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A compact four-dimensional manifold whose metric tensor has a positive determinant (named the Euclid ball) is considered. The Euclid ball can be immersed in the Minkovskian space (which has the negative determinant) and can exist stably through the history of the universe. Since the Euclid ball has the same solution as the Schwarzschild black hole on its three-dimensional surface, an asymptotic observer can not distinguish them. If large fraction of whole energy of the pre-universe was encapsulated in Euclid balls, they behave as the dark matter in the current universe. Euclid balls already existed at the end of the cosmological inflation, and can have a heavy mass in this model, they can be a seed of supper-massive black-holes, which are necessary to initiate a forming of galaxies in the early universe. The $gamma$-ray burst at early universe is also a possible signal of the Euclidean ball.
The effect of stellar aberration seems to be one of the simplest phenomena in astronomical observations. But there is a large literature about it betraying a problem of asymmetry between observer motion and source motion. This paper addresses the pro
In this paper we consider a three dimensional Kropina space and obtain the partial differential equation that characterizes a minimal surfaces with the induced metric. Using this characterization equation we study various immersions of minimal surfac
We prove that under some assumptions on the mean curvature the set of umbilical points of an immersed surface in a $3$-dimensional space form has positive measure. In case of an immersed sphere our result can be seen as a generalization of the celebrated Hopf theorem.
We consider the online search problem in which a server starting at the origin of a $d$-dimensional Euclidean space has to find an arbitrary hyperplane. The best-possible competitive ratio and the length of the shortest curve from which each point on
Cyclostationary processes are those signals whose have vary almost periodically in statistics. It can give rise to random data whose statistical characteristics vary periodically with time although these processes not periodic functions of time. Inte