Ultrasound-assisted three-component synthesis of 3-(5-amino-1H-pyrazol-4-yl)-3-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-enyl)indolin-2-ones in water

Indium(III) chloride was found to be an efficient catalyst for the synthesis of 3-(5-amino-1H-pyrazol-4-yl)-3-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-enyl)indolin-2-ones by one-pot, three-component reaction of dimedone, 1H-pyrazol-5-amines and isatins in water under ultrasonic irradiation. The advantages of this method are the use of a readily available catalyst, easy workup, excellent yields, and the use of water as a solvent that is considered to be relatively environmentally benign.     

An estimator of the stable tail dependence function based on the empirical beta copula

The replacement of indicator functions by integrated beta kernels in the definition of the empirical tail dependence function is shown to produce a smoothed version of the latter estimator with the same asymptotic distribution but superior finite-sample performance. The link of the new estimator with the empirical beta copula enables a simple but effective resampling scheme.     

Numerical study of melting in an enclosure with discrete protruding heat sources

In order to explore the capability of a solid–liquid phase change material (PCM) for cooling electronic or heat storage applications, melting of a PCM in a vertical rectangular enclosure was studied. Three protruding generating heat sources are attached on one of the vertical walls of the enclosure, and generating heat at a constant and uniform volumetric rate. The horizontal walls are adiabatic. The power generated in heat sources is dissipated in PCM (n-eicosane with the melting temperature, T_m = 36 °C) that filled the rectangular enclosure. The advantage of using PCM is that it is able to absorb high amount of heat generated by heat sources due to its relatively high energy density. To investigate the thermal behaviour and thermal performance of the proposed system, a mathematical model based on the mass, momentum and energy conservation equations was developed. The governing equations are next discretised using a control volume approach in a staggered mesh and a pressure correction equation method is employed for the pressure–velocity coupling. The PCM energy equation is solved using the enthalpy method. The solid regions (wall and heat sources) are treated as fluid regions with infinite viscosity and the thermal coupling between solid and fluid regions is taken into account using the harmonic mean of the thermal conductivity method. The dimensionless independent parameters that govern the thermal behaviour of the system were next identified. After validating the proposed mathematical model against experimental data, a numerical investigation was next conducted in order to examine the thermal behaviour of the system by analyzing the flow structure and the heat transfer during the melting process, for a given values of governing parameters.     

The operator dose assessment of landmine detection systems using the neutron backscattering method

Personal safety issue is one of the major limitations in landmine detection by nuclear techniques. In this paper, the dose rate received by the operator of different hand-held landmine detection systems using the neutron backscattering method was investigated. Monte Carlo method was used to simulate a computational model of the body, instruments with different shielding configurations and soil with various moisture contents. The effective dose received by the different organs of the operator has been estimated by using two different approximation methods including average equivalent dose and dose equivalent assessment. The results obtained by these two methods were compared. The common results showed that the operator dose rate depends on the facility shielding, soil moisture level, and source-to-operator distance. Also, although the absorbed dose received by most organs generally decreases as a function of source to operator distance, for some organs such as kidneys and lungs it firstly increases when source-to-operator distance increases up to 0.7–1.2 m and after that the absorbed dose decreases. Furthermore, the results showed that the effective dose received by the operator has its maximum value when the source to operator distance is 0.60 m.     

Improvement in corrosion resistance of micro arc oxidation coating formed on AZ91D magnesium alloy via applying a nano-crystalline sol–gel layer

