SiC/Al-based composite foams were prepared by a two-step foaming method.The influence of the SiC content and its distribution uniformity on the foaming stability,cell structure,and mechanical properties of the aluminu...SiC/Al-based composite foams were prepared by a two-step foaming method.The influence of the SiC content and its distribution uniformity on the foaming stability,cell structure,and mechanical properties of the aluminum foams was investigated.The macro/micro-features of the aluminum foams were characterized and analyzed.Results demonstrate that an appropriate increase in SiC content and the uniform distribution of SiC can improve the foaming stability,optimize the cell diameter and cell wall thickness,ameliorate the cell distribution,and enhance the hardness and compressive strength of the aluminum foams.However,either insufficient or excessive SiC leads to uneven distribution of SiC particles,which is unfavorable to foaming stability and good cell structure formation.With 6wt%SiC,both the foaming stability and cell structure of the aluminum foam reach the optimal state,resulting in the highest compressive strength and optimal energy absorption capacity.展开更多
Photoacoustic-computed tomography is a novel imaging technique that combines high absorption contrast and deep tissue penetration capability,enabling comprehensive three-dimensional imaging of biological targets.Howev...Photoacoustic-computed tomography is a novel imaging technique that combines high absorption contrast and deep tissue penetration capability,enabling comprehensive three-dimensional imaging of biological targets.However,the increasing demand for higher resolution and real-time imaging results in significant data volume,limiting data storage,transmission and processing efficiency of system.Therefore,there is an urgent need for an effective method to compress the raw data without compromising image quality.This paper presents a photoacoustic-computed tomography 3D data compression method and system based on Wavelet-Transformer.This method is based on the cooperative compression framework that integrates wavelet hard coding with deep learning-based soft decoding.It combines the multiscale analysis capability of wavelet transforms with the global feature modeling advantage of Transformers,achieving high-quality data compression and reconstruction.Experimental results using k-wave simulation suggest that the proposed compression system has advantages under extreme compression conditions,achieving a raw data compression ratio of up to 1:40.Furthermore,three-dimensional data compression experiment using in vivo mouse demonstrated that the maximum peak signal-to-noise ratio(PSNR)and structural similarity index(SSIM)values of reconstructed images reached 38.60 and 0.9583,effectively overcoming detail loss and artifacts introduced by raw data compression.All the results suggest that the proposed system can significantly reduce storage requirements and hardware cost,enhancing computational efficiency and image quality.These advantages support the development of photoacoustic-computed tomography toward higher efficiency,real-time performance and intelligent functionality.展开更多
Dear Editor,The letter proposes a tensor low-rank orthogonal compression(TLOC)model for a convolutional neural network(CNN),which facilitates its efficient and highly-accurate low-rank representation.Model compression...Dear Editor,The letter proposes a tensor low-rank orthogonal compression(TLOC)model for a convolutional neural network(CNN),which facilitates its efficient and highly-accurate low-rank representation.Model compression is crucial for deploying deep neural network(DNN)models on resource-constrained embedded devices.展开更多
To achieve the potential performance gain of massive multiple-input multiple-output(MIMO)systems,base stations(BS)require downlink channel state information(CSI)fed back by users to execute beamforming design,especial...To achieve the potential performance gain of massive multiple-input multiple-output(MIMO)systems,base stations(BS)require downlink channel state information(CSI)fed back by users to execute beamforming design,especially in the frequency division duplex(FDD)systems.However,due to the enormous number of antennas in massive MIMO systems,the feedback overhead of downlink CSI acquisition is extremely large.To address this issue,deep learning(DL)techniques have been introduced to de velop high-accuracy feedback strategies under limited backhaul constraints.In this paper,we provide an overview of DL-based CSI compression and feedback approaches in massive MIMO systems.Specifically,we introduce the conventional CSI compression and feedback schemes and the existing problems.Besides,we elaborate on various DL techniques employed in CSI compression from the perspective of network architecture and analyze the advantages of different techniques.We also enumerate the applications of DL-based methods for solving practical challenges in CSI compression and feedback.In addition,we brief the remaining issues in deep CSI compression and indicate potential directions in future wireless networks.展开更多
Rock brittleness is a critical property in geotechnical and energy engineering,as it directly influences the prediction of rock failure and stability assessment.Although numerous methods have been developed to evaluat...Rock brittleness is a critical property in geotechnical and energy engineering,as it directly influences the prediction of rock failure and stability assessment.Although numerous methods have been developed to evaluate brittleness,many fail to comprehensively account for the impacts of microstructural changes,mineralogical characteristics,and stress conditions on energy evolution during failure.This study proposes a novel approach for brittleness evaluation based on the energy evolution throughout the post-peak failure process,integrating two micromechanical mechanisms:crack propagation and frictional sliding.A new brittleness index is defined as the ratio of generated surface energy to released elastic energy,providing a unified framework for assessing both Class I and Class II mechanical behaviors.The brittleness of cyan,white,and gray sandstones was investigated under various confining pressures and moisture conditions using X-ray diffraction(XRD),scanning electron microscopy(SEM),and conventional triaxial compression(CTC)tests.The results demonstrate that brittleness decreases with increasing confining pressure,due to suppressed crack propagation,and increases under saturated conditions,as moisture enhances crack propagation.By establishing connections between mineral composition,microstructural features,and stress-induced responses,the proposed method overcame limitations of previous approaches and offered a more precise tool for evaluating rock brittleness under diverse environmental scenarios.展开更多
