Stratified cluster randomisation trial design is widely employed in biomedical research and cluster size has been frequently used as the stratifying factor.Conventional sample size calculation methods have assumed the...Stratified cluster randomisation trial design is widely employed in biomedical research and cluster size has been frequently used as the stratifying factor.Conventional sample size calculation methods have assumed the cluster sizes to be constant within each stratum,which is rarely true in practice.Ignoring the random variability in cluster size leads to underestimated sample sizes and underpowered clinical trials.In this study,we proposed to directly incorporate the variability in cluster size(represented by coefficient of variability)into sample size calculation.This approach provides closed-form sample size formulas,and is flexible to accommodate arbitrary randomisation ratio and varying numbers of clusters across strata.Simulation study shows that the proposed approach achieves desired power and type I error over a wide spectrum of design configurations,including different distributions of cluster sizes.An application example is presented.展开更多
Magnesium and its alloys have been initially applied to biliary tract surgery.Currently,few reports on the degradation behavior of magnesium in the bile environment were investigated.Thus,in-depth research on the degr...Magnesium and its alloys have been initially applied to biliary tract surgery.Currently,few reports on the degradation behavior of magnesium in the bile environment were investigated.Thus,in-depth research on the degradation behavior of Mg and its alloys in bile is beneficial to the further application of Mg in biliary tract surgery.In this study,the degradation behavior of HP-Mg(HPM)and Mg-2 wt.%Zn(MZ2)alloys in human bile and Hanks balanced salt solution(HBSS)was systematically investigated.The MZ2 alloy biliary stent was implanted into the porcine common bile duct to study the degradation behavior of MZ2 alloy in vivo,and to verify the biosafety of MZ2 alloys degradation in the bile duct.It was found that the degradation product layer formed by MZ2 alloys in bile consisted of three layers,including organic matter(fatty acid,etc.),calcium and magnesium phosphate,and Mg(OH)2/MgO,respectively from the outside to the inside.The multi-layered degradation product layer slowed down the corrosion of the Mg matrix.During the 21 days of stent implantation,the degradation rate of the MZ2 stent was about 0.83 mm/y,there was no blockage and stenosis of the tube diameter,and the bile drainage function was normal.展开更多
This study examines the potential impacts o climate change on Lake Biwa,Japan’s largest freshwate lake,with a focus on temperature,wind speed,and pre cipitation variations.Leveraging data from the IPCC Sixth Assessme...This study examines the potential impacts o climate change on Lake Biwa,Japan’s largest freshwate lake,with a focus on temperature,wind speed,and pre cipitation variations.Leveraging data from the IPCC Sixth Assessment Report,including CCP scenarios,projecting a significant temperature rise of 3.3–5.7℃in the case o very high GHG emission power,the research investigates how these shifts may influence dissolved oxygen levels in Lake Biwa.Through a one-dimensional model incorporat ing sediment redox reactions,various scenarios where ai temperature and wind speed are changed are simulated.I is revealed that a 5℃increase in air temperature leads to decreasing 1-2 mg/L of dissolved oxygen concentrations from the surface layer to the bottom layer,while a decrease in air temperature tends to elevate 1–3 mg/L of oxygen lev els.Moreover,doubling wind speed enhances surface laye oxygen but diminishes it in deeper layers due to increased mixing.Seasonal variations in wind effects are noted with significant surface layer oxygen increases from 0.4to 0.8 mg/L during summer to autumn,increases from 0.4 to 0.8 mg/L in autumn to winter due to intensified vertica mixing.This phenomenon impacts the lake’s oxygen cycle year-round.In contrast,precipitation changes show limited impact on oxygen levels,suggesting minor influence com pared to other meteorological factors.The study suggests the necessity of comprehensive three-dimensional models that account for lake-specific and geographical factors fo accurate predictions of future water conditions.A holistic approach integrating nutrient levels,water temperature,and river inflow is deemed essential for sustainable management of Lake Biwa’s water resources,particularly in addressing precipitation variations.展开更多
The mechanical properties of stratified rocks are closely related not only to the stress state but also to the inherent structural anisotropy,which can be represented by the occurrence of bedding planes.This research ...The mechanical properties of stratified rocks are closely related not only to the stress state but also to the inherent structural anisotropy,which can be represented by the occurrence of bedding planes.This research aims to enhance the understanding of the anisotropic deformation and failure behaviors of stratified rocks by proposing a novel coupled elastoplastic-damage constitutive model.In this constitutive model,a scalar anisotropic parameter(stress-structure mixed invariant)based on the Pietruszczak–Mroz anisotropic theory is incorporated into a nonlinear yield surface,which accounts for the combined effects of the stress state and bedding structure on the anisotropic strength behaviors of stratified rocks.A damage-driven function governs the expansion and contraction of the anisotropic yield surface in the pre-peak strain hardening and post-peak strain-softening regions.The strength and deformation characteristics under multiaxial stress conditions are represented by incorporating the Lode's angle into the yield and plastic potential functions.Numerical simulations are conducted to facilitate a comparison with the conventional and true triaxial compression test data for several stratified rocks.The simulation results demonstrate good agreement with the test data,validating the effectiveness of the proposed constitutive model.This study provides theoretical and technical support for addressing engineering challenges involving stratified rocks.展开更多
