Basic equations are derived for kinematical force-free fields of a magnetic arch in a perfect conducting fluid, and the stationary and unsteady similarity solutions are discussed in this paper.
Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal fie...Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasma β (the ratio between gas pressure and magnetic pressure) is taken to be so small (β = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the threshold is exceeded. The energy threshold is found to be larger than that of the corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope. This gives an example showing that a force-free magnetic field may have an energy larger than the corresponding open field energy if part of the field lines is allowed to be detached from the solar surface. The implication of such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic fields.展开更多
To examine the impact of anthropogenic land reconstruction,particularly the consolidation of small terraces into larger fields,on soil organic carbon(SOC),total nitrogen(TN)dynamics,rice yield,and its components,soil ...To examine the impact of anthropogenic land reconstruction,particularly the consolidation of small terraces into larger fields,on soil organic carbon(SOC),total nitrogen(TN)dynamics,rice yield,and its components,soil and plant samples were collected from seven newly reconstructed fields in Japanese Andosols in Tochigi,Japan.Samples were obtained from both the former low-and high-elevation sides within each field plot.During harvest season,nine rice plants were randomly selected from each plot(0.675 m^(2),comprising 3 rows and 3 hills per row),collected from a 3-m stretch along both the east(former low side)and west(former high side)ridges.Soil cores were collected from identical plots at two depths(0–15 and 15–30 cm)and combined into one composite sample per layer.Rice plant samples were air-dried for two weeks until reaching constant moisture content,after which stems and ears were separated and weighed to determine biomass,yield,yield components,and nitrogen uptake.This indicated that land reconstruction significantly affected rice yield and its components between the two sides of all field plots.SOC,TN,and their decomposition following land reconstruction showed notable changes,especially in the 15–30 cm subsurface soil layer.Additionally,grain weight demonstrated significant correlation with SOC,TN,and carbon decomposition in both the 0–15 and 15–30 cm layers,indicating that soil fertility to a depth of 30 cm was crucial for rice productivity after land reconstruction.展开更多
This study presents preliminary results of tidal-induced magnetic field signals extracted from 9 months of data collected by the Macao Science Satellite-1(MSS-1) from November 2023 to July 2024. Tidal signals were iso...This study presents preliminary results of tidal-induced magnetic field signals extracted from 9 months of data collected by the Macao Science Satellite-1(MSS-1) from November 2023 to July 2024. Tidal signals were isolated using sequential modeling techniques by subtracting non-tidal field model predictions from observed magnetic data. The extracted MSS-1 results show strong agreement with those from the Swarm and CryoSat satellites. MSS-1 effectively captures key large-scale tidal-induced magnetic anomalies, mainly due to its unique 41-degree low-inclination orbit, which provides wide coverage of local times. This finding underscores the strong potential of MSS-1 to recover high-resolution global tidal magnetic field models as more MSS-1 data become available.展开更多
With the continuous upgrading of traditional manufacturing industries and the rapid rise of emerging technology fields,the performance requirements for the permanent magnet synchronous motors(PMSMs)have become higher ...With the continuous upgrading of traditional manufacturing industries and the rapid rise of emerging technology fields,the performance requirements for the permanent magnet synchronous motors(PMSMs)have become higher and higher.The importance of fast and accurate electromagnetic thermal coupling analysis of such motors becomes more and more prominent.In view of this,the surfacemounted PMSM(SPMSM)equipped with unequally thick magnetic poles is taken as the main object and its electromagnetic thermal coupling analytical model(ETc AM)is investigated.First,the electromagnetic analytical model(EAM)is studied based on the modified subdomain method.It realizes the fast calculation of key electromagnetic characteristics.Subsequently,the 3D thermal analytical model(TAM)is developed by combining the EAM,the lumped parameter thermal network method(LPTNM),and the partial differential equation of heat flux.It realizes the fast calculation of key thermal characteristics in 3D space.Further,the information transfer channel between EAM and TAM is built with reference to the intrinsic connection between electromagnetic field and temperature field.Thereby,the novel ETcAM is proposed to realize the fast and accurate prediction of electromagnetic and temperature fields.Besides,ETcAM has a lot to commend it.One is that it well accounts for the complex structure,saturation,and heat exchange behavior.Second,it saves a lot of computer resources.It offers boundless possibilities for initial design,scheme evaluation,and optimization of motors.Finally,the validity,accuracy,and practicality of this study are verified by simulation and experiment.展开更多
Aircraft disturbs the adjacent atmospheric environment in flight,forming spatial distribution features of atmospheric density that differ from the natural background,which may potentially be utilized as tracer charact...Aircraft disturbs the adjacent atmospheric environment in flight,forming spatial distribution features of atmospheric density that differ from the natural background,which may potentially be utilized as tracer characteristics to introduce new technologies for indirectly sensing the presence of aircraft.In this paper,the concept of a long-range aircraft detection based on the atmospheric disturbance density field is proposed,and the detection mode of tomographic imaging of the scattering light of an atmospheric disturbance flow field is designed.By modeling the spatial distribution of the disturbance density field,the scattered echo signal images of active light towards the disturbance field at long distance are simulated.On this basis,the characteristics of the