Biomedical subjects

Kwangho Park

Publications and source records attributed to Kwangho Park.

16 recordsLinked to original sources

PubMed2006

Information propagation on modular networks.

Networks with a community (or modular) structure underlie many social and biological phenomena. In such a network individuals tend to form sparsely linked local communities, each having dense internal connections. We investigate the dynamics of information propagation on modular networks by using a three-state epidemic model with a unit spreading rate (i.e., the probability for a susceptible individual to be "infected" with the information is one). We find a surprising, resonancelike phenomenon: the information lifetime on the network can be maximized by the number of modules. The result can be useful for optimizing or controlling information spread on social or biological networks.

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PubMed2006

Synchronization in complex networks with a modular structure.

Networks with a community (or modular) structure arise in social and biological sciences. In such a network individuals tend to form local communities, each having dense internal connections. The linkage among the communities is, however, much more sparse. The dynamics on modular networks, for instance synchronization, may be of great social or biological interest. (Here by synchronization we mean some synchronous behavior among the nodes in the network, not, for example, partially synchronous behavior in the network or the synchronizability of the network with some external dynamics.) By using a recent theoretical framework, the master-stability approach originally introduced by Pecora and Carroll in the context of synchronization in coupled nonlinear oscillators, we address synchronization in complex modular networks. We use a prototype model and develop scaling relations for the network synchronizability with respect to variations of some key network structural parameters. Our results indicate that random, long-range links among distant modules is the key to synchronization. As an application we suggest a viable strategy to achieve synchronous behavior in social networks.

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PubMed2005

Tolerance of scale-free networks against attack-induced cascades.

Scale-free networks can be disintegrated by attack on a single or a very few nodes through the process of cascading failures. By utilizing a prototype cascading model, we previously determined the critical value of the capacity parameter below which the network can become disintegrated due to attack on a single node. A fundamental question in network security, which has not been addressed previously but may be more important and of wider interest, is how to design networks of finite capacity that are safe against cascading breakdown. Here we derive an upper bound for the capacity parameter, above which the network is immune to cascading breakdown. Our theory also yields estimates for the maximally achievable network integrity via controlled removal of a small set of low-degree nodes. The theoretical results are confirmed numerically.

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PubMed2005

Self-organized scale-free networks.

Growth and preferential attachments have been coined as the two fundamental mechanisms responsible for the scale-free feature in complex networks, as characterized by an algebraic degree distribution. There are situations, particularly in biological networks, where growth is absent or not important, yet some of these networks still exhibit the scale-free feature with a small degree exponent. Here we propose two classes of models to account for this phenomenon. We show analytically and numerically that, in the first model, a spectrum of algebraic degree distributions with a small exponent can be generated. The second model incorporates weights for nodes, and it is able to generate robust scale-free degree distribution with larger algebraic exponents. Our results imply that it is natural for a complex network to self-organize itself into a scale-free state without growth.

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PubMed2005

Jamming in complex gradient networks.

Flows of physical quantities in large complex networks, natural or man made, rely in general on some scalar gradients existing in the networks. We investigate, analytically and numerically, under what conditions jamming in gradient flows can occur in random and scale-free networks. We find that the degree of jamming typically increases with the average connectivity of the network. A crossover phenomenon is uncovered where for < k(c) (k(c) denotes a critical connectivity, estimated to be about 10), scale-free networks have a higher level of congestion than random networks with the same , while the opposite occurs for > k(c).

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PubMed2005

Absorbing phase transition with a conserved field.

We study a lattice gas model where the number of particles is conserved during dynamical process. Our model shows a continuous phase transition from a fluctuating phase to two symmetric absorbing states at the critical point in one dimension. We conjecture the values of the critical exponents characterizing the phase transition of our model. We show that the obtained values are in good agreement with those estimated from computer simulations. The critical exponents indicate that our model exhibits an absorbing phase transition which is different from the known ones.

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PubMed2005

Onset of traffic congestion in complex networks.

Free traffic flow on a complex network is key to its normal and efficient functioning. Recent works indicate that many realistic networks possess connecting topologies with a scale-free feature: the probability distribution of the number of links at nodes, or the degree distribution, contains a power-law component. A natural question is then how the topology influences the dynamics of traffic flow on a complex network. Here we present two models to address this question, taking into account the network topology, the information-generating rate, and the information-processing capacity of individual nodes. For each model, we study four kinds of networks: scale-free, random, and regular networks and Cayley trees. In the first model, the capacity of packet delivery of each node is proportional to its number of links, while in the second model, it is proportional to the number of shortest paths passing through the node. We find, in both models, that there is a critical rate of information generation, below which the network traffic is free but above which traffic congestion occurs. Theoretical estimates are given for the critical point. For the first model, scale-free networks and random networks are found to be more tolerant to congestion. For the second model, the congestion condition is independent of network size and topology, suggesting that this model may be practically useful for designing communication protocols.

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PubMed2004

Attack vulnerability of scale-free networks due to cascading breakdown.