Geological sequestration of carbon dioxide(CO_(2))entails the long-term storage of captured emissions from CCUS(Carbon Capture,Utilization,and Storage)facilities in deep saline aquifers to mitigate greenhouse gas accu...Geological sequestration of carbon dioxide(CO_(2))entails the long-term storage of captured emissions from CCUS(Carbon Capture,Utilization,and Storage)facilities in deep saline aquifers to mitigate greenhouse gas accumulation.Among various trapping mechanisms,dissolution trapping is particularly effective in enhancing storage security.However,the stratified structure of saline aquifers plays a crucial role in controlling the efficiency of CO_(2) dissolution into the resident brine.In this study,a two-dimensional numerical model of a stratified saline aquifer is developed,integrating both two-phase flow and mass transfer dynamics.The model captures the temporal evolution of gas saturation,reservoir pressure,and CO_(2) dissolution behavior under varying geological and operational conditions.Specifically,the effects of porosity heterogeneity,permeability distribution,and injection rate on the dissolution process are examined,and sequestration efficiencies across distinct stratigraphic layers are compared.Simulation results reveal that in the early phase of CO_(2) injection,the plume spreads radially along the lower portion of the aquifer.With continued injection,high-saturation regions expand upward and eventually accumulate beneath the shale and caprock layers.Pressure within the reservoir rises in response to CO_(2) injection,propagating both vertically and laterally.CO_(2) migration and dissolution are strongly influenced by reservoir properties,with progressive dissolution occurring in the pore spaces of individual layers.High-porosity zones favor CO_(2) accumulation and enhance local dissolution,whereas low-porosity regions facilitate vertical diffusion.An increase in porosity from 0.25 to 0.30 reduces the radial extent of dissolution in the high-permeability layer by 16.5%.Likewise,increasing permeability promotes radial dispersion;each 10 mD increment extends the CO_(2) dissolution front by approximately 18 m.Elevated injection rates intensify both vertical and lateral plume migration:every 0.25×10^(−6) m/s increase in rate yields an average 100–120 m increase in radial dissolution distance within high-permeability zones.展开更多
This study examined gender differences in modal choice among residents of coastal communities of Yenagoa metropolis in Bayelsa State, Nigeria. The Four-Step model of transportation planning and modal choice provided t...This study examined gender differences in modal choice among residents of coastal communities of Yenagoa metropolis in Bayelsa State, Nigeria. The Four-Step model of transportation planning and modal choice provided the theoretical basis for this study. A survey research design involving a stratified sampling technique was adopted. The descriptives on transport modes, amount and time spent revealed that 10 (76.9%) males and 3 (23.1%) females preferred bicycle as means of transportation, 7 (58.3%) males and 5 (41.7%) females preferred motorcycle, while a significant proportion 90 (53.9%) males and 77 (46.1%) females preferred tricycle, 80 (63.0%) males and 47 (37.0%) females preferred cars/taxis, and 12 (46.2%) males and 14 (53.8%) females preferred mass transit bus. However, 14 (46.7%) males and 16 (53.3%) females in marshy terrain and coastal locations preferred canoes and boats. The result of the logistic regression model revealed that gender modal preference is more likely to be influenced by mode of transportation with a beta weight of 1.140, safety considerations 1.139, ownership of transport 1.135 and distance to place of work 1.073. Hence, this study recommends that a combination of these factors should be incorporated into transport planning to achieve effective transport planning and sustainable development in the Yenagoa metropolis.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
Iread with great interest the recent article by Shin,et al.[1]the authors present an important exploration into the use of drug-coated balloon(DCB)in patients aged≥75 years,a demographic increasingly encountered in m...Iread with great interest the recent article by Shin,et al.[1]the authors present an important exploration into the use of drug-coated balloon(DCB)in patients aged≥75 years,a demographic increasingly encountered in modern cardiovascular practice.The authors conducted a retrospective analysis involving 2050 elderly patients(aged≥75 years)undergoing successful percutaneous coronary intervention(PCI).展开更多
The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures invo...The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures involved.The gravity field is obtained from the GGMplus model,from which 3D inversions at resolutions of 1000,500,and 250 m are performed.Low-gravity anomalies are associated with Sierra Negra(4580 m)and Citlaltépetl(5521 m)volcanoes,as well as with the Chichimeco Dome Complex(~4000 m)(CDC).They are located within a SW-NE anomaly that serves as a constraint to the reconstruction.The associ-ated Bouguer anomaly appears as a continuous low-gravity surface;however,its vertical derivative Dz shows that the sources of those three structures are separated.The fault scarps are complemented with inferred trajectories that suggest the existence of two volcanoes before the collapse at 32 ka:Citlaltépetl and the Ancestral Teteltzingo.Density cross-sections identify three stratified magmatic deposits under the summit of CT.On the summit of CT,there is an anomalous concentration of high-density materials,attributed to the presence of domes and lava flows,which mask the position of the volcano’s chimney.The existence of the Ancestral Teteltzingo volcano(ATE)is inferred NE of CT from the associated density distribution;CDC is at the center of the ATE struc-ture and is interpreted as a resurgent activity at<8 ka.Sierra Negra volcano(SN)shows low-density distributions in and around its summit,contradicting the idea that this is an extinct volcano.展开更多
