Diffuse-porous

ZerstraUtmg, /. annihilation radiation, zerstreuen, v.t. disperse, scatter, disseminate, dissipate, diffuse divert, distract. — zer-streut, p.a. dispersed, etc. diffuse disperse abstracted, distracted, zerstreutporig, a. diffuse-porous. 

Figure 2.1 Light photomicrographs of wood cross-sections illustrating different anatomical features of softwood and hardwood (a) pine (softwood), (b) birch (diffuse porous hardwood), (c) oak (ring porous hardwood). Scale bar = 200 m.

Figure 6. Cross-sectional and longitudinal views of a diffuse-porous wood. Note in cross section that the vessels, the large diameter cells, are essentially the same size throughout the growth ring. Both longitudinal views reveal the vessels (V) are formed as the result of individual vessel cells stacked one on top of the other in the longitudinal direction. The majority of the remaining cells are small diameter fibers. 70 X (Courtesy of N. C. Brown Center for Ultra-structural Studies, S.U.N.Y. College of Environmental Science and Forestry)...

Figure 16. Types of vessel segments found in hardwoods. A and B springwood vessels from a ring-porous wood. Note the short length compared with the diameter. C and D typical vessel elements from diffuse-porous woods with simple perforation plates at each end. E typical diffuse-porous vessel element with scalariform perforation plates at each end. 140X...

Fig. 28.3. Photomicrograph of hardwood cross-sections depicting (a) ring-porous and (b) diffuse porous wood. (Courtesy U.S.D.A Forest Products Laboratory.)...

Figure 10. Light micrograph of the three types of pore patterns of growth increments in hardwoods as seen in cross section. Key A, ring-porous (red oak) B, semi-ring-porous (aspen) and C, diffuse-porous (yellow birch). (Reproduced with permission from Ref. 40. Copyright 1982, Technical Association of the Pulp and Paper Industry Press.)...

Figure 1.21. Vessels throughout the growth Figure 1.22. Large earl)fwood vessels in the ring in the diffuse porous wood of Populus ring porous wood of Quercus robur. x 40. robusta. x 60.

All possible patterns of wood density variation appear in hardwoods. The middle to high density diffuse-porous hardwoods generally follow a pattern of low basic density near the pith and then an increase, followed by a slower increase or levelling off toward the bark. The low density, diffuse-porous woods, such as Populus, seem to have a somewhat higher density at the pith, although some have a uniform density from pith to bark [while Populus deltoids increases in density from pith to bark (Shukla et al,... 

Their diversity of habitat is such that generally one can find a species or hybrid that offers superior growth rates to most other species under almost any condition and, being diffuse-porous hardwoods, the density of their wood is not greatly influenced by their growth rate. A further plus is their genetic diversity. 

Sperry, J, S, Nichols, K, L., Sullivan, J, E, M., and Eastlack, S. E. (1994). Xylem embolism in ring-porous, diffuse-porous, and coniferous trees of Northern Utah and interior Alaska. F.cology 75, 1736- 1752. 

However, the two-sink model as well as other existing adsorption (sink) models do not seem to be able to describe the strong asymmetry between the adsorption/desorption of VOCs on/from indoor surface materials (the desorption process is much slower than the adsorption process). Diffusion combined with internal adsorption is assumed to be capable of explaining the observed asymmetry. Diffusion mechanisms have been considered to play a role in interactions of VOCs with indoor sinks. Dunn and Chen (1993) proposed and tested three unified, diffusion-limited mathematical models to account for such interactions. The phrase unified relates to the ability of the model to predict both the ad/absorption and desorption phases. This is a very important aspect of modeling test chamber kinetics because in actual applications of chamber studies to indoor air quality (lAQ), we will never be able to predict when we will be in an accumulation or decay phase, so that the same model must apply to both. Development of such models is underway by different research groups. An excellent reference, in which the theoretical bases of most of the recently developed sorption models are reviewed, is the paper by Axley and Lorenzetti (1993). The authors proposed four generic families of models formulated as mass transport modules that can be combined with existing lAQ models. These models include processes such as equilibrium adsorption, boundary layer diffusion, porous adsorbent diffusion transport, and conveetion-diffusion transport. In their paper, the authors present applications of these models and propose criteria for selection of models that are based on the boundary layer/conduction heat transfer problem. 

White-Poplar. Poplar is a diffuse porous wood composed of vessels surrounded by fiber cells. There are rays, and a few axial parenchyma strands along the border of the annual rings, but on the whole it is a more homogeneous wood than the species examined so far. 

The quantification of the mobility of different cations in various types of wood, i.e. ring- and diffuse-porous as well as conifer wood. 

Several thousands of hardwood species exist, and each one has its own anatomical pattern. The density, for example, ranges from less than 100 kg m" (i.e., balsa wood) up to more than 1200 kg m" (i.e., ebony wood). They are usually divided into ring-porous and diffuse-porous types, though all intermediate types can be found ... 

Diffuse-porous species have smaller vessels (50-100 pm in diameter) of almost uniform size and distribution throughout the growth ring. In diffuse-porous species, vessel cells are usually connected by scalariform ( ladderlike ) perforation plates. 

FIGURE 40.5 Typical anatomical patterns encountered in temperate species (a) softwood, (b) ring-porous species, and (c) diffuse-porous species. The height of these images represents about 2 mm. (Microphotographs J.C. Mosnier, LERMAB-ENGREF, Nancy, France.)... 

The diffuse-porous hardwoods are fairly permeable too probably, the large number of vessels can offset their smaller diameter (around 50 pm). 

FIGURE 40.15 Capillary-function curves determined using image analysis, (a) Spruce (Picea abies) the cells have thicker walls and smaller radial extension in latewood part, hence the highest value of the capillary-pressure curve. One also has to be aware that full saturation is obtained with a lower amount of water in latewood (the porosity of this part is very small) (b) beech (Fagus sylvatica) because beech is a pore diffuse-porous hardwood species, no significant difference is observed between these parts. The low capillary pressure obtained for saturation values above 0.2 corresponds to the meniscus radii located in the vessel elements. The dramatic increase for low saturation values is due to the small lumen diameters of the parenchyma and fiber cells. 

The situation is more complex with hardwoods. The growth rate has little effect on the wood properties of diffuse-porous hardwoods, but has a marked impact on the density of ring-porous hardwoods. Unlike softwoods, these produce denser wood when fast grown. 

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