Plasma diagnostics of planetary nebulae

Diagnostics for the rarefied plasmas in gaseous nebulae are reviewed, beginning with the pioneering papers of V. A. Ambartsumian. These papers, as well as the diagnostic techniques which have been developed on the basis of ideas contained in them, are discussed. Diagnostic techniques for homogeneous, as well as inhomogeneous, plasmas are described. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 363–383 (August 2008).     

Emission stratification in two-component HII regions with stellar wind

To explain the variety of observed optical emission stratification in the shells around Wolf-Rayet stars, we have calculated the nonstationary cooling of a homogeneous gas layer heated to a temperature (0.4–2) × 10⁵ K. We have assumed that the nebula is ionized by its central star and consists of a rarefied gas and a set of clouds with different densities through which adiabatic shock waves produced by the stellar wind propagate. Based on this model, we have determined the sequence in which the emission in Hα and in nebular oxygen lines appears. The Hα emission attributable to the electron-collision excitation of hydrogen atoms is produced earliest on the periphery of nebulae, the [O III] line emission follows next, and, finally, the Hα recombination emission is produced. The results obtained are in good agreement with the observational data.     

中低压缩性地基上设置沉降后浇带的主裙楼沉降及基底反力分布特征

沉降后浇带是经常采用的主裙楼连接方式,设置沉降后浇带的大底盘高层建筑共同作用分析更复杂。介绍了设置沉降后浇带的大底盘高层建筑的共同作用分析方法：按施工过程中的不同工况分别计算,然后将计算结果叠加;采用有限压缩层地基模型,并考虑回弹再压缩;考虑上部结构刚度分段形成。对于中低压缩性地基上的主裙楼结构,通过对简化模型进行计算分析,得到了不同沉降后浇带设置位置、不同后浇带浇筑时间条件下的沉降、基底反力分布特征：后浇带封闭时间越晚,主裙楼连接处在封闭后产生的差异沉降越小,但主楼最大沉降会增加;与后浇带设置在主楼外第1跨相比较,后浇带设置在主楼外第2跨时,主楼最大沉降减少,主裙楼连接处的差异沉降减小,主楼下平均地基反力降低。     

基于传递矩阵的两相介质波动问题时域显式有限元方法稳定性研究

饱和两相介质波动问题的时域显式有限元方法具有条件稳定性。这类方法的稳定性可通过方法中动力反应时域递推计算格式传递矩阵传递因子的数值进行评估,传递因子的数值越小,方法的稳定性越好。针对饱和两相介质波动问题的两种时域显式有限元方法,基于其动力反应时域递推计算格式的传递矩阵的性质,在两相介质体系物理参数取值不同的条件下,对两种方法稳定性性质的差异进行了对比研究。结果表明：渗透系数的取值对两种时域显式有限元方法稳定性性质的差异具有较为显著的影响。当渗透系数取值较大时,两种方法的稳定性性质没有明显的差异;当渗透系数的取值较小时,两种方法的稳定性性质将表现出明显的差异,方法1的稳定性要优于方法2。     

二维叠后地震数据的平稳随机介质参数估计

随机介质参数估计是随机介质理论应用于地震勘探的关键.本文提出了一种从二维叠后地震数据中估计平稳随机介质参数的方法.文中阐述了二维叠后地震数据与随机介质波阻抗模型的关系,以及随机介质自相关函数参数的估计原理和方法,并结合实例详细介绍了应用功率谱法进行随机介质参数估计的具体步骤;通过多个二维理论模型的估计试验,验证了方法的可行性和正确性;还对实际地震数据进行了随机介质参数的估计试验,结果表明,随机介质参数可以为三角洲沉积相的进一步划分提供参考,反映了该方法有较好的应用前景.相比前人的研究,本文所提出的随机介质参数估计方法是一种真正的二维算法,特别是能给出自相关角度θ的估计,这种基于功率谱的估计方法具有直观且高效率的优点,但也存在着误差较大的问题,需要进一步的改进和完善.     

Feedback through multiple outbursts in the cluster 2A 0335+096

We examine the core of the X-ray bright galaxy cluster 2A 0335+096 using deep Chandra X-ray imaging and spatially resolved spectroscopy, and include new radio observations. The set of around eight X-ray bright blobs in the core of the cluster, appearing like eggs in a bird's nest, contains multiphase gas from ∼0.5 to 2 keV. The morphology of the coolest X-ray emitting gas at 0.5 keV temperature is similar to the Hα emitting nebula known in this cluster, which surrounds the central galaxy. XMM–Newton grating spectra confirm the presence of material at these temperatures, showing reasonable agreement with Chandra emission measures. On scales of 80 to 250 kpc, there is a low temperature, high metallicity, swirl of intracluster medium as seen in other clusters. In the core, we find evidence for a further three X-ray cavities, in addition to the two previously discovered. Enhancements in 1.5 GHz radio emission are correlated with the X-ray cavities. The total  4 PV   enthalpy associated with the cavities is around  5 × 10⁵⁹ erg  . This energy would be enough to heat the cooling region for  ∼5 × 10⁷ yr  . We find a maximum pressure discontinuity of 26 per cent (2σ) across the surface brightness edge to the south-west of the cluster core. This corresponds to an upper limit on the Mach number of the cool core with respect to its surroundings of 0.55.     

The 21-cm power spectrum after reionization

We discuss the 21-cm power spectrum (PS) following the completion of reionization. In contrast to the reionization era, this PS is proportional to the PS of mass density fluctuations, with only a small modulation due to fluctuations in the ionization field on scales larger than the mean-free-path of ionizing photons. We derive the form of this modulation, and demonstrate that its effect on the 21-cm PS will be smaller than 1 per cent for physically plausible models of damped Lyα systems. In contrast to the 21-cm PS observed prior to reionization, in which H  ii regions dominate the ionization structure, the simplicity of the 21-cm PS after reionization will enhance its utility as a cosmological probe by removing the need to separate the PS into physical and astrophysical components. As a demonstration, we consider the Alcock–Paczynski test and show that the next generation of low-frequency arrays could measure the angular distortion of the PS at the per cent level for   z ∼ 3–5  .