As a controllable power generation method requiring no energy storage,Ocean Thermal Energy Conversion(OTEC)technology demonstrates characteristics of abundant reserves,low pollution,and round-the-clock stable operatio...As a controllable power generation method requiring no energy storage,Ocean Thermal Energy Conversion(OTEC)technology demonstrates characteristics of abundant reserves,low pollution,and round-the-clock stable operation.The free-standing cold-water pipe(CWP)in the system withstands various complex loads during operation,posing potential failure risks.To reveal the deformation and stress mechanisms of OTEC CWPs,this study first analyzes wave particle velocity and acceleration to determine wave loads at different water depths.Based on the Euler-Bernoulli beam model,a quasi-static load calculation model for OTEC CWPs was established.The governing equations were discretized using the finite difference method,and matrix equations were solved to analyze bending deformation,bending moments,and surface stresses at discrete points along the pipe.Results indicate that water depths within 50 m represent a critical zone where wave particle velocity,acceleration,and wave loads exhibit significant variations in harmonic patterns,while beyond 50 m depth wave loads decrease linearly.Ocean currents and surface wind-driven currents substantially influence the CWP’s lateral displacement.Considering the effect of clump weights,the maximum lateral displacement occurs at 600–800 m below sea level.Utilizing large-wall-thickness high-strength pipes at the top section significantly enhances the structural safety of the CWP system.展开更多
With the rapid economic development and continuous expansion of human activities,forest degradation—characterized by reduced forest stock within the forest including declining carbon storage—poses significant threat...With the rapid economic development and continuous expansion of human activities,forest degradation—characterized by reduced forest stock within the forest including declining carbon storage—poses significant threats to ecosystem stability.Understanding the current status of forest degradation and assessing potential carbon stocks in China are of strategic importance for making forest restoration efforts and enhancing carbon sequestration capacity.In this study,we used the national forest inventory data from 2009 to 2018 to develop a set of standard measures for assessing degraded forests across China,based on five key indicators:forest accumulation growth rate(FAGR),forest recruitment rate(FRR),tree species reduction rate(TSRR),forest canopy cover reduction rate(FCCRR),and forest disaster level(FDL).Additionally,we estimated standing carbon stock,potential carbon stock,and theoretical space to grow by developing a stand growth model,which accounts for stand density across different site classes,to evaluate the restoration potential of degraded forests.The results indicate that degraded forest area in China is 36.15 million hectares,accounting for 20.10% of a total forest area.Standing carbon stock and potential carbon stock of degraded forests in China are 23.93 million tons and 61.90 million tons,respectively.Overall,degraded forest varies significantly across different regions.The results highlight the important trade-offs among environmental factors,policy decisions,and forest conditions,providing a robust foundation for developing measures to enhance forest quality.展开更多
In this paper,inspired by the running motion gait of a cheetah,an H-shaped bionic piezoelectric robot(H-BPR)based on the standing wave principle is proposed and designed.The piezoelectric robot realizes linear motion,...In this paper,inspired by the running motion gait of a cheetah,an H-shaped bionic piezoelectric robot(H-BPR)based on the standing wave principle is proposed and designed.The piezoelectric robot realizes linear motion,turning motion,and turning motion with different radi by the voltage differential driving method.A prototype with a weight of 38 g and dimensions of 150×80×31 mm^(3) was fabricated.Firstly,the dynamics and kinematics of the piezoelectric robot were analyzed to obtain the trajectory of a point at the end of the piezoelectric robot leg.The motion principle of the piezo-electric robot was analyzed,and then the piezoelectric robot's modal analysis and harmonic response analysis were carried out using finite element analysis software.Finally,an experimental setup was built to verify the effectiveness and high efficiency of the robot's motion,and the effects of frequency,voltage,load,and height of the driving leg on the robot's motion performance were discussed.The performance test results show that the piezoelectric robot has a maximum veloc-ity of 66.79 mm/s at an excitation voltage of 320 V and a load capacity of 55 g.In addition,the H-BPR with unequal drive legs has better climbing performance,and the obtained conclusions are informative for selecting leg heights for piezoelectric robots.展开更多
The turbidity maximum zone(TMZ)is a distinctive aquatic environment marked by consistently higher turbidity compared to upstream and downstream section.In the TMZ,physicochemical properties such as intense light limit...The turbidity maximum zone(TMZ)is a distinctive aquatic environment marked by consistently higher turbidity compared to upstream and downstream section.In the TMZ,physicochemical properties such as intense light limitation,abundant nutrients,and rapid salinity shifts play a crucial role in shaping phytoplankton dynamics.The Qiantang River estuary-Hangzhou Bay(QRE-HZB)is a macrotidal estuary system known for its exceptionally high suspended solids concentration.To investigate the impact of TMZ on the standing crop and size structure of phytoplankton in the QRE-HZB,we conducted three cruises in dry,wet,and dry-to-wet transition seasons during 2022-2023,by assessing parameters including size fractionated chlorophyll a(chl