The space-borne fluxgate magnetometer(FGM)requires regular in-flight calibration to obtain its zero offset.Recently,Wang GQ and Pan ZH(2021a)developed a new method for the zero offset calibration based on the properti...The space-borne fluxgate magnetometer(FGM)requires regular in-flight calibration to obtain its zero offset.Recently,Wang GQ and Pan ZH(2021a)developed a new method for the zero offset calibration based on the properties of Alfvén waves.They found that an optimal offset line(OOL)exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs.Because no pure Alfvén waves exist in the interplanetary magnetic field,calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events.Here,we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset.This procedure includes three parts:(1)selecting potential Alfvénic fluctuation events,(2)obtaining the OOL,and(3)determining the zero offset.We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express.The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis-Smith method.One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler.Our automatic procedure could also be applied to find fluctuation events for the Davis-Smith method.展开更多
In this paper, a very low-offset continuous time amplifier has been presented. It has the fully differential structure and uses an Auto-zeroed offset stabilization technique. This structure consists of two phases in w...In this paper, a very low-offset continuous time amplifier has been presented. It has the fully differential structure and uses an Auto-zeroed offset stabilization technique. This structure consists of two phases in which the offset value is sampled in the first phase and then subtracted from the signal in the second phase. In order to maintain the continuous time topology, the amplifier uses two paths called main-path and sub-path where the main-path is never disconnected from the signal path and as a result the structure will be continuous time. The amplifier is designed to have a total amount of power dissipation about 3 mW in the standard 0.35 μm CMOS process. Furthermore, the proposed Opamp has an offset value lower than 1 μV at a 2.5 kHz Auto-zeroing frequency, unity gain frequency of 6.14 MHz and phase margin of 78.6° with 50 pF loads.展开更多
Abstract Accurate simulation of seismic wave propaga- tion in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments wi...Abstract Accurate simulation of seismic wave propaga- tion in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments with great and rapid structural changes, due for instance to the presence of shadow zones, diffractions and/or edge effects. Different methods, developed to improve seismic model- ing, are typically tested on synthetic configurations against analytical solutions for simple canonical problems or ref- erence methods, or via direct comparison with real data acquired in situ. Such approaches have limitations,especially if the propagation occurs in a complex envi- ronment with strong-contrast reflectors and surface irreg- ularities, as it can be difficult to determine the method which gives the best approximation of the ＂real＂ solution, or to interpret the results obtained without an a priori knowledge of the geologic environment. An alternative approach for seismics consists in comparing the synthetic data with high-quality data collected in laboratory experi- ments under controlled conditions for a known configuration. In contrast with numerical experiments, laboratory data possess many of the characteristics of field data, as real waves propagate through models with no numerical approximations. We thus present a comparison of laboratory-scaled measurements of 3D zero-offset wave reflection of broadband pulses from a strong topographic environment immersed in a water tank with numerical data simulated by means of a spectral-element method and a discretized Kirchhoff integral method. The results indicate a good quantitative fit in terms of time arrivals and acceptable fit in amplitudes for all datasets.展开更多
针对换相失败影响因素分析已经取得一些成果,但故障清除时刻(故障分闸角)对换相失败的影响有待进一步研究。首先基于换相失败过程分析过零点偏移角对关断角的影响;其次基于换相电压时间面积法分析不同故障合闸角对逆变器首次换相失败的...针对换相失败影响因素分析已经取得一些成果,但故障清除时刻(故障分闸角)对换相失败的影响有待进一步研究。首先基于换相失败过程分析过零点偏移角对关断角的影响;其次基于换相电压时间面积法分析不同故障合闸角对逆变器首次换相失败的影响,并进一步分析故障分闸角及过零点偏移角对后续换相失败的影响,发现故障在换相过程中清除引发后续换相失败风险最大;最后以单相接地故障为例,基于PSCAD/EMTDC中的(conseil international des grands reseaux electriques,CIGRE)模型的不同故障合闸角与分闸角的仿真测试结果验证了理论分析的正确性。展开更多
基金financially supported by the Shenzhen Science and Technology Research Program(grant no.JCYJ2021032412141-2034)the National Natural Science Foundation of China(grant nos.41804157,41774171,41774167,41974205,41804157,and 41904156)+3 种基金financial support from the pre-research Project on Civil Aerospace Technologies(grant no.D020103)funded by the China National Space Administrationthe 111 Project(grant no.B18017)the Chinese Academy of Sciences Center for Excellence in Comparative Planetologythe Macao Foundation.
