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Damping Characteristic Analysis and Optimization of Wind-therma.-bundled Power Transmission by LCC-HVDC Systems

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Journal of Modern Power Systems and Clean Energy 2024年第1期12卷 299-312页

作者： Liwen Zheng Shiying ma the Power System Department China Electric Power Research InstituteBeijing 100192China

With the rapid development of renewable energy,wind-therma.-bundled power transmission by line-commutated converter based high-voltage direct current(LCC-HVDC)systems has been widely *** dynamic interaction mechanisms among perma.ent ma.net synchronous generators(PMSGs),synchronous generators(SGs),and LCC-HVDC system become *** deal with this issue,a path analysis method(PAM)is proposed to study the dynamic interaction mechanism,and the damping reconstruction is used to analyze the damping characteristic of the ***,based on the modular modeling,linearized models for the PMSG subsystem,the LCC-HVDC subsystem,and the SG subsystem are ***,based on the closed-loop transfer function diagram of the system,the disturbance transfer path and coupling relationship among subsystems are analyzed by the PAM,and the damping characteristic analysis of the SG-dominated oscillation mode is studied based on the damping *** with the PAM,the sma.l-signal model of the system is obtained and eigenvalue analysis results are ***,the effect of the control parameters on the damping characteristic is analyzed and the conclusions are verified by time-doma.n ***,the penalty functions of the oscillation modes and decay modes are taken as the objective function,and an optimization strategy based on the Monte Carlo method is proposed to solve the parameter optimization *** simulation results are presented to validate the effectiveness of the proposed strategy.

关键词： Wind-therma.-bundled power transmission line-commutated converter based high-voltage direct current(LCC-HVDC) path analysis method(PAM) damping characteristic analysis Monte Carlo method

Finite-time Prescribed Performa.ce Time-Varying Forma.ion Control for Second-Order multi-Agent Systems With Non-Strict Feedback Based on a Neural Network Observer

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IEEE/CAA Journal of Automa.ica Sinica 2024年第4期11卷 1039-1050页

作者： Chi ma.Dianbiao Dong the School of Mechanical Engineering Northwestern Polytechnical UniversityXi’an 710072China

This paper studies the problem of time-varying forma.ion control with finite-time prescribed performa.ce for nonstrict feedback second-order multi-agent systems with unmeasured states and unknown *** eliminate nonlinearities,neural networks are applied to approxima.e the inherent dynamics of the *** addition,due to the limitations of the actual working conditions,each follower agent can only obtain the locally measurable partial state informa.ion of the leader *** address this problem,a neural network state observer based on the leader state informa.ion is ***,a finite-time prescribed performa.ce adaptive output feedback control strategy is proposed by restricting the sliding mode surface to a prescribed region,which ensures that the closed-loop system has practical finite-time stability and that forma.ion errors of the multi-agent systems converge to the prescribed performa.ce bound in finite ***,a numerical simulation is provided to demonstrate the practicality and effectiveness of the developed algorithm.

关键词： Finite-time control multi-agent systems neural network prescribed performa.ce control time-varying forma.ion control

Attitude control of multi-spacecraft systems on SO(3)with stochastic links failure

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Chinese Journal of Aeronautics 2024年第3期37卷 320-331页

作者： KANG Zeyu SHEN Qiang WU Shufan Chris J.DAma.EN mu Zhongcheng School of Aeronautics and Astronautics Shanghai Jiao Tong UniversityShanghai 200240China Institute for Aerospace Studies University of TorontoTorontoOntario M3H 5T6Canada

In this paper,for multi-Spacecraft System(MSS)with a directed communication topology link and a static virtual leader,a controller is proposed to realize attitude consensus and attitude stabilization with stochastic links failure and actuator ***,an MSS attitude error model suitable for a directed topology link and with a static virtual leader based on SO(3)is derived,which considers that the attitude error on SO(3)cannot be defined based on algebraic ***,we design a controller to realize the MSS on SO(3)with attitude consensus and attitude stabilization under stochastic links failure and actuator ***,the simulation results of a multi-spacecraft system with stochastic links failure and a static virtual leader spacecraft are demonstrated to illustrate the efficiency of the attitude controller.

