空间尘埃等离子体Maser效应以及所导致的Langmuir辐射

本从弱湍动等离子体理论出发,由Ｖｌａｓｏｖ方程导出Ｍａｓｅｒ效应作用机制下共振波的演化规律,并且讨论了尘埃等离子体电子束入射情况下,共振Ｌａｎｇｍｕｉｒ波的增长率,研究结果表明,Ｍａｓｅｒ效应比其它不稳定性（如本中论及的束流不稳定性等）能更好的解释空间中反常Ｌａｎｇｍｕｉｒ辐射现象。     

太阳系尘埃等离子体研究

综述了太阳系尘埃等离子体中的充电机制和波动过程以及与之有关的若干空间物理现象,内容包括太阳系等离子体中尘埃表面的平衡电势,带电尘埃在空间环境中的受力与运动,行星环内沿的弥漫扩散,轮辐结构的成困,彗星环境中尘埃的静电爆裂,尘埃彗尾的形态演化,天王星窄环的稳定性等问题．     

空间尘埃动力学的研究动向

讨论了空间尘埃动力学的特性，特别是空间尘埃等离子体的充电，波动和不稳定性现象以及它们在太阳系中的一系列表现。     

彗星等离子体某些特征的讨论

本文讨论了彗星中尘埃粒子的充电机制 ,带电特性和平衡电势的变化规律 ,分析了彗星尘埃的破碎特性和临界半径 ,得出了很有意义的结果     

空间等离子体中相干射电辐射过程的粒子模拟研究

射电辐射机制,尤其是射电暴发现象的相干辐射机制,是天体物理中最复杂、争议最多的电磁辐射机制.由于受到多重物理因素相互牵连的复杂影响,相干射电辐射机制的理论研究存在很大的难度,长期以来在等离子体辐射和电子回旋脉泽辐射这两类相干辐射机制间争议一直不断.近年来,人们开始尝试将粒子数值模拟方法应用于相干射电辐射机制的研究,并已经取得了一些积极的进展.本文将着重介绍近年来的粒子模拟研究工作及其取得的主要进展,并对现存的一些问题和困难进行简要评述.     

动力学阿尔文波的非线性波-波相互作用及其在日地空间等离子体中的应用

动力学阿尔文波是垂直波长接近离子回旋半径或电子惯性长度时的色散阿尔文波,在等离子体粒子加热、加速或反常输运等现象中能起重要作用.因此,在各类天体和空间等离子体环境中动力学阿尔文波的特性也一直是引起人们广泛兴趣和倍受关注的研究课题.本论文系统、深入地研究了不同等离子体环境下动力学阿尔文波的非线性波一波耦合相互作用过程,特别是对不同环境下波一波耦合导致的动力学阿尔文波非线性生长率进行了细致的分析.     

Maser Mapping and Dust Properties of Red Supergiant Winds

Maser emission from the circumstellar envelopes of four late-type red supergiants has been mapped with milli-arcsecond resolution using MERLIN1. The wind is driven by radiation pressure on dust and the structure and kinematics of the masing regions reflect the dust properties. The unbeamed radius of water maser blobs, ∼ 10¹² m, has been measured for the first time. The velocity gradient is used to derive the dust absorption coefficient which increases with radius from ≤ 0.1 to ≤ 1.0 m² kg⁻¹. Comparison with laboratory studies suggests that small crystalline grains are formed near the star and are annealed into astronomical silicates at larger distances. This revised version was published online in September 2006 with corrections to the Cover Date.     

Radiation Pressure and the Poynting-Robertson Effect for Fluffy Dust Particles

A correct understanding of the dynamical effect of solar radiation exerted on fluffy dust particles can be achieved with assistance of a light scattering theory as well as the equation of motion. We reformulate the equation of motion so that the radiation pressure and the Poynting-Robertson effect on fluffy grains are given in both radial and nonradial directions from the center of the Sun. This allows numerical estimates of these radiation forces on fluffy dust aggregates in the framework of the discrete dipole approximation, in which the first term of the scattering coefficients in Mie theory determines the polarizability of homogeneous spheres forming the aggregates.The nonsphericity in shape turns out to play a key role in the dynamical evolution of dust particles, while its consequence depends on the rotation rate and axis of the grains. Unless a fluffy dust particle rapidly revolves on its randomly oriented axis, the nonradial radiation forces may prevent, apart from the orbital eccentricity and semimajor axis, the orbital inclination of the particle from being preserved in orbit around the Sun. However, a change in the inclination is most probably controlled by the Lorentz force as a consequence of the interaction between electric charges on the grains and the solar magnetic field. Although rapidly and randomly rotating grains spiral into the Sun under the Poynting-Robertson effect in spite of their shapes and structures, fluffy grains drift inward on time scales longer at submicrometer sizes and shorter at much larger sizes than spherical grains of the same sizes. Numerical calculations reveal that the dynamical lifetimes of fluffy particles are determined by the material composition of the grains rather than by their morphological structures and sizes. The Poynting-Robertson effect alone is nevertheless insufficient for giving a satisfactory estimate of lifetimes for fluffy dust grains since their large ratios of cross section to mass would reduce the lifetimes by enhancing the collisional probabilities. We also show that the radiation pressure on a dust particle varies with the orbital velocity of the particle but that this effect is negligibly small for dust grains in the Solar System.     

