A note on ray curvature

Although formulae have long existed for ray curvature in an inhomogeneous cold collisionless magnetoplasma, they have not always been applied consistently. General expressions applicable to propagation in a meridional plane in an axially symmetric plasma in the presence of a poloidal potential magnetic field, such as a dipole field, are re-presented, and some previous results re-examined.     

A note on the care and handling of triremes

The authors of'Effects of shipworm on the performance of ancient Mediterranean warships'(Steinmayer & Turfa, 1996) theorise that extensive shipworm damage to warships of the ancient Mediterranean was unavoidable and would have affected naval operations and the outcome of naval battles. However, there is a significant amount of literary evidence for the care and handling of warships and for the battles in which they engaged that they have not taken into account. The purpose of this note is to bring the missing evidence into the discussion and to suggest that ancient seafarers were better able to protect their ships than Steinmayer and Turfa have allowed.     

A note on the diurnal averaging of aeronomical models

We have developed an approximate technique for diurnally time-averaging atmospheric photochemical-dynamical models which eliminates the need for a detailed numerical resolution of sunrise and sunset transitions. In its application, our scheme is equivalent to scaling certain chemical rate constants and photodissociation coefficients by appropriate aeronomical factors. To calculate the scaling factors, we parameterize diurnal variations with a step-function behavior, assuming that each species has a constant day-time and night-time concentration whose ratio we can determine by analyzing the chemical interactions occurring after sunset. Our solution accounts for the effects of night-time reactions on the 24 h average values of species abundances and on the average daily rates of the catalytic processes consuming ozone in the stratosphere. We demonstrate the accuracy of our technique by comparing its predictions to those of a full diurnal simulation; typically, the precision is better than 10%. By contrast, we show that the use of some other well-known computational schemes can result in significantly larger predictive errors—up to an order of magnitude for the N₂O₅ concentration as an extreme example.