The operational demands of a wide range significantly exacerbate combustion instability issues within ramjet combustor.To suppress combustion oscillations,an open-loop control system utilizing Linear Genetic Programmi...The operational demands of a wide range significantly exacerbate combustion instability issues within ramjet combustor.To suppress combustion oscillations,an open-loop control system utilizing Linear Genetic Programming(LGP)has been developed for a full-scale annular ramjet combustor.The LGP is used to generate control laws that include multi-frequency forcing.These laws are then transformed into square waves to actuate the solenoid valve,which modulates the kerosene supply for open-loop control.The results show that the duty cycle has little effect on instability amplitude,whereas an increase in frequency leads to a remarked reduction in combustion amplitude.After five generations evolvements,the pressure amplitude is reduced by 40.6% under the optimal control law generated by LGP.Furthermore,the machine learning process is depicted using a proximity map of control law similarity,with the search pathway visualized by the steepest descent.All individuals go forward to the upper left corner of the map with the evolution process,terminating at the optimal individual of the fifth generation.展开更多
A prototype based on digital radio technology with associated open-loop Doppler signal processing techniques has been developed to measure a spacecraft's line-of-sight velocity. The prototype was tested in China&#...A prototype based on digital radio technology with associated open-loop Doppler signal processing techniques has been developed to measure a spacecraft's line-of-sight velocity. The prototype was tested in China's Chang'E-1 lunar mission relying on S-band telemetry signals transmitted by the sat-ellite,with results showing that the residuals had a RMS value of ～3 mm/s (1σ ) using 1-sec integration,which is consistent with the Chinese conventional USB (Unified S-Band) tracking system. Such preci-sion is mainly limited by the short-term stability of the atomic (e.g. rubidium) clock at the uplink ground station. It can also be improved with proper calibration to remove some effects of the transmission media (such as solar plasma,troposphere and ionosphere),and a longer integration time (e.g. down to 0.56 mm/s at 34 seconds) allowed by the spacecraft dynamics. The tracking accuracy can also be in-creased with differential methods that may effectively remove most of the long-term drifts and some of the short-term uncertainties of the uplink atomic clock,thereby further reducing the residuals to the 1 mm/s level. Our experimental tracking data have been used in orbit determination for Chang'E-1,while other applications (such as the upcoming YH-1 Mars orbiter) based on open-loop Doppler tracking will be initiated in the future. Successful application of the prototype to the Chang'E-1 mission in 2008 is believed to have great significance for China's future deep space exploration.展开更多
As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding...As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding scenarios.This paper discusses interferogram modeling and phase distortion cor-rection techniques for spaceborne DASH interferometers.The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted,and the effectiveness of the analytical expression was verified through numerical simulation.The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms.In contrast,the phase distortion correction algorithm can achieve effective correction.This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer,providing a feasible solution to enhance its measurement accuracy.展开更多
To address the issue of low measurement accuracy caused by noise interference in the acquisition of low fluid flow rate signals with ultrasonic Doppler flow meters,a novel signal processing algorithm that combines ens...To address the issue of low measurement accuracy caused by noise interference in the acquisition of low fluid flow rate signals with ultrasonic Doppler flow meters,a novel signal processing algorithm that combines ensemble empirical mode decomposition(EEMD)and cross-correlation algorithm was proposed.Firstly,a fast Fourier transform(FFT)spectrum analysis was utilized to ascertain the frequency range of the signal.Secondly,data acquisition was conducted at an appropriate sampling frequency,and the acquired Doppler flow rate signal was then decomposed into a series of intrinsic mode functions(IMFs)by EEMD.Subsequently,these decomposed IMFs were recombined based on their energy entropy,and then the noise of the recombined Doppler flow rate signal was removed by cross-correlation filtering.Finally,an ideal ultrasonic Doppler flow rate signal was extracted.Simulation and experimental verification show that the proposed Doppler flow signal processing method can effectively enhance the signal-to-noise ratio(SNR)and extend the lower limit of measurement of the ultrasonic Doppler flow meter.展开更多
This study discusses the scope of application of the Doppler backscattering(DBS)diagnostic for the tokamak with reactor technologies(TRT)project.This involved numerical modeling of the three-dimensional(3D)beam trajec...This study discusses the scope of application of the Doppler backscattering(DBS)diagnostic for the tokamak with reactor technologies(TRT)project.This involved numerical modeling of the three-dimensional(3D)beam trajectories.Calculations were performed to investigate the propagation of microwaves in the V(40–75 GHz)and W(75–110 GHz)frequency ranges with O-mode polarization for the density profile of the base TRT scenario.Our analysis showed that the DBS system antenna on the TRT would need to be tilted in both the poloidal and toroidal directions in order to meet the condition Kperp/Kpar<10%..For the DBS system located in the equatorial plane it was shown that a wide range of poloidal and toroidal angles is available for the successful implementation of the diagnostic to study the core,pedestal and scrape-off layer(SOL)regions.The DBS system located at 35 cm above the equatorial plane would be more limited in measurements only covering the SOL and pedestal regions.A shift of the cut-offs in the toroidal direction highlighted the need for 3D analysis of the DBS data.展开更多