Stratified flow is a common phenomenon in horizontal tubes of two-phase flow systems. However, the existing methods for calculating the wetted angle of the flat interface model and the central angle of the two-circle ...Stratified flow is a common phenomenon in horizontal tubes of two-phase flow systems. However, the existing methods for calculating the wetted angle of the flat interface model and the central angle of the two-circle model rely on solving implicit transcendental equations, which require iterative numerical root-finding methods,thereby introducing computational complexity and inefficiency. This paper proposes the high-precision explicit approximate solutions for the two models, directly correlating the geometric parameters with the flow parameters, thus significantly enhancing the efficiency and accuracy of two-phase flow analysis.展开更多
We present a method to unify the calculation of Green＇s functions for an electromagnetic（EM） transmitting source embedded in a homogeneous stratified medium.A virtual interface parallel to layer interfaces is intro...We present a method to unify the calculation of Green＇s functions for an electromagnetic（EM） transmitting source embedded in a homogeneous stratified medium.A virtual interface parallel to layer interfaces is introduced through the source location.The potentials for Green＇s function are derived by decomposing the partial wave solutions to Helmholtz＇s equations into upward and downward within boundaries.The amplitudes of the potentials in each stratum are obtained recursively from the initial amplitudes at the source level.The initial amplitudes are derived by coupling with the transmitting sources and following the discontinuity of the tangential electric and magnetic fields at the source interface.Only the initial terms are related to the transmitting sources and thus need to be modified for different transmitters,whereas the kernel connected with the stratified media stays unchanged.Hence,the present method can be easily applied to EM transmitting sources with little modification.The application of the proposed method to the marine controlled-source electromagnetic method（MCSEM） demonstrates its simplicity and flexibility.展开更多
Test results of reducing two stroke motorcycle emissions with new type carburettors and electronic fuel injection systems are presented. Analyses and comparison between different systems are discussed. The adoption o...Test results of reducing two stroke motorcycle emissions with new type carburettors and electronic fuel injection systems are presented. Analyses and comparison between different systems are discussed. The adoption of electronically controlled injection and corresponding electronic control technique is an effective measure of prolonged vitality to improve emissions from two stroke motorcycles. Suggestions about the strategic steps of China′s motorcycle emission control are proposed.展开更多
As a main distributed computing system,Spark has been used to solve problems with more and more complex tasks.However,the native scheduling strategy of Spark assumes it works on a homogenized cluster,which is not so e...As a main distributed computing system,Spark has been used to solve problems with more and more complex tasks.However,the native scheduling strategy of Spark assumes it works on a homogenized cluster,which is not so effective when it comes to heterogeneous cluster.The aim of this study is looking for a more effective strategy to schedule tasks and adding it to the source code of Spark.After investigating Spark scheduling principles and mechanisms,we developed a stratifying algorithm and a node scheduling algorithm is proposed in this paper to optimize the native scheduling strategy of Spark.In this new strategy,the static level of nodes is calculated,the dynamic factors such as the length of running tasks,and CPU usage of work nodes are considered comprehensively.And through a series of comparative experiments in alienation cluster,the new strategy costs less running time and lower CPU usage rate than the original Spark strategy,which verifies that the new schedule strategy is more effective one.展开更多
The practice of stratified English teaching is determined by the features of vocational education. In addition, it is an inexorable trend of current higher education reform, and also a fundamental demand of higher voc...The practice of stratified English teaching is determined by the features of vocational education. In addition, it is an inexorable trend of current higher education reform, and also a fundamental demand of higher vocational education and quality-oriented education. This thesis argues for the need of stratified English teaching in high vocational colleges.展开更多
