The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas w...The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.展开更多
Tunable behavior in electrocatalysis by external multifields,such as magnetic field,thermal field,and electric field,is the most promising strategy to expand the theory,design,and synthesis of state-of-the-art catalys...Tunable behavior in electrocatalysis by external multifields,such as magnetic field,thermal field,and electric field,is the most promising strategy to expand the theory,design,and synthesis of state-of-the-art catalysts and the cell in the near future.Here,a systematic investigation for the effect of external magnetic field and thermal field on methanol oxidation reactions(MOR)in magnetic nanoparticles is reported.For Co_(42)Pt_(58)truncated octahedral nanoparticles(TONPs),the catalytic performance in MOR is greatly increased to the maximum of 14.1%by applying a magnetic field up to 3000 Oe,and it shows a monotonical increase with increasing working temperature.The magnetic enhanced effect is closely related to the Co content of Co_(x)Pt_(100-x)TONPs.Furthermore,the enhancement effect under a magnetic field is more obvious for Co_(42)Pt_(58)TONPs annealed at 650℃.First-principle calculation points out that the magnetic fields can facilitate the dehydrogenation of both methanol and water by suppression of entropy of the electron spin and lowering of the activation barrier,where OH_(ad)intermediates on Co sites play a more important role.The application of magnetic fields together with thermal fields in MOR provides a new prospect to manipulate the performance of direct methanol fuel cells,which will accelerate their potential applications.展开更多
During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an el...During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an electromagnetic device is developed and coupled with the welding system. By adjusting the conditions of external magnetic field, forward electromagnetic force is obtained to reduce the momentum of the backward flow of molten metal in weld pool. Consequently, the humping bead can be suppressed by adjusting the external magnetic field. Bead-on-plate welding experiment was conducted on mild steel plates, and the influence of magnetic flux density on the arc deflection angle and weld bead quality is investigated. It is found that external magnetic field can remarkably adjust the momentum of backward flow jet and significantly improve the quality of weld bead.展开更多
Obtaining a uniform interface temperature field plays a crucial role in the interface bonding quality of bimetal compound rolls.Therefore,this study proposes an improved electroslag remelting cladding(ESRC)process usi...Obtaining a uniform interface temperature field plays a crucial role in the interface bonding quality of bimetal compound rolls.Therefore,this study proposes an improved electroslag remelting cladding(ESRC)process using an external magnetic field to improve the uniformity of the interface temperature of compound rolls.The improved ESRC comprises a conventional ESRC circuit and an external coil circuit.A comprehensive 3D model,including multi-physics fields,is proposed to study the effect of external magnetic fields on the multi-phys-ics fields and interface temperature uniformity.The simulated results demonstrate that the nonuniform Joule heat and flow fields cause a non-uniform interface temperature in the conventional ESRC.As for the improved ESRC,the magnetic flux density(B_(coil))along the z-axis is pro-duced by an anticlockwise current of the external coil.The rotating Lorentz force is generated from the interaction between the radial current and axial B_(coil).Therefore,the slag pool flows clockwise,which enhances circumferential effective thermal conductivity.As a result,the uniformity of the temperature field and interface temperature improve.In addition,the magnetic flux density and rotational speed of the simulated results are in good agreement with those of the experimental results,which verifies the accuracy of the improved ESRC model.Therefore,an improved ESRC is efficient for industrial production of the compound roll with a uniform interface bonding quality.展开更多
The external magnetic field is applied to mitigating backward flow jet of molten metal in weld pool so that humping bead may be suppressed during high speed gas metal arc welding（GMAW）. Therefore, the external magne...The external magnetic field is applied to mitigating backward flow jet of molten metal in weld pool so that humping bead may be suppressed during high speed gas metal arc welding（GMAW）. Therefore, the external magnetic field distribution in workpiece is critical to understand the interaction mechanisms of the external magnetic field with molten metal flow. In this study, the steady state external magnetic field induced by excitation device is numerically analyzed by using the the finite element software ANSYS and the three dimensional static magnetic scalar method. The distribution of external transverse magnetic field By in workpiece and arc area is calculated, and the influence of excitation current and air-gap distance on the distribution of transverse magnetic field By has been discussed. The magnetic field distribution in workpiece is measured by using a Tesla-Meter and compared with the simulated result. It is found that both are in good agreement.展开更多