An in-depth understanding of the behaviours of solid propellants under low-velocity impact loads is crucial for enhancing their safety in applications such as aerospace propulsion.This study investigated the dynamic r...An in-depth understanding of the behaviours of solid propellants under low-velocity impact loads is crucial for enhancing their safety in applications such as aerospace propulsion.This study investigated the dynamic responses of single ammonium perchlorate(AP)/octogen(HMX)particles embedded in a hydroxyl-terminated polybutadiene(HTPB)binder under dynamic compression loading via real-time synchrotron-based X-ray phase contrast imaging and a modified split Hopkinson pressure bar(SHPB)system.The compression of the viscoelastic binder and subsequent dynamic fracturing of the AP/HMX particles were captured.During compression,transverse cracks developed within the AP particles,and their propagation led to particle fracturing,resulting in ductile fracturing.Unlike AP,HMX generated numerous short cracks within the internal and edge regions simultaneously,leading to fragmentation and brittle fracturing.Moreover,particle damage reduced the modulus of the sample,shifting its dynamic stress response from nonlinear elasticity to strain softening and further strain hardening as the binder exhibited plastic deformation.A compression simulation incorporating a real particle microscopic structure was established to study the mechanical response of the interface and particles.The simulation results agreed with the experimental observations.These results indicate that the shear stress at the HTPB-AP interface is greater than that at the HTPB-HMX interface,which is a factor influencing the differences in the mesoscale damage mechanisms of the particles.展开更多
Micropillar compression tests were used to investigate the influence of hydrogen on the deformation behavior and hydrogen embrittlement(HE)of nitrogen-alloyed austenitic stainless steel QN_(2)109.Results indicate that...Micropillar compression tests were used to investigate the influence of hydrogen on the deformation behavior and hydrogen embrittlement(HE)of nitrogen-alloyed austenitic stainless steel QN_(2)109.Results indicate that the hydrogen increases the dislocation density,reduces the yield stress,and accelerates the formation and intersection of slip bands,with hydrogen-induced cracks initiating at slip band intersections.X-ray diffraction confirms the absence of martensitic transformation,ruling out the role of martensitic transformation in HE.The micropillar compression technique is highly sensitive for characterizing hydrogen-material interactions,owing to the material’s low hydrogen diffusivity and the small size of its hydrogen-affected zone.These findings align with the hydrogen-enhanced localized plasticity mechanism.展开更多
The deformation and failure of coal walls in front of a working face cause significant difficulties during mining operations.This study reveals the nonuniform distribution of bearing pressure in front of coal walls ba...The deformation and failure of coal walls in front of a working face cause significant difficulties during mining operations.This study reveals the nonuniform distribution of bearing pressure in front of coal walls based on in situ monitoring data and numerical simulation.Therefore,an eccentric compression mechanical model was established to study the deformation and failure characteristics of a coal wall.The slenderness ratio of the compression bar is introduced to define coal walls.The results showed that instability failure occurs when λ>λ_(c) and material failure occurs when λ≤λ_(c).The instability failure-type coal wall spalling was related to the mining height,eccentricity of roof pressure,the horizontal force,and the reaction moment of the floor.The material failure-type coal wall spalling was related to the cohesion,the internal friction angle of the coal,the upper pressure,and the horizontal force of coal walls.Unstable and destructive coal wall peeling usually occurs at a height of 0.5–0.6 times the mining height,while material damage to coal wall peeling is determined to occur within the range of 0.4-0.6 times the mining depth.The findings contribute to the understanding of the deformation and failure of coal walls.展开更多
To investigate the damage evolution caused by stress-driven and sub-critical crack propagation within the Beishan granite under multi-creep triaxial compressive conditions,the distributed optical fiber sensing and X-r...To investigate the damage evolution caused by stress-driven and sub-critical crack propagation within the Beishan granite under multi-creep triaxial compressive conditions,the distributed optical fiber sensing and X-ray computed tomography were combined to obtain the strain distribution over the sample surface and internal fractures of the samples.The Gini and skewness(G-S)coefficients were used to quantify strain localization during tests,where the Gini coefficient reflects the degree of clustering of elements with high strain values,i.e.,strain localization/delocalization.The strain localization-induced asymmetry of data distribution is quantified by the skewness coefficient.A precursor to granite failure is defined by the rapid and simultaneous increase of the G-S coefficients,which are calculated from strain increment,giving an earlier warning of failure by about 8%peak stress than those from absolute strain values.Moreover,the process of damage accumulation due to stress-driven crack propagation in Beishan granite is different at various confining pressures as the stress exceeds the crack initiation stress.Concretely,strain localization is continuous until brittle failure at higher confining pressure,while both strain localization and delocalization occur at lower confining pressure.Despite the different stress conditions,a similar statistical characteristic of strain localization during the creep stage is observed.The Gini coefficient increases,and the skewness coefficient decreases slightly as the creep stress is below 95%peak stress.When the accelerated strain localization begins,the Gini and skewness coefficients increase rapidly and simultaneously.展开更多
