Sufficient conditions are derived for every solution of a nonlinear Schrödinger equation (or inequality) to be oscillatory in an exterior domain of En. Such results apply in particular to the n-dimensional Emden-Fowler equation. The method involves oscillatory behaviour of solutions of a nonlinear ordinary differential inequality satisfied by the spherical mean of a positive solution of the Schrödinger equation.

In a previous publication [1] we determined the structure of some new types of ordered inverse semigroup in which the ordering need not be the natural ordering. At the moment, very little is known about ordered regular semigroups and the purpose of this paper is to generalise the structure theorems in [1] to corresponding theorems on ordered regular semigroups. The results obtained provide an interesting bridge between the theory of semigroups and that of ordered semigroups, these theories currently having very little in common.

A large class of self-adjoint fourth-order differential equations has the property that if one solution is oscillatory then all solutions are oscillatory. This paper establishes necessary and sufficient conditions for this property to hold for a corresponding class of non-self-adjoint differential equations.

The theorems in this paper deal with the analogues for integrals of Hardy's Series Inequality and its generalisations.

It is shown that classical solutions backward in time to the alternatives to the Navier-Stokes equations proposed by Ladyzhenskaya cannot exist for all time. Estimates are obtained for the maximum interval of existence.

In a certain factor analysis model sampling formulae for maximum likelihood estimators of the parameters are found by inverting an augmented information matrix. The formulae were derived previously by other methods; but the techniques here employed may be of some general interest and applicable to other problems.