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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

Estimating Critical Clearing Time of Grid Faults Using DA of State-Reduction Model of Power Systems

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 807-820页

作者： Yang liu Zhongyang Chen huanjin Yao Lin Yi Q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou 510640China China Southern Power Grid Research Institute Guangzhou 510663China

This paper proposes a critical clearing time (CCT) estimation method by the domain of attraction (DA) of a state-reduction model of power systems using sum of squares (SOS) programming. By exploiting the property of the Jacobian matrix and the structure of the boundary of the DA, it is found the DA of the state-reduction model and that of the full model of a power system are topological isomorphism. There are one-to-one correspondence relationships between the number of equilibrium points, the type of equilibrium points, and solutions of the two system models. Based on these findings, an expanding interior algorithm is proposed with SOS programming to estimate the DA of the state-reduction model. State trajectories of the full model can be transformed to those of the state-reduction model by orthogonal or equiradius projection. In this way, CCT of a grid fault is estimated with the DA of the state-reduction model. The calculational burden of SOS programming in the DA estimation using the state-reduction model is rather small compared with using the full model. Simulation results show the proposed expanding interior algorithm is able to provide a tight estimation of DA of power systems with higher accuracy and lower time costs.

关键词： Critical clearing time domain of attraction expanding interior algorithm state-reduction model SOS programming

Implicit Function Based Open-loop Analysis Method for Detecting the SSR Using Identified System Parameters

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CSEE Journal of Power and Energy Systems 2024年第5期10卷 2016-2026页

作者： Luonan Qiu Tianhao Wen Yang liu Q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou 510640China

This paper proposes an implicit function based open-loop analysis method to detect the subsynchronous resonance(SSR),including asymmetric subsynchronous modal attraction(ASSMA)and asymmetric subsynchronous modal repulsion(ASSMR),of doubly-fed induction generator based wind farms(DFIG-WFs)penetrated power *** some important parameters of DFIG-WF are difficult to obtain,reinforcement learning and least squares method are applied to identify those important *** predicting the location of closed-loop subsynchronous oscillation(SSO)modes based on the calculation of partial differentials of characteristic equation,both ASSMA and ASSMR can be *** proposed method in this paper can select SSO modes which move to the right half complex planes as control parameters ***,the proposed open-loop analysis method is adaptive to parameter *** studies are carried out on the 4-machine 11-bus power system to verify properties of the proposed method.

关键词： Open-loop modal analysis reinforcement learning based parameter identification subsynchronous resonance

Expanding Annular Domain Algorithm to Estimate Domains of Attraction for Power System Stability Analysis

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CSEE Journal of Power and Energy Systems 2024年第5期10卷 1925-1934页

作者： Yuqing Lin Tianhao Wen Yang liu Q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou 510640China

This paper presents an Expanding Annular Domain(EAD)algorithm combined with Sum of Squares(SOS)programming to estimate and maximize the domain of attraction(DA)of power *** proposed algorithm can systematically construct polynomial Lyapunov functions for power systems with transfer conductance and reliably determine a less conservative approximated DA,which are quite difficult to achieve with traditional *** linear SOS programming,we begin from an initial estimated DA,then enlarge it by iteratively determining a series of so-called annular domains of attraction,each of which is characterized by level sets of two successively obtained Lyapunov ***,the EAD algorithm is theoretically analyzed in detail and its validity and convergence are shown under certain *** the end,our method is tested on two classical power system cases and is demonstrated to be superior to existing methods in terms of computational speed and conservativeness of results.

