The Upper Cretaceous of Tantou Basin in western Henan has yielded many vertebrate fossils,which are featured by several non-avian dinosaurs.Meanwhile,studies on their eggs were yet inadequate though many eggshells hav...The Upper Cretaceous of Tantou Basin in western Henan has yielded many vertebrate fossils,which are featured by several non-avian dinosaurs.Meanwhile,studies on their eggs were yet inadequate though many eggshells have been reported.The newly discovered material 41HⅤ0199 was excavated from the Upper Cretaceous Qiupa Formation in 2021.The block preserves eight complete eggs arranged in two partial rings that form a partial clutch,and there are some scattered eggshells preserved closely with the block,showing a concave-up to concave-down ratio of 54.5:45.5,which indicates that the scattered eggshells come from the clutch and the clutch had been partially broken before it was buried.Based on morphological and microstructural characteristics,the eggs and eggshells can be assigned to Macroolithus yaotunensis(Elongatoolithidae),an oospecies known to be related to oviraptorids,which leads Yulong mini to be its probable producer.Besides,some eggshells show microstructural signs indicating egg retention,which marks the second example of egg retention in the oofamily Elongatoolithidae.展开更多
Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of sh...Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.展开更多
Combat effectiveness of unmanned aerial vehicle(UAV)formations can be severely affected by the mission execution reliability.During the practical execution phase,there are inevitable risks where UAVs being destroyed o...Combat effectiveness of unmanned aerial vehicle(UAV)formations can be severely affected by the mission execution reliability.During the practical execution phase,there are inevitable risks where UAVs being destroyed or targets failed to be executed.To improve the mission reliability,a resilient mission planning framework integrates task pre-and re-assignment modules is developed in this paper.In the task pre-assignment phase,to guarantee the mission reliability,probability constraints regarding the minimum mission success rate are imposed to establish a multi-objective optimization model.And an improved genetic algorithm with the multi-population mechanism and specifically designed evolutionary operators is used for efficient solution.As in the task-reassignment phase,possible trigger events are first analyzed.A real-time contract net protocol-based algorithm is then proposed to address the corresponding emergency scenario.And the dual objective used in the former phase is adapted into a single objective to keep a consistent combat intention.Three cases of different scales demonstrate that the two modules cooperate well with each other.On the one hand,the pre-assignment module can generate high-reliability mission schedules as an elaborate mathematical model is introduced.On the other hand,the re-assignment module can efficiently respond to various emergencies and adjust the original schedule within a millisecond.The corresponding animation is accessible at bilibili.com/video/BV12t421w7EE for better illustration.展开更多
The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) ...The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) and promote the balance of the carbon cycle.Formate is one of the most economical and practical products of all the electrochemical CO_(2) reduction products.Among the many metal-based electrocatalysts that can convert CO_(2) into formate,Sn-based catalysts have received a lot of attention because of their low-cost,non-toxic characteristics and high selectivity for formate.In this article,the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples,which are mainly divided into monometallic Sn,alloyed Sn,Sn-based compounds and Sn composite catalysts.Finally,the current performance enhancement strategies and future directions of the field are summarized.展开更多
Offboard active decoys(OADs)can effectively jam monopulse radars.However,for missiles approaching from a particular direction and distance,the OAD should be placed at a specific location,posing high requirements for t...Offboard active decoys(OADs)can effectively jam monopulse radars.However,for missiles approaching from a particular direction and distance,the OAD should be placed at a specific location,posing high requirements for timing and deployment.To improve the response speed and jamming effect,a cluster of OADs based on an unmanned surface vehicle(USV)is proposed.The formation of the cluster determines the effectiveness of jamming.First,based on the mechanism of OAD jamming,critical conditions are identified,and a method for assessing the jamming effect is proposed.Then,for the optimization of the cluster formation,a mathematical model is built,and a multi-tribe adaptive particle swarm optimization algorithm based on mutation strategy and Metropolis criterion(3M-APSO)is designed.Finally,the formation optimization problem is solved and analyzed using the 3M-APSO algorithm under specific scenarios.The results show that the improved algorithm has a faster convergence rate and superior performance as compared to the standard Adaptive-PSO algorithm.Compared with a single OAD,the optimal formation of USV-OAD cluster effectively fills the blind area and maximizes the use of jamming resources.展开更多
