Σχολικός εκφοβισμός και θυματοποίηση: Ατομικές και οικογενειακές παράμετροι

The present paper aims at describing the factors that contribute in thedevelopment of bullying and victimization at school. Prior research has identified three distinct groups of children participating in the above phenomenon: bullies, passive victims and aggressive victims (or bully-victims). These groups have different profiles in their intraindividual(personal), as well as their family environments. The most important personal characteristics refer to their temperament, the degree of psycho-pathology issues, gender and age. Further, differences havebeen found in terms of attitudes such as attributions, and in terms of being different in a way that sets the individual apart from a mainstream group. Regarding family parameters, factors such as parentalinvolvement and parental style, as well as parental depression have been shown to be related to child bullying and victimization at school. Among the many explanatory models that have been suggested, verypopular are recently the transactional models, proposing that a bi-directional influence exists between parents and children.

Schema-Based JSON Data Stores in Relational Databases

JSON is a simple, compact and light weighted data exchange format to communicate between web services and client applications. NoSQL document stores evolve with the popularity of JSON, which can support JSON schema-less storage, reduce cost, and facilitate quick development. However, NoSQL still lacks standard query language and supports eventually consistent BASE transaction model rather than the ACID transaction model. This is very challenging and a burden on the developer. The relational database management systems (RDBMS) support JSON in binary format with SQL functions (also known as SQL/JSON). However, these functions are not standardized yet and vary across vendors along with different limitations and complexities. More importantly, complex searches, partial updates, composite queries, and analyses are cumbersome and time consuming in SQL/JSON compared to standard SQL operations. It is essential to integrate JSON into databases that use standard SQL features, support ACID transactional models, and has the capability of managing and organizing data efficiently. In this article, we empower JSON to use relational databases for analysis and complex queries. The authors reveal that the descriptive nature of the JSON schema can be utilized to create a relational schema for the storage of the JSON document. Then, the powerful SQL features can be used to gain consistency and ACID compatibility for querying JSON instances from the relational schema. This approach will open a gateway to combine the best features of both worlds: the fast development of JSON, consistency of relational model, and efficiency of SQL.

Reproductive control via the threat of eviction in the clown anemonefish

In social groups, high reproductive skew is predicted to arise when the reproductive output of a group is limited, and dominant individuals can suppress subordinate reproductive efforts. Reproductive suppression is often assumed to occur via overt aggression or the threat of eviction. It is unclear, however, whether the threat of eviction alone is sufficient to induce reproductive restraint by subordinates. Here, we test two assumptions of the restraint model of reproductive skew by investigating whether resource limitation generates reproductive competition and whether the threat of eviction leads to reproductive restraint in the clown anemonefish Amphiprion percula . First, we use a feeding experiment to test whether reproduction is resource limited, which would create an incentive for the dominant pair to suppress subordinate reproduction. We show that the number of eggs laid increased in the population over the study period, but the per cent increase in fed groups was more than twice that in unfed groups (205% and 78%, respectively). Second, we use an eviction experiment to test whether the dominant pair evicts mature subordinates, which would create an incentive for the subordinates to forgo reproduction. We show that mature subordinates are seven times more likely to be evicted than immature subordinates of the same size. In summary, we provide experimental support for the assumptions of the restraint model by showing that resource limitation creates reproductive competition and a credible threat of eviction helps explain why subordinates forego reproduction. Transactional models of reproductive skew may apply well to this and other simple systems.

A Comparative Study of Transactional and Semantic Approaches for Predicting Cascades on Twitter

The availability of massive social media data has enabled the prediction of people’s future behavioral trends at an unprecedented large scale. Information cascades study on Twitter has been an integral part of behavior analysis. A number of methods based on the transactional features (such as keyword frequency) and the semantic features (such as sentiment) have been proposed to predict the future cascading trends. However, an in-depth understanding of the pros and cons of semantic and transactional models is lacking. This paper conducts a comparative study of both approaches in predicting information diffusion with three mechanisms: retweet cascade, url cascade, and hashtag cascade. Experiments on Twitter data show that the semantic model outperforms the transactional model, if the exterior pattern is less directly observable (i.e. hashtag cascade). When it becomes more directly observable (i.e. retweet and url cascades), the semantic method yet delivers approximate accuracy (i.e. url cascade) or even worse accuracy (i.e. retweet cascade). Further, we demonstrate that the transactional and semantic models are not independent, and the performance gets greatly enhanced when combining both.