Recent advances in studies of the middle and upper atmosphere and their coupling with the lower atmosphere in China are briefly reviewed. This review emphasizes four aspects: (1) Development of instrumentation for mid...Recent advances in studies of the middle and upper atmosphere and their coupling with the lower atmosphere in China are briefly reviewed. This review emphasizes four aspects: (1) Development of instrumentation for middle and upper atmosphere observation; (2) Analyses and observation of middle and upper atmosphere; (3) Theoretical and modeling studies of planetary wave and gravity wave activities in the middle atmosphere and their relation to lower atmospheric processes; (4) Study on the coupling between the stratosphere and the troposphere.展开更多
Propagation of the surface waves along a two-dimensional plasma column and the far-field radiation patterns are studied in thin column approximation. Wave phase and attenuation coefficients are calculated for various ...Propagation of the surface waves along a two-dimensional plasma column and the far-field radiation patterns are studied in thin column approximation. Wave phase and attenuation coefficients are calculated for various plasma parameters. The radiation patterns are shown. Results show that the radiation patterns are controllable by flexibly changing the plasma length and other parameters in comparison to the metal monopole antenna. It is meaningful and instructional for the optimization of the plasma antenna design.展开更多
This paper summarizes the research results obtained by Chinese scientists and/or through international collaborations during 2004 to 2006.Within the context of COSPAR,the progresses in the studies of the middle and up...This paper summarizes the research results obtained by Chinese scientists and/or through international collaborations during 2004 to 2006.Within the context of COSPAR,the progresses in the studies of the middle and upper atmosphere in China in the past two years are introduced with focusing the developments in facilities and instruments,and the advancements in scientific issues,e.g.,dynamics related processes,atmospheric constituents,and the coupling with the lower atmosphere.展开更多
In this paper advances on study of middle and upper atmosphere and their cou pling with lower atmosphere in China in recent two years are briefly reviewed.This review emphasized three aspects, ie. (1) analysis and obs...In this paper advances on study of middle and upper atmosphere and their cou pling with lower atmosphere in China in recent two years are briefly reviewed.This review emphasized three aspects, ie. (1) analysis and observation of mid and upper atmosphere over China; (2) theoretical and modelling study of grav ity wave activities in middle atmosphere and their relation to lower atmospheric processes; (3) coupling between the stratosphere and troposphere.展开更多
Along with the introduction of the concept of dual-channel communication,we utilized the finite-difference time-domain（FDTD） method to simulate and measure the radiation pattern under certain plasma densities and pl...Along with the introduction of the concept of dual-channel communication,we utilized the finite-difference time-domain（FDTD） method to simulate and measure the radiation pattern under certain plasma densities and plasma collision frequencies.Results show that under certain settings,the radiation pattern of a plasma antenna resembles that of a metallic antenna.In contrast to a metallic antenna,a plasma antenna possesses other functionalities,such as dynamic reconfiguration and digital controllability.The data from simulation are similar to the measurement results,indicating that column plasma antenna can realize dual-channel communication.This work confirms the viability of realizing dual-channel communication by column plasma antenna,which adds a new but promising method for modern intelligent communication.展开更多
This paper briefly introduces the history of China's Manned Space Flight Program and concludes the experiments done since 2008,namely,a small satellite and a material science experiment.An outlook of future Chines...This paper briefly introduces the history of China's Manned Space Flight Program and concludes the experiments done since 2008,namely,a small satellite and a material science experiment.An outlook of future Chinese Space Station is also described at the end.展开更多
