Predicting the time-varying auto-spectral density of a spacecraft in high-altitude orbits requires an accurate model for the non-stationary random vibration signals with densely spaced modal frequency. The traditional...Predicting the time-varying auto-spectral density of a spacecraft in high-altitude orbits requires an accurate model for the non-stationary random vibration signals with densely spaced modal frequency. The traditional time-varying algorithm limits prediction accuracy, thus affecting a number of operational decisions. To solve this problem, a time-varying auto regressive （TVAR） model based on the process neural network （PNN） and the empirical mode decomposition （EMD） is proposed. The time-varying system is tracked on-line by establishing a time-varying parameter model, and then the relevant parameter spectrum is obtained. Firstly, the EMD method is utilized to decompose the signal into several intrinsic mode functions （IMFs）. Then for each IMF, the PNN is established and the time-varying auto-spectral density is obtained. Finally, the time-frequency distribution of the signals can be reconstructed by linear superposition. The simulation and the analytical results from an example demonstrate that this approach possesses simplicity, effectiveness, and feasibility, as well as higher frequency resolution.展开更多
The interrupted sampling repeater jamming（ISRJ） is an effective deception jamming method for coherent radar, especially for the wideband linear frequency modulation（LFM） radar. An electronic counter-countermeasure...The interrupted sampling repeater jamming（ISRJ） is an effective deception jamming method for coherent radar, especially for the wideband linear frequency modulation（LFM） radar. An electronic counter-countermeasure（ECCM） scheme is proposed to remove the ISRJ-based false targets from the pulse compression result of the de-chirping radar. Through the time-frequency（TF） analysis of the radar echo signal, it can be found that the TF characteristics of the ISRJ signal are discontinuous in the pulse duration because the ISRJ jammer needs short durations to receive the radar signal. Based on the discontinuous characteristics a particular band-pass filter can be generated by two alternative approaches to retain the true target signal and suppress the ISRJ signal. The simulation results prove the validity of the proposed ECCM scheme for the ISRJ.展开更多
The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new meth...The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform(SR-ST)is presented to improve the stability and accuracy of Q estimation.The variable window of ST is used to solve the time window problem.We add two window factors to the Gaussian window function in the ST.The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal,which reduces the calculation error attributed to the conventional Gaussian window function.Meanwhile,the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy.First,the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments.Second,artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method.Finally,a further comparison between the new method and the conventional spectral ratio method(SR)is conducted using rock field samples,again addressing stability and accuracy.The experimental results show that this method will yield an error of approximately 36%using the conventional Gaussian window function.This problem can be solved by adding the time window factors to the Gaussian window function.The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation(Q>15)is less than 10%.展开更多
A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequ...A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequency extraction becomes curve detection in the image-view. A set of morphological operations are used to implement curve detection. And a map fusion scheme is presented to eliminate the influence of strong direct current （DC） component of echo signal during curve detection. The radar real-life data are used to illustrate the performance of the new approach. Experimental results show that the proposed method can overcome the shortcomings of piecewise-processing-based FFT method and can improve the measuring precision of miss distance.展开更多
Li transient concentration distribution in spherical active material particles can affect the maximum power density and the safe operating regime of the electric vehicles(EVs). On one hand, the quasiexact/exact soluti...Li transient concentration distribution in spherical active material particles can affect the maximum power density and the safe operating regime of the electric vehicles(EVs). On one hand, the quasiexact/exact solution obtained in the time/frequency domain is time-consuming and just as a reference value for approximate solutions;on the other hand, calculation errors and application range of approximate solutions not only rely on approximate algorithms but also on discharge modes. For the purpose to track the transient dynamics for Li solid-phase diffusion in spherical active particles with a tolerable error range and for a wide applicable range, it is necessary to choose optimal approximate algorithms in terms of discharge modes and the nature of active material particles. In this study, approximation methods,such as diffusion length method, polynomial profile approximation method, Padé approximation method,pseudo steady state method, eigenfunction-based Galerkin collocation method, and separation of variables method for solving Li solid-phase diffusion in spherical active particles are compared from calculation fundamentals to algorithm implementation. Furthermore, these approximate solutions are quantitatively compared to the quasi-exact/exact solution in the time/frequency domain under typical discharge modes, i.e., start-up, slow-down, and speed-up. The results obtained from the viewpoint of time-frequency analysis offer a theoretical foundation on how to track Li transient concentration profile in spherical active particles with a high precision and for a wide application range. In turn, optimal solutions of Li solid diffusion equations for spherical active particles can improve the reliability in predicting safe operating regime and estimating maximum power for automotive batteries.展开更多
Multi-radar signal separation is a critical process in modern reconnaissance systems. However, the complicated battlefield is typically confronted with increasing electronic equipment and complex radar waveforms. The ...Multi-radar signal separation is a critical process in modern reconnaissance systems. However, the complicated battlefield is typically confronted with increasing electronic equipment and complex radar waveforms. The intercepted signal is difficult to separate with conventional parameters because of severe overlapping in both time and frequency domains. On the contrary, time-frequency analysis maps the 1D signal into a 2D time-frequency plane, which provides a better insight into the signal than traditional methods. Particularly, the parameterized time-frequency analysis (PTFA) shows great potential in processing such non stationary signals. Five procedures for the PTFA are proposed to separate the overlapped multi-radar signal, including initiation, instantaneous frequency estimation with PTFA, signal demodulation, signal separation with adaptive filter and signal recovery. The proposed method is verified with both simulated and real signals, which shows good performance in the application on multi-radar signal separation.展开更多
