Collective Tunnelling of Strongly Interacting Cold Atoms in a Double-Well Potential

It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually.     

A characterization of projective-planar signed graphs

A signed graph has a plus or minus sign on each edge. A simple cycle is positive or negative depending on whether it contains an even or odd number of negative edges, respectively. We consider embeddings of a signed graph in the projective plane for which a simple cycle is essential if and only if it is negative. We characterize those signed graphs that have such a projective-planar embedding. Our characterization is in terms of a related signed graph formed by considering the theta subgraphs in the given graph.     

The first ruthenium-alkyne-dihydride reported is now recognized as an intermediate in the homogeneous hydrogenation of diphenylacetylene: Crystal structure of (μ-H)2Ru3(CO)9(μ3-η2-∥-C2Ph2)

The title complex (complex1) was the first alkyne-substituted triruthenium dihydrido cluster to be reported and was characterized by spectroscopy as a triangular cluster with the alkyne parallel to a Ru-Ru edge. Recently, we have found that1 is a key intermediate in the homogeneous hydrogenation of diphenylacetylene catalyzed by tetrahedral Ru₄ and FeRu₃ clusters. Since the discovery of1, a great number of complexes with alkynes parallel to a cluster edge have been reported; at present this is the more common bonding mode for alkynes on trinuclear clusters. The structural features of1 allow a comparison with those of other ruthenium-containing derivatives and help to draw suggestions of the role of1 in hydrogenation catalysis.     

Mercury removal from aqueous solution and flue gas by adsorption on activated carbon fibres

The use of two activated carbon fibres, one laboratorial sample prepared from a commercial acrylic textile fibre and one commercial sample of Kynol^®, as prepared/received and modified by reaction with powdered sulfur and H₂S gas in order to increase the sulfur content were studied for the removal of mercury from aqueous solution and from flue gases from a fluidized bed combustor. The sulfur introduced ranged from 1 to 6 wt.% depending on the method used. The most important parameter for the mercury uptake is the type of sulfur introduced rather than the total amount and it was found that the H₂S treatment of ACF leads to samples with the highest mercury uptake, despite the lower sulfur amount introduced. The modified samples by both methods can remove HgCl₂ from aqueous solutions at pH 6 within the range 290-710 mg/g (ACF) which can be favourably compared with other studies already published. The use of a filter made with an activated carbon fibre modified by powdered sulfur totally removed the mercury species present in the flue gases produced by combustion of fossil fuel.     

Thermal behavior of the maleic anhydride modified poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate), PHB has been structurally modified through reaction with maleic anhydride, MA. Transesterification reaction was carried out fixing the PHB and MA and besides time and temperature the concentration of the triethylamine (used as catalyst) was changed. Glass transition, melting and crystallization temperature obtained from DSC curves and thermal degradation temperatures obtained from TG traces were used to evaluate the influence of the reaction conditions on the modification of PHB according to factorial design. On the base of the results the optimum conditions are to perform the PHB modification reaction with MA reaction at 110°C for 1 h with 5% v/v triethylamine.     

Crystal and molecular structure of nitrosyl(1,10-phenanthroline)-bis(triphenylphosphine)iridium(I) Dihexafluorophosphate, [Ir(NO)(phen)(PPh3)2][PF6]2

Summary The structure of [Ir(NO)(phen)(PPh₃)₂][PF₆]₂ has been determined from x-ray diffractometer data. The compound crystallizes in space groupPnam with four molecules in a unit cell witha = 19.924(12),b = 14.793(9) andc = 16.348(9) A. Full-matrix least-squares refinement has led to a final R value of 0.061 for the 4796 observed reflections. The structure consists of well-separated ions, and the geometry around the metal is trigonal bipyramidal with nitrosyl and bidentate 1,10-phenanthroline (in spite of the very narrow bite angle of 75.8°) ligands occupying the equatorial positions and the triphenylphosphine ligands the axial positions. The cation has an imposed crystallographicm symmetry. Important bond lengths are as follows: Ir-P, 2.391(3): Ir-N (nitrosyl) 1.700(12): Ir-N (1,10-phenanthroline) 2.103(12) and 2.142(11): N-O, 1.201(18)A. The nitrosyl ligand is linear [Ir-N-O = 179.9(9)°] so that this complex can be formulated as an NO⁺ complex of iridium(I).     

The crystal structure of tris(acetonitrile)nitrosylbis(triphenylphosphine)iridium(III) dihexafluorophosphate. An unusual iridium nitrosyl hexacoordinate complex

Summary The structure of [Ir(NCMe)₃(NO)(PPh₃)₂][PF₆]₂ has been ] determined by x-ray methods. Crystals are orthorhombic, space groupPca 2₁ , witha = 21.753(14),b = 11.678(10),c = 18.474(12) Å and Z = 4. The structure has been solved from diffractometer data and refined by full-matrix leastsquares to R = 0.076 for 2776 observed reflections. The cation is a hexacoordinate and not a pentacoordinate species as expected. The extra acetonitrile molecule,trans to the nitrosyl ligand, is much more weakly bound to the metal atom [Ir-N 2.360(26) against 1.965(20) and 1.912(14) Å for the other two acetonitriles]. The nitrosyl is bent [Ir-N-O 111(1)° Å] and acts as the formally one-electron donor NO^–.     

General approach for the synthesis of chiral perylenequinones via catalytic enantioselective oxidative biaryl coupling

By using oxygen as the terminal oxidant, copper complexes derived from chiral 1,5-diaza-cis-decalin catalyze the enantioselective oxidative biaryl coupling of highly functionalized naphthols to provide octa- and decasubstituted binaphthalenes with high selectivity (86-90% ee). Products containing very electron-rich naphthalenes were prone to epimerization under the reaction conditions. This epimerization could be suppressed by employing naphthol starting materials with phenol protecting groups that attenuated the electron-rich nature of the naphthalenes. Direct oxidation of the resultant chiral 1,1'-binaphthol framework completed the first asymmetric synthesis of a perylenequinone containing only an axial chirality element.