Semi fractal three leaf clover‐shaped CPW antenna for triple band operation

This article presents a unique and compact coplanar waveguide (CPW) antenna that exhibits triband operation with circular polarization. The single antenna was designed to operate simultaneously in the following bands: WiMAX (3.3–3.6 GHz), wireless local area network (WLAN) (5.15–5.825 GHz), ITS (5.795–6.400 GHz), and ITU‐R (7.725–8.5 GHz). The realization of the triband antenna was achieved by using two semi fractal ring patches resembling the shape of a three leaf clover, and by introducing a pair of symmetrical L‐shaped slits in its ground plane. The antenna's physical parameters were investigated to fully understand their affect on the antenna's performance. The salient parameters obtained from this analysis enabled the optimization of the antenna's overall characteristics. The design concept was confirmed by fabricating the antenna prototype and measuring its characteristics. The proposed antenna has dimensions of 20 × 20 × 1 mm³. Measured results show the antenna exhibits circular polarization in WiMAX and ITU‐R bands, and linear polarization in the WLAN band. The antenna radiates omnidirectionally in the H‐plane, and approximately bidirectionally in the E‐plane. In addition, the antenna presents stable gain over the triband. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:413–418, 2015.     

A new analytical study of MHD stagnation-point flow in porous media with heat transfer

The similarity solution for the MHD Hiemenz flow against a flat plate with variable wall temperature in a porous medium gives a system of nonlinear partial differential equations. These equations are solved analytically by using a novel analytical method (DTM-Padé technique which is a combination of the differential transform method and the Padé approximation). This method is applied to give solutions of nonlinear differential equations with boundary conditions at infinity. Graphical results are presented to investigate influence of the Prandtl number, permeability parameter, Hartmann number and suction/blowing parameter on the velocity and temperature profiles.     

A modified directed search domain algorithm for multiobjective engineering and design optimization

Multiobjective optimization is one of the key challenges in engineering design process. Since the answer to such problem is not unique, a set of evenly distributed solutions is particularly important for a designer. The Directed Search Domain (DSD) method is a numerical optimization approach that has proven to be efficient enough to tackle such optimization problems. In this paper, we propose two modifications to the DSD approach which make the solution algorithm simpler for program implementation. These modifications are related to the control of the search domain and reformulation of the appropriate single objective optimization problem. As a result, the computational efficiency of the method is increased due to the lower number of objective function evaluations. The capabilities of the new approach are demonstrated on a set of test cases.     

Plastic shear buckling of unstiffened stocky plates

A number of moderate to stocky steel and aluminum plates, with various slenderness ratios and boundary conditions are numerically analyzed under the action of pure in-plane shear and the results are validated against available analytical methods. Numerical non-linear finite element analyses are performed to assess different theoretical approaches and to picture buckling behaviors of moderate stocky plates. It is observed that while thick stocky plates possess some post-yield capacity during the hardening stage prior to plastic buckling, moderately thick plates yield and buckle concurrently followed by softening due to sudden loss of stiffness. It is also concluded that changes in the modulus of elasticity and shear modulus should be considered in the analysis and that the secondary bending stresses induced by initial out-of-plane curvature can cause significant reduction in the post-yield capacity and ultimate resistance of stocky plates.     

Image compressed sensing recovery via nonconvex garrote regularization

Multimedia Tools and Applications - Sparsity inducing model is one of the most important components of image compressed sensing (CS) recovery methods. These models are built on the image prior...     

