Hybrid silane-treated glass fabric/epoxy composites: tensile properties by micromechanical approach

The effect of interface modification on the interfacial adhesion and tensile properties of glass fabric/epoxy composites was evaluated in two directions of 0° and +45°. Herein, the glass fabric surface was modified by colloidal nanosilica particles and by a new blend of silane-coupling agents including both reactive and non-reactive silanes. Composite samples with high strength and toughness were obtained. A simultaneous improvement of tensile strength and toughness was observed for an epoxy composite reinforced with a hybrid-sized glass fabric including silane mixture and nanosilica. In fact, the incorporation of colloidal silica into the hybrid sizing dramatically modified the fiber surface texture and created mechanical interlocking between the glass fabric and resin. The results were analyzed by the rule of mixtures (ROM), Halpin–Tsai (H–T), and Chamis equations. It was found that the ROM equations provided approximate upper bound values for all investigated composite samples. In the samples containing nanosilica, the shear and elastic moduli values calculated by the Chamis and ROM equations showed good agreement with those obtained from experiments. However, in other samples, the values calculated by the H–T equation showed a better agreement with the experimental data. The analysis of fracture surfaces indicated that both silane and nanosilica particles had influence on the mode of failures at the interface.     

Three-dimensional numerical analysis of proton exchange membrane fuel cell

A full three-dimensional, non-isothermal computational fluid dynamics model of a proton exchange membrane fuel cell (PEMFC) with both the gas distribution flow channels and the membrane electrode assembly (MEA) has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region are developed and numerically solved using a finite volume based computational fluid dynamics technique. In this research some parameters such as Oxygen consumption and fuel cell performance according to the variation of porosity, thickness of gas diffusion layer, and the effect of the boundary conditions were investigated in more details. Numerical results shown that the higher values of gas diffusion layer porosity improve the mass transport within the cell, and this leads to reduce the mass transport loss. The gas diffusion layer thickness affects the fuel cell mass transport. A thinner gas diffusion layer increases the mass transport, and consequently the performance of the fuel cell. Furthermore, the study of boundary conditions effects showed that by insulating the bipolar surfaces, hydrogen and oxygen consumption at the anode and cathode sides increase; so that the fuel cell performance would be optimized. Finally the numerical results of proposed CFD model are compared with the available experimental data that represent good agreement.     

Prediction of the Physicochemical Properties of Spray-Dried Black Mulberry (Morus nigra) Juice using Artificial Neural Networks

An artificial neural network (ANN) was developed to predict quality changes of spray-dried black mulberry (Morus nigra) powder. In this study, the effects of inlet-air temperature (110, 130, and 150 °C), compressed air flow rate (400, 600, and 800 L/h), and concentration of different carrier types such as 6, 9, and 20 dextrose equivalent maltodextrins, and Arabic gum (8, 12, and 16%), were studied on five performance indices, namely: drying yield, bulk density, color change, total anthocyanin content, and antioxidant activity. A feed-forward multi-layered perceptron trained by back propagation algorithms for six independent variables was developed to predict the five outputs. The (6:14:5)-multi-layered perceptron, namely, a three-layered network having fourteen neurons in the hidden layer resulted in the best-suited model estimating the outputs at all drying runs. Predictive ability of ANN was compared using a separate dataset of 48 unseen experiments based on root mean square error, mean absolute error, and coefficient of determination for each output parameter. The optimum model was able to predict the five output parameters with coefficient of determination higher than 0.905. The results indicated that the experimental and ANN predicted data sets were in good agreement, so it is feasible to use ANN to investigate and predict the properties of black mulberry juice powder.     

Reliability investigation of InGaP/GaAs HBTs under current and temperature stress

The reliability of InGaP/GaAs N–p–n heterojunction bipolar transistors (HBTs) with different base metal contact systems (Au/Zn/Au, Ti/Au, Ti/Pt/Au and the novel Ti/ZrB₂/Au) under current and temperature stress is studied in this paper. We further report results of current stress on three p-GaAs doping impurities namely Zn, Be and C. The effect of O⁺/H⁺ and O⁺/He⁺ ions, used in the fabrication of planar self-aligned HBTs, is also investigated in the stability of device dc current gain. The instability phenomena typical of each factors and their effects on the HBT characteristics are reported.     

