The estimation of glacier flow velocity on a short-term scale is very important for further glacier dynamics research.In this study,10 Sentinel-1 ascending images and 10 Sentinel-1 descending images of Urumqi Glacier ...The estimation of glacier flow velocity on a short-term scale is very important for further glacier dynamics research.In this study,10 Sentinel-1 ascending images and 10 Sentinel-1 descending images of Urumqi Glacier No.1 in 2017 were used to calculate the glacier flow velocity in a high coherence period by DIn SAR technology and MAI technology,while the offset tracking technology was used to estimate the glacier flow velocity in a low coherence period.Then,the monthly three-dimensional flow velocity of the glacier was calculated by the Helmert variance component estimation method.Finally,the accuracy of the estimated glacier flow velocity on a monthly scale was evaluated.The results showed that:(1)the monthly scale motion velocity of Urumqi Glacier No.1 in May,June,July,and August 2017 was 0.273 m/month,0.657 m/month,0.582 m/month,and 0.392 m/month,respectively.(2)The accuracy of glacier surface velocity from May 2017 to August 2017 was 0.033 m/month,0.026 m/month,0.034 m/month and 0.037 m/month,respectively.(3)The accuracy of glacier surface flow velocity from May 2017 to August 2017 was 0.018 m/month,0.031 m/month,0.029 m/month and 0.030 m/month,respectively.Therefore,the research methodology based on the Sentinel-1 ascending and descending data and presented in this paper was applicable to the estimation of monthly-scale flow velocity of mountain glaciers.展开更多
This paper analyzed the existing methods of wave measurement, and described the advantages of GPS applied in measuring the wave. The equations of absolute velocity estimation were discussed, focusing on two methods wi...This paper analyzed the existing methods of wave measurement, and described the advantages of GPS applied in measuring the wave. The equations of absolute velocity estimation were discussed, focusing on two methods with Doppler shill. The error sources and their effect on velocity estimation were analyzed. Then, some tests were carried on to simulate dynamic velocity determination using static data Based on the high-frequency carrier-phase derived Doppler observations, the velocity has been estimated to the precision of 1 cm/s or so, even to the mm/s level. And with the receiver generated Doppler measurements, the precision can reach 3 - 15 cm/s.展开更多
By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the ...By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the estimated velocity is inversely proportional to the frequency step size instead of the carrier frequency of the transmitted signal as the pulse-Doppler （PD） processing, the new algorithm can achieve much wider unambiguous velocity range. Furthermore, non-coherent integration of the sub-pulses with different carrier frequencies can be implemented by Hough trans- form to improve the anti-noise performance. Besides, field experimental results show that the high range resolution profile （HRRP） of a bullet with high speed can be reconstructed correctly without distortion.展开更多
Radial velocity estimation used in wide-band radar systems is investigated.By analyzing the signal of cross-correlation output of adjacent echoes,it is found that the frequency and phase of the cross-correlation outpu...Radial velocity estimation used in wide-band radar systems is investigated.By analyzing the signal of cross-correlation output of adjacent echoes,it is found that the frequency and phase of the cross-correlation output are related to the target’s radial velocity.Since the precision of the phase estimation is higher than that of the frequency,a phase-based velocity estimator is proposed.However,the ambiguity problem exists in the phase estimators,and thus the estimation of the cross-correlation of adjacent echoes(CCAE)is used to calculate the ambiguity number.The root-mean-square-error(RMSE)of the proposed estimator is derived.Simulation results show that the performance of the proposed method is better than that of the frequency-based estimator.展开更多
Estimation of S-wave velocity using logging data has mainly been performed for sandstone, mudstone and oil and gas strata, while its application to hydrate reservoirs has been largely overlooked. In this paper we pres...Estimation of S-wave velocity using logging data has mainly been performed for sandstone, mudstone and oil and gas strata, while its application to hydrate reservoirs has been largely overlooked. In this paper we present petxophysical methods to estimate the S-wave velocity of hydrate reservoirs with the P-wave velocity and the density as constraints. The three models used in this paper are an equivalent model （MBGL）, a three-phase model （TPBE）, and a thermo-elasticity model （TEM）. The MBGL model can effectively describe the internal relationship among the components of the rock, and the estimated P-wave velocities are in good agreement with the measured data （2.8% error）. However, in the