Fault features in mechanical systems often manifest as transient impulses,which can be effectively analyzed using time-frequency analysis(TFA)methods.Recently,a new TFA technique known as the time-reassigned multi-syn...Fault features in mechanical systems often manifest as transient impulses,which can be effectively analyzed using time-frequency analysis(TFA)methods.Recently,a new TFA technique known as the time-reassigned multi-synchrosqueezing transform(TMssT)was proposed to capture these transient impulses for fault diagnosis.However,the TMSST,which is based on the short-time Fourier transform(STFT),suffers from unclear high-frequency re-presentations owing to the fixed sliding window used in the STFT.To address this limitation,the current study combined TMSST with the S-transform and a local maximum method to enhance the time-frequency representation for improved signal analysis.Furthermore,an extractive reconstruction algorithm that binds the maximum value of the spectral envelope is proposed for spectral decomposition.To validate the proposed technique,a simulated noise-added signal and four experimental bearing defect datasets were used.The results demonstrate that the proposed technique can effectively and accurately extract fault features from bearing signals regardless of whether the bearings operate under constant or varying speed conditions.This study offers a novel and efficient approach for fault diagnosis in mechanical systems with complex dynamic behaviors.展开更多
Flooding remains one of the most destructive natural disasters,posing significant risks to both human lives and infrastructure.In India,where a large area is susceptible to flood hazards,the importance of accurate flo...Flooding remains one of the most destructive natural disasters,posing significant risks to both human lives and infrastructure.In India,where a large area is susceptible to flood hazards,the importance of accurate flood frequency analysis(FFA)and flood susceptibility mapping cannot be overstated.This study focuses on the Haora River basin in Tripura,a region prone to frequent flooding due to a combination of natural and anthropogenic factors.This study evaluates the suitability of the Log-Pearson Type Ⅲ(LP-Ⅲ)and Gumbel Extreme Value-1(EV-1)distributions for estimating peak discharges and delineates floodsusceptible zones in the Haora River basin,Tripura.Using 40 years of peak discharge data(1984-2023),the LP-Ⅲ distribution was identified as the most appropriate model based on goodness-of-fit tests.Flood susceptibility mapping,integrating 16 thematic layers through the Analytical Hierarchy Process,identified 8%,64%,and 26%of the area as high,moderate,and low susceptibility zones,respectively,with a model success rate of 0.81.The findings highlight the need for improved flood management strategies,such as enhancing river capacity and constructing flood spill channels.These insights are critical for designing targeted flood mitigation measures in the Haora basin and other flood-prone regions.展开更多
To improve design accuracy and reliability of structures,this study solves the uncertain natural frequencies with consideration for geometric nonlinearity and structural uncertainty.Frequencies of the laminated plate ...To improve design accuracy and reliability of structures,this study solves the uncertain natural frequencies with consideration for geometric nonlinearity and structural uncertainty.Frequencies of the laminated plate with all four edges clamped(CCCC)are derived based on Navier's method and Galerkin's method.The novelty of the current work is that the number of unknowns in the displacement field model of a CCCC plate with free midsurface(CCCC-2 plate)is only three compared with four or five in cases of other exposed methods.The present analytical method is proved to be accurate and reliable by comparing linear natural frequencies and nonlinear natural frequencies with other models available in the open literature.Furthermore,a novel method for analyzing effects of mean values and tolerance zones of uncertain structural parameters on random frequencies is proposed based on a self-developed Multiscale Feature Extraction and Fusion Network(MFEFN)system.Compared with a direct Monte Carlo Simulation(MCS),the MFEFNbased procedure significantly reduces the calculation burden with a guarantee of accuracy.Our research provides a method to calculate nonlinear natural frequencies under two boundary conditions and presentes a surrogate model to predict frequencies for accuracy analysis and optimization design.展开更多
This paper introduces a small perturbation frequency domain thermal analysis model based on the nonlinear dynamics model.The model can be applied to study the high-precision temperature control of thermal systems unde...This paper introduces a small perturbation frequency domain thermal analysis model based on the nonlinear dynamics model.The model can be applied to study the high-precision temperature control of thermal systems under low-frequency complex perturbations.The frequency domain characteristics of the space gravitational wave detection satellite are analyzed,and a multi-channel perturbation structure is established.The effects of three kinds of heat flow perturbations,including external heat flow,power generation power,and waste heat of electronic equipment,on the temperature through five transfer paths are investigated.It has been discovered that the waste heat from electronic equipment inside the satellite has the most noticeable effect on the temperature power spectral density of temperature-sensitive optical loads,serving as the primary factor influencing thermal stability.For complex noise signals,the small perturbation analysis method can decompose the different frequency components or ranges,reducing the problem to linearized analysis and simplifying complex calculations.The results indicate that the temperature power spectral density decreases as signal frequency increases,with low-frequency signals exerting a greater influence on temperature stability.The small perturbation analysis method is a novel and effective method for temperature control of space thermal systems,with high accuracy and stability.展开更多
To explore the electrostatic discharge behavior of charged powders in industrial silos,discharge experiments are conducted based on a full-size industrial silo discharge platform.Electrostatic discharge mode,frequency...To explore the electrostatic discharge behavior of charged powders in industrial silos,discharge experiments are conducted based on a full-size industrial silo discharge platform.Electrostatic discharge mode,frequency,and energy are investigated for powders of different polarities.Although the powders have low charge-to-mass ratios(+0.087μC/kg for the positively charged powders and−0.26μC/kg for the negatively charged ones),electrostatic discharges occur approximately every 10 s,with the maximum discharge energy being 800 mJ.Powder polarity considerably influences discharge energy.The positive powders exhibit higher discharge energy than the negative ones,although discharge frequency remains similar for both.Effects of powder charge,humidity,and mass flow on discharge frequency and discharge energy are quantitatively analyzed,providing important insights for the improvement of safety in industrial powder handling.展开更多