In the field of rock engineering,the influence of water is a dynamic process that exhibits varying effects over time and across different locations.To further understand how water influences the mechanical properties ...In the field of rock engineering,the influence of water is a dynamic process that exhibits varying effects over time and across different locations.To further understand how water influences the mechanical properties and acoustic emission(AE)behavior of rocks,this study conducted uniaxial compression experiments on sandstones with varying degrees of wetting under both natural conditions and water-chemical environments.In addition,the study combined AE equipment with digital image correlation(DIC)to monitor the entire failure process.Using the sliding window algorithm,the variation in the variance of AE characteristic parameters during the process of sandstone loading to failure is analyzed from the perspective of critical slowing down.This analysis enables the effective identification of the early warning signal before failure.The experimental findings suggest that an increase in wetting height results in a gradual decrease in peak stress,accompanied by a concomitant increase in the percentage of shear cracks.The characteristic parameters,including energy,amplitude,and ringing count,all exhibit critical slowing phenomena.The waveform of AE characteristic parameters of the same sample is similar,and the mutation time of the precursor signal is roughly the same.All signals appear in the irreversible plastic deformation stage of microcrack initiation.The integration of critical slowing down theory and the b-value early warning method facilitates a more comprehensive evaluation of the stability of rock mass,thereby significantly enhancing the efficiency and safety of disaster prevention measures.展开更多
We present the first systematic experimental validation of return-current-driven cylindrical implosion scaling in micrometer-sized Cu and Al wires irradiated by J-class femtosecond laser pulses.Employing XFEL-based im...We present the first systematic experimental validation of return-current-driven cylindrical implosion scaling in micrometer-sized Cu and Al wires irradiated by J-class femtosecond laser pulses.Employing XFEL-based imaging with sub-micrometer spatial and femtosecond temporal resolution,supported by hydrodynamic and particle-in-cell simulations,we reveal how return current density depends precisely on wire diameter,material properties,and incident laser energy.We identify deviations from simple theoretical predictions due to geometrically influenced electron escape dynamics.These results refine and confirm the scaling laws essential for predictive modeling in high-energy-density physics and inertial fusion research.展开更多
The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods,and the large-size mined-out area is usually backfilled by multiple backfilling be...The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods,and the large-size mined-out area is usually backfilled by multiple backfilling before the recovery of a secondary stope,resulting in a layered structure of backfill in stope.Therefore,it is significant to investigate the deformation responses and mechanical properties of stratified cemented tailings backfill(SCTB)with different layer structures to remain self-standing as an artificial pillar in the primary stope.The current work examined the effects of enhance layer position(1/3,1/2,and 2/3)and thickness ratio(0,0.1,0.2,and 0.3)on the mechanical properties,deformation,energy evolution,microstructures,and failure modes of SCTB.The results demonstrate that the incorporation of an enhance layer significantly strengthens the deformation and strength of SCTB.Under a confining pressure of 50 kPa,the peak deviatoric stress rises from 525.6 to 560.3,597.1,and 790.5 kPa as the thickness ratio of enhance layer is increased from 0 to 0.1,0.2,and 0.3,representing a significant increase of 6.6%,13.6%,and 50.4%.As the confining pressure increases,the slopes of the curves in the elastic stage become steep,and the plastic phase is extended accordingly.Additionally,the incorporation of the enhance layer significantly improves the energy storage linit of SCTB specimen.As the thickness ratio of the enhance layer increases from 0 to 0.1,0.2,and 0.3,the elastic energy rises from 0.54 to 0.67,0.84,and 1.00 MJ·m^(-3),representing a significant increase of 24.1%,55.6%,and 85.2%.The internal friction angles and cohesions of the SCTB specimens are higher than those of the CTB specimens,however,the cohesion is more susceptible to enhance layer position and thickness ratio than the internal friction angle.The failure style of the SCTB specimen changes from shear failure to splitting bulging failure and shear bulging failure with the presence of an enhance layer.The crack propagation path is significantly blocked by the enhance layer.The findings are of great significance to the application and stability of the SCTB in subsequent stoping backfilling mines.展开更多
The progressive failure characteristics of geomaterial are a remarkable and challenging topic in geotechnical engineering.To study the effect of salt content and temperature on the progressive failure characteristics ...The progressive failure characteristics of geomaterial are a remarkable and challenging topic in geotechnical engineering.To study the effect of salt content and temperature on the progressive failure characteristics of frozen sodium sulfate saline sandy soil,a series of uniaxial compression tests were performed by integrating digital image correlation(DIC)technology into the testing apparatus.The evolution law of the uniaxial compression strength(UCS),the failure strain,and the formation of the shear band of the frozen sodium sulfate saline sandy soil were analyzed.The test results show that within the scope of this study,with the increase of salt content,both the UCS and the shear band angle initially decrease with increasing salt content before showing an increase.In contrast,the failure strain and the width of the shear band exhibit an initial increase followed by a decrease in the samples.In addition,to investigate the brittle failure characteristics of frozen sodium sulfate saline sandy soil,two classic brittleness evaluation methods were employed to quantitatively assess the brittleness level for the soil samples.The findings suggest that the failure characteristics under all test conditions in this study belong to the transition stage between brittle and ductile,indicating that frozen sodium sulfate saline sandy soil exhibits certain brittle behavior under uniaxial compression conditions,and the brittleness index basically decreases and then increases with the rise in salt content.展开更多
