Time-averaged thermal convection in a rotating horizontal annulus with a higher temperature at its inner boundary is studied.The centrifugal force plays a stabilizing role,while thermal convection is determined by the...Time-averaged thermal convection in a rotating horizontal annulus with a higher temperature at its inner boundary is studied.The centrifugal force plays a stabilizing role,while thermal convection is determined by the“thermovibrational mechanism”.Convective flow is excited due to oscillations of a non-isothermal rotating fluid.Thermal vibrational convectionmanifests in the form of two-dimensional vortices elongated along the axis of rotation,which develop in a threshold manner with an increase in the amplitude of fluid oscillations.The objective of the present study is to clarify the nature of another phenomenon,i.e.,three-dimensional convective vortices observed in the experiments both before the excitation of the convection described above and in the supercritical region.The experimental study of the oscillatory and the time-averaged flow fields by particle image velocimetry is accompanied by the theoretical research of inertial waves.It is found that three-dimensional fluid flows owe their origin to inertial waves.This is confirmed by a high degree of agreement between the experimental and theoretical results.Experiments with cavities of different lengths indicate that the vortices are clearly seen in cavities thatmeet the conditions of resonant excitation of inertial modes.Furthermore,the length of the cavity has no effect on heat transfer,which is explained by the comparatively low intensity of the wave-induced flows.The main contribution to heat transfer is due to vortices elongated along the axis of rotation.The novel results are of significant practical importance in various fields.展开更多
In this paper we consider a static spherically symmetric black hole(BH)embedded in a Dehnen-(1,4,0)-type dark matter(DM)halo in the presence of a cloud string.We examine and present data on how the core density of the...In this paper we consider a static spherically symmetric black hole(BH)embedded in a Dehnen-(1,4,0)-type dark matter(DM)halo in the presence of a cloud string.We examine and present data on how the core density of the DM halo parameter and the cloud string parameter affect BH attributes such as quasinormal modes(QNMs)and shadow cast.To do this,we first look into the effective potential of perturbation equations for three types of perturbation fields with different spins:massless scalar field,electromagnetic field and gravitational field.Then,using the sixth-order Wentzel-Kramers-Brillouin approximation,we examine QNMs of the BH disturbed by the three fields and derive quasinormal frequencies.The changes in QNM versus the core density parameter and the cloud string parameter for three disturbances are explored.We also investigate how the core density and the cloud string parameter affect the photon sphere and shadow radius.Interestingly,the study shows that the influence of Dehnen-type DM and cloud strings increases both the photon sphere and the shadow radius.Finally,we employ observational data from Sgr A^(*) and M87^(*) to set limitations on the BH parameters.展开更多
Utilizing the Standardized Precipitation Evapotranspiration Index(SPEI)and ERA5 reanalysis data,this study investigates the variability of spring drought in southern China from 1979 to 2022 and its associated drivers....Utilizing the Standardized Precipitation Evapotranspiration Index(SPEI)and ERA5 reanalysis data,this study investigates the variability of spring drought in southern China from 1979 to 2022 and its associated drivers.The results indicate that southern China experienced interdecadal changes in SPEI over the past several decades,which can be concluded that drought severity intensified from 1979 to 2010,whereas a transition shift towards increased wetness occurred from 2010 to 2022.The first Empirical Orthogonal Function(EOF1)mode of SPEI variability in southern China accounts for 44.37%of the total variance,reflecting a uniform variation of SPEI across the region.In contrast,the second Empirical Orthogonal Function(EOF2),which explains 24.41%of the total variance,reveals a west-east dipole pattern in SPEI variability.Further analysis indicates that the positive phase of EOF1 is primarily driven by warm sea surface temperature anomalies(SSTAs)in the tropical eastern Pacific.These anomalies induce an anomalous anticyclone over the Philippine Sea,enhancing water vapor transport to southern China during spring.The positive phase of EOF2 is jointly influenced by warm SSTAs in the tropical Indian Ocean and the central Pacific;the latter induces anticyclonic anomalies over the Philippine Sea,which enhance water vapor transport from the western Pacific and increase precipitation in the eastern part of southern China.However,the warm SSTAs in the tropical Indian Ocean trigger an anomalous anticyclone over South Asia,inhibiting water vapor transport from the Bay of Bengal to the western part of southern China and thus reducing precipitation there.展开更多
The multiscale variability in summer extreme persistent precipitation(SEPP)in China from 1961 to 2020 was investigated via three extreme precipitation indices:consecutive wet days,total precipitation amount,and daily ...The multiscale variability in summer extreme persistent precipitation(SEPP)in China from 1961 to 2020 was investigated via three extreme precipitation indices:consecutive wet days,total precipitation amount,and daily precipitation intensity.The relationships between precursory and concurrent global oceanic modes and SEPP were identified via a generalized linear model(GLM).The influence of oceanic modes on SEPP was finally investigated via numerical simulations.The results revealed that the climatological SEPP(≥14 days)mainly appears across the Tibetan Plateau,Yunnan–Guizhou Plateau,and South China coast.The first EOF mode for all three indices showed strong signals over the Yangtze River.Further analysis via the GLM suggested that the positive phases of the tropical North Atlantic(TNA)in autumn,ENSO in winter,the Indian Ocean Basin(IOB)in spring,and the western North Pacific(WNP)in summer emerged as the most effective precursory factors of SEPP,which could serve as preceding signals for future predictions,contributing 30.2%,36.4%,38.0%,and 55.6%,respectively,to the GLM.Sensitivity experiments revealed that SST forcing in all four seasons contributes to SEPP over China,whereas the winter and summer SST warming over the Pacific and Indian Ocean(IO)contributes the most.Diagnosis of the hydrological cycle suggested that water vapor advection predominantly originates from the western Pacific and IO in summer,driven by the strengthened subtropical high and Asian summer monsoon(ASM).The enhanced vertical water vapor transport is attributed to stronger upward motion across all four seasons.These findings are helpful for better understanding SEPP variabilities and their prediction under SST warming.展开更多
We present a 3+1 formulation of the light modes in nonlinear electrodynamics described by Plebanski-type Lagrangians,which include post-Maxwellian,Born-Infeld,ModMax,and Heisenberg-Euler-Schwinger QED Lagrangians.In n...We present a 3+1 formulation of the light modes in nonlinear electrodynamics described by Plebanski-type Lagrangians,which include post-Maxwellian,Born-Infeld,ModMax,and Heisenberg-Euler-Schwinger QED Lagrangians.In nonlinear electrodynamics,strong electromagnetic fields modify the vacuum such that it acquires optical properties.Such a field-modified vacuum can possess electric permittivity,magnetic permeability,and a magneto-electric response,inducing novel phenomena such as vacuum birefringence.By exploiting the mathematical structures of Plebanski-type Lagrangians,we establish a streamlined procedure and explicit formulas to determine light modes,i.e.,refractive indices and polarization vectors for a given propagation direction.We also work out the light modes of the various Lagrangians for an arbitrarily strong magnetic field.The 3+1 formulation advanced in this paper has direct applications to the current vacuum birefringence research:terrestrial experiments using permanent magnets/ultra-intense lasers for the subcritical regime and astrophysical observation of X-rays from highly magnetized neutron stars for the near-critical and supercritical regimes.展开更多
