Particles grazing

Regardless of these short-ranged cohesive forces, the formation and stability of particle clusters in a fluidized bed appears to be a multistep process [27], Some shear (as in two particles grazing each other) may be needed to promote collisional cooling, but less than that perhaps in the dense emnlsion of a fluidized bed. Perhaps the lower particle concentration in a babble provides the environment where clnster stability is promoted for the smaller particles. Collisional stresses in the emnlsion may be too high and the cohesive forces may be too low to have long-lasting particle clusters. Indeed, the only evidence of particle clnsters in fluidized beds offered here is that the clusters are located near the bubbles. 

Filtration is a physical separation whereby particles are removed from the fluid and retained by the filters. Three basic collection mechanisms involving fibers are inertial impaction, interception, and diffusion. In collection by inertial impaction, the particles with large inertia deviate from the gas streamlines around the fiber collector and collide with the fiber collector. In collection by interception, the particles with small inertia nearly follow the streamline around the fiber collector and are partially or completely immersed in the boundary layer region. Subsequently, the particle velocity decreases and the particles graze the barrier and stop on the surface of the collector. Collection by diffusion is very important for fine particles. In this collection mechanism, particles with a zig-zag Brownian motion in the immediate vicinity of the collector are collected on the surface of the collector. The efficiency of collection by diffusion increases with decreasing size of particles and suspension flow rate. There are also several other collection mechanisms such as gravitational sedimentation, induced electrostatic precipitation, and van der Waals deposition their contributions in filtration may also be important in some processes. 

HANSEN B, WERNBERG-MOLLER T and wiTTRUP L (1997) Particle grazing efficiency and specific growth of the rotiicx Brachionus plicatilis (Muller)./owmal of Experimental Marine Biology and Ecology 215 217-233. 

Copper supplements can also have an anthelmintic effect. Small amounts of copper oxide wire particles (COWP) were effective against both incoming and established Haemonchus contortus worms (Bang et al., 1990) and a mineral supplement containing elemental copper reduced faecal egg counts in lambs (Lindqvist et al., 2001). Also, Burke et al. (2004) showed a great reduction of faecal egg counts and adult worm burden of H. contortus in COWP-treated lambs. However, Dimander et al. (2003) could not show an effect against GIN in grazing cattle. 

Let us consider what we can learn about cross sections from some general considerations. Consider the reaction of an uncharged particle (a neutron) with a nucleus as shown in Figure 10.7. The neutron makes a grazing collision with the nucleus. The impact parameter b is taken to be the sum of the radii of the projectile and target nuclei. Thus, the cross section can be written as... 

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