This study investigates the relationship between atmospheric stratification (i.e., static stability given by N^(2)) and the vertical energy transfer of stationary planetary waves, and further illustrates the underlyin...This study investigates the relationship between atmospheric stratification (i.e., static stability given by N^(2)) and the vertical energy transfer of stationary planetary waves, and further illustrates the underlying physical mechanism. Specifically, for the simplified case of constant stratospheric N^(2), the refractive index square of planetary waves has a theoretical tendency to increase first and then decrease with an increased N^(2), whereas the group velocity weakens. Mechanistically, this behavior can be understood as an intensified suppression of vertical isentropic surface displacement caused by meridional heat transport of planetary waves under strong N^(2) conditions. Observational analysis corroborates this finding, demonstrating a reduction in the vertical-propagation velocity of waves with increased N^(2). A linear, quasi- geostrophic, mid-latitude beta-plane model with a constant background westerly wind and a prescribed N^(2) applicable to the stratosphere is used to obtain analytic solutions. In this model, the planetary waves are initiated by steady energy influx from the lower boundary. The analysis indicates that under strong N^(2) conditions, the amplitude of planetary waves can be sufficiently increased by the effective energy convergence due to the slowing vertical energy transfer, resulting in a streamfunction response in this model that contains more energy. For N^(2) with a quasi-linear vertical variation, the results bear a resemblance to the constant case, except that the wave amplitude and oscillating frequency show some vertical variations.展开更多
In a Nature Physics report published in late September 2024[1],a team of scientists and engineers at Sandia National Laboratories(Albuquerque,NM,USA)described the results of a laboratory experiment showing that a nucl...In a Nature Physics report published in late September 2024[1],a team of scientists and engineers at Sandia National Laboratories(Albuquerque,NM,USA)described the results of a laboratory experiment showing that a nuclear blast could create a burst of X-rays powerful enough to change the path of a large asteroid that might one day be on a collision course with Earth.展开更多
The metamaterial based on external meshing gears(MEG)is designed based on the principle of external meshing gear transmission.Based on the meshing transmission principle of external meshing gears and planetary gear tr...The metamaterial based on external meshing gears(MEG)is designed based on the principle of external meshing gear transmission.Based on the meshing transmission principle of external meshing gears and planetary gear trains,the internal and external gear rings are designed.Based on the internal and external gear rings,the metamaterial based on inner and outer planetary gear trains(MIP)is designed to study the shear modulus,Young's modulus,and amplitude-frequency characteristics of the metamaterial based on gears at different angles.The effects of the number of planetary gears on the physical characteristics of the MIP are studied.The results show that the MEG can be continuously adjusted by adjusting the shear modulus and Young's modulus due to its meshing characteristics.With the same number of gears,the adjustment range of the MIP is larger than the adjustment range of the MEG.When the number of planetary gears increases,the adjustment range of the MIP decreases.Moreover,when the metamaterial based on gears rotates,the harmonic response changes with the change of the angle.展开更多
This paper introduces a hybrid multi-objective optimization algorithm,designated HMODESFO,which amalgamates the exploratory prowess of Differential Evolution(DE)with the rapid convergence attributes of the Sailfish Op...This paper introduces a hybrid multi-objective optimization algorithm,designated HMODESFO,which amalgamates the exploratory prowess of Differential Evolution(DE)with the rapid convergence attributes of the Sailfish Optimization(SFO)algorithm.The primary objective is to address multi-objective optimization challenges within mechanical engineering,with a specific emphasis on planetary gearbox optimization.The algorithm is equipped with the ability to dynamically select the optimal mutation operator,contingent upon an adaptive normalized population spacing parameter.The efficacy of HMODESFO has been substantiated through rigorous validation against estab-lished industry benchmarks,including a suite of Zitzler-Deb-Thiele(ZDT)and Zeb-Thiele-Laumanns-Zitzler(DTLZ)problems,where it exhibited superior performance.The outcomes underscore the algorithm’s markedly enhanced optimization capabilities relative to existing methods,particularly in tackling highly intricate multi-objective planetary gearbox optimization problems.Additionally,the performance of HMODESFO is evaluated against selected well-known mechanical engineering test problems,further accentuating its adeptness in resolving complex optimization challenges within this domain.展开更多
The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state.The coupling effect of tooth surface roughness and lubrication on meshing character...The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state.The coupling effect of tooth surface roughness and lubrication on meshing characteristics of planetary gear is studied.An improved three-dimensional(3 D)anisotropic tooth surface roughness fractal model is proposed based on the experimental parameters.Considering asperity contact and elastohydrodynamic lubrication(EHL),the contact load and flexibility deformation of the tooth surface are derived,and the deformation compatibility equation of the 3 D loaded tooth contact analysis(3 D-LTCA)method is improved.The asperity of the tooth surface changes the system from EHL to mixed lubrication and reduces the stiffness of the oil film.Compared with the sun planet gear,the asperity has a greater effect on the meshing characteristics of the ring-planet gear.Compared with the proposed method,the comprehensive stiffness obtained by the traditional calculation method considering the lubrication effect is smaller,especially for the ring-planet gear.Compared with roughness,speed and viscosity,the meshing characteristics of planetary gears are most sensitive to torque.展开更多