Addressing issues such as the disconnect between theory and practice and low student engagement in control system education,this paper uses the course“The Working Process of Open-Loop Control Systems”as a case study...Addressing issues such as the disconnect between theory and practice and low student engagement in control system education,this paper uses the course“The Working Process of Open-Loop Control Systems”as a case study to explore the integration of AI technology with the“project-guided and task-driven”teaching model.By constructing a four-dimensional teaching framework of“situation-task-activity-evaluation,”AI tools are embedded in project practices such as the construction of a mechanical timed flower watering device and the optimization of a digital timed flower watering device,achieving precision,interactivity,and personalization in the teaching process.Teaching practice demonstrates that this model significantly enhances students’technical awareness,materialization capabilities,and engineering thinking,providing a reference for the teaching reform of technical courses in high school education.展开更多
Orthogonal time frequency space(OTFS)can resist the Doppler effect and guarantee reliable communication in high-speed scenarios.However,the Doppler rate induced by the relative acceleration between the transmitter and...Orthogonal time frequency space(OTFS)can resist the Doppler effect and guarantee reliable communication in high-speed scenarios.However,the Doppler rate induced by the relative acceleration between the transmitter and receiver degrades the performance of the OTFS.So far,the impact of the Doppler rate on OTFS systems has not been addressed.In this paper,we first introduce the Doppler rate in the OTFS system and derive the delay-Doppler domain input-output relation.In addition,the impact of the Doppler rate on the effective delay-Doppler domain channel is characterized by utilizing the first mean value theorem for definite integrals to avoid complicated integrals.To mitigate the effect of the Doppler rate,a large-scale antenna array is arranged at the receiver to separate each path of the multi-path channel through a high-resolution spatial matched filter beamformer.Next,the Doppler rate estimation scheme for an arbitrary order Doppler rate is proposed based on the successive interference cancellation pattern and the maximization of the spectrum of the ratio of high-order moments between the received samples in the identified branch and the transmitted samples.Finally,the estimation accuracy of the Doppler rate and the error performance of the proposed transceiver are validated by the numerical results.展开更多
The Doppler backscattering(DBS)diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures.Microwave is launched at a frequency that approaches a cutoff...The Doppler backscattering(DBS)diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures.Microwave is launched at a frequency that approaches a cutoff layer in the plasma at an angle oblique to the cutoff layer.A new Q-band multichannel DBS system based on a comb generator has been designed and tested for application on the HL-3 tokamak.With the comb generator and heterodyne scheme,the stability and flexibility of the new DBS system are improved.The new DBS diagnostic has a high output power(~10 dBm),good power flatness(<5 dB in Q-band),and frequency stability,and the inter-frequency separation is tunable remotely.This article introduces the system design,laboratory test results,and initial experimental results from the HL-3 tokamak.With the help of the newly developed multichannel DBS,the turbulence information can be studied with high temporal and spatial resolution.展开更多
Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting t...Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting their potential applications.Therefore,it is imperative to study the creation of lowfrequency signals using antennas with suitable dimensions.In contrast to conventional mechanical antenna techniques,our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect.We also defines the antenna array architecture,the timing sequency,and the radiating element signal waveform,and provides experimental prototypes including 8/64 antennas based on earlier research.In the conducted experiments,121 MHz,40 MHz,and 10 kHz composite signals are generated by 156 MHz radiating element signals.The composite signal spectrum matches the simulations,proving our low-frequency signal generating method works.This holds significant implications for research on generating low-frequency signals with small-sized antennas.展开更多
The fundamental physics of anomalous and normal Doppler resonances between electrons and electromagnetic(EM)waves is analyzed using a quantum model that incorporates angular-momentum conservation.This work extends pri...The fundamental physics of anomalous and normal Doppler resonances between electrons and electromagnetic(EM)waves is analyzed using a quantum model that incorporates angular-momentum conservation.This work extends prior theory by explicitly linking the resonant integer m to the EM wave's angular-momentum quantum number.Numerical simulations based on the volume-preserving algorithm(VPA)further confirm this correspondence.Moreover,a direct comparison of the energy-transfer ratio from translational energy to gyrokinetic energy during resonance,between classical dynamics and quantum predictions,is presented and verified numerically.展开更多
This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moo...This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moon and Mars).A novel autonomous navigation scheme is proposed that integrates laser Doppler velocimetry(LDV)with star trackers(ST)and inertial navigation system(INS).The scheme suppresses slip errors from wheel odometry through non-contact,high-precision laser speed measurement(accuracy better than 0.1%).By deeply fusing multi-source data via a Kalman filter algorithm,high-precision positioning is realized under extreme extraterrestrial conditions such as weak illumination and dust coverage.This solution features high accuracy,non-contact measurement,and anti-interference capabilities,significantly improving the navigation accuracy and autonomy of deep space rovers in complex environments.展开更多
