From calls to communities: a model for time varying social networks

Social interactions vary in time and appear to be driven by intrinsic mechanisms, which in turn shape the emerging structure of the social network. Large-scale empirical observations of social interaction structure have become possible only recently, and modelling their dynamics is an actual challenge. Here we propose a temporal network model which builds on the framework of activity-driven time-varying networks with memory. The model also integrates key mechanisms that drive the formation of social ties - social reinforcement, focal closure and cyclic closure, which have been shown to give rise to community structure and the global connectedness of the network. We compare the proposed model with a real-world time-varying network of mobile phone communication and show that they share several characteristics from heterogeneous degrees and weights to rich community structure. Further, the strong and weak ties that emerge from the model follow similar weight-topology correlations as real-world social networks, including the role of weak ties.Comment: 10 pages, 5 figure

Effects of temporal correlations on cascades: Threshold models on temporal networks

A person's decision to adopt an idea or product is often driven by the decisions of peers, mediated through a network of social ties. A common way of modeling adoption dynamics is to use threshold models, where a node may become an adopter given a high enough rate of contacts with adopted neighbors. We study the dynamics of threshold models that take both the network topology and the timings of contacts into account, using empirical contact sequences as substrates. The models are designed such that adoption is driven by the number of contacts with different adopted neighbors within a chosen time. We find that while some networks support cascades leading to network-level adoption, some do not: the propagation of adoption depends on several factors from the frequency of contacts to burstiness and timing correlations of contact sequences. More specifically, burstiness is seen to suppress cascades sizes when compared to randomised contact timings, while timing correlations between contacts on adjacent links facilitate cascades.Comment: 9 pages, 7 figures, Published versio

Ranking influential spreaders is an ill-defined problem

Finding influential spreaders of information and disease in networks is an important theoretical problem, and one of considerable recent interest. It has been almost exclusively formulated as a node-ranking problem -- methods for identifying influential spreaders rank nodes according to how influential they are. In this work, we show that the ranking approach does not necessarily work: the set of most influential nodes depends on the number of nodes in the set. Therefore, the set of $n$ most important nodes to vaccinate does not need to have any node in common with the set of $n+1$ most important nodes. We propose a method for quantifying the extent and impact of this phenomenon, and show that it is common in both empirical and model networks

Two betweenness centrality measures based on Randomized Shortest Paths

This paper introduces two new closely related betweenness centrality measures based on the Randomized Shortest Paths (RSP) framework, which fill a gap between traditional network centrality measures based on shortest paths and more recent methods considering random walks or current flows. The framework defines Boltzmann probability distributions over paths of the network which focus on the shortest paths, but also take into account longer paths depending on an inverse temperature parameter. RSP's have previously proven to be useful in defining distance measures on networks. In this work we study their utility in quantifying the importance of the nodes of a network. The proposed RSP betweenness centralities combine, in an optimal way, the ideas of using the shortest and purely random paths for analysing the roles of network nodes, avoiding issues involving these two paradigms. We present the derivations of these measures and how they can be computed in an efficient way. In addition, we show with real world examples the potential of the RSP betweenness centralities in identifying interesting nodes of a network that more traditional methods might fail to notice.Comment: Minor updates; published in Scientific Report

American Parties’ Policies towards Europe in the Post-Cold War Era : A Comparative Analysis of the Democratic and Republican Party Platforms

This thesis provides a unique perspective on transatlantic relations in the post-Cold War era: the role of the parties. Democratic and Republican party platforms from the 1992 American presidential elections until the 2016 elections are analyzed to reveal differences in their policies towards Europe. The 14 party platforms were chosen as the material because they are the most important documents the political parties produce. Moreover, there is only limited amount of previous research on party platforms since the focus has been on the actions of the administration or on the candidate speeches and debates instead. The analysis is carried out on two levels: comparison over time to reveal intra-party ideological change, and comparison between the parties to reveal inter-party polarization over policies towards Europe. The method of the thesis is mainly data-driven qualitative content analysis. The theoretical background is based on research about party polarization and partisan ideological differences over foreign policy. The analysis shows that the policies towards Europe vary within the party platforms over time. Intra-party ideological policy shifts appear more clearly in the Republican party platforms, whereas the Democratic party platforms showcase a more balanced ideological foundation. The incumbent/challenger role of the party as well as events in international politics have also influenced policy shifts over time. Additionally, the analysis reveals that Democratic and Republican party platforms are somewhat polarized in their policies towards Europe. As predicted, the parties concentrate on slightly different policies, regions, and institutions when referring to Europe. Most importantly, because of their ideological differences, the two parties have differing or even opposing moral evaluations about and treatment recommendations for the policies and the actors. To conclude, this thesis provides new information about the partisan perspective on transatlantic relations. Some say the party platforms are neglected documents that receive little public attention. Their policies will rarely be realized as such in the real world because of the balance of power in the American political system and unexpected events in international politics. Nonetheless, this thesis proves that intra-party ideological contestation and inter-party polarization exist in transatlantic relations

Improved technique for design of perfect reconstruction FIR QMF banks with lossless polyphase matrices

A technique is developed for the design of analysis filters in an M-channel maximally decimated, perfect reconstruction, finite-impulse-response quadrature mirror filter (FIR QMF) bank that has a lossless polyphase-component matrix E(z). The aim is to optimize the parameters characterizing E(z) until the sum of the stopband energies of the analysis filters is minimized. There are four novel elements in the procedure reported here. The first is a technique for efficient initialization of one of the M analysis filters, as a spectral factor of an Mth band filter. The factorization itself is done in an efficient manner using the eigenfilters approach, without the need for root-finding techniques. The second element is the initialization of the internal parameters which characterize E(z), based on the above spectral factor. The third element is a modified characterization, mostly free from rotation angles, of the FIR E(z). The fourth is the incorporation of symmetry among the analysis filters, so as to minimize the number of unknown parameters being optimized. The resulting design procedure always gives better filter responses than earlier ones (for a given filter length) and converges much faste

Best practices in SECURE partner regions

Smarter Energy Communities in Northern and Arctic Regions (SECURE) project is a project funded by the Northern Periphery and Arctic Programme (NPA). The project runs for three years, from May 2016 to the end of April 2019. SECURE is implemented by eight partners in six countries (Ireland, Sweden, United Kingdom, Finland, Canada, Faroe Islands) and is coordinated by the European Regions Network for the Application of Communications Technology (ERNACT). The project aims at increasing the capacity of the local authorities regarding energy efficiency and use of renewable energy. The best practices have been executed in the SECURE partner regions and have involved public and private instances as well as companies and associations. The practices are examples of actions that can be taken to reduce the carbon footprint and eventually lead to behavioral change by example. The partners have sought for resource-efficient and sustainable practices that can be transferred directly or modified before use in the new setting

Toistuvalla lannoituksella saatava kasvunlisäys kivennäismaiden männiköissä ja kuusikoissa.

25 graphs, 11 tables80 ref. Summaries (En, Fi). Incl. 2 append. table