The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, w...The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, which leverages jet synthesis for drag reduction. A drag control experiment was conducted in a low-speed wind tunnel with a controlled flow velocity of 9.6 m/s(Re = 1.445 × 10^(4)). This study investigated the effects of varying pulse frequencies and actuation voltages on the turbulent boundary layer. Using a hot-wire measurement system, we analyzed the pulsating and time-averaged velocity distributions within the boundary layer to evaluate the streamwise turbulent drag reduction. The results show that the local TDR decreases as the pulse frequency increases, reaching a maximum reduction of approximately 20.97% at a pulse frequency of 50 Hz. In addition, as the actuation voltage increases, the friction coefficient decreases, increasing the drag reduction rate. The maximum drag reduction of approximately 33.34% is achieved at an actuation voltage of 10 kV.展开更多
This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445...This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445×10^(4).Using a hot-wire anemometer and an electrical data acquisition system,the influences of millisecond pulsed plasma actuation with different burst frequencies and duty cycles on the microscale coherent structures near the wall of the turbulent boundary layer(TBL)are studied.The experimental results show that the SBP-PA can effectively reduce the frictional drag of the TBL.When the duty cycle exceeds 30%,the TDR rate is greater than 11%,and the optimal drag reduction rate of 13.69%is obtained at a duty cycle of 50%.Furthermore,optimizing the electrical parameters reveals that increasing the burst frequency significantly reduces the velocity distribution in the logarithmic region of the TBL.When the normalized burst frequency reaches f+=2πf_(p)d/U_(∞)=7.196,the optimal TDR effectiveness is 16.97%,indicating a resonance phenomenon between the pulsed plasma actuation and the microscale coherent structures near the wall.Therefore,reasonably selecting the electrical parameters of the plasma actuator is expected to significantly improve the TDR effect.展开更多
Tri-electrode sliding discharge(TED)plasma actuators are formed by adding a direct current(DC)exposed electrode to conventional dielectric barrier discharge(DBD)plasma actuators.There are three TED modes depending on ...Tri-electrode sliding discharge(TED)plasma actuators are formed by adding a direct current(DC)exposed electrode to conventional dielectric barrier discharge(DBD)plasma actuators.There are three TED modes depending on the polarity and amplitude of the DC supply:DBD discharge,extended discharge and sliding discharge.This paper evaluates the electrical,aerodynamic and mechanical characteristics of a TED plasma actuator based on energy analysis,particle image velocimetry experiments and calculations using the Navier-Stokes equation.The flow control performances of different discharge modes are quantitatively analyzed based on characteristic parameters.The results show that flow control performance in both extended discharge and sliding discharge is more significant than that of DBD,mainly because of the significantly higher(up to 141%)body force of TED compared with DBD.However,conductivity loss is the primary power loss caused by the DC polarity for TED discharge.Therefore,power consumption can be reduced by optimizing the dielectric material and thickness,thus improving the flow control performance of plasma actuators.展开更多
In order to investigate the relationship between the flow-field parameters outside the vehicle and the altitude,this paper takes the Atmospheric Reentry Demonstrator(ARD)with an angle of attack of-20°as the resea...In order to investigate the relationship between the flow-field parameters outside the vehicle and the altitude,this paper takes the Atmospheric Reentry Demonstrator(ARD)with an angle of attack of-20°as the research object and adopts a two-temperature model coupled with the shear-stress transport k-ωturbulence model to focus on the variation of flow-field parameters including flow-field pressure,Mach number and temperature with the reentry altitude.It is found that the flow-field high-pressure region and low-Mach region both appear in the shock layer near the head of the ARD,while the maximum pressure of the surface appears on the windward side of the ARD's head with a toroidal distribution,and the numerical magnitude is inversely proportional to the radius of the torus.With fluid through the shoulder of the ARD flow expansion plays a dominant role,the airflow velocity increases,the Mach number of the windward side of the rear cone increases and the flow-field pressure and surface pressure rapidly decrease.When the fluid passes through the shock layer,the translational-rotation temperature will increase before the vibration-electron temperature,there is a thermal non-equilibrium effect and the two temperatures will rapidly decrease again when approaching the surface of the ARD due to the existence of temperature gradient.At the same time,both the windward side of the shoulder and the back cover of the ARD suffer from a large thermal load and require thermal protection.展开更多