This study investigates the nonlinear dynamic properties of rotating functionally graded sandwich rectangular plates in a thermal environment.The nonlinear vibration equations for a rotating metal-ceramic functionally...This study investigates the nonlinear dynamic properties of rotating functionally graded sandwich rectangular plates in a thermal environment.The nonlinear vibration equations for a rotating metal-ceramic functionally graded sandwich rectangular plate in a thermal environment are derived using classical thin plate theory and Hamilton’s principle,considering geometric nonlinearity,temperature-dependent material properties,and power law distribution of components through the thickness.With cantilever boundary conditions,the flexural nonlinear differential equations of the rectangular sandwich plate are obtained via the Galerkin method.Since the natural vibration differential equations exhibit nonlinear characteristics,the multiscale method is employed to derive the expression for nonlinear natural frequency.An example analysis reveals how the natural frequency of a functionally graded sandwich rectangular plate varies with rotational speed and temperature.Results show that the nonlinear/linear frequency ratio increases with rotational angular velocity Ω and thickness-to-length ratio h/a,follows a cosine-like periodic pattern with the setting angle,and shows a sharp decrease followed by a rapid increase with increasing width-to-length ratio b/a.The derived analytical solutions for nonlinear frequency provide valuable insights for assessing the dynamic characteristics of functionally graded structures.展开更多
The fused quartz hemispherical resonator is the core component of the hemispherical resonator gyroscope.It features a complex shape and is Made from a Material that is difficult to process.Scratches are easily introdu...The fused quartz hemispherical resonator is the core component of the hemispherical resonator gyroscope.It features a complex shape and is Made from a Material that is difficult to process.Scratches are easily introduced during grinding,potentially degrading the mass-stiffness-damping symmetry;however,the underlying mechanisms of this influence have not been fully understood.This paper aims to investigate the effects of scratch defects on the frequency splitting and quality factor of the hemispherical resonator.First,finite element models of the hemispherical resonator with scratches are established.Then,the effects of the mass-stiffness factor,as well as the latitude and length of the scratches,on frequency splitting are analyzed.Furthermore,the impacts of latitude,length,and the first four harmonics of the unbalanced mass caused by scratches on thermoelastic damping and anchor loss are examined.Simulation results indicate that scratches above 55°latitude cause frequency splitting solely due to stiffness changes.Frequency splitting caused by scratches of the same size on the inherent rigidity shaft at the rim is approximately 50%of that near the transition fillet.Frequency splitting varies linearly with the volume of material removed by scratches.Scratches have little effect on thermoelastic damping.The first three harmonics of the unbalanced mass due to scratches at the rim are the primary contributors to anchor loss.Finally,focused ion beam trimming experiments are conducted at different locations on the hemispherical resonator.The trends observed in the experimental results are consistent with the simulation results.This work provides guidance for evaluating the impact of scratches on the performance of hemispherical resonators and for developing appropriate trimming processes.展开更多
The seismic stability of the rock slope at tunnel entrances is very intricate because of the interactions among geological structures and earthquakes.However,the local damage mechanism and the correlation mechanism of...The seismic stability of the rock slope at tunnel entrances is very intricate because of the interactions among geological structures and earthquakes.However,the local damage mechanism and the correlation mechanism of accumulated damage and landslide triggering are not clear.To investigate the correlation between the inherent frequency and seismic characteristics of a layered slope at a tunnel entrance from the perspective of the frequency domain,a three-dimensional finite element modal analysis and Fourier spectrum analysis of shaking table tests were carried out.This work takes the quarry slope at the tunnel entrance in Xiamen City as a case example.The study region is predominantly affected by strong seismic activity,where the rock is primarily composed of granite with varying degrees of weathering.The results show that the seismic energy below the tunnel is mostly focused on the lowfrequency ranges,whereas the energy above the tunnel is gradually transferred to the high-frequency range.By analyzing the peak spectrum value of high-order inherent frequencies for the slope,its seismic damage evolution can be effectively identified,including fracture initiation,accelerated deformation,and sliding instability stages.The seismic response of the slope includes multi-mode interactions,which mainly include bending,torsion,and combined deformation.There are magnification effects of elevation,slope surface,and structural plane in the slope.Moreover,the triggering mechanism of the local deformation and integral sliding for the landslide is identified,which indicates that the lining structure of the tunnel entrance is more prone to seismic damage.This work successfully investigated the seismic damage evolution and failure mechanism of the slope at tunnel entrances in the frequency domain.展开更多
This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first ...This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first solved via Newton-Raphson iteration through a set of nonlinear equations,and then input-output variables are selected to estimate the linear transfer function of the original NTP system without perturbations.The applications and insights of the proposed algorithm are discussed,particularly in guiding existing frequency scan algorithms,which are restricted by time-domain signal generation or measurement.This improvement is achieved through linear stability analysis of NTP systems with perturbations.展开更多
Border-associated macrophages are located at the interface between the brain and the periphery, including the perivascular spaces, choroid plexus, and meninges. Until recently, the functions of border-associated macro...Border-associated macrophages are located at the interface between the brain and the periphery, including the perivascular spaces, choroid plexus, and meninges. Until recently, the functions of border-associated macrophages have been poorly understood and largely overlooked. However, a recent study reported that border-associated macrophages participate in stroke-induced inflammation, although many details and the underlying mechanisms remain unclear. In this study, we performed a comprehensive single-cell analysis of mouse border-associated macrophages using sequencing data obtained from the Gene Expression Omnibus(GEO) database(GSE174574 and GSE225948). Differentially expressed genes were identified, and enrichment analysis was performed to identify the transcription profile of border-associated macrophages. CellChat analysis was conducted to determine the cell communication network of border-associated macrophages. Transcription factors were predicted using the ‘pySCENIC' tool. We found that, in response to hypoxia, borderassociated macrophages underwent dynamic transcriptional changes and participated in the regulation of inflammatory-related pathways. Notably, the tumor necrosis factor pathway was activated by border-associated macrophages following ischemic stroke. The pySCENIC analysis indicated that the activity of signal transducer and activator of transcription 3(Stat3) was obviously upregulated in stroke, suggesting that Stat3 inhibition may be a promising strategy for treating border-associated macrophages-induced neuroinflammation. Finally, we constructed an animal model to investigate the effects of border-associated macrophages depletion following a stroke. Treatment with liposomes containing clodronate significantly reduced infarct volume in the animals and improved neurological scores compared with untreated animals. Taken together, our results demonstrate comprehensive changes in border-associated macrophages following a stroke, providing a theoretical basis for targeting border-associated macrophages-induced neuroinflammation in stroke treatment.展开更多
