Acoustic metamaterials(AMs)exhibit outstanding sound absorption performance due to their customizable design.In this work,a low-frequency sound-absorbing metamaterial plate,which combines a fractal-based labyrinth aco...Acoustic metamaterials(AMs)exhibit outstanding sound absorption performance due to their customizable design.In this work,a low-frequency sound-absorbing metamaterial plate,which combines a fractal-based labyrinth acoustic metamaterial(FLAM)and a micro-perforation panel,is proposed.The theoretical,simulation,and experimental methods are used to comprehensively examine the sound absorption performance.A triangular fractal curve is first introduced,and the combined FLAM model is constructed.An equivalent straight channel model is developed to study the effects of the structural parameters on the sound absorption coefficients.The finite element analysis(FEA)is further conducted to validate the theoretical results.All the findings indicate that the proposed combined FLAM exhibits excellent sound absorption performance at a deep sub-wavelength scale,with absorption coefficients of 0.89,0.98,and 1.00 for the first three fractal orders,respectively.Finally,the prototypes are fabricated,and the impedance tube experiments are conducted,yielding results that align closely with both analytical and FEA results.Notably,the sound absorption performance of large-area sound-absorbing plates is also investigated by splicing two/four FLAMs together,demonstrating a relative absorption bandwidth exceeding 35%.This work offers a viable alternative to low-frequency sound-absorbing materials for potential engineering applications.展开更多
Low-frequency signals play a crucial role in seismic inversion of thin-layer structure and reservoir prediction.However,during seismic exploration,the low-frequency signals are often contaminated,distorted,or even mis...Low-frequency signals play a crucial role in seismic inversion of thin-layer structure and reservoir prediction.However,during seismic exploration,the low-frequency signals are often contaminated,distorted,or even missing due to acquisition limitations,processing artifacts,and ambient noise.Although compressive sensing theory-based sparse inversion can partially recover low-frequency signals,the reconstruction results suffer from significant non-uniqueness.To address this challenge,we propose a sparse inversion approach incorporating spatial structural regularization to enhance low-frequency signal recovery.Due to the interference among seismic waveforms,spatial reflection structure exhibits frequency dependency.Consequently,the spatial structure estimated directly from seismic data differs significantly from the actual low-frequency spatial structure.Therefore,the proposed method estimates spatial reflection structure from seismic data in the neighboring frequency band of the low-frequency signals to be recovered,aiming to reduce the impact of frequency dependency on estimation accuracy.Subsequently,both the sparse structure of reflection coefcients and spatial structure of low-frequency signals are incorporated as regularization terms into the inversion framework,enabling geologically guided recovery of low-frequency components.The proposed method was successfully applied in the Tarim Oileld,eectively restoring low-frequency signals and providing reliable foundational seismic data for reservoir prediction.展开更多
Low-frequency ultrasonic array is commonly used to detect interlayer voids located in high-speed railway ballastless track,which is a typical multilayer concrete bonded structure.The difficulty of detection lies in th...Low-frequency ultrasonic array is commonly used to detect interlayer voids located in high-speed railway ballastless track,which is a typical multilayer concrete bonded structure.The difficulty of detection lies in the fact that the total focusingmethod(TFM)based on a single fixed sound velocity model cannot adapt to the acoustic propagation characteristics of multilayer structures,which is prone to generating artifacts.In addition,the long duration of lowfrequency ultrasonic pulses is prone to causing significant deviations in defect localization.To address these issues,a theoretical model of the layered bonded structure is proposed.The acoustic wave propagation path and travel time calculation are clarified after combining the Fermat’s principle and Snell’s law,and the shortest path ray tracing(SPRT)is proposed,which achieves visual imaging of interlayer voids;The pulse peak delay(PPD)is applied to correct the travel time of low-frequency ultrasonic waves,and the shortest path ray tracing combined with pulse peak delay(PSPRT)is proposed,which significantly improves the localization accuracy of defects.Finally,by integrating the amplitude and phase information of scattered signals,the shortest path ray tracing based on pulse peak delay and sign coherence factor(PPSPRT)is constructed,which significantly enhances the SNR.The test results show that,compared with the conventional TFM,the proposed PPSPRT achieves average SNR improvements of 6.62 dB in numerical simulations and 14.30 dB in field tests,and reduces the average depth localization error of interlayer voids to merely 23.49%and 10.38%of that of TFM under corresponding test conditions,respectively.PPSPRT can provide important guidance for accurate imaging of interlayer voids.展开更多
The demand for noise and vibration control in aerospace and vehicle manufacturing is increasing,but reliable design strategies are still lacking.Here,an integrated acousto-mechanical metastructure is proposed to reali...The demand for noise and vibration control in aerospace and vehicle manufacturing is increasing,but reliable design strategies are still lacking.Here,an integrated acousto-mechanical metastructure is proposed to realize broadband lowfrequency sound absorption and vibration isolation simultaneously.Due to the introduction of bistable substructures,the proposed metastructure achieves quasi-zero stiffness vibration isolation and sound energy dissipation without external loads.Rapid customized design of the optimized metastructure is achieved by the proposed optimization algorithm.An average sound absorption coefficient of 0.8 is realized by optimization design within the frequency range of 350 Hz to 800 Hz.In addition,the proposed acousto-mechanical metastructure exhibits ultra-low broadband vibration isolation performance,with an initial isolation frequency of 40.4 Hz.Theoretical calculations,numerical simulations,and experimental results show that the acoustic performance of the metastructure benefits from the intensive mode density brought by multiple geometric degrees of freedom,while its vibration isolation performance originates from the quasi-zero stiffness beams.Overall,a multi-objective optimization method under a given structural design domain is proposed to optimize the multifunctional metastructure.展开更多
