Hang-Hyun Jo | Catholic University of Korea (original) (raw)

Papers by Hang-Hyun Jo

PLOS ONE, 2015

Walking is a fundamental activity of our daily life not only for moving to other places but also ... more Walking is a fundamental activity of our daily life not only for moving to other places but also for interacting with surrounding environment. While walking on the streets, pedestrians can be aware of attractions like shopping windows. They can be influenced by the attractions and some of them might shift their attention towards the attractions, namely switching behavior. As a first step to incorporate the switching behavior, this study investigates collective effects of switching behavior for an attraction by developing a behavioral model. Numerical simulations exhibit different patterns of pedestrian behavior depending on the strength of the social influence and the average length of stay. When the social influence is strong along with a long length of stay, a saturated phase can be defined at which all the pedestrians have visited the attraction. If the social influence is not strong enough, an unsaturated phase appears where one can observe that some pedestrians head for the attraction while others walk in their desired direction. These collective patterns of pedestrian behavior are summarized in a phase diagram by measuring the proportion of visitors. Measuring the marginal benefits with respect to the strength of the social influence and the average length of stay enables us to identify under what conditions enhancing these variables would be more effective. The findings from this study can be understood in the context of the pedestrian facility management, for instance, for retail stores.

We introduce a 2-layer network model for the study of the immunization dynamics in epidemics. Spr... more We introduce a 2-layer network model for the study of the immunization dynamics in epidemics. Spreading of an epidemic is modeled as an excitatory process in a small-world network (body layer) while immunization by prevention for the disease as a dynamic process in a scale-free network (head layer). It is shown that prevention indeed turns periodic rages of an epidemic into small fluctuation. The study also reveals that, in a certain situation, prevention actually plays an adverse role and helps the disease survive. We argue that the presence of two different characteristic time scales contributes to the immunization dynamics observed.

PLOS ONE, 2015

In social networks of human individuals, social relationships do not necessarily last forever as ... more In social networks of human individuals, social relationships do not necessarily last forever as they can either fade gradually with time, resulting in link aging, or terminate abruptly, causing link deletion, as even old friendships may cease. In this paper, we study a social network formation model where we introduce several ways by which a link termination takes place. If we adopt the link aging, we get a more modular structure with more homogeneously distributed link weights within communities than when link deletion is used. By investigating distributions and relations of various network characteristics, we find that the empirical findings are better reproduced with the link deletion model. This indicates that link deletion plays a more prominent role in organizing social networks than link aging.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2014

Recent empirical studies using large-scale data sets have validated the Granovetter hypothesis on... more Recent empirical studies using large-scale data sets have validated the Granovetter hypothesis on the structure of the society in that there are strongly wired communities connected by weak ties. However, as interaction between individuals takes place in diverse contexts, these communities turn out to be overlapping. This implies that the society has a multilayered structure, where the layers represent the different contexts. To model this structure we begin with a single-layer weighted social network (WSN) model showing the Granovetterian structure. We find that when merging such WSN models, a sufficient amount of interlayer correlation is needed to maintain the relationship between topology and link weights, while these correlations destroy the enhancement in the community overlap due to multiple layers. To resolve this, we devise a geographic multilayer WSN model, where the indirect interlayer correlations due to the geographic constraints of individuals enhance the overlaps betw...

Vulnerability, Uncertainty, and Risk, 2014

In order to account for large variance and fat tail of damage by natural disaster, we study a sim... more In order to account for large variance and fat tail of damage by natural disaster, we study a simple model by combining distributions of disaster and population/property with their spatial correlation. We assume fat-tailed or power-law distributions for disaster and population/property exposed to the disaster, and a constant vulnerability for exposed population/property. Our model suggests that the fat tail property of damage can be determined either by that of disaster or by those of population/property depending on which tail is fatter. It is also found that the spatial correlations of population/property can enhance or reduce the variance of damage depending on how fat the tails of population/property are. In case of tornadoes in the United States, we show that the damage does have fat tail property. Our results support that the standard cost-benefit analysis would not be reliable for social investment in vulnerability reduction and disaster prevention.