disturbance optical signal at the optimal detection resolution are analyzed.The results show that the atmospheric disturbance flow field of the supersonic aircraft presents circular in the light-scattering echo images.The disturbance signal can be further highlighted by differential processing of the adjacent scattering images.As the distance behind the aircraft increases,the diffusion range of the disturbance signal increases,and the signal intensity and contrast with the background decrease.Under the ground-based observation conditions of the aircraft at a height of 10000 m,a Mach number of1.6,and a detection distance of 100 km,the contrast between the disturbance signal and the back-ground was 30 d B at a distance of one time from the rear of the fuselage,and the diffusion diameter of the disturbance signal was 50 m.At a distance eight times the length of the aircraft,the contrast decreased to 10 dB,and the diameter increased to 290 m.The contrast was reduced to 3 dB at a distance nine times the length of the aircraft,and the diameter was diffused to 310 m.These results indicate the possibility of long-range aircraft detection based on the characteristics of the atmospheric density field.展开更多
Nonlinear force-free magnetic field （NLFFF） extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric mag...Nonlinear force-free magnetic field （NLFFF） extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric magnetograms contain magnetic forces and small-scale noises, and fail to be consistent with the force-free assumption of NLFFF models. The procedure for removing the forces and noises in observed data is called preprocessing. In this paper, we extend the preprocessing code of Jiang ＆ Feng to spherical coordinates for a full sphere. We first smooth the observed data with Gaussian smoothing, and then split the smoothed magnetic field into a potential field and a non-potential field. The potential part is computed by a numerical potential field model, and the non-potential part is prepro- cessed using an optimization method to minimize the magnetic forces and magnetic torques. Applying the code to synoptic charts of the vector magnetic field from SDO/HMI, we find it can effectively reduce the noises and forces, and improve the quality of data for a better input which will be used for NLFFF extrapolations applied to the global corona.展开更多
In photocatalysis field,S-scheme heterojunctions show unique advantages and prospects.However,the carrier shielding effect of heterojunctions limits the separation and migration of interfacial charges.In this study,a ...In photocatalysis field,S-scheme heterojunctions show unique advantages and prospects.However,the carrier shielding effect of heterojunctions limits the separation and migration of interfacial charges.In this study,a strategy of“dynamic cascade electric fields to deplete unilaterally accumulated charges”was innovatively proposed to overcome this drawback.By modulating g-C_(3)N_(4)(CN)and Bi_(2)WO_(6)(BWO)using the polarized electric field(PEF)of spontaneously polarized ceramic(SPC),a BWO/SPC-CN composite with cascade internal electric field(IEF)and PEF was successfully constructed for efficient piezophotocatalytic degradation of recalcitrant pollutants.BWO/SPC-CN contributed to 96.8% degradation of carbamazepine,significantly surpassing BWO/CN(70.5%).BWO/SPC-CN performed excellent capacity of harvesting piezoelectric energy due to its unique three-dimensional porous nano-network structure.The PEF of SPC modulated the electronic band structure and thus strengthened the IEF of BWO/SPC-CN,providing a persistent driving force for interfacial charge migration.Moreover,SPC with a strong PEF unilaterally consumed the charges accumulated on CN under periodic piezoelectricity,weakening the shielding electric field to inhibit the recombination of electron-hole pairs.As a consequence,the dynamic cascade PEF-IEF ultimately broke the carrier shielding effect in heterojunction photocatalysis and enhanced interfacial electron transfer.This work provides reliable methods to enhance the interfacial charge transfer in heterojunction and new insights into piezo-photocatalytic mechanism.展开更多
Seepage refers to the flow of water through porous materials.This phenomenon has a crucial role in dam,slope,excavation,tunnel,and well design.Performing seepage analysis usually is a challenging task,as one must cope...Seepage refers to the flow of water through porous materials.This phenomenon has a crucial role in dam,slope,excavation,tunnel,and well design.Performing seepage analysis usually is a challenging task,as one must cope with the uncertainty associated with the parameters such as the hydraulic conductivity in the horizontal and vertical directions that drive this phenomenon.However,at the same time,the data on horizontal and vertical hydraulic conductivities are typically scarce in spatial resolution.In this context,so-called non-traditional approaches for uncertainty quantification(such as intervals and fuzzy variables)offer an interesting alternative to classical probabilistic methods,since they have been shown to be quite effective when limited information on the governing parameters of a phenomenon is available.Therefore,the main contribution of this study is the development of a framework for conducting seepage analysis in saturated soils,where uncertainty associated with hydraulic conductivity is characterized using fuzzy fields.This method to characterize uncertainty extends interval fields towards the domain of fuzzy numbers.In fact,it is illustrated that fuzzy fields are an effective tool for capturing uncertainties with a spatial component,since they allow one to account for available physical measurements.A case study in confined saturated soil shows that with the proposed framework,it is possible to quantify the uncertainty associated with seepage flow,exit gradient,and uplift force effectively.展开更多