Banking sector in Ethiopia is dominant and it is a dense competent area.Due to this the bank managements tend to continually found the strategies that enables them to be competent in this dense competition.These strat...Banking sector in Ethiopia is dominant and it is a dense competent area.Due to this the bank managements tend to continually found the strategies that enables them to be competent in this dense competition.These strategies often focus on handling of customers satisfaction to be strongly compete and pooling more customers.Because,service quality is relevant to keep up their competitive advantage and improve customer satisfaction.So,this study examine the handling of customers satisfaction and assessment of service qualities on Commercial Bank of Ethiopia(CBE)in Addis Ababa at East District by applying SERVQUAL model.This study used convenient and random sampling technique to select the sample respondents and 400 respondents were selected branches of CBE in Addis Ababa at east district.The data sources for this study are primary and secondary data sources.The questionnaires are used as primary data source,which are contained SERVQUAL model and the agreements were measured by applying the five Likert point scales.The correlation result revealed that all dimensions of service quality have a strong and significant statistical relationship with customer satisfaction.The quality of service offered by CBE no meets with the expectation of customer(customers satisfied in somewhat quality service).So,the bank needs to reform service quality for satisfy and attract unsatisfied customers.展开更多
Chang＇e-2, Chinese second lunar probe, was inserted into a 100 km altitude low lunar orbit on October 9th, 2010, its purpose is to continuously photograph the lunar surface and possibly chosen landing sites for futur...Chang＇e-2, Chinese second lunar probe, was inserted into a 100 km altitude low lunar orbit on October 9th, 2010, its purpose is to continuously photograph the lunar surface and possibly chosen landing sites for future lunar missions. The probe will still carry considerable amount of propellant after completing all prescribed tasks in about six months. After the successful launch of Chang＇e-2, we began designing the probe＇s subsequent flight scenario, considering a total impulse of 1 100 m/s for takeoff from low lunar orbit and a maximum 3× 10^6 km distance for Earth-probe telecom- munication. Our first-round effort proposed a preliminary flight scenario that involves consecutive arrivals at the halo orbits around the Earth-Moon L1/L2 and Sun-Earth L1/L2 points, near-Earth asteroid flyby, Earth return, and lunar impact. The designed solution of Chang＇e-2＇s subsequent flight scenario is a multi-segment flight trajectory that serves as a reference for making the final decision on Chang＇e-2＇s extended mission, which is a flight to the Sun-Earth L2 point, and a possible scheme of lunar impact via Earth flyby after remaining at the Sun-Earth L2 point was also presented. The proposed flight trajectory, which possesses acceptable solution accuracy for mission analysis, is a novel design that effectively exploits the invariant manifolds in the circular restricted three-body problem and the patched-manifold-conic method.展开更多
Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with ...Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window.展开更多
Electromagnetic ion cyclotron(EMIC)waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics.Most studies have investigated the effects or characteristics of EMIC ...Electromagnetic ion cyclotron(EMIC)waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics.Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization.However,recent studies have found that the reversal of polarization,which occurs at higher latitudes along the wave propagation path,can change the wave-induced pitch angle diffusion coefficients.Whether such a polarization reversal can influence the global ring current dynamics remains unknown.In this study,we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current-atmosphere interactions model(RAM).The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or>100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized.Additionally,the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal,especially during prestorm time and the recovery phase,but the effects are not large during the main phase.This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E<10 keV,an energy range that is not strongly affected by the polarization reversal.展开更多
This paper focuses on the application of plasma as wireless antenna. In order to reveal the radiation characteristics of column plasma antenna, we chose the finite-difference time- domain （FDTD） numerical analysis m...This paper focuses on the application of plasma as wireless antenna. In order to reveal the radiation characteristics of column plasma antenna, we chose the finite-difference time- domain （FDTD） numerical analysis method to simulate radiation impedance and efficiencies of each channel for a few sets of plasma densities and plasma collision frequencies. Simulation results demonstrate that a plasma antenna shares similar characteristics with a metallic antenna in radiation impedance and efficiency of each channel when an appropriate setting is adopted. Unlike a metallic antenna, a plasma antenna is capable of realizing such functions as dynamic reconfiguration, digital control and dual-channel communication. Thus it is possible to carry out dual-channel communication by plasma antenna, indicating a new path for modern intelligent communication.展开更多