Although magnesium is used in many industries, it is reactive and requires protection against aggressive environments. In this study, oxide coating was formed on AZ91D magnesium alloy using micro-arc oxidation (MAO) process in an alkaline electrolyte. Then, in order to seal the pores in the oxide film, a sol–gel layer was applied to the surface of the MAO coating by dipping. For investigation of heat treatment temperature of the sol–gel layer on the properties of the coatings, two different temperatures (150 and 350 °C) were chosen. Surface morphologies and compositions of the coatings were analyzed by Scanning Electron Microscope and X-ray Diffraction (XRD). Surface roughness of the coatings was also measured. The corrosion behavior of the coatings was evaluated with Electrochemical Impedance Spectroscopy and potentiodynamic polarization tests in 3.5 wt%NaCl solution. The porosity percent of the coatings was measured by potentiodynamic polarization tests results. It is found that the sol–gel layers successfully cover the pores of the MAO coatings. The results of the corrosion tests show that the sol–gel layers significantly increase the corrosion resistance of the substrate by reducing the percent of the porosity. The grain size measurements by XRD analysis shows that the grain size of the sol–gel layer heated in 350 °C is about 50 nm.     

Molecular-imprinted polymer extraction combined with dispersive liquid-liquid micro-extractionfor ultra-preconcentration of mononitrotoluene

Molecular-imprinted polymer (MIP) combined with dispersive liquid-liquid micro-extraction (DLLME) were developed for ultra-preconcentration and determination of mononitrotoluenes in wastewater samples using gas chromatography-flame ionization detector. MIP was synthesized by copolymerization of methacrylic acid-ethylene glycole dimethacrylate-2,2-azobisisobutyronitrile as the initiator that imprinted with 3-nitrotoluene as the template molecule. Effects of several factors, such as type and volume of eluent, adsorption, and desorption times of the analyte on the polymer, and breakthrough volume were investigated. Optimization of 3-nitrotoluene extraction from MIP was studied forward followed by DLLME. Preconcentration factor of MIP-DLLME method was about 2800 under the optimum conditions. The LOD of the proposed method was 0.02?μg/L and a linear dynamic range in the range of 0.04-20?μg/L was obtained. The performance of the present method was evaluated for extraction and determination of nitrotoluene compounds in wastewater samples in the range of microgram per liter and satisfactory results were achieved (RSD<13%).     

Dabsyl chloride derivatisation of melamine followed by high-performance liquid chromatography determination in water samples

A new and sensitive precolumn derivatisation with dabsyl chloride was developed for the analysis of melamine in water samples by high-performance liquid chromatography (HPLC) with visible detection. Derivatisation with dabsyl chloride leads to improving sensitivity and hydrophobicity of melamine. Under optimum conditions of derivatisation and microextraction, the method yielded a linear calibration curve ranging from 10 to 2000 µg L^?1 with a determination coefficient (R²) of 0.9952. Limit of detection (LOD) and limit of quantification (LOQ) were 2.0 and 6.0 µg L^?1, respectively. The relative standard deviation per cent (RSD%) for intraday and inter-day extraction and determination at 20 and 200 µg L^?1 levels of melamine was less than 8.2% (n = 6). Finally, the proposed method was successfully applied for the determination of melamine in different water samples and satisfactory results were obtained (relative recovery ≥91%).     

Catalytic activity of manganese(III)-oxazoline complexes in urea hydrogen peroxide epoxidation of olefins: The effect of axial ligands

The catalytic activity of two manganese(III)-oxazoline complexes [Mn(phox)₂(CH₃OH)₂]ClO₄ and Mn(phox)₃ (Hphox = 2-(2′-hydroxylphenyl)oxazoline), was studied in the epoxidation of various olefins. All of epoxidation reactions were carried out in (1:1) mixture of methanol:dichloromethane at room temperature using urea hydrogen peroxide (UHP) as oxidant and imidazole as co-catalyst. The epoxide yields clearly demonstrate the influence of steric and electronic properties of olefins, the catalysts and nitrogenous bases as axial ligand. [Mn(phox)₂(CH₃OH)₂]ClO₄ catalyst with low steric properties has higher catalytic activity than Mn(phox)₃. The highest epoxide yield (95%) was achieved for indene at the presence of [Mn(phox)₂(CH₃OH)₂]ClO₄ within 5 min. The proximal and distal interactions of strong π-donor axial ligands such as imidazole with the active intermediate are efficiently increased activity of the catalytic system.