Vertical segregation

Air Entrainment. Fine particles generally have a lower permeabiUty than coarse particles, and therefore tend to retain air longer in void spaces. Heavier particles settie more quickly in a duidized mixture than lighter particles. Thus, when a mixture of particles is charged into a bin, it is not uncommon to find a vertical segregation pattern, where the coarser, heavier particles concentrate at the bottom of the bed and the finer, lighter particles concentrate near the top. 

The importance of polydispersity is an interesting clue that it may be possible to tailor the weak interactions between polymer brushes by controlled polydispersity, that is, designed mixtures of molecular weight. A mixture of two chain lengths in a flat tethered layer can be analyzed via the Alexander model since the extra chain length in the longer chains, like free chains, will not penetrate the denser, shorter brush. This is one aspect of the vertical segregation phenomenon discussed in the next section. 

The vertical distribution of biolimiting elements is characterized by deep-water enrichments and surface-water depletions. As described above, this vertical segregation is caused by the remineralization of biogenic particles in the deep sea. Not all particulate matter that sinks into the deep zone is remineralized. Some survives to become buried in the sediments. How much of the biogenic particle flux escapes from surfece waters How much of this particle flux is remineralized in the deep zone How much is lost from the ocean by burial in the sediments What effect does this have on the concentrations of the biolimiting elements ... 

The burial of BSi is the most important mechanism by which dissolved silicon is removed from the ocean. Most of the BSi is deposited by surfece-dwelling plankton whose actions collectively keep surface-water DSi concentrations very low (<5 p-M). Remineralization of sinking detrital BSi leads to vertical segregation of DSi as illustrated in Figure 10.1, with average deepwater concentrations around 100 pM. In the present-day ocean, abiogenic precipitation is important only in locations, such as pore waters and estuaries, where DSi concentrations are very high. 

Summer time conditions of nutrient limitation result from grazing and vertical segregation of nutrients. ... 

Vertical segregation The vertical gradient in biogenic materials, such as nutrients and O2, that is established by the interaction between the biogeochemical cycling of particulate organic matter and the vertical density stratification of the water column. Strongest at mid and low latitudes. 

M 14] [P I3]The fluorescent droplet is moved towards the non-fluorescent droplet and the coalesced droplet is held in place [97] (see also an initial experiment in [98]). By this action, the fluorescent droplet moves underneath the non-fluorescent one. From a top view, a homogeneous texture is yielded however, a vertically segregated fluidic system exists (see Figure 1.37). Mixing takes then place by diffusion and needs about 90 s to be completed. 

Figure 15.6. Photosynthesis and respiration, (a) A well-balanced ecosystem may be characterized by a stationary state between photosynthetic production, P (rate of production of organic material) and heterotrophic respiration, R (rate of destruction of organic matter). Photosynthetic functions and respiratory functions may become vertically segregated in a lake or in the sea. In the surface waters the nutrients become exhausted by photosynthesis, (b) The subsequent destruction (respiration) of organism-produced particles after settling leads to enrichment of the deeper water layers with these nutrient elements and a depletion of dissolved oxygen. The relative compositional constancy of the aquatic biomass and the uptake (P) and release (R) of nutritional elements in relatively constant proportions (see equation 3) are responsible for a co-variance of carbon, nitrate, and phosphate in lakes (during stagnation period) and in the ocean an increase in the concentration of these elements is accompanied by a decrease in dissolved oxygen, (c, d) The constant proportions AC/AN/AP/AO2 typically observed in these waters are caused by the stoichiometry of the P-R processes.

---