Poly[[(4,4′-bipyridine-κN)[μ3-(S)-2-hy­droxy­butane­dioato-κ4 O 1,O 2:O 4:O 4′]zinc] dihydrate]

In the title compound, {[Zn(C4H4O5)(C10H8N2)]·2H2O}n, the ZnII ion displays a distorted tetra­gonal–pyramidal coordination environment with one hy­droxy O and three carboxyl­ate O atoms from three malate anions, and the one remaining position occupied by an N atom from a 4,4′-bipyridine ligand. The pyridine rings of the 4,4′-bipyridine ligand are twisted with respect to each other by a dihedral angle of 35.8 (2)°. The uncoordinated water mol­ecules are linked to the complex mol­ecules by O—H⋯O hydrogen bonds. Each malate anion forms four coordination bonds with three Zn atoms, establishing a layer structure parallel to the ac plane. Adjacent layers are further linked via O—H⋯N hydrogen bonding. π–π stacking between the pyridine rings [face-to-face distance = 3.651 (3) Å] occurs in the crystal structure

Bis[tris­(ethyl­enediamine-κ2 N,N′)cobalt(III)] octa­kis-μ-3-oxido-hexa­deca-μ2-oxido-tetra­deca­oxido-μ12-tetra­oxo­silicato-octa­molybdenum(VI)hexa­vanadium(IV,V) hexa­hydrate

The title compound, [Co(C2H8N2)3]2[SiMo8V4O40(VO)2]·6H2O, was prepared under hydro­thermal conditions. The asymmetric unit consists of a transition metal complex [Co(en)3]3+ cation (en is ethyl­enediamine), one half of an [SiMo8V4O40(VO)2]6− heteropolyanion, two solvent water mol­ecules in general positions and two half-mol­ecules of water located on a mirror plane. In the complex cation, the Co3+ ion is in a distorted octa­hedral coordination environment formed by six N atoms of the three chelating en ligands. One of the en ligands exhibits disorder of its aliphatic chain over two sets of sites of equal occupancy. The [SiMo8V4O40(VO)2]6− heteropolyanion is a four-electron reduced bivanadyl-capped α-Keggin-type molybdenum–vanadium–oxide cluster. In the crystal, it is located on a mirror plane, which results in disorder of the central tetra­hedral SiO4 group: the O atoms of this group occupy two sets of sites related by a mirror plane. Furthermore, all of the eight μ2-oxide groups are also disordered over two sets of sites with equal occupancy. There are extensive inter­molecular N—H⋯O hydrogen bonds between the complex cations and inorganic polyoxidoanions, leading to a three-dimensional supra­molecular network

Competitions of magnetism and superconductivity in FeAs-based materials

Using the numerical unrestricted Hartree-Fock approach, we study the ground state of a two-orbital model describing newly discovered FeAs-based superconductors. We observe the competition of a $(0, \pi)$ mode spin-density wave and the superconductivity as the doping concentration changes. There might be a small region in the electron-doping side where the magnetism and superconductivity coexist. The superconducting pairing is found to be spin singlet, orbital even, and mixed s$_{xy}$ + d$_{x^{2}-y^{2}}$ wave (even parity).Comment: 5 pages, 3 figure

A search for flaring Very-High-Energy cosmic-ray sources with the L3+C muon spectrometer

The L3+C muon detector at the Cern electron-position collider, LEP, is used for the detection of very-high-energy cosmic \gamma-ray sources through the observation of muons of energies above 20, 30, 50 and 100 GeV. Daily or monthly excesses in the rate of single-muon events pointing to some particular direction in the sky are searched for. The periods from mid July to November 1999, and April to November 2000 are considered. Special attention is also given to a selection of known \gamma-ray sources. No statistically significant excess is observed for any direction or any particular source

Investigation on the combustion kinetics of non-caking coal under various ventilation rates

Ventilation provides the oxygen required for coal combustion, but it also accelerates the thermal loss of reaction system. To investigate the influence of ventilation on coal combustion, the characteristic temperatures and stage variation were analyzed. Furthermore, the kinetic mode was determined and the apparent activation energy was calculated. The results indicated that the increase of ventilation rate made the boundary temperatures for different stages decreased. The contribution of thermal decomposition effect to mass loss increased, and the contribution of burning effect correspondingly decreased. The ventilation rate mainly presented an influence on the kinetic mode at the second half of coal burning. The kinetic mode transformed from three-dimensional diffusion to random nucleation and subsequent growth when the ventilation rate reached 200 ml/min. In addition, under the same conversion rate, the apparent activation energy during thermal decomposition first increased and then decreased, and reached the maximum when the ventilation rate was 100 ml/min. The apparent activation energy during coal burning first decreased and then increased, and again decreased, and the increasing trend appeared when the ventilation rate was within 100–150 ml/min. These findings will provide guidance for the control and prevention of coal combustion by adjusting air leakage