222 research outputs found
A necessary flexibility condition of a nondegenerate suspension in Lobachevsky 3-space
We show that some combination of the lengths of all edges of the equator of a
flexible suspension in Lobachevsky 3-space is equal to zero (each length is
taken either positive or negative in this combination).Comment: 20 pages, 13 figure
Cayley-Type Conditions for Billiards within Quadrics in
The notions of reflection from outside, reflection from inside and signature
of a billiard trajectory within a quadric are introduced. Cayley-type
conditions for periodical trajectories for the billiard in the region bounded
by quadrics in and for the billiard ordered game within
ellipsoids in are derived. In a limit, the condition describing periodic
trajectories of billiard systems on a quadric in is obtained.Comment: 10 pages, some corractions are made in Section
Looking backward: From Euler to Riemann
We survey the main ideas in the early history of the subjects on which
Riemann worked and that led to some of his most important discoveries. The
subjects discussed include the theory of functions of a complex variable,
elliptic and Abelian integrals, the hypergeometric series, the zeta function,
topology, differential geometry, integration, and the notion of space. We shall
see that among Riemann's predecessors in all these fields, one name occupies a
prominent place, this is Leonhard Euler. The final version of this paper will
appear in the book \emph{From Riemann to differential geometry and relativity}
(L. Ji, A. Papadopoulos and S. Yamada, ed.) Berlin: Springer, 2017
The Dehn invariants of the Bricard octahedra
We prove that the Dehn invariants of any Bricard octahedron remain constant
during the flex and that the Strong Bellows Conjecture holds true for the
Steffen flexible polyhedron.Comment: 13 pages, 10 figure
On regularity of a boundary point for higher-order parabolic equations: towards Petrovskii-type criterion by blow-up approach
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