The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. We expand the potentiM around the two locM minima of the first-order deconfinement phase transition and extra...The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. We expand the potentiM around the two locM minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.展开更多
We consider an entangled Ising-XY Z diamond chain structure. Quantum correlations for this model are inves- tigated by using quantum discord and trace distance discord. Quantum correlations are obtained for different ...We consider an entangled Ising-XY Z diamond chain structure. Quantum correlations for this model are inves- tigated by using quantum discord and trace distance discord. Quantum correlations are obtained for different values of the anisotropy parameter, magnetic field and temperature. By comparison between quantum correlations, we show that the trace distance discord is always larger than quantum discord. Finally, some novel effects such as increasing the quantum correlations with temperature and constructive role of anisotropy parameter, which may play to the quantum correlations, are observed.展开更多
Using over eight years of Mars Atmosphere and Volatile Evolutio N(MAVEN)data,from November 2014 to May 2023,we have investigated the Martian nightside ionospheric magnetic field distribution under the influence of ups...Using over eight years of Mars Atmosphere and Volatile Evolutio N(MAVEN)data,from November 2014 to May 2023,we have investigated the Martian nightside ionospheric magnetic field distribution under the influence of upstream solar wind drivers,including the interplanetary magnetic field intensity(∣BIMF∣),solar wind dynamic pressure(PS W),solar extreme ultraviolet flux(EUV),and Martian seasons(L s).Our analysis reveals pronounced correlations between magnetic field residuals and both∣BIMF∣and PS W.Correlations observed with EUV flux and Ls were weaker—notably,magnetic field residuals increased during periods of high EUV flux and at Mars perihelion.We find that the IMF penetrates to an altitude of 200 km under a wide range of upstream conditions,penetrating notably deeper under high∣BIMF∣andPSWconditions.Our analysis also indicates that EUV flux and IMF cone angle have minimal impact on IMF penetration depth.Those findings provide useful constraints on the dynamic nature of Martian atmospheric escape processes and their evolution,suggesting that historical solar wind conditions may have facilitated deeper IMF penetration and higher rates of ionospheric escape than are observed now.Moreover,by establishing criteria for magnetic‘quiet’conditions,this study offers new insights into the planet’s magnetic environment under varying solar wind influences,knowledge that should help refine models of the Martian crustal magnetic field.展开更多
Photocatalysis is considered as one of the most promising technologies to generate renewable energy and degrade environmental pollutants.Tremendous efforts have been made to improve photocatalytic efficiency.Among the...Photocatalysis is considered as one of the most promising technologies to generate renewable energy and degrade environmental pollutants.Tremendous efforts have been made to improve photocatalytic efficiency.Among these,tuning spin polarization and introducing an external magnetic field are considered two promising strategies to boost photocatalytic performance.Herein this review highlights the recent breakthroughs through manipulating spin states and applying external magnetic fields for enhancing photocatalytic reactions.The relevant characterization techniques and fundamental mechanisms are summarized.Spin polarization states of photocatalysts have received considerable attention due to their unique roles,including inhibiting the recombination of photoexcited carriers owing to spin orientation constraint,enhancing the reaction product selectivity,and reducing the reaction barriers via optimizing the absorption energy and binding strength.As for the effects of external magnetic field on photocatalytic performance,we mainly discuss the separation enhancement of photoinduced carriers under static and time-varying magnetic fields and the magneto-hydrodynamic effect of charged particles.Lastly,the negative magnetoresistance effect is discussed due to the synergistic effects of the electron spin state and an external magnetic field.These discussions in this review may provide new insights into designing new semiconductors for boosting photocatalytic performance in internal and external magnetic fields.展开更多
We study theoretically the effect of weak external magnetic fields on persistent spin helix states in semiconductor two-dimensional electron gases with both Rashba and linear-in-momentum Dresselhaus spin-orbit couplin...We study theoretically the effect of weak external magnetic fields on persistent spin helix states in semiconductor two-dimensional electron gases with both Rashba and linear-in-momentum Dresselhaus spin-orbit coupling.We show that in the presence of weak external magnetic fields, some basic properties of a persistent spin helix state,including the dispersion relation between the decay time and the magnitude of the wavevector, the maximum decay time and the value of the characteristic magnitude of the wavevector at which the maximum decay time occurs, will all depend sensitively on the directions of applied external magnetic fields.展开更多
