Dynamics in online social networks An increasing number of
today's social interactions occurs using online social media as
communication channels. Some online social networks have become
extremely popular in the last decade. They differ among
themselves in the character of the service they provide to
online users. For instance, Facebook can be seen mainly as a
platform for keeping in touch with close friends and relatives,
Twitter is used to propagate and receive news, LinkedIn
facilitates the maintenance of professional contacts, Flickr
gathers amateurs and professionals of photography, etc. Albeit
different, all these online platforms share an ingredient that
pervades all their applications. There exists an underlying
social network that allows their users to keep in touch with
each other and helps to engage them in common activities or
interactions leading to a better fulfillment of the service's
purposes. This is the reason why these platforms share a good
number of functionalities, e.g., personal communi