Human motion modeling is a core technology in computer animation,game development,and humancomputer interaction.In particular,generating natural and coherent in-between motion using only the initial and terminal frame...Human motion modeling is a core technology in computer animation,game development,and humancomputer interaction.In particular,generating natural and coherent in-between motion using only the initial and terminal frames remains a fundamental yet unresolved challenge.Existing methods typically rely on dense keyframe inputs or complex prior structures,making it difficult to balance motion quality and plausibility under conditions such as sparse constraints,long-term dependencies,and diverse motion styles.To address this,we propose a motion generation framework based on a frequency-domain diffusion model,which aims to better model complex motion distributions and enhance generation stability under sparse conditions.Our method maps motion sequences to the frequency domain via the Discrete Cosine Transform(DCT),enabling more effective modeling of low-frequency motion structures while suppressing high-frequency noise.A denoising network based on self-attention is introduced to capture long-range temporal dependencies and improve global structural awareness.Additionally,a multi-objective loss function is employed to jointly optimize motion smoothness,pose diversity,and anatomical consistency,enhancing the realism and physical plausibility of the generated sequences.Comparative experiments on the Human3.6M and LaFAN1 datasets demonstrate that our method outperforms state-of-the-art approaches across multiple performance metrics,showing stronger capabilities in generating intermediate motion frames.This research offers a new perspective and methodology for human motion generation and holds promise for applications in character animation,game development,and virtual interaction.展开更多
BACKGROUND Critical flicker frequency(CFF)is a quantitative tool for assessing hepatic enceph-alopathy(HE),particularly minimal HE,which is associated with poor prognosis in liver cirrhosis.Alcohol-related liver disea...BACKGROUND Critical flicker frequency(CFF)is a quantitative tool for assessing hepatic enceph-alopathy(HE),particularly minimal HE,which is associated with poor prognosis in liver cirrhosis.Alcohol-related liver disease(ALD)is a leading global cause of cirrhosis;however,the effects of alcohol on CFF and its relationship with liver stiffness(LS)remain underexplored.AIM To study the impact of alcohol withdrawal on CFF and its correlation with LS in ALD patients.METHODS A total of 108 patients were included:93 heavy drinkers hospitalized for detoxi-fication,15 with non-ALD etiologies,and 20 healthy controls.CFF was measured using the Hepatonorm analyzer,and LS via transient elastography(FibroScan).Baseline and post-detoxification assessments were conducted in 57 ALD patients.RESULTS The cohort had a mean age of 53.7±13.8 years,with 74% male participants.CFF measurements were reliable,with 97.2% of patients showing an interquartile range<20%.ALD patients exhibited significantly lower CFF compared to controls.Receiver operating characteristic analysis for overt HE(n=12)yielded an area under the curve of 0.66(95%confidence interval:0.49-0.84,P=0.0142),with an optimal cutoff of 36.5 Hz.CFF significantly improved post-detoxification.Patients with LS>17 kPa had lower CFF,while those with intermediate LS showed no significant difference.CONCLUSION CFF is influenced by HE severity and acute alcohol exposure,showing improvement after detoxification.Its weak correlation with fibrosis stage suggests that CFF serves as a sensitive neurocognitive marker in ALD.展开更多
Highly accurate international height reference frames with long-term stability,global consistency,and homogeneity are crucial for monitoring sea level variations,understanding climate change,managing disasters,and sup...Highly accurate international height reference frames with long-term stability,global consistency,and homogeneity are crucial for monitoring sea level variations,understanding climate change,managing disasters,and supporting other applications that benefit scientific research and societal well-being.Currently,there are over 100 local height reference systems worldwide.Unifying these systems is a pivotal step toward constructing international height reference frames.The method introduced in this study-the gravity frequency shift via Satellite Frequency Signal Transfer(SFST)-represents a groundbreaking relativistic geodetic approach,demonstrating its potential to surpass the constraints of conventional techniques.The advent of high-precision optical atomic clocks(OAC)with an accuracy level of 1×10^(-18) has facilitated this method's implementation.The International Association of Geodesy(IAG)has established the International Height Reference System(IHRS)and its practical realization,the International Height Reference Frame(IHRF).Our study focuses on two neighbouring height systems:the China Height System(CHS)and the Nepal Height System(NHS),separated by the Himalayas and the Xizang plateau.We aim to unify these two systems by determining the geopotential and orthometric height differences between their respective height datum stations:the Qingdao Height Datum Station(QHDS)and the Madar Height Datum Station(MHDS)using a simulation experiment with the method mentioned above.Using an OAC with an accuracy of 1×10^(-18),we identified a geopotential difference of-8.348±0.464 m^(2)s^(-2) and an orthometric height difference of 0.786±0.047 m between QHDS and MHDS.These results suggest that the introduced method could unify any two height systems with fewcentimeter-level precision,emphasizing its significance in contributing to the construction of the IHRS/IHRF with today's required precision.In summary,the SFST technique is a novel geodetic method that offers an alternative for height system unification,delivering centimeter-level precision,surpassing traditional methods,and supporting the development of the IHRF.展开更多