关键词： multi-spacecraft systems Attitude consensus Attitude stabilization Stochastic links failure Super-ma.tingale convergence

Hydration lubrication modulated by water structure at TiO2–aqueous interfaces

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Friction 2024年第4期12卷 591-605页

作者： Pingsu ma.Yuan LIU Ke HAN Yu TIAN Liran ma State Key Laboratory of Tribology in Advanced Equipment Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China

The nature of solid-liquid interfaces is of great significance in *** advances have been ma.e in lubrication based on hydration ***,a detailed molecular-level understanding is still ***,we investigated water molecule behaviors at the TiO2-aqueous interfaces by the sum-frequency generation vibrational spectroscopy(SFG-VS)and atomic force microscope(AFM)to elucidate the fundamental role of solid-liquid interfaces in *** contributions of water structures and hydration effects were revealed,where water structures played the dominant role in lubrication for TiO2 surfaces of varying hydrophilicity,while hydration effects dominated with the increasing of ion *** lubrication is observed on the initial TiO2 surfaces with strongly H-bonded water molecules compared to the hydrophilic TiO2 surfaces with more disordered *** stable ordered water arrangement with strong hydrogen bonds and the shear plane occurring between the ordered water layer and subsequent water layer ma. play a significant role in achieving lower *** adsorbed hydrated molecules with the increasing ionic concentration perturb ordered water but lead to the enhancement of hydration effects,which is the ma.n reason for the improved lubrication for both *** work provides more insights into the detailed molecular-level understanding of the mechanism of hydration lubrication.

关键词： hydration lubrication interfacial water structures hydration effects titanium dioxide(TiO2)

Aero-structural design of joined-wing aircraft based on high-fidelity model

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Chinese Journal of Aeronautics 2024年第4期37卷 363-377页

作者： Cheng HE Fengjiang ZHAN Luchuang ma.Gang CHEN Jianying ma Unma.ned Air Vehicle Research Institute Nanjing University of Aeronautics and AstronauticsNanjing 210016China Key Laboratory of Advanced Technology for Sma.l and Medium-sized UAV Ministry of Industry and Information TechnologyNanjing University of Aeronautics and AstronauticsNanjing 210016China Aerospace System Engineering Shanghai Shanghai 201108China

The joined-wing configuration reduces induced drag and structural weight by connecting the rear wing to the front *** addition,the rear wing can replace the role of the horizontal tail of a conventional aircraft,thus eliminating the aerodynamic drag and weight associated with the horizontal *** particular shape creates a highly coupled relationship between aerodynamics and structure,which must be fully considered during the overall design process to enhance aircraft *** this research,an aero-structural design model of the joined-wing aircraft is constructed based on high-fidelity computational fluid dynamics and structural finite element *** model is able to obtain accurate aerodynamic loads for the non-planar wing and to simulate the statically indeterminate structure of the closed wing *** influence of the joined-wing shape parameters on the aerodynamic and structural disciplines,as well as the influence of geometric nonlinear characteristics,deforma.ion constraints and buckling constraints on the structural weight are all taken into *** model is applied to complete the aero-structural design optimization of a high-altitude long-endurance joined-wing aircraft,and wind tunnel tests are *** test results verify the credibility of the design model proposed and the validity of the design environment.

关键词： Joined-wing configuration Aircraft design Aero-structural design Finite element Wind tunnel test

Effects of fertilization on radial growth of Pinus pinea explored hourly using dendrometers

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Ecological Processes 2024年第1期 25-39页

作者： Verónica Loewe-mu?oz Rodrigo del Río Millar Claudia Delard Rodriguez Mónica Balzarini Chilean Forest Institute (INFOR) Metropolitan Office Centro Nacional de Excelencia Para la Industria de la ma.era(CENAma.) Pontificia Universidad Católica de Chile Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET ) Universidad Nacional de Córdoba Ciudad Universitaria

Background Stone pine(Pinus pinea), a drought-resistant species, has significant socio-economic benefits and increasing interest for the establishment of productive plantations in several countries, especially in a clima.e change context. Monitoring hourly stem diameter variations contributes to the understanding of the tree-growth response to changes in environmental conditions and ma.agement. By monitoring the diameter expansion of tree stems, high-resolution band dendrometers were used to study the development of adult trees growing in a semi-arid coastal environment of central Chile under fertilized and non-fertilized soil conditions through the span of a *** Short cycles( 28 h) occurred at a higher frequency in fertilized trees(16 vs 6). Most of the circadian cycles were regular(24 ± 3 h). The longest cycle duration(59 h) was observed in fertilized trees during spring. In all seasons, each phase of the circadian cycle, especially during the stem diameter increment phase(P3, irreversible growth), started earlier in fertilized than in control trees. P3 duration was significantly longer in fertilized than in control trees in springtime. The ma.imum shrinkage(P1) was observed in summer for both treatments. Stem diameter increased faster in fer-tilized than in control trees throughout the year, with the highest accumulation occurring in spring and the lowest in autumn. The daily variability pattern showed lower growth under high temperature across *** This study highlights the importance of fertilization in enhancing stone pine diameter growth. This cultural practice should be further explored to contribute to the mitigation of clima.e change effects in semi-arid environments.

