Stem density

The porosity of the canopy is therefore n = 1- (n/4)ad. Using stem densities and diameters reported for the short- and tail-form of S. alterniflora [627], ad = 0(0.001)-0(0.01). In these marsh canopies the solid volume fraction ( ad) is sufficiently small to make the porosity effectively 1. However, in some freshwater marshes the solid volume fraction can be as high as 15%, corresponding to ad 0.2, and np = 0.8 (Fox et al., 2002 [196]). In mangrove swamps the solid volume fraction can be as high as 45%, np = 0.55, within the root zone [401],... 

Figure 6.7 Natural vegetation, for which stem density changes over depth, can be represented by a simpler canopy with a step distribution in frontal area density, a(z). This step distribution is generates a step profile of longitudinal velocity, (u).

Forests collect more pollutants than do surrounding surfaces with lower vegetation. For example, the forest edge will disturb the vertical wind profde and induce air turbulence that will in turn increase the dry deposition. The deposition at the front is considerably higher compared to that in the open field (by a factor of between 5 and 20), and also to that within the forest (a factor of 2 to 4). The increased deposition affects the vitality of the trees at the edge. Forest structures (tree species, crown density, stem density) differ widely in terms of aerodynamic roughness and leaf area, and these factors will each influence deposition. 

All the tests were conducted in under-critical flow conditions (Fr <1). 3 water depths were tested. For each water-depth condition, several flow discharges or cross-sectional averaged flow velocities were obtained through adjusting the power of the driving water pumps. Flow velocity was measured by the propeller velocimeter. For each test, the water pumps kept at a constant power value so that the flow can be considered steady. Several stem densities of vegetation were used for each flow depth and velocity condition. 

In this study, the base factor of Manning s n formula expressed in Eq. (2), n was tested for each water depth and condition on bare flume bottom. The adjustment factors nj and n2 were considered to be zero. The adjustment factor n3 for obstruction roughness were considered as the steel bars contribution and tested before each set of test for every flow depth, flow velocity and stem density of vegetation. The correction factor for meandering channels m5 was considered to be zero. Thus Eq. (2) can be written as ... 

The hydi ometer method is simpler in that the density of the suspension, which is related to the concentration, is read direc tly from the stem of the Iwdrometer while the depth is determined by the distance of the hydrometer bulb from the surface (ASTM Spec. Pub. 234, 1959). The method has low resolution but is widely used in soil science studies. 

There is intense interest in titanium. This interest stems from an unusual combination of desirable properties in one metal. It is strong it has low density and it is remarkably resistant to corro-... 

The ID profession has embraced plastics with enthusiasm for several reasons. First, plastics provide enormous freedom of shape compared with traditional materials of design. They also permit product production that is faster and more consistent, and they can do it all at a fraction of the cost for making nonplastic products. This low product cost does not stem from the fact that plastics are low in cost. On a per-pound basis, they are actually more costly than many competing materials. But the processability and relatively low density of plastics (which translates into lower costs per volume) gives them a big economic advantage. The net result is that the ID can now achieve quality products at disposable price levels (216). 

Much of the interest in ring-opening polymerizations stems from the fact that the polymers formed may have lower densities than the monomers from which they are derived (i.e. volume expansion may accompany polymerization).168-171 This is in marked contrast with conventional polymerizations which typically involve a nett volume contraction. Such polymerizations are therefore of particular interest in adhesive, mold filling, and other applications where volume... 

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