Prime manifoldIn topology, a branch of mathematics, a prime manifold is an n-manifold that cannot be expressed as a non-trivial connected sum of two n-manifolds. Non-trivial means that neither of the two is an n-sphere. A similar notion is that of an irreducible n-manifold, which is one in which any embedded (n − 1)-sphere bounds an embedded n-ball. Implicit in this definition is the use of a suitable , such as the category of differentiable manifolds or the category of piecewise-linear manifolds.
4-manifoldIn mathematics, a 4-manifold is a 4-dimensional topological manifold. A smooth 4-manifold is a 4-manifold with a smooth structure. In dimension four, in marked contrast with lower dimensions, topological and smooth manifolds are quite different. There exist some topological 4-manifolds which admit no smooth structure, and even if there exists a smooth structure, it need not be unique (i.e. there are smooth 4-manifolds which are homeomorphic but not diffeomorphic).
Onde gravitationnelleEn physique, une onde gravitationnelle, appelée parfois onde de gravitation, est une oscillation de la courbure de l'espace-temps qui se propage à grande distance de son point de formation. Albert Einstein a prédit l'existence des ondes gravitationnelles en : selon sa théorie de la relativité générale qu’il venait de publier, de même que les ondes électromagnétiques (lumière, ondes radio, rayons X, etc.) sont produites par les particules chargées accélérées, les ondes gravitationnelles seraient produites par des masses accélérées et se propageraient à la vitesse de la lumière dans le vide.
Wave heightIn fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighboring trough. Wave height is a term used by mariners, as well as in coastal, ocean and naval engineering. At sea, the term significant wave height is used as a means to introduce a well-defined and standardized statistic to denote the characteristic height of the random waves in a sea state, including wind sea and swell. It is defined in such a way that it more or less corresponds to what a mariner observes when estimating visually the average wave height.