Multiple filling of gobs will lead to a layered structure of the backfill.To explore the influence of layering structure on the mechanical properties and failure modes of backfill,different backfill specimens were pre...Multiple filling of gobs will lead to a layered structure of the backfill.To explore the influence of layering structure on the mechanical properties and failure modes of backfill,different backfill specimens were prepared with a cement/sand ratio of 1:4,a slurry concentration of 75%,and backfilling times of 1,2,3 and 4,separately.Triaxial cyclic loading and unloading experiments were carried out.The results show that with an increase in backfilling time,the peak strength of backfill decreases as a polynomial function and the peak strain increases as an exponential function.The cyclic load enhances the linear characteristic of backfill deformation.The loading and unloading deformation moduli have a linear negative correlation with the backfilling time.The unloading deformation modulus is always slightly higher than the loading deformation modulus.The failure modes of stratified backfill are mainly characterized by conjugate shear failure at the upper layer and tensile failure across the layer plane,and there is usually no damage in the lower layer away from the loading area.展开更多
An important diplogenetic mineralization event superimposed on pre-existing exhalation sediments in the Tongling area, Anhui province, was triggered by widespread granitic magmatism along the northeastern margin of th...An important diplogenetic mineralization event superimposed on pre-existing exhalation sediments in the Tongling area, Anhui province, was triggered by widespread granitic magmatism along the northeastern margin of the Yangtze Block during 140–135 Ma under extensional tectonic circumstances following the collision between the North China and Yangtze blocks. The main orebodies of the Dongguashan copper deposit, a typical diplogenetic stratified deposit among many polymetallic ore deposits in China, are hosted by strata between Upper Devonian sandstone and Carboniferous limestone, and its mineralization was genetically related to the Qingshanjiao intrusive. The Rb-Sr isotopic isochron of the Qingshanjiao intrusive yields an age of about 136.5±1.4 Ma. The ore-forming fluid reflected by the inclusion fluid in quartz veins is characterized by high temperature and high salinity, and its age was also determined by Rb -Sr isotope dating as 134±11 Ma. Oxygen and hydrogen isotope composition data suggest that the ore-forming fluid was derived mainly from magmatism. By integrating these isotopic dating data, characteristics of fluid inclusions and the geology of the deposit, the mineralization of the Dongguashan copper deposit is divided into two stages. First, a stratiform sedimentary deposit or protore layer formed in the Late Devonian to the Early Carboniferous, while in the second stage the pre-existing protore was superimposed by hydrothermal fluid that was derived from the Yanshanian magmatic activities occurring around 135 Ma ago. This two-stage mineralization formed the Dongguashan statiform copper deposit. Associated “porphyry” mineralization found in the bottom of and in surrounding intrusive rocks of the orebodies might have occurred in the same period as a second-stage mineralization of this deposit.展开更多
In order to capture the mechanism of roadway instability in deep mines, a new approach of Physically Finite Elemental Slab Assemblage (PFESA) is proposed in order to construct a large-scale physical model simulating t...In order to capture the mechanism of roadway instability in deep mines, a new approach of Physically Finite Elemental Slab Assemblage (PFESA) is proposed in order to construct a large-scale physical model simulating the geologically horizontal strata. We carried out physical modeling on the deformation and failure processes of roadways subjected to a plane loading scheme. Our laboratory tests were based on work which incorporated infrared (IR) detection, IR radiation temperature (IRT) statistics, image feature extraction and 2D Fourier transformation, from resulting thermographies. The IRT characterizes the mechanical responses from the roadway after loading with two stages, i.e., IRT evolving at higher levels corresponded to shallow mining (≤500 m) during which the roadway deformed gradually (referred to as the "steady deformation stage"); IRT evolving in a quasi-cyclical manner with multiple peaks corresponded to deep mining (800–2600 m), in which the failure mode for the roadway are dominated by breakage and collapse (called the "unsteady deformation stage"). The IR images and 2D Fourier spectra illustrate detailed information in terms of initiation, nucleation and coalescence of the damage to rock masses and the eventual failure of roadways subject to external loading.展开更多
Combining the advantages of the stratified sampling and the importance sampling, a stratified importance sampling method （SISM） is presented to analyze the reliability sensitivity for structure with multiple failure...Combining the advantages of the stratified sampling and the importance sampling, a stratified importance sampling method （SISM） is presented to analyze the reliability sensitivity for structure with multiple failure modes. In the presented method, the variable space is divided into several disjoint subspace by n-dimensional coordinate planes at the mean point of the random vec- tor, and the importance sampling functions in the subspaces are constructed by keeping the sampling center at the mean point and augmenting the standard deviation by a factor of 2. The sample size generated from the importance sampling function in each subspace is determined by the contribution of the subspace to the reliability sensitivity, which can be estimated by iterative simulation in the sampling process. The formulae of the reliability sensitivity estimation, the variance and the coefficient of variation are derived for the presented SISM. Comparing with the Monte Carlo method, the stratified sampling method and the importance sampling method, the presented SISM has wider applicability and higher calculation efficiency, which is demonstrated by numerical examples. Finally, the reliability sensitivity analysis of flap structure is illustrated that the SISM can be applied to engineering structure.展开更多
基金The work was supported in part by NIH grant[1UL1TR001105]AHRQ grant[R24HS22418]+1 种基金CPRIT grants[RP110562-C1]and[RP120670-C1]NSF grant[IIS-1302497-04].
