The amount of time by which an event is retarded.
From O.Fr. délaier, from dé-→ de- "away, from" + laiier, from laiss(i)er "to leave," from L. laxare "to loosen, release, set free."
Derang, from Mid.Pers. dirang, drang "delay, lateness; long, lasting," Av. drənj- "to fix, fasten, hold," Proto-Iranian *dra(n)j- "to fix, fasten, hold."
Fr.: temps de retard, délai
Same as → delay.
Fr.: neutrons retardés
Neutrons resulting from nuclear fission which are emitted with a measurable time delay. Delayed neutrons are responsible for the ability to control the rate at which power can rise in a reactor. → prompt neutrons.
delayed supernova explosion
oskaft-e bâderang-e abar-now-axtar
Fr.: explosion retardée de supernova
A mechanism predicted by theoretical models of → supernova explosion that operates after the → supernova shock fails to deliver a → prompt supernova explosion. The delayed supernova explosion mechanism assumes that a few tenth of a second after the → iron core collapse, the supernova shock is stalled due to energy dissipation. The material between the → protoneutron star and the stalled shock is mainly disintegrated into neutrons and protons due to the high temperatures (a few MeV) in this region. As the → neutrinos coming from the protoneutron star run through this material, a fraction of the neutrinos are captured by the → nucleons, and their energy is deposited in the material. As a result, the material behind the shock is heated by the neutrinos. If this neutrino heating is efficient enough, the stalled shock can be reinvigorated to bring about a supernova explosion.
Fr.: retard géométrique
One of the two factors contributing to → gravitational lensing time delay that arises from the fact that the bent trajectory is longer than the straight one. The other factor is due to the → Shapiro time delay.
gravitational lensing time delay
derang-e zâyide-ye lenzeš-e gerâneši
Fr.: retard dû à l'effet de lentille gravitationnelle
The difference in light travel times along the various light paths from the source to the observer when the source image is divided into several images because of → gravitational lensing. According to the theory of → general relativity, light rays are deflected in the vicinity of massive objects. If the light source and the deflector are sufficiently well aligned with the observer, and obey some conditions on their distances (→ Einstein radius), we can observe several (generally distorted and magnified) images of the source. A property of → strong lensing is that the light travel time from the source to the observer is generally not identical for the different images. In other words, we not only see several images of one same object, but we also see this object, in each image, at different times. This means, in one image the lensed object will be observed before the other image. Given a physical model of the gravitational lens, the light travel time for each image can be computed. The expression giving the time delay has two components: a term is called → geometric delay, and the second term, known as the → Shapiro time delay. The latter is due to time dilation by the gravitational field of the lens, a direct consequence of general relativity. See also → time delay distance.
Fr.: délai de phase
The ratio of the phase shift of a sinusoidal signal in transmission through a system to the frequency of the signal.
Fr.: retard de Rømer
A time delay caused by the light travel across a → dynamical system. The finite → speed of light causes a delay, for example, between the → primary eclipse and the → secondary eclipse in → binary systems.
Shapiro time delay
Fr.: effet Shapiro
A → general relativity effect whereby an → electromagnetic signal passing near a massive object takes, due to the curved → space-time, a slightly longer time to travel to a target than it would if the mass of the object were not present. The Shapiro time delay is one of the four classic solar system tests of general relativity. Radar reflections from → Mercury and → Mars are consistent with general relativity to an accuracy of about 5%. The Shapiro time delay is a significant contributor in → gravitational lens systems.
time delay distance
apest-e derang-e zamâni
A distance-like quantity derived from → gravitational lensing time delay. It is given by a combination of three angular diameter distances in a strong lens system: DΔt = (1 + zL)[DA(EL)DA(ES) / DA(LS)], where zL is the → redshift of the → gravitational lens, while DA(EL), DA(ES), and DA(LS) are the angular diameter distances from the Earth to the lens, from the Earth to the source, and from the lens to the source, respectively. As each of the distance is proportional to the inverse of H0, DΔt is proportional to 1/H0.