Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is propo...Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.展开更多
Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved vario...Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved various capabilities,but many of them are still under development,such as lowprofile,wideband,circular polarization,multi-band,low-radar cross section(RCS)and reconfigurable features.This paper discusses the theoretical analysis methods and research progress of FP antennas,and explains the realization methods of different features of FP antennas.In order to indicate different technologies for realizing various capabilities,the key technologies and features of some of the latest designs are described.Finally,the research situation and prospects of FP antennas are summarized to guide their research directions in the future.展开更多
This paper presents a method for determining specific models of overhead power lines with presence of corona phenomenon. The obtained models provide stable numerical solutions for computer simulation of transients cau...This paper presents a method for determining specific models of overhead power lines with presence of corona phenomenon. The obtained models provide stable numerical solutions for computer simulation of transients caused by direct lightning strikes. The corona non- linear charge-voltage characteristics obtained from experimental tests are used for identification of the corona parameters based on System Identification Toolbox implemented in Matlab package. Different transfer functions, which give the same waveshapes of overvoltages are de- termined using two parametric models. A circuit representation of the obtained transfer functions is proposed and the corona model is implemented in the EMTP-RV as a hierarchical structure composed of a overhead power line divided into sections with corona branches. Some computer simulations of lightning overvoltages propagated in a typical 220 kV power line due to direct lightning strikes to a line tower are presented. The proposed method and the model implemented in EMTP-RV are still valid for multi-conductor lines and for higher voltages of power lines but new corona nonlinear charge-voltage characteristics are required as an input parameter for the identification procedure.展开更多
Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic a...Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.展开更多
Blast-induced ground vibration,quantified by peak particle velocity(PPV),is a crucial factor in mitigating environmental and structural risks in mining and geotechnical engineering.Accurate PPV prediction facilitates ...Blast-induced ground vibration,quantified by peak particle velocity(PPV),is a crucial factor in mitigating environmental and structural risks in mining and geotechnical engineering.Accurate PPV prediction facilitates safer and more sustainable blasting operations by minimizing adverse impacts and ensuring regulatory compliance.This study presents an advanced predictive framework integrating Cat Boost(CB)with nature-inspired optimization algorithms,including the Bat Algorithm(BAT),Sparrow Search Algorithm(SSA),Butterfly Optimization Algorithm(BOA),and Grasshopper Optimization Algorithm(GOA).A comprehensive dataset from the Sarcheshmeh Copper Mine in Iran was utilized to develop and evaluate these models using key performance metrics such as the Index of Agreement(IoA),Nash-Sutcliffe Efficiency(NSE),and the coefficient of determination(R^(2)).The hybrid CB-BOA model outperformed other approaches,achieving the highest accuracy(R^(2)=0.989)and the lowest prediction errors.SHAP analysis identified Distance(Di)as the most influential variable affecting PPV,while uncertainty analysis confirmed CB-BOA as the most reliable model,featuring the narrowest prediction interval.These findings highlight the effectiveness of hybrid machine learning models in refining PPV predictions,contributing to improved blast design strategies,enhanced structural safety,and reduced environmental impacts in mining and geotechnical engineering.展开更多
This paper addresses the cooperative control problem of multiple unmanned aerial vehicles(multi-UAV)systems.First,a new distributed consensus algorithm for second-order nonlinear multi-agent systems(MAS)is formulated ...This paper addresses the cooperative control problem of multiple unmanned aerial vehicles(multi-UAV)systems.First,a new distributed consensus algorithm for second-order nonlinear multi-agent systems(MAS)is formulated under the leader-following approach.The algorithm provides smooth input signals to the agents’control channels,which avoids the chattering effect generated by the conventional sliding mode-based control protocols.Second,a new formation control scheme is developed by integrating smooth distributed consensus control protocols into the geometric pattern model to achieve three-dimensional formation tracking.The Lyapunov theory is used to prove the stability and convergence of both distributed consensus and formation controllers.The effectiveness of the proposed algorithms is demonstrated through simulation results.展开更多
