With the popularity of indoor wireless network,device-free indoor localization has attracted more and more attention.Unlike device-based localization where the target is required to carry an active transmitter,their f...With the popularity of indoor wireless network,device-free indoor localization has attracted more and more attention.Unlike device-based localization where the target is required to carry an active transmitter,their frequent signal scanning consumes a large amount of energy,which is inconvenient for devices with limited energy.In this work,we propose the MFPL,device-free localization(DFL)system based on WiFi distance measurement.First,we combine multi-subcarrier characteristic of Channel State Information(CSI)with classical Fresnel reflection model to get the linear relationship between the change of the length of reflection path and the subcarrier phase difference.Then we calculate the Fresnel phase difference between subcarrier pairs with different spacing from CSI amplitude time series.Finally,we get the change of the length of the reflection path caused by target moving to achieve distance measurement and localization.Using a combination of subcarriers with different spacing to achieve distance measurement effectively broadens the maximum unambiguous distance of the system.To solve the complex non-linear problem of the intersection of two elliptic equations,we introduce Newton's method to transform the non-linear problem into a linear one.The effectiveness of our approach is verified using commodity WiFi infrastructures.The experimental results show our method achieves a median error of 0.87 m in actual indoor environment.展开更多
When a modular multilevel converter based high voltage direct current(MMC-HVDC)system operates under grid faults,there will be a phase difference between the grid voltage and the converter output.It can be caused by g...When a modular multilevel converter based high voltage direct current(MMC-HVDC)system operates under grid faults,there will be a phase difference between the grid voltage and the converter output.It can be caused by grid voltage phase shifting and the integration effect of the phase-locked loop(PLL)in the converter.The system may exhibit an undesirable transient process with expanded current which is harmful for the converter devices.In this paper,a transient current estimation method is proposed for the scenario of converter-grid phase difference caused by the frequency shifting of the grid side.A piecewise phase calculation model is established to determine the transient phase difference of the system.Then,according to the maximum phase difference calculated by the model,the system stability is assessed and the maximum value of system transient current can be estimated after comparing the maximum phase difference with the critical phase difference and π,Finally,the current estimation results are verified by detailed circuit simulations of a 21-level MMC-HVDC system built in PSCAD.展开更多
By considering higher order approximation to the interaural phase difference, a more general localization equation for stereo sound image with interchannel phase difference is derived. At very low frequency or low int...By considering higher order approximation to the interaural phase difference, a more general localization equation for stereo sound image with interchannel phase difference is derived. At very low frequency or low interchannel phase difference, the equation can be simplified to Makita theory. In general, image position is obviously affected by frequency.It is shown that image position varying with freqllency is the main reason for image width broadening in stereo reproduction with interchannel phase difference. And an extra interaural sound level difference caused by interchannel phase difference is the main reason for image naturalness degrading. In practice, it is necessary to reduce the interchannel phase difference,at least, to less than 60°.展开更多
The microstructure and the stability of Fe73.5Cu1Nb3Si13.5B9 alloy at different stages of phase transformation were investigated through the observation of X-ray difraction and transmission electron microscopy and the...The microstructure and the stability of Fe73.5Cu1Nb3Si13.5B9 alloy at different stages of phase transformation were investigated through the observation of X-ray difraction and transmission electron microscopy and the measurement of magnetic aftereffect （MAE）. It was found that the dependence of the volume fraction of amorphous phase and the MAE in the samples annealed from 450 to 700℃ on the annealing temperature is similar.展开更多
