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X-WR-CALDESC:Events for Namur Institute For Complex Systems
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190919T130000
DTEND;TZID=Europe/Paris:20190919T140000
DTSTAMP:20260406T200203
CREATED:20190905T080838Z
LAST-MODIFIED:20190911T090243Z
UID:587-1568898000-1568901600@www.naxys.be
SUMMARY:Hamza Bennani (University Paris Nanterre)
DESCRIPTION:Titre: Does a Sentiment Shock Help to Predict Monetary Policy: Evidence from the ECB \nAbstract: This paper aims to assess whether sentiment shock is helpful in predicting ECB monetary policy decisions. We use a bag-of-words approach and several dictionar- ies on ECB’s President introductory statements to derive a measure of sentiment. Next\, we orthogonalize the sentiment measure on a set of macroeconomic and finan- cial variables to compute sentiment shock. Finally\, we test whether sentiment shock is useful to predict ECB monetary policy decisions. We find that sentiment shock is significantly and positively related to future ECB policy decisions\, even when controlling for future economic conditions and market expectations about mone- tary policy. Further extensions show that the predictive power of sentiment shock is robust to (i) the scoring method chosen to compute sentiment\, (ii) alternative expectations about monetary policy and (iii) the macroeconomic forecasts used in the monetary policy Taylor rule. However\, we find that the predictive power of sentiment shock is sensitive to the dictionaries used to compute the measure of sentiment. These findings highlight an additional channel by which ECB communication improves monetary policy predictability.
URL:https://www.naxys.be/event/hamza-bennani-university-paris-nanterre/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190905T140000
DTEND;TZID=Europe/Paris:20190905T180000
DTSTAMP:20260406T200203
CREATED:20190905T075842Z
LAST-MODIFIED:20190905T075950Z
UID:583-1567692000-1567706400@www.naxys.be
SUMMARY:Workshop Dynamical processes on networks
DESCRIPTION:14h00-15h00: Hiroya Nakao\, Tokyo Institute of Technology (Japan) \nCollective oscillations and synchronization in networks of coupled dynamical elements \n15h00-15h40: Duccio Fanelli\, Università di Firenze (Italy) \nTuring-like patterns from purely reactive systems \n15h40-16h20: Julien Petit\, UNamur \nDiffusion-based processes: from graphs to graphons \n16h20-16h50: Coffee break \n16h50-17h40: Alexandre Mauroy\, UNamur \nOperator theoretic methods for network identification \n17h40-18h20: Malbor Asllani\, MACSI University of Limerick (Ireland) \nEmergence of non-normality in real life networked systems
URL:https://www.naxys.be/event/workshop-dynamical-processes-on-networks/
LOCATION:E22
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190523T130000
DTEND;TZID=Europe/Paris:20190523T140000
DTSTAMP:20260406T200203
CREATED:20190212T115441Z
LAST-MODIFIED:20190426T055429Z
UID:542-1558616400-1558620000@www.naxys.be
SUMMARY:Pauline Thémans (UNamur)
DESCRIPTION:Title: Pharmacokinetic modeling and strategies for drug dosing recommendation: application to meropenem \nAbstract: Pharmacokinetics (PK) studies the link between the dose and the drug exposure in patients. Thanks to mathematical modeling\, clinical pharmacology is an interesting and promising field of application of control and system theory. We focus on time-dependent antibiotic given by constant intravenous (IV) infusion at regular dosing interval. Meropenem is used as a particular case for which numerical results are reported. \nWe report on the study of two kinds of models: a population pharmacokinetic (popPK) model (empirical approach\, mixed effects modeling) and a physiologically-based pharmacokinetic (PBPK) model (mechanistic approach\, human physiology and drug’s properties considerations). We will describe the results of internal and external validations that were performed. Both models are described by linear time-invariant state-space models. They are shown to be nonnegative and stable\, as expected. \nFrom these models\, the aim is to provide guidelines (decision-making aid) for drug dosing in patients based on relevant patient’s characteristics (covariates) and on other practical conditions (target exposure for efficacy\, dosing interval\, time of infusion\, etc.). The studied approaches are based on open-loop methods. (1) A standard input-output analysis yields the analytical expression of the output trajectories and the asymptotic response. A formula is then derived to compute the dose needed to maintain the (steady) concentration trajectory above a given lower bound. (2) We also describe an optimal control approach on the discrete-time model (minimum principle). \n 
URL:https://www.naxys.be/event/pauline-themans-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190516T130000
DTEND;TZID=Europe/Paris:20190516T140000
DTSTAMP:20260406T200203
CREATED:20190313T092254Z
LAST-MODIFIED:20190509T205830Z
UID:564-1558011600-1558015200@www.naxys.be
SUMMARY:Maxime Lucas (Lancaster University\, UK & University of Florence\, Italy)
DESCRIPTION:Title: Network synchronisation with time-varying parameters\n \nAbstract: Many systems in nature\, especially living systems\, can be modelled as a collection of interacting oscillators. Such systems can exhibit a plethora of behaviours\, amongst which synchronisation\, a state of maximal coherence\, is of crucial importance. Indeed\, the synchronisation of the beat of heart cells is as necessary as the synchronisation of neurons can be a bad pre-seizure sign. So far\, ensembles of oscillators have been studied mostly as closed systems so that all parameters such as coupling or frequencies are constant. Very often\, however\, living systems are open and under the non-negligible influence of their environment\, which is in general varying with time. This in turn influence internal parameters of the systems: the frequency of our heartbeat is far from constant\, for example. Here\, we include time-variability in our mode\, and see the effect it has on the dynamics and its stability.\n\nHere\, we will see how time-variability can benefit or reduce stability in two scenarios: a temporal network (time-varying topology)\, and a network driven by an external oscillator with a time-varying frequency. We will discuss how\, in the first case\, synchronization is negatively affected\, but that the region of synchronization is enlarged in the second case. Moreover\, we will discuss the importance of looking into the dynamics of such systems at both short and long timescales. Time-varying features in models of living systems can bring us closer to realistic models\, and allow us to reveal richer dynamics resulting from it.