Proceedings of the 9th Joint Conference on Information Sciences (JCIS), 2006

In this paper, we studied complexity and entropy density of stock market by modeling ε -machine o... more In this paper, we studied complexity and entropy density of stock market by modeling ε -machine of Korean Composition Stock Price Index (KOSPI) from year 1992 to 2003 using causal-state splitting reconstruction (CSSR) algorithm.

How does individuals' cognition change a system which is a collective behavior of individuals? Or... more How does individuals' cognition change a system which is a collective behavior of individuals? Or how does a system affect individuals' cognition? To examine the interplay between a system and individuals, we study a cognition-based strategic link formation. When a network is not fully observable, individuals' perception of a network plays an important role in decision making. Assuming that a communication link is costly and more accurate perception yields higher network utility, one decides whether to form a link in order to get better knowledge. A newly added link is a change in a network, which affects individuals' perception accuracy back. We characterize the early stage of dynamics that a ring network is a global structure and there exists an agent who keeps the full information once a network is connected. Moreover, we discuss a local linking process which causes clusters and the influence of a positive cost of linking in the coevolution between a network and perception.

Interactions in time-varying complex systems are often very heterogeneous at the topological leve... more Interactions in time-varying complex systems are often very heterogeneous at the topological level (who interacts with whom) and at the temporal level (when interactions occur and how often). While it is known that temporal heterogeneities often have strong effects on dynamical processes, e.g. the burstiness of contact sequences is associated with slower spreading dynamics, the picture is far from complete. In this paper, we show that temporal heterogeneities result in temporal sparsity at the time scale of average inter-event times, and that temporal sparsity determines the amount of slowdown of Susceptible-Infectious (SI) spreading dynamics on temporal networks. This result is based on the analysis of several empirical temporal network data sets. An approximate solution for a simple network model confirms the association between temporal sparsity and slowdown of SI spreading dynamics. Since deterministic SI spreading always follows the fastest temporal paths, our results generalize-paths are slower to traverse because of temporal sparsity, and therefore all dynamical processes are slower as well.

Transportation Research Procedia, 2014

While walking on the streets, pedestrians can aware attractions like shopping windows. Some of th... more While walking on the streets, pedestrians can aware attractions like shopping windows. Some of them might shift their attention towards the attractions, namely switching behavior. As a first step, this study investigates collective effects of the switching behavior for an attraction by means of numerical simulations. Such switching behavior leads some pedestrians head for the attraction, or even all the pedestrians have visited the attraction if the social influence is getting stronger. These collective patterns of pedestrian behavior are summarized in a phase diagram. The findings from this study can be interpreted into pedestrian facility management particularly for retail stores.

Physica a-Statistical Mechanics and Its Applications, 2009

The entropy density is an intuitive and powerful concept to study the complicated nonlinear proce... more The entropy density is an intuitive and powerful concept to study the complicated nonlinear processes derived from physical systems. We develop the minimum entropy density method (MEDM) to detect the structure scale of a given time series, which is defined as the scale in which the uncertainty is minimized, hence the pattern is revealed most. The MEDM is applied to the financial time series of Standard and Poor's 500 index from February 1983 to April 2006. Then the temporal behavior of structure scale is obtained and analyzed in relation to the information delivery time and efficient market hypothesis.

Journal of the Korean Physical Society, 2013

In the Korean traditional board game Yut-Nori, teams compete by moving their pieces on the two-di... more In the Korean traditional board game Yut-Nori, teams compete by moving their pieces on the two-dimensional game board, and the team whose all pieces complete a round trip on the board wins. In every round, teams throw four wooden sticks of the shape of half-cut cylinder and the number of sticks that show belly sides, i.e., the flat sides, determines the number of steps the team's piece can advance on the board. It is possible to pile up one team's pieces if their sites are identical so that pieces as a group can move together afterwards (piling). If a piece of the opponent team is at the new site of one team's piece, the piece is caught and removed from the board, and the team is given one more chance to throw sticks and proceed (catching). For a simplicity, we simulate this game on one-dimensional board with the same number of sites as the original game, and show that catching is more advantageous strategy than piling to win. We also study the avalanche-size distribution in thermodynamic limit to find that it follows an exponential form.

