BACKGROUND: A national standardized emergency medicine(EM) curriculum for medical students, including specific competencies in procedural skills, are absent in many countries. The development of an intensive simulatin...BACKGROUND: A national standardized emergency medicine(EM) curriculum for medical students, including specific competencies in procedural skills, are absent in many countries. The development of an intensive simulating training program in EM, based on a tight schedule, is anticipated to enhance the competency of medical students.METHODS: A 3-day intensive EM training program, consisting of four procedural skills and 8-hour case-based learning(CBL), was developed by experienced physicians from the EM department in Peking Union Medical College Hospital(PUMCH). Medical students from Peking Union Medical College(PUMC) and Tsinghua University(THU) participated in the training. Three written tests were cautiously designed to examine the short-term(immediately after the program) and long-term(6 months after the program) efficacy of the training. After completion of the training program, an online personal appraisal questionnaire was distributed to the students on WeChat(a mobile messaging App commonly used in China) to achieve anonymous self-evaluation.RESULTS: Ninety-seven out of 101 students completed the intensive training and took all required tests. There was a significant increase in the average score after the intensive simulating training program(pre-training 13.84 vs. 15.57 post-training, P<0.001). Compared with the pre-training test, 63(64.9%) students made progress. There was no significant difference in scores between the tests taken immediately after the program and 6 months later(15.57±2.22 vs. 15.38±2.37, P=0.157). Students rated a higher score in all diseases and procedural skills, and felt that their learning was fruitful.CONCLUSIONS: The introduction of a standardized intensive training program in EM focusing on key competencies can improve clinical confidence, knowledge, and skills of medical students toward the specialty. In addition, having such a program can also enhance student’s interest in EM as a career choice which may enhance recruitment into the specialty and workplace planning.展开更多
The lower limb exoskeletons are used to assist wearers in various scenarios such as medical and industrial settings.Complex modeling errors of the exoskeleton in different application scenarios pose challenges to the ...The lower limb exoskeletons are used to assist wearers in various scenarios such as medical and industrial settings.Complex modeling errors of the exoskeleton in different application scenarios pose challenges to the robustness and stability of its control algorithm.The Radial Basis Function(RBF)neural network is used widely to compensate for modeling errors.In order to solve the problem that the current RBF neural network controllers cannot guarantee the asymptotic stability,a neural network robust control algorithm based on computed torque method is proposed in this paper,focusing on trajectory tracking.It innovatively incorporates the robust adaptive term while introducing the RBF neural network term,improving the compensation ability for modeling errors.The stability of the algorithm is proved by Lyapunov method,and the effectiveness of the robust adaptive term is verified by the simulation.Experiments wearing the exoskeleton under different walking speeds and scenarios were carried out,and the results show that the absolute value of tracking errors of the hip and knee joints of the exoskeleton are consistently less than 1.5°and 2.5°,respectively.The proposed control algorithm effectively compensates for modeling errors and exhibits high robustness.展开更多
Variable stiffness mechanisms(VSMs)are a class of compliant mechanisms that can adjust their intrinsic stiffness,which promises to be beneficial in applications needed to interact with the environment,such as collabor...Variable stiffness mechanisms(VSMs)are a class of compliant mechanisms that can adjust their intrinsic stiffness,which promises to be beneficial in applications needed to interact with the environment,such as collaborative robots,wearable robots,and polishing robots.This paper presents the design and optimization of a novel linear VSM,called cLVSM,to produce linear motion,conversely to the majority of VSMs designed to perform rotary motion.By changing the effective length of specially designed circular beams,the cLVSM is capable of continuous stiffness regulation from a minimum value to almost rigid.Different from the VSMs which need rotation-to-translation converting mechanisms for stiffness regulation,the stiffness of the proposed design is adjusted by directly rotating the beams without the use of additional mechanisms,which contributes to improving the structural compactness,and reducing the energy loss and error in transmission.Moreover,the beam rotation needed to regulate the stiffness is almost perpendicular to the beam deflection force,which helps to reduce the torque needed for stiffness regulation.The stiffness model of the proposed VSM is developed using the screw theory,and the design parameters are optimized using the genetic algorithm.The effectiveness of the mathematical model and the performance of the design are verified by simulation and experiments.展开更多
