The soft actuator is characterized by high safety,flexibility,and adaptability.It is capable of both active and passive defor-mations.This paper presents a discrete degree of freedom(DOF)method for soft actuators to r...The soft actuator is characterized by high safety,flexibility,and adaptability.It is capable of both active and passive defor-mations.This paper presents a discrete degree of freedom(DOF)method for soft actuators to reveal DOF characteristics.The method draws on the superposition mechanism of the deformation characteristics of the sarcomere in the skeletal muscles of living organisms.Firstly,the multi-DOF deformation characteristics of the soft actuator are discretized into superimposed combinations of single-DOF micro-units.Then,the soft actuator was determined to contain deformation characteristics such as extension-contraction,bending,and twisting.Eighteen types of micro-units with basic deforma-tion characteristics were obtained depending on the axis and orientation.Further,the mapping relationship between the combination of micro-units and the motion characteristics of the soft actuator based on the GF set theory was established.Finally,an active-passive DOF co-structured soft actuator(APCSA)was developed.The graphical approach analyzes the experimental results,and it can be concluded that active and passive DOFs can coexist in the composite deformation of the soft actuator.展开更多
This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The im...This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The impact of the VGs is assessed through the improved delayed detached eddy simulations(IDDES)after validating predictions against previous experimental measurements and other numerical predictions for the base case.The simulations indicate that strategically installed VGs can reduce the average slipstream velocity(U slipstream)and the upper limit of slipstream velocity(U_(slipstream,max))by~17%and~15%,respectively,as well as moving the peaks downstream by approximately train height,thus reducing the danger posed by slipstream to waiting passengers and trackside workers.Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake.It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs.These latter vortices prevent the merging of vortical airflow around the trailing nose tip,which is otherwise induced by the longitudinal vortex of the train.They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream,limiting outwards advection through interaction with the image pair,and contributing to a decrease in the peak slipstream value.The method proposed offers a simple approach to wake control leading to significant slipstream benefits.展开更多
Heat exchangers play a crucial role in thermal energy systems,with their performance directly impacting efficiency,cost,and environmental impact.Apowerful technique for performance improvement can be given by passive ...Heat exchangers play a crucial role in thermal energy systems,with their performance directly impacting efficiency,cost,and environmental impact.Apowerful technique for performance improvement can be given by passive enhancement strategies,which are characterized by their dependability and minimal external power requirements.This comprehensive review critically assesses recent advancements in such passive methods to evaluate their heat transfer mechanisms,performance characteristics,and practical implementation challenges.Our methodology involves a systematic and comprehensive analysis of various heat transfer enhancement techniques,including surface modifications,extended surfaces,swirl flow devices,and tube inserts.This approach synthesizes and integrates findings from a broad spectrum of experimental investigations and numerical simulations to establish a cohesive understanding of their performance characteristics and underlyingmechanisms.Based on the findings,passive heat transfer techniques result in significant improvements in thermal performance;for instance,corrugated and roughened surfaces increase the heat transfer coefficient by 50%–200%,and advanced insert geometries,such as modified twisted tapes,can increase it by more than 300%,typically accompanied by significant pressure-drop penalties.However,an important finding is the general trade-off between enhanced heat transfer and higher frictional loss,which requires optimization depending on the applications.Finally,this review also provides recommendations that will document the gaps of various passive techniques in heat exchangers to future address.展开更多
Methods allowing passive daytime radiative cooling(PDRC)to be carried out in an energy-efficient and scalable way are potentially important for various disciplines.Here,we report a sustainable strategy for scalable-de...Methods allowing passive daytime radiative cooling(PDRC)to be carried out in an energy-efficient and scalable way are potentially important for various disciplines.Here,we report a sustainable strategy for scalable-designed and color-regulating PDRC coating based on high-crystallinity photonic metamaterial(crystallinity:71.5%;enhanced assembly efficiency:72%),that is derived from the as-prepared 55 wt%solid content poly(methyl methacrylate-butyl acrylate-methacrylic acid)P(MMA-BA-MAA)monodispersed latexes(approaching theoretical limit:59 wt%).Robust meter-scale PDRC coatings are constructed by various industrial modes onto diverse surfaces,addressing bottlenecks like dull appearance,high cost,low efficiency,and hard construction.Notably,the solar reflectance,long-wave infrared emittance,and calculated theoretical cooling power of the designed PDRC coating,respectively,reach~0.94,~0.97,and~95.5 W m^(-2)under solar radiation,which can achieve an average 5.3℃ sub-ambient daytime temperature drop in the summer in Nanjing.The cooling performance,scale preparation,and cost-effectiveness of the PDRC coating have extended into leading position compared with those of state-of-the-art designs.This work provides promising route to reduce carbon emissions and energy consumption for global sustainability.展开更多
Radiative cooling passively emits heat to outer space without energy input,offering promise for energy-efficient thermal management.It is an important solution to promote the low-carbon environmental protection strate...Radiative cooling passively emits heat to outer space without energy input,offering promise for energy-efficient thermal management.It is an important solution to promote the low-carbon environmental protection strategy.With the continuous development of radiative cooling technologies,the material selection,preparation process,structural design,and applica-tion fields have also made more diverse progress.Therefore,this review aims to systematically introduce the fundamental concepts and underlying principles of radiative cooling.A summary of the commonly used materials for radiative cooling is provided.In addition,the advanced fabrication processes and structural designs of radiative cooling materials are further explored and discussed.Subsequently,the unique functions of radiative cooling materials are highlighted to enhance their applicability and usefulness across various fields.An overview of combining radiative cooling materials with different fields is also provided.In reality,these applications hold the potential to improve thermal management across a range of fields.Finally,it summarizes the shortcomings and great potential of radiative cooling materials in various fields.It also looks forward to the future,aiming to promote the progress and widespread adoption of radiative cooling technologies.展开更多
