We report measurements of conditional Eulerian and Lagrangian structure functions in order to assess the effects of nonuniversal properties of the large scales on the small scales in turbulence. We study a 1 ϫ 1 ϫ 1.5 m 3 flow between oscillating grids which produces R = 285 while containing regions of nearly homogeneous and highly inhomogeneous turbulence. Large data sets of three-dimensional tracer particle velocities have been collected using stereoscopic high speed cameras with real-time image compression technology. Eulerian and Lagrangian structure functions are measured in both homogeneous and inhomogeneous regions of the flow. We condition the structure functions on the instantaneous large scale velocity or on the grid phase. At all scales, the structure functions depend strongly on the large scale velocity, but are independent of the grid phase. We see clear signatures of inhomogeneity near the oscillating grids, but even in the homogeneous region in the center we see a surprisingly strong dependence on the large scale velocity that remains at all scales. Previous work has shown that similar correlations extend to very high Reynolds numbers. Comprehensive measurements of these effects in a laboratory flow provide a powerful tool for assessing the effects of shear, inhomogeneity and intermittency of the large scales on the small scales in turbulence.
The 5-oxaporphyrin macrocycle is a modified porphyrin (with an oxygen atom replacing a meso-methine unit) that is produced during heme degradation in biological and chemical systems. We have undertaken an investigation into the chemical reactivity of metal complexes of this macrocycle. Here we report that the diamagnetic zinc(II) and paramagnetic cobalt(II) verdoheme analogues, [Zn(II)(OEOP)](O(2)CCH(3)) and [Co(II)(OEOP)](PF(6)) (OEOP is the monoanion of octaethyl-5-oxaporphyrin), undergo ring opening when treated with alkoxide ions. The zinc(II) complex Zn(II)(OEBOMe), where OEBOMe is the dianion of octaethylmethoxybiliverdin, is sufficiently stable to be isolated in crystalline form, but the cobalt(II) analogue, Co(II)(OEBOMe), is less stable and has been characterized primarily by (1)H NMR spectroscopy in solution. The reactions are accompanied by a color change from blue-green for the verdoheme complexes to yellow-green for the ring-opened compounds. The ring-opened product Zn(II)(OEBOMe) has been subjected to a crystallographic study which reveals that the complex contains a four-coordinate zinc(II) ion whose geometry is significantly controlled by the helical tetrapyrrole ligand so that tetrahedral coordination is not achieved. The structure of this complex is compared to that of a closely related free ligand and those of copper and cobalt complexes of tetrapyrrole ligands that also form helical complexes.
Studies of the reaction of 5-oxaporphyrin iron complexes (verdohemes) with methoxide ion or hydroxide ion have been undertaken to understand the initial step of ring opening of verdohemes. High-spin [ClFe(III)(OEOP)] undergoes a complex series of reactions upon treatment with hydroxide ion in chloroform, and similar species are also detected in dichloromethane, acetonitrile, and dimethyl sulfoxide. Three distinct paramagnetic intermediates have been identified by (1)H NMR spectroscopy. These reactive species are formed by addition of hydroxide to the macrocycle and to the iron as an axial ligand. Treatment of low-spin [(py)(2)Fe(II)(OEOP)]Cl (OEOP is the monoanion of octaethyl-5-oxaporphyrin) with excess methoxide ion in pyridine solution produces [(py)(n)()Fe(II)(OEBOMe)] (n = 1 or 2) ((OEBOMe), dianion of octaethylmethoxybiliverdin), whose (1)H NMR spectrum undergoes marked alteration upon addition of further amounts of methoxide ion. An identical (1)H NMR spectrum, which is characterized by methylene resonances with both upfield and downfield paramagnetic shifts, is formed upon treatment of [Fe(II)(OEBOMe)](2) with methoxide in pyridine solution and results from the formation of [(MeO)Fe(II)(OEBOMe)](-).
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