The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were i...The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation.The results show that the average grain size decreases after application of LFEC.At the same time,the fraction of equiaxed grains increases compared with the ingots that without LFEC.In addition,the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency.When the current frequency increases from 5 Hz to 20 Hz,the average grain size decreases from 5.39 mm to 4.74 mm,and the fraction of equiaxed grains increases from 41.21%to 55.24%.The distribution of Lorentz force,melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software.It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency,thus the melt flow velocity and heat transfer in the melt are promoted.It can facilitate the heterogenous nucleation in the melt,resulting in grain refinement,and further preventing hot cracking of large size ingots.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 variation of the nonlinear contact stiffness induced by the elastic wheel-holding effect between the aircraft and tractor has an important effect on the vibration characteristics of an airfield towbarless traction...The variation of the nonlinear contact stiffness induced by the elastic wheel-holding effect between the aircraft and tractor has an important effect on the vibration characteristics of an airfield towbarless traction system,making it essential for ensuring the safety of this emerging towing-out mode.In this paper,the frequency evolutionary tendency of the traction system is studied and obtained considering the variation of nonlinear contact stiffness for the first time.A novel modal analysis method,based on a derived nonlinear contact relationship,is proposed to investigate the vibration characteristics for mechanical system.Frequency veering and mode exchange phenomena in the low-order modes are observed due to the variation of nonlinear contact stiffness.These findings are further validated by the experimental results of a scaled-down model.In addition,it is also found that the veering critical point will be shifted with the external loads.The study provides valuable insights into the vibration characteristics and frequency veering behavior of similar mechanism-based systems,such as towbarless traction system,and has important implications for improving their design and operational performance.展开更多
Research on the properties of neutron stars with dark energy is a particularly interesting yet unresolved problem in astrophysics.We analyze the influence of dark energy on the equation of state,the maximum mass,the s...Research on the properties of neutron stars with dark energy is a particularly interesting yet unresolved problem in astrophysics.We analyze the influence of dark energy on the equation of state,the maximum mass,the surface gravitational redshift and the Keplerian frequency for the traditional neutron star and the hyperon star matter within the relativistic mean field theory,using the GM1 and TM1 parameter sets by considering the two flavor symmetries of SU(6)and SU(3)combined with the observations of PSR J1614-2230,PSR J0348+0432,PSR J0030+0451,RX J0720.4-3125,and 1E 1207.4-5209.It is found that the existence of dark energy leads to the softened equations of the state of the traditional neutron star and the hyperon star.The radius of a fixed-mass traditional neutron star(or hyperon star)with dark energy becomes smaller,which leads to increased compactness.The existence of dark energy can also enhance the surface gravitational redshift and the Keplerian frequency of traditional neutron stars and hyperon stars.The growth of the Keplerian frequency may cause the spin rate to speed up,which may provide a possible way to understand and explain the pulsar glitch phenomenon.Specifically,we infer that the mass and the surface gravitational redshift of PSR J1748-2446ad without dark energy for the GM1(TM1)parameter set are 1.141 M_(☉)(1.309 M_(☉))and 0.095(0.105),respectively.The corresponding values for the GM1(TM1)parameter set are 0.901 M_(☉)(1.072M_(☉))and 0.079(0.091)if PSR J1748-2446ad contains dark energy withα=0.05.PSR J1748-2446ad may be a low-mass pulsar with a lower surface gravitational redshift under our selected models.展开更多
Water hammer diagnostics is an important fracturing diagnosis technique to evaluate fracture locations and other downhole events in fracturing. The evaluation results are obtained by analyzing shut-in water hammer pre...Water hammer diagnostics is an important fracturing diagnosis technique to evaluate fracture locations and other downhole events in fracturing. The evaluation results are obtained by analyzing shut-in water hammer pressure signal. The field-sampled water hammer signal is often disturbed by noise interference. Noise interference exists in various pumping stages during water hammer diagnostics, with significantly different frequency range and energy distribution. Clarifying the differences in frequency range and energy distribution between effective water hammer signals and noise is the basis of setting specific filtering parameters, including filtering frequency range and energy thresholds. Filtering specifically could separate the effective signal and noise, which is the key to ensuring the accuracy of water hammer diagnosis. As an emerging technique, there is a lack of research on the frequency range and energy distribution of effective signals in water hammer diagnostics. In this paper, the frequency range and energy distribution characteristics of field-sampled water hammer signals were clarified quantitatively and qualitatively for the first time by a newly proposed comprehensive water hammer segmentation-energy analysis method. The water hammer signals were preprocessed and divided into three segments, including pre-shut-in, water hammer oscillation, and leak-off segment. Then, the three segments were analyzed by energy analysis and correlation analysis. The results indicated that, one aspect, the frequency range of water hammer oscillation spans from 0 to 0.65 Hz, considered as effective water hammer signal. The pre-shut-in and leak-off segment ranges from 0 to 0.35 Hz and 0-0.2 Hz respectively. Meanwhile, odd harmonics were manifested in water hammer oscillation segment, with the harmonic frequencies ranging approximately from 0.07 to 0.75 Hz. Whereas integer harmonics were observed in pre-shut-in segment, ranging from 6 to 40 Hz. The other aspect, the energy distribution of water hammer signals was analyzed in different frequency ranges. In 0-1 Hz, an exponential decay was observed in all three segments. In 1-100 Hz, a periodical energy distribution was observed in pre-shut-in segment, an exponential decay was observed in water hammer oscillation, and an even energy distribution was observed in leak-off segment. In 100-500 Hz, an even energy distribution was observed in those three segments, yet the highest magnitude was noted in leak-off segment. In this study, the effective frequency range and energy distribution characteristics of the field-sampled water hammer signals in different segments were sufficiently elucidated quantitatively and qualitatively for the first time, laying the groundwork for optimizing the filtering parameters of the field filtering models and advancing the accuracy of identifying downhole event locations.展开更多
