With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal p...With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet(NEPS)during a substorm at 03:23 UT on 12 February 2008.Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes(THA(P5),THD(P3)and THE(P4))in the magnetotail.In the current sheet with a large plasma beta value(β>2,whereβis the ratio of the plasma thermal pressure to the magnetic pressure),the dipolarization within the substorm onset region,(−10.4,2.8,−2.6)RE_gsm,has a large initial magnetic field elevation angle,θ>60°,θ=arctan(Bz/(Bx2+By2)1/2),and is accompanied by energetic ion(tens to hundred keV)dispersionless injection detected by THD(P3).This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations.The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field,Bt.The maximum value of the elevation angle approaches 85°during the later substorm expansion phase.In the NEPS withβ~1,the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value ofθ<45°and following multi-step enhancements during the substorm expansion phase.The maximum value of the elevation angle approaches to 70°during the later substorm expansion phase.Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.展开更多
Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures ...Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures after they are produced by reconnection. Motivated by this simulation, we revisited the scale size of DFs in the dawn-dusk direction by using Cluster observations during the years when the inter-distance among Cluster spacecraft was between 1000 and 2000 km. We selected the DFs that were detected by more than one spacecraft and estimated the radii of these DFs by a simple geometrical analysis, which is based on comparison of DF normals observed by different spacecraft. We found a few DFs that were only a few ion inertial lengths in the dawn-dusk direction. These results point out the importance of multi-scale coupling during the evolution of DFs.展开更多
The Space Plasma Environment Research Facility(SPERF)for ground simulation of the space plasma environment is a key component of the Space Environment Simulation Research Infrastructure(SESRI),a major national science...The Space Plasma Environment Research Facility(SPERF)for ground simulation of the space plasma environment is a key component of the Space Environment Simulation Research Infrastructure(SESRI),a major national science and technology infrastructure for fundamental research.It is designed to investigate outstanding issues in the space plasma environment,such as energetic particle acceleration,transport,and interaction with electromagnetic waves,as well as magnetic reconnection processes,in magnetospheric plasmas.The Tail-Research EXperiment(TREX)is part of the SPERF for laboratory studies of space physics relevant to magnetic reconnection,dipolarization and hydromagnetic wave excitation in the magnetotail.SPERFTREX is designed to carry out three types of experiments:the tail plasmoid for magnetic reconnection,dipolarization front formation,and magnetohydrodynamic waves excited by highspeed plasma jets.In this paper,the scientific goals and three scenarios of SPERF-TREX for typical processes in space plasmas are presented,and experimental plans for SPERF-TREX are also reviewed,together with the plasma sources applied to generate the plasma with the desired parameters and various magnetic configurations.展开更多
In this paper, the particle acceleration processes around magnetotail dipolarization fronts(DFs) were reviewed. We summarize the spacecraft observations(including Cluster, THEMIS, MMS) and numerical simulations(includ...In this paper, the particle acceleration processes around magnetotail dipolarization fronts(DFs) were reviewed. We summarize the spacecraft observations(including Cluster, THEMIS, MMS) and numerical simulations(including MHD, testparticle, hybrid, LSK, PIC) of these processes. Specifically, we(1) introduce the properties of DFs at MHD scale, ion scale, and electron scale,(2) review the properties of suprathermal electrons with particular focus on the pitch-angle distributions,(3)define the particle-acceleration process and distinguish it from the particle-heating process,(4) identify the particle-acceleration process from spacecraft measurements of energy fluxes, and(5) quantify the acceleration efficiency and compare it with other processes in the magnetosphere(e.g., magnetic reconnection and radiation-belt acceleration processes). We focus on both the acceleration of electrons and ions(including light ions and heavy ions). Regarding electron acceleration, we introduce Fermi,betatron, and non-adiabatic acceleration mechanisms;regarding ion acceleration, we present Fermi, betatron, reflection, resonance, and non-adiabatic acceleration mechanisms. We also discuss the unsolved problems and open questions relevant to this topic, and suggest directions for future studies.展开更多
In order to investigate the suprathermal electron flux(>30 ke V) around dipolarization fronts(DFs), we statistically studied the suprathermal electron flux variations and pitch angle distributions of hundreds of ea...In order to investigate the suprathermal electron flux(>30 ke V) around dipolarization fronts(DFs), we statistically studied the suprathermal electron flux variations and pitch angle distributions of hundreds of earthward propagating DFs observed by THEMIS spacecraft during its tail seasons in years 2008–2009. We focused on the electron flux variations across DFs and electron anisotropies behind DFs. We divided DF into three sectors in the equatorial plane: Dusk, central and dawn sectors. The sectors are defined according to the DF normals with respect to DF's meridian in the equatorial plane(the symmetric line of DF). We found that events with electron flux increases and decreases behind the fronts had no particular dependence on the observation locations. In addition, there was no obvious dependence of electron anisotropy behind DF on the different sectors of DF.展开更多
