Contributions of John Henry Poynting to the understanding of radiation pressure.

The name of Poynting is universally recognized for his development of the well-known expression for the flow of electromagnetic energy. Not so well known is Poynting's series of papers on radiation pressure, with 2011 marking the centenary of the last of his 15 publications on this topic. This paper reviews and assesses his radiation-pressure work, with a level of coverage aimed at the reader familiar with the Maxwell electromagnetic theory and interested in the current understanding of radiation pressure.

Optical Thomas-Reiche-Kuhn sum rules.

The Thomas-Reiche-Kuhn sum rule is a fundamental consequence of the position-momentum commutation relation for an atomic electron and it provides an important constraint on the transition matrix elements for an atom. Analogously, the commutation relations for the electromagnetic field operators in a magnetodielectric medium constrain the properties of the dispersion relations for the medium through four sum rules for the allowed phase and group velocities for polaritons propagating through the medium. These rules apply to all bulk media including the metamaterials designed to provide negative refractive indices.

The enigma of optical momentum in a medium.

It is 100 years since Minkowski and Abraham first gave rival expressions for the momentum of light in a material medium. At the single-photon level, these correspond, respectively, either to multiplying or dividing the free-space value (symbol:see text) by the refractive index (n). The debate that this work started has continued till the present day, punctuated by the occasional publication of 'decisive' experimental demonstrations supporting one or other of these values.

Theory of the radiation pressure on dielectric slabs, prisms and single surfaces.

Two alternative formulations of the Lorentz force theory of radiation pressure on macroscopic bodies are reviewed. The theories treat the medium respectively as formed from individual dipoles and from individual charges. The former theory is applied to the systems of dielectric slab and dielectric prism, where it is shown that the total torque and force respectively agree with the results of the latter theory.

RhoA-kinase and myosin II are required for the maintenance of growth cone polarity and guidance by nerve growth factor.

Growth cones are highly polarized and dynamic structures confined to the tips of axons. The polarity of growth cones is in part maintained by suppression of protrusive activity from the distal axon shaft, a process termed axon consolidation. The mechanistic basis of axon consolidation that contributes to the maintenance of growth cone polarity is not clear.