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- ДокументWhen is the space of semi-additive functionals an absolute (neighbourhood) retract?(2022) Adilbek Atakhanovich Zaitov, Khamidjon KurbanovIn the present paper proved that if for a given compact Hausdorff space X the hyperspace exp(X) is a contractible compact space then the space OSf(X) is also a contractible compact space. As a consequence it is established that the space OSf(X) of semi-additive functionals is absolute (neighbourhood) retract if and only if the hyperspace exp(X) is so.
- ДокументGeodesic Ricci-symmetric pseudo-Riemannian spaces(2022) V. Kiosak, L. Kusik, V. IsaievWe introduced special pseudo-Riemannian spaces, called geodesic A-symmetric spaces, into consideration. It is proven that there are no geodesic symmetric spaces and no geodesic Ricci symmetric spaces, which differ from spaces of constant curvature and Einstein spaces respectively. The research is carried out locally, by tensor methods, without any limitations imposed on a metric and a sign.
- ДокументОскуляторний інтерполяційний ланцюговий дріб Тіле(2022) Mykhailo Pahirya, Yuliya MisloІнтерполяційний ланцюговий дріб Тіле з кратними вузлами є аналогом інтерполяційного многочлена Ерміта в теорії ланцюгових дробів. В роботі досліджується задача побудови оскуляторного (дотичного) до функції f в точці z0 інтерполяційного ланцюгового дробу Тіле (ОІЛДТ). Для обчислення коефіцієнтів OICFT використовуються лише значення функції f та її похідних у точці z0. Запропонований метод знаходження коефіцієнтів ґрунтується на обчислені значень m-кратних сум і не передбачає обчислення значень ганкелевих визначників.
- ДокументOn quasi-geodesic mappings of special pseudo-Riemannian spaces(2022) Irina Kurbatova, M. PistruilThe present paper continues the study of quasi-geodesic mappings f:(Vn, gij, Fih) → (V'n,g'ij, Fih) of pseudo-Riemannian spaces Vn, V'n with a generalized-recurrent structure Fih of parabolic type. By a generalized recurrent structure of parabolic type on Vn we mean an almost Hermitian affinor structure of parabolic type for which the covariant derivative of the structural affinor Fih satisfies the condition F(i,j)h=q(i Fj)h. In the previous paper by the authors [Proc. Intern. Geom. Center, 13:3 (2020) 18-32] it was proved that the class of pseudo-Riemannian spaces with generalized-recurrent structure of parabolic type is closed with respect to the considered mappings and the generalized recurrence vectors in (Vn, gij,Fih) and (V'_n, g'ij, Fih) may be distinct. In this article, it is assumed that the mapping f preserves the generalized recurrence vector qi. We construct geometric objects that are invariant under the quasi-geodesic mapping of generalized-recurrent spaces of parabolic type and recurrent-parabolic spaces. A number of conditions are given on these objects, which lead to the fact that a generalized-recurrent space of parabolic type admits a parabolic K-structure, and a recurrent-parabolic space admits a Kählerian structure of parabolic type. We study special types of these mappings that preserve some tensors of an intrinsic nature.
- ДокументThe flow-curvature of spacelike parametrized curves in the Lorentz plane(2022) Mircea CrasmareanuWe introduce and study a new frame and a new curvature function for a fixed parametrization of a spacelike curve in the Lorentz plane. This new frame is called flow-frame since it involves the time-dependent rotation of the usual Frenet flow.