By applying the convolution-based Hilbert transform in the zonal direction on six-hourly streamfunction fields at200 h Pa, we present the climatology and trends of the local wave period, and zonal and meridional phase...By applying the convolution-based Hilbert transform in the zonal direction on six-hourly streamfunction fields at200 h Pa, we present the climatology and trends of the local wave period, and zonal and meridional phase speeds, of Rossby waves over the globe during the solstice seasons of 1979–2023. While partly similar to and inspired by Fragkoulidis and Wirth(2020), our method differs in its ability to cover both planetary-scale and synoptic-scale waves over not only the extratropics, but also the tropics and subtropics. Based on a physically reasonable global distribution of wave periods, our key new finding is a robust prolonging of wave periods over most regions of the tropics and subtropics during both solstice seasons of 1979–2023, except for the tropical Atlantic, which experiences a shortened wave period during June–July–August of 1979–2022. Both the prolonging and shortening of wave periods are mainly associated with the changes in planetary-scale waves. Regionally varying trends of the zonal phase speed(Cpx) of synoptic waves are consistent in sign with, but smaller in magnitude than, the trends of local zonal wind, confirming the conclusion of Wu and Lu(2023)on the opposite effects of zonal wind and the meridional gradient of potential vorticity on Cpx. Meanwhile, the Cpx trends of planetary-scale waves are relatively weak, and do not exhibit a robust relation with the trend of zonal wind. These new results are helpful toward better understanding the changes in atmospheric waves and extreme events under global warming.展开更多
Urban agriculture is gaining recognition for its potential contributions to environmental resilience and climate change adaptation,providing advantages such as urban greening,reduced heat island effects,and decreased ...Urban agriculture is gaining recognition for its potential contributions to environmental resilience and climate change adaptation,providing advantages such as urban greening,reduced heat island effects,and decreased air pollution.Moreover,it indirectly supports communities during weather events and natural disasters,ensuring food security and fostering community cohesion.However,concerns about planetary health risks persist in highly urbanized and climate-affected areas.Employing electronic databases such as Web of Science and PubMed and adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines,we identified 55 relevant papers to comprehend the planetary health risks associated with urban agriculture,The literature review identified five distinct health risks related to urban agriculture:(1)trace metal risks in urban farms;(2)health risks associated with wastewater irrigation;(3)zoonotic risks;(4)other health risks;and(5)social and economic risks.The study highlights that urban agriculture,while emphasizing environmental benefits,particularly raises concerns about trace metal bioaccumulation in soil and vegetables,posing health risks for populations.Other well studied risks included wastewater irrigation and backyard livestock farming.The main limitations in the available literature were in studying infectious diseases and antibiotic resistance associated with urban agriculture.展开更多
Knowledge of the mechanical behavior of planetary rocks is indispensable for space explorations.The scarcity of pristine samples and the irregular shapes of planetary meteorites make it difficult to obtain representat...Knowledge of the mechanical behavior of planetary rocks is indispensable for space explorations.The scarcity of pristine samples and the irregular shapes of planetary meteorites make it difficult to obtain representative samples for conventional macroscale rock mechanics experiments(macro-RMEs).This critical review discusses recent advances in microscale RMEs(micro-RMEs)techniques and the upscaling methods for extracting mechanical parameters.Methods of mineralogical and microstructural analyses,along with non-destructive mechanical techniques,have provided new opportunities for studying planetary rocks with unprecedented precision and capabilities.First,we summarize several mainstream methods for obtaining the mineralogy and microstructure of planetary rocks.Then,nondestructive micromechanical testing methods,nanoindentation and atomic force microscopy(AFM),are detailed reviewed,illustrating the principles,advantages,influencing factors,and available testing results from literature.Subsequently,several feasible upscaling methods that bridge the micro-measurements of meteorite pieces to the strength of the intact body are introduced.Finally,the potential applications of planetary rock mechanics research to guiding the design and execution of space missions are environed,ranging from sample return missions and planetary defense to extraterrestrial construction.These discussions are expected to broaden the understanding of the microscale mechanical properties of planetary rocks and their significant role in deep space exploration.展开更多
