This paper introduces a novel chattering-free terminal sliding mode control(SMC)strategy to address chaotic behavior in permanent magnet synchronous generators(PMSG)for offshore wind turbine systems.By integrating an ...This paper introduces a novel chattering-free terminal sliding mode control(SMC)strategy to address chaotic behavior in permanent magnet synchronous generators(PMSG)for offshore wind turbine systems.By integrating an adaptive exponential reaching law with a continuous barrier function,the proposed approach eliminates chattering and ensures robust performance under model uncertainties.The methodology combines adaptive SMC with dynamic switching to estimate and compensates for unknown uncertainties,providing smooth and stable control.Finally,the performance and effectiveness of the proposed approach are compared with those of a previous study.展开更多
The drone industry is taking o!,fueled by a boom in the low-altitude economy.According to the Research Report on the Development of China’s Low-altitude Economy(2024),released by CCID Consulting Co.,Ltd.in April,the ...The drone industry is taking o!,fueled by a boom in the low-altitude economy.According to the Research Report on the Development of China’s Low-altitude Economy(2024),released by CCID Consulting Co.,Ltd.in April,the scale of China’s civilian drone industry reached 117.43 billion yuan(US$16.21 billion)in 2023,up 32 percent year-on-year.展开更多
A novel discrete-time reaching law was proposed for uncertain discrete-time system,which contained process noise and measurement noise.The proposed method reserves all the advantages of discrete-time reaching law,whic...A novel discrete-time reaching law was proposed for uncertain discrete-time system,which contained process noise and measurement noise.The proposed method reserves all the advantages of discrete-time reaching law,which not only decreases the band width of sliding mode and strengthens the system robustness,but also improves the dynamic performance and stability capability of the system.Moreover,a discrete-time sliding mode control strategy based on Kalman filter method was designed,and Kalman filter was employed to eliminate the influence of system noise.Simulation results show that there is no chattering phenomenon in the output of controller and the state variables of controlled system,and the proposed algorithm is also feasible and has strong robustness to external disturbances.展开更多
Implementation of efficient vibration control schemes for seismically excited structures is becoming more and more important in recent years.In this study,the influence of different control schemes on the dynamic perf...Implementation of efficient vibration control schemes for seismically excited structures is becoming more and more important in recent years.In this study,the influence of different control schemes on the dynamic performance of a frame structure excited by El Centro wave,with an emphasis on reaching law based control strategies,is examined.Reaching law refers to the reachable problem and criteria for the sliding state of a control system.Three reaching laws are designed to present different sliding mode control strategies by incorporating a state space model that describes structural dynamic characteristics of a frame structure.Both intact and damaged structures are studied by using the aforementioned control strategies.The influence of different structural damage extents,control locations and reaching law based control methods are further investigated.The results show that the structure can be well controlled using the sliding mode strategy when the induced structural damage extent does not exceed the standard percentage for considering the structure was damaged,which is 20%reduction in structure stiffness,as reported in the literature.The control effectiveness is more satisfactory if the control location is the same as the direction of external excitation.Furthermore,to study the chattering phenomenon of the sliding mode control method,approximation and detail components extracted from the phase plots of the sliding mode control system are compared via wavelet transform at different scales.The results show that for the same type of control law,the system behaves with similar chattering phenomenon.展开更多
Forward and backward reaching inverse kinematics(FABRIK)is an efficient two-stage iterative solver for inverse kinematics of spherical-joint manipulator without the calculation of Jacobian matrix.Based on FABRIK,this ...Forward and backward reaching inverse kinematics(FABRIK)is an efficient two-stage iterative solver for inverse kinematics of spherical-joint manipulator without the calculation of Jacobian matrix.Based on FABRIK,this paper presents an incremental control scheme for a free-floating space manipulator consists of revolute joints and rigid links with the consideration of joint constraints and dynamic coupling effect.Due to the characteristics of FABRIK,it can induce large angular movements on specific joints.Apart from that,FABRIK maps three dimensional(3D)problem into two dimensional(2D)problem by a simple geometric projection.This operation can cause infinite loops in some cases.In order to overcome these issues and apply FABRIK on space manipulators,an increments allocation method is developed to constrain the angular movements as well as to re-orient the end-effector.The manipulator is re-positioned based on the momentum conservation law.Instead of pure target position tracking,the orientation control of the end-effector is also considered.Numerical simulation is performed to testify and demonstrate the effectiveness and reliability of the proposed incremental control approach.展开更多
