Evolution et localisation des principaux cations au cours du développement du raisin

L'évolution des principaux cations de la baie de Cabernet Sauvignon a été étudiee de la floraison à la maturation. Les teneurs en calcium, potassium et magnesium ont été déterminées dans la pulpe et la pellicule et au niveau des parois et du contenu intracellulaire des cellules de ces deux tissus. Au cours du développement du raisin, les quantités de cations par baie augmentent; à maturite, les baies présentent 15 fois plus de potassium et deux fois plus de calcium et de magnesium par rapport aux baies vertes. En conséquence, le rapport K/Ca augmente et les proportions respectives de magnésium et de calcium restent relativement constantes. Au cours de la maturation, les cellules de la pellicule s'enrichissent en potassium et en calcium tandis que les cellules de la pulpe accumulent essentiellement du potassium. La repartition du magnésium dans les différentes parties de la baie varie peu. A maturité, les parois cellulaires de la pellicule sont riches en calcium; les cellules de la pulpe sont caracterisées par des quantités importantes de potassium intracellulaire et de faibles teneurs en calcium parietal.Evolution and localisation of the main cations during grape berry developmentThe evolution of the main cations was studied in developing grape berries (Vitis vinifera cv. Cabernet Sauvignon) from anthesis to ripeness. The calcium, potassium and magnesium contents of the skin and the fruit flesh and their distribution within cell wall and cell compartment were determined. The concentrations of these cations on per berry basis increased during the entire period of berry development. The ripe berry showed a potassium level 15 times more than green berries but calcium and magnesium increased only twofold. It resulted in an increase of the K/Ca ratio since Mg/Ca ratio remained constant during berry ontogeny. In contrast to the flesh cells which overall accumulated potassium, skin cells grew richer in potassium and calcium during ripening. There was little change in the magnesium distribution within the different parts of the berry. At maturity, a high calcium content characterised the skin cell wall; the flesh cells contained large quantities of potassium and little wall-calcium

Relation entre la teneur en calcium et la resistance à la digestion enzymatique du tissu pelliculaire au cours de la maturation du raisin

L'évolution du calcium au cours du développement et de la maturation du raisin est irrégulière . Les modifications de la teneur en calcium des fractions pariétales a des conséquences importantes sur les tissus de la baie, principalement sur le tissu pelliculaire dont l'évolution détermine le comportement de la baie face à une agression par un parasite tel que Botrytis cinerea. L'étude de la digestion enzymatique des pellicules de baies de différents cépages au cours de la maturation du raisin révèle que les pellicules les plus résistantes sont celles dont les teneurs en calcium pariétal sont les plus importantes. Plus précisément, la cohésion des parois cellulaires de la pellicule résulte essentiellement de l'état de complexation des substances pectiques chélatables par le calcium.Relation between calcium and resistance to enzymatic digestion of the skin during grape ripeningThe evolution of calcium during grape berry development and ripening is irregular. The changes in calcium content of cell wall will have important consequences, mainly on the skin which is responsible for the berry reaction during attack by pathogenic fungus Like Botrytis cinerea. Our study about the evolution of the susceptibility to enzymatic digestion of berry skin from different cultivars during ripening reveals that the more important the cell wall calcium content, the less susceptible is the skin. Precisely, cell wall cohesion of the skin tissue results in the chelation state of the pectic substances

Emergence of a filamentary structure in the fireball from GRB spectra

It is shown that the concept of a fireball with a definite filamentary structure naturally emerges from the analysis of the spectra of Gamma-Ray Bursts (GRBs). These results, made possible by the recently obtained analytic expressions of the equitemporal surfaces in the GRB afterglow, depend crucially on the single parameter R describing the effective area of the fireball emitting the X- and gamma ray radiation. The X- and gamma ray components of the afterglow radiation are shown to have a thermal spectrum in the co-moving frame of the fireball and originate from a stable shock front described self-consistently by the Rankine-Hugoniot equations. Precise predictions are presented on a correlations between spectral changes and intensity variations in the prompt radiation verifiable, e.g., by the Swift and future missions. The highly variable optical and radio emission depends instead on the parameters of the surrounding medium. The GRB 991216 is used as a prototype for this model.Comment: 9 pages, 3 figures, to appear on International Journal of Modern Physics

Evolution des polyosides des parois cellulaires au cours du développement du raisin

La composition en polyosides pariétaux des baies de raisin a été étudiée de la floraison à la maturité chez deux cépages bordelais, le Cabernet-Sauvignon et la Muscadelle. Les techniques histochimiques et densitométriques utilisées ont permis de suivre l'évolution de trois zones distinctes: la zone pelliculaire la plus externe, la zone pelliculaire sous-jacente et la pulpe. Au cours du développement des baies, les teneurs de la majorité des polyosides pariétaux diminuent, particulièrement chez la Muscadelle. Ce phénomène ne concerne pas la cellulose du tissu pelliculaire dont le taux reste constant lors de la maturation. Chez les deux cépages, les parois cellulaires de la pellicule sont toujours plus riches en polyosides que celles de la pulpe. A maturité, la proportion de pectines pariétales au niveau de la pellicule est plus importante chez le Cabernet Sauvignon. Evolution of cell wall polyosides during grape berry growth and ripeningThe content of cell wall polyosides of grape berries has been studied in two Bordeaux vine cultivars, Cabernet Sauvignon and Muscadelle. Three different zones were determined by histochemical and densitometric technics: external part of the skin, skin underlying cells and flesh. Their changes in polyosides have been followed from flowering to maturity. During the growth of the berries, the level of the cell wall polyosides decreases particularly in Muscadelle variety, whereas during ripening the berry skin cellulose levels remains constant. In the two cultivars, the cell walls of the skin are always richer than the flesh ones. At maturity, there are more pectins in the cell walls of the skin of Cabernet Sauvignon berries