In history,the Earth has encountered frequent and massive impacts.Until today,it is still a collided target for Potentially Hazardous Objects(PHOs),gradually making planetary defense a concerned and important research...In history,the Earth has encountered frequent and massive impacts.Until today,it is still a collided target for Potentially Hazardous Objects(PHOs),gradually making planetary defense a concerned and important research topic in the field of aerospace science.Against this background,this work clarifies and discusses some important scientific issues and various critical technologies of planetary defense.First,the current status of planetary defense research is summarized.Subsequently,the classification and characteristics of PHOs are introduced,focusing on their potential impact on planetary defense and related scientific research issues.For the purpose of protecting the Earth and maintaining space safety,the monitoring and characterization,deflection,and mitigation of PHOs have basically occupied all the attention of planetary defense researchers.Therefore,the critical technologies in planetary defense are discussed from these three aspects,and are also compared and analyzed in depth.Based on the current research progress in planetary defense,the challenges for planetary defense are discussed,and future development directions are also analyzed.Finally,a summary of the entire study is provided.展开更多
I analyze a new X-ray image of the youngest supernova remnant(SNR)in the Galaxy,which is the type Ia SNR G1.9+0.3,and reveal a very clear point-symmetrical structure.Since explosion models of type Ia supernovae(SNe Ia...I analyze a new X-ray image of the youngest supernova remnant(SNR)in the Galaxy,which is the type Ia SNR G1.9+0.3,and reveal a very clear point-symmetrical structure.Since explosion models of type Ia supernovae(SNe Ia)do not form such morphologies,the point-symmetrical morphology must come from the circumstellar material(CSM)into which the ejecta expands.The large-scale point-symmetry that I identify and the known substantial deceleration of the ejecta of SNR G1.9+0.3 suggest a relatively massive CSM of■1M⊙.I argue that the most likely explanation is the explosion of this SN Ia into a planetary nebula.The scenario that predicts a large fraction of SN Ia inside PNe(SNIPs)is the core degenerate scenario.Other SN Ia scenarios might lead to only a very small fraction of SNIPs or none at all.展开更多
The fluctuating planetary gravitational field influences not only activities on the Sun but also on the Earth. A special correlation function describes the harmonics of these fluctuations. Groups of earthquakes form o...The fluctuating planetary gravitational field influences not only activities on the Sun but also on the Earth. A special correlation function describes the harmonics of these fluctuations. Groups of earthquakes form oscillation patterns that differ significantly from randomly chosen control groups. These patterns are suitable as an element of an AI for the probability of earthquakes.展开更多
The goal of this research is to explore the effects of black hole singularities. Methodology is to start with large objects like galaxies and continue to smaller objects within our solar neighbourhood. High-redshift o...The goal of this research is to explore the effects of black hole singularities. Methodology is to start with large objects like galaxies and continue to smaller objects within our solar neighbourhood. High-redshift observations from the James Webb Space Telescope reveal that distant galaxies and their central black holes formed shortly after the Big Bang. An innovation about the speed of light explains how supermassive black holes could have formed primordially. Predictions of Hawking radiation include the possibility of black holes contributing to the energy of stars such as the Sun. Black holes have also been suggested as a source of radiation and magnetic fields in giant planets. Observations of Enceladus raise the possibility that this moon and other objects near Saturn’s Rings contain small singularities. Extrapolations of this methodology indicate that black holes could exist within solar system bodies including planets. Extended discussion describes how their presence could explain mysteries of internal heat, planetary magnetic fields, and processes of solar system formation.展开更多
The transmission system is a critical power component of helicopters, playing an indispensable role in power transmission. Among its key elements, the planetary gear system is an essential part of the helicopter trans...The transmission system is a critical power component of helicopters, playing an indispensable role in power transmission. Among its key elements, the planetary gear system is an essential part of the helicopter transmission architecture. Establishing a dynamic model of the helicopter transmission system and analyzing the dynamic response of the planetary gear system under varying flight conditions are crucial for enhancing the system’s performance and safety. In this study, the transmission system is modeled comprehensively using the lumped mass method and the finite element method, and the dynamic characteristics of the planetary gear system, as reflected on the main gearbox casing under different flight scenarios, are examined. The findings reveal that the resonance frequencies of the planetary gear system remain consistent across various flight conditions, indicating that these frequencies are governed by the inherent structural and dynamic properties of the system. However, the vibration amplitudes at resonance points differ depending on the flight condition. Specifically, the resonance amplitudes at 0.057 kHz and 0.093 kHz during Hovering are significantly lower than those in other conditions, demonstrating that operational scenarios directly influence vibration response.展开更多
