Ionospheric TEC prediction using hybrid method based on ensemble empirical mode decomposition (EEMD) and long short-term memory (LSTM) deep learning model over India

Total electron data (TEC) from GPS nowadays can be used as a tool for understanding the space weather phenomena. The development of prediction model for TEC is quiet crucial and challenging due to the dynamic behavior of the ionosphere, since it depends on different factors such as seasonal, diurnal and spatial variations, solar geomagnetic conditions etc. In this paper, an attempt is made for predicting the GPS derived TEC values for different GNSS stations over India using a hybrid method based on Ensemble empirical mode decomposition (EEMD) and Long Short-Term Memory (LSTM) deep learning method. The daily TEC time series data from the IISc Bangalore (Latitude 13.021, Longitude 77.570), Lucknow (Latitude 26.912, Longitude 80.956) and Hyderabad (Latitude 17.417, Longitude 78.551) stations over India during the period 2008 to 2015 of solar cycle 23 and 24 is used for analysis. The assessment of model performance for testing predicted output compared with LSTM and EMD-LSTM models, and their comparison results show that the hybrid EEMD-LSTM model presents better than the other models.     

多个空间高斯源信号情况下成组三维图像特征提取方法

针对功能磁共振成像数据中含有多个高斯信号源的盲源分离问题,介绍了一种成组典型相关分析方法(Group BSS-CCA)。这个方法的组分析框架参照了GIFT工具箱中的Group ICA算法,具体的典型相关分析方法应用的是Friman等人提出的BSS-CCA算法。以验证该方法的有效性为目的,设计了仿真实验;结果表明,该方法能较好识别出混合在人脑功能磁共振成像数据的2个空间高斯信号。Group BSS-CCA算法对研究人脑的功能磁共振成像数据具有较高的实用价值。     

The N4,5 - OO Auger and “N3” N4,5O2,3 Coster-Kronig spectra of xenon induced by electron impact

The N_4,5OO Auger electron spectrum in the kinetic energy region (14–37) eV has been measured with high resolution at electron incident energies between 71 eV and 2019 eV. The Auger and satellite lines are assigned by comparison with previous literature data. Several states which correspond to the resonant Auger transitions from the 4d_{3/2, 5/2} 6p states are observed. The PCI effects on the N₅-O_2,3O_2,3(¹S₀) Auger peak when the incident electron energy approaches to the N₅ edge (67.55 eV) is investigated and it is found that the dependence of the energy shift on the excess energy, E_exc, is well represented by the function E_exc^β with β = (-1.40 ± 0.05). The ^“N₃^” N_4,5O_2,3 Coster-Kronig spectrum is measured at various electron incident energies. The assignments of the features are made in comparison with a similar spectrum from synchrotron radiation measured by Kivimäki et al. [J. Electron Spectrosc. Relat. Phenom. 1999, 101–103, 43–47]. The Auger spectrum in the kinetic energy regions (68–78) eV and (90–138) eV is observed for the first time in an electron impact experiment and a comparison is made with the photoionization experiment by Hikosaka et al. [Phys. Rev. A 2007, 76, 032708].     

热障涂层的研究进展

主要介绍了热障涂层在现阶段的研究和应用，以及它们的组成和性能。讨论了热障涂层现有的三种涂层制备工艺和寿命预测模型，并对等离子喷涂和电子束物理气相沉积作了详细的对比，同时指出了热障涂层未来的研究方向。     

Aspects related to variability of radiative cooling by NO in lower thermosphere,TEC and O/N2 correlation,and diffusion of NO into mesosphere during the Halloween storms

Nitric Oxide is a very important trace species which plays a significant role acting as a natural thermostat in Earth’s thermosphere during strong geomagnetic activity. In this paper, we present various aspects related to the variation in the NO Infrared radiative flux (IRF) exiting the thermosphere by utilizing the TIMED/SABER (Thermosphere Ionosphere Mesosphere Energetics and Dynamics/ Sounding of the Atmosphere using Broadband Emission Radiometry) observational data during the Halloween storm which occurred in late October 2003. The Halloween storm comprised of three intense-geomagnetic storms. The variability of NO infrared flux during these storm events and its connection to the strength of the geomagnetic storms were found to be different in contrast to similar super storms. The connection between the quantum of energy outflux from the upper atmosphere into space in terms of NO IRF and the duration of storms is established. The NO radiative cooling, and the closely correlated depletion in O/N₂ ratio are controlled by the Joule heating intensity (proxied by AE-index). The collisional excitation rate of NO, calculated using the modelled datasets of WACCM-X (Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension), correlates well with the observed pattern of radiative emission by NO. Observational datasets from TIMED/GUVI (Global Ultra-Violet Imager) and MIT Haystack observatory madrigal GNSS (Global navigation satellite system) total electron content (TEC) database shows that the TEC and O/N₂ enhancement in low-mid northern hemispheric latitudes are mainly controlled by the z-component of Interplanetary magnetic field (IMF-B_z). The penetration of eastward electric field during the storm events is found to be responsible for the overall enhancement of TEC. The contribution of enhanced day-side TEC in observed variation of O/N₂ ratio by GUVI is also reported. It is also seen that during substorms related events the night-time polar region experiences more cooling due to NO than the daytime polar region. The connections between the mid- and low-latitude enhancement in NO IRF with the propagation of LSTIDs (Large-scale traveling ionospheric disturbances) in combination with the O/N₂ variability, and the altitudinal variation in NO flux with the progression of the storm is also investigated. This study presents the evidence on the role of diffusion processes in the large scale enhancement of NO in the mesospheric altitudes.     

