Disorders substitutional

In Type-I diabetes, which is due to the loss of insulin-producing cells as a consequence of autoimmune disorders, substitution of insulin is the most important measure. However, merely to inject one daily dose is not an adequate therapy. Here, the objective is to mimic the daily variations in plasma insulin which are closely related to food intake. One such attempt which has improved microvascular complications is intensified insulino-therapy through multiple daily injections of insulin. Another approach is to develop techniques of islet transplantation and using a bioartificial pancreas. In the case of islet transplantation, tissues will not only respond to changes in blood glucose levels but also to hormones of the entero-insular axis. 

Conceptually, crystals are infinite, three-dimensional, and periodic entities constructed from atoms, ions, and molecules. Periodicity implies that every object contained in its smallest repeating unit, the unit cell, is systematically and infinitely repeated in three dimensions. However, real crystals are prone to lattice and other defects and parts of molecules or even entire molecules often exist in multiple crystallographically independent (or energetically similar) orientations. Moreover, the crystal structure derived from the diffraction pattern is the spatial average over the whole crystal and any deviation from the ideal three-dimensional regularity of the crystal is presented as disorder. Generally, there are two categories of disorder substitutional and positional disorder. 

Fig. 9.13. Sample diagrams of free energy density tp ) versus fractional composition 5 of constituent B for a disordered substitutional solid solution The free...

A brief summary of the diffasion formalism of Agren and Andersson and Agren as applied to a disordered substitutional solid solution is useful. Diffasion is assumed to occur by a vacancy exchange mechanism, in which the equilibrium vacancy concentration is maintained. The partial molar volumes of the substitutional species are assumed to be equal. For a given phase, the flux of species i in the z-direction in volume-flxed frame of reference is given by... 

Materials that contain defects and impurities can exhibit some of the most scientifically interesting and economically important phenomena known. The nature of disorder in solids is a vast subject and so our discussion will necessarily be limited. The smallest degree of disorder that can be introduced into a perfect crystal is a point defect. Three common types of point defect are vacancies, interstitials and substitutionals. Vacancies form when an atom is missing from its expected lattice site. A common example is the Schottky defect, which is typically formed when one cation and one anion are removed from fhe bulk and placed on the surface. Schottky defects are common in the alkali halides. Interstitials are due to the presence of an atom in a location that is usually unoccupied. A... 

There is often a wide range of crystalline soHd solubiUty between end-member compositions. Additionally the ferroelectric and antiferroelectric Curie temperatures and consequent properties appear to mutate continuously with fractional cation substitution. Thus the perovskite system has a variety of extremely usehil properties. Other oxygen octahedra stmcture ferroelectrics such as lithium niobate [12031 -63-9] LiNbO, lithium tantalate [12031 -66-2] LiTaO, the tungsten bron2e stmctures, bismuth oxide layer stmctures, pyrochlore stmctures, and order—disorder-type ferroelectrics are well discussed elsewhere (4,12,22,23). 

Tranquilizers. Fluphena2ine hydrochloride [146-56-5] triduopera2ine hydrochloride [440-17-5], and triduproma2ine [146-54-3] are all triduoromethyl substituted phenothia2ine chemicals useful in the management of psychotic disorders. 

Our results demonstrate that the augmented space recursion and the orbital peeling method in conjunction with the LMTO formalism, constitute a viable and computationally feasible approach to the calculation of phase stability in binary substitutionally disordered alloys. ... 

The crystallographic study of the potassium salt is complicated by disorder but in CsOs03N Os=N is 1.676 A and Os=0 1.739-1.741 A. Assignments of the vibrational spectrum of Os03N is assisted by isotopic substitution the higher frequency absorption is shifted significantly on 15N substitution whereas the band just below 900 cm-1 is scarcely affected (Table 1.7) conversely the latter band is shifted by some 50 cm-1 on replacing l60 by l80 [56], Nitrido salts are discussed later (section 1.12.2). 

Estrogens and progestins are diminished in menopausal or ovarectomized women. In hormone replacement therapy (HRT), these hormones are substituted to alleviate hot flushes, mood changes, sleep disorders, and osteoporosis. 

There are three different substituted benzene compounds with the formula C6H4F2. Assume that the benzene rings pack similarly into their crystal lattices. If the positions of the H and F atoms are statistically disordered in the solid state, which isomer will have the least residual molar entropy ... 

Zinc and cadmium have an oxidation number of +2 in all their compounds. Zinc is an essential element for human health. It is present in many enzymes and plays a role in the expression of DNA and in growth. Zinc is toxic only in very-high amounts. However, cadmium is a deadly poison that disrupts metabolism by-substituting for other essential metals in the body such as zinc and calcium, leading to soft bones and to kidney and lung disorders. 

Iwata N, Cowley DS, Radel M, et al Relationship between a GABA alpha g Pro385Ser substitution and benzodiazepine sensitivity. Am] Psychiatry 156 1447—1449,1999 Jacobson AF, Dominguez RA, Goldstein B, et al Comparison of buspirone and diazepam in generalized anxiety disorder. Pharmacotherapy 5 290—296, 1985 Jaffe JH, Ciraulo DA, Nies A, et al Abuse potential of halazepam and diazepam in patients recently treated for acute alcohol withdrawal. Clin Pharmacol Ther 34 623-630, 1983... 

Nelson, D.G.A., Featherstone, J.D.B., Duncan, J.E and Cuttress, T.W. 1982 Paracrystalline disorder of biologieal and synthetic carbonate-substituted apatites. Journal of Denial Research 61 1274-1281. 

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