Abstract
We present a collision-free jammer selection policy for enhanced wireless secrecy. Jammers, selected from the neighbors of a source, are friendly in the sense that they are willing to help the source to transmit securely by causing interference/collisions to possible eavesdroppers. The proposed jammer selection policy results in the selection of the largest number of jammers that do not cause collisions among themselves. This enables jammers to assist the source to transmit securely by causing interference to eavesdroppers, while sending their own traffic into the network. © 2013 IEEE.

Abstract
We propose a method for creating news context by taking advantage of a folksonomy of web clipping based on online news. We experiment with an ontology-based named entity recognition process and study two different ways of modeling the relationships induced by the coreference of named entities on news clips. We try to establish a context by identifying the community structure for a clip-centric network and for an entity-centric network, based on a small test set from the Breadcrumbs system. Finally, we compare both models, based on the detected news communities, and show the advantages of each network specification.

Abstract
In this article, we detail a system that provides contributes for analyzing and characterizing interactions that occur between participants of online communities. We adapted and applied the Social Network Analysis methodology to online discussion forums to create a dynamical interaction graph. The graph can be embedded in learning managements systems and accessed through a web page. The functionality of the system provides a suitable environment to characterize the interactions between actors and their participations in discussion forums. In the article we describe the use of the system in two real-world situations. Our conclusions lead to the verification and the rapid identification of some important situations that occur in learning communities, such as: the location of actors more or less active; distinction of positions and roles; identification of different ways of organization/interaction in groups; characterization of the interactions of a group or of a community as a whole © 2012 IEEE.

Abstract
Assessing the quality of the clustering process is fundamental in unsupervised clustering. In literature we can find three different clustering validity techniques: external criteria; internal criteria and relative criteria. In this paper, we focus on external criteria and present an algorithm that allows the implementation of external measures to assess clustering quality when the structure of the data set is unknown. To obtain an automatic partition of a data set and to reflect how documents must be grouped according to human intuition we use internal information present in data like descriptions provide by the users as tags and the distance between documents. The results show an evident correlation between manual and automatic classes indicating it is acceptable to use an automatic partition. In addition to presenting an alternative to finding the structure of the data set using meta-data such as tags, we also wanted to test the impact of their integration in the k-means++ algorithm and verify how it influences the quality of the formed clusters, suggesting a model of integration based on the occurrence of tags in document content. The experimental results indicate a positive impact when external measures are calculated, although there was no apparent correlation between the weight assigned to the tags and the quality of the obtained clusters.

Abstract
Computational journalism allows journalists to collect large collections of information chunks from separate sources. The analysis of these collections can reveal hidden relationships between of relationships, but due to their size, diversity, and varying nuances it is necessary to use both computational and human analysis. Breadcrumbs PDL is an adaptive spatial hypermedia system that brings together human cognition and machine computation in order to analyze a collection of usergenerated news clips. The project demonstrates the effectiveness of spatial hypermedia in the domain of computational journalism.

Abstract
Breadcrumbs is a folksonomy of news clips, where users can aggregate fragments of text taken from online news. Besides the textual content, each news clip contains a set of metadata fields associated with it. User-defined tags are one of the most important of those information fields. Based on a small data set of news clips, we build a network of cooccurrence of tags in news clips, and use it to improve text clustering. We do this by defining a weighted cosine similarity proximity measure that takes into account both the clip vectors and the tag vectors. The tag weight is computed using the related tags that are present in the discovered community. We then use the resulting vectors together with the new distance metric, which allows us to identify socially biased document clusters. Our study indicates that using the structural features of the network of tags leads to a positive impact in the clustering process. Copyright 2012 ACM.