First tests of a 800 kJ HTS SMES

SMES using high critical temperature superconductors are interesting for high power pulsed sources. Operation at temperatures above 20 K makes cryogenics easier, enhances stability and improves operation as pulsed power source. In the context of a DGA (Delegation Generate pour l'Armement) project, we have designed and constructed a 800 kJ SMES. The coil is wound with Nexans conductors made of Bi-2212 PIT tapes soldered in parallel. The coil consists in 26 superposed simple pancakes wound and bonded on sliced copper plates coated with epoxy. The rated current is 315 A for an energy of 814 kJ. The external diameter of the coil is 814 mm and its height 222 mm. The cooling at 20 K is only performed by conduction from cryocoolers to make cryogenics very friendly and invisible for the SMES users. The cooling down has been successfully carried out and the thermal system works as designed. After a brief description of the SMES design and construction, some tests will be presented. From a current of 244 A, the SMES delivered 425 kJ to a resistance with a maximum power of 175 kW.Comment: 5 page

Biophysical and molecular determinants of vulnerability to cavitation in young poplars

Poster + Communication oraleTrees acclimate to changing environment. Water transport occurs under negative pressure from the roots to the leaves in the vascular system of the xylem. During water stress, the level of negative pressure can increase drastically and lead to the rupture of the water column. This cavitation event can be critical for the tree. Vulnerability to cavitation (VC) is a highly variable hydraulic trait that depends on the specie and the growing conditions. The anatomical parameters that drive the phenomena are still unknow. Actually, researches focus on the pits structures that are the hydraulic pathway between vessels. In this work, we investigated the impact of different growth conditions on pit structure of young poplars and the relationship with the VC. Xylem formed under stress conditions was analyzed using a multidisciplinary approach: - Ecophysiology: stomatal conductance, transpiration, leaf water potential, VC, primary and secondary growth were measured. - Wood anatomy was investigated at the tissue and cell wall level by optical and TEM microscopy. This approach was associated with X-ray microtomography observations to characterize the spatial distribution of cavitation. - Molecular analysis: We hypothezed that genes involved in VC may be involved in the biosynthesis of the cell wall and pits. We investigated the local transcriptome of the tissues. Preliminary results showed lower stomatal conductance, transpiration and leaf water potential for stressed plants than control plants. X-ray microtomography observations indicated that wood formed under water stress condition is more resistant to embolism. We will discuss the relationship between growth speed and VC

Phenotypic and genetic sources of variability of cavitation resistance in Pinus canariensis

Phenotypic and genetic sources of variability of cavitation resistance in Pinus canariensi

Modelling the mechanical behaviour of pit membranes in bordered pits with respect to cavitation resistance in angiosperms

Background and Aims Various correlations have been identified between anatomical features of bordered pits in angiosperm xylem and vulnerability to cavitation, suggesting that the mechanical behaviour of the pits may play a role. Theoretical modelling of the membrane behaviour has been undertaken, but it requires input of parameters at the nanoscale level. However, to date, no experimental data have indicated clearly that pit membranes experience strain at high levels during cavitation events. Methods Transmission electron microscopy (TEM) was used in order to quantify the pit micromorphology of four tree species that show contrasting differences in vulnerability to cavitation, namely Sorbus aria, Carpinus betulus, Fagus sylvatica and Populus tremula. This allowed anatomical characters to be included in a mechanical model that was based on the Kirchhoff–Love thin plate theory. A mechanistic model was developed that included the geometric features of the pits that could be measured, with the purpose of evaluating the pit membrane strain that results from a pressure difference being applied across the membrane. This approach allowed an assessment to be made of the impact of the geometry of a pit on its mechanical behaviour, and provided an estimate of the impact on air-seeding resistance. Key Results The TEM observations showed evidence of residual strains on the pit membranes, thus demonstrating that this membrane may experience a large degree of strain during cavitation. The mechanical modelling revealed the interspecific variability of the strains experienced by the pit membrane, which varied according to the pit geometry and the pressure experienced. The modelling output combined with the TEM observations suggests that cavitation occurs after the pit membrane has been deflected against the pit border. Interspecific variability of the strains experienced was correlated with vulnerability to cavitation. Assuming that air-seeding occurs at a given pit membrane strain, the pressure predicted by the model to achieve this mechanical state corresponds to experimental values of cavitation sensitivity (P50). Conclusions The results provide a functional understanding of the importance of pit geometry and pit membrane structure in air-seeding, and thus in vulnerability to cavitation

Modélisations numériques des pertes en régime variable dans des tubes supraconducteurs

Les pertes AC dans les câbles supraconducteurs générées par un environnement variable dans le temps impactent la cryogénie et donc la faisabilité industrielle des dispositifs supraconducteurs. Nexans est aujourd'hui sur le point de réaliser des fils cylindriques supraconducteurs pour des câbles de forte puissance. Aucune étude numérique n'a pour l'instant porté sur le calcul des pertes AC dans un ou plusieurs tubes. Cet article présente les étapes de création d'un modèle de calcul de pertes à l'aide d'un logiciel d'éléments finis pour une nouvelle géométrie :tube ou cylindre supraconducteur. La non-linéarité des formules E-J ainsi que les problèmes de convergence ont été traités par l'implémentation d'une formulation en H pour la résolution numérique. Les résultats ont été comparés aux formules analytiques. Dans le but de vérifier l'exactitude du modèle, une série de mesures expérimentales a aussi été réalisée sur un ruban supraconducteur industriel.</p

Couplages poroélastiques dans des branches naturelles et artificielles en lien avec la mécano-perception des plantes

Dans la nature les plantes sont soumises à des sollicitations mécaniques externes qui ont un impact important sur leur croissance. De façon remarquable, cette réponse en croissance n'est pas seulement locale mais aussi non-locale, suggérant un transport de l'information. Récemment, il a été suggéré que ce signal pourrait être une onde de pression générée par la flexion mécanique des branches. Afin de tester cette idée, nous avons élaboré une branche artificielle en élastomère de silicone (PDMS). De façon surprenante, la flexion d'une telle branche génère une surpression dont l'amplitude varie quadratiquement avec la déformation imposée. Pour comprendre l'origine de cette réponse non-linéaire, nous proposons un modèle énergétique simple. Des expériences sur des branches naturelles suggèrent la robustesse de ce mécanisme

Could thioredoxin h be involved in early response to gravitropic stimulation of poplar stems?

