A robust digital predistortion(DPD)technique utilizing negative feedback iteration is introduced for linearizing power amplifiers(PAs)in long term evolution(LTE)/5G systems.Different from the conventional direct learn...A robust digital predistortion(DPD)technique utilizing negative feedback iteration is introduced for linearizing power amplifiers(PAs)in long term evolution(LTE)/5G systems.Different from the conventional direct learning and indirect learning structure,the proposed DPD suggests a two-step method to identify the predistortion.Firstly,a negative feedback based iteration is used to estimate the optimal DPD signal.Then the corresponding DPD parameters are extracted by forward modeling with the input signal and optimal DPD signal.The iteration can be applied to both single-band and dual-band PAs,which will achieve superior linear performance than the conventional direct learning DPD while having a relatively low computational complexity.The measurement is carried out on a broadband Doherty PA(DPA)with a 200 MHz bandwidth LTE signal at 2.1 GHz,and on a 5G DPA with two 10 MHz LTE signals at 3.4/3.6 GHz for validation in dual-band scenarios.展开更多
Waveform control method was commonly adopted to reduce the spatter of CO2 arc welding and improve the weld formation. It certainly would reduce the self-regulation ability of arc due to the adoption of segmented const...Waveform control method was commonly adopted to reduce the spatter of CO2 arc welding and improve the weld formation. It certainly would reduce the self-regulation ability of arc due to the adoption of segmented constant current control which especially led to arc＂ blowout with the abrupt change oat＂ arc＂ length or downward welding. Therefore alterative wire-feed system based on arc voltage negative feedback was put forward to improve the .stability of arc＂ length in this paper. Double closed-loop and double fuzzy P1 regulation were adopted in this system. Fuzzy control of induced voltage was adopted in the inner-loop which improved the stability and fast response of wire-feed system. Fuzz）＂ control of arc＂ voltage negative feedback was used in the outer-loop whose output .served as the input of negative feedback regulation of inner-loop induced voltage. This method could remain arc＂ length and weld penetration unchan, ged on the basils of reducing spatter and improving formation and it was proved by downward welding tests.展开更多
One of the ingredients of the anthropogenic global warming hypothesis is the existence of large positive feedback in the climate system. An example is polar ice that, once melted, turns into blacker water that will in...One of the ingredients of the anthropogenic global warming hypothesis is the existence of large positive feedback in the climate system. An example is polar ice that, once melted, turns into blacker water that will increase radiation absorption and this rein-forces the melting. This causes a run-away scenario with a point of no return. Here it is shown that the polar ice can also have negative feedback aspects, where a melting of polar ice will cause it to reappear.展开更多
Negative feedback serves as a means of correcting and rectifying students’utterances.While content feedback is commonly used in extensive reading course,indirect feedback dominates in written assignments,providing st...Negative feedback serves as a means of correcting and rectifying students’utterances.While content feedback is commonly used in extensive reading course,indirect feedback dominates in written assignments,providing students with opportunities for second thoughts and self-correction.For oral limited-response and open-ended questions,recasts are predominantly used to give students more time to reflect and reduce teacher talk,thereby mitigating anxiety and enhancing learning motivation.展开更多
In order to solve the problem of reliability modeling and the analysis of complex systems with multiple closed-loop feedbacks,a new reliability analysis method for repairable systems with multiple closed-loop feedback...In order to solve the problem of reliability modeling and the analysis of complex systems with multiple closed-loop feedbacks,a new reliability analysis method for repairable systems with multiple closed-loop feedbacks is proposed based on the goal-oriented(GO)methodology.Firstly,the basic theories and advantages of GO method are introduced.Secondly,a type-24B multiple closed-loop feedback structure operator is proposed through GO method with its operation formula given,which expands the types of GO method operators and the application scope of their reliability analysis.Finally,taking a certain type of diesel engine fuel supply system an example,the quantitative and qualitative analysis is carried out through GO method,Monte Carlo simulation as well as FTA respectively.The availability results verify the availability of the proposed type-24B operator in the reliability analysis of multiple closed-loop feedback systems.The qualitative analysis results indicate the accuracy and usability of the GO method as a qualitative analysis method.展开更多