Planetary gear train is a critical transmission component in large equipment such as helicopters and wind turbines. Conducting damage perception of planetary gear trains is of great significance for the safe operation...Planetary gear train is a critical transmission component in large equipment such as helicopters and wind turbines. Conducting damage perception of planetary gear trains is of great significance for the safe operation of equipment. Existing methods for damage perception of planetary gear trains mainly rely on linear vibration analysis. However, these methods based on linear vibration signal analysis face challenges such as rich vibration sources, complex signal coupling and modulation mechanisms, significant influence of transmission paths, and difficulties in separating damage information. This paper proposes a method for separating instantaneous angular speed (IAS) signals for planetary gear fault diagnosis. Firstly, this method obtains encoder pulse signals through a built-in encoder. Based on this, it calculates the IAS signals using the Hilbert transform, and obtains the time-domain synchronous average signal of the IAS of the planetary gear through time-domain synchronous averaging technology, thus realizing the fault diagnosis of the planetary gear train. Experimental results validate the effectiveness of the calculated IAS signals, demonstrating that the time-domain synchronous averaging technology can highlight impact characteristics, effectively separate and extract fault impacts, greatly reduce the testing cost of experiments, and provide an effective tool for the fault diagnosis of planetary gear trains.展开更多
The relationship between the efficiency of NiO/Fe2O3 wet grinding and noisy-power dissipation was studied. The optimal grinding parameters were found as: a slurry water content of 64.10%-85.47%, ball number ratio of 3...The relationship between the efficiency of NiO/Fe2O3 wet grinding and noisy-power dissipation was studied. The optimal grinding parameters were found as: a slurry water content of 64.10%-85.47%, ball number ratio of 360/20, revolution speed of 300.9 r/min, powder-filling ratio of 10.88%, ball-filling ratio of 20.53%-23.88%, and grinding time of approximately 6 h. The discrete element method(DEM) was employed to analyze relationship between the noisy-power dissipation and the grinding efficiency, and equations describing the relationship were derived. The mean particle size of the ground powder decreased with a decrease in the degree of noisy-power dissipation, while the grinding efficiency and the amount of specific impact power used decreased with an increase in the degree of noisy-power dissipation.展开更多
This paper presents an assessment of earth and planetary scientific research in the world in the fifteen years period from 1996 through 2012 and in 2013.The total number of publications in that period was about 4.7%of...This paper presents an assessment of earth and planetary scientific research in the world in the fifteen years period from 1996 through 2012 and in 2013.The total number of publications in that period was about 4.7%of total world scientific output.The top 10 countries in 2012 and in 2013 accounted for 67.6%and 66.7%of world publications in earth and planetary sciences.展开更多
Based on the transformed Eulerian-mean equations, the dynamics of planetary waves are discussed. Both observations and simulations indicate that in the Northern Hemisphere winter there are two waveguides for the merid...Based on the transformed Eulerian-mean equations, the dynamics of planetary waves are discussed. Both observations and simulations indicate that in the Northern Hemisphere winter there are two waveguides for the meridional propagation of quasi-stationary planetary waves. One is the high latitude waveguide, and the other is the low latitude waveguide. These results are in good agreement with theoretical analysis. Moreover, the convergence of EP flux indicates that the stratospheric sudden warming is the result of anomalous planetary wave propagation along the high latitude waveguide and its interaction with mean flows. The tropical quasi-biennial oscillation (QBO) winds, which represent one significant variation of zonal flow in the lower stratosphere at low latitudes, can influence the low latitude waveguide of planetary wave propagation. Our results of the wave-mean flow coupled model show that these tropical winds can also modulate the high latitude waveguide significantly in the case of wave-mean flow interaction.The transport effect of planetary waves on ozone is also analyzed. The residual mean circulation forced by planetary waves indicates that there is strong transport circulation for the dissipative planetary waves. Under the forcing of northward eddy heat transport, a positive transport circulation can result which rises at low latitudes and sinks at high latitudes. At the same time, the modification of planetary wave propagation by the equatorial QBO winds is shown to have an important impact on the transport circulation. The model results indicate that the meridional transport is amplified during the easterly phase of the QBO. This mechanism may explain the interannual variability of ozone in the stratosphere at high latitudes.展开更多
The discovery of a planetary companion to the intermediate-mass late-type giant star HD173416 from precise Doppler surveys of G and K giants at Xinglong station and Okayama Astrophysical Observatory （OAO） is present...The discovery of a planetary companion to the intermediate-mass late-type giant star HD173416 from precise Doppler surveys of G and K giants at Xinglong station and Okayama Astrophysical Observatory （OAO） is presented in this letter. The planet has a minimum mass of 2.7 MJ, an eccentricity of 0.21, a semimajor axis of 1.16 AU and an orbital period of 324 days.展开更多
We investigate the effects of the cooling function in the formation of clumps of protoplanetary disks using two-dimensional smoothed particle hydrody- namic simulations. We use a simple prescription for the cooling ra...We investigate the effects of the cooling function in the formation of clumps of protoplanetary disks using two-dimensional smoothed particle hydrody- namic simulations. We use a simple prescription for the cooling rate of the flow, du/dt = -u/τcool, where u and %ool are the internal energy and cooling timeseale, respectively. We assume the ratio of local＇cooling to dynamical timescale, Ωτcool =β, to be a constant and also a function of the local temperature. We found that for the constantβ and γ = 5/3, fragmentation occurs only forβ ≤ 7. However, in the case ofβ having temperature dependence and γ = 5/3, fragmentation can also occur for larger values ofβ. By increasing the temperature dependence of the cooling timescale, the mass accretion rate decreases, the population of clumps/fragments increases, and the clumps/fragments can also form in the smaller radii. Moreover, we found that the clumps can form even in a low mass accretion rate, ≤10-7M⊙yr-1, in the case of temperature-dependentβ. However, clumps form with a larger mass accretion rate, 〉 10-7M⊙ yr-1, in the case of constantβ.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42261134532,42405059,and U2342212)。
