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.
cross-train. v. cross-trained, cross-trainÂ·ing, cross-trains. v. intr. 1. To undergo or provide training in different tasks or skills: The department has cross-trained in firefighting and emergency medical services. 2. To train in different sports, mainly by alternating regimens, as in running, bicycling, and swimming. v. tr. To train (another) in different tasks or skills.