This article investigates a multi-circular path-following formation control with reinforced transient profiles for nonholonomic vehicles connected by a digraph.A multi-circular formation controller endowed with the fe...This article investigates a multi-circular path-following formation control with reinforced transient profiles for nonholonomic vehicles connected by a digraph.A multi-circular formation controller endowed with the feature of spatial-temporal decoupling is devised for a group of vehicles guided by a virtual leader evolving along an implicit path,which allows for a circumnavigation on multiple circles with an anticipant angular spacing.In addition,notice that it typically imposes a stringent time constraint on time-sensitive enclosing scenarios,hence an improved prescribed performance control(IPPC)using novel tighter behavior boundaries is presented to enhance transient capabilities with an ensured appointed-time convergence free from any overshoots.The significant merits are that coordinated circumnavigation along different circles can be realized via executing geometric and dynamic assignments independently with modified transient profiles.Furthermore,all variables existing in the entire system are analyzed to be convergent.Simulation and experimental results are provided to validate the utility of suggested solution.展开更多
Several therocephalian species,mainly represented by cranial material from the late Permian,have been reported from China in recent years.Here we describe a tiny new baurioid therocephalian,Jiucaiyuangnathus confusus ...Several therocephalian species,mainly represented by cranial material from the late Permian,have been reported from China in recent years.Here we describe a tiny new baurioid therocephalian,Jiucaiyuangnathus confusus gen.et sp.nov.,from the Jiucaiyuan Formation,Xinjiang,China.The new taxon is represented by a partial snout with occluded partial lower jaw and two postcranial skeletons.Although juvenile in stage,the new species is diagnosed by the following features:round pit in middle of lateral surface of maxilla;lacrimal contact nasal;fossa for dentary tooth on the posterior end of the premaxilla,lateral to the anterior choana;two small vertical triangular ridges extending dorsally and ventrally on the vomerine anterior portion,and bordering a thin vomerine foramen laterally;anterior projection of the lateral part of the frontal on the nasal;symphyseal region of the dentary projected anteriorly;5 upper premaxillary teeth,upper and lower canines absent,diastema between the last premaxillary upper incisor and first maxillary tooth present,no diastema separating anterior from posterior dentition in the mandible,10 maxillary teeth and 12 dentary teeth,posterior postcanine expands mesiodistally,having a main large cusps and tiny anterior and posterior accessory cusps in line;neural arches of the atlas fused by the neural spine,neural spine of the axis projected posteriorly,procoracoid foramen lies between procoracoid and scapula.Features of the dentition resembles those of the small baurioid Ericiolacerta parva from South Africa and Silphedosuchus orenburgensis from Russia.The specimens provide the rare opportunity to know in detail the postcranial skeleton of baurioids.展开更多
In this paper,the fixed-time time-varying formation of heterogeneous multi-agent systems(MASs) based on tracking error observer under denial-of-service(DoS) attacks is investigated.Firstly,the dynamic pinning strategy...In this paper,the fixed-time time-varying formation of heterogeneous multi-agent systems(MASs) based on tracking error observer under denial-of-service(DoS) attacks is investigated.Firstly,the dynamic pinning strategy is used to reconstruct the communication channel for the system that suffers from DoS attacks to prevent the discontinuous transmission information of the communication network from affecting MASs formation.Then,considering that the leader state is not available to each follower under DoS attacks,a fixed-time distributed observer without velocity information is constructed to estimate the tracking error between followers and the leader.Finally,adaptive radial basis function neural network(RBFNN) is used to approximate the unknown ensemble disturbances in the system,and the fixed-time time-varying formation scheme is designed with the constructed observer.The effectiveness of the proposed control algorithm is demonstrated by the numerical simulation.展开更多
文摘The Upper Cretaceous of Tantou Basin in western Henan has yielded many vertebrate fossils,which are featured by several non-avian dinosaurs.Meanwhile,studies on their eggs were yet inadequate though many eggshells have been reported.The newly discovered material 41HⅤ0199 was excavated from the Upper Cretaceous Qiupa Formation in 2021.The block preserves eight complete eggs arranged in two partial rings that form a partial clutch,and there are some scattered eggshells preserved closely with the block,showing a concave-up to concave-down ratio of 54.5:45.5,which indicates that the scattered eggshells come from the clutch and the clutch had been partially broken before it was buried.Based on morphological and microstructural characteristics,the eggs and eggshells can be assigned to Macroolithus yaotunensis(Elongatoolithidae),an oospecies known to be related to oviraptorids,which leads Yulong mini to be its probable producer.Besides,some eggshells show microstructural signs indicating egg retention,which marks the second example of egg retention in the oofamily Elongatoolithidae.
