MRI of a knee. MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field.
Noun. 1. aestivation - (zoology) cessation or slowing of activity during the summer; especially slowing of metabolism in some animals during a hot or dry period. estivation. zoological science, zoology-the branch of biology that studies animals.
1. (Zo[o]l.) The state of torpidity induced by the heat and dryness of summer, as in certain snails; -- opposed to {hibernation}. [1913 Webster] 2. (Bot.) The arrangement of the petals in a flower bud, as to folding, overlapping, etc.; prefloration. --Gray. [1913 Webster] [Spelt also {estivation}.] [1913 Webster]