The traditional detailed model of the dual active bridge(DAB)power electronic transformer is characterized by the high dimensionality of its nodal admittance matrix and the need for a small simulation step size,which ...The traditional detailed model of the dual active bridge(DAB)power electronic transformer is characterized by the high dimensionality of its nodal admittance matrix and the need for a small simulation step size,which limits the speed of electromagnetic transient(EMT)simulations.To overcome these limitations,a novel EMT equivalent model based on a generalized branch-cutting method is proposed to improve the simulation efficiency of the DAB model.The DAB topology is first decomposed into two subnetworks through branch-cutting and node-tearing methods without the introduction of a one-time-step delay.Sub-sequently,the internal nodes of each sub-network are eliminated through network simplification,and the equivalent circuit for the port cascade module is derived.The model is then validated through simulations across various operating conditions.The results demonstrate that the model avoids the loss of accuracy associated with one-time-step delay,the relative error across different conditions remains below 1%,and the simulation acceleration ratios improve as the number of modules increases.展开更多
Recent years have witnessed significant advances in the development of novel techniques and methodologies for identifying active ingredients in traditional Chinese medicine(TCM),substantially advancing research and de...Recent years have witnessed significant advances in the development of novel techniques and methodologies for identifying active ingredients in traditional Chinese medicine(TCM),substantially advancing research and development efforts.Spectrum-effect correlation analysis,affinity ultrafiltration,high-content screening(HCS)imaging,and cell membrane chromatography(CMC)have emerged as essential tools,effectively linking TCM chemical constituents to their biological effects,thereby enabling efficient active ingredient screening.Additionally,molecular interaction analysis provides deeper insights into TCM-biomolecule interaction mechanisms,enhancing understanding of its therapeutic potential.Computer-aided techniques facilitate TCM active ingredient identification,optimizing the screening process for efficiency and cost-effectiveness.Molecular probe technology,as an emerging methodology,enables precise and rapid screening for novel therapeutic drug discovery.Ongoing technological advancement in this field indicates promising future developments,potentially leading to more effective and targeted TCM-based therapies.展开更多
This paper investigates the active traveling wave vibration control of an elastic supported rotating porous aluminium conical shell(CS)under impact loading.Piezoelectric smart materials in the form of micro fiber comp...This paper investigates the active traveling wave vibration control of an elastic supported rotating porous aluminium conical shell(CS)under impact loading.Piezoelectric smart materials in the form of micro fiber composites(MFCs)are used as actuators and sensors.To this end,a metal pore truncated CS with MFCs attached to its surface is considered.Adding artificial virtual springs at two edges of the truncated CS achieves various elastic supported boundaries by changing the spring stiffness.Based on the first-order shear deformation theory(FSDT),minimum energy principle,and artificial virtual spring technology,the theoretical formulations considering the electromechanical coupling are derived.The comparison of the natural frequency of the present results with the natural frequencies reported in previous literature evaluates the accuracy of the present approach.To study the vibration control,the integral quadrature method in conjunction with the differential quadrature approximation in the length direction is used to discretize the partial differential dynamical system to form a set of ordinary differential equations.With the aid of the velocity negative feedback method,both the time history and the input control voltage on the actuator are demonstrated to present the effects of velocity feedback gain,pore distribution type,semi-vertex angle,impact loading,and rotational angular velocity on the traveling wave vibration control.展开更多
Electrocatalytic nitrate reduction reaction(NitRR)utilizing water as a hydrogen source under ambient conditions represents a highly promising avenue for sustainable ammonia synthesis and environmental remediation.Howe...Electrocatalytic nitrate reduction reaction(NitRR)utilizing water as a hydrogen source under ambient conditions represents a highly promising avenue for sustainable ammonia synthesis and environmental remediation.However,achieving high efficiency and selectivity in NitRR is fundamentally challenged by the complex lifecycle management of active hydrogen derived from water splitting.This review provides a timely and comprehensive analysis centered on the pivotal role and meticulous regulation of active hydrogen throughout the NitRR process.We first elucidate the distinct functions and characteristics of various hydrogen species,followed by a survey of advanced characterization techniques crucial for monitoring the dynamics of active hydrogen.Critically,three core strategies were systematically dissected to modulate the active hydrogen lifecycle:accelerating water activation and dissociation,enhancing the directional transport of hydrogen species,and precisely tuning active hydrogen coupling pathways while suppressing parasitic hydrogen evolution.By consolidating current understanding from both catalyst design and reaction mechanism perspectives,this review offers a hydrogen-centric roadmap and highlights emerging opportunities for rationally engineering advanced NitRR systems.展开更多
