S³: Material-by-Design for Synthesis, Modeling, and Simulation of Innovative Systems and Devices

Séminaire le 30 Septembre 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Giacomo Oliveri (ELEDIA, University of Trento)


Several new devices and architectures have been proposed in the last decade to exploit the unique features of innovative artificially-engineered materials (such as metamaterials, nanomaterials, biomaterials) with important applications in science and engineering. In such a framework, a new set of techniques belonging to the Material-by-Design (MbD) framework [1]-[5] have been recently introduced to synthesize innovative devices comprising task-oriented artificial materials. MbD is an instance of the System-by-Design paradigm [6][7] defined in short as “How to deal with complexity”. More specifically, MbD considers the problem of designing artificial-material enhanced-devices from a completely new perspective, that is "The application-oriented synthesis of advanced systems comprising artificial materials whose constituent properties are driven by the device functional requirements". The aim of this seminar will be to review the fundamentals, features, and potentialities of the MbD paradigm, as well as to illustrate selected state-of-the-art applications of this design framework in sensing and communications scenarios.

Bio: Giacomo Oliveri received the B.S. and M.S. degrees in Telecommunications Engineering and the PhD degree in Space Sciences and Engineering from the University of Genoa, Italy, in 2003, 2005, and 2009 respectively. He is currently an Tenure Track Associate Professor at the Department of Information Engineering and Computer Science (University of Trento), Professor at CentraleSupélec, member of the Laboratoire des signaux et systèmes (L2S)@CentraleSupélec, and member of the ELEDIA Research Center. He has been a visiting researcher at L2S, Gif-sur-Yvette, France, in 2012, 2013, and 2015, and he has been an Invited Associate Professor at the University of Paris Sud, France, in 2014. In 2016, he has been awarded the "Jean d'Alembert" Scholarship by the IDEX Université Paris-Saclay. He is author/co-author of over 250 peer-reviewed papers on international journals and conferences, which have been cited above 2200 times, and his H-Index is 26 (source: Scopus). His research work is mainly focused on electromagnetic direct and inverse problems, system-by-design and metamaterials, compressive sensing techniques and applications to electromagnetics, and antenna array synthesis. Dr. Oliveri serves as an Associate Editor of the International Journal of Antennas and Propagation, of the Microwave Processing journal, and of the International Journal of Distributed Sensor Networks. He is the Chair of the IEEE AP/ED/MTT North Italy Chapter.

Some results on the existence of equilibria and stability of dc linear networks with constant power loads.

Séminaire le 13 Juillet 2016, 11h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Prof. Robert Griñó, Polytechnic University of Catalonia


The presentation will show some results on the existence of equilibria in dc electrical networks that supply to constant power loads (CPLs). Specifically, a necessary condition for the existence, which is also sufficient for the case one and two CPLs, will be presented. Besides, a sufficient condition, based on the negative imaginary systems concept, that assures local stability for all the range of possible equilibria will be shown for the case of a dc linear network with a single ideal or finite-bandwidth CPL.

Singular perturbations for hyperbolic port-Hamiltonian and non-hyperbolic systems

Séminaire le 13 Juillet 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Prof. Jacquelien Scherpen, University of Groningen


In this talk we explore the methodology of model order reduction based on singular perturbations for a fexible-joint robot within the port-Hamiltonian framework. We show that a fexible-joint robot has a port-Hamiltonian representation which is also a singularly perturbed ordinary differential equation. Moreover, the associated reduced slow subsystem corresponds to a port-Hamiltonian model of a rigid-joint robot. To exploit the usefulness of the reduced models, we provide a numerical example where an existing controller for a rigid robot is implemented. In addition, we provide ideas on how to expand this to planar slow-fast systems at a non-hyperbolic point.  At these type of points, the classical theory of singular perturbations is not applicable and new techniques need to be introduced in order to design a controller that stabilizes such a point. We show for some class of nonlinear systems that using geometric  desingularization (also known as blow up), it is possible to design, in a simple way, controllers that stabilize non-hyperbolic equilibrium points of slow-fast systems. The results are exemplified on the Van der Pol oscillator.

