We report the mechanism of color production in peacock feathers. We find that the cortex in differently colored barbules, which contains a 2D photonic-crystal structure, is responsible for coloration. Simulations reveal that the photonic-crystal structure possesses a partial photonic bandgap along the direction normal to the cortex surface, for frequencies within which light is strongly reflected. Coloration strategies in peacock feathers are very ingenious and simple: controlling the lattice constant and the number of periods in the photonic-crystal structure. Varying the lattice constant produces diversified colors. The reduction of the number of periods brings additional colors, causing mixed coloration. C olor production in nature takes advantage of either structural coloration (1, 2) or pigmentation. Structural colors result from the interaction of light waves with a featured structure having the same order of size as the light wavelength. Structural colors in avian feathers have been usually qualitatively understood by thin-film interference (3Ϫ5) or the scattering from a spongy matrix structure incoherently (6, 7) or coherently (8, 9). Although the structural colors of avian feathers have been studied for a long time (10Ϫ14), many questions remain to be answered. In particular, the precise physical mechanism that produces the diversified colors in peacock tail feathers has not been established. Materials and MethodsThe male peacock tail contains spectacular beauty because of the brilliant, iridescent, diversified colors and the intricate, colorful eye patterns. Peacock feathers serve as an excellent canonical example for investigating structural colors in avian feathers. The structures of the blue, green, yellow, and brown barbules in the eye pattern of a male green peacock (Pavo muticus) feather were characterized by using an optical microscope and a scanning electron microscope. The peacock tail feather has a central stem with an array of barbs on each side. On each side of a barb there is an array of flat barbules. Each barbule has round indentations of typically Ϸ20-30 m, which disperse the incident light, causing coloration. The round indentation has a smoothly curved crescent-like profile in transverse cross section (14).To understand the detailed mechanisms of color production in peacock feathers, a plane-wave expansion method (15) was used to calculate the photonic band structure of the periodic photonic structures. A transfer matrix method (16) was adopted to compute the reflectance spectra to compare with experimental results. Fig. 1 shows the submicron structures of barbules. The transverse cross sections reveal that a barbule consists of a medullar core of Ϸ3 m enclosed by a cortex layer. Interestingly, the cortex of all differently colored barbules contains a 2D photonic-crystal structure (14, 17Ϫ19) made up of melanin rods connected by keratin. The longitudinal cross section shows that the melanin rod length is Ϸ0.7 m. Melanin is created by melanocyte cells, deposited in developing feathers,...

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The real-time health monitoring system is a promising body area network application to enhance the safety of firefighters when they are working in harsh and dangerous environments. Other than monitoring the physiological status of the firefighters, on-body monitoring networks can be also regarded as a candidate solution of motion detection and classification. In this paper, we consider motion classification with features obtained from the on-body radio frequency (RF) channel. Various relevant RF features have been identified and a Support Vector Machine (SVM) has been implemented to facilitate human motion classification. In particular, we distinguish the most frequently appearing human motions of firefighters including standing, walking, running, lying, crawling, climbing and running upstairs with an average true classification rate of 88.69%. Classification performance has been analyzed from three different perspectives including typical classification results, effects of candidate human motions and effects of on-body sensor locations. We prove that even a subset of available RF features provides an acceptable classification rate, which may result in less computational cost and easier implementation by using our proposed scheme.1536-1233 (c)

We present experimental observations and numerical simulations of superlensing effect in liquid surface waves. We use rigid cylinders to create a two-dimensional periodic lattice, in which liquid surface waves propagate. Through the observation of a superlensing effect, we demonstrate the existence of negative refraction in surface waves. In addition, a complete band gap is found.