This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method.It is developed in the context of biocementation as soil improvement tech...This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method.It is developed in the context of biocementation as soil improvement technique,which is used in Civil Engineering applications to produce calcium carbonate through bacterial or enzymatic activity,replacing the use of other binder materials such as cement or resins,and therefore reducing carbon footprint.The microdevice was used to measure urease activity in the soil interstitial fluid,to investigate if bacterial activity could be affected by the presence of the particles and tortuosity from pore geometry.Such analysis is important to understand biocementation mechanism inside the soil and helps to improve the design of such treatment solutions.The device is basically a squared reservoir printed in polypropylene using a 3D printing machine,incorporating stainless steel electrodes in its base.The electrical resistivity was computed adopting Wenner method,by connecting 4 PCB electrodes to a signal generator and an oscilloscope for measuring the voltage when a AC current of 1 mA was applied.Both square and sinusoidal waves with 5 kHz frequency were selected among other frequencies.The measurements were adjusted during the calibration of the microdevice,done using standard salt solutions with known electrical conductivity measured using an electrical conductivity probe.For the bacterial activity measurements,the bacterial and urea solutions were added to a uniform-graded size quarzitic sand(average diameter 0.3 mm)placed inside the microdevice and covering completely the electrodes.Bacterial activity was not affected by the presence of the sand,which confirms that this treatment is effective for this type of soils.展开更多
Purpose–The efficient utilization of recycled concrete powder(RCP)has attracted much attention.To break through the limitation of single activation technology of RCP,this study investigates the effects of a mechanica...Purpose–The efficient utilization of recycled concrete powder(RCP)has attracted much attention.To break through the limitation of single activation technology of RCP,this study investigates the effects of a mechanical-microwave method on the reactivity of RCP.Design/methodology/approach–The mechanical properties,hydration products,and pore structure of RCP-incorporated mortar were evaluated.Findings–The results demonstrate that the combined activation reduces the median particle size of RCP and induces a low-frequency shift in the Si-O-T FT-IR characteristic peaks,signifying depolymerization of the silicate network and formation of highly reactive broken bond sites.Concurrently,decreased Si2p and Al2p binding energies in XPS spectra confirm enhanced surface reactivity.The 28-day strength activity index(SAI)of RCP mortar improved from 65.7(untreated)to 82.2%under optimal activation conditions(90-min ball milling followed by 10-min microwave irradiation),outperforming solely mechanical activation by 3.6–6.1%.Furthermore,combined activation increased chemically bound water content from 22.8 to 33.7%,accompanied by a low-wavenumber shift in FT-IR peaks of hydration products.The total porosity of RCP mortar decreased from 17.2 to 14.6%,indicating a denser pore structure.Originality/value–This study explores the feasibility and potential mechanism of mechanical-microwave activation of RCP,aiming to provide valuable insights for the sustainable development of materials.Using activated RCP in cement-based materials reduces the demand for cement and substantially cuts carbon emissions,thereby making a critical contribution to the construction industry’s green and low-carbon transition.展开更多
Tungsten is considered the most promising plasma-facing material for fusion reactors with exceptional performance.Under certain conditions,activated tungsten dust can be generated through plasma–wall interactions and...Tungsten is considered the most promising plasma-facing material for fusion reactors with exceptional performance.Under certain conditions,activated tungsten dust can be generated through plasma–wall interactions and released into the atmosphere.Activated tungsten migrates downward in the soil after atmospheric deposition.However,effective methods for evaluating the environmental dose of gamma rays emitted by activated tungsten are still lacking.Consequently,a method for evaluating the air-absorbed dose rate of activated tungsten dust was proposed considering soil attenuation.Key parameters including the mass attenuation coefficient and energy absorption build-up factor were determined for the main gamma ray energies of radionuclides within the activated tungsten dust.Additionally,air-absorbed dose rates were calculated by assuming that radioactive sources were located at different soil depths and radii.It was found that a soil depth of 50 cm significantly attenuated the environmental dose by 99.9%,whereas the air-absorbed dose rates within the horizontal distance of 500 cm accounted for 91%of the total dose rate.Therefore,this study underscored the importance of soil attenuation in environmental dose assessments,which must be carefully re-examined for the safety analysis of fusion reactors.展开更多
This paper studies the coupling mechanism between the nonlinear stiffness and damping coefficients of Active Elastic Support/Dry Friction Damper(AESDFD)and rotor system.First,parameters for evaluating the vibration re...This paper studies the coupling mechanism between the nonlinear stiffness and damping coefficients of Active Elastic Support/Dry Friction Damper(AESDFD)and rotor system.First,parameters for evaluating the vibration reduction characteristics are proposed to facilitate the design of the AESDFD.To achieve this,the nonlinear friction force is initially represented as equivalent stiffness and damping coefficients,based on the ball-plate friction model.Second,three evaluation parameters—optimal slipping displacement,loss factor,and controllability—are proposed to reveal the vibration reduction characteristics of the AESDFD,alongside determining the optimal normal force.Subsequently,the finite element method,in conjunction with the ball-plate friction model,is introduced to formulate the governing equation of a low-pressure rotor system equipped with AESDFDs.The steady-state responses of the AESDFDs-rotor system are solved using the harmonic balance method combined with an efficient iteration method.Finally,the solutions are validated on the AESDFDs-rotor system both numerically and experimentally.The results indicate that controllability effectively assesses the vibration reduction performance of the AESDFD and is relatively insensitive to variations in low normal force.Away from the critical speed,the AESDFD suppresses vibration by altering the resonance position of the rotor system through its stiffness coefficient.Near the critical speed,vibration reduction is achieved primarily through energy dissipation by the damping coefficient.If the loss factor is less than one,the stiffness coefficient can diminish the vibration reduction effect of the damping coefficient.Notably,the optimal normal force of the AESDFD achieves optimal vibration reduction effect.This study reveals that changes in rotor system unbalance do not affect the vibration reduction characteristics of the AESDFD,with the same upper limit to the vibration reduction effect of the AESDFD.展开更多
Active Flux is a third order accurate numerical method which evolves cell averages and point values at cell interfaces independently.It naturally uses a continuous reconstruction,but is stable when applied to hyperbol...Active Flux is a third order accurate numerical method which evolves cell averages and point values at cell interfaces independently.It naturally uses a continuous reconstruction,but is stable when applied to hyperbolic problems.In this work,the Active Flux method is extended for the first time to a nonlinear hyperbolic system of balance laws,namely,to the shallow water equations with bottom topography.We demonstrate how to achieve an Active Flux method that is well-balanced,positivity preserving,and allows for dry states in one spatial dimension.Because of the continuous reconstruction all these properties are achieved using new approaches.To maintain third order accuracy,we also propose a novel high-order approximate evolution operator for the update of the point values.A variety of test problems demonstrates the good performance of the method even in presence of shocks.展开更多
The component synthesis active vibration suppression method （CSVS） can be applied to suppress the vibration of flexible systems. By this method, several same or similar time-varying components are arranged according...The component synthesis active vibration suppression method （CSVS） can be applied to suppress the vibration of flexible systems. By this method, several same or similar time-varying components are arranged according to certain rules along the time axis. The synthesized command can suppress the arbitrary unwanted vibration harmonic while achieving the desired rigid body motion. The number of the components increases rapidly when the number of harmonic vibration is growing. In this article, the CSVS based on zero-placement technique is used to construct the synthesized command to suppress the multi-harmonics simultaneously in the discrete domain. The nature of zero-placement method is to put enough zeros to cancel system poles at necessary points. The designed synthesized command has equal time intervals between each component and which is much easier to be implemented. Using this method, the number of components increases linearly with the increasing of the number of being suppressed harmonics. For the spacecraft with flexible appendages, CSVS based on zero-placement is used to design the time optimal large angle maneuver control strategy. Simulations have verified the validity and superiority of the proposed approach.展开更多
A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boun...A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen （1995） is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.展开更多
In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed.Differing from other limit equilibrium methods, an arbitrary slip surface shape wi...In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed.Differing from other limit equilibrium methods, an arbitrary slip surface shape without any assumptions of pre-defined shapes is needed in the current framework, which is verified to find the most probable failure slip surface. Based on the current computational framework, numerical comparisons with experiment, discrete element method and other methods are carried out. In addition, the influences of the inclination of the wall, the soil cohesion, the angle of the internal friction of the soil, the slope inclination of the backfill soil on the critical pressure coefficient of the soil, the point of application of the resultant earth pressure and the shape of the slip surface are also carefully investigated. The results demonstrate that limit equilibrium solution from predefined slip plane assumption, including Coulomb solution, is a special case of current computational framework. It is well illustrated that the current method is feasible to evaluate the characteristics of earth pressure problem.展开更多
The behavior of the active layer of material bed within rotary kilns plays a key role in industrial applications.To obtain its influences on industrial process,different regimes of particle motion have been simulated ...The behavior of the active layer of material bed within rotary kilns plays a key role in industrial applications.To obtain its influences on industrial process,different regimes of particle motion have been simulated by discrete element method(DEM) in three dimensions under variant rotation speeds,filling degree,based on the background of induration process of iron ore pellets.The influences of the mentioned factors on the maximum thickness of the active layer and the average velocity of particles have been investigated.The average velocity of particles increases with Froude number following the power function over a wide range,and the maximum thickness rises with increasing rotation speed in a way of logarithm.The influence of the filling degree f on the maximum thickness exhibits a good linearity under two classic regimes,but the increasing of the average velocity of the active layer is limited at f=0.4.This basic research highlights the impact of the active layer within rotary kilns,and lays a good foundation for the further investigation in mixing and heat transfer within the particle bed inside rotary kilns.展开更多
Active learning in semi-supervised classification involves introducing additional labels for unlabelled data to improve the accuracy of the underlying classifier.A challenge is to identify which points to label to bes...Active learning in semi-supervised classification involves introducing additional labels for unlabelled data to improve the accuracy of the underlying classifier.A challenge is to identify which points to label to best improve performance while limiting the number of new labels."Model Change"active learning quantifies the resulting change incurred in the classifier by introducing the additional label(s).We pair this idea with graph-based semi-supervised learning(SSL)methods,that use the spectrum of the graph Laplacian matrix,which can be truncated to avoid prohibitively large computational and storage costs.We consider a family of convex loss functions for which the acquisition function can be efficiently approximated using the Laplace approximation of the posterior distribution.We show a variety of multiclass examples that illustrate improved performance over prior state-of-art.展开更多