The Appointment Scheduling Problem: The Doctor, Her Patients and The Waiting Room

Séminaire le 8 Juillet 2016, 14h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Prof. Stijn De Vuyst, Ghent University (UGent), Belgium.


We consider the appointment scheduling problem in the case of one doctor who sequentially provides service to the patients in the waiting room, in particular with respect to the incurred waiting times for both the patients and the doctor. This problem is different from a classical single-service queueing system in at least two ways: (1) the arrivals happen at pre-determined instants instead of randomly and (2) equilibrium solutions are of no use here since we need to know the waiting time of each individual patient. Given the length of the session and the consultation time distribution of each of K scheduled patient, we obtain the moments of the patient's waiting time and of the doctor's idle times. We also discuss the complicating factors such as the impact of unpunctuality, i.e. what happens if patients do not arrive exactly as appointed as usually the case in practice. A mild degree of unpunctuality can be handled by our model, but problems arise as soon as patients can overtake each other. Finally, we use the our results to construct suitable heuristics for finding optimal optimal appointment schedules.

Biography: Stijn De Vuyst is currently assistant professor at the Faculty of Engineering and Architecture of Ghent University (UGent), Belgium, in the Department of Industrial Systems Engineering and Product Design. His expertise is in operations research, in particular stochastic modelling, simulation, queueing theory and scheduling with application to the design, planning and performance evaluation of production systems as well as telecommunication systems. He obtained a master degree in Electrical Engineering and a PhD degree in Engineering Sciences at Ghent University. Prior to 2012, he was a post-doctoral researcher affiliated with the department of Telecommunication and Information Processing and for 6 months with the Informatics department at Université Libre de Bruxelles. From 2012 to 2015 he presided the faculty's educational board for the Master program Industrial Engineering and Operations Research. He currently teaches various courses on stochastic simulation, quality engineering and industrial statistics.

Almost Lossless Variable-Length Source Coding on Countably Infinite Alphabets

Séminaire le 8 Juillet 2016, 14h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Prof. Jorge F. Silva, University of Chile, Santiago.


Motivated from the fact that universal source coding on countably infinite alphabets is not feasible, in this talk a notion of almost lossless source coding will be introduced.  This idea —analog to the  weak variable-length source coding proposed by Han 2000— aims at relaxing the lossless block-wise assumption to allow a distortion that vanishes asymptotically as the block-length goes to infinity.  In this almost lossless coding setting, new source coding results will be presented that on one hand show that Shannon entropy characterizes the minimum achievable rate (known statistics), while on the other,  that almost lossless universal source coding becomes feasible for the family of finite entropy stationary and memoryless sources with countably infinite alphabets.

Biography: Jorge F. Silva is Associate Professor at the Electrical Engineering Department and director of the Information and Decision Systems (IDS) Group at the University of Chile, Santiago, Chile. He received the Master of Science (2005) and Ph.D. (2008) in Electrical Engineering from the University of Southern California (USC). He is IEEE member of the Signal Processing and Information Theory Societies and he is associate editor of the  IEEE Transactions on Signal Processing.  Dr. Silva is recipient of the Viterbi Doctoral Fellowship  2007–2008 and Simon Ramo Scholarship 2007–2008 at USC.   Dr. Silva general research interests include: detection and estimation, information theory and statistics, universal source coding, sparse and compressible models and  compressed sensing.

