The second order properties of a process are usually characterized by the autocovariance function. In the stationary case, the parameterization by the partial autocorrelation function is relatively recent. We extend this parameterization to the nonstationary case. The advantage of this function is that it is subject to very simple constraints in comparison with the autocovariance function which...

Stable nite di erence approximations of convection-di usion equations lead to large sparse linear systems of equations whose coe cient matrix is an M{matrix, which is highly non symmetric when the convection dominates. For an e cient iterative solution of such systems, it is proposed to consider in the non symmetric case an algebraic multilevel preconditioning method formerly proposed for pure ...

In this note, I will describe a variety of problems from Ramsey theory on which I would like to see progress made. I will also discuss several recent results which do indeed make progress on some of these problems. AMS Mathematics Subject Classification: 05D10

AMS Mathematics Subject Classification (2000): 34G10

We introduce a continuous version of the contact model which is well-known and widely studied in the lattice case. Under certain general assumptions on the infection spreading characteristics we construct the contact process as a Markov process in the configuration space of the system. 2000 AMS Mathematics Subject Classification: 60K35, 60J75, 60J80, 82C21, 82C22

AMS Mathematics Subject Classification (2000): 35D05, 35L60, 46F30

AMS Mathematics Subject Classification (2000): 05C50

In this paper, we give an extension of the orthogonality results to dominant operators and p-hyponormal or log-hyponormal operators, also we will generalize some commutativity results. AMS 2000 Mathematics Subject Classification. 47B47, 47A30, 47B20.

In this paper we characterize pairs of Rosenberg relations (ρ, σ) with the property that the endomorphism monoid of one of the relations is properly contained in the endomorphism monoid of the other relation. We focus on the situations where one of the relations is a partial order, or a central relation. AMS Mathematics Subject Classification (2000): 08A35, 06A06

The object of the present paper is to characterize K-contact Einstein manifolds satisfying the curvature condition R · C = Q(S,C), where C is the conformal curvature tensor and R the Riemannian curvature tensor. Next we study K-contact Einstein manifolds satisfying the curvature conditions C ·S = 0 and S ·C = 0, where S is the Ricci tensor. Finally, we consider K-contact Einstein manifolds sati...