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BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20241115T130000
DTEND;TZID=Europe/Brussels:20241115T140000
DTSTAMP:20260407T003505
CREATED:20241030T101730Z
LAST-MODIFIED:20241106T122335Z
UID:2224-1731675600-1731679200@www.naxys.be
SUMMARY:Serge Gratton (Toulouse INP)
DESCRIPTION:Title : Adaptive regularization algorithms for Objective-Function-Free Optimization \nAbstract :  \nThis work is about the fastest known optimization method in terms of complexity\, which does not require the evaluation of the objective function. Such methods\, termed Objective-Function-Free Optimization (OFFO)\, have gained popularity recently\, especially in noisy problem contexts\, including deep learning applications. We present an adaptive regularization OFFO algorithm for unconstrained nonconvex optimization. This algorithm is part of the adaptive regularization methods family\, which is known for its optimal worst-case complexity results in the conventional framework where the objective function is evaluated. We demonstrate that these outstanding complexity bounds are maintained with the new algorithm\, even though it relies on significantly less information. Specifically\, we show that using derivatives of degree one to p\, the algorithm will find an 𝛆1-approximate first-order minimizer in at most O(𝛆-(p+1)/p) iterations\, and an (𝛆1\, 𝛆2)-approximate second-order minimizer in at most O(𝛆-(p+1)/p\, 𝛆-(p+1)/(p-1)}) iterations. As a particular case\, the algorithm\, when using first and second derivatives and applied to functions with Lipschitz continuous Hessian\, will find an iterate xk where the gradient’s norm is less than 𝛆1 in at most O(𝛆-3/2) iterations. Numerical experiments demonstrate the excellent performance of this method for noisy problems\, highlighting its robustness and efficiency across various scenarios. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/serge-gratton-toulouse-inp/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240919T133000
DTEND;TZID=Europe/Brussels:20240919T140000
DTSTAMP:20260407T003505
CREATED:20240311T155723Z
LAST-MODIFIED:20240919T083342Z
UID:2123-1726752600-1726754400@www.naxys.be
SUMMARY:Christian Bick (VU Amsterdam)
DESCRIPTION:Title : Higher-order Interaction Networks: Phase Reduction\, Synchronization\, and Global Dynamics  \nAbstract : Synchronization is a fascinating effect of the interaction between coupled oscillatory units and is ubiquitous in many real-world systems. If the coupling between units is sufficiently weak\, phase reductions provide an adequate description of the dynamics. We discuss phase reductions beyond first order that yield phase oscillator networks with higher-order interactions. Specifically\, we discuss how the nonpairwise higher-order phase interactions depend on the shape of the limit cycles and the underlying network structure. If time permits\, we also discuss how higher-order interactions influence the emergence of metastable (synchronization) dynamics induced by heteroclinic cycles. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/christian-bick-vu-amsterdam/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240919T130000
DTEND;TZID=Europe/Brussels:20240919T133000
DTSTAMP:20260407T003505
CREATED:20240518T091027Z
LAST-MODIFIED:20240919T083355Z
UID:2154-1726750800-1726752600@www.naxys.be
SUMMARY:Riccardo Muolo (Tokyo Institute of Technology)
DESCRIPTION:Title : A general theory of phase reduction for systems with higher-order interactions \nAbstract:\n\nSynchronization is a ubiquitous emergent phenomenon in which an ensemble of elementary units behaves in unison due to their interactions [1]. Given the pervasiveness of synchronization\, understanding how it is achieved is a fundamental question. In particular\, the nature of the interactions among oscillators has strong consequences on the transition to synchronization. To tackle this issue\, it is convenient to consider phase models in which each oscillator is described solely in terms of a phase variable. According to phase reduction theory\, the phase model captures the dynamics completely when the coupling among the oscillators is sufficiently weak [2]. If one considers only pairwise interactions\, the synchronization transition is described by the Kuramoto-type model. Despite the versatility of such an approach\, the classical theory of synchronization is solely based on pairwise interactions\, while\, in many natural systems\, the interactions are intrinsically higher-order (many-body) rather than pairwise [3]. In fact\, many examples show that a pairwise description is sufficient not to match the theory with observations and\, additionally\, higher-order interactions appear naturally when phase reduction is performed up to higher orders [4]. It was also shown that extensions of the Kuramoto model including higher-order interactions exhibit an explosive transition and other interesting dynamics [5].\n\nThis seminar will be divided in two parts. In the first part\, I will introduce the phase reduction theory and highlight the universality of phase models and the generality of the approach\, especially when compared to the Master Stability Function [6]. Then\, after discussing the basics of higher-order interactions\, I will present a recent work where we analyzed the collective dynamics of the simplest minimal extension of the Kuramoto-type phase model for identical globally coupled oscillators subject to two- and three-body interactions and showed how the many-body interactions greatly enriches the behaviors of the system [7]. Lastly\, I will show some preliminary results for some general cases\, one where the coupling is not constrained to the all-to-all case [8] and the other in which the phase reduction cannot be performed analytically [9].\nThis is a joint work with Hiroya Nakao (Tokyo Institute of Technology\, Japan)\, Iván León (Universidad de Cantabria\, Spain) and Shigefumi Hata (Kagoshima University\, Japan)\n\nReferences\n[1] Kuramoto Y.\, Chemical Oscillations\, Waves\, and Turbulence. Springer-Verlag\, 1984.\n[2] Nakao H.\, Phase reduction approach to synchronisation of nonlinear oscillators. Cont. Phys.\, 57(2): 188-214\, 2016.\n[3] Battiston F. et al.\, Networks beyond pairwise interactions: Structure and dynamics. Phys. Rep.\, 84: 1-92\, 2020.\n[4] León I. and Pazó D.\, Phase reduction beyond the first order: The case of the mean-field complex Ginzburg-Landau equation. Phys. Rev. E\, 100(1): 012211\, 2019.\n[5] Skardal P.S. and Arenas A.\, Abrupt Desynchronization and Extensive Multistability in Globally Coupled Oscillator Simplexes. Phys. Rev. Lett.\, 122(84): 248301\, 2019.\n[6] Fujisaka\, H.\, and Yamada\, T.\, Stability theory of synchronized motion in coupled-oscillator systems. Prog. Theor. Phys.\, 69(1)\, 32-47\, 1983.\n[7] León I.\, Muolo R.\, Hata S. and Nakao H.\, Higher-order interactions induce anomalous transitions to synchrony. To appear in Chaos\, Dec 2023.\n[8] Muolo R.\, León I.\, Hata S. and Nakao H.\, Phase Reduction Analysis of Collective Dynamics in Systems of Coupled Oscillators with Higher-Order Interactions. In preparation.\n[9] Muolo R. and Nakao H.\, A general framework to study spiking neurons coupled through higher-order interactions. In preparation.\n\n\nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/riccardo-muolo-tokyo-institute-of-technology/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240918T130000