In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic fi...In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic field on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen–Boron(HB) fuel,the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle(from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.展开更多
High efficiency welding has always been one of the hot research subjects at home and overseas. Aiming at the problem of unstable droplet rotating spray transfer process in 450 A thin wire metal active gas arc(MAG) wel...High efficiency welding has always been one of the hot research subjects at home and overseas. Aiming at the problem of unstable droplet rotating spray transfer process in 450 A thin wire metal active gas arc(MAG) welding, a three-dimensional arc-droplet coupled model is established in this paper on the base of fluid dynamics to conduct numerical analysis for droplet transfer behavior with external magnetic controlled MAG welding, and used high-speed camera system to verify the simulation results. The results indicate that without external magnetic field, the droplet is transferred by the way of rotating spray, the arc is changeable and the spatter is serious. The electromagnetic force accelerates the radial liquid beam rotation under direct current(DC) magnetic field, and increases the angle between liquid beam and welding wire axis. Meanwhile, the rotation frequency of the liquid beam reaches 400 Hz, the area of arc column and heat loss increase under DC magnetic field. Based on the alternating magnetic field, the arc is the “bell shaped”, the arc stiffness raises, its temperature achieves 26 000 K, and the maximum speed of the liquid stream beam can reach 500 m/s. And the droplet transfer is more stable, the spatter significantly reduces, and welding quality is effectively improved.展开更多
Permanent magnet rings are presented, which exploit the image effect in the surrounding circular iron shields. The theory is given for a general permanent ring when the magnetization orientation at each coordinate ang...Permanent magnet rings are presented, which exploit the image effect in the surrounding circular iron shields. The theory is given for a general permanent ring when the magnetization orientation at each coordinate angle ψ changes by =(n+1)ψ, where n is a positive or negative integer. For the uniformly magnetized case n=-1, the permanent ring produces no field in its bore, and the field is that of a dipole outside. When the ring is surrounded by a soft iron shield, its field becomes uniform in the bore, and zero outside the ring. The field can be varied continuously by moving the iron shield along the magnet axis. A small variable field device was constructed by using NdFeB permanent rings, which produced a field flux density of 0-0.5 T in the central region.展开更多
The full-potential linearized augmented plane wave plus local orbital method is utilized for exploring the electronic,magnetic,and magneto-optical properties of the NiX_(2)(X=Cl,Br,and I)single layer.The first-princip...The full-potential linearized augmented plane wave plus local orbital method is utilized for exploring the electronic,magnetic,and magneto-optical properties of the NiX_(2)(X=Cl,Br,and I)single layer.The first-principles calculation demonstrates that these compounds are ferromagnetic indirect semiconductors,and the energy band gaps of NiX_(2)for X=Cl,Br,and I are 3.888,3.134,and 2.157 eV,respectively.The magnetic moments of Ni atoms in NiX_(2)monolayer are 1.656,1.588,1.449μB,and their magneto-crystalline anisotropy energies are 0.167,0.029,0.090 meV,respectively.Based on the macro-linear response theory,we systematically studied the influences of the external magnetic field and out-of-plane strain on the magneto-optical Kerr effect(MOKE)spectrum of the NiX_(2)single layer.It is found that,when the external magnetic field is perpendicular to the sample plane,the value of the Kerr rotation angle reaches the maximum,and the single-layer NiI_(2)material has a Kerr rotation angle of 1.89°at the photon energy of 1.986 eV.Besides,the Kerr rotation spectrum of NiCl_(2)and NiBr_(2)monolayers redshift as the out-of-plane strain increases,while NiI_(2)monolayer blueshifts.Accurate computation of the MOKE spectrum of NiX_(2)materials provides an opportunity for applications of 2D magnetic material ranging from sensing to data storing.展开更多
A 3D Magnetohydrodynamics （MHD） arc model in conjunction with an arc move- ment model is applied to simulate the arc rotation as well as to solve its effect on the pressure in an auto-expansion circuit breaker. The ...A 3D Magnetohydrodynamics （MHD） arc model in conjunction with an arc move- ment model is applied to simulate the arc rotation as well as to solve its effect on the pressure in an auto-expansion circuit breaker. The rotation of the arc driven by an external electromagnetic force is simulated in the case with 200 kA of the short circuit current and 16 ms of arc duration. The arc rotating process and the speed of arc rotation have been obtained in the simulation. A comparison of the pressure in the expansion volume with and without an external magnetic field has been carried out based on the calculation results of two cases. The results of the simulation reveal that the arc rotation, which causes more energy exchange between the arc and its sur- rounding gas, can evidently bring about the pressurization in the expansion volume, which would contribute to more effective arc quenching at current zero and further reducing operation power.展开更多
