Link Prediction with Social Vector Clocks

State-of-the-art link prediction utilizes combinations of complex features derived from network panel data. We here show that computationally less expensive features can achieve the same performance in the common scenario in which the data is available as a sequence of interactions. Our features are based on social vector clocks, an adaptation of the vector-clock concept introduced in distributed computing to social interaction networks. In fact, our experiments suggest that by taking into account the order and spacing of interactions, social vector clocks exploit different aspects of link formation so that their combination with previous approaches yields the most accurate predictor to date.Comment: 9 pages, 6 figure

Soft behaviour modelling of user communities

A soft modelling approach for describing behaviour in on-line user communities is introduced in this work. Behaviour models of individual users in dynamic virtual environments have been described in the literature in terms of timed transition automata; they have various drawbacks. Soft multi/agent behaviour automata are defined and proposed to describe multiple user behaviours and to recognise larger classes of user group histories, such as group histories which contain unexpected behaviours. The notion of deviation from the user community model allows defining a soft parsing process which assesses and evaluates the dynamic behaviour of a group of users interacting in virtual environments, such as e-learning and e-business platforms. The soft automaton model can describe virtually infinite sequences of actions due to multiple users and subject to temporal constraints. Soft measures assess a form of distance of observed behaviours by evaluating the amount of temporal deviation, additional or omitted actions contained in an observed history as well as actions performed by unexpected users. The proposed model allows the soft recognition of user group histories also when the observed actions only partially meet the given behaviour model constraints. This approach is more realistic for real-time user community support systems, concerning standard boolean model recognition, when more than one user model is potentially available, and the extent of deviation from community behaviour models can be used as a guide to generate the system support by anticipation, projection and other known techniques. Experiments based on logs from an e-learning platform and plan compilation of the soft multi-agent behaviour automaton show the expressiveness of the proposed model

The influence of biological rhythms on host–parasite interactions

Biological rhythms, from circadian control of cellular processes to annual cycles in life history, are a main structural element of biology. Biological rhythms are considered adaptive because they enable organisms to partition activities to cope with, and take advantage of, predictable fluctuations in environmental conditions. A flourishing area of immunology is uncovering rhythms in the immune system of animals, including humans. Given the temporal structure of immunity, and rhythms in parasite activity and disease incidence, we propose that the intersection of chronobiology, disease ecology, and evolutionary biology holds the key to understanding host–parasite interactions. Here, we review host–parasite interactions while explicitly considering biological rhythms, and propose that rhythms: influence within-host infection dynamics and transmission between hosts, might account for diel and annual periodicity in host–parasite systems, and can lead to a host–parasite arms race in the temporal domain

Time dissemination and synchronization methods to support Galileo timing interfaces

Precise timing is an important factor in the modern information-oriented society and culture. Timing is one of the key technologies for such basic and everyday things, like cellular communications, Internet, satellite navigation and many others. Satellite navigation systems offer cost-efficient and high-performance timing services, and GPS is presently the unchallenged market leader. However, GPS is under military control and does not offer availability and performance guarantees. From a user perspective, this situation will change with the advent of the European satellite navigation system Galileo which shall be operated on a commercial basis by civil entities and shall accept certain liabilities for its services providing also guaranteed service performances. This work is motivated by the new opportunities and challenges related to Galileo timekeeping and applications, and in particular by the necessity to (a) produce and maintain a stable, accurate and robust system timescale which can serve for both accurate prediction of satellite clocks and for the metrological purposes, (b) establish accurate and reliable timing interface to GPS to facilitate Galileo interoperability, (c) maximize user benefits from the new system features like service guarantees and support application development by enabling their certification. The thesis starts with overview of atomic clocks, timekeeping and timing applications. Further Galileo project and system architecture are described and details on Galileo timekeeping concept are given. In addition, the state-of-the-art timekeeping and time dissemination methods and algorithms are presented. Main findings of the thesis focus on (a) Galileo timekeeping. Various options for generation of Galileo system time are proposed and compared with respect to the key performance parameters (stability and reliability). Galileo System Time (GST) stability requirements driven by its navigation and metrological functions are derived. In addition, achievable level of GST stability (considering hardware components) is analyzed. Further, optimization of the present baseline with respect to the design of Galileo Precise Timing Facility (PTF), and its redundancy and switching concepts is undertaken. Finally, performance analysis of different options for generation of the ensemble time is performed and considerations with respect to the role of the ensemble time in Galileo are provided, (b) GPS Galileo timing interface. The magnitude and statistical properties of the time offset are investigated and the impact of the time offset onto the user positioning and timing accuracy is studied with the help of simulated GPS and Galileo observations. Here a novel simulation concept which is based on utilization of GPS data and their scaling for Galileo is proposed. Both GPS and Galileo baseline foresees that the GPS/Galileo time offset shall be determined and broadcast to users in the navigation messages. For this purposes, the offset shall be predicted using available measurement data. Simulations of GPS Galileo time offset determination and prediction are presented. The prediction is made relying on both traditional method and on the advanced techniques like Box-Jenkins prediction (based on the autoregressive moving average approach) and Kalman filter. The end-to-end budgets for different options of GPS Galileo time offset determination are also presented. (c) Galileo interface to timing users (Galileo timing service). The relevance of GST restitution from the metrological point of view is discussed and recognition of GST as a legal time reference is proposed. Assessment of the accuracy of the Galileo timing service is presented. Finally, recommendations for Galileo are provided based on the findings of the thesis

Entrainment and motor emulation approaches to joint action: alternatives or complementary approaches?

Joint actions, such as music and dance, rely crucially on the ability of two, or more, agents to align their actions with great temporal precision. Within the literature that seeks to explain how this action alignment is possible, two broad approaches have appeared. The first, what we term the entrainment approach, has sought to explain these alignment phenomena in terms of the behavioral dynamics of the system of two agents. The second, what we term the emulator approach, has sought to explain these alignment phenomena in terms of mechanisms, such as forward and inverse models, that are implemented in the brain. They have often been pitched as alternative explanations of the same phenomena; however, we argue that this view is mistaken, because, as we show, these two approaches are engaged in distinct, and not mutually exclusive, explanatory tasks. While the entrainment approach seeks to uncover the general laws that govern behavior the emulator approach seeks to uncover mechanisms. We argue that is possible to do both and that the entrainment approach must pay greater attention to the mechanisms that support the behavioral dynamics of interest. In short, the entrainment approach must be transformed into a neuroentrainment approach by adopting a mechanistic view of explanation and by seeking mechanisms that are implemented in the brain