Plos One, 2011

Understanding the patterns of human dynamics and social interaction and the way they lead to the ... more Understanding the patterns of human dynamics and social interaction and the way they lead to the formation of an organized and functional society are important issues especially for techno-social development. Addressing these issues of social networks has recently become possible through large scale data analysis of mobile phone call records, which has revealed the existence of modular or community structure with many links between nodes of the same community and relatively few links between nodes of different communities. The weights of links, e.g., the number of calls between two users, and the network topology are found correlated such that intra-community links are stronger compared to the weak inter-community links. This feature is known as Granovetter's ''The strength of weak ties'' hypothesis. In addition to this inhomogeneous community structure, the temporal patterns of human dynamics turn out to be inhomogeneous or bursty, characterized by the heavy tailed distribution of time interval between two consecutive events, i.e., inter-event time. In this paper, we study how the community structure and the bursty dynamics emerge together in a simple evolving weighted network model. The principal mechanisms behind these patterns are social interaction by cyclic closure, i.e., links to friends of friends and the focal closure, links to individuals sharing similar attributes or interests, and human dynamics by task handling process. These three mechanisms have been implemented as a network model with local attachment, global attachment, and priority-based queuing processes. By comprehensive numerical simulations we show that the interplay of these mechanisms leads to the emergence of heavy tailed inter-event time distribution and the evolution of Granovettertype community structure. Moreover, the numerical results are found to be in qualitative agreement with empirical analysis results from mobile phone call dataset.

EPJ Data Science, 2012

We study spatiotemporal correlations and temporal diversities of handset-based service usages by ... more We study spatiotemporal correlations and temporal diversities of handset-based service usages by analyzing a dataset that includes detailed information about locations and service usages of 124 users over 16 months. By constructing the spatiotemporal trajectories of the users we detect several meaningful places or contexts for each one of them and show how the context affects the service usage patterns. We find that temporal patterns of service usages are bound to the typical weekly cycles of humans, yet they show maximal activities at different times. We first discuss their temporal correlations and then investigate the time-ordering behavior of communication services like calls being followed by the non-communication services like applications. We also find that the behavioral overlap network based on the clustering of temporal patterns is comparable to the communication network of users. Our approach provides a useful framework for handset-based data analysis and helps us to understand the complexities of information and communications technology enabled human behavior. arXiv:1204.2169v3 [physics.soc-ph]

SSRN Electronic Journal, 2000

In this paper, we consider two firms diffusing incompatible technologies and their decision of co... more In this paper, we consider two firms diffusing incompatible technologies and their decision of consumer targeting. The technology adoption is made in two steps. First, once the firms sell their products to their respective targeted consumer, the technology is diffused successively by word-of-mouth communication from the initial consumer to other consumers linked along the network. Then, in the second step, each consumer imitates the technology the neighbors use which fares better, and through this process of imitation, the technology distribution keeps evolving until it reaches the long-run steady state. We demonstrate that the early entrant chooses the minmax location when firms are myopic in the sense that they do not take the imitation possibility into account. If firms consider the possibility of imitation, the best target will tend towards a hub, although the minmax principle in general keeps valid in the sense that it should be the minmax location after considering imitation.

Physical Review E, 2005

We study the effect of spatially correlated noise on coherence resonance (CR) in a Watts-Strogatz... more We study the effect of spatially correlated noise on coherence resonance (CR) in a Watts-Strogatz small-world network of Fitz Hugh-Nagumo neurons, where the noise correlation decays exponentially with distance between neurons. It is found that CR is considerably improved just by a small fraction of long-range connections for an intermediate coupling strength. For other coupling strengths, an abrupt change in CR occurs following the drastic fracture of the clustered structures in the network. Our study shows that spatially correlated noise plays a significant role in the phenomenon of CR through enforcing the clustering of the network.

