Due to the time-varying topology and possible disturbances in a conflict environment,it is still challenging to maintain the mission performance of flying Ad hoc networks(FANET),which limits the application of Unmanne...Due to the time-varying topology and possible disturbances in a conflict environment,it is still challenging to maintain the mission performance of flying Ad hoc networks(FANET),which limits the application of Unmanned Aerial Vehicle(UAV)swarms in harsh environments.This paper proposes an intelligent framework to quickly recover the cooperative coveragemission by aggregating the historical spatio-temporal network with the attention mechanism.The mission resilience metric is introduced in conjunction with connectivity and coverage status information to simplify the optimization model.A spatio-temporal node pooling method is proposed to ensure all node location features can be updated after destruction by capturing the temporal network structure.Combined with the corresponding Laplacian matrix as the hyperparameter,a recovery algorithm based on the multi-head attention graph network is designed to achieve rapid recovery.Simulation results showed that the proposed framework can facilitate rapid recovery of the connectivity and coverage more effectively compared to the existing studies.The results demonstrate that the average connectivity and coverage results is improved by 17.92%and 16.96%,respectively compared with the state-of-the-art model.Furthermore,by the ablation study,the contributions of each different improvement are compared.The proposed model can be used to support resilient network design for real-time mission execution.展开更多
Refractory high-entropy alloys(RHEAs)have promising applications as the new generation of hightemperature alloys in hypersonic vehicles,aero-engines,gas turbines,and nuclear power plants.This study focuses on the micr...Refractory high-entropy alloys(RHEAs)have promising applications as the new generation of hightemperature alloys in hypersonic vehicles,aero-engines,gas turbines,and nuclear power plants.This study focuses on the microstructures and mechanical properties of the NbMoTaW(HfN)_(x)(x=0,0.3,0.7,and 1.0)RHEAs.The alloys consist of multiple phases of body-centered cubic(BCC),hafnium nitride(HfN),or multicomponent nitride(MN)phases.As the x contents increase,the grain size becomes smaller,and the strength gradually increases.The compressive yield strengths of the NbMoTaWHfN RHEA at ambient temperature,1000,1400,and 1800℃ were found to be 1682,1192,792,and 288 MPa,respectively.The high-temperature strength of this alloy is an inspiring result that exceeds the high temperature and strength of most known alloys,including high-entropy alloys,refractory metals,and superalloys.The HfN phase has a significant effect on strengthening due to its high structural stability and sluggish grain coarsening,even at ultra-high temperatures.Its superior properties endow the NbMoTaWHfN RHEA with potential for a wide range of engineering applications at ultra-high temperatures.This work offers a strategy for the design of high-temperature alloys and proposes an ultra-high-temperature alloy with potential for future engineering applications.展开更多
This paper investigates the anti-jamming communication scenario where an intelligent reflecting surface(IRS)is mounted on the unmanned aerial vehicle(UAV)to resist the malicious jamming attacks.Different from existing...This paper investigates the anti-jamming communication scenario where an intelligent reflecting surface(IRS)is mounted on the unmanned aerial vehicle(UAV)to resist the malicious jamming attacks.Different from existing works,we consider the dynamic deployment of IRS-UAV in the environment of the mobile user and unknown jammer.Therefore,a joint trajectory and passive beamforming optimization approach is proposed in the IRS-UAV enhanced networks.In detail,the optimization problem is firstly formulated into a Markov decision process(MDP).Then,a dueling double deep Q networks multi-step learning algorithm is proposed to tackle the complex and coupling decision-making problem.Finally,simulation results show that the proposed scheme can significantly improve the anti-jamming communication performance of the mobile user.展开更多
A new type of lightweight AlNiLa medium entropy amorphous alloy composite ribbons(labled as MEAAC ribbons)were prepared by vacuum arc melting technology and high-speed single roller meltspinning method.The microstruct...A new type of lightweight AlNiLa medium entropy amorphous alloy composite ribbons(labled as MEAAC ribbons)were prepared by vacuum arc melting technology and high-speed single roller meltspinning method.The microstructure and thermal stability of MEAAC ribbons were examined using X-ray diffraction,differential scanning calorimeter,and scanning electron microscope.Meanwhile,the hardness and surface roughness of these ribbons were measured by Vickers microhardness tester and atomic force microscope.The potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS)were applied to investigate the corrosion behavior of these MEAAC ribbons in simulated seawater(3.5wt%NaCl corrosive solution)at room temperature.The results demonstrate that AlNiLa MEAAC ribbons in the as-received state are mainly composed of amorphous phase and intermetallic compounds.The hardness values of all melt-spun ribbons are above 310 HV_(0.1).With the increase of Al content,the linear polarization resistances of four various AlNiLa MEAAC ribbons are negligibly different numerically.It is also found that Al_(45)Ni_(27.5)La_(27.5) MEAAC ribbons have the most positive corrosion potential and the smallest corrosion current density at the same time;hence it may be a kind of potential material for metal surface protection in harsh ocean environment.展开更多
Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed l...Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.展开更多