Background:Ex vivo lung perfusion(EVLP)has emerged as a critical technique for lung preservation and evaluation prior to transplantation.While conventional rat EVLP systems utilize closed-loop dual cannulation of pulm...Background:Ex vivo lung perfusion(EVLP)has emerged as a critical technique for lung preservation and evaluation prior to transplantation.While conventional rat EVLP systems utilize closed-loop dual cannulation of pulmonary artery(PA)and vein,the effect of the simplified model using single PA cannulation with passive venous drainage is unknown.Methods:We developed two EVLP models in rats:a semi-closed circuit with PA-only cannulation and left atrial incision for passive venous drainage(SC-EVLP),and a closed circuit employing both arterial and venous cannulation(C-EVLP).Donor lungs were perfused for a defined duration and subsequently orthotopically transplanted.We evaluated pulmonary function parameters,histopathological injury scores,inflammatory cytokine levels,and apoptotic marker expression at the end of perfusion and posttransplantation.Results:Compared to the conventional EVLP,the SC-EVLP group exhibited significantly lower PA pressure and improved dynamic lung compliance throughout perfusion.Although the levels of tumor necrosis factor-αin the perfusate were higher in the SC-EVLP group,other cytokine levels in the perfusate and bronchoalveolar lavage fluid exhibited no significant differences.Pulmonary edema was reduced in the SC-EVLP group,as indicated by a lower lung wet-to-dry ratio.After transplantation,lungs from the SC-EVLP group exhibited lower histological injury scores,reduced apoptosis,and decreased serum cytokine levels,suggesting attenuated inflammation and tissue damage.Conclusions:In a rat model,single PA cannulation with passive venous drainage reduced pulmonary edema during EVLP and reduced lung injury and systemic inflammation after transplantation.展开更多
The integration of the intelligent reflecting surface(IRS)with simultaneous wireless information and power transfer(SWIPT)has emerged as a cost-effective and efficient solution to enhance the performance of informatio...The integration of the intelligent reflecting surface(IRS)with simultaneous wireless information and power transfer(SWIPT)has emerged as a cost-effective and efficient solution to enhance the performance of information and energy transfer.In this research,a hybrid active/passive IRS-assisted SWIPT system is proposed.Specifically,an active IRS(AIRS)and a passive IRS(PIRS)are deployed in the SWIPT system to facilitate a multiantenna base station(BS)in simultaneously delivering information and energy to multiple information users(IUs)and energy users(EUs).The objective is to maximize the sum throughput by jointly optimizing the transmitter beamforming and the reflection coefficient matrices of the AIRS and the PIRS while satisfying the transmitter power constraints,the energy harvesting(EH)requirements of EUs,and the AIRS amplification power limitations.However,the optimization variables are highly coupled and cannot be solved directly.To tackle this complex problem,we propose an efficient algorithm based on alternating optimization(AO)and semi-definite relaxation(SDR)techniques to obtain high-quality solutions.Simulation results demonstrate that the hybrid active/passive IRSassisted SWIPT system significantly enhances throughput performance and outperforms benchmark systems.展开更多
Patients with complete spinal cord injury retain the potential for volitional muscle activity in muscles located below the spinal injury level.However,because of prolonged inactivity,initial attempts to activate these...Patients with complete spinal cord injury retain the potential for volitional muscle activity in muscles located below the spinal injury level.However,because of prolonged inactivity,initial attempts to activate these muscles may not effectively engage any of the remaining neurons in the descending pathway.A previous study unexpectedly found that a brief clinical round of passive activity significantly increased volitional muscle activation,as measured by surface electromyography.In this study,we further explored the effect of passive activity on surface electromyographic signals during volitional control tasks among individuals with complete spinal cord injury.Eleven patients with chronic complete thoracic spinal cord injury were recruited.Surface electromyography data from eight major leg muscles were acquired and compared before and after the passive activity protocol.The results indicated that the passive activity led to an increased number of activated volitional muscles and an increased frequency of activation.Although the cumulative root mean square of surface electromyography amplitude for volitional control of movement showed a slight increase after passive activity,the difference was not statistically significant.These findings suggest that brief passive activity may enhance the ability to initiate volitional muscle activity during surface electromyography tasks and underscore the potential of passive activity for improving residual motor control among patients with motor complete spinal cord injury.展开更多
Passive thermal management in electronics has disadvantages of low efficiency and high cost.Herein,experimental and numerical studies on the geometric optimization of a hygroscopic-membrane heat sink(HMHS)are conducte...Passive thermal management in electronics has disadvantages of low efficiency and high cost.Herein,experimental and numerical studies on the geometric optimization of a hygroscopic-membrane heat sink(HMHS)are conducted.The HMHS is based on water evaporation from a membrane-encapsulated hygroscopic salt solution,in which pin fins are used for thermal conductivity enhancement.A comprehensive heat and mass transfer model is developed and validated.To obtain the HMHS configuration with the maximum cooling performance,an approach that couples the Taguchi method with numerical simulations is utilized.The contribution ratio of each design factor is determined.Experimentally validated results demonstrate that the maximum temperature reduction provided by the HMHS can be further improved from 15.5℃to 17.8℃after optimization,achieving a temperature reduction of up to 21℃at a fixed heat flux of 25kW/m^(2)when compared with a similarly sized fin heat sink.Remarkably,the optimized HMHS extends the effective cooling time by∼343%compared with traditional phase-change materials,achieving a maximum temperature reduction ranging from 7.0℃to 20.4℃.Meanwhile,the effective heat transfer coefficient achieved is comparable with that of forced liquid cooling.Our findings suggest that the proposed cooling approach provides a new pathway for intermittent thermal management,which is expected to be used for thermal regulation of electronics,batteries,photovoltaic panels,and LED lights.展开更多
