BibSonomy publications for /user/andreab/2006Sat Apr 05 14:58:45 CEST 2008New York, NY, USAKDD '06: Proceedings of the 12th ACM SIGKDD international conference on Knowledge discovery and data mining611--617Structure and evolution of online social networks20062006 analysis flickr imported models network social structure yahoo In this paper, we consider the evolution of structure within large online social networks. We present a series of measurements of two such networks, together comprising in excess of five million people and ten million friendship links, annotated with metadata capturing the time of every event in the life of the network. Our measurements expose a surprising segmentation of these networks into three regions: singletons who do not participate in the network; isolated communities which overwhelmingly display star structure; and a giant component anchored by a well-connected core region which persists even in the absence of stars.We present a simple model of network growth which captures these aspects of component structure. The model follows our experimental results, characterizing users as either passive members of the network; inviters who encourage offline friends and acquaintances to migrate online; and linkers who fully participate in the social evolution of the network.Sat Apr 28 16:14:22 CEST 2007Nonsymmetric entropy I: basic concepts and results20062006 entropy imported liu mandelbrot tagora zipf Sat Apr 28 16:11:21 CEST 2007Maximal nonsymmetric entropy leads naturally to Zipf's law20062006 d4.1 distribution frequency imported mandelbrot tagora word zipf Wed Apr 11 19:19:12 CEST 2007http://xxx.lanl.gov/abs/cs.CY/0605015Proceedings of the National Academy of Sciences United States of America1461Semiotic dynamics and collaborative tagging10420072006 cattuto collaborative d4.1 del.icio.us delicious dynamics folksonomy loreto semiotic semioticdynamic tagging tagora yule yulesimon Collaborative tagging has been quickly gaining ground because of its ability to recruit the activity of web users into effectively organizing and sharing vast amounts of information. Here we collect data from a popular system and investigate the statistical properties of tag co-occurrence. We introduce a stochastic model of user behavior embodying two main aspects of collaborative tagging: (i) a frequency-bias mechanism related to the idea that users are exposed to each other's tagging activity; (ii) a notion of memory - or aging of resources - in the form of a heavy-tailed access to the past state of the system. Remarkably, our simple modeling is able to account quantitatively for the observed experimental features, with a surprisingly high accuracy. This points in the direction of a universal behavior of users, who - despite the complexity of their own cognitive processes and the uncoordinated and selfish nature of their tagging activity - appear to follow simple activity patterns.Wed Apr 11 19:16:19 CEST 2007Europhysics Letters2208-214A Yule-Simon process with memory7620062006 Simon Yule analytic cattuto d4.1 folksonomy loreto memory model servedio study tagora yulesimon The Yule-Simon model has been used as a tool to describe the growth of diverse systems, acquiring a paradigmatic character in many fields of research. Here we study a modified Yule-Simon model that takes into account the full history of the system by means of a hyperbolic memory kernel. We show how the memory kernel changes the properties of preferential attachment and provide an approximate analytical solution for the frequency distribution density as well as for the frequency-rank distribution.Tue Apr 10 15:40:05 CEST 2007New York, NY, USACSCW '06: Proceedings of the 2006 20th anniversary conference on Computer supported cooperative work181--190tagging, communities, vocabulary, evolution20062006 banff d4.1 dynamics imported tagging tags userbehavior A tagging community's vocabulary of tags forms the basis for social navigation and shared expression. We present a user-centric model of vocabulary evolution in tagging communities based on community in uence and personal tendency. We evaluate our model in an emergent tagging system by introducing tagging features into the MovieLens recommender system. We explore four tag selection algorithms for displaying tags applied by other community members. We analyze the algorithms eTue Oct 17 19:20:31 CEST 2006Physical Review Letters11118002Brownian Forces in Sheared Granular Matter9620062006 cnrbest5 experiments fluctuations friction granular model myown prl statistics stick-slip We present results from a series of experiments on a granular medium sheared in a Couette geometry and show that their statistical properties can be computed in a quantitative way from the assumption that the resultant from the set of forces acting in the system performs a Brownian motion. The same assumption has been utilized, with success, to describe other phenomena, such as the Barkhausen effect in ferromagnets, and so the scheme suggests itself as a more general description of a wider class of driven instabilities.