Johnnatan Messias

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Search systems in online social media sites are frequently used to find information about ongoing events and people. For topics with multiple competing perspectives, such as political events or political candidates, bias in the top ranked results significantly shapes public opinion. However, bias does not emerge from an algorithm alone. It is important to(More)
Recently, there have been considerable efforts to use online data to investigate international migration. These efforts show that Web data are valuable for estimating migration rates and are relatively easy to obtain. However, existing studies have only investigated flows of people along migration corridors, i.e. between pairs of countries. In our work, we(More)
The increasing use of smartphones to access social media platforms opens a new wave of applications that explore sentiment analysis in the mobile environment. However, there are various existing sentiment analysis methods and it is unclear which of them are deployable in the mobile environment. This paper provides the first of a kind study in which we(More)
Sentiment analysis has become a key tool to extract knowledge from data containing opinions and sentiments, particularly, data from online social systems. With the increasing use of smartphones to access social media platforms, a new wave of applications that explore sentiment analysis in the mobile environment is beginning to emerge. However, there are(More)
PURPOSE To study the epidemiological, clinical, therapeutic and evolutive aspects of endocarditis in a group of patients aging 12 to 20 years-old (mean 15.5). METHODS Thirty-three consecutive patients (14 males, 19 females) admitted with infective endocarditis were retrospectively studied. RESULTS Infective endocarditis mortality was 42%. Rheumatic(More)
Users of social media sites like Facebook and Twitter rely on crowdsourced content recommendation systems (e.g., Trend-ing Topics) to retrieve important and useful information. Contents selected for recommendation indirectly give the initial users who promoted (by liking or posting) the content an opportunity to propagate their messages to a wider audience.(More)
This large-scale measurement study of Twitter focuses on understanding how users control the longitudinal exposure of their publicly shared social data -- that is, their tweets -- and the limitations of currently used control mechanisms. The study finds that, while Twitter users widely employ longitudinal exposure control mechanisms, they face two(More)
Currently available data about people whose left their home country to live in a foreign country does not adequately capture the standards of contemporary global migration flows. A new trend for migration studies is to study the data from the Internet, either by Social Networks or other data in the WEB. In this study, we collected users data from the social(More)