The conventional linear time-frequency analysis method cannot achieve high resolution and energy focusing in the time and frequency dimensions at the same time,especially in the low frequency region.In order to improv...The conventional linear time-frequency analysis method cannot achieve high resolution and energy focusing in the time and frequency dimensions at the same time,especially in the low frequency region.In order to improve the resolution of the linear time-frequency analysis method in the low-frequency region,we have proposed a W transform method,in which the instantaneous frequency is introduced as a parameter into the linear transformation,and the analysis time window is constructed which matches the instantaneous frequency of the seismic data.In this paper,the W transform method is compared with the Wigner-Ville distribution(WVD),a typical nonlinear time-frequency analysis method.The WVD method that shows the energy distribution in the time-frequency domain clearly indicates the gravitational center of time and the gravitational center of frequency of a wavelet,while the time-frequency spectrum of the W transform also has a clear gravitational center of energy focusing,because the instantaneous frequency corresponding to any time position is introduced as the transformation parameter.Therefore,the W transform can be benchmarked directly by the WVD method.We summarize the development of the W transform and three improved methods in recent years,and elaborate on the evolution of the standard W transform,the chirp-modulated W transform,the fractional-order W transform,and the linear canonical W transform.Through three application examples of W transform in fluvial sand body identification and reservoir prediction,it is verified that W transform can improve the resolution and energy focusing of time-frequency spectra.展开更多
Recent advances in electronics have increased the complexity of radar signal modulation.The quasi-linear frequency modulation(quasi-LFM)radar waveforms(LFM,Frank code,P1−P4 code)have similar time-frequency distributio...Recent advances in electronics have increased the complexity of radar signal modulation.The quasi-linear frequency modulation(quasi-LFM)radar waveforms(LFM,Frank code,P1−P4 code)have similar time-frequency distributions,and it is difficult to identify such signals using traditional time-frequency analysis methods.To solve this problem,this paper proposes an algorithm for automatic recognition of quasi-LFM radar waveforms based on fractional Fourier transform and time-frequency analysis.First of all,fractional Fourier transform and the Wigner-Ville distribution(WVD)are used to determine the number of main ridgelines and the tilt angle of the target component in WVD.Next,the standard deviation of the target component's width in the signal's WVD is calculated.Finally,an assembled classifier using neural network is built to recognize different waveforms by automatically combining the three features.Simulation results show that the overall recognition rate of the proposed algorithm reaches 94.17%under 0 dB.When the training data set and the test data set are mixed with noise,the recognition rate reaches 89.93%.The best recognition accuracy is achieved when the size of the training set is taken as 400.The algorithm complexity can meet the requirements of real-time recognition.展开更多
Climate change and environmental degradation threaten the world and global economic conditions.As one of countries’most important economic components,the financial sector might be an effective tool for reducing and e...Climate change and environmental degradation threaten the world and global economic conditions.As one of countries’most important economic components,the financial sector might be an effective tool for reducing and even reversing environmental degradation.The financial sector can affect sustainability through its lending and investment practices.The sector can play a role in financing sustainable projects and businesses,helping reduce CO_(2) emissions.By aligning its financial objectives with environmental protection,the financial sector can support the transition to a more sustainable future by helping reduce environmental degradation’s negative impacts.This paper examines the domestic financial sector’s impact on CO_(2) emissions in the United States over the 1990:Q1–2022:Q3 period.In this research,the nexus between the domestic financial sector(total debt securities,loans,liabilities,and total financial assets)and Carbon dioxide emissions in the U.S.is investigated by Morlet wavelet analysis.Rest of the world:sector discrepancy transactions,rest of the world:debt securities and loans,gross domestic product,and the square of the gross domestic product,are control variables in the estimated models.Partial wavelet coherency analyses prove that the financial sector reduces CO_(2) emissions at the 5–8-year frequency band during different subsample periods.The financial sector’s instruments can be effective in struggling with climate change.展开更多
In this study,we report an analysis of cylinder head vibration signals at a steady engine speed using short-time Fourier transform(STFT).Three popular time-frequency analysis techniques,i.e.,STFT,analytic wavelet tran...In this study,we report an analysis of cylinder head vibration signals at a steady engine speed using short-time Fourier transform(STFT).Three popular time-frequency analysis techniques,i.e.,STFT,analytic wavelet transform(AWT) and S transform(ST),have been examined.AWT and ST are often applied in engine signal analyses.In particular,an AWT expression in terms of the quality factor Q and an analytical relationship between ST and AWT have been derived.The time-frequency resolution of a Gaussian function windowed STFT was studied via numerical simulation.Based on the simulation,the empirical limits for the lowest distinguishable frequency as well as the time and frequency resolutions were determined.These can provide insights for window width selection,spectrogram interpretation and artifact identification.Gaussian function windowed STFTs were applied to some cylinder head vibration signals.The spectrograms of the same signals from ST and AWT were also determined for comparison.The results indicate that the uniform resolution feature of STFT is not necessarily a disadvantage for time-frequency analysis of vibration signals when the engine is in stationary state because it can more accurately localize the frequency components excited by transient excitations without much loss of time resolution.展开更多