Earthquakes are caused directly by the motion of the stress field,therefore,observing the stress field is significant.Experiments on the relationships among wave velocity,stress factors,and faults show that the wave v...Earthquakes are caused directly by the motion of the stress field,therefore,observing the stress field is significant.Experiments on the relationships among wave velocity,stress factors,and faults show that the wave velocity of rock media under stable stress fields corresponds one-to-one with stress factors.Therefore,the wave velocity gradient can indicate the direction of stress vector,and the gradient divergence can indicate the strength of the stress field.To verify the results,considering the limitations of wave velocity measurement in solid crustal media,two quantities,namely the apparent wave velocity and Poisson ratios relating to wave velocity,were used to refl ect the stress field state.The seismic data of the Tangshan and Luzhou regions were studied separately.The calculated apparent wave velocity and Poisson ratios were interpolated to achieve regional data gridding.The gradients and the gradient divergences of the apparent wave velocity and Poisson ratio fields in the two regions were analyzed,and it was found that their spatial distribution in the same region was the same.They are believed to refl ect the vertical projection of the stress direction vector and strength on the surface in the stress field,consistent with the experimental results.Whether it can eff ectively refl ect the stress field requires further analysis of the specific situation of the local medium and the movement mode of the stress field.展开更多
After the fabrication of magnetic resonance superconducting magnets,the magnetic field inhomogeneity needs to be accurately measured for subsequent shimming.However,conventional measurement methods are susceptible to ...After the fabrication of magnetic resonance superconducting magnets,the magnetic field inhomogeneity needs to be accurately measured for subsequent shimming.However,conventional measurement methods are susceptible to magnetic fields,have poor compatibility,and are difficult to adapt to various types of magnets.This paper proposes a new field measuring system based on a three-axis movable platform.The system utilizes non-magnetic materials and an innovative hand-wheel lifting design that can be adapted to various aperture magnets,thus obviating the necessity for electrically driven equipment and addressing safety concerns in strong magnetic fields.In addition,the measurement system offers high accuracy up to 1 mm and a wide measurable range.The fields of 3 T and 7 T magnets were mapped using the designed system with diameter of spherical volume(DSV)of 160 mm and 130 mm,respectively.Experimental results demonstrate that the magnetic field measurement system has strong compatibility and can accurately map the magnetic field at arbitrary positions,which is critical for shimming studies.展开更多
Nitrate(NO_(3)^(-))accumulation and transport processes in the thick vadose zone affect the evolution of the groundwater NO_(3)^(-)content in intensive agricultural regions.Agricultural land-use change(ALUC),typically...Nitrate(NO_(3)^(-))accumulation and transport processes in the thick vadose zone affect the evolution of the groundwater NO_(3)^(-)content in intensive agricultural regions.Agricultural land-use change(ALUC),typically accompanied by substantial alterations in nitrogen fertilizer application and irrigation practices,is an important influencing factor.This study evaluated the changes in NO_(3)^(-)accumulation and transport in the deep vadose zone(DVZ,below the root zone),and the groundwater NO_(3)^(-)content associated with ALUC from grain to vegetable fields in the North China Plain(NCP).The ALUC from grain to vegetable resulted in nitrate–nitrogen(NO_(3)^(-)-N)accumulation in DVZ increased by 235.5 kg ha^(-1)m^(-1)(163.2%)in the piedmont plain and 224.9 kg ha^(-1)m^(-1)(102.7%)in the central plain,respectively.This change accelerated downward transport velocity in the DVZ(from 0.81±0.47 to 0.89±0.55 m yr^(-1)in the piedmont plain,and from 0.24±0.12 to 0.92±0.12 m yr^(-1)in the central plain)and increased NO_(3)^(-)leaching fluxes.High transport velocity and leaching fluxes resulted in chemical N-fertilizer entering the aquifer in several areas in the piedmont plain.The impact of the agricultural activity intensity changes,accompanied by the ALUC,on groundwater quantity and quality should be considered in similar regions.展开更多
As the plasma current power in tokamak devices increases,a significant number of stray magnetic fields are generated around the equipment.These stray magnetic fields can disrupt the operation of electronic power devic...As the plasma current power in tokamak devices increases,a significant number of stray magnetic fields are generated around the equipment.These stray magnetic fields can disrupt the operation of electronic power devices,particularly transformers in switched-mode power supplies.Testing flyback converters with transformers under strong background magnetic fields highlights electromagnetic compatibility(EMC)issues for such switched-mode power supplies.This study utilizes finite element analysis software to simulate the electromagnetic environment of switched-mode power supply transformers and investigates the impact of variations in different magnetic field parameters on the performance of switched-mode power supplies under strong stray magnetic fields.The findings indicate that EMC issues are associated with transformer core saturation and can be alleviated through appropriate configurations of the core size,air gap,fillet radius,and installation direction.This study offers novel solutions for addressing EMC issues in high magnetic field environments.展开更多
In the electroslag remelting(ESR)process,it mainly relies on thermal experiments or analysis via mechanistic models to realize the physical fields simulation of the electromagnetic field and temperature field coupled ...In the electroslag remelting(ESR)process,it mainly relies on thermal experiments or analysis via mechanistic models to realize the physical fields simulation of the electromagnetic field and temperature field coupled transfer,which has the limitations of high cost,a large amount of calculating data and high computing power requirements.A novel network based on physics-informed neural network(PINN)was designed to realize the fast and high-fidelity prediction of the distribution of electromagnetic field and temperature field in ESR process.The physical laws were combined with the deep learning network through PINN,and physical constraints were embedded to achieve effective solution of partial differential equations(PDEs).PINN was used to minimize the loss function consisting of data error,physical information error and boundary condition error.The physical laws and boundary condition constraints in the ESR process were considered to maintain high PDE solution accuracy under different spatial and temporal resolutions.Automatic differentiation(Autodiff)technique and gradient descent algorithm were used to optimize the network parameters.The experimental results show that compared with the mechanistic models,PINN can effectively replace thermal experiments to realize the physical field simulation of ESR process with only a few experimental data,which can avoid the disadvantages of pure data-driven network simulation that requires a large amount of training data.Moreover,the solution of PINN has good physical interpretability and reliability of simulation results.For simulating electromagnetic field and temperature field distribution,the training time of the network is only 140 and 203 s,and the regression indicators of root mean square error can reach 12.65 and 13.76,respectively.展开更多
