Safety assessment is one of important aspects in health management.In safety assessment for practical systems,three problems exist:lack of observation information,high system complexity and environment interference.Be...Safety assessment is one of important aspects in health management.In safety assessment for practical systems,three problems exist:lack of observation information,high system complexity and environment interference.Belief rule base with attribute reliability(BRB-r)is an expert system that provides a useful way for dealing with these three problems.In BRB-r,once the input information is unreliable,the reliability of belief rule is influenced,which further influences the accuracy of its output belief degree.On the other hand,when many system characteristics exist,the belief rule combination will explode in BRB-r,and the BRB-r based safety assessment model becomes too complicated to be applied.Thus,in this paper,to balance the complexity and accuracy of the safety assessment model,a new safety assessment model based on BRB-r with considering belief rule reliability is developed for the first time.In the developed model,a new calculation method of the belief rule reliability is proposed with considering both attribute reliability and global ignorance.Moreover,to reduce the influence of uncertainty of expert knowledge,an optimization model for the developed safety assessment model is constructed.A case study of safety assessment of liquefied natural gas(LNG)storage tank is conducted to illustrate the effectiveness of the new developed model.展开更多
This paper is focused on developing a tracking controller for a hypersonic cruise vehicle using tangent linearization approach.The design of flight control systems for air-breathing hypersonic vehicles is a highly cha...This paper is focused on developing a tracking controller for a hypersonic cruise vehicle using tangent linearization approach.The design of flight control systems for air-breathing hypersonic vehicles is a highly challenging task due to the unique characteristics of the vehicle dynamics.Motivated by recent results on tangent linearization control,the tracking control problem for the hypersonic cruise vehicle is reduced to that of a feedback stabilizing controller design for a linear time-varying system which can be accomplished by a standard design method of frozen-time control.Through a proper model transformation,it can be proven that the tracking error of the designed closed-loop system decays exponentially.Simulation studies are conducted for trimmed cruise conditions of 110000 ft and Mach 15 where the responses of the vehicle to step changes in altitude and velocity are evaluated.The effectiveness of the controller is demonstrated by simulation results.展开更多
Remaining useful life(RUL)estimation approaches on the basis of the degradation data have been greatly developed,and significant advances have been witnessed.Establishing an applicable degradation model of the system ...Remaining useful life(RUL)estimation approaches on the basis of the degradation data have been greatly developed,and significant advances have been witnessed.Establishing an applicable degradation model of the system is the foundation and key to accurately estimating its RUL.Most current researches focus on age-dependent degradation models,but it has been found that some degradation processes in engineering are also related to the degradation states themselves.In addition,due to different working conditions and complex environments in engineering,the problems of the unit-to-unit variability in the degradation process of the same batch of systems and actual degradation states cannot be directly observed will affect the estimation accuracy of the RUL.In order to solve the above issues jointly,we develop an age-dependent and state-dependent nonlinear degradation model taking into consideration the unit-to-unit variability and hidden degradation states.Then,the Kalman filter(KF)is utilized to update the hidden degradation states in real time,and the expectation-maximization(EM)algorithm is applied to adaptively estimate the unknown model parameters.Besides,the approximate analytical RUL distribution can be obtained from the concept of the first hitting time.Once the new observation is available,the RUL distribution can be updated adaptively on the basis of the updated degradation states and model parameters.The effectiveness and accuracy of the proposed approach are shown by a numerical simulation and case studies for Li-ion batteries and rolling element bearings.展开更多