Autonomous Underwater Vehicles(AUVs)are pivotal for deep-sea exploration and resource exploitation,yet their reliability in extreme underwater environments remains a critical barrier to widespread deployment.Through s...Autonomous Underwater Vehicles(AUVs)are pivotal for deep-sea exploration and resource exploitation,yet their reliability in extreme underwater environments remains a critical barrier to widespread deployment.Through systematic analysis of 150 peer-reviewed studies employing mixed-methods research,this review yields three principal advancements to the reliability analysis of AUVs.First,based on the hierarchical functional division of AUVs into six subsystems(propulsion system,navigation system,communication system,power system,environmental detection system,and emergency system),this study systematically identifies the primary failure modes and potential failure causes of each subsystem,providing theoretical support for fault diagnosis and reliability optimization.Subsequently,a comprehensive review of AUV reliability analysis methods is conducted from three perspectives:analytical methods,simulated methods,and surrogate model methods.The applicability and limitations of each method are critically analyzed to offer insights into their suitability for engineering applications.Finally,the study highlights key challenges and research hotpots in AUV reliability analysis,including reliability analysis under limited data,AI-driven reliability analysis,and human reliability analysis.Furthermore,the potential of multi-sensor data fusion,edge computing,and advanced materials in enhancing AUV environmental adaptability and reliability is explored.展开更多
Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relat...Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relationship between load amplitude,fatigue life,and damage progression in low-carbon steel assemblies.Design/methodology/approach–An experimental approach was adopted using MTS specimens fabricated from St 1203 cold-rolled steel,joined with Grade 8.8 M4 bolts.Cyclic fatigue tests were conducted under zerobased loading at seven distinct force levels.Fracture surfaces were visually analyzed to identify dominant failure mechanisms.Findings–The results revealed a strong inverse correlation between applied cyclic load and fatigue life.Three distinct failure modes were identified:bolt shear at high loads(5.4 kN),interface cracking and slippage at moderate loads(4.9–5.1 kN),and plate tearing or stable fatigue behavior at lower loads(54.1 kN).The results highlight a progressive transition in failure mechanisms,from bolt shear at high loads to plate tearing and interface cracking at lower loads,providing essential insights for fatigue-resistant bolted joint design.Originality/value–This study offers original insights into the fatigue behavior of bolted lap joints using MTS,a relatively underexplored configuration in fatigue assessment.By experimentally evaluating failure modes under varied cyclic load levels,the authors uncover critical transitions in damage mechanisms—from bolt shear to interface cracking and plate tearing—depending on the applied load.Unlike many existing studies focused on numerical modeling or bonded joints alone,this work provides empirical data rooted in real-world fastening conditions using cold-rolled low-carbon steel.展开更多
The rise in construction activities within mountainous regions has significantly increased the frequency of rockfalls.Statistical models for rockfall hazard assessment often struggle to achieve high precision on a lar...The rise in construction activities within mountainous regions has significantly increased the frequency of rockfalls.Statistical models for rockfall hazard assessment often struggle to achieve high precision on a large scale.This limitation arises primarily from the scarcity of historical rockfall data and the inadequacy of conventional assessment indicators in capturing the physical and structural characteristics of rockfalls.This study proposes a physically based deterministic model designed to accurately quantify rockfall hazards at a large scale.The model accounts for multiple rockfall failure modes and incorporates the key physical and structural parameters of the rock mass.Rockfall hazard is defined as the product of three factors:the rockfall failure probability,the probability of reaching a specific position,and the corresponding impact intensity.The failure probability includes probabilities of formation and instability of rock blocks under different failure modes,modeled based on the combination patterns of slope surfaces and rock discontinuities.The Monte Carlo method is employed to account for the randomness of mechanical and geometric parameters when quantifying instability probabilities.Additionally,the rock trajectories and impact energies simulated using Flow-R software are combined with rockfall failure probability to enable regional rockfall hazard zoning.A case study was conducted in Tiefeng,Chongqing,China,considering four types of rockfall failure modes.Hazard zoning results identified the steep and elevated terrains of the northern and southern anaclinal slopes as areas of highest rockfall hazard.These findings align with observed conditions,providing detailed hazard zoning and validating the effectiveness and potential of the proposed model.展开更多
We apply the WKB approximation method,matrix method,and finite difference method to study the gravitational quasi-normal modes of charged spherically symmetric black holes surrounded by quintessence fluid in Rastall g...We apply the WKB approximation method,matrix method,and finite difference method to study the gravitational quasi-normal modes of charged spherically symmetric black holes surrounded by quintessence fluid in Rastall gravity.By comparing the spherically symmetric spacetime metric of charged black holes surrounded by quintessence fluid in Rastall gravity with that of general relativity,we can find that the modifications to general relativity in this modified gravity theory can be described by parameters such asλ,Q,and C_(a),etc.In four-dimensional spacetime,we investigate the impact of charge Q and parameter C_(a) on the gravitational quasi-normal modes of charged black holes surrounded by quintessence field in Rastall gravity.The aim is to search for observational evidence of such black holes in astrophysical observations and,consequently,test the validity of Rastall theory.In five-dimensional(5D)spacetime,we study the impact of the parameter C_(a) on the gravitational quasi-normal modes of Rastall black holes surrounded by quintessence field and summarize the corresponding variation patterns.展开更多
This study explores the nonlinear dynamics of a quasi-zero stiffness(QZS)vibration isolator coupled with a piezoelectric energy harvester connected to an RL-resonant circuit.The model of the system is formulated with ...This study explores the nonlinear dynamics of a quasi-zero stiffness(QZS)vibration isolator coupled with a piezoelectric energy harvester connected to an RL-resonant circuit.The model of the system is formulated with the Lagrangian mechanics,representing a two-degree-of-freedom nonlinear electromechanical system subject to harmonic base excitation under a 1:1 internal resonance condition.The model is normalized,and the conditions dictating monostable and bistable oscillation modes are identified.The bifurcation characteristics of the coupled system are analyzed in both oscillation modes by means of harmonic balance and continuation methods.The vibration isolation performance,with and without the coupled harvester,is evaluated in terms of displacement transmissibility to assess its dual functionalities for vibration isolation and energy harvesting.Analytical results demonstrate that integrating a piezoelectric harvester into a monostable QZS isolator under 1:1 internal resonance does not compromise its vibration isolation capability while enabling efficient energy harvesting at extremely low-frequency base excitation.Furthermore,the system's response under strong base excitation is investigated exclusively for energy harvesting in both monostable and bistable modes,leading to optimal structural parameter design.The conditions for intra-well and inter-well periodic oscillation modes,as well as chaotic responses,are analyzed analytically and validated numerically through stability charts,basins of attraction,bifurcation diagrams,time histories,and Poincarémaps.This work provides a comprehensive understanding of the oscillation dynamics of QZS isolators and offers valuable insights for optimizing their geometric parameters to function as high-performance vibration isolators and/or energy harvesters.展开更多