AIM:To study the relationships between amplitude of low-frequency fluctuations(ALFF)changes and clinical ophthalmic parameters in patients with primary open angle glaucoma(POAG)and analyze the diagnostic value of ALFF...AIM:To study the relationships between amplitude of low-frequency fluctuations(ALFF)changes and clinical ophthalmic parameters in patients with primary open angle glaucoma(POAG)and analyze the diagnostic value of ALFF.METHODS:Twenty-four POAG patients and 24 healthy controls(HCs)underwent resting-state functional magnetic resonance imaging(rs-fMRI).Nonparametric rank-sum tests were used to compare the ALFF values in the slow-4 and slow-5 bands,and Spearman or Pearson correlation analysis was used to assess the correlation between ALFF changes and clinical ophthalmic parameters in POAG patients.Receiver operating characteristic(ROC)curves were used to evaluate the diagnostic performance of the ALFF.RESULTS:There were 16 males in POAG patients(median age 48y)and 12 males in HCs(median age 39y).Compared with HCs,POAG patients presented increased or decreased ALFF values in different brain regions,and similar changes were observed in mild POAG patients.The ALFF values were correlated with retinal nerve fiber layer(RNFL)thickness,inner limiting membrane-retinal pigment epithelium thickness changes and the degree of visual field defects.Analysis of the diagnostic value of the ALFF via ROC curves revealed that the right medial frontal gyrus[area under the curve(AUC)=0.9063]and superior frontal gyrus(AUC=0.9097)had better diagnostic value than did the optic disc area(AUC=0.8019),visual field index(VFI%,AUC=0.8988)and macular parameters.CONCLUSION:POAG patients present altered cortical function that is significantly correlated with the optic nerve and retinal thickness and had good diagnostic value,which may reflect the underlying neuropathological mechanism of POAG.展开更多
High-power extremely low-frequency(ELF)sound sources are essential in marine engineering,and electromagnetic transducers(EMTs)are preferred over piezoelectric and magnetostrictive transducers because of their superior...High-power extremely low-frequency(ELF)sound sources are essential in marine engineering,and electromagnetic transducers(EMTs)are preferred over piezoelectric and magnetostrictive transducers because of their superior output power and compactness.However,achieving high sound pressure levels(SPLs)below 50 Hz in compact EMTs is challenging.In our study,EMT diaphragms were optimized using a negative stiffness structure(NSS)to reduce the stiffness of the vibration system,thereby reducing frequency requirements and increasing output power,as validated by finite element analysis.The NSS diaphragm significantly outperformed conventional designs,increasing transducer output power by 216.23%,achieving a maximum SPL of 170 dB and over 160 dB from 4 to 50 Hz.With dimensions of 150 mm radius and 200 mm height,the EMT is an example of compact design.This research has successfully developed a low-frequency,high power,compact EMT that will enhance offshore technology and research and provide an improved solution for high power ELF sound sources,significantly advancing EMT applications in marine engineering.展开更多
The increasing proportion of power generated by new energy has meant that grid-forming energy storage has become a key method for improving power grid flexibility.However,the small disturbance stability problem has be...The increasing proportion of power generated by new energy has meant that grid-forming energy storage has become a key method for improving power grid flexibility.However,the small disturbance stability problem has become an important challenge.The issue is that grid-forming energy storage is prone to low-frequency oscillation under strong grid conditions.Therefore,this study proposes a multi damping torque model to analyze the small signal stability of grid-forming energy storage converters.The impact of grid strength,operating conditions,and control parameters on the damping characteristics of the low-frequency oscillation by the system was quantitatively evaluated.The results revealed the mechanism underlying the low-frequency oscillation associated with grid-forming energy storage under strong grid conditions and key factors controlling the low-frequency oscillation.The results also provide theoretical guidance for the tuning of grid-forming energy storage control parameters.The accuracy of the multi damping torque model and theoretical analysis were verified using the electromagnetic simulation results.展开更多
Metamaterials can control and manipulate acoustic/elastic waves on a subwavelength scale using cavities or additional components.However,the large cavity and weak stiffness components of traditional metamaterials may ...Metamaterials can control and manipulate acoustic/elastic waves on a subwavelength scale using cavities or additional components.However,the large cavity and weak stiffness components of traditional metamaterials may cause a conflict between vibroacoustic reduction and load-bearing capacity,and thus limit their application.Here,we propose a lightweight multifunctional metamaterial that can simultaneously achieve low-frequency sound insulation,broadband vibration reduction,and excellent load-bearing performance,named as vibroacoustic isolation and bearing metamaterial(VIBM).The advent of additive manufacturing technology provides a convenient and reliable method for the fabrication of VIBM samples.The results show that the compressive strength of the VIBM is as high as 9.71 MPa,which is nearly 87.81%higher than that of the conventional grid structure(CGS)under the same volume fraction.Moreover,the vibration and sound transmission are significantly reduced over a low and wide frequency range,which agrees well with the experimental data,and the reduction degree is obviously larger than that obtained by the CGS.The design strategy can effectively realize the key components of metamaterials and improve their application scenarios.展开更多
Low-frequency vibroseis acquisition has become a routine operation in land seismic surveys,given the advantages of low-frequency signals in characterizing geological structures and enhancing the imaging of deep explor...Low-frequency vibroseis acquisition has become a routine operation in land seismic surveys,given the advantages of low-frequency signals in characterizing geological structures and enhancing the imaging of deep exploration targets.The two key points of low-frequency sweep design techniques include controlling the distortion and improving the output energy during the low-frequency stage.However,the vibrators are limited by the maximum fl ow provided by the hydraulic systems at the low-frequency stage,causing difficulty in satisfying exploration energy requirements.Initially,a theoretical analysis of the low-frequency acquisition performance of vibrators is conducted.A theoretical maximum output force below 10 Hz is obtained by guiding through theoretical formulas and combining actual vibrator parameters.Then,the signal is optimized according to the surface characteristics of the operation area.Finally,detailed application quality control and operational procedures are established.The new low-frequency sweep design method has overcome the maximum flow limitations of the hydraulic system,increased the low-frequency energy,and achieved broadband acquisition.The designed signal has been tested and applied on various types of ground surfaces in the Middle East desert region,yielding good performance.The proposed low-frequency sweep design method holds considerable value for the application of conventional vibroseis in low-frequency acquisition.展开更多
Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibra...Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor.Although these strategies have a certain vibration suppression effect,the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome.In this study,a Magnetorheological Joint Damper(MRJD)is developed.The joint-mounted feature ensures machining flexibility of the robot,and the millisecond response time of the Magnetorheological Fluid(MRF)ensures a large effective spindle speed range.More importantly,the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism,which guarantees the application of MRJD in robotic milling machining.To analyze the influence of the robotic joint angle on the suppression effect of the MRJD,the joint braking coefficient and end braking coefficient were proposed.Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect.Finally,a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization.The experimental results show that the MRJD,which directly improves the joint vibration resistance,can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.展开更多
In order to obtain a lower frequency band gap,this paper proposes a novel locally resonant meta-beam incorporating a softening nonlinear factor.An improved camroller structure is designed in this meta-beam to achieve ...In order to obtain a lower frequency band gap,this paper proposes a novel locally resonant meta-beam incorporating a softening nonlinear factor.An improved camroller structure is designed in this meta-beam to achieve the softening nonlinear stiffness of the local oscillators.Firstly,based on Hamilton's principle and the Galerkin method,the control equations for the coupled system are established.The theoretical band gap boundary is then derived with the modal analysis method.The theoretical results reveal that the band gap of the meta-beam shifts towards lower frequencies due to the presence of a softening nonlinear factor,distinguishing it from both linear metamaterials and those with hardening nonlinear characteristics.Then,the vibration attenuation characteristics of a finite size meta-beam are investigated through numerical calculation,and are verified by the theoretical results.Furthermore,parameter studies indicate that the reasonable design of the local oscillator parameters based on lightweight principles helps to achieve further broadband and efficient vibration reduction in the low-frequency region.Finally,a prototype of the meta-beam is fabricated and assembled,and the formations of the low-frequency band gap and the amplitude-induced band gap phenomenon are verified through experiments.展开更多
This article reports In2O3 thin-film transistors(TFTs) that utilize a CeAlOx/Al2O3 stacked gate dielectric architecture.The CeAlOx gate dielectric films were optimized by doping Al into CeO2,where...This article reports In2O3 thin-film transistors(TFTs) that utilize a CeAlOx/Al2O3 stacked gate dielectric architecture.The CeAlOx gate dielectric films were optimized by doping Al into CeO2,where the adjustment of the Al/Ce atomic ratio effectively suppressed oxygen-vacancy-related defects and optimized gate dielectric leakage current.Due to the large bandgap and high density of Al2O3 prepared via atomic layer deposition(ALD),CeAlOx/Al2O3 stacked gate dielectric exhibits lower leakage current compared to single-layer CeAlOx.We systematically investigated the Al/Ce ratio's dependence on In2O3 TFT performance,identifying an optimal stoichiometry of 3:7(Al:Ce).The CeAlOx/Al2O3-based In2O3 TFT fabricated at this ratio achieved exceptional characteristics:higher saturation mobility(26.86 cm2 V-1 s-1) and on/off current ratio(3.58×107),lower sub threshold swing(0.08 V decade-1) and interface state density(1.39×1012 cm-2),coupled with excellent bias stress stability.By combining low-frequency noise analysis and X-ray photoelectron spectroscopy(XPS),we confirmed that Al doping reduces the trap density in CeO2 while simultaneously enhancing its dielectric properties.Furthermore,a resistive-load inverter based on In2O3 TFT presents a voltage gain up to 15.1 at an applied voltage of 5 V with a typical reverse behavior,demonstrating that In2O3 TFT based on CeAlOx/Al2O3 stacked gate dielectric exhibits potential for application in advanced digital circuits.展开更多
Aiming at the poor performance of the parity check(PC) aided adaptive successive cancellation list(PC-ASCL) decoding algorithm because the PC code in the polar code can only verify odd errors, an optimized parity chec...Aiming at the poor performance of the parity check(PC) aided adaptive successive cancellation list(PC-ASCL) decoding algorithm because the PC code in the polar code can only verify odd errors, an optimized parity check(OPC) code which can verify all odd errors as well as the half even errors is proposed. The OPC code is used to improve the PC-ASCL decoding algorithm, thus an OPC aided ASCL(OPC-ASCL) decoding algorithm is proposed. In the coding stage, the algorithm divides the information sequence into multiple segments, and places an OPC code at the end of each segment to verify the current information sequence, and places a cyclic redundancy check code at the end of the entire information sequence to verify the entire information sequence. In the decoding stage, the algorithm uses the OPC-ASCL decoder to decode. Simulation results show that compared to the PC-ASCL decoding algorithm, the OPC-ASCL decoding algorithm can reduce the complexity and obtain the certain performance gain.展开更多
Quantum error correction technology is based on the principle of redundant encoding,encoding logical quantum information into multiple physical qubits to provide important support for the stable operation of quantum c...Quantum error correction technology is based on the principle of redundant encoding,encoding logical quantum information into multiple physical qubits to provide important support for the stable operation of quantum computers.To address the issues of low decoding accuracy and limited feature extraction in quantum error correction,this paper proposes a toric code decoder based on a syndrome-preliminary error fusion module(SPEFM)and a ResNet architecture.This decoder takes full advantage of the correlations between X and Z errors.In the SPEFM,the syndrome and preliminary error predictions are deeply fused,while a unidirectional Swin transformer architecture is incorporated to extract global error features from the syndrome data,signiffiificantly improving both decoding accuracy and computational efffiificiency.In addition,this paper further extracts local error features from the fused features using the deep residual structure of ResNet,enhancing the decoder's ability to capture quantum error patterns.Experimental results show that the decoder is applicable to different code distances(d=4,6,8,10)under the depolarizing noise model.Its bit error rate is lower than that of the minimum weight perfect matching(MWPM)algorithm,and its logical error rate is lower than both the MWPM algorithm and the ResNet18 decoder.Furthermore,the decoding threshold is increased to 0.163,representing a 3.82%improvement over the MWPM algorithm threshold of 0.157.展开更多