Tactile perception plays a vital role for the human body and is also highly desired for smart prosthesis and advanced robots.Compared to active sensing devices,passive piezoelectric and triboelectric tactile sensors c...Tactile perception plays a vital role for the human body and is also highly desired for smart prosthesis and advanced robots.Compared to active sensing devices,passive piezoelectric and triboelectric tactile sensors consume less power,but lack the capability to resolve static stimuli.Here,we address this issue by utilizing the unique polarization chemistry of conjugated polymers for the first time and propose a new type of bioinspired,passive,and bio-friendly tactile sensors for resolving both static and dynamic stimuli.Specifically,to emulate the polarization process of natural sensory cells,conjugated polymers(including poly(3,4-ethylenedioxythiophen e):poly(styrenesulfonate),polyaniline,or polypyrrole)are controllably polarized into two opposite states to create artificial potential differences.The controllable and reversible polarization process of the conjugated polymers is fully in situ characterized.Then,a micro-structured ionic electrolyte is employed to imitate the natural ion channels and to encode external touch stimulations into the variation in potential difference outputs.Compared with the currently existing tactile sensing devices,the developed tactile sensors feature distinct characteristics including fully organic composition,high sensitivity(up to 773 mV N^(−1)),ultralow power consumption(nW),as well as superior bio-friendliness.As demonstrations,both single point tactile perception(surface texture perception and material property perception)and two-dimensional tactile recognitions(shape or profile perception)with high accuracy are successfully realized using self-defined machine learning algorithms.This tactile sensing concept innovation based on the polarization chemistry of conjugated polymers opens up a new path to create robotic tactile sensors and prosthetic electronic skins.展开更多
This paper investigates the configuration design associated with boundary-constrained swarm flying.An analytic swarm configuration is identified to ensure the passive safety between each pair of spacecraft in the radi...This paper investigates the configuration design associated with boundary-constrained swarm flying.An analytic swarm configuration is identified to ensure the passive safety between each pair of spacecraft in the radial-cross-track plane.For the first time,this work derives the explicit configurable spacecraft amount to clarify the configuration's accommodation capacity while considering the maximum inter-spacecraft separation constraint.For larger-scale design problem that involves hundreds of spacecraft,this paper proposes an optimization framework that integrates a Relative Orbit Element(ROE)affine transformation operation and successional convex optimization.The framework establishes a multi-subcluster swarm structure,allowing decoupling the maintenance issues of each subcluster.Compared with previous design methods,it ensures that the computational cost for constraints verification only scales linearly with the swarm size,while also preserving the configuration optimization capacities.Numerical simulations demonstrate that the proposed analytic configuration strictly meets the design constraints.It is also shown that the proposed framework reduces the handled constraint amount by two orders compared with direct optimization,while achieving a remarkable swarm safety enhancement based on the existing analytic configuration.展开更多
The corrosion behavior of Ti–6Al–2Zr–1Mo–1V(TA15)alloy fabricated through selective laser melting(SLM)technology and traditional wrought technology in hydrochloric acid solutions was investigated using electrochem...The corrosion behavior of Ti–6Al–2Zr–1Mo–1V(TA15)alloy fabricated through selective laser melting(SLM)technology and traditional wrought technology in hydrochloric acid solutions was investigated using electrochemical testing and surface characterizations,including electron backscattered diffraction,scanning electron microscopy,and X-ray photoelectron spectroscopy analyses.The results showed that both types of TA15 alloy underwent spontaneous passivation reactions in HCl solution,and with the increase in HCl concentration,the surface of SLM-TA15 sample exhibited larger and deeper pits.In comparison to SLM-TA15 sample,the pits on the wrought-TA15 sample were shallower and the surface was more uniform.Analysis of the passive current density,breakdown potential,and electrochemical impedance revealed that the corrosion resistance of both alloys decreased as the concentration of HCl increased,and SLM sample exhibited poorer corrosion resistance compared with the wrought sample.Analysis of Mott–Schottky test curves and calculation of passive film thickness indicated that the passive film of wrought-TA15 sample was superior to that of SLM-TA15 sample.展开更多
Passive source imaging can reconstruct body wave reflections similar to those of active sources through seismic interferometry(SI).It has become a low-cost,environmentally friendly alternative to active source seismic...Passive source imaging can reconstruct body wave reflections similar to those of active sources through seismic interferometry(SI).It has become a low-cost,environmentally friendly alternative to active source seismic,showing great potential.However,this method faces many challenges in practical applications,including uneven distribution of underground sources and complex survey environments.These situations seriously affect the reconstruction quality of virtual shot records,resulting in unguaranteed imaging results and greatly limiting passive source seismic exploration applications.In addition,the quality of the reconstructed records is directly related to the time length of the noise records,but in practice it is often difficult to obtain long-term,high-quality noise segments containing body wave events.To solve the above problems,we propose a deep learning method for reconstructing passive source virtual shot records and apply it to passive source time-lapse monitoring.This method combines the UNet network and the BiLSTM(Bidirectional Long Short-Term Memory)network for extracting spatial features and temporal features respectively.It introduces the spatial attention mechanism to establish a hybrid SUNet-BiLSTM-Attention(SBA)network for supervised training.Through pre-training and fine-tuning training,the network can accurately reconstruct passive source virtual shot records directly from short-time noisy segments containing body wave events.The experimental results of theoretical data show that the virtual shot records reconstructed by the network have high resolution and signal to noise ratio(SNR),providing high-quality data for subsequent monitoring and imaging.Finally,to further validate the effectiveness of proposed method,we applied it to field data collected from gas storage in northwest China.The reconstruction results of field data effectively improve the quality of virtual records and obtain more reliable time-lapse imaging monitoring results,which have significant practical value.展开更多
