Aircraft disturbs the adjacent atmospheric environment in flight,forming spatial distribution features of atmospheric density that differ from the natural background,which may potentially be utilized as tracer charact...Aircraft disturbs the adjacent atmospheric environment in flight,forming spatial distribution features of atmospheric density that differ from the natural background,which may potentially be utilized as tracer characteristics to introduce new technologies for indirectly sensing the presence of aircraft.In this paper,the concept of a long-range aircraft detection based on the atmospheric disturbance density field is proposed,and the detection mode of tomographic imaging of the scattering light of an atmospheric disturbance flow field is designed.By modeling the spatial distribution of the disturbance density field,the scattered echo signal images of active light towards the disturbance field at long distance are simulated.On this basis,the characteristics of the disturbance optical signal at the optimal detection resolution are analyzed.The results show that the atmospheric disturbance flow field of the supersonic aircraft presents circular in the light-scattering echo images.The disturbance signal can be further highlighted by differential processing of the adjacent scattering images.As the distance behind the aircraft increases,the diffusion range of the disturbance signal increases,and the signal intensity and contrast with the background decrease.Under the ground-based observation conditions of the aircraft at a height of 10000 m,a Mach number of1.6,and a detection distance of 100 km,the contrast between the disturbance signal and the back-ground was 30 d B at a distance of one time from the rear of the fuselage,and the diffusion diameter of the disturbance signal was 50 m.At a distance eight times the length of the aircraft,the contrast decreased to 10 dB,and the diameter increased to 290 m.The contrast was reduced to 3 dB at a distance nine times the length of the aircraft,and the diameter was diffused to 310 m.These results indicate the possibility of long-range aircraft detection based on the characteristics of the atmospheric density field.展开更多
Single-wall carbon nanotubes(SWCNTs)have attracted significant attention as a thermal management material because of their high thermal conductivity and excellent thermal stability.However,decreasing the great thermal...Single-wall carbon nanotubes(SWCNTs)have attracted significant attention as a thermal management material because of their high thermal conductivity and excellent thermal stability.However,decreasing the great thermal contact resistance at the tube-tube junctions of SWCNT assemblies is a prerequisite for its practical applications.We report a strategy to address this issue by welding the junctions of SWC-NTs together and introducing hexagonal boron nitride(h-BN)encapsulating layers to the surface of the SWCNT bundles.By changing the partial pressure of the BN precursor in a two-step atmospheric-pressure chemical vapor deposition process,amorphous BN nanoparticles and crystalline h-BN were deposited to weld and encapsulate the SWCNT network in sequence.The introduction of the BN led to an in-plane thermal conductivity∼3.8 times higher than that of the SWCNT film,as measured by optothermal Ra-man method.Molecular dynamics simulations demonstrate that the BN welding and encapsulating facil-itate thermal transport by reducing thermal resistance at the tube-tube junctions.Our work brings new insights into facilitating the heat transport in low-dimensional nanomaterial assemblies through struc-tural design.展开更多
Rapid urbanization has resulted in pervasive occurrence of antibiotic resistance genes(ARGs)in urban aquatic ecosystems.However,limited information is available concerning the ARG profiles and the forces responsible f...Rapid urbanization has resulted in pervasive occurrence of antibiotic resistance genes(ARGs)in urban aquatic ecosystems.However,limited information is available concerning the ARG profiles and the forces responsible for their assembly in urban landscape lagoon systems.Here,we employed high-throughput quantitative PCR(HT-q PCR)to characterize the spatial variations of ARGs in surface and core sediments of Yundang Lagoon,China.The results indicated that the average richness and absolute abundance of ARGs were 11 and 53 times higher in the lagoon sediments as compared to pristine reference Tibetan lake sediments,highlighting the role of anthropogenic activities in ARG pollution.Co-occurrence network analysis indicated that various anaerobic prokaryotic genera belonging to Alpha-,Deltaproteobacteria,Bacteroidetes,Euryarchaeota,Firmicutes and Synergistetes were the potential hosts of ARGs.The partial least squares-path modeling(PLS-PM)analysis revealed positive and negative indirect effects of physicochemical factors and heavy metals on the lagoon ARG profiles,via biotic factors,respectively.The horizontal(mediated by mobile genetic elements)and vertical(mediated by prokaryotic communities)gene transfer may directly contribute the most to drive the abundance and composition of ARGs,respectively.Furthermore,the neutral community model demonstrated that the assembly of sediment ARG communities was jointly governed by deterministic and stochastic processes.Overall,this study provides novel insights into the diversity and distribution of ARGs in the benthic habitat of urban lagoon systems and underlying mechanisms for the spread and proliferation of ARGs.展开更多