Super-resolution(SR)for the camera array-based infrared light field(IRLF)images aims to reconstruct high-resolution sub-aperture images(SAIs)from their low-resolution counterparts.Existing SR methods mainly focus on e...Super-resolution(SR)for the camera array-based infrared light field(IRLF)images aims to reconstruct high-resolution sub-aperture images(SAIs)from their low-resolution counterparts.Existing SR methods mainly focus on exploiting the spatial and angular information of SAIs and have achieved promising results in the visible band.However,they fail to adaptively correct the nonuniform noise in IRLF images,resulting in over-smoothness or artifacts in their results.This study proposes a novel method that reconstructs high-resolution IRLF images while correcting the nonuniformity.The main idea is to decompose the structure and nonuniform noise into high-and low-frequency components and then learn the frequency correlations to help correct the nonuniformity.To learn the frequency correlation,intra-and inter-frequency units are designed.The former learns the correlation of neighboring pixels within each component,aiming to reconstruct the structure and coarsely remove nonuniform noise.The latter models the correlation of contents between different components to reconstruct fine-grained structures and reduce residual noise.Both units are equipped with our designed triple-attention mechanism,which can jointly exploit spatial,angular,and frequency information.Moreover,we collected two real-world IRLF-image datasets with significant nonuniformity,which can be used as a common base in the field.Qualitative and quantitative comparisons demonstrate that our method outperforms state-of-the-art approaches with a clearer structure and fewer artifacts.The code is available at https://github.com/DuYou2023/IRLF-FSR.展开更多
Iodine is an essential element for the synthesis of thyroid hormones.Iodine deficiency increases the burden on thyroid function and causes harm to health.The identification of convenient and reliable biomarkers for as...Iodine is an essential element for the synthesis of thyroid hormones.Iodine deficiency increases the burden on thyroid function and causes harm to health.The identification of convenient and reliable biomarkers for assessing iodine nutritional status is essential for evaluating iodine intake.Urinary iodine concentration(UIC)is commonly used for population level iodine status assessment but is less reliable for individuals.A 24-h urine sample is more accurate but difficult to collect[1].Thyroid volume(Tvol)and goiter rate are suitable for evaluating the long-term iodine nutritional status in populations[2].Blood indicator collection is an invasive procedure.展开更多
During direct chilling(DC)casting of ZK61 alloys,the primary and secondary cooling causes strong thermal gradients,which leads to the uneven crystallization rate and thermal contraction in different positions of the i...During direct chilling(DC)casting of ZK61 alloys,the primary and secondary cooling causes strong thermal gradients,which leads to the uneven crystallization rate and thermal contraction in different positions of the ingot.The consequences manifested appearance of heterogeneous grains,huge casting stresses,and even hot cracking flaws.In this paper,chemical and physical methods were integrated to produce large-scale magnesium(Mg)alloy ingots.A φ525 mm ZK61-RE alloy ingot that was refined,homogeneous,and free from hot cracking was obtained via the DC process coupled with a differential low frequency pulsed magnetic field(DLPM).The effects of rare earth(RE)and DLPM on the hot cracking tendency were investigated,and the mechanism of hot cracking formation and modification in largescale ingots was revealed.The findings indicate that the addition of moderate amounts of RE lessens the tendency of hot cracking in large-scale ZK61 alloy ingots.This is mainly attributed to the addition of RE increases the content of the second phase,thus enhancing the ability of the eutectic liquid phase to feed the cracking.With the introduction of DLPM,the grain sizes are significantly refined and homogenized,and there is no obvious hot cracking observed in the ingot.This is because the coupling of the DLPM provides a more homogeneous temperature field,leading to the synchronization of the solidification process,and the consequent reduction of the casting stress,thus reducing the driving force for the formation of hot cracking.In addition,the casting conditions are modified to enhance the ability of solidification feeding and the resistance to hot cracking.This work provides theoretical and practical references for the preparation of large-scale high-quality Mg alloy ingots.展开更多
Recently,many Sequential Recommendation methods adopt self-attention mechanisms to model user preferences.However,these methods tend to focus more on low-frequency information while neglecting highfrequency informatio...Recently,many Sequential Recommendation methods adopt self-attention mechanisms to model user preferences.However,these methods tend to focus more on low-frequency information while neglecting highfrequency information,which makes them ineffective in balancing users’long-and short-term preferences.At the same time,manymethods overlook the potential of frequency domainmethods,ignoring their efficiency in processing frequency information.To overcome this limitation,we shift the focus to the combination of time and frequency domains and propose a novel Hybrid Time-Frequency Dual-Branch Transformer for Sequential Recommendation,namely HyTiFRec.Specifically,we design two hybrid filter modules:the learnable hybrid filter(LHF)and the window hybrid filter(WHF).We combine these with the Efficient Attention(EA)module to form the dual-branch structure to replace the self-attention components in Transformers.The EAmodule is used to extract sequential and global information.The LHF andWHF modules balance the proportion of different frequency bands,with LHF globally modulating the spectrum in the frequency domain and WHF retaining frequency components within specific local frequency bands.Furthermore,we use a time domain residual information addition operation in the hybrid filter module,which reduces information loss and further facilitates the hybrid of time-frequency methods.Extensive experiments on five widely-used real-world datasets show that our proposed method surpasses state-of-the-art methods.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