Topological Interference Management

Séminaire le 28 Juin 2016, 14h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Dr Syed Ali Jafar


Abstract:

Studies of the degrees of Freedom (DoF) of wireless communication networks often focus on clever ways to exploit an abundance of channel knowledge which is rarely available in practice while ignoring topological aspects that are the basis of most robust interference management schemes. Topological interference management refers to a complementary perspective where the focus is on exploiting network topology under limited channel knowledge. Progress in this direction includes the discovery that optimal interference avoidance is essentially the index coding problem, that interference alignment plays a central role in this problem even though no precise knowledge of channel realizations is available, a new set of conditions for the approximate optimality of treating interference as noise, novel outer bounds based on aligned image sets, and connections to network coding problems such as distributed storage repair, multiple unicasts and private information retrieval. This talk will summarize the advances in the broad area of topological interference management and highlight some of the key open problems.

Biography:

Syed Ali Jafar received his B. Tech. from IIT Delhi, India, in 1997, M.S. from Caltech, USA, in 1999, and Ph.D. from Stanford, USA, in 2003, all in Electrical Engineering. His industry experience includes positions at Lucent Bell Labs, Qualcomm Inc. and Hughes Software Systems. He is a Professor in the Department of Electrical Engineering and Computer Science at the University of California Irvine, Irvine, CA USA. His research interests include multiuser information theory, wireless communications and network coding.

Dr. Jafar received the Blavatnik National Laureate in Physical Sciences and Engineering in 2015, the UCI Academic Senate Distinguished Mid-Career Faculty Award for Research in 2015, the School of Engineering Mid-Career Excellence in Research Award in 2015, the School of Engineering Maseeh Outstanding Research Award in 2010, the ONR Young Investigator Award in 2008, and the NSF CAREER award in 2006. His co-authored papers received the IEEE Information Theory Society Best Paper Award in 2009, IEEE Communications Society Best Tutorial Paper Award in 2013, IEEE Communications Society Heinrich Hertz Award in 2015, IEEE Signal Processing Society Young Author Best Paper Award (to student co-authors) in 2015, an IEEE GLOBECOM Best Paper Award in 2012 and an IEEE GLOBECOM Best Paper Award in 2014. Dr. Jafar received the UC Irvine EECS Professor of the Year award five times, in 2006, 2009, 2011, 2012, and 2014, from the Engineering Students Council and the Teaching Excellence Award in 2012 from the School of Engineering. He was a University of Canterbury Erskine Fellow in 2010 and an IEEE Communications Society Distinguished Lecturer for 2013-2014. Dr. Jafar was recognized as a Thomson Reuters Highly Cited Researcher and included by Sciencewatch among The World's Most Influential Scientific Minds in 2014 and again in 2015. He served as Associate Editor for IEEE Transactions on Communications 2004-2009, for IEEE Communications Letters 2008-2009 and for IEEE Transactions on Information Theory 2009-2012. Dr. Jafar was elevated to IEEE Fellow, Class of 2014, for contributions to analyzing the capacity of wireless communication networks.

A Delay-Based Sustained Oscillator : Oregonator Based Model

Séminaire le 14 Juin 2016, 15h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Hakki Ulas UNAL (L2S, Anadolu University)


Many metabolic and  physiological processes occur in some periodic fashion. The phenomena has been known for a long time,  however, the underlying mechanism of such oscillatory behaviour has not been  fully understood.  Belousov-Zhabotinskii reaction, which exhibits oscillatory behaviour that are analogous to ones observed in certain biological systems, is often utilized to better understand the  oscillatory mechanism in  these systems. The reaction is very complicated, however, its oscillatory behaviour is described by a simple model, called Oregonator.  By the mass-action kinetics, the model can be described  by three  variables, which correspond to concentration of some chemical reactants.  In this talk,  delay-based Oregonator model obtained by the use of delay-mass-action kinetics will  be discussed. Some qualitative analysis on the  model will also be presented.

Mass-Action Kinetic Models

Séminaire le 14 Juin 2016, 14h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
VijaySekhar Chellaboina, (Mahindra Ecole Centrale)


In this talk, we present a general construction of the mass-action kinetic equations in a state-space form. Next, we discuss the nonnegativity of solutions to the kinetic equations and the inverse problem of constructing a reaction network having specified essentially non- negative dynamics. The problem of reducibility of the kinetic equations is next considered as well as the stability of the equilibria of the kinetic equations. Specifically, Lyapunov methods are employed to show boundedness and convergence of solutions. Finally, the zero deficiency result for mass-action kinetics in standard matrix terminology is presented.