Lower limb rehabilitation exoskeleton robots integrate sensing, control, and other technologies and exhibit the characteristics of bionics, robotics, information and control science, medicine, and other interdisciplin...Lower limb rehabilitation exoskeleton robots integrate sensing, control, and other technologies and exhibit the characteristics of bionics, robotics, information and control science, medicine, and other interdisciplinary areas. In this review, the typical products and prototypes of lower limb exoskeleton rehabilitation robots are introduced and stateof-the-art techniques are analyzed and summarized. Because the goal of rehabilitation training is to recover patients’ sporting ability to the normal level, studying the human gait is the foundation of lower limb exoskeleton rehabilitation robot research. Therefore, this review critically evaluates research progress in human gait analysis and systematically summarizes developments in the mechanical design and control of lower limb rehabilitation exoskeleton robots. From the performance of typical prototypes, it can be deduced that these robots can be connected to human limbs as wearable forms;further, it is possible to control robot movement at each joint to simulate normal gait and drive the patient’s limb to realize robot-assisted rehabilitation training. Therefore human–robot integration is one of the most important research directions, and in this context, rigid-flexible-soft hybrid structure design, customized personalized gait generation, and multimodal information fusion are three key technologies.展开更多
An online TL （transmission line） impedance TPIS （transmission line parameter identification system） using PMU （phasor measurement unit） was recently developed and implemented at CSG （china southern power grid c...An online TL （transmission line） impedance TPIS （transmission line parameter identification system） using PMU （phasor measurement unit） was recently developed and implemented at CSG （china southern power grid company）, Traditional approaches for TL impedance calculation only approximate the effect of conductor sags and ignore the dependence of impedances on temperature variation. Utilizing PMU measurements may improve the accuracy of TL parameters calculation. The challenge is that the parameters identified are very sensitive to noise and errors in PMU measurements, which are difficult to quantify and can be uncertain under different system operating/loading condition, TPIS provides an innovative yet practical problem formulation for TL sequence parameter estimation based on least-squares with linear constraints. A bootstrapping-based resampling technique is developed and a new metric is proposed to determine the credibility of the estimated sequence impedances. This paper discusses the proposed methodologies, challenges, as well as implementation issues identified during the development of TPIS.展开更多
The paper takes the Shanghai-Nanjing expressway as the research subject and takes the samples of the Total Suspended Particulates (TSP) on both sides of the highway as samples to analyze the pollution and the pattern ...The paper takes the Shanghai-Nanjing expressway as the research subject and takes the samples of the Total Suspended Particulates (TSP) on both sides of the highway as samples to analyze the pollution and the pattern of pollution distribution. The study shows that the concentration of TSP is very high, even six times of the national limit value.展开更多
Summary What is already known about this topic?Myopia has been identified as a significant emerging challenge and policy priority among children and adolescents in China by the Ministry of Education and seven other de...Summary What is already known about this topic?Myopia has been identified as a significant emerging challenge and policy priority among children and adolescents in China by the Ministry of Education and seven other departments.Limited research has been conducted to investigate the collective impact of outdoor time and other modifiable factors on the incidence of myopia.展开更多
Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluores...Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration（FRI） and differential fluorescence spectroscopy（DFS）. Humic-like（H-L） and fulvic-like（F-L） materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5.Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants（p Ka） were calculated by use of results of DFS and the modified Stern-Volmer relationship. The p Kaof H-L, F-L, tryptophan-like and tyrosine-like materials of FA subfractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of p Ka for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like（P-L）materials had greater affinities for protons than did either H-L or F-L materials. The dicarboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.展开更多
What is known as StahPs Theorem in power engineering circles is used to justify a convergence guarantee of the Holomorphic Embedding Method(HEM)as it applies to powerflow(PF)problem.In this two-part paper,we examine i...What is known as StahPs Theorem in power engineering circles is used to justify a convergence guarantee of the Holomorphic Embedding Method(HEM)as it applies to powerflow(PF)problem.In this two-part paper,we examine in more detail the implications of Stahl's theorems to both theoretical and numerical convergence for a wider range of problems to which these theorems are now being applied.We show that the difference between StahPs extremal domain and the function's domain is responsible for theoretical nonconvergence and that the fundamental cause of numerical nonconvergence is the magnitude of logarithmic capacity of the branch cut,a concept central to understanding nonconvergence.We introduce theorems using the necessary mathematical parlance and then translate the language to show its implications to convergence of nonlinear problems in general and specifically to the PF problem.We show that,among other possibilities,the existence of Chebotarev points,which are embedding specific,are a possible theoretical impediment to convergence・The theoretical foundation of Part I is necessary for understanding the numerical behavior of HEM discussed in Part II.展开更多