In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a ...In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a specifically designed test setup.The energy attenuation of stress waves was measured by the relative index between the output voltage of sensors and the excitation voltage at the actuator.Based on the experimental results of concrete cube and cylinder specimens,the effect of excitation frequencies,excitation amplitude,wave propagation paths and the curing age on the output signals of sensors are evaluated.The results show that the relative voltage attenuation coefficient RVAC is an effective indicator for measuring the attenuation of stress waves through the interior of concrete.展开更多
The performance of structures with active variable stiffness (AVS) systems exhibits strong nonlinearity due to the variety with time of the stiffness of each storey unit,in which the AVS system is installed.Hence,the ...The performance of structures with active variable stiffness (AVS) systems exhibits strong nonlinearity due to the variety with time of the stiffness of each storey unit,in which the AVS system is installed.Hence,the classical dynamic analysis method for linear structures,such as the mode-superposition method,is not applicable to structures with AVS systems.In this paper,an approximate analysis method is proposed for displacement responses of structures with AVS systems.Firstly,an equivalent relationship between single-degree-of-freedom (SDOF) structures equipped with AVS systems and so-called fictitious linear structures is established.Then,an approximate mode-superposition (AMS) method is presented for multi-degree-of-freedom (MDOF) structures equipped with AVS systems.The accuracy of this method is investigated through extensive parametrical study using different types of earthquake excitations,and some modification is made to the method. Numerical calculation results indicate that the modified AMS method is effective for estimating the maximum displacements relative to the ground and the maximum interstorey drifts of MDOF structures equipped with AVS systems.展开更多
A B-spline active contour model based on finite element method is presented, into which the advantages of a B-spline active contour attributing to its fewer parameters and its smoothness is built accompanied with redu...A B-spline active contour model based on finite element method is presented, into which the advantages of a B-spline active contour attributing to its fewer parameters and its smoothness is built accompanied with reduced computational complexity and better numerical stability resulted from the finite element method. In this model, a cubic B-spline segment is taken as an element, and the finite element method is adopted to solve the energy minimization problem of the B-spline active contour, thus to implement image segmentation. Experiment results verify that this method is efficient for B-spline active contour, which attains stable, accurate and faster convergence.展开更多
Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between pil...Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.展开更多
The depth of upper fault point is the key data for ascertaining the active age of a buried fault on a plain. The difference of depth obtained from same fault may be dozens to several hundred meters when using differen...The depth of upper fault point is the key data for ascertaining the active age of a buried fault on a plain. The difference of depth obtained from same fault may be dozens to several hundred meters when using different geophysical methods. It can result in the absolutely opposite conclusions when judging fault activity. Because of a lack of an artificial earthquake source with wide band and high central frequency, many kinds of methods have to be used together. The higher the frequency of the artificial earthquake wave, electromagnetic wave and sonic wave, the higher the resolution. However the attenuation is also very fast and the exploration depth is very shallow. The reverse is also true. The frequency of artificial seismic waves is in the tens of Hz. Its exploration depth is big and the resolution is poor. The frequency of radar electromagnetic waves is about a million Hz, indicating that the resolving power is better, but the exploration depth is very shallow. However, the acoustic frequency is thousands of Hz, its resolving power is better than that of the artificial earthquake method and the exploration depth is larger than that of the radar method. So it is suitable for extra shallow exploration in the thick deposit strata of the Quaternary. The preliminary results detected using the high frequency acoustic method in extra shallow layers indicates that previous inferences about some fault activity in the eastern part of the North China plain may need to be greatly corrected.展开更多
In this paper, the incremental harmonic balance method is employed to solve the periodic solution that a vibration active control system with double time delays generates, and the stability analysis of which is achiev...In this paper, the incremental harmonic balance method is employed to solve the periodic solution that a vibration active control system with double time delays generates, and the stability analysis of which is achieved by the Poincare theorem. The system stability regions can be obtained in view of time delay and feedback gain, the variation of which is also studied. It turns out that along with the increase of time delay, the active control system is not always from stable to unstable, and the system can be from stable to unstable state, whereas the system can be from unstable to stable state. The extent that the two times delays impact to the relative magnitude of the two feedback gains. the condition of the well-matched feedback gains. control strategy of time-delayed feedback.展开更多
基金The Technology Project of State Grid Corporation of China Headquarters(No.5400-202318547A-3-2-ZN).
