Design superiority

Despite rather intensive efforts to design superior inhibitors to Zanamivir or 4-amino-4-deoxy-Neu5Ac2en by replacement of the group at C-4, no improvements have been realized. This reflects the importance and complexity of both electrostatic interactions and the extensive multi-atom intermolecular hydrogen-bond networks that assure the high affinities observed for 9 and 1. 

In order to design superior catalyst systems and expand the applications of these first generation catalysts, it was necessary to understand the fundamental mechanism of ruthenium-catalyzed olefin metathesis reactions. Initial investigations focused on the activity of 1 and its derivatives for the catalytic RCM of diethyl diallylmalonate (Eq. 4.14) [86]. These studies revealed that, in all cases, the overall catalytic activity was inhibited by the addition of free phosphine, and that the turnover rate was inversely proportional to the concentration of added phosphine. This indicated that phosphine dissociation was required for catalytic activity, and further suggested that olefin metathesis may be initiated by the substitution of a phosphine ligand with an olefin substrate. 

At the beginning of the Second World War, the almost overwhelming propaganda of German technical achievement was countered by a British emphasis on craft and design superiority. Barnes Wallis s design for a medium bomber dispersed structure evenly to avoid vulnerable concentrations of spars. The celebrated ability to absorb damage complicated construction hand-built rather than production-line assembly. 

A great deal of experimental work has also been done to identify and quantify the ha2ards of explosive operations (30—40). The vulnerabiUty of stmctures and people to shock waves and fragment impact has been well estabUshed. This effort has also led to the design of protective stmctures superior to the conventional barricades which permit considerable reduction ia allowable safety distances. In addition, a variety of techniques have been developed to mitigate catastrophic detonations of explosives exposed to fire. 

Recent advances in Eischer-Tropsch technology at Sasol include the demonstration of the slurry-bed Eischer-Tropsch process and the new generation Sasol Advanced Synthol (SAS) Reactor, which is a classical fluidized-bed reactor design. The slurry-bed reactor is considered a superior alternative to the Arge tubular fixed-bed reactor. Commercial implementation of a slurry-bed design requires development of efficient catalyst separation techniques. Sasol has developed proprietary technology that provides satisfactory separation of wax and soHd catalyst, and a commercial-scale reactor is being commissioned in the first half of 1993. 

Etom the customer s point of view, there is an optimal level of standardization. Increased standardization lowers costs but restricts choice. Furthermore, if a single minimal performance product standard is rigorously invoked in an industry, competition in a free market ultimately may lead the manufacturer of a superior product to save costs by lowering his product quaHty to the level of the standard, thus denying other values to the customer. Again, excessive standardization, especially as appHed to design or how the product performance is to be achieved, effectively can limit technological innovation. 

As engineered stmctures, nonwovens can be designed to have appearances, textures, and other aesthetic properties comparable to traditional wovens and knits, and performance and functional properties superior to traditional wovens and knits. Nonwovens are, indeed, a distinct class of fiber-based materials with the characteristics of fabric and many of its useful properties. 

Similady, hquid-crystal polymers exhibit considerable order in the hquid state, either in solution (lyotropic) or melt (thermotropic). When crystallized from solution or melt, they have a high degree of extended-chain crystallinity, and thus have superior mechanical properties. Kevlar (Du Pont) is an aromatic polyamide (atamid) with the repeating unit designated as (2). It is spun into... 

The acetabular component is as integral to successful total hip arthroplasty as is the femoral hip stem component. The life of the acetabular component depends on proper placement and bone preparation in the acetabular region of the hip girdle, proper use of bone cement, and superior component design. 

Of course, the above appHes when staying within a given tread design and at equivalent tread stiffness. Tire designs that allow water to be channeled out of the tread mbber/road contact area are significantly superior to those that do not, even when more contact area is available. Tread element stiffness plays an important role in traction capabiUties as softer treads have less column stiffness and reduce tread void areas, ie, there is more mbber on the road but this is offset if water channeling is significantly reduced. 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

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