Harmonic Structures of Gyrosynchrotron Radiation and Cyclotron Maser Instability

1 INTRODUCTIONSolar microwave bursts are usually produced by dtherellt radiation mechanisxns: gyroresonance absorption, Coulomb brernsstrahlung of the thermal baCkground plasma, as well asgyrosynchrotron radiation of the nonihermal electrons (Hildebrandt et al. 1998). Meanwhile,cyclotron or synchrotron maser instabilities may be responsible for microwave spaaes, blips, andtype ill bursts (Wu 1985; Huang 1987; Huang et al. 1996; Huang 1998), which are usuajly superposed on the ambient mi…     

Atmospheric Disturbances and Radiation Impulses Caused by Large-Meteoroid Impacts on the Surface of Mars. I. Formation and Evolution of Dust Cloud

We consider the mechanisms of the formation of dust ejected from craters produced by large-meteoroid impacts on the Martian surface, as well as the mechanisms of the elevation of dust that already existed on the surface, due to impulsed aeolian processes. Detailed numerical calculations of the dust injection, the shock wave propagation, and the formation and evolution of the dust cloud are carried out for vertical impacts of meteoroids with sizes from 1 m to 100 m. The results of these calculations show that dust raised by a 1-m impactor is sufficient to produce a local dust storm, while the mass of dust formed in impacts of large bodies is comparable to the mass of a regional or even a global dust storm. The impact detection rates for 1-, 5-, 20-, and 100-m-sized meteoroids are estimated to be a few impact events per year, one event in every 5–6 years, one event in every 300–800 years, and one event in every 5000–20000 years, respectively. In the last case, the thickness of the global layer of precipitated dust and small fragments, which has been formed through impacts over a period of 10⁷–10⁸ years, is comparable to the thickness of the global dust layer on the Martian surface. In the first case, the mass of raised dust is greater than that for typical dust devils. The speed of impulsed wind at large distances from the impact site is shown to exceed the critical speed at which the blowing-off of dust from the surface begins. Some factors that may enhance the dust ejection have been previously ignored in numerical calculations. We discuss here the role of these factors. The second part of our study deals with the determination of the impact-induced radiation impulse and the estimation of its effect on the rise of dust.     

Amplification by Stimulated Emission in Rydberg Matter Clusters as the Source of Intense Maser Lines in Interstellar Space

The detailed processes giving maser line radiation from various molecules in space are not well understood, as can be seen from many recent detailed studies of maser line emission with high spatial and velocity resolution, and with polarization measurements. We now propose an improved maser mechanism based on amplification of the original molecular line emission by stimulated emission in Rydberg Matter (RM) clouds in HII regions, containing clusters H _N and (H₂) _N . This mechanism will amplify the molecular lines, depending on the position, velocity, cluster size and state of excitation of the clusters in the RM cloud. RM will only support certain frequencies, corresponding to rotational transitions of the clusters. The bond lengths in the RM clusters are known within 1% from radio frequency emission measurements in the laboratory, and it is now shown that all the commonly studied maser lines agree well with stimulated emission transitions in several types of RM clusters simultaneously. This may explain the strongly varying intensities of neighboring or related maser lines, an important effect that is not well understood previously. It is also pointed out that the magnetic field due to RM is of the same order of magnitude as observed from the Zeeman splitting in maser lines; thus, the molecules that are the original sources of the lines may be embedded in the RM clouds, for example in dense HII regions that are likely to be RM regions.     

Plasma Collective Effects in the Presence of Dust

Charged dust particles strongly affect collective processes in plasmas. Here we review recent advances in the theoretical study of collective effects in dusty plasmas. In particular, we consider processes of charging of dust by plasma currents, wave propagation and scattering, properties of Alfvén waves, and discuss collective effects in plasma-dust crystals.     

The Experiment and Analysis on VLBI Observations of Space Passive Hydrogen Maser

China plans to establish a lunar orbital VLBI (Very Long Baseline Interferometer) station around 2025, which will carry a space passive hydrogen maser as the time and frequency reference. Since it is the first time to use a space passive hydrogen maser for VLBI observation, its feasibility needs to be studied and verified. Therefore, we carried out VLBI observations using the space passive hydrogen maser as the frequency reference. In the experiment, the active hydrogen atomic clock and space passive hydrogen maser were used as the frequency standard, and the alternate VLBI observations of China’s Mars probe TW1 (Tianwen 1) were carried out using the 25 m radio telescope at Sheshan, Shanghai, and other VLBI stations. The results of data processing and analysis show that the standard deviation of VLBI residual group delay based on both active hydrogen atomic clock and space passive hydrogen maser are within 0.5 ns, which indicates that the space passive hydrogen maser can meet the accuracy requirements of VLBI measurement for deep space exploration, and verify its feasibility as the frequency standard of lunar orbital VLBI stations.     

星载氢钟VLBI观测实验及分析

中国计划于2025年左右建立月球轨道VLBI (Very Long Baseline Interferometer)测站,将会搭载被动型星载氢钟作为时间频率标准.由于是首次在VLBI观测中使用星载氢钟,需要研究和验证其可行性.因此,利用星载氢钟作为频率基准开展了VLBI观测.实验时,分别使用主动型地面氢钟和被动型星载氢钟作为频率基准,利用上海天文台佘山25 m射电望远镜和其他测站对我国火星探测器天问一号进行了交替VLBI观测.数据处理分析结果表明,基于地面氢钟与星载氢钟的VLBI残余群时延标准差均在0.5 ns以内,表明星载氢钟可满足深空探测VLBI测定轨的精度要求,验证了其作为月球VLBI测站频率基准的可行性.     

Perturbations in the Nodal Period of Artificial Satellites Caused by the Terrestrial Infrared Radiation Pressure

Considering the terrestrial infrared radiaton pressure as a disturbing factor, its influence on the nodal period of an artificial satellite moving in a quasi-circular orbit is estimated.