What has become known as Stahl's Theorem in power-engineering circles has been used to justify a convergence guarantee of the Holomorphic Embedding Method(HEM)as it applies to the power-flow problem.In this,the se...What has become known as Stahl's Theorem in power-engineering circles has been used to justify a convergence guarantee of the Holomorphic Embedding Method(HEM)as it applies to the power-flow problem.In this,the second part of a two-part paper,we examine implications to numerical convergence of the HEM and the numerical properties of a Pade approximant algorithm.We show that even if the point of interest is within the convergence domain,numerical convergence of the sequence of Pade approximants computed with finite precision is not guaranteed.We propose a convergence factor equation that can be used to both estimate the convergence rate and the capacity of the branch cut.We also show that the study of convergence properties of the Pade approximant is the study of the location of the branch-points of the function,which in turn dictate branch-cut topology and capacity and,therefore,convergence rate.展开更多
This article is the second part of Active Power Correction Strategies Based on Deep Reinforcement Learning.In Part II,we consider the renewable energy scenarios plugged into the large-scale power grid and provide an a...This article is the second part of Active Power Correction Strategies Based on Deep Reinforcement Learning.In Part II,we consider the renewable energy scenarios plugged into the large-scale power grid and provide an adaptive algorithmic implementation to maintain power grid stability.Based on the robustness method in Part I,a distributed deep reinforcement learning method is proposed to overcome the infuence of the increasing renewable energy penetration.A multi-agent system is implemented in multiple control areas of the power system,which conducts a fully cooperative stochastic game.Based on the Monte Carlo tree search mentioned in Part I,we select practical actions in each sub-control area to search the Nash equilibrium of the game.Based on the QMIX method,a structure of offine centralized training and online distributed execution is proposed to employ better practical actions in the active power correction control.Our proposed method is evaluated in the modified global competition scenario cases of“2020 Learning to Run a Power Network.Neurips Track 2”.展开更多
This paper proposes a voltage stability constrained optimal power flow(VSC-OPF)for an unbalanced distribution system with distributed generators(DGs)based on semidefinite programming(SDP).The AC optimal power flow(ACO...This paper proposes a voltage stability constrained optimal power flow(VSC-OPF)for an unbalanced distribution system with distributed generators(DGs)based on semidefinite programming(SDP).The AC optimal power flow(ACOPF)for unbalanced distribution systems is formulated as a chordal relaxation-based SDP model.The minimal singular value(MSV)of the power flow Jacobian matrix is adopted to indicate the voltage stability margin.The Jacobian matrix can be explicitly expressed by ACOPF state variables.The nonlinear constraint on the Jacobian MSV is then replaced with its maximal convex subset using linear matrix inequality(LMI),which can be incorporated in the SDP-based ACOPF formulation.A penalty technique is leveraged to improve the exactness of the SDP relaxation.Case studies performed on several IEEE test systems validate the effectiveness of the proposed method.展开更多
Online estimation of electromechanical oscillation parameters provides essential information to prevent system instability and blackout and helps to identify event categories and locations.We formulate the problem as ...Online estimation of electromechanical oscillation parameters provides essential information to prevent system instability and blackout and helps to identify event categories and locations.We formulate the problem as a state space model and employ the extended Kalman filter to estimate oscillation frequencies and damping factors directly based on data from phasor measurement units.Due to considerations of communication burdens and privacy concerns,a fully distributed algorithm is proposed using diffusion extended Kalman filter.The effectiveness of proposed algorithms is confirmed by both simulated and real data collected during events in State Grid Jiangsu Electric Power Company.展开更多
