frequency can be tuned to any value below the fundamental frequency of an uncoupled Van de...
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Wikipedia, a paradigmatic example of online knowledge space is organized in a collaborative, bottom-up way with voluntary contributions, yet it maintains a level of reliability comparable to that of traditional encyclopedias. The lack of... more
Wikipedia, a paradigmatic example of online knowledge space is organized in a collaborative, bottom-up way with voluntary contributions, yet it maintains a level of reliability comparable to that of traditional encyclopedias. The lack of selected professional writers and editors makes the judgement about quality and trustworthiness of the articles a real challenge. Here we show that a self-consistent metrics for the network defined by the edit records captures well the character of editors’ activity and the articles’ level of complexity. Using our metrics, one can better identify the human-labeled high-quality articles, e.g., “featured” ones, and differentiate them from the popular and controversial articles. Furthermore, the dynamics of the editor-article system is also well captured by the metrics, revealing the evolutionary pathways of articles and diverse roles of editors. We demonstrate that the collective effort of the editors indeed drives to the direction of article improvem...
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Research Interests: Geography, Mathematical Physics, Condensed Matter Physics, Quantum Physics, Social Behaviour, and 10 moreMedicine, Epidemiological Modelling, Stochastic processes, Population, Non Linear Dynamics, Pandemics, Statistics and Probability, Geographical Spread, Pandemic, and Coronavirus Disease 2019 (COVID-19)
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We study the robustness of an evolving system that is driven by successive inclusions of new elements or constituents with m random interactions to older ones. Each constitutive element in the model stays either active or is temporarily... more
We study the robustness of an evolving system that is driven by successive inclusions of new elements or constituents with m random interactions to older ones. Each constitutive element in the model stays either active or is temporarily inactivated depending upon the influence of the other active elements. If the time spent by an element in the inactivated state reaches T W , it gets extinct. The phase diagram of this dynamic model as a function of m and T W is investigated by numerical and analytical methods and as a result both growing (robust) as well as non-growing (volatile) phases are identified. It is also found that larger time limit T W enhances the system’s robustness against the inclusion of new elements, mainly due to the system’s increased ability to reject ‘falling-together’ type attacks. Our results suggest that the ability of an element to survive in an unfavourable situation for a while, either as a minority or in a dormant state, could improve the robustness of the...
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Research Interests: Computer Science, Algorithms, Physics, Communication, Science Policy, and 15 moreSocial Networking, Ecology, Medicine, Multidisciplinary, Probability, Biological Sciences, Social behavior, Humans, Data Collection, PLoS one, Social Behavior, Friends, Internet, social network formation, and Residence Characteristics
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Here we present an agent-based model where agents interact with other agents by playing a hybrid of dictator and ultimatum games in a co-evolving social network. The basic assumption about the behaviour of the agents in both games is that... more
Here we present an agent-based model where agents interact with other agents by playing a hybrid of dictator and ultimatum games in a co-evolving social network. The basic assumption about the behaviour of the agents in both games is that they try to attain superior socioeconomic positions relative to other agents. As the model parameters we have chosen the relative proportions of the dictator and ultimatum game strategies being played between a pair of agents in a single social transaction and a parameter depicting the living costs of the agents. The motivation of the study is to examine how different types of social interactions affect the formation of social structures and networks, when the agents have a tendency to maximize their socioeconomic standing. We find that such social networks of agents invariably undergo a community formation process from simple chain-like structure to more complex networks as the living cost parameter is increased. The point where this occurs, depen...
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In human relations individuals' gender and age play a key role in the structures and dynamics of their social arrangements. In order to analyze the gender preferences of individuals in interaction with others at different stages of... more
In human relations individuals' gender and age play a key role in the structures and dynamics of their social arrangements. In order to analyze the gender preferences of individuals in interaction with others at different stages of their lives we study a large mobile phone dataset. To do this we consider four fundamental gender-related caller and callee combinations of human interactions, namely male to male, male to female, female to male, and female to female, which together with age, kinship, and different levels of friendship give rise to a wide scope of human sociality. Here we analyse the relative strength of these four types of interaction using a large dataset of mobile phone communication records. Our analysis suggests strong age dependence for an ego of one gender choosing to call an individual of either gender. We observe a strong opposite sex bonding across most of their reproductive age. However, older women show a strong tendency to connect to another female that i...
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The last centuries have seen a great surge in our understanding and control of “simple” physical,chemical, and biological processes through data analysis and the mathematical modeling of theirunderlying dynamics [...]
