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X-WR-CALNAME:Namur Institute For Complex Systems
X-ORIGINAL-URL:https://www.naxys.be
X-WR-CALDESC:Events for Namur Institute For Complex Systems
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TZID:Europe/Paris
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DTSTART:20160327T010000
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DTSTART:20161030T010000
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DTSTART:20171029T010000
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DTSTART:20191027T010000
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END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180329T130000
DTEND;TZID=Europe/Paris:20180329T140000
DTSTAMP:20260408T151641
CREATED:20180131T211858Z
LAST-MODIFIED:20180324T213728Z
UID:314-1522328400-1522332000@www.naxys.be
SUMMARY:Jean Teyssandier (Cornell University\, USA)
DESCRIPTION:Title: Orbital evolution during planet-⁠disc interactions \nAbstract: The origin and wide distribution of eccentricities and inclinations in planetary systems remains to be explained\, in particular in the context of planet-disc interactions. In this talk I will present a study of the evolution of eccentricity in discs and planets that combines methods from celestial mechanics and hydrodynamics\, and takes the form of a linear secular theory. I will compare the predictions of this linear theory against direct hydrodynamical simulations and show how eccentricity can grow. I will discuss what these results imply for the orbital structure of protoplanetary discs and young planetary systems. I will also discuss how moderate inclinations can be generated via similar mechanisms.
URL:https://www.naxys.be/event/jean-teyssandier-cornell-university-usa/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180308T130000
DTEND;TZID=Europe/Paris:20180308T140000
DTSTAMP:20260408T151641
CREATED:20180214T105809Z
LAST-MODIFIED:20181016T114613Z
UID:355-1520514000-1520517600@www.naxys.be
SUMMARY:Alexey Medvedev (UNamur)
DESCRIPTION:Title:   Modelling structure and predicting dynamics of discussion threads in online boards using Hawkes processesAbstract:  Online social platforms provide a fruitful source of information about social interaction. Depending on the platform\, various tree-like cascading patterns emerge as a consequence of such interaction. For example\, on Twitter or on Facebook people interact via resharing messages\, which turns into cascade trees of reshares\, in email networks people forward messages to their peers resulting in trees of email forwards\, in online boards like Digg or Reddit people interact via discussing particular posts\, which leaves a trace of discussion trees. The two main questions arise: what is the shape of these cascades and how to predict the dynamics of their evolution? The question of evolution of discussion threads is now gradually being understood. By now researchers studied only the structural evolution of discussion trees and the dynamical properties are left out of consideration. Nevertheless\, there was proposed a sort of a mean-field model for dynamics and structure\, however by the design the model has limited utility in practice. We consider cascades given by discussion trees of posts in online board Reddit. The dataset of Reddit discussion threads consists of all posts and comments submitted to Reddit from Jan\, 2008 till Jan\, 2015. The dataset in total contains more than 150 million posts and around 1.4 billion comments. We propose a model of discussion trees generation based on the self-exciting Hawkes processes\, which represents both the tree structure and temporal information. We use the dataset of Reddit discussion threads to show that structurally trees resemble Galton-Watson trees with a special root offspring distribution\, and distinct the cases when the dynamics of comments attraction can be well predicted using Hawkes processes.
URL:https://www.naxys.be/event/alexey-medvedev-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180301T130000
DTEND;TZID=Europe/Paris:20180301T140000
DTSTAMP:20260408T151641
CREATED:20180131T211528Z
LAST-MODIFIED:20180213T140748Z
UID:312-1519909200-1519912800@www.naxys.be
SUMMARY:Alexandre Bovet (UNamur - UCL)
DESCRIPTION:Title: Opinion dynamics and fake versus traditional news influence in Twitter \nAbstract: We investigate the opinion of Twitter users during the 2016 US elections using a large scale dataset of more than 170 millions tweets. We develop a method to infer the opinion of Twitter users regarding the candidates by using a combination of natural language processing of the tweet contents\, machine learning classification and analysis of the hashtags co-occurrence network. We study the temporal social networks formed by the interactions among millions of Twitter users and infer the support of each user to the presidential candidates. The resulting Twitter opinion trend follows the New York Times National Polling Average\, which represents an aggregate of hundreds of independent traditional polls\, with remarkable accuracy.\nGoing beyond the daily opinion analysis and analyzing the level of activity\, the repartition of the supporters between the strongly connected giant component and the rest of the network and the daily fluctuations in the number of users reveal a clear dichotomy between the behavior of supporters of each candidate. Although Clinton supporters are the majority in Twitter\, Trump supporters are generally more active and more constant in their support\, while Clinton supporters are less active and show their support only occasionally.\nTo understand the role of information diffusion on Twitter opinion dynamics\, we consider tweets containing URLs directing to news outlet websites. In particular\, we compare websites known to diffuse fake news compared to traditional\, fact-based\, news outlets. We find that 29% of the tweets linking to news outlets points to websites containing fake or extremely biased news. Analyzing the information diffusion networks\, we find that user diffusing fake news form more connected and less heterogeneous networks than users in traditional news diffusion networks. While influencers of traditional news outlets are journalists and public figures with verified Twitter accounts\, most influencers of fake news and extremely biased websites are unknown users or users with deleted Twitter accounts. Finally\, an analysis of the activity dynamics of influencers reveals that influencers of tradition news are driving the most part of Twitter while fake news influencers are\, in fact\, mostly driven by the activity of Trump supporters.