Progress towards an accurate determination of the Boltzmann constant by Doppler spectroscopy

In this paper, we present significant progress performed on an experiment dedicated to the determination of the Boltzmann constant, k, by accurately measuring the Doppler absorption profile of a line in a gas of ammonia at thermal equilibrium. This optical method based on the first principles of statistical mechanics is an alternative to the acoustical method which has led to the unique determination of k published by the CODATA with a relative accuracy of 1.7 ppm. We report on the first measurement of the Boltzmann constant by laser spectroscopy with a statistical uncertainty below 10 ppm, more specifically 6.4 ppm. This progress results from improvements in the detection method and in the statistical treatment of the data. In addition, we have recorded the hyperfine structure of the probed saQ(6,3) rovibrational line of ammonia by saturation spectroscopy and thus determine very precisely the induced 4.36 (2) ppm broadening of the absorption linewidth. We also show that, in our well chosen experimental conditions, saturation effects have a negligible impact on the linewidth. Finally, we draw the route to future developments for an absolute determination of with an accuracy of a few ppm.Comment: 22 pages, 11 figure

On the structure of the burst and afterglow of Gamma-Ray Bursts I: the radial approximation

We have proposed three paradigms for the theoretical interpretation of gamma-ray bursts (GRBs). (1) The relative space-time transformation (RSTT) paradigm emphasizes how the knowledge of the entire world-line of the source from the moment of gravitational collapse is a necessary condition to interpret GRB data. (2) The interpretation of the burst structure (IBS) paradigm differentiates in all GRBs between an injector phase and a beam-target phase. (3) The GRB-supernova time sequence (GSTS) paradigm introduces the concept of induced supernova explosion in the supernovae-GRB association. These three paradigms are illustrated using our theory based on the vacuum polarization process occurring around an electromagnetic black hole (EMBH theory) and using GRB 991216 as a prototype. We illustrate the five fundamental eras of the EMBH theory: the self acceleration of the $e^+e^-$ pair-electromagnetic plasma (PEM pulse), its interaction with the baryonic remnant of the progenitor star (PEMB pulse). We then study the approach of the PEMB pulse to transparency, the emission of the proper GRB (P-GRB) and its relation to the ``short GRBs''. Finally the three different regimes of the afterglow are described within the fully radiative and radial approximations. The best fit of the theory leads to an unequivocal identification of the ``long GRBs'' as extended emission occurring at the afterglow peak (E-APE). The relative intensities, the time separation and the hardness ratio of the P-GRB and the E-APE are used as distinctive observational test of the EMBH theory and the excellent agreement between our theoretical predictions and the observations are documented. The afterglow power-law indexes in the EMBH theory are compared and contrasted with the ones in the literature, and no beaming process is found for GRB 991216.Comment: 96 pages, 40 figures, to appear on Int. Journ. Mod. Phys.

Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia

We report on our ongoing effort to measure the Boltzmann constant, $k_B,$ using the Doppler broadening technique on ammonia. This paper presents some of the improvements made to the mid-infrared spectrometer including the use of a phase-stabilized quantum cascade laser, a lineshape analysis based on a refined physical model and an improved fitting program 2 increasing the confidence in our estimates of the relevant molecular parameters, and a first evaluation of the saturation parameter and its impact on the measurement of k B. A summary of the systematic effects contributing to the measurement is given and the optimal experimental conditions for mitigating those effects in order to reach a competitive measurement of $k_B$ at a part per million accuracy level are outlined

Relative space-time transformations in GRBs

The GRB 991216 and its relevant data acquired from the BATSE experiment and RXTE and Chandra satellites are used as a prototypical case to test the theory linking the origin of gamma ray bursts (GRBs) to the process of vacuum polarization occurring during the formation phase of a black hole endowed with electromagnetic structure (EMBH). The relative space-time transformation paradigm (RSTT paradigm) is presented. It relates the observed signals of GRBs to their past light cones, defining the events on the worldline of the source essential for the interpretation of the data. Since GRBs present regimes with unprecedently large Lorentz $\gamma$ factor, also sharply varying with time, particular attention is given to the constitutive equations relating the four time variables: the comoving time, the laboratory time, the arrival time at the detector, duly corrected by the cosmological effects. This paradigm is at the very foundation of any possible interpretation of the data of GRBs.Comment: AASTeX, 10 pages, 2 figures, to appear in Ap. J. Let