URL:https://www.naxys.be/event/maxime-lucas-marseille/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190507T130000
DTEND;TZID=Europe/Paris:20190507T140000
DTSTAMP:20260406T200203
CREATED:20190220T180356Z
LAST-MODIFIED:20190425T133242Z
UID:557-1557234000-1557237600@www.naxys.be
SUMMARY:Debmalya Das (Harish-Chandra Research Institute\, Allahabad\, India)
DESCRIPTION:Title: The Quantum Chesire Cat: some new aspects and possibilities \nAbstract: Quantum Chesire Cat is a counterintuitive phenomenon that provides a new window into the nature of the quantum systems in relation to multiple degrees of freedom associated with a single physical entity. Under suitable pre and postselections\, a photon (the cat) can be decoupled from its circular polarization (its grin). In this talk\, we will explore whether the grin without the cat can be teleported to a distant location. This will be a totally disembodied teleportation protocol. Based on the original Quantum Chesire Cat setup\, we design a protocol where the circular polarization is successfully teleported between two spatially separated parties even though the photon is not physically present with them. The process raises questions in our understanding about properties of quantum system. We further demonstrate this by swapping the grins of two Quantum Chesire Cats. We also briefly discuss about a few interesting new aspects of the original Quantum Chesire Cat protocol.
URL:https://www.naxys.be/event/debmalya-das-harish-chandra-research-institute-allahabad-india/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190502T130000
DTEND;TZID=Europe/Paris:20190502T140000
DTSTAMP:20260406T200203
CREATED:20190306T132149Z
LAST-MODIFIED:20190425T133454Z
UID:562-1556802000-1556805600@www.naxys.be
SUMMARY:Nathanaël Kasoro Mulenda (University of Kinshasa\, DRC)
DESCRIPTION:Title: PercoMCV: A hybrid approach of community detection in social networks \nAbstract: Knowledge extraction in social networks is a needful tool as it touches every aspect of our lives such as politic\, socio-economic\, scientific\, etc. Community detection is one of the objectives of this specific tool used for knowledge extraction in social networks. \nMany algorithms of knowledge extraction from social networks have been developed these last years. However\, many of them are not constant\, effective and accurate when facing these social networks with many edges. \nIn this paper\, we propose a new approach of community detection in social networks with many links between communities. The proposed approach has two steps. In the first step\, the algorithm attempts to determine all communities that the clique percolation algorithm may find. In the second step\, the algorithm computes the Eigenvector Centrality method on the output of the first step in order to measure the influence of network nodes and reduce the rate of the unclassified nodes. \nTo assess this new approach\, we test it on different types of networks. Relevant communities that have been detected testifies effectiveness and performance of the approach over other community detection algorithms. \n  \n 
URL:https://www.naxys.be/event/nathanael-kasoro-mulenda-university-of-kinshasa/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190430T140000
DTEND;TZID=Europe/Paris:20190430T150000
DTSTAMP:20260406T200203
CREATED:20190424T105807Z
LAST-MODIFIED:20190424T105918Z
UID:574-1556632800-1556636400@www.naxys.be
SUMMARY:Joni Virta (Aalto University\, Helsinki\, Finland)
DESCRIPTION:Title: Statistical properties of second-order tensor decompositions \nAuthors: Joni Virta\, Christoph Kösner\, Niko Lietzén\, Klaus Nordhausen \nAbstract: Two classical tensor decompositions are considered from a statistical viewpoint: the Tucker decomposition and the higher order singular value decomposition (HOSVD). Both decompositions are shown to be consistent estimators of the parameters of a certain noisy latent variable model. The decompositions’ asymptotic properties allow comparisons between them. Also inference for the true latent dimension is discussed. The theory is illustrated with examples.
URL:https://www.naxys.be/event/joni-virta/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190425T130000
DTEND;TZID=Europe/Paris:20190425T140000
DTSTAMP:20260406T200203
CREATED:20181119T095453Z
LAST-MODIFIED:20190401T131233Z
UID:509-1556197200-1556200800@www.naxys.be
SUMMARY:Oscar Godoy (University of Cádiz\, Spain)
DESCRIPTION:Title: Functional and multitrophic mechanisms of species coexistence \nAbstract: Ecologists have been investigating for decades the mechanisms that maintain the diversity of species within ecological communities. In particular\, several functional traits and interactions with mutualists have been thought to promote the stabilizing effect of niche differences on population dynamics of competing species. These effects occur because higher intraspecific compared to interspecific competition limits species abundance when they are common yet buffer them again extinction when they are rare. Recent advances in coexistence theory have now the opportunity to rigorously evaluate such relationships by coupling experimental and observational approaches to species population models\, and surprisingly\, they are showing a much more complex mapping that previously thought. As an example\, most of the plant functional traits widely measured in the literature does not provide a demographic signature of niche differences\, instead\, they promote competitive imbalances between species that lead to competitive exclusion. Only traits and phenotypic plasticity related to light and water use efficiency promote niche partitioning between species. In a similar fashion\, multitrophic interactions that plant species establish with floral visitors are an equalising rather than a stabilizing\, which promote species coexistence by decreasing the competitive ability of superior competitors and increase that of inferior competitors. Although the examples I will provide are mostly for plant species\, the underlying ecological mechanisms are common to any taxa type\, so I expect a fruitful discussion of how these ideas and experiments can be extended to other ecological systems.
