All Years Seminars
[INMA] 2008-12-09 (14.00) : "Trajectory planning of vertical pointing movements: using gravity to move the arm"
At Euler building
Speaker :
Crevecoeur, Frédéric
Abstract : This study aims at better understanding how the central nervous system (CNS) integrates the action of the gravitational torque on the upper limb when we perform a vertical movement such as replacing a cup on a shelf. Particular kinematic properties of vertical pointing movements have provided evidence for an integration of the action of gravity in the motor plan. However, it remains unclear how the CNS achieves this integration and optimal control approaches considering minimum joint torque input failed to explain the kinematic properties observed in normal gravity condition. In this experiment, we asked subjects to perform vertical pointing movements in different gravitational conditions, normal (1g), hyper (1.8g) and micro gravity (~0g). We used a model that considers minimal motoneuron discharge to test the hypothesis that gravity is integrated in an energy-optimal way. The observed behaviors are consistent with the model's predictions although the strategies vary across subjects, movement's direction and gravity condition. The analysis of subjects' strategies permit to better understand the nature of mechanism underlying adaptation of motor control to altered gravity condition.
[INMA] 2008-12-03 (16.00) : CHAIRE FRANQUI - (Teoretical) Computer Science is Everywhere
At Aud. BARB92, Place Sainte Barbe
Speaker :
Erik DEMAINE (MIT, U.S.A.)
Abstract : Theoretical computer science, and the algorithmic way of thinking,
transcends our traditional boundaries. I believe that algorithms are relevant
to every discipline of study, and will give eclectic examples from the arts and
sciences to business and society. The examples span the spectrum from serious
topics like protein folding and decoding Inka khipu to fun topics like juggling
and magic.
[INMA] 2008-11-27 (16.30) : Colloquium CESAME-MAPA "Un survol de l'homologie de contact"
At Auditoire Ch.-J. de La Vallée Poussin (cycl 01)
Speaker :
Frédéric BOURGEOIS (ULB)
Abstract : L'homologie de contact est un invariant pour les structures de contact, dont la définition est basée sur les courbes holomorphes.
Dans cet exposé, on esquissera la construction de l'homologie de contact, puis on illustrera certaines de ses applications et on discutera de certaines de ses propriétés.
[INMA] 2008-11-25 (14.00) : "Microbial Fuel Cells : Principles and Optimization by Multi Unit Approach"
At Euler building
Speaker :
Michel PERRIER (Ecole Polytechnique de Montréal)
Abstract :
Multi-unit optimization is an extremum seeking method (real-time
steady state optimization of a dynamic system by controlling the
gradient), where the gradient is obtained using finite difference of
the outputs of multiple identical units driven with different
inputs. The major limitation of this approach is that the
convergence is established only when units are identical. This talk
addresses the convergence of the multi-unit scheme with
non-identical units. With a simple quadratic approximation of the
objective function, it is shown that the scheme converges only when
the difference between the inputs is either larger than or in a
direction opposite to that of the difference between their optimum
values. Also, it is shown that the best value for the difference
between the inputs is not zero, but determined by the deviation
between the units.
The multi-unit algorithm is applied to the maximization of power
production in a stack of two continuous flow microbial fuel cells
(MFCs) to maximize power output by manipulating external resistances
of two aircathode membraneless MFCs. The experiment demonstrated fast
convergence toward optimal external resistance and algorithm stability during external
perturbations (e.g. temperature variations). Rate of the algorithm convergence was much faster
than in traditional maximum power point tracking algorithms (MPPT), which are based on
temporal perturbations.
[INMA] 2008-11-18 (14.00) : "Coordination on nonlinear spaces"
At Euler building
Speaker :
Sarlette, Alain
Abstract : Recently, numerous authors have studied algorithms for interacting individual agents that lead to a coordinated behavior of the overall swarm. Mostly, the agents are assumed to evolve on a vector space.
This talk extends the theoretical study of coordination to nonlinear but highly symmetric spaces, like the spheres or Lie groups. The focus is on consequences of the geometry and associated symmetries of the setting. It shows that new fundamental problems appear in this context, proposes appropriate definitions and various control methods to circumvent undesired phenomena. Two main "coordination" tasks are considered: (i) achieving a particular configuration of the agents and (ii) performing "coordinated motions".
Seminars
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secretaire-inma@uclouvain.be
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