A novel method is developed by utilizing the fractional frequency based multirange rulers to precisely position the passive inter-modulation(PIM)sources within radio frequency(RF)cables.The proposed method employs a s...A novel method is developed by utilizing the fractional frequency based multirange rulers to precisely position the passive inter-modulation(PIM)sources within radio frequency(RF)cables.The proposed method employs a set of fractional frequencies to create multiple measuring rulers with different metric ranges to determine the values of the tens,ones,tenths,and hundredths digits of the distance.Among these rulers,the one with the lowest frequency determines the maximum metric range,while the one with the highest frequency decides the highest achievable accuracy of the position system.For all rulers,the metric accuracy is uniquely determined by the phase accuracy of the detected PIM signals.With the all-phase Fourier transform method,the phases of the PIM signals at all fractional frequencies maintain almost the same accuracy,approximately 1°(about 1/360 wavelength in the positioning accuracy)at the signal-to-noise ratio(SNR)of 10 d B.Numerical simulations verify the effectiveness of the proposed method,improving the positioning accuracy of the cable PIM up to a millimeter level with the highest fractional frequency operating at 200 MHz.展开更多
This paper investigates how to achieve integrated sensing and communication(ISAC)based on a cell-free radio access network(CF-RAN)architecture with a minimum footprint of communication resources.We propose a new passi...This paper investigates how to achieve integrated sensing and communication(ISAC)based on a cell-free radio access network(CF-RAN)architecture with a minimum footprint of communication resources.We propose a new passive sensing scheme.The scheme is based on the radio frequency(RF)fingerprint learning of the RF radio unit(RRU)to build an RF fingerprint library of RRUs.The source RRU is identified by comparing the RF fingerprints carried by the signal at the receiver side.The receiver extracts the channel parameters from the signal and estimates the channel environment,thus locating the reflectors in the environment.The proposed scheme can effectively solve the problem of interference between signals in the same time-frequency domain but in different spatial domains when multiple RRUs jointly serve users in CF-RAN architecture.Simulation results show that the proposed passive ISAC scheme can effectively detect reflector location information in the environment without degrading the communication performance.展开更多
Musculoskeletal Symptoms(MSS)often arise from prolonged maintenance of bent postures in the neck and trunk during surgical procedures.To prevent MSS,a passive exoskeleton utilizing carbon fiber beams to offer support ...Musculoskeletal Symptoms(MSS)often arise from prolonged maintenance of bent postures in the neck and trunk during surgical procedures.To prevent MSS,a passive exoskeleton utilizing carbon fiber beams to offer support to the neck and trunk was proposed.The application of support force is intended to reduce muscle forces and joint compression forces.A nonlinear mathematical model for the neck and trunk support beam is presented to estimate the support force.A validation test is subsequently conducted to assess the accuracy of the mathematical model.Finally,a preliminary functional evaluation test is performed to evaluate movement capabilities and support provided by the exoskeleton.The mathematical model demonstrates an accuracy for beam support force within a range of 0.8–1.2 N Root Mean Square Error(RMSE).The exoskeleton was shown to allow sufficient Range of Motion(ROM)for neck and trunk during open surgery training.While the exoskeleton showed potential in reducing musculoskeletal load and task difficulty during simulated surgery tasks,the observed reduction in perceived task difficulty was deemed non-significant.This prompts the recommendation for further optimization in personalized adjustments of beams to facilitate improvements in task difficulty and enhance comfort.展开更多
With the development of wireless communication,the fifth generation mobile communication technology(5G)has emerged as a hot topic in highspeed railway communication system and has moved towards industrial application....With the development of wireless communication,the fifth generation mobile communication technology(5G)has emerged as a hot topic in highspeed railway communication system and has moved towards industrial application.Investigating the radio propagation characteristics in 5G high-speed train(HST)scenarios is essential for enhancing wireless coverage and overall system performance.We propose a novel 5G passive sounding scheme to extract channel impulse responses(CIRs)using channel state information reference signals(CSI-RS)from the target 5G base station(BS).Detailed procedures for timefrequency synchronization,CSI-RS detection and extraction are presented through simulations.Through the laboratory work involving absolute power calibration,phase coherence calibration and power delay profile(PDP)validation,we validate the accuracy and performance of the developed platform.Furthermore,a measurement campaign was conducted in HST scenarios encompassing both residential and undeveloped areas.The path loss(PL)model and the channel characteristics including stationarity interval(SI),multipath components(MPCs),shadow fading(SF),Rician K-factor,root mean square(RMS)delay spread and received correlation coefficients are analyzed and fitted.The estimated channel characteristics and the statistical model presented in this paper will contribute to the research on HST radio propagation and the development of 5G railway communication systems.展开更多
We conduct optical-tweezers experiments to investigate the average potential energies of passive plates harmonically trapped in bacterial suspensions.Our results show that the mean potential energies along both the ma...We conduct optical-tweezers experiments to investigate the average potential energies of passive plates harmonically trapped in bacterial suspensions.Our results show that the mean potential energies along both the major and minor axes increase with bacterial concentration but decrease with trap stiffness.Notably,the average potential energy along the major axis consistently exceeds that along the minor axis.This discrepancy from equilibrium systems is primarily attributed to the distinct bacterial flow fields and direct bacterium–plate collisions near the major and minor axes,as evidenced by the higher orientational order around the plate along the major compared to the minor axis,despite identical bacterial densities in these regions.Our findings highlight the critical role of hydrodynamic interactions in determining the potential energy of passive objects immersed in an active bath.展开更多
基金The Central Government Guides Local Foundation for Science and Technology Development(Grant No.YDZJSX2024B004).
