Flow of second-order fluid in a curved duct with square cross-section

This paper investigates the inertial and creeping flow of a second-order fluid in a curved duct with a square cross-section. Numerical modeling is employed to analyze fluid flow, and the governing equations are discretized using the finite difference method on a staggered mesh. The marker-and-cell method is employed to allocate the parameters on the staggered mesh, and static pressure is calculated using the artificial compressibility approach. The effect of centrifugal force due to the curvature of the duct and the opposing effects of the first and second normal stress difference on the flow field are investigated. In addition, the order-of-magnitude technique is used to derive the force balance relations for the core region of flow. Based on these relations, the performance mechanism of centrifugal force and normal stress differences on the generation of secondary flows is considered. We also present an analytical relation for the axial velocity profile and flow resistance ratio of creeping flow. For this kind of flow, previous studies have investigated the effect of the first normal stress difference on the transition from one pair to two pairs of vortices while we show that the negative second normal stress difference has the opposite effect on this transition and can stabilize the flow.     

Fast Fourier transformation with continuous cyclic voltammetry at an Au microelectrode for the determination of morphine in a flow injection system

For the fast morphine monitoring in flow injection systems a highly sensitive method is being introduced in this work. The fast Fourier transformation with continuous cyclic voltammetry (FFTCV) in a flowing solution as a detection system was applied for the prompt morphine monitoring. Here it should be stressed that this technique is simple, precise, accurate, time saving and economical. This research includes the observation of the effects of various parameters on the sensitivity of the detection system. Eventually, it was concluded that the best condition was obtained within the pH value of 2, scan rate value of 40 V s⁻¹, accumulation potential of 400 mV and accumulation time of 0.6 s.In detail, the noteworthy advantages which this method illustrates in comparison with other reported methods are the following; no necessity for the oxygen removal from the test solution, a sub-nano molar detection limit and the fast determination of any such compound in a wide variety of chromatographic methods.The method proved to be linear over the concentration range of 285-305,300 pg mL⁻¹ (r = 0.999) with a detection limit and a quantitation limit of 95.5 and 285 pg mL⁻¹, respectively. Consequently, the method illustrates the requisite accuracy, sensitivity, precision and selectivity to assay morphine in its tablets and biological fluids.     

<Emphasis Type="Italic">Bis</Emphasis>(macrocyclic)dinickel(II) complexes containing phenylene bridges between 13-membered triaza dioxa macrocyclic ligands: <Emphasis Type="Italic">in-situ</Emphasis> one pot template synthesis,characterization and catalytic oxidation of cyclohexene

A new series of bis(macrocyclic)dinickel(II) complexes containing phenylene bridges between 13-membered triaza dioxa macrocyclic subunits have been synthesized via in-situ One Pot Template Condensation (IOPTC) of nitrogen–nitrogen linker, CH₂O and 1,8-diamino-3,6-dioxaoctane and nickel(II) in a 1:4:2:2 molar ratio. These complexes have been found to be effective catalysts for the selective oxidation of cyclohexene to 2-cyclohexene-1-one and 2-cyclohexene-2-ol with molecular oxygen as the oxidant.     

Rapid and Direct Spectrofluorometric and Chemometrics Methods for the Simultaneous Determination of Two Dansyl Derivatives

ABSTRACT

In this study the simultaneous molecular spectrofluorometric determination of ultratrace amounts of two dansyl chloride derivatives, DMNPS (5-(dimethylamino)naphthalene-1-sulfonyl 4-phenylsemicarbazide) and DMNPH (2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide), was accomplished using a genetic algorithm joint partial least squares (GA-PLS) technique that leads to very low detection limits (lower than 10^?6 mol/L) The linear dynamic ranges of the compounds were 1–6 µ mol L^?1 and 1–7 µ mol L^?1 for DMNPS and DMNPH, respectively. Quantification was performed using the emission wavelength range from 360 to 600 nm with an optimum calibration sample number of 25 and prediction sample number of 7. The technique was proved to be beneficial.     

Very fast and efficient synthesis of some novel substituted 2-arylbenzimidazoles in water using ZrOCl2·nH2O on montmorillonite K10 as catalyst

Abstract  A simple and eco-friendly protocol for the synthesis of some novel substituted 2-arylbenzimidazoles was developed. In this process, these compounds were prepared in water as the solvent using ZrOCl₂·nH₂O supported on montmorillonite K10 as an efficient water tolerating Lewis acid. The reaction was performed under mild conditions with good to excellent yields and remarkable chemoselectivity in the absence of any byproduct. Graphical Abstract        

Selective determination of penicillamine by on-line vapor-phase generation combined with Fourier transform infrared spectrometry

In this work, an on-line system with vapor-phase generation (VPG) and Fourier transform infrared (FTIR) spectrometric detection has been developed as a direct and highly selective analytical technique for the assay of penicillamine (PA). Potassium iodate solution was injected into a reactor, heated at 75 °C, containing PA. The CO generated under these conditions was transported by means of N₂ gas carrier stream to an infrared gas cell and corresponding FTIR spectra were acquired in a continuous mode. The maximum absorbance of CO band at 2170 cm⁻¹, corrected by a baseline established between 2240 and 2000 cm⁻¹ at a nominal resolution of 2 cm⁻¹, was selected as a measurement criterion. Initially, the effect of different chemical, physical and spectroscopic parameters, such as concentration and volume of oxidant, pH, equilibrium time, reactor temperature, reactor volume, N₂ carrier flow rate and number of scans on the analytical signals were evaluated by using a short path length (10 cm) IR gas cell. At optimum experimental conditions, the method provided a relatively broad linear dynamic range of 4-380 mg L⁻¹, a limit of detection of 0.5 mg L⁻¹, a sampling frequency of 15 h⁻¹ and a relative standard deviation (R.S.D.) of 1.6%. Further, the method was successfully applied to the determination of PA in pharmaceutical formulations and results compared well with those obtained by a reference colorimetric method.     

Extraction and characterization of native heteroxylans from delignified corn stover and aspen

Dimethylsulfoxide-solubilized polysaccharides from delignified corn stover and aspen were characterized. The biomass was delignified by two different techniques; a standard acid chlorite and a pulp and paper QPD technique comprising chelation (Q), peroxide (P), and acid-chlorite (D). Major polysaccharides in all fractions were diversely substituted xylan. Xylan acetylation was intact after chlorite delignification and, as expected, xylan from QPD-delignified fraction was de-acetylated by the alkaline peroxide step. The study of DMSO-extractable xylans from chlorite-delignified biomass revealed major differences in native acetylation patterns between corn stover and aspen xylan. Xylan from cell walls of corn stover contains 2-O- and 3-O-mono-acetylated xylan and [MeGlcA-α-(1 → 2)][3-OAc]-xylp units. In addition, aspen xylan also contains 2,3-di-O-acetylated xylose. 1,4-β-d-xylp residues substituted with MeGlcA at O-2 position are absent in chlorite-delignified aspen xylan. Sugar composition in accord with NMR-spectroscopic data indicated that corn stover xylan is arabinosylated while aspen xylan is not. We have shown that corn stover xylan has similar structure with xylans from other plants of Poales order. No evidence was found to indicate the presence of 1,4-β-d-[MeGlcA-α-(1 → 2)][Ara-α-(1 → 3)]-xylp in corn stover xylan fractions.