Objective:To investigate the detection rate and sonographic characteristics of color Doppler ultrasound in the diagnosis of papillary thyroid microcarcinoma(PTMC).Methods:A retrospective analysis was conducted on 50 c...Objective:To investigate the detection rate and sonographic characteristics of color Doppler ultrasound in the diagnosis of papillary thyroid microcarcinoma(PTMC).Methods:A retrospective analysis was conducted on 50 cases of PTMC confirmed by postoperative pathology from January 2020 to December 2024,all of which underwent preoperative color Doppler ultrasound examination.The detection rate was calculated,and the two-dimensional ultrasound characteristics and CDFI manifestations were analyzed.Results:Among the 50 cases of PTMC confirmed by pathology,the detection rate of color Doppler ultrasound was 88.00%,and the diagnostic accuracy rate was 96.00%.Two-dimensional ultrasound characteristics:The mean lesion size was(6.83±1.51)mm;42 cases(84.00%)had irregular shapes;45 cases(90.00%)had unclear boundaries;46 cases(92.00%)had hypoechoic lesions;38 cases(76.00%)exhibited microcalcifications;and 40 cases(80.00%)had an aspect ratio≥1.CDFI characteristics:The highest proportion was grade Ⅱ,with 23 cases(46.00%);39 cases(78.00%)had an RI≥0.7,and the average RI value was(0.75±0.06).Conclusion:Color Doppler ultrasound demonstrates a high detection rate for PTMC,with typical features including hypoechogenicity,irregular shape,microcalcifications,and high RI,making it the preferred imaging modality for early clinical diagnosis of PTMC.展开更多
BACKGROUND Pre-eclampsia is a significant challenge in obstetric care and adversely affects the feto-maternal outcomes,causing significant perinatal morbidity and mortality.Early detection of women at higher risk of d...BACKGROUND Pre-eclampsia is a significant challenge in obstetric care and adversely affects the feto-maternal outcomes,causing significant perinatal morbidity and mortality.Early detection of women at higher risk of developing pre-eclampsia in the first trimester provides a vital opportunity to initiate timely prophylactic therapies.First-trimester uterine artery Doppler is gaining prominence as a promising tool in early risk stratification.AIM To assess the role of uterine artery Doppler in screening for pre-eclampsia at 11-14 weeks of gestation.METHODS Pregnant women attending routine antenatal care between 11 weeks and 14 weeks of gestation and undergoing first-trimester nuchal translucency screening were offered enrolment in the study.After calculating gestational age from the last menstrual period or fetal biometry(crown-rump length),Doppler ultrasound of bilateral uterine arteries was performed,and relevant Doppler parameters were recorded.Patients were followed until delivery for development of preeclampsia.RESULTS Out of a total of 342 participants,42 women(12.28%)developed preeclampsia,while the remaining 300 women(87.71%)had a normal pregnancy without preeclampsia.The mean uterine artery pulsatility index was significantly elevated in the pre-eclampsia group(1.9455±0.36)compared to the normal group(1.474±0.52)(P<0.001).Using a pulsatility index threshold of 1.622,the receiver operating characteristic curve analysis demonstrated a sensitivity of 75%(95%confidence internal:0.66-0.82),specificity of 86%(95%confidence internal:0.78-0.91),positive predictive value of 84.27%,and negative predictive value of 77.48%with a diagnostic accuracy of 80.5%.The area under the curve was 0.896,indicating good diagnostic performance.Uterine artery notching was observed in 88%of the pre-eclampsia group compared to 16%in the control group,a difference that was statistically significant(P<0.001).CONCLUSION Uterine artery Doppler in the first trimester at 11-14 weeks of gestation showed a good diagnostic value for forecasting the development of pre-eclampsia and holds promise as a valuable tool for early risk stratification.展开更多
Objective:To investigate the diagnostic value of transcranial Doppler ultrasound(TCD)in elderly patients with cerebrovascular disease and emotional disorder.Methods:Sixty-seven patients with cerebrovascular disease ag...Objective:To investigate the diagnostic value of transcranial Doppler ultrasound(TCD)in elderly patients with cerebrovascular disease and emotional disorder.Methods:Sixty-seven patients with cerebrovascular disease aged 60 years or above and with white matter hyperintensity(WMH)on magnetic resonance imaging(MRI)were enrolled in the study.The patients were divided into two groups according to Hamilton Depression Scale(HAMD)score:vascular depression group(WMH with depression)and non-depressive group(WMH without depression).TCD was performed in both groups,and the results of vascular pulsatility index(PI)and average blood flow velocity(Vm)were compared.Results:A total of 67 elderly patients were enrolled,with 33 cases in the vascular depression group and 34 in the non-depression group according to HAMD scores.(1)No statistically significant differences were observed between the two groups in age,gender,smoking history,alcohol consumption history,hypertension history,diabetes history,ischemic stroke history,hemorrhagic stroke history,coronary heart disease history,white matter score,and white matter grading(P>0.05).(2)The Vm on both sides of the anterior cerebral artery(ACA)and middle cerebral artery(MCA)in the vascular depression group was significantly lower than that in the non-depressive group(P<0.05).However,no statistically significant difference was found in Vm on both sides of the terminal internal carotid artery(TICA)between the two groups(P>0.05).(3)The PI on both sides of the ACA and MCA in the vascular depressive group was significantly higher than that in the non-depression group(P<0.05),while no statistically significant difference was observed in TICA PI values(P>0.05).(4)No statistically significant differences were found in Vm and PI values of the left ACA and MCA compared to the right side in the vascular depression group(P>0.05).Conclusion:The hemodynamic disturbance of vascular depression can be manifested as increased resistance and slowed flow velocity of intracranial small arteries.Transcranial Doppler ultrasound is a valuable method for dynamic evaluation and auxiliary diagnosis of vascular depression.展开更多