DTEND;TZID=Europe/Brussels:20240918T140000
DTSTAMP:20260407T003505
CREATED:20240729T174819Z
LAST-MODIFIED:20240822T130014Z
UID:2166-1726664400-1726668000@www.naxys.be
SUMMARY:Keisuke Taga (Waseda University)
DESCRIPTION:Title : Nonlinear pattern formation of tape peeling \nAbstract : \nWhen we look closely at the peel front of the adhesives\, we can find two kinds of structures. One of them is a tunnel structure which can be found in slow peeling. Then for fast peeling\, the tunnel structure collapses and a without tunnel structure occurs . And at the intermediate peel speed\, these two structures switch chaotic. From the experimental observation\,this chaotic switching gives Sierpinski-gasket like fractal random patterns in the peel trace of the adhesive tapes[1].\n\nIn this talk\, I introduce a model for the pattern formation of the peel trace by considering the deformation of the peel front based on the Newton equation\, then we compare its scaling properties to the previous experimental result [2].\n\n[1] Y. Yamazaki and A. Toda\, Physica D 214 120 (2006).\n[2] K. Taga and Y. Yamazaki\, J. Phys. Soc. Jpn.\, 92\, 4\, 043001 (2023).\n\nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/keisuke-taga-waseda-university/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20240911
DTEND;VALUE=DATE:20240914
DTSTAMP:20260407T003505
CREATED:20240821T075330Z
LAST-MODIFIED:20240821T075346Z
UID:2176-1726012800-1726271999@www.naxys.be
SUMMARY:WIVACE Workshop 2024
DESCRIPTION:XVIII International Workshop on Artificial Life and Evolutionary Computation\nNamur\, Belgium\, 11-13 September 2024\nThe International Workshop on Artificial Life and Evolutionary Computation aims at bringing together researchers to present and share their results and ideas in a multidisciplinary context. The workshop provides a forum for the discussion of new research directions and applications in Artificial Life\, Evolutionary Computation and in related fields\, where different disciplines and research areas could effectively meet. \nMore information : https://events.info.unamur.be/wivace2024/index.html
URL:https://www.naxys.be/event/wivace-2024/
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20240909
DTEND;VALUE=DATE:20240914
DTSTAMP:20260407T003505
CREATED:20240821T075509Z
LAST-MODIFIED:20240821T075524Z
UID:2179-1725840000-1726271999@www.naxys.be
SUMMARY:Mathematics for Industry 2024
DESCRIPTION:Study week Mathematics for Industry 2024\nFrom 9 to 13 September 2024\, the Belgian network BE-MATHS-IN on applied mathematics for industry and innovation\, which gathers applied mathematical researchers at all Belgian universities\, organizes its third Belgian study week “Mathematics for Industry”\, which will be held at the TRAKK co-working center in Namur. \nThe Mathematics for Industry study week is an intensive problem-solving workshop that brings together young researchers\, postdocs\, scientists and industrialists. In the course of one week\, small groups of researchers of different backgrounds will intensively brainstorm and work together to model and solve real-world challenges provided by industry. On Monday\, each company representative presents their problem\, after which the participants choose a problem to work on for the remainder of the week along with the industrial partner. On Friday morning\, each group presents their solution to the chosen problem. \nThe study week warmly welcomes a broad scientific audience: from applied and computational sciences (applied mathematics\, engineering\, statistics\, …) to pure sciences (mathematics\, physics\, chemistry\, biology\, …). \nMore information : https://be-maths-in.be/mfi24/
URL:https://www.naxys.be/event/mathematics-for-industry-2024/
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20240905
DTEND;VALUE=DATE:20240906
DTSTAMP:20260407T003505
CREATED:20240821T074925Z
LAST-MODIFIED:20240905T100021Z
UID:2173-1725494400-1725580799@www.naxys.be
SUMMARY:naXys Research Day
DESCRIPTION:The naXys Research Day takes place at La Bergerie de Lives (100 rue de Mosanville\, 5000 Namur). \nSchedule\n13.00-13.30 Welcome  and words of the President\, A.-S. Libert \n13.30-13.45 Meet Jeanick Pignolet\, Executive assistant \n13.45-14.30 Flash talks  (3 minutes / 3 slides)  by naXys PhD students \n14.30-15.15 Design the research poles – SPACE | BIO | OPTICS | AI | ECO | ROBUST \n15.15-15.30 Feedback  \nCOFFEE BREAK (15.30 – 16.10) \n16.10-17.50 Interdisciplinary talks (15′ + 5′) by naXys post-docs and PI \n17.50-18.00 Conclusion \nCOCKTAIL DINNER (18.00) \nProgram\nFLASH TALKS  \n\nAlexandru Caliman\, Long-term stability of planetary systems\nArunima Sidker\, Stress echoes: how past environments shape population responses to future stress\nAntoine Hubermont\, Predictive maintenance as a multi label classification problem\nBaptiste Perez Riaza\, Empirical insights into crypto-assets using network inference\nCharles Modera\, Generation of High-Frequency Gravitational Waves Using Resonant Cavities\nDavoud Alahvirdi\, Traffic monitoring and management by swarm of drone\nFrançois-Grégoire Bierwart\, Koopman-based framework for stability analysis of dynamical systems\nJulien Pietquin\, Urban traffic networks with unmanned aerial vehicules\nLoic Warscotte\, Weighing vehicules with piezo material\nMarie Dorchain\, Turing patterns on higher-order structures\nMartin Moriamé\, Control of synchronization in Higher-order networks\nNemanja Antonic\, BABOTS: the design and control of biological animal robots\nNicolas Roy\, Surrogate-Assisted Heuristic Optimization in Photonic Device Engineering\nWilliams Dhelonga\, Probing the universe with the light sail or the Einstein Dirac fermions\nYun Li\, Biodiversity shifts mediate global change effects on trophic pyramids\n\n  \nINTERDISCIPLINARY TALKS \n\nAlexis Coyette\, JUICE – Constraining the interior of the Galilean Moons\nGonzalo Marcello Ramirez-Avila\, Modeling posible chronobiological strategies for improving radiotherapy treatments\nJean-Yves Gnabo\, Climate Risk Exposure : A Comparative Analysis of Sustainable and Conventional Funds\nMaxime Boucher\, On directional runs and their local and asymptotic properties\nMohammed Alkhateeb\, Tunneling time problem in relativistic quantum field theory
