An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 7 Search : boundary
karân (#)

Fr.: limite, bord   

1) General: Something that indicates a border or limit; the border or limit so indicated.
2) Thermodynamics: A conceptual closed surface useful in separating and distinguishing a system from its surroundings.
3) Math.: In topology, the boundary of a subset S of a topological space X is the set of points which can be approached both from S and from the outside of S.
4) Electronics: An area of meeting of P-type and N-type → semiconductor materials where the → donor and → acceptor concentrations are equal.

From Fr., from O.Fr. bodne, from M.L. bodina, butina "boundary, boundary marker."

Karân, karâné, kenâr from Mid.Pers. karânag, Av. karana- "boundary."

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.

boundary effect
  اسکر ِ کران   
oskar-e karân

Fr.: effet de bords   

An effect that forbids or invalidate locally the use of an idealized model of a system in which one or several of its dimensions are supposed to be infinite.

boundary; → effect.

boundary layer
  لایه‌ی ِ کرانی   
lâye-ye karâni

Fr.: couche limite   

A layer of fluid that is formed wherever a fluid flows past a solid surface and the effects of → viscosity are important. The boundary level forms because as the fluid moves past the object, the molecules which are in direct contact with the surface stick to the surface. The molecules just above the surface are slowed down in their collisions with the molecules sticking to the surface. These molecules in turn slow down the flow just above them, but less effectively. This creates a thin layer of fluid near the surface in which the velocity changes from zero at the surface to the free stream value away from the surface. The boundary layer may be either → laminar or → turbulent in character, depending on the value of the → Reynolds number. The concept of boundary level was first put forward by Ludwig Prandlt (1875-1953) in 1904.

boundary; → layer.

laminar boundary layer
  لایه‌ی ِ کرانی ِ ورقه‌ای   
lâye-ye karâni-ye varaqe-yi

Fr.: Couche limite laminaire   

In a fluid flow, layer next to a fixed boundary. The fluid velocity is zero at the boundary but the molecular viscous stress is large because the velocity gradient normal to the wall is large. → turbulent boundary layer.

laminar; → boundary; → layer.

no boundary hypothesis
  انگاره‌ی ِ گیتی بی کران ِ آغازین   
engâre-ye giti bi karân-e âqâzin

Fr.: l'hypothèse de l'Univers sans limite initiale   

The proposal whereby the → Universe would not have begun with a → singularity. Instead, the → Big Bang would be an ordinary point of → space-time. The proposal, advanced by James Hartle and Stephen Hawking (1983) results from an attempt to combine aspects of → general relativity and → quantum mechanics. Based on an imaginary time assumption, it predicts a closed Universe that would start at a single point, that can be compared to the North Pole of the Earth on a two-dimensional space. Before the → Planck era there was space, but the real time began with the Big Bang event. → Hartle-Hawking initial state.

boundary; → hypothesis.

turbulent boundary layer
  لایه‌یِ کرانیِ آشوبناک   
lâye-ye karâni-ye âš:ubnâk

Fr.: couche limite turbulente   

The layer in which the Reynolds stresses are much larger than the viscous stresses. When the → Reynolds number is sufficiently high, there is a turbulent layer adjacent to the → laminar boundary layer.

turbulent; → boundary; → layer.