In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The ...In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).展开更多
To broaden the frequency regulation range of piezoelectric motors,this paper proposes a piezoelectric vibrator that operates in multiple in-plane vibration modes with distinct resonance frequencies.The piezoelectric v...To broaden the frequency regulation range of piezoelectric motors,this paper proposes a piezoelectric vibrator that operates in multiple in-plane vibration modes with distinct resonance frequencies.The piezoelectric vibrator was constructed by reasonably arranging multiple groups of piezoelectric ceramic(PZT)sheets based on the most typical rectangular plate piezoelectric motors.Suitable working modes were selected,and the excitation method of these operating modes was also analyzed.Besides,interactions between selected operating modes were also investigated.The finite element software,ANSYS,was adopted to optimize the structural parameters of the vibrator through modal analysis to match the resonance frequencies of specific modes.After that,whether the selected operating modes can be successfully motivated was verified by harmonic response analysis.Finally,the vibration characteristics of piezoelectric vibrators under conventional vibration modes and multiple modes were acquired by transient analysis,respectively.Simulation results reveal that under dual-frequency excitation scheme 1,response displacements of the driving point are relatively larger.This strategy not only facilitates the excitation of B4 mode but also enables control over the ratio of horizontal to vertical displacements of the driving point.Additionally,incorporating B4 mode expands the frequency adjustment range of piezoelectric vibrators.展开更多
A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number...A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number 2.92 supersonic inflow,with stagnation pressureof 2.4 MPa and stagnation temperature of 1600 K.Reynolds-averaged Navier-Stokes simulationswere conducted to characterize the mixing process and flow field structure.This study identifiedfour distinct LA ignition modes.Under the specified condition,laser ablation in zero and negativedefocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition(LADI)mode and Laser Ablation Re-Ignition(LARI)mode,correspondingly.LA ignition in alocal small cavity,created by depressing the flow field regulator,could facilitate the ignition modetransforming from LARI mode to Laser Ablation Transition Ignition(LATI)mode.On the otherhand,the elevation of the flow field regulator effectively inhibited the forward propagation of theinitial flame kernel and reduced the dissipation of LA plasma,further enhancing the LADI mode.Based on these characteristics,the LADI mode was subdivided into strong(LADI-S)and weak(LADI-W)modes.Facilitating the transition of ignition modes through alterations in the local flowfield could contribute to attaining a more effective and stable LA ignition.展开更多
Objective:To investigate the delivery modes of women with repeat pregnancies involving uterine scars and their effects on both mothers and neonates.Methods:A study was conducted on 100 patients treated at Shenzhen Mat...Objective:To investigate the delivery modes of women with repeat pregnancies involving uterine scars and their effects on both mothers and neonates.Methods:A study was conducted on 100 patients treated at Shenzhen Maternity and Child Healthcare Hospital from July 2023 to July 2024.The participants were divided into a control group and an observation group,with 50 cases in each.The division was based on the indications for prior cesarean section,cervical maturity,postpartum complications,and thickness of the cesarean scar.The control group underwent cesarean delivery,while the observation group experienced vaginal delivery.The two groups were compared in terms of intrapartum blood loss,postpartum blood loss within 2 hours,length of hospital stay,Apgar scores at 1-minute post-birth,and incidences of neonatal fever and jaundice.Results:The observation group had significantly lower intrapartum blood loss,postpartum blood loss within 2 hours,and shorter hospital stays compared to the control group(P<0.05).Additionally,the Apgar scores at 1 minute post-birth were significantly higher in the observation group(P<0.05).The incidence of neonatal fever and jaundice was significantly lower in the observation group(P<0.05).These differences were statistically significant.Conclusion:Vaginal delivery has high clinical value for women with repeat pregnancies involving uterine scars.It reduces maternal intrapartum and postpartum blood loss,shortens hospital stays,improves neonatal Apgar scores,and decreases the incidences of neonatal fever and jaundice.This method is worthy of clinical application and promotion.展开更多
Natural gas hydrate widely exists in the South China Sea as clean energy.A three-phase transition layer widely exists in low permeability Class I hydrates in the Shenhu offshore area.Therefore,taking into account the ...Natural gas hydrate widely exists in the South China Sea as clean energy.A three-phase transition layer widely exists in low permeability Class I hydrates in the Shenhu offshore area.Therefore,taking into account the low-permeability characteristics with an average permeability of 5.5 mD and moderate heterogeneity,a 3-D geological model of heterogeneous Class I hydrate reservoirs with three-phase transition layers is established by Kriging interpolation and stochastic modeling method,and a numerical simulation model is used to describe the depressurization production performance of the reservoir.With the development of depressurization,a specific range of complete decomposition zones appear both in the hydrate and transition layers.The entire decomposition zone of the whole reservoir tends to outward and upward diffusion.There is apparent methane escape in the three-phase transition layer.Due to the improvement of local permeability caused by the phase transition of hydrate dissociation,some methane accumulation occurs at the bottom of the hydrate layer,forming a local methane enrichment zone.The methane migration trends in reservoirs are mainly characterized by movement toward production wells and hydrate layers under the influence of gravity.However,due to the permeability limitation of hydrate reservoirs,many fluids have not been effectively produced and remain in the reservoir.Therefore,to improve the effective pressure drop of the reservoir,the perforation method and pressure reduction method were optimized by analyzing the influencing factors based on the gas production rate.The comparative study demonstrates that perforating through the free gas layer combined with one-time depressurization can enhance the effective depressurization and improve production performance.The gas production rate from perforating through the free gas layer can be twice as high as that from perforating through the transition layer.This study can provide theoretical support for the utilization of marine energy.展开更多