We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts （DFs） in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by m...We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts （DFs） in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS space- craft in the near-Earth magnetotail （-10 Re）. We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic （LSK） simulation results. The LSK simulation reproduced the sudden ion energy flux enhance- ment concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.展开更多
It has been confirmed that dipolarization fronts(DFs)are the result of the interchange instability in the Earth's magnetotail.In this paper,we use a Hall MHD model to simulate the evolution of the interchange inst...It has been confirmed that dipolarization fronts(DFs)are the result of the interchange instability in the Earth's magnetotail.In this paper,we use a Hall MHD model to simulate the evolution of the interchange instability that produces DFs along the leading edge.A test particle simulation is performed to study the physical phenomenon of ion acceleration at the DF.The numerical simulation indicates that almost all particles move earthward and dawnward and then drift to the tail.The DF-reflected ion population at the duskside appears earlier as a consequence of the asymmetric Hall electric field.Ions that are distributed in a dawn-dusk asymmetric semicircle behind the DF tend to be accelerated to higher energies(>13.5 keV).These high-energy particles eventually concentrate in the dawnside.Ions experience effective acceleration by the dawnward electric field,while they drift through the dawn flank at the front,toward the tail.展开更多
We numerically investigate the breathing dynamics induced by collision between bright solitons in a binary dipolar Bose–Einstein condensates, whose dipole–dipole interaction and contact interaction are attractive. W...We numerically investigate the breathing dynamics induced by collision between bright solitons in a binary dipolar Bose–Einstein condensates, whose dipole–dipole interaction and contact interaction are attractive. We identify three special breathing structures, such as snakelike special breathing structure, mixed breathing structure, and divide breathing structure.The characteristics of these breathing structures can be described by breathing frequency ?, maximum breathing amplitude A and lifetime τ, which can be manipulated by atomic number Ni and interspecies scattering length a12. Meanwhile, the above breathing structures can realize the process of quasi-transition with a reasonable Ni and a12. Additionally, the collision of two special breathing structures also can bring more abundant breathing dynamics. Our results provide a reference for the study of soliton interactions and deepen the understanding of soliton properties in a binary dipolar Bose–Einstein condensates.展开更多
The prevalent view endorses that the force of gravitation of the earth is directed towards the centre of the planet, in consequence of which, temperature and pressure at the deepest part of the planet must be very hig...The prevalent view endorses that the force of gravitation of the earth is directed towards the centre of the planet, in consequence of which, temperature and pressure at the deepest part of the planet must be very high. This view leads to the conclusion that the inner core or deepest part of the planet, though constituted of iron through which magnetic lines of force emanate, cannot be magnetic. The author has shown that amongst the earth’s three geospheres, fluid outer core that occurs between mantle and inner core, is a void zone which, because of the association of some particles from the mantle, apparently shows fluid characteristics. Occurrence of a virtually void zone in the planet’s deep interior separated by a solid mantle and iron inner core would generate a reversely directed gravitational force due to which pressure and temperature at the deepest part of the earth would be sufficiently low. Hence, the earth’s solid inner core, constituted of iron, is a dipolar permanent magnet. The paper envisages that the concept of reverse gravity presented here needs to be validated by physicists since it is an original view. The concept put forward here, not only explains the cause of earth’s magnetic phenomena, but also elucidates continental drifting and several other features of the planet in a scientifically accepted manner, thereby refuting the possibility of occurrence of convection current in the mantle which is solid and rigid.展开更多