Goal oriented( GO) methodology is a kind of success oriented system reliability analysis method and has been used widely.The repairable system with dual input closed-loop feedback link( DICLFL) considering shutdown co...Goal oriented( GO) methodology is a kind of success oriented system reliability analysis method and has been used widely.The repairable system with dual input closed-loop feedback link( DICLFL) considering shutdown correlation didn't make reliability analysis accurately based on existing GO methodology. So, a reliability analysis method used to deal with DICLFL considering shutdown correlation is provided based on GO methodology.Firstly, a new operator, which is used to describe DICLFL considering shutdown correlation,whose number is 1,is created and named as Type 9C operator. And then,the formulas of type 9C operator are derived based on Markov process theory. Finally,the new method presented in this paper is adopted to conduct the reliability analysis of an electro-hydraulic servo speed control system. The analysis result is compared with those of Monte Carlo simulation and fault tree analysis( FTA). The comparison results show that this new reliability analysis method based on GO methodology is feasible and meaningful for reliability analysis of repairable systems with DICLFL considering shutdown correlation.Meantime,it will be useful for more other applications.展开更多
This paper proposes a separated trajectory tracking controller for fishing ships at sea state level 6 to solve the trajectory tracking problem of a fishing ship in a 6-level sea state,and to adapt to different working...This paper proposes a separated trajectory tracking controller for fishing ships at sea state level 6 to solve the trajectory tracking problem of a fishing ship in a 6-level sea state,and to adapt to different working environments and safety requirements.The nonlinear feedback method is used to improve the closed-loop gain shaping algorithm.By introducing the sine function,the problem of excessive control energy of the system can be effectively solved.Moreover,an integral separation design is used to solve the influence of the integral term in conventional PID controllers on the transient performance of the system.In this paper,a common 32.98 m large fiberglass reinforced plastic(FRP)trawler is adopted for simulation research at the winds scale of Beaufort No.7.The results show that the track error is smaller than 3.5 m.The method is safe,feasible,concise and effective and has popularization value in the direction of fishing ship trajectory tracking control.This method can be used to improve the level of informatization and intelligence of fishing ships.展开更多
Conspecific negative density dependencies(CNDDs)foster biodiversity through reducing the chances of competitive exclusion in plant communities and have therefore fascinated ecologists.A major driver of CNDDs is plant-...Conspecific negative density dependencies(CNDDs)foster biodiversity through reducing the chances of competitive exclusion in plant communities and have therefore fascinated ecologists.A major driver of CNDDs is plant-soil feedback,and a lot of the literature assumes that the triggers of CNDDs concur with those for plant-soil feedback.Here,we suggest that a core assumption of a lot of the literature on CNDDs,that CNDDs are stronger in AM-associated than ECM-associated trees,is not quite as well supported as widely claimed.We think that dismissing this very important consideration prevents us from identifying a major gap in the literature on CNDDs.The vast majority of the literature on mycorrhiza-induced CNDDs originates from temperate systems,but the findings are extrapolated across divergent ecosystems.We then develop the argument that likely propagule limitations for arbuscular mycorrhizal trees in temperate forests might be inducing stronger CNDDs than they do at propagule sufficiency,which arbuscular mycorrhizal trees usually experience in other systems.We are thus contributing a new hypothesis in the field of mycorrhizal ecology with the potential to unify observations across scales and biomes.展开更多
As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up wi...As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed.By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence,the dimensional accuracy is improved.This work focuses on the development of this steering model.Since the method used does not increase cycle time,it is attractive for high-volume industrial applications.More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology.The results show that by activating the automated closed-loop feedback system,the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending.Since the steering model permits the direct use of additional process data,such as instant wall thickness and cross sectional distortions,it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.展开更多