URL:https://www.naxys.be/event/alexandre-bovet-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180222T130000
DTEND;TZID=Europe/Paris:20180222T140000
DTSTAMP:20260408T151641
CREATED:20180214T201338Z
LAST-MODIFIED:20180214T201349Z
UID:366-1519304400-1519308000@www.naxys.be
SUMMARY:naXys extended Board meeting
DESCRIPTION:
URL:https://www.naxys.be/event/naxys-extended-board-meeting/
LOCATION:E25
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180220T130000
DTEND;TZID=Europe/Paris:20180220T140000
DTSTAMP:20260408T151641
CREATED:20180131T211209Z
LAST-MODIFIED:20180208T112833Z
UID:309-1519131600-1519135200@www.naxys.be
SUMMARY:François Lamoline (UNamur)
DESCRIPTION:Title: Well-Posedness of Boundary Controlled and Observed Stochastic Port-Hamiltonian systems \nAbstract: On finite-dimensional spaces\, the well-posedness is not a concern and is usually not even mentioned. However\, on infinite-dimensional spaces\, establishing the well-posedness is of paramount importance and paves the way for dealing with control/estimation\, transfer function\, etc. In this talk\, stochastic port-Hamiltonian systems on infinite-dimensional spaces governed by Ito stochastic differential equations and with boundary control and observation operators are introduced and some properties of this new class of systems are studied. They are an extension of stochastic port-Hamiltonian systems defined on a finite-dimensional state space. The concept of well-posedness in the sense of Weiss and Salamon is generalized to the stochastic context. Under this extended definition\, stochastic port-Hamiltonian systems are shown to be well-posed. The theory is illustrated on an example of a vibrating string subject to a Hilbert-space valued Gaussian white noise process.
URL:https://www.naxys.be/event/francois-lamoline-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180215T130000
DTEND;TZID=Europe/Paris:20180215T140000
DTSTAMP:20260408T151641
CREATED:20180131T210945Z
LAST-MODIFIED:20180208T112729Z
UID:307-1518699600-1518703200@www.naxys.be
SUMMARY:Eve-Aline Dubois (UNamur)
DESCRIPTION:Titre: The early times of stationary cosmologies \nAbstract: The Steady-state model of Bondi and Gold\, on the one hand\, and Hoyle’s model on the other hand are the most famous examples of stationary cosmologies. However\, they are actually quite different in terms of motivations and content and were not the only stationary models. In this talk\, we will look back at the very beginning of relativistic cosmology and the first stationary cosmological models. They were lead by various motivations and suggest a surprising phenomenon: creation of matter. From Einstein to Hoyle\, we will follow the different stationary cosmologies\, their development and their interplay.
URL:https://www.naxys.be/event/eve-aline-dubois-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20180125T130000
DTEND;TZID=Europe/Paris:20180125T140000
DTSTAMP:20260408T151641
CREATED:20180122T091928Z
LAST-MODIFIED:20180122T113112Z
UID:262-1516885200-1516888800@www.naxys.be
SUMMARY:Justin Buhendwa Nyenyezi (UNamur)
DESCRIPTION:Title: Polynomial preconditioners versus matrix-splitting preconditioners for linear systems arising in 3D medical image registration \nAbstract: Many methods exist to solve large sparse linear systems. However\, a given method may perform well for a particular problem while it may not work as well for another [2]. For designing ecient system solvers\, one may analyze structures of general operators or matrices used by the algorithms. In non-rigid medical image registration\, matrices are derived from physical principles\, modelled as Partial Dierential Equations (PDEs). Although these systems are often sparse and structured\, they are very large and ill-conditioned. Thus\, their solvers are time consuming and their complexity in operation counts is polynomial. As a consequence\, fast and superfast direct methods reveal numerical instabilities and thus lead to breakdowns or inaccurate solutions. The most used alternative are iterative system solvers that enable a reduction of the number of expensive operations such as matrix-vector products and thus a speed up of the registration process. Although iterative solvers provide only an approximation of the solution\, they are well suited for very large systems when cheap and well suited preconditioners are available. Preconditioners may be stationary (Jacobi\, Gauss-Seidel or SOR) and non-stationary (e.g\, polynonmial or low-rank inverse approximation).\nIn this study\, we are especially interested in benchmarking [3\, 4] iterative system solvers on a large set of 3D medical images. These system solvers are based on the Conjugate Gradient method but dierent from the preconditioning techniques [6\, 5] . The ongoing results conrm [4] that there is no single system solver that is the best for all the problems. However\, the results indicate which solver has the highest probability of being the best within a factor f ∈ [1\, ∞[ and considering a limited computional budget in terms of time and storage require-\nments.\nReferences\n[1] Oseledets\, Ivan and Tyrtyshnikov\, Eugene and Zamarashkin\, Nickolai. Evaluation of optimization methods for nonrigid medical image registration using mutual information and B-splines. Image Processing\, IEEE Transactions on\, 16:12\,28792890\, 2007.\n[2] Barrett\, Richard and & all. Templates for the solution of linear systems: building blocks for iterative methods. SIAM \, 1994.\n[3] Moré\, Jorge J and Wild\, Stefan M. Benchmarking derivative-free optimization algorithms. SIAM Journal on Optimization \, 20:1\,172191\, 2009.\n[4] Gould\, Nicholas and Scott\, Jennifer. The State-of-the-Art of Preconditioners for Sparse Linear Least-Squares Problems. ACM Transactions on Mathematical Software (TOMS) \, 43:4\,36\, 2017.\n[5] Nocedal\, Jorge and Wright\, Stephen J. Numerical optimization. Springer New York \, 2\, 2006.\n[6] SAAD\,Yousef Iterative methods for sparse linear systems. Society for Industrial and Applied Mathematics \, 2003.