a),turbidity,Secchi depth,temperature,salinity,nutrients,and mesozooplankton.Results reveal significant variations in the TMZ and associated environmental factors in different periods,which markedly influenced the phytoplankton chl-a concentration,size structure,and cell activity(pheophytin/chl a).The chl-a concentration was high with micro-phytoplankton predominance in wet season,while nano-phytoplankton dominated in dry season.Within the TMZ,lower chl-a concentrations and pico-chl-a contributions,alongside higher pheophytin/chl-a and micro-chl-a contributions,were observed.The Spearman’s rank correlation and generalized additive model analyses indicated strong correlations of chl-a concentrations with turbidity,nutrients,and mesozooplankton.Redundancy analysis further revealed that salinity,nutrients,and turbidity significantly regulated variations in size structure.Phytoplankton mortality within the TMZ was primarily driven by high turbidity and salinity fluctuations,reflecting the vigorous resuspension and mixing of freshwater and seawater in the QRE-HZB.These findings highlight that the standing crop and size structure of phytoplankton were strongly regulated by the TMZ and associated physicochemical factors in the macrotidal QRE-HZB.展开更多
In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-levelλ-type atomic medium via superposition of asymmetric and symmetric standing wave fields.Our anal...In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-levelλ-type atomic medium via superposition of asymmetric and symmetric standing wave fields.Our analysis provides an understanding of the precise spatial localization of atomic positions at the atomic level,utilizing advanced theoretical approaches and principles of quantum mechanics.The dynamical behavior of a three-level atomic system is thoroughly analyzed using the density matrix formalism within the realm of quantum mechanics.A theoretical approach is constructed to describe the interaction between the system and external fields,specifically a control field and a probe field.The absorption spectrum of the probe field is thoroughly examined to clarify the spatial localization of the atom within the proposed configuration.A theoretical investigation found that symmetric and asymmetric superposition phenomena significantly influence the localized peaks within a two-dimensional spatial domain.Specifically,the emergence of one and two sharp localized peaks was observed within a one-wavelength domain.We observed notable influences of the intensity of the control field,probe field detuning and decay rates on atomic localization.Ultimately,we have achieved an unprecedented level of ultrahigh resolution and precision in localizing an atom within an area smaller thanλ/35×λ/35.These findings hold promise for potential applications in fields such as Bose-Einstein condensation,nanolithography,laser cooling,trapping of neutral atoms and the measurement of center-of-mass wave functions.展开更多
Panchen Rinpoche Concludes Xizang Tour Panchen Erdeni Chos-kyi rGyal-po,a member of the Standing Committee of the National Committee of the Chinese People's Political Consultative Conference and vice president of ...Panchen Rinpoche Concludes Xizang Tour Panchen Erdeni Chos-kyi rGyal-po,a member of the Standing Committee of the National Committee of the Chinese People's Political Consultative Conference and vice president of the Buddhist Association of China,flew back to Beijing on Dec.23 of 2025 after completing a six-month tour of southwest China's Xizang Autonomous Region,during which he performed regular duties,Buddhist rituals and social activities.展开更多
A gathering was held on December 9,2025,at theTashilhunpo Monastery in Xigaze,southwest China's Xizang Autonomous Region,to commemorate the 30th anniversary of the enthronement of Panchen Erdeni Chos-kyi rGyal-po....A gathering was held on December 9,2025,at theTashilhunpo Monastery in Xigaze,southwest China's Xizang Autonomous Region,to commemorate the 30th anniversary of the enthronement of Panchen Erdeni Chos-kyi rGyal-po.Panchen Rinpoche is a member of the Standing Committee of the National Committee of the Chinese People's Political Consultative Conference and vice president of the Buddhist Association of China.The Tashilhunpo Monastery has been Panchen Rinpoche's traditional seat.展开更多
The Hainan FTP is a game changer,and those who seize the opportunities it offers early will be in an advantageous position As it provides a vital new model for China’s international trade and logistics,the Hainan Fre...The Hainan FTP is a game changer,and those who seize the opportunities it offers early will be in an advantageous position As it provides a vital new model for China’s international trade and logistics,the Hainan Free Trade Port(FTP)stands out among similar opening-up initiatives.展开更多
Stand age plays a crucial role in forest biomass estimation and carbon cycle modeling.Assessing the uncertainty of stand age prediction models and identifying the key driving factors in the modeling process have becom...Stand age plays a crucial role in forest biomass estimation and carbon cycle modeling.Assessing the uncertainty of stand age prediction models and identifying the key driving factors in the modeling process have become major challenges in forestry research.In this study,we selected the Shaanxi-Gansu-Ningxia region of Northeast China as the research area and utilized multi-source datasets from the summer of 2019 to extract information on spectral,textural,climatic,water balance,and stand characteristics.By integrating the Random Forest(RF)model with Monte Carlo(MC)simulation,we constructed six regression models based on different combina-tions of features and evaluated the uncertainty of each model.Furthermore,we investigated the driving factors influencing stand age modeling by analyzing the effects of different types of features on age inversion.Model performance and accuracy were assessed