The dynamics of network power response play a crucial role in system stability.However,the integration of power electronic equipment leads to amplitude and angular frequency(abbreviated as"frequency")time-va...The dynamics of network power response play a crucial role in system stability.However,the integration of power electronic equipment leads to amplitude and angular frequency(abbreviated as"frequency")time-varying characteristics of the node voltage during dynamic processes.As a result,traditional calcu-lation methods for and characteristics of the power response of the network based on phasor and impe-dance lose their validity.Therefore,this paper undertakes mathematical calculations to reveal the power response of a network under excitation by voltage with time-varying amplitude and frequency(TVAF),relying on the original mathematical relationships and superimposed step response.Then,the multi-timescale characteristics of both the active and reactive power of the network are explored physically.Additionally,this paper reveals a new phenomenon of storing and releasing the active and reactive power of the network.To meet practical engineering requirements,a simplified power expression is presented.Finally,the theoretical analysis is validated through time-domain simulations.展开更多
Radiofrequency ablation(RFA)is a form of minimally invasive procedure that precisely ablates abnormal lesions or hyperplastic tissues through thermal energy generated by the radiofrequency current at the tip electrode...Radiofrequency ablation(RFA)is a form of minimally invasive procedure that precisely ablates abnormal lesions or hyperplastic tissues through thermal energy generated by the radiofrequency current at the tip electrode of the flexible catheter,which aims to partially or fully restore the function of the corresponding tissues or organs.Accurate prediction and control of thermal fields are crucial for clinical thermal ablation to ensure precise control of the ablation lesion size and prevent excessive burning of healthy tissues.In this study,an axisymmetric analytical model is developed for the electrothermal analysis of RFA in the cambered tissue surface and verified with the finite element analysis(FEA),which incorporates both the thermal field induced by the radiofrequency current and Pennes'biothermal effect.This model utilizes analytically derived electric and thermal fields to accurately predict the increase in the tissue temperature and the time-varying size of ablation lesion in the tissue.Furthermore,the parameters such as the input current density,curvature,and convective heat transfer coefficient of blood have a significant effect on the thermal field and thus the ablation lesion size.This electrothermal analytical model with a large curvature may provide a theoretical foundation and guidance for the future RFA applications on large-curvature biological surfaces,thereby enhancing accuracy,reducing the need for re-ablation,and lowering the costs associated with the design and production of ablation catheters.展开更多
This study investigates how the uncertainty surrounding cryptocurrency affects cryptocurrency returns(CR)by employing various wavelet techniques.We concentrate on the recently published cryptocurrency uncertainty inde...This study investigates how the uncertainty surrounding cryptocurrency affects cryptocurrency returns(CR)by employing various wavelet techniques.We concentrate on the recently published cryptocurrency uncertainty index(UCRY)and the top eight cryptocurrencies by market capitalization from December 30,2013,to June 30,2023.Our results showed that the UCRY index strongly predicted CR.In particular,the UCRY index has a leading position at all frequencies for all cryptocurrencies in our sample.Additionally,when the impacts of economic policy uncertainty and the volatility index are eliminated,the significant comovement of UCRY-CR remains unchanged for the short-,medium-,and long-term investment horizons.Therefore,we conclude that the UCRY-CR relationship is both persistent and pervasive.Our study contributes toward the literature on the relationships between cryptocurrencies and market uncertainties,as well as toward investors who use uncertainty indices to design investment strategies for their portfolios.展开更多
This study explores theoretical insights and experimental results on monitoring load-carrying capacity degradation in bridge spans through frequency analysis.Experiments were conducted on real bridge structures,includ...This study explores theoretical insights and experimental results on monitoring load-carrying capacity degradation in bridge spans through frequency analysis.Experiments were conducted on real bridge structures,including the Binh Thuan Bridge,focusing on analyzing the power spectral density(PSD)of vibration signals under random traffic loads.Detailed digital models of various bridge spans with different structural designs and construction periods were developed to ensure diversity.The study utilized PSD to analyze the vibration signals from the bridge spans under various loading conditions,identifying the vibration frequencies and the corresponding response regions.The research correlated the observed frequency changes of PSD with the actual deterioration of the bridges over time,identifying patterns that indicate a reduction in stiffness.Experiments demonstrated that frequency changes,particularly in high-frequency regions,are directly related to a reduction in the stiffness of bridge spans.This supports the hypothesis that natural frequencies can serve as effective indicators of structural damage.Furthermore,the emergence and shift of resonant frequency regions provide valuable insights into the extent of damage in actual bridge spans,highlighting the potential for using changes in resonant frequency regions as a new tool for structural damage detection.展开更多
The 193 nm deep-ultraviolet(DUV)laser plays a critical role in advanced semiconductor chip manufacturing[1,2],micro-nano material characterization[3,4]and biomedical analysis[5,6],due to its high spatial resolution an...The 193 nm deep-ultraviolet(DUV)laser plays a critical role in advanced semiconductor chip manufacturing[1,2],micro-nano material characterization[3,4]and biomedical analysis[5,6],due to its high spatial resolution and short wavelength.Efficient and compact 193 nm DUV laser source thus becomes a hot research area.Currently,193 nm Ar F excimer gas laser is widely employed in DUV lithography systems and serves as the enabling technology for 7 and 5 nm semiconductor fabrication.展开更多
Six new lanthanide complexes:[Ln(3,4-DEOBA)3(4,4'-DM-2,2'-bipy)]2·2C_(2)H_(5)OH,[Ln=Dy(1),Eu(2),Tb(3),Sm(4),Ho(5),Gd(6);3,4-DEOBA-=3,4-diethoxybenzoate,4,4'-DM-2,2'-bipy=4,4'-dimethyl-2,2'...Six new lanthanide complexes:[Ln(3,4-DEOBA)3(4,4'-DM-2,2'-bipy)]2·2C_(2)H_(5)OH,[Ln=Dy(1),Eu(2),Tb(3),Sm(4),Ho(5),Gd(6);3,4-DEOBA-=3,4-diethoxybenzoate,4,4'-DM-2,2'-bipy=4,4'-dimethyl-2,2'-bipyridine]were successfully synthesized by the volatilization of the solution at room temperature.The crystal structures of six complexes were determined by single-crystal X-ray diffraction technology.The results showed that the complexes all have a binuclear structure,and the structures contain free ethanol molecules.Moreover,the coordination number of the central metal of each structural unit is eight.Adjacent structural units interact with each other through hydrogen bonds and further expand to form 1D chain-like and 2D planar structures.After conducting a systematic study on the luminescence properties of complexes 1-4,their emission and excitation spectra were obtained.Experimental results indicated that the fluorescence lifetimes of complexes 2 and 3 were 0.807 and 0.845 ms,respectively.The emission spectral data of complexes 1-4 were imported into the CIE chromaticity coordinate system,and their corre sponding luminescent regions cover the yellow light,red light,green light,and orange-red light bands,respectively.Within the temperature range of 299.15-1300 K,the thermal decomposition processes of the six complexes were comprehensively analyzed by using TG-DSC/FTIR/MS technology.The hypothesis of the gradual loss of ligand groups during the decomposition process was verified by detecting the escaped gas,3D infrared spectroscopy,and ion fragment information detected by mass spectrometry.The specific decomposition path is as follows:firstly,free ethanol molecules and neutral ligands are removed,and finally,acidic ligands are released;the final product is the corresponding metal oxide.CCDC:2430420,1;2430422,2;2430419,3;2430424,4;2430421,5;2430423,6.展开更多