Patent foramen ovale(PFO)is a common congenital heart disorder associated with stroke,decompression sickness and migraine.Combining synchronized contrast transcranial Doppler with contrast transthoracic echocardiograp...Patent foramen ovale(PFO)is a common congenital heart disorder associated with stroke,decompression sickness and migraine.Combining synchronized contrast transcranial Doppler with contrast transthoracic echocardiography has important clinical significance and can improve the accuracy of detecting right-left shunts(RLSs)in patients with PFO.In this letter,regarding an original study presented by Yao et al,we present our insights and discuss how to better help clinicians evaluate changes in PFO-related RLS.展开更多
The research on ocean dynamics information plays a crucial role in understanding ocean phenomena, assessing marine environmental impacts, and guiding engineering designs. The Doppler information observed by radars ref...The research on ocean dynamics information plays a crucial role in understanding ocean phenomena, assessing marine environmental impacts, and guiding engineering designs. The Doppler information observed by radars reflects sea surface dynamics, to which ocean waves make important contributions. Low-incidence-angle real aperture radar(RAR)demonstrates great potential for independently observing vectorial Doppler information on the ocean surface. To systematically characterize and accurately estimate the wave-induced Doppler frequency shift(WVF) from lowincidence-angle RAR, this study conducts comprehensive influencing factor analysis and establishes sea-stateparameterized WVF models. First, a simulated WVF dataset is generated under a rotating low-incidence-angle RAR.The feature parameters of WVF are then determined by analysing contributing factors including wind waves, swells,and sea state parameters. Furthermore, two WVF models(WVF_Ku P9 with 9 inputs and WVF_Ku P4 with 4 inputs) are constructed by the Transformer encoder for different application scenarios. Both models achieve high accuracy for WVF estimation with root mean square errors(RMSE) of 1.874 Hz and 2.716 Hz, respectively. The reliability and superiority of the proposed models are validated through comparisons with the Ka DOP, which is a typical geophysical model function(GMF). The findings in this paper advance the understanding of WVF characteristics and generation mechanisms. The proposed estimation models can provide reliable estimates, offering critical references for lowincidence-angle RAR applications such as ocean surface current retrieval.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
Objective:To investigate the evaluation value of cardiac color Doppler echocardiography(CDE)in assessing poor prognosis in patients with coronary atherosclerotic heart disease(CAD).Methods:A retrospective review was c...Objective:To investigate the evaluation value of cardiac color Doppler echocardiography(CDE)in assessing poor prognosis in patients with coronary atherosclerotic heart disease(CAD).Methods:A retrospective review was conducted of 106 patients with coronary artery disease(CAD)who were treated in the hospital’s cardiovascular department between January 2023 and June 2024.All participants received baseline comprehensive Doppler echocardiography(CDE)assessments.Based on whether they experienced a Major Adverse Cardiovascular Event(MACE)within one year of follow-up,the patients were categorized into either a MACE group or a non-MACE group.The study compared baseline clinical information and CDE parameters,specifically left ventricular ejection fraction(LVEF),wall motion score index(WMSI),and mitral annular E/e’ratio,between the two groups.Independent predictors of MACE were identified using multivariate logistic regression analysis.Results:A total of 29 out of the 106 patients experienced MACE during the oneyear follow-up.Compared with the non-MACE group,the MACE group had a higher prevalence of diabetes mellitus.In terms of CDE parameters,the MACE group had a lower LVEF than the non-MACE group(p<0.05),while WMSI,average E/e’,pulmonary artery systolic pressure(PASP),and mitral regurgitation(MR)proportion were all higher in the MACE group than in the non-MACE group(p<0.05).Multifactor logistic regression analysis revealed that after adjusting for confounding factors such as diabetes,WMSI(OR=3.003,95%CI:1.226–7.356,p=0.016)and mean E/e’(OR=1.281,95%CI:1.006–1.539,p=0.008)were independent predictors of the occurrence of major adverse cardiovascular events(MACE).Conclusion:WMSI and E/e’diagnosed by color Doppler echocardiography(CDE)hold significant and independent assessment value for predicting poor prognosis in patients with coronary artery disease(CAD).展开更多
基金support from the National Natural Science Foundation of China(No.12002372)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology(No.2022QNRC001)the Natural Science Foundation of Hunan Province,China(No.2021JJ40674)。
文摘The operational demands of a wide range significantly exacerbate combustion instability issues within ramjet combustor.To suppress combustion oscillations,an open-loop control system utilizing Linear Genetic Programming(LGP)has been developed for a full-scale annular ramjet combustor.The LGP is used to generate control laws that include multi-frequency forcing.These laws are then transformed into square waves to actuate the solenoid valve,which modulates the kerosene supply for open-loop control.The results show that the duty cycle has little effect on instability amplitude,whereas an increase in frequency leads to a remarked reduction in combustion amplitude.After five generations evolvements,the pressure amplitude is reduced by 40.6% under the optimal control law generated by LGP.Furthermore,the machine learning process is depicted using a proximity map of control law similarity,with the search pathway visualized by the steepest descent.All individuals go forward to the upper left corner of the map with the evolution process,terminating at the optimal individual of the fifth generation.