using the root mean square error(RMSE),mean absolute error(MAE),and the coefficient of determination(R^(2)),while the relative root mean square error(rRMSE)was employed to quantify model uncertainty.The results indicate that the scenarios with more obvious improve-ment in accuracy and effective reduction in uncertainty were Scenario 3 with the inclusion of climate and water balance information(RMSE=25.54 yr,MAE=18.03 yr,R^(2)=0.51,rRMSE=19.17%)and Scenario 5 with the inclusion of stand characterization informa-tion(RMSE=18.47 yr,MAE=13.05 yr,R^(2)=0.74,rRMSE=16.99%).Scenario 6,incorporating all feature types,achieved the highest accuracy(RMSE=17.60 yr,MAE=12.06 yr,R^(2)=0.77,rRMSE=14.19%).In this study,elevation,minimum temperature,and diameter at breast height(DBH)emerged as the key drivers of stand-age modeling.The proposed method can be used to identify drivers and to quantify uncertainty in stand-age estimation,providing a useful reference for improving model accuracy and uncertainty assessment.展开更多
A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration character...A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.展开更多
Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach ...Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number.Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge(upper limit)to the angle that a Chapman-Jouguet(CJ)detonation occurs(lower limit).For pathological detonation cases,however,the CJ detonation cannot be achieved,and thus the lower limit of the standing window of ODW should be revisited.In present study,two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation,that is,the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process,have been used for studying standing behavior of ODW.The steady detonation polar analysis of ODW is carried out for both reaction systems.The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW.Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics,Mach number of incoming flow and heat effect of reactions.It is found that the standing window of ODW is determined by the specific heat ratio,the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow,regardless of whether the detonation is pathological or not.展开更多
The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section ...The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm, excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM （full width at half maximum of density distribution） is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3：9：10.展开更多
It was attempted to enhance and accelerate the separation of oxidation inclusions from magnesium alloy melt by virtue of ultrasonic agglomeration technology.In order to investigate the feasibility and effectiveness of...It was attempted to enhance and accelerate the separation of oxidation inclusions from magnesium alloy melt by virtue of ultrasonic agglomeration technology.In order to investigate the feasibility and effectiveness of standing waves for ultrasonic purification of magnesium alloy melt,numerical simulation and relevant experiment were carried out.The numerical simulation was broken into two main aspects.On one hand,the ultrasonic field propagations within the cells with various shapes were characterized by numerical solutions of the wave equation and with a careful choice of geometry a nearly idealized standing wave field was finally obtained.On the other hand,within such a standing wave field the agglomeration behavior of oxidation inclusions in magnesium alloy melt was analyzed and discussed.The agglomeration time and agglomeration position of oxidation inclusions were predicted with numerical simulation method.The results show that the oxidation inclusions whose apparent densities are close to the density of the melt can agglomerate at wave nodes in a short time which to a great extent enhances and accelerates the separation of oxidation inclusions from magnesium alloy melt.展开更多
Estimating the volume growth of forest ecosystems accurately is important for understanding carbon sequestration and achieving carbon neutrality goals.However,the key environmental factors affecting volume growth diff...Estimating the volume growth of forest ecosystems accurately is important for understanding carbon sequestration and achieving carbon neutrality goals.However,the key environmental factors affecting volume growth differ across various scales and plant functional types.This study was,therefore,conducted to estimate the volume growth of Larix and Quercus forests based on national-scale forestry inventory data in China and its influencing factors using random forest algorithms.The results showed that the model performances of volume growth in natural forests(R^(2)=0.65 for Larix and 0.66 for Quercus,respectively)were better than those in planted forests(R^(2)=0.44 for Larix and 0.40 for Quercus,respectively).In both natural and planted forests,the stand age showed a strong relative importance for volume growth(8.6%–66.2%),while the edaphic and climatic variables had a limited relative importance(<6.0%).The relationship between stand age and volume growth was unimodal in natural forests and linear increase in planted Quercus forests.And the specific locations(i.e.,altitude and aspect)of sampling plots exhibited high relative importance for volume growth in planted forests(4.1%–18.2%).Altitude positively affected volume growth in planted Larix forests but controlled volume growth negatively in planted Quercus forests.Similarly,the effects of other environmental factors on volume growth also differed in both stand origins(planted versus natural)and plant functional types(Larix versus Quercus).These results highlighted that the stand age was the most important predictor for volume growth and there were diverse effects of environmental factors on volume growth among stand origins and plant functional types.Our findings will provide a good framework for site-specific recommendations regarding the management practices necessary to maintain the volume growth in China's forest ecosystems.展开更多
