An a posteriori error estimate for vertex-centered finite volume discretizations of immiscible incompressible two-phase flow

International audienceIn this paper we derive an a posteriori error estimate for the numerical approximation of the solution of a system modeling the flow of two incompressible and immiscible fluids in a porous medium. We take into account the capillary pressure, which leads to a coupled system of two equations: parabolic and elliptic. The parabolic equation may become degenerate, i.e., the nonlinear diffusion coefficient may vanish over regions that are not known a priori. We first show that, under appropriate assumptions, the energy-type-norm differences between the exact and the approximate nonwetting phase saturations, the global pressures, and the Kirchhoff transforms of the nonwetting phase saturations can be bounded by the dual norm of the residuals. We then bound the dual norm of the residuals by fully computable a posteriori estimators. Our analysis covers a large class of conforming, vertex-centered finite volume-type discretizations with fully implicit time stepping. As an example, we focus here on two approaches: a ''mathematical'' scheme derived from the weak formulation, and a phase-by-phase upstream weighting ''engineering'' scheme. Finally, we show how the different error components, namely the space discretization error, the time discretization error, the linearization error, the algebraic solver error, and the quadrature error can be distinguished and used for making the calculations efficient

Error estimates for the gradient discretisation of degenerate parabolic equation of porous medium type

International audienceThe gradient discretisation method (GDM) is a generic framework for the spatial discretisation of partial differential equations. The goal of this contribution is to establish an error estimate for a class of degenerate parabolic problems, obtained under very mild regularity assumptions on the exact solution. Our study covers well-known models like the porous medium equation and the fast diffusion equations, as well as the strongly degenerate Stefan problem. Several schemes are then compared in a last section devoted to numerical results

Organisation subcellulaire et remobilisation métabolique lors de la senescence foliaire chez le colza en réponse aux stress abiotiques

Brassica napus est une des cultures oléagineuse majeure dans le monde. En raison de sa faible efficacité d’utilisation de l’azote (NUE) comparée aux autres grandes cultures, la gestion de cette ressource présente un objectif écologique et économique majeur pour cette culture. La remobilisation des nutriments des organes sources vers les organes puits est une composante de la NUE qui se déroule durant la sénescence et qui est associée aux processus de recyclages métaboliques et à des modifications de la structure foliaire. L’objectif de cette thèse était de comprendre et de quantifier ces modifications structurales afin d’évaluer à travers ces processus les capacités de remobilisation du colza en fonction de son génotype et de son statut nutritionnel (eau et azote). La structure foliaire a été étudiée grâce à la relaxométrie RMN qui donne accès au statut et à la distribution de l’eau au niveau cellulaire. Ces travaux de thèse ont mis en évidence que la distribution des temps de relaxation transversale (T2) dépend non seulement de la structure cellulaire, mais aussi de l’organisation tissulaire. Cette étude a aussi mis en évidence le processus d’élargissement cellulaire et d’hydratation pendant la sénescence, spécifiquement dans le parenchyme palissadique. Il a été également démontré que le signal RMN reflète la déstructuration progressive se déroulant durant la sénescence au niveau subcellulaire et est un marqueur de sénescence précis permettant de suivre le développement de la feuille. De plus, le statut nutritionnel de la plante modifié par les carences azotées ou le stress hydrique, impacte grandement la sénescence séquentielle et les conséquences en termes d’efficacité de la remobilisation peuvent être suivies par RMN. Ce travail a permis de renforcer les connaissances sur la structure et le fonctionnement de la feuille au niveau tissulaire et cellulaire. De plus, il a été démontré que le signal de relaxométrie RMN donne accès à des informations sur la structure foliaire inaccessible par des méthodes courantes. Une des principales applications de ce travail serait le phénotypage, particulièrement la sélection de génotypes caractérisés par une forte efficacité de remobilisation en particulier en cas de carence azoté ou de stress hydrique.Brassica napus is one of the major oil crops of the world. Due to its low NUE (Nitrogen Use Efficiency) compared to other species, Nitrogen management presents a major economic and environmental goal for improvement of that crop production. As a component of NUE, nutrient remobilization from source to sink tissues takes place mainly during the leaf senescence and is associated to metabolic recycling processes and modification of the cellular organization and structure. The aim of this work was therefore to understand and estimate the amplitude of these structural modifications with the objective to appreciate through these processes remobilization performance according to oilseed rape genotypes and nutritional status in terms of nitrogen and water supply. The leaf structure was investigated through NMR relaxometry, providing access to cellular water status and distribution. The present work demonstrated that the transverse relaxation time (T2) distribution depends on both leaf tissue structure and cellular compartmentalization. The study revealed a process of cell enlargement and hydration during leaf senescence, specifically in the palisade parenchyma and showed that the T2 relaxation time was able to discriminate parenchyma tissues at an early phase of senescence induction. Moreover, the NMR relaxometry signal was shown to reflect specific chronological loss of sub-cellular structuring all along the senescence process progression and was demonstrated to be an accurate non-invasive monitoring method of leaf development. Finally, plant nutrition status experienced through nitrogen and water availability limitation has been demonstrated to strongly affect regular sequential leaf senescence. Consequences on remobilization efficiency by stress conditions have been also assessed through the NMR signal. This work has improved the understanding of leaf structure and functioning at the cell and tissue levels after the onset and during the progression of senescence. Moreover, it was demonstrated that NMR relaxometry provides access to leaf structural information that are not accessible with currently used techniques for plant structural investigations. One of the main applications would be for plant phenotyping, especially for selecting genotypes with higher nutrient remobilization efficiency especially under environmental stresses like nitrogen and water limitations for sustainable oil and protein production

Leaf Development Monitoring and Early Detection of Water Deficiency by Low Field Nuclear Magnetic Resonance Relaxation in Nicotiana tabacum Plants

