星历误差对双星定位系统定位精度的影响

双星定位系统是我国自行研制开发的一种区域性卫星定位系统,其定位体制与 GPS 不同,并且其定位精度受到诸多因素的影响,其中星历误差的影响是不可忽略的因素。文中重点研究了星历误差对其定位精度的影响,并推导出了其数学误差模型,在一定条件下给出了其仿真结果,为分析其他误差因素对其定位精度的影响奠定了基础。     

风力机柔性叶片振动变形对其气动阻尼的影响分析

为了研究大型水平轴风力机柔性叶片的振动变形对其气动阻尼的影响,用叶素动量理论计算了风力机叶片气动力,用有限元法计算了结构动力响应,基于能量损失法建立了风力机的气动阻尼分析模型.重点分析了叶片振动扭角、挥舞倾角、摆振倾角对攻角的影响,考虑了挥舞速度,摆振速度对入流速度、入流角的影响.以某5MW海上风力机为例,分析计算了风力机整个叶片的气动阻尼.结果表明挥舞倾角、扭角对挥舞方向气动阻尼影响较大,会使其减小;摆振倾角对摆振方向气动阻尼的影响较大,会使其增大;振动变形对气动阻尼沿叶片的分布没有影响.     

金属橡胶材料静态特性的研究

金属橡胶材料是一种新型阻尼材料,且影响其特性的参数有很多。本文从其本构关系出发,通过改变不同的影响参数,针对不同形状、不同几何尺寸的构件,进行了理论分析和试验研究,总结出了影响其特性的参数及其变化规律,为进一步地设计和更好地应用金属橡胶构件提供有意义的依据。      

轻小型超声速射流控制元件性能影响因素研究

为优化轻小型超声速射流控制元件切换性能,对影响其切换性能的主要流道参数进行了研究。通过数值计算方法,得出了不同流道参数对射流控制元件主流切换性能的影响规律。计算结果显示,控制口径、扩张径、劈距对其切换性能的影响较大,且存在明显的变化规律和极限值,突破极限值将导致射流控制元件无法实现切换;而扩张半角对其切换性能影响不明显。结合数值计算结果,加工制造射流控制元件,其外形直径在0.1m以内,重量2.5kg以内。热气试验结果显示,此轻小型超声速射流控制元件能够实现快速稳定的切换,平均切换时间仅为6.6ms。     

突片射流冲击冷却换热特性的实验

对涡激励突片的单排圆形射流冲击冷却特性进行了实验研究.主要对突片堵塞比、突片形状和突片安装角度对冲击换热特性的影响进行了实验研究, 并揭示了其影响规律.研究结果表明:在研究的参数范围内, 突片的几何形状及安装角对射流冲击换热有较显著的影响, 并根据其影响规律, 对突片的结构设计提出了有价值的参考意见.      

SiC颗粒增强Al-Li基复合材料力学性能试验研究

对SiC颗粒增强Al -Li基复合材料开展了包套挤压技术研究 ,研究了SiC颗粒含量、挤压比和热处理工艺参数对复合材料力学性能的影响规律 ,探讨了其影响机制     

连续玻璃纤维增强尼龙的介质腐蚀效应

通过重量变化、力学性能测试以及 SEM断口分析对实验室制备的连续玻璃纤维增强尼龙 (GF/PA-66)在酸、碱、汽油、机油、丙酮等介质中的行为进行了探讨 ,发现 GF/PA-66具有良好的耐油性 ,而酸、碱对其性能影响较大 ,极性介质丙酮对其性能也有一定影响     

光纤光栅传感器动态解调方式的误差分析

主要介绍了扫描PZT器件法等四种典型动态解调方法的适用性,分析了其误差主要来源,并推导了其计算公式;分析了光强波动对几种解调方法解调精度的影响,评价了其影响程度,并得出了根据被测对象频率来选择解调方式的结论.     

高超声速楔形模型飞行流场数值模拟

针对典型的高超声速飞行器结构模型,利用COMSOL Multiphysics多物理场耦合软件对其流场进行建模仿真.研究了楔形头部对高超声速气流的影响,分析了气流流过楔形模型时的流线、压力、温度分布.对不同楔角的模型进行了模拟,观察其对气流速度分布的影响.依据数值模拟的结果对高超声速气流流场的流动特性进行了细节分析.     

飞机起落架收放系统传动性能影响因素分析

飞机起落架液压收放系统的传动性能与系统或元件的结构参数、工作条件参数以及负载参数等有关.文中在对收放系统传动时间、传动速度等传动性能计算的基础上分析影响其性能的主要因素,比较其影响程度,并进一步探讨了判断故障原因的方法.     

差值法与比值法的误差修正效果比较研究及应用

差值法与比值法对不同测量系统的误差修正效果不一样。本文将两种方法的比较用一个比值来描述,并用推得的公式进行量化表示。在进一步的应用研究中,理论分析与实验数据相互印证,同时得到许多有益的结论,有助于全面掌握测量系统的误差来源,从而灵活选择各种修正方法以获得更加准确的测量结果。     

论政府经济职能与非经济职能的关系

政府职能是由政府经济职能与政府非经济职能(包括政治职能和社会职能)构成的职能体系.政府经济职能与非经济职能是政府应该履行的不同职能,两者之间存在着相同之处,也存在着不同之处;两者相互依存,相互制约.政府经济职能目标与非经济职能目标既存在协调的一面,也存在相冲突的一面.在政府要实现的职能目标中,政府优先选择的顺序是不同的,政府经济职能与非经济职能之间相互依存、相互制约的关系决定了政府职能机构体系的复杂性,也决定了政府要有效地履行其职能,就必须使政府各职能部门相互配合和协调.     