In the re-entry phase of a ballistic missile,decoys can be deployed as a mean to overburden enemy defenses.This results in a single track being split into multiple track-lets.Tracking of these track-lets is a critical...In the re-entry phase of a ballistic missile,decoys can be deployed as a mean to overburden enemy defenses.This results in a single track being split into multiple track-lets.Tracking of these track-lets is a critical task as any miss in the tracking procedure can become a cause of a major threat.The tracking process becomes more complicated in the presence of clutter.The low detection rate is one of the factors that may contribute to increasing the difficulty level in terms of tracking in the cluttered environment.This work introduces a new algorithm for the split event detection and target tracking under the framework of the joint integrated probabilistic data association(JIPDA)algorithm.The proposed algorithm is termed as split event-JIPDA(SE-JIPDA).This work establishes the mathematical foundation for the split target detection and tracking mechanism.The performance analysis is made under different simulation conditions to provide a clear insight into the merits of the proposed algorithm.The performance parameters in these simulations are the root mean square error(RMSE),confirmed true track rate(CTTR)and confirmed split true track rate(CSTTR).展开更多
The network reliability is difficult to be evaluated because of the complex relationship among the network components.It can be quite different for different users running different applications on the same network.Th...The network reliability is difficult to be evaluated because of the complex relationship among the network components.It can be quite different for different users running different applications on the same network.This paper proposes a new concept and a model of application reliability.Different from the existing models that ignores the effects of applications,the proposed application reliability model considers the effects of different applications on the network performance and different types of network faults and makes the analysis of network components relationship possible.This paper also provides a method to evaluate the application reliability when the data flow satisfies Markov properties.Finally,a case study is presented to illustrate the proposed network reliability model and the analysis method.展开更多
The main contribution of this paper is the design of an event-triggered formation control for leader-following consensus in second-order multi-agent systems(MASs)under communication faults.All the agents must follow t...The main contribution of this paper is the design of an event-triggered formation control for leader-following consensus in second-order multi-agent systems(MASs)under communication faults.All the agents must follow the trajectories of a virtual leader despite communication faults considered as smooth time-varying delays dependent on the distance between the agents.Linear matrix inequalities(LMIs)-based conditions are obtained to synthesize a controller gain that guarantees stability of the synchronization error.Based on the closed-loop system,an event-triggered mechanism is designed to reduce the control law update and information exchange in order to reduce energy consumption.The proposed approach is implemented in a real platform of a fleet of unmanned aerial vehicles(UAVs)under communication faults.A comparison between a state-of-the-art technique and the proposed technique has been provided,demonstrating the performance improvement brought by the proposed approach.展开更多
Metal superhydrophobic surfaces with anisotropic wettability and adhesion have become more and more important due to their promising applications. Herein, we report a new fabrication strategy through a combination of ...Metal superhydrophobic surfaces with anisotropic wettability and adhesion have become more and more important due to their promising applications. Herein, we report a new fabrication strategy through a combination of pulsed laser ablation and low-temperature annealing post-processing. An inclined cone structure array is made on stainless steel surfaces, and then 120 °C low-temperature annealing is applied. Such surface displays excellent mechanical durability and anisotropic superhydrophobicity. It is demonstrated experimentally that the contact angle of water droplets on the surface is different along the parallel(167° ±2°) and perpendicular directions(157° ±2°) of the inclined cone structure. The sliding behaviors of water droplets and mechanical durability of the inclined cone structures are studied. These surfaces obtained in a short time with environmentally friendly fabrication can be applied in industries for water harvesting, droplet manipulation, and pipeline transportation.展开更多
This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm ...This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm uses a GCMPN cost function to combat the impul-sive interference.To further accelerate the convergence rate in the sparse and the block-sparse system identification processes,the proportionate versions of the proposed algorithm,the L0-norm GCMPN-SAF(L0-GCMPN-SAF)and the block-sparse GCMPN-SAF(BSGCMPN-SAF)algorithms are also developed.Moreover,the convergence analysis of the proposed algorithm is provided.Simulation results show that the proposed algorithms have a better performance than some other state-of-the-art algorithms in the literature with respect to the convergence rate and the tracking capability.展开更多
