An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13116 Search : far
Debye length
  درازای ِ دبی   
derâzâ-ye Debye (#)

Fr.: longueur de Debye   

A characteristic length scale in a → plasma, determined by the temperature and number density of the charged particles. The Debye length (in cm) is given by the expression: λD = 743(Te/ne)1/2, where Te is the electron temperature in → electron-volts and ne is the electron density in cm-3. Particles which pass each other at distances smaller than the Debye length interact directly. Outside the Debye length particle interactions are dominated by collective effects. In typical laboratory plasmas the Debye length is small compared with the plasma dimension, so that collective effects are important.

debye (D); → length.

Debye model
  مدل ِ دبی   
model-e Debye (#)

Fr.: modèle de Debye   

An extension of the → Einstein model accounting for → specific heats, based on the concept of → elastic waves in → crystals. In this model specific heat is given by: CV = 9R[(4/x2)∫ y2/(ey - 1)dy - x/(ex - 1)], integrating from 0 to x, where R is the → gas constant, k is → Boltzmann's constant, x = hνmax/k, and y = hν/k. The parameter TD = hνmax/k is the characteristic → Debye temperature of the crystal. At low temperatures the specific heat prediction by this model is in good agreement with observations (→ Debye law), in contrast to Einstein's model.

debye; → temperature.

Debye temperature
  دمای ِ دبی   
damâ-ye Debye (#)

Fr.: température de Debye   

The characteristic → temperature of the → crystal as given by the → Debye model of → specific heats.

debye; → temperature.

deca-
  دکا-   
dekâ- (#)

Fr.: déca-   

Prefix meaning "ten" and "ten times" used in terms belonging to the metric system.

From Fr. déca-, from L. deca-, dec-, from Gk. deka "ten;" cf. Av. dasa "ten," Mod.Pers. dah "ten," Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Dekâ-, from Fr. as above.

decay
  ۱) تباهیدن؛ ۲) تباهی، فروپاشی   
1) tabâhidan (#); 2) tabâhi (#), forupâši (#)

Fr.: 1) se désintegrer, se désexciter; 2) désintegration, désexcitation   

1a) To become decomposed.
1b) Of a radioactive nucleus, to disintegrate spontaneously into one or more different nuclei, accompanied by the emission of → alpha particles, → beta particles, → positrons, and/or → gamma rays.
2a) Decomposition.
2b) The → transition of a system from an → excited state to a less excited one. Radiative decay refers to the process when the energy difference between the states is taken away by radiation. Likewise, collisional decay is when the energy difference is removed by a target during a collision.
2c) Of a spacecraft, a gradual decrease in the radius of its orbit over time, caused by aerodynamic drag of the atmosphere and other forces. The rate of orbit decay rises as the spacecraft falls and encounters increasing atmospheric density, eventually resulting in reentry.
alpha decay; → beta decay; → dark matter decay; → decay chain; → decay constant; → decay mode; → decay product; → decay time; → inverse beta decay; → Ohmic decay time; → orbit decay; → radioactive decay; → turbulence decay.

From O.Fr. decair, from V.L. *decadere "to fall off," from L. cadere "to fall," PIE base *kad- "to fall" (cf. Pers. Gilaki katan "to fall," ba.ka.tam "I fell," dakatan "to fall (in a marsh, in a pit)," vakatan "to fall from tiredness, be exhausted," fakatan "to fall from (lose) reputation," Pers. Laki: katen "to fall," kat "he fell," beko "fall!," Pers. Tabari: dakətə "fallen," dakətən "to crash down," dakət.gu "stray cow," Arm. chacnum "to fall").

