This paper investigates the attitude tracking control problem for the cruise mode of a dual-system convertible unmanned aerial vehicle(UAV)in the presence of parameter uncertainties,unmodeled uncertainties and wind di...This paper investigates the attitude tracking control problem for the cruise mode of a dual-system convertible unmanned aerial vehicle(UAV)in the presence of parameter uncertainties,unmodeled uncertainties and wind disturbances.First,a fixed-time disturbance observer(FXDO)based on the bi-limit homogeneity theory is designed to estimate the lumped disturbance of the convertible UAV model.Then,a fixed-time integral sliding mode control(FXISMC)is combined with the FXDO to achieve strong robustness and chattering reduction.Bi-limit homogeneity theory and Lyapunov theory are applied to provide detailed proof of the fixed-time stability.Finally,numerical simulation experimental results verify the robustness of the proposed algorithm to model parameter uncertainties and wind disturbances.In addition,the proposed algorithm is deployed in a open-source UAV autopilot and its effectiveness is further demonstrated by hardware-in-the-loop experimental results.展开更多
An in-pixel histogramming time-to-digital converter(hTDC)based on octonary search and 4-tap phase detection is presented,aiming to improve frame rate while ensuring high precicion.The proposed hTDC is a 12-bit two-ste...An in-pixel histogramming time-to-digital converter(hTDC)based on octonary search and 4-tap phase detection is presented,aiming to improve frame rate while ensuring high precicion.The proposed hTDC is a 12-bit two-step converter consisting of a 6-bit coarse quantization and a 6-bit fine quantization,which supports a time resolution of 120 ps and multiphoton counting up to 2 GHz without a GHz reference frequency.The proposed hTDC is designed in 0.11μm CMOS process with an area consumption of 6900μm^(2).The data from a behavioral-level model is imported into the designed hTDC circuit for simulation verification.The post-simulation results show that the proposed hTDC achieves 0.8%depth precision in 9 m range for short-range system design specifications and 0.2%depth precision in 48 m range for long-range system design specifications.Under 30×10^(3) lux background light conditions,the proposed hTDC can be used for SPAD-based flash LiDAR sensor to achieve a frame rate to 40 fps with 200 ps resolution in 9 m range.展开更多
To facilitate rapid analysis of the oscillation stability mechanism in modular multilevel converter-based high voltage direct current(MMC-HVDC)systems and streamline the simulation process for determining MMC impedanc...To facilitate rapid analysis of the oscillation stability mechanism in modular multilevel converter-based high voltage direct current(MMC-HVDC)systems and streamline the simulation process for determining MMC impedance characteristics,a simplified mathematical simulation model for MMC closed-loop impedance is developed using the harmonic state space method.This model considers various control strategies and includes both AC-side and DC-side impedance models.By applying a Nyquist criterion-based impedance analysis method,the stability mechanisms on the AC and DC sides of the MMC are examined.In addition,a data-driven oscillation stability analysis method is also proposed,leveraging a global sensitivity algorithm based on fast model results to identify key parameters influencing MMC oscillation stability.Based on sensitivity analysis results,a parameter adjustment strategy for oscillation suppression is proposed.The simulation results from the MATLAB/Simulinkbased MMC model validate the effectiveness of the proposed method.展开更多
在英语中,常用来表示“改变”的动词有alter,change N convert^modify^revise%shift^transcribe、transform、vary等。本文将就以上九个动词的词义和用法进行辨析,并列举一些教材和辞书中的典型实例加以说明。1.alter:用作及物或不及物...在英语中,常用来表示“改变”的动词有alter,change N convert^modify^revise%shift^transcribe、transform、vary等。本文将就以上九个动词的词义和用法进行辨析,并列举一些教材和辞书中的典型实例加以说明。1.alter:用作及物或不及物动词,表示对事实、过程、设计、计划、方案、政策、意见、习惯、价格、地貌、容貌等的改变,也可表示对衣服的改动而使其更加合身。展开更多
The filter capacitor stack is one of the main acoustic noise sources in high-voltage DC(HVDC) converter stations.As HVDC systems are built more and more recently,it is significant to research the audible noise of filt...The filter capacitor stack is one of the main acoustic noise sources in high-voltage DC(HVDC) converter stations.As HVDC systems are built more and more recently,it is significant to research the audible noise of filter capacitors.In this paper,the current situation of research on vibration and audible noise of filter capacitors in HVDC converter stations,which is departed into three parts—generation mechanism,prediction methods,and reduction measures,is presented and the research achievements are discussed.Scholars have built the model that the alternating electric