The quality evaluation of cork planks in relation to porosity may use image analysis techniques. Results are presented on the number, dimensions, form and orientation of the lenticular channels in tangential, transverse and radial sections of cork planks of different thickness and qualities. The porosity coefficient (% pore area in relation to total area) varied between 1.1%-I8.9% and 2.1%-16.4%, respectively in tangential and transverse/radial sections and is determined mostly by the number of pores larger than 0.8mm 2 and by their average area, The porosity may be used to define cork quality classes. Due to the heterogeneous porosity distribution in cork plunks, an assessment of quality made on small cork samples will give a result with a large error. For an error below 15%, the observation in the tangential section should be made on a sample with a minimum area of 225cm 2 (e.g. 15 cm 15cm) and in the transverse and radial sections on a sample with a minimum length of 15cm.

We investigate the thermodynamic equilibrium states of a rotating thin shell, i.e., a ring, in a (2+1)-dimensional spacetime with a negative cosmological constant. The inner and outer regions with respect to the shell are given by the vacuum anti-de Sitter and the rotating Bañados-TeitelbomZanelli spacetimes, respectively. The first law of thermodynamics on the thin shell, together with three equations of state for the pressure, the local inverse temperature and the thermodynamic angular velocity of the shell, yields the entropy of the shell, which is shown to depend only on its gravitational radii. When the shell is pushed to its own gravitational radius and its temperature is taken to be the Hawking temperature of the corresponding black hole, the entropy of the shell coincides with the Bekenstein-Hawking entropy. In addition, we consider simple ansätze for the equations of state, as well as a power-law equation of state where the entropy and the thermodynamic stability conditions can be examined analytically.

Résumé -La croissance et la qualité du liège ont été caractérisées pour cinq suberaies de la région de production du bassin du fleuve Sado (Alcácer do Sal, Portugal), par un prélèvement d'échantillons sur 40 arbres par peuplement. En moyenne, l'épaisseur du liège était de 33,8 mm, dont 75 % du total appartenant aux classes commerciales au dessus de 27 mm, aptes au bouchonnage, et la porosité, mesurée par analyse d'image, 4,6 %. La qualité du liège montre une grande variabilité entre arbres d'une même suberaie et aussi entre suberaies. L'accroissement annuel moyen du liège pour un cycle de production de 8 ans complets était 4,1 mm. La croissance des années qui suivent le déliégeage est plus grande et diminue pendant le cycle. Pour cette région, le cycle de production de 9 ans est adapté aux débouchés industriels de la matière première. Les résultats montrent l'importance de la variabilité entre arbres de la croissance du liège et surtout de sa qualité. liège / croissance / qualité / porosité / variabilitéAbstract -Characterization of cork growth and quality in one region of production. Cork growth and quality were characterised in 5 cork oak stands within the production area of the Sado basin (Alcácer do Sal, Portugal) based on a field sampling on 40 trees/stand. Cork thickness was on average 33.8 mm, with 75% of the samples in the commercial classes above 27 mm suitable for production of stoppers. Porosity measured by image analysis was 4.6% on average. Between tree and between stand variability of cork quality was large. The annual average cork growth for a production cycle with 8 complete growth years was 4.1 mm, being highest during the years following cork extraction and decreasing during the cycle. For this region, a production cycle of 9 years is adequate for raw-material industrial requirements. The results show the importance of between tree variability in growth and especially in quality.cork / growth / quality / porosity / variability

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