基金Supported by the Innovation Research Plan of CAS,the National Natural Science Foundation of China (Grant Nos. 10973031 and 40904006)the CAS Key Research Program (Grant No. KJCX2-YW-T13-2), and Beijing Aerospace Command and Control Center
文摘A prototype based on digital radio technology with associated open-loop Doppler signal processing techniques has been developed to measure a spacecraft's line-of-sight velocity. The prototype was tested in China's Chang'E-1 lunar mission relying on S-band telemetry signals transmitted by the sat-ellite,with results showing that the residuals had a RMS value of ～3 mm/s (1σ ) using 1-sec integration,which is consistent with the Chinese conventional USB (Unified S-Band) tracking system. Such preci-sion is mainly limited by the short-term stability of the atomic (e.g. rubidium) clock at the uplink ground station. It can also be improved with proper calibration to remove some effects of the transmission media (such as solar plasma,troposphere and ionosphere),and a longer integration time (e.g. down to 0.56 mm/s at 34 seconds) allowed by the spacecraft dynamics. The tracking accuracy can also be in-creased with differential methods that may effectively remove most of the long-term drifts and some of the short-term uncertainties of the uplink atomic clock,thereby further reducing the residuals to the 1 mm/s level. Our experimental tracking data have been used in orbit determination for Chang'E-1,while other applications (such as the upcoming YH-1 Mars orbiter) based on open-loop Doppler tracking will be initiated in the future. Successful application of the prototype to the Chang'E-1 mission in 2008 is believed to have great significance for China's future deep space exploration.
文摘As an advanced device for observing atmospheric winds,the spaceborne Doppler Asymmetric Spatial Heterodyne(DASH)interferometer also encounters challenges associated with phase distortion,par-ticularly in limb sounding scenarios.This paper discusses interferogram modeling and phase distortion cor-rection techniques for spaceborne DASH interferometers.The modeling of phase distortion interferograms with and without Doppler shift for limb observation was conducted,and the effectiveness of the analytical expression was verified through numerical simulation.The simulation results indicate that errors propagate layer by layer while using the onion-peeling inversion algorithm to handle phase-distorted interferograms.In contrast,the phase distortion correction algorithm can achieve effective correction.This phase correction method can be successfully applied to correct phase distortions in the interferograms of the spaceborne DASH interferometer,providing a feasible solution to enhance its measurement accuracy.
基金supported by National Natural Science Foundation of China(No.61973234)Tianjin Science and Technology Plan Project(No.22YDTPJC00090)。
文摘To address the issue of low measurement accuracy caused by noise interference in the acquisition of low fluid flow rate signals with ultrasonic Doppler flow meters,a novel signal processing algorithm that combines ensemble empirical mode decomposition(EEMD)and cross-correlation algorithm was proposed.Firstly,a fast Fourier transform(FFT)spectrum analysis was utilized to ascertain the frequency range of the signal.Secondly,data acquisition was conducted at an appropriate sampling frequency,and the acquired Doppler flow rate signal was then decomposed into a series of intrinsic mode functions(IMFs)by EEMD.Subsequently,these decomposed IMFs were recombined based on their energy entropy,and then the noise of the recombined Doppler flow rate signal was removed by cross-correlation filtering.Finally,an ideal ultrasonic Doppler flow rate signal was extracted.Simulation and experimental verification show that the proposed Doppler flow signal processing method can effectively enhance the signal-to-noise ratio(SNR)and extend the lower limit of measurement of the ultrasonic Doppler flow meter.