URL:https://www.naxys.be/event/naxys-research-day-2024/
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240613T130000
DTEND;TZID=Europe/Brussels:20240613T140000
DTSTAMP:20260407T003505
CREATED:20240516T101736Z
LAST-MODIFIED:20240524T131753Z
UID:2150-1718283600-1718287200@www.naxys.be
SUMMARY:Corbinian Schlösser (INRIA Paris)
DESCRIPTION:Title : Identifying low dimensional systems from high dimensional observations \nAbstract : Motivated by the increasing availability of motion data through multiple sensors and cameras\, we address the problem of identifying low-dimensional autonomous systems for which only high-dimensional measurements are observed. We do not assume prior knowledge on the latent dimension or its dynamics. However\, we assume that the observation map is injective which implies that the observations follow an autonomous system. This is our starting point for reducing a general and non-linear identification problem towards a (tractable) convex optimization problem. We discuss different obstacles that came across our route\, several limiting factors\, and situations for which our approach provides feasible solutions to the identification problem. This is joint and ongoing work with Francis Bach and Alessandro Rudi. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/corbinian-schlosser/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20240524
DTEND;VALUE=DATE:20240525
DTSTAMP:20260407T003505
CREATED:20240209T151207Z
LAST-MODIFIED:20240209T151207Z
UID:2102-1716508800-1716595199@www.naxys.be
SUMMARY:Interdisciplinary Training School for Doctoral students (EFID 2024)
DESCRIPTION:
URL:https://www.naxys.be/event/interdisciplinary-training-school-for-doctoral-students-efid-2024/
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240521T130000
DTEND;TZID=Europe/Brussels:20240521T140000
DTSTAMP:20260407T003505
CREATED:20240425T131125Z
LAST-MODIFIED:20240507T094101Z
UID:2143-1716296400-1716300000@www.naxys.be
SUMMARY:Williams Dhelonga (UNamur)
DESCRIPTION:Title : Exploring Weak measurements within the Einstein-Dirac Cosmological framework. \nAbstract : Our study applies the Two-State Formalism alongside weak measurements within a spatially homogeneous and isotropic cosmological framework\, wherein Dirac spinors are intricately coupled to classical gravity. To elucidate this\, we provide detailed formulations for computing the weak values of the energy-momentum tensors\, the Z component of spin\, and the characterization of pure states. Weak measurements appear to be a generalization and extension of the computation already made by Finster an Hainzl\, in A spatially homogeneous and isotropic Einstein-Dirac cosmology. Our analysis reveals that the acceleration of the Universe expansion can be understood as an outcome of postselection\, underscoring the effectiveness of weak measurement as a discerning approach for gauging cosmic acceleration. https://arxiv.org/abs/2405.02108 \n\nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/williams-dhelonga-unamur/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240425T130000
DTEND;TZID=Europe/Brussels:20240425T140000
DTSTAMP:20260407T003505
CREATED:20240212T203641Z
LAST-MODIFIED:20240408T104821Z
UID:2106-1714050000-1714053600@www.naxys.be
SUMMARY:Jean-François de Kemmeter (UNamur)
DESCRIPTION:Title : Random walks on networks with limiting nodes carrying capacities \nAbstract : \nOver the last years\, network science has emerged as an efficient tool to model complex systems composed of numerous interconnected entities. In particular\, the interplay between network structure and dynamics on networks has long been recognized as a cornerstone of network science and is at the core of various applications such as community detection. Among those dynamical processes on networks\, random walks are ubiquitous stochastic processes that describe\, in their “standard” formulation\, the displacement of an entity that hops from node to node following at random the available connections. \nIn this talk\, we will focus on a class of random walks in which multiple random walkers travel across the network under the constraint of limiting nodes carrying capacities\, a feature of most real-life networks. We will discuss how the outcomes of the dynamics differ from the “standard” random walk and depend on the network structure. \nThis is based on joint work with Malbor Asllani and Timoteo Carletti. \nMore information: https://arxiv.org/abs/2112.02549 https://arxiv.org/abs/2307.14083 \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/jean-francois-de-kemmeter-unamur/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240415T130000
DTEND;TZID=Europe/Brussels:20240415T140000
DTSTAMP:20260407T003505
CREATED:20240304T135013Z
LAST-MODIFIED:20240321T095121Z
UID:2117-1713186000-1713189600@www.naxys.be
SUMMARY:Benoît Bonnet-Weill (CNRS)
DESCRIPTION:Title : A Set-Valued Approach to Koopman Operators for Control Systems\n \nAbstract : In this talk\, I will present a new approach that we recently put forth together with Milan Korda (LAAS-CNRS) to define and study the properties of Koopman operators for general nonlinear control systems\, based on the theory of set-valued analysis. In this framework\, the Koopman operators at some given time are defined as the multi-mappings which\, to a given function observable\, associate the collection of its evaluations along all possible flows of the control systems. \nStarting from this general construct\, we were able to obtain relevant set-valued counterparts of all the basic results of Koopman theory\, namely the existence of an infinitesimal generator\, whose dynamics precisely encodes a rich subclass of observables\, an adapted version of the spectral mapping theorem relating their respective point spectra\, and a characterisation of the dual (also known as Perron-Frobenius) semigroup as a family of time-dependent operators acting on measures. \nBesides its conceptual soundness\, our approach provides theoretical grounding for a class of practical methods used for solving control problems by leveraging the Koopman framework\, which revolve around the idea of bundling together the classical Koopman operators stemming from a collection of fixed control inputs. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/benoit-bonnet-weill-cnrs/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240404T130000