Séminaire d'Automatique du Plateau de Saclay : Robust perfomance by a stable controller for infinite-dimensional plants

Séminaire le 8 Juin 2016, 11h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Hakki Ulas Unal (Anadolu University)


In a feedback system, besides the stabilization, the controllers are often designed to meet some performance specifications defined by H∞ norm minimization of corresponding sensitivity functions. From the practical point of view, if it is possible, it is desired the controller to be designed is stable. In this work, stable controller design to minimize the H∞ norm of the corresponding sensitivity function in a feedback system with a single-input single-output biproper infinite-dimensional real plant is considered. The plant may have infinitely many poles and simple zeros in the right-half-plane, however, its zeros are assumed to satisfy some growth condition. Interpolation-based approach will be used to design such a controller and a numerical example will be presented.

Séminaire d'Automatique du Plateau de Saclay :On Control Lyapunov-Krasovskii Functionals and Stabilization in the Sample-and-Hold Sense of Nonlinear Time-Delay Systems

Séminaire le 8 Juin 2016, 10h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Pierdomenico Pepe (Università degli Studi dell'Aquila)


This talk deals with the stabilization in the sample-and-hold sense of nonlinear systems described by retarded functional differential equations. The notion of stabilization in the sample-and-hold sense has been introduced in 1997 by Clarke, Ledyaev, Sontag and Subbotin, for nonlinear delay-free systems. Roughly speaking, a state feedback (continuous or not) is said to be a stabilizer in the sample-and-hold sense if, for any given large ball and small ball of the origin, there exists a suitable small sampling period such that the feedback control law obtained by sampling and holding the above state feedback, with the given sampling period, keeps uniformly bounded all the trajectories starting in any point of the large ball and, moreover, drives all such trajectories into the small ball, uniformly in a maximum finite time, keeping them in, thereafter. In this talk suitable control Lyapunov-Krasovski functionals will be introduced and suitable induced state feedbacks (continuous or not), and it will be shown that these state feedbacks are stabilizers in the sample-and- hold sense, for fully nonlinear time-delay systems. Moreover, in the case of time-delay systems, implementation by means of digital devices often requires some further approximation due to non availability in the buffer of the value of the system variables at some past times, as it can be frequently required by the proposed state feedback. In order to cope with this problem, well known approximation schemes based on first order splines are used. It is shown, for fully nonlinear retarded systems, that, by sampling at suitable high frequency the system (finite dimensional) variable, stabilization in the sample-and-hold sense is still guaranteed, when the holden input is obtained as a feedback of the (first order) spline approximation of the (infinite dimensional) system state, whose entries are available at sampling times, and the state feedback is Lipschitz on any bounded subset of the Banach state space

Séminaire d'Automatique du Plateau de Saclay : Optimal control and Lyapunov functions applied to the satellite attitude control

Séminaire le 24 Mai 2016, 11h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Nadjim Horri (Coventry University)


The use of Lyapunov functions is generally limited to proving the stability of a system with a given control law. In this presentation, Lyapunov functions are used to formulate optimal control problems as pointwise nonlinear programmes. These optimisation problems are equivalent to inverse optimal control problems. This approach is applied to satellite attitude control. The optimal attitude control problems under consideration will be the minimisation of the norm of the control torque subject to constraints on the convergence rate of a Lyapunov function. This approach improves the tradeoff between rapidity and energy consumption compared to a benchmark controller, which is taken to be a PD type controller without loss of generality. The phase space trajectories show that the solutions to some fundamental open loop optimization problems are particular cases of optimal control problem formulations based on the convergence rates of Lyapunov functions. This is the case of the minimum time single axis attitude control problem, which is a special case of the problem of maximizing the convergence rate of a Lyapunov function under maximum torque limitations. It is also the case of the problem of minimising toque for fixed manoeuvre time. The solution to this problem is a particular case of the problem of minimizing the norm of the control torque under a Lyapunov convergence rate constraint.