Ultra-compact serpentine inlet faces serve inlet-engine compatibility issues due to flow distortion.To ensure inlet-engine compatibility over a wide range of Mach number,novel active flow control techniques with the a...Ultra-compact serpentine inlet faces serve inlet-engine compatibility issues due to flow distortion.To ensure inlet-engine compatibility over a wide range of Mach number,novel active flow control techniques with the ability of being opened or adjusted as needed draw many attentions in recent years.In this paper,a feedback control system was developed based on the method of microjet blowing.The proposed system includes a pressure adjusting valve to adjust the control effort,a dynamic pressure sensor to sense the inlet distortion intensity,a signal processing instrument to calculate the Root-Mean-Squared(RMS)pressure,and a controller to implement feedback control.To achieve high quality closed-loop controls at dynamic conditions,a novel nondimensional feedback method was developed.The advantage of this nondimensional method was validated at both off-design and arbitrarily changing Mach number conditions.With a sectional PI control law,the RMS control error reduced more than 56%at arbitrary changing conditions.Works in this paper also showed that the dynamics of this nondimensional system can be simplified as a stable second-order overdamped system.展开更多
The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD sy...The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.展开更多
In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of...In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of optimal adaptation transmission mode. However, in practice, there is an undesirable but non-negligible effect, namely the asymmetric interference, that makes the assumptions no longer valid. In this paper, a simple closed-loop feedback method of compensating interference asymmetry in TDD multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is proposed. The system makes the estimated interference at transmit-side be able to track the instantaneous receive-side interference dynamically. The proposed method maintains constant frame error rate (FER) by adopting adaptive modulation coding (AMC) and power loading. The final simulations have verified the effectiveness of the new method.展开更多
Over the past three decades, neurophysiologists studying the neural circuitry responsible for control of skeletal muscles have developed several different general theories of sensorimotor control. These have usually i...Over the past three decades, neurophysiologists studying the neural circuitry responsible for control of skeletal muscles have developed several different general theories of sensorimotor control. These have usually invoked one or more of the sources of proprioceptive signals (e.g. muscle spindle and Golgi tendon organ afferents) in positive or negative feed-back loops to the homonymous alpha motoneurones. In this paper we consider to analyze the role of posi-tive feedback in combination of negative feedback due to important role of them in stabilizing the neu-romuscular system.展开更多
The design and fabrication of an ultra-broadband power amplifier based on a GaN HEMT, which operates in the frequency range from 3 to 8 GHz, is presented in this paper. A TGF2023-02 GaN HEMT chip from Tri Quint is ado...The design and fabrication of an ultra-broadband power amplifier based on a GaN HEMT, which operates in the frequency range from 3 to 8 GHz, is presented in this paper. A TGF2023-02 GaN HEMT chip from Tri Quint is adopted and modeled. A novel negative feedback structure is applied in the circuit. The measured results show that the amplifier module has a wide range frequency response that is almost consistent with those of simulation at frequencies from 3 to 6.5 GHz. The measured power gain is greater than 7 dB between 3 and 6.5 GHz.The saturated output power is 38.5 dBm under DC bias of Vds =D28 V, Vgs D =-3：5 V at the frequency of 5.5 GHz.展开更多
The reasons for inducing quadrature error and offset error are analyzed and the expressions of quadrature error and offset error are induced. The open-loop system analysis indicates that, in order to avoid the appeara...The reasons for inducing quadrature error and offset error are analyzed and the expressions of quadrature error and offset error are induced. The open-loop system analysis indicates that, in order to avoid the appearance of harmonic peaks, the frequency difference δf between drive mode and sense mode must be less than 1/（2Qy）. In order to eliminate the effects of the quadrature error and the offset error, as well as the inherent non- linearity in the capacitance-type sensors, a closed-loop feedback control circuit with quadrature correction is designed. The experimental results indicate that the quadrature error and offset error are corrected. By comparing with open-loop detection, the closed-loop feedback control circuit with quadrature correction decreases the non-linearity of the scale factor from 16. 02% to 0. 35 %, widens the maximum rate capability from ± 270 （°）/s to ± 370 （°）/s and increases the stability of zero bias from 155. 2 （°）/h to 60. 6 （°）/h.展开更多
