Scientific Glossary
- Dark energy: Hypothetical form of energy permeating the universe thought to be responsible for the acceleration of the expansion of the universe.
- Dark matter: Matter of unknown composition, thought to be more than five times more abundant in the universe than ordinary baryons. Although it does not emit or reflect enough light to be detected directly, its presence has been inferred from its gravitational effects on stars and galaxies.
- Deuterium: Isotope of hydrogen, whose nucleus contains one proton and one neutron.
- Dihalide: A molecule containing two atoms of chlorine, bromine, or iodine.
- Direct-gap semiconductor: Conduction and valence bands overlap sufficiently for electrons in the conduction band to recombine with holes in the valence band.
- Dispersion compensation: A method for preventing the degradation of optical signals over distance.
- Dissociative recombination: Process in which a positive molecular ion recombines with an electron, resulting in the dissociation of the newly formed neutral molecule.
- Doping (semiconductors): The intentional introduction of impurities into a semiconductor to change its electrical properties.
- Dynamo action: Process by which motion in the Sun's convective interior acts to continuously regenerate a magnetic field.