Motivated by a result on weak Markov dilations, we define a notion of characteristic function for ergodic and coisometric row contractions with a one-dimensional invariant subspace for the adjoints. This extends a definition given by G.Popescu. We prove that our characteristic function is a complete unitary invariant for such tuples and show how it can be computed. Mathematics Subject Classific...

* Correspondence: [email protected] Department of Natural Sciences, Hong Duc University, Thanh Hoa, Vietnam Abstract In this paper, we prove a fixed point theorem for generalized weak contractions satisfying rational expressions in partially ordered metric spaces. The result is a generalization of a recent result of Harjani et al. (Abstr. Appl. Anal, Vol.2010, 1-8, 2010). An example is also gi...

Received: December 21, 2010 Accepted: January 7, 2011 doi:10.5539/jmr.v3n2p151 Abstract In this paper, we study fixed point theorems for multi-valued weak contractions. We show that the Picard projection iteration converges to a fixed point, give a rate of convergence and generalize Collage theorem. This work includes results on multi-valued contraction mappings studied by (Kunze, H.E., La Torr...

In this paper, we shall establish two fixed point theorems by following the concept of [9, 21] and using weak contractions of the integral type. Our results are generalizations of the classical Banach’s fixed point theorem [1, 2, 3, 4, 5, 7, 25] as well as extensions of some other results of Berinde [4, 5, 6, 7], Berinde and Berinde [8], Branciari [9], Chatterjea [10], Kannan [16] and Zamfiresc...

I construct normal del Pezzo surfaces, and regular weak del Pezzo surfaces as well, with positive irregularity q > 0. This can happen only over nonperfect fields. The surfaces in question are twisted forms of nonnormal del Pezzo surfaces, which were classified by Reid. The twisting is with respect to the flat topology and infinitesimal group scheme actions. The twisted surfaces appear as generi...