A fully differential R-MOSFET-C fourth-order Bessel active lowpass filter employing fully differential operational amplifier,passive resistors,and current-steering MOS transistors as a variable resistor is proposed.T...A fully differential R-MOSFET-C fourth-order Bessel active lowpass filter employing fully differential operational amplifier,passive resistors,and current-steering MOS transistors as a variable resistor is proposed.This proposed implementation relies on the tunability of current-steering MOS transistors operating in the triode region counteracting the concert deviation of resistor in the integrated circuit manufacturing technology in orde r that the group delay of Bessel active filter could be designed accurately.The amplifier is not only with voltage common-mode negative feedback,but also with current common-mode negative feedback,which will benefit for the stability of its D C operating point.0.75μs group delay fourth-order Bessel lowpass filter,whic h is synthesized according to passive doubly terminated RLC prototype lowpass filter,demonstrates better than -65dB THD using 100kHz,2.5V pp signal in Taiwan UMC 2P2M(2-poly,2-metal)5.0V,0.5μm CMOS technology.展开更多
Transistors are nonlinear devices, which can produce nonlinear distortion in amplifier while amplifying signals. For weak nonlinear distortion, the expressions of total harmonic distortion (THD), the second order in...Transistors are nonlinear devices, which can produce nonlinear distortion in amplifier while amplifying signals. For weak nonlinear distortion, the expressions of total harmonic distortion (THD), the second order intermodulation distortion(IM2 ), the third order intermodulation distortion(IM 3) and intercept point(IP 3) are deduced. With the aid of software Multisim, we simulate transistor common emitter amplifier, transistor common emitter amplifier with resistor in emitter, differential amplifier and differential amplifier with resistor between emitters. The simulational results and theoretical analyses are almost the same.展开更多
In this study, the temporal structure of the variation of North Atlantic Oscillation （NAO） and its impact on regional climate variability are analyzed using various datasets. The results show that blocking formation...In this study, the temporal structure of the variation of North Atlantic Oscillation （NAO） and its impact on regional climate variability are analyzed using various datasets. The results show that blocking formations in the Atlantic region are sensitive to the phase of the NAO. Sixty-seven percent more winter blocking days are observed during the negative phase compared to the positive phase of the NAO. The average length of blocking during the negative phase is about 11 days, which is nearly twice as long as the 6-day length observed during the positive phase of the NAO. The NAO-related differences in blocking frequency and persistence are associated with changes in the distribution of the surface air temperature anomaly, which, to a large extent, is determined by the phase of the NAO. The distribution of regional cloud amount is also sensitive to the phase of the NAO. For the negative phase, the cloud amounts are significant, positive anomalies in the convective zone in the Tropics and much less cloudiness in the mid latitudes. But for the positive phase of the NAO, the cloud amount is much higher in the mid-latitude storm track region. In the whole Atlantic region, the cloud amount shows a decrease with the increase of surface air temperature. These results suggest that there may be a negative feedback between the cloud amount and the surface air t.emperature in the Atlantic region.展开更多
A model-flee compound controller design method is proposed to achieve the wide frequency bandwidth requirement of flight simulators. The method based on quantitative feedback theory, acquires system uncertainty under ...A model-flee compound controller design method is proposed to achieve the wide frequency bandwidth requirement of flight simulators. The method based on quantitative feedback theory, acquires system uncertainty under different working conditions through closed-loop identification with power spectrum estimation. Then in controller designing, it makes a trade, off between the strict requirements for magnitude-frequency characteristics and those for phase-frequency characteristics of flight simulators, by converting the indices of magnitude-frequency characteristics of flight simulators into quantitative feedback theory-based tracking specification bounds and using feedforward controller to attain the required phase-flequency characteristics. Simulation and experimental results indicate that, when used to design inner flame controller of flight simulator, the proposed method can fulfill the requirements for wide frequency bandwidth indices. Compared with other controller design methods, it has the property of model-free and transparency.展开更多
基金National Key R&D Program of China under Grant No.2018YFB1801603 and No.2017YFF0206201National Sci⁃ence and Technology Major Project under Grant 2017ZX03001024,NSFC under Grant No.61801259 and Beijing National Research Center for Infor⁃mation Science and Technology(BNRist).
