Constraint chemical

Tiepolo M, Vaimucci R, Zanetti A, Bramm R, Foley SF, Bottazzi P, Oberti R (1998) Fine-scale stractural control of REE site-preference the case of amphibole. Mineral Mag 62A 1517-1518 Tiepolo M, Varmucci R, Oberti R, Foley SF, Botazzi P, Zanetti A (2000a) Nb and Ta incorporation and fractionation in titanian pargasite and kaersutite crystal-chemical constraints and implications for natural systems. Earth Planet Sci Lett 176 185-201... 

If this reaction were in a turbulent flow, excess oxidizer will be present due to the unmixedness of the fuel and oxygen in the turbulent stream. Hence, r will effectively be larger for a turbulent reaction than the molecular chemical constraint.)... 

Incorporation of Chemical Constraints. To complete the model of the oxide-electrolyte interface, it is necessary to return to the preceding section on models of chemical reactions to find values of ctq, CT-p and 172 calculated from chemical considerations. 

In the absence of specific adsorption at the IHP, a is simply set equal to zero. The chemical constraint for a 2 is given directly by Equation 9. 

The chemical constraint reduces the number of possible reactions considerably, and consequently it leads to a much narrower molar mass distribution. Furthermore, the extent of reaction a of the A-group can cover all values from zero to unity, but the extent of reaction P of the equally reactive 5-groups cannot become larger than P=a/(f-l). One important consequence of this strict constraint is that gelation can never occur [1,13]. A much higher branching density than by random polycondensation can be achieved. For this reason one nowadays speaks of hyperbranching. 

Navrotsky A. (1985). Crystal chemical constraints on the thermochemistry of minerals. In Reviews in Mineralogy, vol. 14, P. H. Ribbe (series ed.), Mineralogical Society of America. Navrotsky A. (1994). Physics and Chemistry of Earth Materials Cambridge University Press. 

In the case where it is preferred to choose only one process technology to produce a single chemical, constraints (4.4) and (4.5) can be included for each intermediate and product chemical type, respectively ... 

The multipole formalism described by Stewart (1976) deviates from Eq. (3.35) in several respects. It is a deformation density formalism in which the deformation from the IAM density is described by multipole functions with Slater-type radial dependence, without the K-type expansion and contraction of the valence shell. While Eq. (3.35) is commonly applied using local atomic coordinate systems to facilitate the introduction of chemical constraints (chapter 4), Stewart s formalism has been encoded using a single crystal-coordinate system. 

If individual atomic coordinate systems are used, as is common when chemical constraints are applied in the least-squares refinement, they must first be rotated to have a common orientation. The transformation of the population parameters under coordinate-system rotation is described in section D.5 of appendix D (Cromer et al. 1976, Su 1993, Su and Coppens 1994). 

Francl et al. (1996) examined the conditioning of the least squares matrix in the fitting procedure, and conclude that the method cannot be used to assign statistically valid charges to all atoms in a given molecule. This problem cannot be alleviated by the selection of more sampling points, and thus may require the introduction of chemical constraints to reduce the number of charges to be determined. 

The principle of maximum symmetry requires that the crystal structure adopted by a given compound be the most symmetric that can satisfy the chemical constraints. We therefore expect to find high-symmetry environments around atoms wherever possible, but such environments are subject to constraints such as the relationship between site symmetry and multiplicity (eqn (10.2)) and the constraint that each atom will inherit certain symmetries from its bonded neighbours. The problems that arise when we try to match the symmetry that is inherent in the bond graph with the symmetry allowed by the different space groups are discussed in Section 11.2.2.4. 

Chemistry-based approaches start by postulating a structure that satisfies the rules of chemistry and then look for ways in which this structure can be mapped into three-dimensional space. The chemical constraints are the ones that... 

Bond valences can be used in conjunction with other techniques, particularly powder diffraction where, for example, light atoms are difficult to refine in the presence of heavy atoms. Adding the chemical constraints of the bond valence model can stabilize the refinement, particularly in the case of superstructures that have high pseudo-symmetry (Thompson et al. 1999). 

Folding of polypeptides is subject to an array of physical and chemical constraints. A sampling of the prominent folding rules that have emerged provides an opportunity to introduce some simple motifs. 

The chemical constraints related to physical chemistry in the origin of petroleum should be more clearly defined than in the other subdisciplines, but the complexity of the situation becomes overwhelming. Physicochemical aspects are widespread, fitting into two major areas one dealing with reaction kinetics and thermodynamics, and the other with physical relationships including colloid chemistry. 

In many cases, high yields (>75% based on polymer loading) of the final product were obtained. Some drawbacks to this approach include partial dehalogenation of (67) back to (65) during the Stille coupling, the presence of Pd impurities in some products, and structural and chemical constraints imposed by the bromination reaction. 

A catalyst design strategy based on ternary metal oxides with catalytic and chemical constraints limited the desired set of catalyst compositions to about 100000, a number that could be tested in the scanning mass spectrometer [46]. A feed gas mixture of C2H6, 02, and Ar (4 1 5) was created using a set of digital... 

However, as cell growth proceeds, the physical as well as chemical constraints of the triblock terpolymers inhibit pronounced growth within the PB phase. Instead, the nucleated cells tend to grow into the SAN/PMMA phase. As the PPE/PS phase still stores a significant amount of carbon dioxide, the blowing agent is subsequently transported along the interface towards the foam cells. Apparently the PPE/PS phase still acts similar to a solid phase. 

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