文摘This study investigates the relationship between atmospheric stratification (i.e., static stability given by N^(2)) and the vertical energy transfer of stationary planetary waves, and further illustrates the underlying physical mechanism. Specifically, for the simplified case of constant stratospheric N^(2), the refractive index square of planetary waves has a theoretical tendency to increase first and then decrease with an increased N^(2), whereas the group velocity weakens. Mechanistically, this behavior can be understood as an intensified suppression of vertical isentropic surface displacement caused by meridional heat transport of planetary waves under strong N^(2) conditions. Observational analysis corroborates this finding, demonstrating a reduction in the vertical-propagation velocity of waves with increased N^(2). A linear, quasi- geostrophic, mid-latitude beta-plane model with a constant background westerly wind and a prescribed N^(2) applicable to the stratosphere is used to obtain analytic solutions. In this model, the planetary waves are initiated by steady energy influx from the lower boundary. The analysis indicates that under strong N^(2) conditions, the amplitude of planetary waves can be sufficiently increased by the effective energy convergence due to the slowing vertical energy transfer, resulting in a streamfunction response in this model that contains more energy. For N^(2) with a quasi-linear vertical variation, the results bear a resemblance to the constant case, except that the wave amplitude and oscillating frequency show some vertical variations.
文摘In a Nature Physics report published in late September 2024[1],a team of scientists and engineers at Sandia National Laboratories(Albuquerque,NM,USA)described the results of a laboratory experiment showing that a nuclear blast could create a burst of X-rays powerful enough to change the path of a large asteroid that might one day be on a collision course with Earth.
基金supported by the Guangxi Science and Technology Major Program of China(Nos.AA23073019 and AA24263074)the National Natural Science Foundation of China(No.52265004)+7 种基金the Guangxi Natural Science Fund for Distinguished Young Scholars of China(No.2024JJG160014)the Innovation Project of Guangxi Graduate Education of China(No.YCSW2024119)the Open Fund of State Key Laboratory of Intelligent Manufacturing Equipment and Technology of China(No.IMETKF2025021)the Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance-Central South University of China(No.Kfkt2023-06)the Open Fund of High-end Basic Component Innovation Station of China(No.KY01080030124001)the Open Fund for Academician Mao Ming's Workstation of China(No.XSJSFW-QNKXJ-202404-007)the Technology Innovation Platform Project of China Aviation Engine Group Corporation(No.CXPT-2023-044)the Open Fund for Innovation Workstation in the National Defense Science and Technology Innovation Special Zone(Xi'an Jiaotong University).
文摘The metamaterial based on external meshing gears(MEG)is designed based on the principle of external meshing gear transmission.Based on the meshing transmission principle of external meshing gears and planetary gear trains,the internal and external gear rings are designed.Based on the internal and external gear rings,the metamaterial based on inner and outer planetary gear trains(MIP)is designed to study the shear modulus,Young's modulus,and amplitude-frequency characteristics of the metamaterial based on gears at different angles.The effects of the number of planetary gears on the physical characteristics of the MIP are studied.The results show that the MEG can be continuously adjusted by adjusting the shear modulus and Young's modulus due to its meshing characteristics.With the same number of gears,the adjustment range of the MIP is larger than the adjustment range of the MEG.When the number of planetary gears increases,the adjustment range of the MIP decreases.Moreover,when the metamaterial based on gears rotates,the harmonic response changes with the change of the angle.
基金supported by the Serbian Ministry of Education and Science under Grant No.TR35006 and COST Action:CA23155—A Pan-European Network of Ocean Tribology(OTC)The research of B.Rosic and M.Rosic was supported by the Serbian Ministry of Education and Science under Grant TR35029.
文摘This paper introduces a hybrid multi-objective optimization algorithm,designated HMODESFO,which amalgamates the exploratory prowess of Differential Evolution(DE)with the rapid convergence attributes of the Sailfish Optimization(SFO)algorithm.The primary objective is to address multi-objective optimization challenges within mechanical engineering,with a specific emphasis on planetary gearbox optimization.The algorithm is equipped with the ability to dynamically select the optimal mutation operator,contingent upon an adaptive normalized population spacing parameter.The efficacy of HMODESFO has been substantiated through rigorous validation against estab-lished industry benchmarks,including a suite of Zitzler-Deb-Thiele(ZDT)and Zeb-Thiele-Laumanns-Zitzler(DTLZ)problems,where it exhibited superior performance.The outcomes underscore the algorithm’s markedly enhanced optimization capabilities relative to existing methods,particularly in tackling highly intricate multi-objective planetary gearbox optimization problems.Additionally,the performance of HMODESFO is evaluated against selected well-known mechanical engineering test problems,further accentuating its adeptness in resolving complex optimization challenges within this domain.
