The variability of eta Car: A tool for the LBV phenomenon

We discuss the historical light curve of the most peculiar superluminous star Car, and the spectroscopic variations during the last 100 y. After the nova-like spectral evolution following the 1889 light maximum, the star underwent many shell episodes which were characterized by a large fading of the higher ionization emission lines. We describe the most recent 1992 event when the Hei and [Nii] emission lines nearly faded out, and a broad P Cygni absorption appeared in the Hi and Hei lines. A recurrence time of about 5 years is suggested from the times of the spectroscopic episodes and the IR light curve. The results are discussed in the light of possible models.     

The nature of the luminous blue variable AG carinae

After many years of permanence at minimum, the luminous blue variable AG Car started in mid 1990 a new brightening phase. We review the spectroscopic variations of the star since 1949, and discuss the nature of the circumstellar nebula. We give evidence that, like in Car, also in AG Car dust is continuously condensing from the stellar wind. We suggest that the star could be partially reddened by the circumstellar dust, which could affect the estimates of the stellar distance. An extended HII halo is present outside the ring nebula, which should be associated with the wind of a previous cooler evolutionary stage of AG Car.     

Chemistry of the solar nebula

The composition, mineralogy and texture of chondritic meteorites suggest they are relatively unaltered relicts of the condensation and accretion processes which took place in the primitive solar nebula. Chondrites thus are thought to contain a unique record of the physico-chemical conditions which prevailed at the time and place (asteroid belt) of their origin. Elemental abundance patterns are an important clue to the events and processes. Most elements can be placed in one of four groups according to their observed fractionation behavior in chondritic material: refractory, siderophile, normally depleted and strongly depleted. This grouping can be explained in terms of four events which presumably took place during cooling, condensation and accretion in the nebula. In order of inferred occurrence these are: (1) partial loss of the initial condensates rich in refractory elements at T > 1300K, (2) partial loss of metallic Fe-Ni grains, perhaps because they were magnetic, at 1000 to 700K, (3) partial remelting and outgassing of the condensate (chondrule formation) at 600 to 350K, and (4) accretion, when the P-T conditions controlled the volatile content (500 to 350K). Total gas pressure at the time and place of accretion is estimated to fall between 10^-–6 and 10^–-4 atm.Contribution No. 80, Center for Meteorite Studies.     

Measurements of solar total irradiance and its variability

The development of electrically self calibrated cavity pyrheliometric instrumentation that occurred in the early 20th century provided the technological base for experiments to detect variability of the solar total irradiance. Experiments from ground based observatories, aircraft and balloons during the 1st half of the 20th century were unable to achieve sufficient accuracy or long term precision to unambiguously detect irradiance variations of solar origin. Refinements in pyrheliometric technology during the 1960's and 1970's and the accessibility of extended experimental opportunities above the Earth's atmosphere in recent years have provided the first direct observations of solar total irradiance variability and provided the cornerstone observations of a long term database on solar irradiance. A program of solar irradiance monitoring has evolved to sustain the database over at least 22 years, corresponding to a single cycle of solar magnetic activity, and the shortest well identified cycle of climate variation. Direct links between total irradiance variations, solar magnetic activity and the solar global 5 min oscillation phenomena have been derived from recent space flight observations by the SMM/ACRIM I experiment.     

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.     

轴流压气机低转速特性表达方式的改进及应用

针对常规压气机特性图在低转速区域适用性较差的问题,首先给出一种改进的轴流压气机特性表达方法,在特性模型中用基于出口气流参数的换算转速代替基于进口气流参数的换算转速。然后将这种改进应用于压气机低转速特性的外推估算分析,结合压气机零转速特性线的特点,提出了基于改进特性图的外推方法,并给出了外推结果的合理性判断准则。实例表明,改进后的特性图非常适合表达发动机起动和风车状态的压气机特性,在该图上进行低转速特性的外推计算行之有效且结果准确性高,很好地解决了压气机低转速特性难以获取的难题。     

