Low-fi'equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been de...Low-fi'equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been developed. However, few researches focus on how to optimize the test mass install position in order to improve the vibration transmissibility. An active low-frequency vertical vibration isolation system based on an earlier instrument, the Super Spring, is designed and implemented. The system, which is simple and compact, consists of two stages: a parallelogram-shaped linkage to ensure vertical motion, and a simple spring-mass system. The theoretical analysis of the vibration isolation system is presented, including terms erroneously ignored before. By carefully choosing the mechanical parameters according to the above analysis and using feedback control, the resonance frequency of the system is reduced from 2.3 to 0.03 Hz, a reduction by a factor of more than 75. The vibration isolation system is installed as an inertial reference in an absolute gravimeter, where it improved the scatter of the absolute gravity values by a factor of 5. The experimental results verifies the improved performance of the isolation system, making it particularly suitable for precision experiments. The improved vertical vibration isolation system can be used as a prototype for designing high-performance active vertical isolation systems. An improved theoretical model of this active vibration isolation system with beam-pivot configuration is proposed, providing fundamental guidelines for vibration isolator design and assembling.展开更多
Anthropogenic activities have become more and more important in characterizing the landscape, but their impacts are still restricted by natural environments. This paper discusses the interactions of anthropogenic acti...Anthropogenic activities have become more and more important in characterizing the landscape, but their impacts are still restricted by natural environments. This paper discusses the interactions of anthropogenic activity, vegetation activity and topography through describing the spatial distribution of land cover and vegetation activity (represented by Normalized Difference Vegetation Index, NDVI) along topographic gradient in a mountainous area of southwestern China. Our results indicate that the existing landscape pattern is controlled by anthropogenic activities as well as topographic factors. Intensive anthropogenic activities mainly occur in areas with relatively low elevation, gentle and concave slopes, as these areas are easy and convenient to attain for human. Because of the destruction by human, some land cover types (mainly grassland and shrub) are only found in relatively harsher environments. This study also finds that topographic wetness index (W) used in other places only reflects runoff generation capacity, but not indicate the real spatial pattern of soil water content in this area. The relationships between NDVI and W, and NDVI and length slope factor (LSF) show that runoff and erosion have complex effects on vegetation activity. Greater values of W and LSF will lead to stronger capacity to produce runoff and transport sediment, and thereby increase soil water content and soil deposition, whereas beyond a certain threshold runoff and erosion are so strong that they would destruct vegetation growth. This study provides information needed to successfully restore native vegetation, improve land management, and promote sustainable development in mountainous areas, especially for developing regions.展开更多
We applied a primitive equation ocean model to simulate submesoscale activities and processes over the shelf of the northern South China Sea(NSCS) with a one-way nesting technology for downscaling.The temperature and ...We applied a primitive equation ocean model to simulate submesoscale activities and processes over the shelf of the northern South China Sea(NSCS) with a one-way nesting technology for downscaling.The temperature and density fields showed that submesoscale activities were ubiquitous in the NSCS shelf.The vertical velocity was considerably enhanced in submesoscale processes and could reach an average of 58 m per day in the subsurface.At this point,the mixed layer depth also was deepened along the front,and the surface kinetic energy also increased with the intense vertical movement induced by submesoscale activity.Thus,submesoscale stirring/mixing is important for tracers,such as temperature,salinity,nutrients,dissolved organic,and inorganic carbon.This result may have implication for climate and biogeochemical investigations.展开更多
The characteristics of vertical crustal movement in Chinese mainland are studied, and the ideas and principles for dividing active blocks according to the map of recent vertical crustal deformation rate in China is pr...The characteristics of vertical crustal movement in Chinese mainland are studied, and the ideas and principles for dividing active blocks according to the map of recent vertical crustal deformation rate in China is proposed. As a result, Chinese mainland is divided into 2 first-grade blocks, the east and west block, 6 second-grade blocks, the Northeast China, North China, East China, Xizang (Tibet), Gansu-Qinghai-Xizang (Gan-Qing-Zang) and Xinjiang block, and 16 third-grade blocks. The boundaries of active blocks divided in this paper are generally consistent with the pattern of neotectonic movement with some local difference. It shows that the recent crustal activity in Chinese mainland inherits the neotectonic movement occurred since the Quaternary, while some new activity tendencies appear.展开更多
In this paper, solar active region (AR) 6891 is studied. The long term temporal (over a 8 day period) relationahip between vertical current evolution and flare are examined. We found that the day to day variation of t...In this paper, solar active region (AR) 6891 is studied. The long term temporal (over a 8 day period) relationahip between vertical current evolution and flare are examined. We found that the day to day variation of the flare number in the active region is more closly associated with the variation of net current intensity than that of total current intensity. The increase in negative current in the weak following polarity area is due to the reduction in negative current in the strong preceding area.展开更多
通过对可编程逻辑控制器(Programma blelogic contro ller,PLC)的梯形图语言及指令表语言的分析,提出了基于AOV(Activity on vertex)有向图和二叉树实现梯形图与指令表程序相互转换的算法。转换算法将梯形图映射为AOV图,并由其建立二叉...通过对可编程逻辑控制器(Programma blelogic contro ller,PLC)的梯形图语言及指令表语言的分析,提出了基于AOV(Activity on vertex)有向图和二叉树实现梯形图与指令表程序相互转换的算法。转换算法将梯形图映射为AOV图,并由其建立二叉树来表示指令间的逻辑关系,通过遍历二叉树实现PLC梯形图与指令表的转换。文中给出一个转换实例,介绍了算法思想及其实现步骤。该算法具有通用性,适于复杂控制逻辑的梯形图,已成功用于水电自动化监控系统中的PLC编程软件平台。展开更多
Mercury and its derivatives are hazardous environmental pollutants and could affect the aquatic ecosystems and human health by biomagnification. Lake sediments can provide important historical information regarding ch...Mercury and its derivatives are hazardous environmental pollutants and could affect the aquatic ecosystems and human health by biomagnification. Lake sediments can provide important historical information regarding changes in pollution levels and thus trace anthropogenic or natural influences. This research investigates the 100-year history of mercury (Hg) deposition in sediments from Chao Lake, a shallow eutrophic lake in China. The results indicate that the Hg deposition history can be separated into three stages (pre-1960s, 1960s–1980s, and post-1980s) over the last 100 years. Before the 1960s, Hg concentrations in the sediment cores varied little and had no spatial difference. Since the 1960s, the concentration of Hg began to increase gradually, and showed a higher concentration of contamination in the western half of the lake region than in the eastern half of the lake region due to all kinds of centralized human-input sources. The influences of anthropogenic factors and hydrological change are revealed by analyzing correlations between Hg and heavy metals (Fe, Co, Cr, Cu, Mn, Pb, and Zn), stable carbon and nitrogen isotopes (d13C and d15N), nutrients, particle sizes, and meteorological factors. The results show that Hg pollution intensified after the 1960s, mainly due to hydrological change, rapid regional development and urbanization, and the proliferation of anthropogenic Hg sources. Furthermore, the temperature, wind speed, and evaporation are found to interactively influence the environmental behaviors and environmental fate of Hg.展开更多
The mesozooplankton in both epipelagic and mesopelagic zones is essentially important for the study of ecosystem and biological carbon pump. Previous studies showed that the diel vertical migration (DVM) pattern of me...The mesozooplankton in both epipelagic and mesopelagic zones is essentially important for the study of ecosystem and biological carbon pump. Previous studies showed that the diel vertical migration (DVM) pattern of mesozooplankton varied among ecosystems. However, that pattern was largely unknown in the Western Pacific Warm Pool (WPWP). The vertical distribution, DVM and community structure of mesozooplankton from the surface to 1 000 m were compared at Stas JL7K (WPWP) and MA (North Pacific Subtropical Gyre, NPSG). Two sites showed similarly low biomass in both epipelagic and mesopelagic zones, which were in accordance with oligotrophic conditions of these two ecosystems. Stronger DVM (night/day ratio) was found at JL7K (1.31) than that at MA (1.09) on surface 0–100 m, and an obvious night increase of