Plasma electron density is one of the most fundamental parameters in the study of tokamak plasma physics.The method of plasma electron density measuring and processing on the Joint Texas Experimental Tokamak(J-TEXT) w...Plasma electron density is one of the most fundamental parameters in the study of tokamak plasma physics.The method of plasma electron density measuring and processing on the Joint Texas Experimental Tokamak(J-TEXT) was presented in this paper.The principle of the plasma electron density measuring by hydrogen cyanide(HCN) laser interferometer was introduced.Room temperature triglycine sulface(TGS) detector was used to obtain the beat signal of HCN,and phase difference was measured by high-speed acquisition card DAQ2010.Based on the signal characteristics,a specific HCN processing algorithm was designed to eliminate the baseline offset accurately and process overturns of HCN signals effectively.As a result,plasma electron density with high accuracy and low noise has been obtained during the J-TEXT tokamak experiment.展开更多
The inhomogenous ocean waveguide, which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate, is one of the causes that make the array gain deviate from its ideal value. The relation...The inhomogenous ocean waveguide, which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate, is one of the causes that make the array gain deviate from its ideal value. The relationship between the array gain and the fluctuant acoustic channel is studied theoretically. The analytical expression of the array gain is derived via an acoustic channel transfer function on the assumption that the ambient noise field is isotropic. The expression is expanded via the Euler formula to give an insight into the effect of the fluctuant acoustic channel on the array gain. The result demonstrates that the amplitude fluctuation of the acoustic channel transfer functions has a slight effect on the array gain; however, the uniformity of the phase difference between the weighting coefficient and the channel transfer function on all the hydrophones in the array is a major factor that leads the array gain to further deviate from its ideal value. The numerical verification is conducted in the downslope waveguide, in which the gain of a horizontal uniform linear array(HLA) with a wide-aperture operating in the continental slope area is considered. Numerical result is consistent with the theoretical analysis.展开更多
With the target at simplicity like facilitating the mechanical system,the quadruped robots usually have limited degrees of freedom per leg.Addressing the robot whose legs have only two degrees of freedom,this paper ex...With the target at simplicity like facilitating the mechanical system,the quadruped robots usually have limited degrees of freedom per leg.Addressing the robot whose legs have only two degrees of freedom,this paper explores several turning strategies including altering the median value,changing the phase difference,and modifying the amplitude.The insights of the proposed methods are that we break down the symmetries which exist during the process of the robot locomotion and rebuild them.Since we probe into the turning feasibility from the points of the median value,phase difference and amplitude in the sine functions,these turning methods are feature of universality.In order to evaluate these methods,this paper presents a new way to weigh the stability,which can be easily applied to practical robots.Experiments demonstrate that the quadruped turns around with little effort and endeavor.展开更多
Generator synchronization is an important and frequent operation in rural small hydropower station. In order to ensure that generator can be paralleled in the grid automatically,efficiently,and stably in the rural sma...Generator synchronization is an important and frequent operation in rural small hydropower station. In order to ensure that generator can be paralleled in the grid automatically,efficiently,and stably in the rural small hydropower station whose parallel in operation still needs to be accomplished manually. This paper described an automatic quasi-synchronizing device,based on 89C52 Single-chip Microcomputer(SCM) . Its hardware includes three modules and its software is structuralized. The device structure is simple,and its reliability is high and the maintenance is easy. Besides,convenient Human Machine Interface(HMI) makes the parameter setting simple and flexible.展开更多
The phase difference Δξ between locked islands(2/1 and 3/1) has been found to influence the heat transport on the thermal quench during disruptions by numerical modeling [Hu Q et al 2019Nucl.Fusion 59,016005].To ver...The phase difference Δξ between locked islands(2/1 and 3/1) has been found to influence the heat transport on the thermal quench during disruptions by numerical modeling [Hu Q et al 2019Nucl.Fusion 59,016005].To verify this experimentally,a set of resonant magnetic perturbation(RMP) coils is required to excite coupled magnetic islands with different Δξ.The spectrum analysis shows that the current RMP coils on J-TEXT can only produce sufficient 2/1 and 3/1RMP fields with a limited phase difference of Δξ∈[-75°,75°].In order to broaden the adjustable range of Δξ,a set of coils on the high field side(HFS) is proposed to generate 2/1 and 3/1 RMP fields with Δξ=180°.As a result,RMPs with adjustable Δξ∈[-180°,180°] and sufficient amplitudes could be achieved by applying the HFS coils and the low field side(LFS)coils.This work provides a feasible solution for flexible adjustment of the phase difference between m and m+1 RMP,which might facilitate the study of major disruptions and their control.展开更多