Poly(ε-caprolactone)/nano fluoridated hydroxyapatite scaffolds for bone tissue engineering: in vitro degradation and biocompatibility study

In this study, biodegradation and biocompatibility of novel poly(ε-caparolactone)/nano fluoridated hydroxyapatite (PCL–FHA) scaffolds were investigated. The FHA nanopowders were prepared via mechanical alloying method and had a chemical composition of Ca₁₀ (PO₄)₆OH_2–x F _x (where x values were selected equal to 0.5 and 2.0). In order to fabricate PCL–FHA scaffolds, 10, 20, 30 and 40 wt% of the FHA were added to the PCL. The PCL–FHA scaffolds were produced by the solvent casting/particulate leaching using sodium chloride particles (with diameters of 300–500 μm) as the porogen. The phase structure, microstructure and morphology of the scaffolds were evaluated using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Porosity of the scaffolds was measured using the Archimedes’ Principle. In vitro degradation of PCL–FHA scaffolds was studied by incubating the samples in phosphate buffered saline at 37°C and pH 7.4 for 30 days. Moreover, biocompatibility was evaluated by MTT assay after seeding and culture of osteoblast-like cells on the scaffolds. Results showed that the osteoblast-like cells attached to and proliferated on PCL–FHA and increasing the porosity of the scaffolds increased the cell viability. Also, degradation rate of scaffolds were increased with increasing the fluorine content in scaffolds composition.     

Impact of Artificial Compressibility on the Numerical Solution of Incompressible Nanofluid Flow

The numerical solution of compressible flows has become more prevalent than that of incompressible flows. With the help of the artificial compressibility approach, incompressible flows can be solved numerically using the same methods as compressible ones. The artificial compressibility scheme is thus widely used to numerically solve incompressible Navier-Stokes equations. Any numerical method highly depends on its accuracy and speed of convergence. Although the artificial compressibility approach is utilized in several numerical simulations, the effect of the compressibility factor on the accuracy of results and convergence speed has not been investigated for nanofluid flows in previous studies. Therefore, this paper assesses the effect of this factor on the convergence speed and accuracy of results for various types of thermo-flow. To improve the stability and convergence speed of time discretizations, the fifth-order Runge-Kutta method is applied. A computer program has been written in FORTRAN to solve the discretized equations in different Reynolds and Grashof numbers for various grids. The results demonstrate that the artificial compressibility factor has a noticeable effect on the accuracy and convergence rate of the simulation. The optimum artificial compressibility is found to be between 1 and 5. These findings can be utilized to enhance the performance of commercial numerical simulation tools, including ANSYS and COMSOL.     

A single-stage operational amplifier with enhanced transconductance and slew rate for switched-capacitor circuits

The DVB-T2 standard for digital terrestrial broadcasting supports the use of quadrature amplitude modulation constellations where the constellation points are rotated in the I–Q plane. This combined with a cyclic delay of the Q component provides improved performance in some fading channels. The complexity of the optimal demapping process for rotated constellations is however significantly higher than for non-rotated constellations. This makes the DVB-T2 demapper one of the most computationally complex parts of a receiver. In this article, we examine possible simplifications of the demapping process suitable for implementation on a general purpose computer containing a modern graphics processing unit (GPU). Furthermore, we measure the performance in terms of throughput, as well as accuracy, of the implemented algorithms. The implementations are designed to interface efficiently to a previously implemented real-time capable GPU-based low-density parity-check channel decoder.     

Growth and characterization of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La_5/8Sr_3/8MnO₃ (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was ?17.21 % for LSMO/MgO film followed by ?15.65 % for LSMO/Si and ?14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T_P) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T_C) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T_C such as 363 and 352 K are the high T_C that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature.     

Experiments on conical shell reducers under uniform external pressure

In previous studies, a proliferation of research work has been undertaken on the buckling behavior of shell structures particularly conical shells. Nonetheless, no experimental studies are found in the literature on the buckling of a full and real configured model of a slender shell reducer with two cylindrical end boundaries. To this end, buckling behavior of three conical shell reducers under uniform peripheral pressure was investigated and evaluated experimentally in this paper. In addition, relevant FE simulations as well as theoretical predictions were taken into account to compare buckling load and modes of deformation. Derived results were aimed at generalizing the data for conical reducers in full scale within the range of this study.