Measuring and modelling the reflectance spectra of male Swinhoe's pheasant feather barbules

A range of iridescent colour appearances are presented by male Swinhoe''s pheasants'' (Lophura swinhoii) mantle feathers. Two distinct regions of the open pennaceous portion of its feathers display particularly conspicuous angle-dependent reflection. A bright blue band appears in one region at normal incidence that spatially shifts to another at higher illumination angles. The two-dimensional photonic crystal-like nanostructures inside the barbules of these two regions are similar. However, this study found that the spatial variation in their colour appearance results from a continuously changing orientation of barbules with respect to the alignment of their associated barb. A multi-layered rigorous coupled-wave analysis approach was used to model the reflections from the identified intra-barbule structures. Well-matched simulated and measured reflectance spectra, at both normal and oblique incidence, support our elucidation of the origin of the bird''s distinctive feather colour appearance.     

Estimates of the errors when determining the direction and localization of the magnetic-field source of a dipole model

Stationary methods for the direction finding and localization of a magnetic-field source of a dipole model in real time are considered. For each method, an analytical estimate is made of the root mean square deviation of the measurement errors. The estimates are made using computer modeling of the errors. The limiting ranges when the equipment contains flux-gate magnetometers and gradiometers are determined. The methods are compared with respect to stability, range, and accuracy and the best method is chosen. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 30–35, May, 2008.