文摘The space-borne fluxgate magnetometer(FGM)requires regular in-flight calibration to obtain its zero offset.Recently,Wang GQ and Pan ZH(2021a)developed a new method for the zero offset calibration based on the properties of Alfvén waves.They found that an optimal offset line(OOL)exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs.Because no pure Alfvén waves exist in the interplanetary magnetic field,calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events.Here,we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset.This procedure includes three parts:(1)selecting potential Alfvénic fluctuation events,(2)obtaining the OOL,and(3)determining the zero offset.We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express.The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis-Smith method.One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler.Our automatic procedure could also be applied to find fluctuation events for the Davis-Smith method.
文摘In this paper, a very low-offset continuous time amplifier has been presented. It has the fully differential structure and uses an Auto-zeroed offset stabilization technique. This structure consists of two phases in which the offset value is sampled in the first phase and then subtracted from the signal in the second phase. In order to maintain the continuous time topology, the amplifier uses two paths called main-path and sub-path where the main-path is never disconnected from the signal path and as a result the structure will be continuous time. The amplifier is designed to have a total amount of power dissipation about 3 mW in the standard 0.35 μm CMOS process. Furthermore, the proposed Opamp has an offset value lower than 1 μV at a 2.5 kHz Auto-zeroing frequency, unity gain frequency of 6.14 MHz and phase margin of 78.6° with 50 pF loads.
基金the INSIS Institute of the French CNRS,Aix-Marseille Universitythe Carnot Star Institute,the VISTA Projectthe Norwegian Research Council through the ROSE Project for financial support
文摘Abstract Accurate simulation of seismic wave propaga- tion in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments with great and rapid structural changes, due for instance to the presence of shadow zones, diffractions and/or edge effects. Different methods, developed to improve seismic model- ing, are typically tested on synthetic configurations against analytical solutions for simple canonical problems or ref- erence methods, or via direct comparison with real data acquired in situ. Such approaches have limitations,especially if the propagation occurs in a complex envi- ronment with strong-contrast reflectors and surface irreg- ularities, as it can be difficult to determine the method which gives the best approximation of the ＂real＂ solution, or to interpret the results obtained without an a priori knowledge of the geologic environment. An alternative approach for seismics consists in comparing the synthetic data with high-quality data collected in laboratory experi- ments under controlled conditions for a known configuration. In contrast with numerical experiments, laboratory data possess many of the characteristics of field data, as real waves propagate through models with no numerical approximations. We thus present a comparison of laboratory-scaled measurements of 3D zero-offset wave reflection of broadband pulses from a strong topographic environment immersed in a water tank with numerical data simulated by means of a spectral-element method and a discretized Kirchhoff integral method. The results indicate a good quantitative fit in terms of time arrivals and acceptable fit in amplitudes for all datasets.
文摘针对换相失败影响因素分析已经取得一些成果,但故障清除时刻(故障分闸角)对换相失败的影响有待进一步研究。首先基于换相失败过程分析过零点偏移角对关断角的影响;其次基于换相电压时间面积法分析不同故障合闸角对逆变器首次换相失败的影响,并进一步分析故障分闸角及过零点偏移角对后续换相失败的影响,发现故障在换相过程中清除引发后续换相失败风险最大;最后以单相接地故障为例,基于PSCAD/EMTDC中的(conseil international des grands reseaux electriques,CIGRE)模型的不同故障合闸角与分闸角的仿真测试结果验证了理论分析的正确性。