In order to further study the reliability of macro evaluation indexes,molecular dynamics (MD) was applied to the evaluation of asphalt binder.Micro evaluation indexes (potential energy,surface free energy,solubility p...In order to further study the reliability of macro evaluation indexes,molecular dynamics (MD) was applied to the evaluation of asphalt binder.Micro evaluation indexes (potential energy,surface free energy,solubility parameter and diffusion coefficient) of asphalt binder in different service phases (virgin,modified,aged and rejuvenated) were simulated.Combined with the variation characteristics of asphalt binder macro evaluation indexes (permeability,ductility,viscosity and softening point) in different service phases,the cross-scale correlation of macro-micro evaluation indexes was explored.The results show that the macro and micro evaluation indexes of asphalt binder have different characteristics in different service phases.The essence of the variation in the properties of asphalt binders is the difference in micro composition.In addition,there is a certain correlation between macro and micro evaluation indexes,which can be described by the gray relation theory.The cross-scale correlation of macro-micro evaluation indexes can provide a certain theoretical basis for the development of asphalt binder.展开更多
The impact of magnetic field on the corrosion behavior of Al-Mg-xR_(E)/Fe alloys in NaCl solutions with concentrations of 1.5wt%,3.5wt%,and 5.5wt%were studied by microstructure observation,immersion test,and electroch...The impact of magnetic field on the corrosion behavior of Al-Mg-xR_(E)/Fe alloys in NaCl solutions with concentrations of 1.5wt%,3.5wt%,and 5.5wt%were studied by microstructure observation,immersion test,and electrochemical test.The combined impacts of magnetic field and chloride ion concentration on the corrosion behavior of Al-Mg alloys with various electrode potential phases were discussed.The results indicate that Al-3.0Mg-xR_(E)/Fe alloys corrode faster and have a higher pitting corrosion potential in the NaCl solution with a higher concentration.In addition,a magnetic field can lower the pitting sensitivity and corrosion rate of Al-3.0Mg and Al-3.0Mg-0.2R_(E)/Fe alloys in NaCl solution with different concentrations.However,at a higher concentration of NaCl solution,the magnetic field has a weaker inhibiting effect on corrosion rate and pitting sensitivity.In NaCl solutions with concentrations of 1.5wt%and 3.5wt%,the corrosion rate and pitting sensitivity of Al-3.0Mg-1.0R_(E)/Fe alloys can be reduced by a magnetic field.However,in NaCl solution with the concentration of 5.5wt%,the corrosion rate of the alloys is increased by a magnetic field.展开更多
Phasor measurement units(PMUs)provide useful data for real-time monitoring of the smart grid.However,there may be time-varying deviation in phase angle differences(PADs)between both ends of the transmission line(TL),w...Phasor measurement units(PMUs)provide useful data for real-time monitoring of the smart grid.However,there may be time-varying deviation in phase angle differences(PADs)between both ends of the transmission line(TL),which may deteriorate application performance based on PMUs.To address that,this paper proposes two robust methods of correcting time-varying PAD deviation with unknown parameters of TL(ParTL).First,the phenomena of time-varying PAD deviation observed from field PMU data are presented.Two general formulations for PAD estimation are then established.To simplify the formulations,estimation of PADs is converted into the optimal problem with a single ParTL as the variable,yielding a linear estimation of PADs.The latter is used by second-order Taylor series expansion to estimate PADs accurately.To reduce the impact of possible abnormal amplitude data in field data,the IGG(Institute of Geodesy&Geophysics,Chinese Academy of Sciences)weighting function is adopted.Results using both simulated and field data verify the effectiveness and robustness of the proposed methods.展开更多