force caused by the voltage conduces to the vibration,which propagates to the enclosure and radiates audible noise.As a result,the parts contributing most to the generation of audible noise are the top and the bottom of capacitors. In the noise level prediction respect,several methods have been prospected including impact hammer,sweep frequency, impact current,monopole and Kirchhoff formula method,which are suitable for single capacitors or capacitors stacks individually.However,the sweep frequency method is restricted by experiment condition,and the impact current method needs further research and verified.On the other hand,CIGRE WG14.26 provides three sound reduction measures,but all of them are not so practicable,while MPP absorber and compressible space absorber prospected by Dr.Wu Peng are proved to be effective.The sound barriers are also considered by scholars,and the acoustic directivity performance of capacitors is also researched.Besides,the developing direction of each research field is prospected in corresponding part.展开更多
The convertion of solar energy into hydrogen energy with high energy density by photocatalysis is a green and eco-friendly avenue to solve the energy crisis and environmental pollution issues 1,2.Unfortunately,most ph...The convertion of solar energy into hydrogen energy with high energy density by photocatalysis is a green and eco-friendly avenue to solve the energy crisis and environmental pollution issues 1,2.Unfortunately,most photocatalysts usually suffer from the rapid quenching of photogenerated carriers and depressed interfacial H_(2)-generation dynamics 3,4.To overcome the above shortcomings,cocatalysts are widely employed to promote the separation of photocarriers and to create active sites for surface catalytic reactions 5.For a superb cocatalyst,its active sites usually play a key role in the overall performance of photocatalytic H_(2) evolution because the active sites can not only provide a large number of adsorption centers to enrich H+,but also present an outstanding catalytic efficiency to convert H+into H_(2) by reducing its reaction overpotential 6.Thus,the active-site number and efficiency of cocatalysts should be maximized as much as possible to greatly boost the cocatalytic H2-evolution activity by photocatalysis.展开更多
An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insul...An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insulated bushing,rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge.The measurement of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment.An additional challenge is the""mixed"voltage stress on the bushing insulation,which has both ac and dc high-voltage components.There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation.As a result,the analysis and interpretation of PD data for HVDC equipment is more complex;PD pulses may occur in response to the ac,dc,or switching transient voltage stresses.In this paper,an online PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed.The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients,caused during switching,trigger some PD events.Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities.The findings from the online PD measurements are verified with physical evidence,found after the bushing was removed from service,suggested internal PD had occurred inside the bushing.展开更多
The multi-string LED in parallel is a popular structure in backlight and lighting applications.The current balancing for each string is required to achieve uniform luminance and reliable operation.The conventional act...The multi-string LED in parallel is a popular structure in backlight and lighting applications.The current balancing for each string is required to achieve uniform luminance and reliable operation.The conventional active current sharing technique using a switching converter or a linear switch is very complex,and needs extra components.The conventional coupled inductor based current sharing method is much more simple,but needs too many coupled inductors.展开更多
A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump...A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area. The PMU chip is designed with MagnaChip＇s 0.25 μ high-voltage process. The driving currents of ELVDD and ELVSS are more than 50 mA when a SPICE simulation is done.展开更多