This paper develops a discrete-time sliding mode controller with a power rate exponential reaching law approach to enhance the performance of a pneumatic artificial muscle system in both reaching time and chattering r...This paper develops a discrete-time sliding mode controller with a power rate exponential reaching law approach to enhance the performance of a pneumatic artificial muscle system in both reaching time and chattering reduction.The proposed method dynamically adapts to the variation of the switching function,which is based on an exponential term and a power rate term of the sliding surface.Thus,the controlled system can achieve high tracking performance while still obtain chattering-free control.Moreover,the effectiveness of the proposed method is validated through multiple experimental tests,focused on a dual pneumatic artificial muscle system.Finally,experimental results show the effectiveness of the proposed approach in this paper.展开更多
Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are ...Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are involved in the SMC operation, namely reaching mode and sliding mode.In the reaching mode, the system state is forced to reach the sliding surface in a finite time.The major drawback of the SMC approach is the occurrence of chattering in the sliding mode, which is undesirable in most applications.Generally, the trade-off between chattering reduction and fast reaching time must be considered in the conventional SMC design.This paper proposes SMC design with a novel reaching law called the exponential rate reaching law(ERRL) to reduce chattering, and the control structure of the converter is designed based on the multiinput SMC that is applied to a three-phase AC/DC power converter.The simulation and experimental results show the effectiveness of the proposed technique.展开更多
Hemiparesis is common following stroke. The ability to reach and grasp is a necessary component of many daily life functional tasks, hence reduced upper limb function has an impact on the ability to perform activities...Hemiparesis is common following stroke. The ability to reach and grasp is a necessary component of many daily life functional tasks, hence reduced upper limb function has an impact on the ability to perform activities of daily living. In hemiparetic patients, the unrestricted and unguided repetition of a motor task may reinforce compensatory movements. Trunk restraint allowed the patients to use joint ranges that were present but not recruited during unrestrained reaching. Later, studies combined the trunk restraint training with additional therapeutic interventions. With the growing number of studies on this intervention in the stroke population, there is the need to consolidate this evidence to determine the potential use of trunk restraint training in improving arm reaching in neurological rehabilitation particularly for stroke patients. A considerable research effort had assessed the effects of trunk restraint training on the recovery of reaching movements in hemiparetic patients. This review identified 5 relevant trials in which one trial is a pilot study. Among 5 trials, three trials recorded the movement kinematics (outcome measure) by Optotrak Motion analysis System, in the other two trials the movement kinematics (outcome measure) were analysed by a 6 – camera, 3D Motion analysis system and 10 – camera Motion Analysis System respectively. The effect size for the intervention was calculated by Cohen’s d. In this review, for the meta-analysis we used trunk displacement, trunk flexion, elbow extension, Smoothness and hand trajectory straightness (movement variables in kinematic analysis). The results of our review demonstrated that the use of trunk restraint as a treatment paradigm aimed at decreasing compensatory strategies has the potential of becoming an effective therapy. Further studies are necessary to determine the long term effect of the trunk restraint training.展开更多
I paid great attention to the Alibaba program that nurtures entrepreneurs. We must conduct dialogue with African governments, so that they support young entrepreneurs and cultivate ecommerce systems." These are t...I paid great attention to the Alibaba program that nurtures entrepreneurs. We must conduct dialogue with African governments, so that they support young entrepreneurs and cultivate ecommerce systems." These are the words of Dr. Mukhissa Kituyi, secretary general of the United Nations Conference on Trade and Development (UNCTAD), who paid a visit to the headquarters of the Alibaba Group on June 28, 2018 to speak with 29 African entrepreneurs, who were receiving training under the “African Entrepreneur Training Program.”展开更多