The effect of deformation resistance of AlCr_(1.3)TiNi_(2) eutectic high-entropy alloys under various current densities and strain rates was investigated during electrically-assisted compression.Results show that at c...The effect of deformation resistance of AlCr_(1.3)TiNi_(2) eutectic high-entropy alloys under various current densities and strain rates was investigated during electrically-assisted compression.Results show that at current density of 60 A/mm^(2) and strain rate of 0.1 s^(−1),the ultimate tensile stress shows a significant decrease from approximately 3000 MPa to 1900 MPa with reduction ratio of about 36.7%.However,as current density increases,elongation decreases due to intermediate temperature embrittlement.This is because the current induces Joule effect,which then leads to stress concentration and more defect formation.Moreover,the flow stress is decreased with the increase in strain rate at constant current density.展开更多
The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compressio...The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compression tests,CT scanning,SEM,and EDS tests were conducted on cemented gangue backfill samples(CGBSs)with various carbon nanotube concentrations(P_(CNT))that satisfied fractal theory for the PSD of aggregates.The mechanical properties,energy dissipations,and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed.The results indicate that appropriate carbon nanotubes(CNTs)effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging,and the optimal effect appears at P_(CNT)of 0.08wt%.Taking PSD fractal dimension(D)of 2.500 as an example,compared to that of CGBS without CNT,the peak strength(σ_(p)),axial peak strain(ε_(1,p)),elastic strain energy(Ue),and dissipated energy(U_(d))increased by 12.76%,29.60%,19.05%,and90.39%,respectively.However,excessive CNTs can reduce the mechanical properties of CGBSs due to CNT agglomeration,manifesting a decrease inρ_(p),ε_(1,p),and the volumetric strain increment(Δε_(v))when P_(CNT)increases from 0.08wt%to 0.12wt%.Moreover,the addition of CNTs improved the integrity of CGBS after macroscopic failure,and crack extension in CGBSs appeared in two modes:detour and pass through the aggregates.Theσ_(p)and U_(d)firstly increase and then decrease with increasing D,and porosity shows the opposite trend.Theε_(1,p)andΔε_(v)are negatively correlated with D,and CGBS with D=2.150 has the maximum deformation parameters(ε_(1,p)=0.05079,Δε_(v)=0.01990)due to the frictional slip effect caused by coarse aggregates.With increasing D,the failure modes of CGBSs are sequentially manifested as oblique shear failure,"Y-shaped"shear failure,and conjugate shear failure.展开更多
Microbially induced calcium carbonate precipitation(MICP)technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regu...Microbially induced calcium carbonate precipitation(MICP)technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength,better durability and environmental friendli-ness,as well as a good engineering application prospect.In this paper,the shear strength of sand column was tested by triaxial compression tests,and the strength index was obtained.In order to further study the micro-strength mechanism and the failure process,based on the discrete element method,a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation,particle mor-phology,content ratio of induced calcium carbonate,pore distribution characteristics,inter-particle cementation and so on.The failure process of MICP cemented sand column under load was analysed by numerical simulation,and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions.The results indicate that compared with the actual triaxial tests of MICP cemented sand column,although there are deviations in stress and strain,cohesion and internal friction angle,the numerical simulation shows similar development law and intensity amplitude,and the same failure trend.The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.展开更多
AZ31/Al/Ta composites were prepared using the vacuum hot compression bonding(VHCB)method.The effect of hot compressing temperature on the interface microstructure evolution,phase constitution,and shear strength at the...AZ31/Al/Ta composites were prepared using the vacuum hot compression bonding(VHCB)method.The effect of hot compressing temperature on the interface microstructure evolution,phase constitution,and shear strength at the interface was investigated.Moreover,the interface bonding mechanisms of the AZ31/Al/Ta composites during the VHCB process were explored.The results demonstrate that as the VHCB temperature increases,the phase composition of the interface between Mg and Al changes from the Mg-Al brittle intermetallic compounds(Al_(12)Mg_(17)and Al_(3)Mg_(2))to the Al-Mg solid solution.Meanwhile,the width of the Al/Ta interface diffusion layer at 450℃increases compared to that at 400℃.The shear strengths are 24 and 46 MPa at 400 and 450℃,respectively.The interfacial bonding mechanism of AZ31/Al/Ta composites involves the coexistence of diffusion and mechanical meshing.Avoiding the formation of brittle phases at the interface can significantly improve interfacial bonding strength.展开更多
基金Doctoral Startup Fund(20192066,20212028)Laijin Excellent Doctoral Fund(20202021)+1 种基金Scientific and Technological Innovation of Colleges and Universities in Shanxi Province(2020L0342)Fundamental Research Program of Shanxi Province(202303021222178)。
文摘SiC/Al-based composite foams were prepared by a two-step foaming method.The influence of the SiC content and its distribution uniformity on the foaming stability,cell structure,and mechanical properties of the aluminum foams was investigated.The macro/micro-features of the aluminum foams were characterized and analyzed.Results demonstrate that an appropriate increase in SiC content and the uniform distribution of SiC can improve the foaming stability,optimize the cell diameter and cell wall thickness,ameliorate the cell distribution,and enhance the hardness and compressive strength of the aluminum foams.However,either insufficient or excessive SiC leads to uneven distribution of SiC particles,which is unfavorable to foaming stability and good cell structure formation.With 6wt%SiC,both the foaming stability and cell structure of the aluminum foam reach the optimal state,resulting in the highest compressive strength and optimal energy absorption capacity.