Tabâhidan, verbal form of tabâhi, noun form of tabâh "spoiled, ruined, destroyed," Mid.Pers. tapâh "spoiled, destroyed." Maybe related to Mod.Pers. tâb "affliction, pain, torment; heat, burning," tab "fever," tâbidan, tâftan "to shine," tafsidan "to become hot," Av. tāp-, taf- "to warm up, heat," tafsat "became hot," tāpaiieiti "to create warmth," cf. Skt. tap- "to spoil, injure, damage; to suffer; to heat, be/become hot," tapati "burns," L. tepere "to be warm," tepidus "warm," PIE base *tep- "warm."

decay chain
  زنجیره‌ی ِ تباهی   
zanjire-ye tabâhi

Fr.: chaîne de désintégration   

A series of nuclear decays produced by successive → daughter products, when the daughters are themselves → radioactive. For example, the decay chain N1N2N3→ ... in which the parent nuclide N1 decays to the daughter N2, which in turn decays to N3. Each → radionuclide in the decay chain can → branch to more than one daughter.

decay; → chain.

decay constant
  پایای ِ تباهی   
pâyâ-ye tabâhi

Fr.: constante de désintégration   

A constant of proportionality occurring in the formula expressing spontaneous → decay of → radionuclides. The number of atoms decaying is given by N = N0e-kt, where N0 is the number of nuclei in the given volume of the substance at instant t = 0, N is the number of nuclei at t, and k is decay constant. Decay constant is related to → half-life by τ = ln2/k, roughly 0.693/k.

decay; → constant.

decay mode
  ترز ِ تباهی، مد ِ ~   
tarz-e tabâhi, mod-e ~

Fr.: mode de désintégration   

A possible type of decay of a → radionuclide or → elementary particle. In general, a given particle may decay by more than one decay mode. Usually the number of decay modes is one or two. There are, however, → nuclides which have many decay modes; for example the nuclide 11Li has seven decay modes.

decay; → mode.

decay product
  فر‌آورده‌ی ِ تباهی   
farâvarde-ye tabâhi

Fr.: produit de désintégration   

A → stable nuclide or → radioactive nuclide formed by the → disintegration of a → radioactive isotope, either directly or as a result of a → decay chain. Also called → daughter product. For example, the decay product of 238U is 206Pb, after passing through the following chain: 238U → 234Th (4.5 billion yr) → 234Pa (24 days) → 234U (1 min) → 230Th (245,000 yr) → 226Ra (76,000 yr) → 222Rn (1,600 yr) → 218Po (3.8 d) → 214Pb (3 m) → 214Bi (27 m) → 214Po (160 microseconds) → 210Pb (22 yr) → 210Bi (5 d) → 210Po (138 d) → 206Pb.

decay; → product.

decay time
  زمان ِ تباهی   
zamân-e tabâhi (#)

Fr.: temps d'amortissement   

The time required for the amplitude of a vibrating system to decrease to 1/e of its initial value.
Of an orbiting object, its lifetime in a non stable orbit.

decay; → time.

decelerate
  واشتابیدن؛ واشتاباندن   
vâšetâbidan (#); vâšetâbândan (#)

Fr.: décélérer   

(v.intr.) To slow down. (v.tr.) To decrease the velocity of.

From → de- + (ac)celerate, from → accelerate.

Vâšetâbidan, from vâ-de- + šetâbidan, → accelerate.

deceleration
  واشتاب   
vâšetâb (#)

Fr.: décéleration   

The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration.

Verbal noun of decelerate.

deceleration parameter
  پارامون ِ واشتاب   
pârâmun-e vâšetâb

Fr.: paramètre de décéleration   

A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by: q(t) = -R(t)R ..(t)/R .2(t), where R(t) represents the size of the Universe at time t. See also → expansion parameter; compare with → acceleration parameter.

deceleration; → parameter.

deci-
  دسی-   
desi- (#)

Fr.: déci-   

Prefix used in the metric system to mean on-tenth.

From Fr. déci-, from L. decimus "tenth," from decem "ten," cf. Av. dasa "ten," Mod.Pers. dah "ten," Gk. deka, Skt. dasa, PIE *dekm (Dan. ti, Du. tien, Ger. zehn, E. ten, Fr. dix).