mesopelagic biomass was observed at JL7K, which was probably due to migrators from bathypelagic zone. Active carbon flux by DVM of zooplankton was estimated to be 0.23 mmol/(m2·d) at JL7K and 0.16 mmol/(m2·d) at MA. The community structure analysis showed that calanoid copepods, cnidarians and appendicularians were the main contributors to DVM of mesozooplankton at both sites. We also compared the present result with previous studies of the two ecosystems, and suggested that the DVM of mesozooplankton was more homogeneous within the WPWP and more variable within the NPSG, though both ecosystems showed typically extremely oligotrophic conditions. The different diel vertical migration strength of mesozooplankton between NPSG and WPWP implied different efficiency of carbon pump in these two ecosystems.展开更多
Di erential braking and active steering have already been integrated to overcome their shortcomings. However, existing research mainly focuses on two-axle vehicles and controllers are mostly designed to use one contro...Di erential braking and active steering have already been integrated to overcome their shortcomings. However, existing research mainly focuses on two-axle vehicles and controllers are mostly designed to use one control method to improve the other. Moreover, many experiments are needed to improve the robustness; therefore, these control methods are underutilized. This paper proposes an integrated control system specially designed for multi-axle vehicles, in which the desired lateral force and yaw moment of vehicles are determined by the sliding mode control algorithm. The output of the sliding mode control is distributed to the suitable wheels based on the abilities and potentials of the two control methods. Moreover, in this method, fewer experiments are needed, and the robustness and simultaneity are both guaranteed. To simplify the optimization system and to improve the computation speed, seven simple optimization subsystems are designed for the determination of control outputs on each wheel. The simulation results show that the proposed controller obviously enhances the stability of multi-axle trucks. The system improves 68% of the safe velocity, and its performance is much better than both di erential braking and active steering. This research proposes an integrated control system that can simultaneously invoke di erential braking and active steering of multi-axle vehicles to fully utilize the abilities and potentials of the two control methods.展开更多
Control of the vertical instability of the plasma in the SUNIST spherical tokamak is studied. A proportional-derivative (PD) position controller is employed in a control system which consists of a massless plasma, a...Control of the vertical instability of the plasma in the SUNIST spherical tokamak is studied. A proportional-derivative (PD) position controller is employed in a control system which consists of a massless plasma, active coils and a passive conducting vessel. Stability conditions axe determined and the feedback control with different combinations of both active and passive coils, available on SUNIST, is emphasized. The simulation results are also discussed.展开更多
基金Supported by Tsinghua University’s Scientific Research Initiative Program,China(Grant No.2010THZ05)
文摘Low-fi'equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been developed. However, few researches focus on how to optimize the test mass install position in order to improve the vibration transmissibility. An active low-frequency vertical vibration isolation system based on an earlier instrument, the Super Spring, is designed and implemented. The system, which is simple and compact, consists of two stages: a parallelogram-shaped linkage to ensure vertical motion, and a simple spring-mass system. The theoretical analysis of the vibration isolation system is presented, including terms erroneously ignored before. By carefully choosing the mechanical parameters according to the above analysis and using feedback control, the resonance frequency of the system is reduced from 2.3 to 0.03 Hz, a reduction by a factor of more than 75. The vibration isolation system is installed as an inertial reference in an absolute gravimeter, where it improved the scatter of the absolute gravity values by a factor of 5. The experimental results verifies the improved performance of the isolation system, making it particularly suitable for precision experiments. The improved vertical vibration isolation system can be used as a prototype for designing high-performance active vertical isolation systems. An improved theoretical model of this active vibration isolation system with beam-pivot configuration is proposed, providing fundamental guidelines for vibration isolator design and assembling.
