For most children, the National Heart, Lung, and Blood Institute recommends one cholesterol screening test between the ages of 9 and 11, and another cholesterol screening test between the ages of 17 and 21.
Wiktionary (0.00 / 0 votes) Rate this definition: fixation (Noun). The act of fixing, or the state of being fixed or fixated. fixation (Noun). The act of uniting chemically with a solid substance or in a solid form; reduction to a non-volatile condition; -- said of gaseous elements. fixation (Noun). The act or process of ceasing to be fluid and becoming firm.
Nitrogen fixation. Nitrogen fixation is the process by which nitrogen is taken from its stable gas form (N2) in air and changes into other nitrogen compounds (such as ammonia, nitrate and nitrogen dioxide) useful for other chemical processes. It is an important part of the nitrogen cycle. Nitrogen is fixed in biological and non-biological ways: