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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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Modeling and simulation of bow wave effect in probe and drogue aerial refueling

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Chinese Journal of Aeronautics 2016年第2期29卷 448-461页

作者： Dai Xunhua Wei Zibo Quan quan School of Automation Science and Electrical Engineering Beihang University

In a probe and drogue aerial refueling system, the bow wave of the receiver aircraft will produce a strong aerodynamic effect on the drogue once the receiver follows the drogue at a close distance. It is a major difficulty of docking control in the probe and drogue refueling. This paper analyses the bow wave effect and presents a simple method to model it. Firstly, the inviscid flow around the receiver is modeled based on the stream function defined by basic stream singularities. Secondly, a correction function is developed to eliminate the error caused by the absence of air vis- cosity. Then, the aerodynamic coefficients are used to calculate the induced aerodynamic force on the drogue. The obtained model is in an analytical form that can be easily applied to the controller design and the real-time simulations. In the verification part, computational fluid dynamics （CFD） simulation tests are conducted to validate the obtained flow fields and aerodynamic forces. Finally, the modeling method is applied to an F-16 receiver aircraft in a previously developed autonomous aerial refueling simulation system. The simulations results are analyzed and compared with the NASA flight-test data, which demonstrates the effectiveness of the proposed method.

关键词： Aerial refueling Aerodynamic Bow wave Modeling Probe and drogueUAV

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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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Enhanced geographic information system-based mapping of local climate zones in Beijing, China

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Science China(Technological Sciences) 2019年第12期62卷 2243-2260页

作者： quan JinLing State Key Laboratory of Resources and Environmental Information System Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of Sciences

The vague urban-rural dichotomy severely restricts effective comparisons and communications among urban heat island studies.A local climate zone(LCZ) scheme has therefore been developed to classify urban and natural landscapes in a standardized and universal manner. Despite LCZ mapping efforts in worldwide cities, this study attempts to propose an enhanced geographic information system-based workflow to enable the hierarchical classification of LCZs with fewer indicators but higher accuracies while considering supplementary classes and subclasses. Specifically, five morphological and coverage indicators that were easily obtained and well differentiated among LCZs were derived from a city street map and satellite images, and 25 LCZs(including 16 standard, 3 supplementary, and 6 sub-classified zones) were determined at a block-level according to the indicator hierarchy and criteria. The method was performed over Beijing, China, and evaluations by field surveys and google earth images showed a high accuracy with little noise and sharp boundaries, outperforming the widely-used remote sensing-based method of the World Urban Database and Access Portal Tools, particularly in terms of building height and heavy industry. Results also demonstrate that the Beijing core was dominated by open(including extremely open) mid-rise buildings(28.7%) and open lowrise buildings(12.8%), forming an inner-low-middle-high-outer-low annular building-height pattern. Significant land surface temperature differences were detected among the LCZs, where the low-rise and compact LCZs had higher temperatures than the mid-/high-rise and open LCZs during daytime, and subclasses LCZ XB/C/D(LCZ XE/F) generated lower(higher) temperatures than their parent classes in May. This method was proposed to augment the LCZ mapping system and further support applications(e.g., urban planning/management and climate/weather modeling) in high-density cities similar to Beijing.

关键词： geographic information system(GIS) remote sensing local climate zone(LCZ) land surface temperature urban morphology

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Coating Qualities Evaluation for Alkali-Metal Atomic Vapor Cells Based on Frustrated Total Internal Reflection

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Chinese Physics Letters 2014年第3期31卷 38-42页

作者： quan Wei Science and Technology on Inertial Laboratory Beihang University Beijing 100191 Fundamental Science on Novel Instrument and Navigation System Technology Laboratory Beihang University Beijing 100191

To realize accurate measurement of coating thickness and surface reliefs for alkali-metal vapor cells, a measurement method based on frustrated total internal reflection （FTIR） is proposed. Firstly, the phenomenon of frustrated total internal reflection and the theory of coating thickness measurement based on FTIR are introduced. Then a coating thickness measuring system based on FTIR is established and the coating thickness measuring experiment is carried out. Next, surface reliefs are obtained by analyzing distributions of the data of coating thickness. The experimental results indicate that the FTIR method can measure coating thickness exactly with an accuracy better than 2 nm, which can satisfy the evaluation of coating qualities for alkali-metal vapor cells.

关键词： METAL vapors RESEARCH ALKALI metals TOTAL internal reflection (Optics) SURFACE coatings PHYSICS research

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Repetitive Control for TORA Benchmark:An Additive-state-decomposition-based Approach

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International Journal of Automation and computing 2015年第3期12卷 289-296页

作者： Quan quan Kai-Yuan Cai Department of Automatic Control Beijing University of Aeronautics and Astronautics

The repetitive control(RC) or repetitive controller problem for nonminimum phase nonlinear systems is both challenging and practical. In this paper, we consider an RC problem for the translational oscillator with a rotational actuator(TORA), which is a nonminimum phase nonlinear system. The major difficulty is to handle both a nonminimum phase RC problem and a nonlinear problem simultaneously. For such purpose, a new RC design, namely the additive-state-decomposition-based approach, is proposed,by which the nonminimum phase RC problem and the nonlinear problem are separated. This makes RC for the TORA benchmark tractable. To demonstrate the effectiveness of the proposed approach, a numerical simulation is given.

关键词： Additive state decomposition repetitive control translational oscillator with a rotational actuator(TORA) rotational-translation

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Cooling the Earth:a polymer-based selective thermal emitter for all-day radiative cooling

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Science China Chemistry 2021年第3期64卷 339-340页

作者： quan-Hong Yang Nanoyang Group State Key Laboratory of Chemical EngineeringSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin 300350China Joint School of National University of Singapore and Tianjin University International Campus of Tianjin UniversityTianjin UniversityFuzhou 350207China

From fundamental thermodynamics considerations, cooling is more challenging than heating in reducing the energy consumption and relieving the greenhouse effect. While most of the currently used cooling methods require energy and resources to carry heat away, radiative cooling has attracted much attention since it can dissipate heat to outer atmosphere through a transparency window without any energy consumption [1,2].

关键词： Earth transparency thermodynamics

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Robust Hybrid Control for Ballistic Missile Longitudinal Autopilot

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Chinese Journal of Aeronautics 2011年第6期24卷 777-788页

作者： WAEL Mohsen Ahmeda WAEL Mohsen Ahmed QUan quan Department of Automatic Control School of Automation Science and Electrical Engineering Beihang University Beijing 100191 China State Key Laboratory of Virtual Reality Technology and Systems Beihang University Beijing 100191 China

This paper investigates the boost phase＇s longitudinal autopilot of a ballistic missile equipped with thrust vector control. The existing longitudinal autopilot employs time-invariant passive resistor-inductor-capacitor （RLC） network compensator as a control strategy, which does not take into account the time-varying missile dynamics. This may cause the closed-loop system instability in the presence of large disturbance and dynamics uncertainty. Therefore, the existing controller should be redesigned to achieve more stable vehicle response. In this paper, based on gain-scheduling adaptive control strategy, two different types of optimal controllers are proposed. The first controller is gain-scheduled optimal tuning-proportional-integral-derivative （PID） with actuator constraints, which supplies better response but requires a priori knowledge of the system dynamics. Moreover, the controller has oscillatory response in the presence of dynamic uncertainty. Taking this into account, gain-scheduled optimal linear quadratic （LQ） in conjunction with optimal tuning-compensator offers the greatest scope for controller improvement in the presence of dynamic uncertainty and large disturbance. The latter controller is tested through various scenarios for the validated nonlinear dynamic flight model of the real ballistic missile system with autopilot exposed to external disturbances.

关键词： ballistic missiles attitude control gain-scheduling optimal tuning-control LQ optimal regulators

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CATALYTIC ACTIVITIES OF RARE-EARTH CALIXARENE COMPLEXES IN POLYMER SYNTHESES

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Chinese Journal of Polymer Science 2005年第6期23卷 593-602页

作者： Zhi-quan Shen Institute of Polymer Science Zhejiang University Hangzhou 310027 China

The studies of our group on the catalytic activities of rare earth calixarene complexes in polymer syntheses are reviewed. Rare earth calixarene complexes are effect catalysts for the polymerizations of butadiene, isoprene, ethylene, styrene, propylene oxide, styrene oxide, trimethylene carbonate and 2,2-dimethyl-trimethylene carbonate.

关键词： Rare earth complex Calixarene Polymer synthesis.

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Docking control for probe-drogue refueling: An additive-state-decomposition-based output feedback iterative learning control method

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Chinese Journal of Aeronautics 2020年第3期33卷 1016-1025页

作者： Jinrui REN Quan quan Cunjia LIU Kai-Yuan CAI School of Automation Science and Electrical Engineering Beihang UniversityBeijing 100083China Department of Aeronautical and Automotive Engineering Loughborough UniversityLeicestershire LE113TUUnited Kingdom

Designing a controller for the docking maneuver in Probe-Drogue Refueling(PDR) is an important but challenging task, due to the complex system model and the high precision *** order to overcome the disadvantage of only feedback control, a feedforward control scheme known as Iterative Learning Control(ILC) is adopted in this ***, Additive State Decomposition(ASD) is used to address the tight coupling of input saturation, nonlinearity and the property of Non Minimum Phase(NMP) by separating these features into two subsystems(a primary system and a secondary system).After system decomposition, an adjoint-type ILC is applied to the Linear Time-Invariant(LTI) primary system with NMP to achieve entire output trajectory tracking, whereas state feedback is used to stabilize the secondary system with input *** two controllers designed for the two subsystems can be combined to achieve the original control goal of the PDR ***, to compensate for the receiverindependent uncertainties, a correction action is proposed by using the terminal docking error,which can lead to a smaller docking error at the docking *** tests have been carried out to demonstrate the performance of the proposed control method, which has some advantages over the traditional derivative-type ILC and adjoint-type ILC in the docking control of PDR.

关键词： Additive state decomposition Adjoint operator Docking control Iterative learning control Probe-drogue refueling Stable inversion

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