DTEND;TZID=Europe/Brussels:20240404T140000
DTSTAMP:20260407T003505
CREATED:20231030T130708Z
LAST-MODIFIED:20240305T142426Z
UID:2051-1712235600-1712239200@www.naxys.be
SUMMARY:Valentin Delchevalerie (UNamur)
DESCRIPTION:Title : SO(2) and O(2) Equivariance in Image Recognition with Bessel-Convolutional Neural Networks \nAbstract : For many years\, it has been shown how much exploiting equivariances can be beneficial when solving image analysis tasks. For example\, the superiority of convolutional neural networks (CNNs) compared to dense networks mainly comes from an elegant exploitation of the translation equivariance. Patterns can appear at arbitrary positions and convolutions take this into account to achieve translation invariant operations through weight sharing. Nevertheless\, images often involve other symmetries that can also be exploited. It is the case of rotations and reflections that have drawn particular attention and led to the development of multiple equivariant CNN architectures. Among all these methods\, Bessel-convolutional neural networks (B-CNNs) exploit a particular decomposition based on Bessel functions to modify the key operation between images and filters and make it by design equivariant to all the continuous set of planar rotations\, and also include the incorporation of reflection and multi-scale equivariances. \nMore information: https://arxiv.org/abs/2304.09214  https://proceedings.neurips.cc/paper/2021/hash/f18224a1adfb7b3dbff668c9b655a35a-Abstract.html \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/valentin-delchevalerie-unamur/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240321T130000
DTEND;TZID=Europe/Brussels:20240321T140000
DTSTAMP:20260407T003505
CREATED:20240209T150814Z
LAST-MODIFIED:20240321T095156Z
UID:2098-1711026000-1711029600@www.naxys.be
SUMMARY:Jean-Charles Delvenne (UCLouvain)
DESCRIPTION:Title : Markov chains\, transport theory and statistical physics \nAbstract : \nWe look at the following motivating problem: how to move an electronic memory from a ‘zero’ state to a ‘one’ state\, at minimal energy cost?\n\nMathematically\, this amounts to design a Markov chain  that drives a certain probability measure (encoding a ‘zero’) towards another one (a ‘one’) through an ‘optimal’ path — an avatar of Gaspard Monge’s so-called ‘earth mover problem’\, at the core of transport theory.\n\n We explore various recent results and conjectures around this theme at the interface of statistical physics and Markov chain theory. We support these by illustrations on realistic simulations on electronic memories.\n\nThe seminar will exceptionally take place in Room S06 (and not S08) at the Faculty of Sciences.
URL:https://www.naxys.be/event/jean-charles-delvenne-uclouvain/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240314T130000
DTEND;TZID=Europe/Brussels:20240314T140000
DTSTAMP:20260407T003505
CREATED:20240122T163629Z
LAST-MODIFIED:20240301T100046Z
UID:2088-1710421200-1710424800@www.naxys.be
SUMMARY:Michaël Fanuel (Université de Lille)
DESCRIPTION:Title : Sparsification of the magnetic Laplacian with statistical guarantees \nAbstract : \n  \nLaplacian matrices are discrete analogues of Laplacian differential operators\, which have applications in several areas of applied mathematics such as network science\, machine learning\, control\, etc.\nA Laplacian matrix is in general associated with a graph.\nIn this talk\, we consider the problem of finding a controlled approximation of a Laplacian matrix — called a sparsifier — which only has a few non-zero entries.\nThis (sparse) matrix is associated with a graph with fewer edges\, and is often cheaper to inverse. \nMore specifically\, we consider a U(1)-connection graph\, that is\, a graph where each oriented edge is endowed with a unit modulus complex number which is simply conjugated under orientation flip. A natural replacement for the usual graph Laplacian is then the so-called magnetic Laplacian\, a Hermitian matrix which includes information about the graph’s connection. Connection graphs and magnetic Laplacians appear\, e.g.\, in the problem of angular synchronization (signal processing).In the context of large and dense graphs\, we study spectral sparsifiers of the magnetic Laplacian\, i.e.\, spectral approximations based on subgraphs with few edges. Our approach relies on sampling variants of spanning forests using a custom determinantal point process\, a distribution over edges that favours diversity (and which originates from quantum physics).\nIn a word\, the connected components of our spanning forests are either trees or cycle-rooted trees. The latter partially capture the angular inconsistencies of the connection graph\, and thus provide a way to compress information contained in the connection.\nOne of our contributions is to provide statistical guarantees for a choice of natural estimators of the connection Laplacian based on batches of spanning forests. \nInterestingly\, when the connection graph has weakly inconsistent cycles\, samples of this distribution can be obtained by using a loop-erased random walk.\nThis sampling algorithm is called CyclePopping and is actually rather performant in practice. The law of the number of steps to complete CyclePopping is also known exactly if the connection graph has weakly inconsistent cycles.\nWe shall briefly discuss our contribution in the analysis of this algorithm. \nThis is a joint work with Rémi Bardenet (CNRS & ULille) https://arxiv.org/abs/2208.14797. \n\nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/michael-fanuel-universite-de-lille/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240229T130000
DTEND;TZID=Europe/Brussels:20240229T140000
DTSTAMP:20260407T003505
CREATED:20231115T130540Z
LAST-MODIFIED:20240223T080934Z
UID:2060-1709211600-1709215200@www.naxys.be
SUMMARY:Morine Delhelle (UCLouvain)
