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By
Fra, Alberto; Migliori, Grazia
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Recently Tallini introduced the definition ofcomposition of two designs with suitable parameters. In this paper we study the Steiner systems obtained by composition of two given ovaloids, investigating the existence of possible Steiner subsystems of them. Furthermore we give an evaluation of the number of these Steiner systems, which are not isomorphic.
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By
Wähling, Heinz
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A sharply 2transitive (3transitive) groupT can be described by means of a neardomainF (a KTfield(F,ε)). We show, thatT has a least nontrivial normal subgroupA (S(F,ε)), ifF is a nearfield or if CharF≠ 2. In this case the nontrivial normal subgroups ofT correspond bijectively with all normal subgroupsF^{*} (the multiplicative group ofF) containing a setD (D(Q)). IfF is a nearfield or ifF has a suitable central element, then the group S(F,ε) is simple.
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By
Ghosh, Amalendu; Sharma, Ramesh
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2 Citations
We study a generalization of Kcontact and (k, μ)contact manifolds, and show that if such manifolds of dimensions ≥ 5 are conformally flat, then they have constant curvature +1. We also show under certain conditions that such manifolds admitting a nonhomothetic closed conformal vector field are isometric to a unit sphere. Finally, we show that such manifolds with parallel Ricci tensor are either Einstein, or of zero
$${\xi}$$
sectional curvature.
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By
Aquino, Cícero P.; Lima, Henrique F.; Santos, Fábio R.; Velásquez, Marco Antonio L.
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2 Citations
We deal with spacelike hypersurfaces immersed with some constant rth mean curvature in a steady state type spacetime, that is, a generalized Robertson–Walker spacetime of the type
$${\mathbb{R} \times_{e^t} M^n}$$
. In this setting, supposing that the fiber M^{n} of the ambient space has nonnegative constant sectional curvature, we establish characterization results concerning domains of the spacelike slices
$${\{t\} \times M^n}$$
. Afterwards, we apply such characterization results to study the uniqueness of complete spacelike hypersurfaces with one end in such a ambient space.
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By
Choi, Miekyung; Kim, Young Ho; Yoon, Dae Won
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4 Citations
We study the surfaces of revolution with the nondegenerate second fundamental form in Minkowski 3space. In particular, we investigate the surfaces of revolution satisfying an equation in terms of the position vector field and the 2ndLaplacian in Minkowski 3space. As a result, we give some new examples of the surfaces of revolution with lightlike axis in Minkowski 3space.
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By
Artzy, Rafael; Kiss, György
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1 Citations
The notion of shape in the Gaussian plane was introduced by Lester [5] and extended by Artzy [1]. In this paper we generalize this notion in the affine planesAG(2,q) over the Galois fieldGF(q), q=p^{r} andp an odd prime. We investigate the existence of shaperegular polygons and the correspondence between shaperegularity and affineregularity.
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By
Baker, Catharine A.
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1 Citations
In “Order and topology in projective Hjelmslev planes”, the authors introduced the notions of preorder and order on projective Hjelmslev planes (PHplanes); cf. [3: 3.7, 5.3]. They also showed that in both ordered and preordered uniform PHplanes singular segments are uniquely determined by their endpoints. In this note, we show that the notions of order and preorder actually coincide on uniform PHplanes.
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By
Jin, HaiLin; Leng, GangSong; Guo, Qi
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In 1988, H. Groemer gave a stability theorem for the area of convex domains of constant width. In this paper, we obtain a stability theorem for the wellknown Minkowski measure of asymmetry for convex domains of constant width.
