Night-time total electron content enhancements at equatorial anomaly region in China

This paper presents small scale (duration ?1 h, ΔTEC ? 1TECU) night-time total electron content (TEC) enhancements observed at the equatorial anomaly region in China, for the first time. The data is from a GPS receiver chain established in 2005 by Institute of Center for Space Science and Applied Research, Chinese Academy of Sciences and a GPS receiver of International GPS Service (IGS), located between Fuzhou (26.1°N, 119.3°E) and Nanning (22.8°N, 108.3°E). Two other GPS observations of IGS taken at higher latitude were also used to investigate the localization of such phenomenon. The characteristics of the night-time TEC enhancement are examined with two case studies. The TEC increases about 1–3TECU, intermittently. While the night-time TEC enhancement mainly occurs at the equatorial anomaly region, it can be observed at middle latitude as well. The spatial size of the enhancement region is less than 5° in longitude. The primary statistical study shows that the TEC enhancement is more often observed in spring and autumn, but rarely in summer. It has no dependence on geomagnetic activity. The enhancement can occur both before and after midnight.     

The effect of total solar eclipse of October 3, 2005, on the total electron content over Europe

GPS observations from EUREF permanent GPS network were used to observe the response of TEC (Total Electron Content) to the total solar eclipse on October 3, 2005, under quiet geomagnetic conditions of the daytime ionosphere. The effect of the eclipse was detected in diurnal variations and more distinctly in the variations of TEC along individual satellite passes. The trough-like variations with a gradual decrease and followed by an increase of TEC at the time of the eclipse were observed over a large region. The depression of TEC amounted to 3–4 TECU. The maximum depression was observed over all stations located at the maximum path of the solar eclipse. The delay of a minimum level of TEC with respect to the maximum phase of the eclipse was about 20–30 min.     

脉冲微分系统关于部分变元的强稳定性

介绍了一种新的稳定性——脉冲微分系统的解关于部分变元的强稳定性,并进而讨论了该类稳定性问题. 首先建立了两个重要的引理,然后再借助于逐段连续的Lyapunov函数,得到了脉冲微分系统的零解关于部分变元强稳定性的一些判定定理.最后阐述了这些定理的应用.      

Temporal evolution analysis of storm-enhanced density during an intense magnetic storm on March 2015

An intense Storm Enhancement Density (SED) event with the magnetic storm occurred on 17–24 March 2015 has been investigated. The morphological character of the SED during different phase of the magnetic storm is examined and compared with the non-storm time. Three intensity indexes, i.e., “general” SED index, “heavy” SED index and “severe” SED index, are defined to represent the intensity of SED respectively represented by the numbers of the ionospheric total electron content (TEC) grids with TEC > 60 TECu, TEC > 80 TECu and TEC > 100 TECu. The temporal evolution of the SED intensity indexes during a time span covering the non-storm time and the magnetic storm time have also been investigated. The SED exhibits a shape with two parallel slender troughs in the middle and low latitudes during the non-storm time and then gradually develops into an ellipse structure as the development of magnetic storm. The intensity of SED and the fluctuation of the TEC evolution are generally corresponding to the fluctuation of Dst index. The analyzing results enrich our understanding of the temporal and spatial evolution of the ionospheric SED.     

面向多电飞机的脉冲波形下局部放电规律

为满足多电飞机（MEA）的大功率用电需求，系统工作电压需要进一步提高，而较高电压会增加相关部件的绝缘失效风险。面向多电飞机特定工作场景和参数，搭建了模拟飞机电作动器中的绕组间绝缘故障测试平台，开展了1 kHz范围内的局部放电（PD）大量重复实验，研究了特定电压幅值、正弦波和方波脉冲波形下局部放电幅值、放电重复率和放电相位等统计特征，并计算评估了不同频率值下多电飞机中的局部放电行为。实验结果表明：在设定频域范围内，方波脉冲下的起始放电电压（PDIV）都低于正弦，方波脉冲波形对绝缘影响更大；随着频率升高，放电幅值逐渐降低，但放电重复率几乎呈线性增长；放电时刻集中于上升沿/下降沿末端。以50 Hz作为对比基准频率，1 kHz时的放电幅值降低80%，而放电重复率增加11.92倍，较高频率下多次累积的小幅值击穿成为威胁绝缘失效的主要原因。计算分析认为高频下空间电荷场强变化导致的放电延迟时间减少和周期数目增加分别导致局部放电脉冲幅值降低和放电重复率增加。本实验结果有助于针对多电飞机电气系统和相关装备开展针对性绝缘测试和评估，并有望为多电飞机向大功率高电压方向的设计提供参考和借鉴。     

On the detection of anomalous seismo-ionospheric behavior in the presence of space weather stimuli for large earthquakes

