2004 Vol. 24, No. 3
2004, 24(3): 161-168.
Abstract:
The collisionless shocks are the common phenomena in the interplanetary and interstellar space. They are also the important fundamental subject in the research of plasma physics, space physics and astrophysics. Numerical simulation is widely used in the study of collisionless shocks. Corresponding to the particle simulation, the method of solving the ideal MHD equations with WENO scheme has been presented to simulate the space collisionless shock. Based on the method, the interaction between the quasi-perpendicular collisionless shocks and two kinds of interplanetary structure——C inversed magnetic field and plasmoid with high density has been studied, and the results have also been compared with those of particle simulation, to consider the feasibility and the accuracy of MHD method in the simulation of collisionless shock. The comparison between the results of two method shows that, the MHD simulation can provide most results that are observed in the particle simulation, thus it is feasible to simulate the quasi-perpendicular collisionless shock with MHD method when the dynamic effects can be omitted. It also has a higher computational efficiency than the particle simulation, and will be easier to extend to the 2D or 3D simulation. However, the MHD simulation does not include the effect caused by single particle. So it lacks the capacity to describe the dynamic effects such as the dissipation and detailed structure of collisionless shocks. If the phenomena caused by these effects are not so important in specific research topics, the MHD simulation still can provide satisfied results. In some other cases, MHD simulation can be a convenient way to forecast the behavior of large-scale particle simulation.
The collisionless shocks are the common phenomena in the interplanetary and interstellar space. They are also the important fundamental subject in the research of plasma physics, space physics and astrophysics. Numerical simulation is widely used in the study of collisionless shocks. Corresponding to the particle simulation, the method of solving the ideal MHD equations with WENO scheme has been presented to simulate the space collisionless shock. Based on the method, the interaction between the quasi-perpendicular collisionless shocks and two kinds of interplanetary structure——C inversed magnetic field and plasmoid with high density has been studied, and the results have also been compared with those of particle simulation, to consider the feasibility and the accuracy of MHD method in the simulation of collisionless shock. The comparison between the results of two method shows that, the MHD simulation can provide most results that are observed in the particle simulation, thus it is feasible to simulate the quasi-perpendicular collisionless shock with MHD method when the dynamic effects can be omitted. It also has a higher computational efficiency than the particle simulation, and will be easier to extend to the 2D or 3D simulation. However, the MHD simulation does not include the effect caused by single particle. So it lacks the capacity to describe the dynamic effects such as the dissipation and detailed structure of collisionless shocks. If the phenomena caused by these effects are not so important in specific research topics, the MHD simulation still can provide satisfied results. In some other cases, MHD simulation can be a convenient way to forecast the behavior of large-scale particle simulation.
2004, 24(3): 169-181.
Abstract:
In view of the distribution features of the temperature and density across the different regions of the quiet magnetotail, the same non-uniform distributions of the temperature and density are used as the initial state of the simulation study. In this report, three cases with the different distributions of initial By component are investigated. The numerical results illustrate the characteristic evolution of three kinds of magnetic structures. For the varying magnetic field at a given point in the neutral sheet, the hodograms of the typical events are performed. From another point of view, the hodograms of three cases show the features of flux rope structure, plasmoids with Complex closed magnetic field lines and two-dimension "magnetic island", respectively. It was demonstrated from the observations that most plasmoids in the magnetotail are the flux rope structures with a large core field. Monitoring the development of a flux rope structure, the profiles of the directional velocity vx, vy, vz and magnetic field strength B in it as a function of the distance x are given. The computing values of vx and B are approximately consistent with the observed values in the near and middle tail by Geotail. Moreover, in comparison with Jin et al.’s simulation with a constant initial temperature, in the present work the temperature of plasmoids increases and the density of plasmoids decreases notably, and so the difference between the numerical results and observation is reduced.
In view of the distribution features of the temperature and density across the different regions of the quiet magnetotail, the same non-uniform distributions of the temperature and density are used as the initial state of the simulation study. In this report, three cases with the different distributions of initial By component are investigated. The numerical results illustrate the characteristic evolution of three kinds of magnetic structures. For the varying magnetic field at a given point in the neutral sheet, the hodograms of the typical events are performed. From another point of view, the hodograms of three cases show the features of flux rope structure, plasmoids with Complex closed magnetic field lines and two-dimension "magnetic island", respectively. It was demonstrated from the observations that most plasmoids in the magnetotail are the flux rope structures with a large core field. Monitoring the development of a flux rope structure, the profiles of the directional velocity vx, vy, vz and magnetic field strength B in it as a function of the distance x are given. The computing values of vx and B are approximately consistent with the observed values in the near and middle tail by Geotail. Moreover, in comparison with Jin et al.’s simulation with a constant initial temperature, in the present work the temperature of plasmoids increases and the density of plasmoids decreases notably, and so the difference between the numerical results and observation is reduced.
