A note on θ-tightness

In questo lavoro chiariamo il ruolo che la θ-tightness (introdotta dagli autori in [2]) ha nel determinare alcune estensioni di sottoinsiemi di uno spazio topologico.     

A note on linear θ-derivations on JB1-triples

In this paper we prove a generalization of the stability of the functional equation in the spirit of Hyers, Ulam and Rassias. Also we introduce the concept of linear θ-derivations on JB¹-triple, and prove the generalization of the stability of the functional equation in the spirit of Hyers, Ulam and Rassias of linear θ-derivations on JB¹-triple. For resent results see [1], [2], [3].     

2–3 brother trees

2–3 brother trees form a dense class of search trees havingO(logN) insertion and deletion algorithms. In this paper we provide anO(logN) insertion algorithm and show that these trees have much better density and storage utilization than 2–3 trees. Thus we demonstrate that the brother property which has so far been used only for binary trees can be usefully applied to 2–3 trees.Work supported partially by a Natural Sciences and Engineering Research Council of Canada Grant No. A-7700 and partially by the German Academic Exchange Service under Nato Research Grant No. 430/402/584/8.     

μ-complete Souslin trees on μ+

Summary We prove thatµ=µ ^<µ , 2 ^µ =µ ⁺ and there is a non-reflecting stationary subset ofµ ⁺ composed of ordinals of cofinality < imply that there is a -complete Souslin tree onµ ⁺.The second author thanks the Binational Science Foundation for supporting this research. Publication no. 449     

Boundedness of the θ-type Calderon-Zygmund Operators on Weighted Herz-type

In this paper, we will discuss the boundedness of θ-type Calderdn-Zygmund operator on weighted Herz-type Hardy spaces.     

Möbius bilipschitz homogeneous arcs on the plane

A möbius bilipschitz mapping is an η-quasimöbius mapping with the linear distortion function η(t) = Kt. We show that if an open Jordan arc γ ? C with distinct endpoints a and b is homogeneous with respect to the family F_K of möbius bilipschitz automorphisms of the sphere C with K specified then γ has bounded turning RT(γ) in the sense of Rickman and, consequently, γ is a quasiconformal image of a rectilinear segment. The homogeneity of γ with respect to F_K means that for all x, y ∈ γ {a, b} there exists f ∈ F_K with f(γ) = γ and f(x) = y. In order to estimate RT(γ) from above, we introduce the condition BR(δ) of bounded rotation of γ, and then the explicit bound depends only on K and δ.     

Einstein–Weyl structures on contact metric manifolds

In this paper we study Einstein-Weyl structures in the framework of contact metric manifolds. First, we prove that a complete K-contact manifold admitting both the Einstein-Weyl structures W ^± = (g, ±ω) is Sasakian. Next, we show that a compact contact metric manifold admitting an Einstein-Weyl structure is either K-contact or the dual field of ω is orthogonal to the Reeb vector field, provided the Reeb vector field is an eigenvector of the Ricci operator. We also prove that a contact metric manifold admitting both the Einstein-Weyl structures and satisfying is either K-contact or Einstein. Finally, a couple of results on contact metric manifold admitting an Einstein-Weyl structure W = (g, f η) are presented.      

Inequivalent contact structures on Boothby–Wang five-manifolds

We consider contact structures on simply-connected five-manifolds which arise as circle bundles over simply-connected symplectic four-manifolds and show that invariants from contact homology are related to the divisibility of the canonical class of the symplectic structure. As an application we find new examples of inequivalent contact structures in the same equivalence class of almost contact structures with non-zero first Chern class.     

Invariant affinor and sub-Kähler structures on homogeneous spaces

We consider G-invariant affinor metric structures and their particular cases, sub-Kähler structures, on a homogeneous space G/H. The affinor metric structures generalize almost Kähler and almost contact metric structures to manifolds of arbitrary dimension. We consider invariant sub-Riemannian and sub-Kähler structures related to a fixed 1-form with a nontrivial radical. In addition to giving some results for homogeneous spaces of arbitrary dimension, we study these structures separately on the homogeneous spaces of dimension 4 and 5.