文摘Stratified cluster randomisation trial design is widely employed in biomedical research and cluster size has been frequently used as the stratifying factor.Conventional sample size calculation methods have assumed the cluster sizes to be constant within each stratum,which is rarely true in practice.Ignoring the random variability in cluster size leads to underestimated sample sizes and underpowered clinical trials.In this study,we proposed to directly incorporate the variability in cluster size(represented by coefficient of variability)into sample size calculation.This approach provides closed-form sample size formulas,and is flexible to accommodate arbitrary randomisation ratio and varying numbers of clusters across strata.Simulation study shows that the proposed approach achieves desired power and type I error over a wide spectrum of design configurations,including different distributions of cluster sizes.An application example is presented.
基金supported by the Sci-ence and technology commission of Shanghai Municipal-ity(No.19441905600)the Shanghai Jiao Tong University Interdisciplinary(Biomedical Engineering)Research Fund(No.ZH2018ZDA09)+2 种基金Clinical Research Plan of SHDC(No.SHDC2020CR3036B)China Postdoctoral Science Founda-tion(No.2021M702090)Changshu Science and Technology Program(Industrial)Project(No.CG202107).
文摘Magnesium and its alloys have been initially applied to biliary tract surgery.Currently,few reports on the degradation behavior of magnesium in the bile environment were investigated.Thus,in-depth research on the degradation behavior of Mg and its alloys in bile is beneficial to the further application of Mg in biliary tract surgery.In this study,the degradation behavior of HP-Mg(HPM)and Mg-2 wt.%Zn(MZ2)alloys in human bile and Hanks balanced salt solution(HBSS)was systematically investigated.The MZ2 alloy biliary stent was implanted into the porcine common bile duct to study the degradation behavior of MZ2 alloy in vivo,and to verify the biosafety of MZ2 alloys degradation in the bile duct.It was found that the degradation product layer formed by MZ2 alloys in bile consisted of three layers,including organic matter(fatty acid,etc.),calcium and magnesium phosphate,and Mg(OH)2/MgO,respectively from the outside to the inside.The multi-layered degradation product layer slowed down the corrosion of the Mg matrix.During the 21 days of stent implantation,the degradation rate of the MZ2 stent was about 0.83 mm/y,there was no blockage and stenosis of the tube diameter,and the bile drainage function was normal.
基金Open Access funding provided by Kobe UniversityThis research was partially performed by the Environment Research and Technology Development Fund(2RL-2301)of the Environmental Restoration and Conservation Agency provided by Ministry of the Environment of Japan.
文摘This study examines the potential impacts o climate change on Lake Biwa,Japan’s largest freshwate lake,with a focus on temperature,wind speed,and pre cipitation variations.Leveraging data from the IPCC Sixth Assessment Report,including CCP scenarios,projecting a significant temperature rise of 3.3–5.7℃in the case o very high GHG emission power,the research investigates how these shifts may influence dissolved oxygen levels in Lake Biwa.Through a one-dimensional model incorporat ing sediment redox reactions,various scenarios where ai temperature and wind speed are changed are simulated.I is revealed that a 5℃increase in air temperature leads to decreasing 1-2 mg/L of dissolved oxygen concentrations from the surface layer to the bottom layer,while a decrease in air temperature tends to elevate 1–3 mg/L of oxygen lev els.Moreover,doubling wind speed enhances surface laye oxygen but diminishes it in deeper layers due to increased mixing.Seasonal variations in wind effects are noted with significant surface layer oxygen increases from 0.4to 0.8 mg/L during summer to autumn,increases from 0.4 to 0.8 mg/L in autumn to winter due to intensified vertica mixing.This phenomenon impacts the lake’s oxygen cycle year-round.In contrast,precipitation changes show limited impact on oxygen levels,suggesting minor influence com pared to other meteorological factors.The study suggests the necessity of comprehensive three-dimensional models that account for lake-specific and geographical factors fo accurate predictions of future water conditions.A holistic approach integrating nutrient levels,water temperature,and river inflow is deemed essential for sustainable management of Lake Biwa’s water resources,particularly in addressing precipitation variations.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52109143 and 12062026)the Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(China Institute of Water Resources and Hydropower Research)(Grant No.IWHRSKL-KF202305).