Lattice engineering and distortion have been considered one kind of effective strategies for discovering advanced materials.The instinct chemical flexibility of high-entropy oxides(HEOs)motivates/accelerates to tailor...Lattice engineering and distortion have been considered one kind of effective strategies for discovering advanced materials.The instinct chemical flexibility of high-entropy oxides(HEOs)motivates/accelerates to tailor the target properties through phase transformations and lattice distortion.Here,a hybrid knowledge-assisted data-driven machine learning(ML)strategy is utilized to discover the A_(2)B_(2)O_(7)-type HEOs with low thermal conductivity(κ)through 17 rare-earth(RE=Sc,Y,La-Lu)solutes optimized A-site.A designing routine integrating the ML and high throughput first principles has been proposed to predict the key physical parameter(KPPs)correlated to the targetedκof advanced HEOs.Among the smart-designed 6188(5RE_(0.2))_(2)Zr_(2)O_(7)HEOs,the best candidates are addressed and validated by the princi-ples of severe lattice distortion and local phase transformation,which effectively reduceκby the strong multi-phonon scattering and weak interatomic interactions.Particularly,(Sc_(0.2)Y_(0.2)La_(0.2)Ce_(0.2)Pr_(0.2))_(2)Zr_(2)O_(7)with predictedκbelow 1.59 Wm^(−1)K^(−1)is selected to be verified,which matches well with the ex-perimentalκ=1.69 Wm^(−1)K^(−1)at 300 K and could be further decreased to 0.14 Wm^(−1)K^(−1)at 1473 K.Moreover,the coupling effects of lattice vibrations and charges on heat transfer are revealed by the cross-validations of various models,indicating that the weak bonds with low electronegativity and few bond-ing charge density and the lattice distortion(r∗)identified by cation radius ratio(r A/r B)should be the KPPs to decreaseκefficiently.This work supports an intelligent designing strategy with limited atomic and electronic KPPs to accelerate the development of advanced multi-component HEOs with proper-ties/performance at multi-scales.展开更多
In recent years,there has been significant research on the application of deep learning(DL)in topology optimization(TO)to accelerate structural design.However,these methods have primarily focused on solving binary TO ...In recent years,there has been significant research on the application of deep learning(DL)in topology optimization(TO)to accelerate structural design.However,these methods have primarily focused on solving binary TO problems,and effective solutions for multi-material topology optimization(MMTO)which requires a lot of computing resources are still lacking.Therefore,this paper proposes the framework of multiphase topology optimization using deep learning to accelerate MMTO design.The framework employs convolutional neural network(CNN)to construct a surrogate model for solving MMTO,and the obtained surrogate model can rapidly generate multi-material structure topologies in negligible time without any iterations.The performance evaluation results show that the proposed method not only outputs multi-material topologies with clear material boundary but also reduces the calculation cost with high prediction accuracy.Additionally,in order to find a more reasonable modeling method for MMTO,this paper studies the characteristics of surrogate modeling as regression task and classification task.Through the training of 297 models,our findings show that the regression task yields slightly better results than the classification task in most cases.Furthermore,The results indicate that the prediction accuracy is primarily influenced by factors such as the TO problem,material category,and data scale.Conversely,factors such as the domain size and the material property have minimal impact on the accuracy.展开更多
We reported on the mechanical properties and microstructural evolution of a W_(20)Ta_(30)Mo_(20)C_(30)(at.%)re-fractory high-entropy composite(RHEC).The RHEC exhibited outstanding yield strength at both 2273 and 1873 ...We reported on the mechanical properties and microstructural evolution of a W_(20)Ta_(30)Mo_(20)C_(30)(at.%)re-fractory high-entropy composite(RHEC).The RHEC exhibited outstanding yield strength at both 2273 and 1873 K.Microstructural investigations revealed that the as-cast RHEC had a triple-phase structure con-sisting of FCC dendrites,HCP matrix,HCP-BCC eutectic structure,and FCC-BCC eutectoid structure,and exhibited high-density defects owing to the complex phase transformations during solidification.After annealing at 2273 K,the precipitation of the BCC phase from the FCC dendrites and the decomposition of the HCP phase into the FCC-BCC eutectoid structure was observed to significantly refine the grain sizes of all triple phases.After compression at 2273 K,the ceramic phases and solid solution precipitated out from each other,which helps to avoid persistent softening after the yielding of RHEC.Further analyses sug-gested that the dominant deformation mechanisms of the BCC phase and HCP phase are dislocation glide and transformation-induced plasticity;whereas those of the FCC phase are twinning-and transformation-induced plasticity.The outstanding yield strength of this RHEC at ultrahigh temperatures may originate from the high-content ceramic phases and the structural metastability of the multi-principal composition.These findings provide a novel strategy to design RHECs by alloying high-content nonmetallic elements,which contributes to further breaking through their performance limits at ultrahigh temperatures.展开更多
Nitride-reinforced(HfNbTaTiV)_(90)N_(10) high-entropy alloy aiming at high-temperature applications is de-signed in this paper.Abundant FCC nitride phases are formed in situ in theBCC matrix by arc melt-ing technique,...Nitride-reinforced(HfNbTaTiV)_(90)N_(10) high-entropy alloy aiming at high-temperature applications is de-signed in this paper.Abundant FCC nitride phases are formed in situ in theBCC matrix by arc melt-ing technique,without complex deformation or heat treatment.The(HfNbTaTiV)_(90)N_(10) alloy exhibits a remarkable yield strength of 2716 MPa and ultimate compressive strength of 2833 MPa with a plas-tic strain of 10%at room temperature.Besides,the alloy remains a high yield strength of 279 MPa at 1400℃.The nitride phases play an essential role in maintaining the excellent strength-ductility com-bination at room temperature and enhancing the high-temperature softening resistance.Alternating BCC and FCC phases possess the semi-coherent interface,which not only strengthens the BCC matrix but also promotes the compatible deformation of the duplex microstructure.The lattice coherency structure of the semi-coherent interface is conducive to the slip transfer of partial dislocations through the interface,which facilitates the accommodation of plastic deformation.The cross-slip of the screw dislocations ef-fectively eliminates stress concentration and leads to good ductility of the dual-phase alloy.The results demonstrate that the nitride phases achieve coordinate deformation with the matrix without deteriorat-ing the ductility of the(HfNbTaTiV)_(90)N_(10) alloy.展开更多