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Mitigate noisy data for sma.t IoT via GAN based ma.hine unlearning

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Science China(Informa.ion Sciences) 2024年第3期67卷 62-78页

作者： Zhuo ma.Yilong YANG Yang LIU Xinjing LIU Jianfeng ma School of Cyber Engineering Xidian University State Key Laboratory of Integrated Services Networks (ISN)

With the development of IoT applications, ma.hine learning drama.ically improves the utility of variable IoT systems such as autonomous driving. Although the pretrain-finetune framework can cope well with data heterogeneity in complex IoT scenarios, the data collected by sensors often contain unexpected noisy data, e.g., out-of-distribution(OOD) data, which leads to the reduced performa.ce of fine-tuned models. To resolve the problem, this paper proposes mu GAN, a method that can mitigate the side-effect of OOD data via the generative adversarial network(GAN)-based ma.hine unlearning. mu GAN follows a straightforward but effective idea to mitigate the performa.ce loss caused by OOD data, i.e., “flashbacking” the model to the condition where OOD data are excluded from model training. To achieve the goal, we design an adversarial game, where a discriminator is trained to identify whether a sample belongs to the training set by observing the confidence score. Meanwhile, a generator(i.e., the target model) is updated to fool the discriminator into believing that the OOD data are not included in the training set but others do. The experimental results show that benefiting from the high unlearning rate(more than 90%) and retention rate(99%), mu GAN succeeds in lowering the model performa.ce degradation caused by OOD data from 5.88% to 0.8%.

关键词： ma.hine unlearning generative adversarial network out of distribution data Internet of Thing neural network

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CToMP: a cycle-task-oriented memory protection scheme for unma.ned systems

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Science China(Informa.ion Sciences) 2024年第6期67卷 399-417页

作者： Chengyan ma.Ning XI Di LU Yebo FENG Jianfeng ma School of Cyber Engineering Xidian University School of Computer Science and Technology Xidian University Department of Computer and Informa.ion Science University of Oregon

Memory corruption attacks(MCAs) refer to ma.icious behaviors of system intruders that modify the contents of a memory location to disrupt the norma. operation of computing systems, causing leakage of sensitive data or perturbations to ongoing processes. Unlike general-purpose systems, unma.ned systems cannot deploy complete security protection schemes, due to their limitations in size, cost and *** in unma.ned systems are particularly difficult to defend against. Furthermore, MCAs have diverse and unpredictable attack interfaces in unma.ned systems, severely impacting digital and physical sectors. In this paper, we first generalize, model and taxonomize MCAs found in unma.ned systems currently, laying the foundation for designing a portable and general defense approach. According to different attack mechanisms,we found that MCAs are ma.nly categorized into two types — return2libc and return2shellcode. To tackle return2libc attacks, we model the erratic operation of unma.ned systems with cycles and then propose a cycle-task-oriented memory protection(CToMP) approach to protect control flows from tampering. To defend against return2shellcode attacks, we introduce a secure process stack with a randomized memory address by leveraging the memory pool to prevent Shellcode from being executed. Moreover, we discuss the mechanism by which CTo MP resists the return-oriented programming(ROP) attack, a novel variant of return2libc attacks. Finally, we implement CTo MP on CUAV V5+ with Ardupilot and Crazyflie. The evaluation and security analysis results demonstrate that the proposed approach CTo MP is resilient to various MCAs in unma.ned systems with low footprints and system overhead.

关键词： unma.ned system memory corruption attack memory protection system security randomized memory address

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A commentary of"Artificial intelligence models bring new breakthroughs in global accurate weather forecasting":Top 10 Scientific Advances of 2023,China

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Fundamental Research 2024年第3期4卷 690-692页

作者： mu mu Bo Qin Guokun Dai Department of Atmospheric and Oceanic Sciences&Institute of Atmospheric Sciences Fudan UniversityShanghai 200438China Key Laboratoryof PolarAmospherecean-iceSystemfor Weatherand Clima.e Ministryof EducationFudan Universityhanghai200438China

Skillful weather forecasts have the potential to save lives,support emergency ma.agement,and mitigate economic and social losses,which capture the public's *** present framework of numerical weather prediction(NWP)can trace its origins back to the 1950s,by solving partial differential equations(PDEs)that describe atmospheric motion,to infer future atmospheric *** forecasts typically require several hours on a supercomputer with hundreds of nodes for the upcoming *** the various numerical models used by operational centers,the Integrated Forecasting System(IFS)from the European Centre for Medium-Range Weather Forecasts(ECMWF)stands out for its superior skills in medium-range weather *** quiet revolution of NwP has also been evaluated by the World Meteorological Organization as one of the most significant scientific,technological and social advances in the twentieth century[1].

关键词： weather forecasting breakthrough