URL:https://www.naxys.be/event/oscar-godoy-university-of-cadiz-spain/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190423T130000
DTEND;TZID=Europe/Paris:20190423T140000
DTSTAMP:20260406T200203
CREATED:20190124T081010Z
LAST-MODIFIED:20190327T103542Z
UID:537-1556024400-1556028000@www.naxys.be
SUMMARY:Emmanuel Flachaire (Aix-Marseille University\, France)
DESCRIPTION:Title: Pareto Models for Top Incomes \nAuthors: Arthur Charpentier (UQAM) and Emmanuel Flachaire (Aix-Marseille University) \nAbstract: Top incomes are often related to Pareto distribution. To date\, economists have mostly used Pareto Type I distribution to model the upper tail of income and wealth distribution. It is a parametric distribution\, with an attractive property\, that can be easily linked to economic theory. In this paper\, we first show that modelling top incomes with Pareto Type I distribution can lead to severe over-estimation of inequality\, even with millions of observations. To overcome this problem\, we then show that other Pareto distributions should be used. Two applications illustrate these characteristics\, with the distribution of income in South Africa in 2012 and the distribution of wealth in the United States in 2013.
URL:https://www.naxys.be/event/emmanuel-flachaire/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190409T130000
DTEND;TZID=Europe/Paris:20190409T140000
DTSTAMP:20260406T200203
CREATED:20190304T222416Z
LAST-MODIFIED:20190304T222416Z
UID:560-1554814800-1554818400@www.naxys.be
SUMMARY:Liubov Tupikina (CRI\, Paris Descartes\, France & MIPT\, Moscow\, Russia)
DESCRIPTION:Title: Heterogeneous spreading in network models \nAbstract: I will present some of our recent results on the random walks on networks with spatial and temporal heterogeneity. In particular\, I will discuss how the influence of heterogeneities can be encoded into the dynamics of continuous time random walk model. Continuous limits of heterogeneous continuous time random walks can lead to various diffusion equations\, which opens new questions about general description of spreading in heterogeneous media. Then I will talk about some applications of the heterogeneous random walk model to the epidemiological models on static or temporal networks and some potential applications to the real data.
URL:https://www.naxys.be/event/liubov-tupikina-cri-paris-descartes-france-mipt-moscow-russia/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190404T130000
DTEND;TZID=Europe/Paris:20190404T140000
DTSTAMP:20260406T200203
CREATED:20181205T224534Z
LAST-MODIFIED:20190401T131104Z
UID:520-1554382800-1554386400@www.naxys.be
SUMMARY:Gyuri Barabas (University of Linköping\, Sweden)
DESCRIPTION:Title: The evolution of trait variance creates a tension between species and functional diversity\n\nAbstract: It seems intuitively obvious that species diversity begets functional (trait) diversity: the more plant species there are\, the more varied their leaf chemistry will be; more species of crops provide more kinds of food; etc. In this talk I argue that the evolution of trait variance challenges this view. In a trait-based eco-evolutionary model\, I show that when species richness is low\, individual species evolve large trait variation\, while in species-rich communities species avoid competition by evolving narrow trait breadths. This effect can be so strong that those communities with more but narrower species will cover a smaller fraction of the available trait space than those with fewer but intraspecifically more variable ones. The expected positive relationship between species and functional diversity is thus overhauled\, a result which proved extremely robust to changes in model setup and parameterization. I finish by presenting and discussing empirical data consistent with this claim.
URL:https://www.naxys.be/event/gyuri-barabas/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190322T140000
DTEND;TZID=Europe/Paris:20190322T163000
DTSTAMP:20260406T200203
CREATED:20190109T223801Z
LAST-MODIFIED:20190214T124300Z
UID:524-1553263200-1553272200@www.naxys.be
SUMMARY:Making the most of your presentation by Principiae
DESCRIPTION:Abstract: Strong presentation skills are a key to success for researchers\, yet many speakers are at a loss to tackle the task. Systematic as they otherwise can be in their work\, they go at it intuitively or haphazardly\, with much good will but seldom good results. In this talk\, Dr Doumont proposes a systematic way to prepare and deliver an oral presentation: he covers structure\, slides\, and delivery\, as well as stage fright.\n \nSpeaker: An engineer (UCLouvain) and PhD in applied physics (Stanford)\, Jean-luc Doumont is acclaimed worldwide for his no-nonsense approach\, his highly applicable\, often life-changing recommendations on a wide range of topics\, and Trees\, maps\, and theorems\, his book about “effective communication for rational minds.” \nFor additional information\, visit www.principiae.be. \nA drink will follow the conference. \n  \nRegistration\nRegistration is free but mandatory through the following web form. \nPhD students will receive a certificate with ECTS mention for their doctoral training. \n 
URL:https://www.naxys.be/event/making-the-most-of-your-presentation-principiae/
LOCATION:E13\, 8 Rempart de la Vierge\, Namur\, Belgium
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190312T130000
DTEND;TZID=Europe/Paris:20190312T140000
DTSTAMP:20260406T200203
CREATED:20190117T152123Z
LAST-MODIFIED:20190304T222141Z
UID:526-1552395600-1552399200@www.naxys.be
SUMMARY:Anna Kiriliouk (UNamur)
DESCRIPTION:Title: Climate event attribution using multivariate peaks-over-thresholds modelling \nAbstract: Quantifying the human influence on climate change and identifying potential causes is a highly relevant research area which is often referred to as detection and attribution. A common approach is to compare the probability of an extreme event in the factual world to the probability of an extreme event in a counterfactual world\, i.e.\, a world that might have been if no humans would have existed. The event probabilities can be calculated using large scale climate model runs that simulate the evolution of the climate with and without anthropogenic forcings. The Fraction of Attributable Risk (FAR) is defined as the relative ratio of event probabilities in the factual and in the counterfactual world. Estimating the FAR will allow us to quantify the extent to which human activities have increased the risk of occurrence of an extreme event. We propose a model for the FAR based on the multivariate generalized Pareto distribution\, i.e.\, the asymptotic distribution of suitably normalized exceedances over a high threshold. The model is used to quantify the increased risk of an extreme rainfall event in central Europe. \n 