A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vort...A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vorticity gradient tensor(or the so-called vorticity strain rate tensor).The new subgrid-scale stress model is taken into account the effect of the vortex motions in turbulence,which is reflected on the anti-symmetric part of the velocity gradient tensor.In addition,the eddy viscosity of the new model reproduces the proper scaling as O(y^3)near the wall.Then,the new SGS model is applied in large-eddy simulation of the spanwise rotating turbulent channel flow.Different simulating cases are selected to test the new model.The results demonstrate that the present model can well predict the mean velocity profiles,the turbulence intensities,and the rotating turbulence structures.In addition,it needs no a second filter,and is convenient to be used in the engineering rotational flows.展开更多
This paper investigates the finite-thickness effect of two superimposed fluids on bubbles and spikes in Richtmyer–Meshkov instability(RMI) for arbitrary Atwood numbers by using the method of the small parameter expan...This paper investigates the finite-thickness effect of two superimposed fluids on bubbles and spikes in Richtmyer–Meshkov instability(RMI) for arbitrary Atwood numbers by using the method of the small parameter expansion up to the second order. When the thickness of the two fluids tends to be infinity, our results can reproduce the classical results where RMI happens at the interface separating two semi-infinity-thickness fluids of different densities. It is found that the thickness has a large influence on the amplitude evolution of bubbles and spikes compared with those in classical RMI. Based on the thickness relationship of the two fluids, the thickness effect on bubbles and spikes for four cases is discussed. The thickness encourages(or reduces)the growth of bubbles or spikes, depending on not only Atwood number, but also the relationship of the thickness ratio of the heavy and light fluids, which is explicitly determined in this paper.展开更多
The subgrid-scale(SGS)kinetic energy has been used to predict the SGS stress in compressible flow and it was resolved through the SGS kinetic energy transport equation in past studies.In this paper,a new SGS eddy-visc...The subgrid-scale(SGS)kinetic energy has been used to predict the SGS stress in compressible flow and it was resolved through the SGS kinetic energy transport equation in past studies.In this paper,a new SGS eddy-viscosity model is proposed using artificial neural network to obtain the SGS kinetic energy precisely,instead of using the SGS kinetic energy equation.Using the infinite series expansion and reserving the first term of the expanded term,we obtain an approximated SGS kinetic energy,which has a high correlation with the real SGS kinetic energy.Then,the coefficient of the modelled SGS kinetic energy is resolved by the artificial neural network and the modelled SGS kinetic energy is more accurate through this method compared to the SGS kinetic energy obtained from the SGS kinetic energy equation.The coefficients of the SGS stress and SGS heat flux terms are determined by the dynamic procedure.The new model is tested in the compressible turbulent channel flow.From the a posterior tests,we know that the new model can precisely predict the mean velocity,the Reynolds stress,the mean temperature and turbulence intensities,etc.展开更多
The rapid development of cyber technology and the increase of flexible resources have transformed the distribution network into a cyber-physical distribution system,while the accompanying multidimensional uncertaintie...The rapid development of cyber technology and the increase of flexible resources have transformed the distribution network into a cyber-physical distribution system,while the accompanying multidimensional uncertainties have brought new planning challenges.In this paper,an innovative approach is proposed to effectively leverage distributed resources while considering the impact of cyber-physical coupling in distribution network planning.A cyber-physical integrated planning model of the distribution network is proposed,considering the effects of spatial-temporal flexible resources and multi-network coupling.Specifically,a three-layer optimization model is established and analyzed by the simulate anneal-particle swarm optimization algorithm.The upper layer achieves the optimization of the location and configuration of energy storage systems and smart terminal units.The middle layer optimizes the data load migration strategy using spatial-temporal flexible resources to solve the voltage exceeding problem caused by high penetration of distributed power access,while the lower layer optimizes the cyber side communication topology,improving the convergence speed and control performance of the distribution network.Then,the optimization model is analyzed iteratively with objective functions including total planning cost,operation excess loss and distributed control performance.Finally,the effectiveness and economy of the proposed planning scheme is verified and compared to traditional methods.展开更多