The perception of gravity is essential for plant development. Trees constantly develop specialized woody tissues, termed « reaction wood » to correct inclined branch and stem growth in order to adopt an optimal position. Despite the economical impact of reaction wood occurrence and itsimportance from a developmental point of view, the perception and response to the gravitational stimulus have not been extensively studied in woody species in which primary and secondary growth occur. Using complementary approaches (proteomics, qRT-PCR, immunolocalization), we have compared straight polar stems to stems that were inclined at 35° from the vertical axis for periods of time varying from 10 min to 6 hours depending on the experiments. The proteomics approach revealed that thirty six percent of the identified proteins that were differentially expressed after gravistimulation were established as potential Thioredoxin targets. qRT-PCR indicated an early induction of Thioredoxin h expression following gravistimulation. In situ immunolocalization indicated that Thioredoxin h protein co-localized with the amyloplasts located in the endodermalcells which may be specialized in gravity perception. These investigations suggest the involvement of Thioredoxin h in the first events of signal transduction in inclined poplar stems, leading to reaction wood formation

Xylem embolism and bubble formation during freezing suggest complex dynamics of pressure-tension in Betula pendula stems

Freeze-thaw-induced embolism is a key limiting factor for perennial plants in frost-exposed environments. Gas bubbles are formed during freezing, when the low chemical potential of the ice reaches a critical cavitation threshold and expand during thawing. However, when water freezes, its volume increases by 9%, generating local pressures, which can limit the formation of bubbles. To characterize local dynamic of pressure-tension and physical state of the sap during freeze-thaw cycles, we simultaneously used ultrasonic acoustic emissions analysis and synchrotron-based High Resolution Computed Tomography on the diffuse-porous species Betula pendula. Visualization of individual air-filled vessels was performed to measure freeze-thaw induced embolism after successive freeze-thaw cycles down to -10C or -20C during the leafy and the leafless periods. We also measured the distribution of gas bubbles and made additional continuous monitoring of embolism spreading using a dedicated cooling system that allowed X-ray scanning during freezing and thawing. Experiments confirmed that ultrasonic emissions occurred after the onset of ice formation, together with bubble formation, whereas the development of embolism took place after thawing in all cases. The pictures of frozen tissues indicated that upon freezing the balance between negative pressure generated by the low water potential of the ice and the positive pressure induced by the volumetric increase of ice can provoke inward flow from the cell wall toward the lumen of the vessels. We found no evidence that wider vessels within a tissue were more prone to embolism although the occurrence of gas bubbles in larger conduits would make them prone to earlier embolism. These results highlight the need to monitor local pressure as well as ice and air distribution during xylem freezing to understand the mechanism leading to frost-induced embolism.Comment: 41 pages, 7 figures, 4 supplementary figure

Photosynthesis, leaf hydraulic conductance and embolism dynamics in the resurrection plant Barbacenia purpurea

The main parameters determining photosynthesis are stomatal and mesophyll conductance and electron transport rate, and for hydraulic dynamics they are leaf hydraulic conductance and the spread of embolism. These parameters have scarcely been studied in desiccation-tolerant (resurrection) plants exposed to drought. Here, we characterized photosynthesis and hydraulics during desiccation and rehydration in a poikilochlorophyllous resurrection plant, Barbacenia purpurea (Velloziaceae). Gas exchange, chlorophyll fluorescence, and leaf water status were monitored along the whole dehydration-rehydration cycle. Simultaneously, embolism formation and hydraulic functioning recovery were measured at leaf level using micro-computed tomography imaging. Photosynthesis and leaf hydraulic conductance ceased at relatively high water potential (?1.28 and ?1.54?MPa, respectively), whereas the onset of leaf embolism occurred after stomatal closure and photosynthesis cessation (<?1.61?MPa). This sequence of physiological processes during water stress may be associated with the need to delay dehydration, to prepare the molecular changes required in the desiccated state. Complete rehydration occurred rapidly in the mesophyll, whereas partial xylem refilling, and subsequent recovery of photosynthesis, occurred at later stages after rewatering. These results highlight the importance of stomata as safety valves to protect the vascular system from embolism, even in a plant able to fully recover after complete embolism.Este trabajo fue apoyado por el proyecto PGC2018-093824-B-C41 del Ministerio de Ciencia, Innovación y Universidades (España), el Fondo Europeo de Desarrollo Regional (FEDER), y La Région Auvergne-Rhône-Alpes "Pack Ambition International 2020" a través del proyecto "ThirsTree" 20-006175-01, 20-006175-02. MN recibió el apoyo de la beca predoctoral BES-2015-072578, financiada por el Ministerio de Economía y Competitividad (MINECO) y el Fondo Social Europeo; y las becas postdoctorales Juan de la Cierva-Formación (FJC2020-043902-I y FJC2020-042856-I), financiadas por MCIN/AEI/10.13039/501100011033 (España) y la Unión Europea ("NextGenerationEU/PRTR").Barbacenia purpureaPublishe