文摘The mechanical properties of stratified rocks are closely related not only to the stress state but also to the inherent structural anisotropy,which can be represented by the occurrence of bedding planes.This research aims to enhance the understanding of the anisotropic deformation and failure behaviors of stratified rocks by proposing a novel coupled elastoplastic-damage constitutive model.In this constitutive model,a scalar anisotropic parameter(stress-structure mixed invariant)based on the Pietruszczak–Mroz anisotropic theory is incorporated into a nonlinear yield surface,which accounts for the combined effects of the stress state and bedding structure on the anisotropic strength behaviors of stratified rocks.A damage-driven function governs the expansion and contraction of the anisotropic yield surface in the pre-peak strain hardening and post-peak strain-softening regions.The strength and deformation characteristics under multiaxial stress conditions are represented by incorporating the Lode's angle into the yield and plastic potential functions.Numerical simulations are conducted to facilitate a comparison with the conventional and true triaxial compression test data for several stratified rocks.The simulation results demonstrate good agreement with the test data,validating the effectiveness of the proposed constitutive model.This study provides theoretical and technical support for addressing engineering challenges involving stratified rocks.
基金supported by the National Natural Science Foundation of China(No.52306187)the Fundamental Research Funds for the Central Universities of China(Grant No.3132024205)the Open Fund of Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education(Grant No.LOEC-202004).
文摘Geological sequestration of carbon dioxide(CO_(2))entails the long-term storage of captured emissions from CCUS(Carbon Capture,Utilization,and Storage)facilities in deep saline aquifers to mitigate greenhouse gas accumulation.Among various trapping mechanisms,dissolution trapping is particularly effective in enhancing storage security.However,the stratified structure of saline aquifers plays a crucial role in controlling the efficiency of CO_(2) dissolution into the resident brine.In this study,a two-dimensional numerical model of a stratified saline aquifer is developed,integrating both two-phase flow and mass transfer dynamics.The model captures the temporal evolution of gas saturation,reservoir pressure,and CO_(2) dissolution behavior under varying geological and operational conditions.Specifically,the effects of porosity heterogeneity,permeability distribution,and injection rate on the dissolution process are examined,and sequestration efficiencies across distinct stratigraphic layers are compared.Simulation results reveal that in the early phase of CO_(2) injection,the plume spreads radially along the lower portion of the aquifer.With continued injection,high-saturation regions expand upward and eventually accumulate beneath the shale and caprock layers.Pressure within the reservoir rises in response to CO_(2) injection,propagating both vertically and laterally.CO_(2) migration and dissolution are strongly influenced by reservoir properties,with progressive dissolution occurring in the pore spaces of individual layers.High-porosity zones favor CO_(2) accumulation and enhance local dissolution,whereas low-porosity regions facilitate vertical diffusion.An increase in porosity from 0.25 to 0.30 reduces the radial extent of dissolution in the high-permeability layer by 16.5%.Likewise,increasing permeability promotes radial dispersion;each 10 mD increment extends the CO_(2) dissolution front by approximately 18 m.Elevated injection rates intensify both vertical and lateral plume migration:every 0.25×10^(−6) m/s increase in rate yields an average 100–120 m increase in radial dissolution distance within high-permeability zones.
文摘This study examined gender differences in modal choice among residents of coastal communities of Yenagoa metropolis in Bayelsa State, Nigeria. The Four-Step model of transportation planning and modal choice provided the theoretical basis for this study. A survey research design involving a stratified sampling technique was adopted. The descriptives on transport modes, amount and time spent revealed that 10 (76.9%) males and 3 (23.1%) females preferred bicycle as means of transportation, 7 (58.3%) males and 5 (41.7%) females preferred motorcycle, while a significant proportion 90 (53.9%) males and 77 (46.1%) females preferred tricycle, 80 (63.0%) males and 47 (37.0%) females preferred cars/taxis, and 12 (46.2%) males and 14 (53.8%) females preferred mass transit bus. However, 14 (46.7%) males and 16 (53.3%) females in marshy terrain and coastal locations preferred canoes and boats. The result of the logistic regression model revealed that gender modal preference is more likely to be influenced by mode of transportation with a beta weight of 1.140, safety considerations 1.139, ownership of transport 1.135 and distance to place of work 1.073. Hence, this study recommends that a combination of these factors should be incorporated into transport planning to achieve effective transport planning and sustainable development in the Yenagoa metropolis.
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.
文摘Iread with great interest the recent article by Shin,et al.[1]the authors present an important exploration into the use of drug-coated balloon(DCB)in patients aged≥75 years,a demographic increasingly encountered in modern cardiovascular practice.The authors conducted a retrospective analysis involving 2050 elderly patients(aged≥75 years)undergoing successful percutaneous coronary intervention(PCI).
基金supported by IIMAS and the Geophysics Institute,both at UNAMmaterial support from both institutions.This research did not receive any specific grant from funding agencies in the public,commer-cial,or nonprofit sectors.
