An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) (adj.) Tied, confined by bonds. → bound cluster, → bound charge, → bound system.
2) (n) a boundary; a limit.

1) p.p. of → bind. 2) → boundary.

Any electric charge which is bound to an atom or molecule, in contrast to free charge, such as metallic conduction electrons, which is not. Also known as → polarization charge.

→ bound; → charge.

A cluster of astronomical objects, such as stars or galaxies, held together by their mutual gravitational attraction. → bound system.

Bound, p.p. of → bind; → cluster.

Xušé, → cluster; bandidé p.p. of bandidan, → bind.

Any → occurrence of a → variable  x in an x-bound part of a → wff.

→ bound; → occurrence.

The orbit described by an object around a central gravitational force in a system whose total energy is negative. An elliptical orbit.

Bound, p.p. of → bind; → orbit.

Madâr, → orbit; bandidé, p.p. of bandidan, → bind.

A system composed of several material bodies the total energy of which (the sum of kinetic and potential energies) is negative, e.g. a → bound cluster.

Bound, p.p. of → bind; → system.

Aâžmân, → system; bandidé p.p. of bandidan, → bind.

A transition between two energy levels of an electron bound to a nucleus. The electron remains tied to the nucleus before and after the transition. → bound-free transition; → free-free emission.

Bound, p.p. of → bind; → transition.

A transition in which a bound electron is liberated. → free-bound emission; → free-free emission.

Bound, p.p. of → bind; → free.

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."

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.

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.

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.

General: Having bounds or limits.
Math.: Of a function, having a range with an upper bound and a lower bound.

Adj. from → bound.

The function y = f(x) in a given range of the argument x if there exists a positive number M such that for all values of x in the range under consideration the inequality | f(x) | ≤ M will be fulfilled. → unbounded function.

→ bounded; → function.

An → H II region which lacks enough matter to absorb all → Lyman continuum photons of the → exciting star(s). In such an H II region a part of the ionizing photons escape into the → interstellar medium. See also → ionization-bounded H II region.

→ density; → bounded; → region.

The radiation emitted when a → free electron is captured by an → ion. See also: → free-free emission; → bound-free transition.

→ free; → bound; → emission.

Objects held in orbit about each other by their → gravitational attraction. Such objects are part of a → bound system.

→ gravitational; → bound.

An H II region whose → exciting star(s) do not have enough → Lyman continuum photons to ionize the whole region. → density-bounded H II region.

→ ionization; → bounded; → H II region.

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.

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.