基金financial support of the Ministry of Science and Higher Education of the Russian Federation in the framework of the state contract in the field of science(No.FSEG-2024-0005)。
文摘This study discusses the scope of application of the Doppler backscattering(DBS)diagnostic for the tokamak with reactor technologies(TRT)project.This involved numerical modeling of the three-dimensional(3D)beam trajectories.Calculations were performed to investigate the propagation of microwaves in the V(40–75 GHz)and W(75–110 GHz)frequency ranges with O-mode polarization for the density profile of the base TRT scenario.Our analysis showed that the DBS system antenna on the TRT would need to be tilted in both the poloidal and toroidal directions in order to meet the condition Kperp/Kpar<10%..For the DBS system located in the equatorial plane it was shown that a wide range of poloidal and toroidal angles is available for the successful implementation of the diagnostic to study the core,pedestal and scrape-off layer(SOL)regions.The DBS system located at 35 cm above the equatorial plane would be more limited in measurements only covering the SOL and pedestal regions.A shift of the cut-offs in the toroidal direction highlighted the need for 3D analysis of the DBS data.
文摘Addressing issues such as the disconnect between theory and practice and low student engagement in control system education,this paper uses the course“The Working Process of Open-Loop Control Systems”as a case study to explore the integration of AI technology with the“project-guided and task-driven”teaching model.By constructing a four-dimensional teaching framework of“situation-task-activity-evaluation,”AI tools are embedded in project practices such as the construction of a mechanical timed flower watering device and the optimization of a digital timed flower watering device,achieving precision,interactivity,and personalization in the teaching process.Teaching practice demonstrates that this model significantly enhances students’technical awareness,materialization capabilities,and engineering thinking,providing a reference for the teaching reform of technical courses in high school education.
基金supported in part by the Fundamental Research Funds for the Central Universities under Grant No.2022JBQY004the National Natural Science Foundation of China under Grant Nos.62471026 and 62221001+3 种基金the Zhongguancun Xin Xi Disruptive Technology Innovation Foundation under Grant No.ZZ-2024-001the Joint Funds for Railway Fundamental Research of National Natural Science Foundation of China under Grant No.U2368201the Postdoctoral Fellowship Program and China Postdoctoral Science Foundation BX20240471ZTE Industry-University-Institute Cooperation Funds under Grant No.HC-CN-03-2019-12。
文摘Orthogonal time frequency space(OTFS)can resist the Doppler effect and guarantee reliable communication in high-speed scenarios.However,the Doppler rate induced by the relative acceleration between the transmitter and receiver degrades the performance of the OTFS.So far,the impact of the Doppler rate on OTFS systems has not been addressed.In this paper,we first introduce the Doppler rate in the OTFS system and derive the delay-Doppler domain input-output relation.In addition,the impact of the Doppler rate on the effective delay-Doppler domain channel is characterized by utilizing the first mean value theorem for definite integrals to avoid complicated integrals.To mitigate the effect of the Doppler rate,a large-scale antenna array is arranged at the receiver to separate each path of the multi-path channel through a high-resolution spatial matched filter beamformer.Next,the Doppler rate estimation scheme for an arbitrary order Doppler rate is proposed based on the successive interference cancellation pattern and the maximization of the spectrum of the ratio of high-order moments between the received samples in the identified branch and the transmitted samples.Finally,the estimation accuracy of the Doppler rate and the error performance of the proposed transceiver are validated by the numerical results.
基金supported by National Natural Science Foundation of China(Nos.12105087,12275096,and 11922503)the Joint Funds of the National Natural Science Foundation of China(No.U21A20440)the Science and Technology Planning Project of Sichuan Province(No.2023YFG0139)。
文摘The Doppler backscattering(DBS)diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures.Microwave is launched at a frequency that approaches a cutoff layer in the plasma at an angle oblique to the cutoff layer.A new Q-band multichannel DBS system based on a comb generator has been designed and tested for application on the HL-3 tokamak.With the comb generator and heterodyne scheme,the stability and flexibility of the new DBS system are improved.The new DBS diagnostic has a high output power(~10 dBm),good power flatness(<5 dB in Q-band),and frequency stability,and the inter-frequency separation is tunable remotely.This article introduces the system design,laboratory test results,and initial experimental results from the HL-3 tokamak.With the help of the newly developed multichannel DBS,the turbulence information can be studied with high temporal and spatial resolution.
基金Science and Technology Project of Aerospace Information Research Institute,Chinese Academy of Sciences(Y910340Z2F)Science and Technology Project of BBEF(E3E2010201)。
文摘Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting their potential applications.Therefore,it is imperative to study the creation of lowfrequency signals using antennas with suitable dimensions.In contrast to conventional mechanical antenna techniques,our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect.We also defines the antenna array architecture,the timing sequency,and the radiating element signal waveform,and provides experimental prototypes including 8/64 antennas based on earlier research.In the conducted experiments,121 MHz,40 MHz,and 10 kHz composite signals are generated by 156 MHz radiating element signals.The composite signal spectrum matches the simulations,proving our low-frequency signal generating method works.This holds significant implications for research on generating low-frequency signals with small-sized antennas.
