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: 20 Search : condition
Abbe sine condition
  بوتار ِ سینوس ِ آبه   
butâr-e sinus-e Abbe

Fr.: condition des sinus d'Abbe   

In → geometric optics, a condition for eliminating → spherical aberration and → coma in an → optical system. It is expressed by the relationship: sin u'/U' = sin u/U, where u and U are the angles, relative to the → optical axis, of any two rays as they leave the object, and u' and U' are the angles of the same rays where they reach the image plane. A system which satisfies the sine condition is called → aplanatic.

Named after Ernst Karl Abbe (1840-1905), a German physicist; → sine; → condition.

adiabatic initial conditions
  بوتارهای ِ آغازین ِ بی‌دررو   
butârhâ-ye âqâzin-e bidarrow

Fr.: conditions initiales adiabatiques   

The assumption whereby the density fluctuations in the very → early Universe would be produced by compressing or decompressing of all components of a homogeneous Universe. The adiabatic initial conditions lead to coherent oscillations in the form of peaks in the → temperature anisotropy spectrum. See also → acoustic peak, → baryon acoustic oscillation.

adiabatic; → initial; → condition.

boundary conditions
  بوتارها‌ی ِ کران، ~ کرانی   
butârhâ-ye karân, ~ karâni

Fr.: conditions à la limite   

1) Math: Restriction on the limits of applicability of an equation. In a differential equation, conditions that allow to fix the constant of integration and reach a unique solution. The number of boundary conditions necessary to determine a solution matches the order of the equation.
2) Physics: Conditions needed to determine the evolution of a system, given the physical laws.

boundary; → condition.

condition
  بوتار   
butâr

Fr.: condition   

1) Physics: The state of a physical system at a given time. Also called → physical condition.
2) Math: A premise, statement, or restriction upon which a mathematical result or consequence depends. → initial conditions; → boundary conditions.

From O.Fr. condition, from L. condicionem (nom. condicio) "agreement, situation," from condicere "to speak with, talk together," from → com- "together" + dicere "to speak," from PIE *deik- "to point out;" cf. Av. daēs- "to show; assign; make known," Skt. dis- "to show, point toward," disati "shows," Gk. deiknunai "to show," O.H.G. zeigon, Ger. zeigen "to show," E. token "indication, sign."

Butâr, from Mid.Pers. but past tense stem of butan Mod.Pers. budan "to be, become," → exist, + -âr noun suffix (as in raftâr, jostâr, goftâr, kerdâr).

conditional
  بوتاری، بوتارمند   
butâri, butârmand

Fr.: conditionnel   

1) Imposing, containing, subject to, or depending on a condition or conditions; not absolute; made or allowed on certain terms.
2a) Logic: (of a proposition) Asserting that the existence or occurrence of one thing or event depends on the existence or occurrence of another thing or event.
2b) (of a → syllogism) Containing at least one → conditional proposition as a → premise (Dictionary.com).
2c) The "if ... then" relation.

condition; → -al.

conditional introduction
  اندرهازش ِ بوتاری   
andarhâzeš-e butâri

Fr.: introduction conditionnelle   

A derivation rule that begins with an → assumption in a → subproof and allows for deriving a conditional outside the subproof. The derived conditional consists of the assumed proposition as the → antecedent and the derived conclusion in the subproof as the → consequent.

conditional; → introduction.

conditional probability
  شوانایی ِ بوتاری   
šavânâyi-ye butâri

Fr.: probabilité conditionnelle   

Of an event B in relationship to an event A, the probability that event B occurs given that event A has already occurred. The notation for conditional probability is P(B|A), read as the probability of B given A: P(B|A) = P(A ∩ B)/P(A). → Bayes' theorem.

conditional; → probability.

conditional proof
  آوین ِ بوتاری   
âvin-e butâri

Fr.: preuve conditionnelle   

A → proof in which one assumes the → truth of one of the → premises to show that if that premise is true then the → argument is → valid.

conditional; → proof.

conditional proposition
  گزاره‌ی ِ بوتاری   
gozâre-ye butâri

Fr.: proposition conditionelle   

A compound → proposition in which one → clause asserts something as true provided that the other clause is true. A conditional statement consists of two parts, a hypothesis in the "if" clause and a conclusion in the "then"clause. For instance, "If it rains, then they cancel school." It rains is the hypothesis. "They cancel school" is the conclusion. The clause following if is traditionally called the → antecedent, whereas the clause following then is called the → consequent.

conditional; → proposition.

Dirichlet condition
  بوتار ِ دیریکله   
butâr-e Dirichlet

Fr.: condition de Dirichlet   

One of the following conditions for a → Fourier series to converge:
1) The function f(x) is defined and single valued, except possibly at a finite number of points in the interval -π, +π.
2) f(x) has a period of 2π.
3) f(x) and f'(x) are → piecewise continuous functions on -π, +π.
Then, the Fourier series converges to:
(a) f(x) if x is a point of continuity.
(b) (f(x + 0) + f(x - 0))/2, if x is a point of discontinuity.

