Neutral points on the boundary of the closed magnetosphere

Theoretical studies of a field-free plasma incident upon a magnetic dipole lead to a closed magnetosphere with two neutral points in the noon magnetic meridian, at a latitude of ± 70°–75° and a geocentric distance of approximately 10 R_E. The position of the neutral points with respect to the dipole axis is not greatly affected by the angle of incidence of the solar wind. Although the field magnitude near the neutral points is only a fraction of the dipole field, the direction is seen to reverse on opposite sides of the neutral point. Near the boundary the field direction is parallel to the boundary and tends to point towards the neutral point in the Northern hemisphere.     

Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

The Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP’s ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This paper summarizes the IMAP mission at the start of Phase A development.     

Novel single-phase AC/DC converter with two PWM control schemes

A novel single-phase AC/DC converter with two pulsewidth modulation (PWM) schemes is proposed to draw a sinusoidal line current with nearly unity power factor, achieve balanced neutral point voltage and regulate the DC bus voltage. With the aid of neutral point clamped scheme, a three-level voltage pattern is generated on the AC side of the proposed rectifier. To track the tine current command derived from a voltage controller and a phase-locked loop circuit, a hysteresis current control scheme is used in the inner loop control. A capacitor voltage compensator is employed to achieve the balanced neutral point voltage. To investigate the effectiveness of the proposed control scheme, the simulation and experimental results based on a laboratory prototype circuit are performed.     

The Dynamic Heliosphere: Outstanding Issues

Properties of the heliospheric interface, a complex product of an interaction between charged and neutral particles and magnetic fields in the heliosphere and surrounding Circumheliospheric Medium, are far from being fully understood. Recent Voyager spacecraft encounters with the termination shock and their observations in the heliosheath revealed multiple energetic particle populations and noticeable spatial asymmetries not accounted for by the classic theories. Some of the challenges still facing space physicists include the origin of anomalous cosmic rays, particle acceleration downstream of the termination shock, the role of interstellar magnetic fields in producing the global asymmetry of the interface, the influence of charge exchange and interstellar neutral atoms on heliospheric plasma flows, and the signatures of solar magnetic cycle in the heliosheath. These and other outstanding issues are reviewed in this joint report of working groups 4 and 6.     

电分相电弧对全向信标电磁辐射特性的分析

为了分析电气化铁路高速列车电分相电弧对机场全向信标（VOR）的影响,研究其电磁发射特性。利用电磁干扰接收机与频谱仪,分别以点频和扫频方式,对电气化铁路电分相点和普通点进行了大量辐射测试。分析测试数据的异方差性,改进回归分析方法,拟合出电弧在全向信标频段的幅频特性曲线,分析弓网电弧电磁辐射对机场全向信标的影响。结果表明：电分相电磁辐射是随机的,在电分相处比普通点大;现代电气化铁路高速列车经过电分相的测试数据异方差性比较明显,普通的最小二乘估计方法不适用;当电气化铁路电分相点与飞机距离小于4.944 km时,可能会对VOR信号产生影响。     

弓网电弧辐射特性及对机场下滑信标的影响

为获得弓网电弧辐射特性及从理论上分析其对机场下滑信标的影响。选择典型电气化动车线路,首先基于CISPR16-1标准,利用电磁干扰接收机对电分相和普通点处的弓网电弧电磁辐射进行点频测试,获得了其在下滑信标台频谱内的辐射特性,然后基于电波传播理论,以电气化轨道平行跑道为例,分析了弓网电弧电磁辐射对飞机导航的影响。结果表明：电弧电磁辐射具有一定的随机特性,普通点处产生的电磁辐射场强小于电分相处;普通点的电磁辐射不会对飞机的导航产生干扰;当轨道距跑道中心的距离分别为700、120和60 m时,电分相拉弧点距下滑信标台天线的距离应分别小于3 291、546和249 m时才不会对飞机的导航产生干扰。本结果能够为轨道电气化和民用航空这两大工业体系在机场区域的电磁兼容性设计提供依据。     

