deep reinforcement learning forresource allocation has been investigated extensively owing to its ability of handling model-free and end-to-end problems. However, its slow convergence and high time complexity during ...
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deep reinforcement learning forresource allocation has been investigated extensively owing to its ability of handling model-free and end-to-end problems. However, its slow convergence and high time complexity during online training hinder its practical use in dynamic wireless systems. To reduce the training complexity, we resort to graph reinforcement learning for leveraging two kinds of relational priors inherent in many wireless communication problems: topology information and permutation properties. To harness the two priors, we first conceive a method to convert the state matrix into a state graph,and then propose a graph deep deterministic policy gradient(ddPG) algorithm with the desired permutation property. To demonstrate how to apply the proposed methods, we consider a representative problem of using reinforcement learning, predictive power allocation, which minimizes the energy consumption while ensuring the quality-of-service of each userrequesting video streaming. We derive the time complexity required by training the proposed graph ddPG algorithm and fully-connected neural network-basedddPG algorithm in each time step. Simulations show that the graph ddPG algorithm converges much faster and needs much lower time and space complexity than existing ddPG algorithms to achieve the same learning performance.
A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this *** complex deformation characteristics of IF are considered in the modeling process,which can acc...
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A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this *** complex deformation characteristics of IF are considered in the modeling process,which can accurately describe the strain and stress states in *** on strain analysis,the model can predict the material thickness distribution and neck height after *** considering contact area,strain characteristics,material thickness changes,and friction,the model can predict specific moments and corresponding values of maximum axial forming force and maximum horizontal forming force during *** addition,an IF experiment involving different tool diameters,flanging diameters,and opening hole diameters is *** the basis of the experimental strain paths,the strain characteristics of different deformation zones are studied,and the stable strain ratio is quantitatively described through two dimensionless parameters:relative tool diameter andrelative hole ***,the changing of material thickness and forming force in IF,and the variation of minimum material thickness,neck height,maximum axial forming force,and maximum horizontal forming force with flanging parameters are studied,and the reliability of the analytical model is verified in this ***,the influence of the horizontal forming force on the tool design and the fluctuation of the forming force are explained.
In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of un...
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In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of unknown external ***,VTs are constructed for each QUAV,and the QUAV is restricted into the corresponding VT by the artificial potential field,which is distributed around the boundary of the ***,the collisions between QUAVs are ***,the boundaries of the VTs are flexible by the modification signals,which are generated by the self-regulating auxiliary systems,to make the repulsive force smaller and give more buffer space for QUAVs without ***,a novel ET mechanism is designed by introducing the concept of prediction to the traditional fixed threshold ET ***,a disturbance observer is proposed to deal with the adverse effects of the unknown external *** this basis,a distributed ET collision avoidance coordinated controller is ***,the proposed controller is quantized by the hysteresis uniform quantizer and then sent to the actuator only at the ET *** boundedness of the closed-loop signals is verified by the Lyapunov ***,simulation and experimental results are performed to demonstrate the superiority of the proposed control method.
Terahertz(THz)wireless communication has been recognized as a powerful technology to meet the everincreasing demand of ultra-high rate *** order to achieve efficient andreliable wireless communications over THz bands...
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Terahertz(THz)wireless communication has been recognized as a powerful technology to meet the everincreasing demand of ultra-high rate *** order to achieve efficient andreliable wireless communications over THz bands,it is extremely necessary to find an appropriate waveform for THz *** this paper,performance comparison of various single-carrier and multi-carrier waveforms over THz channels will be ***,first,a system model for terahertz communication is briefly described,which includes amplifier nonlinearity,propagation characteristic,phase noise,***,the transceiver architectures related to both single-carrier and multi-carrier waveforms are presented,as well as their corresponding signal processing *** evaluate the suitability of the waveforms,key performance metrics concerning power efficiency,transmission performance,and computational complexity are *** results are provided to compare and validate the performance of different waveforms,which demonstrate the outstanding performance of discrete-Fourier-Transform spread Orthogonal Frequency division Multiplexing(dFT-s-OFdM)to THz communications when compared to Cyclic Prefix-OFdM(CP-OFdM)and other single-carrier waveforms.
With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable ***,the virtual synchronous generator(VSG)control is recognized as the m...
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With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable ***,the virtual synchronous generator(VSG)control is recognized as the mainstream control strategy for grid-forming *** permanent magnet synchronous generator(PMSG)based wind generation systems connected to power grid via VSG-controlled grid-forming inverters,some novel impacts on the low-frequency oscillations(LFOs)emerge in power *** first impact involves the negative/positive damping effect on *** this paper,the small-signal torque model of VSG-controlled PMSGbased wind generation systems is established based on the damping torque analysis method,revealing the influence mechanism of machine-side dynamics on LFOs and proving the necessity of the double-mass model for accurate stability *** second impact is the resonance effect between torsional oscillation and ***,this paper uses the open-loop resonance analysis method to study the resonance mechanism and to predict the root ***,a damping enhancement strategy is proposed to weaken and eliminate the negative damping effect of machine-side dynamics on LFOs and the resonance effect between torsional oscillation and ***,the analysis result is validated through a case study involving the connection of the VSG-controlled PMSG-based wind generation system to the IEEE 39-bus AC grid,supporting the industrial application and stable operation of VSG-controlled PMSGbased wind generation systems.
The complexity and uncertainty in power systems cause great challenges to controlling power *** a populardata-driven technique,deep reinforcement learning(drL)attracts attention in the control of power ***,drL has so...