基金supported by the National Key R&D Program of China[Grant No.2023YFF0713600]the National Natural Science Foundation of China[Grant No.62275062]+3 种基金Project of Shandong Innovation and Startup Community of High-end Medical Apparatus and Instruments[Grant No.2023-SGTTXM-002 and 2024-SGTTXM-005]the Shandong Province Technology Innovation Guidance Plan(Central Leading Local Science and Technology Development Fund)[Grant No.YDZX2023115]the Taishan Scholar Special Funding Project of Shandong Provincethe Shandong Laboratory of Advanced Biomaterials and Medical Devices in Weihai[Grant No.ZL202402].
文摘Photoacoustic-computed tomography is a novel imaging technique that combines high absorption contrast and deep tissue penetration capability,enabling comprehensive three-dimensional imaging of biological targets.However,the increasing demand for higher resolution and real-time imaging results in significant data volume,limiting data storage,transmission and processing efficiency of system.Therefore,there is an urgent need for an effective method to compress the raw data without compromising image quality.This paper presents a photoacoustic-computed tomography 3D data compression method and system based on Wavelet-Transformer.This method is based on the cooperative compression framework that integrates wavelet hard coding with deep learning-based soft decoding.It combines the multiscale analysis capability of wavelet transforms with the global feature modeling advantage of Transformers,achieving high-quality data compression and reconstruction.Experimental results using k-wave simulation suggest that the proposed compression system has advantages under extreme compression conditions,achieving a raw data compression ratio of up to 1:40.Furthermore,three-dimensional data compression experiment using in vivo mouse demonstrated that the maximum peak signal-to-noise ratio(PSNR)and structural similarity index(SSIM)values of reconstructed images reached 38.60 and 0.9583,effectively overcoming detail loss and artifacts introduced by raw data compression.All the results suggest that the proposed system can significantly reduce storage requirements and hardware cost,enhancing computational efficiency and image quality.These advantages support the development of photoacoustic-computed tomography toward higher efficiency,real-time performance and intelligent functionality.
基金supported by the Science and Technology Innovation Key R&D Program of Chongqing(CSTB2025TIAD-STX0032)National Key Research and Development Program of China(2024YFF0908200)+1 种基金the Chongqing Technology Innovation and Application Development Special Key Project(CSTB2024TIAD-KPX0018)the Southwest University Graduate Student Research Innovation(SWUB24051)。
文摘Dear Editor,The letter proposes a tensor low-rank orthogonal compression(TLOC)model for a convolutional neural network(CNN),which facilitates its efficient and highly-accurate low-rank representation.Model compression is crucial for deploying deep neural network(DNN)models on resource-constrained embedded devices.
基金supported by ZTE Industry-University-Institute Cooperation Funds under Grant No.IA20240319003the NSFC under Grant No.62571112。
文摘To achieve the potential performance gain of massive multiple-input multiple-output(MIMO)systems,base stations(BS)require downlink channel state information(CSI)fed back by users to execute beamforming design,especially in the frequency division duplex(FDD)systems.However,due to the enormous number of antennas in massive MIMO systems,the feedback overhead of downlink CSI acquisition is extremely large.To address this issue,deep learning(DL)techniques have been introduced to de velop high-accuracy feedback strategies under limited backhaul constraints.In this paper,we provide an overview of DL-based CSI compression and feedback approaches in massive MIMO systems.Specifically,we introduce the conventional CSI compression and feedback schemes and the existing problems.Besides,we elaborate on various DL techniques employed in CSI compression from the perspective of network architecture and analyze the advantages of different techniques.We also enumerate the applications of DL-based methods for solving practical challenges in CSI compression and feedback.In addition,we brief the remaining issues in deep CSI compression and indicate potential directions in future wireless networks.
基金supported by the National Natural Science Foundation of China(Grant No.42277147)Ningbo Public Welfare Research Program(Grant No.2024S081)Ningbo Natural Science Foundation(Grant No.2024J186).
文摘Rock brittleness is a critical property in geotechnical and energy engineering,as it directly influences the prediction of rock failure and stability assessment.Although numerous methods have been developed to evaluate brittleness,many fail to comprehensively account for the impacts of microstructural changes,mineralogical characteristics,and stress conditions on energy evolution during failure.This study proposes a novel approach for brittleness evaluation based on the energy evolution throughout the post-peak failure process,integrating two micromechanical mechanisms:crack propagation and frictional sliding.A new brittleness index is defined as the ratio of generated surface energy to released elastic energy,providing a unified framework for assessing both Class I and Class II mechanical behaviors.The brittleness of cyan,white,and gray sandstones was investigated under various confining pressures and moisture conditions using X-ray diffraction(XRD),scanning electron microscopy(SEM),and conventional triaxial compression(CTC)tests.The results demonstrate that brittleness decreases with increasing confining pressure,due to suppressed crack propagation,and increases under saturated conditions,as moisture enhances crack propagation.By establishing connections between mineral composition,microstructural features,and stress-induced responses,the proposed method overcame limitations of previous approaches and offered a more precise tool for evaluating rock brittleness under diverse environmental scenarios.
基金supported by the National Natural Science Foundation of China(U2341288 and 12302492)。
文摘An in-depth understanding of the behaviours of solid propellants under low-velocity impact loads is crucial for enhancing their safety in applications such as aerospace propulsion.This study investigated the dynamic responses of single ammonium perchlorate(AP)/octogen(HMX)particles embedded in a hydroxyl-terminated polybutadiene(HTPB)binder under dynamic compression loading via real-time synchrotron-based X-ray phase contrast imaging and a modified split Hopkinson pressure bar(SHPB)system.The compression of the viscoelastic binder and subsequent dynamic fracturing of the AP/HMX particles were captured.During compression,transverse cracks developed within the AP particles,and their propagation led to particle fracturing,resulting in ductile fracturing.Unlike AP,HMX generated numerous short cracks within the internal and edge regions simultaneously,leading to fragmentation and brittle fracturing.Moreover,particle damage reduced the modulus of the sample,shifting its dynamic stress response from nonlinear elasticity to strain softening and further strain hardening as the binder exhibited plastic deformation.A compression simulation incorporating a real particle microscopic structure was established to study the mechanical response of the interface and particles.The simulation results agreed with the experimental observations.These results indicate that the shear stress at the HTPB-AP interface is greater than that at the HTPB-HMX interface,which is a factor influencing the differences in the mesoscale damage mechanisms of the particles.
基金support from the National Natural Science Foundation of China(Grant No.U24A20105 and 52071209)the Major Scientific and Technological Innovation Project of CITIC Group(Grant No.2022ZXKYA06100,with Hongzhou Lu as the principal grant recipient)the Program of Shanghai Academic and Technology Research Leader(Grant No.18XD1402200).
文摘Micropillar compression tests were used to investigate the influence of hydrogen on the deformation behavior and hydrogen embrittlement(HE)of nitrogen-alloyed austenitic stainless steel QN_(2)109.Results indicate that the hydrogen increases the dislocation density,reduces the yield stress,and accelerates the formation and intersection of slip bands,with hydrogen-induced cracks initiating at slip band intersections.X-ray diffraction confirms the absence of martensitic transformation,ruling out the role of martensitic transformation in HE.The micropillar compression technique is highly sensitive for characterizing hydrogen-material interactions,owing to the material’s low hydrogen diffusivity and the small size of its hydrogen-affected zone.These findings align with the hydrogen-enhanced localized plasticity mechanism.
基金Youth Innovation Team of Shandong Higher Education Institutions,Grant/Award Number:2022KJ214Shandong Postdoctoral Science Foundation,Grant/Award Number:SDCXZG‐202303031+2 种基金China Postdoctoral Science Foundation,Grant/Award Number:2023M732109National Natural Science Foundation of China,Grant/Award Number:52209141Natural Science Foundation of Shandong Province,China,Grant/Award Number:ZR2021QE069。
文摘The deformation and failure of coal walls in front of a working face cause significant difficulties during mining operations.This study reveals the nonuniform distribution of bearing pressure in front of coal walls based on in situ monitoring data and numerical simulation.Therefore,an eccentric compression mechanical model was established to study the deformation and failure characteristics of a coal wall.The slenderness ratio of the compression bar is introduced to define coal walls.The results showed that instability failure occurs when λ>λ_(c) and material failure occurs when λ≤λ_(c).The instability failure-type coal wall spalling was related to the mining height,eccentricity of roof pressure,the horizontal force,and the reaction moment of the floor.The material failure-type coal wall spalling was related to the cohesion,the internal friction angle of the coal,the upper pressure,and the horizontal force of coal walls.Unstable and destructive coal wall peeling usually occurs at a height of 0.5–0.6 times the mining height,while material damage to coal wall peeling is determined to occur within the range of 0.4-0.6 times the mining depth.The findings contribute to the understanding of the deformation and failure of coal walls.
基金supported by the National Natural Science Foundation of China(Grant No.52339001).
文摘To investigate the damage evolution caused by stress-driven and sub-critical crack propagation within the Beishan granite under multi-creep triaxial compressive conditions,the distributed optical fiber sensing and X-ray computed tomography were combined to obtain the strain distribution over the sample surface and internal fractures of the samples.The Gini and skewness(G-S)coefficients were used to quantify strain localization during tests,where the Gini coefficient reflects the degree of clustering of elements with high strain values,i.e.,strain localization/delocalization.The strain localization-induced asymmetry of data distribution is quantified by the skewness coefficient.A precursor to granite failure is defined by the rapid and simultaneous increase of the G-S coefficients,which are calculated from strain increment,giving an earlier warning of failure by about 8%peak stress than those from absolute strain values.Moreover,the process of damage accumulation due to stress-driven crack propagation in Beishan granite is different at various confining pressures as the stress exceeds the crack initiation stress.Concretely,strain localization is continuous until brittle failure at higher confining pressure,while both strain localization and delocalization occur at lower confining pressure.Despite the different stress conditions,a similar statistical characteristic of strain localization during the creep stage is observed.The Gini coefficient increases,and the skewness coefficient decreases slightly as the creep stress is below 95%peak stress.When the accelerated strain localization begins,the Gini and skewness coefficients increase rapidly and simultaneously.
基金support from the National Natural Science Foundation of China(Grant Nos.52104207 and 52374214)the Shandong Provincial Youth Innovation Team Development Program for Higher Education Institutions(Grant No.2023KJ305).
