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On inversions of van der Grinten projections

Tomáš Bayer, Milada Kočandrlová (2021)

Applications of Mathematics

Approximately 150 map projections are known, but the inverse forms have been published for only two-thirds of them. This paper focuses on finding the inverse forms of van der Grinten projections I--IV, both by non-linear partial differential equations and by the straightforward inverse of their projection equations. Taking into account the particular cases, new derivations of coordinate functions are also presented. Both the direct and inverse equations have the analytic form, are easy to implement...

On Levi-flat hypersurfaces tangent to holomorphic webs

Arturo Fernández-Pérez (2011)

Annales de la faculté des sciences de Toulouse Mathématiques

We investigate real analytic Levi-flat hypersurfaces tangent to holomorphic webs. We introduce the notion of first integrals for local webs. In particular, we prove that a k -web with finitely many invariant subvarieties through the origin tangent to a Levi-flat hypersurface has a holomorphic first integral.

On metrics of positive Ricci curvature conformal to M × 𝐑 m

Juan Miguel Ruiz (2009)

Archivum Mathematicum

Let ( M n , g ) be a closed Riemannian manifold and g E the Euclidean metric. We show that for m > 1 , M n × 𝐑 m , ( g + g E ) is not conformal to a positive Einstein manifold. Moreover, M n × 𝐑 m , ( g + g E ) is not conformal to a Riemannian manifold of positive Ricci curvature, through a radial, integrable, smooth function, ϕ : 𝐑 𝐦 𝐑 + , for m > 1 . These results are motivated by some recent questions on Yamabe constants.

On minimal homothetical hypersurfaces

Lin Jiu, Huafei Sun (2007)

Colloquium Mathematicae

We give a classification of minimal homothetical hypersurfaces in an (n+1)-dimensional Euclidean space. In fact, when n ≥ 3, a minimal homothetical hypersurface is a hyperplane, a quadratic cone, a cylinder on a quadratic cone or a cylinder on a helicoid.

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