S³: Condition monitoring using vibration signals

Séminaire le 24 Mai 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle des séminaires du L2S
Asoke K. Nandi


Condition monitoring of machines is an essential part of smooth, efficient, safe, and productive operation of machines. In this presentation, focus will be on rotating machines and in the use of vibration signals. Classification of vibration signals to different states of machines has been achieved through the developments and applications of signal processing and machine learning. This presentation will cover research efforts and some case studies carried out over many years.

Bio: Professor Asoke K. Nandi received the degree of Ph.D. in Physics from the University of Cambridge, Cambridge (UK). He held academic positions in several universities, including Oxford (UK), Imperial College London (UK), Strathclyde (UK), and Liverpool (UK) as well as Finland Distinguished Professorship in Jyvaskyla (Finland). In 2013 he moved to Brunel University London (UK), to become the Chair and Head of Electronic and Computer Engineering. Professor Nandi is a Distinguished Visiting Professor at Tongji University (China) and an Adjunct Professor at University of Calgary (Canada).
In 1983 Professor Nandi contributed to the discovery of the three fundamental particles known as W+, W− and Z0 (by the UA1 team at CERN), providing the evidence for the unification of the electromagnetic and weak forces, which was recognized by the Nobel Committee for Physics in 1984. His current research interests lie in the areas of signal processing and machine learning, with applications to communications, gene expression data, functional magnetic resonance data, and biomedical data. He has made many fundamental theoretical and algorithmic contributions to many aspects of signal processing and machine learning. He has much expertise in “Big Data”, dealing with heterogeneous data, and extracting information from multiple datasets obtained in different laboratories and different times. He has authored over 500 technical publications, including 200 journal papers as well as four books, entitled Automatic Modulation Classification: Principles, Algorithms and Applications (Wiley, 2015), Integrative Cluster Analysis in Bioinformatics (Wiley, 2015), Automatic Modulation Recognition of Communications Signals (Springer, 1996), and Blind Estimation Using Higher-Order Statistics (Springer, 1999),. Recently he published in Blood, BMC Bioinformatics, IEEE TWC, NeuroImage, PLOS ONE, Royal Society Interface, and Signal Processing. The h-index of his publications is 63 (Google Scholar).

Professor Nandi is a Fellow of the Royal Academy of Engineering and also a Fellow of seven other institutions including the IEEE and the IET. Among the many awards he received are the Institute of Electrical and Electronics Engineers (USA) Heinrich Hertz Award in 2012, the Glory of Bengal Award for his outstanding achievements in scientific research in 2010, the Water Arbitration Prize of the Institution of Mechanical Engineers (UK) in 1999, and the Mountbatten Premium, Division Award of the Electronics and Communications Division, of the Institution of Electrical Engineers (UK) in 1998.

Séminaire d'Automatique du Plateau de Saclay : Inverse optimal control: the sub-Riemannian case

Séminaire le 24 Mai 2016, 10h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Frédéric Jean (ENSTA)


An inverse control problem is formulated as follows: given a set of trajectories and a control system, find a cost such that these paths are optimal. The first question to ask is the uniqueness of the solution of such a problem. For general classes of costs the problem appears to be very difficult, even with a trivial dynamics. We are therefore interested in this issue for the class of costs which are quadratic in the control, when the dynamics depend linearly in the control (Riemannian and sub-Riemannian case). In this case we can reduce the problem to the question of the existence of geodesically equivalent metrics and the existing results will be described, from the theorem of Levi-Civita (1890) to those we obtained recently with Sofya Maslovskaya and Igor Zelenko.

