Prompt efficiency of energy harvesting by magnetic coupling of an improved bi-stable system

In order to improve the transform efficiency of bi-stable energy harvester（BEH）,this paper proposes an advanced bi-stable energy harvester（ABEH）,which is composed of two bi-stable beams coupling through their magnets.Theoretical analyzes and simulations for the ABEH are carried out.First,the mathematical model is established and its dynamical equations are derived.The formulas of magnetic force in two directions are given.The potential energy barrier of ABEH is reduced and the snap-through is liable to occur between potential wells.To demonstrate the ABEH＇s advantage in harvesting energy,comparisons between the ABEH and the BEH are carried out for both harmonic and stochastic excitations.Our results reveal that the ABEH＇s inter-well response can be elicited by a low-frequency excitation and the harvester can attain frequent jumping between potential wells at fairly weak random excitations.Thus,it can generate a higher output power.The present findings prove that the ABEH is preferable in harvesting energy and can be optimally designed such that it attains the best harvesting performance.

Demand Charge under Nonsinusoidal Conditions

This paper aims to present a new point of view about the active power measurement, for billing purposes, measured at the PCC （point of common coupling） between the utility and the consumer when harmonic distortions are involved. Depending on theorigin of it, the active power can result in higher or lower values in comparison to the fundamental component. The consequences are higher costs for the consumer or losses for the electric utility. Using computational simulations and theoretical analysis, these aspects are evaluated and compared.

Harmonic generation at air–soil interface by femtosecond laser filament

We observe the third-harmonic generation and second-harmonic generation together with element fluorescence from the interaction of a femtosecond laser filament with a rough surface sample（sandy soil） in non-phasematched directions. The harmonics prove to originate from the phase-matched surface harmonics and air filament, then scatter in non-phase-matched directions due to the rough surface. These harmonics occurr when the sample is in the region before and after the laser filament, where the laser intensity is not high enough to excite the element fluorescence. The observed harmonics are related to the element spectroscopy, which will benefit the understanding of the interaction of the laser filament with a solid and be helpful for the application on filament induced breakdown spectroscopy.

Temporal and spatial differentiation in microhabitat use: Implications for reproductive isolation and ecological niche specification

Niche differentiation enables ecologically similar species to coexist by lessening competition over food and/or shelters and may be critical for reproductive isolation between closely related species in close proximity.Be­cause no extra traits need to evolve,spatial and temporal differentiation may readily take place to complement other isolating mechanisms.Two closely related treefrog species occur together in Korea:the endangered Hyla suweonensis and the widespread Hyla japonica.Advertisement calls are differentiated,but it is unclear whether call difference is sufficient for reproductive isolation.We tracked individuals of both species to study fine-scale differentiation in microhabitat use in the diel cycle of the breeding season using a harmonic direction finder.tracking male movement patterns of both species revealed spatial and temporal differentiation in microhabitat use for calling and resting during the breeding season.Males of both H.suweonensis and H.japonica occurred in all 5 microhabitats identified in this study:rice paddy,ground,buried,grass and bush.Both treefrog species showed general similarities in calling from rice paddies and resting in grass and bush.However,H.suweonensis moved into rice paddies and produced advertisement calls 3 h earlier than H.japonica.These differences like­ly minimize contact between the species and provide an additional isolating mechanism.In addition,the activity of H.suweonensis may be contributing to the decline of this species,as resting in grass would increase dangers from predatory birds and habitat disturbance.