Isotope …, "m" are the atomic masses of each individual isotope, and "x", …, "x" are the relative abundances of these isotopes. Several applications exist that capitalize on properties of the various isotopes of a given element. Isotope separation is a significant technological challenge, particularly with heavy elements such as uranium or plutonium. Lighter elements such as lithium, carbon, nitrogen, and oxygen are commonly separated by gas diffusion of their compounds such as CO and NO. The separation of hydrogen and deuterium is unusual because it is based on chemical rather than physical properties, for example in the Girdler sulfide process.
Standard weight in fish relationships representing a species across its range are used. As fish grow in length, they increase in weight. The relationship between weight and length is not linear. The relationship between length ("L") and weight ("W") can be expressed as: When the equation is for standard weight, the standard weight for a given length is written as W. The exponent "b" is close to 3.0 for most species. The coefficient "a" varies between species. If the exponent "b" is greater than three for a certain fish species, that species tends to become relatively fatter or have more girth as it grows