TPBE model, the solid, liquid and gas phases axe considered to be independent of each other, and the estimation results are relatively low （46.6% error）. The TEM model is based on the sensitivity of the gas hydrate to temperature and pressure, and the accuracy of the estimation results is also high （3.6% error）. Before the estimation, the occurrence patterns of hydrates in the Shenhu area were examined, and occurrence state one （the hydrate is in solid form in the reservoir） was selected for analysis. By using the known P-wave velocity and density as constraints, a reasonable S-wave velocity value （ranging from 400 to 1100 m s 1 and for a hydrate layer of 1100 m s 1） can be obtained through multiple iterations. These methods and results provide new data and technical support for further research on hydrates and other geological features in the Shenhu area.展开更多
In this paper, a novel adaptive filtering algorithm using real-time deviation of velocity estimation is presented for maneuvering target tracking. This new algorithm will be called adaptive filtering algorithm of velo...In this paper, a novel adaptive filtering algorithm using real-time deviation of velocity estimation is presented for maneuvering target tracking. This new algorithm will be called adaptive filtering algorithm of velocity estimation. A number of simulation results indicate that the algorithm not only has good performance on tracking maneuvering target, but also greatly improves the capacity for tracking non-maneuvering target. So it is worthy to be applied widely in practice.展开更多
After introducing the principle of float car data (FCD), this paper gives the primary flow of pre-handing and map- matching of the FCD. After analyzing the percentage of coverage of FCD on the road network, large quan...After introducing the principle of float car data (FCD), this paper gives the primary flow of pre-handing and map- matching of the FCD. After analyzing the percentage of coverage of FCD on the road network, large quantity of heritage database of routing status is used to estimate the routing velocity when lack of FCD on parts road segments. Multi liner regression model is then put forwarded by considering the spatial correlativity among the road network, and some model parameters are deduced when time series is classified in day and week. Besides, error of velocity probability and error of status probability are achieved based on the result from field testing while the feasibility and reliability of the velocity estimation model is obtained as well. Finally, as a case study in Shanghai center area, the whole routing velocity in the road network is estimated and published in real time.展开更多
Objective We aimed to clarify the association between estimated pulse wave velocity(ePWV)and the changes in ePWV with all-cause mortality among middle-aged and elderly Chinese.Methods Data were obtained from the China...Objective We aimed to clarify the association between estimated pulse wave velocity(ePWV)and the changes in ePWV with all-cause mortality among middle-aged and elderly Chinese.Methods Data were obtained from the China Health and Retirement Longitudinal Study(CHARLS)from 2011-2018.The ePWV was calculated using an equation that included age and mean blood pressure(MBP).The ΔePWV was assessed as the difference in ePWV between the first two waves.Cox proportional hazard models were used to determine the association between ePWV and ΔePWV with all-cause mortality after adjustment for potential confounders.Results Of 13,116 participants during a median follow-up of 7.0 years,1,356 deaths occurred.An increased ePWV was independently associated with all-cause mortality.The hazard ratio[95% confidence interval(CI)]for participants from the 1^(st)-4^(th) quartile groups was 1.00,1.69(1.31-2.18),3.09(2.44-3.91),and 8.54(6.78-10.75),respectively.Each standard deviation(SD)increment of ePWV increased the risk of all-cause mortality by 132%.Furthermore,theΔePWV was significantly associated with a 1.28-fold(95%CI,1.18-1.38)risk of all-cause mortality per SD increment.Conclusion This cohort study provided novel evidence from a Chinese population that an increased ePWV or progression of the ePWV was independently associated with all-cause mortality,which highlighted the importance of mitigating ePWV progression in clinical practice.展开更多
