Fr.: diffusion ambipolaire
A physical process which allows a → molecular cloud to decouple from → interstellar magnetic field in order to undergo → gravitational collapse. A cloud of pure molecular gas would form stars very fast through collapse since neutral matter does not respond to the magnetic field. However, the magnetic field holds up a collapse because the ions present in the cloud collide with the neutrals and tie them to the field. The collapse can then only proceed if the magnetic field can be separated from the gas. In denser molecular cores the ionization degree decreases substantially and therefore neutrals and ions decouple.
A defect of vision due to abnormal development, without detectable organic lesion of the eye.
From Gk. amblyopia "dim-sightedness," from amblys "dulled, blunt" + ops, → eye.
Tambalcašmi, literally "eye laziness," from tambal "lazy" + cašm, → eye.
An artificially produced → radioactive→ chemical element; symbol Am. → Atomic number 95; → atomic weight of most stable → isotope 243; → melting point about 1,175°C; → boiling point about 2,600°C; → specific gravity 13.67 at 20°C; → valence +2, +3, +4, +5, or +6. Its most stable isotope, 243Am, has → half-life of 7.4 x 103 years.
From America, where it was first synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, and Albert Ghiorso, who bombarded plutonium-239 with neutrons to form plutonium-241, which decays to form americium-241.
An irritating, colorless, gaseous compound of → nitrogen and → hydrogen (NH3), which is lighter than air and readily soluble in water. It is formed in nature as a by-product of protein metabolism in animals. Ammonia is used in the preparation of many substances containing nitrogen, such as fertilizers, explosives, refrigerants, and so on.
Coined in 1782 by Swedish chemist Torbern Bergman (1735-1784) for gas obtained from ammoniac, a salt and a gum resin containing ammonium chloride found near temple of Jupiter Ammon in Libya, from Gk. ammoniakos "belonging to Ammon" (Egyptian God).
Âmoniyâk, loan from Fr.
Fr.: maser à ammoniac, ~ NH3
A maser source in which excited → ammonia molecules (NH3) produce → maser emission. The first device to demonstrate the principle of → stimulated emission of radiation used ammonia molecules (Gordon et al. 1954). The hydrogen atoms of ammonia molecules have a rotation motion whereas the nitrogen atom oscillates between two positions, above and below the plane of the hydrogen atoms. These arrangements do not represent exactly the same energy, and therefore the molecule exists in two energy states. The difference in energy between the states corresponds to a frequency of 23.87 GHz, or 1.25 cm. In astrophysics, ammonia maser emission has been detected toward active star formation regions, such as W51. → interstellar masers.
Fr.: astéroïde Amor
A → near-Earth asteroid (NEA) with → perihelion distances between 1.017 and 1.3 → astronomical units. The Amor asteroids approach the orbit of the Earth from beyond, but do not intersect it. Most Amors do cross the orbit of Mars. It is estimated that 32% of the total number of NEAs are Amors. One of the larger Amors is → Eros.
Quantity; measure; the sum total of two or more quantities or sums.
From M.E. amounten "to ascend," from O.Fr. amonter, from amont "upward," from L. ad montem "to the hill," from ad "to" + mons, mont "hill," → mountain.
Masâk, from Mid.Pers. masâk "size, amount, magnitude," from mas "great, large," Av. masan "greatness, importance," from mas-; maz- "long, large; great"; cp. Skt. maha "great, mighty" (Mod.Pers. mah "great, large"), Gk. megas "great, large" L. magnus "great," PIE *meg- "great".
The → SI unit of → electric current; symbol A. It is defined by taking the fixed numerical value of the → elementary charge, e, to be 1.602 176 634 × 10-19 when expressed in the unit → coulomb (C), which is equal to A s, where the → second (s) is defined in terms of ΔνCs.
Named after the French physicist and mathematician André-Marie Ampère (1775-1836), one of the pioneers in studying electricity, who laid the foundation of electromagnetic theory.
