Different grassland managements significantly change carbon fluxes in an alpine meadow.

Alpine meadow plays vital roles in regional animal husbandry and the ecological environment. However, different grassland managements affect the structure and function of the alpine meadow. In this study, we selected three typical grassland managements including free grazing, enclosure, and artificial grass planting and conducted a field survey to study the effects of grassland managements on carbon fluxes in an alpine meadow. The carbon fluxes were observed by static chamber and environmental factors including vegetation and soil characteristics were measured simultaneously. Our results show that the alpine meadow was a CO2 and CH4 sink, and grassland managements had a significant effect on all CO2 fluxes, including gross ecosystem production (GEP, P< 0.001), net ecosystem production (NEP, P< 0.001) and ecosystem respiration (ER, P< 0.001) but had no significant effect on CH4 fluxes (P > 0.05). The ranking of GEP under the different grassland managements was enclosure > free grazing > artificial grass planting. Furthermore, NEP and ER at enclosure plots were significantly higher than those of the free grazing and artificial grass planting plots. In addition, different grassland managements also affected the vegetation and soil characteristics of the alpine meadow. The aboveground biomass of artificial grass planting was significantly higher than that of the free grazing and enclosure plots. The vegetation coverage under three different grassland managements was ranked in the order of enclosure > artificial grass planting > free grazing and significant differences were observed among them. Moreover, significant differences in the number of species (P< 0.01) and the Margalef richness index (P< 0.05) were detected under three different grassland managements. Further analysis of the relationship between environmental factors and carbon fluxes revealed that GEP and NEP of the alpine meadow were positively correlated with vegetation coverage, the number of species, and the Margalef richness index. Therefore, grassland restoration should be configured with multiple species, which could improve carbon sink capacity while considering the functions of grassland restoration and production.

Principal stress lines based design method of lightweight and low vibration amplitude gear web.

A lightweight and low vibration amplitude web design method was investigated to reduce gear weight and noise. It was based upon the relationship between length and orthogonality that the principal stress lines were designed at the gear web. By constructing a vibration control model with gear design parameters, the optimal distance was calculated. By offsetting the principal stress lines at the optimal distance, the lightweight gear web with the low vibration amplitude was then generated. A vibration experimental platform was built to verify the novel gear vibration performances, and it was compared with other gears with the same web's porosity to verify loading performance. The experimental results indicated that compared with the solid gear, the novel gear is 20.50% lighter and with a 29.46% vibration amplitude reduction.

Michell truss design for lightweight gear bodies.

A new method for lightweight gear design based on Michell Trusses Design method was investigated in this research to compare with the traditional Topology Optimization method. A workflow with detailed steps was established using example of constructing Michell Trusses to make lightening holes at the gear's web. In this workflow, Michell Trusses are generated from a set of concentric circles. By solving the equation with the variables of concentric circles (complexity), the optimal orthogonality of trusses can be determined. Real experiments were conducted to compare the two design methods in the aspects of design costs and product mechanical property, including recording the time consumed in each link and detecting the force of failure of gears by a testing platform. The results indicate that this new method can significantly reduce design time while maintain the same power-to-weight ratio as the Topology Optimization design, which potentially provide a new research direction for lightweight structural modeling in mechanical engineering and aviation industry. The experimental product developed in this research demonstrated the promising prospects for real world applications.