curvature xamidegi (#) Fr.: courbure A measure of the amount by which a curve, a surface, or any other
manifold deviates from a straight line, a plane, or a hyperplane. In particular,
The reciprocal of the radius of the circle which most nearly approximates a
curve at a given point. From L. curvatura, from curvatus, p.p. of curvare "to bend," from curvus "curved," → curve. Xamidegi, from xamidé "curved," from xamidag "curved" + noun suffix -i. |
curvature constant pârâmun-e xamidegi Fr.: paramètre de courbure A parameter occurring in the → Friedmann equations of → general relativity describing the geometry of → space-time. A spatially → open Universe is defined by k = -1, a → closed Universe by k = + 1 and a → flat Universe by k = 0. See also the → Robertson-Walker metric. See also → curvature of space-time. |
curvature of space-time xamidegi-ye fazâ-zamân (#) Fr.: courbure de l'espace-temps According to → general relativity, → space-time is curved by the presence of → matter. The curvature is described in terms of → Riemann's geometry. In → cosmological models three types of curvature are considered: positive (spherical, → closed Universe), zero (Euclidean, → flat Universe), and negative (hyperbolic, → open Universe). See also → curvature constant. → curvature; → space-time. |
field curvature xamidegi-ye meydân (#) Fr.: courbure de champ An aberration in an optical instrument, common in Schmidt telescopes, in which the focus changes from the center to the edge of the field of view. Owing to this aberration, a straight object looks curved in the image. |
primordial curvature perturbation partureš-e xamidegi-ye bonâqâzin Fr.: perturbation de courbure primordiale In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe. → primordial; → curvature; → perturbation. |
Riemann curvature tensor tânsor-e xamidegi-ye Riemann Fr.: tenseur de courbure de Riemann A 4th → rank tensor that characterizes the deviation of the geometry of space from the Euclidean type. The curvature tensor R^{λ}_{μνκ} is defined through the → Christoffel symbols Γ^{λ}_{μν} as follows: R^{λ}_{μνκ} = (∂Γ^{λ}_{μκ})/(∂x^{ν}) - (∂Γ^{λ}_{μν})/(∂x^{κ}) + Γ^{η}_{μκ}Γ^{λ}_{ην} - Γ^{η}_{μν}Γ^{λ}_{ηκ}. → Riemannian geometry; → curvature; → tensor. |
space-time curvature xamidegi-ye fazâ-zamân Fr.: courbure de l'espace-temps |