Desi-, from Fr. déci-, as above.

decibel (dB)
  دسی‌بل   
desibel (#)

Fr.: décibel   

A dimensionless unit used to express relative difference in power or intensity, usually between two acoustic or electric signals. It is defined as n [dB] = 10 log (P1/P0), with → natural logarithm. One decibel equals one-tenth of a → bel (B).

deci-; → bel (B).

decide
  واسونیدن   
vâsunidan

Fr.: décider   

To make a choice or come to a conclusion about something. → decision, → rule of decision.

M.E. deciden, from O.Fr. decider, from L. decidere "to decide, determine," literally "to cut off," from → de-"off" + caedere "to cut, chop, beat, hew."

Vâsunidan, from vâ- "off, away," → de-, + sun "to cut;" cf. Kurd. Soriani su, sun "to sharpen, whet;" Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun "to sharpen, whet;" Mod.Pers. sân "whetstone," variants fasân, afsân, awsân; Av. si-, sā- "to cut;" cf. Skt. śā- "to sharpen, whet;" + -idan infinitive suffix.

decider
  واسوننده   
vâsunandé

Fr.: décideur   

Someone who decides, or something that allows to determine.

decide; → -er.

decimal
  دهدهی   
dahdahi (#)

Fr.: décimal   

Referring to or based in the number 10; relating to tens or tenths.

M.L. decimalis "of tithes or tenths," from L. decimus "tenth," from decem, → ten.

Dahi , of or relating to dah, → ten; dahdahi literally "ten by ten."

decimal fraction
  برخه‌ی ِ دهدهی   
barxe-ye dahdahi

Fr.: fraction décimale   

A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.

decimal; → fraction.

decimal logarithm
  لگاریتم ِ دهدهی   
logâritm-e dahdahi

Fr.: logarithme décimal   

common logarithm.

decimal; → logarithm.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer aga air Alf Alg alk Alp alt alu amm ana And ang ani ano ant ant Ap apo app app Aqu Arc arg arr asc ass ast ast asy atm ato att aur aut axi B-m bad Bal bar bar Bay Bed ber Bet bif bim bin bio bis bla ble blu Bod Bol bor bou Bra Bre bro bul C-t Cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che chl Cir cir cir Cla cli clo clu co- coc coh col col col Com com com com com com com com Com con con con con con con con con con con con con coo Cor Cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dua dus dwa dyn DZ Ear ecc eco edi EHB Ein ela ele ele ele ele ell eme emp end Eng ent epi equ equ era ESP eth Eur evi exa exc exe exi exp exp ext ext ext fac fal far fec Fer fer fie fin fir fis fla Flo flu fog for for Fou fra fre fre Fro fun G s Gal gal gal Gar gau geg gen geo geo geo ger gla gly gra gra gra gra gra Gre gro GYR Had Hal hap Har HD hea hel hel Hen Her hex hig Hil hol Hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp in- inc Ind ind ine inf inf inf ini ins ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jor jum K c Kep Ker kin kno lab Lam Lan Lap las lat Le lef len lev lig lig lin lin lin liq Lit loc log lon lou LS lun lun Lym M s Mag mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mol mon mor mov mul mur mys nan nat nav nec Nep neu New New NGC nob nom non non nor nos nuc nuc num nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi P-w pal par par par par Pas pat pej per per per per per per pha Phe pho pho pho phy pin pla Pla pla pla pla plu poi pol pol Pol pol por pos pot Poy pre pre pre pre pri pri pri pro pro pro pro pro pro Psa pul pum Q i qua qua qua qua R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set Sha sha shi sho sid sig sim sin Sir ske sli Smo soc sof sol sol sol sol sou sou spa spe spe Spe spe sph spi Spi spr sta sta sta sta sta ste ste ste Sto str str sub sub sub suc sun sup sup sup sup sur swa syn syn tac tas tel tem ter tes the the the the thi thr tid til tip ton tor tou tra tra tra tra Tri tri tru tsu tur two Typ UHE ult unc uni uni uni upg ura uti val var vec Vel ver Ver vie Vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>