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Chinese Physics C 2024年第8期48卷 198-212页

作者： Zhi-Chao Wang xian Gao School of Physics and Astronomy Sun Yat-sen UniversityZhuhai 519082China

We investigate a class of gravity theories respecting only spatial covariance,termed spatially covariant gravity,in the presence of an auxiliary scalar *** examine the conditions on the Lagrangian required to eliminate scalar degrees of freedom,allowing only two tensorial degrees of freedom to *** of strict constraint analysis,in this paper,we employ the perturbation method and focus on the necessary conditions to evade the scalar mode at the linear order in perturbations around a cosmological *** with a general action and solving the auxiliary perturbation variables in terms of a would-be dynamical scalar mode,we derive the condition to remove its kinetic term,thus ensuring that no scalar mode *** an application of the general condition,we study a polynomial-type Lagrangian as a concrete example,in which all monomials are spatially covariant scalars containing two *** find that the auxiliary scalar field is essential,and new terms in the Lagrangian are *** analysis provides insights into constructing gravity theories with two degrees of freedom in the extended framework of spatially covariant gravity.

关键词： modified gravity cosmological perturbation theory gravitational theory

Cretaceous magmatic arc in Hainan and the peri-South china Sea asevidenced by geochemical fingerprinting of granitoids in the region

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Geoscience Frontiers 2024年第5期15卷 355-371页

作者： Xiao-Yan Jiang Yildirim Dilek xian-Hua Li State Key Laboratory of Ore Deposit Geochemistry Institute of GeochemistryChinese Academy of SciencesGuiyang 550081China State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China Department of Geology and Environmental Earth science Miami UniversityOxfordOH 45056USA

Mesozoic magmatic rocks occur widely in the South china Block and are generally interpreted as the manifestations of the subduction of the Paleo-Pacific oceanic lithosphere beneath *** magmatism in southeast(SE)china continued from the Late Permian through the Late Cretaceous with an inferred lull between 12. Ma and 115 Ma that is known in the literature as the Cretaceous"magmatic quiescence".We report in-situ zircon U-Pb ages,Hf-O and whole-rock Sr-Nd isotopes,and whole-rock geochemistry of Cretaceous granitoids on Hainan Island and discuss their magmatic evolution within the framework of the Late Mesozoic geodynamics of SE *** recognize two main stages of the emplacement of Cretaceous granitoids on Hainan,first around 12. Ma and then around 100-95 Ma,displaying high-K calc-alkaline,I-type geochemical *** in both age groups are enriched in LILE and LREE,but depleted in Nb,Ta,Ba,Sr,and *** 12. Ma granites have zircon ε_(Hf)(t)values of-2.6 to 2.3 corresponding to Hf crustal model ages,ranging from 0.79 Ga to 1.03 Ga,and δ^(18)O values ranging from 6.9‰to 7.7‰.Zircons from 100-95 Ma granites have ε_(Hf)(t)values of-4.2.to 1.1 corresponding to Hf crustal model ages of 1.08 Ga to 1.42.Ga,and δ^(18)O values ranging from 6.7‰to 8.4‰.Increasing ε_(Hf)(t)values of the Cretaceous Hainan granites with younger crystallization ages indicate addition of more juvenile components and reworking of crustal material into their melt *** ε_(Nd)(t)values of the 12. Ma and 100-95 Ma granitoids range between-4.1 to-0.4 and-7.7 to-4.0,*** calculated two-stage model age of the 100-95 Ma granitoids clusters between 1.2. Ga and 1.53 *** isotopic data suggest that magmas of the Cretaceous granitoids were produced by partial melting of Mesoproterozoic metabasaltic rocks,which make up much of the crystalline basement of the southern Cathaysia *** geochemical and isotopic characteristics of the Cretaceous granitoids on H

关键词： I-type granites Cretaceous Hainan Island Southeast china Magmatic arc peri-South china Sea region

Limit Theorems for Critical Galton-Watson Processes with Immigration Stopped at Zero

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Acta Mathematica Sinica,English Series 2024年第2期40卷 435-450页

作者： Dou Dou LI Mei ZHANG xian Yu ZHANG College of Statistics and Data science Faculty of ScienceBeijing University of TechnologyBeijing 100124P.R.China Laboratory of Mathematics and Complex Systems(Ministry of Education) School of Mathematical SciencesBeijing Normal UniversityBeijing 100875P.R.China

In this paper,we consider a critical Galton-Watson branching process with immigration stopped at zero *** precise estimation on the probability generating function of the n-th population are obtained,and the tail prob... 详细信息

关键词： Branching immigration critical life period limit theorems

Quasi-shadowing for Z^(d)-actions

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Acta Mathematica Sinica,English Series 2024年第6期40卷 1563-1580页

作者： Juan PAN xian Kun REN Yun Hua ZHOU School of Mathematics and Statistics Chongqing Technology and Business UniversityChongqing 400067P.R.China College of Mathematics and Statistics Chongqing UniversityChongqing 401331P.R.China

A diffeomorphism is non-uniformly partially hyperbolic if it preserves an ergodic measure with at least one zero Lyapunov *** prove that a C^(1)-smooth Z^(d)-action has the quasishadowing property if one of the genera... 详细信息

关键词： Quasi-shadowing Z^(d)-action non-uniformly partially hyperbolic ergodic measure

Spontaneous Recovery in Directed Dynamical Networks

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engineering 2024年第6期37卷 208-214页

作者： Xueming Liu xian Yan H.Eugene Stanley School of Artificial Intelligence and Automation&The MOE engineering Research Center of Autonomous Intelligent Unmanned Systems&the Key Laboratory of Image Processing Huazhong University of Science and TechnologyWuhan 430074China Center for Polymer Studies Department of PhysicsBoston UniversityBostonMA 02215USA

Complex networked systems,which range from biological systems in the natural world to infrastructure systems in the human-made world,can exhibit spontaneous recovery after a failure;for example,a brain may spontaneously return to normal after a seizure,and traffic flow can become smooth again after a *** studies on the spontaneous recovery of dynamical networks have been limited to undirected ***,most real-world networks are *** fill this gap,we build a model in which nodes may alternately fail and recover,and we develop a theoretical tool to analyze the recovery properties of directed dynamical *** find that the tool can accurately predict the final fraction of active nodes,and the prediction accuracy decreases as the fraction of bidirectional links in the network increases,which emphasizes the importance of directionality in network *** to different initial states,directed dynamical networks may show alternative stable states under the same control parameter,exhibiting hysteresis *** addition,for networks with finite sizes,the fraction of active nodes may jump back and forth between high and low states,mimicking repetitive failure-recovery *** findings could help clarify the system recovery mechanism and enable better design of networked systems with high resilience.

关键词： Network resilience Directed dynamical networks Spontaneous recovery

Controlled flight of a self-powered micro blimp driven by insect-sized flapping-wing thrusters

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Chinese Journal of Aeronautics 2024年第6期37卷 127-136页

作者： xian YU Zhiwei LIU Jiaming LENG Mingjing QI Xiaojun YAN School of Energy and Power engineering Beihang UniversityBeijing 100191China Collaborative Innovation Center of Advanced Aero-Engine Beijing 100191China National Key Laboratory of science and technology on Aero-Engine Aero-thermodynamics Beihang UniversityBeijng 100191China Beijing Key Laboratory of Aero-Engine Structure and Strength Beihang UniversityBeijing 100191China

Micro aerial platforms face significant challenges in achieving long controlled endurance as most of the energy is consumed to overcome the weight of the *** this study,we present a controllable micro blimp that addresses this issue through the use of a helium-filled *** micro blimp has a long axis of 2. cm and is propelled by four insect-sized flapping-wing thrusters,each weighing 80 mg and with a wingspan of 3.5 *** distributed thrusters enable controlled motions and provide the micro blimp with an advantage in flight endurance compared to multirotors or flapping-wing micro aerial vehicles at the same size *** enhance the performance of the controlled flight,we propose a wireless control module that enables manipulation from a distance of up to 100 ***,a smartphone application is developed to send instructions to the circuit board,allowing the blimp to turn left and right,ascend and descend,and achieve a combination of these movements *** findings demonstrate that this micro blimp is one of the smallest controlled self-powered micro blimps to date.

关键词： Microairvehicle Aircraft control Self-powered micro blimp Flapping-wing thruster Wireless flight

Communication Resource-Efficient Vehicle Platooning Control With Various Spacing Policies

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IEEE/CAA Journal of Automatica Sinica 2024年第2期11卷 362-376页

作者： Xiaohua Ge Qing-Long Han xian-Ming Zhang Derui Ding IEEE School of science Computing and Engineering TechnologiesSwinburne University of TechnologyMelbourne VIC 3122Australia

Platooning represents one of the key features that connected automated vehicles may possess as it allows multiple automated vehicles to be maneuvered cooperatively with small headways on roads. However, a critical challenge in accomplishing automated vehicle platoons is to deal with the effects of intermittent and sporadic vehicle-to-vehicle data transmissions caused by limited wireless communication resources. This paper addresses the co-design problem of dynamic event-triggered communication scheduling and cooperative adaptive cruise control for a convoy of automated vehicles with diverse spacing policies. The central aim is to achieve automated vehicle platooning under various gap references with desired platoon stability and spacing performance requirements, while simultaneously improving communication efficiency. Toward this aim, a dynamic event-triggered scheduling mechanism is developed such that the intervehicle data transmissions are scheduled dynamically and efficiently over time. Then, a tractable co-design criterion on the existence of both the admissible event-driven cooperative adaptive cruise control law and the desired scheduling mechanism is derived. Finally, comparative simulation results are presented to substantiate the effectiveness and merits of the obtained results.