This paper introduces an algorithm for beamforming systems by the aid of multidimensional harmonic retrieval(MHR).This algorithm resolves problems,removes limitations of sampling and provides a more robust beamformer....This paper introduces an algorithm for beamforming systems by the aid of multidimensional harmonic retrieval(MHR).This algorithm resolves problems,removes limitations of sampling and provides a more robust beamformer.A new sample space is created that can be used for estimating weights of a new beamforming called spatial-harmonics retrieval beamformer(SHRB).Simulation results show that SHRB has a better performance,accuracy,and applicability and more powerful eigenvalues than conventional beamformers.A simple mathematical proof is provided.By changing the number of harmonics,as a degree of freedom that is missing in conventional beamformers,SHRB can achieve more optimal outputs without increasing the number of spatial or temporal samples.We will demonstrate that SHRB offers an improvement of 4 dB in signal to noise ratio(SNR) in bit error rate(BER) of 10~(-4) over conventional beamformers.In the case of direction of arrival(DOA) estimation,SHRB can estimate the DOA of the desired signal with an SNR of-25 dB,when conventional methods cannot have acceptable response.展开更多
In addition to the conventional Franklin Rod,many non-conventional air terminals are being used as lightning protection devices.As cited in previous works,these non-conventional devices emit space charge in the vicini...In addition to the conventional Franklin Rod,many non-conventional air terminals are being used as lightning protection devices.As cited in previous works,these non-conventional devices emit space charge in the vicinity of the terminals during the process of lightning stroke.A number of factors affect the performance of these lightning protection devices,among them are geometry and dimension of the devices,location of the device above the ground,height of the cloud above the ground,and polarity of the lightning stroke.The performance of these lightning protection devices has been a topic of discussion by researchers for many years.Some studies focused on the magnitude of emission current from these devices as a criterion to evaluate their performances.The critical flashover voltage(CFO)between the devices and a metal screen simulating cloud can also be used as another criterion to evaluate the performance of the devices.Laboratory measurements were conducted in controlled conditions on different types of lightning protection devices to compare their performance.Four different types of devices were used in the present study:Franklin Rod,TerraStat models TS 100,TS 400,and Spline Ball Ionizer.The study focused on the CFO voltage of the air gap between devices and the metal screen.The CFO voltage was evaluated using standard switching and lightning impulses.The measurements were recorded for positive as well as negative polarity.The air gap between the devices and metal screen was selected at 2 m and 3 m.The results obtained provide a better understanding of the electrical performance of lightning protection devices.展开更多
PZT-based valveless micropump is a microactuator that can be used for controlling and delivering tiny amounts of fluids,and diffuser/nozzle plays an important role when this type of micropump drives the fluid flowing ...PZT-based valveless micropump is a microactuator that can be used for controlling and delivering tiny amounts of fluids,and diffuser/nozzle plays an important role when this type of micropump drives the fluid flowing along a specific direction.In this paper,a numerical model of micropump has been proposed,and the fluidic properties of diffuser/nozzle have been simulated with ANSYS.With the method of finite-element analysis,the increased pressure drop between inlet and outlet of diffuser/nozzle induces the increment of flow rate in both diffuser and nozzle simultaneously,but the increasing rate of diffuser is faster than that of nozzle.The L/R,ratio of L(length of cone pipe) and R(radius of minimal cross section of cone pipe) plays an important role in fluidic performance of diffuser and nozzle as well,and the mean flow rate will decrease with increment of L/R.The mean flow rate reaches its peak value when L/R with the value of 10 regardless the divergence angle of diffuser or nozzle.The simulation results indicate that the fluidic properties of diffuser/nozzle can be defined by its geometric structure,and accordingly determine the efficiency of micropump.展开更多