S³: Time Frequency Array Signal Processing: Multi-Dimensional processing for non-stationary signals

Séminaire le 20 Mai 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Adel Belouchrani


Conventional time-frequency analysis methods are being extended to data arrays, and there is a potential for a great synergistic development of new advanced tools by exploiting the joint properties of time-frequency methods and array signal processing methods. Conventional array signal processing assumes stationary signals and mainly employs the covariance matrix of the data array. This assumption is motivated by the crucial need in practice for estimating sample statistics by resorting to temporal averaging under the additional hypothesis of ergodic signals. When the frequency content of the measured signals is time varying (i.e., nonstationary signals), this class of approaches can still be applied. However, the achievable performances in this case are reduced with respect to those that would be achieved in a stationary environment. Instead of considering the nonstationarity as a shortcoming, Time Frequency Array Processing   takes advantage of the nonstationarity by considering it as a source of information in the design of efficient algorithms in such environments. This talk deals with this  relationship between time-frequency methods and array signal processing methods. Recent results on the performance analysis of the Time Frequency MUSIC algorithm will be also presented.

Bio: Adel Belouchrani was born in Algiers, Algeria, on May 5, 1967. He received the State Engineering degree in 1991 from Ecole Nationale Polytechnique (ENP), Algiers, Algeria, the M.S. degree in signal processing from the Institut National Polytechnique de Grenoble (INPG), France, in 1992, and the Ph.D. degree in signal and image processing from Télécom Paris (ENST), France, in 1995. He was a Visiting Scholar at the Electrical Engineering and Computer Sciences Department, University of California, Berkeley, from 1995 to 1996. He was with the Department of Electrical and Computer Engineering, Villanova University, Villanova, PA, as a Research Associate from 1996 to 1997. From 1998 to 2005, he has been with the Electrical Engineering Department of ENP as Associate Professor. He is currently and since 2006 Full Professor at ENP. His research interests are in statistical signal processing, (blind) array signal processing, time-frequency analysis and time-frequency array signal processing with applications in biomedical and telecommunications. Professor Adel Belouchrani is an IEEE Senior Member and has published over 180 technical publications including 48  journal papers, 4 book chapters and 4 patents that have been cited over 5400 times according Google Scholar  and  over 2000 time according to ISI Web Of Science. He has supervised over 19 PhD students. Professor Adel Belouchrani is currently Associated Editor of the IEEE Transactions on Signal Processing and Editorial board member of the Digital signal processing Journal (Ed. Elsevier).  He has been recently nominated  as a founding member of the Algerian Academy of Science  and Technology.

Control of Fuel Cell Hybrid Power Systems

Séminaire le 9 Mai 2016, 15h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Prof. Jian Chen, College of Control Science and Engineering, Zhejiang University, Hangzhou, China


with the environment and energy crisis worsening, fuel cells have shown significant potential as an alternative energy conversion device with high efficiency and low environmental impact. In particular, Fuel cells are promising for new energy automotive applications. Fuel cell hybrid power systems usually include fuel cells and lithium-Ion batteries. In this presentation, I will talk about control of fuel cell systems, SOC Estimation of Lithium-Ion Batteries, and adaptive control strategies of fuel cell/battery hybrid power systems.

Biography: Jian Chen (M’06-SM’10) received the B.E. and M.E. degrees from Zhejiang University, Hangzhou, China, in 1998 and 2001, respectively, and the Ph.D. degree from Clemson University, South Carolina, USA, in 2005. From 2006 to 2008, he was as a research fellow working on fuel cell modeling and ­control at the University of Michigan, Ann Arbor, MI, USA. He joined IdaTech LLC, Oregen, USA, working on fuel cell back power systems and Proterra Inc., South Carolina, USA, working on the National Fuel Cell Bus Program, in 2008 and 2012, respectively. In 2013, he joined the Department of Control Science and Engineering, Zhejiang University, Hangzhou, China. Dr. Chen is currently a professor with the College of Control Science and Engineering, Zhejiang University, Hangzhou, China. He has been supported by the Chinese Recruitment Program of Global Youth Experts since 2012 and received the Major Program of National Natural Science Foundation of China on Modeling and Control of Fuel Cell vehicles in 2014. His research interests include fuel cell modeling and control, battery management, visual servo techniques, and nonlinear control.