This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large ruptur...This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large rupture strain and fibre-reinforced polymer(FRP)with high strength-to-weight ratio.To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular(PFT)standing support,a series of compression tests were conducted.Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket.Compression tests were also conducted on cementitious grout-filled PVC tubular(PT)support and cementitious grout-filled FRP tubular(FT)support.These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability(>20%of the overall height of the support).In addition,the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support.Furthermore,using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support.These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents(i.e.PVC and FRP)and infill material.展开更多
Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which ca...Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which can be used to calculate the wave particle velocity and wave pressure, is suitable to the complicated topography whose relative depth (d/lambda(0), ratio of the characteristic water depth to the characteristic wavelength in deep-water) is equal to or smaller than one. The governing equations are discretized with the improved 2-D Crank-Nicolson method in which the first-order derivatives are corrected by Taylor series expansion, And the general boundary conditions with an arbitrary reflection coefficient and phase shift are adopted in the model. The surface elevation, horizontal and vertical velocity components and wave pressure of standing waves are numerically calculated. The results show that the numerical model can effectively simulate the complicated standing waves, and the general boundary conditions possess good adaptability.展开更多
Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstan...Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves(SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation.This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.展开更多
In this paper bottom scours in front of vertical breakwaters by standing waves are systematically investigated, the scouring patterns, criterion for differentiating the scouring patterns and scouring mechanism are dis...In this paper bottom scours in front of vertical breakwaters by standing waves are systematically investigated, the scouring patterns, criterion for differentiating the scouring patterns and scouring mechanism are discussed ; a formula of maximum depth of scouring trough considering sediment size is given; and influence of mound foundation on bottom scours is investigated.展开更多
We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach.An expression is derived for the radiation force on a multilayered spher...We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach.An expression is derived for the radiation force on a multilayered sphere centered on the axis of a Gaussian standing wave propagating in an ideal fluid,The effects of the sound absorption of the materials and sound wave on acoustic radiation force of a multilayered sphere immersed in water are analyzed,with particular emphasis on the shell thickness of every layer,and the width of the Gaussian beam.The results reveal that the existence of particle trapping behavior depends on the choice of the non-dimensional frequency ka,as well as the shell thickness of each layer.This study provides a theoretical basis for the development of acoustical tweezers in a Gaussian standing wave,which may benefit the improvement and development of acoustic control technology,such as trapping,sorting,and assembling a cell,and drug delivery applications.展开更多
For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. ...For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. In this paper, a coupling calculation is carried out based on a practical model for the loop antenna. The ion cyclotron wave coupling performance depends greatly on the antenna current propagation constant and the phase of standing wave. For a small antenna-current-propagation constant, the antenna coupling performance is more sensitive to a π/2 change in the phase of standing wave.展开更多
基金funded by Nansha District Science and Technology Project(Grant Number.2024ZD008)funded by China Geological Survey(Grant number:No.DD20230066,DD20242659).
文摘As a controllable power generation method requiring no energy storage,Ocean Thermal Energy Conversion(OTEC)technology demonstrates characteristics of abundant reserves,low pollution,and round-the-clock stable operation.The free-standing cold-water pipe(CWP)in the system withstands various complex loads during operation,posing potential failure risks.To reveal the deformation and stress mechanisms of OTEC CWPs,this study first analyzes wave particle velocity and acceleration to determine wave loads at different water depths.Based on the Euler-Bernoulli beam model,a quasi-static load calculation model for OTEC CWPs was established.The governing equations were discretized using the finite difference method,and matrix equations were solved to analyze bending deformation,bending moments,and surface stresses at discrete points along the pipe.Results indicate that water depths within 50 m represent a critical zone where wave particle velocity,acceleration,and wave loads exhibit significant variations in harmonic patterns,while beyond 50 m depth wave loads decrease linearly.Ocean currents and surface wind-driven currents substantially influence the CWP’s lateral displacement.Considering the effect of clump weights,the maximum lateral displacement occurs at 600–800 m below sea level.Utilizing large-wall-thickness high-strength pipes at the top section significantly enhances the structural safety of the CWP system.