文摘The soft actuator is characterized by high safety,flexibility,and adaptability.It is capable of both active and passive defor-mations.This paper presents a discrete degree of freedom(DOF)method for soft actuators to reveal DOF characteristics.The method draws on the superposition mechanism of the deformation characteristics of the sarcomere in the skeletal muscles of living organisms.Firstly,the multi-DOF deformation characteristics of the soft actuator are discretized into superimposed combinations of single-DOF micro-units.Then,the soft actuator was determined to contain deformation characteristics such as extension-contraction,bending,and twisting.Eighteen types of micro-units with basic deforma-tion characteristics were obtained depending on the axis and orientation.Further,the mapping relationship between the combination of micro-units and the motion characteristics of the soft actuator based on the GF set theory was established.Finally,an active-passive DOF co-structured soft actuator(APCSA)was developed.The graphical approach analyzes the experimental results,and it can be concluded that active and passive DOFs can coexist in the composite deformation of the soft actuator.
基金Project(52372370)supported by the National Natural Science Foundation of ChinaProject(2023ZZTS0379)supported by the Graduate Student Independent Innovation Project of Central South University,ChinaProject(202206370058)supported by the China Scholarship Council。
文摘This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators(VGs)onto the upper surface of the tail car.The impact of the VGs is assessed through the improved delayed detached eddy simulations(IDDES)after validating predictions against previous experimental measurements and other numerical predictions for the base case.The simulations indicate that strategically installed VGs can reduce the average slipstream velocity(U slipstream)and the upper limit of slipstream velocity(U_(slipstream,max))by~17%and~15%,respectively,as well as moving the peaks downstream by approximately train height,thus reducing the danger posed by slipstream to waiting passengers and trackside workers.Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake.It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs.These latter vortices prevent the merging of vortical airflow around the trailing nose tip,which is otherwise induced by the longitudinal vortex of the train.They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream,limiting outwards advection through interaction with the image pair,and contributing to a decrease in the peak slipstream value.The method proposed offers a simple approach to wake control leading to significant slipstream benefits.
文摘Heat exchangers play a crucial role in thermal energy systems,with their performance directly impacting efficiency,cost,and environmental impact.Apowerful technique for performance improvement can be given by passive enhancement strategies,which are characterized by their dependability and minimal external power requirements.This comprehensive review critically assesses recent advancements in such passive methods to evaluate their heat transfer mechanisms,performance characteristics,and practical implementation challenges.Our methodology involves a systematic and comprehensive analysis of various heat transfer enhancement techniques,including surface modifications,extended surfaces,swirl flow devices,and tube inserts.This approach synthesizes and integrates findings from a broad spectrum of experimental investigations and numerical simulations to establish a cohesive understanding of their performance characteristics and underlyingmechanisms.Based on the findings,passive heat transfer techniques result in significant improvements in thermal performance;for instance,corrugated and roughened surfaces increase the heat transfer coefficient by 50%–200%,and advanced insert geometries,such as modified twisted tapes,can increase it by more than 300%,typically accompanied by significant pressure-drop penalties.However,an important finding is the general trade-off between enhanced heat transfer and higher frictional loss,which requires optimization depending on the applications.Finally,this review also provides recommendations that will document the gaps of various passive techniques in heat exchangers to future address.
基金support of the National Natural Science Foundation of China(grant 22508184 to X.Q.Y.,grant 21736006 to S.C.,and grant 22278225 to S.C.)supported by the Natural Funding Program of Jiangsu Province(grant BK20250610 to X.Q.Y.).
文摘Methods allowing passive daytime radiative cooling(PDRC)to be carried out in an energy-efficient and scalable way are potentially important for various disciplines.Here,we report a sustainable strategy for scalable-designed and color-regulating PDRC coating based on high-crystallinity photonic metamaterial(crystallinity:71.5%;enhanced assembly efficiency:72%),that is derived from the as-prepared 55 wt%solid content poly(methyl methacrylate-butyl acrylate-methacrylic acid)P(MMA-BA-MAA)monodispersed latexes(approaching theoretical limit:59 wt%).Robust meter-scale PDRC coatings are constructed by various industrial modes onto diverse surfaces,addressing bottlenecks like dull appearance,high cost,low efficiency,and hard construction.Notably,the solar reflectance,long-wave infrared emittance,and calculated theoretical cooling power of the designed PDRC coating,respectively,reach~0.94,~0.97,and~95.5 W m^(-2)under solar radiation,which can achieve an average 5.3℃ sub-ambient daytime temperature drop in the summer in Nanjing.The cooling performance,scale preparation,and cost-effectiveness of the PDRC coating have extended into leading position compared with those of state-of-the-art designs.This work provides promising route to reduce carbon emissions and energy consumption for global sustainability.
基金National Natural Science Foundation of China Excellent Youth Fund(No.52222509)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.52021003)+3 种基金National Key Research and Development Program of China(No.2018YFA0703300)National Natural Science Foundation of China(No.52105298)Science and Technology Development Program of Jilin Province(No.SKL202402005)"Fundamental Research Funds for the Central Universities".
文摘Radiative cooling passively emits heat to outer space without energy input,offering promise for energy-efficient thermal management.It is an important solution to promote the low-carbon environmental protection strategy.With the continuous development of radiative cooling technologies,the material selection,preparation process,structural design,and applica-tion fields have also made more diverse progress.Therefore,this review aims to systematically introduce the fundamental concepts and underlying principles of radiative cooling.A summary of the commonly used materials for radiative cooling is provided.In addition,the advanced fabrication processes and structural designs of radiative cooling materials are further explored and discussed.Subsequently,the unique functions of radiative cooling materials are highlighted to enhance their applicability and usefulness across various fields.An overview of combining radiative cooling materials with different fields is also provided.In reality,these applications hold the potential to improve thermal management across a range of fields.Finally,it summarizes the shortcomings and great potential of radiative cooling materials in various fields.It also looks forward to the future,aiming to promote the progress and widespread adoption of radiative cooling technologies.