Ⅰ. SOLAR-TERRESTRIAL SCIENCESThe solar-terrestrial sciences study how the solar energy, momentum and mass transfer through the interplanetary space, the earth magnetosphere, the ionosphere and the neutral atmosphere,...Ⅰ. SOLAR-TERRESTRIAL SCIENCESThe solar-terrestrial sciences study how the solar energy, momentum and mass transfer through the interplanetary space, the earth magnetosphere, the ionosphere and the neutral atmosphere, and their influence on earth environment. The solar-terrestrial sciences are also called, sometimes, the solar-terrestrial physics, solar-terrestrial relations,展开更多
A set of magnetic-line-coordinate systems is used to much simplify the conservation equation of space electric currents in an anisotropic electric conductivity medium. Analytic expressions of eletric potential pattern...A set of magnetic-line-coordinate systems is used to much simplify the conservation equation of space electric currents in an anisotropic electric conductivity medium. Analytic expressions of eletric potential pattern in near-earth space are then obtained under a rather general condition. Discussions of simplified expressions of the electric potential pattern in various special regions, i.e. lower altitudes, equatorial region, polar region and higher altitudes, are given. It is shown that they can all be expressed as the solutions of the Riccatitype differential equations or even simpler solutions.展开更多
Chaotic phenomena in the magnetopause boundary region are studied in the MHD framework by using the Fourier truncation method. The MHD system is considered as a one-dimensional current sheet with a co-existing velocit...Chaotic phenomena in the magnetopause boundary region are studied in the MHD framework by using the Fourier truncation method. The MHD system is considered as a one-dimensional current sheet with a co-existing velocity shear and continuous energy transfer. The nonlinearity of the system, the evolution processes and properties of its different attractors are analysed. The possible routs and parameter conditions for chaos onset are also investigated. Numerical solutions show that when the Reynolds number (R) and the magnetic Reynolds number (Km) are very large, chaos appears in the system and its onset may provide a physical mechanism leading to turbulent reconnection at the magnetopause.展开更多
As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components d...As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components do indeed agree. This results indicate that the IMF By penetrates plasmoids and the magnetic structures must therefore be three-dimensional. In this note, the dynamical processes of magnetotail in the course of a substorm are studied using a MHD code with two-dimensions and three components on the basis of two types of initial equilibrium solutions of the quiet magnetotail. The numerical results of two cases illustrate various features of time evolution of By component that correspond to two kinds of plasmoid-like structures: one is associated with a flux rope core and the other resembles a 'closed loop' plamoid. Therefore, the occurrence of various magnetic structures in the magnetotail might be related to nonsteady driven reconnection with different distributions of the By component.展开更多
The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons ...The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons by magnetic field dipolarization is hard to occur at X>–10 RE because the time-scale of dipolarization(several minutes) is much larger than the gyroperiod of protons there(several seconds). In this paper, we present a case of nonadiabatic acceleration of plasma sheet ions observed by Cluster on October 30, 2006 at(XGSM, YGSM)=(-7.7, 4.7) RE. The nonadiabatic acceleration of ions is caused not by previously reported magnetospheric dipolarization but by the ultra low frequency(ULF) waves during magnetospheric dipolarization. The nonadiabatic acceleration of ions generates a new energy flux structure of ions, which is characterized by the usual energy flux increase of ions(28–80 ke V) and a concurrent energy flux decrease of ions in a lower energy range(10 e V–20 ke V). These new observations constitute a complete physical picture: The lower energy ions absorb the wave energy, and thus get accelerated to higher energy. We use a nonadiabatic model to interpret the ion energy flux variations. Both analytic and simulation results are in good agreement with the observations. This indicates that the nonadiabatic acceleration associated with ULF waves superposed on dipolarized magnetic field is an effective mechanism for ion energization in the near-Earth plasma sheet. The presented energy flux structures can be used as a proxy to identify the similar dynamic process.展开更多