基金supported by National Key Research and Development Program of China(No.2021YFD2200405(S.R.L.))Natural Science Foundation of China(Grant No.31971653).
文摘With the rapid economic development and continuous expansion of human activities,forest degradation—characterized by reduced forest stock within the forest including declining carbon storage—poses significant threats to ecosystem stability.Understanding the current status of forest degradation and assessing potential carbon stocks in China are of strategic importance for making forest restoration efforts and enhancing carbon sequestration capacity.In this study,we used the national forest inventory data from 2009 to 2018 to develop a set of standard measures for assessing degraded forests across China,based on five key indicators:forest accumulation growth rate(FAGR),forest recruitment rate(FRR),tree species reduction rate(TSRR),forest canopy cover reduction rate(FCCRR),and forest disaster level(FDL).Additionally,we estimated standing carbon stock,potential carbon stock,and theoretical space to grow by developing a stand growth model,which accounts for stand density across different site classes,to evaluate the restoration potential of degraded forests.The results indicate that degraded forest area in China is 36.15 million hectares,accounting for 20.10% of a total forest area.Standing carbon stock and potential carbon stock of degraded forests in China are 23.93 million tons and 61.90 million tons,respectively.Overall,degraded forest varies significantly across different regions.The results highlight the important trade-offs among environmental factors,policy decisions,and forest conditions,providing a robust foundation for developing measures to enhance forest quality.
基金supported by the National Natural Science Foundation of China(No.12372005)the Aeronautical Science Foundation of China(No.ASFC-2024Z070050001)the Natural Science Foundation of Liaoning Province(2024-MSBA-32).
文摘In this paper,inspired by the running motion gait of a cheetah,an H-shaped bionic piezoelectric robot(H-BPR)based on the standing wave principle is proposed and designed.The piezoelectric robot realizes linear motion,turning motion,and turning motion with different radi by the voltage differential driving method.A prototype with a weight of 38 g and dimensions of 150×80×31 mm^(3) was fabricated.Firstly,the dynamics and kinematics of the piezoelectric robot were analyzed to obtain the trajectory of a point at the end of the piezoelectric robot leg.The motion principle of the piezo-electric robot was analyzed,and then the piezoelectric robot's modal analysis and harmonic response analysis were carried out using finite element analysis software.Finally,an experimental setup was built to verify the effectiveness and high efficiency of the robot's motion,and the effects of frequency,voltage,load,and height of the driving leg on the robot's motion performance were discussed.The performance test results show that the piezoelectric robot has a maximum veloc-ity of 66.79 mm/s at an excitation voltage of 320 V and a load capacity of 55 g.In addition,the H-BPR with unequal drive legs has better climbing performance,and the obtained conclusions are informative for selecting leg heights for piezoelectric robots.
基金Supported by the National Key Research and Development Program of China(No.2021 YFC 3101702)the Key R&D Program of Zhejiang(No.2022 C 03044)+2 种基金the Scientific Research Fund of the Second Institute of Oceanography,MNR(No.JG 1521)the Project of State Key Laboratory of Satellite Ocean Environment Dynamics,Second Institute of Oceanography(No.SOEDZZ 2202)the National Program on Global Change and Air-Sea Interaction(Phase Ⅱ)-Hypoxia and Acidification Monitoring and Warning Project in the Changjiang River estuary,and Long-term Observation and Research Plan in the Changjiang River estuary and Adjacent East China Sea(LORCE)Project(No.SZ 2001)。
文摘The turbidity maximum zone(TMZ)is a distinctive aquatic environment marked by consistently higher turbidity compared to upstream and downstream section.In the TMZ,physicochemical properties such as intense light limitation,abundant nutrients,and rapid salinity shifts play a crucial role in shaping phytoplankton dynamics.The Qiantang River estuary-Hangzhou Bay(QRE-HZB)is a macrotidal estuary system known for its exceptionally high suspended solids concentration.To investigate the impact of TMZ on the standing crop and size structure of phytoplankton in the QRE-HZB,we conducted three cruises in dry,wet,and dry-to-wet transition seasons during 2022-2023,by assessing parameters including size fractionated chlorophyll a(chl a),turbidity,Secchi depth,temperature,salinity,nutrients,and mesozooplankton.Results reveal significant variations in the TMZ and associated environmental factors in different periods,which markedly influenced the phytoplankton chl-a concentration,size structure,and cell activity(pheophytin/chl a).The chl-a concentration was high with micro-phytoplankton predominance in wet season,while nano-phytoplankton dominated in dry season.Within the TMZ,lower chl-a concentrations and pico-chl-a contributions,alongside higher pheophytin/chl-a and micro-chl-a contributions,were observed.The Spearman’s rank correlation and generalized additive model analyses indicated strong correlations of chl-a concentrations with turbidity,nutrients,and mesozooplankton.Redundancy analysis further revealed that salinity,nutrients,and turbidity significantly regulated variations in size structure.Phytoplankton mortality within the TMZ was primarily driven by high turbidity and salinity fluctuations,reflecting the vigorous resuspension and mixing of freshwater and seawater in the QRE-HZB.These findings highlight that the standing crop and size structure of phytoplankton were strongly regulated by the TMZ and associated physicochemical factors in the macrotidal QRE-HZB.