Focused on the non-statlonarity and real-time analysis of signal in flutter test with progression variable speed （FTPVS）, a new method of recursive time-frequency analysis is presented. The time-varying system is tr...Focused on the non-statlonarity and real-time analysis of signal in flutter test with progression variable speed （FTPVS）, a new method of recursive time-frequency analysis is presented. The time-varying system is tracked on-line by building a time-varying parameter model, and then the relevant parameter spectrum can be obtained. The feasibility and advantages of the method are examined by digital simulation. The results of FTPVS at low-speed wind-tunnel promise the engineering application perspective of the method.展开更多
With the continuous improvement of Synthetic Aperture Radar(SAR) resolution, interpreting the small targets like aircraft in SAR images becomes possible and turn out to be a hot spot in SAR application research. Howev...With the continuous improvement of Synthetic Aperture Radar(SAR) resolution, interpreting the small targets like aircraft in SAR images becomes possible and turn out to be a hot spot in SAR application research. However, due to the complexity of SAR imaging mechanism, interpreting targets in SAR images is a tough problem. This paper presents a new aircraft interpretation method based on the joint time-frequency analysis and multi-dimensional contrasting of basic structures. Moreover, SAR data acquisition experiment is designed for interpreting the aircraft. Analyzing the experiment data with our method, the result shows that the proposed method largely makes use of the SAR data information. The reasonable results can provide some auxiliary support for the SAR images manual interpretation.展开更多
With the increasingly complex and changeable electromagnetic environment,wireless communication systems are facing jamming and abnormal signal injection,which significantly affects the normal operation of a communicat...With the increasingly complex and changeable electromagnetic environment,wireless communication systems are facing jamming and abnormal signal injection,which significantly affects the normal operation of a communication system.In particular,the abnormal signals may emulate the normal signals,which makes it very challenging for abnormal signal recognition.In this paper,we propose a new abnormal signal recognition scheme,which combines time-frequency analysis with deep learning to effectively identify synthetic abnormal communication signals.Firstly,we emulate synthetic abnormal communication signals including seven jamming patterns.Then,we model an abnormal communication signals recognition system based on the communication protocol between the transmitter and the receiver.To improve the performance,we convert the original signal into the time-frequency spectrogram to develop an image classification algorithm.Simulation results demonstrate that the proposed method can effectively recognize the abnormal signals under various parameter configurations,even under low signal-to-noise ratio(SNR)and low jamming-to-signal ratio(JSR)conditions.展开更多
0 INTRODUCTION.The global availability of digital elevation model(DEM)data,such as 90-m Shuttle Radar Topography Mission(SRTM)DEM and 30-m Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital ...0 INTRODUCTION.The global availability of digital elevation model(DEM)data,such as 90-m Shuttle Radar Topography Mission(SRTM)DEM and 30-m Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model(ASTER GDEM),has been extensively utilized in morphotectonic analyses(e.g.,Wang et al.,2024;Cheng et al.,2018;Pérez-Pe?a et al.,2010;El Hamdouni et al.,2008).展开更多
BACKGROUND Myocardial ischemia/reperfusion(I/R)injury,which is associated with high morbidity and mortality,is a main cause of unexpected myocardial injury after acute myocardial infarction.However,the underlying mech...BACKGROUND Myocardial ischemia/reperfusion(I/R)injury,which is associated with high morbidity and mortality,is a main cause of unexpected myocardial injury after acute myocardial infarction.However,the underlying mechanism remains unclear.Circular RNAs(circRNAs),which are formed from protein-coding genes,can sequester microRNAs or proteins,modulate transcription and interfere with splicing.Authoritative studies suggest that circRNAs may play an important role in myocardial I/R injury.AIM To explore the role and mechanism of circRNAs in myocardial I/R injury.METHODS We constructed a myocardial I/R injury model using ligation of the left anterior descending coronary artery,and evaluated the success of the validated model using triphenyltetrazolium chloride and hematoxylin-eosin staining.Then,left ventricular samples from different groups were selected for mRNA-sequence,and differential gene screening was performed on the obtained results.The differentially obtained mRNAs were divided into up-regulated and down-regulated according to their expression levels,and Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)functional enrichment analysis were performed,respectively.Then,the obtained circRNA and microRNA(miRNA)were paired for analysis,and the binding sites of miRNA and mRNA were virtual screened.Finally,the obtained circRNA,miRNA and mRNA were constructed by ceRNA mutual most useful network.RESULTS We used an RNA sequencing array to investigate the expression signatures of circRNAs in myocardial I/R injury using three samples from the I/R group and three samples from the sham group.A total of 142 upregulated and 121 downregulated circRNAs were found to be differentially expressed(fold change≥2,P<0.05).GO and KEGG functional analyses of these circRNAs were performed.GO analysis revealed that these circRNAs were involved mainly in cellular and intracellular processes.KEGG analysis demonstrated that 6 of the top 20 pathways were correlated with cell apoptosis.Furthermore,a circRNA-miRNA coexpression network and ceRNA network based on these genes were constructed,revealing that mmu-circ-0001452,mmu-circ-0001637,and mmu-circ-0000870 might be key regulators of myocardial I/R injury.CONCLUSION This research provides new insights into the mechanism of myocardial I/R,which mmu-circ-0001452,mmu-circ-0001637,and mmu-circ-0000870 are expected to be new therapeutic targets for myocardial I/R injury.展开更多
The world-class Jiaodong gold province in the North China Craton hosts over 5000 t of Au resource and is characterized by abundant visible gold mineralization.However,the critical processes controlling the formation o...The world-class Jiaodong gold province in the North China Craton hosts over 5000 t of Au resource and is characterized by abundant visible gold mineralization.However,the critical processes controlling the formation of visible gold in this province remain poorly understood.To solve this problem,integrated microtextural,trace elemental,and sulfur isotopic analyses of pyrite from the high-grade Linglong gold deposit in the Jiaodong gold province were conducted in this study.Two distinct pyrite types were identified within auriferous quartz-sulfide veins:(1)Py1 aggregates in quartz-pyrite veins(hydrothermal stageⅡ),and(2)euhedral to subhedral,coarse-grained Py2 crystals in quartz-polymetallic sulfide veins(hydrothermal stageⅢ).Microtextural and elemental analyses revealed that visible gold predominantly occurs as intergranular particles between primary pyrite crystals within Py1 aggregates.The Py1 exhibits complex microtextures with abundant mineral inclusions of polymetallic sulfides and has low concentrations of Au(median:0.032 ppm)with a narrowδ^(34)S range(4.86‰-6.75‰),indicative of rapid crystallization under unstable,disequilibrium conditions.By contrast,the Py2 is texturally homogeneous and contains higher Au concentrations(median:0.304 ppm)with progressively increasingδ^(34)S values(5.25‰-10.14‰)over time,suggesting slow crystal growth under more stable,near-equilibrium conditions.Based on the microtextural and geochemical information,it is proposed that fluid boiling occurred only during the hydrothermal stage Ⅱ,which resulted in the unstable physicochemical environment and rapid deposition of gold.During the boiling processes,gold colloids likely occurred and promoted the formation of visible gold.展开更多
