Relations entre l'allongement et l'épaississement de la pousse annuelle des rejets de châtaignier (Castanea sativa Mill) au cours des deux premières années de leur développement

L'étude a pour objectif de préciser les relations entre l'allongement et l'épaississement de la pousse annuelle au cours de 2 premières années du développement des rejets de souche chez le châtaignier. Elle est fondée sur une comparaison directe, à partir de graphiques, de l'allongement et de l'épaississement de chacune des pousses au cours de l'activité annuelle des rejets. L'évolution relative de ces deux paramètres est traduite par des courbes sur lesquelles apparaissent des «vagues» de fluctuation liées au fait qu'un type d'activité est momentanément prépondérant sur l'autre et inversement. Les rejets ont un comportement hétérogène. Le nombre de «vagues» de fluctuation varie de 1 à 4, avec des comportements intermédiaires pour lesquels les 2e et 3e vagues sont seulement amorcées. Un faible nombre de rejets ne présente pas de «vagues» marquées. Les «vagues» sont d'autant plus nombreuses que la croissance de la pousse est plus importante et plus durable. La fin de la période évolutive allongement-épaississement correspond, pour un tiers des rejets, à un ralentissement progressif de la croissance en longueur alors que l'activité cambiale tend à devenir prédominante. Par contre, pour un autre tiers des rejets, l'allongement initialement prédominant s'interrompt assez brusquement, l'activité cambiale reprend alors très nettement. L'influence exercée par la souche sur la croissance des rejets est peu apparente. Ces résultats sont discutés dans les termes de déterminisme externe ou interne du comportement des rejets, ainsi que par comparaison avec les données précédemment acquises par nous sur le même matériel.Relationships between elongation and diameter growth of the annual sprout during the first 2 years of development in chestnut tree stump shoots (Castanea sativa Mill). The present investigation aims to clarify the relationships between elongation and diameter growth of the annual sprout during the first 2 yr of development in chestnut tree stump shoots. The analysis is based on the direct comparison of the diagrams on lengthening and basal diameter growth of each annual sprout. The relative evolution of these 2 parameters is demonstrated by the curves on which fluctuation waves appear. They indicate that one type of growth activity prevails temporarily over the other , and conversely (figs 9-14). Stump shoot behaviour is variable; their final length and diameter are very heterogeneous (figs 1-4). The same holds true for duration of elongation activity phase (figs 5, 6). However, duration of diameter growth phase is more homogeneous (figs 7, 8). The number of fluctuation waves varies from 1 to 4 (figs 9, 10, 12, 14) with intermediate behavioural types in which the second and third waves are only initiated (figs 11, 13). Some stumps do not show marked fluctuation waves (fig 15). In one third of them, the '1 wave', '2 wave' or 'two and a half wave' stump shoots are dominated by stump shoots with only 1 elongation activity phase. On the other hand, most of the '3 wave', 'three and a half-wave' and '4 wave' stump shoots are dominant and their significant elongation shows 2 successive phases of activity. In another third of the stump shoots the end of the growth evolution period corresponds to a gradual decrease in the elongation speed when cambial activity tends to become predominant (figs 12, 14). Conversely, in the remaining third initially predominant elongation stops abruptly when cambial activity starts again (figs 9, 10, 15). Stump influence on the growth of shoots is low. Our results are discussed in terms of the external or internal determinism of stump shoot behaviour and also by comparison with our previous results obtained on the same material

Croissance de la pousse annuelle au cours des deux premières années du développement des rejets de châtaignier (Castanea sativa Mill). Mise en évidence d'un rythme endogène, influence du facteur thermique

L'étude a pour objectif de préciser la cinétique de la croissance de la pousse annuelle au cours des 2 premières années du développement des rejets de souche chez le châtaignier. L'analyse de la croissance résulte d'observations concernant l'allongement de la pousse, l'accroissement du diamètre à sa base, le nombre de feuilles. Les variations des différents paramètres sont comparées à celles de la température. L'allongement, l'épaississement et le nombre de feuilles ne varient pas de façon simultanée. Ainsi, la croissance en épaisseur de la pousse se poursuit après l'arrêt de l'allongement et de l'activité plastochronique. D'autre part, la durée de la période de croissance montre de fortes variations individuelles. Cependant, la croissance de la pousse s'établit le plus souvent en 2 phases principales au cours de la période d'activité annuelle. Ce comportement est particulièrement remarquable dans le cas de l'allongement où les 2 périodes d'activité sont séparées par une période de repos plus ou moins profond et prolongé. Parfois l'allongement se limite à la 1re phase d'activité. Les caractéristiques de l'allongement d'une même pousse peuvent être très différentes au cours des 2 phases d'activité, la longueur finale de la pousse étant mieux corellée avec l'allongement pendant la 2nde phase que pendant la première. Enfin, c'est seulement au cours de la 1re phase de l'allongement qu'on a pu mettre en évidence des correspondances entre les variations de la température et de la croissance.Growth of the annual sprout during the first two years In chestnut tree stump shoots (Castanea sativa Mill). The influence of temperature. The present investigation aims to clarify the growth kinetics of the annual sprout during the 1st 2 years in the development of chestnut stump shoots. The growth is evaluated from observations of elongation, diameter growth, and number of leaves. The variations of these different parameters are compared with those of mean temperatures. The study of the sprout elongation during the 1st and the 2nd year reveals the presence of 2 phases of activity separated by deep and long rest periods. This takes place during late June or early July (figs 2a, 3a). A few sprouts stop lengthening at the end of the 1st active phase (fig 1a). The correlations between lengthening and temperatures are generally significant within the 1st active phase (fig 4) but non-significant within the 2nd. The variations in the number of leaves (figs 1b, 2b) correspond roughly to those of lengthening. However, the correlations between number of leaves and temperatures are seldomly significant (fig 5). The diameter growth of the sprouts also includes 2 main phases of activity, but the fluctuation periodicity is different from that of lengthening. In particular, the diameter growth continues after the lenghtening one (figs 1c, 2c, 3c). The correlations between diameter growth and temperature are never significant (fig 6). The growth of the annual sprout during the 1st 2 years in chestnut stump shoots is divided into 2 main phases of activity. However, the different parameters used to characterize the growth of the sprout do not vary simultaneously. The fluctuation in lengthening and the number of leaves seem to be synchronous, but this is not the case for diameter thickening. Finally, large individual variations can occur throughout the duration of the growing period and the growth velocity. For any given shoot, the characteristics of the 2 successive phases of activity can be very different so that the final size of the sprout correlates better with the growing characteristics during the 2nd phase rather than during the first