Background Menarche is a substantial milestone of female puberty.Timing of age at menarche is considered the key to understanding the potential linkages with women’s health outcomes later in life.This study aimed to ...Background Menarche is a substantial milestone of female puberty.Timing of age at menarche is considered the key to understanding the potential linkages with women’s health outcomes later in life.This study aimed to explore the secular trends and urban‒rural disparities in the median age at menarche among Chinese Han girls from 1985 to 2019.Methods Data were extracted from the 1985,1995,2005,2014,and 2019 Chinese National Surveys on Students’Constitution and Health,which were nationally representative cross-sectional studies,and a total of 173,535 Han girls aged 9–18 years were examined.Girls were asked whether menarche had occurred.The median age at menarche was estimated by probit analysis.Z tests were used to compare the differences between survey years and between urban and rural areas.Results The median age at menarche among Chinese Han girls decreased from 13.37 years in 1985 to 12.00 years in 2019,and the overall decrease was more significant in rural areas(1.77 years)than in urban areas(0.99 years).The average five-year change in the decrease in the median age at menarche showed an accelerating and then slowing pace;and it was observed similarly in both urban and rural areas.The urban‒rural disparities shrank from 0.64 years in 1985 to 0.44 years in 1995,then to 0.27 years in 2005,0.24 years in 2014,and finally to−0.14 years in 2019.Conclusions The median age at menarche among Chinese Han girls continued to decline from 1985 to 2019 but at a slowing pace in the last five years.Urban‒rural disparities gradually narrowed.Sexual and reproductive health education and interventions to prevent the decline in the age of menarche are needed,especially in rural areas.展开更多
WITH the increasing integration of renewable energies,power electronic devices and flexible loads,modern power systems are becoming more sophisticated and facing higher uncertainty.Traditional model-based methods cann...WITH the increasing integration of renewable energies,power electronic devices and flexible loads,modern power systems are becoming more sophisticated and facing higher uncertainty.Traditional model-based methods cannot fully satisfy the analysis and control requirements of modern power systems duo to its complexity and uncertainty.展开更多
Controlled islanding is considered to be the last countermeasure to prevent a system-wide blackout in case of cascading failures.It splits the system into self-sustained islands to maintain transient stability at the ...Controlled islanding is considered to be the last countermeasure to prevent a system-wide blackout in case of cascading failures.It splits the system into self-sustained islands to maintain transient stability at the expense of possible loss of load.Generator coherence identification is critical to controlled islanding scheme as it helps identify the optimal cut-set to maintain the transient stability of the post-islanding systems.This paper presents a novel approach for online generator coherency identification using phasor measurement unit(PMU) data and dynamic time warping(DTW).Results from the coherence identification are used to further cluster non-generator buses using spectral clustering with the objective of minimizing power flow disruptions.The proposed approach is validated and compared to existing methods on the IEEE39-bus system and WECC 179-bus system, through which its advantages are demonstrated.展开更多
基金supported by grants from Chinese Academy of Medical Science Teaching Reform Research Fund(2018zlgc0101)Chinese Academy of Medical Science Online Open Course Construction Fund(J2009022861)+1 种基金CAMS Innovation Fund for Medical Sciences(CIFMS)(serial number 2021-1-I2M-020)CAMS Innovation Fund for Medical Sciences(CIFMS)(serial number 2020-I2M-C&T-B-014).
文摘BACKGROUND: A national standardized emergency medicine(EM) curriculum for medical students, including specific competencies in procedural skills, are absent in many countries. The development of an intensive simulating training program in EM, based on a tight schedule, is anticipated to enhance the competency of medical students.METHODS: A 3-day intensive EM training program, consisting of four procedural skills and 8-hour case-based learning(CBL), was developed by experienced physicians from the EM department in Peking Union Medical College Hospital(PUMCH). Medical students from Peking Union Medical College(PUMC) and Tsinghua University(THU) participated in the training. Three written tests were cautiously designed to examine the short-term(immediately after the program) and long-term(6 months after the program) efficacy of the training. After completion of the training program, an online personal appraisal questionnaire was distributed to the students on WeChat(a mobile messaging App commonly used in China) to achieve anonymous self-evaluation.RESULTS: Ninety-seven out of 101 students completed the intensive training and took all required tests. There was a significant increase in the average score after the intensive simulating training program(pre-training 13.84 vs. 15.57 post-training, P<0.001). Compared with the pre-training test, 63(64.9%) students made progress. There was no significant difference in scores between the tests taken immediately after the program and 6 months later(15.57±2.22 vs. 15.38±2.37, P=0.157). Students rated a higher score in all diseases and procedural skills, and felt that their learning was fruitful.CONCLUSIONS: The introduction of a standardized intensive training program in EM focusing on key competencies can improve clinical confidence, knowledge, and skills of medical students toward the specialty. In addition, having such a program can also enhance student’s interest in EM as a career choice which may enhance recruitment into the specialty and workplace planning.