The quark anomalous magnetic moment(AMM)is dynamically generated through spontaneous chiral symmetry breaking.It has been revealed that,even though its exact form is still unknown,the quark AMM is essential to explori...The quark anomalous magnetic moment(AMM)is dynamically generated through spontaneous chiral symmetry breaking.It has been revealed that,even though its exact form is still unknown,the quark AMM is essential to exploring quark matter properties and QCD phase structure under external magnetic fields.In this study,we take three different forms of the quark AMM and investigate its influence on the chiral phase transition under a magnetic field.In general,a negative(positive)quark AMM acts as a magnetic-catalyzer(magnetic-inhibitor)for chiral symmetry breaking.It is found that a constant quark AMM drives an unexpected 1st order chiral phase transition,a quark AMM proportional to the chiral condensate flips the sign on the chiral condensate,and a quark AMM proportional to the square of the chiral condensate suppresses the magnetic enhancement in the chiral condensate at finite temperatures while retaining the chiral crossover phase transition.We also evaluate the intrinsic temperature dependence of the effective AMM form by fitting the effective model result of the chiral condensate to lattice QCD data,which may have a nontrivial correlation with the chiral phase transition.展开更多
A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are...A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coecient on the temperature is shown to be linearly changed over a wide range of temperature.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.12065015)the Hongliu Firstlevel Discipline Construction Project of Lanzhou University of Technology。
文摘The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFB2005800)the Natural Science Foundation of China(Grant Nos.52130103,52071026,51971026,and 11874082)+4 种基金the NSFC-ISF Joint Research Program(Grant No.51961145305)the State Key Laboratory for Advanced Metals and Materials(Grant No.2019Z-10)Beijing Natural Science Foundation Key Program(Grant No.Z190007)the Postdoctoral International Exchange Program(Grant No.YJ20210027)the Fundamental Research Funds for the Central Universities Grant(Grant No.FRF-TP-16-001C2).
文摘Tunable behavior in electrocatalysis by external multifields,such as magnetic field,thermal field,and electric field,is the most promising strategy to expand the theory,design,and synthesis of state-of-the-art catalysts and the cell in the near future.Here,a systematic investigation for the effect of external magnetic field and thermal field on methanol oxidation reactions(MOR)in magnetic nanoparticles is reported.For Co_(42)Pt_(58)truncated octahedral nanoparticles(TONPs),the catalytic performance in MOR is greatly increased to the maximum of 14.1%by applying a magnetic field up to 3000 Oe,and it shows a monotonical increase with increasing working temperature.The magnetic enhanced effect is closely related to the Co content of Co_(x)Pt_(100-x)TONPs.Furthermore,the enhancement effect under a magnetic field is more obvious for Co_(42)Pt_(58)TONPs annealed at 650℃.First-principle calculation points out that the magnetic fields can facilitate the dehydrogenation of both methanol and water by suppression of entropy of the electron spin and lowering of the activation barrier,where OH_(ad)intermediates on Co sites play a more important role.The application of magnetic fields together with thermal fields in MOR provides a new prospect to manipulate the performance of direct methanol fuel cells,which will accelerate their potential applications.
基金The authors are grateful to the financial support for this research from the National Natural Science Foundation of China，the Research Fund for the Doctoral Program of Higher Education of China
文摘During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an electromagnetic device is developed and coupled with the welding system. By adjusting the conditions of external magnetic field, forward electromagnetic force is obtained to reduce the momentum of the backward flow of molten metal in weld pool. Consequently, the humping bead can be suppressed by adjusting the external magnetic field. Bead-on-plate welding experiment was conducted on mild steel plates, and the influence of magnetic flux density on the arc deflection angle and weld bead quality is investigated. It is found that external magnetic field can remarkably adjust the momentum of backward flow jet and significantly improve the quality of weld bead.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51874084 and 52174303)the Fundamental Research Funds for the Central Universities of China(No.N2125026).