Floor tile glass-ceramic glaze for improvement of glaze surface properties

Simultaneous improvement of surface hardness and glossiness of floor tile glaze, without changing its firing temperature, was the main purpose of the present paper. Thus, various glazes in the system of CaO–MgO–SiO₂–Al₂O₃–ZrO₂ were prepared and their crystallization behaviors within a fast firing cycle were investigated. With increasing amounts of calcium and magnesium oxides to base glass, the optimum glass-ceramic glaze was obtained. The results showed that with increasing of CaO and MgO part weights in frit, the crystallization peak temperature was gradually decreased and the intensities of diopside and zirconium silicate were increased. The comparison of micro hardness for the optimum glass ceramic glaze derived in this work with a traditional one used in floor tile industries indicates an improvement of 21%. It was found that the glaze hardness not only depend on the amount and type of crystalline phases, but also on the residual glass composition. Furthermore, it was observed that the glaze micro hardness is only slightly affected by thermal expansion mismatch of body and glaze.     

On the modeling of a piezoelectrically actuated microsensor for simultaneous measurement of fluids viscosity and density

This paper deals with the analysis of a novel micro–electro-mechanical (MEM) fluid density and viscosity sensor. The proposed sensor consists of a micro-beam and a sensing micro-plate immersed in a fluid. In order to actuate longitudinally the micro-beam and micro-plate, the sensor includes a pair of piezoelectric layers bonded to the upper and lower surfaces of the micro-beam and subjected to an AC voltage. The coupled governing partial differential equations of longitudinal vibration of the micro-beam and fluid field have been derived. The obtained governing differential equations with time varying boundary conditions have been transformed to an enhanced form with homogenous boundary conditions. The enhanced equations have been discretized over the beam and fluid domains using a Galerkin based reduced order model. The dynamic response of the sensing plate for different piezoelectric actuation voltages and different exciting frequencies has been investigated. The effects of viscosity and density of fluids and geometrical parameters of the sensor on the response of the sensing plate have been studied.     

Catalytic Friedel–Crafts Acylation and Benzoylation of Aromatic Compounds Using Activated Hematite as a Novel Heterogeneous Catalyst

Catalytic Friedel–Crafts acylation of benzene and unactivated benzenes such as chlorobenzene and nitrobenzene have been successfully carried out using activated hematite (α‐Fe₂O₃) as a new, heterogeneous and green catalyst. Sonication of neat α‐Fe₂O₃ in a water bath under air atmosphere at room temperature followed by heating at 200 °C, dramatically increase the activity of α‐Fe₂O₃. With the catalyst loading as low as 5.0 mol%, a wide variety of benzene derivatives were easily converted into the corresponding acylated products in a clean and high‐yielding acylation reaction. It was found that the activated α‐Fe₂O₃ could be efficiently recycled and reused several times by simple washing with ethyl acetate, this cannot be attained with most of the traditional catalysts.     

Mechanical behavior of a FGM micro-beam subjected to a nonlinear electrostatic pressure

The present article studies the mechanical behavior of a FGM micro-beam subjected to a nonlinear electrostatic pressure. The FGM micro-beam is made of metal and ceramic and material properties vary continuously along the beam thickness according to a power-law. The nonlinear equation of dynamic motion of the FGM micro-beam is derived. By solving the equation of the static deflection, equilibrium positions of the micro-beam are determined and shown in the state control space. To study the stability of the fixed points, the trajectories of the beam motion are illustrated in the phase plane for different initial conditions. In order to find the response of the micro-beam to a step DC applied voltage, the nonlinear equation of motion is solved using a Galerkin based reduced order model. Moreover, time histories and phase portraits for different applied voltages are illustrated. The effect of different power law exponent on the stability of the micro-beam is studied.     

Removal,preconcentration and spectrophotometric determination of picric acid in water samples using modified magnetic iron oxide nanoparticles as an efficient adsorbent

A simple, fast and sensitive spectrophotometric method is developed for removal, preconcentration and determination of trace amounts of picric acid in water samples. Magnetic iron oxide nanoparticles (MIONPs) were synthesized and characterized by transmission electron microscopy (TEM). The magnetic nanoparticles were coated with cetyltrimethylammonium bromide (CTAB) and were applied for fast separation, preconcentration and spectrophotometric determination of picrate anion (the ion of picric acid) in an aqueous solution. The separation, preconcentration procedure is fast and will be completed in 2 min. Methanol is used for desorption of adsorbed picrate anion. The effects of important parameters such as pH of aqueous medium, CTAB dosage, adsorbent amount, temperature, electrolyte concentration, desorbing solvent and interfering ions on the adsorption of picrate anion were investigated. The method showed good linearity for the determination of picric acid in the concentration range of 0.02–1.00 μg mL^? 1 with a regression coefficient of 0.999. The limit of detection (LOD) is obtained to be 0.007 μg mL^? 1. The relative standard deviation (RSD) for 0.03 μg mL^? 1 and 0.8 μg mL^? 1 of picric acid were 3.98% and 1.97% respectively. Picric acid was separated, preconcentrated and determined successfully in spiked samples of Karoon River water.     

Full-Wave Analyses for a Multi-Layered Microstrip Patch Antenna

This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques.