Broad-line and Multi-wave Band Emission from Blazars

We study the correlations of the flux of the broad-line emission ($F_{BLR}$) with the X-ray emission flux, optical emission flux at 5500 \AA and radio emission flux at 5 GHz, respectively, for a large sample of 50 Blazars (39 flat-spectrum radio quasars (FSRQs) and 11 BL Lac objects). Our main results are as follows. There are very strong correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ in both states for 39 FSRQs and the slopes of the linear regression equations are almost equal to 1. There are weak correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ for 11 BL Lac objects in both states, and the slopes of the linear regression equations are close to 1. There are significant correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ for 50 blazars in both states, the slopes of both the linear regression equations are also close to 1. These results support a close link between relativistic jets and accretion on to the central Kerr black hole. On the other hand, we find that BL Lac objects have low accretion efficiency $\eta$, whereas FSRQs have high accretion efficiency $\eta$. The unified model of FSRQs and BL Lac objects is also discussed.Comment: 15 pages, 8 figure

The long-term optical behavior of MRK421

All data available in B band for the BL Lac object MRK421 from 22 publications are used to construct a historical light curve, dating back to 1900. It is found that the light curve is very complicated and consists of a set of outbursts with very large duration. The brightness of MRK421 varies from 11.6 magnitude to more than 16 magnitude. Analyses with Jurkevich method of computing period of cyclic phenomena reveal in the light curve two kinds of behaviors. The first one is non-periodic with rapid, violent variations in intensity on time scales of hours to days. The second one is periodic with a possible period of $23.1\pm 1.1$ years. Another possible period of $15.3\pm 0.7$ years is not very significant. We have tested the robustness of the Jurkevich method. The period of about one year found in the light curves of MRK421 and of other objects is a spurious period due to the method and the observing window. We try to explain the period of $23.1 \pm1.1$ years under the thermal instability of a slim accretion disk around a massive black hole of mass of $2 *10^6 M_\odot$.Comment: Tex, 14 pages, 5 Postscript figures. Accepted for publication in A&A Supplement Serie

Nonperturbative signatures in pair production for general elliptic polarization fields

The momentum signatures in nonperturbative multiphoton pair production for general elliptic polarization electric fields are investigated by employing the real-time Dirac-Heisenberg-Wigner formalism. For a linearly polarized electric field we find that the positions of the nodes in momenta spectra of created pairs depend only on the electric field frequency. The polarization of external fields could not only change the node structures or even make the nodes disappear but also change the thresholds of pair production. The momentum signatures associated to the node positions in which the even-number-photon pair creation process is forbid could be used to distinguish the orbital angular momentum of created pairs on the momenta spectra. These distinguishable momentum signatures could be relevant for providing the output information of created particles and also the input information of ultrashort laser pulses.Comment: 8 pages, 4 figures, submitted to Europhysics Letter

Spike Effects on Drag Reduction for Hypersonic Lifting Body

A high lift-to-drag ratio is considered crucial for high-altitude and long-endurance hypersonic vehicles. One of the simplest and most useful methods is to install an aerospike in front of the vehicle’s nose. In this paper, the flight aerodynamic characteristics are investigated by simulating and comparing the lifting body with or without the aerospikes at Ma=8. The flowfields around aerospikes using different spike lengths and a hemispherical disk along with the lifting body are analyzed. The results of aerodynamic characteristics indicate that L/D=2 is the best ratio of the spike length to the nose diameter. By comparing with the baseline model, the maximum drag reduction of the nose’s part is 49.3% at α=8  deg using a hemispherical disk. In addition, three shapes of aerospike disks are compared to search for the best disk for hypersonic drag reduction. The best drag reduction is found for the double flat-faced disk aerospike, which gives a pressure drag reduction of 60.5% of the nose’s part at α=8  deg. Furthermore, when the flight angle of attack increases, the drag increases significantly. Employing a certain installation angle is shown to effectively improve the drag reduction around the angle of attack and results in improving the lift-to-drag ratio. At the end, the lift-to-drag ratio of the final optimized design is 9.1% better than that of the baseline model. The pressure center is moved forward by 1.6%, barely influencing the vertical static stability of the vehicle

Higher-order conservative interpolation between control-volume meshes: Application to advection and multiphase flow problems with dynamic mesh adaptivity

© 2016 .A general, higher-order, conservative and bounded interpolation for the dynamic and adaptive meshing of control-volume fields dual to continuous and discontinuous finite element representations is presented. Existing techniques such as node-wise interpolation are not conservative and do not readily generalise to discontinuous fields, whilst conservative methods such as Grandy interpolation are often too diffusive. The new method uses control-volume Galerkin projection to interpolate between control-volume fields. Bounded solutions are ensured by using a post-interpolation diffusive correction. Example applications of the method to interface capturing during advection and also to the modelling of multiphase porous media flow are presented to demonstrate the generality and robustness of the approach