基金Key Science and Technology Program of Shaanxi Province,Grant/Award Number:2024SF2-GJHX-45National Natural Science Foundation of China,Grant/Award Number:82472191The Natural Science Foundation of Shaanxi Province,Grant/Award Number:2024JC-ZDXM-49。
文摘Background:Ex vivo lung perfusion(EVLP)has emerged as a critical technique for lung preservation and evaluation prior to transplantation.While conventional rat EVLP systems utilize closed-loop dual cannulation of pulmonary artery(PA)and vein,the effect of the simplified model using single PA cannulation with passive venous drainage is unknown.Methods:We developed two EVLP models in rats:a semi-closed circuit with PA-only cannulation and left atrial incision for passive venous drainage(SC-EVLP),and a closed circuit employing both arterial and venous cannulation(C-EVLP).Donor lungs were perfused for a defined duration and subsequently orthotopically transplanted.We evaluated pulmonary function parameters,histopathological injury scores,inflammatory cytokine levels,and apoptotic marker expression at the end of perfusion and posttransplantation.Results:Compared to the conventional EVLP,the SC-EVLP group exhibited significantly lower PA pressure and improved dynamic lung compliance throughout perfusion.Although the levels of tumor necrosis factor-αin the perfusate were higher in the SC-EVLP group,other cytokine levels in the perfusate and bronchoalveolar lavage fluid exhibited no significant differences.Pulmonary edema was reduced in the SC-EVLP group,as indicated by a lower lung wet-to-dry ratio.After transplantation,lungs from the SC-EVLP group exhibited lower histological injury scores,reduced apoptosis,and decreased serum cytokine levels,suggesting attenuated inflammation and tissue damage.Conclusions:In a rat model,single PA cannulation with passive venous drainage reduced pulmonary edema during EVLP and reduced lung injury and systemic inflammation after transplantation.
基金National Natural Science Foundation of China(No.62301141)。
文摘The integration of the intelligent reflecting surface(IRS)with simultaneous wireless information and power transfer(SWIPT)has emerged as a cost-effective and efficient solution to enhance the performance of information and energy transfer.In this research,a hybrid active/passive IRS-assisted SWIPT system is proposed.Specifically,an active IRS(AIRS)and a passive IRS(PIRS)are deployed in the SWIPT system to facilitate a multiantenna base station(BS)in simultaneously delivering information and energy to multiple information users(IUs)and energy users(EUs).The objective is to maximize the sum throughput by jointly optimizing the transmitter beamforming and the reflection coefficient matrices of the AIRS and the PIRS while satisfying the transmitter power constraints,the energy harvesting(EH)requirements of EUs,and the AIRS amplification power limitations.However,the optimization variables are highly coupled and cannot be solved directly.To tackle this complex problem,we propose an efficient algorithm based on alternating optimization(AO)and semi-definite relaxation(SDR)techniques to obtain high-quality solutions.Simulation results demonstrate that the hybrid active/passive IRSassisted SWIPT system significantly enhances throughput performance and outperforms benchmark systems.
基金supported by the Fundamental Research Funds for Central Public Welfare Research Institute,No.2020CZ-5(to WS and GS)the National Natural Science Foundation of China,No.31970970(to JSR)Fundamental Research Funds for the Central Universities,No.YWF-23-YG-QB-010(to JSR)。
文摘Patients with complete spinal cord injury retain the potential for volitional muscle activity in muscles located below the spinal injury level.However,because of prolonged inactivity,initial attempts to activate these muscles may not effectively engage any of the remaining neurons in the descending pathway.A previous study unexpectedly found that a brief clinical round of passive activity significantly increased volitional muscle activation,as measured by surface electromyography.In this study,we further explored the effect of passive activity on surface electromyographic signals during volitional control tasks among individuals with complete spinal cord injury.Eleven patients with chronic complete thoracic spinal cord injury were recruited.Surface electromyography data from eight major leg muscles were acquired and compared before and after the passive activity protocol.The results indicated that the passive activity led to an increased number of activated volitional muscles and an increased frequency of activation.Although the cumulative root mean square of surface electromyography amplitude for volitional control of movement showed a slight increase after passive activity,the difference was not statistically significant.These findings suggest that brief passive activity may enhance the ability to initiate volitional muscle activity during surface electromyography tasks and underscore the potential of passive activity for improving residual motor control among patients with motor complete spinal cord injury.
基金National Natural Science Foundation of China,Grant/Award Number:52322812Shenzhen Science and Technology Program,Grant/Award Number:JCYJ20230807114905012Research Grants Council of Hong Kong,Grant/Award Numbers:CityU 11215621,CityU 11218922。
文摘Passive thermal management in electronics has disadvantages of low efficiency and high cost.Herein,experimental and numerical studies on the geometric optimization of a hygroscopic-membrane heat sink(HMHS)are conducted.The HMHS is based on water evaporation from a membrane-encapsulated hygroscopic salt solution,in which pin fins are used for thermal conductivity enhancement.A comprehensive heat and mass transfer model is developed and validated.To obtain the HMHS configuration with the maximum cooling performance,an approach that couples the Taguchi method with numerical simulations is utilized.The contribution ratio of each design factor is determined.Experimentally validated results demonstrate that the maximum temperature reduction provided by the HMHS can be further improved from 15.5℃to 17.8℃after optimization,achieving a temperature reduction of up to 21℃at a fixed heat flux of 25kW/m^(2)when compared with a similarly sized fin heat sink.Remarkably,the optimized HMHS extends the effective cooling time by∼343%compared with traditional phase-change materials,achieving a maximum temperature reduction ranging from 7.0℃to 20.4℃.Meanwhile,the effective heat transfer coefficient achieved is comparable with that of forced liquid cooling.Our findings suggest that the proposed cooling approach provides a new pathway for intermittent thermal management,which is expected to be used for thermal regulation of electronics,batteries,photovoltaic panels,and LED lights.