Solid oxide fuel cells (SOFCs) are considered to be one of the most important clean,distributed resources. However,SOFCs present a challenging control problem owing to their slow dynamics,nonlinearity and tight operat...Solid oxide fuel cells (SOFCs) are considered to be one of the most important clean,distributed resources. However,SOFCs present a challenging control problem owing to their slow dynamics,nonlinearity and tight operating constraints. A novel data-driven nonlinear control strategy was proposed to solve the SOFC control problem by combining a virtual reference feedback tuning (VRFT) method and support vector machine. In order to fulfill the requirement for fuel utilization and control constraints,a dynamic constraints unit and an anti-windup scheme were adopted. In addition,a feedforward loop was designed to deal with the current disturbance. Detailed simulations demonstrate that the fast response of fuel flow for the current demand disturbance and zero steady error of the output voltage are both achieved. Meanwhile,fuel utilization is kept almost within the safe region.展开更多
Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are ...Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are involved in the SMC operation, namely reaching mode and sliding mode.In the reaching mode, the system state is forced to reach the sliding surface in a finite time.The major drawback of the SMC approach is the occurrence of chattering in the sliding mode, which is undesirable in most applications.Generally, the trade-off between chattering reduction and fast reaching time must be considered in the conventional SMC design.This paper proposes SMC design with a novel reaching law called the exponential rate reaching law(ERRL) to reduce chattering, and the control structure of the converter is designed based on the multiinput SMC that is applied to a three-phase AC/DC power converter.The simulation and experimental results show the effectiveness of the proposed technique.展开更多
Superhydrophobic surfaces have attracted extensive interests and researches into their fundamentals and potential applications.Laser texturing provides the convenience to fabricate the hierarchical micro/nanostructure...Superhydrophobic surfaces have attracted extensive interests and researches into their fundamentals and potential applications.Laser texturing provides the convenience to fabricate the hierarchical micro/nanostructures for superhydrophobicity.However,after laser texturing,long wettability transition time from superhydrophilicity to superhydrophobicity is a barrier to mass production and practical industrial applications.External stimuli have been applied to change the surface composition and/or the surface morphology to reduce wettability transition time.Herein,by temperature tuning,wettability transition of laser textured brass surfaces is investigated.Scanning electron microscopy and surface contact angle measurement are employed to characterize the surface morphology and wettability behavior of the textured brass surfaces.By low-temperature heating(100℃~150℃),partial deoxidation of the top Cu O layer occurs to form hydrophobic Cu_2O.Therefore,superhydrophobicity without any chemical coating and surface modification could be achieved in a short time.Furthermore,after low-temperature heating,the low adhesive force between the water droplet and the sample surface is demonstrated for the laser textured brass surface.This study provides a simple method to fabricate the micro/nanostructure surfaces with controllable wettability for the potential applications.展开更多
The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna(PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup.To distinguish the contri...The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna(PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup.To distinguish the contribution of in-gap photocurrent and antenna structure to far-field radiation,polarization-dependent THz field was measured and quantified as the illuminating laser beam moved along the bias field within the gap region of electrodes. The result suggests that, although the far-field THz radiation originates from the in-gap photocurrent, the antenna structure of butterfly-shaped PCA dominates the overall THz radiation. In addition, to explore the impact of photoconductive material,radiation properties of butterfly-shaped PCAs fabricated on both low-temperature-grown GaAs(LT-GaAs) and semi-insulating GaAs(Si-GaAs) were characterized and compared. Consistent with previous experiments, it is observed that while Si-GaAs-based PCA can emit higher THz field than LT-GaAs-based PCA at low laser power, it would saturate more severely as laser power increased and eventually be surpassed by LT-GaAs-based PCA. Beyond that, it is found the severe saturation effect of Si-GaAs was due to the longer carrier lifetime and higher carrier mobility, which was confirmed by the numerical simulation.展开更多
基金supported by the National Natural Science Foundation of China (U1609209)National Natural Science Foundation of China (61605162)+2 种基金NSFC-Liaoning Province united foundation (U1608259)National Natural Science Foundation of China (51501219)the financial support from the China Scholarship Council
文摘Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.
基金supported by the National Natural Science Foundation of China(61671238,61471368)the Fundamental Research Funds for the Central Universities(NJ20160008,56XAA19052)+2 种基金the Jiangsu Planned Projects for Postdoctoral Research Funds(1601009B)the Equipment Advanced Research Foundation of China(61402090103)the Natural Sciences and Engineering Research Council(NSERC)of Canada.