Microsphere and microcylinder-assisted microscopy(MAM)has grown steadily over the last decade and is still an intensively studied optical far-field imaging technique that promises to overcome the fundamental lateral r...Microsphere and microcylinder-assisted microscopy(MAM)has grown steadily over the last decade and is still an intensively studied optical far-field imaging technique that promises to overcome the fundamental lateral resolution limit of microscopy.However,the physical effects leading to resolution enhancement are still frequently debated.In addition,various configurations of MAM operating in transmission mode as well as reflection mode are examined,and the results are sometimes generalized.We present a rigorous simulation model of MAM and introduce a way to quantify the resolution enhancement.The lateral resolution is compared for microscope arrangements in reflection and transmission modes.Furthermore,we discuss different physical effects with respect to their contribution to resolution enhancement.The results indicate that the effects impacting the resolution in MAM strongly depend on the arrangement of the microscope and the measurement object.As a highlight,we outline that evanescent waves in combination with whispering gallery modes also improve the imaging capabilities,enabling super-resolution under certain circumstances.This result is contrary to the conclusions drawn from previous studies,where phase objects have been analyzed,and thus further emphasizes the complexity of the physical mechanisms underlying MAM.展开更多
Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both g...Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both global and regional climates.This study assesses the performance of models participating in phase 6 of the Coupled Model Intercomparison Project in simulating interannual variability modes of Northern Hemisphere 500-hPa geopotential height during winter and summer,distinguishing predictable(potentially predictable on seasonal or longer timescales)and unpredictable(intraseasonal and essentially unpredictable at long range)components,using reanalysis data and a variance decomposition method.Although most models effectively capture unpredictable modes in reanalysis,their ability to reproduce dominant predictable modes-specifically the Pacific-North American pattern,Arctic Oscillation,and Western Pacific Oscillation in winter,and the East Atlantic and North Atlantic Oscillations in summer-varies notably.An optimal ensemble is identified to distinguish(a)predictable-external modes,dominated by external forcing,and(b)predictable-internal modes,associated with slow internal variability,during the historical period(1950-2014)and the SSP5-8.5 scenario(2036-2100).Under increased radiative forcing,the leading winter/summer predictable-external mode exhibits a more uniform spatial distribution,remarkably larger trend and annual variance,and enhanced height-sea surface temperature(SST)covariance under SSP5-8.5 compared to historical conditions.The dominant winter/summer predictable-internal modes also exhibit increased variance and height-SST covariance under SSP5-8.5,along with localized changes in spatial configuration.Minimal changes are observed in spatial distribution or variance for dominant winter/summer unpredictable modes under SSP5-8.5.This study,from a predictive perspective,deepens our understanding of model uncertainties and projected changes in circulations.展开更多
To ensure the safe implementation of underground reservoirs in abandoned coal mines,this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading....To ensure the safe implementation of underground reservoirs in abandoned coal mines,this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading.Specimens with coal-to-concrete height ratios ranging from 0.5:1 to 3:1 were tested,with damage evolution continuously monitored using acoustic emission techniques.Results indicate that while the peak strength of pure materials decreases by approximately 1 MPa under cyclic stress compared to uniaxial compression,composite specimens exhibit strength enhancements exceeding 5 MPa.However,the peak strength of composite specimens decreases with increasing coal height,from 30 MPa at CR0.5 to 20 MPa at CR3.0.The damage state was assessed using the dynamic elastic strain energy index and Felicity ratio,which revealed that composite specimens are more prone to early damage accumulation.Spatial acoustic emission localization further reveals distinct failure modes across specimens with varying height ratios.To elucidate these differences,interfacial effects were incorporated into a modified twin-shear unified strength theory.The refined model accurately predicts the internal strength distribution and failure characteristics of the composite structures.These findings provide a theoretical basis for the structural design and safe operation of underground reservoir dams.展开更多
Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin,which has garnered significant attention due to the potential economic value.However,most research has concentrated pr...Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin,which has garnered significant attention due to the potential economic value.However,most research has concentrated primarily on the coal seams of the Taiyuan and Shanxi formations,with limited reports on the Benxi Formation.To address this gap,our study focused on elucidating the geochemical characteristics and origins of the lithium enrichment in the No.8 coal of the Benxi Formation through the use of optical microscopy and inductively coupled plasma mass spectrometry(ICP-MS).The results showed that the No.8 coal was a bituminous coal,characterized by medium ash yield,low volatile matter,high total sulfur content and medium vitrinite proportion.The No.8 coal was enriched in Li(average 91.7 ppm,CC=6.55)and Zr(average 191 ppm,CC=5.30),the unusual enrichment of Li being primarily located in the middle of the coal.The minerals in the coal were predominantly clay minerals,along with minor amounts of pyrite,quartz and calcite.The occurrence mode of Li in the No.8 coal was associated with aluminosilicate minerals,presumably kaolinite.Based on geochemical characteristics,the sedimentary source of the No.8 coal was intermediate-felsic volcanic rock from the Yinshan oldland.The enrichment of Li can be attributed to the supply of terrestrial debris from the Yinshan oldland and the depositional environment.Our analysis identifies three distinct stages of lithium enrichment,emphasizing the critical role played by the terrestrial debris,as well as the acidic to partially reducing conditions,in facilitating this process.In conclusion,our study sheds light on the mechanisms underlying lithium enrichment in the No.8 coal of the Benxi Formation,highlighting the significance of geological factors in shaping the distribution and concentration of critical metals in coal.展开更多
The elliptic integral method(EIM) is an efficient analytical approach for analyzing large deformations of elastic beams. However, it faces the following challenges.First, the existing EIM can only handle cases with kn...The elliptic integral method(EIM) is an efficient analytical approach for analyzing large deformations of elastic beams. However, it faces the following challenges.First, the existing EIM can only handle cases with known deformation modes. Second,the existing EIM is only applicable to Euler beams, and there is no EIM available for higher-precision Timoshenko and Reissner beams in cases where both force and moment are applied at the end. This paper proposes a general EIM for Reissner beams under arbitrary boundary conditions. On this basis, an analytical equation for determining the sign of the elliptic integral is provided. Based on the equation, we discover a class of elliptic integral piecewise points that are distinct from inflection points. More importantly, we propose an algorithm that automatically calculates the number of inflection points and other piecewise points during the nonlinear solution process, which is crucial for beams with unknown or changing deformation modes.展开更多
基金funded by the Ministry of Education of the Russian Federation within the framework of a state assignment,number 1023032300071-6-2.3.1.