Effectiveness evaluation of the joint operation system is an important basis for the demonstration and development of weapon equipment.With the consideration that existing models of system effectiveness evaluation sel...Effectiveness evaluation of the joint operation system is an important basis for the demonstration and development of weapon equipment.With the consideration that existing models of system effectiveness evaluation seldom describe the structural relationship among equipment clearly as well as reflect the dynamic,the analog-to-digital converter-graphical evaluation and review technique(ADC-GERT)network parameter estimation model is proposed based on the ADC model and the joint operation system structure.Firstly,analysis of the joint operation system structure and operation process is conducted to build the GERT network,where equipment subsystems are nodes and activities are directed arches.Then the mission effectiveness of equipment subsystems is calculated by the ADC model.The probability transfer parameters are modified by the mission effectiveness of equipment subsystems based on the Bayesian theorem,with the ADC-GERT network parameter estimation model constructed.Finally,a case study is used to validate the efficiency and dynamic of the ADC-GERT network parameter estimation model.展开更多
An adaptive chaotic gradient descending optimization algorithm for single objective optimization was presented. A local minimum judged by two rules was obtained by an improved mutative-step gradient descending method....An adaptive chaotic gradient descending optimization algorithm for single objective optimization was presented. A local minimum judged by two rules was obtained by an improved mutative-step gradient descending method. A new optimal minimum was obtained to replace the local minimum by mutative-scale chaotic search algorithm whose scales are magnified gradually from a small scale in order to escape local minima. The global optimal value was attained by repeatedly iterating. At last, a BP (back-propagation) neural network model for forecasting slag output in matte converting was established. The algorithm was used to train the weights of the BP neural network model. The simulation results with a training data set of 400 samples show that the training process can be finished within 300 steps to obtain the global optimal value, and escape local minima effectively. An optimization system for operation parameters, which includes the forecasting model, is achieved, in which the output of converter increases by 6.0%, and the amount of the treated cool materials rises by 7.8% in the matte converting process.展开更多
With the development of current electronic technology, numerous high-speed data acquisition systems provide a variety of potential benefits. This article describes a high-speed data acquisition system which consists o...With the development of current electronic technology, numerous high-speed data acquisition systems provide a variety of potential benefits. This article describes a high-speed data acquisition system which consists of ECL logic and TTL logic devices, samples and stores data with a 1 GHz clock. This system is accomplished easily and works stably. A performance test of this system has been undertaken and the results show that the effective number of bits （ENOB） is more than 6.5 bits.展开更多
In the modern wireless communication system,the manipulation for polarization of electromagnetic wave plays a important role in improving the capacity and reliability of communication.In this paper,a multifunctional p...In the modern wireless communication system,the manipulation for polarization of electromagnetic wave plays a important role in improving the capacity and reliability of communication.In this paper,a multifunctional polarization converter(MFPC)based on the multilayer reconfigurable metasurface is proposed,which can assist the source antenna to transmit and receive multiple polarization signals.The MFPC consists of a grating which can filter out the undesired polarization and four layers of metasurfaces incorporated with PIN diodes.The functions of the MFPC include LTC and LTL polarization conversions,co-polarization transmission and reflection for arbitrary polarization.By changing the states of PIN diodes,the functions of MFPC can be dynamically switched.Loaded on the aperture of source antenna,the proposed MFPC can serve as a transmissive array with multiple polarization channels,and can also provide EM protection for source antenna by reflecting the incoming interference waves.Cascading of the metasurfaces produces Fabry-Perot resonance in the MFPC,and it contributes to the realization of LTC and LTL polarization conversions.To verify the performance of the proposed MFPC,the prototype is fabricated and tested.The measured results show that the fractional bandwidths of four functions are all higher than 31.9% with transmission or reflection coefficients higher than-2 d B.The frequency band of each function is mainly concentrated in S-band.The measured data are in agreement with the simulated results.展开更多