The effect of oxygen vacancies on the adsorption and activation of CO_(2) on the surface of different phases of ZrO_(2) is investigated by density functional theory(DFT)calculations.The calculations show that the oxyg...The effect of oxygen vacancies on the adsorption and activation of CO_(2) on the surface of different phases of ZrO_(2) is investigated by density functional theory(DFT)calculations.The calculations show that the oxygen vacancies contribute greatly to both the adsorption and activation of CO_(2).The adsorption energy of CO_(2) on the c-ZrO_(2),t-ZrO_(2) and,m-ZrO_(2) surfaces is enhanced to 5,4,and 3 folds with the help of oxygen vacancies,respectively.Moreover,the energy barrier of CO_(2) dissociation on the defective surfaces of c-ZrO_(2),t-ZrO_(2),and m-ZrO_(2) is reduced to 1/2,1/4,and 1/5 of the perfect surface with the assistance of oxygen vacancies.Furthermore,the activation of CO_(2) on the ZrO_(2) surface where oxygen vacancies are present,and changes from an endothermic reaction to an exothermic reaction.This finding demonstrates that the presence of oxygen vacancies promotes the activation of CO_(2) both kinetically and thermodynamically.These results could provide guidance for the high-efficient utilization of CO_(2) at an atomic scale.展开更多
We propose a novel modified frequency-shifted interferometer, where a Mach–Zehnder interferometer is added in order to obtain wavelength information. We use the Hilbert transform to extract the wavelength information...We propose a novel modified frequency-shifted interferometer, where a Mach–Zehnder interferometer is added in order to obtain wavelength information. We use the Hilbert transform to extract the wavelength information from the phase of the interference pattern and construct the relationship between phase and wavelength. The laser wavelength measurement experiment is used to verify the compound interferometer. Experimental results demonstrated that our method could obtain the wavelength from the phase, which is of great significance for demodulation of the fiber Bragg grating based on a frequency-shifted interferometer.展开更多
Chirped fiber grating was used in dispersion compensator. We tried to use the same phase mask to write fiber grating of different wavelength with two methods to reduce the price of the fiber grating.
The Floating nuclear power plant grid is composed of power generation,in-station power supply and external power delivery.To ensure the safety of the nuclear island,the in-station system adopts a special power supply ...The Floating nuclear power plant grid is composed of power generation,in-station power supply and external power delivery.To ensure the safety of the nuclear island,the in-station system adopts a special power supply mode,while the external power supply needs to be adapted to different types of external systems.Because of frequent single phase-ground faults and various fault forms,the fault line selection protection should be accurate,sensitive and adaptive.This paper presents a fault line selection method in cooperation with multi-mode grounding control.Based on the maximum united energy entropy ratio(MUEER),the optimal wavelet basis function and decomposition scale are adaptively chosen,while the fault line is selected by wavelet transform modulus maxima(WTMM).For high-impedance faults(HIFs),to enlarge the fault feature,the system grounding mode can be switched by the multi-mode grounding control.Based on the characteristic of HIFs,the fault line can be selected by comparing phase differences of zero-sequence current mutation and fault phase voltage mutation before and after the fault.Simulation results using MATLAB/Simulink show the effectiveness of the proposed method in solving the protection problems.展开更多
Understanding dynamic stability of a ship on a resonance frequency is important because comparatively smaller external forces and moments generate larger motions.The roll motion is most susceptible because of smaller ...Understanding dynamic stability of a ship on a resonance frequency is important because comparatively smaller external forces and moments generate larger motions.The roll motion is most susceptible because of smaller restoring moments.Most studies related to the failure modes such as parametric roll and dead ship condition,identified by second generation of intact stability criteria(SGISC)are performed at a resonance frequency.However,the nature of resonance,where the model experiences an incremental roll motion,has not been well understood.In this study,nonlinear unsteady computational fluid dynamics(CFD)simulations were conducted to investigate the resonance phenomenon using a containership under a sinusoidal roll exciting moment.To capture the complexity of the phenomenon,simulations were conducted over a range of frequencies to cover the resonance frequency including lower and higher amplitudes.In addition to the resonance frequency,the phase shift between roll exciting moment and roll angle,as well as the phase difference between acceleration and roll angle,were found to have significant effects on the occurrence of resonance.展开更多
基金This work is supported in part by National Natural Science Foundation of China(61771083,61704015)the Program for Changjiang Scholars and Innovative Research Team in University(IRT1299)+2 种基金Fundamental and Frontier Research Project of Chongqing(Nos.cstc2017jcyjAX0380,cstc2015jcyjBX0065)Sichuan Science and Technology Program(2018GZ0184)University Outstanding Achievement Transformation Project of Chongqing(No.KJZH17117).
