Rigid-site points

Let s - 2, Ns be a set of isotopomers of a parent molecule 5=1, and let a = 1, Na, enumerate the atoms in the molecule. (Eventually, only substituted atoms will be relevant.) In the present notation, the sites of the atoms are referred to the PAS of the parent 5=1, and are hence defined by the position vectors (in the rigid mass point model). Let the mass change upon substitution of atom a be Ama(s) for isotopomer 5, we then have ... 

Pipes, particularly small-bore pipes, often have failed by fatigue because their support was insufficient and tlie pipes were free to vibrate. On other occasions, pipes failed because their support was too rigid and tliey were not fi ee to expand. Supports for pipes usually are constructed on site, and often it is not apparent until start-up tliat tlie supports are inadequate. Even at tliis point, tlie necessary reinforcement may not be done because it is not considered a priority at start-up. 

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