Shell thickening

Apart from gastropods, harmful effects of TBT have also been demonstrated in oysters (Environmental Health Criteria 116, Thain and Waldock 1986). Early work established that adult Pacific oysters (Crassostrea gigas) showed shell thickening caused by the development of gel centers when exposed to 0.2 pg/L of TBT fluoride (Alzieu et al. 1982). Subsequent work established the no observable effect level (NOEL) for shell thickening in this, the most sensitive of the tested species, at about 20 ng/L. It has been suggested that shell thickening is a consequence of the effect of TBT on mitochondrial oxidative phosphorylation (Alzieu et al. 1982). Reduced ATP production may retard the function of Ca++ ATPase, which is responsible for the Ca++ transport that leads to CaCOj deposition during the course of shell formation. Abnormal calcification causes distortion of the shell layers. 

This situation is termed pore-mouth poisoning. As poisoning proceeds the inactive shell thickens and, under extreme conditions, the rate of the catalytic reaction may become limited by the rate of diffusion past the poisoned pore mouths. The apparent activation energy of the reaction under these extreme conditions will be typical of the temperature dependence of diffusion coefficients. If the catalyst and reaction conditions in question are characterized by a low effectiveness factor, one may find that poisoning only a small fraction of the surface gives rise to a disproportionate drop in activity. In a sense one observes a form of selective poisoning. 

Waldock, MJ. and J.E. Thain. 1983. Shell thickening in Crassostrea gigas organotin antifouhng or sediment induced Mar. Pollut. Bull. 14 41 I -415. 

C. gigas 0.15 Reduced growth and shell thickening after 8 weeks 11... 

In summary, the microimaging technique provides a powerful tool to study directly the mechanism of converting water droplets to hydrate particles. The results reported indicate that provided the gas hydrate former can diffuse into the interior droplet, hydrate growth can proceed in the bulk interior droplet away from the hydrate shell-water interface, as well by growing out from the hydrate shell resulting in shell thickening. 

Chitosan Crustaceans (controlled enzymatic degradation of shells) Thickening for paints cosmetics, make-up, diet products... 

Solvent Evaporation. This encapsulation technology involves removing a volatile solvent from either an oil-in-water, oil-in-oil, or water-in-oH-in-water emulsion (19,20). In most cases, the shell material is dissolved in a volatile solvent such as methylene chloride or ethyl acetate. The active agent to be encapsulated is either dissolved, dispersed, or emulsified into this solution. Water-soluble core materials like hormonal polypeptides are dissolved in water that contains a thickening agent before dispersion in the volatile solvent phase that contains the shell material. This dispersed aqueous phase is gelled thermally to entrap the polypeptide in the dispersed aqueous phase before solvent evaporation occurs (21). 

In gluing, the adhesive must not saturate veneers or wood chips, but must remain in the glue line on the surface of the chips or between the pHes. The adhesives are generally of high viscosity so that they remain in the glue line. Thickeners and extenders, such as powdered pecan shells and wheat flour, are often used. 

The two limiting cases for the distribution of deactivated catalyst sites are representative of some of the situations that can be encountered in industrial practice. The formation of coke deposits on some relatively inactive cracking catalysts would be expected to occur uniformly throughout the catalyst pore structure. In other situations the coke may deposit as a peripheral shell that thickens with time on-stream. Poisoning by trace constituents of the feed stream often falls in the pore-mouth category. 

All but the polyurethane are characterized by methylene backbones with ligands that are sufficiently polar to make them water soluble. Thus, upon dissolution in water, the polarity of the water molecule associates with the polarity of the acrylic or acrylamide groups to form a shell. We discussed hydrophilic polyurethanes that are typically cross-linked and are not (but could be) considered effective thickeners. Nevertheless they too have hydration shells developed due to the influence of the polyethylene glycol backbone. The extent of that shell is determined by the hydro-philicity of the ligand the acrylic > acrylamide > alcohol > polyurethane. The volume... 

Starch is used in frozen foods for the same reason it is used in fresh, refrigerated or canned foods, i.e. for thickening, low-temperature stability and control of the flow character of the food. Freezing exacerbates syneresis in other components of the food system, such as fruit tissue, increasing the demand for water entrainment by the starch. Frozen dinners are cooked, cooled, packaged and flash frozen. Fruit pie fillings are mixed, heated, cooled, filled into shells and flash frozen. Freezing introduces stability demands beyond the other forms of distribution. The stability of the starch... 

In H. nana, the shell material is described as being deposited against the inside of the capsule (204). The shell/capsule is well developed in the Pseudophyllidea, Tetraphyllidea and Trypanorhyncha. It is often poorly developed or absent in the Cyclophyllidea (Fig. 7.1(a)), in which case (especially in the Taeniidae) the embryophore (see below) is thickened and essentially functions as a protective shell . A subshell membrane has been described in some eggs (Fig. 7.1(a)). 

Rapid increase in temperature is desirable at temperatures below those at which substantial liquid formation occurs (C9,B27,S21,C11,W9,G26). Most of the belite, and almost all of the other product phases, subsequently either melt or react in the presence of the melt, and there is no merit in promoting crystal growth or removal of imperfections, which would impede these processes. Slow heating may also allow the decomposition products of the clay minerals to transform into less reactive phases. It can also lead to the formation of microstructures unfavourable to the later reactions Chromy (C9) found that it allowed the belite shells around the silica particles to thicken, producing composites slow to react with lime. In contrast, rapid heating increases movement of the liquid phase, when this forms, and thus improves the mixing of the calcareous and siliceous constituents (Cl 1). 

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