Colorectal cancer(CRC)is a type of malignant tumor that seriously threatens human health and life,and its treatment has always been a difficulty and hotspot in research.Herein,this study for the first time reports tha...Colorectal cancer(CRC)is a type of malignant tumor that seriously threatens human health and life,and its treatment has always been a difficulty and hotspot in research.Herein,this study for the first time reports that antipsychotic aripiprazole(Ari)against the proliferation of CRC cells both in vitro and in vivo,but with less damage in normal colon cells.Mechanistically,the results showed that5-hydroxytryptamine 2B receptor(HTR2B)and its coupling protein G protein subunit alpha q(Gaq)were highly distributed in CRC cells.Ari had a strong affinity with HTR2B and inhibited HTR2B downstream signaling.Blockade of HTR2B signaling suppressed the growth of CRC cells,but HTR2B was not found to have independent anticancer activity.Interestingly,the binding of Gaq to HTR2B was decreased after Ari treatment.Knockdown of Gaq not only restricted CRC cell growth,but also directly affected the antiCRC efficacy of Ari.Moreover,an interaction between Ari and Gaq was found in that the mutation at amino acid 190 of Gaq reduced the efficacy of Ari.Thus,these results confirm that Gaq coupled to HTR2B was a potential target of Ari in mediating CRC proliferation.Collectively,this study provides a novel effective strategy for CRC therapy and favorable evidence for promoting Ari as an anticancer agent.展开更多
航天继电器作为液体运载火箭等大型结构件复杂电子系统中的关键部件之一,其工作状态直接决定整个系统能否正常工作.本文针对航天继电器使用过程中所面临的高价值样本缺乏、系统复杂、复杂环境干扰等难题,基于考虑属性可靠度的置信规则库...航天继电器作为液体运载火箭等大型结构件复杂电子系统中的关键部件之一,其工作状态直接决定整个系统能否正常工作.本文针对航天继电器使用过程中所面临的高价值样本缺乏、系统复杂、复杂环境干扰等难题,基于考虑属性可靠度的置信规则库(belief rule base with attribute reliability,BRB-r)专家系统提出了一种新的考虑环境干扰的航天继电器故障诊断与容错控制框架.在所提出的新框架中,对航天继电器输出监测指标进行分析,基于BRB-r建立航天继电器故障诊断模型,通过其工作状态评估结果,分为功能正常、功能缺陷和功能丧失3种;然后,针对3种状态分别设计3种控制策略:保持原控制输入、重构控制率和切换备份继电器.本文所提方法通过实验室所搭建的JRC-7M航天继电器测试系统进行了实验验证.展开更多
This paper investigates a switching control strategy for the altitude motion of a morphing aircraft with variable sweep wings based on Q-learning.The morphing process is regarded as a function of the system states and...This paper investigates a switching control strategy for the altitude motion of a morphing aircraft with variable sweep wings based on Q-learning.The morphing process is regarded as a function of the system states and a related altitude motion model is established.Then,the designed controller is divided into the outer part and inner part,where the outer part is devised by a combination of the back-stepping method and command filter technique so that the’explosion of complexity’problem is eliminated.Moreover,the integrator structure of the altitude motion model is exploited to simplify the back-stepping design,and disturbance observers inspired from the idea of extended state observer are devised to obtain estimations of the system disturbances.The control input switches from the outer part to the inner part when the altitude tracking error converges to a small value and linear approximation of the altitude motion model is applied.The inner part is generated by the Q-learning algorithm which learns the optimal command in the presence of unknown system matrices and disturbances.It is proved rigorously that all signals of the closed-loop system stay bounded by the developed control method and controller switching occurs only once.Finally,comparative simulations are conducted to validate improved control performance of the proposed scheme.展开更多
As the key part of Prognostics and Health Management(PHM), Remaining Useful Life(RUL) estimation has been extensively investigated in recent years. Current RUL estimation studies considering the intervention of im...As the key part of Prognostics and Health Management(PHM), Remaining Useful Life(RUL) estimation has been extensively investigated in recent years. Current RUL estimation studies considering the intervention of imperfect maintenance activities usually assumed that maintenance activities have a single influence on the degradation level or degradation rate, but not on both.Aimed at this problem, this paper proposes a new degradation modeling and RUL estimation method taking the influence of imperfect maintenance activities on both the degradation level and the degradation rate into account. Toward this end, a stochastic degradation model considering imperfect maintenance activities is firstly constructed based on the diffusion process. Then, the Probability Density Function(PDF) of the RUL is derived by the convolution operator under the concept of First Hitting Time(FHT). To implement the proposed RUL estimation method,the Maximum Likelihood Estimation(MLE) is utilized to estimate the degradation related parameters based on the Condition Monitoring(CM) data, while the Bayesian method is utilized to estimate the maintenance related parameters based on the maintenance data. Finally, a numerical example and a practical case study are provided to demonstrate the superiority of the proposed method. The experimental results show that the proposed method could greatly improve the RUL estimation accuracy for the degrading equipment subjected to imperfect maintenance activities.展开更多
Mycophenolic acid(MPA,1)and its derivatives are first-line immunosuppressants used in organ transplantation and for treating autoimmune diseases.Despite chemical synthetic achievements,the biosynthetic formation of a ...Mycophenolic acid(MPA,1)and its derivatives are first-line immunosuppressants used in organ transplantation and for treating autoimmune diseases.Despite chemical synthetic achievements,the biosynthetic formation of a seven-carbon carboxylic acid pharmacophore side chain of 1,especially the processes involving the cleavage of the prenyl side chain between DHMP(4)and DMMPA(5),remains unknown.In this work,we identified a membrane-bound prenyltransferase,PgMpaA,that transfers FPP to 4 to yield FDHMP(6).Compound 6 undergoes the first cleavage step via a new globin-like enzyme PgMpaB to form a cryptic intermediate 12.Heterologous expression of PgMpa genes in Aspergillus nidulans demonstrates that the second cleavage step(from 12 to 5)of 1 is a PgMpa clusterindependent process in vivo.Our results,especially the discovery of the broad tolerance of substrates recognized by PgMpaB,set up a strategy for the formation of"pseudo-isopentenyl"natural products using fungal globin-like enzymes.展开更多