URL:https://www.naxys.be/event/justin-buhendwa-nyenyezi-unamur/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171221T130000
DTEND;TZID=Europe/Paris:20171221T140000
DTSTAMP:20260408T151641
CREATED:20171116T160642Z
LAST-MODIFIED:20171205T202348Z
UID:248-1513861200-1513864800@www.naxys.be
SUMMARY:Anthony Hendrickx
DESCRIPTION:Title: Algorithme génétique et Rotifères Bdelloïdes: les mathématiques au service de la biologie \nRésumé: Existant depuis 1962\, les algorithmes génétiques se sont toujours basés sur un mode de reproduction sexuée\, la reproduction asexuée entraînant une accumulation de mutations délétères\, censée provoquer l’extinction de l’espèce. Cependant\, l’espèce du Bdelloïde\, malgré son mode de reproduction asexuée\, survit depuis des dizaines de millions d’années dans des milieux extrêmes et variés. Cette incroyable faculté semble être expliquée par l’observation\, chez cette espèce\, de phénomènes connus sous les noms de conversion génique et transfert horizontal. L’objectif de ce mémoire était de modéliser\, sous forme d’algorithmes génétiques\, l’évolution asexuée du Rotifère Bdelloïde\, afin d’étudier l’importance et l’influence de ces deux phénomènes. Des relations mathématiques connues en génétique\, liant taux de mutation\, longueur d’ADN et taux de conversion génique\, sont retrouvées numériquement\, permettant de valider et de simplifier notre modélisation. L’utilité du phénomène de conversion génique\, permettant de rendre nos algorithmes plus stables\, robustes et précis qu’un algorithme génétique classique\, est ensuite démontrée. Enfin\, l’importance du mécanisme de transfert horizontal\, améliorant l’efficacité du modèle asexué\, est mise en évidence\, permettant d’envisager un algorithme plus efficace que les modèles classiques.
URL:https://www.naxys.be/event/anthony-hendrickx/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171214T130000
DTEND;TZID=Europe/Paris:20171214T140000
DTSTAMP:20260408T151641
CREATED:20171116T160402Z
LAST-MODIFIED:20171207T091559Z
UID:246-1513256400-1513260000@www.naxys.be
SUMMARY:Sébastien Clesse (UCL - UNamur)
DESCRIPTION:Title:  Is Dark Matter made of Primordial Black Holes? \nAbstract: The detection of gravitational waves by Advanced-LIGO/VIRGO has opened a wide new field of astronomy.   Strangely\, the merging rate of massive black holes was found to be compatible with the rate expected if they constitute the Dark Matter.  This has revived the interest for Primordial Black Holes (PBH) formed in the early Universe constituting a fraction or even the totality of Dark Matter .  This scenario is however well constrained by other astrophysical observations.  I will review the pros and cons of this scenario\, in the view of the most recent results and observations\, and I will emphasize how PBH Dark Matter could resolve some long-standing cosmological and astrophysical puzzles.   The presentation will be understandable by a broad audience of mathematicians\, physicists and students.
URL:https://www.naxys.be/event/sebastien-clesse-ucl-unamur/
LOCATION:E22
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171207T130000
DTEND;TZID=Europe/Paris:20171207T140000
DTSTAMP:20260408T151641
CREATED:20171116T160011Z
LAST-MODIFIED:20171206T202424Z
UID:243-1512651600-1512655200@www.naxys.be
SUMMARY:Henri Vanhomwegen (UNamur)
DESCRIPTION:Title: Mutual funds styles distinctiveness and financial performance insights from Europe \nAsbtract: Do mutual funds following a same style adopt similar investment strategies? Are these potential differences more salient over certain periods? What drives a mutual fund to be distinct from its peers? Does it pay? Those are central questions for both academics and market practitioners that we aim to address in this paper. More generally\, we propose to study the degree of commonality among European equity mutual funds over time\, and its impact on financial performance. To this end\, we use several market-based measures of commonality among 4957 European equity mutual fund returns over the 1999-2016 period. We pay a particular attention to the computation of adequate metrics\, the so-called « strategy distinctiveness index » applying up-to-date techniques from statistics and machine learning to generate clusters of mutual funds associated to “styles”\, from which we can gauge how similar or distinct a mutual fund is from its peers (i.e. the mutual funds belonging to the same cluster or style). Our results show marked changes in the level of commonality over time\, distinctiveness among European mutual funds decreasing sharply before the crisis before going up and eventually reaching a new low in the recent months. We find strong evidence regarding the contribution of fund-level as well as cluster characteristics to strategy distinctiveness. Turning to financial performance\, our results show a strong and robust\, positive impact of strategy distinctiveness on financial performance.
