Assessment of ecosystem health based on landscape pattern in ecologically fragile regions at different spatial scales: A case study of Dianchi Lake basin, China

In the process of urbanization, maintaining ecosystem health in ecologically fragile regions is an inevitable requirement for sustainable development in the future, but the ecological health status varies greatly at different spatial scales. Determining the appropriate spatial scale of ecological health assessment is the basis and premise of ecological management and environmental protection policy making. Taking Dianchi Lake basin as the research area, based on the vigor-organization-resilience (VOR) model and landscape pattern index, this study established an assessment system of ecological health to evaluate the ecosystem health status from quadrat, ecological and administrative scales, with the aim to determine a reasonable evaluation scale and strengthen regional sustainability. The results show that: 1) The suitable spatial grain of landscape pattern analysis in Dianchi Lake basin is 150 m. 2) The average values of ecosystem health indices at quadrat scale, ecological scale and administrative scale are 0.5466, 0.4977 and 0.5373, respectively, demonstrating a sub-health state. 3) The most suitable scale for ecological health assessment of Dianchi Lake basin is ecological scale, because taking sub-watershed as ecological unit can ensure the integrity of the evaluated ecosystem to the greatest extent. Multiscale assessment is helpful for eco-environmental management departments to understand the ecosystem health status at different scales and provide a scientific basis for regional eco-environmental management decisions

Aerodynamic Drag Reduction on Speed Skating Helmet by Surface Structures

The aerodynamic drag for speed skating helmets with surface structures was investigated in this work by using numerical and experimental methods. Computational fluid dynamic (CFD) research was performed to analyze the detail of the flow field around the helmets. The simplified helmet models, with riblet and bump surface structures, were analyzed using the CFD simulations. The pressure distribution and velocity field around the helmets were obtained through the CFD analysis. The CFD results showed that the boundary layer separation position was obviously delayed, and the pressure changed to a higher value at the back area for structured helmets. Therefore, the aerodynamic drag for the structured helmet was lower than that of the original model. According to the CFD results, three types of helmets, with the of riblet and bump surface structure printed on the helmets by using flexible film, were tested in a wind tunnel. A full-scaled skater mannequin of half a body was used in the experiment to simulate the actual skating process. Compared with the original helmet, a drag reduction rate of 7% was achieved for the helmet with the bump at the middle region in the wind tunnel experiment, at the average speed in competitions for skaters

Nanobead-reinforced outmost shell of solid-electrolyte interphase layers for suppressing dendritic growth of lithium metal

Plating-stripping reversibility of lithium metal is improved by reinforcing the solid-electrolyte interphase layer by inorganic nanobeads. The outmost solid-electrolyte interphase shell is clearly identified, which is the passive layer formed on current collectors (or lithium metal) before the first lithium metal deposition. The outmost shell is intrinsically brittle and fragile so that it is easily broken by lithium metal dendrites growing along the progress of plating. Lithium metal deposit is not completely stripped back to lithium ions. On the other hand, lithium metal cells containing inorganic nanobeads in electrolyte show high reversibility between plating and stripping. The nanobeads are incorporated into the outmost shell during its formation. The nanobead-reinforced outmost shell having mechanically durable toughness suppresses dendritic growth of lithium metal, not allowing the dendrites to penetrate the shell. In addition to the mechanical effect of nanobeads, the LiF-rich solid-electrolyte interphase layer formation is triggered by HF generated by the reaction of the moisture adsorbed on oxide nanobeads with PF6 −. The LiF-rich composition is responsible for facile lithium ion transfer through the passive layers

Polypyrrole-assisted oxygen electrocatalysis on perovskite oxides

Nitrogen-containing electrocatalysts, such as metal-nitrogen-carbon (M-N-C) composites and nitrogen-doped carbons, are known to exhibit high activities for an oxygen reduction reaction (ORR). Moreover, even if the mechanism by which nitrogen improves the activities is not completely understood, a strong electronic interaction between nitrogen and active sites has been found in these composites. Herein, we demonstrate a case in which nitrogen improves the electroactivity, but in the absence of a strong interaction with other components. The overpotentials of the ORR and oxygen evolution reaction (OER) on perovskite oxide catalysts were significantly reduced simply by mixing the catalyst particles with polypyrrole/carbon composites (pPy/C). Any strong interactions between pPy (a nitrogen-containing compound) and active sites of the catalysts are not confirmed. A scenario based on the sequential task allocation between pPy and oxide catalysts for the ORR was proposed: (1) molecular oxygen is incorporated into pPy as a form of superoxide (pPy(+)O(2)(-)), (2) the superoxide is transferred to the active sites of perovskite catalysts, and (3) the superoxide is completely reduced along the 4e ORR process.clos