基金supported by the National Science Foundation of China(Grant Nos.12372361,12102427,12372335 and 12102202)the Fundamental Research Funds for the Central Universities(Grant No.30923010908)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX23_0520).
文摘Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.
基金supported by the National Key Research and Development Plan(Grant No.2021YFB3302501)the National Natural Science Foundation of China(Grant Nos.12102077,12161076,U2241263).
文摘Combat effectiveness of unmanned aerial vehicle(UAV)formations can be severely affected by the mission execution reliability.During the practical execution phase,there are inevitable risks where UAVs being destroyed or targets failed to be executed.To improve the mission reliability,a resilient mission planning framework integrates task pre-and re-assignment modules is developed in this paper.In the task pre-assignment phase,to guarantee the mission reliability,probability constraints regarding the minimum mission success rate are imposed to establish a multi-objective optimization model.And an improved genetic algorithm with the multi-population mechanism and specifically designed evolutionary operators is used for efficient solution.As in the task-reassignment phase,possible trigger events are first analyzed.A real-time contract net protocol-based algorithm is then proposed to address the corresponding emergency scenario.And the dual objective used in the former phase is adapted into a single objective to keep a consistent combat intention.Three cases of different scales demonstrate that the two modules cooperate well with each other.On the one hand,the pre-assignment module can generate high-reliability mission schedules as an elaborate mathematical model is introduced.On the other hand,the re-assignment module can efficiently respond to various emergencies and adjust the original schedule within a millisecond.The corresponding animation is accessible at bilibili.com/video/BV12t421w7EE for better illustration.
基金Project(52204378)supported by the National Natural Science Foundation of China。
文摘The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) and promote the balance of the carbon cycle.Formate is one of the most economical and practical products of all the electrochemical CO_(2) reduction products.Among the many metal-based electrocatalysts that can convert CO_(2) into formate,Sn-based catalysts have received a lot of attention because of their low-cost,non-toxic characteristics and high selectivity for formate.In this article,the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples,which are mainly divided into monometallic Sn,alloyed Sn,Sn-based compounds and Sn composite catalysts.Finally,the current performance enhancement strategies and future directions of the field are summarized.
基金the National Natural Science Foundation of China(Grant No.62101579).