The composition of the modern aerospace system becomes more and more complex.The performance degradation of any device in the system may cause it difficult for the whole system to keep normal working states.Therefore,...The composition of the modern aerospace system becomes more and more complex.The performance degradation of any device in the system may cause it difficult for the whole system to keep normal working states.Therefore,it is essential to evaluate the performance of complex aerospace systems.In this paper,the performance evaluation of complex aerospace systems is regarded as a Multi-Attribute Decision Analysis(MADA)problem.Based on the structure and working principle of the system,a new Evidential Reasoning(ER)based approach with uncertain parameters is proposed to construct a nonlinear optimization model to evaluate the system performance.In the model,the interval form is used to express the uncertainty,such as error in testing data and inaccuracy in expert knowledge.In order to analyze the subsystems that have a great impact on the performance of the system,the sensitivity analysis of the evaluation result is carried out,and the corresponding maintenance strategy is proposed.For a type of Inertial Measurement Unit(IMU)used in a rocket,the proposed method is employed to evaluate its performance.Then,the parameter sensitivity of the evaluation result is analyzed,and the main factors affecting the performance of IMU are obtained.Finally,the comparative study shows the effectiveness of the proposed method.展开更多
Dear Editor,Polyene macrolides are a group of natural products with potent antifungal activity (Caffrey et al., 2016). Candicidin/FR-008, a potent broad-spectrum anti-fungal agent, is produced by several Streptomycete...Dear Editor,Polyene macrolides are a group of natural products with potent antifungal activity (Caffrey et al., 2016). Candicidin/FR-008, a potent broad-spectrum anti-fungal agent, is produced by several Streptomycetes, including Streptomycetes sp. strain FR-008 (Chen et al., 2003), S. griseus 3570(Campelo and Gil, 2002) and S. albus J1074 (Olano et al.,2014). Due to its medical importance, considerable effort has been applied to elucidate its biosynthetic pathway and identify key regulatory genes (Chen et al., 2003;Zhang et al.,2015).展开更多
The design of the gain-scheduled H_(2)/H_(∞)filter for polytopic discrete-time systems is investigated.By introducing additional slack variables,a new mixed H_(2)/H_(∞)performance criterion is proposed,which provide...The design of the gain-scheduled H_(2)/H_(∞)filter for polytopic discrete-time systems is investigated.By introducing additional slack variables,a new mixed H_(2)/H_(∞)performance criterion is proposed,which provides a decoupling between the Lyapunov matrix and system matrices.Based on the new performance criterion,a sufficient condition for the existence of the gain-scheduled H_(2)/H_(∞)filter is derived.Furthermore,the filter design problem is converted into a convex optimization problem with linear matrix inequality(LMI)constraints.Simulation results show the effectiveness of the proposed approach.展开更多
基金supported in part by the National Natural Science Foundation of China(61833016,61751304,61873273,61702142,61773388)the Key Research and Development Plan of Hainan(ZDYF2019007)Shaanxi Outstanding Youth Science Foundation(2020JC-34)。
文摘Safety assessment is one of important aspects in health management.In safety assessment for practical systems,three problems exist:lack of observation information,high system complexity and environment interference.Belief rule base with attribute reliability(BRB-r)is an expert system that provides a useful way for dealing with these three problems.In BRB-r,once the input information is unreliable,the reliability of belief rule is influenced,which further influences the accuracy of its output belief degree.On the other hand,when many system characteristics exist,the belief rule combination will explode in BRB-r,and the BRB-r based safety assessment model becomes too complicated to be applied.Thus,in this paper,to balance the complexity and accuracy of the safety assessment model,a new safety assessment model based on BRB-r with considering belief rule reliability is developed for the first time.In the developed model,a new calculation method of the belief rule reliability is proposed with considering both attribute reliability and global ignorance.Moreover,to reduce the influence of uncertainty of expert knowledge,an optimization model for the developed safety assessment model is constructed.A case study of safety assessment of liquefied natural gas(LNG)storage tank is conducted to illustrate the effectiveness of the new developed model.