Introduction Cells can sense and respond to the mechanical microenvironment by converting forces into biochemical signals inside the cells,i.e.mechanotransduction<sup>[1-3]</sup>.Focal adhesions are the ma...Introduction Cells can sense and respond to the mechanical microenvironment by converting forces into biochemical signals inside the cells,i.e.mechanotransduction<sup>[1-3]</sup>.Focal adhesions are the major sites of interaction between a cell and its extracellular matrix（ECM）microenvironment,thus outside mechanical signals can be sensed at focal adhesions through transmembrane receptor integrins.In particular,it has been shown that matrix elasticity can control the cell fate<sup>[4]</sup>by modulating the interactions between ECM proteins and their receptor integrins<sup>[5,6]</sup>.For example,different rigidity of polyacrylamide（PA）gels can lead to different density of ECM ancho-展开更多
Optimal activation of T cells requires at least 2signals. Signal one is generated by interactionsbetween T cell receptor and antigenic peptide-majorhistocompatibility complex on antigen-presentingcells. Signal two is ...Optimal activation of T cells requires at least 2signals. Signal one is generated by interactionsbetween T cell receptor and antigenic peptide-majorhistocompatibility complex on antigen-presentingcells. Signal two is delivered by co-stimulatory ligandson antigen-presenting cells to their receptors on展开更多
基金supported by National Natural Science Foundation of China (Grant Nos.52072309 and 62303379)Beijing Institute of Spacecraft System Engineering Research Project (Grant NO.JSZL2020203B004)+1 种基金Natural Science Foundation of Shaanxi Province,Chinese (Grant NOs.2023-JC-QN-0003 and 2023-JC-QN-0665)Industry-University-Research Innovation Fund of Ministry of Education for Chinese Universities (Grant NO.2022IT189)。
文摘This paper investigates the attitude tracking control problem for the cruise mode of a dual-system convertible unmanned aerial vehicle(UAV)in the presence of parameter uncertainties,unmodeled uncertainties and wind disturbances.First,a fixed-time disturbance observer(FXDO)based on the bi-limit homogeneity theory is designed to estimate the lumped disturbance of the convertible UAV model.Then,a fixed-time integral sliding mode control(FXISMC)is combined with the FXDO to achieve strong robustness and chattering reduction.Bi-limit homogeneity theory and Lyapunov theory are applied to provide detailed proof of the fixed-time stability.Finally,numerical simulation experimental results verify the robustness of the proposed algorithm to model parameter uncertainties and wind disturbances.In addition,the proposed algorithm is deployed in a open-source UAV autopilot and its effectiveness is further demonstrated by hardware-in-the-loop experimental results.
基金National Key Research and Development Program of China(2022YFB2804401)。
文摘An in-pixel histogramming time-to-digital converter(hTDC)based on octonary search and 4-tap phase detection is presented,aiming to improve frame rate while ensuring high precicion.The proposed hTDC is a 12-bit two-step converter consisting of a 6-bit coarse quantization and a 6-bit fine quantization,which supports a time resolution of 120 ps and multiphoton counting up to 2 GHz without a GHz reference frequency.The proposed hTDC is designed in 0.11μm CMOS process with an area consumption of 6900μm^(2).The data from a behavioral-level model is imported into the designed hTDC circuit for simulation verification.The post-simulation results show that the proposed hTDC achieves 0.8%depth precision in 9 m range for short-range system design specifications and 0.2%depth precision in 48 m range for long-range system design specifications.Under 30×10^(3) lux background light conditions,the proposed hTDC can be used for SPAD-based flash LiDAR sensor to achieve a frame rate to 40 fps with 200 ps resolution in 9 m range.
基金National Natural Science Foundation of China(52307127)State Key Laboratory of Power System Operation and Control(SKLD23KZ07)。
文摘To facilitate rapid analysis of the oscillation stability mechanism in modular multilevel converter-based high voltage direct current(MMC-HVDC)systems and streamline the simulation process for determining MMC impedance characteristics,a simplified mathematical simulation model for MMC closed-loop impedance is developed using the harmonic state space method.This model considers various control strategies and includes both AC-side and DC-side impedance models.By applying a Nyquist criterion-based impedance analysis method,the stability mechanisms on the AC and DC sides of the MMC are examined.In addition,a data-driven oscillation stability analysis method is also proposed,leveraging a global sensitivity algorithm based on fast model results to identify key parameters influencing MMC oscillation stability.Based on sensitivity analysis results,a parameter adjustment strategy for oscillation suppression is proposed.The simulation results from the MATLAB/Simulinkbased MMC model validate the effectiveness of the proposed method.
