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Solar forcing of desert vegetation and drought frequency during the last 2700 years in the interior Qaidam Basin, northeastern Tibetan Plateau

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Science China Earth Sciences 2020年第4期63卷 561-574页

作者： quan li Key Laboratory of Land Surface Pattern and Simulation Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijing 100101China

Knowledge of long-term change in vegetation and climate in semi-arid/arid regions is essential for the study of current climate and development of mitigation strategies against severe drought. Here, a fossil pollen record of annually-varved core from Sugan Lake in interior Qaidam Basin was quantitatively analyzed to reconstruct changes in vegetation, floristic diversity and drought frequency. Results of biomization suggested that regional vegetation was desert vegetation with three short-term occupations of temperate steppe/xerophytic shrub during the last 2700 years. Floristic diversity generally increased/decreased with the expansion/degradation of desert vegetation. Moisture fluctuations showed three distinct stages(extremely dry between 742 BC and ~AD500, relatively wet with an increasing trend between ~AD500 and 1200 and relatively wet with frequent fluctuations after AD1200), interrupted by 14 drought events. Spectral analysis and continuous wavelet transform of moisture variation revealed 200-and 120-year cycles. According to cross-wavelet transform analysis, major drought frequency of ~200-year was explicitly correlated to solar activity. It's suggested that the centennial-scale drought frequency was mainly driven by solar activity, through modulation of large-scale atmospheric circulation. Furthermore, the effect of surface temperature–evaporation and uplifting/subsiding air flow should be notable. The climatic drought in interior Qaidam Basin could be intensified under the continuous global warming.

关键词： Pollen Vegetation change Drought frequency Qaidam Basin Northeastern Tibetan Plateau

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Spatial variability and long-term change in pollen diversity in Nam Co catchment(central Tibetan Plateau): Implications for alpine vegetation restoration from a paleoecological perspective

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Science China Earth Sciences 2018年第3期61卷 270-284页

作者： li quan Key Laboratory of Land Surface Pattern and Simulation Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences

Pollen diversity offers abundant clues into the floristic diversity and history of vegetation change. Few palynological studies investigated modem pollen diversity or the past floristic diversity on the Tibetan Plateau （TP）. Based on modem pollen assemblages from 37 topsoils and 63 surface lake sediments in the Nam Co catchment on the central TP, this study quantitatively explored spatial distribution of modem pollen diversity using Shannon-Wiener index （H） and palynological richness （E（Tn）, n=600）. Pollen diversity indices showed spatial variability among vegetation types, reflecting the differences in terrestrial floristic diversity in the lake catchment. Their values were high in the southeastern region of the lake catchment which is covered by alpine steppe, while values were low for alpine meadow and marsh meadow. The pollen diversity in lacustrine pollen assemblage could be an effective proxy to document past floristic diversity. The past floristic diversity in the lake catchment, recovered from a fossil pollen record ofNMLC-1, showed a long-term change of ascending overlaid by several rapid diversity changes during the last 8400 years due to the downward shift of altitudinal vegetation belt driven by a general climatic cooling. The results imply that under the environmental challenge of climate warming and vegetation degradation, alpine vegetation restoration in the Nam Co catchment and the central TP should pay attention to altitudinal vegetation belt and zonal vegetation of alpine steppe, and use the long-term change of floristic diversity as a historical analogue.

关键词： Pollen diversity Palynological richness Vegetation restoration Nam Co Lake Tibetan Plateau

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Nonlinear autopilot design for interceptors with tail fins and pulse thrusters via θ–D approach

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Journal of Systems Engineering and Electronics 2014年第2期25卷 273-280页

作者： quan li Di Zhou School of Astronautics Harbin Institute of Technology

The missile autopilot for an interceptor with tail fins and pulse thrusters is designed via the θ-D approach. The nonlin- ear dynamic model of the pitch and yaw motion of the missile is transformed into a linear-like structure with state-dependent coef- ficient （SDC） matrices. Based on the linear-like structure, a θ-D feedback controller is designed to steer the missile to track refer- ence acceleration commands. A sufficient condition that ensures the asymptotic stability of the tracking system is given based on Lyapunov＇s theorem. Numerical results show that the proposed autopilot achieves good tracking performance and the closed-loop tracking system is asymptotically stable.

关键词： blended control nonlinear control suboptimal control,θ-D approach.