DESCRIPTION:Title : Copula based dependent censoring in cure models with covariates \nAbstract : In survival data analysis\, datasets with both a cure fraction (individuals who will never experience the event of interest) and dependent censoring (loss to follow-up for a reason related to the event of interest before the occurrence of that event) are not scarce\, and appropriate models and methods must be considered to avoid biased estimators of the survival function or incorrect conclusions in clinical trials. Delhelle and Van Keilegom proposed a fully parametric model for the bivariate distribution of survival (T) and censoring (C) times\, that takes these features into account. The model depends on a parametric copula (with an unknown association parameter) and on parametric marginal distributions for T and C. An advantage is that it allows one to estimate the strength of the dependence and the cure rate. \n\n\n\nThis talk presents an improvement of this model. Administrative censoring is considered separately from dependent censoring\, and covariates are included in the model. \n\n\n\nAuthors : Morine Delhelle (Institute of Statistics\, Biostatistics and Actuarial Science\, UCLouvain\, Belgium) and Ingrid Van Keilegom (ORSTAT\, KU Leuven\, Belgium) \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/morine-delhelle-uclouvain/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20240208
DTEND;VALUE=DATE:20240209
DTSTAMP:20260407T003505
CREATED:20231114T111145Z
LAST-MODIFIED:20231114T111145Z
UID:2058-1707350400-1707436799@www.naxys.be
SUMMARY:Women and Girls in Science
DESCRIPTION:The International Day of Women and Girls in Science takes place every 11th of February\, following the declaration by the General Assembly of the United Nations on 22nd of December 2015. \nThis annual event aims at promoting the access of women and girls to science and technology as well as their full and fair participation. It reminds the important role of women in the scientific community and constitutes a great opportunity to encourage girls and young women to participate in the scientific developments.
URL:https://www.naxys.be/event/women-and-girls-in-science/
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20240201T130000
DTEND;TZID=Europe/Brussels:20240201T140000
DTSTAMP:20260407T003505
CREATED:20240122T162902Z
LAST-MODIFIED:20240209T151004Z
UID:2085-1706792400-1706796000@www.naxys.be
SUMMARY:Johan Barthélemy (University of Wollongong\, NVIDIA)
DESCRIPTION:Title : Accelerating Simulations with NVIDIA Modulus \nAbstract : High-fidelity simulations in science and engineering are computationally expensive and time-prohibitive for quick iterative use cases\, from design analysis to optimization. \nNVIDIA Modulus\, the open source physics machine learning platform\, turbocharges such use cases by building physics-based deep learning models that are order of magnitudes. faster than traditional methods and offer high-fidelity simulation results.  Once trained\, the model can perform quick forward passes\, making it ideal for applications that demand fast responses\, such as real-time simulations of large complex systems. \nModulus is a offers a suite Physics-ML model architectures\, including Fourier neural operators. It provides an end-to-end pipeline for training models\, from geometry ingestion to training and inference\, with explicit parameter specifications for a wide range of applications.  The framework is also integrated with NVIDIA Omniverse for enhanced visualization and is tailored for high-performance\, leveraging technologies for multi-GPU computing and multinode scaling. \nThis seminar will present the key features\, use cases\, and performance aspects of NVIDIA Modulus\, providing attendees with a understanding of its capabilities and applications. \nThe seminar will take place in Room S07 at the Faculty of Sciences.
URL:https://www.naxys.be/event/johan-barthelemy-university-of-wollongong-nvidia/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20231214T130000
DTEND;TZID=Europe/Brussels:20231214T140000
DTSTAMP:20260407T003505
CREATED:20231025T110858Z
LAST-MODIFIED:20240209T151012Z
UID:2042-1702558800-1702562400@www.naxys.be
SUMMARY:André Füzfa (UNamur)
DESCRIPTION:Title: Fundamentals of relativistic astrodynamics and rocketry \nAbstract: \nAstrodynamics traditionally denotes the study of controlled flight paths of human-made spacecraft (Kaplan\, 1976). This term originates from the prehistory of the space age\, at a time where only archaic Newtonian dynamics were used for determining interplanetary spaceflights at extremely low velocities (in the km/s range). \nAfter briefly reviewing basic rocketry in this primitive language\, we will introduce space cadets to the modern geometric formalism that is now state-of-the-art for interstellar navigation. Relativistic trajectories in curved space-time are described by non-geodesic worldlines of particles submitted to the action of an external four-force. We will show how to use your relativistic inertial guidance system to monitor the evolution of both the rest mass of your starship and the apparent weight inside it\, through the space-time orientation of the total four-force. Then\, several well-known models of deep space propulsion will be reviewed: Ackeret’s rocket and the relativistic Tsiolkowsky equation\, thermal and radiation rockets\, Bussard’s ramjet and finally lightsails. We will end the course by two relativistic astrodynamical applications : basic interstellar transfer and ascent trajectories from a compact object. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/andre-fuzfa-unamur/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20231109T130000
DTEND;TZID=Europe/Brussels:20231109T140000
DTSTAMP:20260407T003505
CREATED:20230915T093744Z
LAST-MODIFIED:20231025T111007Z
UID:2017-1699534800-1699538400@www.naxys.be
SUMMARY:Tamas Kovács (Institute of Physics\, Eötvös University\, Hungary)