文摘The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures involved.The gravity field is obtained from the GGMplus model,from which 3D inversions at resolutions of 1000,500,and 250 m are performed.Low-gravity anomalies are associated with Sierra Negra(4580 m)and Citlaltépetl(5521 m)volcanoes,as well as with the Chichimeco Dome Complex(~4000 m)(CDC).They are located within a SW-NE anomaly that serves as a constraint to the reconstruction.The associ-ated Bouguer anomaly appears as a continuous low-gravity surface;however,its vertical derivative Dz shows that the sources of those three structures are separated.The fault scarps are complemented with inferred trajectories that suggest the existence of two volcanoes before the collapse at 32 ka:Citlaltépetl and the Ancestral Teteltzingo.Density cross-sections identify three stratified magmatic deposits under the summit of CT.On the summit of CT,there is an anomalous concentration of high-density materials,attributed to the presence of domes and lava flows,which mask the position of the volcano’s chimney.The existence of the Ancestral Teteltzingo volcano(ATE)is inferred NE of CT from the associated density distribution;CDC is at the center of the ATE struc-ture and is interpreted as a resurgent activity at<8 ka.Sierra Negra volcano(SN)shows low-density distributions in and around its summit,contradicting the idea that this is an extinct volcano.
基金supported by the General Research Fund from the Research Grants Council of the Hong Kong Special Administrative Region of China (No. PolyU 15210624)。
文摘Stratified flow is a common phenomenon in horizontal tubes of two-phase flow systems. However, the existing methods for calculating the wetted angle of the flat interface model and the central angle of the two-circle model rely on solving implicit transcendental equations, which require iterative numerical root-finding methods,thereby introducing computational complexity and inefficiency. This paper proposes the high-precision explicit approximate solutions for the two models, directly correlating the geometric parameters with the flow parameters, thus significantly enhancing the efficiency and accuracy of two-phase flow analysis.
基金supported by CNSF(Granted No.40874050)Chinese High Technology Project(Granted No.2011YQ05006010)
文摘We present a method to unify the calculation of Green＇s functions for an electromagnetic（EM） transmitting source embedded in a homogeneous stratified medium.A virtual interface parallel to layer interfaces is introduced through the source location.The potentials for Green＇s function are derived by decomposing the partial wave solutions to Helmholtz＇s equations into upward and downward within boundaries.The amplitudes of the potentials in each stratum are obtained recursively from the initial amplitudes at the source level.The initial amplitudes are derived by coupling with the transmitting sources and following the discontinuity of the tangential electric and magnetic fields at the source interface.Only the initial terms are related to the transmitting sources and thus need to be modified for different transmitters,whereas the kernel connected with the stratified media stays unchanged.Hence,the present method can be easily applied to EM transmitting sources with little modification.The application of the proposed method to the marine controlled-source electromagnetic method（MCSEM） demonstrates its simplicity and flexibility.
文摘Test results of reducing two stroke motorcycle emissions with new type carburettors and electronic fuel injection systems are presented. Analyses and comparison between different systems are discussed. The adoption of electronically controlled injection and corresponding electronic control technique is an effective measure of prolonged vitality to improve emissions from two stroke motorcycles. Suggestions about the strategic steps of China′s motorcycle emission control are proposed.
基金This work is supported by the National Natural Science Foundation of China(Grant No.61472248,61772337)the SJTU-Shanghai Songheng Content Analysis Joint Lab.
文摘As a main distributed computing system,Spark has been used to solve problems with more and more complex tasks.However,the native scheduling strategy of Spark assumes it works on a homogenized cluster,which is not so effective when it comes to heterogeneous cluster.The aim of this study is looking for a more effective strategy to schedule tasks and adding it to the source code of Spark.After investigating Spark scheduling principles and mechanisms,we developed a stratifying algorithm and a node scheduling algorithm is proposed in this paper to optimize the native scheduling strategy of Spark.In this new strategy,the static level of nodes is calculated,the dynamic factors such as the length of running tasks,and CPU usage of work nodes are considered comprehensively.And through a series of comparative experiments in alienation cluster,the new strategy costs less running time and lower CPU usage rate than the original Spark strategy,which verifies that the new schedule strategy is more effective one.
文摘The practice of stratified English teaching is determined by the features of vocational education. In addition, it is an inexorable trend of current higher education reform, and also a fundamental demand of higher vocational education and quality-oriented education. This thesis argues for the need of stratified English teaching in high vocational colleges.
基金the National Natural Science Foundation of China(No.51374033)the Key Projects of the National Key Research and Development Program(No.YS2017YFSF040004).