The last decade has witnessed significant progress and extensive applications of unmanned aerial vehicles(UAVs),thanks to their exceptional mobility,cost-effectiveness,and versatile deployment capabilities.1 With cont...The last decade has witnessed significant progress and extensive applications of unmanned aerial vehicles(UAVs),thanks to their exceptional mobility,cost-effectiveness,and versatile deployment capabilities.1 With continuous advances in sensing,communication,and processing technologies,using UAV swarms to provide cost-effective services in future smart cities is expected to become ubiquitous.These services encompass a wide spectrum of applications,ranging from large-scale infrastructure inspection,geospatial land surveying,and traffic/crowd monitoring,to three-dimensional terrain mapping.2 In these scenarios,UAVs are typically equipped with onboard sensors such as cameras and LiDARs,to gather environmental information by analyzing the sensor data such as captured videos and point clouds.The key technologies to achieve autonomous information-gathering flight for UAV swarms include information extraction from sensor data,transmission and fusion of the extracted information among UAVs,and planning and coordination of their trajectories to ensure safe and efficient mission accomplishment.展开更多
High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated tempera...High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated temperatures are promising candidates for high-temperature structural materials.In this work,a WTaMoNbTi RHEA with adequate room temperature plasticity and considerable strength at 1600℃was fabricated by vacuum arc-melting.The room temperature fracture strain of the as-cast WTaMoNbTi RHEA was 7.8%,which was about 5.2 times that of the NbMoTaW alloy.The alloy exhibited a strong resistance to high-temperature softening,with a high yield strength of 173 MPa and compressive strength of 218 MPa at 1600℃.The WTaMoNbTi RHEA possessed excellent phase stability in the range of room temperature to 2000℃.The dendritic grains grew into equiaxed grains after compression test at 1600℃due to the dynamic recrystallization process at high temperature.This work presents a promising high-temperature structural material that can be applied at 1600℃.展开更多
In this work,the effect of Re alloying on the phase composition,crystal structure,and mechanical properties of NbMoTaWRe_(x) (x=0,0.27,0.57,0.92,1.33) refractory high-entropy alloys (RHEAs) were systematically investi...In this work,the effect of Re alloying on the phase composition,crystal structure,and mechanical properties of NbMoTaWRe_(x) (x=0,0.27,0.57,0.92,1.33) refractory high-entropy alloys (RHEAs) were systematically investigated by combining the calculation of phase diagram(CALPHAD),first-principle calculations and experiment.The theoretical predictions showed good consistency with the experimental results.As the increase in Re content,the theoretical results showed that all considered alloys have a single body-centered cubic (bcc) structure and the lattice constant and ductility were decreased,while the elastic moduli and hardness were improved.To avoid extreme brittleness,a strategic suggestion was given for the design of Re-containing RHEAs in the future.展开更多
Dissipative Kerr solitons(DKSs)with mode-locked pulse trains in high-Q optical microresonators possess lownoise and broadband parallelized comb lines,having already found plentiful cutting-edge applications.However,th...Dissipative Kerr solitons(DKSs)with mode-locked pulse trains in high-Q optical microresonators possess lownoise and broadband parallelized comb lines,having already found plentiful cutting-edge applications.However,thermal bistability and thermal noise caused by the high microresonator power and large temperature exchange between microresonator and the environment would prevent soliton microcomb formation and deteriorate the phase and frequency noise.Here,a novel method that combines rapid frequency sweep with optical sideband thermal compensation is presented,providing a simple and reliable way to get into the single-soliton state.Meanwhile,it is shown that the phase and frequency noises of the generated soliton are greatly reduced.Moreover,by closing the locking loop,an in-loop repetition rate fractional instability of 5.5×10^(-15)at 1 s integration time and a triangular linear repetition rate sweep with 2.5 MHz could be realized.This demonstration provides a means for the generation,locking,and tuning of a soliton microcomb,paving the way for the application of single-soliton microcombs in low-phase-noise microwave generation and laser ranging.展开更多
The thermal issue is of great importance during the layout design of heat source components in systems engineering,especially for high functional-density products.Thermal analysis requires complex simulation,which lea...The thermal issue is of great importance during the layout design of heat source components in systems engineering,especially for high functional-density products.Thermal analysis requires complex simulation,which leads to an unaffordable computational burden to layout optimization as it iteratively evaluates different schemes.Surrogate modeling is an effective method for alleviating computation complexity.However,the temperature field prediction(TFP)with complex heat source layout(HSL)input is an ultra-high dimensional nonlinear regression problem,which brings great difficulty to traditional regression models.The deep neural network(DNN)regression method is a feasible way for its good approximation performance.However,it faces great challenges in data preparation for sample diversity and uniformity in the layout space with physical constraints and proper DNN model selection and training for good generality,which necessitates the efforts of layout designers and DNN experts.To advance this cross-domain research,this paper proposes a DNN-based HSL-TFP surrogate modeling task benchmark.With consideration for engineering applicability,sample generation,dataset evaluation,DNN model,and surrogate performance metrics are thoroughly investigated.Experiments are conducted with ten representative state-of-the-art DNN models.A detailed discussion on baseline results is provided,and future prospects are analyzed for DNN-based HSL-TFP tasks.展开更多
We present a theoretical analysis of a novel multi-channel light amplification photonic system on chip,where the nonlinear Raman amplification phenomenon in the silicon(Si)wire waveguide is considered.Particularly,a c...We present a theoretical analysis of a novel multi-channel light amplification photonic system on chip,where the nonlinear Raman amplification phenomenon in the silicon(Si)wire waveguide is considered.Particularly,a compact and temperature insensitive Mach–Zehnder interferometer filter working as demultiplexer is also exploited,allowing for the whole Si photonic system to be free from thermal interference.The propagation of the multi-channel pump and Stokes lights is described by a rigorous theoretical model that incorporates all relevant linear and nonlinear optical effects,including the intrinsic waveguide optical losses,first-and second-order frequency dispersion,self-phase and cross-phase modulation,phase shift and two-photon absorption,free-carriers dynamics,as well as the inter-pulse Raman interaction.Notably,to prevent excessive drift of the transmission window of the demultiplexer caused by ambient temperature variations and high thermo-optical coefficient of Si,an asymmetric waveguide width is adopted in the upper and lower arms of each Mach–Zehnder interferometer lattice cell.A Chebyshev half-band filter is utilized to achieve a flat pass-band transmission,achieving a temperature sensitivity of<1.4 pm=K and over 100 K temperature span.This all-Si amplifier shows a thermally robust behavior,which is desired by future Si-on-insulator(SOI)applications.展开更多
