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・ Oriented strand board
・ Oriented structural straw board
・ Orienteering
・ Orienteering (Scouting)
・ Orienteering Association of Hong Kong
・ Orienteering at the World Games
・ Orienteering Australia
・ Orienteering map
・ Orienteering USA
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・ Orientering
・ Orientia
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・ Orienticaelum
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Orientifold
・ Orientin
・ Orienting response
・ Orienting system
・ Orientius
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・ Orientophiaris
・ Orientopsaltria
・ Orientoreicheia
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・ Orientozeuzera aeglospila
・ Orientozeuzera brechlini
・ Orientozeuzera caudata
・ Orientozeuzera celebensis
・ Orientozeuzera halmahera


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Orientifold : ウィキペディア英語版
Orientifold
In theoretical physics orientifold is a generalization of the notion of orbifold, proposed by Augusto Sagnotti in 1987. The novelty is that in the case of string theory the non-trivial element(s) of the orbifold group includes the reversal of the orientation of the string. Orientifolding therefore produces unoriented strings—strings that carry no "arrow" and whose two opposite orientations are equivalent. Type I string theory is the simplest example of such a theory and can be obtained by orientifolding type IIB string theory.
In mathematical terms, given a smooth manifold \mathcal, two discrete, freely acting, groups G_ and G_ and the worldsheet parity operator \Omega_ (such that \Omega_ : \sigma \to 2\pi - \sigma) an orientifold is expressed as the quotient space \mathcal/(G_ \cup \Omega G_). If G_ is empty, then the quotient space is an orbifold. If G_ is not empty, then it is an orientifold.
== Application to string theory ==

In string theory \mathcal is the compact space formed by rolling up the theory's extra dimensions, specifically a six-dimensional Calabi-Yau space. The simplest viable compact spaces are those formed by modifying a torus.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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