基金Project(2024A1515240020)supported by the Guangdong Basic and Applied Basic Research Foundation,China。
文摘The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state.The coupling effect of tooth surface roughness and lubrication on meshing characteristics of planetary gear is studied.An improved three-dimensional(3 D)anisotropic tooth surface roughness fractal model is proposed based on the experimental parameters.Considering asperity contact and elastohydrodynamic lubrication(EHL),the contact load and flexibility deformation of the tooth surface are derived,and the deformation compatibility equation of the 3 D loaded tooth contact analysis(3 D-LTCA)method is improved.The asperity of the tooth surface changes the system from EHL to mixed lubrication and reduces the stiffness of the oil film.Compared with the sun planet gear,the asperity has a greater effect on the meshing characteristics of the ring-planet gear.Compared with the proposed method,the comprehensive stiffness obtained by the traditional calculation method considering the lubrication effect is smaller,especially for the ring-planet gear.Compared with roughness,speed and viscosity,the meshing characteristics of planetary gears are most sensitive to torque.
基金the support from the National Natural Science Foundation of China (Grant No. 42175070)supported by the National Natural Science Foundation of China (Grant No. 42288101)supported by the National Key Scientific and Technological Infrastructure project “Earth System Numerical Simulation Facility” (Earth Lab)。
文摘By applying the convolution-based Hilbert transform in the zonal direction on six-hourly streamfunction fields at200 h Pa, we present the climatology and trends of the local wave period, and zonal and meridional phase speeds, of Rossby waves over the globe during the solstice seasons of 1979–2023. While partly similar to and inspired by Fragkoulidis and Wirth(2020), our method differs in its ability to cover both planetary-scale and synoptic-scale waves over not only the extratropics, but also the tropics and subtropics. Based on a physically reasonable global distribution of wave periods, our key new finding is a robust prolonging of wave periods over most regions of the tropics and subtropics during both solstice seasons of 1979–2023, except for the tropical Atlantic, which experiences a shortened wave period during June–July–August of 1979–2022. Both the prolonging and shortening of wave periods are mainly associated with the changes in planetary-scale waves. Regionally varying trends of the zonal phase speed(Cpx) of synoptic waves are consistent in sign with, but smaller in magnitude than, the trends of local zonal wind, confirming the conclusion of Wu and Lu(2023)on the opposite effects of zonal wind and the meridional gradient of potential vorticity on Cpx. Meanwhile, the Cpx trends of planetary-scale waves are relatively weak, and do not exhibit a robust relation with the trend of zonal wind. These new results are helpful toward better understanding the changes in atmospheric waves and extreme events under global warming.
文摘Urban agriculture is gaining recognition for its potential contributions to environmental resilience and climate change adaptation,providing advantages such as urban greening,reduced heat island effects,and decreased air pollution.Moreover,it indirectly supports communities during weather events and natural disasters,ensuring food security and fostering community cohesion.However,concerns about planetary health risks persist in highly urbanized and climate-affected areas.Employing electronic databases such as Web of Science and PubMed and adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines,we identified 55 relevant papers to comprehend the planetary health risks associated with urban agriculture,The literature review identified five distinct health risks related to urban agriculture:(1)trace metal risks in urban farms;(2)health risks associated with wastewater irrigation;(3)zoonotic risks;(4)other health risks;and(5)social and economic risks.The study highlights that urban agriculture,while emphasizing environmental benefits,particularly raises concerns about trace metal bioaccumulation in soil and vegetables,posing health risks for populations.Other well studied risks included wastewater irrigation and backyard livestock farming.The main limitations in the available literature were in studying infectious diseases and antibiotic resistance associated with urban agriculture.
基金supported by China Postdoctoral Science Foundation(No.2023TQ0247)Shenzhen Science and Technology Program(No.JCYJ20220530140602005)+2 种基金the Fundamental Research Funds for the Central Universities(No.2042023kfyq03)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515111071)the Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(No.GZB20230544).
文摘Knowledge of the mechanical behavior of planetary rocks is indispensable for space explorations.The scarcity of pristine samples and the irregular shapes of planetary meteorites make it difficult to obtain representative samples for conventional macroscale rock mechanics experiments(macro-RMEs).This critical review discusses recent advances in microscale RMEs(micro-RMEs)techniques and the upscaling methods for extracting mechanical parameters.Methods of mineralogical and microstructural analyses,along with non-destructive mechanical techniques,have provided new opportunities for studying planetary rocks with unprecedented precision and capabilities.First,we summarize several mainstream methods for obtaining the mineralogy and microstructure of planetary rocks.Then,nondestructive micromechanical testing methods,nanoindentation and atomic force microscopy(AFM),are detailed reviewed,illustrating the principles,advantages,influencing factors,and available testing results from literature.Subsequently,several feasible upscaling methods that bridge the micro-measurements of meteorite pieces to the strength of the intact body are introduced.Finally,the potential applications of planetary rock mechanics research to guiding the design and execution of space missions are environed,ranging from sample return missions and planetary defense to extraterrestrial construction.These discussions are expected to broaden the understanding of the microscale mechanical properties of planetary rocks and their significant role in deep space exploration.
