All Years Seminars
[INMA] 2008-04-24 (16.30) : La conjecture de Poincaré et la classification des 3-variétés.
At Euler building
Speaker :
Pascal Lambrechts
( UCL
)
Abstract :
D'après le magazine Science, l'évènement scientifique de l'année 2006 fut la résolution de la conjecture de Poincaré
par Grigori Perelman. Dans cet exposé j'expliquerai cette conjecture et des idées élémentaires de sa preuve.
Mais j'expliquerai aussi que Perelman a en fait démontré beaucoup plus que la conjecture de Poincaré puisqu'il semble avoir achevé un formidable programme de recherche initié
par Thurston à la fin des années 1970. Ce programme proposait une classification des variétés de dimension 3 grâce à l'existence de géométries homogènes sur ces variétés, en analogie avec un phénomène analogue en dimension 2 bien connu selon lequel toute surface compacte orientable admet une géométrie à courbure constante.
[INMA] 2008-04-22 (14.00) : Interactions Between Explicit and Implicit Timing
At Euler building
Speaker :
Jérémy Badler
( CESAME
)
Abstract :
When stimuli are temporally regular, their prediction depends on an
implicit representation of elapsed time. However, it is unclear
whether the underlying timing mechanism is separable from a
conscious, explicit perception of time. To address the question,
human subjects had to predict the duration of an interval either
explicitly, with a button press, or implicitly, by accurately
tracking with the eyes a suddenly-moving target. Performing the
tasks concurrently yielded a delay in response times for both
modalities compared to single-task trials. This suggests that implicit
and explicit time representations are partially independent, and invoking
them simultaneously increases the attentional load on the brain.
[INMA] 2008-04-15 (14.00) : Iterative filtering for a dynamical reputation system
At Euler building
Speaker :
de Kerchove D'Exaerde, Cristobald
Abstract :
I introduces a novel iterative method that
assigns a reputation to $n+m$ items: n raters and m objects.
Each rater evaluates a subset of objects leading to a nxm
evaluation matrix with a certain sparsity pattern. From this
evaluation matrix we give a nonlinear formula to define the
reputation of raters and objects. I also provide an iterative
algorithm that superlinearly converges to the unique vector of
reputations and this for any evaluation matrix. In contrast to
classical outliers detection, no evaluation is discarded in this
method but each one is taken into account with different weights
for the reputation of the objects. The complexity of one iteration
step is linear in the number of evaluations, making our algorithm
efficient for large data set. Experiments show good robustness of
the reputation of the objects against cheaters and spammers and
good detection properties of cheaters and spammers.
[INMA] 2008-04-08 (14.00) : Evaluating scientific products by means of citation-based models: a first analysis and validation
At Euler building
Speaker :
Gianna Del Corso
( University of Pisa
)
Abstract :
Some integrated models for ranking scientific publications together
with authors and journals are presented and analyzed. The models rely
on certain adiacency matrices obtained from the relations of citation,
authorship and publication, which concurr to forming a suitable
irreducible stochastic matrix whose Perron vector provides the
ranking. Some perturbation theorems concerning the Perron vector of
nonnegative irreducible matrices are proved. These theoretical
results provide a validation of the consistency and effectiveness
of our models. Several paradigmatic examples are reported together
with some results obtained on a real set of data.
[INMA] 2008-03-18 (Unknown) : 27th Benelux Meeting on Systems and Control - NO SEMINAR !!
At Heeze, The Netherlands
Speaker :
( )
Abstract :
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