文摘Multiple filling of gobs will lead to a layered structure of the backfill.To explore the influence of layering structure on the mechanical properties and failure modes of backfill,different backfill specimens were prepared with a cement/sand ratio of 1:4,a slurry concentration of 75%,and backfilling times of 1,2,3 and 4,separately.Triaxial cyclic loading and unloading experiments were carried out.The results show that with an increase in backfilling time,the peak strength of backfill decreases as a polynomial function and the peak strain increases as an exponential function.The cyclic load enhances the linear characteristic of backfill deformation.The loading and unloading deformation moduli have a linear negative correlation with the backfilling time.The unloading deformation modulus is always slightly higher than the loading deformation modulus.The failure modes of stratified backfill are mainly characterized by conjugate shear failure at the upper layer and tensile failure across the layer plane,and there is usually no damage in the lower layer away from the loading area.
基金supported by the National Science Foundation of China(grant Nos.49873016,40221301)the Ph.D.Programs Foundation of the Ministry of Education of China(No.20020284035)
文摘An important diplogenetic mineralization event superimposed on pre-existing exhalation sediments in the Tongling area, Anhui province, was triggered by widespread granitic magmatism along the northeastern margin of the Yangtze Block during 140–135 Ma under extensional tectonic circumstances following the collision between the North China and Yangtze blocks. The main orebodies of the Dongguashan copper deposit, a typical diplogenetic stratified deposit among many polymetallic ore deposits in China, are hosted by strata between Upper Devonian sandstone and Carboniferous limestone, and its mineralization was genetically related to the Qingshanjiao intrusive. The Rb-Sr isotopic isochron of the Qingshanjiao intrusive yields an age of about 136.5±1.4 Ma. The ore-forming fluid reflected by the inclusion fluid in quartz veins is characterized by high temperature and high salinity, and its age was also determined by Rb -Sr isotope dating as 134±11 Ma. Oxygen and hydrogen isotope composition data suggest that the ore-forming fluid was derived mainly from magmatism. By integrating these isotopic dating data, characteristics of fluid inclusions and the geology of the deposit, the mineralization of the Dongguashan copper deposit is divided into two stages. First, a stratiform sedimentary deposit or protore layer formed in the Late Devonian to the Early Carboniferous, while in the second stage the pre-existing protore was superimposed by hydrothermal fluid that was derived from the Yanshanian magmatic activities occurring around 135 Ma ago. This two-stage mineralization formed the Dongguashan statiform copper deposit. Associated “porphyry” mineralization found in the bottom of and in surrounding intrusive rocks of the orebodies might have occurred in the same period as a second-stage mineralization of this deposit.
基金Projects 2006CB202200 supported by the Special Funds for the Major State Basic Research ProjectIRT0656 by the Innovative Team Development Project of the State Educational Ministry of China
文摘In order to capture the mechanism of roadway instability in deep mines, a new approach of Physically Finite Elemental Slab Assemblage (PFESA) is proposed in order to construct a large-scale physical model simulating the geologically horizontal strata. We carried out physical modeling on the deformation and failure processes of roadways subjected to a plane loading scheme. Our laboratory tests were based on work which incorporated infrared (IR) detection, IR radiation temperature (IRT) statistics, image feature extraction and 2D Fourier transformation, from resulting thermographies. The IRT characterizes the mechanical responses from the roadway after loading with two stages, i.e., IRT evolving at higher levels corresponded to shallow mining (≤500 m) during which the roadway deformed gradually (referred to as the "steady deformation stage"); IRT evolving in a quasi-cyclical manner with multiple peaks corresponded to deep mining (800–2600 m), in which the failure mode for the roadway are dominated by breakage and collapse (called the "unsteady deformation stage"). The IR images and 2D Fourier spectra illustrate detailed information in terms of initiation, nucleation and coalescence of the damage to rock masses and the eventual failure of roadways subject to external loading.
基金National Natural Science Foundation of China (10572117,10802063,50875213)Aeronautical Science Foundation of China (2007ZA53012)+1 种基金New Century Program For Excellent Talents of Ministry of Education of China (NCET-05-0868)National High-tech Research and Development Program (2007AA04Z401)
文摘Combining the advantages of the stratified sampling and the importance sampling, a stratified importance sampling method （SISM） is presented to analyze the reliability sensitivity for structure with multiple failure modes. In the presented method, the variable space is divided into several disjoint subspace by n-dimensional coordinate planes at the mean point of the random vec- tor, and the importance sampling functions in the subspaces are constructed by keeping the sampling center at the mean point and augmenting the standard deviation by a factor of 2. The sample size generated from the importance sampling function in each subspace is determined by the contribution of the subspace to the reliability sensitivity, which can be estimated by iterative simulation in the sampling process. The formulae of the reliability sensitivity estimation, the variance and the coefficient of variation are derived for the presented SISM. Comparing with the Monte Carlo method, the stratified sampling method and the importance sampling method, the presented SISM has wider applicability and higher calculation efficiency, which is demonstrated by numerical examples. Finally, the reliability sensitivity analysis of flap structure is illustrated that the SISM can be applied to engineering structure.
