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: 13046 Search : far
Fermi constant
  پایای ِ فرمی   
pâyâ-ye Fermi

Fr.: constante de Fermi   

The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. CF = 1.167 x 10-5 GeV-2.

Fermi; → constant.

Fermi energy
  کاروژ ِ فرمی   
kâruž-e Fermi

Fr.: énergie de Fermi   

The energy of the highest occupied quantum state in a system of fermions at absolute zero temperature. See also → Fermi sea.

fermi; → energy.

Fermi Gamma-ray Space Telescope
  دوربین ِ فضایی ِ پرتوهای ِ گاما فرمی   
Durbin-e fazâyi-ye partowhâ-ye gâmâ Fermi

Fr.: Télescope spatial à rayons gamma Fermi   

A space observatory, formerly named GLAST, devoted to the study of → gamma rays emitted from astrophysical objects. Developed by NASA in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States, Fermi was launched on June 11, 2008. The main instrument, the Large Area Telescope (LAT), is an imaging → camera covering the energy range from about 20 → MeV to more than 300 → GeV. Such gamma rays are emitted only in the most extreme conditions, by particles moving very nearly at the → speed of light. The LAT's → field of view covers about 20% of the sky at any time, and it scans continuously, covering the whole sky every three hours. Another instrument, the Gamma-ray Burst Monitor (GBM) has a field of view several times larger than the LAT and provides → spectral coverage of → gamma-ray burst that extends from the lower limit of the LAT down to 10 → keV.

Fermi; → gamma ray; → space; → telescope.

Fermi interaction
  اندرژیرش ِ فرمی   
andaržirš-e Fermi

Fr.: interaction de Fermi   

An old explanation, proposed by Enrico Fermi, of the → weak interaction.

fermi; → interaction.

Fermi level
  تراز ِ فرمی   
tarâz-e Fermi

Fr.: niveau de Fermi   

A measure of the → energy of the least tightly held → electrons within a → solid at a → non-zero → temperature. The value of the Fermi level at → absolute zero (-273.15 °C) is called the → Fermi energy and is a constant for each solid. In other words, the Fermi level is any → energy level having the probability that it is exactly half filled with electrons in the → Fermi-Dirac statistics. Levels of lower energy than the Fermi level tend to be entirely filled with electrons, whereas energy levels higher than the Fermi tend to be empty.

Fermi; → level.

Fermi paradox
  پارادخش ِ فرمی   
pârâdaxš-e Fermi

Fr.: paradoxe de Fermi   

The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.

fermi; → paradox.

Fermi pressure
  فشار ِ فرمی   
fešâr-e Fermi

Fr.: pression de Fermi   

Same as → degeneracy pressure.

fermi; → pressure.

Fermi sea
  دریای ِ فرمی   
daryâ-ye Fermi

Fr.: mer de Fermi   

A large aggregate of single-state → fermions of lowest energy. When the temperature is lowered to absolute zero, all electrons in solids attempt to get into the lowest available energy level. However, electrons cannot all occupy the lowest energy, or ground state, in virtue of the → Pauli exclusion principle. They stack up in the lowest energy states, with two fermions in each state, one spin up and one spin down. Such assemblage of filled states is called the Fermi "sea," and this state of matter is called → degenerate. All states with energy less than the Fermi energy are filled, and all states above the Fermi energy are empty.

fermi; → sea.

Fermi-Dirac statistics
  آمار ِ فرمی-دیراک   
âmâr-e Fermi-Dirac (#)

Fr.: distribution Fermi-Dirac   

The statistical distribution of → fermions over the energy states for a system in → thermodynamic equilibrium. In other words, the probability that a given energy level be occupied by a fermion.

fermi, → Dirac function; → statistics.