Using in-situ measurements from the Cassini spacecraft in 2013, we report an Earth substorm-like loading-unloading process at Saturn's distant magnetotail. We found that the loading process is featured with two di...Using in-situ measurements from the Cassini spacecraft in 2013, we report an Earth substorm-like loading-unloading process at Saturn's distant magnetotail. We found that the loading process is featured with two distinct processes: a rapid loading process that was likely driven by an internal source and a slow loading process that was likely driven by solar wind. Each of the two loading processes could also individually lead to an unloading process. The rapid internal loading process lasts for ~ 1-2 hours; the solar wind driven loading process lasts for ~ 3-18 hours and the following unloading process lasts for ~1-3 hours. In this letter, we suggest three possible loadingunloading circulations, which are fundamental in understanding the role of solar wind in driving giant planetary magnetospheric dynamics.展开更多
Pyrolysis has the potential of transforming waste into recyclable products. Pyrolytic carbon black (PCB) is one of the most important products from the pyrolysis of used tires. Techniques for surface modifications of ...Pyrolysis has the potential of transforming waste into recyclable products. Pyrolytic carbon black (PCB) is one of the most important products from the pyrolysis of used tires. Techniques for surface modifications of PCB have been developed. One of the most significant applications for modified PCB is to reinforce the rubber matrix to obtain high added values. The transverse relaxation and the chain dynamics of vulcanized rubber networks with PCB and modified PCB were studied and compared with those of the commercial carbon blacks using selective 1H transverse relaxation (T2) experiments and dipolar correlation effect (DCE) experiments on the stimulated echo. Demineralization and coupling agent modification not only intensified the interactions between the modified PCB and the neighboring polyisoprene chains, but also increased the chemical cross-link density of the vulcanized rubber with modified PCB. The mechanical testing of the rubbers with different kinds of carbon blacks showed that the maximum strain of the rubber with modified PCB was improved greatly. The mechanical testing results confirmed the conclusion obtained by nuclear magnetic resonance (NMR). PCB modified by the demineralization and NDZ-105 titanate coupling agent could be used to replace the commercial semi-reinforcing carbon black.展开更多
The determination of natural products stereochemistry remains a formidable task.Residual dipolar couplings(RDCs)induced by anisotropic media are a powerful tool for determination of the stereochemistry of organic mole...The determination of natural products stereochemistry remains a formidable task.Residual dipolar couplings(RDCs)induced by anisotropic media are a powerful tool for determination of the stereochemistry of organic molecule in solution.This review will provide a short introduction on RDCs-based methodology for the structural elucidation of natural products.Special attention is given to the current availability of alignment media in organic solvents.The applications of RDCs for structural analysis of some examples of natural products were discussed and summarized.Graphical Abstract This review provides a short introduction on RDCs-based methodology for the structural elucidation of natural products.Special attention is given to the current availability of alignment media in organic solvents.The applications of RDCs for structural analysis of some examples of natural products were discussed and summarized.展开更多
We study the formation of vortices in a dipolar Bose-Einstein condensate in a synthetic magnetic field by numerically solving the Gross-Pitaevskii equation. The formation process depends on the dipole strength, the ro...We study the formation of vortices in a dipolar Bose-Einstein condensate in a synthetic magnetic field by numerically solving the Gross-Pitaevskii equation. The formation process depends on the dipole strength, the rotating frequency, the potential geometry, and the orientation of the dipoles. We make an extensive comparison with vortices created by a rotating trap, especially focusing on the issues of the critical rotating frequency and the vortex number as a function of the rotating frequency. We observe that a higher rotating frequency is needed to generate a large number of vortices and the anisotropic interaction manifests itself as a perceptible difference in the vortex formation. Furthermore, a large dipole strength or aspect ratio also can increase the number of vortices effectively. In particular, we discuss the validity of the Feynman rule.展开更多
A series of “H-shaped” organic dimers （azobenzene derivatives） exhibit linear absorption red shift compared with their corresponding monomers experimentally. Dipolar interaction model is not appropriate for the az...A series of “H-shaped” organic dimers （azobenzene derivatives） exhibit linear absorption red shift compared with their corresponding monomers experimentally. Dipolar interaction model is not appropriate for the azobenzene derivatives due to the small distance between two “D-π-A” chains. Energy transfer model is suggested for explanation of the absorption red shift. Two necessary conditions for energy transfer were verified. In addition, bi-exponential florescence-delay behavior of the dimer as well as Bella＇s quantum chemistry calculation shows evidence of energy transfer.展开更多