Direct numerical simulation(DNS)of transition over a hypersonic lifting body model HyTRV developed by China Aerodynamics Research and Development Center is performed.The free-stream parameters are:the free-stream Mach...Direct numerical simulation(DNS)of transition over a hypersonic lifting body model HyTRV developed by China Aerodynamics Research and Development Center is performed.The free-stream parameters are:the free-stream Mach number is 6,the unit Reynolds number is 10000/mm,the free-stream temperature is 79 K,the angle of attack is 0,and the wall temperature is 300 K.Weak random blowing-and-suction perturbations in the leading range are used to trigger the transition.A high order finite-difference code OpenCFD developed by the authors is used for the simulation,and grid convergence test shows that the transition locations are grid-convergence.DNS results show that transition occurs in central area of the lower surface and the concaved region of the upper surface,and the transition regions are also the streamline convergence regions.The transition mechanisms in different regions are investigated by using the spectrum and POD analysis.展开更多
文摘Aircraft disturbs the adjacent atmospheric environment in flight,forming spatial distribution features of atmospheric density that differ from the natural background,which may potentially be utilized as tracer characteristics to introduce new technologies for indirectly sensing the presence of aircraft.In this paper,the concept of a long-range aircraft detection based on the atmospheric disturbance density field is proposed,and the detection mode of tomographic imaging of the scattering light of an atmospheric disturbance flow field is designed.By modeling the spatial distribution of the disturbance density field,the scattered echo signal images of active light towards the disturbance field at long distance are simulated.On this basis,the characteristics of the disturbance optical signal at the optimal detection resolution are analyzed.The results show that the atmospheric disturbance flow field of the supersonic aircraft presents circular in the light-scattering echo images.The disturbance signal can be further highlighted by differential processing of the adjacent scattering images.As the distance behind the aircraft increases,the diffusion range of the disturbance signal increases,and the signal intensity and contrast with the background decrease.Under the ground-based observation conditions of the aircraft at a height of 10000 m,a Mach number of1.6,and a detection distance of 100 km,the contrast between the disturbance signal and the back-ground was 30 d B at a distance of one time from the rear of the fuselage,and the diffusion diameter of the disturbance signal was 50 m.At a distance eight times the length of the aircraft,the contrast decreased to 10 dB,and the diameter increased to 290 m.The contrast was reduced to 3 dB at a distance nine times the length of the aircraft,and the diameter was diffused to 310 m.These results indicate the possibility of long-range aircraft detection based on the characteristics of the atmospheric density field.
基金supported by the National Key R&D Program of China(No.2022YFA1203303)the National Natural Science Foundation of China(Nos.52472054,52130209,and 52072376).
文摘Single-wall carbon nanotubes(SWCNTs)have attracted significant attention as a thermal management material because of their high thermal conductivity and excellent thermal stability.However,decreasing the great thermal contact resistance at the tube-tube junctions of SWCNT assemblies is a prerequisite for its practical applications.We report a strategy to address this issue by welding the junctions of SWC-NTs together and introducing hexagonal boron nitride(h-BN)encapsulating layers to the surface of the SWCNT bundles.By changing the partial pressure of the BN precursor in a two-step atmospheric-pressure chemical vapor deposition process,amorphous BN nanoparticles and crystalline h-BN were deposited to weld and encapsulate the SWCNT network in sequence.The introduction of the BN led to an in-plane thermal conductivity∼3.8 times higher than that of the SWCNT film,as measured by optothermal Ra-man method.Molecular dynamics simulations demonstrate that the BN welding and encapsulating facil-itate thermal transport by reducing thermal resistance at the tube-tube junctions.Our work brings new insights into facilitating the heat transport in low-dimensional nanomaterial assemblies through struc-tural design.