BACKGROUND Hepatocellular carcinoma(HCC)is among the most aggressive primary liver cancers,leading to significant global mortality.While early diagnosis improves prognosis,treatment decisions,particularly between surg...BACKGROUND Hepatocellular carcinoma(HCC)is among the most aggressive primary liver cancers,leading to significant global mortality.While early diagnosis improves prognosis,treatment decisions,particularly between surgical resection and radiofrequency ablation(RFA),remain controversial.AIM To clarify this issue using sentiment analysis of medical literature alongside a meta-analysis of overall survival(OS).METHODS We included studies comparing liver resection and RFA,excluding case reports,editorials,and studies without relevant outcomes.A systematic search in PubMed and Web of Science identified 197 studies.Abstracts underwent sentiment analysis using Python’s Natural Language Toolkit library,categorizing them as favoring resection,ablation,or neutral.We also performed a meta-analysis using a random-effects model on 11 studies reporting hazard ratios(HRs)for OS.RESULTS Sentiment analysis revealed that 75.1%of abstracts were neutral,14.2%favored resection,and 10.7%favored RFA.The meta-analysis showed a significant survival advantage for liver resection,with a pooled HR of 0.5924(95%confidence interval:0.540-0.649).Heterogeneity was moderate(I²=39.98%).Despite the meta-analysis demonstrating clear survival benefits of liver resection,most abstracts maintained a neutral stance.This discrepancy highlights potential biases or hesitancy in drawing definitive conclusions.CONCLUSION The study emphasizes the need for clinicians to prioritize robust statistical evidence over narrative impressions.Liver resection remains the preferred treatment for HCC in eligible patients.展开更多
Actuator dynamics introduce a synchronization disparity between commanded displacements transmitted to the actuator and the actual displacements generated by the actuator,thereby affecting its precision and potentiall...Actuator dynamics introduce a synchronization disparity between commanded displacements transmitted to the actuator and the actual displacements generated by the actuator,thereby affecting its precision and potentially leading to instability in real-time hybrid simulation(RTHS).This study aims to elucidate the relationship between calculated and measured displacements by analyzing their magnitude and phase in the frequency domain via transformations.The physical implications of these relationships are explored in the context of frequency domain evaluation indices(FEI),the transfer function of actuator dynamics,and delay compensation.Formulations for achieving perfect compensation of actuator dynamics are developed,and an enhanced compensation approach,termed improved windowed frequency domain evaluation index-based compensation(IWFEI),is introduced.The efficacy of IWFEI is assessed using a RTHS benchmark model,with perturbed simulations conducted to validate its robustness.Uncertainties inherent in actuator dynamics are represented as random variables in these simulations.Comparative analysis of the mean values and variances of evaluation criteria demonstrates that IWFEI enables more accurate and robust compensation.Furthermore,strong correlations observed among criteria in the time and frequency domains underscore the effectiveness of the proposed frequency domain-based compensation method in mitigating amplitude errors and phase delays in RTHS.展开更多
Energy storage-equipped photovoltaic(PV-storage)systems can meet frequency regulation requirements under various operating conditions,and their coordinated support for grid frequency has become a future trend.To addre...Energy storage-equipped photovoltaic(PV-storage)systems can meet frequency regulation requirements under various operating conditions,and their coordinated support for grid frequency has become a future trend.To address frequency stability issues caused by low inertia and weak damping,this paper proposes a multi-timescale frequency regulation coordinated control strategy for PV-storage integrated systems.First,a self-synchronizing control strategy for grid-connected inverters is designed based on DC voltage dynamics,enabling active inertia support while transmitting frequency variation information.Next,an energy storage inertia support control strategy is developed to enhance the frequency nadir,and an active frequency support control strategy for PV system considering a frequency regulation deadband is proposed,where the deadband value is determined based on the power regulation margin of synchronous generators,allowing the PV-storage system to adaptively switch between inertia support and primary frequency regulation under different disturbance conditions.This approach ensures system frequency stability while fully leveraging the regulation capabilities of heterogeneous resources.Finally,the real-time digital simulation results of the PV-storage integrated system demonstrate that,compared to existing control methods,the proposed strategy effectively reduces the rate of change of frequency and improves the frequency nadir under various disturbance scenarios,verifying its effectiveness.展开更多
With the increasing penetration of renewable energy,the coordination of energy storage with thermal power for frequency regulation has become an effective means to enhance grid frequency security.Addressing the challe...With the increasing penetration of renewable energy,the coordination of energy storage with thermal power for frequency regulation has become an effective means to enhance grid frequency security.Addressing the challenge of improving the frequency regulation performance of a thermal-storage primary frequency regulation system while reducing its associated losses,this paper proposes a multi-dimensional cooperative optimization strategy for the control parameters of a combined thermal-storage system,considering regulation losses.First,the frequency regulation losses of various components within the thermal power unit are quantified,and a calculation method for energy storage regulation loss is proposed,based on Depth of Discharge(DOD)and C-rate.Second,a thermal-storage cooperative control method based on series compensation is developed to improve the system’s frequency regulation performance.Third,targeting system regulation loss cost and regulation output,and considering constraints on output overshoot and system parameters,an improved Particle Swarm Optimization(PSO)algorithm is employed to tune the parameters of the low-pass filter and the series compensator,thereby reducing regulation losses while enhancing performance.Finally,simulation results demonstrate that the total loss cost of the proposed control strategy is comparable to that of a system with only thermal power participation.However,the thermal power loss cost is reduced by 42.16%compared to the thermal-only case,while simultaneously improving system frequency stability.Thus,the proposed strategy effectively balances system frequency stability and economic efficiency.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.62271230)Shandong Provincial Central Guidance on Local Science and Technology Development Fund(Grant No.YDZX2022178).