A modified correlated spectroscopy （COSY） revamped with asymmetric Z-gradient echo detection sequence was designed to investigate the influence of diffusion hehaviour on intermolecular double-quantum coherence signa...A modified correlated spectroscopy （COSY） revamped with asymmetric Z-gradient echo detection sequence was designed to investigate the influence of diffusion hehaviour on intermolecular double-quantum coherence signal attenuation during the pre-acquisition period. Theoretical formulas were deduced and experimental measurements and simulations were performed. It is found that the diffusion behaviour of intermolecular double-quantum coherence in the pre-acquisition period may be different from that of conventional single-quantum coherence, depending on the relative orientation of diffusion weighting gradients to coherence selection gradients. When the orientation of the diffusion weighting gradients is parallel or anti-parallel to the orientation of the coherence selection gradients, the diffusion is modulated by the distant dipolar field. This study is helpful for understanding the signal properties in intermolecular double-quantum coherence magnetic resonance imaging.展开更多
This paper analyses the heteronuclear Cosy Revamped by Asymmetric Z-gradient Echo Detection pulse sequence. General theoretical expressions of the pulse sequence with arbitrary flip angles were derived by using dipola...This paper analyses the heteronuclear Cosy Revamped by Asymmetric Z-gradient Echo Detection pulse sequence. General theoretical expressions of the pulse sequence with arbitrary flip angles were derived by using dipolar field treatment and signals originating from heteronuclear intermolecular single-quantum coherences （iSQCs） in highly-polarized two spin-1/2 systems were mainly discussed in order to find the optimal flip angles. The results show that signals from heteronuclear iSQCs decay slower than those from intermolecular double-quantum coherences or intermolecular zero-quantum coherences. Magical angle experiments validate that the signals are from heteronuclear iSQCs and insensitive to the imperfection of radio-frequency flip angles. All experimental observations are in excellent agreement with theoretical predictions. The quantum-mechanical treatment leads to similar predictions to the dipolar field treatment.展开更多
The main idea of this paper is to find an analytical formula for the input conductance of an elevated ferrite film circu-lator to match it systematically to the desired matching network. For solving the ferrite loaded...The main idea of this paper is to find an analytical formula for the input conductance of an elevated ferrite film circu-lator to match it systematically to the desired matching network. For solving the ferrite loaded dielectric resonator included in stripline elevated ferrite film circulator, the off diagonal components of the permeability tensor are taken as the perturbation. The electromagnetic fields computations are done for unperturbed structure. The dipolar resonant frequencies corresponding to harmonics of the resonant modes are then calculated using the perturbation integrals. The quality factor of the circulator is derived in terms of these dipolar resonant frequencies. Energy integrals are calculated to find the energy stored in the ferrite and dielectic layers. An analytical expression for the input conductance of the elevated ferrite film circulators is derived by using the quality factor and energy integrals. In this expression the ferrite and dielectric layers can have different permittivities. Some discussions about the effect of ferrite film thickness and permittivity mismatch on the bandwidth of the circulator are investigated by HFSS commercial software.展开更多
The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocea...The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocean（SPO） in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.展开更多
We study quantum tunneling of a dipolar Bose-Einstein condensate in optical lattice when the spin system initially is prepared in a squeezed coherent state. It is found that there exists quantum tunneling between latt...We study quantum tunneling of a dipolar Bose-Einstein condensate in optical lattice when the spin system initially is prepared in a squeezed coherent state. It is found that there exists quantum tunneling between lattices l and l ＋ 1, l and l - 1, respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength limit, quantum tunneling disappears between lattices l and l ＋ 1, and that l and l - 1. Correspondingly, the magnetic soliton appears.展开更多
For the numerical simulation of the fractional quantum Hall(FQH) effects on a finite disk, the rotational symmetry is the only symmetry that is used in diagonalizing the Hamiltonian. In this work, we propose a method ...For the numerical simulation of the fractional quantum Hall(FQH) effects on a finite disk, the rotational symmetry is the only symmetry that is used in diagonalizing the Hamiltonian. In this work, we propose a method of using the weak translational symmetry for the center of mass of the many-body system. With this approach, the bulk properties, such as the energy gap and the magneto-roton excitation are consistent with those in the closed manifolds like the sphere and torus. As an application, we consider the FQH phase and its phase transition in the fast rotated dipolar fermions. We thus demonstrate the disk geometry having versatility in analyzing the bulk properties beside the usual edge physics.展开更多
基金supported by the National Natural Science Foundation of China(NSFC)under grants 41731070,41674167,41574161the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences,grants XDA15052500,XDA15350201 and XDA15011401the Specialized Research Fund for State Key Laboratories of China.