文摘With the popularity of indoor wireless network,device-free indoor localization has attracted more and more attention.Unlike device-based localization where the target is required to carry an active transmitter,their frequent signal scanning consumes a large amount of energy,which is inconvenient for devices with limited energy.In this work,we propose the MFPL,device-free localization(DFL)system based on WiFi distance measurement.First,we combine multi-subcarrier characteristic of Channel State Information(CSI)with classical Fresnel reflection model to get the linear relationship between the change of the length of reflection path and the subcarrier phase difference.Then we calculate the Fresnel phase difference between subcarrier pairs with different spacing from CSI amplitude time series.Finally,we get the change of the length of the reflection path caused by target moving to achieve distance measurement and localization.Using a combination of subcarriers with different spacing to achieve distance measurement effectively broadens the maximum unambiguous distance of the system.To solve the complex non-linear problem of the intersection of two elliptic equations,we introduce Newton's method to transform the non-linear problem into a linear one.The effectiveness of our approach is verified using commodity WiFi infrastructures.The experimental results show our method achieves a median error of 0.87 m in actual indoor environment.
基金supported by the National Natural Science Foundation of China under Grants 51877159,51637007the Fundamental Research Funds for Central Universities Program 2042019kf0195。
文摘When a modular multilevel converter based high voltage direct current(MMC-HVDC)system operates under grid faults,there will be a phase difference between the grid voltage and the converter output.It can be caused by grid voltage phase shifting and the integration effect of the phase-locked loop(PLL)in the converter.The system may exhibit an undesirable transient process with expanded current which is harmful for the converter devices.In this paper,a transient current estimation method is proposed for the scenario of converter-grid phase difference caused by the frequency shifting of the grid side.A piecewise phase calculation model is established to determine the transient phase difference of the system.Then,according to the maximum phase difference calculated by the model,the system stability is assessed and the maximum value of system transient current can be estimated after comparing the maximum phase difference with the critical phase difference and π,Finally,the current estimation results are verified by detailed circuit simulations of a 21-level MMC-HVDC system built in PSCAD.
文摘By considering higher order approximation to the interaural phase difference, a more general localization equation for stereo sound image with interchannel phase difference is derived. At very low frequency or low interchannel phase difference, the equation can be simplified to Makita theory. In general, image position is obviously affected by frequency.It is shown that image position varying with freqllency is the main reason for image width broadening in stereo reproduction with interchannel phase difference. And an extra interaural sound level difference caused by interchannel phase difference is the main reason for image naturalness degrading. In practice, it is necessary to reduce the interchannel phase difference,at least, to less than 60°.
基金National Natural &ience Foundation of China!(No. 59671020).
文摘The microstructure and the stability of Fe73.5Cu1Nb3Si13.5B9 alloy at different stages of phase transformation were investigated through the observation of X-ray difraction and transmission electron microscopy and the measurement of magnetic aftereffect （MAE）. It was found that the dependence of the volume fraction of amorphous phase and the MAE in the samples annealed from 450 to 700℃ on the annealing temperature is similar.
