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Abrupt vegetation shifts caused by gradual climate changes in central Asia during the Holocene

Science China Earth Sciences 2017年第7期60卷 1317-1327页

作者： ZHAO yan liu YaoLiang GUO ZhengTang FANG Keyan LI Quan CAO XianYong Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences Beijing 100101 China University of Chinese Academy of Sciences Beijing 100049 China Key Laboratory of Cenozoic Geology and Environment Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences Beijing 100101 China College of Geographical Sciences Fujian Normal University Fuzhou 350007 China Alfred Wegener Institute Helmholtz Center for Polar and Marine Research 14473 Potsdam Germany

Understanding the response of ecosystems to past climate is critical for evaluating the impacts of future climate changes.A large-scale abrupt shift of vegetation in response to the Holocene gradual climate changes has been well documented for the Sahara-Sahel ecosystem. Whether such a non-linear response is of universal significance remains to be further addressed. Here,we examine the vegetation-climate relationships in central Asia based on a compilation of 38 high-quality pollen records. The results show that the Holocene vegetation experienced two major abrupt shifts, one in the early Holocene(Shift I, establishing shift) and another in the late Holocene(Shift II, collapsing shift), while the mid-Holocene vegetation remained rather stable. The timings of these shifts in different regions are asynchronous, which are not readily linkable with any known abrupt climate shifts,but are highly correlated with the local rainfalls. These new findings suggest that the observed vegetation shifts are attributable to the threshold effects of the orbital-induced gradual climate changes. During the early Holocene, the orbital-induced precipitation increase would have first reached the threshold for vegetation "establishment" for moister areas, but significantly later for drier areas. In contrast, the orbital-induced precipitation decrease during the late Holocene would have first reached the threshold, and led to the vegetation "collapse" for drier areas, but delayed for moister areas. The well-known 4.2 kyr BP drought event and human intervention would have also helped the vegetation collapses at some sites. These interpretations are strongly supported by our surface pollen-climate analyses and ecosystem simulations. These results also imply that future climate changes may cause abrupt changes in the dry ecosystem once the threshold is reached.

关键词： Fossil pollen Vegetation response Threshold effects Holocene climate Central Asia

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Stiffness Degradation Modeling for Composite Wind Turbine Blades Based on Full-Scale Fatigue Testing

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Journal of Beijing Institute of Technology 2023年第4期32卷 517-528页

作者： Haixia Kou Kongyuan wei yanhu liu Xuyao Zhang School of Mechanical Engineering Lanzhou JiaoTong UniversityLanzhou 730070China School of Mechatronics Engineering Lanzhou University of TechnologyLanzhou 730050China School of New Energy and Power Engineering Lanzhou JiaoTong UniversityLanzhou 730070China

In order to provide more insights into the damage propagation composite wind turbine blades(blade)under cyclic fatigue loading,a stiffness degradation model for blade is proposed based on the full-scale fatigue testing of a blade.A novel non-linear fatigue damage accumulation model is proposed using the damage assessment theories of composite laminates for the first ***,a stiffness degradation model is established based on the correlation of fatigue damage and residual stiffness of the composite ***,a stiffness degradation model for the blade is presented based on the full-scale fatigue *** scientific rationale of the proposed stiffness model of blade is verified by using full-scale fatigue test data of blade with a total length of 52.5 *** results indicate that the proposed stiffness degradation model of the blade agrees well with the fatigue testing results of this *** work provides a basis for evaluating the fatigue damage and lifetime of blade under cyclic fatigue loading.

关键词： composite wind turbine blades fatigue damage stiffness degradation model full-scale fatigue testing

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An Energy-Efficient Query Based on Variable Region for Large-Scale Smart Grid

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China Communications 2016年第10期13卷 119-136页

作者： yan Wang Qingxu Deng Genghao liu Xiuping Hao Baoyan Song School of Computer Science and Engineering Northeastern University School of Information Liaoning University

The state-of-the-art query techniques in power grid monitoring systems focus on querying history data, which typically introduces an unwanted lag when the systems try to discover emergency situations. The monitoring data of large-scale smart grids are massive, dynamic and highly dimensional, so global query, the method widely adopted in continuous queries in Wireless Sensor Networks(WSN), is rendered not suitable for its high energy consumption. The situation is even worse with increasing application complexity. We propose an energy-efficient query technique for large-scale smart grids based on variable regions. This method can query an arbitrary region based on variable physical windows, and optimizes data retrieve paths by a key nodes selection strategy. According to the characteristics of sensing data, we introduce an efficient filter into the each query subtree to keep non-skyline data from being retrieved. Experimental results show that our method can efficiently return the overview situation of any query region. Compared to TAG and ESA, the average query efficiency of our approach is improved by 79% and 46%, respectively; the total energy consumption of regional query is decreased by 82% and 50%, respectively.