Novel composites of HfNbTaTiZrV refractory high-entropy alloy(RHEA)reinforced with 0–4 vol.%Al_(2)O_(3)particles have been synthesized by vacuum arc melting.The microstructure evolution,compressive mechanical propert...Novel composites of HfNbTaTiZrV refractory high-entropy alloy(RHEA)reinforced with 0–4 vol.%Al_(2)O_(3)particles have been synthesized by vacuum arc melting.The microstructure evolution,compressive mechanical properties at room and elevated temperatures,as well as strengthening mechanism of the composites were analyzed.The HfNbTaTiZrV RHEA reinforced with 4 vol.%Al_(2)O_(3)displayed excellent phase stability at elevated temperatures.A superior compressive yield strength of 2700 MPa at room temperature,1392 MPa at 800°C,and 693 MPa at 1000°C was obtained for this composite.The improved yield strength resulted from multiple strengthening mechanisms caused by Al_(2)O_(3)addition,including solution strengthening,interstitial strengthening,grain boundary strengthening,and dispersion strengthening.Besides,the effects of interstitial strengthening increased with temperature and was the main strengthening mechanism at elevated temperatures.These findings not only promote the development of oxidereinforced RHEAs for challenging engineering applications but also provide guidelines for the design of light refractory materials with multiple strengthening mechanisms.展开更多
Entropy-stabilized multi-component alloys have been considered to be prospective structural materials attributing to their impressive mechanical and functional properties.The local chemical complexions,microstates and...Entropy-stabilized multi-component alloys have been considered to be prospective structural materials attributing to their impressive mechanical and functional properties.The local chemical complexions,microstates and configurational transformations are essential to reveal the structure–property relationship,thus,to promote the development of advanced multicomponent alloys.In the present work,effects of local lattice distortion(LLD)and microstates of various configurations on the equilibrium volume(V0),total energy,Fermi energy,magnetic moment(μMag)and electron work function(Φ)and bonding structures of the Fe–Mn–Al medium entropy alloy(MEA)have been investigated comprehensively by first-principles calculations.It is found that theΦandμMag of those MEA are proportional to the V 0,which is dominated by lattice distortion.In terms of bonding charge density,both the strengthened clusters or the so-called short-range order structures and the weakly bonded spots or weak spots are characterized.While the presence of weakly bonded Al atoms implies a large LLD/mismatch,the Fe–Mn bonding pairs result in the formation of strengthened clusters,which dominate the local microstates and the configurational transitions.The variations ofμMag are associated with the enhancement of the nearest neighbor magnetic Fe and Mn atoms,attributing to the LLD caused by Al atoms,the local changes in the electronic structures.This work provides an atomic and electronic insight into the microstate-dominated solid-solution strengthening mechanism of Fe–Mn–Al MEA.展开更多
Surface electromyography(EMG) is a bioelectrical signal that recognizes speech contents in a non-acoustic form. Activity detection is an important research direction in EMG research. However, in the low signal-to-nois...Surface electromyography(EMG) is a bioelectrical signal that recognizes speech contents in a non-acoustic form. Activity detection is an important research direction in EMG research. However, in the low signal-to-noise ratio(SNR) environment, it is difficult for traditional methods to obtain accurate active signals. This paper proposes a new energy-based spectral subtraction backtracking(E-SSB) method to segment EMG active signal in the low SNR environment. Compared with traditional energy detection, the algorithm in this paper adds spectral subtraction(SS) to filter out the clutter, and raises a retrospective idea to improve the classification performance. The experiment results show the proposed activity detection method is more effective than other methods in the low SNR environment.展开更多
In the satellite overall design phase,it is a crucial step to perform satellite layout design to guarantee that the aggregation of electronic components can operate normally and stably in an appropriate temperature en...In the satellite overall design phase,it is a crucial step to perform satellite layout design to guarantee that the aggregation of electronic components can operate normally and stably in an appropriate temperature environment.In order to handle the satellite payload placement problem of the DongFangHong 4(DFH-4)platform,the heat pipe-constrained component layout optimization(HCLO)problem is proposed with the HCLO model formulated.Through careful investigation,it can be divided into two optimization subproblems that can be solved subsequently.Based on the divide-and-conquer strategy,an integer linear programming-(ILP-)assisted two-stage layout optimization method is proposed.In stage one,component-heat pipe distribution optimization is performed using the ILP technique so that specific heat pipes occupied by each component can be determined and the horizontal movement range of components can be reduced.In stage two,the detailed component layout optimization is investigated to obtain the final positions of components.First,the sequence layout sampling(SeqLS)method is used to generate one nonoverlap initial layout.Next,swap operation between components is incorporated to reduce the centroid deviation.Finally,sequential quadratic programming(SQP)search is conducted based on the generated promising initial layout solutions.Therefore,the SeqLS-based heuristic layout search algorithm is proposed in the second stage.Two layout test cases,including 15 components and 90 components,respectively,are investigated to demonstrate the validity and efficacy of the proposed layout design method.Experimental results show that it is promising to apply such a two-stage approach for satellite payload placement in engineering.展开更多
基金the National Natural Science Foundation of China(NNSFC)(Grant Nos.72001213 and 72301292)the National Social Science Fund of China(Grant No.19BGL297)the Basic Research Program of Natural Science in Shaanxi Province(Grant No.2021JQ-369).
