We present a comprehensive solution to the classical problem of electromagnetic scattering by aggregates of an arbitrary number of arbitrarily configured spheres that are isotropic and homogeneous but may be of different size and composition. The profile of incident electromagnetic waves is arbitrary. The analysis is based on the framework of the Mie theory for a single sphere and the existing addition theorems for spherical vector wave functions. The classic Mie theory is generalized. Applying the extended Mie theory to all the spherical constituents in an aggregate simultaneously leads to a set of coupled linear equations in the unknown interactive coefficients. We propose an asymptotic iteration technique to solve for these coefficients. The total scattered field of the entire ensemble is constructed with the interactive scattering coefficients by the use of the translational addition theorem a second time. Rigorous analytical expressions are derived for the cross sections in a general case and for all the elements of the amplitude-scattering matrix in a special case of a plane-incident wave propagating along the z axis. As an illustration, we present some of our preliminary numerical results and compare them with previously published laboratory scattering measurements.

Electromagnetic scattering by an aggregate of spheres

Classical and quantum mechanics of the damped harmonic oscillator

Resonant multiple scattering of light

The probability of a photon (x-ray, gamma-ray, bremsstrahlung, etc) of a given energyE undergoing absorption or scattering when traversing a layer of materialZ can be expressed quantitatively in terms of a linear attenuation coefficient (cm 1 ). Since is dependent on the material's density, (g cm 3 ), which can be variable, the quantity usually tabulated is the mass attenuation coefficient = (cm 2 g 1 ) in which the dependence on the density has been removed. =, in turn, can be obtained as the sum of the different types of possible interactions of photons with atoms of the material. For photon energies below 1 MeV the major interaction processes to be considered are incoherent (Compton) scattering, coherent (Rayleigh) scattering and atomic photoeffect absorption. Above 1 MeV one must also include nuclear-field pair production and atomic-field (triplet) production, and above 5 MeV one in principle should include photonuclear absorption, although the latter is neglected in data tabulations up to the present time. This review includes a selective history of measurements and theory relating to = from the turn of the century up to the present time, and is intended to provide a basis for further calculations and critical tabulations of photon cross section data, particularly as required by users in radiation medicine and biology. The mass energy-absorption coefficient en= is also briefly discussed.

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Review of photon interaction cross section data in the medical and biological context

Particle sizing by quasi-elastic light scattering

Large grained long life push-pull fatigue specimens of 99-999% purity copper have been examined at 10% and 50% of the expected life. Carbon replicas of slip striations were examined, interference microscopy was used to measure the displacement across the striations and dislocation structure was examined by transmission electron microscopy. The total length of slip striation in a given area was measured as a function of fatigue life. After polishing the surface the pattern of slip striations which appeared when cycling was resumed was identical to that removed by polishing. The observations indicate that the slip striations are produced by a very large number of related dislocation sources situated in the planes of the striations. Intrusions and extrusions may be built up by the operation of two dislocation sources near the surface on closely adjacent parallel planes, one operated by a tensile stress and the other by the compressive stress. It is suggested that annealing a specimen after half the ...

C. Roberts

Papers

Slip line and dislocation structures in fatigued copper