搅拌摩擦加工调控镁合金组织与耐腐蚀性能的发展现状与趋势

近年来,航空航天领域轻量化进程发展迅速,镁合金在其中扮演着越来越重要的角色.然而,镁合金耐腐蚀性不佳的特点制约了镁合金的应用范围.本文综述了搅拌摩擦加工技术调控含第二相镁合金耐腐蚀性能的研究现状,从动态再结晶和加速第二相破碎、固溶两个角度,论述了搅拌摩擦加工调控镁合金组织的基本原理,并分析了搅拌摩擦加工改善含粗大第二相...     

纳米CuO/AP复合粒子的制备及催化性能研究

采用溶剂-非溶剂法制备出了以纳米CuO为核、AP为壳的CuO／AP复合粒子。TEM、KRD及从的测试结果表明。复合粒子中只有CuO和AP存在,且AP包覆于CuO的外表,而DSC对复合粒子催化性能的测试结果表明。纳米CuO／AP复合粒子中AP的高温分解峰温度下降到101℃,较CuO-AP的简单混合物提前了5．64℃,而且复合粒子中AP的低温分解峰消失,在完成由斜方晶系向立方晶系的晶型转变后,便直接进入了高温分解,这为改善推进剂燃速提供了一条可行途径。     

硼粒子直径对点火位置及燃烧效率的影响研究

采用颗粒轨道模型对非壅塞固冲发动机补燃室内不同直径硼粒子的点火及燃烧进行了数值模拟。其中,气相反应简化为一种等效气体的燃烧,硼粒子与O2的燃烧反应模型采用涡耗散模型。硼粒子的点火过程采用King模型,燃烧过程采用化学动力学控制的燃烧模型。结果表明,直径较小的硼粒子能够在补燃室头部点火,且能随气流旋转,驻留时间较长,燃烧较为充分,直径较大的硼粒子与此相反。     

Investigation of PMSE dependence on high energy particle precipitation during their simultaneous occurrence

This paper is based on the observations of Polar Mesosphere Summer Echoes (PMSE) with the EISCAT VHF 224?MHz radar during the summer month 08–12 July 2013. The effect of high energy particle precipitation on PMSE intensity, particularly during their simultaneous occurrence for longer time interval (longer than or equal to 3-h) has been investigated. The correlation between the two phenomena has been computed using the Spearman rank and Pearson linear correlation coefficient. The variations in high energy particle precipitation reaching down to altitude of 91?km and PMSE intensity in the altitude range of 80–90?km are positively correlated. The electron density irregularity due to ionization caused by precipitating particles might be one of the possible reasons for this positive correlation. Moreover, some other background parameters i.e. K-indices (proxy of high energy particle precipitation) and electron fluxes during the simultaneous occurrence of the two phenomena also support one of the possible reasons given for explanation of the observed positive correlation. The X-rays and proton fluxes have no noticeable effect on PMSE echoes in this study.     

Acceleration of charged particles by fluctuating and steady electric fields in a X-type magnetic field

Release of stored magnetic energy via particle acceleration is a characteristic feature of astrophysical plasmas. Magnetic reconnection is one of the mechanisms for releasing energy from magnetized plasmas. Collisionless magnetic reconnection could provide both the energy release mechanism and the particle accelerator in space plasmas. Here we studied particle acceleration when fluctuating (in-time) electric fields are superposed on an static X-type magnetic field in collisionless hot solar plasma. This system is chosen to mimic the reconnective dissipation of a linear MHD disturbance. Our results are compared to particle acceleration from constant electric field superposed on an X-type magnetic field. The constant electric field configuration represents the effects of steady state magnetic reconnection. Time evolution of ion and electron distributions are obtained by numerically integrating particle trajectories. The frequencies of the electric field represent a turbulent range of waves. Depending on the frequency and amplitude of the electric field, electrons and ions are accelerated to different degrees and have energy distributions of bimodal form consisting of a lower energy part and a high energy tail. For frequencies (ω in dimensioless units) in the range 0.5 ? ω ? 1.0 a substantial fraction (20%–30%) of the proton distribution is accelerated to gamma-ray producing energies. For frequencies in the range 1 ? ω ? 100.0 the bulk of the electron distribution is accelerated to hard X-ray producing energies. The acceleration mechanism is important for solar flares and solar noise storms but it could be applicable to all collisionless astrophysical plasmas.     

