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perfection farsâxtegi, farsâzeš Fr.: perfection The state or quality of being or becoming perfect. |
perfectionism farsâxtgerâyi, farsâxtgari Fr.: perfectionisme 1) Any of various doctrines holding that religious, moral, social, or political
perfection is attainable. → perfection; → -ism. |
perfectionist farsâxtgerâ, farsâxtgar Fr.: perfectioniste 1) A person who adheres to or believes in → perfectionism. → perfection; → -ist. |
pericynthion pirâmâh Fr.: périlune The point in the orbit of a satellite around the Moon closest to the Moon; opposite of → apocynthion. |
perihelion pirâhur Fr.: périhélie The nearest point to the Sun in an orbit around the Sun; opposite of → aphelion. Perihelion, from L. perihelium, from → peri- + helios "sun," cognate with L. sol, Skt. surya, Av. hvar-, Mod.Pers. xor, hur, O.H.G. sunna, Ger. Sonne, E. sun; PIE *sawel- "sun". Pirâhur, from pirâ-, → peri-, + hur "sun," as above; |
perihelion advance pišraft-e pirâhur Fr.: avance du périhélie |
perihelion distance apest-e pirâhuri Fr.: distance au périhélie The distance between the → Sun and an → object in orbit around it when they are at their closest approach. → perihelion; → distance. |
perihelion precession pišÃ¢yÃ¢n-e pirÃ¢huri Fr.: prÃ©cession du pÃ©rihÃ©lie → perihelion; → precession. |
period-luminosity relation bâzâneš-e dowré-tâbandegi Fr.: relation période-luminosité A → correlation between the periods and luminosities of → Cepheid variable stars: Cepheids with longer periods are intrinsically more luminous than those with shorter periods. The relation was discovered by Henrietta Leavitt in 1912 when studying Cepheids in the → Small Magellanic Cloud. Once the period of a Cepheid variable is determined from observations, the period-luminosity relation can be used to derive its luminosity. Since luminosity is a function of → distance, the distance can then be calculated with the luminosity. The period-luminosity relation is an invaluable tool for the measurements of distances out to the nearest galaxies and thus for studying the structure of our own Galaxy and of the Universe. → period; → luminosity; → relation. |
period-mean density relation bâzâneš-e dowré-cagâli-ye miyângin Fr.: relation période-densité moyenne A relation that gives a rough estimate of the oscillation period of a → pulsating star as a function of its mean density. This relation is obtained by considering how long it would take a sound wave to travel across the diameter of a model star: Π ≅ (3π/2γGρ)^{1/2}, where ρ is the mean density, γ the ratio of → specific heats (C_{p}/C_{v}), and G the → gravitational constant. This relation shows that the pulsation period of a star is inversely proportional to the square root of its mean density. And this is the reason why the pulsation periods decrease along the → instability strip from the luminous, very tenuous → supergiants to the faint, very dense → white dwarfs. |
periodic function karyâ-ye dowreyi Fr.: fonction périodique A function f(x) if for all x, f(x + P) = f(x), where P is a positive constant. The least value of P > 0 is called the period of f(x). |
periodic motion jonbeš-e dowreyi Fr.: mouvement périodique Any motion that recurs in identical forms at equal intervals of time. |
peripheral vision did-e pirâbari Fr.: vision périphérique In optics, the ability to see over large angles of view. → peripheral; → vision. |
permission parzâmeš Fr.: permission The act of permitting. Authorization granted to do something. |
permitted transition gozareš-e parzâmidé Fr.: transition permise A transition between two quantum mechanical states that does not violate the quantum mechanical selection rules. → permitted; → transition. |
permutation permuteš, jâygašt Fr.: permutation Math.: A rearrangement of the elements of a set in a particular order. The number of permutations of n objects is equal to n! (→ factorial n). For example, there are 24 permutations of letters A, B, C, and D (4! = 1 × 2 × 3 × 4). The number of permutations of n objects taken r at a time is denoted by ^{n}P_{r} and equals n! / (n - r)!. For example, the number of permutation of A, B, C, and D taken two at a time is 12. If n objects are of k different kinds, with r_{1} alike of one kind, permutations of n objects equals n! / r_{1}! r_{2}! ... r_{k}!, where r_{1} + r_{2} + ... r_{k} = n. Verbal noun of → permute. Permuteš, verbal noun of → permute. |
perpetual motion jonbeš-e hamišegi Fr.: mouvement perpétuel The motion of a hypothetical machine which, once set in motion, will go on for ever without any losses due to → friction or other forms of → dissipation of energy and without receiving any external energy. |
personal equation hamugeš-e tanumi Fr.: équation personnelle A systematic observational error due to the characteristics of the observer. |
personification tanumâreš Fr.: personnification 1) The attribution of human nature or character to animals, inanimate objects, or
abstract notions, especially as a rhetorical figure. Verbal noun of → personify. |
perturbation partureš Fr.: perturbation 1) Any departure introduced into a steady state of a system.
The magnitude is often assumed to be small so
that the resulting terms in the dependent variables may be neglected.
The term "perturbation" is therefore sometimes used as synonymous with "small perturbation." Verbal noun of → perturb. |
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