URL:https://www.naxys.be/event/anna-kiriliouk-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190307T130000
DTEND;TZID=Europe/Paris:20190307T140000
DTSTAMP:20260406T200203
CREATED:20181105T082321Z
LAST-MODIFIED:20190327T103510Z
UID:507-1551963600-1551967200@www.naxys.be
SUMMARY:Ines Wilms (Maastricht University\, Netherlands)
DESCRIPTION:Title: Multi-class Vector AutoRegressive Models for Multi-Market Commodity Data \nAbstract: Vector AutoRegressive (VAR) models form a special case of multivariate regression models in that the response variables are observed over time and modeled as a function of their own past values. We use VAR models to study dynamics among agricultural\, metal and energy commodity returns. As the increasing integration of the world economy suggests commodity dynamics to be comparable for different markets\, we aim to jointly analyze these dynamics across markets. To this end\, we introduce a sparse estimator of the Multi-Class Vector AutoRegressive model. We jointly estimate several VAR models\, one for each market (“class”)\, to borrow strength across markets. Our methodology encourages effects to be similar across markets\, while still allowing for small differences between them. Moreover\, we focus on multi-class estimation of high-dimensional VAR models\, i.e. models with a large number of time series relative to the time series length. Therefore\, our estimate is sparse: unimportant effects are estimated as exactly zero\, which facilitates the interpretation of the results. \nThis is joint work with Luca Barbaglia and Christophe Croux
URL:https://www.naxys.be/event/ines-wilms/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190215T120000
DTEND;TZID=Europe/Paris:20190215T140000
DTSTAMP:20260406T200203
CREATED:20190215T093208Z
LAST-MODIFIED:20190215T093208Z
UID:552-1550232000-1550239200@www.naxys.be
SUMMARY:naXys board meeting
DESCRIPTION:
URL:https://www.naxys.be/event/naxys-board-meeting-3/
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190214T130000
DTEND;TZID=Europe/Paris:20190214T140000
DTSTAMP:20260406T200203
CREATED:20190117T152245Z
LAST-MODIFIED:20190123T132905Z
UID:528-1550149200-1550152800@www.naxys.be
SUMMARY:Martin Gueuning (UNamur)
DESCRIPTION:Title: Information Diffusion on Twitter: exploiting the timings of Retweets \nAbstract: Online social networks such as Twitter have emerged as influential platforms for real-time information diffusion. Due to various factors\, a tweet may become viral and initiate a cascade of retweets. In this work\, we first show how the timings of the retweets reveal information about how the tweet propagated on the underlying network. In particular\, we show under which circumstances the transition of the tweet from one group to another on Twitter leaves fingerprints on its retweets timings [1]. Then\, we leverage these findings to address the question of multi-targets selection for maximal information diffusion. We present SmartInf\, an algorithm providing a list of influential users of the network only based on an historic of popular cascades\, or refining the list when the ego networks of the users may be extracted. We illustrate the performance of SmartInf against the baselines on both real-world and simulated data [2] . \n[1] Temporal patterns of (re)tweets reveal cascade migration. AK Bhowmick\, M Gueuning\, JC Delvenne\, R Lambiotte\, B Mitra. Proceedings of the 2017 IEEE/ACM International Conference on Advances in in Social Networks Analysis and Mining.\n[2] Temporal patterns of (re)tweets help to detect influential nodes for information diffusion in social networks. AK Bhowmick\, M Gueuning\, JC Delvenne\, R Lambiotte\, B Mitra. Submitted. \n 
URL:https://www.naxys.be/event/martin-gueuning-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181220T130000
DTEND;TZID=Europe/Paris:20181220T140000
DTSTAMP:20260406T200203
CREATED:20181120T102045Z
LAST-MODIFIED:20181122T115758Z
UID:513-1545310800-1545314400@www.naxys.be
SUMMARY:Justin Delloye (Luxembourg Institute of Socio-Economic Research LISER)
DESCRIPTION:Title: A New Approach to Complexity in Economic Geography \nAbstract: The design of efficient regional policies calls for a reliable understanding of complex regional dynamics. Dedicated scientific efforts have historically been split up in two distinct research strands that are Location Theory and Complex Systems. In this presentation\, I propose a conciliating modelling approach and I use it to address multiple equilibria issues in a model of New Economic Geography. In this field\, the question of equilibrium selection traditionally reduces to a dependence on initial conditions. In more recent core-periphery models\, the introduction of heterogeneous preferences generates exogenous shocks and therefore complex path-dependent dynamics. However\, these recent models use averaging procedures which prevent them from discussing path-dependent dynamics. Starting from the footloose entrepreneur model\, this method proposes a novel approach to adjustment dynamics\, based on stochastic migration models\, by which the dynamics of the population distribution is a continuous-time Markov chain. Using a diffusion approximation\, it computes the evolution of the transition probability function in the state space of the regional system\, which enables to discuss in particular the appearance of multiple peaks\, denoting substantial divergences of sample paths. It enables further to identify\, in explicit time units and at both short- and long-term horizons\, periods when heterogeneous preferences may substantially affect the regional dynamic. Thus\, this method raises new opportunities to improve the operational potential of New Economic Geography models.
