Dynamic modeling and structural optimization of a bistable electromagnetic vibration energy harvester

A novel bistable electromagnetic vibration energy harvester (BEMH) is constructed and optimized in this study, based on a nonlinear system consisting mainly of a flexible membrane and a magnetic spring. A large-amplitude transverse vibration equation of the system is established with the general nonlinear geometry and magnetic force. Firstly, the mathematical model, considering the higher-order nonlinearities given by nonlinear Galerkin method, is applied to a membrane with a co-axial magnet mass and magnetic spring. Secondly, the steady vibration response of the membrane subjected to a harmonic base motion is obtained, and then the output power considering electromagnetic effect is analytically derived. On this basis, a parametric study in a broad frequency domain has been achieved for the BEMH with different radius ratios and membrane thicknesses. It is demonstrated that model predictions are both in close agreement with results from the finite element simulation and experiment data. Finally, the proposed efficient solution method is used to obtain an optimizing strategy for the design of multi-stable energy harvesters with the similar flexible structure

古唐詩合解箋注 : 十二卷附古詩四卷 / (清)王堯衢註, (清)模宏遠校, (清)桓廣心校

Avec mode text

Job demands, job resources and safety outcomes: The roles of emotional exhaustion and safety compliance

The aim of this study was to assess the effectiveness of the job demands-resources (JD-R) model in explaining the relationship of job demands and resources with safety outcomes (i.e., workplace injuries and near-misses). We collected self-reported data from 670 crude oil production workers from three subcompanies of a major oilfield company in China. The results of a structural equation analysis indicated that job demands (psychological and physical demands) and job resources (decision latitude, supervisor support and coworker support) could affect emotional exhaustion and safety compliance, and thus influence the occurrence of injuries and near-misses. The implications of the present findings regarding both the JD-R model and occupational safety research were discussed. (C) 2012 Elsevier Ltd. All rights reserved

Carbon nanotubes from post-consumer waste plastics: Investigations into catalyst metal and support material characteristics

Carbon nanotubes were produced from post-consumer mixed waste plastics using a pyrolysis-catalysis process. The catalysts used were Ni-Fe bimetals supported over four different porous materials. The Ni-Fe/MCM41 catalyst displayed the highest catalytic activity for the pyrolysis-catalysis of the waste plastics in terms of carbon material yield at 55.60 wt.%. The order of catalytic activity was Ni-Fe/MCM41> Ni-Fe/ZSM5> Ni-Fe/Beta > Ni-Fe/NKF5, which was closely related to their differences in catalyst pore volume and catalyst reducibility. Formation of Ni-Fe alloy with fine particle dispersion over the Ni-Fe/MCM41 catalyst is suggested to be crucial for the promotion of the decomposition of the carbon precursors and subsequent precipitation to form carbon nanotubes. Whereas, the large catalyst particle size for the Ni-Fe/Beta catalyst led to irregular carbon shapes with a simultaneous decrease in purity and graphitization of the nanotubes. By-product production of hydrogen in large quantities (38.10 mmol H2  g−1plastic) could be used as process fuel