The ultracold neutron(UCN)transport code,MCUCN,designed initially for simulating UCN transportation from a solid deuterium(SD_2)source and neutron electric dipole moment experiments,could not simulate UCN storage and ...The ultracold neutron(UCN)transport code,MCUCN,designed initially for simulating UCN transportation from a solid deuterium(SD_2)source and neutron electric dipole moment experiments,could not simulate UCN storage and transportation in a superfluid4He(SFHe,He-Ⅱ)source accurately.This limitation arose from the absence of an4He upscattering mechanism and the absorption of3He.And the provided source energy distribution in MCUCN is different from that in SFHe source.This study introduced enhancements to MCUCN to address these constraints,explicitly incorporating the4He upscattering effect,the absorption of3He,the loss caused by impurities on converter wall,UCN source energy distribution in SFHe,and the transmission through negative optical potential.Additionally,a Python-based visualization code for intermediate states and results was developed.To validate these enhancements,we systematically compared the simulation results of the Lujan Center Mark3 UCN system by MCUCN and the improved MCUCN code(iMCUCN)with UCNtransport simulations.Additionally,we compared the results of the SUN1 system simulated by MCUCN and iMCUCN with measurement results.The study demonstrates that iMCUCN effectively simulates the storage and transportation of ultracold neutrons in He-Ⅱ.展开更多
In erasure-coded storage systems,updating data requires parity maintenance,which often leads to significant I/O amplification due to“write-after-read”operations.Furthermore,scattered parity placement increases disk ...In erasure-coded storage systems,updating data requires parity maintenance,which often leads to significant I/O amplification due to“write-after-read”operations.Furthermore,scattered parity placement increases disk seek overhead during repair,resulting in degraded system performance.To address these challenges,this paper proposes a Cognitive Update and Repair Method(CURM)that leverages machine learning to classify files into writeonly,read-only,and read-write categories,enabling tailored update and repair strategies.For write-only and read-write files,CURM employs a data-differencemechanism combined with fine-grained I/O scheduling to minimize redundant read operations and mitigate I/O amplification.For read-write files,CURM further reserves adjacent disk space near parity blocks,supporting parallel reads and reducing disk seek overhead during repair.We implement CURM in a prototype system,Cognitive Update and Repair File System(CURFS),and conduct extensive experiments using realworld Network File System(NFS)and Microsoft Research(MSR)workloads on a 25-node cluster.Experimental results demonstrate that CURMimproves data update throughput by up to 82.52%,reduces recovery time by up to 47.47%,and decreases long-term storage overhead by more than 15% compared to state-of-the-art methods including Full Logging(FL),ParityLogging(PL),ParityLoggingwithReservedspace(PLR),andPARIX.These results validate the effectiveness of CURM in enhancing both update and repair performance,providing a scalable and efficient solution for large-scale erasure-coded storage systems.展开更多
Controlling low-frequency noise presents a significant challenge for traditional sound absorption materials,such as foams and fibrous substances.Recently developed acoustic absorption metamaterials,which rely on local...Controlling low-frequency noise presents a significant challenge for traditional sound absorption materials,such as foams and fibrous substances.Recently developed acoustic absorption metamaterials,which rely on local resonance can effectively balance the volume occupation and low-frequency absorption performance.However,these materials often exhibit a very narrow and fixed absorption band.Inspired by Helmholtz resonators and bistable structures,we propose bistable reconfigurable acoustic metamaterials(BRAMs)that offer multiband low-frequency absorption.These BRAMs are fabricated using shape-memory polylactic acid(SM-PLA)via four-dimension(4D)printing technology.Consequently,the geometry and absorption performance of the BRAMs can be adjusted by applying thermal stimuli(at 55℃)to switch between two stable states.The BRAMs demonstrate excellent low-frequency absorption with multiband characteristics,achieving an absorption coefficient of 0.981 at 136 Hz and 0.998 at 230 Hz for stable state I,and coefficients of 0.984 at 156 Hz and 0.961 at 542 Hz for stable state II.It was found that the BRAMs with different inclined plate angles had linear recovery stages,and the recovery speeds range from 0.75 mm/s to 1.1 mm/s.By combining a rational structural design and 4D printing,the reported reconfigurable acoustic metamaterials will inspire further studies on the design of dynamic and broadband absorption devices.展开更多
Karst landscapes are developed on soluble rocks(primarily limestone),covering about 10-15%of Earth’s ice-free land surface(Ford and Williams,2007).Their unique geological properties have given rise to complex,heterog...Karst landscapes are developed on soluble rocks(primarily limestone),covering about 10-15%of Earth’s ice-free land surface(Ford and Williams,2007).Their unique geological properties have given rise to complex,heterogeneous,and“island-like”habitats that,combined with periodic drought,high calcium,and lownutrient stresses,foster high species diversity and endemism(Clements et al.,2006;Hao et al.,2015;Oliver et al.,2017;Monro et al.,2018).These conditions make karst ecosystems ideal“natural laboratories”for studying speciation and adaptive evolution(Clements et al.,2006;Oliver et al.,2017).展开更多
This paper conducts an empirical study on students'code modification behaviors in incremental programming projects by analyzing 40771 code submissions from 371 students through abstract syntax tree(AST)difference ...This paper conducts an empirical study on students'code modification behaviors in incremental programming projects by analyzing 40771 code submissions from 371 students through abstract syntax tree(AST)difference analysis and manual annotation.The study investigates the distribution of code modification types to prior-phase code during iterative development,identifies cross-phase error types,and analyzes refactoring strategies.The findings reveal that error correction and code refactoring constitute the primary types of cross-phase code modifications.Among cross-phase latent errors,special case neglect represents the dominant error type,indicating insufficient coverage of special scenarios in existing test suites.Variable renaming emerges as the most prevalent refactoring behavior,reflecting students'emphasis on code readability.These research findings provide empirical evidence for optimizing incremental curriculum design,improving test cases,and cultivating students'code maintenance capabilities in programming education.展开更多
基金the National Natural Science Foundation of China(Grant Nos.U2241264 and 11972051).