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As a step towards studying human-agent collectives, we conduct an online game with human participants cooperating on a network. The game is presented in the context of achieving group formation through local coordination. The players set... more
As a step towards studying human-agent collectives, we conduct an online game with human participants cooperating on a network. The game is presented in the context of achieving group formation through local coordination. The players set initially to a small-world network with limited information on the location of other players, coordinate their movements to arrange themselves into groups. To understand the decision-making process, we construct a data-driven model of agents based on probability matching. The model allows us to gather insight into the nature and degree of rationality employed by the human players. By varying the parameters in agent-based simulations, we are able to benchmark the human behaviour. We observe that while the players use the neighbourhood information in limited capacity, the perception of risk is optimal. We also find that for certain parameter ranges, the agents are able to act more efficiently when compared to the human players. This approach would all...
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Timings of human activities are marked by circadian clocks which in turn are entrained to different environmental signals. In an urban environment the presence of artificial lighting and various social cues tend to disrupt the natural... more
Timings of human activities are marked by circadian clocks which in turn are entrained to different environmental signals. In an urban environment the presence of artificial lighting and various social cues tend to disrupt the natural entrainment with the sunlight. However, it is not completely understood to what extent this is the case. Here we exploit the large-scale data analysis techniques to study the mobile phone calling activity of people in large cities to infer the dynamics of urban daily rhythms. From the calling patterns of about 1,000,000 users spread over different cities but lying inside the same time-zone, we show that the onset and termination of the calling activity synchronizes with the east-west progression of the sun. We also find that the onset and termination of the calling activity of users follows a yearly dynamics, varying across seasons, and that its timings are entrained to solar midnight. Furthermore, we show that the average mid-sleep time of people livi...
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Research Interests: Crack propagation, Computer Simulation, Copper, Physical sciences, Dislocations, and 14 moreCrack Initiation, CHEMICAL SCIENCES, Grain Boundary, Room Temperature, Microstructures, Elastic Modulus, Brittle Fracture, Stress Concentration, Molecular Dynamic Simulation, Effective Medium Theory, Structural model, Mechanical Property, Speed of Sound, and Point Defect
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We study the influence of seasonally and geographically related daily dynamics of daylight and ambient temperature on human resting or sleeping patterns using mobile phone data of a large number of individuals. We observe two daily... more
We study the influence of seasonally and geographically related daily dynamics of daylight and ambient temperature on human resting or sleeping patterns using mobile phone data of a large number of individuals. We observe two daily inactivity periods in the people's aggregated mobile phone calling patterns and infer these to represent the resting times of the population. We find that the nocturnal resting period is strongly influenced by the length of daylight, and that its seasonal variation depends on the latitude, such that for people living in two different cities separated by eight latitudinal degrees, the difference in the resting periods of people between the summer and winter in southern cities is almost twice that in the northern cities. We also observe that the duration of the afternoon resting period is influenced by the temperature, and that there is a threshold from which this influence sets in. Finally, we observe that the yearly dynamics of the afternoon and noctu...
Big Data has become the primary source of understanding the structure and dynamics of the society at large scale. The network of social interactions can be considered as a multiplex, where each layer corresponds to one communication... more
Big Data has become the primary source of understanding the structure and dynamics of the society at large scale. The network of social interactions can be considered as a multiplex, where each layer corresponds to one communication channel and the aggregate of all of them constitutes the entire social network. However, usually one has information only about one of the channels or even a part of it, which should be considered as a subset or sample of the whole. Here we introduce a model based on a natural bilateral communication channel selection mechanism, which for one channel leads to consistent changes in the network properties. For example, while it is expected that the degree distribution of the whole social network has a maximum at a value larger than one, we get a monotonically decreasing distribution as observed in empirical studies of single-channel data. We also find that assortativity may occur or get strengthened due to the sampling method. We analyze the far-reaching c...
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... 10 The resulting phase diagrams in the HT plane for R5=0.25 and R5=0 are shown in Fig. 3(a), and for R5 =0.01 and R5 =0 in Fig. ... The same symmetry arguments therefore apply to the terms ( 11 IbtM ,^6 1 ) as to the terms I b1pI2. ...
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We have constructed a dynamic face model, which is based on the anatomical structures of a real face. Accurate head geometry was obtained from Magnetic Resonance Images (MRIs). An image segmentation program was used to convert the... more
We have constructed a dynamic face model, which is based on the anatomical structures of a real face. Accurate head geometry was obtained from Magnetic Resonance Images (MRIs). An image segmentation program was used to convert the volumetric MRI data to a polygonal representation of the head. The most detailed models we have used have contained approximately 35000 vertices and 70000 polygons. We have constructed separate models for the behavior of the skin, muscles and skull. Contracting the modeled muscles produces facial movements.
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In order to characterize in detail the nature of temporally inhomogeneous spreading processes we introduce a novel dynamic mean field model to investigate analytically the effect of non-Poissonian or bursty inter-event time distributions... more
In order to characterize in detail the nature of temporally inhomogeneous spreading processes we introduce a novel dynamic mean field model to investigate analytically the effect of non-Poissonian or bursty inter-event time distributions on the Susceptible-Infected (SI) spreading dynamics. The exact solution shows that for early and intermediate times bursty dynamics accelerates the spreading as compared to a corresponding Poisson-like process with the same mean activity and lower bound of the inter-event times. The late time dynamics in finite systems is the opposite, where the power law distribution of inter-event times results in a slower and algebraic convergence to the asymptotics as compared to the exponential decay of the Poisson-like process.