文摘Obtaining a uniform interface temperature field plays a crucial role in the interface bonding quality of bimetal compound rolls.Therefore,this study proposes an improved electroslag remelting cladding(ESRC)process using an external magnetic field to improve the uniformity of the interface temperature of compound rolls.The improved ESRC comprises a conventional ESRC circuit and an external coil circuit.A comprehensive 3D model,including multi-physics fields,is proposed to study the effect of external magnetic fields on the multi-phys-ics fields and interface temperature uniformity.The simulated results demonstrate that the nonuniform Joule heat and flow fields cause a non-uniform interface temperature in the conventional ESRC.As for the improved ESRC,the magnetic flux density(B_(coil))along the z-axis is pro-duced by an anticlockwise current of the external coil.The rotating Lorentz force is generated from the interaction between the radial current and axial B_(coil).Therefore,the slag pool flows clockwise,which enhances circumferential effective thermal conductivity.As a result,the uniformity of the temperature field and interface temperature improve.In addition,the magnetic flux density and rotational speed of the simulated results are in good agreement with those of the experimental results,which verifies the accuracy of the improved ESRC model.Therefore,an improved ESRC is efficient for industrial production of the compound roll with a uniform interface bonding quality.
基金The authors are grateful to the financial support for this research from the National Natural Science Foundation of China （ Grant No. 51275276） and the Research Fund for the Doctoral Program of Higher Education of China （ Grant No. 20120131130009）.
文摘The external magnetic field is applied to mitigating backward flow jet of molten metal in weld pool so that humping bead may be suppressed during high speed gas metal arc welding（GMAW）. Therefore, the external magnetic field distribution in workpiece is critical to understand the interaction mechanisms of the external magnetic field with molten metal flow. In this study, the steady state external magnetic field induced by excitation device is numerically analyzed by using the the finite element software ANSYS and the three dimensional static magnetic scalar method. The distribution of external transverse magnetic field By in workpiece and arc area is calculated, and the influence of excitation current and air-gap distance on the distribution of transverse magnetic field By has been discussed. The magnetic field distribution in workpiece is measured by using a Tesla-Meter and compared with the simulated result. It is found that both are in good agreement.
基金Supported by the National Natural Science Foundation of China under Grant No 11405122the China Postdoctoral Science Foundation under Grant No 2014M550483
文摘The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model. We expand the potentiM around the two locM minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.
基金Supported by the Azerbaijan Shahid Madani University
文摘We consider an entangled Ising-XY Z diamond chain structure. Quantum correlations for this model are inves- tigated by using quantum discord and trace distance discord. Quantum correlations are obtained for different values of the anisotropy parameter, magnetic field and temperature. By comparison between quantum correlations, we show that the trace distance discord is always larger than quantum discord. Finally, some novel effects such as increasing the quantum correlations with temperature and constructive role of anisotropy parameter, which may play to the quantum correlations, are observed.
基金supported by the National Natural Science Foundation of China(Grant No.42304186)China Postdoctoral Science Foundation(2023M743466)+3 种基金the Key Research Program of Chinese Academy of Sciences(Grant No.ZDBS-SSW-TLC00103)the Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.s IGGCAS-201904,IGGCAS-202102)supported by the International Space Science Institute(ISSI)in Bern and Beijing,through ISSI/ISSI-BJ International Team project“Understanding the Mars Space Environment through Multi-Spacecraft Measurements”(ISSI Team project#23–582ISSIBJ Team project#58).