Development of robust electrocatalyst for oxygen reduction reaction(ORR)in a seawater electrolyte is the key to realize seawater electrolyte-based zinc-air batteries(SZABs).Herein,constructing a local electric field c...Development of robust electrocatalyst for oxygen reduction reaction(ORR)in a seawater electrolyte is the key to realize seawater electrolyte-based zinc-air batteries(SZABs).Herein,constructing a local electric field coupled with chloride ions(Cl-)fixation strategy in dual single-atom catalysts(DSACs)was proposed,and the resultant catalyst delivered considerable ORR performance in a seawater electrolyte,with a high half-wave potential(E_(1/2))of 0.868 V and a good maximum power density(Pmax)of 182 mW·cm^(−2)in the assembled SZABs,much higher than those of the Pt/C catalyst(E_(1/2):0.846 V;Pmax:150 mW·cm^(−2)).The in-situ characterization and theoretical calculations revealed that the Fe sites have a higher Cl^(−)adsorption affinity than the Co sites,and preferentially adsorbs Cl^(−)in a seawater electrolyte during the ORR process,and thus constructs a low-concentration Cl^(−)local microenvironment through the common-ion exclusion effect,which prevents Cl^(−)adsorption and corrosion in the Co active centers,achieving impressive catalytic stability.In addition,the directional charge movement between Fe and Co atomic pairs establishes a local electric field,optimizing the adsorption energy of Co sites for oxygen-containing intermediates,and further improving the ORR activity.展开更多
A recent study demonstrated that solid-state photochemically induced dynamic nuclear polarization(photo-CIDNP)can achieve significant 1H NMR hyperpolarization at high magnetic fields(9.4 T and 21.1 T).This was accompl...A recent study demonstrated that solid-state photochemically induced dynamic nuclear polarization(photo-CIDNP)can achieve significant 1H NMR hyperpolarization at high magnetic fields(9.4 T and 21.1 T).This was accomplished using a specially designed donor-chromophore-acceptor(D-C-A)molecule,which exhibits an excited state electron-electron interaction that is finely tuned to match the proton Larmor frequency under high-field conditions[1].展开更多
Spiral waves,as a typical self-organized structure with chiral characteristics,are widely found in excitable media such as cardiac tissues,chemical reactions,and neural networks.Based on the Fitz Hugh–Nagumo model,we...Spiral waves,as a typical self-organized structure with chiral characteristics,are widely found in excitable media such as cardiac tissues,chemical reactions,and neural networks.Based on the Fitz Hugh–Nagumo model,we investigated the mechanisms underlying the effects of direct current electric fields(DCEF),alternating current electric fields(ACEF),and polarized electric fields(PEF)on the interaction and annihilation processes of counter-rotating spiral waves.We found that in a direct current electric field,the drift direction of the spiral wave is determined jointly by its chirality and the electric field direction,which allows selective attraction or repulsion.In an alternating current electric field,the annihilation behavior of spiral waves can be influenced by the phase and intensity of the electric field,where a specific range of parameters induces resonance drift and eventual annihilation.On the other hand,the polarized electric field exhibits a more complex modulation capability on spiral waves:the trajectory and annihilation efficiency of spiral waves can be regulated by both the intensity and phase of the polarized electric field.These results reveal the potential feasibility of regulating multichiral spiral waves through multiple electric fields,providing theoretical insight for the control of spiral waves in relevant systems.展开更多
The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of ...The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of the Martian bow shocks were first found from the Mars Atmosphere and Volatile EvolutioN(MAVEN)observations.The present study aims to test whether this effect is also present in the shocks observed by Mars Express(MEX).We find that the bow shocks above the crustal field regions are enlarged,resulting in a north−south asymmetry and a longitude dependence in the shock size.The longitude dependence is more pronounced for near-subsolar shocks,and more dispersed for near-terminator shocks.The enlarged shocks are also observed to have shifted tailward from the longitudes of the strongest crustal fields.Due to a dawnside bias in MEX shock crossings,the enlarged shocks generally display a westward shift from the strongest crustal field region.These results confirm that stretches of the mini-magnetosphere are also present in the MEX shock observations.展开更多
Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds nu...Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.展开更多
In this paper we present certain bilinear estimates for commutators on Besov spaces with variable smoothness and integrability,and under no vanishing assumptions on the divergence of vector fields.Such commutator esti...In this paper we present certain bilinear estimates for commutators on Besov spaces with variable smoothness and integrability,and under no vanishing assumptions on the divergence of vector fields.Such commutator estimates are motivated by the study of well-posedness results for some models in incompressible fuid mechanics.展开更多
文摘Basic equations are derived for kinematical force-free fields of a magnetic arch in a perfect conducting fluid, and the stationary and unsteady similarity solutions are discussed in this paper.