文摘Offboard active decoys(OADs)can effectively jam monopulse radars.However,for missiles approaching from a particular direction and distance,the OAD should be placed at a specific location,posing high requirements for timing and deployment.To improve the response speed and jamming effect,a cluster of OADs based on an unmanned surface vehicle(USV)is proposed.The formation of the cluster determines the effectiveness of jamming.First,based on the mechanism of OAD jamming,critical conditions are identified,and a method for assessing the jamming effect is proposed.Then,for the optimization of the cluster formation,a mathematical model is built,and a multi-tribe adaptive particle swarm optimization algorithm based on mutation strategy and Metropolis criterion(3M-APSO)is designed.Finally,the formation optimization problem is solved and analyzed using the 3M-APSO algorithm under specific scenarios.The results show that the improved algorithm has a faster convergence rate and superior performance as compared to the standard Adaptive-PSO algorithm.Compared with a single OAD,the optimal formation of USV-OAD cluster effectively fills the blind area and maximizes the use of jamming resources.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.62173312 and 61803348in part by the National Major Scientific Instruments Development Project under Grant No.61927807+3 种基金in part by the Program for the Innovative Talents of Higher Education Institutions of ShanxiShanxi Province Science Foundation for Excellent Youthsin part by the Shanxi"1331 Project"Key Subjects Construction(1331KSC)in part by Graduate Innovation Project of Shanxi Province under Grant No.2021Y617。
文摘This article investigates a multi-circular path-following formation control with reinforced transient profiles for nonholonomic vehicles connected by a digraph.A multi-circular formation controller endowed with the feature of spatial-temporal decoupling is devised for a group of vehicles guided by a virtual leader evolving along an implicit path,which allows for a circumnavigation on multiple circles with an anticipant angular spacing.In addition,notice that it typically imposes a stringent time constraint on time-sensitive enclosing scenarios,hence an improved prescribed performance control(IPPC)using novel tighter behavior boundaries is presented to enhance transient capabilities with an ensured appointed-time convergence free from any overshoots.The significant merits are that coordinated circumnavigation along different circles can be realized via executing geometric and dynamic assignments independently with modified transient profiles.Furthermore,all variables existing in the entire system are analyzed to be convergent.Simulation and experimental results are provided to validate the utility of suggested solution.
文摘Several therocephalian species,mainly represented by cranial material from the late Permian,have been reported from China in recent years.Here we describe a tiny new baurioid therocephalian,Jiucaiyuangnathus confusus gen.et sp.nov.,from the Jiucaiyuan Formation,Xinjiang,China.The new taxon is represented by a partial snout with occluded partial lower jaw and two postcranial skeletons.Although juvenile in stage,the new species is diagnosed by the following features:round pit in middle of lateral surface of maxilla;lacrimal contact nasal;fossa for dentary tooth on the posterior end of the premaxilla,lateral to the anterior choana;two small vertical triangular ridges extending dorsally and ventrally on the vomerine anterior portion,and bordering a thin vomerine foramen laterally;anterior projection of the lateral part of the frontal on the nasal;symphyseal region of the dentary projected anteriorly;5 upper premaxillary teeth,upper and lower canines absent,diastema between the last premaxillary upper incisor and first maxillary tooth present,no diastema separating anterior from posterior dentition in the mandible,10 maxillary teeth and 12 dentary teeth,posterior postcanine expands mesiodistally,having a main large cusps and tiny anterior and posterior accessory cusps in line;neural arches of the atlas fused by the neural spine,neural spine of the axis projected posteriorly,procoracoid foramen lies between procoracoid and scapula.Features of the dentition resembles those of the small baurioid Ericiolacerta parva from South Africa and Silphedosuchus orenburgensis from Russia.The specimens provide the rare opportunity to know in detail the postcranial skeleton of baurioids.
文摘In this paper,the fixed-time time-varying formation of heterogeneous multi-agent systems(MASs) based on tracking error observer under denial-of-service(DoS) attacks is investigated.Firstly,the dynamic pinning strategy is used to reconstruct the communication channel for the system that suffers from DoS attacks to prevent the discontinuous transmission information of the communication network from affecting MASs formation.Then,considering that the leader state is not available to each follower under DoS attacks,a fixed-time distributed observer without velocity information is constructed to estimate the tracking error between followers and the leader.Finally,adaptive radial basis function neural network(RBFNN) is used to approximate the unknown ensemble disturbances in the system,and the fixed-time time-varying formation scheme is designed with the constructed observer.The effectiveness of the proposed control algorithm is demonstrated by the numerical simulation.
