Changes in plant species richness distribution in Tibetan alpine grasslands under different precipitation scenarios

Species richness is the core of biodiversity-ecosystem functioning (BEF) research. Nevertheless, it is difficult to accurately predict changes in plant species richness under different climate scenarios, especially in alpine biomes. In this study, we surveyed plant species richness from 2009 to 2017 in 75 alpine meadows (AM), 199 alpine steppes (AS), and 71 desert steppes (DS) in the Tibetan Autonomous Region, China. Along with 20 environmental factors relevant to species settlement, development, and survival, we first simulated the spatial pattern of plant species richness under current climate conditions using random forest modelling. Our results showed that simulated species richness matched well with observed values in the field, showing an evident decrease from meadows to steppes and then to deserts. Summer precipitation, which ranked first among the 20 environmental factors, was further confirmed to be the most critical driver of species richness distribution. Next, we simulated and compared species richness patterns under four different precipitation scenarios, increasing and decreasing summer precipitation by 20% and 10%, relative to the current species richness pattern. Our findings showed that species richness in response to altered precipitation was grassland-type specific, with meadows being sensitive to decreasing precipitation, steppes being sensitive to increasing precipitation, and deserts remaining resistant. In addition, species richness at low elevations was more sensitive to decreasing precipitation than to increasing precipitation, implying that droughts might have stronger influences than wetting on species composition. In contrast, species richness at high elevations (also in deserts) changed slightly under different precipitation scenarios, likely due to harsh physical conditions and small species pools for plant recruitment and survival. Finally, we suggest that policymakers and herdsmen pay more attention to alpine grasslands in central Tibet and at low elevations where species richness is sensitive to precipitation changes

Climate Variability Rather Than Livestock Grazing Dominates Changes in Alpine Grassland Productivity Across Tibet

Alpine grasslands on the Tibetan Plateau, being vulnerable to environmental and anthropogenic changes, have experienced dramatic climate change and intensive livestock grazing during the last half-century. Climate change, coupled with grazing activities, has profoundly altered alpine grassland function and structure and resulted in vast grassland degradation. To restore degraded grasslands, the Central Government of China has implemented the Ecological Security Barrier Protection and Construction Project since 2008 across the Tibetan Autonomous Region. However, the relative effect of climate change and grazing activities on the variation in alpine grassland productivity is still under debate. In this study, we quantified how aboveground net primary production (ANPP) varied before (2000-2008) and after (2009-2017) starting the project across different alpine grasslands and how much variance in ANPP could be attributed to climate change and grazing disturbance, in terms of temperature, precipitation, solar radiation, and grazing intensity. Our results revealed that Tibet's climate got warmer and wetter, and grazing intensity decreased after starting the project. Mean ANPP increased at approximately 81% of the sites, on average from 27.0 g C m(-2) during 2000-2008 to 28.4 g C m(-2) during 2009-2017. The ANPP positively correlated with annual temperature and precipitation, but negatively with grazing intensity for both periods. Random forest modeling indicated that grazing intensity (14.5%) had a much lower influence in controlling the dynamics of grassland ANPP than precipitation (29.0%), suggesting that precipitation variability was the key factor for alpine grassland ANPP increase across Tibet

Research and Implementation of Instrument System on a Light-Duty Electric Aircraft Simulator

Considering the demands of the instrument system on a light-duty electric aircraft simulator, a semi-physical simulation instrument system, which is based on virtual reality and microcontroller technologies, is designed and implemented. Meanwhile, some key technologies are discussed and a general development method is put forward in this paper. After being completed, this simulated instrument system is connected with the flight-computing system to test its performances. The results show that it has real effect, stable operation and real time response. In practice, the instrument system not only meets the demands of the light-duty electric aircraft simulator, but also can be seen as a certain reference to develop the instrument system of other aircraft simulators

Highly Conductive In-SnO2/RGO Nano-Heterostructures with Improved Lithium-Ion Battery Performance

The increasing demand of emerging technologies for high energy density electrochemical storage has led many researchers to look for alternative anode materials to graphite. The most promising conversion and alloying materials do not yet possess acceptable cycle life or rate capability. In this work, we use tin oxide, SnO2, as a representative anode material to explore the influence of graphene incorporation and In-doping to increase the electronic conductivity and concomitantly improve capacity retention and cycle life. It was found that the incorporation of In into SnO2 reduces the charge transfer resistance during cycling, prolonging life. It is also hypothesized that the increased conductivity allows the tin oxide conversion and alloying reactions to both be reversible, leading to very high capacity near 1200 mAh/g. Finally, the electrodes show excellent rate capability with a capacity of over 200 mAh/g at 10C