文摘Due to the time-varying topology and possible disturbances in a conflict environment,it is still challenging to maintain the mission performance of flying Ad hoc networks(FANET),which limits the application of Unmanned Aerial Vehicle(UAV)swarms in harsh environments.This paper proposes an intelligent framework to quickly recover the cooperative coveragemission by aggregating the historical spatio-temporal network with the attention mechanism.The mission resilience metric is introduced in conjunction with connectivity and coverage status information to simplify the optimization model.A spatio-temporal node pooling method is proposed to ensure all node location features can be updated after destruction by capturing the temporal network structure.Combined with the corresponding Laplacian matrix as the hyperparameter,a recovery algorithm based on the multi-head attention graph network is designed to achieve rapid recovery.Simulation results showed that the proposed framework can facilitate rapid recovery of the connectivity and coverage more effectively compared to the existing studies.The results demonstrate that the average connectivity and coverage results is improved by 17.92%and 16.96%,respectively compared with the state-of-the-art model.Furthermore,by the ablation study,the contributions of each different improvement are compared.The proposed model can be used to support resilient network design for real-time mission execution.
基金supported by the National Key Research and Development Program of China(2023YFE0201600 and 2018YFC1902400)the National Natural Science Foundation of China(51975582)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Refractory high-entropy alloys(RHEAs)have promising applications as the new generation of hightemperature alloys in hypersonic vehicles,aero-engines,gas turbines,and nuclear power plants.This study focuses on the microstructures and mechanical properties of the NbMoTaW(HfN)_(x)(x=0,0.3,0.7,and 1.0)RHEAs.The alloys consist of multiple phases of body-centered cubic(BCC),hafnium nitride(HfN),or multicomponent nitride(MN)phases.As the x contents increase,the grain size becomes smaller,and the strength gradually increases.The compressive yield strengths of the NbMoTaWHfN RHEA at ambient temperature,1000,1400,and 1800℃ were found to be 1682,1192,792,and 288 MPa,respectively.The high-temperature strength of this alloy is an inspiring result that exceeds the high temperature and strength of most known alloys,including high-entropy alloys,refractory metals,and superalloys.The HfN phase has a significant effect on strengthening due to its high structural stability and sluggish grain coarsening,even at ultra-high temperatures.Its superior properties endow the NbMoTaWHfN RHEA with potential for a wide range of engineering applications at ultra-high temperatures.This work offers a strategy for the design of high-temperature alloys and proposes an ultra-high-temperature alloy with potential for future engineering applications.
基金This work was supported in part by the National Natural Science Foundation of China(No.61971474,No.61771488)in part by the Beijing Nova Program under Grant Z201100006820121in part by China Postdoctoral Science Foundation Funded Project under Grant 2019T120071.
文摘This paper investigates the anti-jamming communication scenario where an intelligent reflecting surface(IRS)is mounted on the unmanned aerial vehicle(UAV)to resist the malicious jamming attacks.Different from existing works,we consider the dynamic deployment of IRS-UAV in the environment of the mobile user and unknown jammer.Therefore,a joint trajectory and passive beamforming optimization approach is proposed in the IRS-UAV enhanced networks.In detail,the optimization problem is firstly formulated into a Markov decision process(MDP).Then,a dueling double deep Q networks multi-step learning algorithm is proposed to tackle the complex and coupling decision-making problem.Finally,simulation results show that the proposed scheme can significantly improve the anti-jamming communication performance of the mobile user.
基金by the National Key R&D Program of China(No.2018YFC1902400)the National Natural Science Foundation of China(No.51975582)the Natural Science Foundation of Beijing,China(No.2212055)。
文摘A new type of lightweight AlNiLa medium entropy amorphous alloy composite ribbons(labled as MEAAC ribbons)were prepared by vacuum arc melting technology and high-speed single roller meltspinning method.The microstructure and thermal stability of MEAAC ribbons were examined using X-ray diffraction,differential scanning calorimeter,and scanning electron microscope.Meanwhile,the hardness and surface roughness of these ribbons were measured by Vickers microhardness tester and atomic force microscope.The potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS)were applied to investigate the corrosion behavior of these MEAAC ribbons in simulated seawater(3.5wt%NaCl corrosive solution)at room temperature.The results demonstrate that AlNiLa MEAAC ribbons in the as-received state are mainly composed of amorphous phase and intermetallic compounds.The hardness values of all melt-spun ribbons are above 310 HV_(0.1).With the increase of Al content,the linear polarization resistances of four various AlNiLa MEAAC ribbons are negligibly different numerically.It is also found that Al_(45)Ni_(27.5)La_(27.5) MEAAC ribbons have the most positive corrosion potential and the smallest corrosion current density at the same time;hence it may be a kind of potential material for metal surface protection in harsh ocean environment.
基金supported by the National Natural Science Foundation of China(Nos.52105233 and 52275366)the Tianjin Science and Technology Plan Project(No.22JCYBJC01590).
文摘Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.
基金supported by National defense ba-sic scientific research(Grant Nos.2022-JCKY-JJ-1086 and 211-CXCY-N103-03-04-00).
