Flow past a square cylinder at low Reynolds numbers

Results are presented for the flow past a stationary square cylinder at zero incidence for Reynolds number, Re ? 150. A stabilized finite‐element formulation is employed to discretize the equations of incompressible fluid flow in two‐dimensions. For the first time, values of the laminar separation Reynolds number, Re_s, and separation angle, θ_s, at Re_s are predicted. Also, the variation of θ_s with Re is presented. It is found that the steady separation initiates at Re = 1.15. Contrary to the popular belief that separation originates at the rear sharp corners, it is found to originate from the base point, i.e. θ_s=180^° at Re = Re_s. For Re > 5, θ_s approaches the limit of 135 ^°. The length of the separation bubble increases approximately linearly with increasing Re. The drag coefficient varies as Re^?0.66. Flow characteristics at Re ? 40 are also presented for elliptical cylinders of aspect ratios 0.2, 0.5, 0.8 and 1 (circle) having the same characteristic dimension as the square and major axis oriented normal to the free‐stream. Compared with a circular cylinder, the flow separates at a much lower Re from a square cylinder leading to the formation of a bigger wake (larger bubble length and width). Consequently, at a given Re, the drag on a square cylinder is more than the drag of a circular cylinder. This suggests that a cylinder with square section is more bluff than the one with circular section. Among all the cylinder shapes studied, the square cylinder with sharp corners generates the largest amount of drag. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactions of nucleophiles with triarylpropenones and triarylbutenones

From a study of the reactions of nucleophiles with 1,2,3-triaryl-propenones and-butenones in a chemical ionization source it has been found that stronger nucleophiles, such as, MeO^?, EtO^? and MeS^?, attack the α,β-unsaturated system at the β-carbon (Michael addition) or the carbonyl carbon giving rise to tetrahedral adducts, while weaker nucleophiles, such as, Cl^? form the adduct ion by H-bonding with the β-hydrogen. The effect of substituents and source temperature supports the operation of these processes. The triaryl butenone did not give the adduct ion with MeO^? as deprotonation leads to a stable [M ? H]^? ion.     

Separation and preconcentration of metal ions and their estimation in vitamin, steel and milk samples using o-vanillin-immobilized silica gel

o-Vanillin-immobilized silica gel has been used for the adsorption and estimation of copper, cobalt, iron and zinc by both batch and column techniques. Metal ions were quantitatively retained on the column packed with immobilized silica gel in the pH range 4.0-6.0 for Cu, 5.0-6.0 for Co, 4.5-6.0 for Fe and 6.0-8.0 for Zn. The distribution coefficient D determined for each metal was as follows (ml g(-1)): Fe, 5.4x10(2); Cu, 4.9x10(2); Zn, 4.4x10(2); Co, 3.8x10(2). Methods have been developed to estimate zinc, copper and cobalt in milk, steel and vitamin samples, respectively.     

Zusammensetzung und Stabilität des Thallium(I)-Komplexes der β-Mercaptopropionsäure

Zusammenfassung Durch potentiometrische und konduktometrische Titrationen wird die genaue Zusammensetzung des Komplexes untersucht, der sich aus Thallium(I) und -Mercaptopropionsäure in wäßriger 0,1m-KNO₃-Lösung bildet. Es zeigt sich, daß Thallium nur einen einzigen Komplex bildet. Er ist farblos, hat die Molzusammensetzung 11 und liegt besonders im pH-Bereich 9,0–10,5 vor. Durch Anwendung der vonCalvin undMelchior erweiterten Meßmethode vonBjerrum wird für drei verschiedene Temperaturen der Wert der Komplexbildungskonstante bestimmt. Als Werte für logK ergaben sich bei 20° 2,775, bei 30° 2,850 und bei 40° 2,935. Die Werte der thermodynamischen Zustandsfunktionen berechnen sich für die Komplexbildung zu G=–3,95 kcal/Mol, H=–3,34 kcal/Mol und S=+2,01 cal/grad.

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The precise nature of the complex formation between Thallium(I) and -mercaptopropionic acid in aqueous 0.1M-KNO₃ has been investigated by potentiometric and conductometric titration techniques. It was found that Tl(I) forms only one, 11, colourless complex predominating at pH 9.0–10.5. The stability constant of the complex has been determined by applyingCalvin andMelchior's extention ofBjerrum's method at three different temperatures. The logK values were found to be 2.775, 2.850 and 2.935 at 20, 30 and 40° C respectively. The thermodynamic functions of complexation, G, H and S were also evaluated at 30° C and found to be –3.95 K-cal/mole, –3.34 K-cal/mole and +2.01 Cal/deg. respectively.