We present a solid 226 nm deep ultraviolet laser system pumped by a Nd:YAG laser.A diamond Raman laser with a 1485 nm wavelength was generated up to 2.53 mJ pumped by a 9.7 mJ 1064 nm laser,which is the highest pulse ...We present a solid 226 nm deep ultraviolet laser system pumped by a Nd:YAG laser.A diamond Raman laser with a 1485 nm wavelength was generated up to 2.53 mJ pumped by a 9.7 mJ 1064 nm laser,which is the highest pulse energy of a second Stokes diamond Raman laser pumped by a 1064 nm laser as we know.Then,the Raman laser is mixed with the frequency-quadrupled 1064 nm laser to produce the 226 nm laser.The maximum output pulse energy at 226 nm reaches 0.49 mJ.The overall conversion efficiency from1064 to 226 nm is up to 1.14%,which is significantly higher than conventional optical parametric oscillator technology for the generation of 226 nm laser.The 226 nm laser system has been used in a laser-induced fluorescence(LIF)experiment of oxygen two-photon to demonstrate its potential for LIF measurements.展开更多
Developing highly efficient,inexpensive catalysts for oxygen electrocatalysis in alkaline electrolytes(i.e.,the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER))is essential for constructing advanc...Developing highly efficient,inexpensive catalysts for oxygen electrocatalysis in alkaline electrolytes(i.e.,the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER))is essential for constructing advanced energy conversion techniques(such as electrolyzers,fuel cells,and metal–air batteries).Recent achievements in efficient noble metal-free ORR and OER catalysts make the replacement of conventional noble metal counterparts a realistic possibility.In particular,various electronic structure regulation strategies have been employed to endow these oxygen catalysts with attractive physicochemical properties and strong synergistic effects,providing significant fundamental understanding to advance in this direction.This review article summarizes recently developed electronic structure regulation strategies for three types of noble metal-free oxygen catalysts:transition metal compounds,single-atom catalysts,and metal-free catalysts.We begin by briefly presenting the basic ORR and OER reaction mechanisms,following this with an analysis of the fundamental relationship between electronic structure and intrinsic electrocatalytic activity for the three categories of catalysts.Subsequently,recent advances in electronic structure regulation strategies for noble metal-free ORR and OER catalysts are systematically dis-cussed.We conclude by summarizing the remaining challenges and presenting our outlook on the future for designing and synthesizing noble metal-free oxygen electrocatalysts.展开更多
Freestanding MXene-based macroforms have gained significant attention as versatile components in electrochemical energy storage applications owing to their interconnected conductive network,strong mechanical strength,...Freestanding MXene-based macroforms have gained significant attention as versatile components in electrochemical energy storage applications owing to their interconnected conductive network,strong mechanical strength,and customizable surface chemistries derived from MXene nanosheets.This comprehensive review article encompasses key aspects related to the synthesis of MXene nanosheets,strategies for structure design and surface medication,surface modification,and the diverse fabrication methods employed to create freestanding MXene-based macroform architectures.The review also delves into the recent advancements in utilizing freestanding MXene macroforms for electrochemical energy storage applications,offering a detailed discussion on the significant progress achieved thus far.Notably,the correlation between the macroform’s structural attributes and its performance characteristics is thoroughly explored,shedding light on the critical factors influencing efficiency and durability.Despite the remarkable development,the review also highlights the existing challenges and presents future perspectives for freestanding MXenebased macroforms in the realms of high-performance energy storage devices.By addressing these challenges and leveraging emerging opportunities,the potential of freestanding MXene-based macroforms can be harnessed to enable groundbreaking advancements in the field of energy storage.展开更多