文摘The traditional detailed model of the dual active bridge(DAB)power electronic transformer is characterized by the high dimensionality of its nodal admittance matrix and the need for a small simulation step size,which limits the speed of electromagnetic transient(EMT)simulations.To overcome these limitations,a novel EMT equivalent model based on a generalized branch-cutting method is proposed to improve the simulation efficiency of the DAB model.The DAB topology is first decomposed into two subnetworks through branch-cutting and node-tearing methods without the introduction of a one-time-step delay.Sub-sequently,the internal nodes of each sub-network are eliminated through network simplification,and the equivalent circuit for the port cascade module is derived.The model is then validated through simulations across various operating conditions.The results demonstrate that the model avoids the loss of accuracy associated with one-time-step delay,the relative error across different conditions remains below 1%,and the simulation acceleration ratios improve as the number of modules increases.
基金supported by the National Natural Science Foundation of China (Nos. 22175078, 52373287, 82404846, and 22467002)the Natural Science Foundation of Jiangsu Province of China (No. BK20241597)the Fundamental Research Funds for the Central Universities (No. 2632024TD05)
文摘Recent years have witnessed significant advances in the development of novel techniques and methodologies for identifying active ingredients in traditional Chinese medicine(TCM),substantially advancing research and development efforts.Spectrum-effect correlation analysis,affinity ultrafiltration,high-content screening(HCS)imaging,and cell membrane chromatography(CMC)have emerged as essential tools,effectively linking TCM chemical constituents to their biological effects,thereby enabling efficient active ingredient screening.Additionally,molecular interaction analysis provides deeper insights into TCM-biomolecule interaction mechanisms,enhancing understanding of its therapeutic potential.Computer-aided techniques facilitate TCM active ingredient identification,optimizing the screening process for efficiency and cost-effectiveness.Molecular probe technology,as an emerging methodology,enables precise and rapid screening for novel therapeutic drug discovery.Ongoing technological advancement in this field indicates promising future developments,potentially leading to more effective and targeted TCM-based therapies.
基金Supported by the National Natural Science Foundation of China(Nos.12272056 and 11832002)。
文摘This paper investigates the active traveling wave vibration control of an elastic supported rotating porous aluminium conical shell(CS)under impact loading.Piezoelectric smart materials in the form of micro fiber composites(MFCs)are used as actuators and sensors.To this end,a metal pore truncated CS with MFCs attached to its surface is considered.Adding artificial virtual springs at two edges of the truncated CS achieves various elastic supported boundaries by changing the spring stiffness.Based on the first-order shear deformation theory(FSDT),minimum energy principle,and artificial virtual spring technology,the theoretical formulations considering the electromechanical coupling are derived.The comparison of the natural frequency of the present results with the natural frequencies reported in previous literature evaluates the accuracy of the present approach.To study the vibration control,the integral quadrature method in conjunction with the differential quadrature approximation in the length direction is used to discretize the partial differential dynamical system to form a set of ordinary differential equations.With the aid of the velocity negative feedback method,both the time history and the input control voltage on the actuator are demonstrated to present the effects of velocity feedback gain,pore distribution type,semi-vertex angle,impact loading,and rotational angular velocity on the traveling wave vibration control.
基金financially supported by the National Natural Science Foundation of China(22179035)the Science Fund for Distinguished Young Scholars of Heilongjiang Province(JQ2022B001)the Fundamental Research Funds for the Universities of Heilongjiang Province of China(2023-KYYWF1440)。
文摘Electrocatalytic nitrate reduction reaction(NitRR)utilizing water as a hydrogen source under ambient conditions represents a highly promising avenue for sustainable ammonia synthesis and environmental remediation.However,achieving high efficiency and selectivity in NitRR is fundamentally challenged by the complex lifecycle management of active hydrogen derived from water splitting.This review provides a timely and comprehensive analysis centered on the pivotal role and meticulous regulation of active hydrogen throughout the NitRR process.We first elucidate the distinct functions and characteristics of various hydrogen species,followed by a survey of advanced characterization techniques crucial for monitoring the dynamics of active hydrogen.Critically,three core strategies were systematically dissected to modulate the active hydrogen lifecycle:accelerating water activation and dissociation,enhancing the directional transport of hydrogen species,and precisely tuning active hydrogen coupling pathways while suppressing parasitic hydrogen evolution.By consolidating current understanding from both catalyst design and reaction mechanism perspectives,this review offers a hydrogen-centric roadmap and highlights emerging opportunities for rationally engineering advanced NitRR systems.
基金FCT I.P,for the funding through CALCITE Project(ref.PTDC/ECI-EGC/1086/2021).