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Kinetics and mechanism of oxidation of hydrazinium ion with peroxomonophosphoric acid in acid perchlorate solutions and role of trace iodide ions

The reaction of peroxomonophosphoric acid and hydrazinium ion in acid perchlorate solutions occurs as per stoichiometry (i), and the rate law (ii) at large [N₂H₅ ⁺], where K′_d is the first acid dissociation constant of H₃PO₅ and k ₁ and k ₂ are rate constants found to be 2.6 × 10^?4 s^?1 and 5.0 × 10^?2 M^?1 s^?1, respectively, at 35°. The reaction is greatly catalyzed by iodide ions. The mechanism involves a redox cycle I^?/I₂ and the rate is independent of [N₂H₅ ⁺] in the presence of iodide ions. K′_d was found to be 0.55 M^?1 and independent of temperature.     

IR and Raman spectra,density functional computations of vibrational spectrum,molecular geometry,atomic charges,and some molecular properties of 3‐aminobenzonitrile molecule

Geometry, vibrational wavenumbers, and several thermodynamic parameters have been calculated using ab initio quantum chemical methods for the 3‐aminobenzonitrile molecule for the first time. The results were compared with experimental values. With the help of specific scaling procedures, the observed vibrational wavenumbers were analyzed and assigned to different normal modes of the molecule. In general, the error obtained was very low. Using potential energy distribution (PED), the contributions of the different modes to each wavenumber were determined. Other general conclusions were also deduced. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Effect of fluorine substitution on the OH-radical-induced electron-transfer reaction in aqueous solutions of fluorinated alkyl iodides

The transient optical absorption bands formed at λ_max=340 and 435 nm, on reaction of ^√OH radicals in aerated acidic aqueous solutions of 1,1,1-trifluoro-2-iodoethane at low and high solute concentration, have been assigned to monomer and dimer radical cations, respectively. The deprotonation of the solute radical cations is the rate-determining step for the decay of the dimer radical cations. The stability constant for the dimer radical cation is determined to be 50 dm³ mol⁻¹ at 25°C. The dimer radical cation is a strong one-electron oxidant. Quantum chemical calculations and experimental results confirm that fluorine reduces the electron density at iodine and the ^√OH-radical-induced oxidation of fluoroiodoalkanes becomes a difficult process compared to iodoalkanes.     

ON THE NATURE OF CHLOROPHYLL a IN AQUEOUS MICELLAR SYSTEMS

Abstract— Absorption and fluorescence spectra of chlorophyll a in aqueous micellar solutions were studied. Solutions in anionic micelles gave an absorption band at 740 nm, attributable to microcrystal- line chlorophyll a. Solutions in cationic and nonionic micelles do not show this band. The positions of the spectral bands in anionic micelles and the possible structure of microcrystalline form are discussed. A comparison is made of the behaviour of microcrystalline form in hydrocarbon solvents and in micellar solutions.     

Azulenes and related substances—XV : Azuleno[2,1-a]azulene (part 1): reaction of 3,6,7,8-tetrahydrodibenzopentalene with diazomethane; synthesis of 11H-indeno[2,1-a]azulene

In an attempt to synthesise azuleno[2,1-a]azulene (1), Cu⁺ ion-catalysed reaction of diazomethane with 3,6,7,8-tetrahydrodibenzopentalene (4) has been investigated. Addition occurred to only one of the aromatic rings to give chiefly 1,2-benzo-4,5-cycloheptatrieno-3,6,7,8-tetrahydropentalene (13/14). Dehydrogenation of 13/14 to 11H-indeno[2.1-a]azulene has been carried out.     

Uncatalyzed chemical oscillations in the aqueous acidic bromate oxidation of veratraldehyde

Oscillatory behavior in the uncatalyzed aqueous acidic bromate oxidation of 3,4-dimethoxybenzaldehyde (veratraldehyde) is reported. The generally used H₂SO₄ can be substituted by HNO₃, HClO₄, CCl₃ COOH and H₃PO₄ in this system. The length of the induction period is found to be dependent on the initial concentrations of the reagents and this effect is more prominent in the case of acidity. The precipitate accumulated in the reaction during oscillations has been identified. A plausible mechanism is also suggested. Experiments with allyl alcohol, a bromine scavenger, suggest that elemental bromine formed in the reaction has a role in the mechanism together with or besides bromide inons.

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3,4- () . H₂SO₄ HNO₃, HClO₄, CCl₃ COOH H₃PO₄ . . , , . . , , , , , .