Ning Ning Chung

Threshold effect and entanglement enhancement through local squeezing of initial separable states in continuous-variable systems

We investigate the dynamical enhancement of entanglement by means of local squeezing of initial separable Gaussian states in two coupled harmonic oscillator systems. Interestingly, the maximum generation of entanglement between the two modes is not a monotonically increasing function of the squeezing parameter. Instead, there exists a critical degree of squeezing rc for the maximum entanglement to be enhanced. For the coupled oscillator systems considered, we have derived the analytical expressions of rc.

Spectral analysis on explosive percolation

We study the spectral properties of the process of explosive percolation. In particular, we explore how the maximum eigenvalue of the adjacency matrix of a network which governs the spreading efficiency evolves as the density of connection increases. Interestingly, for networks with connectivity that grow in an explosive way, information spreading and mass transport are found to be carried out inefficiently. In the conventional explosive percolation models that we studied, the sudden emergences of large-scale connectivity are found to come with relatively lowered efficiency of spreading. Nevertheless, the spreading efficiency of the explosive model can be increased by introducing heterogeneous structures into the networks.

Influence of network structure on cooperative dynamics in coupled socio-ecological systems

Interactions in real-world social and biological organizations are complex. Spatial structures or social networks enable clusters of cooperators to outcompete defectors when the altruistic act of a cooperator benefits only its neighbors. In this context, it had been shown that cooperation is favored if the benefit-to-cost ratio of the altruistic act exceeds the average number of interactions. This implies that cooperation survives better in societies with less social ties. For coupled socio-ecological systems in which an unselfish act is assumed to benefit all users who have open access to the resource, we show that when social sanction is present, the opposite can happen: cooperation can be easily promoted in populations where virtually everyone knows everyone else but not in populations that possess fewer connections.

Adaptive self-organization of Bali’s ancient rice terraces

Significance In Bali, the cooperative management of rice terraces extends beyond villages to whole watersheds. To understand why, we created a model that explores how cooperation can propagate from pairs of individuals to extended groups, creating a resilient system of bottom-up management that both increases and equalizes harvests. Spatial patterns of collective crop management—observable in Google Earth—closely match the predictions of the model. The spatial patterning that emerges is nonuniform and scale-free. Although the model parameters here are tuned to Bali, similar mechanisms of emergent global control should be detectible in other anthropogenic landscapes using multispectral imagery. Recognizing this signature of emergent system-wide cooperation may help planners to avoid unproductive changes to successful bottom-up systems of environmental management. Spatial patterning often occurs in ecosystems as a result of a self-organizing process caused by feedback between organisms and the physical environment. Here, we show that the spatial patterns observable in centuries-old Balinese rice terraces are also created by feedback between farmers’ decisions and the ecology of the paddies, which triggers a transition from local to global-scale control of water shortages and rice pests. We propose an evolutionary game, based on local farmers’ decisions that predicts specific power laws in spatial patterning that are also seen in a multispectral image analysis of Balinese rice terraces. The model shows how feedbacks between human decisions and ecosystem processes can evolve toward an optimal state in which total harvests are maximized and the system approaches Pareto optimality. It helps explain how multiscale cooperation from the community to the watershed scale could persist for centuries, and why the disruption of this self-organizing system by the Green Revolution caused chaos in irrigation and devastating losses from pests. The model shows that adaptation in a coupled human–natural system can trigger self-organized criticality (SOC). In previous exogenously driven SOC models, adaptation plays no role, and no optimization occurs. In contrast, adaptive SOC is a self-organizing process where local adaptations drive the system toward local and global optima.

Impact of edge removal on the centrality betweenness of the best spreaders

The control of epidemic spreading is essential to avoid potential fatal consequences and also, to lessen the unforeseen socio-economic impact. The need for effective control is exemplified during the severe acute respiratory syndrome (SARS) epidemy in 2003, which has inflicted nearly a thousand deaths as well as bankruptcies of airlines and related businesses. In this article, we examine the efficacy of control strategies on the propagation of infectious diseases based on removing connections within real-world airline networks with the associated economic and social costs taken into account through defining appropriate quantitative measures. We uncover the surprising results that removing less busy connections can be far more effective in hindering the spread of the disease than removing the more popular connections. Since disconnecting the less popular routes tends to incur less socio-economic cost, our finding suggests the possibility of trading minimal reduction in connectivity of an important hub with efficiencies in epidemic control. In particular, we demonstrate the performance of various local epidemic control strategies, and show how our approach can predict their cost effectiveness through the spreading control characteristics.

