An → elementary particle that does not participate in the → strong interaction. The Lepton family includes → electrons, → muons, tau leptons, → neutrinos and their → antiparticles. The lepton is a → fermion.
From Gk, lepto-, combining form of leptos "small, slight" + -on a suffix used in the names of subatomic particles (gluon; meson; neutron), quanta (photon; graviton), and other minimal entities or components.
Fr.: dégénérescence des leptons
Postulate that the magnitude of the lepton number density is comparable to or larger than the thermal radiation photon number density, so relaxation to equilibrium produces a degenerate sea of neutrinos. Degenerate neutrinos would suppress the number of neutrons relative to protons in the very early Universe; degenerate antineutrinos would suppress the number of protons relative to neutrons. Either case would affect BBNS (Peebles, P. et al., 2009, Finding the Big Bang, Cambridge: UK, Cambridge Univ. Press).
dowrân-e leptoni (#)
Fr.: ère leptonique
The era following the hadronic era, when the Universe consisted mainly of leptons and photons. It began when the temperature dropped below 1012 degrees kelvin some 10-4 seconds after the Big Bang, and it lasted until the temperature fell below 1010 degrees kelvin, at an era of about 1 second.
adad-e leptoni (#)
Fr.: nombre leptonique
In particle physics, a quantum number attributed to elementary particles which is conserved in nuclear reactions. It is +1 for a lepton, -1 for an antilepton and 0 for other particles.
The Hare. A small → constellation in the southern hemisphere at about 6h right ascension, 20° south declination. Abbreviation: Lep; genitive: Leporis.
L. lepus "hare."
Xarguš "rabbit, hare," literally "ass-ear," Mid.Pers. xargôš, from xar "donkey, ass" (Mid.Pers. xar "donkey;" Av. xara- "donkey;" cf. Skt. khára- "donkey, mule") + guš, → ear.
Lesath (Upsilon Scorpii)
A bright blue star of → apparent visual magnitudeV = 2.70, that with → Shaula (Lambda Scorpii) makes up the Scorpion's stinger. Among its other designations: HR 6508 and HIP 85696. Lesath is 580 → light-years away. Lesath and Shaula appear very close on the sky (less than a degree apart), but they are not physically related. Lesath is a → subgiant of → spectral type B2 IV with a → luminosity of about 7,380 Msun. It has a radius of about 6 Rsun, and a → surface temperature of about 22,000 K.
Lesath, from Ar. al-Las'ah (
1) vât (#); 2) nâmé (#)
1) A symbol or character representing a sound of which words are formed
used in writing and printing a language.
M.E., from O.Fr. letre "character, letter; missive," from L. littera "letter of the alphabet," litterae (plural) "epistle, literature"
1) Vât "letter, word," from vat- "to speak, say;" cf. (Kurd.) wittin
"to speak, say," → article,
(Nâyin) vâte, (Qohrud) vâta, (Sangesar) -vât-/vân,
(Zazaki) vâtiš, (Awromani) wâtay/wâc-,
(Farizand) -vât/-vaj, (Gaz) vâ-/vât, related to Pers.
vâžé "word;" Mid.Pers. vâc, vâcak "word, speech;"
âva "voice, sound," âvâz "voice, sound, song,"
bâng "voice, sound, clamour" (Mid.Pers. vâng);
Av. vacah- "word," vaocanghê "to decalre" (by means of speech), from
vac- "to speak, say;" cf. Skt. vakti "speaks, says," vacas- "word;"
Gk. epos "word;" L. vox "voice;" PIE base *wek- "to speak."
A position with respect to a given or specified base. → energy level.
From O.Fr. livel, from L. libella "a balance, level," diminutive of libra "balance, scale."
Tarâz "level; a level," from tarâzu "balance, scales," Mid.Pers. tarâzên-, taraênidan "to weigh," Proto-Iranian *tarāz-, from *tarā- "balance, scale" ( cf. Skt. tulā- "scales, balance, weight," from tul- "to weigh, make equal in weight, equal," tolayati "weighs, balances," L. tollere "to raise," Gk. talanton "balance, weight," Atlas "the Bearer" of Heaven," Lith. tiltas "bridge;" PIE base telə- "to lift, weigh") + Av. az- "to convey, conduct, drive," azaiti drives" (cf. Skt. aj- "to dive, sling," ájati "drives," ajirá- "agile, quick," Gk. agein "to lead, guide, drive, carry off," L. agere "to do, set in motion, drive," from PIE root *ag- "to drive, move," → act).
level of significance
Fr.: niveau de significativité
Same as → significance level.
A rigid bar that pivots about a point and is used to move or lift a load at one end by applying force to the other end. → lever arm.
M.E. levere, levour; O.Fr. levier "a lifter, a lever," agent noun from lever "to raise," from L. levare "to raise," from levis "light" in weight.
Ahrom, of unknown etymology.
bâzu-ye ahrom (#)
Fr.: bras de levier
A physical process occurring in stellar atmospheres whereby → radiation pressure selectively pushes certain elements outward, leading to an atmospheric overabundance of such elements.
from levitate modeled on gravitate, from L. levitas "lightness," from levis "light."
A combining form meaning "left" and "counterclockwise," used in the formation of compound words, such as → levorotation, levocardia, levoglucose, etc. The variant lev- occurs before vowels. Compare → dextro-.
From L. laevo-, from laevus, cf. Gk. laios, Russ. levyj, + epenthetic vowel -o-.
Cap-, from cap "left," of unknown etymology.
The counterclockwise rotation of the → plane of polarization of light (as observed when looking straight through the incoming light) by certain substances.
Adj. related to → levorotation.
Adj. related to → levorotation.
A branch of → linguistics that deals with the principle and methods of writing dictionaries.
A branch of → linguistics that studies the formation, meaning, and use of words and their idiomatic combinations. In contrast to → terminology, lexicology is based on words and does not conceive of meaning unless it is related to the word.
Fr.: bouteille de Leyde
An early form of → capacitors which is a glass jar coated inside and outside about half way up the side with metal foil. A chain connects the inner coating to a rod which usually terminates in a small brass knob. The jar is charged by connecting the knob, that is the inner metal coating, to a charged body, meanwhile grounding the outer coating. Same as Leiden jar
Named after Leyden (Leiden) the city where it was invented by the Dutch scientist Pieter van Musschenbroek in 1745, independently from the German Ewald Georg von Kleist; jar a usually "cylindrical vessel," from M.Fr. jarre, from Provençal jarra, from Ar. jarrah.
Botri, → bottle.
Li I line
xatt-e Li I
Fr.: raie Li I
Fr.: géante rich en Li
A → giant star whose observed → lithium abundance is much higher (A(Li) ~ 2.95) than that predicted by stellar → evolutionary models. Standard evolutionary models predict severe → depletion of surface Li → abundance, which is as low as 1.4 → dex in K giants, a factor of about 80 lower than the maximum value of about 3.3 dex observed in → main sequence stars. Observations confirm model predictions showing much less Li compared to model predictions in most → red giant branch (RGB) stars (Kumar et al., 2018, J. Astrophys. Astr. 39, 25 and references therein).