Bayesian coronal seismology

In contrast to the situation in a laboratory, the study of the solar atmosphere has to be pursued without direct access to the physical conditions of interest. Information is therefore incomplete and uncertain and inference methods need to be employed to diagnose the physical conditions and processes. One of such methods, solar atmospheric seismology, makes use of observed and theoretically predicted properties of waves to infer plasma and magnetic field properties. A recent development in solar atmospheric seismology consists in the use of inversion and model comparison methods based on Bayesian analysis. In this paper, the philosophy and methodology of Bayesian analysis are first explained. Then, we provide an account of what has been achieved so far from the application of these techniques to solar atmospheric seismology and a prospect of possible future extensions.     

RATAN-600 and RadioAstron reveal the neutrino-associated blazar TXS 0506+056 as a typical variable AGN

The possible association with the high-energy neutrino event IceCube-170922A has sparked interest in the blazar TXS 0506+056. We present 72 instantaneous 1–22 GHz spectra measured over the past 20 years with the RATAN-600 telescope and compare them with the results of observations of 700 variable Active Galactic Nuclei (AGN) studied within the same program. The recent radio flare of TXS 0506+056 started from a minimum in 2013 and reached its first peak in December 2017 and a second peak in May-June 2018. This was the third strong radio flare in this source since 1997. The spectrum remains nearly flat during the flares. The spectral shape and variability pattern observed in TXS 0506+056 are typical for variable AGN. RadioAstron Space VLBI observations in 2013–2015 did not detect TXS 0506+056 on space-ground baselines of more than 9 Earth diameters. However, an observation on 23 September 2015 resulted in the detection of interferometric signal on 6 Earth diameter baselines at 18 cm close to the detection limit. We consider the possibility that TXS 0506+056 and other AGN may accelerate relativistic protons more efficiently than electrons. Relativistic protons are necessary to produce both the high-energy neutrinos observed in the IceCube Observatory and the high AGN brightness temperatures implied by the RadioAstron detection. They may also provide the main contribution to the observed synchrotron radiation of parsec-scale AGN jets. This supports the suggestion that relativistic protons may play a much more important part in extragalactic astrophysics than earlier anticipated.     

Numerical investigation of flow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor ‘‘Radiver’’ with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance. The results demonstrate that tandem design and clocking fraction (λ_s) significantly affects the compressor performance. The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller. The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary. In order to restrain the inducer wake and exducer shock losses, parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained. The modified tandem impeller with 25% clocking arrangement shows an 8.45% stall margin increase and maintains the total pressure ratio and efficiency as the conventional design, which proves the potential of tandem impeller to improve compressor stage performance. It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.     

一个太阳硬X射线爆的观测特性

本文分析了1981年4月27日的一个特大高能爆发。它在硬X射线(HXR)、γ射线和微波(MW)记录上显示一一对应的多脉冲结构。文中讨论了这些脉冲的寿命、时延与HXR的能量、MW的波长之间的关系,发现时延量与湍动加速所预期的值相符合。提出了各脉冲期间的谱呈软→硬→软的演化,可能是由高能电子受到加速的看法。还对产生HXR的高能电子的谱指数、电子总数和MW源区的磁场也作了估计。      

电流片的稳定性问题

本文从理想磁流体力学出发,分析了固结在光球层上的半圆弧形电流片的线性稳定性。主要结论是:当沿电流方向的磁场小于某临界值时,电流片将不稳定,且最先引起不稳定的扰动模沿电流方向的波数近似为电流片圆弧直径的倒数。      

S-08钢真空熔模精密铸造工艺研究

通过工艺试验和系统分析,研究出一套用真空感应铸造炉生产S-08钢铸件的工艺方法,解决S—08钢真空熔模精密铸造过程中的关键工艺技术问题,使S-08钢铸造的液氧／煤油发动机低压壳体、氧主阀下壳体等关键铸件满足高压、高冲击的负荷指标。     

天基微小空间碎片探测研究

随着空间碎片数量的不断增多,天基微小空间碎片探测已经成为一个热点．首先介绍了空间碎片在低地球轨道上的分布情况以及它对于航天器的危害,然后介绍了国外微小碎片探测器的基本情况,并在这些探测结果的基础上提出了一个探测器方案．这种探测器的传感器采用了新型的压电材料聚偏二氟乙稀(PVDF),使用了飞行时间法(TOF)准确测定空间碎片的飞行速度,以及快脉冲分析系统分析碎片的质量．     

铝颗粒云燃烧研究进展

为探究铝颗粒云燃烧特性,把握其研究进展,并为后续研究工作提供参考,本文首先简述了铝颗粒点火、燃烧过程,总结了铝颗粒燃烧机理;其次,综述了铝颗粒云燃烧的实验、理论和模拟研究进展,从不同维度分析了影响颗粒云火焰速度的关键参数,并提出颗粒云燃烧的研究方向,包括提升颗粒云燃烧实验颗粒分散均匀性与表征精度、降低火焰传播速度等实验结果散差、改善颗粒云燃烧理论预测模型精度及构建实用的颗粒云燃烧模拟CFD模型。     

Probing the origin of the iron Kα line around stellar and supermassive black holes using X-ray polarimetry

Asymmetric, broad iron lines are a common feature in the X-ray spectra of both X-ray binaries (XRBs) and type-1 Active Galactic Nuclei (AGN). It was suggested that the distortion of the Fe Kα emission results from Doppler and relativistic effects affecting the radiative transfer close to the strong gravitational well of the central compact object: a stellar mass black hole (BH) or neutron star (NS) in the case of XRBs, or a super massive black hole (SMBH) in the case of AGN. However, alternative approaches based on reprocessing and transmission of radiation through surrounding media also attempt to explain the line broadening. So far, spectroscopic and timing analyzes have not yet convinced the whole community to discriminate between the two scenarios. Here we study to which extent X-ray polarimetric measurements of black hole X-ray binaries (BHXRBs) and type-1 AGN could help to identify the possible origin of the line distortion. To do so, we report on recent simulations obtained for the two BH flavors and show that the proposed scenarios are found to behave differently in polarization degree and polarization angle. A relativistic origin for the distortion is found to be more probable in the context of BHXRBs, supporting the idea that the same mechanism should lead the way also for AGN. We show that the discriminating polarization signal could have been detectable by several X-ray polarimetry missions proposed in the past.     

The effective temperatures of O-type stars from UV spectroscopy

We present an analysis of high resolution spectra in the far-UV – UV range (∼905–2000 Å) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) T_eff scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.