a galaxy that emits usually large amounts of energy from a very compact central source, such as Seyfert galaxies, radio galaxies, and quasars Also called active galactic nucleus
A galaxy emitting unusually high quantities of radiation from an active galactic nucleus at its center. Some active galaxies emit more energy in radio wavelengths than they do visible light. Seyfert galaxies are examples of active galaxies. See more at galactic nucleus.
- Active hydrogen
. hydrogen in the form of single atoms, rather than molecules, which makes it extremely reactive.
- Active hyperemia
active hyperemia active hyperemia n. Hyperemia due to increased flow of arterial blood in dilated capillaries. Also called arterial hyperemia, fluxionary hyperemia. Historical Examples The first two produce venous or passive hyperemia, and the third, arterial or active hyperemia. Surgery, with Special Reference to Podiatry Maximilian Stern
- Active immunity
immunity in an organism resulting from its own production of antibody or lymphocytes. Historical Examples The increased ingestion of bacteria in active immunity would seem to depend upon the presence of immune opsonins in the serum. Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 2 Various An active immunity is thus induced in susceptible […]
- Active ingredient
noun the chemically active part of a chemical compound Contemporary Examples I take a triptan called Treximet, which also includes a dose of the painkiller naproxen, the active ingredient in Aleve. Presidents Can Have Migraines Dana Goldstein July 19, 2011 The National Institute on Drug Abuse reports the prevalence of MDMA (the active ingredient in […]