Séminaire d'Automatique du Plateau de Saclay: Virtual Inertia Emulation and Placement in Power Grids

Séminaire le 15 Avril 2016, 11h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Florian Dörfler (ETH Zurich)


A major transition in the operation of electric power grids is the replacement of bulk generation based on synchronous machines by distributed generation based on low-inertia power electronic sources. The accompanying "loss of rotational inertia" and the fluctuations by renewable sources jeopardize the system stability, as testified by the ever-growing number of frequency incidents. As a remedy, numerous studies demonstrate how virtual inertia can be emulated through various devices, but few of them address the question of "where" to place this inertia. It is however strongly believed that the placement of virtual inertia hugely impacts system efficiency, as demonstrated by recent case studies. We carry out a comprehensive analysis in an attempt to address the optimal inertia placement problem, considering a linear network-reduced power system model along with an H2 performance metric accounting for the network coherency. The optimal inertia placement problem turns out to be non-convex, yet we provide a set of closed-form global optimality results for particular problem instances as well as a computational approach resulting in locally optimal solutions. We illustrate our results with a three-region power grid case study and compare our locally optimal solution with different placement heuristics in terms of different performance metrics.

Séminaire d'Automatique du Plateau de Saclay: A modular design of incremental Lyapunov functions for microgrid control

Séminaire le 15 Avril 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Claudio De Persis (Groningen University)


In this talk we propose a Lyapunov based analysis of microgrids. The starting point is an energy function comprising the kinetic energy associated with the elements that emulate the rotating machinery and terms taking into account the reactive power stored in the lines and dissipated on shunt elements. We then shape this energy function with the addition of an adjustable voltage-dependent term, and construct incremental storage functions satisfying suitable dissipation inequalities. The choice of the voltage-dependent term depends on the voltage dynamics/controller under investigation. Several microgrids dynamics that have similarities or coincide with dynamics already considered in the literature are captured in this incremental energy analysis framework. These incremental storage functions allow for a complete analysis of the coupled microgrid obviating the need for simplifying linearization techniques and for the restrictive decoupling assumption in which the frequency dynamics is fully separated from the voltage one.

Improved Millimeter-Wave Radar Concealed-Threat Person Scanning

Séminaire le 8 Avril 2016, 14h00 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Carey M. Rappapor


Metal-detecting airport security scanners for airline passengers are being replaced by millimeter-wave imagers. These new systems are much better at revealing concealed manmade objects, but they can be improved. At our Advanced Imaging Technology Lab at Northeastern University in Boston, we are developing a custom-designed elliptical toroid reflector antenna which allows multiple overlapping beams for focused wide-angle illumination to speed data acquisition and accurately image strongly inclined body surfaces.  We have developed the concept of the Blade Beam Reflector both as a single transmitting antenna and a multi-beam Toroidal Reflector, with multiple feeds. Each feed generates a different incident beam with different viewing angles, while still maintaining the blade beam configuration of narrow slit illumination in the vertical direction.  Having multiple transmitters provides horizontal resolution and imaging of full 120 deg. of body.  Furthermore, the reflector can simultaneously be used for receiving the scattered field, with high gain, overlapping, high vertical resolution beams for each transmitting or receiving array element. The multistatic transmitting and receiving array configuration sensing avoids dihedral artifacts from body crevices and reduces non-specular drop-outs, and will leads to a faster, higher resolution, and less expensive security system.