Velocity incorporates user dynamic characteristics,facilitating more precise predictions about the positioning.However,the positioning,velocity,and timing services derived from Global Navigation Satellite System(GNSS)...Velocity incorporates user dynamic characteristics,facilitating more precise predictions about the positioning.However,the positioning,velocity,and timing services derived from Global Navigation Satellite System(GNSS)undergo accuracy degradation in urban environments due to multipath/Non-Line of Sight(NLOS)effects.Fault detection and exclusion(FDE)methods can mitigate these effects.However,the existing methods,such as the multi-hypothesis separation solution(MHSS),exhibit high computational burdens and cannot perform accurate exclusion due to the excessive fault modes.In response,a fault detection and correction(FDC)method is developed to address outliers arising from multipath/NLOS in the Doppler measurements.To alleviate computational demands while simultaneously improving velocity estimation accuracy,multipath/NLOS sparsity assumptions and grouping constraints are introduced.Specifically,the grouping-sparsity enforcing Least Absolute Shrinkage and Selection Operator(GS-LASSO)is introduced to jointly detect and correct multipath/NLOS-induced outliers.A grouping strategy based on sky-map and carrier-to-noise ratio is introduced,which is coupled with a new cost function to improve sparsity estimation.To facilitate the implementation,a solver and parameter-tuning method incorporating false alarm rates are developed.The performance of GS-LASSO is compared with that of MHSS.The results show that GS-LASSO reduces greater velocity errors in the urban environment,while requiring limited computational load.展开更多
A gas puff imaging(GPI)diagnostic has been developed and operated on EAST since 2012,and the time-delay estimation(TDE)method is used to derive the propagation velocity of fluctuations from the two-dimensional GPI dat...A gas puff imaging(GPI)diagnostic has been developed and operated on EAST since 2012,and the time-delay estimation(TDE)method is used to derive the propagation velocity of fluctuations from the two-dimensional GPI data.However,with the TDE method it is difficult to analyze the data with fast transient events,such as edge-localized mode(ELM).Consequently,a method called the spatial displacement estimation(SDE)algorithm is developed to estimate the turbulence velocity with high temporal resolution.Based on the SDE algorithm,we make some improvements,including an adaptive median filter and super-resolution technology.After the development of the algorithm,a straight-line movement and a curved-line movement are used to test the accuracy of the algorithm,and the calculated speed agrees well with preset speed.This SDE algorithm is applied to the EAST GPI data analysis,and the derived propagation velocity of turbulence is consistent with that from the TDE method,but with much higher temporal resolution.展开更多
An improved multidirectional velocity model was proposed for more accurately locating micro-seismic events in rock engineering. It was assumed that the stress wave propagation velocities from a micro-seismic source to...An improved multidirectional velocity model was proposed for more accurately locating micro-seismic events in rock engineering. It was assumed that the stress wave propagation velocities from a micro-seismic source to three nearest monitoring sensors in a sensor's array arrangement were the same. Since the defined objective function does not require pre-measurement of the stress wave propagation velocity in the field, errors from the velocity measurement can be avoided in comparison to three traditional velocity models. By analyzing 24 different cases, the proposed multidirectional velocity model iterated by the Simplex method is found to be the best option no matter the source is within the region of the sensor's array or not. The proposed model and the adopted iterative algorithm are verified by field data and it is concluded that it can significantly reduce the error of the estimated source location.展开更多
In the railway industry, re-adhesion control plays an important role in attenuating the slip occurrence due to the low adhesion condition in the wheel-rail inter- action. Braking and traction forces depend on the norm...In the railway industry, re-adhesion control plays an important role in attenuating the slip occurrence due to the low adhesion condition in the wheel-rail inter- action. Braking and traction forces depend on the normal force and adhesion coefficient at the wheel-rail contact area. Due to the restrictions on controlling normal force, the only way to increase the tractive or braking effect is to maximize the adhesion coefficient. Through efficient uti- lization of adhesion, it is also possible to avoid wheel-rail wear and minimize the energy consumption. The adhesion between wheel and rail is a highly nonlinear function of many parameters like environmental conditions, railway vehicle speed and slip velocity. To estimate these unknown parameters accurately is a very hard and competitive challenge. The robust adaptive control strategy presented in this paper is not only able to suppress the wheel slip in time, but also maximize the adhesion utilization perfor- mance after re-adhesion process even if the wheel-rail contact mechanism exhibits significant adhesion uncer- tainties and/or nonlinearities. Using an optimal slip velocity seeking algorithm, the proposed strategy provides a satisfactory slip velocity tracking ability, which was demonstrated able to realize the desired slip velocity without experiencing any instability problem. The control torque of the traction motor was regulated continuously to drive the railway vehicle in the neighborhood of the opti- mal adhesion point and guarantee the best traction capacity after re-adhesion process by making the railway vehicle operate away from the unstable region. The results obtained from the adaptive approach based on the second- order sliding mode observer have been confirmed through theoretical analysis and numerical simulation conducted in MATLAB and Simulink with a full traction model under various wheel-rail conditions.展开更多
Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters.Normally,this technique requires the assumption of late...Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters.Normally,this technique requires the assumption of lateral homogeneity,which makes the horizontal slowness components at depths of downhole receivers equal to those measured at the surface.Any violations of this assumption,such as lateral heterogeneity or nonzero dip of intermediate interfaces,lead to distortions in reconstructed slowness surfaces and,consequently,to errors in estimated anisotropic parameters.In this work,we relax the assumption of lateral homogeneity and discuss how to correct vertical seismic profile data for weak lateral heterogeneity.We describe a procedure of downward continuation of recorded traveltimes that accounts for the presence of both vertical inhomogeneity and weak lateral heterogeneity,which produces correct slowness surfaces at depths of downhole receivers,noticing that sufficiently dense receiver coverage along a borehole is required to separate influences of vertical and lateral heterogeneity on measured traveltimes and obtain accurate estimates of the slowness surfaces.Once the slowness surfaces are found and a desired type of anisotropic model to be inverted is selected,the corresponding anisotropic parameters,providing the best fit to the estimated slownesses,can be obtained.We invert the slowness surfaces of P-waves for parameters of the simplest anisotropic model describing dipping fractures(transversely isotropic medium with a tilted symmetry axis).Five parameters of this model,namely,the P-wave velocity V0 in the direction of the symmetry axis,Thomsen's anisotropic coefficients e and d,the tilt n,and the azimuth b of the symmetry axis,can be estimated in a stable manner when maximum source offset is greater than half of receiver depth.展开更多
The error caused by irreversible demagnetization damages the accurate velocity tracking of an in-wheel motor in a mobile robot.A current feedforward vector control system based on ESO is proposed to compensate it for ...The error caused by irreversible demagnetization damages the accurate velocity tracking of an in-wheel motor in a mobile robot.A current feedforward vector control system based on ESO is proposed to compensate it for the demagnetization motor.A demagnetization mathematical model is established to describe a permanent magnet synchronous motor,which took the change of permanent magnet flux linkage parameters as a factor to count the demagnetization error in velocity tracking.The uncertain disturbance estimation model of the control system is built based on ESO,which eliminates the system error by the feedforward current compensation.It is compared with the vector control method in terms of control accuracy.The simulation results show that the current feedforward vector control method based on ESO reduces the velocity tracking error greatly in conditions of motor demagnetization less than 30%.It is effective to improve the operation accuracy of the mobile robot.展开更多
In this paper,we consider the density-dependent magnetohydrodynamic equations with vacuum,and provide a regularity criterion involving the velocity and magnetic fields in Besov space of negative order,which improves[J...In this paper,we consider the density-dependent magnetohydrodynamic equations with vacuum,and provide a regularity criterion involving the velocity and magnetic fields in Besov space of negative order,which improves[Jishan FAN,Fucai LI,G.NAKAMURA,Zhong TAN,Regularity criteria for the three-dimensional magnetohydrodynamic equations.J.Differential Equations,2014,256（8）：2858 2875]in some sense.The method is to establish a new bilinear estimate.展开更多
High-frequency noise,often caused by system jitter and environmental factors,can obscure the true motion of particles.This study presents a Fourier transform-based particle velocity optimization framework designed to ...High-frequency noise,often caused by system jitter and environmental factors,can obscure the true motion of particles.This study presents a Fourier transform-based particle velocity optimization framework designed to improve the accuracy of velocity estimation in particle tracking experiments.High-frequency noise,often caused by system jitter and environmental factors,can obscure the true motion of particles.To address this,we propose an adaptive low-pass filtering approach where the cutoff frequency is optimized through a numerical search algorithm to minimize the error between the filtered velocity and the ground truth trajectory.Our results demonstrate that an optimal cutoff frequency of approximately 1 Hz offers the best balance between noise reduction and signal preservation.The framework is further enhanced by its adaptability to different experimental conditions,making it applicable to a wide range of particle tracking scenarios.This approach offers a more effective solution for overcoming noise-related challenges in particle tracking,providing a valuable tool for precise motion analysis in various scientific fields.展开更多
