Structural variability

A sequence alignment establishes the correspondences between the amino adds in th unknown protein and the template protein (or proteins) from wliich it will be built. Th three-dimensional structures of two or more related proteins are conveniently divided int structurally conserved regions (SCRs) and structurally variable regions (SVRs). Ihe structural conserved regions correspond to those stretches of maximum sequence identity or sequenc... 

Structural Variables. The properties of a foamed plastic can be related to several variables of composition and geometry often referred to as stmctural variables. 

Table 14.1 Influence of structure variables on the properties of polyfvinyl formal)...

There are a number of structural variables which can considerably affect the properties of the aliphatic polyamides ... 

The micropore volume varied from -0.15 to -0.35 cmVg. No clear trend was observed with respect to the spatial variation. Data for the BET surface area are shown in Fig. 14. The surface area varied from -300 to -900 mVg, again with no clear dependence upon spatial location withm the monolith. The surface area and pore volume varied by a factor -3 withm the monolith, which had a volume of -1900 cm. In contrast, the steam activated monolith exhibited similar imcropore structure variability, but in a sample with less than one fiftieth of the volume. Pore size, pore volume and surface area data are given in Table 2 for four large monoliths activated via Oj chemisorption. The data in Table 2 are mean values from samples cored from each end of the monolith. A comparison of the data m Table 1 and 2 indicates that at bum-offs -10% comparable pore volumes and surface areas are developed for both steam activation and Oj chemisorption activation, although the process time is substantially longer in the latter case. 

The voluminous experimental information about the linkage between structural variables and properties of polymers is assembled in books, notably that by van Krevelen (1990). In effect, such books encapsulate much empirical knowledge on how to formulate polymers for specific applications (Uhlherr and Theodorou 1998). What polymer modellers and simulators strive to achieve is to establish more rigorous links between structural variables and properties, to foster more rational design of polymers in future. 

First, we must realize that many variables exist in any structural design. We can make a list of structural variables such as sizes, lengths of objects, materials, laminae orientations, and so on. those variables all have influence just as column length, moment of inertia, and Young s modulus influence column-buckling loads. The complete list of design variables will be called the vector Xj, and that vector will have N components. That list constitutes the definition of the structural configuration. 

Old and new values for-structure variables, in atomic units (bohrs and radians]... 

These equations describe the full oxidation of a conducting polymer Submitted to a potential step under electrochemically stimulated confer-mational relaxation control as a function of electrochemical and structural variables. The initial term of /(f) includes the evolution of the current consumed to relax the structure. The second term indicates an interdependence between counter-ion diffusion and conformational changes, which are responsible for the overall oxidation and swelling of the polymer under diffusion control. 

Further studies of the 2-substituted 5-nitroanilines, conducted by Kier and coworkers, searched for a linear combination of structural variables that describes a line, plane, or surface that separates the molecule classes in the optimum manner. They found that sweetness correlated very well with the substituent polarizability-constants for the 2-substituent, implicating the involvement of the 2-substituents in dispersive-binding interactions at the receptor. This is in agreement with the results of Hansch " and McFarland. The correlation equation was not, however, reported. 

Bhatnagar K. and Meisami E. (1998). Vomeronasal organ in bats and primates extremes of structural variability and its phylogenetic implications. Microsc Res Tech 43, 465-475. 

The study of how fluids interact with porous solids is itself an important area of research [6], The introduction of wall forces and the competition between fluid-fluid and fluid-wall forces, leads to interesting surface-driven phase changes, and the departure of the physical behavior of a fluid from the normal equation of state is often profound [6-9]. Studies of gas-liquid phase equilibria in restricted geometries provide information on finite-size effects and surface forces, as well as the thermodynamic behavior of constrained fluids (i.e., shifts in phase coexistence curves). Furthermore, improved understanding of changes in phase transitions and associated critical points in confined systems allow for material science studies of pore structure variables, such as pore size, surface area/chemistry and connectivity [6, 23-25],... 

In fact there is substantial structural variability among the five instances of the helical tubuland structure described above, in the form of variable placements of the diol hosts along the twofold axes, and variable a dimensions of the lattice, both of which have marked influence on the size and shape of the canals. Full analysis of these effects is provided elsewhere 8) and the major results only are reported here. As a consequence of steric repulsions between the bridge on the syn face and methyl substituents R on adjacent molecules presenting an anti face to the canal, as shown in Fig. 8, the molecules presenting the anti face are moved along the twofold axes, farther... 

RA Gross. Bacterial polyesters Structural variability in microbial synthesis. In SW Shalaby, ed. Biomedical Polymers Designed-to-Degrade Systems. Cincinnati, OH Hanser/Gardner, 1994, pp 173-188. 

Variations in local geometries of organic compounds are often subtle and below the resolution of most experimental structural techniques. Thus, the full extent of structural variability was at first not so much apparent from experimental structural studies, but from ab initio gradient optimized geometries (Schafer 1982G, 1983G). 

Among the main molecular structural variables in EPDMs that are stipulated by catalyst systems and that affect the vulcanizate tensile properties we may mention molecular weight (MW) and MWD, degree of unsaturation (LG=C 1) and its distribution in the polymer, composition (C S) and monomer sequence length distribution along molecular chains, and long-chain branching if present. Effect of... 

The first ingredient in any theory for the rheology of a complex fluid is the expression for the stress in terms of the microscopic structure variables. We derive an expression for the stress-tensor here from the principle of virtual work. In the case of flexible polymers the total stress arises to a good approximation from the entropy of the chain paths. At equilibrium the polymer paths are random walks - of maximal entropy. A deformation induces preferred orientation of the steps of the walks, which are therefore no longer random - the entropy has decreased and the free energy density/increased. So... 

In several cases, a series of compounds containing the chalcogens O, S, Se, and Te has been prepared, and the behavior of the compounds under oxidizing conditions evaluated and compared. In other cases, a more limited set of compounds has been evaluated in the same way. In another subset, the impact of substituents has been examined. Finally, the impact of other structural variables, such as the hybridization of the atoms and the structure of the groups to which the chalcogen is attached, have been explored. 

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