Bio — Carey M. Rappaport received five degrees from the Massachusetts Institute of Technology:  the SB in Mathematics, the SB, SM, and EE in Electrical Engineering in June 1982, and the PhD in Electrical Engineering in June 1987.  He is married to Ann W. Morgenthaler, and has two children, Sarah and Brian. Prof. Rappaport joined the faculty at Northeastern University in Boston, MA in 1987.  He has been Professor of Electrical and Computer Engineering since July 2000. In 2011, he was appointed College of Engineering Distinguished Professor.  He was Principal Investigator of an ARO-sponsored Multidisciplinary University Research Initiative on Humanitarian Demining, Co-Principal Investigator of the NSF-sponsored Engineering Research Center for Subsurface Sensing and Imaging Systems (CenSSIS), and Co-Principal Investigator and Deputy Director of the DHS-sponsored Awareness and Localization of Explosive Related Threats (ALERT) Center of Excellence. Prof. Rappaport has authored over 400 technical journal and conference papers in the areas of microwave antenna design, electromagnetic wave propagation and scattering computation, and bioelectromagnetics, and has received two reflector antenna patents, two biomedical device patents and three subsurface sensing device patents.  He was awarded the IEEE Antenna and Propagation Society's H.A. Wheeler Award for best applications paper, as a student in 1986.  He is a member of Sigma Xi and Eta Kappa Nu professional honorary societies.

S³: Topological Pattern Selection in Recurrent Networks

Séminaire le 1 Avril 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Alireza Bahraini


One of the differences between memory function of hypocampus and  neural networks situated at neocortex is that in the  latter memory operation still reflect the topography informing synaptic connections. This means that the activity of a unit relates also to its position in the tissue.
We introduce two approaches for incorporating the information of the geometry  of the underlying neural network into its dynamics. This phenomenon is carried out based on two probability rules for selecting storing patterns. First  a Gibbs type distribution inspired by the architecture of the network is applied. We are then led to a second method to introduce topological effects on the dynamics of the network. In both approaches a significant enhancement on the capacity of the network is observed after considerable rigorous computations.

Some References:
1- Bahraini,A, .  Abbassian,A.  Topological Pattern Selection in Recurrent Networks, Journal of Neural Networks, 31, 2012, 22-32.
2- Roudi, Y, Treves, A,. An associative Network with Spatially Organized Connectivity,2004, Journal of Statistical Mechanics.
3- Gallan, R., F., On how network architecture determines the dominant patterns of spontaneous neural activity, PLoS One , 2008.

Bio: I obtained my DEA in 2001 and my PhD in 2004 at University Paris 7 under the supervision of Professor Daniel Bennequin. The title of my thesis was Super-symmetry and Complex Geometry. I joined the department of mathematical sciences of Sharif university of technology as an assistant
professor in 2004 and in 2012 I became an associate professor at the same department.

S³: Solving large-scale inverse problems using forward-backward based methods

Séminaire le 11 Mars 2016, 10h30 à CentraleSupelec (Gif-sur-Yvette) Salle du conseil du L2S - B4.40
Audrey Repett: post-doctoral researcher at the Heriot-Watt university, in Scotland


Recent developments in imaging and data analysis techniques came along with an increasing need for fast convex optimization methods for solving large scale problems.  A simple optimization strategy to minimize the sum of a Lipschitz differentiable function and a non smooth function is the forward-backward algorithm. In this presentation, several approaches to accelerate convergence speed and to reduce complexity of this algorithm will be proposed. More precisely, in a first part, preconditioning methods adapted to non convex minimization problems will be presented, and in a second part, stochastic optimization techniques will be described in the context of convex optimization. The different proposed methods will be used to solve several inverse problems in signal and image processing.

Bio: Audrey Repetti is a post-doctoral researcher at the Heriot-Watt university, in Scotland. She received her M.Sc. degree from the Université Pierre et Marie Curie (Paris VI) in applied mathematics, and her Ph.D. degree from the Université Paris-Est Marne-la-Vallée in signal and image processing. Her research interests include convex and non convex optimization, and signal and image processing.

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