基金Supported by the National Natural Science Foundation of China
文摘Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasma β (the ratio between gas pressure and magnetic pressure) is taken to be so small (β = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the threshold is exceeded. The energy threshold is found to be larger than that of the corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope. This gives an example showing that a force-free magnetic field may have an energy larger than the corresponding open field energy if part of the field lines is allowed to be detached from the solar surface. The implication of such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic fields.
基金support of the Japanese Government(Monbukagakusho)Scholarship for his studies in Japansupported by the Yamagata University YU-COE(S)program and by the Advanced Agri-food System Research Center of Yamagata University,Japan+2 种基金financially supported by a Japan Society for the Promotion of Science(JSPS)Grant-in-Aid for Scientific Research(26310304)Yamagata University YU-COE(S)programby the Advanced Agri-food System Research Center of Yamagata University,Japan。
文摘To examine the impact of anthropogenic land reconstruction,particularly the consolidation of small terraces into larger fields,on soil organic carbon(SOC),total nitrogen(TN)dynamics,rice yield,and its components,soil and plant samples were collected from seven newly reconstructed fields in Japanese Andosols in Tochigi,Japan.Samples were obtained from both the former low-and high-elevation sides within each field plot.During harvest season,nine rice plants were randomly selected from each plot(0.675 m^(2),comprising 3 rows and 3 hills per row),collected from a 3-m stretch along both the east(former low side)and west(former high side)ridges.Soil cores were collected from identical plots at two depths(0–15 and 15–30 cm)and combined into one composite sample per layer.Rice plant samples were air-dried for two weeks until reaching constant moisture content,after which stems and ears were separated and weighed to determine biomass,yield,yield components,and nitrogen uptake.This indicated that land reconstruction significantly affected rice yield and its components between the two sides of all field plots.SOC,TN,and their decomposition following land reconstruction showed notable changes,especially in the 15–30 cm subsurface soil layer.Additionally,grain weight demonstrated significant correlation with SOC,TN,and carbon decomposition in both the 0–15 and 15–30 cm layers,indicating that soil fertility to a depth of 30 cm was crucial for rice productivity after land reconstruction.
基金financially supported by the National Natural Science Foundation of China(42250102,42250101)the Macao Foundation and Macao Science and Technology Development Fund(0001/2019/A1)the Pre-research Project on Civil Aerospace Technologies funded by China National Space Administration(D020303)。
文摘This study presents preliminary results of tidal-induced magnetic field signals extracted from 9 months of data collected by the Macao Science Satellite-1(MSS-1) from November 2023 to July 2024. Tidal signals were isolated using sequential modeling techniques by subtracting non-tidal field model predictions from observed magnetic data. The extracted MSS-1 results show strong agreement with those from the Swarm and CryoSat satellites. MSS-1 effectively captures key large-scale tidal-induced magnetic anomalies, mainly due to its unique 41-degree low-inclination orbit, which provides wide coverage of local times. This finding underscores the strong potential of MSS-1 to recover high-resolution global tidal magnetic field models as more MSS-1 data become available.
基金supported by the Project of National Natural Science Foundation of China under Grant 52077122。
文摘With the continuous upgrading of traditional manufacturing industries and the rapid rise of emerging technology fields,the performance requirements for the permanent magnet synchronous motors(PMSMs)have become higher and higher.The importance of fast and accurate electromagnetic thermal coupling analysis of such motors becomes more and more prominent.In view of this,the surfacemounted PMSM(SPMSM)equipped with unequally thick magnetic poles is taken as the main object and its electromagnetic thermal coupling analytical model(ETc AM)is investigated.First,the electromagnetic analytical model(EAM)is studied based on the modified subdomain method.It realizes the fast calculation of key electromagnetic characteristics.Subsequently,the 3D thermal analytical model(TAM)is developed by combining the EAM,the lumped parameter thermal network method(LPTNM),and the partial differential equation of heat flux.It realizes the fast calculation of key thermal characteristics in 3D space.Further,the information transfer channel between EAM and TAM is built with reference to the intrinsic connection between electromagnetic field and temperature field.Thereby,the novel ETcAM is proposed to realize the fast and accurate prediction of electromagnetic and temperature fields.Besides,ETcAM has a lot to commend it.One is that it well accounts for the complex structure,saturation,and heat exchange behavior.Second,it saves a lot of computer resources.It offers boundless possibilities for initial design,scheme evaluation,and optimization of motors.Finally,the validity,accuracy,and practicality of this study are verified by simulation and experiment.
