Davenport has proved (3) that any cubic form in 32 or more variables with rational coefficients has a non-trivial rational zero. He has also announced that he has subsequently been able to reduce the number of variables to 29. Following the method of (3), we shall prove that any cubic form over any algebraic number field has a non-trivial zero in that field, provided that the number of variables is at least 54. The following is the precise form of our result.

Let be a commutative normed algebra whose elements are functions on a Banach space, and in which the product is of convolution type. We show how , under reasonable assumptions upon its semi-group of translation operators and rather severe restrictions upon its semi-simplicity, can be renormed so that its completion contains mean Gâteaux or Fréchet differentials of all its members. In this way the function algebra can be embedded in an algebra of generalized functions defined as strong limits of functions, which admits strong differentiation as an everywhere-defined operation. The differentials show most of the properties of point-wise Gâteaux differentials. The completion of is an example of what I have called in (3) an ‘inflation’.

Let L be the lattice of all points with integer coordinates in the real affine plane R2 (with respect to some fixed coordinate system). Let X be a finite rectilinear simplicial complex in R2 whose 0-simplexes are points of L. Suppose X is pure and the frontier Ẋ of X is a Jordan curve; then there is a well-known formula for the area of X in terms of the number of points of L which lie in X and Ẋ respectively, namely

where L(X) (resp. L(Ẋ)) is the number of points of L which lie in X (resp. Ẋ), and μ(X) is the area of X, normalized so that a fundamental parallelogram of L has unit area.

We recall that a bounded linear operator T in a Hilbert space or finite-dimensional unitary space is said to be normal if T commutes with its adjoint operator T*, i.e. TT* = T*T. Most of the proofs given in the literature for the spectral theorem for normal operators, even in the finite-dimensional case, appeal to the corresponding results for Hermitian or unitary operators.

Dual integral equations involving Bessel functions occur in the solution of some boundary-value problems in potential theory with conditions prescribed on a circular disc and a considerable amount of attention has been given to the solution of such equations (cf. (1)). The method of solving these dual integral equations is very similar to that employed in the solution of certain dual series equations involving Legendre functions. Equations of this type occur in problems in potential theory with conditions prescribed on a spherical cap and their solution has been obtained by Collins (2). No definite mathematical connexion has, however, been established between these dual series and dual integral equations and the object of this note is to establish such a connexion.

In a previous paper (3) one of us reported an expansion for the exponential integral

in terms of Bessel functions. In this note, we shall obtain the more general formula

where n is any positive integer, γ is Euler's constant and

It reduces to that in (3) when n = 1.

It was shown by Birkhoff ((1), p. 253) that every spherically symmetric solution of the field equations of general relativity for empty space,

may be reduced, by suitable coordinate transformations, to the static Schwarzschild form:

where m is a constant. This result is known as Birkhoff's theorem and excludes the possibility of spherically symmetric gravitational radiation. Different proofs of the theorem have been given by Eiesland(2), Tolman(3), and Bonnor ((4), p. 167).

The familiar classical dynamical theory treats only a restricted class of dynamical systems. For a Lagrangian depending on n generalized coordinates, the n generalized velocities, and (perhaps) the time the usual theory considers only the normal case in which the Hessian matrix of the Lagrangian with respect to the generalized velocities has rank n. But the rank of this Hessian matrix can be less than n in a given dynamical system. Dynamical systems with this property are called degenerate in the present work. Some important physical systems do in fact belong to this degenerate class: for instance, Einstein's theory of the gravitational field, the theory of the electromagnetic field in terms of the electromagnetic potentials, and the theory of the neutral vector meson field. This circumstance makes it necessary to have a general theory of degenerate dynamical systems (and of the associated degenerate variational problems).

The 4-dimensional tensor calculus is used to derive the retarded fields of an accelerated electric dipole of constant moment. Following the analogous case of the accelerated charge, it is shown that the result can be expressed concisely in terms of ordinary three-vectors. The radiation field is discussed for important cases including that of the slowly moving dipole. Cases are cited to exhibit the existence of a forward beam of radiation for uniform circular motion.

A derivation is given of the general solution of the static baryon Low equation for KΛ-scattering. This model has previously been used by Low to indicate possible ambiguities in the terms elementary and bound-state as applied to particles. The solution derived here can be used to establish this result from a general viewpoint which may possibly be applicable to more realistic models.

This paper obtains an exact description of the statistical mechanics of a one-dimensional system of charged particles moving in a uniform neutralizing background of positive charge. These results are compared with the behaviour of a one-dimensional system of equal numbers of positive and negative charged particles. Although the thermodynamics of the two systems do differ, the discrepancy is small enough to indicate that the assumption of a uniform background of positive charge, common in statistical mechanical treatments of a plasma in equilibrium, may provide a good approximation to a real system of discrete charges.

The effect of heat transfer on boundary-layer growth is considered for the problem of a main stream of small Mach number which is instantaneously released past a heated cylinder, or alternatively the cylinder is accelerated impulsively into a stream at rest. In particular the effect of different values of the given wall temperature on the interval to separation and the thickness of the boundary layer is investigated. It is found that the former is decreased and the latter increased by the presence of heat transfer.

The methods of papers I and II (1), (2) are applied to a problem in classical elastodynamics.

The simple concept of minimum potential energy of the classical theory of elasticity, first applied to solve inclusion problems (1) by one of the authors (R. D. B.), who considered spherical and circular inclusions, has now been extended to solve elliptic inclusion problems. The complex-variable method of determining the elastic field, first enunciated by A. C. Stevenson in the U.K. and N. I. Muskhelishvili in the U.S.S.R., has been used to determine the elastic field in the infinite material (the matrix) around the inclusion. Strain energies are calculated. The equilibrium size of an elliptic inclusion of elastic (Lamé's) constants λ1 and μ1, differing from those of matrix, for which the constants are λ and μ, has been determined.

An independent check on the calculations has been made by testing the continuity of normal and shearing stresses. The results also agree with the known results for the much simpler case when inclusion and matrix are of the same material.

This paper treats an extension of the problem considered by the authors in a recent paper (1). The minimum energy principle of the classical theory of elasticity was used in the above paper for evaluating the elastic field when an elliptic region (the inclusion, which could be of a material different from the rest) undergoes spontaneous dimensional change in an otherwise unstrained infinite medium (the matrix). By modification of this method, it has been possible to deal with the case when the inclusion is spherical or circular and the matrix is under uniform tension at infinity (2). The present paper deals with the much more general case when the matrix is under tension, at infinity, inclined at any angle to the major axis of the elliptic inclusion. The solution has been possible by the combination of the complex variable method coupled with minimum energy principle and superposition methods of linear elasticity theory. As a consequence we immediately derive almost without further calculation many particular cases, viz. (i) the inclusion problem in a matrix under axial tension parallel to either of the axes, (ii) under all round uniform tension (or pressure) etc. It is obvious that the results for the respective cases of a circular inclusion can be deduced from these results.

It also solves the problem of composite sections under external forces at infinity because of the complete freedom in choosing the elastic constant of the inclusion which can be different from that of the matrix. As a corollary, it solves the problem of a cavity under stress at infinity.

A new and simple proof is given of the known theorem that, if T1, T2,… is an infinite sequence of finite trees, then there exist i and j such that i < j and Ti is homeomorphic to a subtree of Tj.