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feedforward pišxord Fr.: In a self-regulatory system, monitoring a disturbance before it enters the → system to apply corrections before the disturbance has influenced the system. See also → feedback. |
feedhorn karnâ, karnâ-ye xorând Fr.: cornet d'alimentation In a → radio telescope, a device located at the → focal point of the → antenna. It receives the → radio waves which the antenna collects and guides them to the → detector. |
feel sohidan (#) Fr.: sentir 1) To perceive or examine by touch. M.E. felen, from O.E. felan "to touch;" cf. O.S. gifolian, O.Fr.fela, Du. voelen, O.H.G. vuolen, Ger. fühlen "to feel;" from PIE root *pal- "to touch, feel, shake, strike softly" (cognates: Gk. psallein "to pluck (the harp)," L. palpare "to touch softly, stroke"). Sohidan, from Mid.Pers. sôhistan "to feel, to touch," sôhešn "feeling, sense," of unknown origin. Note Pers. sahestan "to fear," from Proto-Ir. *θrah- "to shake; to fear;" Pers. tars, harâs, sham "fear;" may be they are of different roots. |
feeling soheš (#) Fr.: sensation 1) The function or the power of perceiving by touch. Verbal noun of "to → feel." |
feminine mâdin (#) Fr.: féminin 1) Characteristic of or appropriate or unique to women. M.E. feminin, from O.Fr. femenin "feminine, female; with feminine qualities," from L. femininus "feminine," from femina "woman, female," literally "she who suckles," from root of felare "to suck, suckle;" cf. Gk. thele "mother's breast, nipple," thelys "female, fruitful;" Pers. dâyé, dâyah "(wet-nurse);" PIE root *d^{h}e(i)- "to suck, suckle." Mâdin, from mâdé "female," from Mid.Pers. mâdag, "female," from mâd, → mother. |
feminism zâd-zan-bâvari (#) Fr.: féminisme 1) Belief in the social, political, and economic freedom of women and
equality of the sexes. Feminism is closely tied to democracy and
→ secularism. From Fr. féminisme, from féminin "feminine, female," from L. femininus "feminine" (originally in the grammatical sense), from femina "woman, female," literally "she who suckles," cognates fecund "fruitful, fertile," felix "happy," fetus "offspring, pregnancy;" PIE base *d^{h}eh(i)- "to suck, suckle;" cf. Gk. thele "mother's breast;" Pers. dâyé "wet nurse." Zâd-zan-bâvari, from zâdzan "free woman" (on the model of zâdmard "free man, valiant man, generous man," zâdsarv "tall and upright cypress tree"), from zâd, contraction of âzâd, → free, + zan, → woman, + bâvari, → -ism. |
femto- femto- (#) Fr.: femto- In the International System of Units, a prefix meaning 10^{-15}. From Danish and Norwegian femten "fifteen," from O.N. fimmtān (Sw. femton, Du. vüftien, Ger. fünfzehn, E. fifteen, Pers. pânzdah), ultimately from PIE base *penk^{w}e "five" (cf. Mod.Pers. panj, Av. panca, Skt. pánca, Gk. pente, L. quinque) + PIE *dekm "ten" (cf. Mod.Pers. dah, Av. dasa, Skt. dáśa, Arm. tasn, Gk. deka, L. decem, Ger. zehn, E. ten, Fr. dix). |
Fermat number adad-e Fermat Fr.: nombre de Fermat Any number of the form 2^{2n} + 1, where n is a connective → integer. If Fermat number is → prime, it is called a → Fermat prime. → Fermat's principle; → number. |
Fermat prime naxost-e Fermat Fr.: nombre de Fermat premier A → Fermat number, 2^{2n} + 1, that is a → prime number. The only known Fermat primes are: 3, 5, 17, 257, and 65537, corresponding to n = 0, 1, 2, 3, and 4. → Fermat's principle; → prime. |
Fermat's last theorem vâpasin farbin-e Fermat Fr.: dernier théorème de Fermat In → number theory, the statement that for all → integers, the equation x^{n} + y^{n} = z^{n} has no solution in → positive integer. After 358 years of effort by mathematicians to prove the theorem, a complete proof was found by Andrew Wiles in 1995. → Fermat's principle; → last; → theorem. |
Fermat's principle parvaz-e Fermat Fr.: principe de Fermat The path taken by a ray of light going from one point to another through any set of media is such that the time taken is a minimum. This principle governs the light propagation and determines the geodesics of optical paths. Put forward by Pierre de Fermat (1601-1665), French mathematician, born at Beaumont-de-Lomagne; → principle |
fermi fermi (#) Fr.: fermi A unit of length equal to 10^{-13} cm. After Enrico Fermi (1901-1954), the Italian-born American physicist who was a key figure in the development of nuclear physics. He was awarded the 1938 Nobel Prize for Physics. |
Fermi constant pâyâ-ye Fermi Fr.: constante de Fermi The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. C_{F} = 1.167 x 10^{-5} GeV^{-2}. |
Fermi energy 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 Gamma-ray Space Telescope 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 interaction andaržirš-e Fermi Fr.: interaction de Fermi An old explanation, proposed by Enrico Fermi, of the → weak interaction. → fermi; → interaction. |
Fermi level 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 paradox 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 pressure fešâr-e Fermi Fr.: pression de Fermi Same as → degeneracy pressure. |
Fermi sea 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. |
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