Professor of Physics,
Deputy Director, Centre for Quantum Technologies,
Fellow of the University Scholars Programme (USP)
MY LATEST RESEARCH
S Ma, L Feng, C P Monterola and C H Lai
Importance of small degree nodes in assortative networks with degree-weight correlations
It has been known that assortative network structure plays an important role in spreading dynamics for unweighted networks. Yet its influence on weighted networks is not clear, in particular when weight is strongly correlated with the degrees of the nodes as we empirically observed in Twitter. Here we use the self-consistent probability method and revised non-perturbative HMF method to investigate this influence on both SIR and SIS spreading dynamics. Both our simulation and theoretical results show that while the critical threshold is not signicantly influenced by the assortativity, the prevalence in the supercritical regime shows a cross-over under dierent degree-weight
correlations. In particular, unlike the case of random mixing networks, in assortative networks, the negatively degree-weight correlation leads to higher prevalence in their spreading beyond the critical transmissivity than that of the positively correlated. In addition, the previously observed inhibition effect on spreading velocity by assortative structure is not apparent in negatively degree-weight correlated networks, while enhanced for that of the positively correlated. Detailed investigation into the degree distribution of the infected nodes reveals that small degree nodes play essential roles in the supercritical phase of both SIR and SIS spreadings. Our results have direct implications on viral information spreading over online social networks and epidemic spreading over contact networks.
H S Sugiarto, J S Lansing, N N Chung, C H Lai, S A Cheong and L Y Chew,
Social cooperation and disharmony in communities mediated through common pool resource exploitation
Physical Review Letters 118, 208301 (2017)
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.
N N Chung, L Y Chew and C H Lai
The Science of the American Presidential Election
Like the process of desertification, a switching of social opinion can be enduring and irreversible. When a majority opinion loses its attractiveness and becomes a minority opinion, recovering the original level of attractiveness does not necessary bring popularity of the opinion back. In the American presidential election, irrevocable transitions of opinion are observed in states where voters’ decisions on whether to vote for a party depend highly on opinion of the majority. Analysis from an opinion transition model predicts that the Democrats could end up losing the 2016 presidential election if President Obama’s approval rating falls below 48.5%.