基金supported by the National Magnetic Confinement Fusion Energy Program of China(Grant No.2019YFE03020001)。
文摘The fundamental physics of anomalous and normal Doppler resonances between electrons and electromagnetic(EM)waves is analyzed using a quantum model that incorporates angular-momentum conservation.This work extends prior theory by explicitly linking the resonant integer m to the EM wave's angular-momentum quantum number.Numerical simulations based on the volume-preserving algorithm(VPA)further confirm this correspondence.Moreover,a direct comparison of the energy-transfer ratio from translational energy to gyrokinetic energy during resonance,between classical dynamics and quantum predictions,is presented and verified numerically.
文摘This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moon and Mars).A novel autonomous navigation scheme is proposed that integrates laser Doppler velocimetry(LDV)with star trackers(ST)and inertial navigation system(INS).The scheme suppresses slip errors from wheel odometry through non-contact,high-precision laser speed measurement(accuracy better than 0.1%).By deeply fusing multi-source data via a Kalman filter algorithm,high-precision positioning is realized under extreme extraterrestrial conditions such as weak illumination and dust coverage.This solution features high accuracy,non-contact measurement,and anti-interference capabilities,significantly improving the navigation accuracy and autonomy of deep space rovers in complex environments.
文摘Objective:To investigate the detection rate and sonographic characteristics of color Doppler ultrasound in the diagnosis of papillary thyroid microcarcinoma(PTMC).Methods:A retrospective analysis was conducted on 50 cases of PTMC confirmed by postoperative pathology from January 2020 to December 2024,all of which underwent preoperative color Doppler ultrasound examination.The detection rate was calculated,and the two-dimensional ultrasound characteristics and CDFI manifestations were analyzed.Results:Among the 50 cases of PTMC confirmed by pathology,the detection rate of color Doppler ultrasound was 88.00%,and the diagnostic accuracy rate was 96.00%.Two-dimensional ultrasound characteristics:The mean lesion size was(6.83±1.51)mm;42 cases(84.00%)had irregular shapes;45 cases(90.00%)had unclear boundaries;46 cases(92.00%)had hypoechoic lesions;38 cases(76.00%)exhibited microcalcifications;and 40 cases(80.00%)had an aspect ratio≥1.CDFI characteristics:The highest proportion was grade Ⅱ,with 23 cases(46.00%);39 cases(78.00%)had an RI≥0.7,and the average RI value was(0.75±0.06).Conclusion:Color Doppler ultrasound demonstrates a high detection rate for PTMC,with typical features including hypoechogenicity,irregular shape,microcalcifications,and high RI,making it the preferred imaging modality for early clinical diagnosis of PTMC.
文摘BACKGROUND Pre-eclampsia is a significant challenge in obstetric care and adversely affects the feto-maternal outcomes,causing significant perinatal morbidity and mortality.Early detection of women at higher risk of developing pre-eclampsia in the first trimester provides a vital opportunity to initiate timely prophylactic therapies.First-trimester uterine artery Doppler is gaining prominence as a promising tool in early risk stratification.AIM To assess the role of uterine artery Doppler in screening for pre-eclampsia at 11-14 weeks of gestation.METHODS Pregnant women attending routine antenatal care between 11 weeks and 14 weeks of gestation and undergoing first-trimester nuchal translucency screening were offered enrolment in the study.After calculating gestational age from the last menstrual period or fetal biometry(crown-rump length),Doppler ultrasound of bilateral uterine arteries was performed,and relevant Doppler parameters were recorded.Patients were followed until delivery for development of preeclampsia.RESULTS Out of a total of 342 participants,42 women(12.28%)developed preeclampsia,while the remaining 300 women(87.71%)had a normal pregnancy without preeclampsia.The mean uterine artery pulsatility index was significantly elevated in the pre-eclampsia group(1.9455±0.36)compared to the normal group(1.474±0.52)(P<0.001).Using a pulsatility index threshold of 1.622,the receiver operating characteristic curve analysis demonstrated a sensitivity of 75%(95%confidence internal:0.66-0.82),specificity of 86%(95%confidence internal:0.78-0.91),positive predictive value of 84.27%,and negative predictive value of 77.48%with a diagnostic accuracy of 80.5%.The area under the curve was 0.896,indicating good diagnostic performance.Uterine artery notching was observed in 88%of the pre-eclampsia group compared to 16%in the control group,a difference that was statistically significant(P<0.001).CONCLUSION Uterine artery Doppler in the first trimester at 11-14 weeks of gestation showed a good diagnostic value for forecasting the development of pre-eclampsia and holds promise as a valuable tool for early risk stratification.