基金Supported by National Key R&D Program of China(Grant No.2022YFB4701200)National Natural Science Foundation of China(NSFC)(Grant Nos.T2121003,52205004).
文摘The lower limb exoskeletons are used to assist wearers in various scenarios such as medical and industrial settings.Complex modeling errors of the exoskeleton in different application scenarios pose challenges to the robustness and stability of its control algorithm.The Radial Basis Function(RBF)neural network is used widely to compensate for modeling errors.In order to solve the problem that the current RBF neural network controllers cannot guarantee the asymptotic stability,a neural network robust control algorithm based on computed torque method is proposed in this paper,focusing on trajectory tracking.It innovatively incorporates the robust adaptive term while introducing the RBF neural network term,improving the compensation ability for modeling errors.The stability of the algorithm is proved by Lyapunov method,and the effectiveness of the robust adaptive term is verified by the simulation.Experiments wearing the exoskeleton under different walking speeds and scenarios were carried out,and the results show that the absolute value of tracking errors of the hip and knee joints of the exoskeleton are consistently less than 1.5°and 2.5°,respectively.The proposed control algorithm effectively compensates for modeling errors and exhibits high robustness.
基金Supported by National Key R&D Program of China(Grant No.2022YFB4701200)Ningbo Municipal Key Projects of Science and Technology Innovation 2025 Plan(Grant No.2022Z070)National Natural Science Foundation of China(Grant No.52205004).
文摘Variable stiffness mechanisms(VSMs)are a class of compliant mechanisms that can adjust their intrinsic stiffness,which promises to be beneficial in applications needed to interact with the environment,such as collaborative robots,wearable robots,and polishing robots.This paper presents the design and optimization of a novel linear VSM,called cLVSM,to produce linear motion,conversely to the majority of VSMs designed to perform rotary motion.By changing the effective length of specially designed circular beams,the cLVSM is capable of continuous stiffness regulation from a minimum value to almost rigid.Different from the VSMs which need rotation-to-translation converting mechanisms for stiffness regulation,the stiffness of the proposed design is adjusted by directly rotating the beams without the use of additional mechanisms,which contributes to improving the structural compactness,and reducing the energy loss and error in transmission.Moreover,the beam rotation needed to regulate the stiffness is almost perpendicular to the beam deflection force,which helps to reduce the torque needed for stiffness regulation.The stiffness model of the proposed VSM is developed using the screw theory,and the design parameters are optimized using the genetic algorithm.The effectiveness of the mathematical model and the performance of the design are verified by simulation and experiments.
基金Supported by National Key R&D Program of China(Grant No.2016YFE0105000)National Natural Science Foundation of China(Grant No.91848104)
文摘Lower limb rehabilitation exoskeleton robots integrate sensing, control, and other technologies and exhibit the characteristics of bionics, robotics, information and control science, medicine, and other interdisciplinary areas. In this review, the typical products and prototypes of lower limb exoskeleton rehabilitation robots are introduced and stateof-the-art techniques are analyzed and summarized. Because the goal of rehabilitation training is to recover patients’ sporting ability to the normal level, studying the human gait is the foundation of lower limb exoskeleton rehabilitation robot research. Therefore, this review critically evaluates research progress in human gait analysis and systematically summarizes developments in the mechanical design and control of lower limb rehabilitation exoskeleton robots. From the performance of typical prototypes, it can be deduced that these robots can be connected to human limbs as wearable forms;further, it is possible to control robot movement at each joint to simulate normal gait and drive the patient’s limb to realize robot-assisted rehabilitation training. Therefore human–robot integration is one of the most important research directions, and in this context, rigid-flexible-soft hybrid structure design, customized personalized gait generation, and multimodal information fusion are three key technologies.
文摘An online TL （transmission line） impedance TPIS （transmission line parameter identification system） using PMU （phasor measurement unit） was recently developed and implemented at CSG （china southern power grid company）, Traditional approaches for TL impedance calculation only approximate the effect of conductor sags and ignore the dependence of impedances on temperature variation. Utilizing PMU measurements may improve the accuracy of TL parameters calculation. The challenge is that the parameters identified are very sensitive to noise and errors in PMU measurements, which are difficult to quantify and can be uncertain under different system operating/loading condition, TPIS provides an innovative yet practical problem formulation for TL sequence parameter estimation based on least-squares with linear constraints. A bootstrapping-based resampling technique is developed and a new metric is proposed to determine the credibility of the estimated sequence impedances. This paper discusses the proposed methodologies, challenges, as well as implementation issues identified during the development of TPIS.