A diverse range of light and waves,spanning from near-infrared to ultraviolet,alongside ultrasound,have proven effective in propelling nanomotors.This review encapsulates the advancements in nanomotor research propell...A diverse range of light and waves,spanning from near-infrared to ultraviolet,alongside ultrasound,have proven effective in propelling nanomotors.This review encapsulates the advancements in nanomotor research propelled by waves of varying frequencies.It delves into the driving mechanisms and control methodologies of different nanomotor types,emphasizing the role of frequency.Nanomotors can be classified based on the frequency of the driving wave,encompassing ultraviolet light-driven,visible light-driven,near-infrared-driven,and ultrasounddriven variants.Each category corresponds to distinct propulsion mechanisms,including momentum transfer,photothermal effects,self-electrophoresis,and acoustic radiation force.Notably,visible light and near-infrared radiation predominantly propel momentum transfer nanomotors,while photothermal nanomotors are chiefly active within the infrared spectrum.Ultraviolet light drives most self-electrophoretic nanomotors,while ultrasound-driven nanomotors respond to acoustic radiation force.Furthermore,precise control over nanomotor speed and direction is achievable by adjusting the frequency of incident waves within a narrow range,modulating wave absorption rates.Lastly,this paper explores microwave nanomotors,an area yet to be reported,shedding light on potential driving mechanisms.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
Dynamic disturbances with various frequencies could trigger different failure modes of deep excavations.Superimposed on this static stress are dynamic disturbances due to various dynamic vibrations,e.g.excavation blas...Dynamic disturbances with various frequencies could trigger different failure modes of deep excavations.Superimposed on this static stress are dynamic disturbances due to various dynamic vibrations,e.g.excavation blasting,blasting,tunnel boring machine(TBM)vibration,rockburst wave,earthquakes.Specifically,these dynamic sources are characterized by a wide range of wave frequencies f,resulting in differences in failure modes.A series of true-triaxial compression tests were conducted on granite to simulate the excavation-induced stress path in three-dimensional(3D)stresses.Subsequently,a dynamic disturbance with various frequencies was applied to a cuboid specimen,to reveal the behavior associated with brittle failure.The dynamic disturbance with frequencies f of 5 Hz,10 Hz,and 40 Hz generates less disturbed energy components in the granite together with higher peak strength.However,dynamic disturbances with f of 20 Hz and 30 Hz resulted in a lower peak strength;the peak strength of the rock increases sp albeit it decreases at first,then increases.This U-shaped phenomenon relates to the natural frequency of the granite under such stress conditions.Different rock lithologies consisting of diverse mineral composition,respond differently to each sensitive resonance frequency.Interestingly,the weak disturbance stress with a high frequency f and low amplitude A increases the ratio of crack damage to peak strength(scd/sp)in the granite.This leads to the inhibition of the expansion of the granite during the dynamic disturbance process.Multiple penetrating tensileeshear cracks appear in the s3-direction as the disturbance frequency f increases.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
The radio frequency(RF)fingerprint technique is a robust method for security enhancement of the physical layer by leveraging the unique RF imperfections inherent in various wireless devices.Among these imperfections,t...The radio frequency(RF)fingerprint technique is a robust method for security enhancement of the physical layer by leveraging the unique RF imperfections inherent in various wireless devices.Among these imperfections,the carrier frequency offset(CFO)stands out as a primary RF fingerprint(RFF)of the transmitter,offering the potential to distinguish among different transmitters.However,accurately estimating CFO in time-varying channels poses significant challenges due to multipath effects and Doppler shifts.In this paper,we focus on estimating CFO for wireless device identification in the orthogonal frequency division multiplexing(OFDM)communication system.To achieve precise CFO estimation under time-varying channels,we propose a frequency domain correlation and spline interpolation(FCSI)algorithm.This approach utilizes pilots distributed across different subcarriers to correlate with prior local sequences,facilitating accurate CFO estimation.Classification is then performed based on the Euclidean distance between the prior RFF and the tested RFF dataset.Simulation results demonstrate that the proposed Mconsecutive average method effectively reduces the classification error rate in the challenging high-frequency(HF)skywave channel environment.展开更多
In the image fusion field,fusing infrared images(IRIs)and visible images(VIs)excelled is a key area.The differences between IRIs and VIs make it challenging to fuse both types into a high-quality image.Accordingly,eff...In the image fusion field,fusing infrared images(IRIs)and visible images(VIs)excelled is a key area.The differences between IRIs and VIs make it challenging to fuse both types into a high-quality image.Accordingly,efficiently combining the advantages of both images while overcoming their shortcomings is necessary.To handle this challenge,we developed an end-to-end IRI andVI fusionmethod based on frequency decomposition and enhancement.By applying concepts from frequency domain analysis,we used the layering mechanism to better capture the salient thermal targets from the IRIs and the rich textural information from the VIs,respectively,significantly boosting the image fusion quality and effectiveness.In addition,the backbone network combined Restormer Blocks and Dense Blocks;Restormer blocks utilize global attention to extract shallow features.Meanwhile,Dense Blocks ensure the integration between shallow and deep features,thereby avoiding the loss of shallow attributes.Extensive experiments on TNO and MSRS datasets demonstrated that the suggested method achieved state-of-the-art(SOTA)performance in various metrics:Entropy(EN),Mutual Information(MI),Standard Deviation(SD),The Structural Similarity Index Measure(SSIM),Fusion quality(Qabf),MI of the pixel(FMI_(pixel)),and modified Visual Information Fidelity(VIF_(m)).展开更多
基金supported by the National Natural Science Foundation of China(Grant No.72161034).