URL:https://www.naxys.be/event/justin-delloye-luxembourg-institute-of-socio-economic-research-liser/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181213T130000
DTEND;TZID=Europe/Paris:20181213T140000
DTSTAMP:20260406T200203
CREATED:20181019T202631Z
LAST-MODIFIED:20181122T092014Z
UID:501-1544706000-1544709600@www.naxys.be
SUMMARY:Fabian Bastin (Université de Montréal)
DESCRIPTION:Title: Staffing optimization in call centers \nAbstract: Call centers are prominent in modern life\, and labor intensive. We aim to determine the minimum number of agents in a multi-skill call center\, while ensuring the desired level of quality of service to customers. We consider the case where the arrival rates cannot be forecast perfectly\, leading to a two-stage stochastic optimization problem. The arrival rates are modeled as random variables with large variance (uncertainty) in the first stage of the staffing decision process. The number of agents can however be adjusted in a second stage\, under some penalty costs\, when the information on the arrival rates is more accurate. The quality of service is measured by the service level\, defined as the proportion of calls answered within a given time\, called the acceptable wait threshold. Since the number of calls coming into the call center is unknown\, we only require that the service level constraints are satisfied with given (high) probabilities. These constraints cannot be evaluated analytically and are approximated using sample averages computed using simulation. We use a decomposition approach\, based on the L-shaped method\, to efficiently address the resulting optimization problem. We provide numerical studies to illustrate the performance of the decomposition algorithm\, along with a validation study of the approach. \nJoint work with Anh Thuy Ta\, Wyean Chan\, and Pierre L’Ecuyer.
URL:https://www.naxys.be/event/fabian-bastin-universite-de-montreal/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181206T130000
DTEND;TZID=Europe/Paris:20181206T140000
DTSTAMP:20260406T200203
CREATED:20181016T113010Z
LAST-MODIFIED:20181207T091454Z
UID:491-1544101200-1544104800@www.naxys.be
SUMMARY:Thomas Parmentier (UGhent)
DESCRIPTION:Title: Ants and their associates as a model system to test host-symbiont network dynamics \nAbstract: An extremely large number of organisms engage in symbiotic relationships with ants. Interestingly\, these relationships are highly variable in terms of host-specificity and span the entire mutualism-antagonism continuum. In this talk\, we present different types of network analyses focusing on ant-symbiont interactions. We argue that ant-symbiont communities are highly suitable to test a wide range of network hypotheses in terrestrial ecosystems.  \n 
URL:https://www.naxys.be/event/thomas-parmentier-kuleuven-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181129T130000
DTEND;TZID=Europe/Paris:20181129T140000
DTSTAMP:20260406T200203
CREATED:20181016T113244Z
LAST-MODIFIED:20181026T090642Z
UID:493-1543496400-1543500000@www.naxys.be
SUMMARY:Germain Van Bever (UNamur)
DESCRIPTION:Title: Symmetric Component Analysis and Functional Independent Component Analysis \nAbstract: With the increase in measurement precision\, functional data is becoming common practice. Relatively few techniques for analysing such data have been developed\, however\, and a first step often consists in reducing the dimension via Functional PCA\, which amounts to diagonalising the covariance operator. Joint diagonalisation of a pair of scatter functionals has proved useful in many different setups\, such has Independent Component Analysis (ICA)\, Invariant Coordinate Selection (ICS)\, etc.\nAfter an introduction to classical ICA techniques (and a look into several extensions of ICS)\, the main part of this talk will consist in extending the Fourth Order Blind Identification procedure to the case of data on a separable Hilbert space (with classical FDA setting being the go-to example). In the finite-dimensional setup\, this procedure provides a matrix Γ such that ΓX has independent components\, if one assumes that the random vector X satisfies X = ΨZ\, where Z has independent marginals and Ψ is an invertible mixing matrix. When dealing with distributions on Hilbert spaces\, two major problems arise: (i) the notion of marginals is not naturally defined and (ii) the covariance operator is\, in general\, non invertible. These limitations are tackled by reformulating the problem in a coordinate-free manner and by imposing natural restrictions on the mixing model.\nThe proposed procedure is shown to be Fisher consistent and affine invariant. A sample estimator is provided and its convergence rates are derived. The procedure is amply illustrated on simulated and real datasets.\nReferences\n[1] J.-F. Cardoso\, Source Separation Using Higher Moments Proceedings of IEEE international conference on acoustics\, speech and signal processing 2109-2112.\n[2] D. Tyler\, F. Critchley\, L. Dumbgen and H. Oja\, Invariant Co-ordinate Selection J. R. Statist. Soc. B.\, 2009\, 71\, 549–592.\n[3] J. Ramsay and B.W. Silverman Functional Data Analysis 2nd edn. Springer\, New York\, 2006.
URL:https://www.naxys.be/event/germain-van-bever-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181122T130000
DTEND;TZID=Europe/Paris:20181122T140000
DTSTAMP:20260406T200203
CREATED:20181016T113538Z
LAST-MODIFIED:20181112T140039Z
UID:495-1542891600-1542895200@www.naxys.be
SUMMARY:Alexis Coyette (UNamur)
DESCRIPTION:Title: Modeling the rotation of Titan \nAbstract: Observation of the rotation of synchronously rotating satellites can help to probe their interior. We study here the variations in rotation rate and the polar motion of Titan due to (1) the gravitational force exerted by Saturn at orbital period and (2) exchanges of angular momentum between the seasonally varying atmosphere and the solid surface. The deviation of the mass distribution from hydrostaticity can significantly increase the diurnal libration and decrease the amplitude of the seasonal libration. By including a large spectrum of atmospheric perturbations\, the smaller than synchronous rotation rate measured by Cassini in the 2004–2009 period (Meriggiola et al.\, 2016) could be explained by the atmospheric forcing. The effect of the non-hydrostatic mass distribution is less important for polar motion\, which is more sensitive to flow in the subsurface ocean. For some interior models of Titan\, the amplitude of its polar motion can be resonantly amplified. Future observations of the polar motion of Titan could help constraining some properties of its interior structure as the ice shell thickness and ocean density.
