modulation transfer function (MTF)
karyâ-ye tarâvaž-e degarâhangeš
Fr.: fonction de transfert de modulation
A measure of the ability of an optical system to reproduce (transfer) various levels of detail from the object to the image, as shown by the degree of contrast (modulation) in the image. → optical transfer function.
Any device for effecting the process of modulation.
from L. modulator, from → modulate + -tor a suffix forming personal agent nouns from verbs.
Vâhangâr, from vâhang, → modulation, + -âr, contraction of âvar agent noun of âvardan "to bring; to cause, produce" (Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring; to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry").
A distinct and separable element of a spacecraft or space station.
From M.Fr. module, from L. modulus "small measure," diminutive of modus "measure, manner," → mode.
A real, positive quantity that measures the magnitude of some number. For instance, the modulus of a complex number is the square root of the sum of the squares of its components. Often it means, simply, the numerical ("absolute") value of an algebraic quantity.
From L. modulus, → module.
Peymun, variant of peymâné "a measure either for dry or wet goods; a bushel, cup, bowl," from peymudan, peymâyidan "to measure," from Mid.Pers. patmudan, paymudan "to measure (against)," from *pati-māya-. The first element *pati- "against, back" (cf. Mod.Pers. pâd- "agaist, contrary to;" Mid.Pers. pât-; O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti; Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti). The second element from *mā- "to measure;" O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure." Apart from peymâné, several other terms in Mod.Pers. are related to this second element, which occurs also as mun, mân, man, mâ, mu, and mây: pirâmun "perimeter," âzmun, âzmây- "test, trial," peymân "measuring, agreement," man "a measure weighing forty seers"), nemudan, nemâ- "to show, display," âmâdan, âmây- "to prepare."
modulus of rigidity
Fr.: module de rigidité
Same as → shear modulus.
Describing a quantity of substance that is proportional to its molecular weight. Relating to a → mole.
Fr.: concentration molaire
Of a gas included in the composition of a → gas mixture, the ratio of the number of moles of this gas to the total number of moles of all the gases in the mixture. Same as mole fraction and mole-fraction concentration.
molar heat capacity
gonjâyeš-e garmâyi-ye moli
Fr.: capacité thermique molaire
molar heat of vaporization
garmâ-ye boxâreš-e moli
Fr.: chaleur de vaporisation molaire
The amount of heat energy required to vaporize 1 mole of a liquid at its → boiling point, usually expressed in kJ/mol.
mol, molekul-geram, atom-geram
The molecular weight of a substance expressed in grams. Specifically, a mole is an amount containing the same number of units as there are atoms in 12 grams of carbon-12, i.e., 6.023 x 1023.
From Ger. Mole, short for Molekül, from Fr. → molecule.
Of or pertaining to or caused by molecules.
Molekuli, from molekul→ molecule + -i adj. suffix.
bând-e molekuli (#)
Fr.: bande moléculaire
abr-e molekuli (#)
Fr.: nuage moléculaire
A relatively dense, cold region of interstellar matter where the atoms are primarily bound together as molecules rather than free atoms or ionized particles. Molecular clouds represent the coldest and densest phase of the → interstellar medium. They consist primarily of → molecular hydrogen (H2), with temperatures in the range 10-100 K. Molecular hydrogen is not directly observable under most conditions in molecular clouds. Therefore, almost all current knowledge about the properties of molecular clouds has been deduced from observations of molecules such as → carbon monoxide (CO), which have strong emission lines mainly in the → millimeter portion of the → electromagnetic spectrum. So far 129 molecular species have been detected in molecular clouds, among which complex organic molecules. → Dust grains in molecular clouds play a crucial role in the formation of molecules. Molecular clouds are the principal sites where stars form. → giant molecular cloud; → Orion molecular cloud.
Fr.: grumeau moléculaire
One of many compact and dense sub-structures in a → molecular cloud. Their typical sizes are about 0.5-10 → parsecs and their masses range from about 50 to 103 → solar masses. The gas temperatures are about 10-20 K, and the number densities from about 103 to 104 cm-3.
Fr.: formule moléculaire
The formula of a chemical compound, showing the kind and arrangement of atoms.
hdirožen-e molekuli (#)
Fr.: hydrogène moléculaire
A molecule consisting of two hydrogen atoms (H2) which is the most abundant molecule in the Universe. Molecular hydrogen plays a fundamental role in many astrophysical contexts. It is found in all regions where → self-shielding against the ultraviolet photons, responsible for its → photodissociation, is sufficiently large. Containing two identical hydrogen atoms, H2 is highly symmetric. Due to this property, the molecule has no → dipole moment and all → rotation-vibrational transitions within the electronic → ground state are → quadrupolar with low → spontaneous emission → Einstein coefficient values. The molecule exists in two almost independent states, namely → orthohydrogen and → parahydrogen. H2 may be excited through several mechanisms, including: 1) → far ultraviolet (FUV) induced → optical pumping and → collisional excitation in → photodissociation regions (PDRs) associated with → star formation; 2) → hard X-rays penetrating and heating regions within → molecular clouds, which in turn excite H2 via collisions with electrons or hydrogen atoms; and 3) collisional excitation of H2 due to acceleration produced by interstellar → shock waves. H2 is thought to be chiefly produced via surface reactions on → interstellar grains, but the exact formation mechanism is not fully understood.
Fr.: flot moléculaire
An outflow of molecular material, often → bipolar, observed in the regions of → star formation. Molecular outflows are thought to be driven by → bipolar jets from → protostars. They are probably → bow shocks which have had time to cool and be observable in molecular lines. Molecular outflows are poorly → collimated compared to the jets and tend to be slow moving (velocities 10-20 km s-1). Some bipolar outflows may be driven by → stellar winds.
Fr.: polarisabilité moléculaire
The ability of a molecular entity to be distorted from its normal shape by an external → electric field. When a molecule is subjected to an electric field there is a small displacement of electrical centers which induces a dipole in the molecule. More specifically, the molecular polarizability α is defined as the ratio of the induced → dipole moment (p) to the local electric field (E) that produces this dipole moment: α = p/E (in cgse units).
Fr.: proposition moléculaire
Fr.: vibration moléculaire
The dynamical motion of chemically bound atoms which constantly change their position with each other. The vibration of molecules is treated within → quantum theory. Therefore, the energy of molecular vibration can only take → discrete values. To a first approximation, molecular vibrations can be approximated as → simple harmonic oscillator assigned to each mode.