Physical Review E, 2012

Queuing models provide insight into the temporal inhomogeneity of human dynamics, characterized b... more Queuing models provide insight into the temporal inhomogeneity of human dynamics, characterized by the broad distribution of waiting times of individuals performing tasks. We study the queuing model of an agent trying to execute a task of interest, the priority of which may vary with time due to the agent's "state of mind." However, its execution can be disrupted by other tasks of random priorities. By considering the priority of the task of interest either decreasing or increasing algebraically in time, we analytically obtain and numerically confirm the bimodal and unimodal waiting time distributions with power-law decaying tails, respectively. These results are also compared to the updating time distribution of papers in the arXiv and the processing time distribution of papers in Physical Review journals. Our analysis helps to understand the human task execution behavior in a more realistic scenario.

Physical Review E, 2013

To understand the origin of bursty dynamics in natural and social processes we provide a general ... more To understand the origin of bursty dynamics in natural and social processes we provide a general analysis framework, in which the temporal process is decomposed into sub-processes and then the bursts in sub-processes, called contextual bursts, are combined to collective bursts in the original process. For the combination of sub-processes, it is required to consider the distribution of different contexts over the original process. Based on minimal assumptions for inter-event time statistics, we present a theoretical analysis for the relationship between contextual and collective inter-event time distributions. Our analysis framework helps to exploit contextual information available in decomposable bursty dynamics.

Physical Review E, 2010

We study collective helping behavior and bystander effects in a coevolving helping network model.... more We study collective helping behavior and bystander effects in a coevolving helping network model. A node and a link of the network represents an agent who renders or receives help and a friendly relation between agents, respectively. A helping trial of an agent depends on relations with other involved agents and its result (success or failure) updates the relation between the helper and the recipient. We study the network link dynamics and its steady states analytically and numerically. The full phase diagram is presented with various kinds of active and inactive phases and the nature of phase transitions are explored. We find various interesting bystander effects, consistent with the field study results, of which the underlying mechanism is proposed.

PLOS ONE, 2015

Walking is a fundamental activity of our daily life not only for moving to other places but also ... more Walking is a fundamental activity of our daily life not only for moving to other places but also for interacting with surrounding environment. While walking on the streets, pedestrians can be aware of attractions like shopping windows. They can be influenced by the attractions and some of them might shift their attention towards the attractions, namely switching behavior. As a first step to incorporate the switching behavior, this study investigates collective effects of switching behavior for an attraction by developing a behavioral model. Numerical simulations exhibit different patterns of pedestrian behavior depending on the strength of the social influence and the average length of stay. When the social influence is strong along with a long length of stay, a saturated phase can be defined at which all the pedestrians have visited the attraction. If the social influence is not strong enough, an unsaturated phase appears where one can observe that some pedestrians head for the attraction while others walk in their desired direction. These collective patterns of pedestrian behavior are summarized in a phase diagram by measuring the proportion of visitors. Measuring the marginal benefits with respect to the strength of the social influence and the average length of stay enables us to identify under what conditions enhancing these variables would be more effective. The findings from this study can be understood in the context of the pedestrian facility management, for instance, for retail stores.

We introduce a 2-layer network model for the study of the immunization dynamics in epidemics. Spr... more We introduce a 2-layer network model for the study of the immunization dynamics in epidemics. Spreading of an epidemic is modeled as an excitatory process in a small-world network (body layer) while immunization by prevention for the disease as a dynamic process in a scale-free network (head layer). It is shown that prevention indeed turns periodic rages of an epidemic into small fluctuation. The study also reveals that, in a certain situation, prevention actually plays an adverse role and helps the disease survive. We argue that the presence of two different characteristic time scales contributes to the immunization dynamics observed.

