Helsinki Institute for Information Technology

About: Helsinki Institute for Information Technology is a facility organization based out in Espoo, Finland. It is known for research contribution in the topics: Population & Bayesian network. The organization has 630 authors who have published 1962 publications receiving 63426 citations.

Where Is the Soho of Rome? Measures and Algorithms for Finding Similar Neighborhoods in Cities

Abstract: Data generated on location-aware social media provide rich information about the places (shopping malls, restaurants, cafes , etc) where citizens spend their time. That information can, in turn, be used to describe city neighborhoods in terms of the activity that takes place therein. For example, the data might reveal that citizens visit one neighborhood mainly for shopping , while another for its dining venues. In this paper, we present a methodology to analyze such data, describe neighborhoods in terms of the activity they host, and discover similar neighborhoods across cities. Using millions of Foursquare check-ins from cities in Eu-rope and the US, we conduct an extensive study on features and measures that can be used to quantify similarity of city neighborhoods. We find that the earth-mover's distance outper-forms other candidate measures in finding similar neighborhoods. Subsequently, using the earth-mover's distance as our measure of choice, we address the issue of computational efficiency: given a neighborhood in one city, how to efficiently retrieve the k most similar neighborhoods in other cities. We propose a similarity-search strategy that yields significant speed improvement over the brute-force search, with minimal loss in accuracy. We conclude with a case study that compares neighborhoods of Paris to neighborhoods of other cities.

A local 2-approximation algorithm for the vertex cover problem

Abstract: We present a distributed 2-approximation algorithm for the minimum vertex cover problem. The algorithm is deterministic, and it runs in (Δ + 1)2 synchronous communication rounds, where Δ is the maximum degree of the graph. For Δ = 3, we give a 2-approximation algorithm also for the weighted version of the problem.

Designing for privacy and self-presentation in social awareness

Abstract: Social awareness applications are based on the idea of a group sharing real-time context information via personal and ubiquitous terminals. Studies of such applications have shown that users are not only concerned with the preservation privacy through non-disclosure. Instead, disclosure is manipulated for the constant presentation of self to the group in everyday social situations. Basing on 3 years of research with the mobile social awareness system ContextContacts, established findings in social psychology and ubiquitous computing, we propose a number of design principles to support users in this management of privacy and presentation. These principles are to apply even if disclosure is automated, and include support for lightweight permissions, assuming reciprocity, appearing differently to different audiences, providing for feedback on presentation and allowing lying. These principles are applied in interaction design and protocol engineering for the next version of a mobile awareness system called ContextContacts.

Forest management and regional tree composition drive the host preference of saproxylic beetle communities

Abstract: Summary 1. Among saproxylic beetles, many early colonizers prefer particular host species. Ranking of preferred hosts of local saproxylic beetle communities is critical for effective dead-wood management in forests, but is rarely done because experiments with numerous tree species are labour and cost intensive. 2. We analysed the host preference of local saproxylic beetle communities on logs of 13 tree species in relation to management (unmanaged and managed beech stands, conifer plantations on natural beech sites) in three regions of Germany during the most critical period for host specificity, that is the first two years after harvesting. Hosts were ranked quantitatively based on the ordinal ranking of hosts by single beetle species, which in turn was based on the variation in beetle abundance. First, we employed a Bradley–Terry model in which ranking was derived from paired comparisons of host trees. Then, a model-based recursive partitioning of the Bradley–Terry model tested whether host preference of beetle communities is affected by stand management, region and decay progress of dead wood. 3. Our results indicated that beetle communities overall avoided logs of Fraxinus, Pseudotsuga, Larix and Tilia, and Carpinus ranked highest in preference. Carpinus also ranked highest for communities of broadleaf specialists; Picea abies ranked highest for communities of conifer specialists. Model-based recursive partitioning revealed that ranking of local hosts in conifer stands differed from that of broadleaf stands, and that ranking of hosts in broadleaf stands differed between regions, but only in the first year for both. 4. Synthesis and applications. Early-colonizing saproxylic beetle communities vary locally in their choice of host trees. Therefore, forest managers should focus on the enrichment of dead wood of regional tree species and tree species of the local stand to successfully promote earlycolonizing beetle.