The air temperature of Wuli,which is located in seasonal frozen ground zone,is rising by 13 ℃ yearly.This paper discusses the days that each ground layers' temperature lags behind the surface temperature in reach...The air temperature of Wuli,which is located in seasonal frozen ground zone,is rising by 13 ℃ yearly.This paper discusses the days that each ground layers' temperature lags behind the surface temperature in reaching extremum.The results were shown:The time of each ground layers' lagging days was increasing;the lagging day in warm season was longer than that in cold season;the growth rate of lagging days in warm season was 0.5 d/y,while the growth rate of lagging days in cold season was 0.7 d/y.展开更多
CHINESE and Nigerian media should be aware of their growing influence at home and abroad and should strive to present unbiased news coverage, including stories about each other＇s respective country. Agreement on this...CHINESE and Nigerian media should be aware of their growing influence at home and abroad and should strive to present unbiased news coverage, including stories about each other＇s respective country. Agreement on this important step in ongoing cooperation between the two sides was reached by media representatives attending a me- dia forum on September 19 in Abuja, Nigeria.展开更多
To foster a new development paradigm with domestic circulation as the core and domestic and international circulations reinforcing each other,Chinese enterprises are undertaking a lead role in making better use of bot...To foster a new development paradigm with domestic circulation as the core and domestic and international circulations reinforcing each other,Chinese enterprises are undertaking a lead role in making better use of both domestic and international markets and resources to achieve stronger and more sustainable development and promote construction of an open world economy.Considering the new paradigm,how should Chinese enterprises further develop in the overseas markets?At the Chinese Enterprise Global Image Summit 2020 held in Beijing on November 3,representatives from government departments,business companies,think tanks,and media outlets shared strategies.展开更多
Poised on the edge of Northeast Asia,where China meets the Korean Peninsula and Russia’s Far East,Jilin Province emerges as a mosaic-its identity woven from rugged borderlands,industrial legacy and 21st-century ambit...Poised on the edge of Northeast Asia,where China meets the Korean Peninsula and Russia’s Far East,Jilin Province emerges as a mosaic-its identity woven from rugged borderlands,industrial legacy and 21st-century ambition.展开更多
Chaqg'e is the Chinese moon goddess.Named after'her,the Chang'e-6 lunar module returned to Earth this June carrying 1,935.3 grams of rocks and dust from the far side of the moon.A world first,the unique sa...Chaqg'e is the Chinese moon goddess.Named after'her,the Chang'e-6 lunar module returned to Earth this June carrying 1,935.3 grams of rocks and dust from the far side of the moon.A world first,the unique samples-more viscous and clumpier than previously collected lunar specimens-will be distributed globally for scientific analysis.展开更多
We report a continuous-wave Er：ZBLAN fiber laser with the operation wavelength reaching 3.68 μm.The midinfrared Er：ZBLAN fiber laser is pumped with the dual-wavelength sources consisting of a commercial laser diode...We report a continuous-wave Er：ZBLAN fiber laser with the operation wavelength reaching 3.68 μm.The midinfrared Er：ZBLAN fiber laser is pumped with the dual-wavelength sources consisting of a commercial laser diode at 970 nm and a homemade Tm-doped fiber laser at 1973 nm.By increasing the launched pump power at1973 nm,the laser wavelength can be switched from 3.52 to 3.68 μm.The maximum output power of 0.85 W is obtained with a slope efficiency of 25.14% with respect to the 1973 nm pump power.In the experiment,the laser emission at 3.68 μm is obtained with a significant power of 0.62 W,which is the longest emission wavelength in free-running Er：ZBLAN fiber lasers.展开更多
We present the long-term stability of the integrating sphere cold atom clock（ISCAC） and analyze its systematic limitations. The relative frequency instability of 2.6 × 10-15 is reached for an averaging time of ...We present the long-term stability of the integrating sphere cold atom clock（ISCAC） and analyze its systematic limitations. The relative frequency instability of 2.6 × 10-15 is reached for an averaging time of 2 ×105 s. The second-order Zeeman effect and the cavity pulling effect in ISCAC, which would induce the frequency drift from the clock transition, are analyzed. The analytical and experimental results indicate that the cavity pulling effect is the main contribution to the long-term frequency instability of the ISCAC. Further technical improvements to the microwave cavity are also discussed.展开更多
