椭圆外切2n+1边形中切顶线三角形有向面积的定值定理及其应用

本文给出椭圆外切2n 1边形中一类切顶线三角形有向面积的一个定值定理及其若干推论，其中包括射影几何中著名的Brisanchon定理在椭圆外切三角形中的情形。     

The BOOMERANG experiment

The BOOMERANG (Balloon Observations Of Millimetric Extragalactic RAdiation aNd Geophysics) experiment is an international effort to measure the Cosmic Microwave Background (CMB) anisotropy on angular scales of 20 to 4°, with unprecedented sensitivity, sky and spectral coverage. The telescope will be flown from Antarctica by NASA-NSBF with a long duration stratospheric balloon (7–14 days), and is presently scheduled for flight in 1995–1996. The experiment is designed to produce an image of the Cosmic Microwave Background with high sensitivity and large sky coverage. These data will tightly constrain the baryon density, the reionization history, and the formation of large-scale structure in the universe. BOOMERANG will test technologies and return science data that are essential to the design of a future space-borne mission to map CMB anisotropy.     

Author Index

Authors Index

Author Index     

The optical constants of gypsum particles as analog of Martian sulfates

Various indications seem to suggest that in the past the Martian climate allowed the presence of liquid water on the surface of the planet. It is therefore reasonable to think that bodies of standing water were once present in basins such as craters or depressions and that evaporite deposits of sulfates could have formed in these basins. The identification of such deposits, which might have survived in some regions of the planet, could confirm the present hypothesis about the ancient climate on Mars. Recent analyses of Mars spectra, obtained by ground-based observations, show bands consistent with sulfate features. If such data have to be interpreted with the aid of synthetic spectra, the knowledge of the complex refractive index of some sulfate is necessary. In this work we present the optical constants of submicron particles of gypsum (a typical hydrate–sulfate very common on Earth), derived by means of the dispersion theory from transmission spectra. We have performed the calculation of the optical constants in the wavelength range 2–70 μm, also in view of the wide spectral range covered by the Planetary Fourier Spectrometer (PFS) on board of the ESA space mission Mars Express. The data have been compared with optical constants obtained by other authors from reflectance measurements of particulate samples.     

Role of shielding in modulating the effects of solar particle events: Monte Carlo calculation of absorbed dose and DNA complex lesions in different organs.

Distributions of absorbed dose and DNA clustered damage yields in various organs and tissues following the October 1989 solar particle event (SPE) were calculated by coupling the FLUKA Monte Carlo transport code with two anthropomorphic phantoms (a mathematical model and a voxel model), with the main aim of quantifying the role of the shielding features in modulating organ doses. The phantoms, which were assumed to be in deep space, were inserted into a shielding box of variable thickness and material and were irradiated with the proton spectra of the October 1989 event. Average numbers of DNA lesions per cell in different organs were calculated by adopting a technique already tested in previous works, consisting of integrating into "condensed-history" Monte Carlo transport codes--such as FLUKA--yields of radiobiological damage, either calculated with "event-by-event" track structure simulations, or taken from experimental works available in the literature. More specifically, the yields of "Complex Lesions" (or "CL", defined and calculated as a clustered DNA damage in a previous work) per unit dose and DNA mass (CL Gy-1 Da-1) due to the various beam components, including those derived from nuclear interactions with the shielding and the human body, were integrated in FLUKA. This provided spatial distributions of CL/cell yields in different organs, as well as distributions of absorbed doses. The contributions of primary protons and secondary hadrons were calculated separately, and the simulations were repeated for values of Al shielding thickness ranging between 1 and 20 g/cm2. Slight differences were found between the two phantom types. Skin and eye lenses were found to receive larger doses with respect to internal organs; however, shielding was more effective for skin and lenses. Secondary particles arising from nuclear interactions were found to have a minor role, although their relative contribution was found to be larger for the Complex Lesions than for the absorbed dose, due to their higher LET and thus higher biological effectiveness.     

结构非线性对颤振特性的影响

基于描述函数法，对操纵系统的结构非线性问题，提出了用于描述函数法的耦合模态和非耦合的综合计算模型，使用跨音速非定常空气动力，对扑动间隙和旋转间隙进行研究，揭示了全动水平尾翼振动的根源主要是操纵间隙造成的，为其它同类问题提供了可行的工程分析方法。     

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.     

遥感卫星自截断SPIHT压缩译码技术

链表式SPIHT算法是目前公认最好的压缩方案,但是由于其传输中具有极差的抗误码特性,在遥感图像数据压缩中的应用具有一定局限性。本文提出的自截断式SPIHT压缩算法使得译码器在出现“致使性”误码的情况下能够自动中止该帧数据流译码,使得误码不至于扩散到整幅图像之中。为SPIHT算法在遥感图像数据压缩中的应用提供了理论依据。     

国外卫星的两种检漏方法分析

：介绍了国外卫星“真空检漏法”和“累积检漏法”的检漏原理和主要操作步骤。对这两种方法的检漏特点进行了分析与评估，认为国产卫星选择真空检漏法较妥。