URL:https://www.naxys.be/event/henri-vanhomwegen-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171130T130000
DTEND;TZID=Europe/Paris:20171130T140000
DTSTAMP:20260408T151641
CREATED:20171108T082310Z
LAST-MODIFIED:20171129T200900Z
UID:226-1512046800-1512050400@www.naxys.be
SUMMARY:Marco Sansottera (University of Milan)
DESCRIPTION:Title: On the continuation of degenerate periodic orbits via normal form: full dimensional resonant tori \nAbstract: We reconsider the classical problem of the continuation of degenerate periodic orbits in Hamiltonian systems. In particular we focus on periodic orbits that arise from the breaking of a completely resonant maximal torus. We here propose a suitable normal form construction that allows to identify and approximate the periodic orbits which survive to the breaking of the resonant torus. Our algorithm allows to treat the continuation of approximate orbits which are at leading order degenerate\, hence not covered by classical averaging methods. We discuss possible future extensions and applications to localized periodic orbits in chains of weakly coupled oscillators.
URL:https://www.naxys.be/event/marco-sansottera-university-of-milan-2/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171123T130000
DTEND;TZID=Europe/Paris:20171123T140000
DTSTAMP:20260408T151641
CREATED:20171108T082106Z
LAST-MODIFIED:20171113T081151Z
UID:224-1511442000-1511445600@www.naxys.be
SUMMARY:Yérali Gandica (UNamur)
DESCRIPTION:Title: Language as a signature of collective identity: Wikipedia editing across twelve languages
URL:https://www.naxys.be/event/yeralica-gandica-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171116T130000
DTEND;TZID=Europe/Paris:20171116T140000
DTSTAMP:20260408T151641
CREATED:20171027T115436Z
LAST-MODIFIED:20171113T081252Z
UID:216-1510837200-1510840800@www.naxys.be
SUMMARY:Astero Provata (National Center for Scientific Research Demokritos\, Athens)
DESCRIPTION:Title: The influence of the network connectivity in the spatial patterns of chimera states \nAbstract: Chimera states emerge in systems of nonlocally coupled identical oscillators and are characterized by the coexistence of alternating coherent and incoherent domains. These hybrid states appear unexpectedly since all elementary oscillators in the network are identical and are identically coupled. A characteristic feature of chimera states is their mean frequency profile: In the coherent regions\, all elements have equal\, constant mean phase velocity\, while in the incoherent ones the frequency profiles take arc shapes.  Here we present synchronization properties leading to chimera states in networks of coupled neuronal oscillators. To understand the influence of connectivity in the chimera form we investigate the Leaky Integrate and Fire (LIF) model under different connectivity architectures. In the case of nonlocal connectivity\, we show evidence of a coexistence state where multileveled chimera patterns are formed and they coexist with domains consisting of near-threshold elements. The oscillating elements form complex mean phase velocity profiles while the potentials of the near-threshold elements present small fluctuations and never drop to the resting state. We study different synchronization patterns in the parameter space of the LIF system when the oscillators are nonlocally coupled in 1\, 2 and 3 spatial dimensions. We also investigate the effects of different connectivity schemes: nonlocal connectivity\, reflecting coupling\, diagonal or hierarchical (fractal) connectivity. \n– Tsigkri-DeSmedt\, N.D.\, Hizanidis\, J.\, Schöll\, E.\, Hövel\, P.\, Provata\, A.\nChimeras in leaky integrate-and-fire neural networks: effects of reflecting connectivities\,\nEuropean Physical Journal B 90(7)\,139 (2017). \n– Tsigkri-DeSmedt\, N.D.\, Hizanidis\, J.\, Hövel\, P.\, Provata\, A.\nMulti-chimera states and transitions in the Leaky Integrate-and-Fire model with nonlocal and hierarchical connectivity\,\nEuropean Physical Journal: Special Topics 225(6-7)\, pp. 1149-1164 (2016). \n– Schmidt\, A.\, Kasimatis\, T.\, Hizanidis\, J.\, Provata\, A.\, Hövel\, P.\nChimera patterns in two-dimensional networks of coupled neurons\nPhysical Review E 95(3)\,032224 (2017).