基金supported by the National Natural Science Foundation of China(Nos.31470539 and U1805244)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019QZKK0503)+1 种基金the 9th China-Croatia Science and Technology cooperation committee program(No.9–21)supported by the China Scholarship Council(No.201804910668)。
文摘Rapid urbanization has resulted in pervasive occurrence of antibiotic resistance genes(ARGs)in urban aquatic ecosystems.However,limited information is available concerning the ARG profiles and the forces responsible for their assembly in urban landscape lagoon systems.Here,we employed high-throughput quantitative PCR(HT-q PCR)to characterize the spatial variations of ARGs in surface and core sediments of Yundang Lagoon,China.The results indicated that the average richness and absolute abundance of ARGs were 11 and 53 times higher in the lagoon sediments as compared to pristine reference Tibetan lake sediments,highlighting the role of anthropogenic activities in ARG pollution.Co-occurrence network analysis indicated that various anaerobic prokaryotic genera belonging to Alpha-,Deltaproteobacteria,Bacteroidetes,Euryarchaeota,Firmicutes and Synergistetes were the potential hosts of ARGs.The partial least squares-path modeling(PLS-PM)analysis revealed positive and negative indirect effects of physicochemical factors and heavy metals on the lagoon ARG profiles,via biotic factors,respectively.The horizontal(mediated by mobile genetic elements)and vertical(mediated by prokaryotic communities)gene transfer may directly contribute the most to drive the abundance and composition of ARGs,respectively.Furthermore,the neutral community model demonstrated that the assembly of sediment ARG communities was jointly governed by deterministic and stochastic processes.Overall,this study provides novel insights into the diversity and distribution of ARGs in the benthic habitat of urban lagoon systems and underlying mechanisms for the spread and proliferation of ARGs.
基金supported by the National Natural Science Foundation of China(Grants 91852203 and 11472278)the National Key Research and Development Program of China(Grant 2016YFA04-01200)+1 种基金Science Challenge Project(Grant TZ2016001)Strategic Priority Research Program of Chinese Academy of Sciences(Grants XDA17030100 and XDC01000000)。
文摘A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vorticity gradient tensor(or the so-called vorticity strain rate tensor).The new subgrid-scale stress model is taken into account the effect of the vortex motions in turbulence,which is reflected on the anti-symmetric part of the velocity gradient tensor.In addition,the eddy viscosity of the new model reproduces the proper scaling as O(y^3)near the wall.Then,the new SGS model is applied in large-eddy simulation of the spanwise rotating turbulent channel flow.Different simulating cases are selected to test the new model.The results demonstrate that the present model can well predict the mean velocity profiles,the turbulence intensities,and the rotating turbulence structures.In addition,it needs no a second filter,and is convenient to be used in the engineering rotational flows.
基金supported by National Natural Science Foundation of China (Nos. U1530261,91852203,and 11472278)the Innovation Fund of Fundamental Technology Institute of All Value In Creation (No. JCY2015A005)+2 种基金the Natural Science Foundation of Sichuan Province (Nos. 18ZA0260,and 2018JY0454)the Natural Science Foundation of Mianyang Normal University (Nos. HX2017007,MYSY2017JC06 and MYSY2018T004)the National High-Tech Inertial Confinement Fusion Committee
文摘This paper investigates the finite-thickness effect of two superimposed fluids on bubbles and spikes in Richtmyer–Meshkov instability(RMI) for arbitrary Atwood numbers by using the method of the small parameter expansion up to the second order. When the thickness of the two fluids tends to be infinity, our results can reproduce the classical results where RMI happens at the interface separating two semi-infinity-thickness fluids of different densities. It is found that the thickness has a large influence on the amplitude evolution of bubbles and spikes compared with those in classical RMI. Based on the thickness relationship of the two fluids, the thickness effect on bubbles and spikes for four cases is discussed. The thickness encourages(or reduces)the growth of bubbles or spikes, depending on not only Atwood number, but also the relationship of the thickness ratio of the heavy and light fluids, which is explicitly determined in this paper.
