Stress concentration around a hole in a radially inhomogeneous plate

The stress concentration factor around a circular hole in an infinite plate subjected to uniform biaxial tension and pure shear is considered. The plate is made of a functionally graded material where both Young’s modulus and Poisson’s ratio vary in the radial direction. For plane stress conditions, the governing differential equation for the stress function is derived and solved. A general form for the stress concentration factor in case of biaxial tension is presented. Using a Frobenius series solution, the stress concentration factor is calculated for pure shear case. The stress concentration factor for uniaxial tension is then obtained by superposition of these two modes. The effect of nonhomogeneous stiffness and varying Poisson’s ratio upon the stress concentration factors are analyzed. A reasonable approximation in the practical range of Young’s modulus is obtained for the stress concentration factor in pure shear loading.     

Enhancing the selectivity of an iron binding hydrogel

Iron overload is a critical clinical condition that can be controlled by diet and the use of iron-specific chelating agents. An effective oral formulation of an iron chelator should be nontoxic and selective toward iron while maintaining high affinity for iron. In this study, hydrogels containing 2,3 dihydroxybenzoic acid (2,3 DHBA), a portion of the metal chelating domain of enterobactin, were synthesized as a potential non-absorbed chelator for iron in the gastrointestinal tract. A series of polymeric chelators with various hydrogel:DHBA ratios were prepared. The iron-binding properties of the hydrogels were found to depend on the concentration of 2,3 DHBA groups on polymer chains. A 0.005 ratio of PAAm:DHBA was found to have an optimum affinity (log K = 27.01), selectivity, and high binding capacity for Fe(III).     

Higgs interchange and bound states of superheavy fermions

Hypothetical superheavy fourth-generation fermions with a very small coupling with the rest of the Standard Model can give rise to long enough lived bound states. The production and the detection of these bound states would be experimentally feasible at the LHC. Extending, in the present study, the analysis of other authors, a semirelativistic wave equation is solved using an accurate numerical method to determine the binding energies of these possible superheavy fermion-bound states. The interaction given by the Yukawa potential of the Higgs boson exchange is considered; the corresponding relativistic corrections are calculated by means of a model based on the covariance properties of the Hamiltonian. We study the effects given by the Coulomb force. Moreover, we calculate the contributions given by the Coulombic and confining terms of the strong interaction in the case of superheavy quark bound states. The results of the model are critically analysed.     

Morpholine Catalyzed One‐pot Multicomponent Synthesis of Compounds Containing Chromene Core in Water

A series of dihydropyrano[c]chromene was obtained via condensation of aldehyde, malononitrile and 4‐hydroxycoumarin in water catalyzed by morpholine, as a one‐pot reaction. The significance of our findings relates to reducing the use of organic solvents, potentially toxic and hazardous materials, as well as its simplicity, good yields, mild conditions, and lower costs.     

Pulsed Current Electrochemical Synthesis of Nickel Nanoclusters and Application as Catalyst for Hydrogen and Oxygen Revolution

The main objective of this research is to prepare nickel nanoparticles with more porous structure by the pulsed current electrochemical method. A nickel optimized nanopowder was synthesized by using nickel chloride (0.005 M) as precursor, silver nitrate as a nucleation agent (at 0.5% mole of nickel salt in the starting solution), polyvinyl pyrrolidone (PVP) as structure director (with PVP/Ni = 1.7 g/g), ammonia (2 M), and hydrazine as reduction agent (with Hydrazine/Ni = 16 g/g) by pulsed current of 58 mA cm⁻² with a frequency of 12 Hz. The morphology and particle size of each synthesized sample was studied by scanning electron microscopy (SEM). The obtained results showed that temperature has no considerable effect on the morphology and particle size of nickel nanopowder. The nickel nanopowder synthesized in optimum conditions has excellent uniform and a more porous structure including nanoclusters with a particle size of approximately 10–20 nm. The obtained results indicate that the pulsed current electrochemical method can be used as a confident and controllable method for the preparation of nickel nanoparticles. Optimized nickel nanoclusters were used as catalyst for hydrogen and oxygen revolutions. Cyclic Voltammetry results showed that the synthesized nanoclusters can facilitate hydrogen reduction and increase hydrogen and oxygen revolution rates.     