Fermi-Pasta-Ulam problem
  پراسه‌ی ِ فرمی-پستا-اولام   
parâse-ye Fermi-Pasta-Ulam

Fr.: expérience Fermi-Pasta-Ulam   

A computer experiment that was aimed to study the → thermalization process of a → solid. In other words, the goal was to see whether there is an approximate → equipartition of energy in the system, which would mean that the motion is → chaotic. Using computer simulation, Fermi-Pasta-Ulam studied the behavior of a chain of 64 mass particles connected by → nonlinear springs. In fact, they were looking for a theoretical physics problem suitable for an investigation with one of the very first computers, the he MANIAC (Mathematical Analyzer, Numerical Integrator and Computer). They decided to study how a → crystal evolves toward → thermal equilibrium by simulating a chain of particles, linked by a quadratic interaction potential, but also by a weak nonlinear interaction. Fermi-Pasta-Ulam assumed that if the interaction in the chain were nonlinear, then an exchange of energy among the normal modes would occur, and this would bring forth the equipartition of energy, i.e. the thermalization. Contrary to expectations, the energy revealed no tendency toward equipartition. The system had a simple quasi-periodic behavior, and no → chaoticity was observed. This result, known as the Fermi-Pasta-Ulam paradox, shows that → nonlinearity is not enough to guarantee the equipartition of energy (see, e.g., Dauxois et al., 2005, Eur. J. Phys., 26, S3).

E. Fermi, J. Pasta, S. Ulam, 1955, Los Alamos report LA-1940; → problem.

fermion
  فرمیون   
fermion (#)

Fr.: fermion   

An elementary particle, such as → electron, → proton, or → neutron, having a half integral value of → spin. Fermions obey the → Pauli exclusion principle.

From Fermi → fermi + → -on.

ferric
  فریک   
ferrik

Fr.: ferrique   

Of or containing → iron, especially in the trivalent state. More specifically, iron with an → oxidation number of +3; also denoted iron(III) or Fe3+.

Ferric, from L. ferrum "iron," + → -ic.

ferric iron
  آهن ِ فریک   
âhan-e ferrik

Fr.: fer ferrique, fer trivalent   

Iron in a plus-3 → oxidation state. Ferric iron needs to share three electrons with an oxygen molecule to make the ion neutral.

ferric; → iron.

ferro-
  آهن-، فرو-   
âhan-, ferro-

Fr.: ferro-   

Indicating a property of → iron or the presence of iron.

Ferro-, variant ferri-, combining form of L. ferrum "iron."

Âhan-, → iron.

ferroelectric
  آهن‌برق‌مند   
âhanbarqmand

Fr.: ferroélectrique   

Characterized by the presence of a spontaneous → electric dipole while not exposed to an external electric field. → ferroelectricity.

ferro-; → electric.

ferroelectricity
  آهن‌برق‌مندی   
âhanbarqmandi

Fr.: ferroélectricité   

A property observed in certain materials characterized by the presence of a spontaneous electric polarization even in the absence of an external electric field. In the ferroelectric state the center of positive charge of the material does not coincide with the center of negative charge. This phenomenon is explained by spontaneous alignment of these permanent moments along the same direction. The term comes from the similarity with → ferromagnetism, but iron is not a ferroelectric. Ferroelectricity disappears above a critical temperature. Ferroelectric materials have been a fertile field for the study of → phase transitions.

ferro-; → electricity.

ferromagnet
  آهن‌مغنات   
âhanmeqnât

Fr.: ferro-aimant   

A ferroamagnetic substance, which possesses → ferromagnetism.

ferro-; → magnet.

ferromagnetic
  آهن‌مغناتی   
âhanmeqnâti

Fr.: ferromagnétique   

Relative to or characterized by → ferromagnetism.

ferro-; → magnetic.