基金financially supported by the Sichuan Science and Technology Program(2022YFS0025 and 2024YFFK0133)supported by the“Fundamental Research Funds for the Central Universities of China.”。
文摘Tactile perception plays a vital role for the human body and is also highly desired for smart prosthesis and advanced robots.Compared to active sensing devices,passive piezoelectric and triboelectric tactile sensors consume less power,but lack the capability to resolve static stimuli.Here,we address this issue by utilizing the unique polarization chemistry of conjugated polymers for the first time and propose a new type of bioinspired,passive,and bio-friendly tactile sensors for resolving both static and dynamic stimuli.Specifically,to emulate the polarization process of natural sensory cells,conjugated polymers(including poly(3,4-ethylenedioxythiophen e):poly(styrenesulfonate),polyaniline,or polypyrrole)are controllably polarized into two opposite states to create artificial potential differences.The controllable and reversible polarization process of the conjugated polymers is fully in situ characterized.Then,a micro-structured ionic electrolyte is employed to imitate the natural ion channels and to encode external touch stimulations into the variation in potential difference outputs.Compared with the currently existing tactile sensing devices,the developed tactile sensors feature distinct characteristics including fully organic composition,high sensitivity(up to 773 mV N^(−1)),ultralow power consumption(nW),as well as superior bio-friendliness.As demonstrations,both single point tactile perception(surface texture perception and material property perception)and two-dimensional tactile recognitions(shape or profile perception)with high accuracy are successfully realized using self-defined machine learning algorithms.This tactile sensing concept innovation based on the polarization chemistry of conjugated polymers opens up a new path to create robotic tactile sensors and prosthetic electronic skins.
基金co-supported by the National Natural Science Foundation of China(Nos.52272408,U21B2008)the Guangdong Basic and Applied Basic Research Foundation,China(No.2023B1515120018)。
文摘This paper investigates the configuration design associated with boundary-constrained swarm flying.An analytic swarm configuration is identified to ensure the passive safety between each pair of spacecraft in the radial-cross-track plane.For the first time,this work derives the explicit configurable spacecraft amount to clarify the configuration's accommodation capacity while considering the maximum inter-spacecraft separation constraint.For larger-scale design problem that involves hundreds of spacecraft,this paper proposes an optimization framework that integrates a Relative Orbit Element(ROE)affine transformation operation and successional convex optimization.The framework establishes a multi-subcluster swarm structure,allowing decoupling the maintenance issues of each subcluster.Compared with previous design methods,it ensures that the computational cost for constraints verification only scales linearly with the swarm size,while also preserving the configuration optimization capacities.Numerical simulations demonstrate that the proposed analytic configuration strictly meets the design constraints.It is also shown that the proposed framework reduces the handled constraint amount by two orders compared with direct optimization,while achieving a remarkable swarm safety enhancement based on the existing analytic configuration.
基金supported by the National Natural Science Foundation of China(Grant Nos.51971067 and 52001080)Beijing Natural Science Foundation(Grant No.3232005).
文摘The corrosion behavior of Ti–6Al–2Zr–1Mo–1V(TA15)alloy fabricated through selective laser melting(SLM)technology and traditional wrought technology in hydrochloric acid solutions was investigated using electrochemical testing and surface characterizations,including electron backscattered diffraction,scanning electron microscopy,and X-ray photoelectron spectroscopy analyses.The results showed that both types of TA15 alloy underwent spontaneous passivation reactions in HCl solution,and with the increase in HCl concentration,the surface of SLM-TA15 sample exhibited larger and deeper pits.In comparison to SLM-TA15 sample,the pits on the wrought-TA15 sample were shallower and the surface was more uniform.Analysis of the passive current density,breakdown potential,and electrochemical impedance revealed that the corrosion resistance of both alloys decreased as the concentration of HCl increased,and SLM sample exhibited poorer corrosion resistance compared with the wrought sample.Analysis of Mott–Schottky test curves and calculation of passive film thickness indicated that the passive film of wrought-TA15 sample was superior to that of SLM-TA15 sample.
基金supported by the CNPC-SWPU Innovation Alliance Technology Cooperation Project(2020CX020000)the Natural Science Foundation of Sichuan Province(24NSFSC0808)the China Scholarship Council(202306440144).
文摘Passive source imaging can reconstruct body wave reflections similar to those of active sources through seismic interferometry(SI).It has become a low-cost,environmentally friendly alternative to active source seismic,showing great potential.However,this method faces many challenges in practical applications,including uneven distribution of underground sources and complex survey environments.These situations seriously affect the reconstruction quality of virtual shot records,resulting in unguaranteed imaging results and greatly limiting passive source seismic exploration applications.In addition,the quality of the reconstructed records is directly related to the time length of the noise records,but in practice it is often difficult to obtain long-term,high-quality noise segments containing body wave events.To solve the above problems,we propose a deep learning method for reconstructing passive source virtual shot records and apply it to passive source time-lapse monitoring.This method combines the UNet network and the BiLSTM(Bidirectional Long Short-Term Memory)network for extracting spatial features and temporal features respectively.It introduces the spatial attention mechanism to establish a hybrid SUNet-BiLSTM-Attention(SBA)network for supervised training.Through pre-training and fine-tuning training,the network can accurately reconstruct passive source virtual shot records directly from short-time noisy segments containing body wave events.The experimental results of theoretical data show that the virtual shot records reconstructed by the network have high resolution and signal to noise ratio(SNR),providing high-quality data for subsequent monitoring and imaging.Finally,to further validate the effectiveness of proposed method,we applied it to field data collected from gas storage in northwest China.The reconstruction results of field data effectively improve the quality of virtual records and obtain more reliable time-lapse imaging monitoring results,which have significant practical value.