PLOS ONE, 2015

In social networks of human individuals, social relationships do not necessarily last forever as ... more In social networks of human individuals, social relationships do not necessarily last forever as they can either fade gradually with time, resulting in link aging, or terminate abruptly, causing link deletion, as even old friendships may cease. In this paper, we study a social network formation model where we introduce several ways by which a link termination takes place. If we adopt the link aging, we get a more modular structure with more homogeneously distributed link weights within communities than when link deletion is used. By investigating distributions and relations of various network characteristics, we find that the empirical findings are better reproduced with the link deletion model. This indicates that link deletion plays a more prominent role in organizing social networks than link aging.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2014

Recent empirical studies using large-scale data sets have validated the Granovetter hypothesis on... more Recent empirical studies using large-scale data sets have validated the Granovetter hypothesis on the structure of the society in that there are strongly wired communities connected by weak ties. However, as interaction between individuals takes place in diverse contexts, these communities turn out to be overlapping. This implies that the society has a multilayered structure, where the layers represent the different contexts. To model this structure we begin with a single-layer weighted social network (WSN) model showing the Granovetterian structure. We find that when merging such WSN models, a sufficient amount of interlayer correlation is needed to maintain the relationship between topology and link weights, while these correlations destroy the enhancement in the community overlap due to multiple layers. To resolve this, we devise a geographic multilayer WSN model, where the indirect interlayer correlations due to the geographic constraints of individuals enhance the overlaps betw...

Vulnerability, Uncertainty, and Risk, 2014

In order to account for large variance and fat tail of damage by natural disaster, we study a sim... more In order to account for large variance and fat tail of damage by natural disaster, we study a simple model by combining distributions of disaster and population/property with their spatial correlation. We assume fat-tailed or power-law distributions for disaster and population/property exposed to the disaster, and a constant vulnerability for exposed population/property. Our model suggests that the fat tail property of damage can be determined either by that of disaster or by those of population/property depending on which tail is fatter. It is also found that the spatial correlations of population/property can enhance or reduce the variance of damage depending on how fat the tails of population/property are. In case of tornadoes in the United States, we show that the damage does have fat tail property. Our results support that the standard cost-benefit analysis would not be reliable for social investment in vulnerability reduction and disaster prevention.

Proceedings of the 9th Joint Conference on Information Sciences (JCIS), 2006

In this paper, we studied complexity and entropy density of stock market by modeling ε -machine o... more In this paper, we studied complexity and entropy density of stock market by modeling ε -machine of Korean Composition Stock Price Index (KOSPI) from year 1992 to 2003 using causal-state splitting reconstruction (CSSR) algorithm.

How does individuals' cognition change a system which is a collective behavior of individuals? Or... more How does individuals' cognition change a system which is a collective behavior of individuals? Or how does a system affect individuals' cognition? To examine the interplay between a system and individuals, we study a cognition-based strategic link formation. When a network is not fully observable, individuals' perception of a network plays an important role in decision making. Assuming that a communication link is costly and more accurate perception yields higher network utility, one decides whether to form a link in order to get better knowledge. A newly added link is a change in a network, which affects individuals' perception accuracy back. We characterize the early stage of dynamics that a ring network is a global structure and there exists an agent who keeps the full information once a network is connected. Moreover, we discuss a local linking process which causes clusters and the influence of a positive cost of linking in the coevolution between a network and perception.

Interactions in time-varying complex systems are often very heterogeneous at the topological leve... more Interactions in time-varying complex systems are often very heterogeneous at the topological level (who interacts with whom) and at the temporal level (when interactions occur and how often). While it is known that temporal heterogeneities often have strong effects on dynamical processes, e.g. the burstiness of contact sequences is associated with slower spreading dynamics, the picture is far from complete. In this paper, we show that temporal heterogeneities result in temporal sparsity at the time scale of average inter-event times, and that temporal sparsity determines the amount of slowdown of Susceptible-Infectious (SI) spreading dynamics on temporal networks. This result is based on the analysis of several empirical temporal network data sets. An approximate solution for a simple network model confirms the association between temporal sparsity and slowdown of SI spreading dynamics. Since deterministic SI spreading always follows the fastest temporal paths, our results generalize-paths are slower to traverse because of temporal sparsity, and therefore all dynamical processes are slower as well.