基金supported by the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(No.XDA1502030505)。
文摘In history,the Earth has encountered frequent and massive impacts.Until today,it is still a collided target for Potentially Hazardous Objects(PHOs),gradually making planetary defense a concerned and important research topic in the field of aerospace science.Against this background,this work clarifies and discusses some important scientific issues and various critical technologies of planetary defense.First,the current status of planetary defense research is summarized.Subsequently,the classification and characteristics of PHOs are introduced,focusing on their potential impact on planetary defense and related scientific research issues.For the purpose of protecting the Earth and maintaining space safety,the monitoring and characterization,deflection,and mitigation of PHOs have basically occupied all the attention of planetary defense researchers.Therefore,the critical technologies in planetary defense are discussed from these three aspects,and are also compared and analyzed in depth.Based on the current research progress in planetary defense,the challenges for planetary defense are discussed,and future development directions are also analyzed.Finally,a summary of the entire study is provided.
基金supported by a grant from the Israel Science Foundation(769/20)。
文摘I analyze a new X-ray image of the youngest supernova remnant(SNR)in the Galaxy,which is the type Ia SNR G1.9+0.3,and reveal a very clear point-symmetrical structure.Since explosion models of type Ia supernovae(SNe Ia)do not form such morphologies,the point-symmetrical morphology must come from the circumstellar material(CSM)into which the ejecta expands.The large-scale point-symmetry that I identify and the known substantial deceleration of the ejecta of SNR G1.9+0.3 suggest a relatively massive CSM of■1M⊙.I argue that the most likely explanation is the explosion of this SN Ia into a planetary nebula.The scenario that predicts a large fraction of SN Ia inside PNe(SNIPs)is the core degenerate scenario.Other SN Ia scenarios might lead to only a very small fraction of SNIPs or none at all.
文摘The fluctuating planetary gravitational field influences not only activities on the Sun but also on the Earth. A special correlation function describes the harmonics of these fluctuations. Groups of earthquakes form oscillation patterns that differ significantly from randomly chosen control groups. These patterns are suitable as an element of an AI for the probability of earthquakes.
文摘The goal of this research is to explore the effects of black hole singularities. Methodology is to start with large objects like galaxies and continue to smaller objects within our solar neighbourhood. High-redshift observations from the James Webb Space Telescope reveal that distant galaxies and their central black holes formed shortly after the Big Bang. An innovation about the speed of light explains how supermassive black holes could have formed primordially. Predictions of Hawking radiation include the possibility of black holes contributing to the energy of stars such as the Sun. Black holes have also been suggested as a source of radiation and magnetic fields in giant planets. Observations of Enceladus raise the possibility that this moon and other objects near Saturn’s Rings contain small singularities. Extrapolations of this methodology indicate that black holes could exist within solar system bodies including planets. Extended discussion describes how their presence could explain mysteries of internal heat, planetary magnetic fields, and processes of solar system formation.
文摘The transmission system is a critical power component of helicopters, playing an indispensable role in power transmission. Among its key elements, the planetary gear system is an essential part of the helicopter transmission architecture. Establishing a dynamic model of the helicopter transmission system and analyzing the dynamic response of the planetary gear system under varying flight conditions are crucial for enhancing the system’s performance and safety. In this study, the transmission system is modeled comprehensively using the lumped mass method and the finite element method, and the dynamic characteristics of the planetary gear system, as reflected on the main gearbox casing under different flight scenarios, are examined. The findings reveal that the resonance frequencies of the planetary gear system remain consistent across various flight conditions, indicating that these frequencies are governed by the inherent structural and dynamic properties of the system. However, the vibration amplitudes at resonance points differ depending on the flight condition. Specifically, the resonance amplitudes at 0.057 kHz and 0.093 kHz during Hovering are significantly lower than those in other conditions, demonstrating that operational scenarios directly influence vibration response.
文摘Planetary gear train is a critical transmission component in large equipment such as helicopters and wind turbines. Conducting damage perception of planetary gear trains is of great significance for the safe operation of equipment. Existing methods for damage perception of planetary gear trains mainly rely on linear vibration analysis. However, these methods based on linear vibration signal analysis face challenges such as rich vibration sources, complex signal coupling and modulation mechanisms, significant influence of transmission paths, and difficulties in separating damage information. This paper proposes a method for separating instantaneous angular speed (IAS) signals for planetary gear fault diagnosis. Firstly, this method obtains encoder pulse signals through a built-in encoder. Based on this, it calculates the IAS signals using the Hilbert transform, and obtains the time-domain synchronous average signal of the IAS of the planetary gear through time-domain synchronous averaging technology, thus realizing the fault diagnosis of the planetary gear train. Experimental results validate the effectiveness of the calculated IAS signals, demonstrating that the time-domain synchronous averaging technology can highlight impact characteristics, effectively separate and extract fault impacts, greatly reduce the testing cost of experiments, and provide an effective tool for the fault diagnosis of planetary gear trains.
