(psychology) Aimless, often self-comforting behavior displayed when in doubt, blocked or frustrated. / (more broadly) Something done needlessly when procrastinating.

Making indirect use of solar energy by first converting it to another form (e.g. by using solar panels).

(biology) Movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

(grammar) A participle indicating an ongoing or completed action or state in the active voice, where a noun modified by the participle is taken to represent the agent of the action denoted by the verb.

plural of activation analysis

(chemistry) Any of several similar radiochemical techniques of analysis in which a subatomic particle or gamma ray is captured by a nuclide to form a second stable nuclide which is then measured.

The increase in rate of a chemical reaction caused by the presence of a catalyst. / An amount of catalyst, expressed as the increase of the rate of its reaction.

plural of active couple

(chemistry) A transitional structure, in an energetically excited state, that forms between the reactants of a chemical reaction and breaks down to form the products

plural of neutron activation analysis