ABSTRACT
Tannin-based rigid foams of different bulk densities and their carbonized counterparts were investigated for the first time by X-ray microtomography. This method allowed acquisition of three-dimensional pictures of such highly porous materials. Through mathematical treatment of the images, extremely useful physical characteristics such as porosity, fraction of open cells, connectivity, tortuosity, and pore-size distribution were determined as a function of the foam's density. The obtained information was compared with independent data derived from pycnometry measurements and scanning electron microscope image analysis. The agreement was shown to be acceptable in the limit of the accuracy of the laboratory microtomograph (4 microm). Moreover, recalculating properties like permeability were shown to be quite possible based on the results of standard microtomography data.
ABSTRACT
Intra-annual radial growth variations of two Norway spruce trees (Picea abies (L.) Karst.) were monitored over 4 years, at four heights up the stem, by means of point-dendrometers. The trees were then felled and radial wood samples were cut from the radii that had been monitored by the dendrometers and analyzed for density. From the radial growth measurements recorded by the dendrometers, we related positions within the rings to dates, thus making possible investigation of the relationships between changes within the rings in wood density and fluctuations in climate or growth rate. Radial growth started in early April and ended, with large intra-annual differences, in August or September. Short-term variations in growth rate were related to fluctuations in climate parameters and soil water reserves. The sensitivity of radial growth to climate decreased with stem height. Wood density responded strongly to drought events, and a dry period in June 1996 induced false-ring formation. Wood density was relatively independent of growth rate and climatic conditions during the first part of the growing season, but increased with decreasing radial growth rate later in the growing season.
