Spreading to localized targets in complex networks.

As an important type of dynamics on complex networks, spreading is widely used to model many real processes such as the epidemic contagion and information propagation. One of the most significant research questions in spreading is to rank the spreading ability of nodes in the network. To this end, substantial effort has been made and a variety of effective methods have been proposed. These methods usually define the spreading ability of a node as the number of finally infected nodes given that the spreading is initialized from the node. However, in many real cases such as advertising and news propagation, the spreading only aims to cover a specific group of nodes. Therefore, it is necessary to study the spreading ability of nodes towards localized targets in complex networks. In this paper, we propose a reversed local path algorithm for this problem. Simulation results show that our method outperforms the existing methods in identifying the influential nodes with respect to these localized targets. Moreover, the influential spreaders identified by our method can effectively avoid infecting the non-target nodes in the spreading process.We thank an anonymous reviewer for helpful suggestions which improve this paper. This work is supported by the National Natural Science Foundation of China (Nos 61603046 and 11547188), Natural Science Foundation of Beijing (No. 16L00077) and the Young Scholar Program of Beijing Normal University (No. 2014NT38)

Are virtual currencies virtuous? Ethical and environmental issues

International audienceCryptocurrencies have gained in popularity and generated a great deal of enthusiasm in recent years with regard to the sustained increase in the number of transactions achieved by miners. On what scale can we consider the process and uses of virtual money to be ethical? What are the misuses related to their use? In this chapter, we study the ethical and environmental issues of cryptocurrencies. First, regarding the environmental issue, the major cryptocurrencies use a large amount of electricity for mining, which has a significant impact on the energy production system and global warming. Second, we discuss the new type of Dark economy that has emerged with these currencies, thanks to the anonymity of transactions. We particularly emphasize the unethical use of cryptocurrencies, namely the virtual money laundering and tax evasion, the financing of illegal activities (i.e. illicit products, terrorist financing) and cyber-attacks. Third, we develop the ethical use of virtual money and show that this kind of currency, which guarantees the protection of privacy and anonymity of transactions, can be a good solution to mitigate transaction costs and reduce poverty. They can also be beneficial in the context of debt crises and hyperinflation. Thus, cryptocurrencies per se are not evil; it is their uses that can be