文摘With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet(NEPS)during a substorm at 03:23 UT on 12 February 2008.Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes(THA(P5),THD(P3)and THE(P4))in the magnetotail.In the current sheet with a large plasma beta value(β>2,whereβis the ratio of the plasma thermal pressure to the magnetic pressure),the dipolarization within the substorm onset region,(−10.4,2.8,−2.6)RE_gsm,has a large initial magnetic field elevation angle,θ>60°,θ=arctan(Bz/(Bx2+By2)1/2),and is accompanied by energetic ion(tens to hundred keV)dispersionless injection detected by THD(P3).This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations.The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field,Bt.The maximum value of the elevation angle approaches 85°during the later substorm expansion phase.In the NEPS withβ~1,the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value ofθ<45°and following multi-step enhancements during the substorm expansion phase.The maximum value of the elevation angle approaches to 70°during the later substorm expansion phase.Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.
基金supported by the National Natural Science Foundation of China (NSFC) under grant 41774154 and 41504123the Science Foundation of Jiangxi Province under grant 20122BAB21 2002+1 种基金the Nanchang University graduate innovation special fund project under grant CX2017106the Key Industry Innovation Chain of Shaanxi under grant 2018JQ4032
文摘Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures after they are produced by reconnection. Motivated by this simulation, we revisited the scale size of DFs in the dawn-dusk direction by using Cluster observations during the years when the inter-distance among Cluster spacecraft was between 1000 and 2000 km. We selected the DFs that were detected by more than one spacecraft and estimated the radii of these DFs by a simple geometrical analysis, which is based on comparison of DF normals observed by different spacecraft. We found a few DFs that were only a few ion inertial lengths in the dawn-dusk direction. These results point out the importance of multi-scale coupling during the evolution of DFs.
基金supported by the State Commission of Development and Reform of ChinaNational Natural Science Foundation of China(Nos.42261134533,11261140326,11405038)。
文摘The Space Plasma Environment Research Facility(SPERF)for ground simulation of the space plasma environment is a key component of the Space Environment Simulation Research Infrastructure(SESRI),a major national science and technology infrastructure for fundamental research.It is designed to investigate outstanding issues in the space plasma environment,such as energetic particle acceleration,transport,and interaction with electromagnetic waves,as well as magnetic reconnection processes,in magnetospheric plasmas.The Tail-Research EXperiment(TREX)is part of the SPERF for laboratory studies of space physics relevant to magnetic reconnection,dipolarization and hydromagnetic wave excitation in the magnetotail.SPERFTREX is designed to carry out three types of experiments:the tail plasmoid for magnetic reconnection,dipolarization front formation,and magnetohydrodynamic waves excited by highspeed plasma jets.In this paper,the scientific goals and three scenarios of SPERF-TREX for typical processes in space plasmas are presented,and experimental plans for SPERF-TREX are also reviewed,together with the plasma sources applied to generate the plasma with the desired parameters and various magnetic configurations.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41404133, 41874188, 41574153, 40621003 & 41431071)supported by the project (Grant No. KP19-270)+1 种基金Christine GABRIELSE was supported by NASA (Grant No. NAS5-02099)the support by NASA’s MMS project at Sw RI and NSF (Grant Nos. AGS1602510, NASA NNX16AI39G/80NSSC18K1534, 80NSSC18K0570 & 80NSSC18K0693)
文摘In this paper, the particle acceleration processes around magnetotail dipolarization fronts(DFs) were reviewed. We summarize the spacecraft observations(including Cluster, THEMIS, MMS) and numerical simulations(including MHD, testparticle, hybrid, LSK, PIC) of these processes. Specifically, we(1) introduce the properties of DFs at MHD scale, ion scale, and electron scale,(2) review the properties of suprathermal electrons with particular focus on the pitch-angle distributions,(3)define the particle-acceleration process and distinguish it from the particle-heating process,(4) identify the particle-acceleration process from spacecraft measurements of energy fluxes, and(5) quantify the acceleration efficiency and compare it with other processes in the magnetosphere(e.g., magnetic reconnection and radiation-belt acceleration processes). We focus on both the acceleration of electrons and ions(including light ions and heavy ions). Regarding electron acceleration, we introduce Fermi,betatron, and non-adiabatic acceleration mechanisms;regarding ion acceleration, we present Fermi, betatron, reflection, resonance, and non-adiabatic acceleration mechanisms. We also discuss the unsolved problems and open questions relevant to this topic, and suggest directions for future studies.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.41174147,41274170 and 41331070)Natural Science Foundation of Jiangxi Province(Grant No.20142BCB23006)
文摘In order to investigate the suprathermal electron flux(>30 ke V) around dipolarization fronts(DFs), we statistically studied the suprathermal electron flux variations and pitch angle distributions of hundreds of earthward propagating DFs observed by THEMIS spacecraft during its tail seasons in years 2008–2009. We focused on the electron flux variations across DFs and electron anisotropies behind DFs. We divided DF into three sectors in the equatorial plane: Dusk, central and dawn sectors. The sectors are defined according to the DF normals with respect to DF's meridian in the equatorial plane(the symmetric line of DF). We found that events with electron flux increases and decreases behind the fronts had no particular dependence on the observation locations. In addition, there was no obvious dependence of electron anisotropy behind DF on the different sectors of DF.