URL:https://www.naxys.be/event/alexis-coyette-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181108T130000
DTEND;TZID=Europe/Paris:20181108T140000
DTSTAMP:20260406T200203
CREATED:20181010T085015Z
LAST-MODIFIED:20181011T060140Z
UID:489-1541682000-1541685600@www.naxys.be
SUMMARY:Elio Tuci (UNamur)
DESCRIPTION:Title: Three recent research works in swarm robotics \nAbstract: In this talk\, I briefly illustrate objectives and achievements of three experiments that I have recently conducted with the support of my PhD students. All three works fall into the research area of swarm robotics/swarm intelligence.\nIn the first study\, we have developed a control system to allow a swarm of robots to cooperatively transport objects that due to their mass\, cannot be moved by single robots. The controller is a dynamic neural network synthesised using evolutionary computation techniques. The study shows that the robots do not need to feel forces to coordinate their action in order to find a common direction of transport.\nIn the second study\, we have looked at the process of aggregation in swarm of robots with “informed robots”. These are robots that have been instructed on which site to aggregate\, among those available in the environment. Our study looks at the proportion of informed robots required to gather all the swarm on a selected aggregation site.\nIn the third study\, we have tested a probabilistic adaptive defence mechanism to allow a swarm of agents to limit the disruptive effects of a communication manipulation attack implemented as modification of data in transit events. The results of our study show that the proposed mechanism can be largely effective in multiple context differing for the proportion of malicious agents carrying out the attack.\nI am happy to provide further details/readings for each of these works and to discuss about potential collaborations with anyone interested in pursuing interdisciplinary research work in the area of bio-inspired robotics\, swarm robotics\, swarm intelligence.
URL:https://www.naxys.be/event/elio-tuci-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20181025T130000
DTEND;TZID=Europe/Paris:20181025T140000
DTSTAMP:20260406T200203
CREATED:20181010T063010Z
LAST-MODIFIED:20181010T084458Z
UID:484-1540472400-1540476000@www.naxys.be
SUMMARY:Alexandre Mayer (UNamur)
DESCRIPTION:Title: An evolutionary computing approach to optical engineering \nAbstract: We present a genetic algorithm that we developed in order to address computationally expensive optimization problems in optical engineering. The idea consists in working with a population of individuals that represent possible solutions to the problem. The best individuals are selected. They generate new individuals for the next generation. Random mutations in the coding of parameters are introduced. This strategy is repeated from generation to generation until the algorithm converges to the global optimum of the problem considered. For computationally expensive problems\, it makes sense to analyze the data collected by the algorithm in order to infer more rapidly the final solution. The objective is ideally to determine the global optimum by a single run of the genetic algorithm and with a reduced number of fitness evaluations. The use of a mutation operator that acts on randomly-shifted Gray codes contributes to this objective by helping the genetic algorithm to escape local optima and by enabling a wider diversity of displacements. These techniques reduce the computational cost of optical engineering problems\, where the design parameters have a finite resolution and are limited to a realistic range.
URL:https://www.naxys.be/event/alexandre-mayer-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180920T140000
DTEND;TZID=Europe/Paris:20180920T213000
DTSTAMP:20260406T200203
CREATED:20180820T112245Z
LAST-MODIFIED:20180918T131910Z
UID:426-1537452000-1537479000@www.naxys.be
SUMMARY:naXys kick-off meeting
DESCRIPTION:Founded in 2010 as a research center\, naXys has recently evolved into an Institute. Join us to celebrate our kick-off meeting. \nProgram\n14h: Welcome & Introduction by Prof. Carine Michiels\, UNamur Vice-Rector for Research and Prof. Anne-Sophie Libert\, Director of naXys\n14h30: Prof. Vito Latora (Queen Mary University of London\, UK)\, Complex networks with many layers\n15h15: Prof. Damien Ernst (ULiège\, Belgium)\, Uber-like models for the electrical industry\n16h: Coffee break\n16h30: Prof. Carlos Melian (EAWAG\, ETH Domain\, Switzerland)\, Tangling the webs of life\n17h15: Prof. Glenn Magerman (ULB\, Belgium)\, Production networks in economics\n18h-21h30 : Poster session & Walking dinner \nRegistration\nRegistration is free but mandatory\, before Wednesday\, September 13th\, through the following web form. \nWe strongly encourage poster submissions in all naXys research directions. PhD students will receive certificate with ECTS mention for their doctoral training. \nAbstracts\nProf. Vito Latora (Queen Mary University of London\, UK)\, Complex networks with many layers\n\nNetworks constitute the backbone of complex systems\, from the human brain to computer communications\, transport infrastructures to online social systems and metabolic reactions to financial markets. Characterising their structure improves our understanding of the physical\, biological\, economic and social phenomena that shape our world. As a result\, complex networks have become an essential ingredient in the background of any scientist [1]. In this seminar I will present an overview of the new theory and methods of network science\, of the main results found\, and of some of the still open challenges.\nI will concentrate\, in particular\, on the structure and dynamics of multi-layer networks [2][3]\, namely multiplex networks and temporal networks\, discussing cases where the presence of many layers gives rise to the emergence of novel behaviours\, otherwise unobserved in single-layer networks [4-6]. \n[1] V. Latora\, V. Nicosia and G. Russo\, Complex Networks: Principles\, Methods and Applications\, Cambridge University Press (2017)\n[2] Structural measures for multiplex networks Battiston\, Nicosia\, Latora\, Phys. Rev. E89\, 032804 (2014)\n[3] Growing multiplex networks V. Nicosia\, G. Bianconi\, V. Latora\, M. Barthelemy\, Phys. Rev. Lett. 111\, 058701 (2013)\n[4] Structural reducibility of multilayer networks\,  M. De Domenico\, V. Nicosia\, A. Arenas\, V. Latora\, Nature  Comm 6\, 6864 (2015)\n[5] Collective phenomena emerging from the interactions between dynamical processes in multiplex networks\, Nicosia\, Skardal\, Arenas\, Latora\, Phys. Rev. Lett. 118\, 138302 (2017)\n[6] Mobility and congestion in dynamical multilayer networks with finite storage capacity Manfredi\, Di Tucci\, Latora\, Phys. Rev. Lett. 120\, 068301 (2018)\n\n\nProf. Damien Ernst (ULiège\, Belgium)\, Uber-like models for the electrical industry\n\n\nDuring this presentation Professor Ernst will present new organizational models for the