文摘In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-levelλ-type atomic medium via superposition of asymmetric and symmetric standing wave fields.Our analysis provides an understanding of the precise spatial localization of atomic positions at the atomic level,utilizing advanced theoretical approaches and principles of quantum mechanics.The dynamical behavior of a three-level atomic system is thoroughly analyzed using the density matrix formalism within the realm of quantum mechanics.A theoretical approach is constructed to describe the interaction between the system and external fields,specifically a control field and a probe field.The absorption spectrum of the probe field is thoroughly examined to clarify the spatial localization of the atom within the proposed configuration.A theoretical investigation found that symmetric and asymmetric superposition phenomena significantly influence the localized peaks within a two-dimensional spatial domain.Specifically,the emergence of one and two sharp localized peaks was observed within a one-wavelength domain.We observed notable influences of the intensity of the control field,probe field detuning and decay rates on atomic localization.Ultimately,we have achieved an unprecedented level of ultrahigh resolution and precision in localizing an atom within an area smaller thanλ/35×λ/35.These findings hold promise for potential applications in fields such as Bose-Einstein condensation,nanolithography,laser cooling,trapping of neutral atoms and the measurement of center-of-mass wave functions.
文摘Panchen Rinpoche Concludes Xizang Tour Panchen Erdeni Chos-kyi rGyal-po,a member of the Standing Committee of the National Committee of the Chinese People's Political Consultative Conference and vice president of the Buddhist Association of China,flew back to Beijing on Dec.23 of 2025 after completing a six-month tour of southwest China's Xizang Autonomous Region,during which he performed regular duties,Buddhist rituals and social activities.
文摘A gathering was held on December 9,2025,at theTashilhunpo Monastery in Xigaze,southwest China's Xizang Autonomous Region,to commemorate the 30th anniversary of the enthronement of Panchen Erdeni Chos-kyi rGyal-po.Panchen Rinpoche is a member of the Standing Committee of the National Committee of the Chinese People's Political Consultative Conference and vice president of the Buddhist Association of China.The Tashilhunpo Monastery has been Panchen Rinpoche's traditional seat.
文摘The Hainan FTP is a game changer,and those who seize the opportunities it offers early will be in an advantageous position As it provides a vital new model for China’s international trade and logistics,the Hainan Free Trade Port(FTP)stands out among similar opening-up initiatives.
基金Under the auspices of the Natural Science Foundation of China(No.32371875,32001249)。
文摘Stand age plays a crucial role in forest biomass estimation and carbon cycle modeling.Assessing the uncertainty of stand age prediction models and identifying the key driving factors in the modeling process have become major challenges in forestry research.In this study,we selected the Shaanxi-Gansu-Ningxia region of Northeast China as the research area and utilized multi-source datasets from the summer of 2019 to extract information on spectral,textural,climatic,water balance,and stand characteristics.By integrating the Random Forest(RF)model with Monte Carlo(MC)simulation,we constructed six regression models based on different combina-tions of features and evaluated the uncertainty of each model.Furthermore,we investigated the driving factors influencing stand age modeling by analyzing the effects of different types of features on age inversion.Model performance and accuracy were assessed using the root mean square error(RMSE),mean absolute error(MAE),and the coefficient of determination(R^(2)),while the relative root mean square error(rRMSE)was employed to quantify model uncertainty.The results indicate that the scenarios with more obvious improve-ment in accuracy and effective reduction in uncertainty were Scenario 3 with the inclusion of climate and water balance information(RMSE=25.54 yr,MAE=18.03 yr,R^(2)=0.51,rRMSE=19.17%)and Scenario 5 with the inclusion of stand characterization informa-tion(RMSE=18.47 yr,MAE=13.05 yr,R^(2)=0.74,rRMSE=16.99%).Scenario 6,incorporating all feature types,achieved the highest accuracy(RMSE=17.60 yr,MAE=12.06 yr,R^(2)=0.77,rRMSE=14.19%).In this study,elevation,minimum temperature,and diameter at breast height(DBH)emerged as the key drivers of stand-age modeling.The proposed method can be used to identify drivers and to quantify uncertainty in stand-age estimation,providing a useful reference for improving model accuracy and uncertainty assessment.
