Fr.: état de Cassini
A state characterizing a system which obeys → Cassini's laws.
Fr.: état propre
Fr.: état éléctronique
In molecular quantum mechanics, any of → quantum states corresponding to a particular → electron configuration (i.e. an arrangement of the electron(s) in certain → orbitals). The electron configuration with the lowest energy is called the → ground state. All higher energy states are called → excited states.
Fr.: état d'énergie
Same as → energy level.
equation of state
Fr.: équation d'état
In physics and thermodynamics, the equation that describes the relationship between pressure, density, and temperature, e.g. → ideal gas law, → van der Waals equation, → polytropic process, → virial equation of state.
equation of state parameter
pârâmun-e hamugeš-e hâlat
Fr.: paramètre de l'équation d'état
In cosmology, a → dimensionless parameter introduced by the → equation of state representing the ratio of the pressure to the energy density of a fluid, such as the → dark energy: w = p/ρ. The → deceleration or → acceleration of an → expanding Universe depends on this parameter (→ accelerating Universe). A number of numerical values of this parameter are as follows: for the → cosmological constant: w = -1, for → non-relativistic matter (present-day → baryons): w = 0, and for → relativistic matter (photons, neutrinos): w = +1/3. Together with Ω(dark energy) and Ω(matter), w provides a three-parameter description of the dark energy. The simplest parametrization of the dark energy is w = constant, although w might depend on → redshift.
estât-e tarâzmandi, hâlat-e ~
Fr.: état d'équilibre
hâlat-e barangixté (#)
Fr.: état excité
The condition of a particle or system of particles (especially an atom, nucleus, molecule) after absorbing energy from outside and transiting to a higher → energy level than that of its → ground state. Excited states are transitory as they lose energy through emissions or collisions and return to ground state.
hâlat-e zaminé (#)
Fr.: état fondamental
The lowest energy state of an atom, molecule, or ion, when all electrons are in their lowest possible energy levels, i.e. not excited.
Hartle-Hawking initial state
estât-e âqâzin-e Hartle-Hawking
Fr.: état initial de Hartle-Hawking
A proposal regarding the initial state of the → Universe prior to the → Planck era. This → no boundary hypothesis assumes an imaginary time in that epoch. In other words, there was no real time before the → Big Bang, and the Universe did not have a beginning. Moreover, this model treats the Universe like a quantum particle, in an attempt to encompass → quantum mechanics and → general relativity; and attributes a → wave function to the Universe. The wave function has a large value for our own Universe, but small, non-zero values for an infinite number of other possible, parallel Universes.
Fr.: état de Hoyle
An → excited state in the
→ triple alpha process leading to the production of
the most abundant → isotope of → carbon.
The existence of this state is of extreme astrophysical importance concerning the
→ nucleosynthesis of 12C in stellar
In honor of the British astrophysicist Fred Hoyle (1915-2001), who predicted this state in 1953 (Hoyle et al. 1953, Physical Review 92, 1095); it was discovered by W. A. Fowler in 1957; → state.
Fr.: état macroscopique
Same as → macrostate.
Statistical physics: A state of a physical system that is described in terms of the system's overall or average properties at a macroscopic level (→ temperature, → pressure, → density, → internal energy, etc.). A macrostate will generally consist of many different → microstates. In defining a macrostate we ignore what is going on at the microscopic (atomic/molecular) level. The → probability of a certain macrostate is determined by how many microstates correspond to this macrostate. Therefore, the greater the number of microstates which lead to a particular macrostate, the greater the probability of observing that macrostate. Same as → macroscopic state. See also → entropy, → Boltzmann's entropy formula, → multiplicity.
Fr.: état métastable
An excited state in an atom, which is at the origin of the spectral lines called → forbidden lines. The time duration of the excited state being relatively long, under laboratory conditions the atom cannot pass directly to the ground state by emitting radiation. In the extremely rarefied interstellar medium, however, such highly improbable transitions do occur.
Fr.: état microscopique
Same as → microstate.
Statistical physics: For a system made up of a large number of components, a state of the system which is specified by describing the current dynamical variables of each constituting component. For example, for a gas system composed of a large number of molecules, the microstate is defined by the set of quantities which defines the state of each molecule in the system (position, velocity, vibration, etc.). In practice, it is impossible to know perfectly the microstate of a system. The aim of → statistical physics is to relate the macroscopic (average ) observables (→ pressure, → temperature, → internal energy) to the microstate of the system. Also called → microscopic state. See also → macrostate and → multiplicity.
Fr.: état fondamental
Of an atom, the same as → ground state.
Fr.: état d'oxydation
Same as → oxidation number.
Fr.: état quantique
Fr.: état singulet
In atomic physics, the electronic state of an atom or molecule for which the total → spin angular momentum is zero.