or a hypersonic flight vehicle with highly coupling nonlinear,a sliding mode controller based on reaching law is designed for its longitudinal motion model.Two proposals of reaching law are designed.One of which is a ...or a hypersonic flight vehicle with highly coupling nonlinear,a sliding mode controller based on reaching law is designed for its longitudinal motion model.Two proposals of reaching law are designed.One of which is a variable exponential reaching law,the other one is compound reaching law which consists of a conventional exponential reaching law and a power rate reaching law.The reaching law controller can speed up the system states arriving at the sliding mode condition,at the same time,it can guarantee better robustness.Simulation analysis is conducted for trimmed cruise condition of 110,000 ft and Mach 15,in which the responses of the vehicle to a step change of altitude and velocity respectively are analyzed.Simulation results show that the controller based on variable exponential reaching law enables the system to faster tracking speed than the conventional reaching law.Moreover the compound reaching law controller has shorter tracking time and strong robustness against parameters uncertainties.展开更多
[Objective]Implementation of the Ten-Year Fishing Ban policy may alter fish diversity and niche characteristics of dominant species in spawning grounds within the National Nature Reserve for Rare and Endemic Fish in t...[Objective]Implementation of the Ten-Year Fishing Ban policy may alter fish diversity and niche characteristics of dominant species in spawning grounds within the National Nature Reserve for Rare and Endemic Fish in the Upper Yangtze River.This study initiated continuous monitoring of natural spawning habitats from February 2022 to assess these ecological changes.[Methods]Environmental DNA(eDNA)metabarcoding was employed to analyze fish species composition,biodiversity patterns,and niche parameters of dominant species.Water sampling followed the CEN/TS 19461 standard across five monitoring transects(ZT1-ZT5).[Results]The eDNA analysis detected 45 species of fish belonging to 38 genera,13 families,and 3 orders were detected through environmental DNA(eDNA)in this survey,including 10 species endemic to the upper reaches of the Yangtze River,such as Procypris rabaudi and Myxocyprinus asiaticus.The fish community was mainly composed of bottom-dwelling,settling ovum-producing,omnivorous fish.The variation ranges of the Chao1 index,ACE index,Shannon index,and Simpson index are 736~996,719~965,1.58~3.23,and 0.83~0.99,respectively,indicating that fish species in spawning sites are abundant and community distribution uniformity is high.All indexes are highest at ZT1 monitoring points.Cluster analysis showed that,at a certain similarity level,fish community types in spawning sites could be basically divided into two groups:ZT1,ZT3,and ZT5 clustered together,and ZT2 and ZT4 clustered together,indicating similar fish community habitats.There are 9 dominant fish species in typical deep pool habitats in the reserve,with niche widths(Bi)ranging from 1.13 to 3.87.The dominant fish species are broad and medium niche fish,such as Cyprinus carpio and Hemiculter tchangi,with the niche overlap index(Oik)of some dominant fish species reaching more than 0.95.This indicates fierce competition for resources among the fish in this spawning ground.[Conclusion]The Zhutuo spawning ground demonstrates high species richness with homogeneous community structure and intense resource competition.This study establishes an eDNA-based monitoring framework that enhances conventional survey method,providing critical baseline data for adaptive management under the fishing moratorium regime.展开更多
The global issue of climate change presents young entrepreneurs with opportunities to explore new business models.FACED with the severe challenges presented by global climate change,pursuing a green lifestyle is a way...The global issue of climate change presents young entrepreneurs with opportunities to explore new business models.FACED with the severe challenges presented by global climate change,pursuing a green lifestyle is a way to achieve sustainable development.Many countries are exploring ways to reach a balance between economic development and environmental protection.展开更多
文摘This paper introduces a novel chattering-free terminal sliding mode control(SMC)strategy to address chaotic behavior in permanent magnet synchronous generators(PMSG)for offshore wind turbine systems.By integrating an adaptive exponential reaching law with a continuous barrier function,the proposed approach eliminates chattering and ensures robust performance under model uncertainties.The methodology combines adaptive SMC with dynamic switching to estimate and compensates for unknown uncertainties,providing smooth and stable control.Finally,the performance and effectiveness of the proposed approach are compared with those of a previous study.
文摘The drone industry is taking o!,fueled by a boom in the low-altitude economy.According to the Research Report on the Development of China’s Low-altitude Economy(2024),released by CCID Consulting Co.,Ltd.in April,the scale of China’s civilian drone industry reached 117.43 billion yuan(US$16.21 billion)in 2023,up 32 percent year-on-year.