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In this paper, fractal compression methods are reviewed. Three new methods are developed and their results are compared with the results obtained using four previously published fractal compression methods. Furthermore, we have compared... more
In this paper, fractal compression methods are reviewed. Three new methods are developed and their results are compared with the results obtained using four previously published fractal compression methods. Furthermore, we have compared the results of these methods with the standard JPEG method. For comparison, we have used an extensive set of image quality measures. According to these tests, fractal methods do not yield significantly better compression results when compared with conventional methods. This is especially the case when high coding accuracy (small compression ratio) is desired.
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Age and gender are two important factors that play crucial roles in the way organisms allocate their social effort. In this study, we analyse a large mobile phone dataset to explore the way life history influences human sociality and the... more
Age and gender are two important factors that play crucial roles in the way organisms allocate their social effort. In this study, we analyse a large mobile phone dataset to explore the way life history influences human sociality and the way social networks are structured. Our results indicate that these aspects of human behaviour are strongly related to age and gender such that younger individuals have more contacts and, among them, males more than females. However, the rate of decrease in the number of contacts with age differs between males and females, such that there is a reversal in the number of contacts around the late 30s. We suggest that this pattern can be attributed to the difference in reproductive investments that are made by the two sexes. We analyse the inequality in social investment patterns and suggest that the age- and gender-related differences we find reflect the constraints imposed by reproduction in a context where time (a form of social capital) is limited.
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ABSTRACT Part 1: Disorder and dynamical systems. Reflections on the beguiling but wayward spherical model -- Phase transitions in vector spin glasses -- Transitions, dynamics and disorder: From equilibrium to nonequilibrium systems --... more
ABSTRACT Part 1: Disorder and dynamical systems. Reflections on the beguiling but wayward spherical model -- Phase transitions in vector spin glasses -- Transitions, dynamics and disorder: From equilibrium to nonequilibrium systems -- Two-dimensional growth in a three component mixture with competing interactions -- Glassy dynamics at the edge of chaos.Part 2: Structures and glasses. Flexibility in biomolecules -- Lattice dynamics of carbon nanotubes -- Glassy behavior due to kinetic constraints: From topological foam to backgammon -- On glass transition with rapid cooling effects -- The dielectric loss function and the search for simple models for relaxation in glass formers -- The theory of turing pattern formation -- The dioctadecylamine monolayer: Non-equilibrium phase domains.Electrical and magnetic properties. Multiple scattering effects in the second harmonic generation of light reflection from a randomly rough metal surface -- Theory for large-scale electronic structure calculations -- Symmetric magnetic clusters -- Optical and Fermi-edge singularities in one-dimensional semiconductor quantum wires -- Probing the magnetic coupling in multilayers using domain wall excitations -- Density of electronic states in the quantum percolation problem -- Power terms in the construction of thermodynamic functions for melting description.
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Each stage of the human life course is characterised by a distinctive pattern of social relations. We study how the intensity and importance of the closest social contacts vary across the life course, using a large database of mobile... more
Each stage of the human life course is characterised by a distinctive pattern of social relations. We study how the intensity and importance of the closest social contacts vary across the life course, using a large database of mobile communication from a European country. We first determine the most likely social relationship type from these mobile phone records by relating the age and gender of the caller and recipient to the frequency, length, and direction of calls. We then show how communication patterns between parents and children, romantic partner, and friends vary across the six main stages of the adult family life course. Young adulthood is dominated by a gradual shift of call activity from parents to close friends, and then to a romantic partner, culminating in the period of early family formation during which the focus is on the romantic partner. During middle adulthood call patterns suggest a high dependence on the parents of the ego, who, presumably often provide allopa...
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ABSTRACT
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We study a statistical model consisting of $N$ basic units which interact with each other by exchanging a physical entity, according to a given microscopic random law, depending on a parameter $\lambda$. We focus on the equilibrium or... more
We study a statistical model consisting of $N$ basic units which interact with each other by exchanging a physical entity, according to a given microscopic random law, depending on a parameter $\lambda$. We focus on the equilibrium or stationary distribution of the entity exchanged and verify through numerical fitting of the simulation data that the final form of the equilibrium distribution is that of a standard Gamma distribution. The model can be interpreted as a simple closed economy in which economic agents trade money and a saving criterion is fixed by the saving propensity $\lambda$. Alternatively, from the nature of the equilibrium distribution, we show that the model can also be interpreted as a perfect gas at an effective temperature $T(\lambda)$, where particles exchange energy in a space with an effective dimension $D(\lambda)$.