Sesame – An Experiment of the Rosetta Lander Philae: Objectives and General Design

SESAME is an instrument complex built in international co-operation and carried by the Rosetta lander Philae intended to land on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of this instrument suite are to measure mechanical and electrical properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface. Most of the sensors are mounted within the six soles of the landing gear feet in order to provide good contact with or proximity to the cometary surface. The measuring principles, instrument designs, technical layout, operational concepts and the results from the first in-flight measurements are described. We conclude with comments on the consequences of the last minute change of the target comet and how to improve and to preserve the knowledge during the long-duration Rosetta mission.     

Plasma flow variations and energetic protons upstream of the earth’s bow shock: A statistical study

Foreshock is a special region located upstream of the Earth’s bow shock characterized by the presence of various plasma waves and fluctuations caused by the interaction of the solar wind plasma with particles reflected from the bow shock or escaping from the magnetosphere. On the other hand, foreshock fluctuations may modify the bow shock structure and, being carried through the magnetosheath, influence the magnetopause. During the years 1995–2000, the INTERBALL-1 satellite made over 10,000 hours of plasma and energetic particles measurements in the solar wind upstream of the Earth’s bow shock. We have sorted intervals according to the level of solar wind ion flux fluctuations and/or according to the flux of back-streaming energetic protons. An analysis of connection between a level of ion flux fluctuations and fluxes of high-energy protons and their relation to the IMF orientation is presented.     

Advances in modeling gradual solar energetic particle events

Solar energetic particles pose one of the most serious hazards to space probes, satellites and astronauts. The most intense and largest solar energetic particle events are closely associated with fast coronal mass ejections able to drive interplanetary shock waves as they propagate through interplanetary space. The simulation of these particle events requires knowledge of how particles and shocks propagate through the interplanetary medium, and how shocks accelerate and inject particles into interplanetary space. Several models have appeared in the literature that attempt to model these energetic particle events. Each model presents its own simplifying assumptions in order to tackle the series of complex phenomena occurring during the development of such events. The accuracy of these models depends upon the approximations used to describe the physical processes involved in the events. We review the current models used to describe gradual solar energetic particle events, their advances and shortcomings, and their possible applications to space weather forecasting.     

Solar Energetic Particle Charge States: An Overview

The ionic charge distributions of solar energetic particles (SEP) as observed in interplanetary space provide fundamental information about the origin of these particles, and the acceleration and propagation processes at the Sun and in interplanetary space. In this paper we review the measurements of ionic charge states of energetic particles in interplanetary space and discuss their implication for our understanding of SEP sources, and acceleration and propagation processes.     

Inner radiation belt source of helium and heavy hydrogen isotopes

Nuclear interactions between inner zone protons and atoms in the upper atmosphere provide the main source of energetic H and He isotopes nuclei in the radiation belt. This paper reports on the specified calculations of these isotope intensities using various inner zone proton intensity models (AP-8 and SAMPEX/PET PSB97), the atmosphere drift-averaged composition and density model MSIS-90, and cross-sections of the interaction processes from the GNASH nuclear model code. To calculate drift-averaged densities and energy losses of secondaries, the particles were tracked in the geomagnetic field (modelled through IGRF-95) by integrating numerically the equation of the motion. The calculations take into account the kinematics of nuclear interactions along the whole trajectory of trapped proton. The comparison with new data obtained from the experiments on board RESURS-04 and MITA satellites and with data from SAMPEX and CRRES satellites taken during different phases of solar activity shows that the upper atmosphere is a sufficient source for inner zone helium and heavy hydrogen isotopes. The calculation results are energy spectra and angular distributions of light nuclear isotopes in the inner radiation belt that may be used to develop helium inner radiation belt model and to evaluate their contribution to SEU (single event upset) rates.