Numerical simulations of a continuously injected relativistic electron beam relaxation into a plasma with large-scale density gradients

In this paper the influence of large-scale decreasing and increasing gradients of the density of magnetized plasma on the relaxation process of a continuously injected relativistic electron beam with an energy of 660 keV ($v_b=0.9c$) and a pitch-angle distribution is studied using particle-in-cell numerical simulations. It is found that for the selected parameters in the case of a smoothly decreasing gradient and in a homogeneous plasma the formation of spatially limited plasma oscillations of large amplitude occurs. In such cases, modulation instability develops and a long-wave longitudinal modulation of the ion density is formed. In addition, the large amplitude of plasma waves accelerates plasma electrons to energies on the order of the beam energy. In the case of increasing and sharply decreasing gradients, a significant decrease in the amplitude of plasma oscillations and the formation of a turbulent ion density spectrum are observed. The possibility of acceleration of beam electrons to energies more than 2 times higher than the initial energy of the beam particles is also demonstrated. This process takes place not only during beam propagation in growing plasma density, but also in homogeneous plasma due to interaction of beam particles with plasma oscillations of large amplitude.     

不同钝化工艺SiO2薄膜的辐射缺陷

为研究不同钝化工艺栅介质用SiO₂薄膜的高能电子辐射缺陷特征，采用能量为1 MeV的高能电子在辐照注量为1×10¹⁵ e/cm²、5×10¹⁵ e/cm²和1×10¹⁶e/cm²下对三种不同钝化工艺（I，700 nm SiN + 500 nm PSG;II，1.2 μm SiN;III，700 nm PSG + 500 nm SiN）的SiO₂薄膜进行了辐照试验。拉曼光谱和X射线光电子能谱结果表明I和III钝化工艺SiO₂薄膜形成了非晶硅及双氧根离子，傅立叶红外光谱结果表明I钝化工艺SiO₂薄膜形成缺陷结构未知的A₁、A₂、B₁及B₂缺陷；II钝化工艺SiO₂薄膜形成A₁、B₁、及 缺陷；III钝化工艺SiO₂薄膜形成A₁、及B₂缺陷。     

Investigation of the planar midlatitude ionospheric trend under different levels of solar activity

A better understanding of the ionosphere through accurate mathematical models is no doubt a crucial element. This study focuses on the challenging problem of building a model representing the complex structure of the midlatitude ionosphere. Previous studies have shown that a regional planar model is suitable in representing the total electron content (TEC) trend in the midlatitude ionosphere in both hemispheres. In this study, the planar trend model for 12 non-overlapping northern hemisphere regions in three groups of geographically near 4 regions is further investigated under different levels of solar activity; low, moderate and high. To that end, the coefficients of the model are estimated in the least squares sense using total electron content values from global ionospheric maps (GIMs) for the years 2009, 2012 and 2014. Subsequently, these coefficients are used to reconstruct estimated TEC maps which are then compared with actual GIM-TEC by investigating their difference in normalized $L_2$ norm squared sense. The regional planar trend model provides a particularly successful representation in the years 2012 and 2014 for which the solar activity level is the dominant factor determining the TEC trend. Under low solar activity conditions of 2009, other factors such as ocean currents, temperature variations and meteorological phenomena are suspected to have a considerable effect in some regions depending on their geographic location and on seasonal trends in those regions. As an example, studies show that under the influence of the Pacific Decadal Oscillation (PDO) and Siberian High (SH), a significant cooling trend between 2004 and 2018 in autumn is observed in Eurasia, which, in conjunction with the low solar activity levels, may be related to the deviations from the actual GIM-TEC in 2009 in these regions. As solar radiation increases, however, such bottom-side forcings are masked in 2012 and 2014 and these deviations are no longer observed.     

推进剂管理装置的可靠性增长及试验验证

采用原始的焊接方式焊接筛网式推进剂管理装置的收集器合格率低、可靠性差。为此,采用纯钛箔作为过渡层进行了不锈钢筛网与钛合金支压板的电阻缝焊试验以及随后这两者与钛合金骨架的电子束焊试验,然后进行了地面力学环境下的振动试验,以验证焊接方式改进后收集器的可靠性。焊接试验结果表明,纯钛箔过渡层一方面可以大幅降低筛网在电阻缝焊时的焊接热量,有效地减小筛网的热变形;另一方面可以在电阻缝焊后形成牢固、封闭的纯钛/不锈钢筛网焊缝过渡区,有效地增加电子束焊时筛网的变形抗力,从而使得焊接后试样的合格率和性能大幅提高。振动试验结果表明,焊接方式改进后收集器的可靠度置信下限从0.90增加到了0.96。     

The global response of terrestrial ionosphere to the December 2015 space weather event

This paper investigates the ionospheric storm of December 19–21, 2015, which was initiated by two successive CME eruptions that caused a G3 space weather event. We used the in situ electron density (N_e) and electron temperature (T_e) and the Total Electron Content (TEC) measurements from SWARM-A satellite, as well as the O/N₂ observations from TIMED/GUVI to study the ionospheric impact. The observations reveal the longitudinal and hemispherical differences in the ionospheric response to the storm event. A positive ionospheric storm was observed over the American, African and Asian regions on 20 December, and the next day showed a negative storm. Both these exhibited hemispheric differences. A positive storm was observed over the East Pacific region on 21 December. It is seen that the net effect of both the disturbance dynamo electric field and composition differences become important in explaining the observed variability in topside ionospheric densities. In addition, we also discuss the T_e variations that occurred as a consequence of the space weather event.