基金funded by the Basic scientific research fund projects(Youth Project)of the Educational Department of Liaoning Province in 2023(Grants No.JYTQN2023451)Liaoning Institute of Science and Technology doctoral research initiation fund project in 2023(Grants No.2307B27)+2 种基金Basic Research Project of Higher Education Institutions of Liaoning Provincial Department of Education(Grants No.2024JYTYB-12)the Basic scientific research fund projects(Youth Project)of the Educational Department of Liaoning Province in 2023(Grants No.JYTQN2024-21)Liaoning Institute of Science and Technology doctoral research initiation fund project in 2023(Grants No.2307B26)。
文摘The estimation of glacier flow velocity on a short-term scale is very important for further glacier dynamics research.In this study,10 Sentinel-1 ascending images and 10 Sentinel-1 descending images of Urumqi Glacier No.1 in 2017 were used to calculate the glacier flow velocity in a high coherence period by DIn SAR technology and MAI technology,while the offset tracking technology was used to estimate the glacier flow velocity in a low coherence period.Then,the monthly three-dimensional flow velocity of the glacier was calculated by the Helmert variance component estimation method.Finally,the accuracy of the estimated glacier flow velocity on a monthly scale was evaluated.The results showed that:(1)the monthly scale motion velocity of Urumqi Glacier No.1 in May,June,July,and August 2017 was 0.273 m/month,0.657 m/month,0.582 m/month,and 0.392 m/month,respectively.(2)The accuracy of glacier surface velocity from May 2017 to August 2017 was 0.033 m/month,0.026 m/month,0.034 m/month and 0.037 m/month,respectively.(3)The accuracy of glacier surface flow velocity from May 2017 to August 2017 was 0.018 m/month,0.031 m/month,0.029 m/month and 0.030 m/month,respectively.Therefore,the research methodology based on the Sentinel-1 ascending and descending data and presented in this paper was applicable to the estimation of monthly-scale flow velocity of mountain glaciers.
基金supported by the Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology(MRE201233)Key Laboratory of Surveying and Mapping Technology on Island and ReefState Bureau of Surveying and Mapping(2012B04)
文摘This paper analyzed the existing methods of wave measurement, and described the advantages of GPS applied in measuring the wave. The equations of absolute velocity estimation were discussed, focusing on two methods with Doppler shill. The error sources and their effect on velocity estimation were analyzed. Then, some tests were carried on to simulate dynamic velocity determination using static data Based on the high-frequency carrier-phase derived Doppler observations, the velocity has been estimated to the precision of 1 cm/s or so, even to the mm/s level. And with the receiver generated Doppler measurements, the precision can reach 3 - 15 cm/s.
基金Supported by the Fund of National Defense Industry Innovative Team(231)
文摘By analyzing the signal model of stepped-frequency waveform, a novel method for velocity measurement is proposed. The method is based on Doppler frequency difference which is achieved by using Hough transform. As the estimated velocity is inversely proportional to the frequency step size instead of the carrier frequency of the transmitted signal as the pulse-Doppler （PD） processing, the new algorithm can achieve much wider unambiguous velocity range. Furthermore, non-coherent integration of the sub-pulses with different carrier frequencies can be implemented by Hough trans- form to improve the anti-noise performance. Besides, field experimental results show that the high range resolution profile （HRRP） of a bullet with high speed can be reconstructed correctly without distortion.
基金the National Natural Science Foundation of China(61471012).
文摘Radial velocity estimation used in wide-band radar systems is investigated.By analyzing the signal of cross-correlation output of adjacent echoes,it is found that the frequency and phase of the cross-correlation output are related to the target’s radial velocity.Since the precision of the phase estimation is higher than that of the frequency,a phase-based velocity estimator is proposed.However,the ambiguity problem exists in the phase estimators,and thus the estimation of the cross-correlation of adjacent echoes(CCAE)is used to calculate the ambiguity number.The root-mean-square-error(RMSE)of the proposed estimator is derived.Simulation results show that the performance of the proposed method is better than that of the frequency-based estimator.