文摘Using over eight years of Mars Atmosphere and Volatile Evolutio N(MAVEN)data,from November 2014 to May 2023,we have investigated the Martian nightside ionospheric magnetic field distribution under the influence of upstream solar wind drivers,including the interplanetary magnetic field intensity(∣BIMF∣),solar wind dynamic pressure(PS W),solar extreme ultraviolet flux(EUV),and Martian seasons(L s).Our analysis reveals pronounced correlations between magnetic field residuals and both∣BIMF∣and PS W.Correlations observed with EUV flux and Ls were weaker—notably,magnetic field residuals increased during periods of high EUV flux and at Mars perihelion.We find that the IMF penetrates to an altitude of 200 km under a wide range of upstream conditions,penetrating notably deeper under high∣BIMF∣andPSWconditions.Our analysis also indicates that EUV flux and IMF cone angle have minimal impact on IMF penetration depth.Those findings provide useful constraints on the dynamic nature of Martian atmospheric escape processes and their evolution,suggesting that historical solar wind conditions may have facilitated deeper IMF penetration and higher rates of ionospheric escape than are observed now.Moreover,by establishing criteria for magnetic‘quiet’conditions,this study offers new insights into the planet’s magnetic environment under varying solar wind influences,knowledge that should help refine models of the Martian crustal magnetic field.
基金the National Natural Science Foundation of China(Nos.61774055,51871138,and U2102212)the Science and Technology Committee of Shanghai(No.19010500400)。
文摘Photocatalysis is considered as one of the most promising technologies to generate renewable energy and degrade environmental pollutants.Tremendous efforts have been made to improve photocatalytic efficiency.Among these,tuning spin polarization and introducing an external magnetic field are considered two promising strategies to boost photocatalytic performance.Herein this review highlights the recent breakthroughs through manipulating spin states and applying external magnetic fields for enhancing photocatalytic reactions.The relevant characterization techniques and fundamental mechanisms are summarized.Spin polarization states of photocatalysts have received considerable attention due to their unique roles,including inhibiting the recombination of photoexcited carriers owing to spin orientation constraint,enhancing the reaction product selectivity,and reducing the reaction barriers via optimizing the absorption energy and binding strength.As for the effects of external magnetic field on photocatalytic performance,we mainly discuss the separation enhancement of photoinduced carriers under static and time-varying magnetic fields and the magneto-hydrodynamic effect of charged particles.Lastly,the negative magnetoresistance effect is discussed due to the synergistic effects of the electron spin state and an external magnetic field.These discussions in this review may provide new insights into designing new semiconductors for boosting photocatalytic performance in internal and external magnetic fields.
基金Supported by the National Natural Science Foundation of China under Grant No.10874049
文摘We study theoretically the effect of weak external magnetic fields on persistent spin helix states in semiconductor two-dimensional electron gases with both Rashba and linear-in-momentum Dresselhaus spin-orbit coupling.We show that in the presence of weak external magnetic fields, some basic properties of a persistent spin helix state,including the dispersion relation between the decay time and the magnitude of the wavevector, the maximum decay time and the value of the characteristic magnitude of the wavevector at which the maximum decay time occurs, will all depend sensitively on the directions of applied external magnetic fields.
文摘In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic field on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen–Boron(HB) fuel,the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle(from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.
基金Major Scientific and Technological Project of Gansu Province(No.22ZD6GA008)the National Natural Science Foundation of China(No.51775256).
文摘High efficiency welding has always been one of the hot research subjects at home and overseas. Aiming at the problem of unstable droplet rotating spray transfer process in 450 A thin wire metal active gas arc(MAG) welding, a three-dimensional arc-droplet coupled model is established in this paper on the base of fluid dynamics to conduct numerical analysis for droplet transfer behavior with external magnetic controlled MAG welding, and used high-speed camera system to verify the simulation results. The results indicate that without external magnetic field, the droplet is transferred by the way of rotating spray, the arc is changeable and the spatter is serious. The electromagnetic force accelerates the radial liquid beam rotation under direct current(DC) magnetic field, and increases the angle between liquid beam and welding wire axis. Meanwhile, the rotation frequency of the liquid beam reaches 400 Hz, the area of arc column and heat loss increase under DC magnetic field. Based on the alternating magnetic field, the arc is the “bell shaped”, the arc stiffness raises, its temperature achieves 26 000 K, and the maximum speed of the liquid stream beam can reach 500 m/s. And the droplet transfer is more stable, the spatter significantly reduces, and welding quality is effectively improved.
