Carbocations are species bearing a formal + charge on carbon. The have sp2 hybridization and trigonal planar geometry, with an empty p orbital on carbon, perpendicular to the plane containing the substituents (see diagrams shown to the right).
Aortic cross-clamp. An aortic cross-clamp is a surgical instrument used in cardiac surgery to clamp the aorta and separate the systemic circulation from the outflow of the heart. An aortic cross-clamping procedure serves, for example, in the repairing of coarctation of the aorta.
A similar type of clamp to the screw band, also with a solid screw, is the Marman clamp. Spring clamps. Spring clamps are typically made from a strip of spring steel, cut so that one side has a narrow protrusion centered on the end, and the other side a pair of narrow protrusions on either side.