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Structure and property of the hydrogen bonding complex between triazines and water

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Science China Chemistry 2006年第3期49卷 209-213页

作者： li quan College of Chemistry Sichuan Normal University Chengdu 610066 China

Density functional theory B3LYP is employed to obtain the optimized geometries of the ground state and interaction energy for triazines and water complexes. The results show that the 1,2,3-triazine-water, 1,2,4-triazine-water and 1,3,5-triazine-water complex on the ground state have Cs, Cs and C1 symmetry, and strong hydrogen bonding interaction with ?17.83, ?17.38 and ?13.55 kJ/mol after basis set superposition error and zero-point vibration energy correction, respectively, and large red-shift for the symmetric H─O stretching vibration frequencies forming N···H─O hydrogen bond in the triazines complex. The first singlet (n, π*) vertical excitation energy of the monomer and the hydrogen bonding complexes between triazines and water is investigated by time-dependent density functional theory.

关键词： triazines, hydrogen bond, vertical excitation, density functional theory.

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TWO DIMENSIONAL RIEMANN PROBLEM FOR GASDYNAMICS SYSTEM IN THREE PIECES

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Journal of Computational Mathematics 1999年第3期17卷 327-336页

作者： li, Jie-quan Yang, Shu-li Acad Sinica Inst Math Beijing 100080 Peoples R China Acad Sinica Inst Appl Math Beijing 100080 Peoples R China

The Riemann problem for two-dimensional flow of polytropic gas with three constant initial data is considered. Under the assumption that each interface of initial data outside of the origin projects exactly one planar wave of shock, rarefaction wave or contact discontinuity, it is proved that only two kinds of combinations, JRS and Js, are reasonable. Numerical solutions are obtained by using a nonsplitting second order accurate MmB Scheme, and they efficiently reflect the complicated configurations and the geometric structure of solutions of gas dynamics system. (Author abstract) 10 Refs.

关键词： two-dimensional Riemann problem MmB scheme gas dynamics

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Effects of Phase Composition on Microstructure and Mechanical Properties of Lu_2O_3-doped Porous Silicon Nitride Ceramics

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Journal of Materials Science & Technology 2011年第6期27卷 529-533页

作者： quan li Xiaowei Yin National Key Laboratory of Thermostructure Composite Materials Northwestern Polytechnical University Xi'an 710072 China

Porous silicon nitride ceramics（Si3N4） were fabricated by pressureless sintering using different particle size of silicon nitride ***2O3 was used as sintering *** to phase relationships in the ternary system Si3N4-SiO2-Lu2O3,porous Si3N4 ceramics with different phase composition were designed through the change of the content of SiO2 which was formed by the oxidation at 800℃ in *** Si3N4 with different phase compositions was obtained after sintering at 1800℃ in N2atmosphere.A small content of SiO2 favored the formation of secondary phase Lu4Si2O7N2,while large content of SiO2 favored the formation of secondary phase Lu2Si2O7 and *** Si3N4 ceramics with secondary phase Lu4Si2O7N2 had a flexural strength of 207 MPa,while that with secondary phase Si2N2O and Lu2Si2O7 had lower flexural strength.

关键词： Porous silicon nitride ceramics Secondary phase SiO2

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Preparation and Characterization of Antibacterial Polyacrylonitrile-based Activated Carbon Fiber Supporting Nano-ZnO

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Chemical Research in Chinese Universities 2013年第5期29卷 1011-1015页

作者： li quan-ming College of Quartermaster Science and Technology Jilin University Changchun 130062 P. R. China

Polyacrylonitrile（PAN）-based activated carbon fiber（PACF） supporting nano-ZnO（PACF/nano-ZnO） was prepared by spin, pretreatment, carbonization, and KOH chemical activation at an activation temperature of 950℃ for 40 min. Nano-ZnO content, distribution and antibacterial properties of the PACF/nano-ZnO were studied. The pore structure and surface properties of the PACF/nano-ZnO were studied by Brunauer-Emmett-Teller（BET）, N2/77 K isothermal adsorption. The specific surface area increased markedly after the activation process and it was several hundred times greater than that before the process. The PACF/nano-ZnO shows a strong adsorption for Staphylococ- cus aureus（S, aureus） and Escherichia coli（E, coli） and antibacterial activity against them. As an experimental result, antibacterial properties of PACF/nano-ZnO increased with increasing the concentration of nano-ZnO panicles, which suggests it is a promising antibacterial material.