Synthesis and Characterization of Nanostructure Materials as Catalysts for Environmental and Energy Storage Applications

Environmental pollution and energy depletion are the two major issues we human beings have faced for the 21st century and even beyond. The bloom of nanotechnologies has brought new hope for solving these issues, along with the progress being made in engineering and information technologies. The work in this thesis only represents one piece of science like many others. Herein, the creation of novel materials and their screening as promising functionalized catalysts, targeting applications for example, in volatile organic compounds(VOC) abatement, heterogeneous oxidation, and solar energy driven water splitting towards H2 production as a substituting fuel for fossil fuel are sought. In the end, a novel nickel doped manganese oxide/graphene oxide composite was presented as a superior anode material for lithium ion batteries by achieving large capacities, good rate capabilities, and cycling stabilities. For environmental applications, a novel material, manganese-containing MFI type Mn-ZSM-5 zeolite was synthesized by a facile one-step hydrothermal method using tetrapropylammonium hydroxide (TPAOH) and manganese (III)-acetylacetonate as organic template and manganese salts, respectively. Direct evidence of the incorporation of Mn in the zeolite framework sites was observed by performing structural parameter refinements, and supported by data collected from other characterization techniques such as: IR, Raman, UV-Vis, TGA, N2-adsorption, SEM, TEM, EDX, and XPS. The unique optical properties of Mn-ZSM-5 from UV-vis spectra show two absorption peaks at 250 nm and 500 nm. The unique absorption was interpreted by studying photophysical properties of a model Mn(O-SiH3)4- compound, an Mn-embedded zeolite cluster, and model Mn oxides utilizing Time-Dependent Density Functional Theory (TD-DFT). The catalytic activity was studied in both gas phase benzyl alcohol oxidation and toluene oxidation reactions with remarkable oxidative activity presented for the first time. These reactions result in a 55 % yield of benzaldehyde, and 65 % total conversion of toluene to carbon dioxide for the 2% Mn-ZSM-5. Severe climate changes and depleting fossil fuel supplies call for sustainable energy conversion systems and storage techniques. The storage of solar energy by formation of fuel molecules, i.e. H2 and methanol provides a viable way to replace our current reliance on fossil fuels. In all these solar fuel productions, a large amount of protons and electrons are needed as the fuel sources and reducing equivalents, respectively. Water, as an inexpensive and abundant source can produce protons and electrons after being oxidized. Consequently, water oxidation (WO) has received extensive research efforts which mainly focus on development of accessible catalysts to drive WO at low overpotentials. In this regard, manganese has a leading role in catalyzing water oxidation efficiently with many unmatchable merits: low toxicity, high availability, and low cost. More importantly, manganese is Nature’s choice as catalyst for producing oxygen via the photosynthesis system II (PSII). Our study over a variety of manganese oxide structures and their catalytic activities in the oxygen evolution reaction (OER) showed an order of activity was followed: α-MnO2\u3e AMO \u3e β-MnO2 \u3e δ-MnO2, which has uncovered a clearly structure-property relationship of MnO2 in catalyzing OER

Research and Implementation of Instrument System on a Light-Duty Electric Aircraft Simulator

Considering the demands of the instrument system on a light-duty electric aircraft simulator, a semi-physical simulation instrument system, which is based on virtual reality and microcontroller technologies, is designed and implemented. Meanwhile, some key technologies are discussed and a general development method is put forward in this paper. After being completed, this simulated instrument system is connected with the flight-computing system to test its performances. The results show that it has real effect, stable operation and real time response. In practice, the instrument system not only meets the demands of the light-duty electric aircraft simulator, but also can be seen as a certain reference to develop the instrument system of other aircraft simulators

Research and Implementation of Instrument System on a Light-Duty Electric Aircraft Simulator

Considering the demands of the instrument system on a light-duty electric aircraft simulator, a semi-physical simulation instrument system, which is based on virtual reality and microcontroller technologies, is designed and implemented. Meanwhile, some key technologies are discussed and a general development method is put forward in this paper. After being completed, this simulated instrument system is connected with the flight-computing system to test its performances. The results show that it has real effect, stable operation and real time response. In practice, the instrument system not only meets the demands of the light-duty electric aircraft simulator, but also can be seen as a certain reference to develop the instrument system of other aircraft simulators