文摘Time-averaged thermal convection in a rotating horizontal annulus with a higher temperature at its inner boundary is studied.The centrifugal force plays a stabilizing role,while thermal convection is determined by the“thermovibrational mechanism”.Convective flow is excited due to oscillations of a non-isothermal rotating fluid.Thermal vibrational convectionmanifests in the form of two-dimensional vortices elongated along the axis of rotation,which develop in a threshold manner with an increase in the amplitude of fluid oscillations.The objective of the present study is to clarify the nature of another phenomenon,i.e.,three-dimensional convective vortices observed in the experiments both before the excitation of the convection described above and in the supercritical region.The experimental study of the oscillatory and the time-averaged flow fields by particle image velocimetry is accompanied by the theoretical research of inertial waves.It is found that three-dimensional fluid flows owe their origin to inertial waves.This is confirmed by a high degree of agreement between the experimental and theoretical results.Experiments with cavities of different lengths indicate that the vortices are clearly seen in cavities thatmeet the conditions of resonant excitation of inertial modes.Furthermore,the length of the cavity has no effect on heat transfer,which is explained by the comparatively low intensity of the wave-induced flows.The main contribution to heat transfer is due to vortices elongated along the axis of rotation.The novel results are of significant practical importance in various fields.
基金supported by the National Natural Science Foundation of China under Grant No.11675143the National Key Research and Development Program of China under Grant No.2020YFC2201503。
文摘In this paper we consider a static spherically symmetric black hole(BH)embedded in a Dehnen-(1,4,0)-type dark matter(DM)halo in the presence of a cloud string.We examine and present data on how the core density of the DM halo parameter and the cloud string parameter affect BH attributes such as quasinormal modes(QNMs)and shadow cast.To do this,we first look into the effective potential of perturbation equations for three types of perturbation fields with different spins:massless scalar field,electromagnetic field and gravitational field.Then,using the sixth-order Wentzel-Kramers-Brillouin approximation,we examine QNMs of the BH disturbed by the three fields and derive quasinormal frequencies.The changes in QNM versus the core density parameter and the cloud string parameter for three disturbances are explored.We also investigate how the core density and the cloud string parameter affect the photon sphere and shadow radius.Interestingly,the study shows that the influence of Dehnen-type DM and cloud strings increases both the photon sphere and the shadow radius.Finally,we employ observational data from Sgr A^(*) and M87^(*) to set limitations on the BH parameters.
基金Natural Science Foundation of Guangdong Province,China(2024A1515011352)National Natural Science Founda-tion of China(42275020)+2 种基金Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhu-hai)(311021001)Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies(2020B1212060025)Shanghai Frontiers Science Center of Atmosphere-Ocean Interaction(FDAOS-OP202401)。
文摘Utilizing the Standardized Precipitation Evapotranspiration Index(SPEI)and ERA5 reanalysis data,this study investigates the variability of spring drought in southern China from 1979 to 2022 and its associated drivers.The results indicate that southern China experienced interdecadal changes in SPEI over the past several decades,which can be concluded that drought severity intensified from 1979 to 2010,whereas a transition shift towards increased wetness occurred from 2010 to 2022.The first Empirical Orthogonal Function(EOF1)mode of SPEI variability in southern China accounts for 44.37%of the total variance,reflecting a uniform variation of SPEI across the region.In contrast,the second Empirical Orthogonal Function(EOF2),which explains 24.41%of the total variance,reveals a west-east dipole pattern in SPEI variability.Further analysis indicates that the positive phase of EOF1 is primarily driven by warm sea surface temperature anomalies(SSTAs)in the tropical eastern Pacific.These anomalies induce an anomalous anticyclone over the Philippine Sea,enhancing water vapor transport to southern China during spring.The positive phase of EOF2 is jointly influenced by warm SSTAs in the tropical Indian Ocean and the central Pacific;the latter induces anticyclonic anomalies over the Philippine Sea,which enhance water vapor transport from the western Pacific and increase precipitation in the eastern part of southern China.However,the warm SSTAs in the tropical Indian Ocean trigger an anomalous anticyclone over South Asia,inhibiting water vapor transport from the Bay of Bengal to the western part of southern China and thus reducing precipitation there.
基金jointly funded by the National Natural Science Foundation of China(Grant Nos.42122035,42288101,42130605,72293604,42475179,and 42475020)the support of the Guangdong Provincial Observation and Research Station for Tropical Ocean Environment in Western Coastal Waters(GSTOEW)+2 种基金Key Laboratory of Space Ocean Remote Sensing and ApplicationCMAGDOU Joint Laboratory for Marine MeteorologyKey Laboratory of Climate Resources and Environment in Continental Shelf Sea and Deep Ocean(LCRE)。
文摘The multiscale variability in summer extreme persistent precipitation(SEPP)in China from 1961 to 2020 was investigated via three extreme precipitation indices:consecutive wet days,total precipitation amount,and daily precipitation intensity.The relationships between precursory and concurrent global oceanic modes and SEPP were identified via a generalized linear model(GLM).The influence of oceanic modes on SEPP was finally investigated via numerical simulations.The results revealed that the climatological SEPP(≥14 days)mainly appears across the Tibetan Plateau,Yunnan–Guizhou Plateau,and South China coast.The first EOF mode for all three indices showed strong signals over the Yangtze River.Further analysis via the GLM suggested that the positive phases of the tropical North Atlantic(TNA)in autumn,ENSO in winter,the Indian Ocean Basin(IOB)in spring,and the western North Pacific(WNP)in summer emerged as the most effective precursory factors of SEPP,which could serve as preceding signals for future predictions,contributing 30.2%,36.4%,38.0%,and 55.6%,respectively,to the GLM.Sensitivity experiments revealed that SST forcing in all four seasons contributes to SEPP over China,whereas the winter and summer SST warming over the Pacific and Indian Ocean(IO)contributes the most.Diagnosis of the hydrological cycle suggested that water vapor advection predominantly originates from the western Pacific and IO in summer,driven by the strengthened subtropical high and Asian summer monsoon(ASM).The enhanced vertical water vapor transport is attributed to stronger upward motion across all four seasons.These findings are helpful for better understanding SEPP variabilities and their prediction under SST warming.
基金supported by the Ultrashort Quantum Beam Facility operation program(Grant No.140011)through APRI,GISTalso by the Institute of Basic Science(Grant No.IBSR038-D1).
文摘We present a 3+1 formulation of the light modes in nonlinear electrodynamics described by Plebanski-type Lagrangians,which include post-Maxwellian,Born-Infeld,ModMax,and Heisenberg-Euler-Schwinger QED Lagrangians.In nonlinear electrodynamics,strong electromagnetic fields modify the vacuum such that it acquires optical properties.Such a field-modified vacuum can possess electric permittivity,magnetic permeability,and a magneto-electric response,inducing novel phenomena such as vacuum birefringence.By exploiting the mathematical structures of Plebanski-type Lagrangians,we establish a streamlined procedure and explicit formulas to determine light modes,i.e.,refractive indices and polarization vectors for a given propagation direction.We also work out the light modes of the various Lagrangians for an arbitrarily strong magnetic field.The 3+1 formulation advanced in this paper has direct applications to the current vacuum birefringence research:terrestrial experiments using permanent magnets/ultra-intense lasers for the subcritical regime and astrophysical observation of X-rays from highly magnetized neutron stars for the near-critical and supercritical regimes.