Optical components from a new vitrifying liquid crystal

New low molar mass liquid crystalline vitrifying materials have been synthesized and tested for application in optical films. The molecules were based on spiro compounds derived from pentaerythritol and mesogenic groups derived from cyanobiphenylyl moieties. The resulting materials showed glass transition temperatures as high as 85 degrees C and nematic to isotropic phase transition temperatures up to 222 degrees C. Crystallization from the melt was strongly suppressed. Well-aligned, solid, birefringent layers were obtained from the materials by spincoating. Uniaxially oriented layers with an optic axis tilted with respect to the substrate were obtained by spincoating the liquid crystals on pretilt amplification layers. When an anisotropic dye was incorporated in the liquid crystals, polarizers with a tilted absorption axis were obtained. In addition, the compounds were found to be suitable as hosts for photo-induced reorientation of photo-isomerizable dyes.     

Preparation and characterization of a composite PDMS membrane on CA support

Polydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C₃H₈, CO₂, CH₄, and H₂ in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C₃H₈, compared to the lighter ones, such as CO₂, CH₄, and H₂. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C₃H₈/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C₃H₈ over CO₂, CH₄, and H₂, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley & Sons, Ltd.     

C3H8 separation from CH4 and H2 using a synthesized PDMS membrane: Experimental and neural network modeling

A polydimethylsiloxane (PDMS) membrane was synthesized and permeation behavior of ternary gas mixtures including C₃H₈, CH₄ and H₂ through it was studied as a function of operating parameters. Mixed gas permeability values were also compared with pure gas data as well as literature to validate experimental results. The aim was to predict separation factor (SF) of C₃H₈ as a function of feed temperature, pressure, flow rate and C₃H₈ concentration with the aid of artificial neural network (ANN) technique. Multilayer perceptron (MLP), which is the most common type of feedforward neural network (FFNN), was used for prediction. The Levenberg–Marquardt training method was initially employed to train the net. Then, optimum numbers of hidden layers and nodes in each layer were determined. The selected structure (4:4:5:1) was finally used to predict SF of C₃H₈ for different inputs in the domain of training data. The modeling results showed that there is an excellent agreement between the experimental data and the predicted values, with mean absolute errors of less than 1%. Both modeling and experimental results confirmed that increasing feed temperature, feed pressure and C₃H₈ concentration in feed debilitates separation performance; however, SF increases with increasing feed flow rate. As a result, ANN can be recommended for the modeling of mixed gas transport through dense membranes such as PDMS.     

Quantitative Analysis of Sertraline in Human Serum by LC with Fluorescence Detection After Pre-Column Derivatization with 4-Chloro-7-nitrobenzofurazan

An accurate and sensitive reversed-phase high-performance liquid chromatographic method for analysis of sertraline in human serum, using 4-chloro-7-nitrobenzofurazan as pre-column derivatization agent, is described. The drug and an internal standard (azithromycin) were extracted from serum by use of a mixture of diethyl ether and chloroform, and subjected to pre-column derivatization with the reagent. Analysis of the resulting derivatives was performed on a 250 mm × 4.0 mm cyano column with 63:37 (v/v) methanol–sodium phosphate buffer (0.05 M, pH 3.7) containing 2 mL L^?1 triethylamine as mobile phase. Detector response was monitored at excitation and emission wavelengths of 470 and 537 nm, respectively. The calibration plot was linear over the concentration range 2–640 ng mL^?1. The lower limits of detection and quantification were 0.5 and 2 ng mL^?1, respectively. The method was validated for specificity, sensitivity, linearity, precision, accuracy, and stability and shown to be accurate (intra-day and inter-day accuracy from 0.3 to 4.2%) and precise (intra-day and inter-day precision from 2.4 to 15.5%). The drug was detected at concentrations as low as 2 ng mL^?1 in 0.5 mL serum and the method described can be easily applied to human single-dose pharmacokinetic studies of sertraline.     

Ligandless-dispersive liquid-liquid microextraction of trace amount of copper ions

In the present work, a new ligandless-dispersive liquid-liquid microextraction (LL-DLLME) method has been developed for preconcentration trace amounts of copper as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach 1,2-dicholorobenzene and ethanol were used as extraction and dispersive solvents, respectively. Some factors influencing on the extraction efficiency of copper and its subsequent determination were studied and optimized, such as the extraction and dispersive solvent type and volume, pH of sample solution, extraction time and salting out effect. Under the optimal conditions, the calibration curve was linear in the range of 1.0 ng mL⁻¹-0.6 μg mL⁻¹ of copper with R² = 0.9985. Detection limit was 0.5 ng mL⁻¹ in original solution (3S_b/m) and the relative standard deviation for seven replicate determination of 0.2 μg mL⁻¹ copper was ±1.4%. The proposed method has been applied for determination of copper in standard and water samples with satisfactory results.