The interpretation of the XUV solar spectrum

This paper reviews (a) the earth's ionosphere, and (b) the solar atmosphere, in relation to the recent observations of solar XUV. The expected ionospheric characteristics are derived as directly as possible from the XUV observations and then compared with the well-known D-, E-, and F-layer formations. The comparison leads to (1) a high ionospheric recombination coefficient decreasing rapidly with height, (2) contributions to the E-layer from both UV and X-rays, and (3) very little difference in the solar cycle variations from the D-, E-, and F-layers although intensity variations are greater from high than low ions. The flux measurements of the identified XUV solar emission lines give information on the numbers of ions in the solar atmosphere. This makes it possible to derive (1) the amount of solar material in each temperature range, (2) the chemical abundances, and (3) the physical differences between quiet solar atmosphere, centres of activity, and flares. When the new dielectronic recombination coefficients are well investigated it should be possible to redetermine the distribution of solar material with temperature. The fitting of such results to chromospheric and coronal models provides many problems.     

The evolutionary status of eta Car based on historical and modern optical and infrared photometry

We present a photometric study of the luminous early-type star Car. The star's secular brightness increase is due largely to the expansion of the Homunculus. Car is a LBV with a possible B0.5V companion. The combined effect of Balmer-line emission, and of warm and cold dust radiation explains the star's other light variations.     

直升机机身外形对气动特性的影响

基于FLUENT流体力学软件,进行了直升机机身流场的数值模拟和分析。描述了网格生成方法,给出了计算迭代步骤和流程图。针对ROBIN机身绕流场进行了计算,并与可得到的实验结果进行了对比,验证了计算结果的可靠性。在此基础上,以NUAA模型机身为算例,改变机身尾部、截面和头部形状对其流场进行了对比计算,给出了表面压强系数分布、机身阻力等计算结果,讨论了直升机机身外形参数对气动特性的影响,得出了一些有意义的结论。     

X-ray and optical variability at the hour timescale for 1E 0630+178 (GEMINGA) and its proposed optical couterpart

Einstein and EXOSAT data on the soft X-ray source IE 0630+178, the proposed counterpart of the -ray source GEMINGA, are analyzed for variability on the time scale of one to three hours. The EXOSAT September 1983 data, with an uninterrupted strech of over 10 hours offer the most interesting case. In parallel, a similar analysis is presented for the first time, for the optical data of the m_V21 proposed counterpart. About 30 CCD exposures, of 15 min. each, taken over two consecutive nights at the 3.6 m CFH telescope, yield evidence of variability, when compared to the data of similar nearby objects in the field.Visiting astronomer at the Canada-France-Hawaii Telescope, operated by the National Concil of Research, Canada, the Centre National de la Recherche Scientifique, France, and the University of Hawaii.     

Concerning the interpretation of the ultraviolet radiation from B stars

Measurements of the shape of the ultraviolet spectrum from B stars are compared with the theoretical spectra predicted from a homogeneous series of eight model atmospheres which are known to be close to a state of radiative equilibrium and to give a good representation of the ordinarily observed spectral region. The broad-band photometer measurements of Byram, Chubb, and Friedman in the region 1314 indicate that the stars become brighter in the ultraviolet as their temperature increases. The theoretical spectra reproduce this trend. However, the theoretical spectra are about three times as bright at 1314 relative to their brightness at 5560 as is observed.The spectral observations at 50Å resolution of Stecher and Milligan of six absorption-line stars are compared in detail with theoretical spectra. The observed shape of the spectrum is reproduced well by the models from 2600 to longer wavelengths. At wavelengths shorter than 2600 Å, the observed fluxes from B stars are less than the predicted fluxes. At 2000 the deficiency is between a factor two and a factor four. The spectrum of Canis Majoris is observed to have a different shape from that found for four other early-type stars. In the case of Canis Majoris the deficiency at 2000 is about a factor 13.The proper manner in which to compare theory and observation is discussed and some astrophysical terminology is explained. Theoretical fluxes, , are given in Table 1 for eight early B type model atmospheres at wavelengths between the Lyman limit and 6251. These fluxes have been computed without consideration of the opacity due to line blanketing. It is shown that line blanketing can probably account for the differences noted between predicted and observed ultra-violet spectra of B stars. It is not necessary at present to invoke unusual sources of opacity in the stellar atmosphere or in the space between the star and the earth in order to explain the observations. Spectra of B stars in the 2000 region at sufficient resolution to show the line spectrum would clarify the problem.     

