浅谈冬季恶劣天气签派放行攻略

针对冬季机场容易出现的恶劣天气特点,主要从降雪跑道结冰、大雾低能见两个主要恶劣天气着手,分析飞行签派员放行攻略。     

Observational appearances of isolated stellar-mass black hole accretion – Theory and observations

General properties of accretion onto isolated stellar-mass black holes in the Galaxy are discussed. An analysis of plasma internal energy growth during the infall is performed. Adiabatic heating of collisionless accretion flow due to magnetic adiabatic invariant conservation is 25% more efficient than in the standard non-magnetized gas case. It is shown that magnetic field line reconnections in discrete current sheets lead to significant nonthermal electron component formation, which leads to a formation of a hard (UV, X-ray, up to gamma), highly variable spectral component in addition to the standard synchrotron optical component first derived by Shvartsman generated by thermal electrons in the magnetic field of the accretion flow. Properties of accretion flow emission variability are discussed. Observation results of two single black hole candidates – gravitational lens MACHO-1999-BLG-22 and radio-loud X-ray source with featureless optical spectrum J1942+10 – in optical band with high temporal resolution are presented and interpreted in the framework of the proposed model.     

Limit cycles of accretion disks in the Rapid Burster and GRS 1915+105

The Rapid Burster is known to show rapidly repetitive bursts (Type II bursts). An interesting feature of the Type II burst is an approximate proportionality of the burst duration to the time to the next burst. The time sequence from a burst to the following quiescent phase can be said to be a time-scale invariant high (burst phase)–low (quiescent phase) transition. The Galactic superluminal source, GRS 1915+105 exhibits a variety of the time variation of the X-ray flux and often repeats transitions between a high-flux level and a low-flux level. In such high–low transitions, Belloni et al. (1997b) found an approximate proportionality between the duration of the low-flux phase and that of the following high-flux phase, over a wide range of the time scale. This low–high transition can again be said to be time-scale invariant. However, an interesting difference between the two time scale invariant transitions is an opposite order of the high and low-flux phase in the time-scale invariant sequence. In the case of the Rapid Burster, the high-flux (burst) phase is the first, while the low-flux phase is the first in the case of GRS1915+105. A limit cycle between an accretion disk in a state of the standard-disk and that in a state of the ADAF (advection dominated accretion flow) is discussed to explain the time-scale invariant high–low (or low–high) transition as well as the difference between the neutron star system and the black-hole system, qualitatively. A phenomenological relation of the accretion disk change with mass ejections from the central part of the disk is also discussed.     

Testing the no-hair theorem with observations of black holes in the electromagnetic spectrum

According to the no-hair theorem, astrophysical black holes are uniquely described by their mass and spin. In this paper, we review a new framework for testing the no-hair hypothesis with observations in the electromagnetic spectrum. The approach is formulated in terms of a Kerr-like spacetime containing a quadrupole moment that is independent of both mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric quadrupole has to be zero. We show how upcoming VLBI imaging observations of Sgr A∗ as well as spectroscopic observations of iron lines from accreting black holes with IXO may lead to the first astrophysical test of the no-hair theorem.     

The relevance of the Eddington limit to thick accretion disks

Thick accretion disks with narrow funnels around massive black holes are considered promising models for active galactic nuclei. These models assume a supercritical accretion rate and emit collimated beams with super-Eddington luminosities. We have made approximate calculations of the interaction between the emerging radiation and the walls for an optically thin funnel. The results are sensitive to the sound velocity and to the viscosity parameter α. They suggest that a significant particle luminosity can accompany the radiation in the super-Eddington case. By applying an Eddington type limit based on mechanical equilibrium to a suitably chosen interior surface in the disk, we find that energy transport, if radiative, can strongly limit the efficiency of these models.     

