Sediment densities

HBsAg was the first viral antigen to be produced in transgenic plants. The protein self-assembles into subviral mammalian particles of 22 nm, and is virtually indistinguishable from serum-derived and yeast-derived HBsAg in both infected sera as well as commercial vaccines with respect to size, density sedimentation, and immunogenicity. 

Aquifer- sediment (constitutive degrader of TCE) 100 ml serum bottles 25 flM TCE within 24 h at high cell density, but not at all at lower densities. Sediment microcosms high densities removed all TCE overnight, lower densities took much longer (weeks). (1993)... 

FIGURE 11.21 When a salt is added to a colloidal dispersion (a), the repulsive forces between the colloidal particles are reduced and aggregation occurs (b). Eventually, the aggregated particles fall to the bottom of the container as low-density sediment (c). 

Fig. 3.16 Extractor used for the preparation of pore water from low density sediments (modified after Schluter 1990).

Diapiric traps are caused by differences in the density of sediment layers. In the ordinary way as sediments are buried they become compacted due to the overburdenpres-sure. They lose porosity and their density increases. There are two exceptions to this general rule in which low-density sediments may be overlain by denser sediment. This situation is inherently unstable. The deeper less dense material is displaced upward as the overburden bears... 

For large partides (> 1 pm and high density) sedimentation may occur during the measurement. In this case one can use a rectangular cell and observe the par-tides horizontally from the side of the glass cell. 

In most colloidal suspensions tire particles have a tendency to sediment. At infinite dilution, spherical particles with a density difference Ap with tire solvent will move at tire Stokes velocity... 

Generally, Httle is known in advance concerning the degree of homogeneity of most sampled systems. Uniformity, rarely constant throughout bulk systems, is often nonrandom. During the production of thousands of tons of material, size and shape distribution, surface and bulk composition, density, moisture, etc, can vary. Thus, in any bulk container, the product may be stratified into zones of variable properties. In gas and Hquid systems, particulates segregate and concentrate in specific locations in the container as the result of sedimentation (qv) or flotation (qv) processes. 

In sohd—sohd separation, the soHds are separated iato fractions according to size, density, shape, or other particle property (see Size reduction). Sedimentation is also used for size separation, ie, classification of soHds (see Separation, size separation). One of the simplest ways to remove the coarse or dense soHds from a feed suspension is by sedimentation. Successive decantation ia a batch system produces closely controUed size fractions of the product. Generally, however, particle classification by sedimentation does not give sharp separation (see Size MEASUREMENT OF PARTICLES). 

Particles in the gradient may be separated on the basis of sedimentation rate a sample introduced at the top of the preformed gradient setties according to density and si2e of particles, but the mn is terminated before the heaviest particles reach the bottom of the tube. If the density of all the particles ties within the range of the density limits of the gradient, and the mn is not terminated until all particles have reached an equiUbtium position in the density field, equiUbtium separation takes place. The steepness of the gradient can be varied to match the breadth of particle densities in the sample. 

Sohds in either phase are sedimented to the underside of the disks and shde outward along the surfaces because of their density. The aggregated sohds must move by free settling from the outer edges of the disks to the bowl wall some may be reentrained into new feed material, and carried into the disk stack, which accounts in part for actual performance falling short of theoretical prediction. 

The particle size deterrnined by sedimentation techniques is an equivalent spherical diameter, also known as the equivalent settling diameter, defined as the diameter of a sphere of the same density as the irregularly shaped particle that exhibits an identical free-fall velocity. Thus it is an appropriate diameter upon which to base particle behavior in other fluid-flow situations. Variations in the particle size distribution can occur for nonspherical particles (43,44). The upper size limit for sedimentation methods is estabHshed by the value of the particle Reynolds number, given by equation 11 ... 

In the United States, a number of physical tests are performed on siUcon carbide using standard AGA-approved methods, including particle size (sieve) analysis, bulk density, capillarity (wettabiUty), friabiUty, and sedimentation. Specifications for particle size depend on the use for example, coated abrasive requirements (134) are different from the requirements for general industrial abrasives. In Europe and Japan, requirements are again set by ISO and JSA, respectively. Standards for industrial grain are approximately the same as in the United States, but sizing standards are different for both coated abrasives and powders. 

Glassification. Classification (2,12,26,28) or elutriation processes separate particles by the differences in how they settle in a Hquid or moving gas stream. Classification can be used to eliminate fine or coarse particles, or to produce a narrow particle size distribution powder. Classification by sedimentation iavolves particle settling in a Hquid for a predetermined time to achieve the desired particle size and size distribution or cut. Below - 10 fim, where interparticle forces can be significant, gravitational-induced separation becomes inefficient, and cyclone and centrifugation techniques must be used. Classification also separates particles by density and shape. Raw material separation by differential sedimentation is commonly used in mineral processiag. 

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