An exact algebraic representation for the 2D elastodynamic Green's tensor is derived. A new displacement potential decomposition is employed which yields, in conjunction with the Pekeris–Cagniard–de Hoop method, the exact representation. The first motions of the major arrivals are evaluated in terms of their polarizations, radiation patterns, geometrical spreading and wave-front singularities. The tensorial components of the Rayleigh wave on the free surface are found and solutions for dipolar line source discussed. We also investigate diffracted phases first noticed by Lapwood in his 1949 paper [13].

Polynomial identities satisfied by the generators of the Lie groups O(n) and U(n) are rederived. Using these identities the reduced matrix elements of the Lie groups U(n) and O(n) are evaluated as rational functions of the IR labels occurring in the canonical chains

This method does not require an explicit realization of the Lie algebras and their representations using bosons. Finally, trace formulae encountered previously by several authors for finite dimensional irreducible representations are shown to hold on arbitrary representations admitting an infinitesimal character.

Necessary and sufficient conditions for optimality in the control of linear differential systems ẋ = Ax + Bu with Stieltjes boundary conditions , where ν is an r × n matrix valued measure of bounded variation, are obtained, Feedback-like control is given in the case of quadratic performance.

The algebraic structure of relativistic wave equations of the form

is considered. This leads to the problem of finding all Lie algebras L which contain the Lorentz Lie algebra so(3, 1) and also contain a “four-vector” αμ a such an L gives rise to a family of wave equations. The simplest possibility is the Bhabha equations where L≅so(5). Some authors have claimed that this is the only one, but it is shown that there are many other possibilities still in accord with physical requirements. Known facts about representations, along with Dynkin's theory of the embeddings of Lie algebras, are used to obtain a partial classification of wave equations. The discrete transformations C, P, T are also discussed, along with reality properties. Finally, a simple example of a family of wave equations based on L = sp(12) is considered in detail. The so(3, 1) content and mass spectra are given for the low order members of the family, and the problem of causality is briefly discussed.

Geometric programming is now a well-established branch of optimization theory which has its origin in the analysis of posynomial programs. Geometric programming transforms a mathematical program with nonlinear objective function and nonlinear inequality constraints into a dual problem with nonlinear objective function and linear constraints. Although the dual problem is potentially simpler to solve, there are certain computational difficulties to be overcome. The gradient of the dual objective function is not defined for components whose values are zero. Moreover, certain dual variables may be constrained to be zero (geometric programming degeneracy).

To resolve these problems, a means to find a solution in the relative interior of a set of linear equalities and inequalities is developed. It is then applied to the analysis of dual geometric programs.

In order to use the method of asymptotic matching for low frequencies, the equations of plane elastostatics are reformulated in terms of the two scalar potentials commonly used in plane elastodynamics. It is shown that the resulting equations of plane elastostatics can be reduced to those first obtained by Muskhelishvili. The use of the formulation is illustrated by considering the case of the plane diffraction of a P wave by a circular, cylindrical cavity of small radius. The results agree with those obtained from the exact solution of the problem.

Page 242, bottom line.

Page 243, right side of equation (6).

Page 243, right side of equations (8) and (9).

Page 250, line 4 of Section 7.