文摘This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method.It is developed in the context of biocementation as soil improvement technique,which is used in Civil Engineering applications to produce calcium carbonate through bacterial or enzymatic activity,replacing the use of other binder materials such as cement or resins,and therefore reducing carbon footprint.The microdevice was used to measure urease activity in the soil interstitial fluid,to investigate if bacterial activity could be affected by the presence of the particles and tortuosity from pore geometry.Such analysis is important to understand biocementation mechanism inside the soil and helps to improve the design of such treatment solutions.The device is basically a squared reservoir printed in polypropylene using a 3D printing machine,incorporating stainless steel electrodes in its base.The electrical resistivity was computed adopting Wenner method,by connecting 4 PCB electrodes to a signal generator and an oscilloscope for measuring the voltage when a AC current of 1 mA was applied.Both square and sinusoidal waves with 5 kHz frequency were selected among other frequencies.The measurements were adjusted during the calibration of the microdevice,done using standard salt solutions with known electrical conductivity measured using an electrical conductivity probe.For the bacterial activity measurements,the bacterial and urea solutions were added to a uniform-graded size quarzitic sand(average diameter 0.3 mm)placed inside the microdevice and covering completely the electrodes.Bacterial activity was not affected by the presence of the sand,which confirms that this treatment is effective for this type of soils.
基金sponsored by Science and Technology Research and Development Plan of China National Railway Group Co.,Ltd.(L2022G009)National Natural Science Foundation of China(52438002)+1 种基金Research Project of China Academy of Railway Science Corporation Limited(2024YJ254)New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Purpose–The efficient utilization of recycled concrete powder(RCP)has attracted much attention.To break through the limitation of single activation technology of RCP,this study investigates the effects of a mechanical-microwave method on the reactivity of RCP.Design/methodology/approach–The mechanical properties,hydration products,and pore structure of RCP-incorporated mortar were evaluated.Findings–The results demonstrate that the combined activation reduces the median particle size of RCP and induces a low-frequency shift in the Si-O-T FT-IR characteristic peaks,signifying depolymerization of the silicate network and formation of highly reactive broken bond sites.Concurrently,decreased Si2p and Al2p binding energies in XPS spectra confirm enhanced surface reactivity.The 28-day strength activity index(SAI)of RCP mortar improved from 65.7(untreated)to 82.2%under optimal activation conditions(90-min ball milling followed by 10-min microwave irradiation),outperforming solely mechanical activation by 3.6–6.1%.Furthermore,combined activation increased chemically bound water content from 22.8 to 33.7%,accompanied by a low-wavenumber shift in FT-IR peaks of hydration products.The total porosity of RCP mortar decreased from 17.2 to 14.6%,indicating a denser pore structure.Originality/value–This study explores the feasibility and potential mechanism of mechanical-microwave activation of RCP,aiming to provide valuable insights for the sustainable development of materials.Using activated RCP in cement-based materials reduces the demand for cement and substantially cuts carbon emissions,thereby making a critical contribution to the construction industry’s green and low-carbon transition.
基金supported by the National Natural Science Foundation of China(No.12375314)。
文摘Tungsten is considered the most promising plasma-facing material for fusion reactors with exceptional performance.Under certain conditions,activated tungsten dust can be generated through plasma–wall interactions and released into the atmosphere.Activated tungsten migrates downward in the soil after atmospheric deposition.However,effective methods for evaluating the environmental dose of gamma rays emitted by activated tungsten are still lacking.Consequently,a method for evaluating the air-absorbed dose rate of activated tungsten dust was proposed considering soil attenuation.Key parameters including the mass attenuation coefficient and energy absorption build-up factor were determined for the main gamma ray energies of radionuclides within the activated tungsten dust.Additionally,air-absorbed dose rates were calculated by assuming that radioactive sources were located at different soil depths and radii.It was found that a soil depth of 50 cm significantly attenuated the environmental dose by 99.9%,whereas the air-absorbed dose rates within the horizontal distance of 500 cm accounted for 91%of the total dose rate.Therefore,this study underscored the importance of soil attenuation in environmental dose assessments,which must be carefully re-examined for the safety analysis of fusion reactors.