X-ray observations of black-hole accretion disks

Our current theoretical and observational understandings of the accretion disks around Galactic black-holes are reviewed. Historically, a simple phenomenological accretion disk model has been used to interpret X-ray observations. Although such a phenomenological interpretation is still useful, high quality X-ray data from contemporary instruments allow us to test more realistic accretion disk models. In a simple and ideal case, the standard optically thick accretion disk model is successful to explain observations, such that the inner disk radius is constant at three times the Schwarzschild radius over large luminosity variations. However, when disk luminosity is close to or exceeds the Eddington luminosity, the standard disk model breaks, and we have to consider the “slim disk” solution in which radial energy advection is dominant. Recent observations of Ultra-luminous X-ray sources (ULXs), which may not be explained by the standard disk model, strongly suggest the slim disk solution. We compare theoretical X-ray spectra from the slim disk with observed X-ray spectra of ULXs. We have found that the slim disk model is successful to explain ULX spectra, in terms of the massive stellar black-holes with several tens of solar mass and the super-Eddington mass accretion rates. In order to explain the large luminosities (>10⁴⁰ ergs s⁻¹) of ULXs, “intermediate black-holes” (>100M) are not required. Slim disks around massive stellar black-holes of up to several tens of solar mass would naturally explain the observed properties of ULXs.     

Self-similar problems of the time-dependant discs accretion and the nature of the temporary X-ray sources

Self-similar solutions, obtained by means of non-linear hydrodynamic equations, describing the picture of the time-dependant discs accretion. Some of the solutions describe the evolution of the accumulating disc, which is created around the neutron star with a strong magnetic field. Others give the time evolution of the initial narrow material ring, thrown at a certain distance around the gravitation centre. Practically all problems of the time-dependant disc accretion, asymptotically come to the above mentioned solutions.It is shown that the time-dependant disc accretion of the gas of the neutron star from the accumulating disc cause recurrent X-ray outbursts. The fall of the X-ray luminosity at the maximum stage depends of the time to a certain degree; is near the ones which are observed in the time-dependant X-ray sources. The model of the time-dependant X-ray sources is explained in the framework of the time-dependant disc accretion of magnetized neutron star with a strong magnetic field.     

Delayed outburst of H 1743–322 in 2003 and relation with its other outbursts

The Galactic transient black hole candidate H 1743–322 exhibited a long duration outburst in 2003 after more than two and a half decades of inactivity. The 2003 event was extensively studied in multi-wavelength bands by many groups. The striking feature is that the total energy released is extremely high as compared to that in tens of outbursts which followed. In this paper, we look at this event and study both the spectral and temporal properties of the source using two component advective flow (TCAF) paradigm. We extract accretion flow parameters for each observation from spectral properties of the decay phase and determine the mass of the black hole. We computed the energy released during all the known outbursts since 2003 and showed that on an average, the energy release in an outburst is proportional to the duration of the quiescent state just prior to it, with the exception of the 2004 outburst. A constant rate of supply of matter from the companion cannot explain the energy release in 2004 outburst. However, if the energy release of 2003 is incomplete and the leftover is released in 2004, then the companion’s rate of matter supply can be constant since 1977 till date. We believe that erratic behaviour of viscosity at the accumulation radius $X_p$ of matter as well as location the $X_p$ itself, rather than the random variation of mass transfer rate from the companion, could be responsible for non-uniformity in outburst pattern. We discuss several factors on which the waiting time and duration of the next outburst could depend.     

直升机旋翼桨叶翼型积冰的数值模拟

本文对直升机旋翼桨叶翼型积冰进行了数值模拟.建立了空气、水滴两相流控制方程,通过求解气体欧拉方程得到空气流场,求解水滴控制方程得到翼型表面的水滴收集率.根据结冰表面的对流换热特性,使用积冰数值模拟的热力学模型确定翼型表面的积冰量,利用冰层时间推进法模拟积冰过程,采用积冰法向生长模型预测积冰形状;对NACA0012翼型在不同环境温度下的积冰进行了预测,最后对预测结果进行了分析.