It is not difficult to construct an unbounded set E on the positive real line such that, if x1, x2 belong to E, then x1/x2 is never equal to an integer. Our object is to show that it is possible to find such a set E which is measurable and of infinite Lebesgue measure. We were led to consider this problem through a study of those sets E, which are of infinite measure, yet, for each x > 0, nx є E for only a finite number of integers n. Sets of this type were first discovered by C. G. Lekkerkerker [2]. The set that we consider has both these properties. For another result on lattice points in sets of infinite measure see [1].

A positive integer n is called a square-full integer, if p2 divides n, whenever p is a prime divisor of n. It is clear that each square-full integer can be written in the form a2b3, where a and b are positive integers; moreover, this representation is unique if we stipulate that b is square-free.

Generating functions for the number of linearly independent invariants of a set of tensors under a given group of transformations are given by the theory of group representations. For the full and proper orthogonal groups these generating functions are in the form of definite integrals. The classical theory of algebraic invariants gives generating functions for the number of invariants of tensors under two-dimensional unimodular transformations, these generating functions being algebraic expressions. Because of a correspondence between the two-dimensional unimodular group and the three-dimensional proper orthogonal group, the corresponding generating functions are equivalent. The main result of this paper is an explicit demonstration of this equivalence. In addition, algebraic generating functions for the three-dimensional full orthogonal group are obtained and the use of the algebraic generating functions illustrated by applying them to a third order symmetric tensor.

In recent papers [1, 2] I have given expressions for the stresses and displacement due to elastic distributions in an infinite isotropic elastic solid bounded internally by a spherical hollow, the boundary of which is either stress or displacement free. This paper gives corresponding results for a semi-infinite elastic solid together with expressions for the stresses and displacement due to thermoelastic distributions in such a solid, the boundary of which is maintained at a constant temperature and is either stress or displacement free.

The concept of uniform regularity of a measure on a compact space—a property which allows uniform approximation of the measure on all compact sets—was introduced and discussed in [1], [2] and [3]. Further some extensions of the notion of uniform regularity are given in [4] and [6].

Introduction. This paper describes a natural way to associate fractal setsto a certain class of absolutely convergent series in In Theorem 1 we give sufficient conditions for such series. Theorem 2 shows that each analytic function gives a different fractal series for each number in a certain open set. Theorem 3 gives the Hausdorff dimension of the associated sets to fractal series, under suitable conditions on the series. This theorem can be applied to some standard series in analysis, such as the binomial, exponential and trigonometrical complex series. The associated sets to geometrical complex series are selfsimilar sets previously studied by M. F. Barnsley from a different (dynamical) point of view (see refs. [5], [6]).

The general features of the interaction of hydrodynamic and electromagnetic effects, when an electrically conducting fluid medium is in motion in the presence of a magnetic field, are now well established. A discussion of these effects in which the equations of the system are set out and an analogy is drawn between the behaviour of the magnetic field and that of vorticity in a viscous fluid, is given by Batchelor [1]. The development of the subject may be divided broadly into two sections. First, there are the problems of engineering interest, such as flow of conducting fluid in pipes, with associated problems of stability, and secondly there are the problems of astrophysical and geophysical interest.

Throughout the paper, let

be forms with rational integer coefficients of degrees d1, …, ds all at least 2 with n ≥ 4. Let p be a prime and Q a box in ℝn,

Let ℳ denote the class of all finite positive Borel measures μ in Rn with compact support. We define the Fourier transform of μεℳ by writing

and the α-energy of μ is given by

First, a special case of Knaster's problem is proved implying that each symmetric convex body in ℝ3 admits an inscribed cube. It is deduced from a theorem in equivariant topology, which says that there is no S4–equivariant map from SO(3) to S2, where S4 acts on SO(3) on the right as the rotation group of the cube, and on S2 on the right as the symmetry group of the regular tetrahedron. Some generalizations are also given.

1.1. Let A = (aμν) be a normal triangular matrix, i.e., one for which aμμ ≠ 0 (μ ≥ 0), aμν = 0 (ν > μ).

where (i) 0≤m<n, (ii) Rμ>0 (μ≥0), (iii) K is a constant, depending on the matrix A and the sequence {Rμ}, but independent of m, n and the finite sequence {sν}.

Let

be two sets of n ≥ 1 consecutive integers with s ≤ t. In this note we are concerned with one-to-one mappings of Γ onto II. If i → f(i) is such a mapping then for i ∈ Γ we write Fi for the highest common factor (i, f(i)), and if Fi = 1 for all i ∈ Γ we say that f is a coprime mapping. Our principal result is

THEOREM 1. If Γ = {1, 2, …, n} and Π = {n+1, n+2, …, 2n} then a one-to-one coprime mapping of Γ onto II can be constructed.