Social Cooperation and Disharmony in Communities Mediated through Common Pool Resource Exploitation

It was theorized that when a society exploits a shared resource, the system can undergo extreme phase transition from full cooperation in abiding by a social agreement, to full defection from it. This was shown to happen in an integrated society with complex social relationships. However, real-world agents tend to segregate into communities whose interactions contain features of the associated community structure. We found that such social segregation softens the abrupt extreme transition through the emergence of multiple intermediate phases composed of communities of cooperators and defectors. Phase transitions thus now occur through these intermediate phases which avert the instantaneous collapse of social cooperation within a society. While this is beneficial to society, it nonetheless costs society in two ways. First, the return to full cooperation from full defection at the phase transition is no longer immediate. Community linkages have rendered greater societal inertia such that the switch back is now typically stepwise rather than a single change. Second, there is a drastic increase in social disharmony within the society due to the greater tension in the relationship between segregated communities of defectors and cooperators. Intriguingly, these results on multiple phases with its associated phenomenon of social disharmony are found to characterize the level of cooperation within a society of Balinese farmers who exploit water for rice production.

Kinship structures create persistent channels for language transmission

Significance Associations between genes and languages occur even with sustained migration among communities. By comparing phylogenies of genes and languages, we identify one source of this association. In traditional tribal societies, marriage customs channel language transmission. When women remain in their natal community and men disperse (matrilocality), children learn their mothers’ language, and language correlates with maternally inherited mitochondrial DNA. For the converse kinship practice (patrilocality), language instead correlates with paternally inherited Y chromosome. Kinship rules dictating postmarital residence can persist for many generations and determine population genetic structure at the community scale. The long-term association of languages with genetic clades created by kinship systems provides information about language transmission, and about the structure and persistence of social groups. Languages are transmitted through channels created by kinship systems. Given sufficient time, these kinship channels can change the genetic and linguistic structure of populations. In traditional societies of eastern Indonesia, finely resolved cophylogenies of languages and genes reveal persistent movements between stable speech communities facilitated by kinship rules. When multiple languages are present in a region and postmarital residence rules encourage sustained directional movement between speech communities, then languages should be channeled along uniparental lines. We find strong evidence for this pattern in 982 individuals from 25 villages on two adjacent islands, where different kinship rules have been followed. Core groups of close relatives have stayed together for generations, while remaining in contact with, and marrying into, surrounding groups. Over time, these kinship systems shaped their gene and language phylogenies: Consistently following a postmarital residence rule turned social communities into speech communities.

Network extreme eigenvalue: From mutimodal to scale-free networks.

The extreme eigenvalues of adjacency matrices are important indicators on the influence of topological structures to the collective dynamical behavior of complex networks. Recent findings on the ensemble averageability of the extreme eigenvalue have further authenticated its applicability to the study of network dynamics. However, the ensemble average of extreme eigenvalue has only been solved analytically up to the second order correction. Here, we determine the ensemble average of the extreme eigenvalue and characterize its deviation across the ensemble through the discrete form of random scale-free network. Remarkably, the analytical approximation derived from the discrete form shows significant improvement over previous results, which implies a more accurate prediction of the epidemic threshold. In addition, we show that bimodal networks, which are more robust against both random and targeted removal of nodes, are more vulnerable to the spreading of diseases.

Dynamical Relation between Quantum Squeezing and Entanglement in Coupled Harmonic Oscillator System

In this paper, we investigate into the numerical and analytical relationship between the dynamically generated quadrature squeezing and entanglement within a coupled harmonic oscillator system. The dynamical relation between these two quantum features is observed to vary monotically, such that an enhancement in entanglement is attained at a fixed squeezing for a larger coupling constant. Surprisingly, the maximum attainable values of these two quantum entities are found to consistently equal to the squeezing and entanglement of the system ground state. In addition, we demonstrate that the inclusion of a small anharmonic perturbation has the effect of modifying the squeezing versus entanglement relation into a nonunique form and also extending the maximum squeezing to a value beyond the system ground state.

Large-Scale Connectivity vs. Spreading Efficiency: Spectral Analysis on Explosive Percolation

Some of the results of a spectral analysis of the process of explosive percolation on complex networks (Chung et al., Europhys Lett 101:66003, 2013) are presented here. More specifically, we explore how the maximum eigenvalues of the adjacency matrix of a network, which governs the spreading efficiency, evolves as the density of network connections are increased. We find that for networks with connectivity that grow in an explosive way, information spreading and mass transport are carried out inefficiently. When we looked into the conventional explosive percolation models, the sudden emergency of large connectivity comes with relatively lowered efficiency of spreading. Nevertheless, the spreading efficiency of the explosive models can be improved by introducing heterogeneous structures into the networks.