Search results for "49"

Algebraic-geometric techniques for the feedback classification and robustness of the optimal control of a pair of Bloch equations with application to…

2017

The aim of this article is to classify the singular trajectories associated with the optimal control problems of a pair of controlled Bloch equations. The motivation is to analyze the robustness of the optimal solutions to the contrast and the time-minimal saturation problem, in magnetic resonance imaging, with respect to the parameters and B1-inhomogeneity. For this purpose, we use various computer algebra algorithms and methods to study solutions of polynomial systems of equations and inequalities which are used for classification issues: Gröbner basis, cylindrical algebraic decomposition of semi-algebraic sets, Thom's isotopy lemma.

One-parameter family of Clairaut-Liouville metrics

2007

Riemannian metrics with singularities are considered on the $2$-sphere of revolution. The analysis of such singularities is motivated by examples stemming from mechanics and related to projections of higher dimensional (regular) sub-Riemannian distributions. An unfolding of the metrics in the form of an homotopy from the canonical metric on $\SS^2$ is defined which allows to analyze the singular case as a limit of standard Riemannian ones. A bifurcation of the conjugate locus for points on the singularity is finally exhibited.

Modelling biogeochemical processes in sediments from the north-western Adriatic Sea: response to enhanced particulate organic carbon fluxes

2018

This work presents the result of a study carried out in the north-western Adriatic Sea, by combining two different types of biogeochemical models with field sampling efforts. A longline mussel farm was taken as a local source of perturbation to the natural particulate organic carbon (POC) downward flux. This flux was first quantified by means of a pelagic model of POC deposition coupled to sediment trap data, and its effects on sediment bioirrigation capacity and organic matter (OM) degradation pathways were investigated constraining an early diagenesis model by using original data collected in sediment porewater. The measurements were performed at stations located inside and outside the ar…

Assessing the potential long-term increase of oceanic fossil fuel CO2 uptake due to CO2-calcification feedback

2007

International audience; Plankton manipulation experiments exhibit a wide range of sensitivities of biogenic calcification to simulated anthropogenic acidification of the ocean, with the "lab rat" of planktic calcifiers, Emiliania huxleyi apparently not representative of calcification generally. We assess the implications of this observational uncertainty by creating an ensemble of realizations of an Earth system model that encapsulates a comparable range of uncertainty in calcification response to ocean acidification. We predict that a substantial reduction in marine carbonate production is possible in the future, with enhanced ocean CO2 sequestration across the model ensemble driving a 4?1…

Temporal coherence in mirrorless optical parametric oscillators

2012

International audience; One of the unique features of mirrorless optical parametric oscillators based on counterpropagating three-wave interactions is the narrow spectral width of the wave generated in the backward direction. In this work, we in- vestigate experimentally and numerically the influence that a strong phase modulation in the pump has on the spectral bandwidths of the parametric waves and on the efficiency of the nonlinear interaction. The effects of group-velocity mismatch and group-velocity dispersion are elucidated. In particular, it is shown that the substan- tial increase in temporal coherence of the backward-generated wave can be obtained even for pumping with a temporally…

Multifunctionality: refocusing a spreading, loose and fashionable concept for looking at sustainability?

2008

International audience; The notion of agriculture's Multifunctionality (MF) emerged in the 1980s. It then followed two trajectories since the 1990s: a conflicting period linked to its use in the international trade negotiations on the one hand, a spreading in terms of meaning, use and geographically on the other hand. Specific meanings appeared in connection with policy making, at national or international levels, or through the involvement of new disciplines. Yet, very few authors discuss the implication of the chosen meaning on their findings. To explore and take advantage of using this word and to deliver it from its controversial use in international trade negotiations, it is absolutely…

Influence de l’alimentation potassique et azotée sur le dépérissement du porte-greffe 161-49C

2019

Dépérissements du 161-49C _ Influence de l'alimentation potassique et azotée

2020

Le 161-49C (croisement Vitis berlandieri x Vitis riparia) est un porte-greffe jugé « qualitatif » qui a été largement utilisé pour les plantations et les complantations. Cependant, depuis une dizaine d’années, hormis sur le vignoble charentais, des problèmes de dépérissements graves et inexpliqués sont signalés, notamment en Bourgogne.Au vu de l’enjeu économique au sein du vignoble Bourguignon, le Bureau Interprofessionnel des Vins de Bourgogne (BIVB) cofinance un projet de recherche sur ce sujet : c’est le projet Aptitude. Ce projet vise à caractériser l’existence de possibles corrélations entre la nature physico-chimique des sols et l’intensité des dépérissements. Une attention particuliè…

Dietary ω3 fatty acids & metabolic syndrome in the rat: consequences on sensitivity and retinal functionality

2014

International audience; Purpose: High fructose diets have been widely used to trigger metabolic syndrome (MetS) in rodents. Insulin resistance is a major risk factor for the development of type 2 diabetes leading in 30 to 40% of the cases to the development of diabetic retinopathy in humans. In the other hand, ω3 fatty acids have been associated with the prevention of MetS. Few studies have been interested in the early changes occurring in the retina after induction of MetS and to potential of ω3 fatty acids to reverse those effects. Methods: 96 male Brown Norway rats (6 weeks of age) were fed for 3 and 8 days with either of the four following diets (n=8 in each group): a regular chow diet …

Polyunsaturated fatty acids and plasmalogens in diabetics

2013

PurposePlasmalogens are phospholipids characterized by a vinyl ether bond and a preferential esterification of polyunsaturated fatty acids (PUFA). We have previously shown that the lack of plasmalogens leads to retinal hyper-capillarization. We hypothesize that plasmalogens are negative regulators of vascular development, and aimed to check their circulating levels in diabetic patients with a retinopathy. MethodsBlood samples were collected from 88 patients and 14 control subjects. Among diabetics we had 14 patients without diabetic retinopathy (DR), 12 with a mild non proliferative DR, 12 with a moderate non proliferative DR, 22 with a severe non proliferative DR and 24 with a proliferativ…