The escalating global energy demand underscores the urgency of developing sustainable battery technologies.Zinc-air batteries(ZABs)have emerged as promising candidates due to their costeffectiveness,safety,and high en...The escalating global energy demand underscores the urgency of developing sustainable battery technologies.Zinc-air batteries(ZABs)have emerged as promising candidates due to their costeffectiveness,safety,and high energy density[1-4].Conventional ZABs typically rely on a four-electron(4e-)oxygen reduction reaction(ORR)in strongly alkaline electrolytes.展开更多
Early diagnosis of lung cancer can effectively reduce the mortality of patients.Doctors use low-dose spiral CT to detect lung nodules,which is timeconsuming and prone to omissions.Deep learning has achieved good resul...Early diagnosis of lung cancer can effectively reduce the mortality of patients.Doctors use low-dose spiral CT to detect lung nodules,which is timeconsuming and prone to omissions.Deep learning has achieved good results in the field of medical image sub-processing,which can reduce the pressure of doctors to a certain extent.However,in the actual lung CT images,the images containing lung nodules account for less than 1%of the total images.The lack of data increases the difficulty of detecting lung nodules by using deep learning methods.This paper proposes an amplification method using deep convolutional anti-generation network(DCGAN)to generate lung nodule data.Compared with different amplification methods,and the effectiveness of this method is confirmed.Experiments can prove that the use of DCGAN to generate data can better solve the problems of high false positive rate and low sensitivity of lung nodule classification than the graphical data amplification mode.Compared with the existing methods,this experimental method greatly improves the accuracy,sensitivity and F1 score of lung nodule detection,and achieves good results of 99.98%,99.15%and 99.55%,respectively.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61971345 and 52107174)。
文摘The primary objective in aircraft transportation is to minimize turbulent drag, thereby conserving energy and reducing emissions. We propose a sector-shaped counter-flow dielectric barrier discharge plasma actuator, which leverages jet synthesis for drag reduction. A drag control experiment was conducted in a low-speed wind tunnel with a controlled flow velocity of 9.6 m/s(Re = 1.445 × 10^(4)). This study investigated the effects of varying pulse frequencies and actuation voltages on the turbulent boundary layer. Using a hot-wire measurement system, we analyzed the pulsating and time-averaged velocity distributions within the boundary layer to evaluate the streamwise turbulent drag reduction. The results show that the local TDR decreases as the pulse frequency increases, reaching a maximum reduction of approximately 20.97% at a pulse frequency of 50 Hz. In addition, as the actuation voltage increases, the friction coefficient decreases, increasing the drag reduction rate. The maximum drag reduction of approximately 33.34% is achieved at an actuation voltage of 10 kV.
基金supported by National Natural Science Foundation of China(Nos.61971345 and 12175177)the Foundation for Key Laboratories of National Defense Science and Technology of China(No.614220120030810).
文摘This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445×10^(4).Using a hot-wire anemometer and an electrical data acquisition system,the influences of millisecond pulsed plasma actuation with different burst frequencies and duty cycles on the microscale coherent structures near the wall of the turbulent boundary layer(TBL)are studied.The experimental results show that the SBP-PA can effectively reduce the frictional drag of the TBL.When the duty cycle exceeds 30%,the TDR rate is greater than 11%,and the optimal drag reduction rate of 13.69%is obtained at a duty cycle of 50%.Furthermore,optimizing the electrical parameters reveals that increasing the burst frequency significantly reduces the velocity distribution in the logarithmic region of the TBL.When the normalized burst frequency reaches f+=2πf_(p)d/U_(∞)=7.196,the optimal TDR effectiveness is 16.97%,indicating a resonance phenomenon between the pulsed plasma actuation and the microscale coherent structures near the wall.Therefore,reasonably selecting the electrical parameters of the plasma actuator is expected to significantly improve the TDR effect.