基金supported by the National Natural Science Foundation of China (6071000260904007)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in Universitythe State Key Laboratory of Robotics and System (SKLRS200801AO3)
文摘This paper is focused on developing a tracking controller for a hypersonic cruise vehicle using tangent linearization approach.The design of flight control systems for air-breathing hypersonic vehicles is a highly challenging task due to the unique characteristics of the vehicle dynamics.Motivated by recent results on tangent linearization control,the tracking control problem for the hypersonic cruise vehicle is reduced to that of a feedback stabilizing controller design for a linear time-varying system which can be accomplished by a standard design method of frozen-time control.Through a proper model transformation,it can be proven that the tracking error of the designed closed-loop system decays exponentially.Simulation studies are conducted for trimmed cruise conditions of 110000 ft and Mach 15 where the responses of the vehicle to step changes in altitude and velocity are evaluated.The effectiveness of the controller is demonstrated by simulation results.
基金supported by the National Key R&D Program of China(2018YFB1306100)the National Natural Science Foundation of China(61922089,61833016,62073336,61903376,61773386)the National Science Foundation of Shannxi Province(2020JQ-489,2020JM-360).
文摘Remaining useful life(RUL)estimation approaches on the basis of the degradation data have been greatly developed,and significant advances have been witnessed.Establishing an applicable degradation model of the system is the foundation and key to accurately estimating its RUL.Most current researches focus on age-dependent degradation models,but it has been found that some degradation processes in engineering are also related to the degradation states themselves.In addition,due to different working conditions and complex environments in engineering,the problems of the unit-to-unit variability in the degradation process of the same batch of systems and actual degradation states cannot be directly observed will affect the estimation accuracy of the RUL.In order to solve the above issues jointly,we develop an age-dependent and state-dependent nonlinear degradation model taking into consideration the unit-to-unit variability and hidden degradation states.Then,the Kalman filter(KF)is utilized to update the hidden degradation states in real time,and the expectation-maximization(EM)algorithm is applied to adaptively estimate the unknown model parameters.Besides,the approximate analytical RUL distribution can be obtained from the concept of the first hitting time.Once the new observation is available,the RUL distribution can be updated adaptively on the basis of the updated degradation states and model parameters.The effectiveness and accuracy of the proposed approach are shown by a numerical simulation and case studies for Li-ion batteries and rolling element bearings.