基金Project(50721063) supported by the National Natural Science Foundation of China
文摘A novel discrete-time reaching law was proposed for uncertain discrete-time system,which contained process noise and measurement noise.The proposed method reserves all the advantages of discrete-time reaching law,which not only decreases the band width of sliding mode and strengthens the system robustness,but also improves the dynamic performance and stability capability of the system.Moreover,a discrete-time sliding mode control strategy based on Kalman filter method was designed,and Kalman filter was employed to eliminate the influence of system noise.Simulation results show that there is no chattering phenomenon in the output of controller and the state variables of controlled system,and the proposed algorithm is also feasible and has strong robustness to external disturbances.
文摘Implementation of efficient vibration control schemes for seismically excited structures is becoming more and more important in recent years.In this study,the influence of different control schemes on the dynamic performance of a frame structure excited by El Centro wave,with an emphasis on reaching law based control strategies,is examined.Reaching law refers to the reachable problem and criteria for the sliding state of a control system.Three reaching laws are designed to present different sliding mode control strategies by incorporating a state space model that describes structural dynamic characteristics of a frame structure.Both intact and damaged structures are studied by using the aforementioned control strategies.The influence of different structural damage extents,control locations and reaching law based control methods are further investigated.The results show that the structure can be well controlled using the sliding mode strategy when the induced structural damage extent does not exceed the standard percentage for considering the structure was damaged,which is 20%reduction in structure stiffness,as reported in the literature.The control effectiveness is more satisfactory if the control location is the same as the direction of external excitation.Furthermore,to study the chattering phenomenon of the sliding mode control method,approximation and detail components extracted from the phase plots of the sliding mode control system are compared via wavelet transform at different scales.The results show that for the same type of control law,the system behaves with similar chattering phenomenon.
基金supported by the National Natural Science Foundation of China(Nos.61803312,91848205 and 61725303).
文摘Forward and backward reaching inverse kinematics(FABRIK)is an efficient two-stage iterative solver for inverse kinematics of spherical-joint manipulator without the calculation of Jacobian matrix.Based on FABRIK,this paper presents an incremental control scheme for a free-floating space manipulator consists of revolute joints and rigid links with the consideration of joint constraints and dynamic coupling effect.Due to the characteristics of FABRIK,it can induce large angular movements on specific joints.Apart from that,FABRIK maps three dimensional(3D)problem into two dimensional(2D)problem by a simple geometric projection.This operation can cause infinite loops in some cases.In order to overcome these issues and apply FABRIK on space manipulators,an increments allocation method is developed to constrain the angular movements as well as to re-orient the end-effector.The manipulator is re-positioned based on the momentum conservation law.Instead of pure target position tracking,the orientation control of the end-effector is also considered.Numerical simulation is performed to testify and demonstrate the effectiveness and reliability of the proposed incremental control approach.
文摘This paper develops a discrete-time sliding mode controller with a power rate exponential reaching law approach to enhance the performance of a pneumatic artificial muscle system in both reaching time and chattering reduction.The proposed method dynamically adapts to the variation of the switching function,which is based on an exponential term and a power rate term of the sliding surface.Thus,the controlled system can achieve high tracking performance while still obtain chattering-free control.Moreover,the effectiveness of the proposed method is validated through multiple experimental tests,focused on a dual pneumatic artificial muscle system.Finally,experimental results show the effectiveness of the proposed approach in this paper.
文摘Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are involved in the SMC operation, namely reaching mode and sliding mode.In the reaching mode, the system state is forced to reach the sliding surface in a finite time.The major drawback of the SMC approach is the occurrence of chattering in the sliding mode, which is undesirable in most applications.Generally, the trade-off between chattering reduction and fast reaching time must be considered in the conventional SMC design.This paper proposes SMC design with a novel reaching law called the exponential rate reaching law(ERRL) to reduce chattering, and the control structure of the converter is designed based on the multiinput SMC that is applied to a three-phase AC/DC power converter.The simulation and experimental results show the effectiveness of the proposed technique.
