On almost nexus semi-symmetric designs

In this paper we survey two classes of semi-symmetric designs that are shown to be equivalent to distance-regular graphs of diameter 2 or 3, and obtain some non-existence results for both classes of design when the graph has diameter 3.     

The existence of weakly symmetric and weakly Ricci-symmetric Sasakian manifolds admitting a quarter-symmetric metric connection

The object of the present work is to obtain a necessary condition for the existence of weakly symmetric and weakly Ricci-symmetric Sasakian manifolds admitting a quarter-symmetric metric connection.     

On the automorphism groups of symmetric graphs admitting an almost simple group

This paper investigates the automorphism group of a connected and undirected G-symmetric graph Γ where G is an almost simple group with socle T. First we prove that, for an arbitrary subgroup M of containing G, either T is normal in M or T is a subgroup of the alternating group A_k of degree . Then we describe the structure of the full automorphism group of G-locally primitive graphs of valency d, where d≤20 or is a prime. Finally, as one of the applications of our results, we determine the structure of the automorphism group for cubic symmetric graph Γ admitting a finite almost simple group.     

Some classes of Kenmotsu manifolds with respect to semi-symmetric metric connection

In this paper, we study conharmonic curvature tensor in Kenmotsu manifolds with respect to semi-symmetric metric connection and also characterize conharmonically flat, conharmonically semi-symmetric and φ-conharmonically flat Kenmotsu manifolds with respect to semi-symmetric metric connection.     

On almost pseudo-conformally symmetric Ricci-recurrent manifolds with applications to relativity

The object of the present paper is to study almost pseudo-conformally symmetric Ricci-recurrent manifolds. The existence of almost pseudo-conformally symmetric Ricci-recurrent manifolds has been proved by an explicit example. Some geometric properties have been studied. Among others we prove that in such a manifold the vector field ? corresponding to the 1-form of recurrence is irrotational and the integral curves of the vector field ? are geodesic. We also study some global properties of such a manifold. Finally, we study almost pseudo-conformally symmetric Ricci-recurrent spacetime. We obtain the Segre’ characteristic of such a spacetime.     

Canonical connection on a class of Reimannian almost product manifolds

The canonical connection on a Reimannian almost product manifold is an analogue to the Hermitian connection on an almost Hermitian manifold. In this paper we consider the canonical connection on a class of Reimannian almost product manifolds with non-integrable almost product structure.     

On pseudo quasi-Einstein manifolds

The object of the present paper is to introduce a type of non-flat semi-Riemannian manifold, called pseudo quasi-Einstein manifold and to study some geometric and global properties of such a manifold. Also the existence of such a manifold is ensured by several non-trivial examples.     

Canonical-type connection on almost contact manifolds with B-metric

The canonical-type connection on the almost contact manifolds with B-metric is constructed. It is proved that its torsion is invariant with respect to a subgroup of the general conformal transformations of the almost contact B-metric structure. The basic classes of the considered manifolds are characterized in terms of the torsion of the canonical-type connection.     

On almost constant-type manifolds

We introduce the class of almost constant-type manifolds and prove some theorems concerning Ricci tensors, scalar curvatures, bisectional curvatures and curvature identities. The above class is also studied in relation to other known classes of almost hermitian manifolds.To Adriano Barlotti with friendship and esteemThis work has been partially supported by a contribution of Ministero Ricerca Scientifica e Tecnologica.     

A-manifolds admitting a functorial connection

A connection for a large class of \(G\) -structures is defined by means of a generic condition on the adjoint bundle, and it is compared with the standard connections for classical \(G\) -structures. A characterization of the (not necessarily commutative) finite-dimensional \(\mathbb R \) -algebras \(A\) for which \(GL(r,A)\) -structures admit such a connection is obtained.     

On the complete decomposition of curvature tensors of Riemannian manifolds with symmetric connection

We give a complete decomposition of the space of curvature tensors with the symmetry properties as the curvature tensor associated with a symmetric connection of Riemannian manifold. We solve the problem under the action ofS0(n). The dimensions of the factors, the projections, their norms and the quadratic invariants of a curvature tensor are determined. Several applications for Riemannian manifolds with symmetric connection are given. The group of projective transformations of a Riemannian manifold and its subgroups are considered.     

On conformally flat almost Hermitian manifolds

We study some of 2n-dimensional conformally flat almost Hermitian manifolds with J-(anti)-invariant Ricci tensor. Received 13 May 2000; revised 15 February 2001.     

On Stepanov-like (pseudo) almost automorphic functions

We prove new composition theorems for Stepanov-like almost automorphic and Stepanov-like pseudo-almost automorphic functions. An application is given to a class of evolution equations with Stepanov-like pseudo-almost automorphic perturbations.