Formation de la bille de pied en culture d'arbres à bois précieux

The study has synthesized the knowledges we have about pruning of fast growing broadleaved species to form a straight, cylindrical and sound bole of high quality. We have followed the form evolution of wild cherries, ashes, sycamore and walnut, pruned or not, on agroforestry plots. With a grid discribing the main form defects, we have characterized each species by the number and the seriouness of its defects. The relationships between pruning intensity and the growth of trees and/or the appearance of epicormic shoots are studied in part through the construction of a software simulating the "structure-fonction" relationships of the walnut. / L'étude fait le point sur les connaissances acquises en matière de taille de formation et d'élagage des feuillus précieux en culture d'arbre pour former une bille de pied droite, cylindrique et sans noeud de haute valeur ajoutée. L'évolution de la forme de merisiers, frênes, érables et noyers, de leurs défauts de forme, avec ou sans taille, a été suivie pendant six ans sur le réseau agroforestier. Grâce à une grille de définition des principaux défauts, nous avons caractérisé chaque espèce quant à ses besoins en taille des points de vue gravité et nombre de défauts. Par ailleurs, les relations entre intensité de taille et perte de croissance et/ou production de gourmands sont abordées par la construction d'un logiciel de simulation de la croissance d'un arbre représentant en particulier les relations "structures-fonctions"

Magnetic field induced by elliptical instability in a rotating spheroid

International audienceThe tidal or elliptical instability of rotating fluid flows is generated by the resonant interaction of inertial waves. In a slightly elliptically deformed rotating sphere, the most unstable linear mode is called the spin-over mode and is a solid body rotation versus an axis aligned with the maximum strain direction. In the non viscous case, this instability corresponds to the median moment of inertia instability of solid rotating bodies. This analogy is furthermore illustrated by an elliptical top experiment, which shows the expected inviscid heteroclinic behaviour. In geophysics, the elliptical instability may appear in the molten liquid cores of rotating planets, which are slightly deformed by tidal gravitational effects of close bodies. It may then participate to the general outer core dynamics and possibly to the geodynamo process. In this context, Kerswell and Malkus (Kerswell, R.R. and Malkus, W.V.R., Tidal instability as the source for Io's magnetic signature, Geophys. Res. Lett., 1998, 25, 603-606) showed that the puzzling magnetic field of the Jovian satellite Io may indeed be induced by the elliptically unstable motions of its liquid core that deflect Jupiter magnetic field. Our magnetohydrodynamics experiment is a toy-experiment of this geophysical situation and demonstrates for the first time the possibility of an induction of a magnetic field by the flow motions due to the elliptical instability. A full analytical calculation of the magnetic dipole induced by the spin-over is presented. Finally, exponential growths of this induced magnetic field in a slightly deformed rotating sphere filled with Galinstan liquid metal are measured for different rotating rates. Their growth rates compare well with theoretical predictions in the limit of a vanishing Lorentz force

Quelle place pour une alimentation low-carb ou à index glycémique bas dans le diabète gestationnel ? [What is the place of a low carbohydrate or low glycemic index diet in gestational diabetes treatment?]

There is no real consensus on the ideal nutritional approach to recommend for gestational diabetes (GDM) treatment. A carbohydrates reduction (low-carb) is frequently suggested, although many studies have not found any consistent beneficial effects. On the other hand, according to recent meta-analyses, a low glycemic index (GI) diet would have favorable effects for the mother and the child. Although the clinical and practical value of GI is still being studied, a low GI diet seems to be the most appropriate approach in GDM. In addition, soluble fibers may have a beneficial metabolic impact in the short time of pregnancy. More evidence on the impact of these nutritional approaches in the short and long term for mother and child is needed

Reactive hypoglycaemia during the OGTT after gestational diabetes mellitus: Metabolic implications and evolution.

Gestational diabetes (GDM) presents an increased cardio-metabolic risk and is diagnosed with an oral glucose tolerance test (OGTT). Reactive hypoglycaemia (RH) during the OGTT in pregnancy is associated with adverse outcomes. Although postpartum OGTT after GDM is recommended, the occurrence and implications of RH are unknown. We investigated the prevalence, metabolic implications and longitudinal evolution of RH at 6-8 weeks postpartum in women with a history of GDM. Between 2011 and 2021, we consecutively followed 1237 women with previous GDM undergoing an OGTT at 6-8 weeks postpartum. RH was defined as 2-h glucose <3.9 mmoL/L after the OGTT. Metabolic outcomes were compared in women with and without RH (RH+/RH-). We also included a subcohort of 191 women with data on insulin sensitivity/secretion indices (MATSUDA, HOMA-IR, insulin-adjusted-secretion ISSI-2). The postpartum prevalence of RH was 12%. RH+ women had a more favourable metabolic profile including a 2-5-times lower prevalence of glucose intolerance and metabolic syndrome at 6-8 weeks postpartum compared to RH- (all p ≤ 0.034). In the subcohort, women with RH+ had higher insulin sensitivity, higher ISSI-2 and an earlier glucose peak after OGTT (p ≤ 0.049) compared to RH- women at the same time point. Insulin resistance increased and ISSI-2 decreased over the first year postpartum in both groups. These changes were associated with a 50% reduction in overall RH prevalence at 1-year postpartum. Some of the favourable profiles of RH+ persisted at 1-year postpartum, without group differences in the longitudinal metabolic changes. At 6-8 weeks postpartum, RH was frequent in women after GDM and associated with a better metabolic profile including increased insulin sensitivity and higher insulin-adjusted-secretory capacity. RH might be a marker of favourable metabolic prognosis in women with a history of GDM

Formation de la bille de pied en culture d'arbres a bois precieux

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