The deep seabed is known for its abundant reserves of various mineral resources.Notably,the Clarion Clipperton(C-C)mining area in the northeast Pacific Ocean,where China holds exploration rights,is particularly rich i...The deep seabed is known for its abundant reserves of various mineral resources.Notably,the Clarion Clipperton(C-C)mining area in the northeast Pacific Ocean,where China holds exploration rights,is particularly rich in deep-sea polymetallic nodules.These nodules,which are nodular and unevenly distributed in seafloor sediments,have significant industrial exploitation value.Over the decades,the deep-sea mining industry has increasingly adopted systems that combine rigid and flexible risers supported by large surface mining vessels.However,current systems face economic and structural stability challenges,hindering the development of deep-sea mining technology.This paper proposes a new structural design for a deep-sea mining system based on flexible risers,validated through numerical simulations and experimental research.The system composition,function and operational characteristics are comprehensively introduced.Detailed calculations determine the production capacity of the deep-sea mining system and the dimensions of the seabed mining subsystem.Finite element numerical simulations analyze the morphological changes of flexible risers and the stress conditions at key connection points under different ocean current incident angles.Experimental research verifies the feasibility of collaborative movement between two tethered underwater devices.The proposed deep-sea mining system,utilizing flexible risers,significantly advances the establishment of a commercial deep-sea mining system.The production calculations and parameter determinations provide essential references for the system’s future detailed design.Furthermore,the finite element simulation model established in this paper provides a research basis,and the method established in this paper offers a foundation for subsequent research under more complex ocean conditions.The control strategy for the collaborative movement between two tethered underwater devices provides an effective solution for deep-sea mining control systems.展开更多
Osteoporosis is a known risk factor for rotator cuff tears(RCTs),but the causal correlation and underlying mechanisms remain unclear.This study aims to evaluate the impact of osteoporosis on RCT risk and investigate t...Osteoporosis is a known risk factor for rotator cuff tears(RCTs),but the causal correlation and underlying mechanisms remain unclear.This study aims to evaluate the impact of osteoporosis on RCT risk and investigate their genetic associations.Using data from the UK Biobank(n=457871),cross-sectional analyses demonstrated that osteoporosis was significantly associated with an increased risk of RCTs(adjusted OR[95%CI]=1.38[1.25–1.52]).A longitudinal analysis of a subset of patients(n=268117)over 11 years revealed that osteoporosis increased the risk of RCTs(adjusted HR[95%CI]=1.56[1.29–1.87]),which is notably varied between sexes in sex-stratified analysis.Causal inference methods,including propensity score matching,inverse probability weighting,causal random forest and survival random forest models further confirmed the causal effect,both from cross-sectional and longitudinal perspectives.展开更多
A new time-frequency analysis method is proposed in this study using a multi-rate signal decomposition technique for the analysis of non-stationary signals. The method uses a multi-rate filter bank for an improved non...A new time-frequency analysis method is proposed in this study using a multi-rate signal decomposition technique for the analysis of non-stationary signals. The method uses a multi-rate filter bank for an improved non-stationary signal decomposition treatment, and uses the Wigner-Ville distribution(WVD) analysis for signal reconstruction. The method presented in this study can effectively resolves the time and frequency resolution issue for non-stationary signal analysis and the cross-term issue typically encountered in time-frequency analysis.The feasibility and accuracy of the proposed method are evaluated and verified in a numerical simulation.展开更多
Objective: To analyze the non-periodic, unstable and even chaotic echoes scattered from microbubbles which are extremely sensitive and may easily collapse, fragment or shrink when ultrasound contrast agents are expose...Objective: To analyze the non-periodic, unstable and even chaotic echoes scattered from microbubbles which are extremely sensitive and may easily collapse, fragment or shrink when ultrasound contrast agents are exposed to ultrasound (US) irradiation. Methods: The combined time-frequency analysis was applied to the original signals instead of the traditional Fourier spectral analysis technique. Results: The results obtained from simulation as well as experiment showed that the subharmonic, 2nd harmonic and ultra harmonic of the microbubbles occurred during the oscillation and varied with time. The dependence on the incident ultrasonic amplitude and microbubble parameters were established. Conclusion: The transient echoes backscattered from the ultrasound agent in the evaluation of the blood perfusion can be analyzed thoroughly by the technique of combined-frequency analysis and the time detail of the frequency contents can be revealed.展开更多
基金Aeronautical Science Foundation of China (20071551016)
文摘Predicting the time-varying auto-spectral density of a spacecraft in high-altitude orbits requires an accurate model for the non-stationary random vibration signals with densely spaced modal frequency. The traditional time-varying algorithm limits prediction accuracy, thus affecting a number of operational decisions. To solve this problem, a time-varying auto regressive （TVAR） model based on the process neural network （PNN） and the empirical mode decomposition （EMD） is proposed. The time-varying system is tracked on-line by establishing a time-varying parameter model, and then the relevant parameter spectrum is obtained. Firstly, the EMD method is utilized to decompose the signal into several intrinsic mode functions （IMFs）. Then for each IMF, the PNN is established and the time-varying auto-spectral density is obtained. Finally, the time-frequency distribution of the signals can be reconstructed by linear superposition. The simulation and the analytical results from an example demonstrate that this approach possesses simplicity, effectiveness, and feasibility, as well as higher frequency resolution.