关键词： Domain of attraction Lyapunov functions power system transient stability sum of squares programming

Microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with different prestrain levels

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Journal of Materials Science & Technology 2024年第4期171卷 80-93页

作者： Y.h.Zhang h.Li Z.W.Yang X.liu Q.F.Gu State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China Shaanxi Key Laboratory of high-Performance Precision Forming Technology and Equipment Northwestern Polytechnical UniversityXi’an 710072China

Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation *** application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to ***-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA ***,microstructure evolution and deformation mechanisms of Ni_(47)Ti_(44)Nb_(9)SMA subjected to vari-ous prestrain levels are still *** this end,microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with prestrain levels of 8%-16%at-28℃(M_(s)+30℃)were *** results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16%.Whereas stageⅡand stageⅢend at prestrains of∼8%and∼12%,*** stageⅡ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix andβ-Nb *** stageⅢ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(001)compound twins are introduced as a result of the(001)deformation twinning in stress-induced ***{20-1}martensite twins are gradually introduced in stageⅣ.Correspondingly,after subsequent unloading and heating,a higher density of{114}austenite twins form in the specimen with a larger prestrain of 16%.With increasing prestrain from 8%to 16%,the recoverable strainε_(re)^(T)upon heating increases first and then ***ε_(re)^(T)obtains a maximum of 7.03%at 10%prestrain and de-creases to 6.17%at 16%*** increase ofε_(re)^(T)can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(001)compound *** the decrease ofε_(re)^(T)is mainly associated with the irrecoverable strain by{20−1}martensite *** effe

关键词： Ni_(47)Ti_(44)Nb_(9)shape memory alloy Wide transformation hysteresis Thermomechanical loading Microstructure evolution Shape memory behaviors Stress-induced martensitic transformation Deformation twinning

Uncovering the hierarchical clusters in the heat-affected zone of an electron beam weldedα/βtitanium alloy joint

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Journal of Materials Science & Technology 2024年第7期174卷 120-132页

作者： C.Xu X.h.Shao h.J.Yang M.Lv h.Q.liu X.L.Ma Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China Suzhou laboratory Suzhou 215028China Department of Mechanical Engineering Kyushu UniversityFukuoka 819-0395Japan Bay Area Center for Electron Microscopy Songshan Lake Materials LaboratoryDongguan 523808China

Using high-resolution transmission Kikuchi diffraction(TKD)and transmission electron microscopy(TEM),we examined the hierarchical clusters that form in situ in the heat-affected zone(hAZ),which are com-monly referred to as“ghost”structures,of bimodal titanium alloy Ti-5Al-2Sn-2Zr-4Mo-4Cr(wt%,TC17).The ghost structures are enriched with Al elements but poor in Mo and Cr compared to the surroundingβ*** results show that the ghost structure in middle-hAZ mainly consists ofα_(L)laths with a high-angle grain boundary,which exhibits the classic Burgers orientation relationship(BOR)with the host matrix,while it encircles theα_(P)grains in *** the ghost structure is evidenced to form via in-complete martensitic *** results further confirm that the ghost structure is composed ofαL and tinyβ_(L)laths with BOR,with the former being enriched with Al and poor with Cr and Mo,while the latter is the ***,twoα_(L)variant clusters with a check-mark morphology are fre-quently observed viewed along[0001]_(αL)//[110]_(βL)directions,which are dominated by the crystallographic and geometrical relationships betweenαandβ*** on the microstructural characterization,it is hypothesized that the ghost structure is transformed from the initialα_(P)phase,due to the coupling ef-fect of high thermal stress(which induces the formation of a large number of dislocations)and element diffusion caused by sudden temperature increase and plunge cooling in the hAZ during the welding pro-cess.

关键词： TC17 titanium alloy Electron beam welding(EBW) The ghost structure Transmission Kikuchi diffraction(TKD) Transmission electron microscopy(TEM)

Demand-Responsive Transportation Vehicle Routing Optimization Based on Two-Stage Method

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Computers, Materials and Continua 2024年第1期81卷 443-469页

作者： Ma J. liu h. Chen L. School of Railway Transportation Shanghai Institute of Technology Shanghai 201418 China

