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Fr.: composition chimique
Fr.: composé chimique
A substance whose molecules are made up of atoms of at least two different elements.
bonpâr-e šimiyâyi (#), onsor-e ~ (#)
Fr.: élément chimique
A substance which consists entirely of atoms of the same → atomic number and cannot be decomposed or changed into another substance using chemical means. Currently 118 chemical elements are known, the most abundant being → hydrogen. → periodic table.
Fr.: enrichissement chimique
The → process by which the relative → abundance of a given → chemical element or → species in an → astrophysical object is increased. For example the the → increase of the → heavy element content of the → interstellar medium due to → stellar evolution.
Fr.: équation chimique
fargašt-e šimiyâyi (#)
Fr.: évolution chimique
A cumulative change in the chemical properties, or more specifically, the relative abundances of chemical elements in an astrophysical system.
âmizeš-e šimiyâyi, ~ šimik
Fr.: mélange chimique
Fr.: potentiel chimique
For a given component in a → gas mixture, the change in → Gibbs free energy (G) with respect to change in amount of the component (n), when pressure, temperature, and amounts of other components remain constant: ∂G/∂n. Components are in equilibrium if their chemical potentials are equal.
vâžireš-e šimiyâyi, vâkoneš-e ~
Fr.: réaction chimique
Fr.: séparation chimique
The physical processes that can cause certain elements to migrate in a → stellar atmosphere. These processes are thought to be important in creating the chemical peculiarities seen in → Am stars and → Ap stars.
Fr.: espèce chimiique
chemically peculiar star
setâre-ye šimikâné afd
Fr.: étoile chimiquement particulière
A → main sequence star of
→ spectral type A or B
(→ A-type star, → B-type star)
identified by the presence of anomalously strong or weak
→ absorption lines of certain elements
in their spectra.
CP stars have been divided into four main classes on the basis of their
spectra: 1) non-magnetic metallic-lined (CP1,
→ Am star), magnetic (CP2,
→ Ap star), non-magnetic mercury-manganese (CP3,
→ HgMn star), and
helium-weak (CP4, → He-weak star).
The production and emission of light via a → chemical reaction.
A kind of → adsorption in which the forces involved are → valence forces of the same kind as those operating in the formation of → chemical compounds. Same as → chemical adsorption. See also → physisorption.
The science of the composition, structure, properties, and reactions of chemical elements and compounds and their interactions with matter and energy.
Chemistry, from chemist, from Gk. chemia "alchemy" + -ry, from M.E. -rie, from O.Fr.
Šimi, from Fr. as above.
A combining form meaning "chemical, chemically induced, chemistry," used in the formation of compound terms like → chemosynthesis. Also chem- (before a vowel) and chemi- (before elements of L. origin).
In biochemistry, the ability to produce organic compounds using energy contained in inorganic molecules. Chemosynthesis is similar to → photosynthesis. Instead of using light as an energy source to make food, energy or compounds from chemical reactions is used. Most chemosynthetic organisms are bacteria.
The first mission, conducted by the → European Space Agency, dedicated to searching for → exoplanetary transits by performing ultra-high precision → photometry on bright stars already known to host planets. Launched on 18 December 2019, Cheops is a small spacecraft with a launch mass (including propellant) of approximately 280 kg. It has a single instrument: a high precision → photometer with a 300 mm effective aperture telescope and a single → charge-coupled device (CCD) → detector covering → visible to → near-infrared wavelengths. The mission's main science goals are to measure the bulk density of → super-Earths and Neptunes orbiting bright stars and provide suitable targets for future in-depth characterization studies of → exoplanets in these mass and size ranges.
CHEOPS, short for CHaracterising ExOPlanet Satellite.
tâbeš-e Čerenkov (#)
rayonnement de Čerenkov
Visible radiation emitted when → charged particles pass through a transparent medium faster than the speed of light in that medium.
Named after Pavel A. Čerenkov (1904-1990), Russian physicist, who discovered the phenomenon. He shared the Nobel prize 1958 in physics with Ilya Frank and Igor Tamm, who in 1937 gave the theoretical explanation for this radiation.
Fr.: loi du chi-deux
A probability density function, denoted χ2, that gives the distribution of the sum of squares of k independent random variables, each being drawn from the normal distribution with zero mean and unit variance. The integer k is the number of degrees of freedom. The distribution has a positive skew; the skew is less with more degrees of freedom. As degrees of freedom increase, the chi-square distribution approaches a normal distribution. The most common application is chi-square tests for goodness of fit of an observed distribution to a theoretical one. If χ2 = 0 the agreement is perfect.