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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.
1) A person between birth and puberty; a son or daughter; an offspring.
M.E.; O.E. cild "fetus, infant;" akin to Goth. kilthai "womb."
Fr.: calendrier chimois
A → lunisolar calendar (Chinese: yīnyáng li), which is now mainly used for determining cultural festivals. It is based on astronomical observations of the Sun's annual apparent motion (→ ecliptic) and → lunar phases. The calendar starts at Chinese New Year and consists of 12 or 13 → lunar months. The ecliptic is divided into 24 sections (jiéqi) of 15° each. In general, Chinese New Year falls on the day of the second new Moon after the → winter solstice on approximately December 22. Since 12 months are about 11 days shorter than the → tropical year, a → leap month is inserted to keep the calendar in tune with the seasons. An ordinary → lunar year has 353-355 days while a → leap year has 383-385 days. Therefore, the → solstices and → equinoxes move 11 (or 10 or 12) days later. Each 13-month leap year is about 19 days too long, so the solstices and equinoxes jump 19 (or 18 or 20) days earlier. Each year is assigned a name consisting of two components within a 60-year cycle. The first component is a celestial stem. The second component is a terrestrial branch; it features the names of animals in a zodiac cycle consisting of 12 animals. Each of the two components is used sequentially. Therefore, the first year of the 60-year cycle becomes jia-zi, the second year is yi-chou, and so on. One starts from the beginning when the end of a component is reached. The 60th year is gui-hai. The current 60-year cycle started on 2 February 1984. The leap year must be inserted if there are 13 new moons from the start of the 11th month in the first year to the start of the 11th month in the second year. The beginnings of the Chinese calendar can be traced back to the 14th century BC. Legend has it that the Emperor Huang-di invented the calendar in 2637 BC. The calendar has been adopted by several southeast Asian cultures. The Chinese calendar has undergone several reforms, the last one in 1645. For more details, see, e.g., Helmer Aslaksen, The Mathematics of the Chinese calendar, e-paper.
Chinese adj. of China, from Pers. Cin [Chin], from Qin the first imperial dynasty of China (221 to 206 BC); → calendar.
The quality of an object that is not superimposable on its mirror image.
From Gk. cheir "hand;" from PIE *ghes- "hand."
Xirâl, loan from Gk., as above.
The geometric property of a rigid object that is → chiral.
An object, discovered in 1977, which was initially assumed to be an asteroid, but subsequent observations showed it to be a weak comet with a detectable coma. Its orbit, lying now between those of Saturn and Uranus, is unstable on time scales of a million years.
In Gk. mythology, Xειρων (Cheiron or Chiron) was the wisest of the Centaurs; he was not a drunkard like other Centaurs. Chiron was tutor to Jason and Heracles. He was the only immortal centaur.
Fr.: compression d'impulsion
1) Telecommunications: A signal in which the wave frequency increases or
decreases, linearly or exponentially, with time.
Chirp "a short, high-pitched sound, such as that made by certain birds or insects," from M.E. chirpen, of onomatopoeic origin.
Cirp loanword from E., as above.
Fr.: figure de Chladni
Named after Ernst Chladni (1756-1827), German physicist; → figure.
1) A negative ion, ClO3- derived from chloric acid.
asid klorik (#)
Fr.: acide chlorique
A colorless, strong acid HClO3, formed by the action of dilute sulfuric acid on barium chlorate.
A gaseous → chemical element of the halogen group, which is greenish yellow and poisonous; symbol Cl. → Atomic number 17; → atomic weight 35.453; → melting point -100.98°C; → boiling point -34.6°C. Chlorine is about two and one-half times as dense as air. It is used for water purification, in the making of bleaching powder. Its compounds occur as common → salt (sodium chloride), NaCl, in sea water and as rock salt. Chlorine is the first poison gas to be used in warfare (by German army, the Second Battle of Ypres, 1915). It has several → radioactive isotopes, in particular 36Cl with a half-life of 3 × 105 years. Chlorine was discovered by the Swedish pharmacist and chemist Carl-Wilhelm Scheele (1742-1786) in 1774. In 1810, the English chemist Humphry Davy (1778-1829) proved it was an element and gave it the name chlorine.
The most common type of → meteorites containing → chondrules. These → stony meteorites make up about 86% of all meteorites. An important feature of the chondrites is that, with the exception of a few highly → volatile elements, they have the same composition as the Sun.
Chondrite, from chondr-, from chondros "grain", + suffix → -ite.
Millimeter-sized grains of → silicate sometimes found in large numbers in → chondrite meteorites. They are essentially glassy beads made by a violent but brief heating event that caused dust grains to form melt droplets. However, the cause of the heating remains unknown.
From Gk. chondr-, from chondros "grain," + diminutive suffix → -ule.