文摘Lattice engineering and distortion have been considered one kind of effective strategies for discovering advanced materials.The instinct chemical flexibility of high-entropy oxides(HEOs)motivates/accelerates to tailor the target properties through phase transformations and lattice distortion.Here,a hybrid knowledge-assisted data-driven machine learning(ML)strategy is utilized to discover the A_(2)B_(2)O_(7)-type HEOs with low thermal conductivity(κ)through 17 rare-earth(RE=Sc,Y,La-Lu)solutes optimized A-site.A designing routine integrating the ML and high throughput first principles has been proposed to predict the key physical parameter(KPPs)correlated to the targetedκof advanced HEOs.Among the smart-designed 6188(5RE_(0.2))_(2)Zr_(2)O_(7)HEOs,the best candidates are addressed and validated by the princi-ples of severe lattice distortion and local phase transformation,which effectively reduceκby the strong multi-phonon scattering and weak interatomic interactions.Particularly,(Sc_(0.2)Y_(0.2)La_(0.2)Ce_(0.2)Pr_(0.2))_(2)Zr_(2)O_(7)with predictedκbelow 1.59 Wm^(−1)K^(−1)is selected to be verified,which matches well with the ex-perimentalκ=1.69 Wm^(−1)K^(−1)at 300 K and could be further decreased to 0.14 Wm^(−1)K^(−1)at 1473 K.Moreover,the coupling effects of lattice vibrations and charges on heat transfer are revealed by the cross-validations of various models,indicating that the weak bonds with low electronegativity and few bond-ing charge density and the lattice distortion(r∗)identified by cation radius ratio(r A/r B)should be the KPPs to decreaseκefficiently.This work supports an intelligent designing strategy with limited atomic and electronic KPPs to accelerate the development of advanced multi-component HEOs with proper-ties/performance at multi-scales.
基金supported in part by National Natural Science Foundation of China under Grant Nos.51675525,52005505,and 62001502Post-Graduate Scientific Research Innovation Project of Hunan Province under Grant No.XJCX2023185.
文摘In recent years,there has been significant research on the application of deep learning(DL)in topology optimization(TO)to accelerate structural design.However,these methods have primarily focused on solving binary TO problems,and effective solutions for multi-material topology optimization(MMTO)which requires a lot of computing resources are still lacking.Therefore,this paper proposes the framework of multiphase topology optimization using deep learning to accelerate MMTO design.The framework employs convolutional neural network(CNN)to construct a surrogate model for solving MMTO,and the obtained surrogate model can rapidly generate multi-material structure topologies in negligible time without any iterations.The performance evaluation results show that the proposed method not only outputs multi-material topologies with clear material boundary but also reduces the calculation cost with high prediction accuracy.Additionally,in order to find a more reasonable modeling method for MMTO,this paper studies the characteristics of surrogate modeling as regression task and classification task.Through the training of 297 models,our findings show that the regression task yields slightly better results than the classification task in most cases.Furthermore,The results indicate that the prediction accuracy is primarily influenced by factors such as the TO problem,material category,and data scale.Conversely,factors such as the domain size and the material property have minimal impact on the accuracy.
基金This work is supported by the National Key Research and Development Program of China(Grant No.2018YFC1902400)the National Natural Science Foundation of China(Grant No.51975582)the Key Research and Development Program of Jiangsu Province(Grant No.BE2021088).
文摘We reported on the mechanical properties and microstructural evolution of a W_(20)Ta_(30)Mo_(20)C_(30)(at.%)re-fractory high-entropy composite(RHEC).The RHEC exhibited outstanding yield strength at both 2273 and 1873 K.Microstructural investigations revealed that the as-cast RHEC had a triple-phase structure con-sisting of FCC dendrites,HCP matrix,HCP-BCC eutectic structure,and FCC-BCC eutectoid structure,and exhibited high-density defects owing to the complex phase transformations during solidification.After annealing at 2273 K,the precipitation of the BCC phase from the FCC dendrites and the decomposition of the HCP phase into the FCC-BCC eutectoid structure was observed to significantly refine the grain sizes of all triple phases.After compression at 2273 K,the ceramic phases and solid solution precipitated out from each other,which helps to avoid persistent softening after the yielding of RHEC.Further analyses sug-gested that the dominant deformation mechanisms of the BCC phase and HCP phase are dislocation glide and transformation-induced plasticity;whereas those of the FCC phase are twinning-and transformation-induced plasticity.The outstanding yield strength of this RHEC at ultrahigh temperatures may originate from the high-content ceramic phases and the structural metastability of the multi-principal composition.These findings provide a novel strategy to design RHECs by alloying high-content nonmetallic elements,which contributes to further breaking through their performance limits at ultrahigh temperatures.
基金supported by the National Natural Science Foun-dation of China(No.51975582)the Jiangsu Provincial Key Re-search and Development Program(No.BE2021088).
文摘Nitride-reinforced(HfNbTaTiV)_(90)N_(10) high-entropy alloy aiming at high-temperature applications is de-signed in this paper.Abundant FCC nitride phases are formed in situ in theBCC matrix by arc melt-ing technique,without complex deformation or heat treatment.The(HfNbTaTiV)_(90)N_(10) alloy exhibits a remarkable yield strength of 2716 MPa and ultimate compressive strength of 2833 MPa with a plas-tic strain of 10%at room temperature.Besides,the alloy remains a high yield strength of 279 MPa at 1400℃.The nitride phases play an essential role in maintaining the excellent strength-ductility com-bination at room temperature and enhancing the high-temperature softening resistance.Alternating BCC and FCC phases possess the semi-coherent interface,which not only strengthens the BCC matrix but also promotes the compatible deformation of the duplex microstructure.The lattice coherency structure of the semi-coherent interface is conducive to the slip transfer of partial dislocations through the interface,which facilitates the accommodation of plastic deformation.The cross-slip of the screw dislocations ef-fectively eliminates stress concentration and leads to good ductility of the dual-phase alloy.The results demonstrate that the nitride phases achieve coordinate deformation with the matrix without deteriorat-ing the ductility of the(HfNbTaTiV)_(90)N_(10) alloy.