文摘Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved various capabilities,but many of them are still under development,such as lowprofile,wideband,circular polarization,multi-band,low-radar cross section(RCS)and reconfigurable features.This paper discusses the theoretical analysis methods and research progress of FP antennas,and explains the realization methods of different features of FP antennas.In order to indicate different technologies for realizing various capabilities,the key technologies and features of some of the latest designs are described.Finally,the research situation and prospects of FP antennas are summarized to guide their research directions in the future.
基金Project supported by the National Science Center, Poland
文摘This paper presents a method for determining specific models of overhead power lines with presence of corona phenomenon. The obtained models provide stable numerical solutions for computer simulation of transients caused by direct lightning strikes. The corona non- linear charge-voltage characteristics obtained from experimental tests are used for identification of the corona parameters based on System Identification Toolbox implemented in Matlab package. Different transfer functions, which give the same waveshapes of overvoltages are de- termined using two parametric models. A circuit representation of the obtained transfer functions is proposed and the corona model is implemented in the EMTP-RV as a hierarchical structure composed of a overhead power line divided into sections with corona branches. Some computer simulations of lightning overvoltages propagated in a typical 220 kV power line due to direct lightning strikes to a line tower are presented. The proposed method and the model implemented in EMTP-RV are still valid for multi-conductor lines and for higher voltages of power lines but new corona nonlinear charge-voltage characteristics are required as an input parameter for the identification procedure.
基金Supported by Bissell Distinguished Professor Endowment Fund at UNC-Charlotte。
文摘Although there are numerous optical spectroscopy techniques and methods that have been used to extract the fundamental bandgap of a semiconductor,most of them belong to one of these three approaches:(1)the excitonic absorption,(2)modulation spectroscopy,and(3)the most widely used Tauc-plot.The excitonic absorption is based on a many-particle theory,which is physically the most correct approach,but requires more stringent crystalline quality and appropriate sample preparation and experimental implementation.The Tauc-plot is based on a single-particle theo⁃ry that neglects the many-electron effects.Modulation spectroscopy analyzes the spectroscopy features in the derivative spectrum,typically,of the reflectance and transmission under an external perturbation.Empirically,the bandgap ener⁃gy derived from the three approaches follow the order of E_(ex)>E_(MS)>E_(TP),where three transition energies are from exci⁃tonic absorption,modulation spectroscopy,and Tauc-plot,respectively.In principle,defining E_(g) as the single-elec⁃tron bandgap,we expect E_(g)>E_(ex),thus,E_(g)>E_(TP).In the literature,E_(TP) is often interpreted as E_(g),which is conceptual⁃ly problematic.However,in many cases,because the excitonic peaks are not readily identifiable,the inconsistency be⁃tween E_(g) and E_(TP) becomes invisible.In this brief review,real world examples are used(1)to illustrate how excitonic absorption features depend sensitively on the sample and measurement conditions;(2)to demonstrate the differences between E_(ex),E_(MS),and E_(TP) when they can be extracted simultaneously for one sample;and(3)to show how the popular⁃ly adopted Tauc-plot could lead to misleading results.Finally,it is pointed out that if the excitonic absorption is not ob⁃servable,the modulation spectroscopy can often yield a more useful and reasonable bandgap than Tauc-plot.
基金the Deanship of Scientific Research at Northern Border University,Arar,KSA for funding this research work through the project number"NBUFFMRA-2025-2461-09"。
文摘Blast-induced ground vibration,quantified by peak particle velocity(PPV),is a crucial factor in mitigating environmental and structural risks in mining and geotechnical engineering.Accurate PPV prediction facilitates safer and more sustainable blasting operations by minimizing adverse impacts and ensuring regulatory compliance.This study presents an advanced predictive framework integrating Cat Boost(CB)with nature-inspired optimization algorithms,including the Bat Algorithm(BAT),Sparrow Search Algorithm(SSA),Butterfly Optimization Algorithm(BOA),and Grasshopper Optimization Algorithm(GOA).A comprehensive dataset from the Sarcheshmeh Copper Mine in Iran was utilized to develop and evaluate these models using key performance metrics such as the Index of Agreement(IoA),Nash-Sutcliffe Efficiency(NSE),and the coefficient of determination(R^(2)).The hybrid CB-BOA model outperformed other approaches,achieving the highest accuracy(R^(2)=0.989)and the lowest prediction errors.SHAP analysis identified Distance(Di)as the most influential variable affecting PPV,while uncertainty analysis confirmed CB-BOA as the most reliable model,featuring the narrowest prediction interval.These findings highlight the effectiveness of hybrid machine learning models in refining PPV predictions,contributing to improved blast design strategies,enhanced structural safety,and reduced environmental impacts in mining and geotechnical engineering.
