All Years Seminars
[INMA] 2012-03-13 (14.00) : Production d'un couple étalon adapté à une balance gravitationnelle réalisée à l'Observatoire Royal de Belgique
At Euler building
Speaker :
François WIELANT (UCL)
Abstract :
Le laboratoire d'instrumentation géodynamique de
l¿Observatoire Royal de Belgique a développé un instrument à partir
d¿un Pendule Vertical Symétrique (Symmetrical Vertical Pendulum, SVP),
dont le but est d'établir une nouvelle mesure de la constante G. Ce
pendule est utilisé comme balance de couples, introduits par le champ
de pesanteur terrestre local g, ainsi que par un actionneur
gravitationnel (paire de masses attractives en mouvement). La
rotation (dans le champ de pesanteur terrestre) des aiguilles d¿une
montre à Quartz fixée sur le bras pendulaire est utilisée pour
produire un couple de comparaison périodique d'amplitude
constante. Cette présentation traite de la conception d'un dispositif
de calibration en vue de pouvoir étalonner le couple généré par les
aiguilles de la montre, au sein d'un instrument pendulaire spécifique
(fixer le rapport d'échelle entre les amplitudes des deux couples). Ce
dispositif de calibration est constitué d'un moteur DC miniaturisé,
effectuant une translation dans le champ de pesanteur d'un corps de
masse connue avec grande précision (micro masse). La maîtrise du
déplacement du corps de masse connue, au sein de l'instrument
pendulaire, procure la précision attendue d'un système
d'étalonnage. La qualité de l¿étalonnage proposée réside dans la
maitrise du déplacement de la micro masse conduisant à un couple
étalon de l'ordre de 10-7 Nm.
[INMA] 2012-03-06 (14.00) : Constructive Feedback Linearization Of Mechanical Systems With Friction and Underactuation Degree One
At Euler building
Speaker :
Lopez-Martinez, Manuel
Abstract :
In this talk we present a constructive methodology to
control a class of unstable underactuated mechanical systems
with underactuation degree one, by means of classical feedback
linearization and Lyapunov design. The design is presented
proposing a dummy output that allows to solve the problem in a constructive way.
We prove that the proposed output solves the problem obtaining
an explicit and compact control law.
The stability result of the obtained solution does
not change when taking into account the friction effects even in the
unactuated coordinate. The new result is applied to obtain a
(almost) global stabilizing scheme for the VTOL aircraft model
with strong input coupling.
[INMA] 2012-02-28 (14.00) : Optimal experiment design for open and closed loop identification
At Euler building
Speaker :
Gevers, Michel
Abstract :
Optimal experiment design for system identification was a
very active research topic in the 1970's: the results at that time
focused on the minimization of different measures of the parameter
covariance matrix. The research on this topic disappeared for more
than a decade. In the mid eighties new results became available that
focused on quality criteria that took account of the objective for
which the model was estimated. These results were based on approximate
variance formulae for the estimated transfer functions, under the
assumption that the model order goes to infinity. Experiment design
experienced a sudden revival of activity from around 2003 under a
triple influence: the advent of new expressions for the variance of
estimated quantities that did not require an assumption of model order
going to infinity, the introduction of the concept of "least costly
identification design", and the development of new optimal design
techniques for identification that convert the optimization problem
into semi-definite programs that can be solved using Linear Matrix
Inequalities. In this talk we shall first review the development of
optimal experiment design. We shall then present new results that
allow one to solve the optimal closed loop experiment design problem,
where the optimization is performed jointly with respect to the
controller and the spectrum of the external excitation. Our results
are based on the partial positive definite matrix completion theorem.
[INMA] 2012-02-23 (16.30) : COLLOQUIUM CESAME/MAPA: Mathematics of pde constrained optimization
At CYCL01 (de Hemptinne)
Speaker :
Prof. Dr. Michael HINZE (Fachbereich Mathematik, University of Hamburg)
Abstract : We discuss control problems with PDEs as subsidiary conditions and
take special emphasis on (i) the proper functional analytic setting,
(ii) tailored discrete concepts in the presence of additional
pointwise constraints, and on
(iii) structure exploiting solution algorithms.
The theoretical results are supported by numerical experiments.
[INMA] 2012-02-21 (14.00) : Random Walks on Networks: Dynamics and Teleportation
At Euler building
Speaker :
Lambiotte, Renaud
Abstract :
In this talk, I will focus on two problems related to random walks on networks. First, I will focus on random teleportation, which is a necessary evil for ranking and clustering directed networks based on random walks. Teleportation enables ergodic solutions, but the solutions must necessarily depend on the exact implementation and parametrization of the teleportation. For example, in the commonly used PageRank algorithm, the teleportation rate must trade off a heavily biased solution with a uniform solution. Here we show that teleportation to links rather than nodes enables a much smoother trade-off and effectively more robust results, and discuss the effect of teleportation on clustering. In the second part of my talk, I will focus on random walks on temporal networks, i.e. networks evolving in time. In particular, I will examine the effects of inter-event statistics on the dynamics of edges, and apply the concept of a generalized master equation to the study of continuous-time random walks on networks.
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