Discharges in the Stratosphere and Mesosphere

In the present paper salient features of discharges in the stratosphere and mesosphere (namely sprites, halos, blue starters, blue jets, gigantic jets and elves), are discussed. The electrostatic field due to charge imbalance during lightning processes may lead to stratospheric/mesospheric discharges either through the conventional breakdown based on streamers and leaders or relativistic runaway mechanism. Most (not all) of the observed features of sprites, halos and jets are explained by this processes. Development and evolution of streamers are based on the local transient electrostatic field and available ambient electron density which dictate better probability in favor of positive cloud-to-ground discharges, and thus explains the polarity asymmetry in triggering sprites and streamers. Elves are generated by electromagnetic pulse radiated by return stroke currents of cloud-to-ground/inter-cloud discharges. Generation of the both donut and pancake shape elves are explained. Electrodynamic features of thunderstorms associated with stratospheric/mesospheric discharges are summarized including current and charge moment associated with relevant cloud-to-ground discharges. The hypothesis relating tropospheric generated gravity waves and mesospheric discharges are also discussed. Finally some interesting problems are listed.     

The massive star distribution in the Galaxy and the Magellanic Clouds

The numbers and distribution of Population I O-type stars and Wolf-Rayet stars are reviewed. The numbers of known WR stars in the Galaxy, the LMC and the SMC are 185, 114, and 9, respectively. Distances and galactic distributions determined by various authors are compared. The single star and binary distributions are discussed in the light of evolutionary studies.     

Blue and red supergiants and the age structure of the NGC 330 region

We analysed new UBVRI CCD photometry of the massive, blue SMC cluster NGC 330 and its surrounding field. The age structure and a new reddening value for the stellar population in this region of the SMC are derived and the implications for star formation in this part of the SMC and for stellar evolution are discussed.Based on observations obtained at ESO, La Silla     

Aging avionics: the problems and the challenges

Aging avionics have become a problem because aircraft are being kept in service far longer than the original plan. This paper discusses the four key problems of aging avionics: (1) determining the systems that are the high cost drivers in order to select those that should receive priority; (2) determining the requirements for the replacement; (3) identifying alternative technologies that will satisfy the requirements and are affordable; and (4) determining the funding required and acquiring the funding needed to replace the aging avionics. Challenges encountered in solving these problems include management and technical. The problem of aging avionics is not limited to a single aircraft, but occurs across all aircraft. Cost-effective modernization requires cutting horizontally across all aging aircraft, and coordination with the end users and the existing management structure. A key technical challenge is to select an architecture that is upgradeable since the funding limitations may ensure parts will become obsolete prior to the completion of a drawn-out production.     

Coupling between the outer magnetosphere and the high-latitude ionosphere

The coupling between the ionosphere and the outer magnetosphere depends on the topology of the geomagnetic field. Some aspects of the closed and open magnetospheric models are briefly discussed.The assumption that the geomagnetic field lines are equipotentials is critisized both on observational and on theoretical grounds. Measurements of H Doppler profiles, of precipitating particles above the ionosphere, and of charged particle densities in the magnetosphere indicate the existence of electric fields, E_\\, parallel with the magnetic field.Two different models of E_\\ are considered. Both models violate the condition of frozen-in magnetic fields. In one of them there are occasional transient electric field impulses along the field lines which cause precipitation splashes. The other model invokes electrostatic fields which vanish occasionally due to instabilities. This gives rise to precipitation splashes of about equal numbers of ions and electrons.The latter model seems to be favoured by known satellite data concerning the pitch angle distributions of electrons above the ionosphere.It is suggested that electric fields in space should be measured by satellites and rockets. Expected values of the fields in different regions of space are given.     

On the Derivation and Numerical Evaluation of the Weibull-Rician Distribution

The Weibull-Rician distribution and density functions are derived by a method based on conditional probability. The derivation is much simpler than the usual Rician approach, giving both the distribution and density as single integrals that are easy to evaluate numerically.     

鸭式旋翼/机翼飞机的技术发展及其关键技术

介绍了鸭式旋翼/机翼飞机的发展背景与发展过程,分析了其技术特点及优势,提出了发展鸭式旋翼/机翼飞机的两个重要关键技术,并给出了一些解决方法和途径,最后对鸭式旋翼/机翼飞机的应用前景进行了展望。所述内容对今后开展CRW无人机研究具有一定的参考价值和意义。     

Geomagnetic micropulsations and diagnostics of the magnetosphere

Plasma oscillations in a wide range of spectrum exist in the magnetosphere. Part of them penetrate the ionosphere and are recorded on the earth's surface. In the range of frequencies from millihertz to several hertz, the so-called micropulsations (ULF) are observed. In the range from hundred of hertz to several kilohertz the low-frequency emissions (VLF) are registered. Both types of emissions contain interesting and important information on the physical parameters of the magnetosphere and on the processes developing in it. The following paper describes the main problems of the diagnostics of the magnetosphere, which are based on the surface observations of micropulsations.In the first part of the paper, a short summary of theoretical conceptions on micropulsations is given. The main part of the paper describes the methods of diagnostics of the location of the boundary of the magnetosphere, of cold-plasma concentration in the outer regions of the magnetosphere, as well as of the energies and fluxes of fast charged particles in the geomagnetic trap. Some experimental results of the diagnostics of the parameters of the magnetosphere are given. Advantages and deficiencies of the existing methods of surface diagnostics are discussed, and the directions of further investigations are traced.