文摘Human motion modeling is a core technology in computer animation,game development,and humancomputer interaction.In particular,generating natural and coherent in-between motion using only the initial and terminal frames remains a fundamental yet unresolved challenge.Existing methods typically rely on dense keyframe inputs or complex prior structures,making it difficult to balance motion quality and plausibility under conditions such as sparse constraints,long-term dependencies,and diverse motion styles.To address this,we propose a motion generation framework based on a frequency-domain diffusion model,which aims to better model complex motion distributions and enhance generation stability under sparse conditions.Our method maps motion sequences to the frequency domain via the Discrete Cosine Transform(DCT),enabling more effective modeling of low-frequency motion structures while suppressing high-frequency noise.A denoising network based on self-attention is introduced to capture long-range temporal dependencies and improve global structural awareness.Additionally,a multi-objective loss function is employed to jointly optimize motion smoothness,pose diversity,and anatomical consistency,enhancing the realism and physical plausibility of the generated sequences.Comparative experiments on the Human3.6M and LaFAN1 datasets demonstrate that our method outperforms state-of-the-art approaches across multiple performance metrics,showing stronger capabilities in generating intermediate motion frames.This research offers a new perspective and methodology for human motion generation and holds promise for applications in character animation,game development,and virtual interaction.
文摘BACKGROUND Critical flicker frequency(CFF)is a quantitative tool for assessing hepatic enceph-alopathy(HE),particularly minimal HE,which is associated with poor prognosis in liver cirrhosis.Alcohol-related liver disease(ALD)is a leading global cause of cirrhosis;however,the effects of alcohol on CFF and its relationship with liver stiffness(LS)remain underexplored.AIM To study the impact of alcohol withdrawal on CFF and its correlation with LS in ALD patients.METHODS A total of 108 patients were included:93 heavy drinkers hospitalized for detoxi-fication,15 with non-ALD etiologies,and 20 healthy controls.CFF was measured using the Hepatonorm analyzer,and LS via transient elastography(FibroScan).Baseline and post-detoxification assessments were conducted in 57 ALD patients.RESULTS The cohort had a mean age of 53.7±13.8 years,with 74% male participants.CFF measurements were reliable,with 97.2% of patients showing an interquartile range<20%.ALD patients exhibited significantly lower CFF compared to controls.Receiver operating characteristic analysis for overt HE(n=12)yielded an area under the curve of 0.66(95%confidence interval:0.49-0.84,P=0.0142),with an optimal cutoff of 36.5 Hz.CFF significantly improved post-detoxification.Patients with LS>17 kPa had lower CFF,while those with intermediate LS showed no significant difference.CONCLUSION CFF is influenced by HE severity and acute alcohol exposure,showing improvement after detoxification.Its weak correlation with fibrosis stage suggests that CFF serves as a sensitive neurocognitive marker in ALD.
基金the National Natural Science Foundation of China(NSFC)(Grant Nos.42030105,42274011,42074019,41974034,42204006)。
文摘Highly accurate international height reference frames with long-term stability,global consistency,and homogeneity are crucial for monitoring sea level variations,understanding climate change,managing disasters,and supporting other applications that benefit scientific research and societal well-being.Currently,there are over 100 local height reference systems worldwide.Unifying these systems is a pivotal step toward constructing international height reference frames.The method introduced in this study-the gravity frequency shift via Satellite Frequency Signal Transfer(SFST)-represents a groundbreaking relativistic geodetic approach,demonstrating its potential to surpass the constraints of conventional techniques.The advent of high-precision optical atomic clocks(OAC)with an accuracy level of 1×10^(-18) has facilitated this method's implementation.The International Association of Geodesy(IAG)has established the International Height Reference System(IHRS)and its practical realization,the International Height Reference Frame(IHRF).Our study focuses on two neighbouring height systems:the China Height System(CHS)and the Nepal Height System(NHS),separated by the Himalayas and the Xizang plateau.We aim to unify these two systems by determining the geopotential and orthometric height differences between their respective height datum stations:the Qingdao Height Datum Station(QHDS)and the Madar Height Datum Station(MHDS)using a simulation experiment with the method mentioned above.Using an OAC with an accuracy of 1×10^(-18),we identified a geopotential difference of-8.348±0.464 m^(2)s^(-2) and an orthometric height difference of 0.786±0.047 m between QHDS and MHDS.These results suggest that the introduced method could unify any two height systems with fewcentimeter-level precision,emphasizing its significance in contributing to the construction of the IHRS/IHRF with today's required precision.In summary,the SFST technique is a novel geodetic method that offers an alternative for height system unification,delivering centimeter-level precision,surpassing traditional methods,and supporting the development of the IHRF.
基金financially supported by the Major Projects in Aviation Engines and Gas Turbines (Grant No.2019-VI-0020-0136)the National Key Research and Development Program of China (Grant Nos.2022YFB3705101&2022YFB3705102)+1 种基金the National Natural Science Foundation of China (Grant No.U1708253)the Fundamental Research Funds for the Central Universities,China (Grant No.N2302005)。
文摘The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation.The results show that the average grain size decreases after application of LFEC.At the same time,the fraction of equiaxed grains increases compared with the ingots that without LFEC.In addition,the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency.When the current frequency increases from 5 Hz to 20 Hz,the average grain size decreases from 5.39 mm to 4.74 mm,and the fraction of equiaxed grains increases from 41.21%to 55.24%.The distribution of Lorentz force,melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software.It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency,thus the melt flow velocity and heat transfer in the melt are promoted.It can facilitate the heterogenous nucleation in the melt,resulting in grain refinement,and further preventing hot cracking of large size ingots.