基金supported by the National Science and Technology Major Project,China,the China Scholarship Council(No.202306290109)National Natural Science Foundation of China(Nos.52472456 and 52361165620)。
文摘This paper studies the coupling mechanism between the nonlinear stiffness and damping coefficients of Active Elastic Support/Dry Friction Damper(AESDFD)and rotor system.First,parameters for evaluating the vibration reduction characteristics are proposed to facilitate the design of the AESDFD.To achieve this,the nonlinear friction force is initially represented as equivalent stiffness and damping coefficients,based on the ball-plate friction model.Second,three evaluation parameters—optimal slipping displacement,loss factor,and controllability—are proposed to reveal the vibration reduction characteristics of the AESDFD,alongside determining the optimal normal force.Subsequently,the finite element method,in conjunction with the ball-plate friction model,is introduced to formulate the governing equation of a low-pressure rotor system equipped with AESDFDs.The steady-state responses of the AESDFDs-rotor system are solved using the harmonic balance method combined with an efficient iteration method.Finally,the solutions are validated on the AESDFDs-rotor system both numerically and experimentally.The results indicate that controllability effectively assesses the vibration reduction performance of the AESDFD and is relatively insensitive to variations in low normal force.Away from the critical speed,the AESDFD suppresses vibration by altering the resonance position of the rotor system through its stiffness coefficient.Near the critical speed,vibration reduction is achieved primarily through energy dissipation by the damping coefficient.If the loss factor is less than one,the stiffness coefficient can diminish the vibration reduction effect of the damping coefficient.Notably,the optimal normal force of the AESDFD achieves optimal vibration reduction effect.This study reveals that changes in rotor system unbalance do not affect the vibration reduction characteristics of the AESDFD,with the same upper limit to the vibration reduction effect of the AESDFD.
基金supported by the Deutsche Forschungsgemeinschaft(DFG)through project 429491391(BA 6878/1-1).
文摘Active Flux is a third order accurate numerical method which evolves cell averages and point values at cell interfaces independently.It naturally uses a continuous reconstruction,but is stable when applied to hyperbolic problems.In this work,the Active Flux method is extended for the first time to a nonlinear hyperbolic system of balance laws,namely,to the shallow water equations with bottom topography.We demonstrate how to achieve an Active Flux method that is well-balanced,positivity preserving,and allows for dry states in one spatial dimension.Because of the continuous reconstruction all these properties are achieved using new approaches.To maintain third order accuracy,we also propose a novel high-order approximate evolution operator for the update of the point values.A variety of test problems demonstrates the good performance of the method even in presence of shocks.
文摘The component synthesis active vibration suppression method （CSVS） can be applied to suppress the vibration of flexible systems. By this method, several same or similar time-varying components are arranged according to certain rules along the time axis. The synthesized command can suppress the arbitrary unwanted vibration harmonic while achieving the desired rigid body motion. The number of the components increases rapidly when the number of harmonic vibration is growing. In this article, the CSVS based on zero-placement technique is used to construct the synthesized command to suppress the multi-harmonics simultaneously in the discrete domain. The nature of zero-placement method is to put enough zeros to cancel system poles at necessary points. The designed synthesized command has equal time intervals between each component and which is much easier to be implemented. Using this method, the number of components increases linearly with the increasing of the number of being suppressed harmonics. For the spacecraft with flexible appendages, CSVS based on zero-placement is used to design the time optimal large angle maneuver control strategy. Simulations have verified the validity and superiority of the proposed approach.
基金supported by the‘New Century Outstanding Talent’Scheme of the Ministry of Education of China(Grant No.NCET-07-0135)
文摘A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen （1995） is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.
基金Financial support from the Key Research Program of Chinese Academy of Sciences (Grant No. KZZD-EW-05-01)the NSFC (Grant Nos. 41101008, 41272346)the Youth Talent Team Program of the Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Opening Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (Grant No. SKLGP2011K010)
文摘In this paper, a generalized limit equilibrium method of solving the active earth pressure problem behind a retaining wall is proposed.Differing from other limit equilibrium methods, an arbitrary slip surface shape without any assumptions of pre-defined shapes is needed in the current framework, which is verified to find the most probable failure slip surface. Based on the current computational framework, numerical comparisons with experiment, discrete element method and other methods are carried out. In addition, the influences of the inclination of the wall, the soil cohesion, the angle of the internal friction of the soil, the slope inclination of the backfill soil on the critical pressure coefficient of the soil, the point of application of the resultant earth pressure and the shape of the slip surface are also carefully investigated. The results demonstrate that limit equilibrium solution from predefined slip plane assumption, including Coulomb solution, is a special case of current computational framework. It is well illustrated that the current method is feasible to evaluate the characteristics of earth pressure problem.
基金Project(FRF-AS-10-0058) supported by the Fundamental Research Funds for the Central Universities,China
文摘The behavior of the active layer of material bed within rotary kilns plays a key role in industrial applications.To obtain its influences on industrial process,different regimes of particle motion have been simulated by discrete element method(DEM) in three dimensions under variant rotation speeds,filling degree,based on the background of induration process of iron ore pellets.The influences of the mentioned factors on the maximum thickness of the active layer and the average velocity of particles have been investigated.The average velocity of particles increases with Froude number following the power function over a wide range,and the maximum thickness rises with increasing rotation speed in a way of logarithm.The influence of the filling degree f on the maximum thickness exhibits a good linearity under two classic regimes,but the increasing of the average velocity of the active layer is limited at f=0.4.This basic research highlights the impact of the active layer within rotary kilns,and lays a good foundation for the further investigation in mixing and heat transfer within the particle bed inside rotary kilns.