基金National Natural Science Foundation of China(62303486)National University of Defense Technology(NUDT)for its 70th anniversary.
文摘The last decade has witnessed significant progress and extensive applications of unmanned aerial vehicles(UAVs),thanks to their exceptional mobility,cost-effectiveness,and versatile deployment capabilities.1 With continuous advances in sensing,communication,and processing technologies,using UAV swarms to provide cost-effective services in future smart cities is expected to become ubiquitous.These services encompass a wide spectrum of applications,ranging from large-scale infrastructure inspection,geospatial land surveying,and traffic/crowd monitoring,to three-dimensional terrain mapping.2 In these scenarios,UAVs are typically equipped with onboard sensors such as cameras and LiDARs,to gather environmental information by analyzing the sensor data such as captured videos and point clouds.The key technologies to achieve autonomous information-gathering flight for UAV swarms include information extraction from sensor data,transmission and fusion of the extracted information among UAVs,and planning and coordination of their trajectories to ensure safe and efficient mission accomplishment.
基金financially supported by the National Key Research and Development Program of China(Grant No.2018YFC1902400)the National Natural Science Foundation of China(Grant No.51975582)。
文摘High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated temperatures are promising candidates for high-temperature structural materials.In this work,a WTaMoNbTi RHEA with adequate room temperature plasticity and considerable strength at 1600℃was fabricated by vacuum arc-melting.The room temperature fracture strain of the as-cast WTaMoNbTi RHEA was 7.8%,which was about 5.2 times that of the NbMoTaW alloy.The alloy exhibited a strong resistance to high-temperature softening,with a high yield strength of 173 MPa and compressive strength of 218 MPa at 1600℃.The WTaMoNbTi RHEA possessed excellent phase stability in the range of room temperature to 2000℃.The dendritic grains grew into equiaxed grains after compression test at 1600℃due to the dynamic recrystallization process at high temperature.This work presents a promising high-temperature structural material that can be applied at 1600℃.
基金financially supported by the National Key R&D Program of China (No.2018YFC1902400)the National Natural Science Foundation of China (No.51975582)the Program of China Scholarship Council (No.202006420036)。
文摘In this work,the effect of Re alloying on the phase composition,crystal structure,and mechanical properties of NbMoTaWRe_(x) (x=0,0.27,0.57,0.92,1.33) refractory high-entropy alloys (RHEAs) were systematically investigated by combining the calculation of phase diagram(CALPHAD),first-principle calculations and experiment.The theoretical predictions showed good consistency with the experimental results.As the increase in Re content,the theoretical results showed that all considered alloys have a single body-centered cubic (bcc) structure and the lattice constant and ductility were decreased,while the elastic moduli and hardness were improved.To avoid extreme brittleness,a strategic suggestion was given for the design of Re-containing RHEAs in the future.
基金National Key Research and Development Program of China(2020YFB2205804)National Natural Science Foundation of China(62075240)+1 种基金Science Fund for Distinguished Young Scholars of Hunan Province(2020JJ2036)Postgraduate Scientific Research Innovation Project of Hunan Province(CX20210004)。
文摘Dissipative Kerr solitons(DKSs)with mode-locked pulse trains in high-Q optical microresonators possess lownoise and broadband parallelized comb lines,having already found plentiful cutting-edge applications.However,thermal bistability and thermal noise caused by the high microresonator power and large temperature exchange between microresonator and the environment would prevent soliton microcomb formation and deteriorate the phase and frequency noise.Here,a novel method that combines rapid frequency sweep with optical sideband thermal compensation is presented,providing a simple and reliable way to get into the single-soliton state.Meanwhile,it is shown that the phase and frequency noises of the generated soliton are greatly reduced.Moreover,by closing the locking loop,an in-loop repetition rate fractional instability of 5.5×10^(-15)at 1 s integration time and a triangular linear repetition rate sweep with 2.5 MHz could be realized.This demonstration provides a means for the generation,locking,and tuning of a soliton microcomb,paving the way for the application of single-soliton microcombs in low-phase-noise microwave generation and laser ranging.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11725211,52005505,and 62001502)Postgraduate Scientific Research Innovation Project of Hunan Province(Grant No.CX20200023).
文摘The thermal issue is of great importance during the layout design of heat source components in systems engineering,especially for high functional-density products.Thermal analysis requires complex simulation,which leads to an unaffordable computational burden to layout optimization as it iteratively evaluates different schemes.Surrogate modeling is an effective method for alleviating computation complexity.However,the temperature field prediction(TFP)with complex heat source layout(HSL)input is an ultra-high dimensional nonlinear regression problem,which brings great difficulty to traditional regression models.The deep neural network(DNN)regression method is a feasible way for its good approximation performance.However,it faces great challenges in data preparation for sample diversity and uniformity in the layout space with physical constraints and proper DNN model selection and training for good generality,which necessitates the efforts of layout designers and DNN experts.To advance this cross-domain research,this paper proposes a DNN-based HSL-TFP surrogate modeling task benchmark.With consideration for engineering applicability,sample generation,dataset evaluation,DNN model,and surrogate performance metrics are thoroughly investigated.Experiments are conducted with ten representative state-of-the-art DNN models.A detailed discussion on baseline results is provided,and future prospects are analyzed for DNN-based HSL-TFP tasks.
基金This work was supported by the National Natural Science Foundation of China(No.11902358)the Scientific Researches Foundation of National University of Defense Technology(Nos.ZK18-03-36 and ZK18-01-03).