惯性颗粒在非均匀加速流中的输运问题

基于新型碳基颗粒增强或碳基纤维材料的再入体热烧蚀问题对飞行器的气动力/热性能影响机制尚不明确。初步研究不考虑化学反应和气体引射效应,把热烧蚀问题中的颗粒剥离问题模化为驻点流中的离散颗粒启动问题。由于高速气流在驻点温度达上万度量级,局部马赫数接近于0,研究近似假设靠近壁面的流体动力学为不可压缩的,并使用不可压缩颗粒解析的直接数值模拟方法（PR-DNS）研究一个惯性颗粒在平面挤压流和壁面驻点流中的动力学,从而揭示在驻点流中的颗粒输运机制。研究发现颗粒在壁面驻点流中的输运机制是水平输运,几乎没有垂直输运,与平行剪切颗粒床输运非常不同,这是驻点流特有的垂直向下挤压作用导致的。     

Energetic Hydrogen and Oxygen Atoms Observed on the Nightside of Mars

We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet. We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach 10⁵ cm⁻² sr⁻¹ s⁻¹, but no oxygen ENA signals above the detection threshold of 10⁴ cm⁻² sr⁻¹ s⁻¹ are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed. Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 10¹⁰ m⁻³ and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 10¹² m⁻³ and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss rate of hydrogen and oxygen due to the production of ENAs.     

Topics in Microphysics of Relativistic Plasmas

Astrophysical plasmas can have parameters vastly different from the more studied laboratory and space plasmas. In particular, the magnetic fields can be the dominant component of the plasma, with energy-density exceeding the particle rest-mass energy density. Magnetic fields then determine the plasma dynamical evolution, energy dissipation and acceleration of non-thermal particles. Recent data coming from astrophysical high energy missions, like magnetar bursts and Crab nebula flares, point to the importance of magnetic reconnection in these objects. In this review we outline a broad spectrum of problems related to the astrophysical relevant processes in magnetically dominated relativistic plasmas. We discuss the problems of large scale dynamics of relativistic plasmas, relativistic reconnection and particle acceleration at reconnecting layers, turbulent cascade in force-fee plasmas. A number of astrophysical applications are also discussed.     

Collisionless Shocks in Partly Ionized Plasma with Cosmic Rays: Microphysics of Non-thermal Components

In this review we discuss some observational aspects and theoretical models of astrophysical collisionless shocks in partly ionized plasma with the presence of non-thermal components. A specific feature of fast strong collisionless shocks is their ability to accelerate energetic particles that can modify the shock upstream flow and form the shock precursors. We discuss the effects of energetic particle acceleration and associated magnetic field amplification and decay in the extended shock precursors on the line and continuum multi-wavelength emission spectra of the shocks. Both Balmer-type and radiative astrophysical shocks are discussed in connection to supernova remnants interacting with partially neutral clouds. Quantitative models described in the review predict a number of observable line-like emission features that can be used to reveal the physical state of the matter in the shock precursors and the character of nonthermal processes in the shocks. Implications of recent progress of gamma-ray observations of supernova remnants in molecular clouds are highlighted.     

时滞依赖状态的脉冲中立型发展微分包含

目的主要考虑一类时滞依赖状态的脉冲中立型发展微分包含;方法在公理化定义的相空间上,利用Ba-nach空间中发展系统理论结合相应的不动点定理;结果时滞依赖状态的中立型泛函微分至少有一个温和解;结论建立此类问题温和解的存在性。     

Magnetic configuration of coronal streamers and threads

We give a short account of the most prominent structures of the intermediate corona. Then we propose an axially symmetrical model for coronal streamers, according to which charged particles move along magnetic surfaces whose sources are electrical currents situated in the vicinity of the photosphere. The simplest current configuration is a pair of coaxial, coplanar, circular, and oppositely directed currents parallel to the photosphere. Magnetic surfaces for this current distribution exhibit a helmet-shaped separatrix and a saddle point. The temperature profile along the streamer can be predicted qualitatively if one takes into account the conservation of an adiabatic invariant in the drift theory of the charged particle motion.     