Named after Peter Gustav Lejeune Dirichlet (1805-1859), German mathematician who made valuable contributions to → number theory, → analysis, and → mechanics; → condition.

Gamow condition
  بوتار ِ گاموف   
butâr-e Gamow

Fr.: condition de Gamow   

The constraint on the → baryon number density at T ~ 109 K in the early → expanding Universe. Gamow recognized that a key to the element buildup is the reaction n + p ↔ d + γ. Deuterium needs to be produced in sufficient abundance for higher elements to form, but if all → neutrons are immediately locked up into → deuterium, no higher elements can form either. The Gamow condition is expressed by nb<σv>t ~ 1, where nb is the baryon number density, σ is the cross section for the reaction at relative → velocity v, and t the expansion time-scale for the → Universe. This means that the time-scale for the above reaction is comparable to the expansion time. From this condition the baryon number density at the start of element buildup is found to be nb ~ (σvt)-1 ~ 1018 cm-3 at T = 109 K (P. J. E. Peebles, 2013, Discovery of the Hot Big Bang: What happened in 1948, arXiv.1310.2146).

Gamow barrier; → condition.

ideal MHD condition
  بوتار ِ MHDی ِ آرمانی   
butâr-e MHD-ye ârmâni

Fr.: MHD idéale   

Magnetohydrodynamics of a plasma with very large (infinite) conductivity. In this limit, Ohm's law reduces to E = -v x B, where E represents electric field, B magnetic field, and v the fluid velocity.

ideal; → magnetohydrodynamics (MHD); → condition.

initial conditions
  بوتارهای ِ آغازین   
butârhâ-ye âqâzin

Fr.: conditions initiales   

1) Conditions at an initial time t = t0 from which a physical system or a given set of mathematical equations evolves.
2) Meteo.: A prescription of the state of a → dynamical system at a specified time; for all subsequent times, the → equation of motion and → boundary conditions determine the state of the system.

initial; → condition.

jump conditions
  بوتارهای ِ جهش   
butârhâ-ye jaheš

Fr.: conditions de saut   

Very different values of pressure and density (or temperature or energy) across a shock wave.

jump; → condition.

MHD condition
  بوتار ِ MHD   
butâr-e MHD

Fr.: condition MHD   

ideal MHD condition.

magnetohydrodynamics (MHD); → condition.

necessary and sufficient conditions
  بوتارهای ِ بایسته و بسنده   
butârhâ-ye bâyesté o basandé

Fr.: conditions nécessaire et suffisante   

If event A must occur for event B to occur, then it is said that A is → necessary for B. If event A may cause B but there could be some other cause as well, then it is said that A is sufficient to cause B. See also → if and only if (iff).

necessary; → and; → sufficient; → condition.

physical condition
  بوتار ِ فیزیکی   
butâr-e fiziki

Fr.: condition physique   

The state of a → physical system regarding its temperature, density, pressure, etc. at a given time.

physical; → condition.

Rankine-Hugoniot conditions
  بوتارهای ِ رانکین-هوگونیو   
butârhâ-ye Rankine-Hugoniot

Fr.: conditions de Rankine-Hugoniot   

Hydrodynamics → conservation laws (which can be extended to → magnetohydrodynamics, MHD) which describe the physical conditions of material across a → shock front. A fluid is completely described by its velocity, density, pressure, specific heat ratio, and magnetic field (in the MHD case). Mass, momentum, and energy fluxes are conserved in the shock, leading to the Rankine-Hugoniot relations. Also called Rankine-Hugoniot jump conditions. See also → jump condition.

Named after William John Rankine, → Rankine scale, and Pierre Henri Hugoniot, → Hugoniot curve; → condition.

Sakharov conditions
  بوتارهای ِ ساخاروف   
butârhâ-ye Sakharov

Fr.: conditions de Sakharov   

The three conditions that are necessary for the generation of a → baryon asymmetry in the → early Universe. These conditions are:
1) The → baryon number should not be → conserved.
2) The → charge conjugation and → CP symmetry should be → violated, and
3) Departure from → thermal equilibrium.

Named after Andrei Sakharov (1921-1989), who in 1967 described these three minimum conditions (A. D. Sakharov, 1967, Zh. Eksp. Teor. Fiz. Pis'ma 5, 32; 1967, JETP Lett. 91B, 24); → condition.

unconditional
  نابوتاری، نابوتارمند   
nâbutâri, nâbutârmand

Fr.: inconditionnel   

Not limited by conditions; absolute.

un-; → conditional.