Search results for " poster"

Parameter-free adaptive step-size multiobjective optimization applied to remote photoplethysmography

2018

International audience; In this work, we propose to reformulate the objective function of Independent Component Analysis (ICA) to make it a better posed problem in the context of Remote photoplethysmography (rPPG). In recent previous works, linear combination coefficients of RGB channels are estimated maximizing the non-Gaussianity of ICA output components. However, in the context of rPPG a priori knowledge of the pulse signal can be incorporated into the component extraction algorithm. To this end, the contrast function of regular ICA is extended with a measure of periodicity formulated using autocorrelation. This novel semi-blind source extraction method for measuring rPPG has the interes…

Hybrid multiple diffraction in semipolar wurtzite materials: (\bf 01\overline{1}2)-oriented ZnMgO/ZnO heterostructures as an illustration

2017

X-ray diffraction has been widely used to characterize the structural properties (strain and structural quality) of semiconductor heterostructures. This work employs hybrid multiple diffraction to analyzer-oriented Zn1−xMgxO layers grown by molecular beam epitaxy on ZnO substrates. In such a low-symmetry material system, additional features appear in symmetric reflection scans, which are described as arising from hybrid multiple diffraction. First, the Bragg conditions necessary for these high-order processes to occur are introduced and applied to explain all the observed satellite reflections, identify the planes that contribute and computea priorithe angles at which they are observed. Fur…

Evaluation of the areal material distribution of paper from its optical transmission image

2011

International audience; The goal of this study was to evaluate the areal mass distribution (defined as the X-ray transmission image) of paper from its optical transmission image. A Bayesian inversion framework was used in the related deconvolution process so as to combine indirect optical information with a priori knowledge about the type of paper imaged. The a priori knowledge was expressed in the form of an empirical Besov space prior distribution constructed in a computationally effective way using the wavelet transform. The estimation process took the form of a large-scale optimization problem, which was in turn solved using the gradient descent method of Barzilai and Borwein. It was de…

Modelling analysis of centroid curves of olfactory habituation in humans

2020

Indexation en cours.; International audience; Previously published experiments established the time-course of olfactory habituation in humans, and extracted 3 centroid curves from clustering analysis that reflected high, middle and low habituation. The aim of the current theoretical study was to further analyse these previous experimental data by developing a mathematical modelling analysis designed for fitting the 3 curves from a general equation. After adjusting equation parameters for each curve, fitting equation outcomes on experimental data yielded high correlation coefficients of 0.9997 – 0.9995 – 0.9962, respectively. A model-based interpretation of olfactory-habituation centroid cur…

Une mesure comparative en didactique des Mathématiques entre une analyse a priori et la contingence

2007

En didactique des Mathématiques, mais plus généralement en sciences humaines, de nombreuses recherches utilisent des analyses qualitatives pour falsifier expérimentalement des hypothèses formulées a priori, c'est-à-dire en amont de la recherche. Une telle approche méthodologique, appliquée à une enquête, s'avère le plus souvent insuffisante pour analyser toutes les variables en jeu dans des phénomènes contingents d'enseignement/ apprentissage, même si dans certains cas (analyse ponctuelle de protocoles, de vidéos, etc.), elle permet de déceler quelques relations intéressantes. Mais si le nombre de sujets devient trop volumineux, l'analyse qualitative ne réussit plus à extraire toutes les re…

On a posteriori error bounds for approximations of the generalized Stokes problem generated by the Uzawa algorithm

2012

In this paper, we derive computable a posteriori error bounds for approximations computed by the Uzawa algorithm for the generalized Stokes problem. We show that for each Uzawa iteration both the velocity error and the pressure error are bounded from above by a constant multiplied by the L2-norm of the divergence of the velocity. The derivation of the estimates essentially uses a posteriori estimates of the functional type for the Stokes problem. peerReviewed

Analysis of errors caused by incomplete knowledge of material data in mathematical models of elastic media

2011

Reliable numerical solution of a class of nonlinear elliptic problems generated by the Poisson-Boltzmann equation

2020

We consider a class of nonlinear elliptic problems associated with models in biophysics, which are described by the Poisson-Boltzmann equation (PBE). We prove mathematical correctness of the problem, study a suitable class of approximations, and deduce guaranteed and fully computable bounds of approximation errors. The latter goal is achieved by means of the approach suggested in [S. Repin, A posteriori error estimation for variational problems with uniformly convex functionals. Math. Comp., 69:481-500, 2000] for convex variational problems. Moreover, we establish the error identity, which defines the error measure natural for the considered class of problems and show that it yields computa…

Pieloplastica open mininvasiva con approccio lombare posteriore: 20 anni di esperienza

2008

Opening New Window in Upper Clival Region: Results from Anatomic Study.

2018

Considering its position located anteriorly to the brainstem, the retrosellar area, in particular the upper clival region and the interpeduncular cistern, is one of the most difficult regions to surgically approach. To date, many different operative solutions have been described, given that this region is attainable by both lateral and median approaches. Lateral routes include the frontolateral, subtemporal, and frontotemporozygomatic approaches with relative variants that have been extensively reported. Among the lateral approaches, the frontotemporozygomatic one is considered particularly useful because it allows better visualization of the retrosellar and suprasellar areas minimizing the…