Action Potential: A reversal of the electrical potential in the plasma membrane of a neuron that occurs when a nerve cell is stimulated; caused by rapid changes in membrane permeability to sodium and potassium.
Reaction: A decline in prices following an advance. Opposite of rally.
Reaction Formation: A defense mechanism, operating unconsciously, in which a person adopts affects, ideas, and behaviours that are the opposites of impulses harboured either consciously or unconsciously. For ex . . . View Full Definition
Reaction Mechanism: A list of all elementary reactions that occur in the course of an overall chemical reaction.
Rarefaction: In sound waves, the opposite of compression. An area of decreased air pressure caused by a sound wave. In a graphical depiction of a cyclical waveform rarefaction occurs when the wave is in . . . View Full Definition
Potentially Responsible Party (PRP): Any individual or company that is potentially responsible for or has contributed to a spill or other contamination at a Superfund site. Whenever possible, EPA requires PRPs to clean up sites . . . View Full Definition
Play-Action Pass: A passing play after the quarterback has faked a hand-off.
Polymerase Chain Reaction (PCR): A method of amplifying or copying DNA fragments that is faster than cloning. The fragments are combined with DNA polymerase, nucleotides, and other components to form a mixture in which the . . . View Full Definition
Potential Difference: Work that must be done to move an electric charge between specified points. Electric potential differences are measured in volts.
Potential Energy: Energy an object possesses by virtue of its position. For example, lifting a mass mby h meters increases its potential energy by mgh, where g is the acceleration due to gravity.