基金supported by the National Key Research and Development Program of China(Grant Nos.2020YFA0711800,2019YFA0405302)NSFC Projects(Grant Nos.12072349,91852203)+1 种基金National Numerical Windtunnel Project,Science Challenge Project(Grant No.TZ2016001)Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDC01000000).
文摘The subgrid-scale(SGS)kinetic energy has been used to predict the SGS stress in compressible flow and it was resolved through the SGS kinetic energy transport equation in past studies.In this paper,a new SGS eddy-viscosity model is proposed using artificial neural network to obtain the SGS kinetic energy precisely,instead of using the SGS kinetic energy equation.Using the infinite series expansion and reserving the first term of the expanded term,we obtain an approximated SGS kinetic energy,which has a high correlation with the real SGS kinetic energy.Then,the coefficient of the modelled SGS kinetic energy is resolved by the artificial neural network and the modelled SGS kinetic energy is more accurate through this method compared to the SGS kinetic energy obtained from the SGS kinetic energy equation.The coefficients of the SGS stress and SGS heat flux terms are determined by the dynamic procedure.The new model is tested in the compressible turbulent channel flow.From the a posterior tests,we know that the new model can precisely predict the mean velocity,the Reynolds stress,the mean temperature and turbulence intensities,etc.
基金supported by National Key R&D Program of China(No.2019YFE0118000).
文摘The rapid development of cyber technology and the increase of flexible resources have transformed the distribution network into a cyber-physical distribution system,while the accompanying multidimensional uncertainties have brought new planning challenges.In this paper,an innovative approach is proposed to effectively leverage distributed resources while considering the impact of cyber-physical coupling in distribution network planning.A cyber-physical integrated planning model of the distribution network is proposed,considering the effects of spatial-temporal flexible resources and multi-network coupling.Specifically,a three-layer optimization model is established and analyzed by the simulate anneal-particle swarm optimization algorithm.The upper layer achieves the optimization of the location and configuration of energy storage systems and smart terminal units.The middle layer optimizes the data load migration strategy using spatial-temporal flexible resources to solve the voltage exceeding problem caused by high penetration of distributed power access,while the lower layer optimizes the cyber side communication topology,improving the convergence speed and control performance of the distribution network.Then,the optimization model is analyzed iteratively with objective functions including total planning cost,operation excess loss and distributed control performance.Finally,the effectiveness and economy of the proposed planning scheme is verified and compared to traditional methods.
基金supported by the National Numerical Windtunnel Projectthe National Key Research and Development Program of China(Grant Nos.2016YFA0401200,2020YFA0711800 and 2019YFA0405300)the National Natural Science Foundation of China(Grant No.91852203 and Grant No.12072349).
文摘Direct numerical simulation(DNS)of transition over a hypersonic lifting body model HyTRV developed by China Aerodynamics Research and Development Center is performed.The free-stream parameters are:the free-stream Mach number is 6,the unit Reynolds number is 10000/mm,the free-stream temperature is 79 K,the angle of attack is 0,and the wall temperature is 300 K.Weak random blowing-and-suction perturbations in the leading range are used to trigger the transition.A high order finite-difference code OpenCFD developed by the authors is used for the simulation,and grid convergence test shows that the transition locations are grid-convergence.DNS results show that transition occurs in central area of the lower surface and the concaved region of the upper surface,and the transition regions are also the streamline convergence regions.The transition mechanisms in different regions are investigated by using the spectrum and POD analysis.
