Fr.: cristal négatif
A uniaxial, birefringent crystal in which the velocity of the extraordinary ray surpasses that of the ordinary ray.
Fr.: rétroaction negative
Fr.: lentille divergente
Same as → divergent lens.
Fr.: nombre négatif
Fr.: polarisation négative
A type of polarization in which the direction of polarization becomes reversed.
Fr.: pression négative
A kind of pressure that contrarily to ordinary pressure pushes inward. In contrast with the → Newtonian mechanics, in → general relativity there are situations in which pressure can be negative. Positive pressure gives rise to attractive gravity, whereas negative pressure creates → repulsive gravity.
Fr.: asymétrie négative
Of a distribution function, a skewness in which the left tail (tail at small end of the distribution) is more pronounced that the right tail (tail at the large end of the distribution). → positive skewness.
An obsolete term denoting a negatively charged electron, as opposed to a positron.
From neighbor, M.E., O.E. neahgebur, from neah→ near + -hood suffix denoting "state or condition of being;" M.E. -hode, -hod; O.E. -had "condition, position," cognate with Ger. -heit, Du. -heid.
A period of → geologic time within the Cenozoic era, between 23 and 2.6 million years ago, which comprises the Miocene and Pliocene epochs.
A colorless, odorless, and tasteless gaseous chemical element; symbol Ne. Atomic number 10, atomic weight 20.179; melting point -248.67°C; boiling point -246.048°C. It was discovered from its bright red spectral lines by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898 from a liquefied air sample. Neon is produced by carbon burning in massive stars and released into the Galaxy when they explode.
From Gk. neon neuter of neos, → new, so called because it was a newly discovered element.
Fr.: combustion du néon
A → nuclear fusion process that takes place in → massive stars and leads to the → production of → oxygen and → magnesium. It requires high temperatures and densities (around 1.2 × 109 K and 4 × 109 kg/m3).
The branch of meteorology that deals with clouds.
From Gk. nephos "cloud," nephele "cloud;" cognate with Pers. nam "moisture;" Av. napta- "moist," nabās-cā- "cloud," nabah- "sky;" L. nebula "mist," nimbus "rainstorm, rain cloud;" Skt. nábhas- "moisture, cloud, mist;" O.H.G. nebul; Ger. Nebel "fog;" O.E. nifol "dark;" PIE base *nebh- "cloud, vapor, fog, moist, sky" + → -logy.
Abršenâsi, from abr "cloud," from Mid.Pers. awr, abr (Laki owr, Baluchi haur, Kurd. Soriani hewr); Av. awra- "rain cloud, rain;" cf. Skt. abhra-"thunder cloud;" Gk. afros "scum, foam;" L. imber "rain;" also Sk. ambha- "water;" Gk. ombros "rain," PIE *mbhros "rain cloud, rain," from *mbh- + -šenâsi→ -logy.
The eighth planet from the Sun (mean distance about 30 A.U.) and the fourth largest by diameter (49,532 km). Neptune is composed of various "ices" and rock with about 15% hydrogen and a little helium. Its atmosphere is mostly hydrogen and helium with a small amount of methane. Its blue color is largely the result of absorption of red light by methane in the atmosphere. Neptune has 13 known moons.
Named for the Roman god of the sea, Gk. Poseidon.
A ductile, silvery radioactive metal, a member of the actinide series; symbol Np. Atomic number 93; atomic weight 237.0482; melting point about 640°C; boiling point 3,902°C (estimated). It was discovered in 1940 by Edwin M. McMillan and Philip H. Abelson, who produced neptunium-239 (half-life 2.3 days) by bombarding uranium with neutrons from a cyclotron at the University of California at Berkeley.
The name derives from the planet → Neptune, since it is the next outer-most planet beyond the planet Uranus in the solar system and this element is the next one beyond uranium in the periodic table.
The outermost satellite of Neptune (radius 150-250 km), discovered on May 1, 1949 by Gerard P. Kuiper. Its period is about 360 days and it has the most eccentric orbit (e = 0.76) of any natural satellite.
Named after the Nereids, the 50 sea-nymph daughters of Nereus, a Gk. sea god.
Fr.: effet de Nernst
When a temperature gradient is maintained through a strip of metal in a magnetic field, the direction of flow being across the lines of force, a potential difference will be produced across the conductor.
Walter Nernst (1864-1941), German physical chemist; → effect.
Oskar, → effect.
Nernst heat theorem
farbin-e garmâ-ye Nernst
Fr.: théorème de Nernst
The entropy change for chemical reactions involving crystalline solid is zero at the absolute zero of temperature. Also known as the third law of thermodynamics.
The outermost natural satellite of → Neptune, discovered in 2002. Also known as Neptune XIII, it follows a highly inclined and highly eccentric orbit at about 48 million km from Neptune. According to preliminary estimates, Neso is about 60 km in diameter.
In Gk. mythology, one of the Nereids, the fifty daughters of Nereus and Doris.
From nest, from M.E., O.E. nest "bird's nest;" cf. M.L.G., M.Du. nest, Ger. Nest, ultimately from PIE *nizdo- (cf. Skt. nidah "resting place, nest," L. nidus "nest," O.C.S. gnezdo, O.Ir. net, Breton nez "nest"), probably from → ni- (PIE) + *sed- "sit" (cf. Pers. nešastan "to sit"), → lander.
Tu-dar-tu literally "inside in inside," from tu "inside, in;" dar, → in-.