关键词： Activated carbon fiber Carbon material Antibacterial activity Microstructure

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High Temperature Behavior of Isothermally Compressed M50 Steel

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Journal of Iron and Steel Research International 2015年第10期22卷 969-976页

作者： li-xing SUN Miao-quan li School of Materials Science and Engineering Northwestern Polytechnical University

The isothermal compression of M50 steel is carried out on a Gleeble-3500 thermo-mechanical simulator in temperature range of 1 223-1 423 K and strain rates range of 10-70 s^-1. The results show that the carbides play a significant role in the flow behavior and microstructure evolution during isothermal compression of M50 steel. The average apparent activation energy for deformation in isothermal compression of M50 steel is （281.1±42.6） kJ·mol^-1 at the strains of 0.4-0.8. The dynamic recrystallization of austenite grains occurs in isothermal compression of M50 steel at 1 363 K and 1 393 K, enhancing with the increase of strain rate and/or strain. The volume fraction of the carbides decreases with the increase of deformation temperature during isothermal compression of M50 steel and the fine carbides inhibit the dynamic recrystallization of austenite grain. With the occurrence of dynamic recrystallization, the austenite grains are refined, leading to a minor increase in the flow stress and apparent activation energy for deformation in isothermal compression of M50 steel. The austenite grains begin to coarsen at 1 423 K and dynamic recrystallization is limited. Hot working of M50 steel should not be performed above 1 393 K in order to achieve good workability.

关键词： M50 steel carbide apparent activation energy dynamic recrystallization isothermal compression

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Holocene peatland development and vegetation changes in the Zoige Basin, eastern Tibetan Plateau

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Science China Earth Sciences 2017年第10期60卷 1826-1837页

作者： SUN XiaoHong ZHAO Yan li quan Key Laboratory of Land Surface Pattern and Simulation Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences Beijing 100101 China University of Chinese Academy of Sciences Beijing 100049 China

Peat sediments and peatland evolution process offer abundant clues into the history of vegetation and climate *** order to reconstruct Holocene peatland, vegetation and climate changes on eastern Tibetan Plateau, we conducted analyses of fossil pollen, loss-on-ignition, and carbon accumulation rate on one peat core from Zoige Basin. Our results show local peatland initiated at 10.3 ka, thrived in the early-mid Holocene, and then began to degrade. Throughout the Holocene, Zoige Basin was dominated by alpine meadow. Coniferous forest on montane regions expanded for several times during 10.5–4.6ka, and then dramatically retreated. Results of peatland property, principal component analysis on fossil pollen suggested the climate maintained warm/wet during 10–5.5 ka, and became relatively cold/dry in the late Holocene. Rapid degradation of peatland, retreat of coniferous forest and climatic drought/cooling occurred at 10.2–10, 9.7–9.5, 8.7–8.5, 7.7–7.4, 6.4–6, 5.5–5.2,4.8–4.5, 4–3.6, 3.1–2.7, 1.4–1.2 and 0.8–0.6 ka. The long-term variations of Holocene climate and vegetation on eastern Tibetan Plateau could be attributed to changes in insolation-driven temperature and Asian Summer Monsoon intensity, while those rapid centennial changes were probably triggered by abrupt monsoon failures and temperature anomalies in the high northern latitudes.

关键词： Holocene Climate change Fossil pollen Peatland Tibetan Plateau

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quantum model for understanding protein misfolding behavior——phase diagram and manual intervention

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Science China(Physics,Mechanics & Astronomy) 2021年第6期64卷 10-16页

作者： Wen-Wen Mao li-Hua Lu You-quan li Zhejiang Province Key Laboratory of quantum Technology&Device and Department of Physics Zhejiang UniversityHangzhou 310027China Collaberative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210008China

The study of protein folding is fundamental and important in the multidisciplinary field because a diversity of diseases,like Alzheimer’s and Parkinson’s are relevant to protein *** current thermodynamic and geometric approaches only phenomenologically describe but do not provide a mechanistic understanding of the competition between correct folding and *** we present a model to understand the misfolding *** the influence of dissipative strength for all possible sequences and comparing the folding time toward different compact structures,we obtain a phase diagram of the dissipative quantum phase transition that enables us to model the *** also investigate how a perturbation in the Hamiltonian affects the transition point,which motivates us to explore possible manual *** results indicate that the manual intervention may be effective for some specific sequence but not for *** approach is expected to lay a foundation for further studies on manual intervention in protein misfolding.

关键词： quantum phase diagram quantum walk mean first-passage time protein folding

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