文摘In the field of rock engineering,the influence of water is a dynamic process that exhibits varying effects over time and across different locations.To further understand how water influences the mechanical properties and acoustic emission(AE)behavior of rocks,this study conducted uniaxial compression experiments on sandstones with varying degrees of wetting under both natural conditions and water-chemical environments.In addition,the study combined AE equipment with digital image correlation(DIC)to monitor the entire failure process.Using the sliding window algorithm,the variation in the variance of AE characteristic parameters during the process of sandstone loading to failure is analyzed from the perspective of critical slowing down.This analysis enables the effective identification of the early warning signal before failure.The experimental findings suggest that an increase in wetting height results in a gradual decrease in peak stress,accompanied by a concomitant increase in the percentage of shear cracks.The characteristic parameters,including energy,amplitude,and ringing count,all exhibit critical slowing phenomena.The waveform of AE characteristic parameters of the same sample is similar,and the mutation time of the precursor signal is roughly the same.All signals appear in the irreversible plastic deformation stage of microcrack initiation.The integration of critical slowing down theory and the b-value early warning method facilitates a more comprehensive evaluation of the stability of rock mass,thereby significantly enhancing the efficiency and safety of disaster prevention measures.
基金partially supported by the Center for Advanced Systems Understanding(CASUS)financed by Germany’s Federal Ministry of Education and Research(BMBF)+2 种基金the Saxon State Government out of the State Budget approved by the Saxon State Parliamentfunding from the European Union’s Just Transition Fund(JTF)within the project Röntgenlaser-Optimierung der Laserfusion(ROLF),Contract No.5086999001co-financed by the Saxon State Government out of the State Budget approved by the Saxon State Parliament.
文摘We present the first systematic experimental validation of return-current-driven cylindrical implosion scaling in micrometer-sized Cu and Al wires irradiated by J-class femtosecond laser pulses.Employing XFEL-based imaging with sub-micrometer spatial and femtosecond temporal resolution,supported by hydrodynamic and particle-in-cell simulations,we reveal how return current density depends precisely on wire diameter,material properties,and incident laser energy.We identify deviations from simple theoretical predictions due to geometrically influenced electron escape dynamics.These results refine and confirm the scaling laws essential for predictive modeling in high-energy-density physics and inertial fusion research.
基金financially supported by the Fundamental Research Funds for the Central Universities,China(No.2023JCCXNY01)Guangxi Key Technologies R&D Program,China(No.2022AB31022).
文摘The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods,and the large-size mined-out area is usually backfilled by multiple backfilling before the recovery of a secondary stope,resulting in a layered structure of backfill in stope.Therefore,it is significant to investigate the deformation responses and mechanical properties of stratified cemented tailings backfill(SCTB)with different layer structures to remain self-standing as an artificial pillar in the primary stope.The current work examined the effects of enhance layer position(1/3,1/2,and 2/3)and thickness ratio(0,0.1,0.2,and 0.3)on the mechanical properties,deformation,energy evolution,microstructures,and failure modes of SCTB.The results demonstrate that the incorporation of an enhance layer significantly strengthens the deformation and strength of SCTB.Under a confining pressure of 50 kPa,the peak deviatoric stress rises from 525.6 to 560.3,597.1,and 790.5 kPa as the thickness ratio of enhance layer is increased from 0 to 0.1,0.2,and 0.3,representing a significant increase of 6.6%,13.6%,and 50.4%.As the confining pressure increases,the slopes of the curves in the elastic stage become steep,and the plastic phase is extended accordingly.Additionally,the incorporation of the enhance layer significantly improves the energy storage linit of SCTB specimen.As the thickness ratio of the enhance layer increases from 0 to 0.1,0.2,and 0.3,the elastic energy rises from 0.54 to 0.67,0.84,and 1.00 MJ·m^(-3),representing a significant increase of 24.1%,55.6%,and 85.2%.The internal friction angles and cohesions of the SCTB specimens are higher than those of the CTB specimens,however,the cohesion is more susceptible to enhance layer position and thickness ratio than the internal friction angle.The failure style of the SCTB specimen changes from shear failure to splitting bulging failure and shear bulging failure with the presence of an enhance layer.The crack propagation path is significantly blocked by the enhance layer.The findings are of great significance to the application and stability of the SCTB in subsequent stoping backfilling mines.
基金supported by the National Natural Science Foundation of China(Grant Nos.42372312,and 42172299)the Pyramid Talent Training Project of Beijing University of Civil Engineering and Architecture(Grant No.JDYC20220807).
文摘The progressive failure characteristics of geomaterial are a remarkable and challenging topic in geotechnical engineering.To study the effect of salt content and temperature on the progressive failure characteristics of frozen sodium sulfate saline sandy soil,a series of uniaxial compression tests were performed by integrating digital image correlation(DIC)technology into the testing apparatus.The evolution law of the uniaxial compression strength(UCS),the failure strain,and the formation of the shear band of the frozen sodium sulfate saline sandy soil were analyzed.The test results show that within the scope of this study,with the increase of salt content,both the UCS and the shear band angle initially decrease with increasing salt content before showing an increase.In contrast,the failure strain and the width of the shear band exhibit an initial increase followed by a decrease in the samples.In addition,to investigate the brittle failure characteristics of frozen sodium sulfate saline sandy soil,two classic brittleness evaluation methods were employed to quantitatively assess the brittleness level for the soil samples.The findings suggest that the failure characteristics under all test conditions in this study belong to the transition stage between brittle and ductile,indicating that frozen sodium sulfate saline sandy soil exhibits certain brittle behavior under uniaxial compression conditions,and the brittleness index basically decreases and then increases with the rise in salt content.