On 24 August 2005, an impulse of solar wind dynamic pressure(Psw) hit the magnetosphere. Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1, we studied the geom...On 24 August 2005, an impulse of solar wind dynamic pressure(Psw) hit the magnetosphere. Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1, we studied the geomagnetic pulsations at auroral latitudes driven by the sharp decrease of Psw at the trailing edge of the impulse. The results show that the sharp decrease of Psw can excite a global pulsation in the frequency range 4.3–11.6 m Hz. The pulsation has a reversal of polarization between two auroral latitude stations, a larger power spectral density(PSD) close to resonant latitude and increasing frequency with decreasing latitude. All these features indicate that the pulsations are associated with field line resonance(FLR). The fundamental resonant frequency(the peak frequency of PSD between 4.3 and 5.8 m Hz) is dependent on magnetic local time and is largest around magnetic local noon. This feature is due to the fact that the size of magnetospheric cavity is dependent on local time and smallest at noon. A second harmonic wave at about 10 m Hz is also observed, which is strongest in the daytime sector, and becomes heavily attenuated in the night sector. The comparison of the PSDs of the pulsations driven by sharp increase and sharp decrease of Psw shows that the frequency of pulsations is negatively proportional to the size of magnetopause. Since the FLR is excited by compressional cavity/waveguide waves, the above results indicate that the resonant frequency in the magnetospheric cavity/waveguide is controlled not only by solar wind parameters but also by magnetic local time of observation point.展开更多
In 1985, Bollinger firstly introduced a repairable system model——a strict consecutive-k-out-of-n: F systems(abbreviated to Bollinger model) in terms ofa nonrepairable system 'consecutive-k-out-of-n: F systems...In 1985, Bollinger firstly introduced a repairable system model——a strict consecutive-k-out-of-n: F systems(abbreviated to Bollinger model) in terms ofa nonrepairable system 'consecutive-k-out-of-n: F systems'. However, some conditions in Bollinger modal were assumed too ideally to be used in engineering. For instance, some states (e.g. FGFFFFFFF, n=9, k=2) have already made the system dislocated, but by the assumptions in展开更多
Using the data taken from Tibet II High Density （HD） Array （1997 February-1999 September） and Tibet-III array （1999 November--2005 November）, our previous northern sky survey for TeV γ-ray point sources has now...Using the data taken from Tibet II High Density （HD） Array （1997 February-1999 September） and Tibet-III array （1999 November--2005 November）, our previous northern sky survey for TeV γ-ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0° to 60.0° in declination （Dec） range, no new TeV T-ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV γ-ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level （C.L.）, the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.40333034,40075007,and 40175002the.Chinese Academy of Sciences under Grant No.KZCX-SW-217.
文摘Recent advances in studies of the middle and upper atmosphere and their coupling with the lower atmosphere in China are briefly reviewed. This review emphasizes four aspects: (1) Development of instrumentation for middle and upper atmosphere observation; (2) Analyses and observation of middle and upper atmosphere; (3) Theoretical and modeling studies of planetary wave and gravity wave activities in the middle atmosphere and their relation to lower atmospheric processes; (4) Study on the coupling between the stratosphere and the troposphere.
文摘Propagation of the surface waves along a two-dimensional plasma column and the far-field radiation patterns are studied in thin column approximation. Wave phase and attenuation coefficients are calculated for various plasma parameters. The radiation patterns are shown. Results show that the radiation patterns are controllable by flexibly changing the plasma length and other parameters in comparison to the metal monopole antenna. It is meaningful and instructional for the optimization of the plasma antenna design.
基金Supported by the National Natural Science Foundation of China(40374056,40333034)Chinese Academy of Science KZCX3-SW-217,KGCX2-SW-408,KGCX3-SYW-403
文摘This paper summarizes the research results obtained by Chinese scientists and/or through international collaborations during 2004 to 2006.Within the context of COSPAR,the progresses in the studies of the middle and upper atmosphere in China in the past two years are introduced with focusing the developments in facilities and instruments,and the advancements in scientific issues,e.g.,dynamics related processes,atmospheric constituents,and the coupling with the lower atmosphere.