基金supported by Chongqing basic research and frontier exploration project(cstc2022ycjh-bgzxm0119,China)。
文摘Colorectal cancer(CRC)is a type of malignant tumor that seriously threatens human health and life,and its treatment has always been a difficulty and hotspot in research.Herein,this study for the first time reports that antipsychotic aripiprazole(Ari)against the proliferation of CRC cells both in vitro and in vivo,but with less damage in normal colon cells.Mechanistically,the results showed that5-hydroxytryptamine 2B receptor(HTR2B)and its coupling protein G protein subunit alpha q(Gaq)were highly distributed in CRC cells.Ari had a strong affinity with HTR2B and inhibited HTR2B downstream signaling.Blockade of HTR2B signaling suppressed the growth of CRC cells,but HTR2B was not found to have independent anticancer activity.Interestingly,the binding of Gaq to HTR2B was decreased after Ari treatment.Knockdown of Gaq not only restricted CRC cell growth,but also directly affected the antiCRC efficacy of Ari.Moreover,an interaction between Ari and Gaq was found in that the mutation at amino acid 190 of Gaq reduced the efficacy of Ari.Thus,these results confirm that Gaq coupled to HTR2B was a potential target of Ari in mediating CRC proliferation.Collectively,this study provides a novel effective strategy for CRC therapy and favorable evidence for promoting Ari as an anticancer agent.
文摘航天继电器作为液体运载火箭等大型结构件复杂电子系统中的关键部件之一,其工作状态直接决定整个系统能否正常工作.本文针对航天继电器使用过程中所面临的高价值样本缺乏、系统复杂、复杂环境干扰等难题,基于考虑属性可靠度的置信规则库(belief rule base with attribute reliability,BRB-r)专家系统提出了一种新的考虑环境干扰的航天继电器故障诊断与容错控制框架.在所提出的新框架中,对航天继电器输出监测指标进行分析,基于BRB-r建立航天继电器故障诊断模型,通过其工作状态评估结果,分为功能正常、功能缺陷和功能丧失3种;然后,针对3种状态分别设计3种控制策略:保持原控制输入、重构控制率和切换备份继电器.本文所提方法通过实验室所搭建的JRC-7M航天继电器测试系统进行了实验验证.
基金supported by the National Natural Science Foundation of China(Nos.61873295,61833016)the Aeronautical Science Foundation of China(No.2016ZA51011).
文摘This paper investigates a switching control strategy for the altitude motion of a morphing aircraft with variable sweep wings based on Q-learning.The morphing process is regarded as a function of the system states and a related altitude motion model is established.Then,the designed controller is divided into the outer part and inner part,where the outer part is devised by a combination of the back-stepping method and command filter technique so that the’explosion of complexity’problem is eliminated.Moreover,the integrator structure of the altitude motion model is exploited to simplify the back-stepping design,and disturbance observers inspired from the idea of extended state observer are devised to obtain estimations of the system disturbances.The control input switches from the outer part to the inner part when the altitude tracking error converges to a small value and linear approximation of the altitude motion model is applied.The inner part is generated by the Q-learning algorithm which learns the optimal command in the presence of unknown system matrices and disturbances.It is proved rigorously that all signals of the closed-loop system stay bounded by the developed control method and controller switching occurs only once.Finally,comparative simulations are conducted to validate improved control performance of the proposed scheme.
基金co-supported by the National Science Foundation of China(NSFC)(Nos.61573365,61603398,61374126,61473094,and 61773386)the Young Talent Fund of University Association for Science and Technology in Shaanxi,Chinathe Young Elite Scientists Sponsorship Program(YESS)by China Association for Science and Technology(CAST)
文摘As the key part of Prognostics and Health Management(PHM), Remaining Useful Life(RUL) estimation has been extensively investigated in recent years. Current RUL estimation studies considering the intervention of imperfect maintenance activities usually assumed that maintenance activities have a single influence on the degradation level or degradation rate, but not on both.Aimed at this problem, this paper proposes a new degradation modeling and RUL estimation method taking the influence of imperfect maintenance activities on both the degradation level and the degradation rate into account. Toward this end, a stochastic degradation model considering imperfect maintenance activities is firstly constructed based on the diffusion process. Then, the Probability Density Function(PDF) of the RUL is derived by the convolution operator under the concept of First Hitting Time(FHT). To implement the proposed RUL estimation method,the Maximum Likelihood Estimation(MLE) is utilized to estimate the degradation related parameters based on the Condition Monitoring(CM) data, while the Bayesian method is utilized to estimate the maintenance related parameters based on the maintenance data. Finally, a numerical example and a practical case study are provided to demonstrate the superiority of the proposed method. The experimental results show that the proposed method could greatly improve the RUL estimation accuracy for the degrading equipment subjected to imperfect maintenance activities.
基金supported by the National Natural Science Foundation of China(31870022)the Fundamental Research Funds for the Central Universities(XDJK2018B035 and 201941001,China)+3 种基金the Scientific Research Starting Foundation of Southwest University(SWU117034,China)the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao,China)(No.2018SDKJ0401-2)Taishan Scholar Youth Expert Program in Shandong Province(tsqn201812021,China)supported by the Venture&Innovation Support Program for Chongqing Overseas Returnees and the Thousand Young Talents Program of China.
文摘Mycophenolic acid(MPA,1)and its derivatives are first-line immunosuppressants used in organ transplantation and for treating autoimmune diseases.Despite chemical synthetic achievements,the biosynthetic formation of a seven-carbon carboxylic acid pharmacophore side chain of 1,especially the processes involving the cleavage of the prenyl side chain between DHMP(4)and DMMPA(5),remains unknown.In this work,we identified a membrane-bound prenyltransferase,PgMpaA,that transfers FPP to 4 to yield FDHMP(6).Compound 6 undergoes the first cleavage step via a new globin-like enzyme PgMpaB to form a cryptic intermediate 12.Heterologous expression of PgMpa genes in Aspergillus nidulans demonstrates that the second cleavage step(from 12 to 5)of 1 is a PgMpa clusterindependent process in vivo.Our results,especially the discovery of the broad tolerance of substrates recognized by PgMpaB,set up a strategy for the formation of"pseudo-isopentenyl"natural products using fungal globin-like enzymes.
基金supported by the National Natural Science Foundation of China(Nos.61773388,61751304,61833016,and 61702142)the Shaanxi Outstanding Youth Science Foundation(No.2020JC-34)the Key Research and Development Plan of Hainan(No.ZDYF2019007)。
文摘The composition of the modern aerospace system becomes more and more complex.The performance degradation of any device in the system may cause it difficult for the whole system to keep normal working states.Therefore,it is essential to evaluate the performance of complex aerospace systems.In this paper,the performance evaluation of complex aerospace systems is regarded as a Multi-Attribute Decision Analysis(MADA)problem.Based on the structure and working principle of the system,a new Evidential Reasoning(ER)based approach with uncertain parameters is proposed to construct a nonlinear optimization model to evaluate the system performance.In the model,the interval form is used to express the uncertainty,such as error in testing data and inaccuracy in expert knowledge.In order to analyze the subsystems that have a great impact on the performance of the system,the sensitivity analysis of the evaluation result is carried out,and the corresponding maintenance strategy is proposed.For a type of Inertial Measurement Unit(IMU)used in a rocket,the proposed method is employed to evaluate its performance.Then,the parameter sensitivity of the evaluation result is analyzed,and the main factors affecting the performance of IMU are obtained.Finally,the comparative study shows the effectiveness of the proposed method.
基金supported by the National Natural Science Foundation of China(31670050,31100069)the Fundamental Research Funds for the Central Universities(XDJK2017B011)。
文摘Dear Editor,Polyene macrolides are a group of natural products with potent antifungal activity (Caffrey et al., 2016). Candicidin/FR-008, a potent broad-spectrum anti-fungal agent, is produced by several Streptomycetes, including Streptomycetes sp. strain FR-008 (Chen et al., 2003), S. griseus 3570(Campelo and Gil, 2002) and S. albus J1074 (Olano et al.,2014). Due to its medical importance, considerable effort has been applied to elucidate its biosynthetic pathway and identify key regulatory genes (Chen et al., 2003;Zhang et al.,2015).
基金supported by the National Natural Science Foundation of China (Grant No.60736026).
文摘The design of the gain-scheduled H_(2)/H_(∞)filter for polytopic discrete-time systems is investigated.By introducing additional slack variables,a new mixed H_(2)/H_(∞)performance criterion is proposed,which provides a decoupling between the Lyapunov matrix and system matrices.Based on the new performance criterion,a sufficient condition for the existence of the gain-scheduled H_(2)/H_(∞)filter is derived.Furthermore,the filter design problem is converted into a convex optimization problem with linear matrix inequality(LMI)constraints.Simulation results show the effectiveness of the proposed approach.