文摘Aircraft disturbs the adjacent atmospheric environment in flight,forming spatial distribution features of atmospheric density that differ from the natural background,which may potentially be utilized as tracer characteristics to introduce new technologies for indirectly sensing the presence of aircraft.In this paper,the concept of a long-range aircraft detection based on the atmospheric disturbance density field is proposed,and the detection mode of tomographic imaging of the scattering light of an atmospheric disturbance flow field is designed.By modeling the spatial distribution of the disturbance density field,the scattered echo signal images of active light towards the disturbance field at long distance are simulated.On this basis,the characteristics of the disturbance optical signal at the optimal detection resolution are analyzed.The results show that the atmospheric disturbance flow field of the supersonic aircraft presents circular in the light-scattering echo images.The disturbance signal can be further highlighted by differential processing of the adjacent scattering images.As the distance behind the aircraft increases,the diffusion range of the disturbance signal increases,and the signal intensity and contrast with the background decrease.Under the ground-based observation conditions of the aircraft at a height of 10000 m,a Mach number of1.6,and a detection distance of 100 km,the contrast between the disturbance signal and the back-ground was 30 d B at a distance of one time from the rear of the fuselage,and the diffusion diameter of the disturbance signal was 50 m.At a distance eight times the length of the aircraft,the contrast decreased to 10 dB,and the diameter increased to 290 m.The contrast was reduced to 3 dB at a distance nine times the length of the aircraft,and the diameter was diffused to 310 m.These results indicate the possibility of long-range aircraft detection based on the characteristics of the atmospheric density field.
基金supported by the National Natural Science Foundation of China (41604140)the Specialized Research Fund for State Key Laboratories and China Postdoctoral Science Foundation Fund
文摘Nonlinear force-free magnetic field （NLFFF） extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric magnetograms contain magnetic forces and small-scale noises, and fail to be consistent with the force-free assumption of NLFFF models. The procedure for removing the forces and noises in observed data is called preprocessing. In this paper, we extend the preprocessing code of Jiang ＆ Feng to spherical coordinates for a full sphere. We first smooth the observed data with Gaussian smoothing, and then split the smoothed magnetic field into a potential field and a non-potential field. The potential part is computed by a numerical potential field model, and the non-potential part is prepro- cessed using an optimization method to minimize the magnetic forces and magnetic torques. Applying the code to synoptic charts of the vector magnetic field from SDO/HMI, we find it can effectively reduce the noises and forces, and improve the quality of data for a better input which will be used for NLFFF extrapolations applied to the global corona.
基金financially supported by the National Natural Science Foundation of China(No.22068007).
文摘In photocatalysis field,S-scheme heterojunctions show unique advantages and prospects.However,the carrier shielding effect of heterojunctions limits the separation and migration of interfacial charges.In this study,a strategy of“dynamic cascade electric fields to deplete unilaterally accumulated charges”was innovatively proposed to overcome this drawback.By modulating g-C_(3)N_(4)(CN)and Bi_(2)WO_(6)(BWO)using the polarized electric field(PEF)of spontaneously polarized ceramic(SPC),a BWO/SPC-CN composite with cascade internal electric field(IEF)and PEF was successfully constructed for efficient piezophotocatalytic degradation of recalcitrant pollutants.BWO/SPC-CN contributed to 96.8% degradation of carbamazepine,significantly surpassing BWO/CN(70.5%).BWO/SPC-CN performed excellent capacity of harvesting piezoelectric energy due to its unique three-dimensional porous nano-network structure.The PEF of SPC modulated the electronic band structure and thus strengthened the IEF of BWO/SPC-CN,providing a persistent driving force for interfacial charge migration.Moreover,SPC with a strong PEF unilaterally consumed the charges accumulated on CN under periodic piezoelectricity,weakening the shielding electric field to inhibit the recombination of electron-hole pairs.As a consequence,the dynamic cascade PEF-IEF ultimately broke the carrier shielding effect in heterojunction photocatalysis and enhanced interfacial electron transfer.This work provides reliable methods to enhance the interfacial charge transfer in heterojunction and new insights into piezo-photocatalytic mechanism.
文摘Seepage refers to the flow of water through porous materials.This phenomenon has a crucial role in dam,slope,excavation,tunnel,and well design.Performing seepage analysis usually is a challenging task,as one must cope with the uncertainty associated with the parameters such as the hydraulic conductivity in the horizontal and vertical directions that drive this phenomenon.However,at the same time,the data on horizontal and vertical hydraulic conductivities are typically scarce in spatial resolution.In this context,so-called non-traditional approaches for uncertainty quantification(such as intervals and fuzzy variables)offer an interesting alternative to classical probabilistic methods,since they have been shown to be quite effective when limited information on the governing parameters of a phenomenon is available.Therefore,the main contribution of this study is the development of a framework for conducting seepage analysis in saturated soils,where uncertainty associated with hydraulic conductivity is characterized using fuzzy fields.This method to characterize uncertainty extends interval fields towards the domain of fuzzy numbers.In fact,it is illustrated that fuzzy fields are an effective tool for capturing uncertainties with a spatial component,since they allow one to account for available physical measurements.A case study in confined saturated soil shows that with the proposed framework,it is possible to quantify the uncertainty associated with seepage flow,exit gradient,and uplift force effectively.
文摘Earthquakes are caused directly by the motion of the stress field,therefore,observing the stress field is significant.Experiments on the relationships among wave velocity,stress factors,and faults show that the wave velocity of rock media under stable stress fields corresponds one-to-one with stress factors.Therefore,the wave velocity gradient can indicate the direction of stress vector,and the gradient divergence can indicate the strength of the stress field.To verify the results,considering the limitations of wave velocity measurement in solid crustal media,two quantities,namely the apparent wave velocity and Poisson ratios relating to wave velocity,were used to refl ect the stress field state.The seismic data of the Tangshan and Luzhou regions were studied separately.The calculated apparent wave velocity and Poisson ratios were interpolated to achieve regional data gridding.The gradients and the gradient divergences of the apparent wave velocity and Poisson ratio fields in the two regions were analyzed,and it was found that their spatial distribution in the same region was the same.They are believed to refl ect the vertical projection of the stress direction vector and strength on the surface in the stress field,consistent with the experimental results.Whether it can eff ectively refl ect the stress field requires further analysis of the specific situation of the local medium and the movement mode of the stress field.