DESCRIPTION:Title: Stability of exoplanetary systems retrieved from scalar time series \nAbstract: In this talk I propose a novel method applied to extrasolar planetary dynamics to describe the system stability. The observations in this field serve the measurements mainly of radial velocity\, transit time\, and/or celestial position. These scalar time series are used to reconstruct the high-dimensional phase space trajectory representing the dynamical evolution of planetary motion. The framework of nonlinear time series analysis and Poincaré recurrences allows us to transform the obtained univariate signals into complex networks whose topology carries the dynamical properties of the underlying system. The proposed scheme does not require neither n-body integration nor best fitting planetary model to perform the stability investigation\, therefore\, the computation time can be reduced drastically compared to those of the standard numerical methods. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/tamas-kovacs-institute-of-physics-eotvos-university-hungary/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20231026T130000
DTEND;TZID=Europe/Brussels:20231026T140000
DTSTAMP:20260407T003505
CREATED:20230925T085126Z
LAST-MODIFIED:20231025T110943Z
UID:2020-1698325200-1698328800@www.naxys.be
SUMMARY:Guillermo Garcia-Sanchez (Spanish National Research Council\, Spain)
DESCRIPTION:Title: From Chaos to Clarity: Revealing Oceanic Transport Pathways In Real-World Applications Through Dynamical Systems \nAbstract: Finding order in the apparent chaos that seems to govern transport processes in the ocean is a challenge. Dynamical system tools\, such as Lagrangian Descriptors reveal time dependent geometries in the ocean that comprise an efficient underlying transport network. In this talk\, I will show how these theoretical approaches are now being applied to address various marine problems\, including oil spills\, harmful algae\, marine litter and search and rescue operations\, bridging the gap between academic theory and real-world applications. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/guillermo-garcia-sanchez-spanish-national-research-council-spain/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20231019T130000
DTEND;TZID=Europe/Brussels:20231019T140000
DTSTAMP:20260407T003505
CREATED:20231009T120842Z
LAST-MODIFIED:20231025T110924Z
UID:2028-1697720400-1697724000@www.naxys.be
SUMMARY:Stefanella Boatto (Federal University of Rio de Janeiro)
DESCRIPTION:Title: Vortex and gravitational modeling : A long journey with a rich mathematical history \nAbstract: \nVortex and gravitational dynamics have long fascinating and interwoven histories\, both for the modeling and for the different areas of mathematics needed to study the corresponding models. Philosophical questions reside behind the modeling part\, as for example how do we define gravity beyond our Euclidean R3 perception? \nAre the laws we are so familiar with\, universal ? What is the geometry of our universe? As for vortices within the boundary of our Solar systems we witness fascinating images of vortex dynamics. Recent beautiful observations of polygonal configurations of vortices present in the atmosphere of Jupiter and Saturn\, and of polygonal jets in the Earth’s atmosphere have revived the interest in the subject. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/stefanella-boatto-federal-university-of-rio-de-janeiro/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230630T130000
DTEND;TZID=Europe/Brussels:20230630T140000
DTSTAMP:20260407T003505
CREATED:20230602T080740Z
LAST-MODIFIED:20230602T080740Z
UID:2011-1688130000-1688133600@www.naxys.be
SUMMARY:Enoch Yeung (UC Santa Barbara (UCSB)\, USA)
DESCRIPTION:Title: Data-Driven State Criticality and Observability with Koopman\nOperator Methods \nAbstract: I will present two major results to show the use of data-\ndriven Koopman methods to identify critical states and observable\nsubspaces to solve problems in synthetic biology. In the first\, I\npresent the use of dynamic mode decomposition (DMD) to model the\ntranscriptome-wide response of a root-isolate bacterium to a novel\nchemical compound. By solving an observability maximization problem\nfor the DMD model\, we find a panel of biomarkers that can act as\neffective biosensors for the compound\, even in field studies with the\nbacterium. This study establishes a new precedent for reasoning about\nstate criticality and system observability\, even without prior\nknowledge of a network model. Second\, I present new theoretical\nresults that show how Koopman methods can be used to evaluate\ncriticality of states to optimize performance of a nonlinear system.\nHistorically\, this problem is solved using either direct sensitivity\nanalysis on a known model or by generating local function\ndistributions that span the nonlinear observable subspace of a system.\nIn the absence of a known model\, I present a new Koopman-based method\nfor estimating the observable subspace of a nonlinear system purely\nfrom data. Our results provide a route for data-driven discovery of\ncritical states that affect an output-based performance measure. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/enoch-yeung-uc-santa-barbara-ucsb-usa/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230601T130000
DTEND;TZID=Europe/Brussels:20230601T140000
DTSTAMP:20260407T003505
CREATED:20230330T132110Z
LAST-MODIFIED:20230516T122104Z
UID:1994-1685624400-1685628000@www.naxys.be
SUMMARY:Ludovic Ducobu (Transilvania University of Brasov\, Romania)
DESCRIPTION:Title: Compact objects and scalar fields in theories of gravity with torsion\, ep. 1 : modelisation \nAbstract:  \nGeneral Relativity [GR] offers an extremely successful framework to describe the gravitational interaction. That being said\, the necessity to question the framework of GR is clear at both the experimental (origin and composition of dark matter and dark energy) and theoretical (search for quantum gravity) levels.\nSince not all these puzzles can be purely reduced to quantum correction problems\, this motivates the study of alternative theories of gravitation already at the classical level.\n\nTo this purpose\, one can follow two distinct but complementary routes. On the one hand\, one can try to modify Einstein’s equations by introducing new fields while maintaining the assumptions related to the geometrical structure of spacetime. On the other hand\, one can precisely question the framework of pseudo-Riemannian geometry as being adapted to the full description of spacetime (typically\, at cosmological scales).\nIn the first case\, scalar-tensor theories of gravity (and especially Horndeski gravity)\, where the new degrees of freedom are encoded by means of a scalar field\, have been extensively investigated in the litterature.\nIn the later case\, a minimal generalisation of GR’s framework consist in relaxing the hypothesis linking the connection to the metric\, leading to the framework of metric-affine gravity. This reveals new starting points to generalise GR through\, for instance\, an examination of the so-called geometrical trinity of gravity.