文摘Hemiparesis is common following stroke. The ability to reach and grasp is a necessary component of many daily life functional tasks, hence reduced upper limb function has an impact on the ability to perform activities of daily living. In hemiparetic patients, the unrestricted and unguided repetition of a motor task may reinforce compensatory movements. Trunk restraint allowed the patients to use joint ranges that were present but not recruited during unrestrained reaching. Later, studies combined the trunk restraint training with additional therapeutic interventions. With the growing number of studies on this intervention in the stroke population, there is the need to consolidate this evidence to determine the potential use of trunk restraint training in improving arm reaching in neurological rehabilitation particularly for stroke patients. A considerable research effort had assessed the effects of trunk restraint training on the recovery of reaching movements in hemiparetic patients. This review identified 5 relevant trials in which one trial is a pilot study. Among 5 trials, three trials recorded the movement kinematics (outcome measure) by Optotrak Motion analysis System, in the other two trials the movement kinematics (outcome measure) were analysed by a 6 – camera, 3D Motion analysis system and 10 – camera Motion Analysis System respectively. The effect size for the intervention was calculated by Cohen’s d. In this review, for the meta-analysis we used trunk displacement, trunk flexion, elbow extension, Smoothness and hand trajectory straightness (movement variables in kinematic analysis). The results of our review demonstrated that the use of trunk restraint as a treatment paradigm aimed at decreasing compensatory strategies has the potential of becoming an effective therapy. Further studies are necessary to determine the long term effect of the trunk restraint training.
文摘I paid great attention to the Alibaba program that nurtures entrepreneurs. We must conduct dialogue with African governments, so that they support young entrepreneurs and cultivate ecommerce systems." These are the words of Dr. Mukhissa Kituyi, secretary general of the United Nations Conference on Trade and Development (UNCTAD), who paid a visit to the headquarters of the Alibaba Group on June 28, 2018 to speak with 29 African entrepreneurs, who were receiving training under the “African Entrepreneur Training Program.”
基金Supported by Pasture Industrialization Technology Research Integration and Application in Mountainous Areas of Guizhou([2014]6017)Phosphate Solubilizing Bacteria Bank Establishment and Phosphate Solubilization Mechanism of Pasture Rhizosphere in Mountainous Areas of Guizhou([2013]2152)
文摘The air temperature of Wuli,which is located in seasonal frozen ground zone,is rising by 13 ℃ yearly.This paper discusses the days that each ground layers' temperature lags behind the surface temperature in reaching extremum.The results were shown:The time of each ground layers' lagging days was increasing;the lagging day in warm season was longer than that in cold season;the growth rate of lagging days in warm season was 0.5 d/y,while the growth rate of lagging days in cold season was 0.7 d/y.
文摘CHINESE and Nigerian media should be aware of their growing influence at home and abroad and should strive to present unbiased news coverage, including stories about each other＇s respective country. Agreement on this important step in ongoing cooperation between the two sides was reached by media representatives attending a me- dia forum on September 19 in Abuja, Nigeria.
文摘To foster a new development paradigm with domestic circulation as the core and domestic and international circulations reinforcing each other,Chinese enterprises are undertaking a lead role in making better use of both domestic and international markets and resources to achieve stronger and more sustainable development and promote construction of an open world economy.Considering the new paradigm,how should Chinese enterprises further develop in the overseas markets?At the Chinese Enterprise Global Image Summit 2020 held in Beijing on November 3,representatives from government departments,business companies,think tanks,and media outlets shared strategies.
文摘Poised on the edge of Northeast Asia,where China meets the Korean Peninsula and Russia’s Far East,Jilin Province emerges as a mosaic-its identity woven from rugged borderlands,industrial legacy and 21st-century ambition.
文摘Chaqg'e is the Chinese moon goddess.Named after'her,the Chang'e-6 lunar module returned to Earth this June carrying 1,935.3 grams of rocks and dust from the far side of the moon.A world first,the unique samples-more viscous and clumpier than previously collected lunar specimens-will be distributed globally for scientific analysis.
基金partially supported by the National Basic Research Program of China(No.2013CBA01505)the Shanghai Excellent Academic Leader Project(No.15XD1502100)+1 种基金the National Natural Science Foundation of China(No.61675130)the National Postdoctoral Program for Innovative Talents(No.190375)
文摘We report a continuous-wave Er：ZBLAN fiber laser with the operation wavelength reaching 3.68 μm.The midinfrared Er：ZBLAN fiber laser is pumped with the dual-wavelength sources consisting of a commercial laser diode at 970 nm and a homemade Tm-doped fiber laser at 1973 nm.By increasing the launched pump power at1973 nm,the laser wavelength can be switched from 3.52 to 3.68 μm.The maximum output power of 0.85 W is obtained with a slope efficiency of 25.14% with respect to the 1973 nm pump power.In the experiment,the laser emission at 3.68 μm is obtained with a significant power of 0.62 W,which is the longest emission wavelength in free-running Er：ZBLAN fiber lasers.