基金supported by the National Natural Science Foundation of China(Nos.41304096 and 41176077)the National Science and Technology Major Project of China(No.2016ZX05024-001-002)+2 种基金the National High-tech R&D Program of China(863 ProgramNo.2013AA0925 01)the Fundamental Research Funds for the Central Universities(No.201762019)
文摘Estimation of S-wave velocity using logging data has mainly been performed for sandstone, mudstone and oil and gas strata, while its application to hydrate reservoirs has been largely overlooked. In this paper we present petxophysical methods to estimate the S-wave velocity of hydrate reservoirs with the P-wave velocity and the density as constraints. The three models used in this paper are an equivalent model （MBGL）, a three-phase model （TPBE）, and a thermo-elasticity model （TEM）. The MBGL model can effectively describe the internal relationship among the components of the rock, and the estimated P-wave velocities are in good agreement with the measured data （2.8% error）. However, in the TPBE model, the solid, liquid and gas phases axe considered to be independent of each other, and the estimation results are relatively low （46.6% error）. The TEM model is based on the sensitivity of the gas hydrate to temperature and pressure, and the accuracy of the estimation results is also high （3.6% error）. Before the estimation, the occurrence patterns of hydrates in the Shenhu area were examined, and occurrence state one （the hydrate is in solid form in the reservoir） was selected for analysis. By using the known P-wave velocity and density as constraints, a reasonable S-wave velocity value （ranging from 400 to 1100 m s 1 and for a hydrate layer of 1100 m s 1） can be obtained through multiple iterations. These methods and results provide new data and technical support for further research on hydrates and other geological features in the Shenhu area.
文摘In this paper, a novel adaptive filtering algorithm using real-time deviation of velocity estimation is presented for maneuvering target tracking. This new algorithm will be called adaptive filtering algorithm of velocity estimation. A number of simulation results indicate that the algorithm not only has good performance on tracking maneuvering target, but also greatly improves the capacity for tracking non-maneuvering target. So it is worthy to be applied widely in practice.
基金supported by National Basic Research Program of China(973 Program)(2012CB720000)National Natural Science Foundation of China(61104187)Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province(BS2012NY003)
文摘After introducing the principle of float car data (FCD), this paper gives the primary flow of pre-handing and map- matching of the FCD. After analyzing the percentage of coverage of FCD on the road network, large quantity of heritage database of routing status is used to estimate the routing velocity when lack of FCD on parts road segments. Multi liner regression model is then put forwarded by considering the spatial correlativity among the road network, and some model parameters are deduced when time series is classified in day and week. Besides, error of velocity probability and error of status probability are achieved based on the result from field testing while the feasibility and reliability of the velocity estimation model is obtained as well. Finally, as a case study in Shanghai center area, the whole routing velocity in the road network is estimated and published in real time.
基金supported by the National Key R&D Program of China[2021YFC2500500]Chinese Academy of Medical Sciences(CAMS)Innovation Fund for Medical Sciences[2021-I2M-1-010]+2 种基金the National Natural Science Foundation of China[82073658]the Taikang Yicai Public Health and Epidemic Control Fund[TKYC-GW-2020]the Research Unit of Prospective Cohort of Cardiovascular Diseases and Cancers of the Chinese Academy of Medical Sciences[2019RU038]。
文摘Objective We aimed to clarify the association between estimated pulse wave velocity(ePWV)and the changes in ePWV with all-cause mortality among middle-aged and elderly Chinese.Methods Data were obtained from the China Health and Retirement Longitudinal Study(CHARLS)from 2011-2018.The ePWV was calculated using an equation that included age and mean blood pressure(MBP).The ΔePWV was assessed as the difference in ePWV between the first two waves.Cox proportional hazard models were used to determine the association between ePWV and ΔePWV with all-cause mortality after adjustment for potential confounders.Results Of 13,116 participants during a median follow-up of 7.0 years,1,356 deaths occurred.An increased ePWV was independently associated with all-cause mortality.The hazard ratio[95% confidence interval(CI)]for participants from the 1^(st)-4^(th) quartile groups was 1.00,1.69(1.31-2.18),3.09(2.44-3.91),and 8.54(6.78-10.75),respectively.Each standard deviation(SD)increment of ePWV increased the risk of all-cause mortality by 132%.Furthermore,theΔePWV was significantly associated with a 1.28-fold(95%CI,1.18-1.38)risk of all-cause mortality per SD increment.Conclusion This cohort study provided novel evidence from a Chinese population that an increased ePWV or progression of the ePWV was independently associated with all-cause mortality,which highlighted the importance of mitigating ePWV progression in clinical practice.
