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| 1 | Effects of anti-symmetric nonlinear viscous damping on the force transmissibility of multi-degree of freedom structures显示文摘In the present study, the concept of the output frequency response function is applied to theoretically investigate the force transmissibility of multi-degree of freedom (MDOF) structures with a nonlinear anti-symmetric viscous damping. The results reveal that an anti-symmetric nonlinear viscous damping can significantly reduce the transmissibility over all resonance regions for MDOF structures while it has almost no effect on the transmissibility over non-resonant and isolation regions. The results indicate that the vibration isolators with an anti-symmetric damping characteristic have great potential to overcome the dilemma in the design of linear viscously damped vibration isolators where an increase of the damping level reduces the force transmissibility over resonant region but increases the transmissibility over non-resonant regions. | Zhike Peng,1, ) and Zhiqiang Lang2 1)State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China 2)Department of Automatic Control and Systems Engineering, University of Sheffeld Mappin Street, Sheffeld, S1 3JD, UK | 2011 | Theoretical & Applied Mechanics Letters2011，1，6： | 1 |
| 2 | Ecology for a crowded planet显示文摘 | Palmer M Bernhardt E Chornesky E Collins S Dobson A Duke C Gold B Jacobson R Kingsland S Kranz R Mappin M Martinez ML Micheli F Morse J Pace M Pascual M Palumbi S Reichman O J Simons A Townsend A Turner M | | 0，，： | 1 |
| 3 | Assessing Mine Water Pollution: Geochemical Principles显示文摘The relative abundance and weathering rate of minerals that produce and consume acidity dictates whether a mine water discharge will be acidic or alkaline. Because metal ion solubility generally decreases with increasing pH, acidic waters are associated with greater risk from dissolved metals loads, while alkaline waters area associated with environmental degradation due to the oxidative precipitation of iron as ochrous deposits in surface water channels. Pyrite weathering produces acidity and dissolved iron loads, while calcite and, to a lesser extent, alumino silicate minerals, provide neutralising capacity that helps maintain circumneutral pH. Relating the relative abundance of these source minerals in the mining environment, and their relative rates of weathering, provides a conceptual framework within which to develop risk assessment and risk management approaches to minewater pollution. In particular the lifetime of contamination, and time scales to reach improved or detereorated mine water discharge quality is critical when assessing environmental impacts and risk, and when choosing treatment technology or selecting other approaches to handling minewater pollution. | Steven A. BanwartDepartment of Civil and Structural Engineering, University of Sheffield, Mappin Street, Sheffield S1, 3JD, UK | 2000 | Tsinghua Science and Technology2000，5，3： | 0 |
| 4 | Natural Biodegradation of Phenolic Compounds in Groundwater显示文摘A combination of field data and theoretical approaches is used to assess the natural attenuation and status of a complex plume of phenolic compounds (phenol, cresols, xylenols) in a deep, consolidated, UK Permo Triassic sandstone aquifer. Biodegradation of the phenolic compounds at concentrations up to 12500mg·L -1 is occurring under aerobic, NO - 3 reducing, Mn/Fe reducing, SO 2- 4 reducing and methanogenic conditions in the aquifer, with the accumulation of inorganic and organic metabolites in the plume. An electron and carbon balance for the plume suggests that only 6% of the source term has been degraded in 50 years. The residual contaminant mass in the plume significantly exceeds estimates of electron acceptor inputs, indicating that the plume will grow. Two detailed vertical profiles through the plume show that contaminant distributions are controlled more by source history than by biodegradation processes. Microbiological and mass balance studies show that biodegradation is greatest at the plume fringe where contaminant concentrations are diluted by transverse mixing. Active bacterial populations exist throughout the plume but biodegradation is inhibited in the plume core by high contaminant concentrations. Stable isotope studies show that SO 2- 4 reduction is particularly sensitive to contaminant concentration. The aquifer is not oxidant deficient but natural attenuation of the phenolic compounds in this system is limited by toxicity from the pollutant load and the bioavailability of electron acceptors. Natural attenuation of these contaminants will increase only after increased dilution of the plume. | David N. Lerner, Steven F. ThorntonDepartment of Civil and Structural Engineering, University of Sheffield, Mappin Street., Sheffield, S1 3JD, UK | 2000 | Tsinghua Science and Technology2000，5，3： | 0 |
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