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The complexity and uncertainty in power systems cause great challenges to controlling power *** a populardata-driven technique,deep reinforcement learning(drL)attracts attention in the control of power ***,drL has some inherent drawbacks in terms of data efficiency and *** paper presents a novel hierarchical task planning(HTP)approach,bridging planning anddrL,to the task of power line flow ***,we introduce a threelevel task hierarchy to model the task and model the sequence of task units on each level as a task planning-Markov decision processes(TP-MdPs).Second,we model the task as a sequential decision-making problem and introduce a higher planner and a lower planner in HTP to handle different levels of task *** addition,we introduce a two-layer knowledge graph that can update dynamically during the planning procedure to assist *** results conducted on the IEEE 118-bus and IEEE 300-bus systems demonstrate our HTP approach outperforms proximal policy optimization,a state-of-the-art deep reinforcement learning(drL)approach,improving efficiency by 26.16%and 6.86%on both systems.
In this study,we investigate the pseudospectrum and spectrum(in)stability of quantum corrected Schwarzschild black ***,we use the hyperboloidal framework to cast the quasinormal mode(QNM)problem into an eigenvalue pro...
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In this study,we investigate the pseudospectrum and spectrum(in)stability of quantum corrected Schwarzschild black ***,we use the hyperboloidal framework to cast the quasinormal mode(QNM)problem into an eigenvalue problem associated with a non-selfadjoint operator,and then the spectrum and pseudospectrum are ***,the invariant subspace method is exploited to improve the computational efficiency for *** investigation into the spectrum(in)stability entails two main *** the one hand,we calculate the spectra of the quantum corrected black hole,then by the means of the migration ratio,the impact of the quantum correction effect on the Schwarzschild black hole has been *** results indicate that the so-called“migration ratio instability”will occur for small black holes with small angular momentum number *** the eikonal limit,the migration ratios remain the same for each *** the other hand,we study the spectrum(in)stability of the quantum corrected black hole by directly adding some particular perturbations into the effective potential,where perturbations are located at the event horizon and null infinity,*** are two interesting observations under the same perturbation energy ***,perturbations at infinity are more capable of generating spectrum instability than those at the event ***,we find that the peak distribution can lead to the instability of QNM spectrum more efficiently than the average distribution.
Grid-following voltage source converter(GFLVSC)and grid-forming voltage source converter(GFM-VSC)have different dynamic characteristics for active power-frequency andreactive power-voltage supports of the power *** p...
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Grid-following voltage source converter(GFLVSC)and grid-forming voltage source converter(GFM-VSC)have different dynamic characteristics for active power-frequency andreactive power-voltage supports of the power *** paper aims to clarify andrecognize the difference between gridfollowing(GFL)and grid-forming(GFM)frequency-voltage support more intuitively and ***,the phasor model considering circuit constraints is established based on the port circuit equations of the *** is revealed that the voltage and active power linearly correspond to the horizontal and vertical axes in the phasor space referenced to the grid voltage ***,based on topological homology,GFL and GFM controls are transformed and mapped into different *** topological similarity of the characteristic curves for GFL and GFM controls is the essential cause of their *** on the above model,it is indicated that GFL-VSC and GFM-VSC possess uniformity with regard to active powerresponse,type of coupling,and phasor *** differ in synchronization,power coupling mechanisms,dynamics,and active power-voltage operation domain in the quasi-steady *** studies are undertaken on GFL-VSC and GFM-VSC integrated into a four-machine two-area *** results verify that the dynamic uniformity anddifference of GFL-VSC and GFM-VSC are intuitively and comprehensively revealed.
The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigatedduring uniaxial tensile ***-situ observations under scanning electron microscopy,transmission ele...
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The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigatedduring uniaxial tensile ***-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation *** findings were discussed with the local strain measurements via digital image *** results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sizedretained austenite(rA),which led to localized stress concentrations and strain hardening and furtherretardation of *** small-sizedrA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier *** volume fraction of rA gradually decreased from 26.8%to 8.2%prior to *** the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.
The demand for anisotropic aerogels with excellent comprehensive properties in cutting-edge fields such as aerospace is *** on the above background,a novel heterocyclic para-aramid nanofiber/reduced graphene oxide(HPA...
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The demand for anisotropic aerogels with excellent comprehensive properties in cutting-edge fields such as aerospace is *** on the above background,a novel heterocyclic para-aramid nanofiber/reduced graphene oxide(HPAN/rGO)composite aerogel was prepared by combining electrospinning and unidirectional *** anisotropic HPAN/rGO composite aerogel exhibited a honeycomb morphology in the direction perpendicular to the growth of ice crystals,and a through-well structure of directed microchannels in the direction parallel to the temperature *** varying the mass ratio of HPAN/rGO,a composite aerogel with an ultra-low density of 5.34-7.81 mg·cm^(-3) and an ultra-high porosity of 98%-99%was *** from the anisotropic structure,the radial and axial thermal conductivities of HPAN/rGO-3 composite aerogel were 29.37 and 44.35 mW·m^(-1)·K^(-1),respectively.A combination of software simulation and experiments was used to analyze the effect of anisotropic structures on the thermal insulation properties of ***,due to the intrinsic self-extinguishing properties of heterocyclic para-aramid and the protection of the graphene carbon layer,the composite aerogel also exhibits excellent flame retardancy properties,and its total heat release rate(THr)was only 5.8 kJ·g^(-1),which is far superior to many reported ***,ultralight anisotropic HPAN/rGO composite aerogels with excellent high-temperature thermal insulation and flame retardancy properties have broad application prospects in complex environments such as aerospace.
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