文摘The paper takes the Shanghai-Nanjing expressway as the research subject and takes the samples of the Total Suspended Particulates (TSP) on both sides of the highway as samples to analyze the pollution and the pattern of pollution distribution. The study shows that the concentration of TSP is very high, even six times of the national limit value.
基金by the China Medical Board(Grant#21-434 to YS)Capital’s Funds for Health Improvement and Research(2022-1G-4251 to YS).
文摘Summary What is already known about this topic?Myopia has been identified as a significant emerging challenge and policy priority among children and adolescents in China by the Ministry of Education and seven other departments.Limited research has been conducted to investigate the collective impact of outdoor time and other modifiable factors on the incidence of myopia.
基金supported by the National Natural Science Foundation of China(Nos.41173084,41521003,41573130,41630645,41703115 and 41503104)the Beijing Natural Science Foundation(No.8162044)the Canada Research Chair program,Einstein Professor Program of the Chinese Academy of Sciences,and the High Level Foreign Experts Program(#GDT20143200016)
文摘Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration（FRI） and differential fluorescence spectroscopy（DFS）. Humic-like（H-L） and fulvic-like（F-L） materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5.Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants（p Ka） were calculated by use of results of DFS and the modified Stern-Volmer relationship. The p Kaof H-L, F-L, tryptophan-like and tyrosine-like materials of FA subfractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of p Ka for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like（P-L）materials had greater affinities for protons than did either H-L or F-L materials. The dicarboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.
基金supported by the Science and Technology Project of SGCC(No.5455HJ160007).
文摘What is known as StahPs Theorem in power engineering circles is used to justify a convergence guarantee of the Holomorphic Embedding Method(HEM)as it applies to powerflow(PF)problem.In this two-part paper,we examine in more detail the implications of Stahl's theorems to both theoretical and numerical convergence for a wider range of problems to which these theorems are now being applied.We show that the difference between StahPs extremal domain and the function's domain is responsible for theoretical nonconvergence and that the fundamental cause of numerical nonconvergence is the magnitude of logarithmic capacity of the branch cut,a concept central to understanding nonconvergence.We introduce theorems using the necessary mathematical parlance and then translate the language to show its implications to convergence of nonlinear problems in general and specifically to the PF problem.We show that,among other possibilities,the existence of Chebotarev points,which are embedding specific,are a possible theoretical impediment to convergence・The theoretical foundation of Part I is necessary for understanding the numerical behavior of HEM discussed in Part II.
基金supported by the Science and Technology Project of SGCC(No.5455HJ160007).
文摘What has become known as Stahl's Theorem in power-engineering circles has been used to justify a convergence guarantee of the Holomorphic Embedding Method(HEM)as it applies to the power-flow problem.In this,the second part of a two-part paper,we examine implications to numerical convergence of the HEM and the numerical properties of a Pade approximant algorithm.We show that even if the point of interest is within the convergence domain,numerical convergence of the sequence of Pade approximants computed with finite precision is not guaranteed.We propose a convergence factor equation that can be used to both estimate the convergence rate and the capacity of the branch cut.We also show that the study of convergence properties of the Pade approximant is the study of the location of the branch-points of the function,which in turn dictate branch-cut topology and capacity and,therefore,convergence rate.
基金supported by the National Key R&D Program of China under Grant 2018AAA0101502.
文摘This article is the second part of Active Power Correction Strategies Based on Deep Reinforcement Learning.In Part II,we consider the renewable energy scenarios plugged into the large-scale power grid and provide an adaptive algorithmic implementation to maintain power grid stability.Based on the robustness method in Part I,a distributed deep reinforcement learning method is proposed to overcome the infuence of the increasing renewable energy penetration.A multi-agent system is implemented in multiple control areas of the power system,which conducts a fully cooperative stochastic game.Based on the Monte Carlo tree search mentioned in Part I,we select practical actions in each sub-control area to search the Nash equilibrium of the game.Based on the QMIX method,a structure of offine centralized training and online distributed execution is proposed to employ better practical actions in the active power correction control.Our proposed method is evaluated in the modified global competition scenario cases of“2020 Learning to Run a Power Network.Neurips Track 2”.
