Hohmann transfer tarâvaž-e Hohmann Fr.: transfert de Hohmann An → orbital maneuver using two timed engine impulses to move a spacecraft between two coplanar circular orbits. It is performed through an elliptic orbit which is tangent to both circles at their periapses (→ periapsis). In honor of Walter Hohmann (1880-1945), German engineer who in his book, The Attainability of Celestial Bodies (1925), described the mathematical principles that govern space vehicle motion, in particular spacecraft transfer between two orbits. |
ohm ohm (#) Fr.: ohm A unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt across its terminals. Named after Georg Simon Ohm (1789-1854), the German physicist who discovered the law which bears his name. |
Ohm's law qânun-e Ohm (#) Fr.: loi d'Ohm 1) For a → conductor at rest, the
→ voltage across the
conductor is equal to the product of the current flowing through it and its
→ resistance. In other words, when such a conductor is
subjected to an electric field E,
the resulting
→ current density, J, is proportional to the
electric field E: J = σE, where σ
is the → conductivity, i.e. the reciprocal of
→ resistivity, ρ = 1/σ. |
Ohmic Ohmi (#) Fr.: ohmique Of or relating to a system which obeys Ohm's law. |
Ohmic decay time zamân-e tabâhi-ye Ohmi Fr.: temps de dissipation ohmique An upper bound on the time scale on which the magnetic field of a system would decay in the absence of any other agent. It is expressed as: τ_{μ} = R^{2} / μ, where R is the scale size of the system, η the magnetic diffusivity (η = 1 / μσ, where μ is the magnetic permeability and σ the electrical conductivity). For a star like the Sun, τ_{μ} ≅ 10^{10} years, so a fossil magnetic field could survive for the star's lifetime on the main sequence. For the Earth, τ_{μ} ≅ 10^{4} years, so a → dynamo is required to explain the persistence of the geomagnetic field. |
Ohmic dissipation eftâl-e ohmi Fr.: dissipation ohmique 1) A loss of electric energy due to conversion into heat when a current
flows through a resistance. Same as Ohmic loss. → Ohmic; → dissipation. |
Ohmic loss dastraft-e Ohmi Fr.: perte ohmique Same as → Ohmic dissipation. |