文摘A robust digital predistortion(DPD)technique utilizing negative feedback iteration is introduced for linearizing power amplifiers(PAs)in long term evolution(LTE)/5G systems.Different from the conventional direct learning and indirect learning structure,the proposed DPD suggests a two-step method to identify the predistortion.Firstly,a negative feedback based iteration is used to estimate the optimal DPD signal.Then the corresponding DPD parameters are extracted by forward modeling with the input signal and optimal DPD signal.The iteration can be applied to both single-band and dual-band PAs,which will achieve superior linear performance than the conventional direct learning DPD while having a relatively low computational complexity.The measurement is carried out on a broadband Doherty PA(DPA)with a 200 MHz bandwidth LTE signal at 2.1 GHz,and on a 5G DPA with two 10 MHz LTE signals at 3.4/3.6 GHz for validation in dual-band scenarios.
文摘Waveform control method was commonly adopted to reduce the spatter of CO2 arc welding and improve the weld formation. It certainly would reduce the self-regulation ability of arc due to the adoption of segmented constant current control which especially led to arc＂ blowout with the abrupt change oat＂ arc＂ length or downward welding. Therefore alterative wire-feed system based on arc voltage negative feedback was put forward to improve the .stability of arc＂ length in this paper. Double closed-loop and double fuzzy P1 regulation were adopted in this system. Fuzzy control of induced voltage was adopted in the inner-loop which improved the stability and fast response of wire-feed system. Fuzz）＂ control of arc＂ voltage negative feedback was used in the outer-loop whose output .served as the input of negative feedback regulation of inner-loop induced voltage. This method could remain arc＂ length and weld penetration unchan, ged on the basils of reducing spatter and improving formation and it was proved by downward welding tests.
文摘One of the ingredients of the anthropogenic global warming hypothesis is the existence of large positive feedback in the climate system. An example is polar ice that, once melted, turns into blacker water that will increase radiation absorption and this rein-forces the melting. This causes a run-away scenario with a point of no return. Here it is shown that the polar ice can also have negative feedback aspects, where a melting of polar ice will cause it to reappear.
文摘Negative feedback serves as a means of correcting and rectifying students’utterances.While content feedback is commonly used in extensive reading course,indirect feedback dominates in written assignments,providing students with opportunities for second thoughts and self-correction.For oral limited-response and open-ended questions,recasts are predominantly used to give students more time to reflect and reduce teacher talk,thereby mitigating anxiety and enhancing learning motivation.
基金supported by the Special Support Project of SASTIND and Technologyof SASTIND(No.JSZL2019XXXB001)。
文摘In order to solve the problem of reliability modeling and the analysis of complex systems with multiple closed-loop feedbacks,a new reliability analysis method for repairable systems with multiple closed-loop feedbacks is proposed based on the goal-oriented(GO)methodology.Firstly,the basic theories and advantages of GO method are introduced.Secondly,a type-24B multiple closed-loop feedback structure operator is proposed through GO method with its operation formula given,which expands the types of GO method operators and the application scope of their reliability analysis.Finally,taking a certain type of diesel engine fuel supply system an example,the quantitative and qualitative analysis is carried out through GO method,Monte Carlo simulation as well as FTA respectively.The availability results verify the availability of the proposed type-24B operator in the reliability analysis of multiple closed-loop feedback systems.The qualitative analysis results indicate the accuracy and usability of the GO method as a qualitative analysis method.