基金the National Natural Science Foundation of China (40621061)the Project of Chinese Academy of Sciences (KZCX2-XB2-02-31) for their financial support
文摘Anthropogenic activities have become more and more important in characterizing the landscape, but their impacts are still restricted by natural environments. This paper discusses the interactions of anthropogenic activity, vegetation activity and topography through describing the spatial distribution of land cover and vegetation activity (represented by Normalized Difference Vegetation Index, NDVI) along topographic gradient in a mountainous area of southwestern China. Our results indicate that the existing landscape pattern is controlled by anthropogenic activities as well as topographic factors. Intensive anthropogenic activities mainly occur in areas with relatively low elevation, gentle and concave slopes, as these areas are easy and convenient to attain for human. Because of the destruction by human, some land cover types (mainly grassland and shrub) are only found in relatively harsher environments. This study also finds that topographic wetness index (W) used in other places only reflects runoff generation capacity, but not indicate the real spatial pattern of soil water content in this area. The relationships between NDVI and W, and NDVI and length slope factor (LSF) show that runoff and erosion have complex effects on vegetation activity. Greater values of W and LSF will lead to stronger capacity to produce runoff and transport sediment, and thereby increase soil water content and soil deposition, whereas beyond a certain threshold runoff and erosion are so strong that they would destruct vegetation growth. This study provides information needed to successfully restore native vegetation, improve land management, and promote sustainable development in mountainous areas, especially for developing regions.
基金Supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Nos.KZCX1-YW-12-04,KZCX2-YW-201)
文摘We applied a primitive equation ocean model to simulate submesoscale activities and processes over the shelf of the northern South China Sea(NSCS) with a one-way nesting technology for downscaling.The temperature and density fields showed that submesoscale activities were ubiquitous in the NSCS shelf.The vertical velocity was considerably enhanced in submesoscale processes and could reach an average of 58 m per day in the subsurface.At this point,the mixed layer depth also was deepened along the front,and the surface kinetic energy also increased with the intense vertical movement induced by submesoscale activity.Thus,submesoscale stirring/mixing is important for tracers,such as temperature,salinity,nutrients,dissolved organic,and inorganic carbon.This result may have implication for climate and biogeochemical investigations.
基金The developing and programming project G19980407 of National Key Basic Researches.
文摘The characteristics of vertical crustal movement in Chinese mainland are studied, and the ideas and principles for dividing active blocks according to the map of recent vertical crustal deformation rate in China is proposed. As a result, Chinese mainland is divided into 2 first-grade blocks, the east and west block, 6 second-grade blocks, the Northeast China, North China, East China, Xizang (Tibet), Gansu-Qinghai-Xizang (Gan-Qing-Zang) and Xinjiang block, and 16 third-grade blocks. The boundaries of active blocks divided in this paper are generally consistent with the pattern of neotectonic movement with some local difference. It shows that the recent crustal activity in Chinese mainland inherits the neotectonic movement occurred since the Quaternary, while some new activity tendencies appear.
文摘In this paper, solar active region (AR) 6891 is studied. The long term temporal (over a 8 day period) relationahip between vertical current evolution and flare are examined. We found that the day to day variation of the flare number in the active region is more closly associated with the variation of net current intensity than that of total current intensity. The increase in negative current in the weak following polarity area is due to the reduction in negative current in the strong preceding area.
文摘通过对可编程逻辑控制器(Programma blelogic contro ller,PLC)的梯形图语言及指令表语言的分析,提出了基于AOV(Activity on vertex)有向图和二叉树实现梯形图与指令表程序相互转换的算法。转换算法将梯形图映射为AOV图,并由其建立二叉树来表示指令间的逻辑关系,通过遍历二叉树实现PLC梯形图与指令表的转换。文中给出一个转换实例,介绍了算法思想及其实现步骤。该算法具有通用性,适于复杂控制逻辑的梯形图,已成功用于水电自动化监控系统中的PLC编程软件平台。
基金The National Key Research and Development Program of China (2017YFA0605003)the National Natural Science Foundation of China (91751114 and 41521003).
文摘Mercury and its derivatives are hazardous environmental pollutants and could affect the aquatic ecosystems and human health by biomagnification. Lake sediments can provide important historical information regarding changes in pollution levels and thus trace anthropogenic or natural influences. This research investigates the 100-year history of mercury (Hg) deposition in sediments from Chao Lake, a shallow eutrophic lake in China. The results indicate that the Hg deposition history can be separated into three stages (pre-1960s, 1960s–1980s, and post-1980s) over the last 100 years. Before the 1960s, Hg concentrations in the sediment cores varied little and had no spatial difference. Since the 1960s, the concentration of Hg began to increase gradually, and showed a higher concentration of contamination in the western half of the lake region than in the eastern half of the lake region due to all kinds of centralized human-input sources. The influences of anthropogenic factors and hydrological change are revealed by analyzing correlations between Hg and heavy metals (Fe, Co, Cr, Cu, Mn, Pb, and Zn), stable carbon and nitrogen isotopes (d13C and d15N), nutrients, particle sizes, and meteorological factors. The results show that Hg pollution intensified after the 1960s, mainly due to hydrological change, rapid regional development and urbanization, and the proliferation of anthropogenic Hg sources. Furthermore, the temperature, wind speed, and evaporation are found to interactively influence the environmental behaviors and environmental fate of Hg.