基金supported by National Natural Science Foundation of China(Grant Nos.41174147,41274170,41331070)China Postdoctoral Science Foundation Funded Project,and the Fundamental Research Fund for theCentral Universities(Grant No.2042014kf0017)
文摘We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts （DFs） in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS space- craft in the near-Earth magnetotail （-10 Re）. We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic （LSK） simulation results. The LSK simulation reproduced the sudden ion energy flux enhance- ment concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.
基金This work was supported by the pre-research projects on Civil Aerospace Technologies funded by China’s National Space Administration(CNSA)(Grant No.D020103)and the National Natural Science Foundation of China(Grant Nos.41474144,41674176).
文摘It has been confirmed that dipolarization fronts(DFs)are the result of the interchange instability in the Earth's magnetotail.In this paper,we use a Hall MHD model to simulate the evolution of the interchange instability that produces DFs along the leading edge.A test particle simulation is performed to study the physical phenomenon of ion acceleration at the DF.The numerical simulation indicates that almost all particles move earthward and dawnward and then drift to the tail.The DF-reflected ion population at the duskside appears earlier as a consequence of the asymmetric Hall electric field.Ions that are distributed in a dawn-dusk asymmetric semicircle behind the DF tend to be accelerated to higher energies(>13.5 keV).These high-energy particles eventually concentrate in the dawnside.Ions experience effective acceleration by the dawnward electric field,while they drift through the dawn flank at the front,toward the tail.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12247103, 12275213, and 12247110)。
文摘We numerically investigate the breathing dynamics induced by collision between bright solitons in a binary dipolar Bose–Einstein condensates, whose dipole–dipole interaction and contact interaction are attractive. We identify three special breathing structures, such as snakelike special breathing structure, mixed breathing structure, and divide breathing structure.The characteristics of these breathing structures can be described by breathing frequency ?, maximum breathing amplitude A and lifetime τ, which can be manipulated by atomic number Ni and interspecies scattering length a12. Meanwhile, the above breathing structures can realize the process of quasi-transition with a reasonable Ni and a12. Additionally, the collision of two special breathing structures also can bring more abundant breathing dynamics. Our results provide a reference for the study of soliton interactions and deepen the understanding of soliton properties in a binary dipolar Bose–Einstein condensates.
文摘The prevalent view endorses that the force of gravitation of the earth is directed towards the centre of the planet, in consequence of which, temperature and pressure at the deepest part of the planet must be very high. This view leads to the conclusion that the inner core or deepest part of the planet, though constituted of iron through which magnetic lines of force emanate, cannot be magnetic. The author has shown that amongst the earth’s three geospheres, fluid outer core that occurs between mantle and inner core, is a void zone which, because of the association of some particles from the mantle, apparently shows fluid characteristics. Occurrence of a virtually void zone in the planet’s deep interior separated by a solid mantle and iron inner core would generate a reversely directed gravitational force due to which pressure and temperature at the deepest part of the earth would be sufficiently low. Hence, the earth’s solid inner core, constituted of iron, is a dipolar permanent magnet. The paper envisages that the concept of reverse gravity presented here needs to be validated by physicists since it is an original view. The concept put forward here, not only explains the cause of earth’s magnetic phenomena, but also elucidates continental drifting and several other features of the planet in a scientifically accepted manner, thereby refuting the possibility of occurrence of convection current in the mantle which is solid and rigid.