文摘Fault features in mechanical systems often manifest as transient impulses,which can be effectively analyzed using time-frequency analysis(TFA)methods.Recently,a new TFA technique known as the time-reassigned multi-synchrosqueezing transform(TMssT)was proposed to capture these transient impulses for fault diagnosis.However,the TMSST,which is based on the short-time Fourier transform(STFT),suffers from unclear high-frequency re-presentations owing to the fixed sliding window used in the STFT.To address this limitation,the current study combined TMSST with the S-transform and a local maximum method to enhance the time-frequency representation for improved signal analysis.Furthermore,an extractive reconstruction algorithm that binds the maximum value of the spectral envelope is proposed for spectral decomposition.To validate the proposed technique,a simulated noise-added signal and four experimental bearing defect datasets were used.The results demonstrate that the proposed technique can effectively and accurately extract fault features from bearing signals regardless of whether the bearings operate under constant or varying speed conditions.This study offers a novel and efficient approach for fault diagnosis in mechanical systems with complex dynamic behaviors.
文摘Flooding remains one of the most destructive natural disasters,posing significant risks to both human lives and infrastructure.In India,where a large area is susceptible to flood hazards,the importance of accurate flood frequency analysis(FFA)and flood susceptibility mapping cannot be overstated.This study focuses on the Haora River basin in Tripura,a region prone to frequent flooding due to a combination of natural and anthropogenic factors.This study evaluates the suitability of the Log-Pearson Type Ⅲ(LP-Ⅲ)and Gumbel Extreme Value-1(EV-1)distributions for estimating peak discharges and delineates floodsusceptible zones in the Haora River basin,Tripura.Using 40 years of peak discharge data(1984-2023),the LP-Ⅲ distribution was identified as the most appropriate model based on goodness-of-fit tests.Flood susceptibility mapping,integrating 16 thematic layers through the Analytical Hierarchy Process,identified 8%,64%,and 26%of the area as high,moderate,and low susceptibility zones,respectively,with a model success rate of 0.81.The findings highlight the need for improved flood management strategies,such as enhancing river capacity and constructing flood spill channels.These insights are critical for designing targeted flood mitigation measures in the Haora basin and other flood-prone regions.
基金the research project funded by the Fundamental Research Funds for the Central Universities(No.HIT.OCEP.2024038)the National Natural Science Foundation of China(No.52372351)the State Key Laboratory of Micro-Spacecraft Rapid Design and Intelligent Cluster,China(No.MS02240107)。
文摘To improve design accuracy and reliability of structures,this study solves the uncertain natural frequencies with consideration for geometric nonlinearity and structural uncertainty.Frequencies of the laminated plate with all four edges clamped(CCCC)are derived based on Navier's method and Galerkin's method.The novelty of the current work is that the number of unknowns in the displacement field model of a CCCC plate with free midsurface(CCCC-2 plate)is only three compared with four or five in cases of other exposed methods.The present analytical method is proved to be accurate and reliable by comparing linear natural frequencies and nonlinear natural frequencies with other models available in the open literature.Furthermore,a novel method for analyzing effects of mean values and tolerance zones of uncertain structural parameters on random frequencies is proposed based on a self-developed Multiscale Feature Extraction and Fusion Network(MFEFN)system.Compared with a direct Monte Carlo Simulation(MCS),the MFEFNbased procedure significantly reduces the calculation burden with a guarantee of accuracy.Our research provides a method to calculate nonlinear natural frequencies under two boundary conditions and presentes a surrogate model to predict frequencies for accuracy analysis and optimization design.
基金supported by the National Key Research and Development Program of China(No.2022YFC2204400)。
文摘This paper introduces a small perturbation frequency domain thermal analysis model based on the nonlinear dynamics model.The model can be applied to study the high-precision temperature control of thermal systems under low-frequency complex perturbations.The frequency domain characteristics of the space gravitational wave detection satellite are analyzed,and a multi-channel perturbation structure is established.The effects of three kinds of heat flow perturbations,including external heat flow,power generation power,and waste heat of electronic equipment,on the temperature through five transfer paths are investigated.It has been discovered that the waste heat from electronic equipment inside the satellite has the most noticeable effect on the temperature power spectral density of temperature-sensitive optical loads,serving as the primary factor influencing thermal stability.For complex noise signals,the small perturbation analysis method can decompose the different frequency components or ranges,reducing the problem to linearized analysis and simplifying complex calculations.The results indicate that the temperature power spectral density decreases as signal frequency increases,with low-frequency signals exerting a greater influence on temperature stability.The small perturbation analysis method is a novel and effective method for temperature control of space thermal systems,with high accuracy and stability.
基金The National Natural Science Foundation of China(No.51976039)。
文摘To explore the electrostatic discharge behavior of charged powders in industrial silos,discharge experiments are conducted based on a full-size industrial silo discharge platform.Electrostatic discharge mode,frequency,and energy are investigated for powders of different polarities.Although the powders have low charge-to-mass ratios(+0.087μC/kg for the positively charged powders and−0.26μC/kg for the negatively charged ones),electrostatic discharges occur approximately every 10 s,with the maximum discharge energy being 800 mJ.Powder polarity considerably influences discharge energy.The positive powders exhibit higher discharge energy than the negative ones,although discharge frequency remains similar for both.Effects of powder charge,humidity,and mass flow on discharge frequency and discharge energy are quantitatively analyzed,providing important insights for the improvement of safety in industrial powder handling.
基金supported by the National Natural Science Foundation of China(No.11772090).
