Shell concept

Daudel, R., Odiot, S., and Brion, H., J. chim. phys. 51, 74, Theory of localizability of corpuscles. I. The concept of box and the geometrical significance of the shell concept in the electrons surrounding atoms. ... 

When G. T. Seaborg in 1944 introduced his actinide concept the theory played not the last role in his decision to place newly discovered elements in a second series where the filling of the 5f-shell takes place, similarly to the lanthanide series where the filling of the 4f-shell takes place. Thus, the filled-shell concept was in accord with the newly found periodicity in chemical properties and resulted in the discovery of all the heavy actinides at that time [20]. 

When Mendeleev constructed his periodic system in 1869 he had actually found the most general and overall systeraatics known in science. He developed this table from his comparison of the chemical and physical properties of the elements, without knowing the underlying reason for it. Since the early stages of quantum mechanics in the 1920 s, it has become clear that the similarity of the properties of the elements depends strongly on the outer electronic structure. The filled-shell concept is in accord with the periodicity of the chemical properties that formed the basis for the concept of the periodic table. 

The Shell concept studies imply that fuel cell sales start with stationary applications to businesses that are willing to pay a premium to ensure highly reliable power without utility voltage fluctuations or outages. This demand helps to drive fuel cell system costs below 500 per kW, providing the stage for transportation uses which incite additional cost drops to 50 per kilowatt in the next half decade. 

The kind of pellet developed in this study has implications outside the limits of its present use in coal gas cleaning. The core-in-shell concept a priori can be extended to reversible reactions where one of the products of reaction can be adsorbed out by the inner core while the reaction continues in the catalytic shell, thus increasing the conversion. The lesson is that novel solutions can be found for challenging problems and, equally important, they can often find applications in a variety of other situations, if only one keeps looking for possibilities. 

However, we can recognize that the essential feature of a Lewis structiu-e is the localized 1-c, 2-c bonding pattern rather than electron pairing per se. Moreover, the a and 3 electrons of open-shell species necessarily experience different Coulomb and exchange forces and may hence lead to different spatial distributions, spin orbitals, and localization patterns. The familiar open-shell concept of different orbitsds for different spins can therefore be extended to a different Lewis structures for different spins (DLSDS) picture, where as usual we associate a Lewis structure with a specified pattern of one-center and two-center (spin-)NBOs. Because the NBO... 

Trappey, J. C., and Liu, C. R. (1990), An Integrated System Shell Concept for Computer Aided Design and Planning, Technical Report TR-ERC-90-2, Purdue University, NSF Engineering Research Center, June. 

For some applications the formation of compact films can be substituted by dispersing polymer pigments in a polymer coating. Instead of pigments for purely conducting polymers, modified pigments have been developed that are based on a core-shell concept. ... 

Figure 6.4 Design configuration of the cold gas quench (a) Prenflo concept as employed in Puertoiiano integrated gasification combined cycle (IGCC) plant [22,23], (b) Shell concept as employed in Buggenum IGCC plant [14,18] (HP - high pressure, IP - intermediate pressure).

For compounds of the transition elements, however, empty valence shell (e.g. 3, Ad or 5d) orbitals are often available, and can markedly decrease their kinetic stability. For example Me4Ti is unstable at room temperature, decomposing to hydrocarbons and other products, whereas Me4Si may be heated to at least SOOT. In transition metals the closed shell concept remains but can apply in several different ways. The commonest of these is where the closed shell consists of 18 electrons, i.e. n, np, and (n-iy . Transition metal atoms are, like atoms of Group lA and IIA elements, inherently electron-deficient, and this electron-deficiency must be satisfied if thermally stable organometallic compounds are to be formed. The 18-electron rule and related ideas are discussed further in Chapter 5. 

HyperChem quantum mechanical calculations are ab initio and semi-empirical. Ab initio calculations use parameters (contracted basis functions) associated with shells, such as an s shell, sp shell, etc., or atomic numbers (atoms). Semi-empirical calculations use parameters associated with specific atomic numbers. The concept of atom types is not used in the conventional quantum mechanics methods. Semi-empirical quantum mechanics methods use a rigorous quantum mechanical formulation combined with the use of empirical parameters obtained from comparison with experiment. If parameters are available for the atoms of a given molecule, the ab initio and semi-empirical calculations have an a priori aspect when compared with a molecular mechanics calculation, letting... 

Gas-Heated Reforming. Gas-heated reforming is an extension of the combined reforming concept where the primary reformer is replaced by a heat-transfer device in which heat for the primary reforming reaction is recovered from the secondary reformer effluent. Various mechanical designs have been proposed which are variants of a shell-and-tube heat exchanger (12,13). 

Two resin systems based on this chemical concept are commercially available from Shell Chemical Company/Technochemie under the COMPIMIDE trademark COMPIMIDE 183 (34) [98723-11-2], for use in printed circuit boards, and COMPIMIDE 796 [106856-59-1], as a resin for low pressure autoclave mol ding (35). Typical properties of COMPIMIDE 183 glass fabric—PCB laminates are provided in Table 8. COMPIMIDE 183 offers a combination of advantageous properties, such as a high glass transition temperature, low expansion coefficient, and flame resistance without bromine compound additives. 

Moving-Bed Type This concept uses a single-pass tube bundle in a vertical shell with the dividea solids flowing by gravity in the tubes. It is little used for sohds. A major difficulty in divided-sohds apphcations is the problem of charging and discharging with uniformity. A second is poor heat-transfer rates. Because of these hmita-tions, this tube-bundle type is not the workhorse for solids that it is for liquid and gas-phase heat exchange. 

The criterion bv which the baU action in mills of various sizes may be compared is the concept of critical speed. It is the theoretical speed at which the centrifugal force on a ball in contacl with the mill shell at the height of its path equals the force on it due to gravity ... 

Stiffnesses for single-layered configurations are treated first to provide a baseline for subsequent discussion. Such stiffnesses should be recognizable in terms of concepts previously encountered by the reader in his study of plates and shells. Next, laminates that are symmetric about their middle surface are discussed and classified. Then, laminates with laminae that are antisymmetrically arranged about their middle surface are described. Finally, laminates with complete lack of middle-surface symmetry, i.e., unsymmetric laminates, are discussed. For all laminates, the question of laminae thicknesses arises. Regular laminates have equal-thickness laminae, and irregular laminates have non-equal-thickness laminae. 

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