基金funded by State Grid Corporation of China(SGCC)under project“Hybrid Energy Storage Management Platform for Integrated Energy System”(No.SGGR0000DLJS1800932).
文摘This paper proposes a voltage stability constrained optimal power flow(VSC-OPF)for an unbalanced distribution system with distributed generators(DGs)based on semidefinite programming(SDP).The AC optimal power flow(ACOPF)for unbalanced distribution systems is formulated as a chordal relaxation-based SDP model.The minimal singular value(MSV)of the power flow Jacobian matrix is adopted to indicate the voltage stability margin.The Jacobian matrix can be explicitly expressed by ACOPF state variables.The nonlinear constraint on the Jacobian MSV is then replaced with its maximal convex subset using linear matrix inequality(LMI),which can be incorporated in the SDP-based ACOPF formulation.A penalty technique is leveraged to improve the exactness of the SDP relaxation.Case studies performed on several IEEE test systems validate the effectiveness of the proposed method.
基金This work is supported by the Science and Technology Project of State Grid Corporation(No.5455HJ160007).
文摘Online estimation of electromechanical oscillation parameters provides essential information to prevent system instability and blackout and helps to identify event categories and locations.We formulate the problem as a state space model and employ the extended Kalman filter to estimate oscillation frequencies and damping factors directly based on data from phasor measurement units.Due to considerations of communication burdens and privacy concerns,a fully distributed algorithm is proposed using diffusion extended Kalman filter.The effectiveness of proposed algorithms is confirmed by both simulated and real data collected during events in State Grid Jiangsu Electric Power Company.
基金The present study was funded by National Natural Science Foundation(82273654 to Y.S.)。
文摘Background Menarche is a substantial milestone of female puberty.Timing of age at menarche is considered the key to understanding the potential linkages with women’s health outcomes later in life.This study aimed to explore the secular trends and urban‒rural disparities in the median age at menarche among Chinese Han girls from 1985 to 2019.Methods Data were extracted from the 1985,1995,2005,2014,and 2019 Chinese National Surveys on Students’Constitution and Health,which were nationally representative cross-sectional studies,and a total of 173,535 Han girls aged 9–18 years were examined.Girls were asked whether menarche had occurred.The median age at menarche was estimated by probit analysis.Z tests were used to compare the differences between survey years and between urban and rural areas.Results The median age at menarche among Chinese Han girls decreased from 13.37 years in 1985 to 12.00 years in 2019,and the overall decrease was more significant in rural areas(1.77 years)than in urban areas(0.99 years).The average five-year change in the decrease in the median age at menarche showed an accelerating and then slowing pace;and it was observed similarly in both urban and rural areas.The urban‒rural disparities shrank from 0.64 years in 1985 to 0.44 years in 1995,then to 0.27 years in 2005,0.24 years in 2014,and finally to−0.14 years in 2019.Conclusions The median age at menarche among Chinese Han girls continued to decline from 1985 to 2019 but at a slowing pace in the last five years.Urban‒rural disparities gradually narrowed.Sexual and reproductive health education and interventions to prevent the decline in the age of menarche are needed,especially in rural areas.
文摘WITH the increasing integration of renewable energies,power electronic devices and flexible loads,modern power systems are becoming more sophisticated and facing higher uncertainty.Traditional model-based methods cannot fully satisfy the analysis and control requirements of modern power systems duo to its complexity and uncertainty.
基金supported by SGCC Science and Technology Program (No.5455HJ160007)
文摘Controlled islanding is considered to be the last countermeasure to prevent a system-wide blackout in case of cascading failures.It splits the system into self-sustained islands to maintain transient stability at the expense of possible loss of load.Generator coherence identification is critical to controlled islanding scheme as it helps identify the optimal cut-set to maintain the transient stability of the post-islanding systems.This paper presents a novel approach for online generator coherency identification using phasor measurement unit(PMU) data and dynamic time warping(DTW).Results from the coherence identification are used to further cluster non-generator buses using spectral clustering with the objective of minimizing power flow disruptions.The proposed approach is validated and compared to existing methods on the IEEE39-bus system and WECC 179-bus system, through which its advantages are demonstrated.