文摘This study investigates the nonlinear dynamic properties of rotating functionally graded sandwich rectangular plates in a thermal environment.The nonlinear vibration equations for a rotating metal-ceramic functionally graded sandwich rectangular plate in a thermal environment are derived using classical thin plate theory and Hamilton’s principle,considering geometric nonlinearity,temperature-dependent material properties,and power law distribution of components through the thickness.With cantilever boundary conditions,the flexural nonlinear differential equations of the rectangular sandwich plate are obtained via the Galerkin method.Since the natural vibration differential equations exhibit nonlinear characteristics,the multiscale method is employed to derive the expression for nonlinear natural frequency.An example analysis reveals how the natural frequency of a functionally graded sandwich rectangular plate varies with rotational speed and temperature.Results show that the nonlinear/linear frequency ratio increases with rotational angular velocity Ω and thickness-to-length ratio h/a,follows a cosine-like periodic pattern with the setting angle,and shows a sharp decrease followed by a rapid increase with increasing width-to-length ratio b/a.The derived analytical solutions for nonlinear frequency provide valuable insights for assessing the dynamic characteristics of functionally graded structures.
基金Supported by National Key Research and Development Program of China(Grant No.2022YFB3403600)the National Natural Science Foundation of China(Grant No.52305461)。
文摘The fused quartz hemispherical resonator is the core component of the hemispherical resonator gyroscope.It features a complex shape and is Made from a Material that is difficult to process.Scratches are easily introduced during grinding,potentially degrading the mass-stiffness-damping symmetry;however,the underlying mechanisms of this influence have not been fully understood.This paper aims to investigate the effects of scratch defects on the frequency splitting and quality factor of the hemispherical resonator.First,finite element models of the hemispherical resonator with scratches are established.Then,the effects of the mass-stiffness factor,as well as the latitude and length of the scratches,on frequency splitting are analyzed.Furthermore,the impacts of latitude,length,and the first four harmonics of the unbalanced mass caused by scratches on thermoelastic damping and anchor loss are examined.Simulation results indicate that scratches above 55°latitude cause frequency splitting solely due to stiffness changes.Frequency splitting caused by scratches of the same size on the inherent rigidity shaft at the rim is approximately 50%of that near the transition fillet.Frequency splitting varies linearly with the volume of material removed by scratches.Scratches have little effect on thermoelastic damping.The first three harmonics of the unbalanced mass due to scratches at the rim are the primary contributors to anchor loss.Finally,focused ion beam trimming experiments are conducted at different locations on the hemispherical resonator.The trends observed in the experimental results are consistent with the simulation results.This work provides guidance for evaluating the impact of scratches on the performance of hemispherical resonators and for developing appropriate trimming processes.
基金funded by the National Natural Science Foundation of China(52574084)the Key Research and Development Projects of Guangdong Province(2019B111108001)+5 种基金the Guangdong Basic and Applied Basic Research Foundation(2024A1515010045)the Natural Science Foundation of Jiangsu Province(BK20231217)the Independent research project of the State Key Laboratory of Subtropical Building and Urban Science(2023ZB15)the Key Laboratory of Geomechanics and Geotechnical Engineering Safety,Chinese Academy of Sciences(SKLGME023001)the Open Research Fund Program of the State Key Laboratory of Hydroscience and Engineering(sklhse-KF-2025-D-02)the Special Project on Basic and Applied Basic Research of the Guangzhou Municipal Science and Technology Bureau(2025A04J3992)。
文摘The seismic stability of the rock slope at tunnel entrances is very intricate because of the interactions among geological structures and earthquakes.However,the local damage mechanism and the correlation mechanism of accumulated damage and landslide triggering are not clear.To investigate the correlation between the inherent frequency and seismic characteristics of a layered slope at a tunnel entrance from the perspective of the frequency domain,a three-dimensional finite element modal analysis and Fourier spectrum analysis of shaking table tests were carried out.This work takes the quarry slope at the tunnel entrance in Xiamen City as a case example.The study region is predominantly affected by strong seismic activity,where the rock is primarily composed of granite with varying degrees of weathering.The results show that the seismic energy below the tunnel is mostly focused on the lowfrequency ranges,whereas the energy above the tunnel is gradually transferred to the high-frequency range.By analyzing the peak spectrum value of high-order inherent frequencies for the slope,its seismic damage evolution can be effectively identified,including fracture initiation,accelerated deformation,and sliding instability stages.The seismic response of the slope includes multi-mode interactions,which mainly include bending,torsion,and combined deformation.There are magnification effects of elevation,slope surface,and structural plane in the slope.Moreover,the triggering mechanism of the local deformation and integral sliding for the landslide is identified,which indicates that the lining structure of the tunnel entrance is more prone to seismic damage.This work successfully investigated the seismic damage evolution and failure mechanism of the slope at tunnel entrances in the frequency domain.
基金supported by China Southern Power Grid Corporation(036000KC23090005(GDKJXM20231027)).
文摘This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first solved via Newton-Raphson iteration through a set of nonlinear equations,and then input-output variables are selected to estimate the linear transfer function of the original NTP system without perturbations.The applications and insights of the proposed algorithm are discussed,particularly in guiding existing frequency scan algorithms,which are restricted by time-domain signal generation or measurement.This improvement is achieved through linear stability analysis of NTP systems with perturbations.
基金supported by Qingdao Key Medical and Health Discipline ProjectThe Intramural Research Program of the Affiliated Hospital of Qingdao University,No. 4910Qingdao West Coast New Area Science and Technology Project,No. 2020-55 (all to SW)。
文摘Border-associated macrophages are located at the interface between the brain and the periphery, including the perivascular spaces, choroid plexus, and meninges. Until recently, the functions of border-associated macrophages have been poorly understood and largely overlooked. However, a recent study reported that border-associated macrophages participate in stroke-induced inflammation, although many details and the underlying mechanisms remain unclear. In this study, we performed a comprehensive single-cell analysis of mouse border-associated macrophages using sequencing data obtained from the Gene Expression Omnibus(GEO) database(GSE174574 and GSE225948). Differentially expressed genes were identified, and enrichment analysis was performed to identify the transcription profile of border-associated macrophages. CellChat analysis was conducted to determine the cell communication network of border-associated macrophages. Transcription factors were predicted using the ‘pySCENIC' tool. We found that, in response to hypoxia, borderassociated macrophages underwent dynamic transcriptional changes and participated in the regulation of inflammatory-related pathways. Notably, the tumor necrosis factor pathway was activated by border-associated macrophages following ischemic stroke. The pySCENIC analysis indicated that the activity of signal transducer and activator of transcription 3(Stat3) was obviously upregulated in stroke, suggesting that Stat3 inhibition may be a promising strategy for treating border-associated macrophages-induced neuroinflammation. Finally, we constructed an animal model to investigate the effects of border-associated macrophages depletion following a stroke. Treatment with liposomes containing clodronate significantly reduced infarct volume in the animals and improved neurological scores compared with untreated animals. Taken together, our results demonstrate comprehensive changes in border-associated macrophages following a stroke, providing a theoretical basis for targeting border-associated macrophages-induced neuroinflammation in stroke treatment.