关键词： smart grid monitoring system wireless sensor network key node skyline query

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Elevated temperature wear behaviour of CeO_2 modified WC-12Co coating

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Journal of Rare Earths 2019年第6期37卷 673-678页

作者： yan liu Guiying yang Zongqiu Hang Hao Fu Naiyuan Xi Hui Chen School of Materials Science and Engineering Southwest Jiaotong University

With the service environment becoming more and more severe, WC-Co coatings are required to apply in high temperature wear condition. In the present study, the sliding wear tests of CeO_2 modified WC-12 Co coatings were conducted at temperature of 450, 550 and 650 ℃. The wear loss and friction coefficient were recorded. The morphologies of wear tracks were observed every 1 h to investigate the dynamic wear mechanisms. The results show that the volume wear loss decreases with temperature *** lowest volume wear loss is obtained at the temperature of 650 ℃ due to oxide films generated in the process of wearing. The wear mechanism is different at the temperature of 450, 550 and 650 0 C. Micro cutting wear, abrasive wear and oxidation wear dominate the wear mechanism at 450, 550 and 650 ℃,respectively. Abrasive wear and oxidation wear are the wear mechanisms at various temperatures.

关键词： CeO2 modified WC-12Co coating Dynamic process Elevated temperature wear mechanism Rare earths

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Electropolishing of NiTi for Improving Biocompatibility

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Journal of Materials Science & Technology 2008年第6期24卷 926-930页

作者： wei WU Xinjie liu Huimin HAN Dazhi yanG Shoudong LU State Key Laboratory for Material Modification by Laser Ion and Electron Beams Dalian University of Technology Dalian 116085 China School of Materials Science and Engineering Dalian University of Technology Dalian 116085 China

A modified electrolyte （CH3COOH-HClO4-A-B） for electropolishing （EP） of NiTi was presented for improving the corrosion resistance and biocompatibility of the alloy. Using the proposed parameters, a homogeneous and uniform surface was obtained. Atomic force microscopy （AFM） revealed that the surface roughness （Ra） for EP sample （23.21 nm） was close to mechanical polishing （MP） sample （19.36 nm）. Analysis by X-ray photoelectron spectroscopy （XPS） showed that Ti/Ni ratio increased from 3.1 for MP sample to 27.6 for EP sample. Measurements using potentiodynamic polarization in Hanks＇ solution showed that no pitting occurred for EP sample even though the applied potential increased up to 1500 mV （vs SCE）, while the MP sample was broken down at 650 mV. The present study indicates that electropolishing NiTi with this modified electrolyte contributes to the improved biocompatibility of NiTi.

关键词： NiTi Electropolishing XPS Corrosion resistance Biocompatibility

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HETEROGENEOUS MULTISCALE METHOD FOR OPTIMAL CONTROL PROBLEM GOVERNED BY ELLIPTIC EQUATIONS WITH HIGHLY OSCILLATORY COEFFICIENTS

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Journal of Computational Mathematics 2018年第5期36卷 644-660页

作者： Liang Ge Ningning yan Lianhai Wang Wenbin liu Danping yang School of Mathematical Sciences University of Jinan Jinan 250022 China Institute of Systems Science Academy of Mathematics and System Science Chinese Academy of Science Beijing 10080 China Shandong Provincial Key Laboratory of Computer Networks Shandong Computer Science Center Jinan 250014 China KBS University of Kent CT2 7PE UK Department of Mathematics East China Normal University Shanghai 200062 China

In this paper, we investigate heterogeneous multiscale method （HMM） for the optimal control problem with distributed control constraints governed by elliptic equations with highly oscillatory coefficients. The state variable and co-state variable are approximated by the multiscale discretization scheme that relies on coupled macro and micro finite elements, whereas the control variable is discretized by the piecewise constant. By applying the well- known Lions＇ Lemma to the discretized optimal control problem, we obtain the necessary and sufficient optimality conditions. A priori error estimates in both L^2 and H^1 norms are derived for the state, co-state and the control variable with uniform bound constants. Finally, numerical examples are presented to illustrate our theoretical results.

关键词： Constrained convex optimal control Heterogeneous multiscale finite element A priori error estimate Elliptic equations with highly oscillatory coefficients.

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Early Pattern of Epstein-Barr Virus Infection in Gastric Epithelial Cells by “Cell-in-cell”

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Virologica Sinica 2019年第3期34卷 253-261页

作者： Wenxing Yue Meijuan Zhu Lielian Zuo Shuyu Xin Jing Zhang Lingzhi liu Shen Li wei Dang Siwei Zhang yan Xie Fanxiu Zhu Jianhong Lu NHC Key Laboratory of Carcinogenesis The Key Laboratory of Carcinogenesis and Cancer Invasion of the Chinese Ministry of Education. Xiangya HospitalCentral South UniversityChangsha 410080China Department of Microbiology School of Basic Medical ScienceCentral South UniversityChangsha 410078China Department of Biological Science Florida State UniversityTallahasseeFL 32306USA

Epstein-Barr virus(EBV)is an important human dsDNA virus,which has been shown to be associated with several malignancies including about 10%of gastric *** EBV enters an epithelial cell has been an interesting project for investigation."Cell-in-cell"infection was recently reported an efficient way for the entry of EBV into nasopharynx epithelial *** present approach was to explore the feasibility of this mode for EBV infection in gastric epithelial cells and the dynamic change of host inflammatory *** EBV-positive lymphoblastic cells of Akata containing a GFP tag in the viral genome were co-cultured with the gastric epithelial cells(GES-1).The infection situation was observed under fluorescence and electron ***-time quantitative PCR and Western-blotting assay were employed to detect the expression of a few specific cytokines and inflammatory *** results demonstrated that EBV could get into gastric epithelial cells by"cell-in-cell"infection but not fully successful due to the host ***-1β,IL-6 and IL-8 played prominent roles in the cellular response to the *** activation of NF-κB and HSP70 was also required for the host antiviral *** results imply that the gastric epithelial cells could powerfully resist the virus invader via cell-in-cell at the early stage through inflammatory and innate immune responses.