摘要Acoustic metamaterials(AMs)exhibit outstanding sound absorption performance due to their customizable design.In this work,a low-frequency sound-absorbing metamaterial plate,which combines a fractal-based labyrinth acoustic metamaterial(FLAM)and a micro-perforation panel,is proposed.The theoretical,simulation,and experimental methods are used to comprehensively examine the sound absorption performance.A triangular fractal curve is first introduced,and the combined FLAM model is constructed.An equivalent straight channel model is developed to study the effects of the structural parameters on the sound absorption coefficients.The finite element analysis(FEA)is further conducted to validate the theoretical results.All the findings indicate that the proposed combined FLAM exhibits excellent sound absorption performance at a deep sub-wavelength scale,with absorption coefficients of 0.89,0.98,and 1.00 for the first three fractal orders,respectively.Finally,the prototypes are fabricated,and the impedance tube experiments are conducted,yielding results that align closely with both analytical and FEA results.Notably,the sound absorption performance of large-area sound-absorbing plates is also investigated by splicing two/four FLAMs together,demonstrating a relative absorption bandwidth exceeding 35%.This work offers a viable alternative to low-frequency sound-absorbing materials for potential engineering applications.
基金supported by the National Natural Science Foundation of China(Grant Number:42574160)the Open Fund(Grant Number:36750000-24-FW0399-0011)of SINOPEC Key Laboratory of Geophysics.
摘要Low-frequency signals play a crucial role in seismic inversion of thin-layer structure and reservoir prediction.However,during seismic exploration,the low-frequency signals are often contaminated,distorted,or even missing due to acquisition limitations,processing artifacts,and ambient noise.Although compressive sensing theory-based sparse inversion can partially recover low-frequency signals,the reconstruction results suffer from significant non-uniqueness.To address this challenge,we propose a sparse inversion approach incorporating spatial structural regularization to enhance low-frequency signal recovery.Due to the interference among seismic waveforms,spatial reflection structure exhibits frequency dependency.Consequently,the spatial structure estimated directly from seismic data differs significantly from the actual low-frequency spatial structure.Therefore,the proposed method estimates spatial reflection structure from seismic data in the neighboring frequency band of the low-frequency signals to be recovered,aiming to reduce the impact of frequency dependency on estimation accuracy.Subsequently,both the sparse structure of reflection coefcients and spatial structure of low-frequency signals are incorporated as regularization terms into the inversion framework,enabling geologically guided recovery of low-frequency components.The proposed method was successfully applied in the Tarim Oileld,eectively restoring low-frequency signals and providing reliable foundational seismic data for reservoir prediction.
基金supported by the National Natural Science Foundation of China(Grant No.12304514).
摘要Low-frequency ultrasonic array is commonly used to detect interlayer voids located in high-speed railway ballastless track,which is a typical multilayer concrete bonded structure.The difficulty of detection lies in the fact that the total focusingmethod(TFM)based on a single fixed sound velocity model cannot adapt to the acoustic propagation characteristics of multilayer structures,which is prone to generating artifacts.In addition,the long duration of lowfrequency ultrasonic pulses is prone to causing significant deviations in defect localization.To address these issues,a theoretical model of the layered bonded structure is proposed.The acoustic wave propagation path and travel time calculation are clarified after combining the Fermat’s principle and Snell’s law,and the shortest path ray tracing(SPRT)is proposed,which achieves visual imaging of interlayer voids;The pulse peak delay(PPD)is applied to correct the travel time of low-frequency ultrasonic waves,and the shortest path ray tracing combined with pulse peak delay(PSPRT)is proposed,which significantly improves the localization accuracy of defects.Finally,by integrating the amplitude and phase information of scattered signals,the shortest path ray tracing based on pulse peak delay and sign coherence factor(PPSPRT)is constructed,which significantly enhances the SNR.The test results show that,compared with the conventional TFM,the proposed PPSPRT achieves average SNR improvements of 6.62 dB in numerical simulations and 14.30 dB in field tests,and reduces the average depth localization error of interlayer voids to merely 23.49%and 10.38%of that of TFM under corresponding test conditions,respectively.PPSPRT can provide important guidance for accurate imaging of interlayer voids.
基金supported by the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation(Grant Nos.GZC20242179 and 2024M764117)。
摘要The demand for noise and vibration control in aerospace and vehicle manufacturing is increasing,but reliable design strategies are still lacking.Here,an integrated acousto-mechanical metastructure is proposed to realize broadband lowfrequency sound absorption and vibration isolation simultaneously.Due to the introduction of bistable substructures,the proposed metastructure achieves quasi-zero stiffness vibration isolation and sound energy dissipation without external loads.Rapid customized design of the optimized metastructure is achieved by the proposed optimization algorithm.An average sound absorption coefficient of 0.8 is realized by optimization design within the frequency range of 350 Hz to 800 Hz.In addition,the proposed acousto-mechanical metastructure exhibits ultra-low broadband vibration isolation performance,with an initial isolation frequency of 40.4 Hz.Theoretical calculations,numerical simulations,and experimental results show that the acoustic performance of the metastructure benefits from the intensive mode density brought by multiple geometric degrees of freedom,while its vibration isolation performance originates from the quasi-zero stiffness beams.Overall,a multi-objective optimization method under a given structural design domain is proposed to optimize the multifunctional metastructure.
基金Supported by National Natural Science Foundation of China(No.82260203).