基金supported in part by the National Natural Science Fundation of China(52225704 and 52107096).
文摘The dynamics of network power response play a crucial role in system stability.However,the integration of power electronic equipment leads to amplitude and angular frequency(abbreviated as"frequency")time-varying characteristics of the node voltage during dynamic processes.As a result,traditional calcu-lation methods for and characteristics of the power response of the network based on phasor and impe-dance lose their validity.Therefore,this paper undertakes mathematical calculations to reveal the power response of a network under excitation by voltage with time-varying amplitude and frequency(TVAF),relying on the original mathematical relationships and superimposed step response.Then,the multi-timescale characteristics of both the active and reactive power of the network are explored physically.Additionally,this paper reveals a new phenomenon of storing and releasing the active and reactive power of the network.To meet practical engineering requirements,a simplified power expression is presented.Finally,the theoretical analysis is validated through time-domain simulations.
基金Project supported by the National Natural Science Foundation of China(Nos.U23A20111 and 12372160)。
文摘Radiofrequency ablation(RFA)is a form of minimally invasive procedure that precisely ablates abnormal lesions or hyperplastic tissues through thermal energy generated by the radiofrequency current at the tip electrode of the flexible catheter,which aims to partially or fully restore the function of the corresponding tissues or organs.Accurate prediction and control of thermal fields are crucial for clinical thermal ablation to ensure precise control of the ablation lesion size and prevent excessive burning of healthy tissues.In this study,an axisymmetric analytical model is developed for the electrothermal analysis of RFA in the cambered tissue surface and verified with the finite element analysis(FEA),which incorporates both the thermal field induced by the radiofrequency current and Pennes'biothermal effect.This model utilizes analytically derived electric and thermal fields to accurately predict the increase in the tissue temperature and the time-varying size of ablation lesion in the tissue.Furthermore,the parameters such as the input current density,curvature,and convective heat transfer coefficient of blood have a significant effect on the thermal field and thus the ablation lesion size.This electrothermal analytical model with a large curvature may provide a theoretical foundation and guidance for the future RFA applications on large-curvature biological surfaces,thereby enhancing accuracy,reducing the need for re-ablation,and lowering the costs associated with the design and production of ablation catheters.
文摘This study investigates how the uncertainty surrounding cryptocurrency affects cryptocurrency returns(CR)by employing various wavelet techniques.We concentrate on the recently published cryptocurrency uncertainty index(UCRY)and the top eight cryptocurrencies by market capitalization from December 30,2013,to June 30,2023.Our results showed that the UCRY index strongly predicted CR.In particular,the UCRY index has a leading position at all frequencies for all cryptocurrencies in our sample.Additionally,when the impacts of economic policy uncertainty and the volatility index are eliminated,the significant comovement of UCRY-CR remains unchanged for the short-,medium-,and long-term investment horizons.Therefore,we conclude that the UCRY-CR relationship is both persistent and pervasive.Our study contributes toward the literature on the relationships between cryptocurrencies and market uncertainties,as well as toward investors who use uncertainty indices to design investment strategies for their portfolios.
文摘This study explores theoretical insights and experimental results on monitoring load-carrying capacity degradation in bridge spans through frequency analysis.Experiments were conducted on real bridge structures,including the Binh Thuan Bridge,focusing on analyzing the power spectral density(PSD)of vibration signals under random traffic loads.Detailed digital models of various bridge spans with different structural designs and construction periods were developed to ensure diversity.The study utilized PSD to analyze the vibration signals from the bridge spans under various loading conditions,identifying the vibration frequencies and the corresponding response regions.The research correlated the observed frequency changes of PSD with the actual deterioration of the bridges over time,identifying patterns that indicate a reduction in stiffness.Experiments demonstrated that frequency changes,particularly in high-frequency regions,are directly related to a reduction in the stiffness of bridge spans.This supports the hypothesis that natural frequencies can serve as effective indicators of structural damage.Furthermore,the emergence and shift of resonant frequency regions provide valuable insights into the extent of damage in actual bridge spans,highlighting the potential for using changes in resonant frequency regions as a new tool for structural damage detection.
基金supported by the National Natural Science Foundation of China(Grant Nos.62450006,62304217,62274157,62127807,62234011,62034008,62074142,62074140)Tianshan Innovation Team Program(Grant No.2022TSYCTD0005)+1 种基金Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0880000)Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant Nos.2023124,Y2023032)。
文摘The 193 nm deep-ultraviolet(DUV)laser plays a critical role in advanced semiconductor chip manufacturing[1,2],micro-nano material characterization[3,4]and biomedical analysis[5,6],due to its high spatial resolution and short wavelength.Efficient and compact 193 nm DUV laser source thus becomes a hot research area.Currently,193 nm Ar F excimer gas laser is widely employed in DUV lithography systems and serves as the enabling technology for 7 and 5 nm semiconductor fabrication.