基金supported by the National Natural Science Foundation of China(61271442)
文摘The interrupted sampling repeater jamming（ISRJ） is an effective deception jamming method for coherent radar, especially for the wideband linear frequency modulation（LFM） radar. An electronic counter-countermeasure（ECCM） scheme is proposed to remove the ISRJ-based false targets from the pulse compression result of the de-chirping radar. Through the time-frequency（TF） analysis of the radar echo signal, it can be found that the TF characteristics of the ISRJ signal are discontinuous in the pulse duration because the ISRJ jammer needs short durations to receive the radar signal. Based on the discontinuous characteristics a particular band-pass filter can be generated by two alternative approaches to retain the true target signal and suppress the ISRJ signal. The simulation results prove the validity of the proposed ECCM scheme for the ISRJ.
基金supported by the Special Fund of the Institute of Geophysics,China Earthquake Administration(Nos.DQJB19B02 and DQJB17T04)
文摘The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform(SR-ST)is presented to improve the stability and accuracy of Q estimation.The variable window of ST is used to solve the time window problem.We add two window factors to the Gaussian window function in the ST.The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal,which reduces the calculation error attributed to the conventional Gaussian window function.Meanwhile,the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy.First,the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments.Second,artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method.Finally,a further comparison between the new method and the conventional spectral ratio method(SR)is conducted using rock field samples,again addressing stability and accuracy.The experimental results show that this method will yield an error of approximately 36%using the conventional Gaussian window function.This problem can be solved by adding the time window factors to the Gaussian window function.The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation(Q>15)is less than 10%.
基金the Ministerial Level Advanced Research Foundation(020045089)
文摘A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequency extraction becomes curve detection in the image-view. A set of morphological operations are used to implement curve detection. And a map fusion scheme is presented to eliminate the influence of strong direct current （DC） component of echo signal during curve detection. The radar real-life data are used to illustrate the performance of the new approach. Experimental results show that the proposed method can overcome the shortcomings of piecewise-processing-based FFT method and can improve the measuring precision of miss distance.
基金the financial support from the National Science Foundation of China(22078190 and 12002196)the National Key Research and Development Program of China(2020YFB1505802)。
文摘Li transient concentration distribution in spherical active material particles can affect the maximum power density and the safe operating regime of the electric vehicles(EVs). On one hand, the quasiexact/exact solution obtained in the time/frequency domain is time-consuming and just as a reference value for approximate solutions;on the other hand, calculation errors and application range of approximate solutions not only rely on approximate algorithms but also on discharge modes. For the purpose to track the transient dynamics for Li solid-phase diffusion in spherical active particles with a tolerable error range and for a wide applicable range, it is necessary to choose optimal approximate algorithms in terms of discharge modes and the nature of active material particles. In this study, approximation methods,such as diffusion length method, polynomial profile approximation method, Padé approximation method,pseudo steady state method, eigenfunction-based Galerkin collocation method, and separation of variables method for solving Li solid-phase diffusion in spherical active particles are compared from calculation fundamentals to algorithm implementation. Furthermore, these approximate solutions are quantitatively compared to the quasi-exact/exact solution in the time/frequency domain under typical discharge modes, i.e., start-up, slow-down, and speed-up. The results obtained from the viewpoint of time-frequency analysis offer a theoretical foundation on how to track Li transient concentration profile in spherical active particles with a high precision and for a wide application range. In turn, optimal solutions of Li solid diffusion equations for spherical active particles can improve the reliability in predicting safe operating regime and estimating maximum power for automotive batteries.
文摘Multi-radar signal separation is a critical process in modern reconnaissance systems. However, the complicated battlefield is typically confronted with increasing electronic equipment and complex radar waveforms. The intercepted signal is difficult to separate with conventional parameters because of severe overlapping in both time and frequency domains. On the contrary, time-frequency analysis maps the 1D signal into a 2D time-frequency plane, which provides a better insight into the signal than traditional methods. Particularly, the parameterized time-frequency analysis (PTFA) shows great potential in processing such non stationary signals. Five procedures for the PTFA are proposed to separate the overlapped multi-radar signal, including initiation, instantaneous frequency estimation with PTFA, signal demodulation, signal separation with adaptive filter and signal recovery. The proposed method is verified with both simulated and real signals, which shows good performance in the application on multi-radar signal separation.