URL:https://www.naxys.be/event/astero-provata-national-center-for-scientific-research-demokritos-athens-greece/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171110T130000
DTEND;TZID=Europe/Paris:20171110T140000
DTSTAMP:20260408T151641
CREATED:20171027T115837Z
LAST-MODIFIED:20171113T081134Z
UID:219-1510318800-1510322400@www.naxys.be
SUMMARY:Olivier Deparis (UNamur)
DESCRIPTION:Title: Alternative expression of the Bloch wave group velocity using the Sturm-Liouville formalism applied to electromagnetic wave propagation in periodic dielectric media
URL:https://www.naxys.be/event/olivier-deparis-unamur/
LOCATION:E22
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171109T121000
DTEND;TZID=Europe/Paris:20171109T133000
DTSTAMP:20260408T151641
CREATED:20171027T115130Z
LAST-MODIFIED:20171027T115130Z
UID:213-1510229400-1510234200@www.naxys.be
SUMMARY:naXys Board meeting
DESCRIPTION:
URL:https://www.naxys.be/event/naxys-board-meeting/
LOCATION:E25
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171102T130000
DTEND;TZID=Europe/Paris:20171102T140000
DTSTAMP:20260408T151641
CREATED:20171027T114745Z
LAST-MODIFIED:20171113T081111Z
UID:208-1509627600-1509631200@www.naxys.be
SUMMARY:Duccio Fanelli (University of Florence\, Italy)
DESCRIPTION:Title: Noise-driven neuromorphic tuned amplifier \nAbstract: Living systems execute an extraordinary plethora of complex functions\, that result from the intertwined interactions among key microscopic actors. Positive and negative feedbacks appear to orchestrate the necessary degree of macroscopic coordination\, by propagating information to distant sites while supporting the processing steps that underly categorization and decision making. Excitatory and inhibitory circuits play\, in this respect\, a role of paramount importance. As an example\, networks of excitatory and inhibitory neurons constitute the primary computational units in the brain cortex and can adjust to different computational modalities\, as triggered by distinct external stimuli. The genetic regulation also relies on sophisticated inhibitory and excitatory loops. Working in this context\, we shall here discuss a minimal model for a discrete collection of agents in mutual interaction via excitatory and inhibitory loops\, bearing universality traits in light of its inherent simplicity. Endogenous-noise stemming from finite size corrections induces quasi-cyclic dynamics that display unusual long-range correlations\, persisting over arbitrary large network structures. When the excitatory and inhibitory species are distributed on a directed network\, the internal noise seeds giant quasi-cycles\, with tunable frequency and amplitude. The system spontaneously behaves as an effective\, stochastic driven pacemaker\, a non-trivial self-organized dynamics that hold general interest\, for its fundamental to applied implications. The phenomenon is characterized analytically. The theoretical prediction is corroborated by direct stochastic simulations.
URL:https://www.naxys.be/event/duccio-fanelli-university-of-florence-italy/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20171030T090000
DTEND;TZID=Europe/Paris:20171030T120000
DTSTAMP:20260408T151641
CREATED:20171027T114049Z
LAST-MODIFIED:20171027T114429Z
UID:204-1509354000-1509364800@www.naxys.be
SUMMARY:VBIH (Virtual Belgium in Health) - Presentation of the results
DESCRIPTION:
URL:https://www.naxys.be/event/vbih-virtual-belgium-in-health-presentation-of-the-results/
LOCATION:E11
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170706T110000
DTEND;TZID=Europe/Paris:20170706T120000
DTSTAMP:20260408T151641
CREATED:20170629T134654Z
LAST-MODIFIED:20170629T134654Z
UID:196-1499338800-1499342400@www.naxys.be
SUMMARY:Alex Matzkin (CNRS/Université de Cergy-Pontoise)
DESCRIPTION:Title: Can the properties of a quantum system vanish? \nAbstract: \nThe Weak Measurements approach is a framework based on implementing non-destructive\, non-perturbing measurements on a quantum system as the system evolves from an initially prepared state to a final state obtained by performing a standard measurement. The result of a weak measurement is called the “weak value” of the weakly measured observable. Weak values have peculiar features. In particular\, a vanishing weak value means that the corresponding system property cannot be found at the location where the observable was weakly measured. This may have striking consequences\, like not being able to detect a particle inside an interferometer although it went in and out\, or observing a spatial separation between a particle and one of its properties. I will describe situations in which quantum properties appear to “vanish” and I will put forward an explanation based on the analysis of null weak values.
URL:https://www.naxys.be/event/alex-matzkin-cnrsuniversite-de-cergy-pontoise/
LOCATION:CH12
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170630T130000
DTEND;TZID=Europe/Paris:20170630T140000
DTSTAMP:20260408T151641
CREATED:20170629T205452Z
LAST-MODIFIED:20170629T205452Z
UID:199-1498827600-1498831200@www.naxys.be
SUMMARY:Marco Sansottera (University of Milan)
DESCRIPTION:Title: Quasi-convexity of the Hamiltonian for non Harmonic or non Keplerian\ncentral potentials. \nAbstract: \nWe consider the planar central motion with a real analytic potential. We\nprove that the corresponding Hamiltonian\, when written in action angle\nvariables\, is almost everywhere quasiconvex\, the only exceptions being\nthe Keplerian and the Harmonic potentials. We deduce persistence of most\nKAM tori for the perturbed planar system. We also deduce a Nekhoroshev\ntype stability result for the perturbed spatial central motion. Such a\nlatter result covers also the case where the central system is put in\ninteraction with a slow system. \n 
URL:https://www.naxys.be/event/marco-sansottera-university-of-milan/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170627T130000
DTEND;TZID=Europe/Paris:20170627T140000
DTSTAMP:20260408T151641
CREATED:20170508T102318Z
LAST-MODIFIED:20170508T102453Z
UID:182-1498568400-1498572000@www.naxys.be
SUMMARY:Jérôme Kunegis (NaXys)
DESCRIPTION:Title: The New KONECT Project at the University of Namur \nAbstract: In this talk I give an overview of the KONECT project\, and highlight some of its applications. The KONECT Project is a project to collect\, analyse and disseminate network datasets as used in various fields of research such as network science\, web science\, etc. The name “KONECT” stands for “Koblenz Network Collection” as the project was  initiated at the University of Koblenz-Landau (Germany)\, but is now maintained at the University of Namur in parallel with my move to this university. This talk will give a motivation for the need of such a project\, highlighting the benefits of performing research on large sets of network datasets\, and why the motto of KONECT is “Everything is a Network”. I will also briefly present recent papers by myself and colleagues that have made use of the KONECT corpus. Finally\, I will give a brief introduction to the Stu build automation tool that I wrote in order to manage the highly parallel and structurally complex computations in KONECT.