基金supported by the National Science Foundation of China (41525016,41404117)
文摘Using in-situ measurements from the Cassini spacecraft in 2013, we report an Earth substorm-like loading-unloading process at Saturn's distant magnetotail. We found that the loading process is featured with two distinct processes: a rapid loading process that was likely driven by an internal source and a slow loading process that was likely driven by solar wind. Each of the two loading processes could also individually lead to an unloading process. The rapid internal loading process lasts for ~ 1-2 hours; the solar wind driven loading process lasts for ~ 3-18 hours and the following unloading process lasts for ~1-3 hours. In this letter, we suggest three possible loadingunloading circulations, which are fundamental in understanding the role of solar wind in driving giant planetary magnetospheric dynamics.
基金Project supported by the National Natural Science Foundation of China (Nos. 20490200 and 20176051), and the Project Based Per-sonnel Exchange Program with the China Scholarship Council and the German Academic Exchange Service
文摘Pyrolysis has the potential of transforming waste into recyclable products. Pyrolytic carbon black (PCB) is one of the most important products from the pyrolysis of used tires. Techniques for surface modifications of PCB have been developed. One of the most significant applications for modified PCB is to reinforce the rubber matrix to obtain high added values. The transverse relaxation and the chain dynamics of vulcanized rubber networks with PCB and modified PCB were studied and compared with those of the commercial carbon blacks using selective 1H transverse relaxation (T2) experiments and dipolar correlation effect (DCE) experiments on the stimulated echo. Demineralization and coupling agent modification not only intensified the interactions between the modified PCB and the neighboring polyisoprene chains, but also increased the chemical cross-link density of the vulcanized rubber with modified PCB. The mechanical testing of the rubbers with different kinds of carbon blacks showed that the maximum strain of the rubber with modified PCB was improved greatly. The mechanical testing results confirmed the conclusion obtained by nuclear magnetic resonance (NMR). PCB modified by the demineralization and NDZ-105 titanate coupling agent could be used to replace the commercial semi-reinforcing carbon black.
基金co-supported by National Natural Science Foundation of China(21572164,U1504207)the Sino-German Center for Research Promotion(GZ1289).
文摘The determination of natural products stereochemistry remains a formidable task.Residual dipolar couplings(RDCs)induced by anisotropic media are a powerful tool for determination of the stereochemistry of organic molecule in solution.This review will provide a short introduction on RDCs-based methodology for the structural elucidation of natural products.Special attention is given to the current availability of alignment media in organic solvents.The applications of RDCs for structural analysis of some examples of natural products were discussed and summarized.Graphical Abstract This review provides a short introduction on RDCs-based methodology for the structural elucidation of natural products.Special attention is given to the current availability of alignment media in organic solvents.The applications of RDCs for structural analysis of some examples of natural products were discussed and summarized.
基金supported by the National Natural Science Foundation of China(Grant No.11274039)the National Basic Research Program of China(Grant No.2013CB922002)the Fundamental Research Funds for the Central Universities of China
文摘We study the formation of vortices in a dipolar Bose-Einstein condensate in a synthetic magnetic field by numerically solving the Gross-Pitaevskii equation. The formation process depends on the dipole strength, the rotating frequency, the potential geometry, and the orientation of the dipoles. We make an extensive comparison with vortices created by a rotating trap, especially focusing on the issues of the critical rotating frequency and the vortex number as a function of the rotating frequency. We observe that a higher rotating frequency is needed to generate a large number of vortices and the anisotropic interaction manifests itself as a perceptible difference in the vortex formation. Furthermore, a large dipole strength or aspect ratio also can increase the number of vortices effectively. In particular, we discuss the validity of the Feynman rule.
文摘A series of “H-shaped” organic dimers （azobenzene derivatives） exhibit linear absorption red shift compared with their corresponding monomers experimentally. Dipolar interaction model is not appropriate for the azobenzene derivatives due to the small distance between two “D-π-A” chains. Energy transfer model is suggested for explanation of the absorption red shift. Two necessary conditions for energy transfer were verified. In addition, bi-exponential florescence-delay behavior of the dimer as well as Bella＇s quantum chemistry calculation shows evidence of energy transfer.