增程式APU混沌退火混合粒子群优化模糊PID动态控制

针对增程式辅助动力单元(APU)工作点切换过程的控制,提出了一种混沌退火混合粒子群(CAHPSO)算法优化模糊比例积分微分(PID)控制的增程式APU动态控制策略。该算法将标准粒子群(PSO)算法与混沌搜索和退火机制融合,强化全局寻优能力,并采用该算法离线优化模糊PID控制参数。为验证该控制策略的有效性,本文建立了APU仿真模型。仿真结果表明:该控制策略可使APU在工作点从热机点逐步切换至高负荷点的过程中稳定时间短,在三个工作点切换控制过程中稳定时间分别为2.92 s,2.88 s,2.79 s;可使APU转速超调率小,在小负荷点向中负荷点切换时超调约0.95%,在其余过程未出现超调;可使APU转矩变化平缓,在中负荷点向高负荷点切换时转矩仅超调0.16 N·m,具有良好的动态控制效果。      

Experimental and numerical study of deposition mechanisms for cold spray additive manufacturing process

Cold spray is an attractive and rapidly developing process for additive manufacturing with high efficiency and precision, repairing and coating, especially in aircraft and aerospace applications. Cold spray additive manufacturing deposits micro-particles with large plastic deformation below their melting point, eliminating heat effect zone which could deteriorate the quality of repairing zone. The particle deposition in cold spray is a complex process which involves high strain rate,high contact...     

Effects of Particle Beams in the Solar Atmosphere

This work addresses the observational and physical effects of particle beams in the solar atmosphere. Mainly electron beams are considered, but also some effects of proton and neutral beams are mentioned. Briefly describing acceleration mechanisms of superthermal particles, the main attention is devoted to effects influencing the particle beam propagation. The collisional energy losses and pitch-angle scattering, return current effects, mirroring in the converging magnetic field, and the scattering in the Alfvén and whistler wave turbulence in specific situations are considered. The role of quasi-linear relaxation is discussed. Examples of observations showing effects of particle beams in the solar atmosphere are presented throughout the paper. Separate chapters are devoted to processes connected with particle beam bombardment of dense layers of the solar atmosphere: hard X-ray and -ray flare emissions, evaporation process, asymmetry of optical chromospheric lines, and impact linear H line polarization. The beam induced energy release processes are also included. The presented effects of particle beams are summarized in the conclusions and future prospects are suggested.     

The Hydrogen Exospheric Density Profile Measured with ASPERA-3/NPD

We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F_10.7=100). We derive estimates for the hydrogen exobase density, n _H = 10¹⁰ m^?3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity.     

波音757右IDG电源输出中线接地点故障分析

以实际维修工作中遇到的波音757右整体驱动发电机（IDG）电源输出中线接地点故障为例．对该故障的现象、特点和难点进行分析和判断,找到了故障的原因,并提出了排故方案和维修建议。     

基于混合粒子群算法的上升段交会弹道快速优化设计

基于梯度搜索的高效性和粒子群搜索的随机性,提出了一种混合粒子群算法,并应用该算法研究了运载火箭上升段交会弹道快速优化设计问题.以运载火箭与目标飞行器在交会时刻的距离最小为目标函数,设计了运载火箭飞行程序,建立了运载火箭上升段交会弹道优化模型,同时分别采用混合粒子群算法、遗传算法和粒子群算法进行求解.仿真结果表明:基于本文算法对运载火箭上升段交会弹道进行优化设计,平均交会位置误差为4.137m,较遗传算法减少了17.940m,平均优化耗时488.922s,较粒子群算法缩短了2342.125s.混合粒子群算法搜索速度较快,收敛精度较高,可用于运载火箭上升段交会弹道的快速优化设计.