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In this paper, we look into the fundamental mechanism to retrieve the power from physical vibrations by using microelectromechanical systems (MEMS) energy harvesters. An analytical model is presented for the velocity-damped resonant generator (VDRG) that delivers electrical power through the power enhancement mechanism using the mechanical resonance of a suspended mass. Deliverable power is also analytically discussed with respect to the theoretical limit, and a view to understand the VDRG behaviors is presented in association with the impedance matching condition and the quality factors. Mechano-electric power conversions including electrostatic induction, electromagnetic induction, and piezoelectric effect are discussed to study the scaling effect. Recent examples of MEMS VDRGs are reviewed and evaluated in terms of the power density.

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Lower Permian volcanism was the first magmatic activity to occur after the collision events in the Mongolian orogenic zone, east China. The Permian volcanic rocks are therefore a key to understanding the dynamics of the unified continental lithosphere. The volcanic rocks consist of basic and intermediate rocks. The intermediate rocks with high initial 87 Sr/ 86 Sr ratios (0.7051 to 0.7052) and low ε Nd values (-0.73 to -3.57) generally overlie the basic rocks in the field. The basic rocks have relatively low initial 87 Sr/ 86 Sr ratios (0.7034 to 0.7051) and high ε Nd values (2.72 to -0.10). Two parallel Rb-Sr isochrons give almost the same age, about 270 Ma. One consists of the basic rocks giving an initial isochron 87 Sr/ 86 Sr ratio of 0.7035. The other consists of the intermediate rocks and one sample of basalt, which give an initial isochron 87 Sr/ 86 Sr value of 0.7051. The strong correlations between SiO 2 and other major elements suggest that fractional crystallization played an important role in the magmatic processes. However, fractional crystallization cannot explain the geochemistry of most incompatible trace elements and Sr-Nd isotope characteristics. The positive correlation between Th/Nb and (La/Sm) N ratios demonstrates the direct relation between the enrichment of the light rare earth elements and the contamination of continental sediments. The high contents of large ion lithosphere elements (LILE) in the Permian volcanic rocks may suggest an additional 'crust + fluid' component, especially in the intermediate rocks, which are highly enriched in Ba (> 400 ppm) relative to the basic rocks (< 200 ppm). We propose that the subduction slab dropped into depleted mantle and released fluid, which induced the mantle metasomatism and LILE enrichment. The metasomatized mantle partially melted and formed the 'primary' magma. This primary magma assimilated with the Proterozoic biotite-quartz schist during its rise, and finally formed the Permian volcanic rocks. Magma assimilated with the Proterozoic biotite-quartz schist in small amounts could have produced the basic rocks, while assimilation of larger amounts of magma (because of longer assimilation time) would generate intermediate rocks. §Author for correspondence: yongfeng@eyou.com