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co-supported by the Key Projects of the Civil Aviation Joint Fund of the National Natural Science Foundation of China(No.U2033208)。
文摘The variation of the nonlinear contact stiffness induced by the elastic wheel-holding effect between the aircraft and tractor has an important effect on the vibration characteristics of an airfield towbarless traction system,making it essential for ensuring the safety of this emerging towing-out mode.In this paper,the frequency evolutionary tendency of the traction system is studied and obtained considering the variation of nonlinear contact stiffness for the first time.A novel modal analysis method,based on a derived nonlinear contact relationship,is proposed to investigate the vibration characteristics for mechanical system.Frequency veering and mode exchange phenomena in the low-order modes are observed due to the variation of nonlinear contact stiffness.These findings are further validated by the experimental results of a scaled-down model.In addition,it is also found that the veering critical point will be shifted with the external loads.The study provides valuable insights into the vibration characteristics and frequency veering behavior of similar mechanism-based systems,such as towbarless traction system,and has important implications for improving their design and operational performance.
基金partially funded by the Horizontal Scientific Research Project of the National Astronomical Observatories of CAS(Grant No.E0900501)and the Theoretical Fundamental Research Special Project of the Changchun Observatory,National Astronomical Observatories,CAS(Grant No.Y990000205)。
文摘Research on the properties of neutron stars with dark energy is a particularly interesting yet unresolved problem in astrophysics.We analyze the influence of dark energy on the equation of state,the maximum mass,the surface gravitational redshift and the Keplerian frequency for the traditional neutron star and the hyperon star matter within the relativistic mean field theory,using the GM1 and TM1 parameter sets by considering the two flavor symmetries of SU(6)and SU(3)combined with the observations of PSR J1614-2230,PSR J0348+0432,PSR J0030+0451,RX J0720.4-3125,and 1E 1207.4-5209.It is found that the existence of dark energy leads to the softened equations of the state of the traditional neutron star and the hyperon star.The radius of a fixed-mass traditional neutron star(or hyperon star)with dark energy becomes smaller,which leads to increased compactness.The existence of dark energy can also enhance the surface gravitational redshift and the Keplerian frequency of traditional neutron stars and hyperon stars.The growth of the Keplerian frequency may cause the spin rate to speed up,which may provide a possible way to understand and explain the pulsar glitch phenomenon.Specifically,we infer that the mass and the surface gravitational redshift of PSR J1748-2446ad without dark energy for the GM1(TM1)parameter set are 1.141 M_(☉)(1.309 M_(☉))and 0.095(0.105),respectively.The corresponding values for the GM1(TM1)parameter set are 0.901 M_(☉)(1.072M_(☉))and 0.079(0.091)if PSR J1748-2446ad contains dark energy withα=0.05.PSR J1748-2446ad may be a low-mass pulsar with a lower surface gravitational redshift under our selected models.
基金support from the National Natural Science Foundation of China(No.52374019).
文摘Water hammer diagnostics is an important fracturing diagnosis technique to evaluate fracture locations and other downhole events in fracturing. The evaluation results are obtained by analyzing shut-in water hammer pressure signal. The field-sampled water hammer signal is often disturbed by noise interference. Noise interference exists in various pumping stages during water hammer diagnostics, with significantly different frequency range and energy distribution. Clarifying the differences in frequency range and energy distribution between effective water hammer signals and noise is the basis of setting specific filtering parameters, including filtering frequency range and energy thresholds. Filtering specifically could separate the effective signal and noise, which is the key to ensuring the accuracy of water hammer diagnosis. As an emerging technique, there is a lack of research on the frequency range and energy distribution of effective signals in water hammer diagnostics. In this paper, the frequency range and energy distribution characteristics of field-sampled water hammer signals were clarified quantitatively and qualitatively for the first time by a newly proposed comprehensive water hammer segmentation-energy analysis method. The water hammer signals were preprocessed and divided into three segments, including pre-shut-in, water hammer oscillation, and leak-off segment. Then, the three segments were analyzed by energy analysis and correlation analysis. The results indicated that, one aspect, the frequency range of water hammer oscillation spans from 0 to 0.65 Hz, considered as effective water hammer signal. The pre-shut-in and leak-off segment ranges from 0 to 0.35 Hz and 0-0.2 Hz respectively. Meanwhile, odd harmonics were manifested in water hammer oscillation segment, with the harmonic frequencies ranging approximately from 0.07 to 0.75 Hz. Whereas integer harmonics were observed in pre-shut-in segment, ranging from 6 to 40 Hz. The other aspect, the energy distribution of water hammer signals was analyzed in different frequency ranges. In 0-1 Hz, an exponential decay was observed in all three segments. In 1-100 Hz, a periodical energy distribution was observed in pre-shut-in segment, an exponential decay was observed in water hammer oscillation, and an even energy distribution was observed in leak-off segment. In 100-500 Hz, an even energy distribution was observed in those three segments, yet the highest magnitude was noted in leak-off segment. In this study, the effective frequency range and energy distribution characteristics of the field-sampled water hammer signals in different segments were sufficiently elucidated quantitatively and qualitatively for the first time, laying the groundwork for optimizing the filtering parameters of the field filtering models and advancing the accuracy of identifying downhole event locations.
基金supported by the National Natural Science Foundation of China(62475199,62075169,U23B2050)the Industry University-Research Cooperation Program of Zhuhai(2220004002828).