Effect of pores and grain size on the elastic and piezoelectric properties of quartz-based materials

The role of grain size and porosity in the piezoelectric and elastic properties of SiO2-based materials was investigated using resonant piezoelectric spectroscopy (RPS) and resonant ultrasound spectroscopy (RUS). RPS performed on agate revealed a piezoelectric effect comparable in magnitude to that in single-crystal quartz. The observed strong piezoelectricity in agate requires preferential orientation of SiO2 during crystal growth. Similarly, in novaculite and sandstone finite (but weak) RPS signals were evident, suggesting that the expected randomization of the piezoelectric quartz grains is incomplete. On the other hand, Vycor, a silica glass with a porosity of 40, showed no evidence of the piezoelectric effect. According to temperature-dependent RPS and RUS measurements, the α-β transition temperature in quartz does not change in polycrystalline samples. Finally, the temperature dependence under heating of the elastic constants is reversible in quartz and agate and irreversible in sandstone and Vycor

Investigating the delay between dust radiation and star-formation in local and distant quenching galaxies

International audienceWe investigate the timescale over which the infrared (IR) luminosity decreases after a complete and rapid quenching of star formation using observations of local and high-redshift galaxies. From spectral energy distribution modelling, we derive the time since quenching of a subsample of 14 galaxies from the Herschel Reference Survey that suffer from ram-pressure stripping due to the environment of the Virgo cluster and of a subsample of 7 rapidly quenched COSMOS galaxies selected through a state-of-the-art statistical method already tested on the determination of galaxy star formation history (SFH). Three out of the seven COSMOS galaxies have an optical spectrum with no emission line, confirming their quenched nature. We obtained the present physical properties of the combined sample (local plus high-redshift) from the long-term SFH properties, as well as the past LIR of these galaxies just before their quenching. We show that this past LIR is consistent with the LIR of reference samples of normally star-forming galaxies with same stellar mass and redshift as each of our quenched galaxies. We put constraints on the present to past IR luminosity ratio as a function of quenching time. The two samples probe different dynamical ranges in terms of quenching age with the HRS galaxies exhibiting longer timescales (0.2–3 Gyr) compared to the COSMOS ones (< 100 Myr). Assuming an exponential decrease in the LIR after quenching, the COSMOS quenched galaxies are consistent with short e-folding times of less than a couple of hundred million years, while the properties of the HRS quenched galaxies are compatible with larger timescales of several hundred million years. For the HRS sample, this result is consistent with the known quenching mechanism that affected them, namely ram pressure stripping due to the environment. For the COSMOS sample, different quenching processes are acting on short to intermediate timescales. Processes such as galaxy mergers, disk instabilities, and environmental effects can produce such strong star formation variability

Macroscopic electrostatic effects in the ATR-FTIR spectrum of modern and archeological bones. Macroscopic electrostatic effects in ATR-FTIR spectra of modern and archaeological bones

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Unraveling weathering episodes in Tertiary regoliths by kaolinite dating (Western Ghats, India)

Secondary minerals in soils can record climatic changes affecting continental surfaces over geological times. Their dating should refine our present knowledge about their potential periods of formation as well as their relations with the ongoing change of climate and erosion/weathering regimes. In the present study, twenty kaolinite samples from two lateritic profiles of the Karnataka plateau, an intensively studied area in the southern India, have been dated using electron paramagnetic resonance (EPR) spectroscopy. Kaolinite ages vary between 0.229(+/- 0.24) Ma to 40.73(+/- 15.37) Ma. Four different groups of age can be identified with ages clustered around 1.0, 3.5, 9.0 and 39.0 Ma. These groups of age indicate local preferential weathering periods that coincide with distinct Indian climatic events described in independent studies, such as monsoon strengthening. Thus, regional or subcontinental factors likely prevailed over global forcing in the imprint of climatic events in the regolith profiles. These results confirm that despite their simple mineralogy, laterites can contain several relictual and coexisting generations of secondary minerals and that EPR dating of kaolinite contributes to unraveling the complex history of continental surfaces over geological periods

Diffusion and viscosity in polysaccharide solutions: Beyond Stokes-Einstein

Non-starch polysaccharides such as arabinoxylans (AXs) have important roles in diet, especially in so-called resistant starch, which results in cholesterol lowering.1 This beneficial effect may arise from viscosity or diffusion phenomena in the gut. In the present study, the diffusion coefficients of a dextran probe in solutions of three AXs of different viscosities were measured. The diffusion coefficients of a dextran probe (MW = 7.0×104) in solutions of three different arabinoxylans over a wide concentration range were carried out using fluorescent recovery after photobleaching (FRAP

Prise en charge du patient en hospitalisation ambulatoire pour la réalisation d’un traitement de radiologie interventionnelle (RI)

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