基金supported by the National Key R&D Program of China(No.2022YFB3904401)。
文摘Velocity incorporates user dynamic characteristics,facilitating more precise predictions about the positioning.However,the positioning,velocity,and timing services derived from Global Navigation Satellite System(GNSS)undergo accuracy degradation in urban environments due to multipath/Non-Line of Sight(NLOS)effects.Fault detection and exclusion(FDE)methods can mitigate these effects.However,the existing methods,such as the multi-hypothesis separation solution(MHSS),exhibit high computational burdens and cannot perform accurate exclusion due to the excessive fault modes.In response,a fault detection and correction(FDC)method is developed to address outliers arising from multipath/NLOS in the Doppler measurements.To alleviate computational demands while simultaneously improving velocity estimation accuracy,multipath/NLOS sparsity assumptions and grouping constraints are introduced.Specifically,the grouping-sparsity enforcing Least Absolute Shrinkage and Selection Operator(GS-LASSO)is introduced to jointly detect and correct multipath/NLOS-induced outliers.A grouping strategy based on sky-map and carrier-to-noise ratio is introduced,which is coupled with a new cost function to improve sparsity estimation.To facilitate the implementation,a solver and parameter-tuning method incorporating false alarm rates are developed.The performance of GS-LASSO is compared with that of MHSS.The results show that GS-LASSO reduces greater velocity errors in the urban environment,while requiring limited computational load.
基金supported by the National Magnetic Confinement Fusion Energy R&D Program of China(Nos.2022YFE03030001,2022YFE03020004 and 2022YFE 03050003)National Natural Science Foundation of China(Nos.12275310,11975275,12175277 and 11975271)+2 种基金the Science Foundation of Institute of Plasma Physics,Chinese Academy of Sciences(No.DSJJ-2021-01)the Collaborative Innovation Program of Hefei Science Center,Chinese Academy of Sciences(No.2021HSC-CIP019)the Users with Excellence Program of Hefei Science Center,Chinese Academy of Sciences(Nos.2021HSC-UE014 and 2021HSCUE012)。
文摘A gas puff imaging(GPI)diagnostic has been developed and operated on EAST since 2012,and the time-delay estimation(TDE)method is used to derive the propagation velocity of fluctuations from the two-dimensional GPI data.However,with the TDE method it is difficult to analyze the data with fast transient events,such as edge-localized mode(ELM).Consequently,a method called the spatial displacement estimation(SDE)algorithm is developed to estimate the turbulence velocity with high temporal resolution.Based on the SDE algorithm,we make some improvements,including an adaptive median filter and super-resolution technology.After the development of the algorithm,a straight-line movement and a curved-line movement are used to test the accuracy of the algorithm,and the calculated speed agrees well with preset speed.This SDE algorithm is applied to the EAST GPI data analysis,and the derived propagation velocity of turbulence is consistent with that from the TDE method,but with much higher temporal resolution.
基金Project(IRT0950)supported by the Cheung Kong Scholars and the Development Plan of Innovative Team,ChinaProject supported by China Scholarship Council
文摘An improved multidirectional velocity model was proposed for more accurately locating micro-seismic events in rock engineering. It was assumed that the stress wave propagation velocities from a micro-seismic source to three nearest monitoring sensors in a sensor's array arrangement were the same. Since the defined objective function does not require pre-measurement of the stress wave propagation velocity in the field, errors from the velocity measurement can be avoided in comparison to three traditional velocity models. By analyzing 24 different cases, the proposed multidirectional velocity model iterated by the Simplex method is found to be the best option no matter the source is within the region of the sensor's array or not. The proposed model and the adopted iterative algorithm are verified by field data and it is concluded that it can significantly reduce the error of the estimated source location.
文摘In the railway industry, re-adhesion control plays an important role in attenuating the slip occurrence due to the low adhesion condition in the wheel-rail inter- action. Braking and traction forces depend on the normal force and adhesion coefficient at the wheel-rail contact area. Due to the restrictions on controlling normal force, the only way to increase the tractive or braking effect is to maximize the adhesion coefficient. Through efficient uti- lization of adhesion, it is also possible to avoid wheel-rail wear and minimize the energy consumption. The adhesion between wheel and rail is a highly nonlinear function of many parameters like environmental conditions, railway vehicle speed and slip velocity. To estimate these unknown parameters accurately is a very hard and competitive challenge. The robust adaptive control strategy presented in this paper is not only able to suppress the wheel slip in time, but also maximize the adhesion utilization perfor- mance after re-adhesion process even if the wheel-rail contact mechanism exhibits significant adhesion uncer- tainties and/or nonlinearities. Using an optimal slip velocity seeking algorithm, the proposed strategy provides a satisfactory slip velocity tracking ability, which was demonstrated able to realize the desired slip velocity without experiencing any instability problem. The control torque of the traction motor was regulated continuously to drive the railway vehicle in the neighborhood of the opti- mal adhesion point and guarantee the best traction capacity after re-adhesion process by making the railway vehicle operate away from the unstable region. The results obtained from the adaptive approach based on the second- order sliding mode observer have been confirmed through theoretical analysis and numerical simulation conducted in MATLAB and Simulink with a full traction model under various wheel-rail conditions.