基金Supported by the National Science Foundation of China(42055402)。
文摘The conventional linear time-frequency analysis method cannot achieve high resolution and energy focusing in the time and frequency dimensions at the same time,especially in the low frequency region.In order to improve the resolution of the linear time-frequency analysis method in the low-frequency region,we have proposed a W transform method,in which the instantaneous frequency is introduced as a parameter into the linear transformation,and the analysis time window is constructed which matches the instantaneous frequency of the seismic data.In this paper,the W transform method is compared with the Wigner-Ville distribution(WVD),a typical nonlinear time-frequency analysis method.The WVD method that shows the energy distribution in the time-frequency domain clearly indicates the gravitational center of time and the gravitational center of frequency of a wavelet,while the time-frequency spectrum of the W transform also has a clear gravitational center of energy focusing,because the instantaneous frequency corresponding to any time position is introduced as the transformation parameter.Therefore,the W transform can be benchmarked directly by the WVD method.We summarize the development of the W transform and three improved methods in recent years,and elaborate on the evolution of the standard W transform,the chirp-modulated W transform,the fractional-order W transform,and the linear canonical W transform.Through three application examples of W transform in fluvial sand body identification and reservoir prediction,it is verified that W transform can improve the resolution and energy focusing of time-frequency spectra.
基金This work was supported by the National Natural Science Foundation of China(91538201)the Taishan Scholar Project of Shandong Province(ts201511020)the project supported by Chinese National Key Laboratory of Science and Technology on Information System Security(6142111190404).
文摘Recent advances in electronics have increased the complexity of radar signal modulation.The quasi-linear frequency modulation(quasi-LFM)radar waveforms(LFM,Frank code,P1−P4 code)have similar time-frequency distributions,and it is difficult to identify such signals using traditional time-frequency analysis methods.To solve this problem,this paper proposes an algorithm for automatic recognition of quasi-LFM radar waveforms based on fractional Fourier transform and time-frequency analysis.First of all,fractional Fourier transform and the Wigner-Ville distribution(WVD)are used to determine the number of main ridgelines and the tilt angle of the target component in WVD.Next,the standard deviation of the target component's width in the signal's WVD is calculated.Finally,an assembled classifier using neural network is built to recognize different waveforms by automatically combining the three features.Simulation results show that the overall recognition rate of the proposed algorithm reaches 94.17%under 0 dB.When the training data set and the test data set are mixed with noise,the recognition rate reaches 89.93%.The best recognition accuracy is achieved when the size of the training set is taken as 400.The algorithm complexity can meet the requirements of real-time recognition.
文摘Climate change and environmental degradation threaten the world and global economic conditions.As one of countries’most important economic components,the financial sector might be an effective tool for reducing and even reversing environmental degradation.The financial sector can affect sustainability through its lending and investment practices.The sector can play a role in financing sustainable projects and businesses,helping reduce CO_(2) emissions.By aligning its financial objectives with environmental protection,the financial sector can support the transition to a more sustainable future by helping reduce environmental degradation’s negative impacts.This paper examines the domestic financial sector’s impact on CO_(2) emissions in the United States over the 1990:Q1–2022:Q3 period.In this research,the nexus between the domestic financial sector(total debt securities,loans,liabilities,and total financial assets)and Carbon dioxide emissions in the U.S.is investigated by Morlet wavelet analysis.Rest of the world:sector discrepancy transactions,rest of the world:debt securities and loans,gross domestic product,and the square of the gross domestic product,are control variables in the estimated models.Partial wavelet coherency analyses prove that the financial sector reduces CO_(2) emissions at the 5–8-year frequency band during different subsample periods.The financial sector’s instruments can be effective in struggling with climate change.
基金Project (No. 2011BAE22B05) supported by the National Key Technologies Supporting Program of China during the 12th Five-Year Plan Period
文摘In this study,we report an analysis of cylinder head vibration signals at a steady engine speed using short-time Fourier transform(STFT).Three popular time-frequency analysis techniques,i.e.,STFT,analytic wavelet transform(AWT) and S transform(ST),have been examined.AWT and ST are often applied in engine signal analyses.In particular,an AWT expression in terms of the quality factor Q and an analytical relationship between ST and AWT have been derived.The time-frequency resolution of a Gaussian function windowed STFT was studied via numerical simulation.Based on the simulation,the empirical limits for the lowest distinguishable frequency as well as the time and frequency resolutions were determined.These can provide insights for window width selection,spectrogram interpretation and artifact identification.Gaussian function windowed STFTs were applied to some cylinder head vibration signals.The spectrograms of the same signals from ST and AWT were also determined for comparison.The results indicate that the uniform resolution feature of STFT is not necessarily a disadvantage for time-frequency analysis of vibration signals when the engine is in stationary state because it can more accurately localize the frequency components excited by transient excitations without much loss of time resolution.
文摘Focused on the non-statlonarity and real-time analysis of signal in flutter test with progression variable speed （FTPVS）, a new method of recursive time-frequency analysis is presented. The time-varying system is tracked on-line by building a time-varying parameter model, and then the relevant parameter spectrum can be obtained. The feasibility and advantages of the method are examined by digital simulation. The results of FTPVS at low-speed wind-tunnel promise the engineering application perspective of the method.
