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sequence of separation units that will isolate desired products from given feed at the minimum cost. Multicomponent products can be specified. An evolutionary Drocedure is Dresented. This method consists of two Dhases. In the first Dhase. a &od initial siructure is created by heuristic methods. In the second phase, the initial structure is successively modified by making evolutionary structural changes. This logic has been programmed on a digital computer and has been tested on several problems. Seader and Westerberg (1977) have addressed the same problem. This work is an extension of the latest work in the field, combining eight heuristic selection rules to provide an initial structure and five evolutionary rules plus a strategy to refine the separation sequence configuration.The product set, the key components, the type of separator, the mass separating agent, if required, are chosen in a systematic way with the help of a heuristic evaluation function. The product set and product recoveries are specified by the user, but the program redefines the product set if it is cheaper to isolate separate species in a product and remix. The system handles distillation and extractive distillation separator types (with any of several mass separating agents) and can readily be extended to other separator types. Recovery and recycle of mass separating agent will be delayed, if the cost of processing will be reduced by using the same agent in several serially connected columns. The final criterion of quality is the total annual cost of the complete sequence, fixed charges plus operating cost. CONCLUSIONS AND SIGNIFICANCEAn evolutionary approach to the synthesis of sharp separations has been proposed. The synthesis problem is decomposed into two phases. In the first phase, an initial feasible structure is created by using heuristic rules. In the second phase, the initial structure obtained in the first phase is successively improved by applying evolutionary rules. The heuristic rules embody knowledge of the general behavior of separation units and separation sequences, and the evolutionary rules question the validity of these heuristic rules for the particular problem under consideration. This approach closely mimics the problem-solving procedures commonly employed by engineers, especially with regard to relatively large systems.The proposed procedure does not suffer from t h e shortcomings of the dynamic programming based synthesis procedures such as the one proposed by Hendry and Hughes (1972). The calculations are performed only on the subproblems selected by the heuristic and evolutionary rules thereby reducing the amount of computer time used. The proposed procedure also does not suffer from the problem of "cycling" (Thompson and King, 1972), since separation types are not selected on the basis of estimated costs. The proposed procedure is practical and has been tested on several problems. For each problem, the procedure creates the best separation sequence in a reasonable amount of computational time.In the course of pro...

Metallothioneins (MTs) are well-characterized low molecular weight, heat-stable cytosolic proteins with exceptional high content of cysteinyl sulfur and are known to bind heavy metals like cadmium (Cd), zinc (Zn), and copper (Cu). Since these proteins are induced on exposure to heavy metals, it is now accepted that they have a detoxifying role during heavy metal toxicity. It has also been suggested that the primary function of Mt is in the homeostasis of the essential metals Zn and Cu. Recently, a role MT in selenium metabolism in primates has been established. Further, MT has gained considerable importance in the clinical disorders related to trace metal metabolism.

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Effects of chronic administration of cadmium and ethanol, alone as well as in combination, on the uptake of cadmium and its interaction with other essential trace elements in various tissues of adult rats were investigated. Cadmium given in combination with ethanol led to a pronounced increase in cadmium absorption and accumulation in all the tissues studied relative to both non-exposed controls and rats treated with cadmium alone. Both cadmium and ethanol exhibited specific effects on copper and zinc levels of the tissues. These effects often were significantly altered when the animals were co-exposed to cadmium and ethanol. The results suggested that although both cadmium and ethanol individually pose a hazard to essential trace metal homeostasis of various organs, co-exposure can pose a major threat since animals exposed to ethanol absorb much more cadmium than their unexposed counterparts.

Male weanling rats were maintained on a thiamine-deficient diet for 4 weeks, and compared with ad libitum and pair-fed controls. Thiamine deficiency led to slow growth and finally a decrease in body weight. Liver and kidney weights of the deficient rats were low, but appropriate to the body weight. Thiamine deficiency also caused a significant decrease in erythrocyte transketolase levels. The decarboxylation of glyoxylate both via the glyoxylate oxidation cycle and α-ketoglutarate:glyoxylate (α-KG:GA) carboligase was significantly lower in the liver and kidney mitochondria, leading to accumulation of glyoxylate in the tissues and its excretion in the urine. Part of the accumulated glyoxylate is converted to oxalate, causing hyperoxaluria.

These findings suggest that hypozincemia with low iron levels may be the possible cause of pica and contradict the contention that low levels of plasma Zn and Fe could be an effect of pica.