基金the National Natural Science Foundation of China(Grant Nos.12175177 and 61971345)the Foundation for Key Laboratories of National Defense Science and Technology of China(Grant No.614220120030810)。
文摘Tri-electrode sliding discharge(TED)plasma actuators are formed by adding a direct current(DC)exposed electrode to conventional dielectric barrier discharge(DBD)plasma actuators.There are three TED modes depending on the polarity and amplitude of the DC supply:DBD discharge,extended discharge and sliding discharge.This paper evaluates the electrical,aerodynamic and mechanical characteristics of a TED plasma actuator based on energy analysis,particle image velocimetry experiments and calculations using the Navier-Stokes equation.The flow control performances of different discharge modes are quantitatively analyzed based on characteristic parameters.The results show that flow control performance in both extended discharge and sliding discharge is more significant than that of DBD,mainly because of the significantly higher(up to 141%)body force of TED compared with DBD.However,conductivity loss is the primary power loss caused by the DC polarity for TED discharge.Therefore,power consumption can be reduced by optimizing the dielectric material and thickness,thus improving the flow control performance of plasma actuators.
基金Project supported by the National Natural Science Foundation of China(Grant No.12175177)the China Postdoctoral Science Foundation(Grant No.2021M693889)。
文摘In order to investigate the relationship between the flow-field parameters outside the vehicle and the altitude,this paper takes the Atmospheric Reentry Demonstrator(ARD)with an angle of attack of-20°as the research object and adopts a two-temperature model coupled with the shear-stress transport k-ωturbulence model to focus on the variation of flow-field parameters including flow-field pressure,Mach number and temperature with the reentry altitude.It is found that the flow-field high-pressure region and low-Mach region both appear in the shock layer near the head of the ARD,while the maximum pressure of the surface appears on the windward side of the ARD's head with a toroidal distribution,and the numerical magnitude is inversely proportional to the radius of the torus.With fluid through the shoulder of the ARD flow expansion plays a dominant role,the airflow velocity increases,the Mach number of the windward side of the rear cone increases and the flow-field pressure and surface pressure rapidly decrease.When the fluid passes through the shock layer,the translational-rotation temperature will increase before the vibration-electron temperature,there is a thermal non-equilibrium effect and the two temperatures will rapidly decrease again when approaching the surface of the ARD due to the existence of temperature gradient.At the same time,both the windward side of the shoulder and the back cover of the ARD suffer from a large thermal load and require thermal protection.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2032136 and U2241288)the Shaanxi Fundamental Science Research Project for Mathematics and Physics(Grant No.23JSY012)。
文摘We present a solid 226 nm deep ultraviolet laser system pumped by a Nd:YAG laser.A diamond Raman laser with a 1485 nm wavelength was generated up to 2.53 mJ pumped by a 9.7 mJ 1064 nm laser,which is the highest pulse energy of a second Stokes diamond Raman laser pumped by a 1064 nm laser as we know.Then,the Raman laser is mixed with the frequency-quadrupled 1064 nm laser to produce the 226 nm laser.The maximum output pulse energy at 226 nm reaches 0.49 mJ.The overall conversion efficiency from1064 to 226 nm is up to 1.14%,which is significantly higher than conventional optical parametric oscillator technology for the generation of 226 nm laser.The 226 nm laser system has been used in a laser-induced fluorescence(LIF)experiment of oxygen two-photon to demonstrate its potential for LIF measurements.
基金supported by European Union's Horizon 2020 research and innovation programme(GrapheneCore3881603)Sachsisches Staatsministerium für Wissenschaft und Kunst(Sonderzuweisung zur Unterstützung profilbestimmender Struktureinheiten),German Research Foundation(DFG)within the Cluster of Excellence,and CRC 1415(grant no.417590517).