文摘Multi-azimuth walkaway vertical seismic profiling is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters.Normally,this technique requires the assumption of lateral homogeneity,which makes the horizontal slowness components at depths of downhole receivers equal to those measured at the surface.Any violations of this assumption,such as lateral heterogeneity or nonzero dip of intermediate interfaces,lead to distortions in reconstructed slowness surfaces and,consequently,to errors in estimated anisotropic parameters.In this work,we relax the assumption of lateral homogeneity and discuss how to correct vertical seismic profile data for weak lateral heterogeneity.We describe a procedure of downward continuation of recorded traveltimes that accounts for the presence of both vertical inhomogeneity and weak lateral heterogeneity,which produces correct slowness surfaces at depths of downhole receivers,noticing that sufficiently dense receiver coverage along a borehole is required to separate influences of vertical and lateral heterogeneity on measured traveltimes and obtain accurate estimates of the slowness surfaces.Once the slowness surfaces are found and a desired type of anisotropic model to be inverted is selected,the corresponding anisotropic parameters,providing the best fit to the estimated slownesses,can be obtained.We invert the slowness surfaces of P-waves for parameters of the simplest anisotropic model describing dipping fractures(transversely isotropic medium with a tilted symmetry axis).Five parameters of this model,namely,the P-wave velocity V0 in the direction of the symmetry axis,Thomsen's anisotropic coefficients e and d,the tilt n,and the azimuth b of the symmetry axis,can be estimated in a stable manner when maximum source offset is greater than half of receiver depth.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51975396)the Natural Science Foundation of Shanxi Province(Grant No.202103021224264).
文摘The error caused by irreversible demagnetization damages the accurate velocity tracking of an in-wheel motor in a mobile robot.A current feedforward vector control system based on ESO is proposed to compensate it for the demagnetization motor.A demagnetization mathematical model is established to describe a permanent magnet synchronous motor,which took the change of permanent magnet flux linkage parameters as a factor to count the demagnetization error in velocity tracking.The uncertain disturbance estimation model of the control system is built based on ESO,which eliminates the system error by the feedforward current compensation.It is compared with the vector control method in terms of control accuracy.The simulation results show that the current feedforward vector control method based on ESO reduces the velocity tracking error greatly in conditions of motor demagnetization less than 30%.It is effective to improve the operation accuracy of the mobile robot.
基金Supported by the Natural Science Foundation of Jiangxi Province(Grant No.20151BAB201010)the National Natural Science Foundation of China(Grant Nos.1150112511361004)
文摘In this paper,we consider the density-dependent magnetohydrodynamic equations with vacuum,and provide a regularity criterion involving the velocity and magnetic fields in Besov space of negative order,which improves[Jishan FAN,Fucai LI,G.NAKAMURA,Zhong TAN,Regularity criteria for the three-dimensional magnetohydrodynamic equations.J.Differential Equations,2014,256（8）：2858 2875]in some sense.The method is to establish a new bilinear estimate.
文摘High-frequency noise,often caused by system jitter and environmental factors,can obscure the true motion of particles.This study presents a Fourier transform-based particle velocity optimization framework designed to improve the accuracy of velocity estimation in particle tracking experiments.High-frequency noise,often caused by system jitter and environmental factors,can obscure the true motion of particles.To address this,we propose an adaptive low-pass filtering approach where the cutoff frequency is optimized through a numerical search algorithm to minimize the error between the filtered velocity and the ground truth trajectory.Our results demonstrate that an optimal cutoff frequency of approximately 1 Hz offers the best balance between noise reduction and signal preservation.The framework is further enhanced by its adaptability to different experimental conditions,making it applicable to a wide range of particle tracking scenarios.This approach offers a more effective solution for overcoming noise-related challenges in particle tracking,providing a valuable tool for precise motion analysis in various scientific fields.