基金Supported by the National Natural Science Foundation of China(No. 40175002, 40075007) and The Chinese Academy of Sciences.
文摘In this paper advances on study of middle and upper atmosphere and their cou pling with lower atmosphere in China in recent two years are briefly reviewed.This review emphasized three aspects, ie. (1) analysis and observation of mid and upper atmosphere over China; (2) theoretical and modelling study of grav ity wave activities in middle atmosphere and their relation to lower atmospheric processes; (3) coupling between the stratosphere and troposphere.
文摘Along with the introduction of the concept of dual-channel communication,we utilized the finite-difference time-domain（FDTD） method to simulate and measure the radiation pattern under certain plasma densities and plasma collision frequencies.Results show that under certain settings,the radiation pattern of a plasma antenna resembles that of a metallic antenna.In contrast to a metallic antenna,a plasma antenna possesses other functionalities,such as dynamic reconfiguration and digital controllability.The data from simulation are similar to the measurement results,indicating that column plasma antenna can realize dual-channel communication.This work confirms the viability of realizing dual-channel communication by column plasma antenna,which adds a new but promising method for modern intelligent communication.
文摘This paper briefly introduces the history of China's Manned Space Flight Program and concludes the experiments done since 2008,namely,a small satellite and a material science experiment.An outlook of future Chinese Space Station is also described at the end.
文摘Banking sector in Ethiopia is dominant and it is a dense competent area.Due to this the bank managements tend to continually found the strategies that enables them to be competent in this dense competition.These strategies often focus on handling of customers satisfaction to be strongly compete and pooling more customers.Because,service quality is relevant to keep up their competitive advantage and improve customer satisfaction.So,this study examine the handling of customers satisfaction and assessment of service qualities on Commercial Bank of Ethiopia(CBE)in Addis Ababa at East District by applying SERVQUAL model.This study used convenient and random sampling technique to select the sample respondents and 400 respondents were selected branches of CBE in Addis Ababa at east district.The data sources for this study are primary and secondary data sources.The questionnaires are used as primary data source,which are contained SERVQUAL model and the agreements were measured by applying the five Likert point scales.The correlation result revealed that all dimensions of service quality have a strong and significant statistical relationship with customer satisfaction.The quality of service offered by CBE no meets with the expectation of customer(customers satisfied in somewhat quality service).So,the bank needs to reform service quality for satisfy and attract unsatisfied customers.
基金supported by the State Key Laboratory of Astronautic Dynamics (2011ADL-DW0202)
文摘Chang＇e-2, Chinese second lunar probe, was inserted into a 100 km altitude low lunar orbit on October 9th, 2010, its purpose is to continuously photograph the lunar surface and possibly chosen landing sites for future lunar missions. The probe will still carry considerable amount of propellant after completing all prescribed tasks in about six months. After the successful launch of Chang＇e-2, we began designing the probe＇s subsequent flight scenario, considering a total impulse of 1 100 m/s for takeoff from low lunar orbit and a maximum 3× 10^6 km distance for Earth-probe telecom- munication. Our first-round effort proposed a preliminary flight scenario that involves consecutive arrivals at the halo orbits around the Earth-Moon L1/L2 and Sun-Earth L1/L2 points, near-Earth asteroid flyby, Earth return, and lunar impact. The designed solution of Chang＇e-2＇s subsequent flight scenario is a multi-segment flight trajectory that serves as a reference for making the final decision on Chang＇e-2＇s extended mission, which is a flight to the Sun-Earth L2 point, and a possible scheme of lunar impact via Earth flyby after remaining at the Sun-Earth L2 point was also presented. The proposed flight trajectory, which possesses acceptable solution accuracy for mission analysis, is a novel design that effectively exploits the invariant manifolds in the circular restricted three-body problem and the patched-manifold-conic method.