基金supported by the National Science Foundation of China(Grant No.52293423 and Grant No.52277031).
文摘After the fabrication of magnetic resonance superconducting magnets,the magnetic field inhomogeneity needs to be accurately measured for subsequent shimming.However,conventional measurement methods are susceptible to magnetic fields,have poor compatibility,and are difficult to adapt to various types of magnets.This paper proposes a new field measuring system based on a three-axis movable platform.The system utilizes non-magnetic materials and an innovative hand-wheel lifting design that can be adapted to various aperture magnets,thus obviating the necessity for electrically driven equipment and addressing safety concerns in strong magnetic fields.In addition,the measurement system offers high accuracy up to 1 mm and a wide measurable range.The fields of 3 T and 7 T magnets were mapped using the designed system with diameter of spherical volume(DSV)of 160 mm and 130 mm,respectively.Experimental results demonstrate that the magnetic field measurement system has strong compatibility and can accurately map the magnetic field at arbitrary positions,which is critical for shimming studies.
基金National Natural Science Foundation of China,No.41930865Project for Innovative Capacity Improvement in Hebei Province,No.225A4201D。
文摘Nitrate(NO_(3)^(-))accumulation and transport processes in the thick vadose zone affect the evolution of the groundwater NO_(3)^(-)content in intensive agricultural regions.Agricultural land-use change(ALUC),typically accompanied by substantial alterations in nitrogen fertilizer application and irrigation practices,is an important influencing factor.This study evaluated the changes in NO_(3)^(-)accumulation and transport in the deep vadose zone(DVZ,below the root zone),and the groundwater NO_(3)^(-)content associated with ALUC from grain to vegetable fields in the North China Plain(NCP).The ALUC from grain to vegetable resulted in nitrate–nitrogen(NO_(3)^(-)-N)accumulation in DVZ increased by 235.5 kg ha^(-1)m^(-1)(163.2%)in the piedmont plain and 224.9 kg ha^(-1)m^(-1)(102.7%)in the central plain,respectively.This change accelerated downward transport velocity in the DVZ(from 0.81±0.47 to 0.89±0.55 m yr^(-1)in the piedmont plain,and from 0.24±0.12 to 0.92±0.12 m yr^(-1)in the central plain)and increased NO_(3)^(-)leaching fluxes.High transport velocity and leaching fluxes resulted in chemical N-fertilizer entering the aquifer in several areas in the piedmont plain.The impact of the agricultural activity intensity changes,accompanied by the ALUC,on groundwater quantity and quality should be considered in similar regions.
基金supported by the Natural Science Foundation of Anhui Province(No.228085ME142)the Comprehensive Research Facility for the Fusion Technology Program of China(No.20180000527301001228)the Open Fund of the Magnetic Confinement Fusion Laboratory of Anhui Province(No.2024AMF04003)。
文摘As the plasma current power in tokamak devices increases,a significant number of stray magnetic fields are generated around the equipment.These stray magnetic fields can disrupt the operation of electronic power devices,particularly transformers in switched-mode power supplies.Testing flyback converters with transformers under strong background magnetic fields highlights electromagnetic compatibility(EMC)issues for such switched-mode power supplies.This study utilizes finite element analysis software to simulate the electromagnetic environment of switched-mode power supply transformers and investigates the impact of variations in different magnetic field parameters on the performance of switched-mode power supplies under strong stray magnetic fields.The findings indicate that EMC issues are associated with transformer core saturation and can be alleviated through appropriate configurations of the core size,air gap,fillet radius,and installation direction.This study offers novel solutions for addressing EMC issues in high magnetic field environments.
基金supported by National Natural Science Foundation of China(52274323 and 524743495)the Postdoctoral Fellowship Program of CPSF under Grant Number GZC20240231.
文摘In the electroslag remelting(ESR)process,it mainly relies on thermal experiments or analysis via mechanistic models to realize the physical fields simulation of the electromagnetic field and temperature field coupled transfer,which has the limitations of high cost,a large amount of calculating data and high computing power requirements.A novel network based on physics-informed neural network(PINN)was designed to realize the fast and high-fidelity prediction of the distribution of electromagnetic field and temperature field in ESR process.The physical laws were combined with the deep learning network through PINN,and physical constraints were embedded to achieve effective solution of partial differential equations(PDEs).PINN was used to minimize the loss function consisting of data error,physical information error and boundary condition error.The physical laws and boundary condition constraints in the ESR process were considered to maintain high PDE solution accuracy under different spatial and temporal resolutions.Automatic differentiation(Autodiff)technique and gradient descent algorithm were used to optimize the network parameters.The experimental results show that compared with the mechanistic models,PINN can effectively replace thermal experiments to realize the physical field simulation of ESR process with only a few experimental data,which can avoid the disadvantages of pure data-driven network simulation that requires a large amount of training data.Moreover,the solution of PINN has good physical interpretability and reliability of simulation results.For simulating electromagnetic field and temperature field distribution,the training time of the network is only 140 and 203 s,and the regression indicators of root mean square error can reach 12.65 and 13.76,respectively.