Fr.: loi d'Ampère, théorème ~
One of the basic relations between → electricity and → magnetism, stating quantitatively the relation of a → magnetic field to the → electric current or changing electric field that produces it. Ampere's law states that the line integral of the magnetic field around an arbitrarily chosen path is proportional to the net electric current enclosed by the path. Also known as Ampère's theorem, Ampère's circuital law.
dâmane-dehi, dâmane-giri (#)
1) General: The act or result of amplifying, enlarging, or extending.
Verbal noun of → amplify.
Fr.: facteur d'amplification
1) Electronics: The extent to which an
→ analogue → amplifier
boosts the strength of a → signal. Also called
Device for reproducing an electrical input at increased intensity.
Agent noun of → amplify.
dâmané dâdan, dâmané gereftan (#)
General:To make larger, greater, or more powerful.
From M.F. amplifier, from L. amplificare "to increase, augmant," from L. amplus "wide, large."
Dâmané, → amplitude; dâdan "to give" (Mid.Pers. dâdan "to give," O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives;" Skt. dadáti "he gives," Gk. didomi "I give," tithenai "to put, set, place;" L. dare "to give, offer;" Rus. delat "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do"); gereftan "to take, seize, catch," (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").
General:The greatness, size, or extent of something.
L. amplitudo "wide extent, width," from amplus "large".
Dâmané "the foot or skirt of a mountain," from dâman "skirt."
a- (#), an- (#); bi- (#); nâ- (#)
Prefix same as → a- "not, without" occurring before a vowel or h in loanwords from Greek.
Prefix meaning: 1) up, upward (anode); 2) back, backward (ananym); 3) again, anew (anagenesis); 4) exceedingly (anamorphism).
From Gk. ana- "up, on, upon, throughout, again," cognate with Av. ana "on, over, along," O.Pers. anâ "throughout," O.E. on; PIE base *ano- "on, upon, above".
Ânâ-, from ana, anâ, Av. and O.Pers. counterparts of Gk. ana-, as above.
The shape resembling a figure of 8 obtained by following the Sun's position in the sky at the same time of day throughout the year. It is a graphical presentation of the → equation of time. Because the Earth's orbit around the Sun is elliptical, the two loops of analemma have different sizes. Analemma figures for different latitudes or different times of day would appear slightly different. The analemma is widest in the period when the Earth is closest to the Sun (December). This is because in this situation the Earth advances in its orbit faster due to the stronger gravitational attraction of the Sun. On the other hand, since the Earth rotates at a constant rate, the Sun appears to rise earlier than average because the Earth advances further in its orbit in one day when the Earth is close to the Sun. The opposite occurs in June when the Earth is further from the Sun.
From L. analemma "the pedestal of a sundial," hence the sundial itself, from Gk. analemma "prop, support," from analambanein, from → ana- "up" + lambanein "to take".
Hurspicak from hur "Sun;" Av. hvar- "sun" (cf. Skt. surya; Gk. hlios; L. sol; O.H.G. sunna; Ger. Sonne; E. sun; PIE *sawel- "sun") + picak "a curled, a twisted figure or object," from picidan "to twist, invove, enttwine, coil."
Fr.: convertisseur analogique-numérique
In electronics, a device that converts the analog signal to → analog-to-digital units or counts.
analog-to-digital unit (ADU)
Fr.: unité analogue-numérique
A number that represents a → charge-coupled device (CCD)'s output and is proportional to the → electron charge created by the → photons, plus the constant → bias offset. The relationship between the ADUs generated and the number of electrons acquired on the CCD is defined by the → CCD gain. Intensities given in ADUs provide a convenient method for comparing images and data generated by different cameras. Also referred to as → count and digital number. In most cases, the analog signal is digitalized by an analog-to-digital (A/D) converter and fed into a computer where further manipulation and analysis are done on what the detector originally produced from the star's photons (Howell, S.B., Handbook of CCD Astronomy, Cambridge Univ. Press, 2000).
Of, relating to, or based on analogy; expressing or implying analogy.