Random vortex-street model for a self-similar plane turbulent jet

We ask what determines the (small) angle of turbulent jets. To answer this question we first construct a deterministic vortex-street model representing the large-scale structure in a self-similar plane turbulent jet. Without adjustable parameters the model reproduces the mean velocity profiles and the transverse positions of the large-scale structures, including their mean sweeping velocities, in a quantitative agreement with experiments. Nevertheless, the exact self-similar arrangement of the vortices (or any other deterministic model) necessarily leads to a collapse of the jet angle. The observed (small) angle results from a competition between vortex sweeping tending to strongly collapse the jet and randomness in the vortex structure, with the latter resulting in a weak spreading of the jet.     

Phase evolution on heat treatment of sodium silicate water glass

Heat treatment of sodium silicate water glass of the nominal composition Na₂O/SiO₂ = 1:3 was carried out from 100 °C up to 800 °C and the advancement of the resulting phases was followed up by powder X-ray diffraction, scanning electron microscopy and thermogravimetry along with differential thermal analysis. The water glass, initially being an amorphous solid, starts to form crystals of β-Na₂Si₂O₅ at about 400 °C and crystallizes the SiO₂ modification cristobalite at about 600 °C that coexists along with β-Na₂Si₂O₅ up to 700 °C. At 750 °C Na₆Si₈O₁₉ appears as a separate phase and beyond 800 °C, the system turns into a liquid.     

Catalytic activity of nanocrystalline ZnM2O4 (M = Fe,Co) prepared via simple and facile synthesis of thermal decomposition of mixed metal complexes of Schiff bases generated from α-ketobutyric acid and diaminoguanidine

Metal complexes ([ML₂], where M = Fe, Co, or Zn; HL = 2-[(6-ethyl-5-oxo-4,5-dihydro-2H-[1,2,4]triazin-3-ylidene)-hydrazono]-butyric acid, C₉H₁₃N₅O₃) of a Schiff base derived from α-ketobutyric acid (α-KBA) and diaminoguanidine (Damgu) were synthesized and characterized using elemental, spectral, and thermal studies. The metal complexes exhibited similar decomposition behavior, with a highly exothermic final decomposition step resulting in the formation of metal oxides. Isomorphism among the complexes was revealed using a powder X-ray diffraction (PXRD) technique. Solid solution precursors ([Zn_1/3M_2/3(L)₂], where M = Fe, Co) were synthesized and characterized using various physico-chemical techniques. A thermal decomposition technique was used to prepare spinel-type zinc cobaltite (ZnCo₂O₄) and zinc ferrite (ZnFe₂O₄) nanocrystalline particles with the synthesized single source precursors. Structural studies using PXRD ascertained the predominant crystal phase to be spinel. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed a mean nanoparticle size of 18 ± 2 nm. Magnetic measurements revealed a weak magnetic behavior in the synthesized spinels. In the aqueous phase, the spinels exhibited catalytic activity, reducing 4-nitrophenol (4-NP) in the presence of NaBH₄ at room temperature. Additionally, the study demonstrated that the catalyst can be recovered and reused for five cycles with a more than 85% conversion efficiency.     

Does the breaking of adsorption-energy scaling relations guarantee enhanced electrocatalysis?

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Crystal structure of bis(triphenylphosphine)-cyclopentadienyl-ruthenium-phenylacetylide chloro-copper(I) acetone solvate

The product of the reaction of (-C₅ H₅)Ru(PPh₃)₂ Cl and CuC₂Ph has been characterized by single-crystal x-ray diffraction techniques and shown to have stoichiometry (-C₅ H₅)Ru(PPh₃)₂Cu(C₂Ph)Cl-(CH₃)₂CO(I). The compound contains a phenylethynyl group -bonded to the ruthenium atom and simultaneously -bonded to a terminal Cu-Cl bond. Crystals of this compound from acetone are monoclinic,P2₁/c, witha = 12.914, = 22.111,c = 16.534 Å, = 110.77 °, andZ — 4. Full-matrix least-squares refinement constraining the phenyl rings of the triphenylphosphines, the cyclopentadienyl ring, and the solvent of crystallization (acetone) as rigid groups yieldedR and weightedR values of 0.084 and 0.075, respectively.     

Strain-stiffening response in transient networks formed by reverse wormlike micelles

Strain-stiffening, that is, an increase in material stiffness at large deformations, is a property of many biological materials. Currently, model systems for the study of this phenomenon are elastic networks (gels) of semiflexible filamentous biopolymers such as actin, keratin, or fibrin. Here, we demonstrate strain-stiffening in a class of viscoelastic solutions, comprising reverse wormlike micelles. These structures are formed by the coassembly of the physiological surfactants, lecithin and bile salt, in an organic solvent, cyclohexane. In contrast to the biopolymer gels, the networks here are transient and are formed by the physical entanglement of relatively flexible worms. Our results suggest that neither a permanent network nor a high filament rigidity is required for strain-stiffening. We suggest a different origin, based on a temporary strain-induced increase in the volume fraction of entangled worms. Our system can also serve as a convenient synthetic model for future studies into this phenomenon.     

A facile route for creating "reverse" vesicles: insights into "reverse" self-assembly in organic liquids

Reverse vesicles are spherical containers in organic liquids (oils) consisting of an oily core surrounded by a reverse bilayer. They are the organic counterparts to vesicles in aqueous solution and could potentially find analogous uses in encapsulation and controlled release. However, few examples of robust reverse vesicles have been reported, and general guidelines for their formation do not exist. We present a new route for forming stable unilamellar reverse vesicles in nonpolar organic liquids, such as cyclohexane and n-hexane. The recipe involves mixing short- and long-chain lipids (lecithins) with a trace of a salt such as sodium chloride. The ratio of short- to long-chain lecithin controls the type and size of self-assembled structure. As this ratio is increased, a spontaneous transition from reverse micelles to reverse vesicles occurs. Small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) confirm the presence of unilamellar vesicles in the corresponding solutions. Average vesicle diameters can be tuned from 60 to 250 nm depending on the sample composition.     

Computational investigations on the general reaction profile and diastereoselectivity in sulfur ylide promoted aziridination

Mechanism and diastereoselectivity of sulfur ylide promoted aziridination reactions were studied by density functional theory with inclusion of solvent effects through the continuum solvation model. The general reaction pathway was modeled for the addition of substituted sulfur ylides (Me(2)S(+)CH(-)R) to an aldimine ((E)-methyl ethylidenecarbamate, MeHC=NCO(2)Me). The nature of the substituents on the ylidic carbon atom substantially affects the reaction profile. The stabilized (R=COMe) and semistabilized (R=Ph) ylides follow a cisoid addition mode leading to trans aziridines via anti betaine intermediates. The simplest model ylide (unstabilized, R=H) underwent cisoid addition in a similar fashion. In the case of stabilized ylides product diastereoselectivity is controlled by the barriers of the elimination step leading to the 2,3-trans aziridine, whereas it is decided in the addition step in the case of semistabilized ylides. The importance of steric and electronic factors in diastereoselective addition (2 and 5) and elimination (5) transition states was established. Comparison of results obtained with the gas-phase optimized geometries and with the fully optimized solvent-phase geometries reveals that the inclusion of solvent effects does not bring about any dramatic changes in the reaction profiles for all three kinds of ylides. In particular, diastereoselectivity for both kinds of ylides was found to be nearly the same in both these approaches.