基金The National Key R&D Program Projects(Grant No.2022YFC2803601)the Natural Science Foundation of Shandong Province(Grant No.ZR2021YQ29)+1 种基金the Natural Science Foundation of Heilongjiang Province(Grant No.YQ2024E036)the Taishan Scholars Project(Grant No.tsqn202312317).
文摘Autonomous Underwater Vehicles(AUVs)are pivotal for deep-sea exploration and resource exploitation,yet their reliability in extreme underwater environments remains a critical barrier to widespread deployment.Through systematic analysis of 150 peer-reviewed studies employing mixed-methods research,this review yields three principal advancements to the reliability analysis of AUVs.First,based on the hierarchical functional division of AUVs into six subsystems(propulsion system,navigation system,communication system,power system,environmental detection system,and emergency system),this study systematically identifies the primary failure modes and potential failure causes of each subsystem,providing theoretical support for fault diagnosis and reliability optimization.Subsequently,a comprehensive review of AUV reliability analysis methods is conducted from three perspectives:analytical methods,simulated methods,and surrogate model methods.The applicability and limitations of each method are critically analyzed to offer insights into their suitability for engineering applications.Finally,the study highlights key challenges and research hotpots in AUV reliability analysis,including reliability analysis under limited data,AI-driven reliability analysis,and human reliability analysis.Furthermore,the potential of multi-sensor data fusion,edge computing,and advanced materials in enhancing AUV environmental adaptability and reliability is explored.
文摘Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relationship between load amplitude,fatigue life,and damage progression in low-carbon steel assemblies.Design/methodology/approach–An experimental approach was adopted using MTS specimens fabricated from St 1203 cold-rolled steel,joined with Grade 8.8 M4 bolts.Cyclic fatigue tests were conducted under zerobased loading at seven distinct force levels.Fracture surfaces were visually analyzed to identify dominant failure mechanisms.Findings–The results revealed a strong inverse correlation between applied cyclic load and fatigue life.Three distinct failure modes were identified:bolt shear at high loads(5.4 kN),interface cracking and slippage at moderate loads(4.9–5.1 kN),and plate tearing or stable fatigue behavior at lower loads(54.1 kN).The results highlight a progressive transition in failure mechanisms,from bolt shear at high loads to plate tearing and interface cracking at lower loads,providing essential insights for fatigue-resistant bolted joint design.Originality/value–This study offers original insights into the fatigue behavior of bolted lap joints using MTS,a relatively underexplored configuration in fatigue assessment.By experimentally evaluating failure modes under varied cyclic load levels,the authors uncover critical transitions in damage mechanisms—from bolt shear to interface cracking and plate tearing—depending on the applied load.Unlike many existing studies focused on numerical modeling or bonded joints alone,this work provides empirical data rooted in real-world fastening conditions using cold-rolled low-carbon steel.
基金supported by the National Natural Science Foundation of China(Grant Nos.42172318 and 42377186)the National Key R&D Program of China(Grant No.2023YFC3007201).
文摘The rise in construction activities within mountainous regions has significantly increased the frequency of rockfalls.Statistical models for rockfall hazard assessment often struggle to achieve high precision on a large scale.This limitation arises primarily from the scarcity of historical rockfall data and the inadequacy of conventional assessment indicators in capturing the physical and structural characteristics of rockfalls.This study proposes a physically based deterministic model designed to accurately quantify rockfall hazards at a large scale.The model accounts for multiple rockfall failure modes and incorporates the key physical and structural parameters of the rock mass.Rockfall hazard is defined as the product of three factors:the rockfall failure probability,the probability of reaching a specific position,and the corresponding impact intensity.The failure probability includes probabilities of formation and instability of rock blocks under different failure modes,modeled based on the combination patterns of slope surfaces and rock discontinuities.The Monte Carlo method is employed to account for the randomness of mechanical and geometric parameters when quantifying instability probabilities.Additionally,the rock trajectories and impact energies simulated using Flow-R software are combined with rockfall failure probability to enable regional rockfall hazard zoning.A case study was conducted in Tiefeng,Chongqing,China,considering four types of rockfall failure modes.Hazard zoning results identified the steep and elevated terrains of the northern and southern anaclinal slopes as areas of highest rockfall hazard.These findings align with observed conditions,providing detailed hazard zoning and validating the effectiveness and potential of the proposed model.
基金Project supported by the National Natural Science Foundation of China(Grant No.42230207)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(Grant No.G1323523064)。
文摘We apply the WKB approximation method,matrix method,and finite difference method to study the gravitational quasi-normal modes of charged spherically symmetric black holes surrounded by quintessence fluid in Rastall gravity.By comparing the spherically symmetric spacetime metric of charged black holes surrounded by quintessence fluid in Rastall gravity with that of general relativity,we can find that the modifications to general relativity in this modified gravity theory can be described by parameters such asλ,Q,and C_(a),etc.In four-dimensional spacetime,we investigate the impact of charge Q and parameter C_(a) on the gravitational quasi-normal modes of charged black holes surrounded by quintessence field in Rastall gravity.The aim is to search for observational evidence of such black holes in astrophysical observations and,consequently,test the validity of Rastall theory.In five-dimensional(5D)spacetime,we study the impact of the parameter C_(a) on the gravitational quasi-normal modes of Rastall black holes surrounded by quintessence field and summarize the corresponding variation patterns.
基金Project supported by the National Key R&D Program of China(No.2023YFE0125900)。
文摘This study explores the nonlinear dynamics of a quasi-zero stiffness(QZS)vibration isolator coupled with a piezoelectric energy harvester connected to an RL-resonant circuit.The model of the system is formulated with the Lagrangian mechanics,representing a two-degree-of-freedom nonlinear electromechanical system subject to harmonic base excitation under a 1:1 internal resonance condition.The model is normalized,and the conditions dictating monostable and bistable oscillation modes are identified.The bifurcation characteristics of the coupled system are analyzed in both oscillation modes by means of harmonic balance and continuation methods.The vibration isolation performance,with and without the coupled harvester,is evaluated in terms of displacement transmissibility to assess its dual functionalities for vibration isolation and energy harvesting.Analytical results demonstrate that integrating a piezoelectric harvester into a monostable QZS isolator under 1:1 internal resonance does not compromise its vibration isolation capability while enabling efficient energy harvesting at extremely low-frequency base excitation.Furthermore,the system's response under strong base excitation is investigated exclusively for energy harvesting in both monostable and bistable modes,leading to optimal structural parameter design.The conditions for intra-well and inter-well periodic oscillation modes,as well as chaotic responses,are analyzed analytically and validated numerically through stability charts,basins of attraction,bifurcation diagrams,time histories,and Poincarémaps.This work provides a comprehensive understanding of the oscillation dynamics of QZS isolators and offers valuable insights for optimizing their geometric parameters to function as high-performance vibration isolators and/or energy harvesters.
