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.     

选区熔化过程多尺度多物理场建模研究进展

选区熔化技术是一种基于粉末床的、能够精确成形复杂零件、调控微观组织和性能的金属增材制造技术,其成形过程的计算机模拟对于生产实践具有重要指导意义。综述了国内外的研究现状,首先介绍选区熔化技术的原理及其特点;然后介绍国内外对选区熔化过程已经开展的计算机模拟技术的研究进展;并进一步重点介绍针对电子束选区熔化过程的多尺度多物理场模型,主要包括:(1)微观尺度电子束与材料相互作用的能量吸收模型;(2)细观尺度从铺粉到粉末加热、熔化、流动、沉积成形全过程的模型;(3)宏观尺度零件成形过程模型。     

OSIRIS-REx: Sample Return from Asteroid (101955) Bennu

In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a flyby of Kuiper Belt object 2014 MU69 on January 1, 2019, and Juno, an orbiting mission that is studying the origin, evolution, and internal structure of Jupiter. The spacecraft departed for near-Earth asteroid (101955) Bennu aboard an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu. The spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with Bennu in November 2018. The science instruments on the spacecraft will survey Bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. The team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess Bennu’s resource potential, refine estimates of its impact probability with Earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. The spacecraft will leave Bennu in 2021 and return the sample to the Utah Test and Training Range (UTTR) on September 24, 2023.

     

Time-Delay Integration Imaging with ICON’s Far-Ultraviolet Imager

A Time-Delay Integration (TDI) image acquisition and processing system has been developed to capture ICON’s Far Ultraviolet (FUV) Spectrographic Imager data. The TDI system is designed to provide variable-range motion-compensated imaging of Earth’s nightside ionospheric limb and sub-limb scenes viewed from Low Earth Orbit in the 135.6 nm emission of oxygen with an integration time of 12 seconds. As a pre-requisite of the motion compensation the TDI system is also designed to provide corrections for optical distortions generated by the FUV Imager’s optical assembly. On the dayside the TDI system is used to process 135.6 nm and 157.0 nm wavelength altitude profiles simultaneously. We present the TDI system’s design methodology and implementation as an FPGA module with an emphasis on minimization of on-board data throughput and telemetry. We also present the methods and results of testing the TDI system in simulation and with Engineering Ground Support Equipment (EGSE) to validate its performance.

     

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Both heliophysics and planetary physics seek to understand the complex nature of the solar wind’s interaction with solar system obstacles like Earth’s magnetosphere, the ionospheres of Venus and Mars, and comets. Studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in context by observations from far and extreme ultraviolet (FUV, EUV), hard X-ray, and energetic neutral atom imagers (ENA). Each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the Kelvin-Helmholtz instability) generates diagnostic plasma density structures. The significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, Venus, and Mars or global magnetospheric/ionospheric convection at Earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. This paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1–2.0 keV) X-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles.The introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. In situ measurements confirm the existence of time- and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at Venus, Mars, comets, and the Earth. However, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. Remote sensing observations provide global information about auroral ovals (FUV and hard X-ray), the terrestrial plasmasphere (EUV), and the terrestrial ring current (ENA). ENA instruments with low energy thresholds (\(\sim1~\mbox{keV}\)) have recently been used to obtain important information concerning the magnetosheaths of Venus, Mars, and the Earth. Recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft X-ray imagers.Section 2 describes proposed dayside interaction mechanisms, including reconnection, the Kelvin-Helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. It focuses upon the questions that remain as yet unanswered, such as the significance of each proposed interaction mode, which can be determined from its occurrence pattern as a function of location and solar wind conditions. Section 3 outlines the physics underlying the charge exchange generation of soft X-rays. Section 4 lists the background sources (helium focusing cone, planetary, and cosmic) of soft X-rays from which the charge exchange emissions generated by solar wind exchange must be distinguished. With the help of simulations employing state-of-the-art magnetohydrodynamic models for the solar wind-magnetosphere interaction, models for Earth’s exosphere, and knowledge concerning these background emissions, Sect. 5 demonstrates that boundaries and regions such as the bow shock, magnetosheath, magnetopause, and cusps can readily be identified in images of charge exchange emissions. Section 6 reviews observations by (generally narrow) field of view (FOV) astrophysical telescopes that confirm the presence of these emissions at the intensities predicted by the simulations. Section 7 describes the design of a notional wide FOV “lobster-eye” telescope capable of imaging the global interactions and shows how it might be used to extract information concerning the global interaction of the solar wind with solar system obstacles. The conclusion outlines prospects for missions employing such wide FOV imagers.     