摘要AIM:To study the relationships between amplitude of low-frequency fluctuations(ALFF)changes and clinical ophthalmic parameters in patients with primary open angle glaucoma(POAG)and analyze the diagnostic value of ALFF.METHODS:Twenty-four POAG patients and 24 healthy controls(HCs)underwent resting-state functional magnetic resonance imaging(rs-fMRI).Nonparametric rank-sum tests were used to compare the ALFF values in the slow-4 and slow-5 bands,and Spearman or Pearson correlation analysis was used to assess the correlation between ALFF changes and clinical ophthalmic parameters in POAG patients.Receiver operating characteristic(ROC)curves were used to evaluate the diagnostic performance of the ALFF.RESULTS:There were 16 males in POAG patients(median age 48y)and 12 males in HCs(median age 39y).Compared with HCs,POAG patients presented increased or decreased ALFF values in different brain regions,and similar changes were observed in mild POAG patients.The ALFF values were correlated with retinal nerve fiber layer(RNFL)thickness,inner limiting membrane-retinal pigment epithelium thickness changes and the degree of visual field defects.Analysis of the diagnostic value of the ALFF via ROC curves revealed that the right medial frontal gyrus[area under the curve(AUC)=0.9063]and superior frontal gyrus(AUC=0.9097)had better diagnostic value than did the optic disc area(AUC=0.8019),visual field index(VFI%,AUC=0.8988)and macular parameters.CONCLUSION:POAG patients present altered cortical function that is significantly correlated with the optic nerve and retinal thickness and had good diagnostic value,which may reflect the underlying neuropathological mechanism of POAG.
基金supported by the National Natural Science Foundation of China(Grant Nos.12272402 and 11972365)the China Agricultural University Education Foundation(Grant No.1101-240001).
摘要High-power extremely low-frequency(ELF)sound sources are essential in marine engineering,and electromagnetic transducers(EMTs)are preferred over piezoelectric and magnetostrictive transducers because of their superior output power and compactness.However,achieving high sound pressure levels(SPLs)below 50 Hz in compact EMTs is challenging.In our study,EMT diaphragms were optimized using a negative stiffness structure(NSS)to reduce the stiffness of the vibration system,thereby reducing frequency requirements and increasing output power,as validated by finite element analysis.The NSS diaphragm significantly outperformed conventional designs,increasing transducer output power by 216.23%,achieving a maximum SPL of 170 dB and over 160 dB from 4 to 50 Hz.With dimensions of 150 mm radius and 200 mm height,the EMT is an example of compact design.This research has successfully developed a low-frequency,high power,compact EMT that will enhance offshore technology and research and provide an improved solution for high power ELF sound sources,significantly advancing EMT applications in marine engineering.
基金funded by Supported by the Science and Technology Project of State Grid Corporation of China(2025220202000070).
摘要The increasing proportion of power generated by new energy has meant that grid-forming energy storage has become a key method for improving power grid flexibility.However,the small disturbance stability problem has become an important challenge.The issue is that grid-forming energy storage is prone to low-frequency oscillation under strong grid conditions.Therefore,this study proposes a multi damping torque model to analyze the small signal stability of grid-forming energy storage converters.The impact of grid strength,operating conditions,and control parameters on the damping characteristics of the low-frequency oscillation by the system was quantitatively evaluated.The results revealed the mechanism underlying the low-frequency oscillation associated with grid-forming energy storage under strong grid conditions and key factors controlling the low-frequency oscillation.The results also provide theoretical guidance for the tuning of grid-forming energy storage control parameters.The accuracy of the multi damping torque model and theoretical analysis were verified using the electromagnetic simulation results.
基金Project supported by the National Natural Science Foundation of China(Nos.11991032 and 52241103)the Hunan Province Graduate Research Innovation Project of China(No.KY0409052440)。
摘要Metamaterials can control and manipulate acoustic/elastic waves on a subwavelength scale using cavities or additional components.However,the large cavity and weak stiffness components of traditional metamaterials may cause a conflict between vibroacoustic reduction and load-bearing capacity,and thus limit their application.Here,we propose a lightweight multifunctional metamaterial that can simultaneously achieve low-frequency sound insulation,broadband vibration reduction,and excellent load-bearing performance,named as vibroacoustic isolation and bearing metamaterial(VIBM).The advent of additive manufacturing technology provides a convenient and reliable method for the fabrication of VIBM samples.The results show that the compressive strength of the VIBM is as high as 9.71 MPa,which is nearly 87.81%higher than that of the conventional grid structure(CGS)under the same volume fraction.Moreover,the vibration and sound transmission are significantly reduced over a low and wide frequency range,which agrees well with the experimental data,and the reduction degree is obviously larger than that obtained by the CGS.The design strategy can effectively realize the key components of metamaterials and improve their application scenarios.
基金The authors would like to express their sincere appreciation to the research project of CNPC Geophysical Key Lab(2022DQ0604-4)National Natural Science Foundation of China(Grant No.42074141).
摘要Low-frequency vibroseis acquisition has become a routine operation in land seismic surveys,given the advantages of low-frequency signals in characterizing geological structures and enhancing the imaging of deep exploration targets.The two key points of low-frequency sweep design techniques include controlling the distortion and improving the output energy during the low-frequency stage.However,the vibrators are limited by the maximum fl ow provided by the hydraulic systems at the low-frequency stage,causing difficulty in satisfying exploration energy requirements.Initially,a theoretical analysis of the low-frequency acquisition performance of vibrators is conducted.A theoretical maximum output force below 10 Hz is obtained by guiding through theoretical formulas and combining actual vibrator parameters.Then,the signal is optimized according to the surface characteristics of the operation area.Finally,detailed application quality control and operational procedures are established.The new low-frequency sweep design method has overcome the maximum flow limitations of the hydraulic system,increased the low-frequency energy,and achieved broadband acquisition.The designed signal has been tested and applied on various types of ground surfaces in the Middle East desert region,yielding good performance.The proposed low-frequency sweep design method holds considerable value for the application of conventional vibroseis in low-frequency acquisition.
基金supported by the National Natural Science Foundation of China(No.U20A20294)the National Natural Science Foundation of China(No.52322511)the National Natural Science Foundation of China(No.52188102).