文摘Objective:To investigate the diagnostic value of transcranial Doppler ultrasound(TCD)in elderly patients with cerebrovascular disease and emotional disorder.Methods:Sixty-seven patients with cerebrovascular disease aged 60 years or above and with white matter hyperintensity(WMH)on magnetic resonance imaging(MRI)were enrolled in the study.The patients were divided into two groups according to Hamilton Depression Scale(HAMD)score:vascular depression group(WMH with depression)and non-depressive group(WMH without depression).TCD was performed in both groups,and the results of vascular pulsatility index(PI)and average blood flow velocity(Vm)were compared.Results:A total of 67 elderly patients were enrolled,with 33 cases in the vascular depression group and 34 in the non-depression group according to HAMD scores.(1)No statistically significant differences were observed between the two groups in age,gender,smoking history,alcohol consumption history,hypertension history,diabetes history,ischemic stroke history,hemorrhagic stroke history,coronary heart disease history,white matter score,and white matter grading(P>0.05).(2)The Vm on both sides of the anterior cerebral artery(ACA)and middle cerebral artery(MCA)in the vascular depression group was significantly lower than that in the non-depressive group(P<0.05).However,no statistically significant difference was found in Vm on both sides of the terminal internal carotid artery(TICA)between the two groups(P>0.05).(3)The PI on both sides of the ACA and MCA in the vascular depressive group was significantly higher than that in the non-depression group(P<0.05),while no statistically significant difference was observed in TICA PI values(P>0.05).(4)No statistically significant differences were found in Vm and PI values of the left ACA and MCA compared to the right side in the vascular depression group(P>0.05).Conclusion:The hemodynamic disturbance of vascular depression can be manifested as increased resistance and slowed flow velocity of intracranial small arteries.Transcranial Doppler ultrasound is a valuable method for dynamic evaluation and auxiliary diagnosis of vascular depression.
文摘Patent foramen ovale(PFO)is a common congenital heart disorder associated with stroke,decompression sickness and migraine.Combining synchronized contrast transcranial Doppler with contrast transthoracic echocardiography has important clinical significance and can improve the accuracy of detecting right-left shunts(RLSs)in patients with PFO.In this letter,regarding an original study presented by Yao et al,we present our insights and discuss how to better help clinicians evaluate changes in PFO-related RLS.
基金The National Natural Science Foundation of China under contract No. 42274159the Project supported by Key Laboratory of Space Ocean Remote Sensing and Application,MNR under contract No.2023CFO016。
文摘The research on ocean dynamics information plays a crucial role in understanding ocean phenomena, assessing marine environmental impacts, and guiding engineering designs. The Doppler information observed by radars reflects sea surface dynamics, to which ocean waves make important contributions. Low-incidence-angle real aperture radar(RAR)demonstrates great potential for independently observing vectorial Doppler information on the ocean surface. To systematically characterize and accurately estimate the wave-induced Doppler frequency shift(WVF) from lowincidence-angle RAR, this study conducts comprehensive influencing factor analysis and establishes sea-stateparameterized WVF models. First, a simulated WVF dataset is generated under a rotating low-incidence-angle RAR.The feature parameters of WVF are then determined by analysing contributing factors including wind waves, swells,and sea state parameters. Furthermore, two WVF models(WVF_Ku P9 with 9 inputs and WVF_Ku P4 with 4 inputs) are constructed by the Transformer encoder for different application scenarios. Both models achieve high accuracy for WVF estimation with root mean square errors(RMSE) of 1.874 Hz and 2.716 Hz, respectively. The reliability and superiority of the proposed models are validated through comparisons with the Ka DOP, which is a typical geophysical model function(GMF). The findings in this paper advance the understanding of WVF characteristics and generation mechanisms. The proposed estimation models can provide reliable estimates, offering critical references for lowincidence-angle RAR applications such as ocean surface current retrieval.
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.
文摘Objective:To investigate the evaluation value of cardiac color Doppler echocardiography(CDE)in assessing poor prognosis in patients with coronary atherosclerotic heart disease(CAD).Methods:A retrospective review was conducted of 106 patients with coronary artery disease(CAD)who were treated in the hospital’s cardiovascular department between January 2023 and June 2024.All participants received baseline comprehensive Doppler echocardiography(CDE)assessments.Based on whether they experienced a Major Adverse Cardiovascular Event(MACE)within one year of follow-up,the patients were categorized into either a MACE group or a non-MACE group.The study compared baseline clinical information and CDE parameters,specifically left ventricular ejection fraction(LVEF),wall motion score index(WMSI),and mitral annular E/e’ratio,between the two groups.Independent predictors of MACE were identified using multivariate logistic regression analysis.Results:A total of 29 out of the 106 patients experienced MACE during the oneyear follow-up.Compared with the non-MACE group,the MACE group had a higher prevalence of diabetes mellitus.In terms of CDE parameters,the MACE group had a lower LVEF than the non-MACE group(p<0.05),while WMSI,average E/e’,pulmonary artery systolic pressure(PASP),and mitral regurgitation(MR)proportion were all higher in the MACE group than in the non-MACE group(p<0.05).Multifactor logistic regression analysis revealed that after adjusting for confounding factors such as diabetes,WMSI(OR=3.003,95%CI:1.226–7.356,p=0.016)and mean E/e’(OR=1.281,95%CI:1.006–1.539,p=0.008)were independent predictors of the occurrence of major adverse cardiovascular events(MACE).Conclusion:WMSI and E/e’diagnosed by color Doppler echocardiography(CDE)hold significant and independent assessment value for predicting poor prognosis in patients with coronary artery disease(CAD).