2004, 24(3): 182-193.
Abstract:
With a theoretical model of ionospheric electric fields, the yearly variation of ionospheric electric fields at mid- and low-latitudes under the condition of low solar and quiet geomagnetic activities were studied. The main results are as follows: when the ionospheric electric fields are calculated individually in the northern or southern hemisphere without including the influence of the other hemisphere （uncoupled）, the electric fields in both hemispheres vary in an obvious annual pattern with an anti-phase; when the electric field was calculated simultaneously in both hemispheres with the influence of the other hemispheres （coupled） included, the electric field varies in a predominant semi-annual pattern. Moreover, quite good consistency was found between the behaviors of semi-annual variation calculated by our theoretical electric field model and an empirical model of Richmond. A simple circuit with the coupling between the northern and southern hemispheres was introduced to interpret the semi-annual variation of electric field. Results from the circuit model reveal that the coupled electric field would show a pronounced semi-annual variation due to the ’coupling effect’ along the magnetic field lines between two hemispheres, whereas the uncoupled electric field have an annual variation in respective hemisphere.
With a theoretical model of ionospheric electric fields, the yearly variation of ionospheric electric fields at mid- and low-latitudes under the condition of low solar and quiet geomagnetic activities were studied. The main results are as follows: when the ionospheric electric fields are calculated individually in the northern or southern hemisphere without including the influence of the other hemisphere （uncoupled）, the electric fields in both hemispheres vary in an obvious annual pattern with an anti-phase; when the electric field was calculated simultaneously in both hemispheres with the influence of the other hemispheres （coupled） included, the electric field varies in a predominant semi-annual pattern. Moreover, quite good consistency was found between the behaviors of semi-annual variation calculated by our theoretical electric field model and an empirical model of Richmond. A simple circuit with the coupling between the northern and southern hemispheres was introduced to interpret the semi-annual variation of electric field. Results from the circuit model reveal that the coupled electric field would show a pronounced semi-annual variation due to the ’coupling effect’ along the magnetic field lines between two hemispheres, whereas the uncoupled electric field have an annual variation in respective hemisphere.
2004, 24(3): 194-202.
Abstract:
Empirical models of ionospheric parameters f0F2 and M（3000）F2 is obtained respectively by analyzing the observed data in Wuhan ionosphere Observatory. In these models, a linear function to describe the relationship between the two parameters and solar 10.7cm flux index is applied, and Fourier series analysis is used to investigate the diurnal and semidiurnal variations of f0F2 over Wuhan, and variations of M（3000）F2 from the first step to the fourth step. The agreement between the prediction and the observed data is satisfactory. Then the NmF2 and hmF2 can be modeled from f0F2 and M（3000）F2; And the oxygen scale height HO can be calculated using the modeled TEC and NmF2. Supposing that the height distribution of electron density fits Chapman α function, the Ne profile is given by inputting the modeled NmF2, hmF2 and HO. By integrating the profile with height in certain range, is estimated the partial electron content and compared with the observed TEC. The result suggests that the electron content integrated from 100km to 1000km are in agreement with the observed TEC at Wuhan. This method is useful for investigating the electron profile of F2 layer around the top, which has scarce observed data.
Empirical models of ionospheric parameters f0F2 and M（3000）F2 is obtained respectively by analyzing the observed data in Wuhan ionosphere Observatory. In these models, a linear function to describe the relationship between the two parameters and solar 10.7cm flux index is applied, and Fourier series analysis is used to investigate the diurnal and semidiurnal variations of f0F2 over Wuhan, and variations of M（3000）F2 from the first step to the fourth step. The agreement between the prediction and the observed data is satisfactory. Then the NmF2 and hmF2 can be modeled from f0F2 and M（3000）F2; And the oxygen scale height HO can be calculated using the modeled TEC and NmF2. Supposing that the height distribution of electron density fits Chapman α function, the Ne profile is given by inputting the modeled NmF2, hmF2 and HO. By integrating the profile with height in certain range, is estimated the partial electron content and compared with the observed TEC. The result suggests that the electron content integrated from 100km to 1000km are in agreement with the observed TEC at Wuhan. This method is useful for investigating the electron profile of F2 layer around the top, which has scarce observed data.