生态文明与中国特色社会主义关系研究述评

自生态文明理念提出以来,国内外学术界对生态文明及其相关问题进行了深入且具有开创性的研究和探索,并取得了大量的理论成果.文章对国内生态文明的研究以及生态文明与中国特色社会主义关系的研究现状进行分析与梳理,指出现有研究中所存在的问题并作简要评论.     

无人机制造外形气动偏差评估方法

气动外形对无人机起着至关重要的作用,有必要对其制造外形的气动偏差进行评估。利用数字摄影测量系统获得无人机制造外形的点云数据;以机头为参考点,将测量点云数据模型与理论模型的坐标系重合,对比重合度并统计无人机制造外形与理论外形的几何偏差分布;根据点云数据进行逆向建模,获得无人机制造外形的三维模型;对无人机理论外形进行CFD计算,与其风洞试验数据进行对比,通过调整网格及计算方法,得到与试验数据相吻合的CFD计算方法;以此方法计算得到无人机制造外形的气动数据,并与无人机的理论气动力进行对比。结果表明:此评估方法能够定量地评估外形制造偏差对无人机气动特性的影响。     

Characteristics of pulsed plasma synthetic jet and its control effect on supersonic flow

The plasma synthetic jet is a novel flow control approach which is currently being studied. In this paper its characteristic and control effect on supersonic flow is investigated both experimentally and numerically. In the experiment, the formation of plasma synthetic jet and its propagation velocity in quiescent air are recorded and calculated with time resolved schlieren method. The jet velocity is up to 100 m/s and no remarkable difference has been found after changing discharge parameters. When applied in Mach 2 supersonic flow, an obvious shockwave can be observed. In the modeling of electrical heating, the arc domain is not defined as an initial condition with fixed temperature or pressure, but a source term with time-varying input power density, which is expected to better describe the influence of heating process. Velocity variation with different heating efficiencies is presented and discussed and a peak velocity of 850 m/s is achieved in still air with heating power density of 5.0 · 1012W/m3. For more details on the interaction between plasma synthetic jet and supersonic flow, the plasma synthetic jet induced shockwave and the disturbances in the boundary layer are numerically researched. All the results have demonstrated the control authority of plasma synthetic jet onto supersonic flow.     

The X-ray and optical variability of the BLRG 3C390.3

We describe the optical emission line and continuum changes in 3C390.3. Also we present new EXOSAT results, and discuss their implication for determination of the X-ray spectrum — spectral index and absorbing column.     

Solar variability and minor constituents in the lower thermosphere and in the mesosphere

Space Science Reviews - The variation in the solar irradiance related for example to the 11-year cycle leads to changes in the photodissociation and photo-ionization of the upper and middle...     

Spectra and time variability of GX 5-1

From a short observation of GX 5-1 with EXOSAT we have derived information on spectral and temporal behaviour in the energy range 1–20 keV. The source was found to be variable on time scales from 10 s to 1 h. Describing the spectrum one is forced to assume at least two spectral components. The best fit is reached using a spectrum composed of two blackbody functions with typical temperatures 1 keV and 2 keV, corresponding to apparent blackbody radii of 43 km and 11 km, respectively (for a distance of 10 kpc). With respect to the hot component there is evidence for variability in temperature as well as in apparent blackbody radius. No periodic variability has been found over the period range 0.25 s to 2000 s. There is no evidence for an iron emission line.