Why should the latitude of the observer be considered when modeling gradual proton events? An insight using the concept of cobpoint

The shape of flux profiles of gradual solar energetic particle (SEP) events depends on several not well-understood factors, such as the strength of the associated shock, the relative position of the observer in space with respect to the traveling shock, the existence of a background seed particle population, the interplanetary conditions for particle transport, as well as the particle energy. Here, we focus on two of these factors: the influence of the shock strength and the relative position of the observer. We performed a 3D simulation of the propagation of a coronal/interplanetary CME-driven shock in the framework of ideal MHD modeling. We analyze the passage of this shock by nine spacecraft located at ∼0.4 AU (Mercury’s orbit) and at different longitudes and latitudes. We study the evolution of the plasma conditions in the shock front region magnetically connected to each spacecraft, that is the region of the shock front scanned by the “cobpoint” (Heras et al., 1995), as the shock propagates away from the Sun. Particularly, we discuss the influence of the latitude of the observer on the injection rate of shock-accelerated particles and, hence, on the resulting proton flux profiles to be detected by each spacecraft.     

Solar Energetic Particle Composition, Energy Spectra, and Space Weather

Recent progress in measuring the composition and energy spectra of solar energetic particles (SEPs) accelerated by CME-driven shocks is reviewed, including a comparison of the observed charge-to-mass dependence of breaks in SEP spectra with model predictions. Also discussed is a comparison of SEP and CME kinetic energies in seventeen large SEP events, and estimates of the SEP radiation dose that astronauts would be subject to once they venture outside the protective cover of Earth’s magnetosphere.     

Particle Acceleration at Interplanetary Shocks

This paper briefly reviews proton acceleration at interplanetary shocks. This is key to describing the acceleration of heavy ions at interplanetary shocks because wave excitation—and hence particle scattering—at oblique shocks is controlled by the protons and not the heavy ions. Heavy ions behave as test particles, and their acceleration characteristics are controlled by the properties of proton-excited turbulence. As a result, the resonance condition for heavy ions introduces distinctly different signatures in abundance, spectra, and intensity profiles, depending on ion mass and charge. Self-consistent models of heavy-ion acceleration and the resulting fractionation are discussed. This includes discussion of the injection problem and the acceleration characteristics of quasi-parallel and quasi-perpendicular shocks.     

一种新型双组元卫星推进剂的研究

通过热力学计算,选择NHO-3作为甲基肼高能添加剂,通过冰点测试、着火延迟期测试确定了NHO-3的含量,该种以甲基肼为主体的新型燃料与氧化剂MON-20组成的双组元推进剂具有冰点低、比冲高、着火延迟期短的优点,可应用于卫星、飞船等领域。     

中性浮力和失重环境人体运动仿真比较研究

为了模拟失重状态,航天技术发达的国家都建立了用于航天员出舱活动训练的中性浮力水槽。但与太空失重环境相比,水中存在的水动阻力会导致两种环境下人体运动反馈的差异性。基于ADAMS多体动力学仿真软件,按照“飞天”舱外航天服的质量分布,建立了着舱外服人体动力学模型。利用此模型仿真比较了水下和失重环境中肘关节屈伸、肩内收外展、肩矢状面内运动时人体躯干的动力学反馈,发现水下环境中模型躯干的转动速度峰值和平均值均较大。研究结果已应用于神舟七号载人飞行任务出舱活动航天员训练,建立的航天员人体动力学模型可应用于我国未来空间站任务出舱活动仿真分析。     

量子真空标准研究进展

2018 年，国际计量局将对国际单位制7 个基本量进行重新定义或重述。基于光学方法的真空计量新方法、新概念进一步发展，促进真空计量标准向量子化迈进，对真空基本量复现以及今后真空国际单位制的重新定义（由压力的SI 单位帕斯卡（Pa）向气体密度单位（mol/m3 或分子个数/m3，变化）具有重要意义。与传统计量技术相比，利用光学方法所建立的量子真空计量标准具有不需要自校、溯源链零长度、响应快、准确度高、可在多个地点及不同时间复现等优点，为真正意义上的绝对原级标准。本文介绍了美国国家标准与技术研究院（NIST）、德国联邦物理技术研究院（PTB）及瑞典国家测试和检定研究院（SNTRI）等机构开展的基于折射率、吸收光谱、冷原子3种光学方法的新一代量子真空计量标准研究进展，对原理、关键技术及难度挑战进行了阐述和分析。     

基于APSE确定高超声速边界层第二模态中性曲线下支

在高超声速边界层流动中,由于存在非平行效应以及激发Mack第二模态时的模态同步机制,因此在进行转捩预测研究时,中性曲线下支的确定需要考虑到这两方面的影响。全文针对高超声速平板边界层,首先采用线性抛物化稳定性方程(LPSE)对考虑感受性的中性曲线下支进行了求解,研究发现该方法存在两大难点:一是计算入口需要给定的离散模态在衰减区求解困难;二是由于存在快、慢模态的同步机制,所以在实际计算时,需要分别计算两次离散模态的演化以确定中性曲线下支,计算效率较低。基于以上问题,本文提出了一种基于伴随抛物化稳定性方程(APSE)来计算非平行边界层稳定性的方法,并以此确定考虑感受性的中性曲线下支位置。该方法从Mack模态的增长区开始进行计算,因此有效地解决了使用LPSE方法计算时所存在的问题。在不同工况下,与线性稳定性理论(LST)以及LPSE给出的预测结果进行了对比。从对比结果中可以看出该方法给出的预测结果与LPSE给定上游主导模态的预测结果一致,同时不必依赖于入口初值的选取且效率更高。该方法有进一步发展的潜力,可以有效地应用于高超声速边界层转捩的预测研究中。     

带网状筋壁板弯曲中性层近似计算方法

文章针对空间站大型密封舱结构对整体壁板弯曲展开尺寸精度有较高的要求,应用塑性弯曲理论及假设,对带网状筋壁板的塑性弯曲过程进行了分析,并通过简化计算确定了壁板弯曲过程中展开中性层与壁板内表面的距离,又根据中性层位置确定了壁板的精确展开长度。经过与弯曲试验数据的对比,表明该简化算法的精度能够满足产品尺寸精度,为相似结构的展开计算提供了依据。     

An investigation of ionospheric disturbances over South Africa during the magnetic storm on 15 May 2005

The effects of the 15 May 2005 severe geomagnetic storm on the South African ionosphere are studied using ground-based and satellite observations. Ionospheric disturbances have less frequently been investigated over mid-latitude regions. Recently, a number of studies investigated their evolution and generation over these regions. This paper reports on the first investigation of travelling ionospheric disturbances (TIDs) over mid-latitude South Africa. Using global positioning system (GPS)-derived total electron content (TEC) variations from the South African network of dual frequency GPS receivers, we were able to examine the effects of the disturbance on the TEC. During this storm, two TEC enhancements were observed at low- and mid-latitudes: the first enhancement was observed between 30–45°S geomagnetic latitudes associated with equatorward neutral winds and the passage of a TID, while the second TEC enhancement is associated with a second TID. In addition, the F-region critical frequency (foF2) values observed at two ionosonde stations show response features that differ from those of the TEC during the disturbance period. The dissimilarity between the TEC and the foF2 suggests that two competing drivers may have existed, i.e., the westward electric field and equatorward neutral wind effects.     

Interplanetary CubeSats system for space weather evaluations and technology demonstration

The paper deals with the mission analysis and conceptual design of an interplanetary 6U CubeSats system to be implemented in the L₁ Earth–Sun Lagrangian Point mission for solar observation and in-situ space weather measurements.