Spectroscopic characterization of cometary samples

After presenting a summary of what is presently known from cometary vibrational spectroscopy, we discuss briefly some possible results to be anticipated from future non-sample-retum cometary missions which, however, will leave a number of key questions unanswered. Major efforts have to be made in the laboratory to properly prepare the analysis of returned cometary samples. We report, in particular, on Raman spectroscopy of cometary analogs (frozen gases and irradiated organic materials) performed in our laboratory applying sufficiently low laser power so as not to significantly alter the sample. Also discussed are our attempts to use REELS (Reflection Electron Energy Loss Spectroscopy) which may yield information not only on the elemental composition of the sample but also on its optical constants, especially in the far UV region.     

Isotopic analysis of cometary organic matter

Carbon isotope ratios have been measured for CN in the coma of comet Halley and for several CHON particles emitted by Halley. Of these, only the CHON-particle data may be reasonably related to organic matter in the cometary nucleus, but the true range of ¹³C/¹²C values in those particles is quite uncertain. The D/H ratio in H₂O in the Halley coma resembles that in Titan/Uranus. The next decade should substantially improve our understanding of the distribution of C, H, N, and O isotopes in cometary organics. The isotopic composition of meteoritic organic matter is better understood and can serve as a useful analog for the cometary case.     

Structural optimization of lifting surfaces with regard to static aeroelasticity

A technique for choosing a rational load-carrying scheme and weight analysis at the early stages of designing lifting surfaces with the use of a special model of the finite element method is proposed. The distribution of structure loads is determined with regard for its deformation. The numerical example is presented.     

The evolution of massive stars

The evolution of stars with masses between 15 M ₀ and 100M ₀ is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution.The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities.Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15M ₀ and a 25M ₀ star from zero-age main sequence (ZAMS) through iron collapse is discussed.The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on evolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface.The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed.The problem of the Wolf-Rayet stars, their origin and the possibilities of their production either as single stars or as massive binaries is examined.Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss.     

Formation and evolution of low-mass Algols

We discuss the origin, evolution and fate of low-mass Algols (LMA) that have components with initial masses less than 2.5 M₀. The semi-major axes of orbits of pre-LMA do not exceed 20–25 R₀. The rate of formation of Algol-type stars is 0.01/year. Magnetic stellar winds may be the factor that determines the evolution of LMA. Most LMA end their lives as double helium degenerate dwarfs with M₁/M₂ 0.88 (like L870-2). Some of them even merge through angular momentum loss caused by gravitational waves.     

Smart flight control surfaces with microelectromechanical systems

Pitch, roll, and yaw moments can be developed by deflecting and changing the geometry of control surfaces. In this paper, smart flight control surfaces are designed using multi-node microelectromechanical systems (MEMS) to displace control surfaces and change the surface geometry. These MEMS augment translational motion microstructures (actuators-sensors), controlling/signal processing integrated circuits (ICs), radiating energy devices and antennas. The desired pitch, roll, and yaw moments are produced, drag can be reduced, and unsteady aerodynamic flows are controlled by smart flight control surfaces. That is, we achieve aerodynamic moment and active flow control capabilities. The major objective here is to report fundamental and applied research in design of smart flight control surfaces with MEMS-based actuator-sensor-IC arrays controlled by hierarchical distributed systems. We demonstrate the feasibility and effectiveness of the application of smart flight control surfaces for coordinated longitudinal and lateral vehicle control     

Common envelope evolution of binary stars

We discuss the common envelope phase in the evolution of binary systems. The problem of the efficiency of energy deposition into envelope ejection is treated in some detail. We describe the implications of common envelope evolution for the shaping of planetary nebulae with close binary nuclei and for double white dwarf systems, considered to be the progenitors of Type I supernovae.     

Common envelope evolution of binary stars

We discuss the common envelope phase in the evolution of binary systems. The problem of the efficiency of energy deposition into envelope ejection is treated in some detail. We describe the implications of common envelope evolution for the shaping of planetary nebulae with close binary nuclei and for double white dwarf systems, considered to be the progenitors of Type I supernovae.     

飞机结构健康监控技术

对于飞机制造商来说,希望有朝一日“视情维修”这个新概念能成为现实。结构完好性监控是向这一目标迈进的重要一步。它使结构部件“感觉”到将要损坏的迹象,从而减少因维修而停飞的时间。它对未来飞机的设计也将产生重大影响。     

Algorithm for calculating geometry of lifting maximum rigidity surfaces

An algorithm for calculating optimal geometry of lifting maximum rigidity surfaces is described.     

复合材料结构件制造技术

作为大飞机关键制造技术之一,复合材料结构件制造技术已经广泛应用于飞机机翼、机身、垂尾、整流罩、中央翼盒等各个关键部位。随着国产大飞机项目的不断进展,复     

飞行器翼面结构型式的确定

飞行器翼面结构型式的选择是结构方案设计阶段的重要内容之一。通过相关参数的统计分析和布局优化设计可以确定翼面结构型式。随着计算技术和拓扑优化技术的发展,结构设计的智能化和自动化水平将不断提高,结构型式的确定将更多地依赖布局优化的结果。     

X-ray binaries and stellar evolution

Observational evidence suggests that most — if not all — binary X-ray sources are neutron stars. The evolutionary status and possible formation mechanisms of the type I (massive) and type II (low-mass) X-ray binaries are discussed. The difference between the standard massive X-ray binaries and the Be/X-ray binaries is ascribed to a somewhat different evolutionary history and status, and possible reasons for the existence of short- and long — period X-ray pulsars are discussed. Type II X-ray sources in globular clusters were most probably formed by capture processes; their formation rate inferred from the observations indicates that only a small fraction ( 1 to 10 percent) of the originally formed neutron stars have remained in their clusters. Type II sources in the galactic bulge may also have formed from cataclysmic binaries in which a white dwarf was driven over the Chandrasekhar limit by accretion.     

几种无损探测新方法

比较真空监测法、激光振动分析法等用于探测结构缺陷的新的无损探测方法,将增强飞机的安全性和经济性。为了提高飞机的安全性,减少飞机检查的时间和成本,一些研究部门正在研制一些新的结构裂缝和结构缺陷的无损监测系统。其中两种技术显示了很好的发展前景,一种是利用可以直接贴在被测表面的传感器进行测量的"比较真空监测"(CVM)法;另一种是激光振动分析法,它又分为多束激光同时测量法和单激光扫描法两种。     

结构健康监控技术的发展现状

正使用传感器监测飞机结构的健康状况从原理上分析是一种非常有效的途径,而且如桑迪亚国家实验室和SMS公司等机构已经对一些真空比较监测传感器开展了广泛的飞行试验,因此,业内人士认为这种监测技术极具应用潜力,如可将非计划维修转化为计划性维修,或者代替耗时耗力的无损检测等。但无论开展哪种应用,均需获得局方的批准,而目前的形势是局方仍较为谨慎。     

复合材料结构修理研究现状

简要介绍了先进复合材料结构修理的研究内容,较详细地评述了修理材料及其固化工艺,并对电子束固化技术用于复合材料结构修理的优势和可能出现的问题及解决途径进行了讨论。     

结构振动疲劳的工程分析方法

介绍了结构振动疲劳的概念；引入了结构在周期振动载荷和随机振动载荷作用下的振动疲劳曲线；提出了振动疲劳的线性和式累积损伤关系式以及振动疲劳的破坏判据；从工程角度给出飞机结构在随机振动载荷作用下的寿命分析方法，即利用正弦共振S-N曲线进行随机分析的方法以及借用声疲劳分析技术计算随机振动疲劳的方法等。     

Chemical and photometric evolution of elliptical galaxies

In this paper we present the new chemical-spectro-photometric models of population synthesis by Bressan, Chiosi & Fagotto (1993). The models are specifically designed for elliptical galaxies. They include the presence of dark matter and galactic winds triggered by the energy deposit from supernovae and winds of massive stars. The models are aimed at studying the UV-excess and its dependence on the metallicity, the color-magnitude relation, and the color evolution as a function of the redshift. It is shown that in order to explain the color-magnitude relation as a result of galactic winds, the energy input from massive stars is required. Supernovae alone cannot provide sufficient energy to start galactic wind before the metallicity and hence colors have got saturated. We show that the main source of the UV-excess are the old, hot HB and AGB manque stars of high metallicity present in varying percentages in the stellar content of a galaxy. Since in our model the mean and maximum metallicity are ultimately driven by the mass of the galaxy, this provides a natural explanation for the observed correlation between UV-excess and metallicity. Finally, looking at the color evolution as function of the redshift, we suggest that a sudden change occurring in the color (1550-V) at the onset of the old, hot HB and AGB manque stars of high metallicity, is a good age indicator. The detection of this feature at a certain redshift would impose firm constraints on the underlying cosmological model of the universe.