Fr.: nombre d'Ekman
A → dimensionless quantity that measures the strength of → viscous forces relative to the → Coriolis force in a rotating fluid. It is given by Ek = ν/(ΩH2), where ν is the → kinematic viscosity of the fluid, Ω is the → angular velocity, and H is the depth scale of the motion. The Ekman number is usually used in describing geophysical phenomena in the oceans and atmosphere. Typical geophysical flows, as well as laboratory experiments, yield very small Ekman numbers. For example, in the ocean at mid-latitudes, motions with a viscosity of 10-2 m2/s are characterized by an Ekman number of about 10-4.
Fr.: Univers ekpyrotique
A cosmological model in which the → Big Bang is not the beginning of the → Universe, but a transitory phase in a more global scenario. The ekpyrotic Universe model is fundamentally different from the → standard cosmology and offers radically different explanations for the cosmological problems (→ homogeneity, → isotropy, → flatness, → magnetic monopoles, etc.). In this highly speculative model → space-time has five dimensions, four spatial and one temporal. Two three-dimensional → branes, one visible and one hidden, collide following the contraction of the extra dimension. The contraction produces a blue shift effect that converts gravitational energy into brane kinetic energy. Some fraction of this kinetic energy is converted into matter and radiation that can fuel the Big Bang. The movement of the hidden brane prior to the collision is under the influence of a potential created by the exchange of appropriate M-theory fields between the branes. The resulting temperature is finite, so the hot Big Bang phase begins without a → singularity. The Universe is homogeneous because the collision and initiation of the Big Bang phase occur nearly simultaneously everywhere. The energetically preferred geometry for the two branes is flat, so their collision produces a flat Big Bang Universe. According to → Einstein's field equations, this means that the total energy density of the Universe is equal to the → critical density. Massive → magnetic monopoles, which are over-abundantly produced in the standard Big Bang theory, are not produced at all in this scenario because the temperature after collision is far too small to produce any of these massive particles. A new version of the model provides the possibility of a cyclic Universe in which the fifth dimension undergoes a cycle of contraction and expansion a number of times, or indefinitely. The Big Bang is therefore not a special event and can happen again and again. Each cycle begins with a Big Bang and ends in a → Big Crunch. At the transition between the Big Crunch and Big Bang, matter and radiation are created, restoring the Universe to the high density required for a new Big Bang phase. In this scenario, the → dark energy that is causing the cosmic acceleration of the Universe today is inter-brane potential energy. Apart from speculation, this model suffers from several fine tunings (J. Khoury et al. 2001, Phys. Rev. D64, 123522 (hep-th/0103239); P. J. Steinhardt & N. Turok, 2002, Phys. Rev. D65, 126003 (hep-th/0111098), and references therein).
Ekpyrotic is inspired by the ancient Stoic doctrine according to which the world ends in a supreme conflagration, called ekpyrosis, and then reborns from the fire (palingenesis), only to be destroyed again at the end of the new cycle; ekpyrosis, from Gk. ek- "out of," → ex-, + → pyro- combining form of pyr, → fire, + -sis a suffix used to form nouns of action, process, state, condition, such as thesis, analysis, catharsis; → Universe.
El Ninyo (#)
Fr.: El Niño
El Niño. A significant warming of the ocean surface over the eastern and central equatorial Pacific that occurs at irregular intervals, generally ranging between two and seven years. El Niño conditions, which are often characterized by "warm events," most often develop after late December during the early months of the year and decay during the following year. → La Nina.
From Sp. El Niño "the child," i.e. "the Christ Child," alluding to the appearance of the current near Christmas. The term was originally applied by fishermen of northern Peru.
Elara (Jupiter VII)
The thirteenth known moon of Jupiter, discovered in 1905 by Charles Perrine.
In Gk. mythology, Elara was the mother by Zeus of the giant Tityus.
From Fr., from Gk. elastos "ductile, flexible," related to elaunein "to strike, beat out."
Kešâyand, from keš stem of kešidan/kašidan "to pull, drag, draw" (Av. karš- "to draw, to plough," karša- "furrow;" cf. Skt. kars-, kársati "to pull, drag, plough," Gk. pelo, pelomai "to be busy, to bustle") + âyand agent form of âmadan "to come; to become," from Mid.Pers. âmatan (O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes;" O.Iranian *āgmatani; Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").
Fr.: collision élastique
A collision between two particles which conserves the total kinetic energy and momentum of the system.
Fr.: déformation élastique
Fr.: limite d'élasticité, ~ élastique
Fr.: diffusion élastique
In a → collision between two → particles,
the reaction in which the total → kinetic energy
of the system, projectile plus target, is the same before the collision as after.
mowj-e kešâyand (#)
Fr.: onde élatique
A wave that propagates by → elastic deformation of the medium. The → propagation takes place by a change in shape that disappears when the forces are removed. In other words, the displaced particles transfer momentum to adjoining particles, and are themselves restored to their original position. A → seismic wave is a type of elastic wave.
The ability of a body which has been → deformed by an applied → force to return to its original shape when the force is removed. Up to a certain point the material obeys → Hooke's law. See also → ductility, → plasticity.
M.E. elbowe, from O.E. elboga, elnboga, from ell + bow. Cognate with Scots elbuck, Du. elleboog, Ger. Ellbogen, Ellenbogen, Dan. albue, Icelandic olbogi, olnbogi "elbow."
Ârenj "elbow," variants âranj, âran "elbow," araš "forearm;" Mid.Pers. âranj, O.Pers. arašan- "cubit," Av. arəθnâ- "elbow," Skt. aratni- "elbow," Iranian stem aratan-, araθn-, borrowed from Iranian into General Slavic as aršin "ell."
Pertaining to, derived from, produced by, or associated with electricity.
Term coined in by the English physicist William Gilbert (1540-1603) in treatise De Magnete (1600), from L. electrum "amber," from Gk. elektron "amber."
Barqi, adj. of barq, → electricity.
Fr.: arc électrique
bâr-e barqi (#)
Fr.: charge électrique
Fr.: circuit électrique
jarayân-e barq (#)
Fr.: courant électrique
dipol-e barqi, diqotbe-ye ~
Fr.: dipôle électrique
1) A type of → charge distribution
consisting of two charges, a
positive and a negative charge of the same magnitude separated by a
distance s, which is small compared to the distance r to
the point P at which the → electric potential
is V and the → electric field
intensity is E.The potential falls as the
square of the distance (1/r2) and the electric
field intensity decreases as
the cube of the distance (1/r3).
Fr.: décharge électrique
The flow of electricity through a gas, resulting in the emission of radiation that is characteristic of the gas and of the intensity of the current.
meydân-e barqi (#)
Fr.: champ électrique
The effect produced by the existence of an → electric charge in the volume of space that surrounds it. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.