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.
As a rule, a large handheld clamp means a more powerful grip and a small spring clamp will provide light gripping pressure. Clamps come in either metal or plastic, and both types are effective at holding things together, but the metal ones are often able to take more abuse.