基金Major State Basic Research Development Program of China (program 973,No. 2008CB717807)ITER Program Supporting Research in China (No. 2010GB108004)
文摘Plasma electron density is one of the most fundamental parameters in the study of tokamak plasma physics.The method of plasma electron density measuring and processing on the Joint Texas Experimental Tokamak(J-TEXT) was presented in this paper.The principle of the plasma electron density measuring by hydrogen cyanide(HCN) laser interferometer was introduced.Room temperature triglycine sulface(TGS) detector was used to obtain the beat signal of HCN,and phase difference was measured by high-speed acquisition card DAQ2010.Based on the signal characteristics,a specific HCN processing algorithm was designed to eliminate the baseline offset accurately and process overturns of HCN signals effectively.As a result,plasma electron density with high accuracy and low noise has been obtained during the J-TEXT tokamak experiment.
基金Project supported by the National Natural Science Foundation of China(Grant No.11534009)
文摘The inhomogenous ocean waveguide, which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate, is one of the causes that make the array gain deviate from its ideal value. The relationship between the array gain and the fluctuant acoustic channel is studied theoretically. The analytical expression of the array gain is derived via an acoustic channel transfer function on the assumption that the ambient noise field is isotropic. The expression is expanded via the Euler formula to give an insight into the effect of the fluctuant acoustic channel on the array gain. The result demonstrates that the amplitude fluctuation of the acoustic channel transfer functions has a slight effect on the array gain; however, the uniformity of the phase difference between the weighting coefficient and the channel transfer function on all the hydrophones in the array is a major factor that leads the array gain to further deviate from its ideal value. The numerical verification is conducted in the downslope waveguide, in which the gain of a horizontal uniform linear array(HLA) with a wide-aperture operating in the continental slope area is considered. Numerical result is consistent with the theoretical analysis.
文摘With the target at simplicity like facilitating the mechanical system,the quadruped robots usually have limited degrees of freedom per leg.Addressing the robot whose legs have only two degrees of freedom,this paper explores several turning strategies including altering the median value,changing the phase difference,and modifying the amplitude.The insights of the proposed methods are that we break down the symmetries which exist during the process of the robot locomotion and rebuild them.Since we probe into the turning feasibility from the points of the median value,phase difference and amplitude in the sine functions,these turning methods are feature of universality.In order to evaluate these methods,this paper presents a new way to weigh the stability,which can be easily applied to practical robots.Experiments demonstrate that the quadruped turns around with little effort and endeavor.
文摘Generator synchronization is an important and frequent operation in rural small hydropower station. In order to ensure that generator can be paralleled in the grid automatically,efficiently,and stably in the rural small hydropower station whose parallel in operation still needs to be accomplished manually. This paper described an automatic quasi-synchronizing device,based on 89C52 Single-chip Microcomputer(SCM) . Its hardware includes three modules and its software is structuralized. The device structure is simple,and its reliability is high and the maintenance is easy. Besides,convenient Human Machine Interface(HMI) makes the parameter setting simple and flexible.
基金supported by the National Magnetic Confinement Fusion Energy R & D Program of China (Nos. 2018YFE0309102 and 2019YFE03010004)National Natural Science Foundation of China (Nos.12075096, 11905078,and 51821005)
文摘The phase difference Δξ between locked islands(2/1 and 3/1) has been found to influence the heat transport on the thermal quench during disruptions by numerical modeling [Hu Q et al 2019Nucl.Fusion 59,016005].To verify this experimentally,a set of resonant magnetic perturbation(RMP) coils is required to excite coupled magnetic islands with different Δξ.The spectrum analysis shows that the current RMP coils on J-TEXT can only produce sufficient 2/1 and 3/1RMP fields with a limited phase difference of Δξ∈[-75°,75°].In order to broaden the adjustable range of Δξ,a set of coils on the high field side(HFS) is proposed to generate 2/1 and 3/1 RMP fields with Δξ=180°.As a result,RMPs with adjustable Δξ∈[-180°,180°] and sufficient amplitudes could be achieved by applying the HFS coils and the low field side(LFS)coils.This work provides a feasible solution for flexible adjustment of the phase difference between m and m+1 RMP,which might facilitate the study of major disruptions and their control.