文摘Six new lanthanide complexes:[Ln(3,4-DEOBA)3(4,4'-DM-2,2'-bipy)]2·2C_(2)H_(5)OH,[Ln=Dy(1),Eu(2),Tb(3),Sm(4),Ho(5),Gd(6);3,4-DEOBA-=3,4-diethoxybenzoate,4,4'-DM-2,2'-bipy=4,4'-dimethyl-2,2'-bipyridine]were successfully synthesized by the volatilization of the solution at room temperature.The crystal structures of six complexes were determined by single-crystal X-ray diffraction technology.The results showed that the complexes all have a binuclear structure,and the structures contain free ethanol molecules.Moreover,the coordination number of the central metal of each structural unit is eight.Adjacent structural units interact with each other through hydrogen bonds and further expand to form 1D chain-like and 2D planar structures.After conducting a systematic study on the luminescence properties of complexes 1-4,their emission and excitation spectra were obtained.Experimental results indicated that the fluorescence lifetimes of complexes 2 and 3 were 0.807 and 0.845 ms,respectively.The emission spectral data of complexes 1-4 were imported into the CIE chromaticity coordinate system,and their corre sponding luminescent regions cover the yellow light,red light,green light,and orange-red light bands,respectively.Within the temperature range of 299.15-1300 K,the thermal decomposition processes of the six complexes were comprehensively analyzed by using TG-DSC/FTIR/MS technology.The hypothesis of the gradual loss of ligand groups during the decomposition process was verified by detecting the escaped gas,3D infrared spectroscopy,and ion fragment information detected by mass spectrometry.The specific decomposition path is as follows:firstly,free ethanol molecules and neutral ligands are removed,and finally,acidic ligands are released;the final product is the corresponding metal oxide.CCDC:2430420,1;2430422,2;2430419,3;2430424,4;2430421,5;2430423,6.
文摘BACKGROUND Hepatocellular carcinoma(HCC)is among the most aggressive primary liver cancers,leading to significant global mortality.While early diagnosis improves prognosis,treatment decisions,particularly between surgical resection and radiofrequency ablation(RFA),remain controversial.AIM To clarify this issue using sentiment analysis of medical literature alongside a meta-analysis of overall survival(OS).METHODS We included studies comparing liver resection and RFA,excluding case reports,editorials,and studies without relevant outcomes.A systematic search in PubMed and Web of Science identified 197 studies.Abstracts underwent sentiment analysis using Python’s Natural Language Toolkit library,categorizing them as favoring resection,ablation,or neutral.We also performed a meta-analysis using a random-effects model on 11 studies reporting hazard ratios(HRs)for OS.RESULTS Sentiment analysis revealed that 75.1%of abstracts were neutral,14.2%favored resection,and 10.7%favored RFA.The meta-analysis showed a significant survival advantage for liver resection,with a pooled HR of 0.5924(95%confidence interval:0.540-0.649).Heterogeneity was moderate(I²=39.98%).Despite the meta-analysis demonstrating clear survival benefits of liver resection,most abstracts maintained a neutral stance.This discrepancy highlights potential biases or hesitancy in drawing definitive conclusions.CONCLUSION The study emphasizes the need for clinicians to prioritize robust statistical evidence over narrative impressions.Liver resection remains the preferred treatment for HCC in eligible patients.
基金Ministry of Science and Technology of China under Grant No.2023YFC3804300National Science Foundation of China under Grant No.52178114。
文摘Actuator dynamics introduce a synchronization disparity between commanded displacements transmitted to the actuator and the actual displacements generated by the actuator,thereby affecting its precision and potentially leading to instability in real-time hybrid simulation(RTHS).This study aims to elucidate the relationship between calculated and measured displacements by analyzing their magnitude and phase in the frequency domain via transformations.The physical implications of these relationships are explored in the context of frequency domain evaluation indices(FEI),the transfer function of actuator dynamics,and delay compensation.Formulations for achieving perfect compensation of actuator dynamics are developed,and an enhanced compensation approach,termed improved windowed frequency domain evaluation index-based compensation(IWFEI),is introduced.The efficacy of IWFEI is assessed using a RTHS benchmark model,with perturbed simulations conducted to validate its robustness.Uncertainties inherent in actuator dynamics are represented as random variables in these simulations.Comparative analysis of the mean values and variances of evaluation criteria demonstrates that IWFEI enables more accurate and robust compensation.Furthermore,strong correlations observed among criteria in the time and frequency domains underscore the effectiveness of the proposed frequency domain-based compensation method in mitigating amplitude errors and phase delays in RTHS.
基金supported by the State Grid Corporation of China under Grant for Science and Technology Projects(No.SGNXJYOOZWJS2500029).
文摘Energy storage-equipped photovoltaic(PV-storage)systems can meet frequency regulation requirements under various operating conditions,and their coordinated support for grid frequency has become a future trend.To address frequency stability issues caused by low inertia and weak damping,this paper proposes a multi-timescale frequency regulation coordinated control strategy for PV-storage integrated systems.First,a self-synchronizing control strategy for grid-connected inverters is designed based on DC voltage dynamics,enabling active inertia support while transmitting frequency variation information.Next,an energy storage inertia support control strategy is developed to enhance the frequency nadir,and an active frequency support control strategy for PV system considering a frequency regulation deadband is proposed,where the deadband value is determined based on the power regulation margin of synchronous generators,allowing the PV-storage system to adaptively switch between inertia support and primary frequency regulation under different disturbance conditions.This approach ensures system frequency stability while fully leveraging the regulation capabilities of heterogeneous resources.Finally,the real-time digital simulation results of the PV-storage integrated system demonstrate that,compared to existing control methods,the proposed strategy effectively reduces the rate of change of frequency and improves the frequency nadir under various disturbance scenarios,verifying its effectiveness.
基金supported by the Science and Technology Development Project of Jilin Province(Project No.YDZJ202301ZYTS284).
文摘With the increasing penetration of renewable energy,the coordination of energy storage with thermal power for frequency regulation has become an effective means to enhance grid frequency security.Addressing the challenge of improving the frequency regulation performance of a thermal-storage primary frequency regulation system while reducing its associated losses,this paper proposes a multi-dimensional cooperative optimization strategy for the control parameters of a combined thermal-storage system,considering regulation losses.First,the frequency regulation losses of various components within the thermal power unit are quantified,and a calculation method for energy storage regulation loss is proposed,based on Depth of Discharge(DOD)and C-rate.Second,a thermal-storage cooperative control method based on series compensation is developed to improve the system’s frequency regulation performance.Third,targeting system regulation loss cost and regulation output,and considering constraints on output overshoot and system parameters,an improved Particle Swarm Optimization(PSO)algorithm is employed to tune the parameters of the low-pass filter and the series compensator,thereby reducing regulation losses while enhancing performance.Finally,simulation results demonstrate that the total loss cost of the proposed control strategy is comparable to that of a system with only thermal power participation.However,the thermal power loss cost is reduced by 42.16%compared to the thermal-only case,while simultaneously improving system frequency stability.Thus,the proposed strategy effectively balances system frequency stability and economic efficiency.