基金support of the Research Project Supported by Shanxi Scholarship Council of China(2022-040)"Chunhui Plan"Collaborative Research Project by the Ministry of Education of China(HZKY20220507)+2 种基金National Natural Science Foundation of China(52104338)Applied Fundamental Research Programs of Shanxi Province(202303021221036)Shandong Postdoctoral Science Foundation(SDCX-ZG-202303027,SDBX2023054).
文摘In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).
基金funded by National Natural Science Foundation of China,grant number 52205292.
文摘To broaden the frequency regulation range of piezoelectric motors,this paper proposes a piezoelectric vibrator that operates in multiple in-plane vibration modes with distinct resonance frequencies.The piezoelectric vibrator was constructed by reasonably arranging multiple groups of piezoelectric ceramic(PZT)sheets based on the most typical rectangular plate piezoelectric motors.Suitable working modes were selected,and the excitation method of these operating modes was also analyzed.Besides,interactions between selected operating modes were also investigated.The finite element software,ANSYS,was adopted to optimize the structural parameters of the vibrator through modal analysis to match the resonance frequencies of specific modes.After that,whether the selected operating modes can be successfully motivated was verified by harmonic response analysis.Finally,the vibration characteristics of piezoelectric vibrators under conventional vibration modes and multiple modes were acquired by transient analysis,respectively.Simulation results reveal that under dual-frequency excitation scheme 1,response displacements of the driving point are relatively larger.This strategy not only facilitates the excitation of B4 mode but also enables control over the ratio of horizontal to vertical displacements of the driving point.Additionally,incorporating B4 mode expands the frequency adjustment range of piezoelectric vibrators.
基金supported by the National Natural Science Foundation of China(Nos.12272408 and 11925207)the Natural Science Foundation for Distinguished Young Scholars of Hunan Province,China(No.2024J12057)。
文摘A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number 2.92 supersonic inflow,with stagnation pressureof 2.4 MPa and stagnation temperature of 1600 K.Reynolds-averaged Navier-Stokes simulationswere conducted to characterize the mixing process and flow field structure.This study identifiedfour distinct LA ignition modes.Under the specified condition,laser ablation in zero and negativedefocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition(LADI)mode and Laser Ablation Re-Ignition(LARI)mode,correspondingly.LA ignition in alocal small cavity,created by depressing the flow field regulator,could facilitate the ignition modetransforming from LARI mode to Laser Ablation Transition Ignition(LATI)mode.On the otherhand,the elevation of the flow field regulator effectively inhibited the forward propagation of theinitial flame kernel and reduced the dissipation of LA plasma,further enhancing the LADI mode.Based on these characteristics,the LADI mode was subdivided into strong(LADI-S)and weak(LADI-W)modes.Facilitating the transition of ignition modes through alterations in the local flowfield could contribute to attaining a more effective and stable LA ignition.
文摘Objective:To investigate the delivery modes of women with repeat pregnancies involving uterine scars and their effects on both mothers and neonates.Methods:A study was conducted on 100 patients treated at Shenzhen Maternity and Child Healthcare Hospital from July 2023 to July 2024.The participants were divided into a control group and an observation group,with 50 cases in each.The division was based on the indications for prior cesarean section,cervical maturity,postpartum complications,and thickness of the cesarean scar.The control group underwent cesarean delivery,while the observation group experienced vaginal delivery.The two groups were compared in terms of intrapartum blood loss,postpartum blood loss within 2 hours,length of hospital stay,Apgar scores at 1-minute post-birth,and incidences of neonatal fever and jaundice.Results:The observation group had significantly lower intrapartum blood loss,postpartum blood loss within 2 hours,and shorter hospital stays compared to the control group(P<0.05).Additionally,the Apgar scores at 1 minute post-birth were significantly higher in the observation group(P<0.05).The incidence of neonatal fever and jaundice was significantly lower in the observation group(P<0.05).These differences were statistically significant.Conclusion:Vaginal delivery has high clinical value for women with repeat pregnancies involving uterine scars.It reduces maternal intrapartum and postpartum blood loss,shortens hospital stays,improves neonatal Apgar scores,and decreases the incidences of neonatal fever and jaundice.This method is worthy of clinical application and promotion.
基金supported by the Sinopec Technology Research and Development Project(No.30000000-22-ZC0607-0235,No.33550000-22-ZC0607-0009)the National Natural Science Foundation of China(No.52334002).
文摘Natural gas hydrate widely exists in the South China Sea as clean energy.A three-phase transition layer widely exists in low permeability Class I hydrates in the Shenhu offshore area.Therefore,taking into account the low-permeability characteristics with an average permeability of 5.5 mD and moderate heterogeneity,a 3-D geological model of heterogeneous Class I hydrate reservoirs with three-phase transition layers is established by Kriging interpolation and stochastic modeling method,and a numerical simulation model is used to describe the depressurization production performance of the reservoir.With the development of depressurization,a specific range of complete decomposition zones appear both in the hydrate and transition layers.The entire decomposition zone of the whole reservoir tends to outward and upward diffusion.There is apparent methane escape in the three-phase transition layer.Due to the improvement of local permeability caused by the phase transition of hydrate dissociation,some methane accumulation occurs at the bottom of the hydrate layer,forming a local methane enrichment zone.The methane migration trends in reservoirs are mainly characterized by movement toward production wells and hydrate layers under the influence of gravity.However,due to the permeability limitation of hydrate reservoirs,many fluids have not been effectively produced and remain in the reservoir.Therefore,to improve the effective pressure drop of the reservoir,the perforation method and pressure reduction method were optimized by analyzing the influencing factors based on the gas production rate.The comparative study demonstrates that perforating through the free gas layer combined with one-time depressurization can enhance the effective depressurization and improve production performance.The gas production rate from perforating through the free gas layer can be twice as high as that from perforating through the transition layer.This study can provide theoretical support for the utilization of marine energy.
基金supported by the German Research Foundation(DFG)(Grant Nos.LE 992/14-3 and LE 992/15-3).
