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.
Learner's definition of CLAMP. [+ object] 1. : to hold or press (things or parts of a thing) tightly together with a device : to fasten or tighten (something) with a clamp. The surgeon clamped the vein. He clamped the two pieces of wood together.