The possibility that a complex network can be brought down by attack on a single or a very few nodes through the process of cascading failures is of significant concern. Here we investigate a recent model for cascading failures in complex networks and uncover a phase-transition phenomenon in terms of the key parameter characterizing the node capacity. For parameter value below the phase-transition point, cascading failures can cause the network to disintegrate almost entirely. We obtain a theoretical estimate for the phase-transition point and provide numerical support.

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PubMed2004

Characterization of weighted complex networks.

To account for possible distinct functional roles played by different nodes and links in complex networks, we introduce and analyze a class of weighted scale-free networks. The weight of a node is assigned as a random number, based on which the weights of links are defined. We utilize the concept of betweenness to characterize the weighted networks and obtain the scaling laws governing the betweenness as functions both of the weight and of the degree. The scaling results may be useful for identifying influential nodes in terms of physical functions in complex networks.

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PubMed2004

Growth of a tensionless interface in anisotropic random media.

We introduce a simple growth model where a tensionless interface grows in random media. In this model, the degree of anisotropy of the random media is controlled by a variable g. When g=0, there is no anisotropic property of the random media. But, the anisotropic property increases as g does from 0. From the numerical simulations, we find that this model belongs to the quenched Herring-Mullins universality class when g=0. Interestingly, however, we find that this model belongs to the quenched Kardar-Parisi-Zhang universality class when g is nonzero.

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PubMed2003

Transition from stable to unstable growth by an inertial force.

We introduce a simple growth model where the growth of the interface is affected by an inertial force and a white noise. The magnitude of the inertial force is controlled by a constant p between 0 and 1. An inertial force increases continuously from 0, as p does from 0 to 1. In our model, the interface starts growing from a flat state. When p p(c), however, the interface width increases continuously without saturation as time elapses. We explain via simple calculation how this interesting phenomenon occurs in our model. We find p(c)=0.5 from the calculation. This critical value is in excellent agreement with the critical value p(c)=0.50(1) found from the simulations of our model.

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PubMed2002

Well-defined set of exponents for a pair contact process with diffusion.

Recently it was suggested that a pair contact process with diffusion (PCPD) might represent an independent new universality class different from the directed percolation (DP) and the parity conservation (PC) class. The dynamics in the PCPD are usually controlled by two independent parameters. The critical exponents for the PCPD are known to have different values for varying values of the two independent parameters. However, once the diffusion and annihilation (or coagulation) rate in the PCPD is tuned in a way that the process without offspring production is exactly solvable, a well-defined set of the exponents for the PCPD is obtained. Then dynamics are controlled by only one independent parameter. The obtained critical exponents are different than those of DP and PC. The critical exponents satisfy the generalized hyperscaling relation within numerical errors.

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PubMed2002

Phase transition in a triplet process.

We argue that the reaction-diffusion process 3A-->4A,3A-->2A exhibits a different type of continuous phase transition from an active into an absorbing phase. Because of the upper critical dimension d(c)> or =4/3 we expect the phase transition in 1+1 dimensions to be characterized by nontrivial fluctuation effects.

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PubMed2002

First-order transition in a particle deposition-evaporation model.

We introduce a simple stochastic growth model where particles of two different species are deposited and evaporated. In the model, a randomly chosen particle of two species is deposited at a rate p and a particle on the edge of the plateau of the interface is evaporated at a rate 1-p. When p p(c2)=0.5015(5), the velocity of the interface is zero. When p(c1)</=p</=p(c2), however, the interface grows with a constant velocity. At both p(c1) and p(c2), the velocity of the interface changes from zero to a constant value discontinuously. The first-order transitions in our model are related to a nonequilibrium phase transition from an active to an inactive phase at the bottom layer of the interface. Interestingly, the first-order transition at p(c1) is triggered by the combination of the parity conserving and the directed percolation dynamics. We explain why the transitions in our model are of first order. Moreover, our model shows two nonequilibrium roughening transitions at p(c1) as well as at p(r)[=0.444(2)].

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PubMed2002

First-order depinning transition of a driven interface in disordered media.

We introduce a simple growth model which exhibits a first-order pinning-depinning (PD) transition in disordered media. In our model, a first-order PD transition is triggered by the local inertia force F(l)=pLv macro where p denotes a constant between 0 and 1, L is the system size, and v macro is the average velocity in a local region of the growing interface. If p p(c), our model shows a first-order PD transition. We measure the critical exponents characterizing the dynamical behavior of our model and explain how a first-order PD transition can occur if p>p(c). Besides the PD transitions, our model exhibits another phase transition from a fluctuating to a nonfluctuating interface with a constant velocity.

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PubMed2001

Stochastic growth models for driven interfaces through random media in two and three dimensions.

We introduce two simple stochastic growth models which describe the motion of the interfaces driven through random media in two and three dimensions. One model describes the motion of the interface driven through isotropic random media, where the dynamics of the interface can be described by the quenched Edwards-Wilkinson (QEW) equation. The other model describes the motion of the interface driven through anisotropic random media, where the dynamics of the interface can be described by the quenched Kardar-Parisi-Zhang (QKPZ) equation. We show via computer simulations that two models belong to the QEW and QKPZ universality class in two and three dimensions, respectively.

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