URL:https://www.naxys.be/event/jerome-kunegis-naxys/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170613T130000
DTEND;TZID=Europe/Paris:20170613T140000
DTSTAMP:20260408T151641
CREATED:20170412T074349Z
LAST-MODIFIED:20170609T144717Z
UID:174-1497358800-1497362400@www.naxys.be
SUMMARY:Pierre-Antoine Absil (UCL)
DESCRIPTION:Title: Averaging diffusion tensors \n  \nAbstract: \nThis talk concerns the problem of averaging a collection of symmetric positive-definite (SPD) matrices. Generally speaking\, averaging methods are required notably to aggregate several noisy measurements of the same object\, or to compute the mean of clusters in k-means clustering algorithms\, or as a subtask in higher-level tasks such as curve fitting. The problem of averaging SPD matrices arises for example in medical imaging (denoising and segmentation tasks in Diffusion Tensor Imaging)\, mechanics (elasticity tensor computation)\, and in video tracking and radar detection tasks. Among several possible definitions for the mean of SPD matrices (including the straightforward arithmetic mean)\, the “Karcher mean” (specifically the least-squares mean in the sense of the so-called affine-invariant metric) is of widespread interest in the research literature\, since it possesses several pleasant properties while being challenging to compute. In this talk\, we will review recent advances in iterative methods that converge to the Karcher mean\, and in methods that approach it using limited resources.\nThis work is in collaboration with Xinru Yuan and Kyle Gallivan (Florida State University)\, Wen Huang (Rice University)\, and Estelle Massart and Julien Hendrickx (UCLouvain).
URL:https://www.naxys.be/event/pierre-antoine-absil-ucl/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170606T130000
DTEND;TZID=Europe/Paris:20170606T140000
DTSTAMP:20260408T151641
CREATED:20170314T141725Z
LAST-MODIFIED:20170323T163200Z
UID:158-1496754000-1496757600@www.naxys.be
SUMMARY:Matteo Polettini (University of Luxembourg)
DESCRIPTION:Title: Effective thermodynamics according to a marginal observer \nAbstract: \nThe celebrated Fluctuation Theorem\, quantifying the extent of breakage of time reversibility in nonequilibrium systems\, pivots on the fact that all currents contributing to the dissipation rate of a system are known. What instead if only some currents are measurable? In general\, the marginal probabilities of fewer currents do not satisfy the full fluctuation symmetry. However\, still many claims can be sustained. We provide a general theory of fluctuation relations for the marginal p.d.f. of the currents of a Markov jump process\, based on the mathematics of the “marginally time-reversed” generator. At the physical level\, the theory has implications regarding the fluctuation-dissipation relations for systems that are only locally at equilibrium\, i.e.\, such that certain currents vanish while all others are arbitrarily far from equilibrium. In particular\, we are able to prove nonequilibrium Green-Kubo relations\, the violation of the Onsager symmetry\, and to provide higher-order signatures of nonequilibrium behavior. \n 
URL:https://www.naxys.be/event/matteo-polettini-university-of-luxembourg/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170601T130000
DTEND;TZID=Europe/Paris:20170601T140000
DTSTAMP:20260408T151641
CREATED:20170602T114520Z
LAST-MODIFIED:20170602T114520Z
UID:191-1496322000-1496325600@www.naxys.be
SUMMARY:Arnaud Dufays (University of Laval)
DESCRIPTION:Title : A new approach to volatility modeling: the High-Dimensional Markov model\nAbstract : A new model — the high-dimensional Markov (HDM) model — is proposed for financial returns and their latent variances. It is also applicable to model directly realized variances. Volatility is modeled as a product of three components: a Markov chain driving volatility persistence\, an independent discrete process capable of generating jumps in the volatility\, and a predictable (data-driven) process capturing the leverage effect. The Markov chain and jump components allow volatility to switch abruptly between thousands of states. The transition probability matrix of the Markov chain is structured in such a way that the multiplicity of the second largest eigenvalue can be greater than one. This distinctive feature generates a high degree of volatility persistence. The statistical properties of the HDM model are derived and an economic interpretation is attached to each component. In-sample results on six financial time series highlight that the HDM model compares favorably to the main existing volatility processes. A forecasting experiment shows that the HDM model significantly outperforms its competitors when predicting volatility over time horizons longer than five days.