基金This work was supported by the Deanship of Scientific Research(DSR)at King Abdulaziz University,Jeddah(G-363-135-1438).
文摘This paper addresses the cooperative control problem of multiple unmanned aerial vehicles(multi-UAV)systems.First,a new distributed consensus algorithm for second-order nonlinear multi-agent systems(MAS)is formulated under the leader-following approach.The algorithm provides smooth input signals to the agents’control channels,which avoids the chattering effect generated by the conventional sliding mode-based control protocols.Second,a new formation control scheme is developed by integrating smooth distributed consensus control protocols into the geometric pattern model to achieve three-dimensional formation tracking.The Lyapunov theory is used to prove the stability and convergence of both distributed consensus and formation controllers.The effectiveness of the proposed algorithms is demonstrated through simulation results.
基金Supported by National Natural Science Foundation of P.R.China(60474038)Science Research Foundation of Beijing Jiaotong University(2005SM005)Specialized Research Fund for the Doctoral Program of Higher Education(20060004002)
文摘In the re-entry phase of a ballistic missile,decoys can be deployed as a mean to overburden enemy defenses.This results in a single track being split into multiple track-lets.Tracking of these track-lets is a critical task as any miss in the tracking procedure can become a cause of a major threat.The tracking process becomes more complicated in the presence of clutter.The low detection rate is one of the factors that may contribute to increasing the difficulty level in terms of tracking in the cluttered environment.This work introduces a new algorithm for the split event detection and target tracking under the framework of the joint integrated probabilistic data association(JIPDA)algorithm.The proposed algorithm is termed as split event-JIPDA(SE-JIPDA).This work establishes the mathematical foundation for the split target detection and tracking mechanism.The performance analysis is made under different simulation conditions to provide a clear insight into the merits of the proposed algorithm.The performance parameters in these simulations are the root mean square error(RMSE),confirmed true track rate(CTTR)and confirmed split true track rate(CSTTR).
基金supported by the Beijing Natural Science Foundation(4113074)
文摘The network reliability is difficult to be evaluated because of the complex relationship among the network components.It can be quite different for different users running different applications on the same network.This paper proposes a new concept and a model of application reliability.Different from the existing models that ignores the effects of applications,the proposed application reliability model considers the effects of different applications on the network performance and different types of network faults and makes the analysis of network components relationship possible.This paper also provides a method to evaluate the application reliability when the data flow satisfies Markov properties.Finally,a case study is presented to illustrate the proposed network reliability model and the analysis method.
文摘The main contribution of this paper is the design of an event-triggered formation control for leader-following consensus in second-order multi-agent systems(MASs)under communication faults.All the agents must follow the trajectories of a virtual leader despite communication faults considered as smooth time-varying delays dependent on the distance between the agents.Linear matrix inequalities(LMIs)-based conditions are obtained to synthesize a controller gain that guarantees stability of the synchronization error.Based on the closed-loop system,an event-triggered mechanism is designed to reduce the control law update and information exchange in order to reduce energy consumption.The proposed approach is implemented in a real platform of a fleet of unmanned aerial vehicles(UAVs)under communication faults.A comparison between a state-of-the-art technique and the proposed technique has been provided,demonstrating the performance improvement brought by the proposed approach.