ferromagnetism
  آهن‌مغنات‌مندی   
âhanmegnâtmandi

Fr.: ferromagnétisme   

A property of certain substances which are enormously more magnetic than any other known substance. Ferromagnetic substances, such as the chemical elements iron, nickel, cobalt, some of the rare earths, and ceratin alloys, achieve maximum → magnetization at relatively low magnetic field strengths. Their large → magnetic permeabilityies (greater than unity) vary with the strength of the applied field. When the temperature of a ferromagnet is increased the property vanishes gradually due to randomizing effects of thermal agitation. Beyond a definite temperature for each substance ( → Curie temperature) it ceases to behave as a ferromagnet and becomes a → paramagnet. Ferromagnetism is due to the alignment of the → magnetic moments of uncompensated electrons in the crystal lattice. Under the influence of an external magnetizing field, all of the uncompensated electrons line up with their → spins in the direction of the field. In contrast with paramagnetic substances, in which spins interact only with an external magnetic field, in ferromagnets the spins interact with each others, each of them trying to align the others in its own direction. This coupling gives rise to a spontaneous alignment of the moments over macroscopic regions called domains. The domains undergo further alignment when the substance is subjected to an applied field. Ferromagnets retain their magnetisation even when the external magnetic field has been removed. See also → antiferromagnetism ; → diamagnetism; → magnetism.

ferro-; → magnetism.

ferrous
  فرور   
fervar

Fr.: ferreux   

Of or containing → iron, especially in the bivalent state. More specifically, iron with → oxidation number of +2, denoted iron(II) or Fe2+.

From L. ferrum "iron," + -ous a suffix forming adjectives that have the general sense "possessing, full of" a given quality.

Fervar, from fer, loan from Fr., + -var adj. suffix.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara arc Ari arr Asi ass ast ast asy atm ato att aut ave axi Bab bal ban bar bar bea Bel Bes bia Big bin bin bip Bla bla bli blu Boh Bon bos Bou bra bri bro bur cal cal can Cap car Car cat Cau cea Cen cen cha Cha cha che chi chr cir cir civ cla clo clo CMB coa coe coh col col col com com com com com com com com com con con con con con con con con con con con coo cop Cor CoR cor cos cos Cou cou CP- cre cri cro cub cur cya Cyg dan dar dau de- deb dec dec dee def deg del den den dep des deu dew dia dif dif dih dip dir dis dis dis dis dis diu doc dop dou DQ dry dus dwa dyn Dys 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 eye fac fal Far fed Fer fer fie fin fir fit fla flo flu fol for for Fou fra fre Fre fro fuz gai Gal Gal gam gas Gau gen gen geo geo geo gia glo gol gra gra gra gra gre gri gui H I hai Ham har Hau hea hec hel hel her HES hie hig his hom hor hot Hub Hul Huy hyd hyd hyl hyp ice ide ima imm imp imp inc ind ind ine inf inf inf inh inn ins ins int int int int int int int int inv ion ion Irr iso iso iso Jal JHK Jul jur Kel Kep kin kne L d Lag lam Lap lar lat law Lea len lep lib lig lin lin lin liq lit loc log lon Los low lum lun Lut Lyr mac mag mag mag mag mag maj man Mar mas mas mat Max mea mec mel Mer Mes met met met mic mid Mil min mir mix mod mod mol mon mor mov mul muo mys nan nat Nav nec nep neu new New NGC Noa nom non non nor not nuc nuc num nyc obj obs obs oce odd OH Omi Oor ope opt opt opt orb ord Ori ort osc out ove oxi pai pan par Par Par par pas pea Pen per per per per Per per pha phl pho pho pho phy Pip Pla pla PLA pla ple plu pol pol pol pol pop pos pos pot Pra pre pre pre pre pri pri pro pro pro pro pro pro pro pse pul pur qua qua qua qua qui rad rad rad rad rad rad raf ran rar ray rea rea rec rec red red ref ref reg rel rel rel rep res res res res ret rev ric rig rin roc ROS rot Rox rus Sad sal sat sca sca Sch sci scy sec sec see sel sem sen Ser sex Sha she sho sid sig sil sim sin siz sle SMA SNR Sof sol sol sol sol sou Sou spa Sp spe spe spe sph spi Spi spr sta sta sta sta sta ste ste ste sto str str Sty sub sub suc sun sup sup sup sup sur Swa syn syn tac tas tel tem ter tes the the the the Tho thr tid tim Tit top tot tra tra TRA tra tre tri tri tru tum tur TY Typ ult una und uni uni uno upp urg UX Van var veg vel ver vib vio vir vis Voi vow wan wat wav WC wea wel whi Wil wir WNh wor X-r yel ytt zer zon > >>