URL:https://www.naxys.be/event/arnaud-dufays-university-of-laval/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170530T130000
DTEND;TZID=Europe/Paris:20170530T140000
DTSTAMP:20260408T151641
CREATED:20170314T141110Z
LAST-MODIFIED:20170602T114233Z
UID:154-1496149200-1496152800@www.naxys.be
SUMMARY:Yannick de Decker (ULB)
DESCRIPTION:Canceled
URL:https://www.naxys.be/event/yannick-de-decker/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170523T130000
DTEND;TZID=Europe/Paris:20170523T140000
DTSTAMP:20260408T151641
CREATED:20170318T163007Z
LAST-MODIFIED:20170514T143251Z
UID:161-1495544400-1495548000@www.naxys.be
SUMMARY:Stefano Berti (University of Lille)
DESCRIPTION:Title: Reaction-transport systems in heterogeneous environments and population dynamics \nAbstract: Understanding the conditions ensuring the persistence of a population or determining the efficiency of its invasion into a new territory are issues of primary importance in population biology. A convenient conceptual framework to study these problems from a theoretical point of view is offered by reaction-transport equations. Taking this modeling approach\, in the first part of the talk I present a study on the evolution of a population in a heterogeneous environment in the presence of advection. The habitat consists of a periodic alternation of favorable and unfavorable patches where the population grows according to logistic dynamics and dies at a fixed rate\, respectively. I show that the population can survive and invade the habitat only above a critical size of the favorable patches and below a critical velocity of the medium. I characterize the survival/extinction transition\, and I present some analytical and numerical results on the invasion speed. Then\, I discuss some limitations of this description\, extending the analysis to a model with a growth term accounting for decreased reproductive power at low population densities. The phenomenology of this model is found to be richer when varying the advection intensity.\nIn the second part of the talk I discuss some effects of discreteness and demographic stochasticity on the extinction dynamics of a population confined in a favorable patch (an oasis) surrounded by a deadly environment. For this purpose\, I introduce an individual-based reaction-diffusion model and investigate its behavior focusing on the average time to extinction and on the quasistationary distribution of the number of individuals that sets in for large enough patch sizes.
URL:https://www.naxys.be/event/stefano-berti/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170509T130000
DTEND;TZID=Europe/Paris:20170509T140000
DTSTAMP:20260408T151641
CREATED:20170308T154206Z
LAST-MODIFIED:20170428T110726Z
UID:152-1494334800-1494338400@www.naxys.be
SUMMARY:Nikos Kouvaris ( University Pompeu Fabra)
DESCRIPTION:Title: Pattern formation in bistable networks: Theory and applications to chemical reactions \n  \nAbstract: \nSelf-organization processes in complex networks is an interdisciplinary research field with great theoretical interest and many potential applications in chemistry and biology. Stationary localized patterns constitute a classical example of self-organization; they can spontaneously be generated by the Turing mechanism\, as it has been reported in both continuous and networked media. However\, an alternative mechanism for the emergence of stationary patterns in networks was recently discovered [1-4]. We have experimentally demonstrated and theoretically analyzed that bistable networks can support a rich variety of stationary patterns determined by the network architecture and the initial conditions [2\,3]. By applying a localized perturbation to a network node or a subset of nodes\, we demonstrate the subsequent spreading\, pinning\, or retraction of the activations; such analysis enables the characterization of the formation of stationary patterns of localized activity. Weak coupling results in trivial pinned states where the activation is stationary. At strong coupling\, a uniform state is expected with active or inactive elements at small or large nodes degree\, respectively. Nontrivial stationary spatial patterns\, corresponding to an activation pinning\, are predicted to occur at nodes with intermediate degrees and at intermediate coupling strengths. The results are confirmed in experiments with networks of coupled bistable electrochemical reactions. Although our experimental system is actually more complex than the simplifying assumptions under which the theory was constructed\, the results show a surprisingly good agreement. This indicates that the found pattern formation mechanism is robust and generic. \nIn this talk we discuss theoretical and experimental studies with bistable chemical reactions organized in tree [1\,2] and star [3] networks. These results are relevant for large random networks [2]. Mechanisms for the control and deliberate design of such patterns [4] will also be considered. \nReferences:\n———–\n1. N. E. Kouvaris\, H. Kori and A. S. Mikhailov\, PLoS ONE 7\, e45029 (2012).\n2. N. E. Kouvaris\, M. Sebek\, A. S. Mikhailov and I. Z. Kiss\, Angew. Chem. Int. Ed.\, 55\, 13267-13270 (2016).\n3. N. E. Kouvaris\, M. Sebek\, A. Iribarne\, A. Diaz-Guilera and I. Z. Kiss\, Phys. Rev. E 95\, 042203 (2017).\n4. N. E. Kouvaris and A. S. Mikhailov\, Europhys. Lett. 102\, 16003 (2013).