基金supported by the DOD National Defense Science and Engineering Graduate(NDSEG)Research Fellowshipsupported by the NGA under Contract No.HM04762110003.
文摘Active learning in semi-supervised classification involves introducing additional labels for unlabelled data to improve the accuracy of the underlying classifier.A challenge is to identify which points to label to best improve performance while limiting the number of new labels."Model Change"active learning quantifies the resulting change incurred in the classifier by introducing the additional label(s).We pair this idea with graph-based semi-supervised learning(SSL)methods,that use the spectrum of the graph Laplacian matrix,which can be truncated to avoid prohibitively large computational and storage costs.We consider a family of convex loss functions for which the acquisition function can be efficiently approximated using the Laplace approximation of the posterior distribution.We show a variety of multiclass examples that illustrate improved performance over prior state-of-art.
基金Funded by the National Natural Science Foundation of China (No.50708065)the National High-tech R&D Program(863 Program )(No.2007-AA-11-Z-113)the Key Projects in the Science and Technology Pillar Program of Tianjin(No.11ZCKFSF00300)
文摘In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a specifically designed test setup.The energy attenuation of stress waves was measured by the relative index between the output voltage of sensors and the excitation voltage at the actuator.Based on the experimental results of concrete cube and cylinder specimens,the effect of excitation frequencies,excitation amplitude,wave propagation paths and the curing age on the output signals of sensors are evaluated.The results show that the relative voltage attenuation coefficient RVAC is an effective indicator for measuring the attenuation of stress waves through the interior of concrete.
基金National Natural Science foundation of China,Grant number 59895410
文摘The performance of structures with active variable stiffness (AVS) systems exhibits strong nonlinearity due to the variety with time of the stiffness of each storey unit,in which the AVS system is installed.Hence,the classical dynamic analysis method for linear structures,such as the mode-superposition method,is not applicable to structures with AVS systems.In this paper,an approximate analysis method is proposed for displacement responses of structures with AVS systems.Firstly,an equivalent relationship between single-degree-of-freedom (SDOF) structures equipped with AVS systems and so-called fictitious linear structures is established.Then,an approximate mode-superposition (AMS) method is presented for multi-degree-of-freedom (MDOF) structures equipped with AVS systems.The accuracy of this method is investigated through extensive parametrical study using different types of earthquake excitations,and some modification is made to the method. Numerical calculation results indicate that the modified AMS method is effective for estimating the maximum displacements relative to the ground and the maximum interstorey drifts of MDOF structures equipped with AVS systems.
基金the National Natural Science Foundation of China (No.59975057).
文摘A B-spline active contour model based on finite element method is presented, into which the advantages of a B-spline active contour attributing to its fewer parameters and its smoothness is built accompanied with reduced computational complexity and better numerical stability resulted from the finite element method. In this model, a cubic B-spline segment is taken as an element, and the finite element method is adopted to solve the energy minimization problem of the B-spline active contour, thus to implement image segmentation. Experiment results verify that this method is efficient for B-spline active contour, which attains stable, accurate and faster convergence.
基金financially supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China under Grant No. 2012BAJ22B06
文摘Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.
文摘The depth of upper fault point is the key data for ascertaining the active age of a buried fault on a plain. The difference of depth obtained from same fault may be dozens to several hundred meters when using different geophysical methods. It can result in the absolutely opposite conclusions when judging fault activity. Because of a lack of an artificial earthquake source with wide band and high central frequency, many kinds of methods have to be used together. The higher the frequency of the artificial earthquake wave, electromagnetic wave and sonic wave, the higher the resolution. However the attenuation is also very fast and the exploration depth is very shallow. The reverse is also true. The frequency of artificial seismic waves is in the tens of Hz. Its exploration depth is big and the resolution is poor. The frequency of radar electromagnetic waves is about a million Hz, indicating that the resolving power is better, but the exploration depth is very shallow. However, the acoustic frequency is thousands of Hz, its resolving power is better than that of the artificial earthquake method and the exploration depth is larger than that of the radar method. So it is suitable for extra shallow exploration in the thick deposit strata of the Quaternary. The preliminary results detected using the high frequency acoustic method in extra shallow layers indicates that previous inferences about some fault activity in the eastern part of the North China plain may need to be greatly corrected.
基金supported by the National Natural Science Foundation of China(11172226)
文摘In this paper, the incremental harmonic balance method is employed to solve the periodic solution that a vibration active control system with double time delays generates, and the stability analysis of which is achieved by the Poincare theorem. The system stability regions can be obtained in view of time delay and feedback gain, the variation of which is also studied. It turns out that along with the increase of time delay, the active control system is not always from stable to unstable, and the system can be from stable to unstable state, whereas the system can be from unstable to stable state. The extent that the two times delays impact to the relative magnitude of the two feedback gains. the condition of the well-matched feedback gains. control strategy of time-delayed feedback.