文摘A novel method is developed by utilizing the fractional frequency based multirange rulers to precisely position the passive inter-modulation(PIM)sources within radio frequency(RF)cables.The proposed method employs a set of fractional frequencies to create multiple measuring rulers with different metric ranges to determine the values of the tens,ones,tenths,and hundredths digits of the distance.Among these rulers,the one with the lowest frequency determines the maximum metric range,while the one with the highest frequency decides the highest achievable accuracy of the position system.For all rulers,the metric accuracy is uniquely determined by the phase accuracy of the detected PIM signals.With the all-phase Fourier transform method,the phases of the PIM signals at all fractional frequencies maintain almost the same accuracy,approximately 1°(about 1/360 wavelength in the positioning accuracy)at the signal-to-noise ratio(SNR)of 10 d B.Numerical simulations verify the effectiveness of the proposed method,improving the positioning accuracy of the cable PIM up to a millimeter level with the highest fractional frequency operating at 200 MHz.
基金supported in part by the National Key Research and Development Program under Grant(2021YFB2900300)by the National Natural Science Foundation of China(NSFC)under Grants 61971127,61871122by the Southeast University-China Mobile Research Institute Joint Innovation Center,and by the Major Key Project of PCL(PCL2021A01-2).
文摘This paper investigates how to achieve integrated sensing and communication(ISAC)based on a cell-free radio access network(CF-RAN)architecture with a minimum footprint of communication resources.We propose a new passive sensing scheme.The scheme is based on the radio frequency(RF)fingerprint learning of the RF radio unit(RRU)to build an RF fingerprint library of RRUs.The source RRU is identified by comparing the RF fingerprints carried by the signal at the receiver side.The receiver extracts the channel parameters from the signal and estimates the channel environment,thus locating the reflectors in the environment.The proposed scheme can effectively solve the problem of interference between signals in the same time-frequency domain but in different spatial domains when multiple RRUs jointly serve users in CF-RAN architecture.Simulation results show that the proposed passive ISAC scheme can effectively detect reflector location information in the environment without degrading the communication performance.
基金funded by China Scholarship Council,Grant Number 201906840121department of rehabilitation medicine,University Medical Center Groningen,University of Groningen,grant number:O/085350.
文摘Musculoskeletal Symptoms(MSS)often arise from prolonged maintenance of bent postures in the neck and trunk during surgical procedures.To prevent MSS,a passive exoskeleton utilizing carbon fiber beams to offer support to the neck and trunk was proposed.The application of support force is intended to reduce muscle forces and joint compression forces.A nonlinear mathematical model for the neck and trunk support beam is presented to estimate the support force.A validation test is subsequently conducted to assess the accuracy of the mathematical model.Finally,a preliminary functional evaluation test is performed to evaluate movement capabilities and support provided by the exoskeleton.The mathematical model demonstrates an accuracy for beam support force within a range of 0.8–1.2 N Root Mean Square Error(RMSE).The exoskeleton was shown to allow sufficient Range of Motion(ROM)for neck and trunk during open surgery training.While the exoskeleton showed potential in reducing musculoskeletal load and task difficulty during simulated surgery tasks,the observed reduction in perceived task difficulty was deemed non-significant.This prompts the recommendation for further optimization in personalized adjustments of beams to facilitate improvements in task difficulty and enhance comfort.
基金supported by Fundamental Research Funds for the Central Universities(No.2024YJS078)the National Natural Science Foundation of China(No.62341127,62221001 and 62171021)+1 种基金the Fundamental Research Funds for the Natural Science Foundation of Jiangsu Province,Major Project(No.BK2021200)the Key Research and Development Program of Zhejiang Province(No.2023C01003)。
文摘With the development of wireless communication,the fifth generation mobile communication technology(5G)has emerged as a hot topic in highspeed railway communication system and has moved towards industrial application.Investigating the radio propagation characteristics in 5G high-speed train(HST)scenarios is essential for enhancing wireless coverage and overall system performance.We propose a novel 5G passive sounding scheme to extract channel impulse responses(CIRs)using channel state information reference signals(CSI-RS)from the target 5G base station(BS).Detailed procedures for timefrequency synchronization,CSI-RS detection and extraction are presented through simulations.Through the laboratory work involving absolute power calibration,phase coherence calibration and power delay profile(PDP)validation,we validate the accuracy and performance of the developed platform.Furthermore,a measurement campaign was conducted in HST scenarios encompassing both residential and undeveloped areas.The path loss(PL)model and the channel characteristics including stationarity interval(SI),multipath components(MPCs),shadow fading(SF),Rician K-factor,root mean square(RMS)delay spread and received correlation coefficients are analyzed and fitted.The estimated channel characteristics and the statistical model presented in this paper will contribute to the research on HST radio propagation and the development of 5G railway communication systems.
基金supports of the National Natural Science Foundation of China(Grant Nos.12304245,12374205,12475031,and 12364029)the Science Foundation of China University of Petroleum,Beijing(Grant Nos.2462023YJRC031 and 2462024BJRC010)+4 种基金the National Key Laboratory of Petroleum Resources and Engineering(Grant No.PRE/DX-2407)the Natural Science Foundation of Shandong Province(Grant No.ZR2024YQ017)the Young Elite Scientist Sponsorship Program by BAST(Grant No.BYESS2023300)the Beijing Institute of Technology Research Fund Program for Young ScholarsThis work was also supported by Beijing National Laboratory for Condensed Matter Physics(Grant Nos.2023BNLCMPKF014 and 2024BNLCMPKF009).
文摘We conduct optical-tweezers experiments to investigate the average potential energies of passive plates harmonically trapped in bacterial suspensions.Our results show that the mean potential energies along both the major and minor axes increase with bacterial concentration but decrease with trap stiffness.Notably,the average potential energy along the major axis consistently exceeds that along the minor axis.This discrepancy from equilibrium systems is primarily attributed to the distinct bacterial flow fields and direct bacterium–plate collisions near the major and minor axes,as evidenced by the higher orientational order around the plate along the major compared to the minor axis,despite identical bacterial densities in these regions.Our findings highlight the critical role of hydrodynamic interactions in determining the potential energy of passive objects immersed in an active bath.