Transportation Research Procedia, 2014

While walking on the streets, pedestrians can aware attractions like shopping windows. Some of th... more While walking on the streets, pedestrians can aware attractions like shopping windows. Some of them might shift their attention towards the attractions, namely switching behavior. As a first step, this study investigates collective effects of the switching behavior for an attraction by means of numerical simulations. Such switching behavior leads some pedestrians head for the attraction, or even all the pedestrians have visited the attraction if the social influence is getting stronger. These collective patterns of pedestrian behavior are summarized in a phase diagram. The findings from this study can be interpreted into pedestrian facility management particularly for retail stores.

Physica a-Statistical Mechanics and Its Applications, 2009

The entropy density is an intuitive and powerful concept to study the complicated nonlinear proce... more The entropy density is an intuitive and powerful concept to study the complicated nonlinear processes derived from physical systems. We develop the minimum entropy density method (MEDM) to detect the structure scale of a given time series, which is defined as the scale in which the uncertainty is minimized, hence the pattern is revealed most. The MEDM is applied to the financial time series of Standard and Poor's 500 index from February 1983 to April 2006. Then the temporal behavior of structure scale is obtained and analyzed in relation to the information delivery time and efficient market hypothesis.

Journal of the Korean Physical Society, 2013

In the Korean traditional board game Yut-Nori, teams compete by moving their pieces on the two-di... more In the Korean traditional board game Yut-Nori, teams compete by moving their pieces on the two-dimensional game board, and the team whose all pieces complete a round trip on the board wins. In every round, teams throw four wooden sticks of the shape of half-cut cylinder and the number of sticks that show belly sides, i.e., the flat sides, determines the number of steps the team's piece can advance on the board. It is possible to pile up one team's pieces if their sites are identical so that pieces as a group can move together afterwards (piling). If a piece of the opponent team is at the new site of one team's piece, the piece is caught and removed from the board, and the team is given one more chance to throw sticks and proceed (catching). For a simplicity, we simulate this game on one-dimensional board with the same number of sites as the original game, and show that catching is more advantageous strategy than piling to win. We also study the avalanche-size distribution in thermodynamic limit to find that it follows an exponential form.

Plos One, 2011

Understanding the patterns of human dynamics and social interaction and the way they lead to the ... more Understanding the patterns of human dynamics and social interaction and the way they lead to the formation of an organized and functional society are important issues especially for techno-social development. Addressing these issues of social networks has recently become possible through large scale data analysis of mobile phone call records, which has revealed the existence of modular or community structure with many links between nodes of the same community and relatively few links between nodes of different communities. The weights of links, e.g., the number of calls between two users, and the network topology are found correlated such that intra-community links are stronger compared to the weak inter-community links. This feature is known as Granovetter's ''The strength of weak ties'' hypothesis. In addition to this inhomogeneous community structure, the temporal patterns of human dynamics turn out to be inhomogeneous or bursty, characterized by the heavy tailed distribution of time interval between two consecutive events, i.e., inter-event time. In this paper, we study how the community structure and the bursty dynamics emerge together in a simple evolving weighted network model. The principal mechanisms behind these patterns are social interaction by cyclic closure, i.e., links to friends of friends and the focal closure, links to individuals sharing similar attributes or interests, and human dynamics by task handling process. These three mechanisms have been implemented as a network model with local attachment, global attachment, and priority-based queuing processes. By comprehensive numerical simulations we show that the interplay of these mechanisms leads to the emergence of heavy tailed inter-event time distribution and the evolution of Granovettertype community structure. Moreover, the numerical results are found to be in qualitative agreement with empirical analysis results from mobile phone call dataset.

