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 spring clamp is most commonly found within woodworking establishments to provide a firm grip while a glue or solvent attaches two or more pieces of lumber together, but perhaps a better example for the novice user would be a jumper cables that can be used to connect two vehicles' batteries when one of them loses a proper charge.