Tetra­kis(μ-6-hydr­oxy-1-naphthoato)bis­[(6-hydr­oxy-1-naphthoato)(1,10-phenanthroline)europium(III)] dihydrate

The title complex, [Eu2(C11H7O3)6(C12H8N2)2]·2H2O, has a centrosymmetric binuclear cage structure in which the two EuIII ions are both nine-coordinated and bridged by 6-hy­droxy-1-naphthoate (L) ligands, with an Eu⋯ Eu separation of 4.1594 (4) Å. The remaining coordination sites are occupied by two N atoms from one 1,10-phenanthroline (phen) and two O atoms from an L ligand. The six 6-hydr­oxy-1-naphthoate groups coordinate each EuIII atom in three different ways, namely μ2-η1:η1-bridging, μ1-η1:η1-chelating, and μ2-η1:η2-chelating/bridging modes. Adjacent discrete dinuclear units are linked into a two-dimensional sheet parallel to (011) by inter­molecular O—H⋯O hydrogen-bonding inter­actions. The sheets are cross-linked by water mol­ecules, forming a three-dimensional network. In addition, π–π stacking inter­actions, with a centroid–centroid separation of 3.547 (2) Å are observed

An hourglass model for the flare of HST-1 in M87

To explain the multi-wavelength light curves (from radio to X-ray) of HST-1 in the M87 jet, we propose an hourglass model that is a modified two-zone system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or Laval nozzle-shaped layer connected by two revolving exponential surfaces surrounding a fast spine, through which plasma blobs flow. Based on the conservation of magnetic flux, the magnetic field changes along the axis of the hourglass. We adopt the result of TG08---the high-energy emission from GeV to TeV can be produced through inverse Compton by the two-zone system, and the photons from radio to X-ray are mainly radiated by the fast inner zone system. Here, we only discuss the light curves of the fast inner blob from radio to X-ray. When a compressible blob travels down the axis of the first bulb in the hourglass, because of magnetic flux conservation, its cross section experiences an adiabatic compression process, which results in particle acceleration and the brightening of HST-1. When the blob moves into the second bulb of the hourglass, because of magnetic flux conservation, the dimming of the knot occurs along with an adiabatic expansion of its cross section. A similar broken exponential function could fit the TeV peaks in M87, which may imply a correlation between the TeV flares of M87 and the light curves from radio to X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1 verifies our prediction based on the model fit to the main peak of the VLA 15 GHz radio light curve.Comment: 14 pages, 2 figures, accepted for publication in A

Risk Assessment Based on Combined Weighting-Cloud Model of Tunnel Construction

In order to reduce the tunnel construction accidents and ensure the safety of personnel, a comprehensive assessment method of tunnel construction risk based on combination weighting and cloud model is constructed according to the characteristics of tunnel construction. The risk assessment index system is established based on researches on engineering geological condition, natural environmental condition, Tunnel engineering design scheme and construction management. On this basis, the tunnel risk is divided into 4 levels and the index risk level standard is proposed. In order to improve the rationality of weighting, a weight calculation method based on AHP, entropy method and Lagrange multiplier method is constructed. Finally, the normal cloud generator is used to form comparison pictures of risk clouds and standard clouds, which demonstrates the risk status of the evaluation indexes at all levels. With reference to Deda Tunnel of Sichuan-Tibet Railway engineering of high integrated risk level, management decision-making is required. The evaluation results are basically consistent with engineering practices, proving that the method has good feasibility and applicability