URL:https://www.naxys.be/event/nikos-kouvaris-university-pompeu-fabra/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170502T130000
DTEND;TZID=Europe/Paris:20170502T140000
DTSTAMP:20260408T151641
CREATED:20170308T152719Z
LAST-MODIFIED:20170416T103118Z
UID:149-1493730000-1493733600@www.naxys.be
SUMMARY:Jan Baert (UGent)
DESCRIPTION:Title: Environmental dependency of biodiversity effects on ecosystem functioning \nAbstract: Expanding human activities are increasingly interfering with Earth’s biogeochemical cycles. This has led to unprecedented global changes in biodiversity and environmental conditions. In the past 3 decades\, ecologists have principally been focusing on whether the functioning of an ecosystem depends on the number of species it contains. There is now ample evidence that biodiversity-ecosystem functioning relationships are generally positive\, and ecosystem function provisioning is at risk by biodiversity loss. However\, evidence is also mounting that the relationship between biodiversity and ecosystem functioning\, and therefore also the consequences of biodiversity changes\, depend on the environmental conditions. In my work\, I ai to explain how biodiversity-ecosystem functioning relationships are affected by changes in environmental conditions. Theoretical models are thereby combined with microcosm experiments to demonstrate how environmental changes lead to predictable changes in biodiversity effects on ecosystem functioning\, and how these changes depend the type of species interactions and species sensitivities to environmental changes. As such\, the presented framework offers new insights in the combined effect of upcoming biodiversity and environmental changes for ecosystem function provisioning.
URL:https://www.naxys.be/event/jan-baert-ugent/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170425T130000
DTEND;TZID=Europe/Paris:20170425T140000
DTSTAMP:20260408T151641
CREATED:20170308T152506Z
LAST-MODIFIED:20170331T155306Z
UID:147-1493125200-1493128800@www.naxys.be
SUMMARY:Francesco Piazza (University of Orléans)
DESCRIPTION:Title: Diffusion of small ligands in complex confining and reactive landscapes:\nthe geometry of chemoreception. \nAbstract: \nThe rate constant that describes the diffusive encounter/reaction between a particle\nand a large sphere can be computed easily by solving the stationary diffusion\n(i.e. Laplace) equation for the particle density with appropriate boundary conditions\nimposed on the surface of the sphere. In one classic\, text-book example\, this calculation is\nused to estimate the binding rate constant of a ligand to a receptor-covered cell.\nBut what happens if the particles are diffusing in the presence of many reactive boundaries\nof different strength (intrinsic reaction rate)\, which compete for the same ligands and amidst\na landscape of inert obstacles? In spite of the apparent overwhelming complexity\, the same mathematical framework as the two-body problem can be used to solve the N-body problem exactly\, by resorting to addition theorems for the appropriate fundamental solutions of the Laplace equation.\nThis powerful mathematical framework allows one to investigate fundamental issues\nthat are central in cell biology and modern nano-sciences\, such as how the specific geometric\nconfigurations of many reactive boundaries shape the overall reaction rate constant.\nWe will illustrate several examples\, including applications to the study of ligand binding\nto arrays of receptors on the surface of a cell and the action of many nano-catalysts embedded within a core-shell nano-reactor.
URL:https://www.naxys.be/event/francesco-piazza-university-of-orleans/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170404T130000
DTEND;TZID=Europe/Paris:20170404T140000
DTSTAMP:20260408T151641
CREATED:20170308T152154Z
LAST-MODIFIED:20170328T210957Z
UID:145-1491310800-1491314400@www.naxys.be
SUMMARY:William Polycarpe (Paris Observatory)
DESCRIPTION:Title: Is Titan responsible for Iapetus’ orbit ? \n  \nAbstract: Latest astrometrical results on Saturnian moons show evidence for high migration rates (Lainey et al. 2012; 2016). The tidal dissipation in the planet is responsible for those large orbital expansions and should therefore be much stronger than usually expected. The idea of significant tidal dissipation in the massive core (Remus et al. 2012) and the convective envelope (Le Guenel et al. 2015; Fuller et al. 2016) of the planet has been brought forward as a likely explanation.\nNevertheless\, high changes in semi-major axes of the moons shuffle up the ideas we had on the past evolution of the system of Saturn. In particular\, depending on tidal mechanisms at play\, several Mean Motion Resonances could have been crossed just a few million years ago.\nIn the frame of high tidal migration\, we investigate the consequences of the past 5:1 mean motion resonance between Titan and Iapetus\, which could have happened between 5 and 500 million years ago. Numerical simulations show that the most common outcome for Iapetus is to be ejected\, as Titan migrates through the resonance. However\, if Titan has a very high recession (Q <2000)\, Iapetus may survive the resonance and come out of it with an eccentricity consistent with today’s value. The effect on Iapetus’ inclination is still under investigation.
URL:https://www.naxys.be/event/william-polycarpe-paris-observatory/
LOCATION:Seminar room\, Rempart de la Vierge 8\, Namur\, 1170
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20170330T080000
DTEND;TZID=Europe/Paris:20170330T170000
DTSTAMP:20260408T151641
CREATED:20170125T090922Z
LAST-MODIFIED:20170125T090922Z
UID:103-1490860800-1490893200@www.naxys.be
SUMMARY:Hands-on session with GIT.
DESCRIPTION: The train to Brussels costs will be re-imbursed by Naxys. The training itself is free of charge. Agenda will be send around well in advance. \nRegistration is free vut mandatory on: http://doodle.com/poll/bdq4aetpkk6kav9w
URL:https://www.naxys.be/event/hands-on-session-with-git/
LOCATION:Brussels
END:VEVENT
END:VCALENDAR