摘要Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor.Although these strategies have a certain vibration suppression effect,the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome.In this study,a Magnetorheological Joint Damper(MRJD)is developed.The joint-mounted feature ensures machining flexibility of the robot,and the millisecond response time of the Magnetorheological Fluid(MRF)ensures a large effective spindle speed range.More importantly,the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism,which guarantees the application of MRJD in robotic milling machining.To analyze the influence of the robotic joint angle on the suppression effect of the MRJD,the joint braking coefficient and end braking coefficient were proposed.Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect.Finally,a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization.The experimental results show that the MRJD,which directly improves the joint vibration resistance,can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.
基金supported by the National Natural Science Foundation of China(Nos.12172014,U224126412332001)。
摘要In order to obtain a lower frequency band gap,this paper proposes a novel locally resonant meta-beam incorporating a softening nonlinear factor.An improved camroller structure is designed in this meta-beam to achieve the softening nonlinear stiffness of the local oscillators.Firstly,based on Hamilton's principle and the Galerkin method,the control equations for the coupled system are established.The theoretical band gap boundary is then derived with the modal analysis method.The theoretical results reveal that the band gap of the meta-beam shifts towards lower frequencies due to the presence of a softening nonlinear factor,distinguishing it from both linear metamaterials and those with hardening nonlinear characteristics.Then,the vibration attenuation characteristics of a finite size meta-beam are investigated through numerical calculation,and are verified by the theoretical results.Furthermore,parameter studies indicate that the reasonable design of the local oscillator parameters based on lightweight principles helps to achieve further broadband and efficient vibration reduction in the low-frequency region.Finally,a prototype of the meta-beam is fabricated and assembled,and the formations of the low-frequency band gap and the amplitude-induced band gap phenomenon are verified through experiments.
基金financially supported by the National Natural Science Foundation of China(Nos.11774001 and 52202156)the Natural Science Foundation of Anhui Higher Education Institution of China(Nos.2023AH040160 and 2024AH051579)+2 种基金Hefei Normal University the High-Level Talent Research Fund(No.2024rcjj09)Hefei Normal University research project(Nos.2024KY60 and 2024KYJX26)Anhui Zhongshi Yike Information Technology Co.,Ltd
摘要This article reports In2O3 thin-film transistors(TFTs) that utilize a CeAlOx/Al2O3 stacked gate dielectric architecture.The CeAlOx gate dielectric films were optimized by doping Al into CeO2,where the adjustment of the Al/Ce atomic ratio effectively suppressed oxygen-vacancy-related defects and optimized gate dielectric leakage current.Due to the large bandgap and high density of Al2O3 prepared via atomic layer deposition(ALD),CeAlOx/Al2O3 stacked gate dielectric exhibits lower leakage current compared to single-layer CeAlOx.We systematically investigated the Al/Ce ratio's dependence on In2O3 TFT performance,identifying an optimal stoichiometry of 3:7(Al:Ce).The CeAlOx/Al2O3-based In2O3 TFT fabricated at this ratio achieved exceptional characteristics:higher saturation mobility(26.86 cm2 V-1 s-1) and on/off current ratio(3.58×107),lower sub threshold swing(0.08 V decade-1) and interface state density(1.39×1012 cm-2),coupled with excellent bias stress stability.By combining low-frequency noise analysis and X-ray photoelectron spectroscopy(XPS),we confirmed that Al doping reduces the trap density in CeO2 while simultaneously enhancing its dielectric properties.Furthermore,a resistive-load inverter based on In2O3 TFT presents a voltage gain up to 15.1 at an applied voltage of 5 V with a typical reverse behavior,demonstrating that In2O3 TFT based on CeAlOx/Al2O3 stacked gate dielectric exhibits potential for application in advanced digital circuits.
基金supported by the National Natural Science Foundation of China(Nos.U21A20447 and 61971079)。
摘要Aiming at the poor performance of the parity check(PC) aided adaptive successive cancellation list(PC-ASCL) decoding algorithm because the PC code in the polar code can only verify odd errors, an optimized parity check(OPC) code which can verify all odd errors as well as the half even errors is proposed. The OPC code is used to improve the PC-ASCL decoding algorithm, thus an OPC aided ASCL(OPC-ASCL) decoding algorithm is proposed. In the coding stage, the algorithm divides the information sequence into multiple segments, and places an OPC code at the end of each segment to verify the current information sequence, and places a cyclic redundancy check code at the end of the entire information sequence to verify the entire information sequence. In the decoding stage, the algorithm uses the OPC-ASCL decoder to decode. Simulation results show that compared to the PC-ASCL decoding algorithm, the OPC-ASCL decoding algorithm can reduce the complexity and obtain the certain performance gain.
基金supported by the Joint Fund of the Natural Science Foundation of Shandong Province,China(Grant Nos.ZR2022LLZ012 and ZR2021LLZ001)the Key Research and Development Program of Shandong Province,China(Grant No.2023CXGC010901)。
摘要Quantum error correction technology is based on the principle of redundant encoding,encoding logical quantum information into multiple physical qubits to provide important support for the stable operation of quantum computers.To address the issues of low decoding accuracy and limited feature extraction in quantum error correction,this paper proposes a toric code decoder based on a syndrome-preliminary error fusion module(SPEFM)and a ResNet architecture.This decoder takes full advantage of the correlations between X and Z errors.In the SPEFM,the syndrome and preliminary error predictions are deeply fused,while a unidirectional Swin transformer architecture is incorporated to extract global error features from the syndrome data,signiffiificantly improving both decoding accuracy and computational efffiificiency.In addition,this paper further extracts local error features from the fused features using the deep residual structure of ResNet,enhancing the decoder's ability to capture quantum error patterns.Experimental results show that the decoder is applicable to different code distances(d=4,6,8,10)under the depolarizing noise model.Its bit error rate is lower than that of the minimum weight perfect matching(MWPM)algorithm,and its logical error rate is lower than both the MWPM algorithm and the ResNet18 decoder.Furthermore,the decoding threshold is increased to 0.163,representing a 3.82%improvement over the MWPM algorithm threshold of 0.157.