基金National Natural Science Foundation of China(52305349)Heilongjiang Touyan Team(HITTY-20190036)+2 种基金Heilongjiang Provincial Natural Science Foundation of China(LH2023E033)CGN-HIT Advanced Nuclear and New Energy Research Institute(CGN-HIT202305)Natural Science Basic Research Program of Shaanxi Province(2023-JC-QN-0518)。
文摘The effect of deformation resistance of AlCr_(1.3)TiNi_(2) eutectic high-entropy alloys under various current densities and strain rates was investigated during electrically-assisted compression.Results show that at current density of 60 A/mm^(2) and strain rate of 0.1 s^(−1),the ultimate tensile stress shows a significant decrease from approximately 3000 MPa to 1900 MPa with reduction ratio of about 36.7%.However,as current density increases,elongation decreases due to intermediate temperature embrittlement.This is because the current induces Joule effect,which then leads to stress concentration and more defect formation.Moreover,the flow stress is decreased with the increase in strain rate at constant current density.
基金financially supported by the National Natural Science Foundation of China(Nos.52174092,51904290,and 52374147)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+2 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the National Key Research and Development Program of China(No.2023YFC3804204)the Major Program of Xinjiang Uygur Autonomous Region S cience and Technology(No.2023A01002)。
文摘The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compression tests,CT scanning,SEM,and EDS tests were conducted on cemented gangue backfill samples(CGBSs)with various carbon nanotube concentrations(P_(CNT))that satisfied fractal theory for the PSD of aggregates.The mechanical properties,energy dissipations,and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed.The results indicate that appropriate carbon nanotubes(CNTs)effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging,and the optimal effect appears at P_(CNT)of 0.08wt%.Taking PSD fractal dimension(D)of 2.500 as an example,compared to that of CGBS without CNT,the peak strength(σ_(p)),axial peak strain(ε_(1,p)),elastic strain energy(Ue),and dissipated energy(U_(d))increased by 12.76%,29.60%,19.05%,and90.39%,respectively.However,excessive CNTs can reduce the mechanical properties of CGBSs due to CNT agglomeration,manifesting a decrease inρ_(p),ε_(1,p),and the volumetric strain increment(Δε_(v))when P_(CNT)increases from 0.08wt%to 0.12wt%.Moreover,the addition of CNTs improved the integrity of CGBS after macroscopic failure,and crack extension in CGBSs appeared in two modes:detour and pass through the aggregates.Theσ_(p)and U_(d)firstly increase and then decrease with increasing D,and porosity shows the opposite trend.Theε_(1,p)andΔε_(v)are negatively correlated with D,and CGBS with D=2.150 has the maximum deformation parameters(ε_(1,p)=0.05079,Δε_(v)=0.01990)due to the frictional slip effect caused by coarse aggregates.With increasing D,the failure modes of CGBSs are sequentially manifested as oblique shear failure,"Y-shaped"shear failure,and conjugate shear failure.
基金sponsored by the National Natural Science Foundation of China(Grant No.12002173,12262027)Research start-up project of Inner Mongolia University of Technology(No.2200000924)key Lab.of University of Geological Hazards and Geotechnical Engineering Defense in Sandy and Drought Regions,Inner Mongolia Autonomous.
文摘Microbially induced calcium carbonate precipitation(MICP)technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength,better durability and environmental friendli-ness,as well as a good engineering application prospect.In this paper,the shear strength of sand column was tested by triaxial compression tests,and the strength index was obtained.In order to further study the micro-strength mechanism and the failure process,based on the discrete element method,a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation,particle mor-phology,content ratio of induced calcium carbonate,pore distribution characteristics,inter-particle cementation and so on.The failure process of MICP cemented sand column under load was analysed by numerical simulation,and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions.The results indicate that compared with the actual triaxial tests of MICP cemented sand column,although there are deviations in stress and strain,cohesion and internal friction angle,the numerical simulation shows similar development law and intensity amplitude,and the same failure trend.The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.
基金National Natural Science Foundation of China(52275308,52301146)Fundamental Research Funds for the Central Universities(2023JG007)Supported by Shi Changxu Innovation Center for Advanced Materials(SCXKFJJ202207)。
文摘AZ31/Al/Ta composites were prepared using the vacuum hot compression bonding(VHCB)method.The effect of hot compressing temperature on the interface microstructure evolution,phase constitution,and shear strength at the interface was investigated.Moreover,the interface bonding mechanisms of the AZ31/Al/Ta composites during the VHCB process were explored.The results demonstrate that as the VHCB temperature increases,the phase composition of the interface between Mg and Al changes from the Mg-Al brittle intermetallic compounds(Al_(12)Mg_(17)and Al_(3)Mg_(2))to the Al-Mg solid solution.Meanwhile,the width of the Al/Ta interface diffusion layer at 450℃increases compared to that at 400℃.The shear strengths are 24 and 46 MPa at 400 and 450℃,respectively.The interfacial bonding mechanism of AZ31/Al/Ta composites involves the coexistence of diffusion and mechanical meshing.Avoiding the formation of brittle phases at the interface can significantly improve interfacial bonding strength.