EPJ Data Science, 2012

We study spatiotemporal correlations and temporal diversities of handset-based service usages by ... more We study spatiotemporal correlations and temporal diversities of handset-based service usages by analyzing a dataset that includes detailed information about locations and service usages of 124 users over 16 months. By constructing the spatiotemporal trajectories of the users we detect several meaningful places or contexts for each one of them and show how the context affects the service usage patterns. We find that temporal patterns of service usages are bound to the typical weekly cycles of humans, yet they show maximal activities at different times. We first discuss their temporal correlations and then investigate the time-ordering behavior of communication services like calls being followed by the non-communication services like applications. We also find that the behavioral overlap network based on the clustering of temporal patterns is comparable to the communication network of users. Our approach provides a useful framework for handset-based data analysis and helps us to understand the complexities of information and communications technology enabled human behavior. arXiv:1204.2169v3 [physics.soc-ph]

SSRN Electronic Journal, 2000

In this paper, we consider two firms diffusing incompatible technologies and their decision of co... more In this paper, we consider two firms diffusing incompatible technologies and their decision of consumer targeting. The technology adoption is made in two steps. First, once the firms sell their products to their respective targeted consumer, the technology is diffused successively by word-of-mouth communication from the initial consumer to other consumers linked along the network. Then, in the second step, each consumer imitates the technology the neighbors use which fares better, and through this process of imitation, the technology distribution keeps evolving until it reaches the long-run steady state. We demonstrate that the early entrant chooses the minmax location when firms are myopic in the sense that they do not take the imitation possibility into account. If firms consider the possibility of imitation, the best target will tend towards a hub, although the minmax principle in general keeps valid in the sense that it should be the minmax location after considering imitation.

Physical Review E, 2005

We study the effect of spatially correlated noise on coherence resonance (CR) in a Watts-Strogatz... more We study the effect of spatially correlated noise on coherence resonance (CR) in a Watts-Strogatz small-world network of Fitz Hugh-Nagumo neurons, where the noise correlation decays exponentially with distance between neurons. It is found that CR is considerably improved just by a small fraction of long-range connections for an intermediate coupling strength. For other coupling strengths, an abrupt change in CR occurs following the drastic fracture of the clustered structures in the network. Our study shows that spatially correlated noise plays a significant role in the phenomenon of CR through enforcing the clustering of the network.

Physical Review E, 2012

Queuing models provide insight into the temporal inhomogeneity of human dynamics, characterized b... more Queuing models provide insight into the temporal inhomogeneity of human dynamics, characterized by the broad distribution of waiting times of individuals performing tasks. We study the queuing model of an agent trying to execute a task of interest, the priority of which may vary with time due to the agent's "state of mind." However, its execution can be disrupted by other tasks of random priorities. By considering the priority of the task of interest either decreasing or increasing algebraically in time, we analytically obtain and numerically confirm the bimodal and unimodal waiting time distributions with power-law decaying tails, respectively. These results are also compared to the updating time distribution of papers in the arXiv and the processing time distribution of papers in Physical Review journals. Our analysis helps to understand the human task execution behavior in a more realistic scenario.

Physical Review E, 2013

To understand the origin of bursty dynamics in natural and social processes we provide a general ... more To understand the origin of bursty dynamics in natural and social processes we provide a general analysis framework, in which the temporal process is decomposed into sub-processes and then the bursts in sub-processes, called contextual bursts, are combined to collective bursts in the original process. For the combination of sub-processes, it is required to consider the distribution of different contexts over the original process. Based on minimal assumptions for inter-event time statistics, we present a theoretical analysis for the relationship between contextual and collective inter-event time distributions. Our analysis framework helps to exploit contextual information available in decomposable bursty dynamics.

Physical Review E, 2010

We study collective helping behavior and bystander effects in a coevolving helping network model.... more We study collective helping behavior and bystander effects in a coevolving helping network model. A node and a link of the network represents an agent who renders or receives help and a friendly relation between agents, respectively. A helping trial of an agent depends on relations with other involved agents and its result (success or failure) updates the relation between the helper and the recipient. We study the network link dynamics and its steady states analytically and numerically. The full phase diagram is presented with various kinds of active and inactive phases and the nature of phase transitions are explored. We find various interesting bystander effects, consistent with the field study results, of which the underlying mechanism is proposed.