\n\nThe aim of this talk is to present the main motivations and features of modified theories of gravity involving scalar fields in both the usual (GR) and metric-affine approaches.\n\nI will first propose a quick overview of Horndeski gravity and of the metric-affine approach of GR; focussing on the so-called Teleparallel theories of gravity and on the Teleparallel equivalent to GR.\nThen\, “unifying” the two approaches\, I will advocate for the interest of modified theories of gravity involving scalar fields in the metric-affine framework.\nI will then present recent results from my own research and discuss the first study of assymptotically flat black holes endowed with scalar hair in a teleparallel generalisation of Horndeski gravity.\nOur study provides an explicit demonstration of how scalar-torsion gravity (and possibly other non-Riemaniann models) provides a richer canvas for the study of phenomenology beyond GR and open the way for novel studies regarding scalarized black hole solutions in non-Riemannian theories of gravity.\n\nThis presentation is based on the work done in [arXiv:2201.11445 [gr-qc]] (https://arxiv.org/abs/2201.11445) and [arXiv:2212.07653 [gr-qc]] (https://arxiv.org/abs/2212.07653) in collaboration with Sebastian Bahamonde\, Daniela Doneva\, Christian Pfeifer and Stoytcho Yazadjiev.\n\n\n\nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/ludovic-ducobu/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230425T130000
DTEND;TZID=Europe/Brussels:20230425T140000
DTSTAMP:20260407T003505
CREATED:20230221T091059Z
LAST-MODIFIED:20230327T154511Z
UID:1950-1682427600-1682431200@www.naxys.be
SUMMARY:Daniele Avitabile (Vrije Universiteit Amsterdam\, The Netherlands)
DESCRIPTION:Title: Bump Attractors and Waves in Networks of Integrate-and-Fire Neurons\n\nAbstract: Bump attractors are localised patterns observed in in vivo experiments of neurobiological networks. They are important for the brain’s navigational system and specific memory tasks. A bump attractor is characterised by a core in which neurons fire frequently\, while those away from the core do not fire. We uncover a relationship between bump attractors and travelling waves in a classical network of excitable\, leaky integrate-and-fire neurons. This relationship bears strong similarities to the one between complex spatiotemporal patterns and waves at the onset of pipe turbulence. We define and study analytical properties of the voltage mapping\, an operator transforming a solution’s firing set into its spatiotemporal profile. This operator allows us to construct localised travelling waves with an arbitrary number of spikes at the core\, and to study their linear stability. A homogeneous “laminar” state exists in the network\, and it is linearly stable for all values of the principal control parameter. We show that one can construct waves with a seemingly arbitrary number of spikes at the core; the higher the number of spikes\, the slower the wave\, and the more its profile resembles a stationary bump. As in the fluid-dynamical analogy\, such waves coexist with the homogeneous state\, are unstable\, and the solution branches to which they belong are disconnected from the laminar state. We provide evidence that the dynamics of the bump attractor displays echoes of the unstable waves.\n\n\nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/daniele-avitabile-vrije-universiteit-amsterdam-the-netherlands/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230420T130000
DTEND;TZID=Europe/Brussels:20230420T140000
DTSTAMP:20260407T003505
CREATED:20230316T134633Z
LAST-MODIFIED:20230417T081156Z
UID:1980-1681995600-1681999200@www.naxys.be
SUMMARY:Philippe Naveau (Laboratoire des Sciences du Climat et de l'Environnement (LSCE) CNRS\, France)
DESCRIPTION:Title: Records Analysis in Climate Attribution \nAbstract: Numerical climate models are complex and combine a large number of physical processes. They are key tools in quantifying the relative contribution of potential anthropogenic causes (e.g.\, the current increase in greenhouse gases) on high-impact atmospheric variables like heavy rainfall or temperatures. These so-called climate extreme event attribution problems are particularly challenging in a non-stationary context. In addition\, global climate models like any in sillico numerical experiments are affected by different types of bias. In this talk\, I will discuss about how to combine to different statistical concepts to assess records changes in the context of extreme event attribution. In addition\, the question of uncertainties quantification that remains a challenge in any climate attribution analysis will be explored from various directions. In particular\, a simple model bias correction step for records will described in detail. To illustrate our approach\, we infer emergence times in precipitation from the CMIP5 and CMIP6 archives. This is joint work with Paula Gonzalez\, Soulivanh Thao and Julien Worms. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/philippe-naveau-laboratoire-des-sciences-du-climat-et-lenvironnement-lsce-cnrs-france/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20230417
DTEND;VALUE=DATE:20230420
DTSTAMP:20260407T003505
CREATED:20230221T093113Z
LAST-MODIFIED:20230221T093332Z
UID:1952-1681689600-1681948799@www.naxys.be
SUMMARY:Francqui Chair 2022-2023
DESCRIPTION:On topology and higher–order dynamics of networks and simplicial complexes \nGuest lecturer: Prof. Ginestra Bianconi\, Queen Mary University London and the Alan Turing Institute (UK) \nProgram: \n* Inaugural lecture\, “Topology shapes higher–order network dynamics”\, Monday\, April 17th 2023\, at 17:00\, Auditorium PA02 \nNext lectures\, room S09 \n* Tuesday 18/4/23\, 10:40 – 12:40 Introduction to simplicial complexes and algebraic topology\, 14:00 – 16:00 Topological Synchronization \n* Wednesday 19/04/23\, 10:40 – 12:40 The Dirac operator on networks and simplicial complexes\, 14:00 – 16:00 Higher–order network dynamics driven by the Dirac operator \nWe invite you to register by March the 31st 2023 following this link. \nThe lectures address Master students\, PhD and researchers interested in dynamical systems\, synchronisation\, network science and high-order models and their interactions. \nPhD students can receive credits for their attendance upon request (please check the box in the registration form).
