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 stitch is a type of counted thread surface embroidery. It uses mostly X-shaped stitches to create a picture or pattern. Partial stitches are also used for shaping and texture, and back stitches are used for creating outlines and small details. Needlepoint is a surface embroidery technique.