Ces dernières années, de nombreuses recherches ont été consacrées à l’étude de la structure extrémale de la somme de deux convexes; signalons, par exemple, les travaux de Bair-Fourneau-Jongmans [3], Edelstein-Fesmire [5], Husain-Tweddle [6], Jongmans [7], Klee [8] et Roy [9]. Dans cette direction, Klee [8] a obtenu ce résultat très intéressant, qui a d’ailleurs été généralisé plus tard par Jongmans [7]: dans un espace euclidien ℝd, tout point extrême z de la somme d’un convexe fermé A et d’un convexe compact B s’écrit de façon unique comme la somme d’un point extrême xz de A et d’un point extrême yz de B; de plus, tout point extrême x de A livre un point extrême y de B tel que z = x + y soit un point extrême de A + B. Par contre, il peut exister des points extrêmes de B dont la somme avec un point extrême de A n’est jamais un point extrême de A + B; cette constatation conduit au problème: est-il possible de caractériser l’ensemble des yz?

Bachelier (1900), Einstein (1905) and Smoluchowski (1915) provided a theory of the peculiar erratic motion of small particles suspended in a liquid, first described in 1826 by the English botanist Brown. In a series of papers beginning in 1920 Wiener undertook a mathematical analysis of Brownian motion.

The purpose of this article is to give an introduction to the study of a class of stochastic partial differential equations and to give a brief review of some of the recent developments in this field. This study has evolved naturally out of the theory of stochastic differential equations initiated in a pioneering paper of K. Itô [13]. In order to set this review in its appropriate setting we begin by considering a simple scalar stochastic differential equation.

The following type of argument is rendered almost believable by its frequent occurrence in elementary courses in statistics. Let ξi be a sequence of independent identically distributed random variables with means μ variances σ2.

These pages summarize recent progress on the oscillation problem for semilinear elliptic partial differential equations of the form

(1)

in unbounded domains Ω in n-dimensional Euclidean space Rn. Our attention is restricted to the second order symmetric equation (1), and completeness is not attempted; the emphasis is on results obtained in the last five years.

In what follows we shall mean by a plane convex body K a compact convex subset of the Euclidean plane having nonempty interior. We shall denote by h (K, θ) the supporting function of K restricted to the unit circle. This measures the signed distances from the origin to the supporting line of K with outward normal (cos θ, sin θ). The right hand and left hand derivatives of h (K, θ) exist everywhere and are equal except on a countable set.

It is well known that

1

where An denotes the number of "up-down" or alternating permutations

2

of 1, 2, …, n. The numbers A2n and A2n+1 are known as the secant and tangent numbers respectively and A2n = (—l)"E2n, where En is the Euler number.

Conditions are given under which the ring of quotients defined by an ideal is semisimple Artinian modulo its Jacobson radical.

A continuous real vector function is said to be nonoscillatory on an interval if at least one of its components is of constant positive or negative sign there. In this note, various existence criteria for nonoscillatory solutions of the system x(m) = (-l)mQ(t)x are established. In some cases, additional monotonicity properties for these solutions are also given.

Let us consider the retarded differential equation

1

for which the following assumptions are made:

(i) p: [t0, ∞) → [0, ∞) is continuous and not identically zero for all large t.

(ii) σ [t0, ∞)→ ℝ is continuous, strictly increasing,

(iii) φ: ℝ → ℝ is continuous, non-decreasing and

In this paper we construct the hitting time distributions for stochastic processes Xk, taking on values amongst the integers 0, 1, …, d -1 for which has a smooth polynomial density with respect to the Lebesgue measure on [0,1].

The aim of this paper is to give a number of characterizations of the rings of the title. In particular, these turn out to be precisely those exchange rings whose idempotents are all central. They are also those rings in which every element is the sum of a unit and a central idempotent.

This note is concerned with some new integral inequalities which are extensions of the results in [2]. The method by which these results are obtained is due to D. C. Benson [1]. Throughout the present note we shall assume 1<p<∞ and f(x) a non-negative measurable function.

Let Tn denote a tournament with vertices labelled 1, …, n. Any undefined terms can be found in [5]. The converse of Tn is the tournament obtained by reversing the orientation of all the arcs in Tn. A tournament is called self-converse (s.c.) if . The transitive tournaments are examples of s.c. tournaments. In this paper we provide a structural characterization of s.c. tournaments and we also characterize the score vectors of s.c. tournaments.

An arithmetic function f is said to be multiplicative if f(mn) = f(m)f(n), whenever (m, n) = 1 and f(1) = 1. The Dirichlet convolution of two arithmetic functions f and g, denoted by f • g, is defined by f • g(n) = Σd|nf(d)g(n/d). Let w(n) denote the product of the distinct prime factors of n, with w(l) = 1. R.

The notion of sequential topological algebra was introduced by this author and Ng [3], Among a number of results concerning these algebras, we showed that each multiplicative linear functional on a sequentially complete, sequential, locally convex algebra is bounded ([3], Theorem 1). From this it follows that every multiplicative linear functional on a sequential F-algebra (complete metrizable) is continuous ([3], Corollary 2).

Abstract. Let denote the graph (k times) where is the strong product of the two graphs G and H. In this paper we prove the conjecture of J. Zaks [3]: For every connected graph G with at least two vertices there exists an integer k = k(G) for which the graph is hamiltonian.

The coarseness, c(G), of a graph G is the maximum number of edge disjoint nonplanar subgraphs contained in G For the n-dimensional cube Qn we obtain the inequalities

The following theorem is proved: Suppose R is a ring with identity which satisfies the identities xkyk = ykxk and xlyl = ylxl, where k and l are positive relatively prime integers. Then R is commutative. This theorem also holds for a group G. Furthermore, examples are given which show that neither R nor G need be commutative if either of the above identities is dropped. The proof of the commutativity of R uses the fact that G is commutative, where G is taken to be the group R* of units in R.

I [1] have shown that

are the only square pseudo-Lucas numbers in the set of pseudo-Lucas numbers defined by

1

In this paper, it is shown that none of the pseudo-Lucas numbers are of the form 2S2, where S is an integer.