electrical industry. These are Uber-type models that are extremely destabilizing for traditional players in the electricity sector. He will explain the different economic forces in place that lead to the emergence of such models. He will also detail  the great opportunities they offer for  accelerating the energy transition and for researchers who are interested in analyzing and controlling very complex systems. \n\nProf. Carlos Melian (EAWAG\, ETH Domain\, Switzerland)\, Tangling the webs of life\n\nMost complex systems consist of elements that interact within and across levels in a broad range of spatiotemporal scales. In biology\, gene interactions and expression dynamics together with plasticity determine the architecture of traits of individuals\, competitive and cooperative interactions among individuals influence population dynamics\, and many types of interactions among species affect the dynamics of communities and ecosystems. Such systems\, usually represented as single networks\, have been partitioned in domains to explain the intricate phenomena that occur at each of the levels and scales\, but can have complex dynamics when interdependencies among networks belonging to different levels or scales occur. In this talk\, I will introduce interdependencies among networks to gain insights about biological systems. I will ask the many open challenges ahead when merging real-world data across levels and scales with process-based modeling to infer the dynamics of interdependent networks. In the end\, I will discuss whether disentangling a single network is enough to understand the origin\, evolution and coexistence of biodiversity on Earth and that we might need data-driven and process-based theory to tangle networks with one another to fully understand the webs of life.\n\n\nProf. Glenn Magerman (ULB\, Belgium)\, Production networks in economics\n\n\nFirms are not isolated islands of production\, but they interact through supplier-buyer relationships and personal network contacts. While intuitive\, this observation is mostly at odds with standard economic reasoning of anonymous markets. However\, the absence of micro data on firm-to-firm transactions has made the development of production network models in economics elusive until very recently\, as it is ex ante hard to understand which mechanisms generate outcomes that are at odds with existing models. In this talk\, I will first discuss some stylized facts on the Belgian production network\, the data which shows unprecedented detail along many dimensions. Second\, I will highlight some elements of the models we develop\, and how they expand typical firm-level models in micro-economics. Next\, I will discuss how these network models can generate new implications for propagation and aggregation (i.e. “micro-to-macro”). Finally\, we will touch upon dynamics.
URL:https://www.naxys.be/event/naxys-kick-off-meeting/
LOCATION:Le Grenier de l’Arsenal\, 11 rue Bruno\, Namur\, Belgium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180621T130000
DTEND;TZID=Europe/Paris:20180621T140000
DTSTAMP:20260406T200203
CREATED:20180521T090404Z
LAST-MODIFIED:20180528T115337Z
UID:414-1529586000-1529589600@www.naxys.be
SUMMARY:Eleonora Andreotti (Università di Torino\, Italy)
DESCRIPTION:Title: Statistical properties of non linear random walks on networks \nAbstract: Random walks simulate various interacting entities (the nodes) which exchange ’particles’ according to the topological structure defined by the links and they are considered to introduce a dynamics on networks. These stochastic dynamical systems can be applied to model complex systems like transportation networks\, ecological systems\, neural networks\, economic systems etc.. In the linear case the statistical properties are defined by single particles dynamics and the equilibrium distribution depends on the network structure. We introduce non linear effects by assuming a finite transportation capacity of the links or a finite capacity in the nodes. As a consequence the transition probabilities depend on the dynamical state of the network and one cannot derive statistical properties of the system from single particle dynamics. We show that non-linear effects can be described by introducing an entropic force among the node states which allows to derive a master equation for the evolution of the probability distribution of the node population. This entropic force has a relevant effect on stationary distribution and the relaxation time scale depends on the numerosity of the population so that the thermodynamics limit is non trivial and the lifetime of the transient state is very long. Using numerical simulation we derive an analytical form of the entropic force and we study the dependence of the stationary distribution on the network topology.
URL:https://www.naxys.be/event/eleonora/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180619T130000
DTEND;TZID=Europe/Paris:20180619T140000
DTSTAMP:20260406T200203
CREATED:20180521T090151Z
LAST-MODIFIED:20180521T090151Z
UID:409-1529413200-1529416800@www.naxys.be
SUMMARY:Takaaki Aoki (Kagawa University\, Japan)
DESCRIPTION:Title: Cities and roads as pattern formation of their co-evolving dynamics on real-world landscape\n\n\nAbstract: Cities and their inter-connected transport networks form part of the fundamental infrastructure developed by human societies. Their organisation reflects a complex interplay between many natural and social factors\, including inter alia natural resources\, landscape\, and climate on the one hand\, combined with business\, commerce\, politics\, diplomacy and culture on the other. Nevertheless\, despite this complexity\, there has been some success in capturing key aspects of city growth and network formation in relatively simple models that include non-linear positive feedback loops. However\, these models are typically embedded in an idealised\, homogeneous space\, leading to regularly-spaced\, lattice-like distributions arising from Turing-type pattern formation. Here we argue that the geographical landscape plays a much more dominant\, but neglected role in pattern formation. To examine this hypothesis\, we evaluate the weighted distance between locations based on a least cost path across the natural terrain\, determined from high-resolution digital topographic databases for the Hokkaido region of Japan. These weights are included in a co-evolving\, dynamical model of both population aggregation in cities\, and movement via an evolving transport network. We compare the results from the stationary state of the system with current population distributions from census data\, and show a reasonable fit\, both qualitatively and quantitatively\, compared with models in homogeneous space. Thus we infer that that addition of weighted topography from the natural landscape to these models is both necessary and almost sufficient to reproduce the majority of the real-world spatial pattern of city sizes and locations in this example.