Drought is the main abiotic stress worldwide affecting harvest quality and quantity of numerous crops. To enable better water management, low field NMR (nuclear magnetic resonance) relaxometry was assessed as a developmental marker and a new method for early detection of water deficiency. The effect of a foliar biostimulant against water stress was also investigated. Two leaves of different ranks (four and eight) were studied. The leaves of different ranks were characterized by different NMR T2 spectra which validated the ability of NMR to describe the developmental stage of tobacco. Results also showed that T2 NMR relaxation spectra allow the detection of mild water stress (80% of the field capacity) through the precise characterization of the leaf water status while other water stress markers (relative water content, photosynthetic related parameters…) were not yet impacted. The agricultural impact of the mild water stress was determined through the nitrogen rate in shoots and amino acids assay six weeks after the beginning of the stress and results shows that foliar application of biostimulant limits the negative consequences of drought. Our results demonstrate the sensitivity of NMR to detect slight changes triggered in the leaf by water stress at the tissue level

Assessment of nutrient remobilization through structural changes of palisade and spongy parenchyma in oilseed rape leaves during senescence

International audienceDifferential palisade and spongy parenchyma structural changes in oilseed rape leaf were demonstrated. These dismantling processes were linked to early senescence events and associated to remobilization processes. During leaf senescence, an ordered cell dismantling process allows efficient nutrient remobilization. However, in Brassica napus plants, an important amount of nitrogen (N) in fallen leaves is associated with low N remobilization efficiency (NRE). The leaf is a complex organ mainly constituted of palisade and spongy parenchyma characterized by different structures and functions concerning water relations and carbon fixation. The aim of the present study was to demonstrate a specific structural evolution of these parenchyma throughout natural senescence in B. napus, probably linked to differential nutrient remobilization processes. The study was performed on 340 leaves from 32 plants during an 8-week development period under controlled growing conditions. Water distribution and status at the cellular level were investigated by low-field proton nuclear magnetic resonance (NMR), while light and electron microscopy were used to observe cell and plast structure. Physiological parameters were determined on all leaves studied and used as indicators of leaf development and remobilization progress. The results revealed a process of hydration and cell enlargement of leaf tissues associated with senescence. Wide variations were observed in the palisade parenchyma while spongy cells changed only very slightly. The major new functional information revealed was the link between the early senescence events and specific tissue dismantling processes

Impact of storage time and temperature of salad heads on the quality of fresh-cut Cichorium endivia

International audienceThe impact of temperature and storage time of escarole salad heads on the quality of processed, fresh-cut salad was investigated. Based on temperatures recorded in a fresh-cut processing plant, salad heads were stored for four different storage times (0, 5, 9, and 12 d) at four temperatures (4, 7, 10, and 12 ◦C) before being processed. A range of quality criteria (technical yield, global visual aspect, pink cut surfaces, mechanical texture, aerobic microflora, respiration rate, atmosphere composition in fresh-cut salad pouches, nuclear magnetic resonance transverse relaxation time) were measured on processing day, after 7 d storage at 4 ◦C of the fresh-cut salad packaged in pouches, and 1 d after pouch opening. The results are presented for salads grown in southeast France and early-season harvest, validated by experimental repetitions with a late-season harvest and salads from another geographical origin. Storage of salad heads caused deterioration of all quality attributes except for total aerobic bacteria. The global visual aspect was the most sensitive to changes in storage conditions of salad heads (significant reduction in quality for 5 d over 7 ◦C). In contrast, mechanical texture (maximum load for the shear test) was only significantly different for the fresh-cut salad prepared from salad heads stored for 9 d at 12 ◦C. For all quality criteria, fresh-cut salads processed from salad heads stored for 5 d at 4 and 7 ◦C were not significantly different from those of non-stored salad heads. For storage time of 5 d or less, a temperature of 7 ◦C is likely as good as 4 ◦C for escarole salad-head storage intended for fresh-cut processing

Thin-body ESD protections in 28nm UTBB-FDSOI: From static to transient behavior

International audienceInnovative Ultra-Thin Body and Buried Oxide FDSOI protections (BBC-T and Z2-FET) are characterized and analyzed in order to assess the CDM time domain behavior. In addition to static (leakage and triggering) control, it is found that front and back gate coupling is a very efficient way to improve the transient responses of the proposed devices

Verhaeren en son temps

Émile Verhaeren est mort accidentellement sur le quai de la gare de Rouen, le 27 novembre 1916. Il effectuait à ce moment des tournées de conférences en faveur du pays occupé. Autant que sa proximité avec la famille royale, cette circonstance a contribué à lui donner la stature d’un poète national, désormais enseigné à l’école et consacré par de nombreuses études. Ce sont quelques autres visages du poète que le présent numéro voudrait présenter, dans ce qu’ils peuvent, en apparence, avoir de mineur, de secondaire ou de marginal, mais qui ont, à leur manière, contribué à façonner l’image que nous en avons. On évoquera ainsi successivement la figure d’un Verhaeren journaliste, chroniqueur mondain ou collaborateur d’un journal politique, le Verhaeren intime et quelques aspects de son audience internationale. Pour enrichir le dossier de cette livraison double, plusieurs articles évoquent aussi ses contemporains et ses proches, de Félicien Rops à Victor Reding, le directeur du théâtre du Parc, de l’éditeur Octave Uzanne aux poètes Albert Mockel et André Fontainas, parmi d’autres. Les différentes approches réunies dans ce dossier complémentaire – études des échanges épistolaires, des rapports entre les arts, des transferts culturels – apportent des éclairages précieux sur l’époque de Verhaeren, cette période de l’histoire des lettres belges qui, pour être désormais bien connue, constitue toujours un terrain d’investigation fertile