基金Technical Basis Projects of China's MIIT(Nos.ZQ092012B003,2012090003)
文摘Goal oriented( GO) methodology is a kind of success oriented system reliability analysis method and has been used widely.The repairable system with dual input closed-loop feedback link( DICLFL) considering shutdown correlation didn't make reliability analysis accurately based on existing GO methodology. So, a reliability analysis method used to deal with DICLFL considering shutdown correlation is provided based on GO methodology.Firstly, a new operator, which is used to describe DICLFL considering shutdown correlation,whose number is 1,is created and named as Type 9C operator. And then,the formulas of type 9C operator are derived based on Markov process theory. Finally,the new method presented in this paper is adopted to conduct the reliability analysis of an electro-hydraulic servo speed control system. The analysis result is compared with those of Monte Carlo simulation and fault tree analysis( FTA). The comparison results show that this new reliability analysis method based on GO methodology is feasible and meaningful for reliability analysis of repairable systems with DICLFL considering shutdown correlation.Meantime,it will be useful for more other applications.
基金supported by Liaoning Provincial Department of Education 2023 Basic Research Projects for Universities and Colleges(Grant No.JYTQN2023131)Liaoning Provincial Science and Technology Program:Cooperative Control and Recognition of Unmanned Vessels for Fishing Vessel Operation Scenarios(Grant No.600024003)Liaoning Provincial Department of Education Scientific Research Funding Project(Grant No.LJKZ0726).
文摘This paper proposes a separated trajectory tracking controller for fishing ships at sea state level 6 to solve the trajectory tracking problem of a fishing ship in a 6-level sea state,and to adapt to different working environments and safety requirements.The nonlinear feedback method is used to improve the closed-loop gain shaping algorithm.By introducing the sine function,the problem of excessive control energy of the system can be effectively solved.Moreover,an integral separation design is used to solve the influence of the integral term in conventional PID controllers on the transient performance of the system.In this paper,a common 32.98 m large fiberglass reinforced plastic(FRP)trawler is adopted for simulation research at the winds scale of Beaufort No.7.The results show that the track error is smaller than 3.5 m.The method is safe,feasible,concise and effective and has popularization value in the direction of fishing ship trajectory tracking control.This method can be used to improve the level of informatization and intelligence of fishing ships.
基金the National Natural Science Foundation of China(Grant:“MycoDisp:Implications of connectance of mycorrhizal habitats for the functioning of ecosystems”,with the grant agreement number C0311-32371721).
文摘Conspecific negative density dependencies(CNDDs)foster biodiversity through reducing the chances of competitive exclusion in plant communities and have therefore fascinated ecologists.A major driver of CNDDs is plant-soil feedback,and a lot of the literature assumes that the triggers of CNDDs concur with those for plant-soil feedback.Here,we suggest that a core assumption of a lot of the literature on CNDDs,that CNDDs are stronger in AM-associated than ECM-associated trees,is not quite as well supported as widely claimed.We think that dismissing this very important consideration prevents us from identifying a major gap in the literature on CNDDs.The vast majority of the literature on mycorrhiza-induced CNDDs originates from temperate systems,but the findings are extrapolated across divergent ecosystems.We then develop the argument that likely propagule limitations for arbuscular mycorrhizal trees in temperate forests might be inducing stronger CNDDs than they do at propagule sufficiency,which arbuscular mycorrhizal trees usually experience in other systems.We are thus contributing a new hypothesis in the field of mycorrhizal ecology with the potential to unify observations across scales and biomes.