基金Supported by the National Natural Science Foundation of China
文摘Previous statistical analyses of a large number of SOHO/MDI full disk longitudinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41974192 and 41821003)Work at Los Alamos was performed under the auspices of the U.S.Department of Energy(Contract No.89233218CNA000001)was partially funded by an NSF grant(Grant No.IAA2027951).
文摘Electromagnetic ion cyclotron(EMIC)waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics.Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization.However,recent studies have found that the reversal of polarization,which occurs at higher latitudes along the wave propagation path,can change the wave-induced pitch angle diffusion coefficients.Whether such a polarization reversal can influence the global ring current dynamics remains unknown.In this study,we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current-atmosphere interactions model(RAM).The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or>100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized.Additionally,the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal,especially during prestorm time and the recovery phase,but the effects are not large during the main phase.This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E<10 keV,an energy range that is not strongly affected by the polarization reversal.
文摘This paper focuses on the application of plasma as wireless antenna. In order to reveal the radiation characteristics of column plasma antenna, we chose the finite-difference time- domain （FDTD） numerical analysis method to simulate radiation impedance and efficiencies of each channel for a few sets of plasma densities and plasma collision frequencies. Simulation results demonstrate that a plasma antenna shares similar characteristics with a metallic antenna in radiation impedance and efficiency of each channel when an appropriate setting is adopted. Unlike a metallic antenna, a plasma antenna is capable of realizing such functions as dynamic reconfiguration, digital control and dual-channel communication. Thus it is possible to carry out dual-channel communication by plasma antenna, indicating a new path for modern intelligent communication.
文摘Ⅰ. SOLAR-TERRESTRIAL SCIENCESThe solar-terrestrial sciences study how the solar energy, momentum and mass transfer through the interplanetary space, the earth magnetosphere, the ionosphere and the neutral atmosphere, and their influence on earth environment. The solar-terrestrial sciences are also called, sometimes, the solar-terrestrial physics, solar-terrestrial relations,
文摘A set of magnetic-line-coordinate systems is used to much simplify the conservation equation of space electric currents in an anisotropic electric conductivity medium. Analytic expressions of eletric potential pattern in near-earth space are then obtained under a rather general condition. Discussions of simplified expressions of the electric potential pattern in various special regions, i.e. lower altitudes, equatorial region, polar region and higher altitudes, are given. It is shown that they can all be expressed as the solutions of the Riccatitype differential equations or even simpler solutions.
基金Project supported by the National Natural Science Foundation of China,and partly by the NationalBasic Research Program(Nonlinear Science).
文摘Chaotic phenomena in the magnetopause boundary region are studied in the MHD framework by using the Fourier truncation method. The MHD system is considered as a one-dimensional current sheet with a co-existing velocity shear and continuous energy transfer. The nonlinearity of the system, the evolution processes and properties of its different attractors are analysed. The possible routs and parameter conditions for chaos onset are also investigated. Numerical solutions show that when the Reynolds number (R) and the magnetic Reynolds number (Km) are very large, chaos appears in the system and its onset may provide a physical mechanism leading to turbulent reconnection at the magnetopause.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 49874035 and 49834040) and the Space Physics Fund of the First-rate University Program.
文摘As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components do indeed agree. This results indicate that the IMF By penetrates plasmoids and the magnetic structures must therefore be three-dimensional. In this note, the dynamical processes of magnetotail in the course of a substorm are studied using a MHD code with two-dimensions and three components on the basis of two types of initial equilibrium solutions of the quiet magnetotail. The numerical results of two cases illustrate various features of time evolution of By component that correspond to two kinds of plasmoid-like structures: one is associated with a flux rope core and the other resembles a 'closed loop' plamoid. Therefore, the occurrence of various magnetic structures in the magnetotail might be related to nonsteady driven reconnection with different distributions of the By component.