文摘We present a theoretical analysis of a novel multi-channel light amplification photonic system on chip,where the nonlinear Raman amplification phenomenon in the silicon(Si)wire waveguide is considered.Particularly,a compact and temperature insensitive Mach–Zehnder interferometer filter working as demultiplexer is also exploited,allowing for the whole Si photonic system to be free from thermal interference.The propagation of the multi-channel pump and Stokes lights is described by a rigorous theoretical model that incorporates all relevant linear and nonlinear optical effects,including the intrinsic waveguide optical losses,first-and second-order frequency dispersion,self-phase and cross-phase modulation,phase shift and two-photon absorption,free-carriers dynamics,as well as the inter-pulse Raman interaction.Notably,to prevent excessive drift of the transmission window of the demultiplexer caused by ambient temperature variations and high thermo-optical coefficient of Si,an asymmetric waveguide width is adopted in the upper and lower arms of each Mach–Zehnder interferometer lattice cell.A Chebyshev half-band filter is utilized to achieve a flat pass-band transmission,achieving a temperature sensitivity of<1.4 pm=K and over 100 K temperature span.This all-Si amplifier shows a thermally robust behavior,which is desired by future Si-on-insulator(SOI)applications.
基金supported by the National Natural Science Foundation of China(Nos.51975582 and 51631003)the Jiangsu Provincial Key Research and Development Program(No.BE2021088)。
文摘Novel composites of HfNbTaTiZrV refractory high-entropy alloy(RHEA)reinforced with 0–4 vol.%Al_(2)O_(3)particles have been synthesized by vacuum arc melting.The microstructure evolution,compressive mechanical properties at room and elevated temperatures,as well as strengthening mechanism of the composites were analyzed.The HfNbTaTiZrV RHEA reinforced with 4 vol.%Al_(2)O_(3)displayed excellent phase stability at elevated temperatures.A superior compressive yield strength of 2700 MPa at room temperature,1392 MPa at 800°C,and 693 MPa at 1000°C was obtained for this composite.The improved yield strength resulted from multiple strengthening mechanisms caused by Al_(2)O_(3)addition,including solution strengthening,interstitial strengthening,grain boundary strengthening,and dispersion strengthening.Besides,the effects of interstitial strengthening increased with temperature and was the main strengthening mechanism at elevated temperatures.These findings not only promote the development of oxidereinforced RHEAs for challenging engineering applications but also provide guidelines for the design of light refractory materials with multiple strengthening mechanisms.
基金financially supported by the Key Project of the Equipment Pre-Research Field Fund of China(No.6140922010302)the National Natural Science Foundation of China(No.51690164)。
文摘Entropy-stabilized multi-component alloys have been considered to be prospective structural materials attributing to their impressive mechanical and functional properties.The local chemical complexions,microstates and configurational transformations are essential to reveal the structure–property relationship,thus,to promote the development of advanced multicomponent alloys.In the present work,effects of local lattice distortion(LLD)and microstates of various configurations on the equilibrium volume(V0),total energy,Fermi energy,magnetic moment(μMag)and electron work function(Φ)and bonding structures of the Fe–Mn–Al medium entropy alloy(MEA)have been investigated comprehensively by first-principles calculations.It is found that theΦandμMag of those MEA are proportional to the V 0,which is dominated by lattice distortion.In terms of bonding charge density,both the strengthened clusters or the so-called short-range order structures and the weakly bonded spots or weak spots are characterized.While the presence of weakly bonded Al atoms implies a large LLD/mismatch,the Fe–Mn bonding pairs result in the formation of strengthened clusters,which dominate the local microstates and the configurational transitions.The variations ofμMag are associated with the enhancement of the nearest neighbor magnetic Fe and Mn atoms,attributing to the LLD caused by Al atoms,the local changes in the electronic structures.This work provides an atomic and electronic insight into the microstate-dominated solid-solution strengthening mechanism of Fe–Mn–Al MEA.
文摘Surface electromyography(EMG) is a bioelectrical signal that recognizes speech contents in a non-acoustic form. Activity detection is an important research direction in EMG research. However, in the low signal-to-noise ratio(SNR) environment, it is difficult for traditional methods to obtain accurate active signals. This paper proposes a new energy-based spectral subtraction backtracking(E-SSB) method to segment EMG active signal in the low SNR environment. Compared with traditional energy detection, the algorithm in this paper adds spectral subtraction(SS) to filter out the clutter, and raises a retrospective idea to improve the classification performance. The experiment results show the proposed activity detection method is more effective than other methods in the low SNR environment.
基金supported by the National Natural Science Foundation of China(Grant Nos.11725211,52005505,and 62001502)the Post-Graduate Scientific Research Innovation Project of Hunan Province(Grant No.CX20200023).
文摘In the satellite overall design phase,it is a crucial step to perform satellite layout design to guarantee that the aggregation of electronic components can operate normally and stably in an appropriate temperature environment.In order to handle the satellite payload placement problem of the DongFangHong 4(DFH-4)platform,the heat pipe-constrained component layout optimization(HCLO)problem is proposed with the HCLO model formulated.Through careful investigation,it can be divided into two optimization subproblems that can be solved subsequently.Based on the divide-and-conquer strategy,an integer linear programming-(ILP-)assisted two-stage layout optimization method is proposed.In stage one,component-heat pipe distribution optimization is performed using the ILP technique so that specific heat pipes occupied by each component can be determined and the horizontal movement range of components can be reduced.In stage two,the detailed component layout optimization is investigated to obtain the final positions of components.First,the sequence layout sampling(SeqLS)method is used to generate one nonoverlap initial layout.Next,swap operation between components is incorporated to reduce the centroid deviation.Finally,sequential quadratic programming(SQP)search is conducted based on the generated promising initial layout solutions.Therefore,the SeqLS-based heuristic layout search algorithm is proposed in the second stage.Two layout test cases,including 15 components and 90 components,respectively,are investigated to demonstrate the validity and efficacy of the proposed layout design method.Experimental results show that it is promising to apply such a two-stage approach for satellite payload placement in engineering.