2004, 24(3): 203-210.
Abstract:
The deployable antenna has been applied widely with development of space science and technology. Recently, the cable net structure becomes more and more popularized for it is not only with light weight and little furl volume, but also able to be made in large size. Considering the flexible cable net deployable antenna, the structural characteristics of the large deployed antenna for satellite have been discussed. And an optimum design model searching for minimum weight （volume）, considering both the size variables and prestress variables is studied. The reflect precision, eigenfrequency, strength and cable’s allowable stress is taken into account in the optimal design. The improved GA method is used to solve it with reasonable results.
The deployable antenna has been applied widely with development of space science and technology. Recently, the cable net structure becomes more and more popularized for it is not only with light weight and little furl volume, but also able to be made in large size. Considering the flexible cable net deployable antenna, the structural characteristics of the large deployed antenna for satellite have been discussed. And an optimum design model searching for minimum weight （volume）, considering both the size variables and prestress variables is studied. The reflect precision, eigenfrequency, strength and cable’s allowable stress is taken into account in the optimal design. The improved GA method is used to solve it with reasonable results.
2004, 24(3): 211-218.
Abstract:
A new second planet superspectrical image series compression coding algorithm is proposed in the paper. The algorithm adopts the still image compression method EBCOT （Embedded Block Coding with Optimized Truncation） as the coding engine, but it can efficiently reduce the redundancy among the frames. In the most documents on multispectral or superspectral images compression, the redundancy among the frames were usually reduced by 3 dimensional compression algorithm, such as 3 dimensional SPIHT, which in general based on 3 dimensional transform. Therefore, the huge memory is necessary when the transform is done, but the hardware system on the second planet must be lightest and with the lowest power consumption, and 3 dimensional compression algorithms are difficult to be used on the remote-sensing second planet. The novelty of the proposed compression coding method is that the interferential imaging characteristic of progressive scan is utilized to do the matching operation in the wavelet domain, when the relative shift between the two successive images is detected by the match method, the difference （error） image of the two images is encoded in stead of the origin image. Therefore the whole coding efficient is improved and the fidelity of the images can be improved by 3—4 dB. Since the complexity and memory is similar to the 2 dimensional compression algorithm, the algorithm is easier than the one based on 3 dimensional wavelet transform to be implemented on the second planet, and the disadvantage of large memory requirement and long encoding delay is overcome also. Numerical experiments on the 512-frame superspectrum image series show that the reconstructed images after using the proposed algorithm exhibit a comparative or even better effect at the same compression ratio than the 3 dimensional methods.
A new second planet superspectrical image series compression coding algorithm is proposed in the paper. The algorithm adopts the still image compression method EBCOT （Embedded Block Coding with Optimized Truncation） as the coding engine, but it can efficiently reduce the redundancy among the frames. In the most documents on multispectral or superspectral images compression, the redundancy among the frames were usually reduced by 3 dimensional compression algorithm, such as 3 dimensional SPIHT, which in general based on 3 dimensional transform. Therefore, the huge memory is necessary when the transform is done, but the hardware system on the second planet must be lightest and with the lowest power consumption, and 3 dimensional compression algorithms are difficult to be used on the remote-sensing second planet. The novelty of the proposed compression coding method is that the interferential imaging characteristic of progressive scan is utilized to do the matching operation in the wavelet domain, when the relative shift between the two successive images is detected by the match method, the difference （error） image of the two images is encoded in stead of the origin image. Therefore the whole coding efficient is improved and the fidelity of the images can be improved by 3—4 dB. Since the complexity and memory is similar to the 2 dimensional compression algorithm, the algorithm is easier than the one based on 3 dimensional wavelet transform to be implemented on the second planet, and the disadvantage of large memory requirement and long encoding delay is overcome also. Numerical experiments on the 512-frame superspectrum image series show that the reconstructed images after using the proposed algorithm exhibit a comparative or even better effect at the same compression ratio than the 3 dimensional methods.
2004, 24(3): 219-225.
Abstract:
In this paper, the pressure correction of the cosmic ray intensity in Yangbajing is investigated. Pressure correction is not only related to the atmospheric pressure, but also to the solar activities. The absolute value of barometric coefficient is biggest when the level of solar activities is highest. And the barometric coefficient is related to the sampling time of data. In the same time, using different sampling time got different barometric coefficient. The pressure correction is made to the raw data of Tibet neutron monitor, and the barometric coefficients of single channel and eight multiplicity channels are calculated.