基金supported by the China Postdoctoral Science Foundation(Grant No.2013M531344)the Fundamental Research Funds for the Central Universities(Grant No.56YAH12039)+1 种基金the National Natural Science Foundation of China(Grant No.41174141)the National Basic Research Program of China("973"Project)(Grant No.2011CB811404)
文摘The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons by magnetic field dipolarization is hard to occur at X>–10 RE because the time-scale of dipolarization(several minutes) is much larger than the gyroperiod of protons there(several seconds). In this paper, we present a case of nonadiabatic acceleration of plasma sheet ions observed by Cluster on October 30, 2006 at(XGSM, YGSM)=(-7.7, 4.7) RE. The nonadiabatic acceleration of ions is caused not by previously reported magnetospheric dipolarization but by the ultra low frequency(ULF) waves during magnetospheric dipolarization. The nonadiabatic acceleration of ions generates a new energy flux structure of ions, which is characterized by the usual energy flux increase of ions(28–80 ke V) and a concurrent energy flux decrease of ions in a lower energy range(10 e V–20 ke V). These new observations constitute a complete physical picture: The lower energy ions absorb the wave energy, and thus get accelerated to higher energy. We use a nonadiabatic model to interpret the ion energy flux variations. Both analytic and simulation results are in good agreement with the observations. This indicates that the nonadiabatic acceleration associated with ULF waves superposed on dipolarized magnetic field is an effective mechanism for ion energization in the near-Earth plasma sheet. The presented energy flux structures can be used as a proxy to identify the similar dynamic process.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.NS2015089)
文摘On 24 August 2005, an impulse of solar wind dynamic pressure(Psw) hit the magnetosphere. Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1, we studied the geomagnetic pulsations at auroral latitudes driven by the sharp decrease of Psw at the trailing edge of the impulse. The results show that the sharp decrease of Psw can excite a global pulsation in the frequency range 4.3–11.6 m Hz. The pulsation has a reversal of polarization between two auroral latitude stations, a larger power spectral density(PSD) close to resonant latitude and increasing frequency with decreasing latitude. All these features indicate that the pulsations are associated with field line resonance(FLR). The fundamental resonant frequency(the peak frequency of PSD between 4.3 and 5.8 m Hz) is dependent on magnetic local time and is largest around magnetic local noon. This feature is due to the fact that the size of magnetospheric cavity is dependent on local time and smallest at noon. A second harmonic wave at about 10 m Hz is also observed, which is strongest in the daytime sector, and becomes heavily attenuated in the night sector. The comparison of the PSDs of the pulsations driven by sharp increase and sharp decrease of Psw shows that the frequency of pulsations is negatively proportional to the size of magnetopause. Since the FLR is excited by compressional cavity/waveguide waves, the above results indicate that the resonant frequency in the magnetospheric cavity/waveguide is controlled not only by solar wind parameters but also by magnetic local time of observation point.
文摘In 1985, Bollinger firstly introduced a repairable system model——a strict consecutive-k-out-of-n: F systems(abbreviated to Bollinger model) in terms ofa nonrepairable system 'consecutive-k-out-of-n: F systems'. However, some conditions in Bollinger modal were assumed too ideally to be used in engineering. For instance, some states (e.g. FGFFFFFFF, n=9, k=2) have already made the system dislocated, but by the assumptions in
基金Supported by Grants-in-Aid for Scientific Research on Priority Areas (712) (MEXT)Japan Society for Promotion of Science(JSPS)+1 种基金National Natural Science Foundation of China (10675134,10533020)Chinese Academy of Sciences
文摘Using the data taken from Tibet II High Density （HD） Array （1997 February-1999 September） and Tibet-III array （1999 November--2005 November）, our previous northern sky survey for TeV γ-ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0° to 60.0° in declination （Dec） range, no new TeV T-ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV γ-ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level （C.L.）, the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.
