NMR apparatus for achieving construction of improved patient access desirably including a generally C-shaped yoke, and devices for reducing the field asymmetry caused by the C-shaped yoke. The piston replaces a tube used in prior art relief valves. -% of units derivable from C5 to C12 \u03b1-olefins, at least 20. The smallest remaining system is allocated to a domain responsive to a determination that the domain can service the smallest remaining system. The catapult further comprises a takeoff damper that generates a damping force having a direction opposite relative to the launching force. Therefore, little friction and resistance is encountered when force fitting a pivot-bearing assembly into the upper portion of the stepped inner bore, thereby avoiding surface damage and the generation of unwanted debris particles.