文摘Developing highly efficient,inexpensive catalysts for oxygen electrocatalysis in alkaline electrolytes(i.e.,the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER))is essential for constructing advanced energy conversion techniques(such as electrolyzers,fuel cells,and metal–air batteries).Recent achievements in efficient noble metal-free ORR and OER catalysts make the replacement of conventional noble metal counterparts a realistic possibility.In particular,various electronic structure regulation strategies have been employed to endow these oxygen catalysts with attractive physicochemical properties and strong synergistic effects,providing significant fundamental understanding to advance in this direction.This review article summarizes recently developed electronic structure regulation strategies for three types of noble metal-free oxygen catalysts:transition metal compounds,single-atom catalysts,and metal-free catalysts.We begin by briefly presenting the basic ORR and OER reaction mechanisms,following this with an analysis of the fundamental relationship between electronic structure and intrinsic electrocatalytic activity for the three categories of catalysts.Subsequently,recent advances in electronic structure regulation strategies for noble metal-free ORR and OER catalysts are systematically dis-cussed.We conclude by summarizing the remaining challenges and presenting our outlook on the future for designing and synthesizing noble metal-free oxygen electrocatalysts.
基金Startup Research Fund of Henan Academy of Sciences,Grant/Award Number:231817001China Scholarship Council(CSC)+2 种基金German Research Foundation(DFG),Grant/Award Number:448719339Sachsisches Staatsministerium furWissenschaft und Kunst(Sonderzuweisung zur Unterstutzung profilbestimmender Struktureinheiten)Federal Ministry of Education and Research(BMBF),Grant/Award Numbers:03XP0390C,03XP0254D。
文摘Freestanding MXene-based macroforms have gained significant attention as versatile components in electrochemical energy storage applications owing to their interconnected conductive network,strong mechanical strength,and customizable surface chemistries derived from MXene nanosheets.This comprehensive review article encompasses key aspects related to the synthesis of MXene nanosheets,strategies for structure design and surface medication,surface modification,and the diverse fabrication methods employed to create freestanding MXene-based macroform architectures.The review also delves into the recent advancements in utilizing freestanding MXene macroforms for electrochemical energy storage applications,offering a detailed discussion on the significant progress achieved thus far.Notably,the correlation between the macroform’s structural attributes and its performance characteristics is thoroughly explored,shedding light on the critical factors influencing efficiency and durability.Despite the remarkable development,the review also highlights the existing challenges and presents future perspectives for freestanding MXenebased macroforms in the realms of high-performance energy storage devices.By addressing these challenges and leveraging emerging opportunities,the potential of freestanding MXene-based macroforms can be harnessed to enable groundbreaking advancements in the field of energy storage.
文摘The escalating global energy demand underscores the urgency of developing sustainable battery technologies.Zinc-air batteries(ZABs)have emerged as promising candidates due to their costeffectiveness,safety,and high energy density[1-4].Conventional ZABs typically rely on a four-electron(4e-)oxygen reduction reaction(ORR)in strongly alkaline electrolytes.
基金beijing Natural Science Foundation(5182018)the Fundamental Research Funds for the Central Universities(PYBZ1834).
文摘Early diagnosis of lung cancer can effectively reduce the mortality of patients.Doctors use low-dose spiral CT to detect lung nodules,which is timeconsuming and prone to omissions.Deep learning has achieved good results in the field of medical image sub-processing,which can reduce the pressure of doctors to a certain extent.However,in the actual lung CT images,the images containing lung nodules account for less than 1%of the total images.The lack of data increases the difficulty of detecting lung nodules by using deep learning methods.This paper proposes an amplification method using deep convolutional anti-generation network(DCGAN)to generate lung nodule data.Compared with different amplification methods,and the effectiveness of this method is confirmed.Experiments can prove that the use of DCGAN to generate data can better solve the problems of high false positive rate and low sensitivity of lung nodule classification than the graphical data amplification mode.Compared with the existing methods,this experimental method greatly improves the accuracy,sensitivity and F1 score of lung nodule detection,and achieves good results of 99.98%,99.15%and 99.55%,respectively.