Demand-responsive transportation (DRT) is a flexible passenger service designed to enhance road efficiency, reduce peak-hour traffic, and boost passenger satisfaction. however, existing optimization methods for initial passenger requests fall short in addressing real-time passenger needs. Consequently, there is a need to develop real-time DRT route optimization methods that integrate both initial and real-time requests. This paper presents a two-stage, multi-objective optimization model for DRT vehicle scheduling. The first stage involves an initial scheduling model aimed at minimizing vehicle configuration, and operational, and CO2 emission costs while ensuring passenger satisfaction. The second stage develops a real-time scheduling model to minimize additional operational costs, penalties for time window violations, and costs due to rejected passengers, thereby addressing real-time demands. Additionally, an enhanced genetic algorithm based on Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is designed, incorporating multiple crossover points to accelerate convergence and improve solution efficiency. The proposed scheduling model is validated using a real network in Shanghai. Results indicate that real-time scheduling can serve more passengers, and improve vehicle utilization and occupancy rates, with only a minor increase in total operational costs. Compared to the traditional NSGA-II algorithm, the improved version enhances convergence speed by 31.7% and solution speed by 4.8%. The proposed model and algorithm offer both theoretical and practical guidance for real-world DRT scheduling. © 2024 The Authors.

关键词： artificial intelligence applications Demand responsive transit genetic algorithm muti-objective optimization

Residue Based Open-Loop Modal Analysis Method for Detecting LFMR of PMSG-WFs Penetrated Power Systems

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CSEE Journal of Power and Energy Systems 2024年第4期10卷 1454-1465页

作者： Luonan Qiu Tianhao Wen Yang liu Q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou510640China

This paper proposes a residue based open-loop modal analysis method to detect low frequency modal resonance(LFMR),including asymmetric low frequency modal attraction(ALFMA)and asymmetric low frequency modal repulsion(ALFMR),of permanent magnetic synchronous generator based wind farms(PMSG-WFs)penetrated power *** formation of ALFMA and ALFMR caused by two open-loop low frequency oscillation(LFO)modes moving close and apart is analyzed in *** predicting the trajectories of closed-loop LFO modes based on calculation of residue of open-loop LFO modes,both ALFMA and ALFMR can be *** proposed method can select LFO modes which move to the right half complex plane as control parameters *** studies are carried out on a three-machine power system and a four-machine 11-bus power system to verify the properties of the proposed method.

关键词： Asymmetric low frequency modal attraction asymmetric low frequency modal repulsion low frequency modal resonance residue based open-loop modal analysis method

Reducing carbon emissions with Geoscience solutions:A look at the contributions of nuclear energy,technology,and green finance

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Geoscience Frontiers 2024年第4期15卷 411-426页

作者： Aifeng liu Muhammad Imran Abdelmohsen A.Nassani Rima h.Binsaeed Khalid Zaman International Business School Shaanxi Normal UniversityXi’anChina Department of Economics The University of HaripurHaripur Khyber Pakhtunkhwa 22620Pakistan Department of Management College of Business AdministrationKing Saud UniversityP.O.Box 71115Riyadh 11587Saudi Arabia

Standards for Low-Carbon Energy Portfolios(LC-EPS)mandate that a certain percentage of a region's electricity generation originate from zero-or low-emissions *** 1995Q1 through 2020Q4,the study used the ARDL-Bounds testing technique to estimate coefficient parameters,Granger causality to draw causal inferences,and variance decomposition analysis to anticipate the factors that will have the greatest impact on carbon emissions in the US *** power significantly impacts carbon emissions,as seen by an inverted U-shaped environmental Kuznets curve,whereas long-term impact of innovation leads to lower *** the other hand,exports of sophisticated technology reduce carbon *** growth has a discernible effect on carbon emissions,nuclear power,innovation,and environmentally friendly ***-tech exports will likely impact carbon emissions most,followed by a demand for nuclear power,innovation,economic expansion,and sustainable finance for the next ten *** results give policymakers helpful insight into how the US economy may reduce carbon emissions and fight climate change via renewable energy and green finance.

关键词： Nuclear energy demand high technology exports Innovation Economic growth Green finance USA