基金supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciencesthe National Natural Science Foundation of China (Nos. 61727821 and 11604353)
文摘We present the long-term stability of the integrating sphere cold atom clock（ISCAC） and analyze its systematic limitations. The relative frequency instability of 2.6 × 10-15 is reached for an averaging time of 2 ×105 s. The second-order Zeeman effect and the cavity pulling effect in ISCAC, which would induce the frequency drift from the clock transition, are analyzed. The analytical and experimental results indicate that the cavity pulling effect is the main contribution to the long-term frequency instability of the ISCAC. Further technical improvements to the microwave cavity are also discussed.
基金supported by the National Natural Science Foundation of China(91216304).
文摘or a hypersonic flight vehicle with highly coupling nonlinear,a sliding mode controller based on reaching law is designed for its longitudinal motion model.Two proposals of reaching law are designed.One of which is a variable exponential reaching law,the other one is compound reaching law which consists of a conventional exponential reaching law and a power rate reaching law.The reaching law controller can speed up the system states arriving at the sliding mode condition,at the same time,it can guarantee better robustness.Simulation analysis is conducted for trimmed cruise condition of 110,000 ft and Mach 15,in which the responses of the vehicle to a step change of altitude and velocity respectively are analyzed.Simulation results show that the controller based on variable exponential reaching law enables the system to faster tracking speed than the conventional reaching law.Moreover the compound reaching law controller has shorter tracking time and strong robustness against parameters uncertainties.
文摘[Objective]Implementation of the Ten-Year Fishing Ban policy may alter fish diversity and niche characteristics of dominant species in spawning grounds within the National Nature Reserve for Rare and Endemic Fish in the Upper Yangtze River.This study initiated continuous monitoring of natural spawning habitats from February 2022 to assess these ecological changes.[Methods]Environmental DNA(eDNA)metabarcoding was employed to analyze fish species composition,biodiversity patterns,and niche parameters of dominant species.Water sampling followed the CEN/TS 19461 standard across five monitoring transects(ZT1-ZT5).[Results]The eDNA analysis detected 45 species of fish belonging to 38 genera,13 families,and 3 orders were detected through environmental DNA(eDNA)in this survey,including 10 species endemic to the upper reaches of the Yangtze River,such as Procypris rabaudi and Myxocyprinus asiaticus.The fish community was mainly composed of bottom-dwelling,settling ovum-producing,omnivorous fish.The variation ranges of the Chao1 index,ACE index,Shannon index,and Simpson index are 736~996,719~965,1.58~3.23,and 0.83~0.99,respectively,indicating that fish species in spawning sites are abundant and community distribution uniformity is high.All indexes are highest at ZT1 monitoring points.Cluster analysis showed that,at a certain similarity level,fish community types in spawning sites could be basically divided into two groups:ZT1,ZT3,and ZT5 clustered together,and ZT2 and ZT4 clustered together,indicating similar fish community habitats.There are 9 dominant fish species in typical deep pool habitats in the reserve,with niche widths(Bi)ranging from 1.13 to 3.87.The dominant fish species are broad and medium niche fish,such as Cyprinus carpio and Hemiculter tchangi,with the niche overlap index(Oik)of some dominant fish species reaching more than 0.95.This indicates fierce competition for resources among the fish in this spawning ground.[Conclusion]The Zhutuo spawning ground demonstrates high species richness with homogeneous community structure and intense resource competition.This study establishes an eDNA-based monitoring framework that enhances conventional survey method,providing critical baseline data for adaptive management under the fishing moratorium regime.
文摘The global issue of climate change presents young entrepreneurs with opportunities to explore new business models.FACED with the severe challenges presented by global climate change,pursuing a green lifestyle is a way to achieve sustainable development.Many countries are exploring ways to reach a balance between economic development and environmental protection.