基金supported by the National Natural Science Foundation of China(52164028,52274297)the Start-up Research Foundation of Hainan University(KYQD(ZR)20008,KYQD(ZR)21125,KYQD(ZR)23169))+1 种基金Collaborative Innovation Center of Marine Science and Technology of Hainan University(XTCX2022HYC14)Innovative Research Project for Postgraduate Students in Hainan Province(Qhyb2024-95).
文摘Development of robust electrocatalyst for oxygen reduction reaction(ORR)in a seawater electrolyte is the key to realize seawater electrolyte-based zinc-air batteries(SZABs).Herein,constructing a local electric field coupled with chloride ions(Cl-)fixation strategy in dual single-atom catalysts(DSACs)was proposed,and the resultant catalyst delivered considerable ORR performance in a seawater electrolyte,with a high half-wave potential(E_(1/2))of 0.868 V and a good maximum power density(Pmax)of 182 mW·cm^(−2)in the assembled SZABs,much higher than those of the Pt/C catalyst(E_(1/2):0.846 V;Pmax:150 mW·cm^(−2)).The in-situ characterization and theoretical calculations revealed that the Fe sites have a higher Cl^(−)adsorption affinity than the Co sites,and preferentially adsorbs Cl^(−)in a seawater electrolyte during the ORR process,and thus constructs a low-concentration Cl^(−)local microenvironment through the common-ion exclusion effect,which prevents Cl^(−)adsorption and corrosion in the Co active centers,achieving impressive catalytic stability.In addition,the directional charge movement between Fe and Co atomic pairs establishes a local electric field,optimizing the adsorption energy of Co sites for oxygen-containing intermediates,and further improving the ORR activity.
基金financially supported by the National Natural Science Foundation of China(Grant No.22325405,22402187 and 22432005).
文摘A recent study demonstrated that solid-state photochemically induced dynamic nuclear polarization(photo-CIDNP)can achieve significant 1H NMR hyperpolarization at high magnetic fields(9.4 T and 21.1 T).This was accomplished using a specially designed donor-chromophore-acceptor(D-C-A)molecule,which exhibits an excited state electron-electron interaction that is finely tuned to match the proton Larmor frequency under high-field conditions[1].
基金supported by the National Natural Science Foundation of China(Grant No.12175080)by Self-Determined Research Funds of Central China Normal University from the Colleges’Basic Research and Operation of MOE(Grant No.CCNU25JC012)。
文摘Spiral waves,as a typical self-organized structure with chiral characteristics,are widely found in excitable media such as cardiac tissues,chemical reactions,and neural networks.Based on the Fitz Hugh–Nagumo model,we investigated the mechanisms underlying the effects of direct current electric fields(DCEF),alternating current electric fields(ACEF),and polarized electric fields(PEF)on the interaction and annihilation processes of counter-rotating spiral waves.We found that in a direct current electric field,the drift direction of the spiral wave is determined jointly by its chirality and the electric field direction,which allows selective attraction or repulsion.In an alternating current electric field,the annihilation behavior of spiral waves can be influenced by the phase and intensity of the electric field,where a specific range of parameters induces resonance drift and eventual annihilation.On the other hand,the polarized electric field exhibits a more complex modulation capability on spiral waves:the trajectory and annihilation efficiency of spiral waves can be regulated by both the intensity and phase of the polarized electric field.These results reveal the potential feasibility of regulating multichiral spiral waves through multiple electric fields,providing theoretical insight for the control of spiral waves in relevant systems.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0503204)the National Natural Science Foundation of China(Grant No.42388101)+3 种基金Youth Innovation Promotion Association CAS(2020065)Young Elite Scientist Sponsorship Program by CAST(YESS20200152)the Key Research Program of the Institute of Geology&Geophysics,CAS(IGGCAS-202102)the Key Research Program of Chinese Academy of Sciences(Grant ZDB-SSW-TLC00103).
文摘The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of the Martian bow shocks were first found from the Mars Atmosphere and Volatile EvolutioN(MAVEN)observations.The present study aims to test whether this effect is also present in the shocks observed by Mars Express(MEX).We find that the bow shocks above the crustal field regions are enlarged,resulting in a north−south asymmetry and a longitude dependence in the shock size.The longitude dependence is more pronounced for near-subsolar shocks,and more dispersed for near-terminator shocks.The enlarged shocks are also observed to have shifted tailward from the longitudes of the strongest crustal fields.Due to a dawnside bias in MEX shock crossings,the enlarged shocks generally display a westward shift from the strongest crustal field region.These results confirm that stretches of the mini-magnetosphere are also present in the MEX shock observations.
基金supported by the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087)and the National Key R&D Program of China(Grant No.2022YFA1204100)。
文摘Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.
文摘In this paper we present certain bilinear estimates for commutators on Besov spaces with variable smoothness and integrability,and under no vanishing assumptions on the divergence of vector fields.Such commutator estimates are motivated by the study of well-posedness results for some models in incompressible fuid mechanics.