基金Funded by the Fundamental Research Funds for the Central Universities (No. 2572021AW10)。
文摘In order to further study the reliability of macro evaluation indexes,molecular dynamics (MD) was applied to the evaluation of asphalt binder.Micro evaluation indexes (potential energy,surface free energy,solubility parameter and diffusion coefficient) of asphalt binder in different service phases (virgin,modified,aged and rejuvenated) were simulated.Combined with the variation characteristics of asphalt binder macro evaluation indexes (permeability,ductility,viscosity and softening point) in different service phases,the cross-scale correlation of macro-micro evaluation indexes was explored.The results show that the macro and micro evaluation indexes of asphalt binder have different characteristics in different service phases.The essence of the variation in the properties of asphalt binders is the difference in micro composition.In addition,there is a certain correlation between macro and micro evaluation indexes,which can be described by the gray relation theory.The cross-scale correlation of macro-micro evaluation indexes can provide a certain theoretical basis for the development of asphalt binder.
基金by the National Natural Science Foundation of China(No.51909071)the Natural Science Foundation of Jiangsu Province(No.BK20190493)the Fundamental Research Funds for the Central Universities(No.B220202040)。
文摘The impact of magnetic field on the corrosion behavior of Al-Mg-xR_(E)/Fe alloys in NaCl solutions with concentrations of 1.5wt%,3.5wt%,and 5.5wt%were studied by microstructure observation,immersion test,and electrochemical test.The combined impacts of magnetic field and chloride ion concentration on the corrosion behavior of Al-Mg alloys with various electrode potential phases were discussed.The results indicate that Al-3.0Mg-xR_(E)/Fe alloys corrode faster and have a higher pitting corrosion potential in the NaCl solution with a higher concentration.In addition,a magnetic field can lower the pitting sensitivity and corrosion rate of Al-3.0Mg and Al-3.0Mg-0.2R_(E)/Fe alloys in NaCl solution with different concentrations.However,at a higher concentration of NaCl solution,the magnetic field has a weaker inhibiting effect on corrosion rate and pitting sensitivity.In NaCl solutions with concentrations of 1.5wt%and 3.5wt%,the corrosion rate and pitting sensitivity of Al-3.0Mg-1.0R_(E)/Fe alloys can be reduced by a magnetic field.However,in NaCl solution with the concentration of 5.5wt%,the corrosion rate of the alloys is increased by a magnetic field.
基金This work was supported by the National Key Research and Development Program of China(2017YFB0902901)National Natural Science Foundation of China(51627811).
文摘Phasor measurement units(PMUs)provide useful data for real-time monitoring of the smart grid.However,there may be time-varying deviation in phase angle differences(PADs)between both ends of the transmission line(TL),which may deteriorate application performance based on PMUs.To address that,this paper proposes two robust methods of correcting time-varying PAD deviation with unknown parameters of TL(ParTL).First,the phenomena of time-varying PAD deviation observed from field PMU data are presented.Two general formulations for PAD estimation are then established.To simplify the formulations,estimation of PADs is converted into the optimal problem with a single ParTL as the variable,yielding a linear estimation of PADs.The latter is used by second-order Taylor series expansion to estimate PADs accurately.To reduce the impact of possible abnormal amplitude data in field data,the IGG(Institute of Geodesy&Geophysics,Chinese Academy of Sciences)weighting function is adopted.Results using both simulated and field data verify the effectiveness and robustness of the proposed methods.
基金supported by the National Natural Science Foundation of China(Grant No.52106179)and the Fundamental Research Program of Shanxi Province,China(Grant No.20210302124017).