基金supported by the Inert Anode Material Production and Application in Electrolytic Production of Aluminium program of the Yunnan Aluminium Yonxin Aluminium Co. Ltd
文摘The relationship between the efficiency of NiO/Fe2O3 wet grinding and noisy-power dissipation was studied. The optimal grinding parameters were found as: a slurry water content of 64.10%-85.47%, ball number ratio of 360/20, revolution speed of 300.9 r/min, powder-filling ratio of 10.88%, ball-filling ratio of 20.53%-23.88%, and grinding time of approximately 6 h. The discrete element method(DEM) was employed to analyze relationship between the noisy-power dissipation and the grinding efficiency, and equations describing the relationship were derived. The mean particle size of the ground powder decreased with a decrease in the degree of noisy-power dissipation, while the grinding efficiency and the amount of specific impact power used decreased with an increase in the degree of noisy-power dissipation.
文摘This paper presents an assessment of earth and planetary scientific research in the world in the fifteen years period from 1996 through 2012 and in 2013.The total number of publications in that period was about 4.7%of total world scientific output.The top 10 countries in 2012 and in 2013 accounted for 67.6%and 66.7%of world publications in earth and planetary sciences.
基金This study was supported by the National Key Programme for Developing Basic Sciences under Grant G1998040900 and by the Chinese Academy of Sciences under Grant KZCX1-10-07.
文摘Based on the transformed Eulerian-mean equations, the dynamics of planetary waves are discussed. Both observations and simulations indicate that in the Northern Hemisphere winter there are two waveguides for the meridional propagation of quasi-stationary planetary waves. One is the high latitude waveguide, and the other is the low latitude waveguide. These results are in good agreement with theoretical analysis. Moreover, the convergence of EP flux indicates that the stratospheric sudden warming is the result of anomalous planetary wave propagation along the high latitude waveguide and its interaction with mean flows. The tropical quasi-biennial oscillation (QBO) winds, which represent one significant variation of zonal flow in the lower stratosphere at low latitudes, can influence the low latitude waveguide of planetary wave propagation. Our results of the wave-mean flow coupled model show that these tropical winds can also modulate the high latitude waveguide significantly in the case of wave-mean flow interaction.The transport effect of planetary waves on ozone is also analyzed. The residual mean circulation forced by planetary waves indicates that there is strong transport circulation for the dissipative planetary waves. Under the forcing of northward eddy heat transport, a positive transport circulation can result which rises at low latitudes and sinks at high latitudes. At the same time, the modification of planetary wave propagation by the equatorial QBO winds is shown to have an important impact on the transport circulation. The model results indicate that the meridional transport is amplified during the easterly phase of the QBO. This mechanism may explain the interannual variability of ozone in the stratosphere at high latitudes.
基金funded by the NSFC under grants 10803010 and 10521001Grants-in-Aid for Scientific Research (B) No.17340056 (H.A.)the Joint program on Search for Extra-solar planets between China and Japan (2008–2010) from the Japan Society for the Promotion of Science.
文摘The discovery of a planetary companion to the intermediate-mass late-type giant star HD173416 from precise Doppler surveys of G and K giants at Xinglong station and Okayama Astrophysical Observatory （OAO） is presented in this letter. The planet has a minimum mass of 2.7 MJ, an eccentricity of 0.21, a semimajor axis of 1.16 AU and an orbital period of 324 days.
文摘We investigate the effects of the cooling function in the formation of clumps of protoplanetary disks using two-dimensional smoothed particle hydrody- namic simulations. We use a simple prescription for the cooling rate of the flow, du/dt = -u/τcool, where u and %ool are the internal energy and cooling timeseale, respectively. We assume the ratio of local＇cooling to dynamical timescale, Ωτcool =β, to be a constant and also a function of the local temperature. We found that for the constantβ and γ = 5/3, fragmentation occurs only forβ ≤ 7. However, in the case ofβ having temperature dependence and γ = 5/3, fragmentation can also occur for larger values ofβ. By increasing the temperature dependence of the cooling timescale, the mass accretion rate decreases, the population of clumps/fragments increases, and the clumps/fragments can also form in the smaller radii. Moreover, we found that the clumps can form even in a low mass accretion rate, ≤10-7M⊙yr-1, in the case of temperature-dependentβ. However, clumps form with a larger mass accretion rate, 〉 10-7M⊙ yr-1, in the case of constantβ.