文摘Super-resolution(SR)for the camera array-based infrared light field(IRLF)images aims to reconstruct high-resolution sub-aperture images(SAIs)from their low-resolution counterparts.Existing SR methods mainly focus on exploiting the spatial and angular information of SAIs and have achieved promising results in the visible band.However,they fail to adaptively correct the nonuniform noise in IRLF images,resulting in over-smoothness or artifacts in their results.This study proposes a novel method that reconstructs high-resolution IRLF images while correcting the nonuniformity.The main idea is to decompose the structure and nonuniform noise into high-and low-frequency components and then learn the frequency correlations to help correct the nonuniformity.To learn the frequency correlation,intra-and inter-frequency units are designed.The former learns the correlation of neighboring pixels within each component,aiming to reconstruct the structure and coarsely remove nonuniform noise.The latter models the correlation of contents between different components to reconstruct fine-grained structures and reduce residual noise.Both units are equipped with our designed triple-attention mechanism,which can jointly exploit spatial,angular,and frequency information.Moreover,we collected two real-world IRLF-image datasets with significant nonuniformity,which can be used as a common base in the field.Qualitative and quantitative comparisons demonstrate that our method outperforms state-of-the-art approaches with a clearer structure and fewer artifacts.The code is available at https://github.com/DuYou2023/IRLF-FSR.
基金supported by the National Natural Science Foundation of China(Grant numbers 82204041)Gansu Provincial Science and Technology Program Funded Projects(Grant numbers 22JR11RA184).
文摘Iodine is an essential element for the synthesis of thyroid hormones.Iodine deficiency increases the burden on thyroid function and causes harm to health.The identification of convenient and reliable biomarkers for assessing iodine nutritional status is essential for evaluating iodine intake.Urinary iodine concentration(UIC)is commonly used for population level iodine status assessment but is less reliable for individuals.A 24-h urine sample is more accurate but difficult to collect[1].Thyroid volume(Tvol)and goiter rate are suitable for evaluating the long-term iodine nutritional status in populations[2].Blood indicator collection is an invasive procedure.
基金Project supported by the Jiangxi Province Key Laboratory of Light Alloy(2024SSY05031)the National Natural Science Foundation of China(52061028)+1 种基金the National Key Research and Development Program of China(2021YFB3501001)the Major Research and Development Projects of Jiangxi Province(20223BBE51021,20213AAE02014)。
文摘During direct chilling(DC)casting of ZK61 alloys,the primary and secondary cooling causes strong thermal gradients,which leads to the uneven crystallization rate and thermal contraction in different positions of the ingot.The consequences manifested appearance of heterogeneous grains,huge casting stresses,and even hot cracking flaws.In this paper,chemical and physical methods were integrated to produce large-scale magnesium(Mg)alloy ingots.A φ525 mm ZK61-RE alloy ingot that was refined,homogeneous,and free from hot cracking was obtained via the DC process coupled with a differential low frequency pulsed magnetic field(DLPM).The effects of rare earth(RE)and DLPM on the hot cracking tendency were investigated,and the mechanism of hot cracking formation and modification in largescale ingots was revealed.The findings indicate that the addition of moderate amounts of RE lessens the tendency of hot cracking in large-scale ZK61 alloy ingots.This is mainly attributed to the addition of RE increases the content of the second phase,thus enhancing the ability of the eutectic liquid phase to feed the cracking.With the introduction of DLPM,the grain sizes are significantly refined and homogenized,and there is no obvious hot cracking observed in the ingot.This is because the coupling of the DLPM provides a more homogeneous temperature field,leading to the synchronization of the solidification process,and the consequent reduction of the casting stress,thus reducing the driving force for the formation of hot cracking.In addition,the casting conditions are modified to enhance the ability of solidification feeding and the resistance to hot cracking.This work provides theoretical and practical references for the preparation of large-scale high-quality Mg alloy ingots.
基金supported by a grant from the Natural Science Foundation of Zhejiang Province under Grant LY21F010016.
文摘Recently,many Sequential Recommendation methods adopt self-attention mechanisms to model user preferences.However,these methods tend to focus more on low-frequency information while neglecting highfrequency information,which makes them ineffective in balancing users’long-and short-term preferences.At the same time,manymethods overlook the potential of frequency domainmethods,ignoring their efficiency in processing frequency information.To overcome this limitation,we shift the focus to the combination of time and frequency domains and propose a novel Hybrid Time-Frequency Dual-Branch Transformer for Sequential Recommendation,namely HyTiFRec.Specifically,we design two hybrid filter modules:the learnable hybrid filter(LHF)and the window hybrid filter(WHF).We combine these with the Efficient Attention(EA)module to form the dual-branch structure to replace the self-attention components in Transformers.The EAmodule is used to extract sequential and global information.The LHF andWHF modules balance the proportion of different frequency bands,with LHF globally modulating the spectrum in the frequency domain and WHF retaining frequency components within specific local frequency bands.Furthermore,we use a time domain residual information addition operation in the hybrid filter module,which reduces information loss and further facilitates the hybrid of time-frequency methods.Extensive experiments on five widely-used real-world datasets show that our proposed method surpasses state-of-the-art methods.
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.