基金Project supported by the National Natural Science Foundation of China (Grant No 10875101)the Natural Science Foundation of Fujian Province, China (Grant No 2008J0028)
文摘A modified correlated spectroscopy （COSY） revamped with asymmetric Z-gradient echo detection sequence was designed to investigate the influence of diffusion hehaviour on intermolecular double-quantum coherence signal attenuation during the pre-acquisition period. Theoretical formulas were deduced and experimental measurements and simulations were performed. It is found that the diffusion behaviour of intermolecular double-quantum coherence in the pre-acquisition period may be different from that of conventional single-quantum coherence, depending on the relative orientation of diffusion weighting gradients to coherence selection gradients. When the orientation of the diffusion weighting gradients is parallel or anti-parallel to the orientation of the coherence selection gradients, the diffusion is modulated by the distant dipolar field. This study is helpful for understanding the signal properties in intermolecular double-quantum coherence magnetic resonance imaging.
基金Project supported by the National Natural Science Foundation of China(Grant Nos 20573084 and 10575085)the Nation Science Foundation of Fujian,China(Grant No A0610005)the Program for New Century Excellent Talents in University of Ministry of Education of China
文摘This paper analyses the heteronuclear Cosy Revamped by Asymmetric Z-gradient Echo Detection pulse sequence. General theoretical expressions of the pulse sequence with arbitrary flip angles were derived by using dipolar field treatment and signals originating from heteronuclear intermolecular single-quantum coherences （iSQCs） in highly-polarized two spin-1/2 systems were mainly discussed in order to find the optimal flip angles. The results show that signals from heteronuclear iSQCs decay slower than those from intermolecular double-quantum coherences or intermolecular zero-quantum coherences. Magical angle experiments validate that the signals are from heteronuclear iSQCs and insensitive to the imperfection of radio-frequency flip angles. All experimental observations are in excellent agreement with theoretical predictions. The quantum-mechanical treatment leads to similar predictions to the dipolar field treatment.
文摘The main idea of this paper is to find an analytical formula for the input conductance of an elevated ferrite film circu-lator to match it systematically to the desired matching network. For solving the ferrite loaded dielectric resonator included in stripline elevated ferrite film circulator, the off diagonal components of the permeability tensor are taken as the perturbation. The electromagnetic fields computations are done for unperturbed structure. The dipolar resonant frequencies corresponding to harmonics of the resonant modes are then calculated using the perturbation integrals. The quality factor of the circulator is derived in terms of these dipolar resonant frequencies. Energy integrals are calculated to find the energy stored in the ferrite and dielectic layers. An analytical expression for the input conductance of the elevated ferrite film circulators is derived by using the quality factor and energy integrals. In this expression the ferrite and dielectric layers can have different permittivities. Some discussions about the effect of ferrite film thickness and permittivity mismatch on the bandwidth of the circulator are investigated by HFSS commercial software.
基金jointly supported by the Special Fund for Public Welfare Industry (meteorology) (Grant No. GYHY201306026)the National Natural Science Foundation of China (Grant Nos. 41421004 and 41522503)
文摘The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocean（SPO） in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.
基金The project partly supported by National Natural Science Foundation of China under Grant No.10574060the Natural Science Foundation of Beijing under Grant No.1072010.
文摘We study quantum tunneling of a dipolar Bose-Einstein condensate in optical lattice when the spin system initially is prepared in a squeezed coherent state. It is found that there exists quantum tunneling between lattices l and l ＋ 1, l and l - 1, respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength limit, quantum tunneling disappears between lattices l and l ＋ 1, and that l and l - 1. Correspondingly, the magnetic soliton appears.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674041,91630205,11474144,and 11847301)Chongqing Research Program of Basic Research and Frontier Technology(Grant No.cstc2017jcyjAX0084)FRF for the Central Universities(Grant No.2019CDJDWL0005)
文摘For the numerical simulation of the fractional quantum Hall(FQH) effects on a finite disk, the rotational symmetry is the only symmetry that is used in diagonalizing the Hamiltonian. In this work, we propose a method of using the weak translational symmetry for the center of mass of the many-body system. With this approach, the bulk properties, such as the energy gap and the magneto-roton excitation are consistent with those in the closed manifolds like the sphere and torus. As an application, we consider the FQH phase and its phase transition in the fast rotated dipolar fermions. We thus demonstrate the disk geometry having versatility in analyzing the bulk properties beside the usual edge physics.
