The stroke-averaged lift forces due to various vortex rings and their mutual interactions are studied using a flapping flight vortex model (Rayner, J. Fluid Mech., vol. 91, 1979, p. 697; Ellington, Phil. Trans. R. Soc. Lond. B, vol. 305, 1984b, p. 115). The vortex system is decomposed into the wing plane (wing-linked) vortex ring, a loop closed by the bound vortex and (arc-shaped) trailing vortex and the wake (the vortex rings shed previously). Using the vorticity moment theory (Wu, AIAA J., vol. 19, 1981, p. 432) we are able to identify the roles of vortex rings in lift production or reduction and express the lift as function of areal contraction or expansion of vortex rings. The wake vortex rings induce areal contraction of the trailing vortex, which should decrease the lift, but this decrease is exactly compensated by the inducing effect of the trailing arc on the wake. The wake reduces the lift through inducing a downwash velocity on the wing plane. The lift force is shown to drop to a minimum at the second half stroke, and then increases to an asymptotic value slightly below the lift at the first half stroke, in such a way following the experimental observation of Birch & Dickinson (Nature, vol. 412, 2001, p. 729). The existence of the negative peak of lift is due to the first shed vortex ring which, just at the second half stroke, lies in the close vicinity to the wing plane, leading to a peak of the wing plane downwash velocity.

A novel and greatly simplified strategy was developed to fabricate high-permittivity dielectric nanocomposites. Interface structure, precursor rheology and dielectric properties of the 0–3 BaTiO3/PVDF–hfp nanocomposite film were investigated.

Surface charge accumulation on cone-type insulators is a remarkable phenomenon in Gas Insulated Line (GIL), especially under DC voltage. It may lead to a considerable reduction of the flashover voltage of insulators. For this respect, this paper focuses on the surface charge distribution on the real insulator after applying DC voltage. In order to study this phenomenon, a set of device for measuring surface voltages on the insulator is designed, base on the electrostatic probe method. After applying different DC voltage amplitudes to the cone-type insulator, the surface voltage distributions, which reflect charge distributions to some extent, are measured by an electrostatic probe in SF 6 gas. Despite of the axial symmetry of the insulator, the measurement results show that the charge distribution is nonaxisymmetrical. The negative charge accumulates mostly under positive DC voltage. On the other hand, no apparent positive charge accumulation is observed on the surface. In areas which are close to electrode, the measured voltage amplitudes are much higher than outer areas.

The X-ray emission from an X-pinch was measured with diamond photoconducting detectors and a pinhole camera, and the results show that the X-ray source of the X-pinch is extremely small in size and high in brightness. As such, the X-pinch could be considered as an X-ray point source having a high spatial coherence that is required by a simplified scheme of X-ray phase-contrast imaging. The X-pinch was used as X-ray source for the phase-contrast imaging of a weakly X-ray-absorbing mosquito and an image with high contrast was obtained.

Based on a Mach-Zehnder interferometer, we report on the first observation of two different modes of wire explosion for nanosized powder production in 5-30 kPa ambient gas, depending on the property of wire material. For wire material with relatively high resistivity, such as titanium, more than one vapor burst was observed. While for wire material with relatively low resistivity, such as copper, the whole wire would explode totally within one single vapor burst.