文摘With the continuous improvement of Synthetic Aperture Radar(SAR) resolution, interpreting the small targets like aircraft in SAR images becomes possible and turn out to be a hot spot in SAR application research. However, due to the complexity of SAR imaging mechanism, interpreting targets in SAR images is a tough problem. This paper presents a new aircraft interpretation method based on the joint time-frequency analysis and multi-dimensional contrasting of basic structures. Moreover, SAR data acquisition experiment is designed for interpreting the aircraft. Analyzing the experiment data with our method, the result shows that the proposed method largely makes use of the SAR data information. The reasonable results can provide some auxiliary support for the SAR images manual interpretation.
基金supported by Natural Science Foundation of China(No.62371231)Natural Science Foundation on Frontier Leading Technology Basic Research Project of Jiangsu under Grant BK20222001Jiangsu Provincial Key Research and Development Program(No.BE2023027).
文摘With the increasingly complex and changeable electromagnetic environment,wireless communication systems are facing jamming and abnormal signal injection,which significantly affects the normal operation of a communication system.In particular,the abnormal signals may emulate the normal signals,which makes it very challenging for abnormal signal recognition.In this paper,we propose a new abnormal signal recognition scheme,which combines time-frequency analysis with deep learning to effectively identify synthetic abnormal communication signals.Firstly,we emulate synthetic abnormal communication signals including seven jamming patterns.Then,we model an abnormal communication signals recognition system based on the communication protocol between the transmitter and the receiver.To improve the performance,we convert the original signal into the time-frequency spectrogram to develop an image classification algorithm.Simulation results demonstrate that the proposed method can effectively recognize the abnormal signals under various parameter configurations,even under low signal-to-noise ratio(SNR)and low jamming-to-signal ratio(JSR)conditions.
基金supported by the National Key Research and Development Project of China(No.2023YFC3007303)the Open Research Project of the Hubei Key Laboratory of Intelligent Geo-Information Processing(No.KLIGIP-2019B08)。
文摘0 INTRODUCTION.The global availability of digital elevation model(DEM)data,such as 90-m Shuttle Radar Topography Mission(SRTM)DEM and 30-m Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model(ASTER GDEM),has been extensively utilized in morphotectonic analyses(e.g.,Wang et al.,2024;Cheng et al.,2018;Pérez-Pe?a et al.,2010;El Hamdouni et al.,2008).
基金Supported by Zhejiang Provincial Natural Science Foundation of China,No.LQ23H020004The Medical and Health Research Project of Zhejiang province,No.2024KY983Basic Medical Health Technology Project of Wenzhou Science and Technology Bureau,No.Y20210818 and No.Y20210140.
文摘BACKGROUND Myocardial ischemia/reperfusion(I/R)injury,which is associated with high morbidity and mortality,is a main cause of unexpected myocardial injury after acute myocardial infarction.However,the underlying mechanism remains unclear.Circular RNAs(circRNAs),which are formed from protein-coding genes,can sequester microRNAs or proteins,modulate transcription and interfere with splicing.Authoritative studies suggest that circRNAs may play an important role in myocardial I/R injury.AIM To explore the role and mechanism of circRNAs in myocardial I/R injury.METHODS We constructed a myocardial I/R injury model using ligation of the left anterior descending coronary artery,and evaluated the success of the validated model using triphenyltetrazolium chloride and hematoxylin-eosin staining.Then,left ventricular samples from different groups were selected for mRNA-sequence,and differential gene screening was performed on the obtained results.The differentially obtained mRNAs were divided into up-regulated and down-regulated according to their expression levels,and Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)functional enrichment analysis were performed,respectively.Then,the obtained circRNA and microRNA(miRNA)were paired for analysis,and the binding sites of miRNA and mRNA were virtual screened.Finally,the obtained circRNA,miRNA and mRNA were constructed by ceRNA mutual most useful network.RESULTS We used an RNA sequencing array to investigate the expression signatures of circRNAs in myocardial I/R injury using three samples from the I/R group and three samples from the sham group.A total of 142 upregulated and 121 downregulated circRNAs were found to be differentially expressed(fold change≥2,P<0.05).GO and KEGG functional analyses of these circRNAs were performed.GO analysis revealed that these circRNAs were involved mainly in cellular and intracellular processes.KEGG analysis demonstrated that 6 of the top 20 pathways were correlated with cell apoptosis.Furthermore,a circRNA-miRNA coexpression network and ceRNA network based on these genes were constructed,revealing that mmu-circ-0001452,mmu-circ-0001637,and mmu-circ-0000870 might be key regulators of myocardial I/R injury.CONCLUSION This research provides new insights into the mechanism of myocardial I/R,which mmu-circ-0001452,mmu-circ-0001637,and mmu-circ-0000870 are expected to be new therapeutic targets for myocardial I/R injury.
基金supported by the National Natural Science Foundation of China(Grant Nos.42302106 and 42102089)National Foundation for Guiding Local Science and Technology Development(Guizhou[2024]043)Innovation and Development Fund of Science and Technology of Institute of Geochemistry,Chinese Academy of Sciences(Grant No.2025-1).