Let Φ : L → ℤ be a positive definite even unimodular quadratic form, L ≅ ℤn; we put f(x) = Φ(x)/2 and call (L, f) a lattice, for short. Let min f be the minimum of the numbers f(x) ≠ 0. Fixing n (a multiple of 8), one is interested in the largest possible minimum. It follows from the theory of modular forms (cf. Sloane [6]) that

The paper is concerned with the Steklov eigenvalue problem on cuboids of arbitrary dimension. We prove a two-term asymptotic formula for the counting function of Steklov eigenvalues on cuboids in dimension $d\geqslant 3$. Apart from the standard Weyl term, we calculate explicitly the second term in the asymptotics, capturing the contribution of the $(d-2)$-dimensional facets of a cuboid. Our approach is based on lattice counting techniques. While this strategy is similar to the one used for the Dirichlet Laplacian, the Steklov case carries additional complications. In particular, it is not clear how to establish directly the completeness of the system of Steklov eigenfunctions admitting separation of variables. We prove this result using a family of auxiliary Robin boundary value problems. Moreover, the correspondence between the Steklov eigenvalues and lattice points is not exact, and hence more delicate analysis is required to obtain spectral asymptotics. Some other related results are presented, such as an isoperimetric inequality for the first Steklov eigenvalue, a concentration property of high frequency Steklov eigenfunctions and applications to spectral determination of cuboids.

Although the theory of supersonic inviscid flow past thin wings and slender bodies has received an enormous amount of attention in recent years, comparatively little attention has been paid to the interaction between wings and finite bodies. The principal reason stems from the extensive numerical work that has to be done in order to form a detailed picture of the flow properties—even with the present generation of highspeed computers the student of this problem is faced with a formidable task. The main effort in this interaction problem has been put into the special case when the body is a circular cylinder symmetrically disposed towards the oncoming flow, and here Nielsen (1951) and Stewartson (1951, unpublished) have shown that a formal solution can be obtained in a simple way in terms of Laplace transforms. Interpretation of these formulae however was still a formidable task, but has been greatly facilitated by the publication of an extensive set of tables of the basic functions (Nielsen 1957). Using these tables a number of workers (Randall 1965, Chan and Sheppard 1965, Treadgold, unpublished, and others) have successfully computed pressure distributions on the wing and the body, except for the neighbourhoods of the lines separating the interaction regions from the remainder of the wing and body. The aim of this paper is to provide formulae for the pressure distributions in these neighbourhoods in order to enable the solutions already obtained to be completed.

§1. Introduction. In this paper, as in [4], we are concerned with integer points (m, n) lying close to the curve

in the sense that

where ║t║ denotes the distance of the real number t from the nearest integer. We shall always suppose that

and that F(x) is at least twice continuously differentiable. Let R be the number of solutions of (1.1) with m an integer, O ≤ m ≤ L. The obvious method of estimating R uses the row-of-teeth or rounding error function

with

It is proved that the sequence is completely uniformly distributed modulo 1 for almost all real numbers x with |x|> 1, if (an) is an arbitrary sequence of distinct positive integers.

In a recent paper [1], R. A. Rankin proved that

where τ(n) is Ramanujan's arithmetical function,

Let F:Z→X be a minimal usco map from the Baire space Z into the compact space X. Then a complete metric space P and a minimal usco G:P→X can be constructed so that for every dense Gδ-subset P1 of P there exist a dense Gδ Z1 of Z and a (single-valued) continuous map f: Z1→P1 such that F(Z)⊂G(f(z)) for every z∈Z1. In particular, if G is single valued on a dense Gδ-subset of P, then F is also single-valued on a dense Gδ-subset of its domain. The above theorem remains valid if Z is Čech complete space and X is an arbitrary completely regular space.

These factorization theorems show that some generalizations of a theorem of Namioka concerning generic single-valuedness and generic continuity of mappings defined in more general spaces can be derived from similar results for mappings with complete metric domains.

The theorems can be used also as a tool to establish that certain topological spaces contain dense completely metrizable subspaces.

In this paper is considered the average size of the 2-Selmer groups of a class of quadratic twists of each elliptic curve over ℚ with ℚ-torsion group ℤ2 × ℤ2. The existence is shown of a positive proportion of quadratic twists of such a curve, each of which has rank 0 Mordell-Weil group.