基金The National Basic Research Program(973 Program)of China under contract No.2015CB755902the China Ocean Mineral Resources Research and Development Association Program under contract No.DY135-E2-2-4+1 种基金the Scientific Research Fund of the Second Institute of Oceanography,SOA under contract No.JG1712the National Natural Science Foundation of China under contract No.41406116
文摘The mesozooplankton in both epipelagic and mesopelagic zones is essentially important for the study of ecosystem and biological carbon pump. Previous studies showed that the diel vertical migration (DVM) pattern of mesozooplankton varied among ecosystems. However, that pattern was largely unknown in the Western Pacific Warm Pool (WPWP). The vertical distribution, DVM and community structure of mesozooplankton from the surface to 1 000 m were compared at Stas JL7K (WPWP) and MA (North Pacific Subtropical Gyre, NPSG). Two sites showed similarly low biomass in both epipelagic and mesopelagic zones, which were in accordance with oligotrophic conditions of these two ecosystems. Stronger DVM (night/day ratio) was found at JL7K (1.31) than that at MA (1.09) on surface 0–100 m, and an obvious night increase of mesopelagic biomass was observed at JL7K, which was probably due to migrators from bathypelagic zone. Active carbon flux by DVM of zooplankton was estimated to be 0.23 mmol/(m2·d) at JL7K and 0.16 mmol/(m2·d) at MA. The community structure analysis showed that calanoid copepods, cnidarians and appendicularians were the main contributors to DVM of mesozooplankton at both sites. We also compared the present result with previous studies of the two ecosystems, and suggested that the DVM of mesozooplankton was more homogeneous within the WPWP and more variable within the NPSG, though both ecosystems showed typically extremely oligotrophic conditions. The different diel vertical migration strength of mesozooplankton between NPSG and WPWP implied different efficiency of carbon pump in these two ecosystems.
基金National Natural Science Foundation of China(Grant No.51505178)China Postdoctoral Science Foundation(Grant No.2014M561289)
文摘Di erential braking and active steering have already been integrated to overcome their shortcomings. However, existing research mainly focuses on two-axle vehicles and controllers are mostly designed to use one control method to improve the other. Moreover, many experiments are needed to improve the robustness; therefore, these control methods are underutilized. This paper proposes an integrated control system specially designed for multi-axle vehicles, in which the desired lateral force and yaw moment of vehicles are determined by the sliding mode control algorithm. The output of the sliding mode control is distributed to the suitable wheels based on the abilities and potentials of the two control methods. Moreover, in this method, fewer experiments are needed, and the robustness and simultaneity are both guaranteed. To simplify the optimization system and to improve the computation speed, seven simple optimization subsystems are designed for the determination of control outputs on each wheel. The simulation results show that the proposed controller obviously enhances the stability of multi-axle trucks. The system improves 68% of the safe velocity, and its performance is much better than both di erential braking and active steering. This research proposes an integrated control system that can simultaneously invoke di erential braking and active steering of multi-axle vehicles to fully utilize the abilities and potentials of the two control methods.
基金supported by National Natural Science Foundation of China (No.10535020)the Foundation for Authors of National Excellent Doctoral Dissertations of China (No.200456)
文摘Control of the vertical instability of the plasma in the SUNIST spherical tokamak is studied. A proportional-derivative (PD) position controller is employed in a control system which consists of a massless plasma, active coils and a passive conducting vessel. Stability conditions axe determined and the feedback control with different combinations of both active and passive coils, available on SUNIST, is emphasized. The simulation results are also discussed.