URL:https://www.naxys.be/event/francqui-chair-2022-2023/
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230413T130000
DTEND;TZID=Europe/Brussels:20230413T140000
DTSTAMP:20260407T003505
CREATED:20230202T103702Z
LAST-MODIFIED:20230202T103828Z
UID:1942-1681390800-1681394400@www.naxys.be
SUMMARY:Hilda A. CERDEIRA (Instituto de Física Teórica\,  UNESP\,  São Paulo\, Brazil)
DESCRIPTION:Title: Phase transition to Synchronization in a system of Swarmalators \nAbstract: Systems of oscillators called Swarmalators\,whose phase and spatial dynamics are coupled\, have been used to describe the dynamics of some living systems. Their collective behavior presents simultaneous aggregation in space and synchronization in phase which in turn leads in some cases to explosive synchronization in a finite population as a function of the coupling parameter between the phases of the internal dynamics. This phenomenon is described using the order parameter and the Hamiltonian formalism. Near the synchronization transition the phase energy of the particles are represented by the XY model\, and they undergo a transition which can be of the first order or second depending on the distribution of natural frequencies of the internal dynamics of the swarmalators. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/hilda-a-cerdeira-instituto-de-fisica-teorica-unesp-sao-paulo-brazil/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230406T130000
DTEND;TZID=Europe/Brussels:20230406T140000
DTSTAMP:20260407T003505
CREATED:20230403T135709Z
LAST-MODIFIED:20230403T135709Z
UID:1996-1680786000-1680789600@www.naxys.be
SUMMARY:Fabian Bastin (University of Montreal (Canada)) - Cinzia Cirillo (University of Maryland (USA))
DESCRIPTION:Title: Large-scale transport model systems: from synthetic population generation to agent-based simulation \nAbstract:  \n1. Generation of synthetic populations exploiting dependency structure transfer (Fabian Bastin) \nThe generation of synthetic populations consists of producing a realistic representation of a target population for modeling and behavioral simulation purposes\, a task that can be tricky when the available multivariate samples are small. Starting from the idea that combining various sources of information makes it possible to design more realistic population generators\, we introduce a new framework based on copulas to generate synthetic data for a population whose only empirical marginal distributions are known\, using a sample from another population sharing a similar dependency structure. We compare the proposed scheme to common methods such as Iterative Proportional Fitting and to modern probabilistic approaches such as Bayesian networks\, variational auto-encoders and generative adversarial networks. We illustrate on American Community Survey data that the method proposed allows to study the structure of the data at different geographical levels in a way that is robust to the peculiarities of the marginal distributions.  \n2. Large scale transportation model systems: an agent-based simulator for the State of Maryland (Cinzia Cirillo) \nThe talk will introduce the architecture of a large-scale microsimulation model that combines population synthesis\, land use models\, transportation choices\, and agent-based transport simulation. This modeling suite overcomes limitations of aggregate four step models and is completely open source. Application of this type of tools will be illustrated in the context of transportation and equity; the first considers the problem of evacuating low-income carless populations during an emergency\, the second evaluates the effects of complete streets on the willingness to walk and bike under different levels of traffic stress. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/fabian-bastin-university-of-montreal-canada-cinzia-cirillo-university-of-maryland-usa/
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Brussels:20230316T130000
DTEND;TZID=Europe/Brussels:20230316T140000
DTSTAMP:20260407T003505
CREATED:20230106T130440Z
LAST-MODIFIED:20230224T113926Z
UID:1883-1678971600-1678975200@www.naxys.be
SUMMARY:Lorena Ballesteros Ferraz (University of Namur)
DESCRIPTION:Title: Geometrical and non–normal properties of weak values \nAuthors: Lorena Ballesteros Ferraz\, Dominique Lambert\, Timoteo Carletti\, Riccardo Muolo\,and Yves Caudano \nAbstract: Quantum measurements are essential to all quantum experiments and are key to developing new quantum technologies. In particular\, weak measurements have attracted much interest\, for both theoretical and experimental reasons. When performing a weak measurement with preselection (which consists of choosing the initial state) and post–selection (which requires a projective measurement after the weak measurement and corresponds to choosing the final state)\, weak values appear. In that case\, the ancilla’s wavefunction is shifted in position by a quantity that is proportional to the real part of the weak value.  \nIts wavefunction is also shifted in momentum by a quantity that is proportional to the imaginary part of the weak value. Even though weak values are regularly studied in terms of their real and imaginary parts\, we focus our analysis in terms of their modulus and argument. In this work\, we have studied the geometrical interpretation of the argument of weak values of general observables in N–level systems. This argument corresponds to a geometric phase (Berry phase) that is associated to the symplectic area generated by the geodesic triangle spanned by the three normalized vectors representing the initial state\, the application of the observable over the initial state and the postselected state. These vectors represent quantum pure states in complex projective space CP^(N–1) and they can be mapped to a subspace of the (𝑁² − 2)–sphere\, a generalization of the Bloch sphere (the usual S² sphere\, used to describe qubits).  \nThe argument of the weak value of an N–level system observable can also be mapped to the sum of N–1 arguments of weak values of two–level projectors up to a phase that specifies the quadrant. Each of these arguments is associated to the solid angle on the Bloch sphere spanned by three vectors representing the pre–selected state\, the observable and the post–selected state. To obtain this decomposition\, we employ the Majorana representation to factor the weak value of the N–level system observable into the product of N–1 weak values of qubit projectors and a real constant. \nStudying the modulus of the weak value provides information on the ability of weak values toamplify minute phenomena as well as their role in improving the estimation of small physicalparameters. Weak values can be written as the expectation value of a non–normal operator.Investigating the non–normal properties of the operator\, we found a direct link with theamplitude of the modulus of the weak value. This paves the way for a deeper understanding of these values from an energetics point of view and links the fields of weak measurements and non–normality. \nThe seminar will take place in Room S08 at the Faculty of Sciences.
URL:https://www.naxys.be/event/lorena-ballesteros-ferraz-university-of-namur/
CATEGORIES:NAXYS Seminar
END:VEVENT
END:VCALENDAR