文摘在英语中,常用来表示“改变”的动词有alter,change N convert^modify^revise%shift^transcribe、transform、vary等。本文将就以上九个动词的词义和用法进行辨析,并列举一些教材和辞书中的典型实例加以说明。1.alter:用作及物或不及物动词,表示对事实、过程、设计、计划、方案、政策、意见、习惯、价格、地貌、容貌等的改变,也可表示对衣服的改动而使其更加合身。
基金Supported by National Natural Science Foundation of China(50907046)
文摘The filter capacitor stack is one of the main acoustic noise sources in high-voltage DC(HVDC) converter stations.As HVDC systems are built more and more recently,it is significant to research the audible noise of filter capacitors.In this paper,the current situation of research on vibration and audible noise of filter capacitors in HVDC converter stations,which is departed into three parts—generation mechanism,prediction methods,and reduction measures,is presented and the research achievements are discussed.Scholars have built the model that the alternating electric force caused by the voltage conduces to the vibration,which propagates to the enclosure and radiates audible noise.As a result,the parts contributing most to the generation of audible noise are the top and the bottom of capacitors. In the noise level prediction respect,several methods have been prospected including impact hammer,sweep frequency, impact current,monopole and Kirchhoff formula method,which are suitable for single capacitors or capacitors stacks individually.However,the sweep frequency method is restricted by experiment condition,and the impact current method needs further research and verified.On the other hand,CIGRE WG14.26 provides three sound reduction measures,but all of them are not so practicable,while MPP absorber and compressible space absorber prospected by Dr.Wu Peng are proved to be effective.The sound barriers are also considered by scholars,and the acoustic directivity performance of capacitors is also researched.Besides,the developing direction of each research field is prospected in corresponding part.
基金funded by the Deanship of Scientific Research(DSR)at King Abdulaziz University,Jeddah,under grant No.RG-72-130-42.
文摘The convertion of solar energy into hydrogen energy with high energy density by photocatalysis is a green and eco-friendly avenue to solve the energy crisis and environmental pollution issues 1,2.Unfortunately,most photocatalysts usually suffer from the rapid quenching of photogenerated carriers and depressed interfacial H_(2)-generation dynamics 3,4.To overcome the above shortcomings,cocatalysts are widely employed to promote the separation of photocarriers and to create active sites for surface catalytic reactions 5.For a superb cocatalyst,its active sites usually play a key role in the overall performance of photocatalytic H_(2) evolution because the active sites can not only provide a large number of adsorption centers to enrich H+,but also present an outstanding catalytic efficiency to convert H+into H_(2) by reducing its reaction overpotential 6.Thus,the active-site number and efficiency of cocatalysts should be maximized as much as possible to greatly boost the cocatalytic H2-evolution activity by photocatalysis.
基金Manitoba Hydro for funding and supporting this research
文摘An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insulated bushing,rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge.The measurement of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment.An additional challenge is the""mixed"voltage stress on the bushing insulation,which has both ac and dc high-voltage components.There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation.As a result,the analysis and interpretation of PD data for HVDC equipment is more complex;PD pulses may occur in response to the ac,dc,or switching transient voltage stresses.In this paper,an online PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed.The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients,caused during switching,trigger some PD events.Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities.The findings from the online PD measurements are verified with physical evidence,found after the bushing was removed from service,suggested internal PD had occurred inside the bushing.
文摘The multi-string LED in parallel is a popular structure in backlight and lighting applications.The current balancing for each string is required to achieve uniform luminance and reliable operation.The conventional active current sharing technique using a switching converter or a linear switch is very complex,and needs extra components.The conventional coupled inductor based current sharing method is much more simple,but needs too many coupled inductors.
文摘A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area. The PMU chip is designed with MagnaChip＇s 0.25 μ high-voltage process. The driving currents of ELVDD and ELVSS are more than 50 mA when a SPICE simulation is done.
基金supported by the National Natural Science Foundation of China(72071111,71801127,71671091)the NSFC and the UK Royal Society joint project(71811530338)+2 种基金the Special Postdoctoral Fund of China(2019TQ0150)the Fundamental Research Funds for the Central Universities of China(NC2019003)the Intelligence Introduction Base of the Ministry of Science and Technology(G20190010178)。
文摘Effectiveness evaluation of the joint operation system is an important basis for the demonstration and development of weapon equipment.With the consideration that existing models of system effectiveness evaluation seldom describe the structural relationship among equipment clearly as well as reflect the dynamic,the analog-to-digital converter-graphical evaluation and review technique(ADC-GERT)network parameter estimation model is proposed based on the ADC model and the joint operation system structure.Firstly,analysis of the joint operation system structure and operation process is conducted to build the GERT network,where equipment subsystems are nodes and activities are directed arches.Then the mission effectiveness of equipment subsystems is calculated by the ADC model.The probability transfer parameters are modified by the mission effectiveness of equipment subsystems based on the Bayesian theorem,with the ADC-GERT network parameter estimation model constructed.Finally,a case study is used to validate the efficiency and dynamic of the ADC-GERT network parameter estimation model.