基金the National Key R&D Program of China(No.2024YFE0110001)the National Natural Science Foundation of China(U1932219)the Mobility Programme endorsed by the Joint Committee of the Sino-German Center(M0728)。
摘要The ultracold neutron(UCN)transport code,MCUCN,designed initially for simulating UCN transportation from a solid deuterium(SD_2)source and neutron electric dipole moment experiments,could not simulate UCN storage and transportation in a superfluid4He(SFHe,He-Ⅱ)source accurately.This limitation arose from the absence of an4He upscattering mechanism and the absorption of3He.And the provided source energy distribution in MCUCN is different from that in SFHe source.This study introduced enhancements to MCUCN to address these constraints,explicitly incorporating the4He upscattering effect,the absorption of3He,the loss caused by impurities on converter wall,UCN source energy distribution in SFHe,and the transmission through negative optical potential.Additionally,a Python-based visualization code for intermediate states and results was developed.To validate these enhancements,we systematically compared the simulation results of the Lujan Center Mark3 UCN system by MCUCN and the improved MCUCN code(iMCUCN)with UCNtransport simulations.Additionally,we compared the results of the SUN1 system simulated by MCUCN and iMCUCN with measurement results.The study demonstrates that iMCUCN effectively simulates the storage and transportation of ultracold neutrons in He-Ⅱ.
基金supported by the National Natural Science Foundation of China(Grant No.62362019)the Natural Science Foundation of Hainan Province(Grant No.624RC482)the Hainan Provincial Higher Education Teaching Reform Research Project(Grant Hnjg2024-27).
摘要In erasure-coded storage systems,updating data requires parity maintenance,which often leads to significant I/O amplification due to“write-after-read”operations.Furthermore,scattered parity placement increases disk seek overhead during repair,resulting in degraded system performance.To address these challenges,this paper proposes a Cognitive Update and Repair Method(CURM)that leverages machine learning to classify files into writeonly,read-only,and read-write categories,enabling tailored update and repair strategies.For write-only and read-write files,CURM employs a data-differencemechanism combined with fine-grained I/O scheduling to minimize redundant read operations and mitigate I/O amplification.For read-write files,CURM further reserves adjacent disk space near parity blocks,supporting parallel reads and reducing disk seek overhead during repair.We implement CURM in a prototype system,Cognitive Update and Repair File System(CURFS),and conduct extensive experiments using realworld Network File System(NFS)and Microsoft Research(MSR)workloads on a 25-node cluster.Experimental results demonstrate that CURMimproves data update throughput by up to 82.52%,reduces recovery time by up to 47.47%,and decreases long-term storage overhead by more than 15% compared to state-of-the-art methods including Full Logging(FL),ParityLogging(PL),ParityLoggingwithReservedspace(PLR),andPARIX.These results validate the effectiveness of CURM in enhancing both update and repair performance,providing a scalable and efficient solution for large-scale erasure-coded storage systems.
基金financially supported by National Key Research and Development Program of China(Grant No.2023YFB4604800)National Natural Science Foundation of China(Grant No.52275331)financial support from the Hong Kong Scholars Program(Grant No.XJ2022014).
摘要Controlling low-frequency noise presents a significant challenge for traditional sound absorption materials,such as foams and fibrous substances.Recently developed acoustic absorption metamaterials,which rely on local resonance can effectively balance the volume occupation and low-frequency absorption performance.However,these materials often exhibit a very narrow and fixed absorption band.Inspired by Helmholtz resonators and bistable structures,we propose bistable reconfigurable acoustic metamaterials(BRAMs)that offer multiband low-frequency absorption.These BRAMs are fabricated using shape-memory polylactic acid(SM-PLA)via four-dimension(4D)printing technology.Consequently,the geometry and absorption performance of the BRAMs can be adjusted by applying thermal stimuli(at 55℃)to switch between two stable states.The BRAMs demonstrate excellent low-frequency absorption with multiband characteristics,achieving an absorption coefficient of 0.981 at 136 Hz and 0.998 at 230 Hz for stable state I,and coefficients of 0.984 at 156 Hz and 0.961 at 542 Hz for stable state II.It was found that the BRAMs with different inclined plate angles had linear recovery stages,and the recovery speeds range from 0.75 mm/s to 1.1 mm/s.By combining a rational structural design and 4D printing,the reported reconfigurable acoustic metamaterials will inspire further studies on the design of dynamic and broadband absorption devices.
基金equally funded by the Joint Funds of the National Natural Science Foundation of China(U2571210)the Strategic Priority Research Program of Kunming Institute of Botany,Chinese Academy of Sciences(KIBXD202401)+2 种基金National Natural Science Foundation of China(32471734)the Yuelushan Laboratory Breeding Projectthe Caiyun Postdoctoral Program of Yunnan Province。
摘要Karst landscapes are developed on soluble rocks(primarily limestone),covering about 10-15%of Earth’s ice-free land surface(Ford and Williams,2007).Their unique geological properties have given rise to complex,heterogeneous,and“island-like”habitats that,combined with periodic drought,high calcium,and lownutrient stresses,foster high species diversity and endemism(Clements et al.,2006;Hao et al.,2015;Oliver et al.,2017;Monro et al.,2018).These conditions make karst ecosystems ideal“natural laboratories”for studying speciation and adaptive evolution(Clements et al.,2006;Oliver et al.,2017).
基金supported by the National Natural Science Foundation of China(Nos.62577007 and 92582204)。
摘要This paper conducts an empirical study on students'code modification behaviors in incremental programming projects by analyzing 40771 code submissions from 371 students through abstract syntax tree(AST)difference analysis and manual annotation.The study investigates the distribution of code modification types to prior-phase code during iterative development,identifies cross-phase error types,and analyzes refactoring strategies.The findings reveal that error correction and code refactoring constitute the primary types of cross-phase code modifications.Among cross-phase latent errors,special case neglect represents the dominant error type,indicating insufficient coverage of special scenarios in existing test suites.Variable renaming emerges as the most prevalent refactoring behavior,reflecting students'emphasis on code readability.These research findings provide empirical evidence for optimizing incremental curriculum design,improving test cases,and cultivating students'code maintenance capabilities in programming education.