软件体系结构的探讨

软件体系结构是软件工程中的一个新兴研究领域,它与软件工程技术的发展有着密切的关系。首先,从软件工程技术的发展了解软件体系结构研究的必然性;然后,给出软件体系结构的概念描述,介绍有关体系结构研究的内容;最后,举出一个实例。     

大型飞机座舱温度控制系统控制律设计

大型飞机座舱温度控制系统具有温度控制非线性、强耦合、大迟滞性等特点,对控制律设计提出很高要求。根据系统设计要求,结合执行机构动作特性,提出了一种新型座舱温度控制律。系统控制方案采用压气机出口温度控制、组件出口温度控制、座舱供气温度控制和座舱区域温度控制四级控制;压气机出口温度目标值根据大气环境温度确定,座舱供气温度目标值根据座舱区域温度控制误差确定,组件出口温度目标值根据座舱供气温度目标值中的最小值确定;使用专家比例-积分-微分(PID)控制方法设计各级温度控制器,温度控制器的设计融入了解耦控制算法和系统保护控制逻辑,控制周期由各级温度控制响应特性确定。系统地面试验与飞行试验结果显示,该座舱温度控制系统响应速度快,抗干扰能力强,控制精度高,满足系统设计要求。     

Boundary discontinuous Fourier analysis of thick beams with clamped and simply supported edges via CUF

This paper presents an analytical solution for static analysis of thick rectangular beams with different boundary conditions.Carrera's Unified Formulation (CUF) is used in order to consider shear deformation theories of arbitrary order.The novelty of the present work is that a boundary discontinuous Fourier approach is used to consider clamped boundary conditions in the analytical solution,unlike Navier-type solutions which are restricted to simply supported beams.Governing equations are obtained by employing the principle of virtual work.The numerical accuracy of results is ascertained by studying the convergence of the solution and comparing the results to those of a 3D finite element solution.Beams subjected to bending due to a uniform pressure load and subjected to torsion due to opposite linear forces are considered.Overall,accurate results close to those of 3D finite element solutions are obtained,which can be used to validate finite element results or other approximate methods.     

超声速PIV示踪粒子布撒技术研究

介绍了上海交通大学高超声速创新技术研究实验室为发展超声速PIV流场测试系统而开发的示踪粒子布撒技术。研究中设计了一套超声速风洞PIV示踪粒子布撒装置,提出了利用发生器罐体内的真空度吸入示踪粒子的加注方式,选定了测试流程时序并得到了较好的粒子布撒效果。通过比较不同的发生器罐注入压力对粒子布撒浓度的影响,得到了效果良好的测试方案。     

The Modulation of Galactic Cosmic Rays in the Heliosphere: Theory and Models

Almost all theoretical and numerical models for the modulation of cosmic ray in the heliosphere are based on Parker's transport equation which contains all the important basic physical processes. The relative importance of the various mechanisms is however not established and may vary significantly over 22 years. The simultaneous measurements of solar wind parameters, heliospheric magnetic field properties and cosmic rays over a wide range of energies and positions in the heliosphere have brought the realization that modulation is much more complicated than what the original drift models predicted. In the process the sophistication of models based on solving Parker's equation has increased by orders of magnitude. A short review of the global modulation of cosmic rays is given from a theoretical and modelling point of view.