Pyramid model

Dowell, A.M. 2002. "Getting from Policy to Practices The Pyramid Model (Or What Is this Standard Really Trying to Do )." Process Safety Progress 21(1). March. 

In previous decades, a pyramid model dominated the treatment of rheumatoid arthritis. Early in the course of the disease, sahcylates were used to control pain and stiffness. If sahcylates were poorly tolerated or began to lose efficacy, they were discontinued and a different NSAID was used. As the efficacy of NSAID therapy waned and joint deterioration progressed, treatment with a DMARD was added. DMARDs were employed... 

This comment serves as justification for selecting some "optimal" geometry as the basis for nomenclating several of the boranes. In particular, rather than using the square pyramid model of Figures 6 or 7, which in the proposed nomenclature would have the name ... 

The low face-selectivity in the previous example can be partially attributed to single-point coordination of the aldehyde to the Lewis acid. Evans and co-workers have used a-alkoxy aldehydes in aldol reactions with much success (Sch. 35) [70]. Thus a variety of silylketene acetals add to 144 in the presence of a copper(bisoxazoline) catalyst with very high selectivity and chemical yields. Reaction with 147, which contains an additional stereoelement, gave a single aldol product 148 with high syn selectivity. The dienol silane 149 also provides high selectivity in the aldol reaction. A square pyramidal model accounts for the observed selectivity. In this model, the substrate binds... 

Figure 1 The pyramid model suggests that the structure of successful drug discovery is built on several interrelated technologies. No single technology is more important than any other.

To answer this problem one makes two identical pyramidal models of CHi, (with C at the apex), and then replace, for instance, the upper right-hand H with a different atom Y in the other model replace the lower right-hand H. Next determine whether or not, by any manipulations except bending or breaking bonds, the models can be made to coincide in all their parts. If the two models are super-imposable, then they represent two molecules of the same structure if the models are not superimposable, then they represent molecules of different structures which, since they have the same molecular formula, are by definition isomers. 

To amplify this point, safety and loss prevention professionals often use the pyramid model to drive home the point that near-misses and other underlying factors, if not addressed, will ultimately lead to an accident. Visualize a pyramid or triangle starting at the bottom, for every 300 equipment damage accidents or... 

Reciprocal salt pair solutions may be represented on an isothermal space model, in the form of either a square-based pyramid or a square prism. Figure 4.30a indicates the pyramidal model the four equilateral triangular faces stand for the four ternary systems AX-AY-W, AY-BY-W, BY-BX-W and AX-BX-W (W = water) for the salt pair represented by the equation... 

Pyramid model for textile recycling categories, by quantity. 

Recently, many titanium compounds have been studied as polymerization catalysts of olefins [5 la-5 If). In these studies, the active center of ethylene polymerization with Ziegler-Natta type catalysts by using a square-pyramidal model is thought to be a weak 7t-bond between ethylene and titanium. The bond length and bond energy are calculated 2.80 A and 7—11 kcal/mole, respectively [51a]. 

The use of chiral copper Lewis acids in enantioselective aldol processes has seen rapid development over the past 10 years. In particular, copper-catalyzed variants of the Mukaiyama aldol reaction received considerable attention in the years leading up to the new millennium. Evans and coworkers first demonstrated Cu(II)/pybox complex (59) as an efficient catalyst for highly enantioselective addition of a variety of silylketene acetals to aldehydes capable ofbidentate coordination (Scheme 17.12) [17]. In reactions utilizing silylketene acetals (61) and (63) with an additional stereoelement, diastereoselectivities and enantioselectivities were also high. A square pyramidal model (65), which has been further supported by a crystal structure of the complex, with the a-alkoxy aldehyde bound in a bidentate fashion accounts for the observed selectivity. 

Figure 4 Schematic illustrations (a) a two-dimensional packing and its Voronoi elements, with dotted lines highlighting particle O and its surrounding particles A-F, and different connections between particles O and A, and between particles O and G (b) a single Voronoi element / together with its neighbors j, k, I, and so on (c) the connection between two neighboring Voronoi polyhedra as a double pyramid model and (d) the simplified connection as a double taper cone model. Reprinted from Cheng and Yu (2013) with permission from ACS.

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