In this paper, the pressure correction of the cosmic ray intensity in Yangbajing is investigated. Pressure correction is not only related to the atmospheric pressure, but also to the solar activities. The absolute value of barometric coefficient is biggest when the level of solar activities is highest. And the barometric coefficient is related to the sampling time of data. In the same time, using different sampling time got different barometric coefficient. The pressure correction is made to the raw data of Tibet neutron monitor, and the barometric coefficients of single channel and eight multiplicity channels are calculated.
2004, 24(3): 226-232.
Abstract:
HY-1 Satellite was launched successfully on May 15th, 2002. It is the first ocean color observation satellite in China. On the other hand it is the first long life experimental and operational small satellite in China. The on-board GPS receiver was successfully used in navigation and give out the precise time. The positioning principle, flow chart and application of the GPS receiver on HY-1 satellite are introduced in this paper. A method to confirm and verify the on orbit positioning data is discussed. Using the Two Line Elements （TLE） from NASA web, the satellite orbit is calculated by the Satellite Tool Kit （STK） software so to obtain the nadir positions, then, the real GPS data at that time are processed and converted to the nadir positions. The nadir geodetic positions from GPS data are compared with those from the TLE. The difference of nadir positions between GPS and TLE methods are given. It is very helpful to give the comparison using the real on-board data.
HY-1 Satellite was launched successfully on May 15th, 2002. It is the first ocean color observation satellite in China. On the other hand it is the first long life experimental and operational small satellite in China. The on-board GPS receiver was successfully used in navigation and give out the precise time. The positioning principle, flow chart and application of the GPS receiver on HY-1 satellite are introduced in this paper. A method to confirm and verify the on orbit positioning data is discussed. Using the Two Line Elements （TLE） from NASA web, the satellite orbit is calculated by the Satellite Tool Kit （STK） software so to obtain the nadir positions, then, the real GPS data at that time are processed and converted to the nadir positions. The nadir geodetic positions from GPS data are compared with those from the TLE. The difference of nadir positions between GPS and TLE methods are given. It is very helpful to give the comparison using the real on-board data.
DING Shijian,
LIU Tao,
SONG Jinfang,
WU Gaode,
SHAO Xiaoxia,
XIA Qichang,
WU Hanji,
JIANG Yuanda,
ZHANG Zhiyuan,
LIU Wenxi,
FENG Xuezhang,
MA Yuli,
LI Qin
2004, 24(3): 233-240.
Abstract:
Separation of two colored model proteins, cytochrome C and hemoglobin, were conducted in the specially self-designed free flow electrophoresis device A3-2 using zone electrophoresis mode under 1 g- and μg- conditions. The results demonstrated that the higher resolution of free flow electrophoresis acquired under the microgravity is obtained. Both onboard LBD detection and measurement of the seperation by the spectrometer demonstrated that the distance between the zone maxima of the two proteins were increased and the dispersion of hemoglobin decreased. The experiments also included: （1） The effect of the glycerol concentration on the separation results; （2） Post-flight analysis of the contents of the fractions. The separation results of 10%, 7%, 4%, 2% and 0% glycerol concentration in the electrophoresis buffer are compared and no significant effect of the glycerol on the separation results are found. So the glycerol and its disadvantages for the clean and storage of the device were excluded finally. Gel electrophoresis and mass spectrometry analysis of the contents of the fractions confirmed that two proteins have been effectively separated.
Separation of two colored model proteins, cytochrome C and hemoglobin, were conducted in the specially self-designed free flow electrophoresis device A3-2 using zone electrophoresis mode under 1 g- and μg- conditions. The results demonstrated that the higher resolution of free flow electrophoresis acquired under the microgravity is obtained. Both onboard LBD detection and measurement of the seperation by the spectrometer demonstrated that the distance between the zone maxima of the two proteins were increased and the dispersion of hemoglobin decreased. The experiments also included: （1） The effect of the glycerol concentration on the separation results; （2） Post-flight analysis of the contents of the fractions. The separation results of 10%, 7%, 4%, 2% and 0% glycerol concentration in the electrophoresis buffer are compared and no significant effect of the glycerol on the separation results are found. So the glycerol and its disadvantages for the clean and storage of the device were excluded finally. Gel electrophoresis and mass spectrometry analysis of the contents of the fractions confirmed that two proteins have been effectively separated.
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