文摘Permanent magnet rings are presented, which exploit the image effect in the surrounding circular iron shields. The theory is given for a general permanent ring when the magnetization orientation at each coordinate angle ψ changes by =(n+1)ψ, where n is a positive or negative integer. For the uniformly magnetized case n=-1, the permanent ring produces no field in its bore, and the field is that of a dipole outside. When the ring is surrounded by a soft iron shield, its field becomes uniform in the bore, and zero outside the ring. The field can be varied continuously by moving the iron shield along the magnet axis. A small variable field device was constructed by using NdFeB permanent rings, which produced a field flux density of 0-0.5 T in the central region.
文摘The full-potential linearized augmented plane wave plus local orbital method is utilized for exploring the electronic,magnetic,and magneto-optical properties of the NiX_(2)(X=Cl,Br,and I)single layer.The first-principles calculation demonstrates that these compounds are ferromagnetic indirect semiconductors,and the energy band gaps of NiX_(2)for X=Cl,Br,and I are 3.888,3.134,and 2.157 eV,respectively.The magnetic moments of Ni atoms in NiX_(2)monolayer are 1.656,1.588,1.449μB,and their magneto-crystalline anisotropy energies are 0.167,0.029,0.090 meV,respectively.Based on the macro-linear response theory,we systematically studied the influences of the external magnetic field and out-of-plane strain on the magneto-optical Kerr effect(MOKE)spectrum of the NiX_(2)single layer.It is found that,when the external magnetic field is perpendicular to the sample plane,the value of the Kerr rotation angle reaches the maximum,and the single-layer NiI_(2)material has a Kerr rotation angle of 1.89°at the photon energy of 1.986 eV.Besides,the Kerr rotation spectrum of NiCl_(2)and NiBr_(2)monolayers redshift as the out-of-plane strain increases,while NiI_(2)monolayer blueshifts.Accurate computation of the MOKE spectrum of NiX_(2)materials provides an opportunity for applications of 2D magnetic material ranging from sensing to data storing.
基金supported by National Natural Science Foundation of China (Nos.51177005 and 51477004)
文摘A 3D Magnetohydrodynamics （MHD） arc model in conjunction with an arc move- ment model is applied to simulate the arc rotation as well as to solve its effect on the pressure in an auto-expansion circuit breaker. The rotation of the arc driven by an external electromagnetic force is simulated in the case with 200 kA of the short circuit current and 16 ms of arc duration. The arc rotating process and the speed of arc rotation have been obtained in the simulation. A comparison of the pressure in the expansion volume with and without an external magnetic field has been carried out based on the calculation results of two cases. The results of the simulation reveal that the arc rotation, which causes more energy exchange between the arc and its sur- rounding gas, can evidently bring about the pressurization in the expansion volume, which would contribute to more effective arc quenching at current zero and further reducing operation power.
基金Supported in part by the National Natural Science Foundation of China(12235016,12221005,11725523,11735007)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB34030000,XDPB15)+1 种基金start-up funding from the University of Chinese Academy of Sciences(UCAS)the Fundamental Research Funds for the Central Universities。
文摘The quark anomalous magnetic moment(AMM)is dynamically generated through spontaneous chiral symmetry breaking.It has been revealed that,even though its exact form is still unknown,the quark AMM is essential to exploring quark matter properties and QCD phase structure under external magnetic fields.In this study,we take three different forms of the quark AMM and investigate its influence on the chiral phase transition under a magnetic field.In general,a negative(positive)quark AMM acts as a magnetic-catalyzer(magnetic-inhibitor)for chiral symmetry breaking.It is found that a constant quark AMM drives an unexpected 1st order chiral phase transition,a quark AMM proportional to the chiral condensate flips the sign on the chiral condensate,and a quark AMM proportional to the square of the chiral condensate suppresses the magnetic enhancement in the chiral condensate at finite temperatures while retaining the chiral crossover phase transition.We also evaluate the intrinsic temperature dependence of the effective AMM form by fitting the effective model result of the chiral condensate to lattice QCD data,which may have a nontrivial correlation with the chiral phase transition.
基金Supported by National Magnetic Confinement Fusion Science Program under Grant No.2013GB111005the Foundation of Civil Aviation University of China under Grant No.08QD07X
文摘A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coecient on the temperature is shown to be linearly changed over a wide range of temperature.