文摘The effect of oxygen vacancies on the adsorption and activation of CO_(2) on the surface of different phases of ZrO_(2) is investigated by density functional theory(DFT)calculations.The calculations show that the oxygen vacancies contribute greatly to both the adsorption and activation of CO_(2).The adsorption energy of CO_(2) on the c-ZrO_(2),t-ZrO_(2) and,m-ZrO_(2) surfaces is enhanced to 5,4,and 3 folds with the help of oxygen vacancies,respectively.Moreover,the energy barrier of CO_(2) dissociation on the defective surfaces of c-ZrO_(2),t-ZrO_(2),and m-ZrO_(2) is reduced to 1/2,1/4,and 1/5 of the perfect surface with the assistance of oxygen vacancies.Furthermore,the activation of CO_(2) on the ZrO_(2) surface where oxygen vacancies are present,and changes from an endothermic reaction to an exothermic reaction.This finding demonstrates that the presence of oxygen vacancies promotes the activation of CO_(2) both kinetically and thermodynamically.These results could provide guidance for the high-efficient utilization of CO_(2) at an atomic scale.
基金supported by the National Natural Science Foundation of China (NSFC)(Nos. 61775173 and 61975157)
文摘We propose a novel modified frequency-shifted interferometer, where a Mach–Zehnder interferometer is added in order to obtain wavelength information. We use the Hilbert transform to extract the wavelength information from the phase of the interference pattern and construct the relationship between phase and wavelength. The laser wavelength measurement experiment is used to verify the compound interferometer. Experimental results demonstrated that our method could obtain the wavelength from the phase, which is of great significance for demodulation of the fiber Bragg grating based on a frequency-shifted interferometer.
文摘Chirped fiber grating was used in dispersion compensator. We tried to use the same phase mask to write fiber grating of different wavelength with two methods to reduce the price of the fiber grating.
基金Project Supported by National Natural Science Foundation of China(No.51877089).Research on the mechanism and fault ride-through integrated strategies of an active power router in hybrid AC and DC distribution grids.
文摘The Floating nuclear power plant grid is composed of power generation,in-station power supply and external power delivery.To ensure the safety of the nuclear island,the in-station system adopts a special power supply mode,while the external power supply needs to be adapted to different types of external systems.Because of frequent single phase-ground faults and various fault forms,the fault line selection protection should be accurate,sensitive and adaptive.This paper presents a fault line selection method in cooperation with multi-mode grounding control.Based on the maximum united energy entropy ratio(MUEER),the optimal wavelet basis function and decomposition scale are adaptively chosen,while the fault line is selected by wavelet transform modulus maxima(WTMM).For high-impedance faults(HIFs),to enlarge the fault feature,the system grounding mode can be switched by the multi-mode grounding control.Based on the characteristic of HIFs,the fault line can be selected by comparing phase differences of zero-sequence current mutation and fault phase voltage mutation before and after the fault.Simulation results using MATLAB/Simulink show the effectiveness of the proposed method in solving the protection problems.
文摘Understanding dynamic stability of a ship on a resonance frequency is important because comparatively smaller external forces and moments generate larger motions.The roll motion is most susceptible because of smaller restoring moments.Most studies related to the failure modes such as parametric roll and dead ship condition,identified by second generation of intact stability criteria(SGISC)are performed at a resonance frequency.However,the nature of resonance,where the model experiences an incremental roll motion,has not been well understood.In this study,nonlinear unsteady computational fluid dynamics(CFD)simulations were conducted to investigate the resonance phenomenon using a containership under a sinusoidal roll exciting moment.To capture the complexity of the phenomenon,simulations were conducted over a range of frequencies to cover the resonance frequency including lower and higher amplitudes.In addition to the resonance frequency,the phase shift between roll exciting moment and roll angle,as well as the phase difference between acceleration and roll angle,were found to have significant effects on the occurrence of resonance.