文摘As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed.By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence,the dimensional accuracy is improved.This work focuses on the development of this steering model.Since the method used does not increase cycle time,it is attractive for high-volume industrial applications.More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology.The results show that by activating the automated closed-loop feedback system,the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending.Since the steering model permits the direct use of additional process data,such as instant wall thickness and cross sectional distortions,it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.
基金supported by the National Natural Science Foundation of China (No.11602291)。
文摘Ultra-compact serpentine inlet faces serve inlet-engine compatibility issues due to flow distortion.To ensure inlet-engine compatibility over a wide range of Mach number,novel active flow control techniques with the ability of being opened or adjusted as needed draw many attentions in recent years.In this paper,a feedback control system was developed based on the method of microjet blowing.The proposed system includes a pressure adjusting valve to adjust the control effort,a dynamic pressure sensor to sense the inlet distortion intensity,a signal processing instrument to calculate the Root-Mean-Squared(RMS)pressure,and a controller to implement feedback control.To achieve high quality closed-loop controls at dynamic conditions,a novel nondimensional feedback method was developed.The advantage of this nondimensional method was validated at both off-design and arbitrarily changing Mach number conditions.With a sectional PI control law,the RMS control error reduced more than 56%at arbitrary changing conditions.Works in this paper also showed that the dynamics of this nondimensional system can be simplified as a stable second-order overdamped system.
基金Project supported by the National Natural Science Foundation of China （Grant No.60472103）, the Shanghai Excellent Academic Leader Project （Grant No.05XP14027）, and the Shanghai Leading Academic Discipline Project （Grant No.T0102）.
文摘The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.
基金the National Natural Science Foundation of China (No. 60572130)the Open Research Fund of National Mobile Communications Research Laboratory,Southeast University+3 种基金the Research Fund of Qing-Lan Engineering, Jiangsu Provincethe Key Project of Natural Science Research Program of Universities, Jiangsu Province (No. 08KJD510001)the Doctorial Fundation of Ministry of Educationthe National Basic Research Program (973) of China (No. 2007CB310607)
文摘In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of optimal adaptation transmission mode. However, in practice, there is an undesirable but non-negligible effect, namely the asymmetric interference, that makes the assumptions no longer valid. In this paper, a simple closed-loop feedback method of compensating interference asymmetry in TDD multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is proposed. The system makes the estimated interference at transmit-side be able to track the instantaneous receive-side interference dynamically. The proposed method maintains constant frame error rate (FER) by adopting adaptive modulation coding (AMC) and power loading. The final simulations have verified the effectiveness of the new method.
文摘Over the past three decades, neurophysiologists studying the neural circuitry responsible for control of skeletal muscles have developed several different general theories of sensorimotor control. These have usually invoked one or more of the sources of proprioceptive signals (e.g. muscle spindle and Golgi tendon organ afferents) in positive or negative feed-back loops to the homonymous alpha motoneurones. In this paper we consider to analyze the role of posi-tive feedback in combination of negative feedback due to important role of them in stabilizing the neu-romuscular system.
基金supported by the Natural Science Foundation of Zhejiang Province(No.Z1110937)
文摘The design and fabrication of an ultra-broadband power amplifier based on a GaN HEMT, which operates in the frequency range from 3 to 8 GHz, is presented in this paper. A TGF2023-02 GaN HEMT chip from Tri Quint is adopted and modeled. A novel negative feedback structure is applied in the circuit. The measured results show that the amplifier module has a wide range frequency response that is almost consistent with those of simulation at frequencies from 3 to 6.5 GHz. The measured power gain is greater than 7 dB between 3 and 6.5 GHz.The saturated output power is 38.5 dBm under DC bias of Vds =D28 V, Vgs D =-3：5 V at the frequency of 5.5 GHz.