URL:https://www.naxys.be/event/takaaki-aoki-kagawa-university-japan/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180607T130000
DTEND;TZID=Europe/Paris:20180607T140000
DTSTAMP:20260406T200203
CREATED:20180418T213241Z
LAST-MODIFIED:20180501T114421Z
UID:398-1528376400-1528380000@www.naxys.be
SUMMARY:Ludovic Renson (University of Bristol\, UK)
DESCRIPTION:Title: Exploring the dynamics of nonlinear experiments using control-based continuation \nAbstract: With the constant drive for better performance and efficiency\, technological boundaries are being pushed to their limits. In mechanics\, this often means that the dynamic behaviour of structures becomes increasingly nonlinear. Nonlinearity can arise\, for instance\, from the large displacements and rotations of flexible components (such as blades in wind turbines). \nWhile a significant effort has been\, and is\, devoted to the mathematical modelling and numerical analysis of such systems\, relatively little research addresses the issue of rigourous experimental testing. In fact\, until now\, there has been no general\, systematic method that can directly measure and characterise nonlinear dynamic behaviour during laboratory tests. Nonlinear systems are still tested as linear ones. Time series are collected for a whole range of excitation parameters and one relies on post-processing tools to understand the behaviour of the system. So far\, this sort of approach has not allowed quantitative comparisons between experiments and mathematical models; hence it is extremely challenging to incorporate nonlinear features into model development and validation processes. \nIn this talk\, I will present a method\, control-based continuation (CBC)\, which uses sensors and actuators to intelligently probe a physical system. Combining feedback control with numerical continuation algorithms\, CBC modifies\, on-line\, the excitation applied to the system in order to isolate the nonlinear behaviour of interest. In this way\, CBC offers the best conditions to analyse these dynamic features in detail\, to follow them as inputs and controllable parameters are changed\, and to detect and track boundaries between qualitatively different types of behaviour.
URL:https://www.naxys.be/event/ludovic-renson-university-of-bristol-uk/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180605T140000
DTEND;TZID=Europe/Paris:20180605T160000
DTSTAMP:20260406T200203
CREATED:20180521T090312Z
LAST-MODIFIED:20180521T090312Z
UID:412-1528207200-1528214400@www.naxys.be
SUMMARY:naXys Board meeting
DESCRIPTION:
URL:https://www.naxys.be/event/naxys-board-meeting-2/
LOCATION:E25
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180523T130000
DTEND;TZID=Europe/Paris:20180523T140000
DTSTAMP:20260406T200203
CREATED:20180409T151620Z
LAST-MODIFIED:20180409T151620Z
UID:383-1527080400-1527084000@www.naxys.be
SUMMARY:Pietro Coletti (University of Hasselt)
DESCRIPTION:Title: Regular school closure & influenza epidemics: a data-driven spatial transmission model for Belgium \n\nAbstract: School closure is often considered as an option to mitigate influenza epidemics because of its potential to reduce transmission in children and then in the community. The policy is still however highly debated because of controversial evidence. Moreover\, the specific mechanisms leading to mitigation are not clearly identified. We introduced a stochastic spatial age-specific metapopulation model to assess the role of holiday-associated behavioral changes and how they affect seasonal influenza dynamics. The model is applied to Belgium\, parameterized with country-specific data on social mixing and travel\, and calibrated to the 2008/2009 influenza season. It includes behavioral changes occurring during weekend vs. week\, and holiday vs. school-term. Several experimental scenarios are explored to identify the relevant social and behavioral mechanisms. \nStochastic numerical simulations show that holidays considerably delay the peak of the season and mitigate its impact. Changes in mixing patterns are responsible for the observed effects\, whereas changes in travel behavior do not alter the epidemic. Weekends are important in slowing down the season by periodically dampening transmission. Christmas holidays have the largest impact on the epidemic\, however later school breaks may help in reducing the epidemic size\, stressing the importance of considering the full calendar. \nChanges in the way individuals establish contacts during holidays are the key ingredient explaining the mitigating effect of regular school closure. Our findings highlight the need to quantify these changes in different demographic and epidemic contexts in order to provide accurate and reliable evaluations of closure effectiveness. They also suggest strategic policies in the distribution of holiday periods to minimize the epidemic impact.
URL:https://www.naxys.be/event/pietro-coletti-university-of-hasselt/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180515T130000
DTEND;TZID=Europe/Paris:20180515T140000
DTSTAMP:20260406T200203
CREATED:20180410T175306Z
LAST-MODIFIED:20181016T115456Z
UID:386-1526389200-1526392800@www.naxys.be
SUMMARY:Nikos Kouvaris (UNamur)
DESCRIPTION:Title: Feedback induced stationary and oscillatory patterns in complex bistable networks \nAbstract: In this talk we will present theoretical and experimental findings on pattern formation in bistable chemical networks. Effects of feedbacks on self-organization phenomena will also be discussed. For regular trees\, an approximate analytical theory for localized stationary patterns under application of global feedbacks is constructed. Using it\, properties of such patterns in different parts of the parameter space are discussed. We will also show that localized oscillatory patterns can be formed in these networks if the global feedback is applied with certain time delay. Linear stability analysis has revealed a critical time delay for which the system undergoes a Hopf bifurcation and exhibits limit cycles of small amplitudes. Furthermore\, we will present results from numerical investigations for large random Erdös-Rényi and scale-free networks. In both kinds of systems localized active patterns consist of a subnetwork\, whose size decreases as the feedback intensity increases. In the later random networks local feedbacks affecting only the hubs or the peripheral nodes are also considered.
URL:https://www.naxys.be/event/nikos-kouvaris-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
END:VCALENDAR