Anomalous behavior of ionospheric total electron content (TEC) prior to earthquake has been observed in many studies. Evidence of such seismo-ionospheric coupling effects suggests that it is plausible to rely on TEC signatures for early earthquake warning. However, the detection of pre-earthquake TEC anomalies (PETA) has not been adopted in practice due to two pertinent issues. Firstly, the effects of space weather activity can affect TEC levels and cause anomalous behavior in the TEC. Usually arbitrary thresholds are set for space weather indices to eliminate TEC anomaly due to space weather effects. Secondly, the choice regarding moving time-window length used to characterise background variation of TEC within the statistical envelope approach has an effect on detection of PETA. While the rule-of-thumb in selecting the moving window length is to have a time window capable of capturing background variability and short-term fluctuations, the length of the time window used in the literature varies with little justification. In this study, a critical examination is conducted on the statistical envelope approach and in particular, to eliminate the effect of space weather activity without the use of arbitrary space indices to detect PETA. A two-part PETA identification procedure is proposed, consisting of wavelet analyses isolating non-earthquake TEC contributions, followed by the statistical envelope method using a moving window length standardized based on observed periodicities and statistical implications is suggested. The approach is tested on a database of 30 large earthquakes (M?≥?7.0). The proposed procedure shows that PETA can be detected prior to earthquakes at higher confidence levels without the need to separately check for space weather activity. More importantly, the procedure was able to detect PETA for studies where it was previously reported that PETA could not be detected or detected convincingly.     

Near real-time PPP-based monitoring of the ionosphere using dual-frequency GPS/BDS/Galileo data

Ionosphere delay is very important to GNSS observations, since it is one of the main error sources which have to be mitigated even eliminated in order to determine reliable and precise positions. The ionosphere is a dispersive medium to radio signal, so the value of the group delay or phase advance of GNSS radio signal depends on the signal frequency. Ground-based GNSS stations have been used for ionosphere monitoring and modeling for a long time. In this paper we will introduce a novel approach suitable for single-receiver operation based on the precise point positioning (PPP) technique. One of the main characteristic is that only carrier-phase observations are used to avoid particular effects of pseudorange observations. The technique consists of introducing ionosphere ambiguity parameters obtained from PPP filter into the geometry-free combination of observations to estimate ionospheric delays. Observational data from stations that are capable of tracking the GPS/BDS/GALILEO from the International GNSS Service (IGS) Multi-GNSS Experiments (MGEX) network are processed. For the purpose of performance validation, ionospheric delays series derived from the novel approach are compared with the global ionospheric map (GIM) from Ionospheric Associate Analysis Centers (IAACs). The results are encouraging and offer potential solutions to the near real-time ionosphere monitoring.     

月球探测器加速度响应预测的时域子结构方法

航天器结构的日益复杂和庞大为全系统级的动力学仿真带来了更大的困难和挑战,目前主要采用动态子结构法来提高分析求解效率,并解决不同设计部门之间的模型共享和技术保护问题。月球探测器软着陆阶段的冲击力学环境一般由加速度冲击响应谱描述,由于高阶振型对结构加速度响应的影响要比对位移响应的影响大得多,所以在小阻尼情况下,经典的基于模态的子结构方法在相同截断频率下对加速度响应的预测精度远低于位移响应。为解决这一问题,引进基于脉冲响应函数的时域子结构(IBS)方法,提出了一种适用于预测加速度响应的降阶形式的迭代求解格式。利用探测器着陆数值模拟试验中测得的缓冲机构作用力作为激励,分别采用固定界面模态综合(CB)法和IBS方法分析了月球探测器的加速度响应。数值算例表明,后者在计算精度和求解效率方面均高于前者,并说明基于脉冲响应函数的子结构方法适于对月球探测器加速度响应进行高精度快速预测。     

Tangent-impulse transfer from elliptic orbit to an excess velocity vector

The two-body orbital transfer problem from an elliptic parking orbit to an excess veloc-ity vector with the tangent impulse is studied. The direction of the impulse is constrained to be aligned with the velocity vector, then speed changes are enough to nullify the relative velocity. First, if one tangent impulse is used, the transfer orbit is obtained by solving a single-variable function about the true anomaly of the initial orbit. For the initial circular orbit, the closed-form solution is derived. For the initial elliptic orbit, the discontinuous point is solved, then the initial true anomaly is obtained by a numerical iterative approach; moreover, an alternative method is proposed to avoid the singularity. There is only one solution for one-tangent-impulse escape trajectory. Then, based on the one-tangent-impulse solution, the minimum-energy multi-tangent-impulse escape trajectory is obtained by a numerical optimization algorithm, e.g., the genetic method. Finally, several examples are provided to validate the proposed method. The numerical results show that the minimum-energy multi-tangent-impulse escape trajectory is the same as the one-tangent-impulse trajectory.     

一类Cohen-Grossberg型BAM脉冲神经网络周期解的存在性和全局指数稳定性

利用Lyapunov泛函、不等式方法及Poincaré映射,建立了一类具有混合时滞的Cohen-Grossberg型BAM脉冲神经网络周期解的存在性和全局指数稳定性的充分性判据。