Head addition, definition

I-. - also head r.t rail addition definition 4. If) lail-to-tail linkages in PVAc 324... 

Most monomers have an asymmetric substitution pattern and the two ends of the double bond are distinct. For mono- and 1,1-disubstituted monomers (Section 4,3.1) it is usual to call the less substituted end "the tail" and the more substituted end "the head". Thus the terminology evolved for two modes of addition head and tail and for the three types of linkages hcad-to-tail, hcad-to-hcad and tail-to-ta.il. For 1,2-di-, tri- and tetrasubstituted monomers definitions of head and tail are necessarily more arbitrary. The term "head" has been used for that end with the most substituents, the largest substituents or the best radical stabilizing substituent (Scheme 4.4). 

Equation 3.11 is due to Blasius(6) and the others are derived from considerations of velocity profile. In addition to the Moody friction factor / = 8R/pu2, the Fanning or Darcy friction factor / = 2R/pu2 is often used. It is extremely important therefore to be clear about the exact definition of the friction factor when using this term in calculating head losses due to friction. 

In view of thousands of publications that have appeared during recent years, it is difficult to summarize all aspects of the chemistry and clinical uses of nitrofurans, not to mention the wide range of experimental studies which were their necessary predecessors. In the clinical section of this chapter each drug will be described under a separate heading with emphasis on the progress in human medicine. The reader should understand in addition that the nitrofurans also have a definite place in veterinary medicine. Besides some basic work which was published soon after the compound under discussion appeared on the market, only the most recent publications have been considered. Hence, the list of references is not to be considered complete. 

We have to understand that sagittal profile describes the position of the body in space. As the body represents a mass, the sagittal profile has not only the task to define the position of the spine in space, but it must also define how the mass of the body (trunk, upper extremities and head) is transmitted to the lower extremities. The trivial fact that the mass of the trunk which is balanced over the pelvis (sacrum) and over the femoral head, can at last be transmitted to the lower extremities is of great significance. It can be easily concluded from this that a definition of the sagittal profile is only possible, if the relationship of these parameters to the position of the sacrum and the femoral heads, in addition to the parameters of the spine, is clearly defined. 

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