关键词： Epstein-Barr virus(EBV) Cell-in-cell infection Gastric epithelial cells Inflammatory response

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DESIGN OF NOVEL HIGH PRESSURE-RESISTANT HYDROTHERMAL FLUID SAMPLE VALVE

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Chinese Journal of Mechanical Engineering 2008年第1期21卷 72-76页

作者： liu wei yanG Canjun WU Shijun XIE Yingjun CHEN Ying State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Hangzhou 310027 China

Sampling study is an effective exploration method, but the most extreme environments of hydrothermal vents pose considerable engineering challenges for sampling hydrothermal fluids. Moreover, traditional sampler systems with sample valves have difficulty in maintaining samples in situ pressure. However, decompression changes have effect on microorganisms sensitive to such stresses. To address the technical difficulty of collecting samples from hydrothermal vents, a new bidirectional high pressure-resistant sample valve with balanced poppet was designed. The sample valve utilizes a soft high performance plastic ＂PEEK＂ as poppet. The poppet with inapposite dimension is prone to occur to plastic deformation or rupture for high working pressure in experiments. To address this issue, based on the fmite element model, simulated results on stress distribution of the poppet with different structure parameters and preload spring force were obtained. The static axial deformations on top of the poppet were experimented. The simulated results agree with the experimental results. The new sample valve seals well and it can withstand high working pressure.

关键词： Hydrothermal vents High pressure-resistant Sample valve Finite element analysis Balanced poppet Bidirectional seal

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Appraisal of an oligomerization behavior of unprotected carbohydrates induced by phosphorus reagent

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Science China Chemistry 2018年第2期61卷 243-250页

作者： Hang Yuan Xu yang Peng Chen yan liu Guo Tang Yufen Zhao Department of Chemical Biology College of Chemistry and Chemical Engineering Key Laboratory for Chemical Biology of Fujian ProvinceXiamen University Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology Ministry of Education Department of Chemistry Tsinghua University

In this article, a novel oligomerization behavior of unprotected monosaccharides was discovered in a one-pot reaction induced by phosphorus reagent at room temperature. The inherent characteristics of the oligomerization reaction were dissected in detail by mass spectrometry based method combined with NMR technology. It was found that the main glycosidic bonding pattern is (1→6) linkage with 66% regioselectivity for each step. The ratio of α-(1→6) and β-(1→6) glycosidic bonds formed is around 1:1. The reactivity of 1-OH group from aldoses and the driving force from penta-coordinated phosphorus intermediates are the two critical factors for the oligomerization, according to the monitoring experiments by ESI-MS and NMR. Besides, the oligomerization reaction has good compatibility for various aldoses and could expand to O-glycosylated modification of peptides in vitro. The above results will provide a novel enlightenment to develop more convenient and higher-efficient methods for the synthesis of oligosaccharide library.

关键词： organic phosphorus activation oligosaccharide oligomerization one-pot unprotected synthesis

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A hindcast of the Bohai Bay oil spill during June to August 2011

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Acta Oceanologica Sinica 2017年第11期36卷 21-26页

作者： yanG Yiqiu LI yan liu Guimei PAN Qingqing WANG Zhaoyi Marine Environmental Forecasting Division National Marine Environmental Forecasting Center State Oceanic Administration Beijing 100081 China

An operational three-dimensional oil spill model is developed by the National Marine Environmental Forecasting Center（NMEFC）, State Oceanic Administration, China, and the model has been running for 9 a. On June 4 and 17,2011, oil is spilled into the sea water from two separate oil platforms in the Bohai Bay, i.e., Platforms B and C of Penglai 19-3 oilfield. The spill causes pollution of thousands of square kilometres of sea area. The NMEFC’s oil spill model is employed to study the Penglai 19-3 oil-spill pollution during June to August 2011. The wind final analysis data of the NMEFC, which is based on a weather research and forecasting（WRF） model, are analyzed and corrected by comparing with the observation data. A corrected current filed is obtained by forcing the princeton ocean model（POM） with the corrected wind field. With the above marine environmental field forcing the oil spill model, the oil mass balance and oil distribution can be produced. The simulation is validated against the observation, and it is concluded that the oil spill model of the NMEFC is able to commendably simulate the oil spill distribution. Thus the NMEFC’s oil spill model can provide a tool in an environmental impact assessment after the event.

关键词： oil spill hindcast Lagrangian random walk oil distribution swept area

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