基金supported by the National Key Research and Development Program of China(2021YFA1401103)the National Natural Science Foundation of China(52473109,52073071)+3 种基金China Scholarship Council(CSC)(202306790056)Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX22_2301)111 Project(B23008)the Innovative Leading Talent Team supported by 2022Wuxi Taihu Talent Program(1096010241230120)。
文摘A diverse range of light and waves,spanning from near-infrared to ultraviolet,alongside ultrasound,have proven effective in propelling nanomotors.This review encapsulates the advancements in nanomotor research propelled by waves of varying frequencies.It delves into the driving mechanisms and control methodologies of different nanomotor types,emphasizing the role of frequency.Nanomotors can be classified based on the frequency of the driving wave,encompassing ultraviolet light-driven,visible light-driven,near-infrared-driven,and ultrasounddriven variants.Each category corresponds to distinct propulsion mechanisms,including momentum transfer,photothermal effects,self-electrophoresis,and acoustic radiation force.Notably,visible light and near-infrared radiation predominantly propel momentum transfer nanomotors,while photothermal nanomotors are chiefly active within the infrared spectrum.Ultraviolet light drives most self-electrophoretic nanomotors,while ultrasound-driven nanomotors respond to acoustic radiation force.Furthermore,precise control over nanomotor speed and direction is achievable by adjusting the frequency of incident waves within a narrow range,modulating wave absorption rates.Lastly,this paper explores microwave nanomotors,an area yet to be reported,shedding light on potential driving mechanisms.
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 National Natural Science Foundation of China(Grant Nos.52222810 and 52178383).
文摘Dynamic disturbances with various frequencies could trigger different failure modes of deep excavations.Superimposed on this static stress are dynamic disturbances due to various dynamic vibrations,e.g.excavation blasting,blasting,tunnel boring machine(TBM)vibration,rockburst wave,earthquakes.Specifically,these dynamic sources are characterized by a wide range of wave frequencies f,resulting in differences in failure modes.A series of true-triaxial compression tests were conducted on granite to simulate the excavation-induced stress path in three-dimensional(3D)stresses.Subsequently,a dynamic disturbance with various frequencies was applied to a cuboid specimen,to reveal the behavior associated with brittle failure.The dynamic disturbance with frequencies f of 5 Hz,10 Hz,and 40 Hz generates less disturbed energy components in the granite together with higher peak strength.However,dynamic disturbances with f of 20 Hz and 30 Hz resulted in a lower peak strength;the peak strength of the rock increases sp albeit it decreases at first,then increases.This U-shaped phenomenon relates to the natural frequency of the granite under such stress conditions.Different rock lithologies consisting of diverse mineral composition,respond differently to each sensitive resonance frequency.Interestingly,the weak disturbance stress with a high frequency f and low amplitude A increases the ratio of crack damage to peak strength(scd/sp)in the granite.This leads to the inhibition of the expansion of the granite during the dynamic disturbance process.Multiple penetrating tensileeshear cracks appear in the s3-direction as the disturbance frequency f increases.
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 ZTE Industry-University-Institute Cooperation Funds under Grant No.IA20240723011National Natural Science Foundation of China under Grant No.62371123+1 种基金Young Elite Scientists Sponsorship Program of the Beijing High Innovation Plan under Grant No.20251077Research Fund of National Mobile Communications Research Laboratory,Southeast University under Grant No.2023A03。
文摘The radio frequency(RF)fingerprint technique is a robust method for security enhancement of the physical layer by leveraging the unique RF imperfections inherent in various wireless devices.Among these imperfections,the carrier frequency offset(CFO)stands out as a primary RF fingerprint(RFF)of the transmitter,offering the potential to distinguish among different transmitters.However,accurately estimating CFO in time-varying channels poses significant challenges due to multipath effects and Doppler shifts.In this paper,we focus on estimating CFO for wireless device identification in the orthogonal frequency division multiplexing(OFDM)communication system.To achieve precise CFO estimation under time-varying channels,we propose a frequency domain correlation and spline interpolation(FCSI)algorithm.This approach utilizes pilots distributed across different subcarriers to correlate with prior local sequences,facilitating accurate CFO estimation.Classification is then performed based on the Euclidean distance between the prior RFF and the tested RFF dataset.Simulation results demonstrate that the proposed Mconsecutive average method effectively reduces the classification error rate in the challenging high-frequency(HF)skywave channel environment.
基金funded by Anhui Province University Key Science and Technology Project(2024AH053415)Anhui Province University Major Science and Technology Project(2024AH040229)+3 种基金Talent Research Initiation Fund Project of Tongling University(2024tlxyrc019)Tongling University School-Level Scientific Research Project(2024tlxyptZD07)TheUniversity Synergy Innovation Programof Anhui Province(GXXT-2023-050)Tongling City Science and Technology Major Special Project(Unveiling and Commanding Model)(200401JB004).
文摘In the image fusion field,fusing infrared images(IRIs)and visible images(VIs)excelled is a key area.The differences between IRIs and VIs make it challenging to fuse both types into a high-quality image.Accordingly,efficiently combining the advantages of both images while overcoming their shortcomings is necessary.To handle this challenge,we developed an end-to-end IRI andVI fusionmethod based on frequency decomposition and enhancement.By applying concepts from frequency domain analysis,we used the layering mechanism to better capture the salient thermal targets from the IRIs and the rich textural information from the VIs,respectively,significantly boosting the image fusion quality and effectiveness.In addition,the backbone network combined Restormer Blocks and Dense Blocks;Restormer blocks utilize global attention to extract shallow features.Meanwhile,Dense Blocks ensure the integration between shallow and deep features,thereby avoiding the loss of shallow attributes.Extensive experiments on TNO and MSRS datasets demonstrated that the suggested method achieved state-of-the-art(SOTA)performance in various metrics:Entropy(EN),Mutual Information(MI),Standard Deviation(SD),The Structural Similarity Index Measure(SSIM),Fusion quality(Qabf),MI of the pixel(FMI_(pixel)),and modified Visual Information Fidelity(VIF_(m)).