文摘Microsphere and microcylinder-assisted microscopy(MAM)has grown steadily over the last decade and is still an intensively studied optical far-field imaging technique that promises to overcome the fundamental lateral resolution limit of microscopy.However,the physical effects leading to resolution enhancement are still frequently debated.In addition,various configurations of MAM operating in transmission mode as well as reflection mode are examined,and the results are sometimes generalized.We present a rigorous simulation model of MAM and introduce a way to quantify the resolution enhancement.The lateral resolution is compared for microscope arrangements in reflection and transmission modes.Furthermore,we discuss different physical effects with respect to their contribution to resolution enhancement.The results indicate that the effects impacting the resolution in MAM strongly depend on the arrangement of the microscope and the measurement object.As a highlight,we outline that evanescent waves in combination with whispering gallery modes also improve the imaging capabilities,enabling super-resolution under certain circumstances.This result is contrary to the conclusions drawn from previous studies,where phase objects have been analyzed,and thus further emphasizes the complexity of the physical mechanisms underlying MAM.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2342210 and 42275043)the National Institute of Natural Hazards,Ministry of Emergency Management of China(Grant Nos.J2223806,ZDJ2024-25 and ZDJ2025-34)。
文摘Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both global and regional climates.This study assesses the performance of models participating in phase 6 of the Coupled Model Intercomparison Project in simulating interannual variability modes of Northern Hemisphere 500-hPa geopotential height during winter and summer,distinguishing predictable(potentially predictable on seasonal or longer timescales)and unpredictable(intraseasonal and essentially unpredictable at long range)components,using reanalysis data and a variance decomposition method.Although most models effectively capture unpredictable modes in reanalysis,their ability to reproduce dominant predictable modes-specifically the Pacific-North American pattern,Arctic Oscillation,and Western Pacific Oscillation in winter,and the East Atlantic and North Atlantic Oscillations in summer-varies notably.An optimal ensemble is identified to distinguish(a)predictable-external modes,dominated by external forcing,and(b)predictable-internal modes,associated with slow internal variability,during the historical period(1950-2014)and the SSP5-8.5 scenario(2036-2100).Under increased radiative forcing,the leading winter/summer predictable-external mode exhibits a more uniform spatial distribution,remarkably larger trend and annual variance,and enhanced height-sea surface temperature(SST)covariance under SSP5-8.5 compared to historical conditions.The dominant winter/summer predictable-internal modes also exhibit increased variance and height-SST covariance under SSP5-8.5,along with localized changes in spatial configuration.Minimal changes are observed in spatial distribution or variance for dominant winter/summer unpredictable modes under SSP5-8.5.This study,from a predictive perspective,deepens our understanding of model uncertainties and projected changes in circulations.
基金supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(No.2024ZD1003903)National Natural Science Foundation of China(Nos.52374078,U24A20616,and 52074043)+1 种基金Sichuan-Chongqing Science and Technology Project Innovation Cooperation Program(No.2024TIAD-CYKJCXX0011)the Fundamental Research Funds for the Central Universities(No.2023CDJKYJH021).
文摘To ensure the safe implementation of underground reservoirs in abandoned coal mines,this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading.Specimens with coal-to-concrete height ratios ranging from 0.5:1 to 3:1 were tested,with damage evolution continuously monitored using acoustic emission techniques.Results indicate that while the peak strength of pure materials decreases by approximately 1 MPa under cyclic stress compared to uniaxial compression,composite specimens exhibit strength enhancements exceeding 5 MPa.However,the peak strength of composite specimens decreases with increasing coal height,from 30 MPa at CR0.5 to 20 MPa at CR3.0.The damage state was assessed using the dynamic elastic strain energy index and Felicity ratio,which revealed that composite specimens are more prone to early damage accumulation.Spatial acoustic emission localization further reveals distinct failure modes across specimens with varying height ratios.To elucidate these differences,interfacial effects were incorporated into a modified twin-shear unified strength theory.The refined model accurately predicts the internal strength distribution and failure characteristics of the composite structures.These findings provide a theoretical basis for the structural design and safe operation of underground reservoir dams.
基金funded by a grant from the National Natural Science Foundation of China(Grant No.41772130)the Natural Science Foundation of Jiangsu Province(Grant No.BK20210521)+4 种基金the Fundamental Research Funds for the Central Universities(Grant No.2021QN1061)‘Energy and Environment Youth Talent Training Program’by China’s Energy Society,China’s Environmental Protection Foundation and the Beijing Energy Society(Grant No.RCJH2022081)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX25_2782)the Graduate Innovation Program of China University of Mining and Technology(No.2025WLKXJ003)the Fundamental Research Funds for the Central Universities(No.202500044)。
文摘Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin,which has garnered significant attention due to the potential economic value.However,most research has concentrated primarily on the coal seams of the Taiyuan and Shanxi formations,with limited reports on the Benxi Formation.To address this gap,our study focused on elucidating the geochemical characteristics and origins of the lithium enrichment in the No.8 coal of the Benxi Formation through the use of optical microscopy and inductively coupled plasma mass spectrometry(ICP-MS).The results showed that the No.8 coal was a bituminous coal,characterized by medium ash yield,low volatile matter,high total sulfur content and medium vitrinite proportion.The No.8 coal was enriched in Li(average 91.7 ppm,CC=6.55)and Zr(average 191 ppm,CC=5.30),the unusual enrichment of Li being primarily located in the middle of the coal.The minerals in the coal were predominantly clay minerals,along with minor amounts of pyrite,quartz and calcite.The occurrence mode of Li in the No.8 coal was associated with aluminosilicate minerals,presumably kaolinite.Based on geochemical characteristics,the sedimentary source of the No.8 coal was intermediate-felsic volcanic rock from the Yinshan oldland.The enrichment of Li can be attributed to the supply of terrestrial debris from the Yinshan oldland and the depositional environment.Our analysis identifies three distinct stages of lithium enrichment,emphasizing the critical role played by the terrestrial debris,as well as the acidic to partially reducing conditions,in facilitating this process.In conclusion,our study sheds light on the mechanisms underlying lithium enrichment in the No.8 coal of the Benxi Formation,highlighting the significance of geological factors in shaping the distribution and concentration of critical metals in coal.
基金supported by the National Natural Science Foundation of China (Nos. 12172388 and 12472400)the Guangdong Basic and Applied Basic Research Foundation of China(No. 2025A1515011975)the Scientific Research Project of Guangdong Polytechnic Normal University of China (No. 2023SDKYA010)
文摘The elliptic integral method(EIM) is an efficient analytical approach for analyzing large deformations of elastic beams. However, it faces the following challenges.First, the existing EIM can only handle cases with known deformation modes. Second,the existing EIM is only applicable to Euler beams, and there is no EIM available for higher-precision Timoshenko and Reissner beams in cases where both force and moment are applied at the end. This paper proposes a general EIM for Reissner beams under arbitrary boundary conditions. On this basis, an analytical equation for determining the sign of the elliptic integral is provided. Based on the equation, we discover a class of elliptic integral piecewise points that are distinct from inflection points. More importantly, we propose an algorithm that automatically calculates the number of inflection points and other piecewise points during the nonlinear solution process, which is crucial for beams with unknown or changing deformation modes.