文摘The world-class Jiaodong gold province in the North China Craton hosts over 5000 t of Au resource and is characterized by abundant visible gold mineralization.However,the critical processes controlling the formation of visible gold in this province remain poorly understood.To solve this problem,integrated microtextural,trace elemental,and sulfur isotopic analyses of pyrite from the high-grade Linglong gold deposit in the Jiaodong gold province were conducted in this study.Two distinct pyrite types were identified within auriferous quartz-sulfide veins:(1)Py1 aggregates in quartz-pyrite veins(hydrothermal stageⅡ),and(2)euhedral to subhedral,coarse-grained Py2 crystals in quartz-polymetallic sulfide veins(hydrothermal stageⅢ).Microtextural and elemental analyses revealed that visible gold predominantly occurs as intergranular particles between primary pyrite crystals within Py1 aggregates.The Py1 exhibits complex microtextures with abundant mineral inclusions of polymetallic sulfides and has low concentrations of Au(median:0.032 ppm)with a narrowδ^(34)S range(4.86‰-6.75‰),indicative of rapid crystallization under unstable,disequilibrium conditions.By contrast,the Py2 is texturally homogeneous and contains higher Au concentrations(median:0.304 ppm)with progressively increasingδ^(34)S values(5.25‰-10.14‰)over time,suggesting slow crystal growth under more stable,near-equilibrium conditions.Based on the microtextural and geochemical information,it is proposed that fluid boiling occurred only during the hydrothermal stage Ⅱ,which resulted in the unstable physicochemical environment and rapid deposition of gold.During the boiling processes,gold colloids likely occurred and promoted the formation of visible gold.
基金Supported by Finance Science and Technology Project of Hainan Province under Grant No.ZDKJ2021027the National Natural Science Foundation of China under Grant No.52231012.
文摘The deep seabed is known for its abundant reserves of various mineral resources.Notably,the Clarion Clipperton(C-C)mining area in the northeast Pacific Ocean,where China holds exploration rights,is particularly rich in deep-sea polymetallic nodules.These nodules,which are nodular and unevenly distributed in seafloor sediments,have significant industrial exploitation value.Over the decades,the deep-sea mining industry has increasingly adopted systems that combine rigid and flexible risers supported by large surface mining vessels.However,current systems face economic and structural stability challenges,hindering the development of deep-sea mining technology.This paper proposes a new structural design for a deep-sea mining system based on flexible risers,validated through numerical simulations and experimental research.The system composition,function and operational characteristics are comprehensively introduced.Detailed calculations determine the production capacity of the deep-sea mining system and the dimensions of the seabed mining subsystem.Finite element numerical simulations analyze the morphological changes of flexible risers and the stress conditions at key connection points under different ocean current incident angles.Experimental research verifies the feasibility of collaborative movement between two tethered underwater devices.The proposed deep-sea mining system,utilizing flexible risers,significantly advances the establishment of a commercial deep-sea mining system.The production calculations and parameter determinations provide essential references for the system’s future detailed design.Furthermore,the finite element simulation model established in this paper provides a research basis,and the method established in this paper offers a foundation for subsequent research under more complex ocean conditions.The control strategy for the collaborative movement between two tethered underwater devices provides an effective solution for deep-sea mining control systems.
基金the Scientific Research Innovation Capability Support Project for Young Faculty(ZYGXQNJSKYCXNLZCXM-H8)Fundamental Research Funds for the Central Universities(2024ZYGXZR077)+3 种基金Guangdong Basic and Applied Basic Research Foundation(2023B1515120006)Guangzhou Basic and Applied Basic Research Foundation(2024A04J5776)the Research Fund(2023QN10Y421)Guangzhou Talent Recruitment Team Program(2024D03J0004),all related to this study.
文摘Osteoporosis is a known risk factor for rotator cuff tears(RCTs),but the causal correlation and underlying mechanisms remain unclear.This study aims to evaluate the impact of osteoporosis on RCT risk and investigate their genetic associations.Using data from the UK Biobank(n=457871),cross-sectional analyses demonstrated that osteoporosis was significantly associated with an increased risk of RCTs(adjusted OR[95%CI]=1.38[1.25–1.52]).A longitudinal analysis of a subset of patients(n=268117)over 11 years revealed that osteoporosis increased the risk of RCTs(adjusted HR[95%CI]=1.56[1.29–1.87]),which is notably varied between sexes in sex-stratified analysis.Causal inference methods,including propensity score matching,inverse probability weighting,causal random forest and survival random forest models further confirmed the causal effect,both from cross-sectional and longitudinal perspectives.
基金the National Natural Science Foundation of China(No.61271387)the Shandong Provincial Government’s Taishan Scholar Program
文摘A new time-frequency analysis method is proposed in this study using a multi-rate signal decomposition technique for the analysis of non-stationary signals. The method uses a multi-rate filter bank for an improved non-stationary signal decomposition treatment, and uses the Wigner-Ville distribution(WVD) analysis for signal reconstruction. The method presented in this study can effectively resolves the time and frequency resolution issue for non-stationary signal analysis and the cross-term issue typically encountered in time-frequency analysis.The feasibility and accuracy of the proposed method are evaluated and verified in a numerical simulation.
文摘Objective: To analyze the non-periodic, unstable and even chaotic echoes scattered from microbubbles which are extremely sensitive and may easily collapse, fragment or shrink when ultrasound contrast agents are exposed to ultrasound (US) irradiation. Methods: The combined time-frequency analysis was applied to the original signals instead of the traditional Fourier spectral analysis technique. Results: The results obtained from simulation as well as experiment showed that the subharmonic, 2nd harmonic and ultra harmonic of the microbubbles occurred during the oscillation and varied with time. The dependence on the incident ultrasonic amplitude and microbubble parameters were established. Conclusion: The transient echoes backscattered from the ultrasound agent in the evaluation of the blood perfusion can be analyzed thoroughly by the technique of combined-frequency analysis and the time detail of the frequency contents can be revealed.