基金Funded by the National Basic Research Program (973 program) (No. 2011CB707602)the Digital Manufacturing Equipment and Technology National Key Laboratory,Huazhong University of Science and Technology (No. DMETKF2009002)National Sciences Foundation-Guangdong Natural Science Foundation,China (No.U0934004)
文摘A contact model for describing the contact mechanics between the stator and slider of the standing wave linear ultrasonic motor was presented. The proposed model starts from the assumption that the vibration characteristics of the stator is not affected by the contact process. A modified friction models was used to analyze the contact problems. Firstly, the dynamic normal contact force, interface friction force, and steady-state characteristics were analyzed. Secondly, the influences of the contact layer material, the dynamic characteristics of the stator, and the pre-load on motor performance were simulated. Finally, to validate the contact model, a linear ultrasonic motor based on in-plane modes was used as an example. The corresponding results show that a set of simulation of motor performances based on the proposed contact mechanism is in good agreement with experimental results. This model is helpful to understanding the operation principle of the standing wave linear motor and thus contributes to the design of these types of motor.
基金co-supported by the National Natural Science Foundation of China(No.11872213)the Open Fund of Key Laboratory of Transient Physics,NJUST(No.6142604180205)the Opening Project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology)(No.KFJJ17-11M)。
文摘Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number.Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge(upper limit)to the angle that a Chapman-Jouguet(CJ)detonation occurs(lower limit).For pathological detonation cases,however,the CJ detonation cannot be achieved,and thus the lower limit of the standing window of ODW should be revisited.In present study,two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation,that is,the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process,have been used for studying standing behavior of ODW.The steady detonation polar analysis of ODW is carried out for both reaction systems.The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW.Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics,Mach number of incoming flow and heat effect of reactions.It is found that the standing window of ODW is determined by the specific heat ratio,the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow,regardless of whether the detonation is pathological or not.
文摘The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm, excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM （full width at half maximum of density distribution） is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3：9：10.
基金Projects(2007CB613701,2007CB613702)supported by the National Basic Research Program of ChinaProjects(50974037,50904018)supported by the National Natural Science Foundation of ChinaProject(NCET-08-0098)supported by the Program for New Century Excellent Talents in University of China
文摘It was attempted to enhance and accelerate the separation of oxidation inclusions from magnesium alloy melt by virtue of ultrasonic agglomeration technology.In order to investigate the feasibility and effectiveness of standing waves for ultrasonic purification of magnesium alloy melt,numerical simulation and relevant experiment were carried out.The numerical simulation was broken into two main aspects.On one hand,the ultrasonic field propagations within the cells with various shapes were characterized by numerical solutions of the wave equation and with a careful choice of geometry a nearly idealized standing wave field was finally obtained.On the other hand,within such a standing wave field the agglomeration behavior of oxidation inclusions in magnesium alloy melt was analyzed and discussed.The agglomeration time and agglomeration position of oxidation inclusions were predicted with numerical simulation method.The results show that the oxidation inclusions whose apparent densities are close to the density of the melt can agglomerate at wave nodes in a short time which to a great extent enhances and accelerates the separation of oxidation inclusions from magnesium alloy melt.
基金supported by the Major Program of the National Natural Science Foundation of China(No.32192434)the Fundamental Research Funds of Chinese Academy of Forestry(No.CAFYBB2019ZD001)the National Key Research and Development Program of China(2016YFD060020602).
