A spacecraft loses all forms of communication, including global positioning system signals, data telemetry, voice communication and so on, when it enters the communication blackout phase. This becomes more and more cr...A spacecraft loses all forms of communication, including global positioning system signals, data telemetry, voice communication and so on, when it enters the communication blackout phase. This becomes more and more critical with the development of reentry vehicle missions since radio blackout brings about many serious issues related to vehicle safety. This paper studies the influence of magnetic field on antenna performance in plasma. The results indicate that the effect of plasma on the antenna performance can be negligible when the magnetic field reaches a certain strength. This provides another way to solve the reentry blackout problem.展开更多
The thermal distortion of an optical reflector surface due to the changing sunlight in a space environment will cause shift and spreading of its reflected focus and thereby influence the performance of space-to-ground...The thermal distortion of an optical reflector surface due to the changing sunlight in a space environment will cause shift and spreading of its reflected focus and thereby influence the performance of space-to-ground laser communication links. Based on the characteristics of a low orbit satellite, the normal shift of a plan mirror caused by thermal distortion is analyzed with the software of the ANSYS of finite element analysis. A general expression of the transmitted beam from a distorted reflector surface and a counting formula for the shifts of the focus center before and after thermal distortion are deduced. The result of simulation shows that the magnitude order of the normal shift of the antenna mirror surface can be as high as tens of μrad.The worse the mirror thermal distortion is, the larger the shift of the received focus center is. And the change of the shifts does not obey a linear rule.展开更多
Objective In order to red uc e the flicker in color plasma display panel (PDP), the highly peaked light outpu t at certain positions and the strong luminance difference among subfields, whic h cause flicker in PDP, i...Objective In order to red uc e the flicker in color plasma display panel (PDP), the highly peaked light outpu t at certain positions and the strong luminance difference among subfields, whic h cause flicker in PDP, is analyzed; and a flicker index method is developed to evaluate flicker in PDP based on the flicker theory and the electroencephalograp h response model for luminance. Methods This method considers f licker as a main result of the fundamental frequency component of luminance supe rimposed on the DC-component, the flicker index is defined as ratio between the positive square roots of the sum of the two square components. Results & Conclusion The calculation results of flicker index indicate that flicker can be obviously weakened via increase of subfield number, symmetrical s election and homogeneous interlaced distribution of major weight subfields . Fli cker can be further reduced by choosing the suitable subfield order according to gray scale region of image.展开更多
基金supported by National High Technology Research and Development Program of China(No.2011AA7022016)National Natural Science Foundation of China(No.11275045)the Sichuan Province Science and Technology Support Program of China(No.13ZC2317)
文摘A spacecraft loses all forms of communication, including global positioning system signals, data telemetry, voice communication and so on, when it enters the communication blackout phase. This becomes more and more critical with the development of reentry vehicle missions since radio blackout brings about many serious issues related to vehicle safety. This paper studies the influence of magnetic field on antenna performance in plasma. The results indicate that the effect of plasma on the antenna performance can be negligible when the magnetic field reaches a certain strength. This provides another way to solve the reentry blackout problem.
基金Funded by 863 project (NO:2002AA107493)youthfounda-tion project of UESTC(NO:JX03018)
文摘The thermal distortion of an optical reflector surface due to the changing sunlight in a space environment will cause shift and spreading of its reflected focus and thereby influence the performance of space-to-ground laser communication links. Based on the characteristics of a low orbit satellite, the normal shift of a plan mirror caused by thermal distortion is analyzed with the software of the ANSYS of finite element analysis. A general expression of the transmitted beam from a distorted reflector surface and a counting formula for the shifts of the focus center before and after thermal distortion are deduced. The result of simulation shows that the magnitude order of the normal shift of the antenna mirror surface can be as high as tens of μrad.The worse the mirror thermal distortion is, the larger the shift of the received focus center is. And the change of the shifts does not obey a linear rule.
基金Thisprojectwassupportedbythe0205ProjectforScienceandTechnology of china edncation ministry.
文摘Objective In order to red uc e the flicker in color plasma display panel (PDP), the highly peaked light outpu t at certain positions and the strong luminance difference among subfields, whic h cause flicker in PDP, is analyzed; and a flicker index method is developed to evaluate flicker in PDP based on the flicker theory and the electroencephalograp h response model for luminance. Methods This method considers f licker as a main result of the fundamental frequency component of luminance supe rimposed on the DC-component, the flicker index is defined as ratio between the positive square roots of the sum of the two square components. Results & Conclusion The calculation results of flicker index indicate that flicker can be obviously weakened via increase of subfield number, symmetrical s election and homogeneous interlaced distribution of major weight subfields . Fli cker can be further reduced by choosing the suitable subfield order according to gray scale region of image.
