二次点火发动机最优增程设计与分析

研究了采用二次点火发动机对火箭弹进行增程的最优设计方法与设计原理，用罚函数法把约束条件构成统一的目标函数，再用直接寻优法进行计算，分析了火箭弹倾角、再点火时间及总冲分配等因素对射程的影响。结果表明，二次点火发动机技术可以实现远程火箭弹增程最大的设计要求，且最优发射角对射程影响极大；总冲分配最佳时，总的阻力消耗最小，增程率越大；再点火时间的影响相对较弱。同时还比较了二次点火发动机工作时的火箭弹弹道与一般弹道的区别，及其对阻力和射程的影响。     

The Cassini Visual And Infrared Mapping Spectrometer (Vims) Investigation

The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth–Moon system.This revised version was published online in July 2005 with a corrected cover date.     

失速起始检测的低频平均频谱幅值法

高速多级轴流式压气机在中低转速的失速起始总是以短周期扰动的形式出现。为了在压气机整机进入深度失速前检测到失速起始信号，通过分析提出了一种基于低频平均频谱幅值的失速起始信号检测方法。对某轴流式压气机压力测量信号的分析结果表明，该方法是准确、可靠和快速的，有望用于失速起始的实时检测。     

昆虫翅悬停飞行中的三维空间旋涡结构

昆虫(果蝇)悬停飞行中,翅膀按照特定的拍动方式往复运动,产生非定常高升力维持身体的平衡.研究昆虫高升力机理,需要探索拍动翼运动引发的三维空间非定常流场的特性,尤其是三维空间非定常涡的发展变化过程.本文将氢气泡流动显示技术应用于动态模型实验,定性的观察拍动翼前缘涡(LEV)的发展破裂过程.并利用数字体视粒子图像测速,DSPIV(Digital Steroscopic Particle Image Velocimetry)技术,测得了拍动翼运动瞬时相位和相位平均的三维空间流场信息(速度向量场、截面涡量场、空间涡量场,以及三维空间流线),揭示了拍动翼展向流动的存在,并结合定性和定量方法多角度说明了前缘涡沿展向发展到破裂的流动结构,并说明了侧缘涡与前缘涡的相互影响.测量结果表明:在雷诺数960的情况下,拍动翼运动至相位时,翼面上前缘涡在距翼根约60%展长的位置发生破裂;翼根至破裂点之间,展向流动稳定,指向翼梢;破裂点以后,展向流改变方向,指向翼根.     

防冰疏水微结构表面的设计

微结构表面具有出色的防水自净性能以及减阻性能,但目前超疏水微结构表面设计制备思路欠缺系统性,很多制备方法也比较复杂,在工程实践方面缺乏指导性。从工程制备的角度,概述了微结构表面设计的经典理论模型和国内外对微结构几何设计的理论研究,探究常用工程材料的理论本征接触角,通过力学平衡分析方法计算仿真确定疏水微观结构几何尺寸、几何截面外形,提出截面线长度及尺寸系数两个疏水微结构设计的参数,归纳了设计疏水微结构的流程,为制备疏水微结构或微结构模具提供理论基础。     

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.     

GNSS超快速产品在全球标准时间复现中的应用

为满足大跨度空间范围内的时间同步需求,对基于共视时间比对原理的标准时间复现系统进行改进,采用全视时间比对方法解决原系统应用基线受限的问题.考虑实时性的要求,使用全球卫星导航系统(GNSS)超快速产品(预测部分)提供卫星位置和卫星钟差,以尽可能消除广播星历和钟差对复现结果的影响.分析了常用的几家机构发布的GNSS超快速产...     

Cyclic variations in the solar lower atmosphere

The Ca K line has been measured regularly nearly every month since 1974 at Kitt Peak. It is well known that the K₁ component of the Ca K line is formed in the temperature minimum region (TMR) of the solar atmosphere. Our study of the data of CaII K profiles over two solar cycles indicates that both in full disc integrated spectra and in center disc spectra, the distance between the red K₁ and the blue K₁ of the profiles and its average intensity show periodic variations. But the variation for the full disc integrated spectra fluctuates in the same way as the sunspot number does, while that for the center disc spectra has a time delay with respect to sunspot number. Non-LTE computations yield a cyclic temperature variation of about 17 K of the TMR in the quiet-Sun atmosphere and a cyclic variation of about 15–20 km in the height position of the TMR.     

带QoP反馈的实时视频服务质量控制框架

分析了实时视频在现有"尽力而为"IP网络上传输所面临的带宽、延迟和丢失等问题,介绍了需要采用的拥塞控制和差错控制等应用级服务质量控制策略,并提出了一种联合的支持应用级服务质量控制的实时视频传输框架.该框架既考虑了网络资源的动态变化和影响,又兼顾了视频的服务质量调整对视频的表现质量的限制因素,充分利用了服务质量和表现质量之间的映射关系,具有更广泛的实用价值.      

An empirical model of the plasma environment around Mercury

Since the flyby observations by Mariner 10 in 1974 and 1975, Mercury has been one of the most interesting objects for space physics and planetary exploration. The MESSENGER and BepiColombo missions now plan to revisit this planet. In order to design plasma instruments for the BepiColombo mission, we have estimated electron and ion fluxes around Mercury with an empirical model, which has been developed for the Earth’s magnetotail. The solar wind data needed as input parameters are derived from Helios observations. The result shows that our predicted electron fluxes at aphelion agree well with the Mariner-10 data. It is also noted that ion instruments must cover a very wide dynamic range of proton fluxes. However, the applicability of the Earth’s magnetospheric model to Mercury is, in itself, an important issue for comparative magnetospheric studies.