文摘Estimating the volume growth of forest ecosystems accurately is important for understanding carbon sequestration and achieving carbon neutrality goals.However,the key environmental factors affecting volume growth differ across various scales and plant functional types.This study was,therefore,conducted to estimate the volume growth of Larix and Quercus forests based on national-scale forestry inventory data in China and its influencing factors using random forest algorithms.The results showed that the model performances of volume growth in natural forests(R^(2)=0.65 for Larix and 0.66 for Quercus,respectively)were better than those in planted forests(R^(2)=0.44 for Larix and 0.40 for Quercus,respectively).In both natural and planted forests,the stand age showed a strong relative importance for volume growth(8.6%–66.2%),while the edaphic and climatic variables had a limited relative importance(<6.0%).The relationship between stand age and volume growth was unimodal in natural forests and linear increase in planted Quercus forests.And the specific locations(i.e.,altitude and aspect)of sampling plots exhibited high relative importance for volume growth in planted forests(4.1%–18.2%).Altitude positively affected volume growth in planted Larix forests but controlled volume growth negatively in planted Quercus forests.Similarly,the effects of other environmental factors on volume growth also differed in both stand origins(planted versus natural)and plant functional types(Larix versus Quercus).These results highlighted that the stand age was the most important predictor for volume growth and there were diverse effects of environmental factors on volume growth among stand origins and plant functional types.Our findings will provide a good framework for site-specific recommendations regarding the management practices necessary to maintain the volume growth in China's forest ecosystems.
基金supported by the Australia government through the Australian Research Council’s Industrial Transformation Research Hub for nanoscience based construction material manufacturing(IH150100006)the Australia Coal Industry’s Research Program(C28068)。
文摘This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large rupture strain and fibre-reinforced polymer(FRP)with high strength-to-weight ratio.To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular(PFT)standing support,a series of compression tests were conducted.Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket.Compression tests were also conducted on cementitious grout-filled PVC tubular(PT)support and cementitious grout-filled FRP tubular(FT)support.These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability(>20%of the overall height of the support).In addition,the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support.Furthermore,using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support.These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents(i.e.PVC and FRP)and infill material.
基金This subject was partly supported by the National Excellent Youth Foundation of China (Grant No. 49825161)
文摘Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which can be used to calculate the wave particle velocity and wave pressure, is suitable to the complicated topography whose relative depth (d/lambda(0), ratio of the characteristic water depth to the characteristic wavelength in deep-water) is equal to or smaller than one. The governing equations are discretized with the improved 2-D Crank-Nicolson method in which the first-order derivatives are corrected by Taylor series expansion, And the general boundary conditions with an arbitrary reflection coefficient and phase shift are adopted in the model. The surface elevation, horizontal and vertical velocity components and wave pressure of standing waves are numerically calculated. The results show that the numerical model can effectively simulate the complicated standing waves, and the general boundary conditions possess good adaptability.
基金supported by the National Key R&D Program of China(No.2017YFE0301201)National Natural Science Foundation of China(No.11975038)the funding support from the State Key Laboratory of Nuclear Physics and Technology,Peking University(No.NPT2021ZZ03)。
文摘Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves(SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation.This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.
文摘In this paper bottom scours in front of vertical breakwaters by standing waves are systematically investigated, the scouring patterns, criterion for differentiating the scouring patterns and scouring mechanism are discussed ; a formula of maximum depth of scouring trough considering sediment size is given; and influence of mound foundation on bottom scours is investigated.
基金Project supported by National Key R&D Program of China(Grant No.2016YFF0203000)the National Natural Science Foundation of China(Grant Nos.11774167 and 61571222)+2 种基金the Fundamental Research Funds for the Central Universities of China(Grant No.020414380001)the Key Laboratory of Underwater Acoustic Environment,Institute of Acoustics,Chinese Academy of Sciences(Grant No.SSHJ-KFKT-1701)the AQSIQ Technology R&D Program of China(Grant No.2017QK125)
文摘We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach.An expression is derived for the radiation force on a multilayered sphere centered on the axis of a Gaussian standing wave propagating in an ideal fluid,The effects of the sound absorption of the materials and sound wave on acoustic radiation force of a multilayered sphere immersed in water are analyzed,with particular emphasis on the shell thickness of every layer,and the width of the Gaussian beam.The results reveal that the existence of particle trapping behavior depends on the choice of the non-dimensional frequency ka,as well as the shell thickness of each layer.This study provides a theoretical basis for the development of acoustical tweezers in a Gaussian standing wave,which may benefit the improvement and development of acoustic control technology,such as trapping,sorting,and assembling a cell,and drug delivery applications.
文摘For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. In this paper, a coupling calculation is carried out based on a practical model for the loop antenna. The ion cyclotron wave coupling performance depends greatly on the antenna current propagation constant and the phase of standing wave. For a small antenna-current-propagation constant, the antenna coupling performance is more sensitive to a π/2 change in the phase of standing wave.