文摘An adaptive chaotic gradient descending optimization algorithm for single objective optimization was presented. A local minimum judged by two rules was obtained by an improved mutative-step gradient descending method. A new optimal minimum was obtained to replace the local minimum by mutative-scale chaotic search algorithm whose scales are magnified gradually from a small scale in order to escape local minima. The global optimal value was attained by repeatedly iterating. At last, a BP (back-propagation) neural network model for forecasting slag output in matte converting was established. The algorithm was used to train the weights of the BP neural network model. The simulation results with a training data set of 400 samples show that the training process can be finished within 300 steps to obtain the global optimal value, and escape local minima effectively. An optimization system for operation parameters, which includes the forecasting model, is achieved, in which the output of converter increases by 6.0%, and the amount of the treated cool materials rises by 7.8% in the matte converting process.
文摘With the development of current electronic technology, numerous high-speed data acquisition systems provide a variety of potential benefits. This article describes a high-speed data acquisition system which consists of ECL logic and TTL logic devices, samples and stores data with a 1 GHz clock. This system is accomplished easily and works stably. A performance test of this system has been undertaken and the results show that the effective number of bits （ENOB） is more than 6.5 bits.
基金supported in part by the Joint Funds of the National Natural Science Foundation of China(G02)(Grant No.U1834203)in part by of the Science and Technology Department of Sichuan Province(S01)(Grant No.2020JDTD0009)。
文摘In the modern wireless communication system,the manipulation for polarization of electromagnetic wave plays a important role in improving the capacity and reliability of communication.In this paper,a multifunctional polarization converter(MFPC)based on the multilayer reconfigurable metasurface is proposed,which can assist the source antenna to transmit and receive multiple polarization signals.The MFPC consists of a grating which can filter out the undesired polarization and four layers of metasurfaces incorporated with PIN diodes.The functions of the MFPC include LTC and LTL polarization conversions,co-polarization transmission and reflection for arbitrary polarization.By changing the states of PIN diodes,the functions of MFPC can be dynamically switched.Loaded on the aperture of source antenna,the proposed MFPC can serve as a transmissive array with multiple polarization channels,and can also provide EM protection for source antenna by reflecting the incoming interference waves.Cascading of the metasurfaces produces Fabry-Perot resonance in the MFPC,and it contributes to the realization of LTC and LTL polarization conversions.To verify the performance of the proposed MFPC,the prototype is fabricated and tested.The measured results show that the fractional bandwidths of four functions are all higher than 31.9% with transmission or reflection coefficients higher than-2 d B.The frequency band of each function is mainly concentrated in S-band.The measured data are in agreement with the simulated results.
基金supported in part by NIH HL098472NSF CBET0846429
文摘Introduction Cells can sense and respond to the mechanical microenvironment by converting forces into biochemical signals inside the cells,i.e.mechanotransduction<sup>[1-3]</sup>.Focal adhesions are the major sites of interaction between a cell and its extracellular matrix（ECM）microenvironment,thus outside mechanical signals can be sensed at focal adhesions through transmembrane receptor integrins.In particular,it has been shown that matrix elasticity can control the cell fate<sup>[4]</sup>by modulating the interactions between ECM proteins and their receptor integrins<sup>[5,6]</sup>.For example,different rigidity of polyacrylamide（PA）gels can lead to different density of ECM ancho-
文摘Optimal activation of T cells requires at least 2signals. Signal one is generated by interactionsbetween T cell receptor and antigenic peptide-majorhistocompatibility complex on antigen-presentingcells. Signal two is delivered by co-stimulatory ligandson antigen-presenting cells to their receptors on
