A new look at the isotropy of narrow-line emission in extragalactic radio sources

We undertake a quantitative investigation, using Monte Carlo simulations, of the amount by which quasars are expected to exceed radio galaxies in optical luminosity in the context of the 'receding torus' model. We compare these simulations with the known behaviour of the [O  III ] λ5007 and [O  II ] λ3727 emission lines and conclude that [O  III ] is the better indicator of the strength of the underlying non-stellar continuum.     

Precise laboratory wavelengths of the Mg I and Mg II resonance transitions at 2853, 2803 and 2796 Å

Strong ultraviolet resonance transitions are observed routinely both in the Galactic interstellar medium and in quasar absorption systems. The quality of the astronomical spectroscopic data now available demands more precise laboratory rest wavelengths. Of particular interest is the accuracy with which one can constrain space–time variations in fundamental constants using quasar spectra. A recent analysis by Webb et al. of 25 quasar spectra using Mg and Fe transitions tentatively suggests that the fine-structure constant was smaller at earlier epochs. To permit a check on this result, and to allow further more extensive investigations, we have carried out a new determination of the laboratory wavelengths of Mg  i  2853 Å, Mg  II  2796 Å and Mg  II  2803 Å by high-resolution Fourier transform spectroscopy. Our results for Mg  II  2796 Å are consistent with the value measured independently by two other groups. To our knowledge, no previous measurements of comparable precision exist for Mg  I  2853 Å and Mg  II  2803 Å.     

Neutral hydrogen absorption observations of the central region of NGC 5929

We present 0.15-arcsec (25-pc) resolution MERLIN observations of neutral hydrogen absorption detected towards the nuclear region of the type 2 Seyfert galaxy NGC 5929. Absorption is detected only towards the north-eastern radio component with a column density of (6.5 ± 0.6) × 10²¹ cm⁻². Based on comparison with an HST WFPC2 continuum image, we propose that the absorption is caused by a 1.5-arcsec structure of neutral gas and dust offset 0.3 arcsec south-east of the nucleus and running NE–SW. A separate cloud of dust is apparent 1.5 arcsec to the south-west of the nucleus in the HST image. A comparison of the centroid velocity (2358 ± 5 km s⁻¹) and full width at half-maximum (43 ± 6 km s⁻¹) of the absorbing gas with previous [O  III ] observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. The main structure is consistent with an inclined ring of gas and dust encircling the active galactic nucleus (AGN); alternatively it may be a bar or inner spiral arm. We do not detect neutral hydrogen absorption or dust obscuration against the radio nucleus (column density < 3.1 × 10²¹ cm⁻²) expected by a torus of neutral gas and dust in unified models of AGNs for a type 2 Seyfert galaxy.     

汶川地震映秀-北川地表破裂带虹口乡段精细填图、位移特征和地震构造分析

同震地表破裂带是地震破裂最直观的表现。地表破裂带的精细填图对理解地震破裂过程及发震机理有着重要意义。我们对5.12汶川地震映秀-北川同震破裂带南部的虹口乡区段开展了较为精细的填图工作,该区段地表破裂带的平面几何和同震位移特征沿走向均显示出公里尺度的横向变化和复杂性。根据同震破裂不连续性特征可把地表破裂分为4段,自南向北依次为深溪沟段、庙坝段、高原新村段和八角庙段。其中,深溪沟段和八角庙段同震垂直位错较大,达.5～6m;庙坝段同震垂直位移量普遍较低,1～2m或更低;  在高原新村附近,地表破裂带分为近平行的南北两支,北支以右旋走滑为主,南支以南东盘逆冲抬升为主,这与与映秀-北川同震破裂总体北西盘抬升的性质相反。本文对高原新村附近的反向陡坎进行了深入的探讨,并综合前人的研究结果,认为是破裂在从深部往上扩展的过程中,在浅表部位顺着发育在虹口东南部的大鱼洞-龙溪飞来峰后缘的具南东倾向的断面继承而成。与北川沙坝附近的反向陡坎一样,说明老断裂带构造几何特征对单次地震破裂的扩展有牵引作用。最后,讨论了八角庙有切割关系的两组断层擦痕的地震学和地质学意义,指出可能指示了映秀-北川断裂面上局部区段震前的初始应力水平较低。     

Slope stability analysis using evolutionary optimization techniques

Slope stability optimization, in the presence of a band of a weak layer between two strong layers, is accounted for in complicated geotechnical problems. Classical optimization algorithms are not suitable for solving such problems as they need a proper preliminary solution to converge to a valid result. Therefore, it is necessary to find a proper algorithm which is capable of finding the best global solution. Recently a lot of metaheuristic algorithms have been proposed which are able to evade local minima effectively. In this study four evolutionary algorithms, including well‐known and recent ones, such as genetic algorithm, differential evolution, evolutionary strategy and biogeography‐based optimization (BBO), are applied in slope stability analysis and their efficiencies are explored by three benchmark case studies. Result show BBO is the most efficient among these evolutionary algorithms and other proposed algorithms applied to this problem. Copyright © 2016 John Wiley & Sons, Ltd.     

Profiles of blue and infrared diffuse interstellar bands

The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) based on the extensive set of high-resolution spectra acquired with the aid of echelle spectrographs installed at the 2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyed diffuse interstellar bands cover the spectral ranges of blue and near-infrared, i.e the DIBs not surveyed by Krełowski & Schmidt . The possible modifications caused by stellar and telluric lines are discussed. The very broad features such as 4430 are not discussed because the shapes of their profiles, extracted from echelle spectra, are very uncertain. The signal-to-noise (S/N) ratios of the spectra are not high enough to enable discussion of the profiles of numerous weak interstellar features discovered recently.     

基于MPGA的复杂应力状态边坡稳定性分析

极限平衡法在边坡稳定性分析中处于主导地位,该算法通常建立在一定的假设之上,没有考虑边坡土体的非线性应力-应变关系,不能用于未达到极限状态以及加固后边坡的稳定性分析。为了解决以上问题,将有限元计算与多种群遗传算法（MPGA）相结合,建立一种基于MPGA的复杂应力状态边坡稳定性分析通用模型,通过数值应力场求解安全系数,并为多种群遗传算法构建适应度函数;再利用多种群遗传算法为安全系数的计算提供滑移面。为了保证分析的高效、合理,根据滑移面发展趋势,动态产生初始滑移面,并增加一个滑移面约束条件。最后,通过均质边坡和软弱夹层边坡两个典型算例分析验证了该方法的合理性;通过分析土钉加固的软弱夹层边坡,证明了该方法可用于加固等复杂应力状态边坡的稳定性分析。