基金Project(A19C2a0019) supported by the Advanced Remanufacturing and Technology Centre (ARTC) under its RIE2020 Advanced Manufacturing and Engineering (AME) IAF PP,Singapore。
文摘Metal superhydrophobic surfaces with anisotropic wettability and adhesion have become more and more important due to their promising applications. Herein, we report a new fabrication strategy through a combination of pulsed laser ablation and low-temperature annealing post-processing. An inclined cone structure array is made on stainless steel surfaces, and then 120 °C low-temperature annealing is applied. Such surface displays excellent mechanical durability and anisotropic superhydrophobicity. It is demonstrated experimentally that the contact angle of water droplets on the surface is different along the parallel(167° ±2°) and perpendicular directions(157° ±2°) of the inclined cone structure. The sliding behaviors of water droplets and mechanical durability of the inclined cone structures are studied. These surfaces obtained in a short time with environmentally friendly fabrication can be applied in industries for water harvesting, droplet manipulation, and pipeline transportation.
文摘This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm uses a GCMPN cost function to combat the impul-sive interference.To further accelerate the convergence rate in the sparse and the block-sparse system identification processes,the proportionate versions of the proposed algorithm,the L0-norm GCMPN-SAF(L0-GCMPN-SAF)and the block-sparse GCMPN-SAF(BSGCMPN-SAF)algorithms are also developed.Moreover,the convergence analysis of the proposed algorithm is provided.Simulation results show that the proposed algorithms have a better performance than some other state-of-the-art algorithms in the literature with respect to the convergence rate and the tracking capability.
文摘This paper introduces an algorithm for beamforming systems by the aid of multidimensional harmonic retrieval(MHR).This algorithm resolves problems,removes limitations of sampling and provides a more robust beamformer.A new sample space is created that can be used for estimating weights of a new beamforming called spatial-harmonics retrieval beamformer(SHRB).Simulation results show that SHRB has a better performance,accuracy,and applicability and more powerful eigenvalues than conventional beamformers.A simple mathematical proof is provided.By changing the number of harmonics,as a degree of freedom that is missing in conventional beamformers,SHRB can achieve more optimal outputs without increasing the number of spatial or temporal samples.We will demonstrate that SHRB offers an improvement of 4 dB in signal to noise ratio(SNR) in bit error rate(BER) of 10~(-4) over conventional beamformers.In the case of direction of arrival(DOA) estimation,SHRB can estimate the DOA of the desired signal with an SNR of-25 dB,when conventional methods cannot have acceptable response.
文摘In addition to the conventional Franklin Rod,many non-conventional air terminals are being used as lightning protection devices.As cited in previous works,these non-conventional devices emit space charge in the vicinity of the terminals during the process of lightning stroke.A number of factors affect the performance of these lightning protection devices,among them are geometry and dimension of the devices,location of the device above the ground,height of the cloud above the ground,and polarity of the lightning stroke.The performance of these lightning protection devices has been a topic of discussion by researchers for many years.Some studies focused on the magnitude of emission current from these devices as a criterion to evaluate their performances.The critical flashover voltage(CFO)between the devices and a metal screen simulating cloud can also be used as another criterion to evaluate the performance of the devices.Laboratory measurements were conducted in controlled conditions on different types of lightning protection devices to compare their performance.Four different types of devices were used in the present study:Franklin Rod,TerraStat models TS 100,TS 400,and Spline Ball Ionizer.The study focused on the CFO voltage of the air gap between devices and the metal screen.The CFO voltage was evaluated using standard switching and lightning impulses.The measurements were recorded for positive as well as negative polarity.The air gap between the devices and metal screen was selected at 2 m and 3 m.The results obtained provide a better understanding of the electrical performance of lightning protection devices.
基金Supported by′111′Project and Chongqing Natural Science Foundation(2006BB2043,2006BB2142)
文摘PZT-based valveless micropump is a microactuator that can be used for controlling and delivering tiny amounts of fluids,and diffuser/nozzle plays an important role when this type of micropump drives the fluid flowing along a specific direction.In this paper,a numerical model of micropump has been proposed,and the fluidic properties of diffuser/nozzle have been simulated with ANSYS.With the method of finite-element analysis,the increased pressure drop between inlet and outlet of diffuser/nozzle induces the increment of flow rate in both diffuser and nozzle simultaneously,but the increasing rate of diffuser is faster than that of nozzle.The L/R,ratio of L(length of cone pipe) and R(radius of minimal cross section of cone pipe) plays an important role in fluidic performance of diffuser and nozzle as well,and the mean flow rate will decrease with increment of L/R.The mean flow rate reaches its peak value when L/R with the value of 10 regardless the divergence angle of diffuser or nozzle.The simulation results indicate that the fluidic properties of diffuser/nozzle can be defined by its geometric structure,and accordingly determine the efficiency of micropump.
基金Projects(51076027,51036002) supported by the National Natural Science Foundation of ChinaProject(20090092110051) supported by the Doctoral Fund of Ministry of Education of China
文摘Solid oxide fuel cells (SOFCs) are considered to be one of the most important clean,distributed resources. However,SOFCs present a challenging control problem owing to their slow dynamics,nonlinearity and tight operating constraints. A novel data-driven nonlinear control strategy was proposed to solve the SOFC control problem by combining a virtual reference feedback tuning (VRFT) method and support vector machine. In order to fulfill the requirement for fuel utilization and control constraints,a dynamic constraints unit and an anti-windup scheme were adopted. In addition,a feedforward loop was designed to deal with the current disturbance. Detailed simulations demonstrate that the fast response of fuel flow for the current demand disturbance and zero steady error of the output voltage are both achieved. Meanwhile,fuel utilization is kept almost within the safe region.
文摘Sliding mode control(SMC) becomes a common tool in designing robust nonlinear control systems, due to its inherent characteristics such as insensitivity to system uncertainties and fast dynamic response.Two modes are involved in the SMC operation, namely reaching mode and sliding mode.In the reaching mode, the system state is forced to reach the sliding surface in a finite time.The major drawback of the SMC approach is the occurrence of chattering in the sliding mode, which is undesirable in most applications.Generally, the trade-off between chattering reduction and fast reaching time must be considered in the conventional SMC design.This paper proposes SMC design with a novel reaching law called the exponential rate reaching law(ERRL) to reduce chattering, and the control structure of the converter is designed based on the multiinput SMC that is applied to a three-phase AC/DC power converter.The simulation and experimental results show the effectiveness of the proposed technique.
基金supported by the National Natural Science Foundation of China (U1609209)Open Program of Laser Precision Machining Engineering Technology Research Center of Fujian Province (2016JZA001)
文摘Superhydrophobic surfaces have attracted extensive interests and researches into their fundamentals and potential applications.Laser texturing provides the convenience to fabricate the hierarchical micro/nanostructures for superhydrophobicity.However,after laser texturing,long wettability transition time from superhydrophilicity to superhydrophobicity is a barrier to mass production and practical industrial applications.External stimuli have been applied to change the surface composition and/or the surface morphology to reduce wettability transition time.Herein,by temperature tuning,wettability transition of laser textured brass surfaces is investigated.Scanning electron microscopy and surface contact angle measurement are employed to characterize the surface morphology and wettability behavior of the textured brass surfaces.By low-temperature heating(100℃~150℃),partial deoxidation of the top Cu O layer occurs to form hydrophobic Cu_2O.Therefore,superhydrophobicity without any chemical coating and surface modification could be achieved in a short time.Furthermore,after low-temperature heating,the low adhesive force between the water droplet and the sample surface is demonstrated for the laser textured brass surface.This study provides a simple method to fabricate the micro/nanostructure surfaces with controllable wettability for the potential applications.
文摘The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna(PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup.To distinguish the contribution of in-gap photocurrent and antenna structure to far-field radiation,polarization-dependent THz field was measured and quantified as the illuminating laser beam moved along the bias field within the gap region of electrodes. The result suggests that, although the far-field THz radiation originates from the in-gap photocurrent, the antenna structure of butterfly-shaped PCA dominates the overall THz radiation. In addition, to explore the impact of photoconductive material,radiation properties of butterfly-shaped PCAs fabricated on both low-temperature-grown GaAs(LT-GaAs) and semi-insulating GaAs(Si-GaAs) were characterized and compared. Consistent with previous experiments, it is observed that while Si-GaAs-based PCA can emit higher THz field than LT-GaAs-based PCA at low laser power, it would saturate more severely as laser power increased and eventually be surpassed by LT-GaAs-based PCA. Beyond that, it is found the severe saturation effect of Si-GaAs was due to the longer carrier lifetime and higher carrier mobility, which was confirmed by the numerical simulation.