文摘The reasons for inducing quadrature error and offset error are analyzed and the expressions of quadrature error and offset error are induced. The open-loop system analysis indicates that, in order to avoid the appearance of harmonic peaks, the frequency difference δf between drive mode and sense mode must be less than 1/（2Qy）. In order to eliminate the effects of the quadrature error and the offset error, as well as the inherent non- linearity in the capacitance-type sensors, a closed-loop feedback control circuit with quadrature correction is designed. The experimental results indicate that the quadrature error and offset error are corrected. By comparing with open-loop detection, the closed-loop feedback control circuit with quadrature correction decreases the non-linearity of the scale factor from 16. 02% to 0. 35 %, widens the maximum rate capability from ± 270 （°）/s to ± 370 （°）/s and increases the stability of zero bias from 155. 2 （°）/h to 60. 6 （°）/h.
文摘A fully differential R-MOSFET-C fourth-order Bessel active lowpass filter employing fully differential operational amplifier,passive resistors,and current-steering MOS transistors as a variable resistor is proposed.This proposed implementation relies on the tunability of current-steering MOS transistors operating in the triode region counteracting the concert deviation of resistor in the integrated circuit manufacturing technology in orde r that the group delay of Bessel active filter could be designed accurately.The amplifier is not only with voltage common-mode negative feedback,but also with current common-mode negative feedback,which will benefit for the stability of its D C operating point.0.75μs group delay fourth-order Bessel lowpass filter,whic h is synthesized according to passive doubly terminated RLC prototype lowpass filter,demonstrates better than -65dB THD using 100kHz,2.5V pp signal in Taiwan UMC 2P2M(2-poly,2-metal)5.0V,0.5μm CMOS technology.
文摘Transistors are nonlinear devices, which can produce nonlinear distortion in amplifier while amplifying signals. For weak nonlinear distortion, the expressions of total harmonic distortion (THD), the second order intermodulation distortion(IM2 ), the third order intermodulation distortion(IM 3) and intercept point(IP 3) are deduced. With the aid of software Multisim, we simulate transistor common emitter amplifier, transistor common emitter amplifier with resistor in emitter, differential amplifier and differential amplifier with resistor between emitters. The simulational results and theoretical analyses are almost the same.
文摘In this study, the temporal structure of the variation of North Atlantic Oscillation （NAO） and its impact on regional climate variability are analyzed using various datasets. The results show that blocking formations in the Atlantic region are sensitive to the phase of the NAO. Sixty-seven percent more winter blocking days are observed during the negative phase compared to the positive phase of the NAO. The average length of blocking during the negative phase is about 11 days, which is nearly twice as long as the 6-day length observed during the positive phase of the NAO. The NAO-related differences in blocking frequency and persistence are associated with changes in the distribution of the surface air temperature anomaly, which, to a large extent, is determined by the phase of the NAO. The distribution of regional cloud amount is also sensitive to the phase of the NAO. For the negative phase, the cloud amounts are significant, positive anomalies in the convective zone in the Tropics and much less cloudiness in the mid latitudes. But for the positive phase of the NAO, the cloud amount is much higher in the mid-latitude storm track region. In the whole Atlantic region, the cloud amount shows a decrease with the increase of surface air temperature. These results suggest that there may be a negative feedback between the cloud amount and the surface air t.emperature in the Atlantic region.
文摘A model-flee compound controller design method is proposed to achieve the wide frequency bandwidth requirement of flight simulators. The method based on quantitative feedback theory, acquires system uncertainty under different working conditions through closed-loop identification with power spectrum estimation. Then in controller designing, it makes a trade, off between the strict requirements for magnitude-frequency characteristics and those for phase-frequency characteristics of flight simulators, by converting the indices of magnitude-frequency characteristics of flight simulators into quantitative feedback theory-based tracking specification bounds and using feedforward controller to attain the required phase-flequency characteristics. Simulation and experimental results indicate that, when used to design inner flame controller of flight simulator, the proposed method can fulfill the requirements for wide frequency bandwidth indices. Compared with other controller design methods, it has the property of model-free and transparency.