关键词： Automated vehicles constant time headway spacing constant spacing cooperative adaptive cruise control event-triggered communication vehicle platooning

Microstructure and mechanical properties of Ti/Al/Ti clad plates prepared via powder-in-tube method

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Journal of Iron and Steel Research International 2024年第3期31卷 670-687页

作者： xian-lei Hu Qin-cheng Xie Yi Yuan Ying Zhi State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819LiaoningChina Suzhou Dongbao Haixing Metal Material technology Co. Ltd.Suzhou 215600JiangsuChina School of Material science and engineering Northeastern UniversityShenyang 110819LiaoningChina

The Ti/Al/Ti clad plates exhibit a broad spectrum of potential ***,the conventional techniques of hot-pressing composite and explosive composite are intricate and environmentally hazardous.A novel method was introduced for preparing clad plates,namely,the powder-in-tube *** method involves a combination of cold rolling,annealing at a temperature of 550℃,and double *** morphology of the intermetallic compound layer was analyzed through the utilization of interface stripping test,tensile test,and microscopic *** interface morphology,interface bonding properties,tensile fracture structures,and properties of plates under the first and second rolling were compared,along with the effects of intermetallic compounds on the interface *** results indicate that the powder-in-tube method,when annealed at 550℃,can produce a composite plate featuring a complete and uniform Ti/Al *** obtained plate exhibits a peeling strength of 2..5 N/mm,tensile strength of 42. MPa,and elongation of 11.5%.Furthermore,a systematic analysis was conducted to determine the causes of performance degra-dation observed during annealing at temperatures of 600 and 650℃.

关键词： Powder-in-tube method-Ti/Al/Ti clad plate Annealing Cold rolling-Mechanical property

Full-domain collaborative deployment method of multiple interference sources and evaluation of its deployment effect

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Defence technology（防务技术） 2024年第2期32卷 572-595页

作者： Yue Wang Fuping Sun xian Wang Jinming Hao Kai Xiao School of Geospatial Information The PLA Information Engineering UniversityZhengzhou 450001HenanChina

This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the attacker and the capability to defend the GNSS during navigation *** evaluation indicators for the jamming effect of GNSS suppressive and deceptive jamming sources are first created,their evaluation models are built,and their detection procedures are sorted out,as the basis for determining the deployment *** principles for collaboratively deploying multi-jamming sources are developed to obtain the deployment structures(including the required number,structures in demand,and corresponding positions)of three single interference sources required by collaboratively ***,simulation and hardware-in-loop testing results are presented to determine a rational configuration of the collaborative deployment of multi-jamming sources in the set situation and further realize the full-domain deployment of an interference network from ground,air to *** evaluation indices for the deployment effect are finally developed to evaluate the deployment effect of the proposed configuration and further verify its reliability and rationality.

关键词： Jamming effect Multiple interference sources Collaborative deployment Effect evaluation Defense capability

An adaptive 3D reconstruction method for asymmetric dual-angle multispectral stereo imaging system on UAV platform

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science china(Information sciences) 2024年第8期67卷 285-299页

作者： Chen WANG xian LI Yanfeng GU Zixu WANG School of Electronics and Information engineering Harbin Institute of Technology Beijing Institute of Control and Electronic technology

A multispectral imaging system often cannot capture 3D spatial information owing to hardware limitations, which diminishes the effectiveness across various domains. To address this problem, we have developed a multispectral stereo imaging system along with an adaptive 3D reconstruction algorithm. Unlike existing unmanned aerial vehicle stereo imaging systems, our multispectral stereo imaging system uses two multispectral cameras with asymmetric spectral bands positioned at different angles. This design enables the acquisition of a higher number of bands and lateral spatial information while maintaining a lightweight structure. This system introduces challenges such as large geometric distortions and intensity differences between multiple bands. To accurately recover 3D spatial information, we propose an adaptive 3D reconstruction method. This method employs a position and orientation system-assisted projection transformation and a normalized threshold adjustment strategy. Finally, mutual information is used to reconstruct the multispectral images densely, effectively addressing nonlinear differences and generating a comprehensive multispectral point cloud. Our stereo system was used for two real data collections in different regions, and the efficacy of the proposed 3D reconstruction method was validated by comparing it with existing methods and commercial software.

关键词： multispectral images 3D reconstruction stereo imaging system unmanned aerial vehicle feature extraction