Three-dimensional study of Ni aluminides in an AlSi12 alloy by means of light optical and synchrotron microtomography

The three-dimensional (3D) microstructure of an AlSi12Ni alloy in as-cast and in solution-treated conditions is characterized by light optical and synchrotron tomography. Eutectic Al–Si alloys containing 1 wt.% Ni in as-cast condition present networks of connected Si lamellae as well as complex 3D shapes of Ni-containing aluminides. The eutectic Si networks disintegrate during solution treatment in the binary Al–Si alloy while they remain connected in the Al–Si–Ni alloy. The contiguity between eutectic Si and Ni-containing aluminides is maintained, when the alloy is solution treated at 540 °C for 24 h. The sphericity of the aluminides is only slightly increased by the solution treatment. The reinforcing role of eutectic Si together with the Ni-containing aluminides is governed by a stable interconnectivity and contiguity of these rigid phases accumulating ～20 vol.%. The 3D data obtained by synchrotron tomography quantify connectivity, shape and volume fraction of eutectic Si and aluminides, whereas their contiguity is verified by light optical sectioning tomography.     

Cyclic Triaxial Tests on Asphalt Concrete as a Water Barrier for Embankment Dams

The seismic behavior of asphaltic concrete used in embankment dams subjected earthquake loads has been studied. In order to evaluate the dynamic behavior, an extensive series of monotonic and cyclic tests were carried out on triaxial specimens of asphalt concrete used in hydraulic structures. The MTS-dynamic equipment at the Norwegian Geotechnical Institute (NGI) was used for this purpose. Temperature and frequency effects on specimen behavior and on specimen degradation have been studied under the cyclic loads in both isotropic and anisotropic initial stress conditions. For investigation of the fatigue behavior, thousands of cyclic loads were imposed on some of the specimens. Moreover, to study any sign of material degradation due to the cyclic loading, the post-cyclic monotonic stress-strain curve was compared with the corresponding curve for specimens that were not first subjected to cyclic loading. Geotechnical parameters to be used in dynamic numerical analysis models are also presented.     

Numerical and experimental investigation on a new modified valve in a valve tray column

This paper reports experimental and computational fluid dynamics (CFD) modeling studies on the performance of three modified valves operating in a valve tray column. The original and modified valves including vnotched, warped and double-valve are tested experimentally. The experimental rig was a Perspex column having a single valve equipped with a fluctuating plate to measure the quality of gas distribution by using laser sensors. Two-stage nested designs were employed to show the repeatability and consistency of the measurements. In the CFD modeling, the volume of fluid (VOF) method was used to model the gas-liquid two-phase flow inside the column. A good agreement was observed between experimental data and the CFD predictions. The results showed that the double-valve layout provides a better gas distribution, smaller bubbles with greater interface area and lower pressure drop in comparison with the original and the two other modified valves.     

Electrospun core-shell nanofibers based on polyethylene oxide reinforced by multiwalled carbon nanotube and silicon dioxide nanofillers: A novel and effective solvent-free electrolyte for lithium ion batteries

Insertion of conductive fillers into solvent-free polymer electrolytes enhances electrochemical behavior of the electrolyte membranes leading to higher ionic conductivity, lower capacity fading, and so on. Although, the presence of the conductive fillers in the polymer matrixes increases the risk of electrical shorting, herein, polyethylene oxide (PEO)-based core-shell nanofibers were prepared via a simple electrospinning method. In the core-shell electrospun fibers, ethylene carbonate (EC) and lithium perchlorate (LiClO₄) were used as a plasticizer and as a lithium salt, respectively. The core component was enwrapped by the PEO/EC/LiClO₄ shell part incorporated with SiO₂ nanoparticles. Various properties of the fabricated membranes were evaluated by changing the ratio of multiwall carbon nanotubes (MWCNTs) in the core part of the nanofibers. The morphology and core-shell structure of the electrospun fibers were studied by FESEM and TEM images. According to FTIR and XRD results, addition of the EC plasticizer and the fillers into the as-spun fibers increased the fraction of free ions and the amorphous regions. From electrochemical impedance spectroscopy studies, the ionic conductivity enhanced by insertion of the plasticizer molecules and the filler particles into the core-shell structures. The highest ionic conductivities of 0.09 and 0.21 mS.cm⁻¹ were obtained for the free-filler and the filler-loaded nanofibrous membranes, respectively. The prepared mats obeyed the Arrhenius behavior ( R²~1 ). Dielectric studies confirmed the obtained data from the ionic conductivities. Furthermore, the capacity residual was enhanced from 69% to 85% by incorporation of the MWCNTs filler into the core component of the electrospun nanofibers. The presented results may facilitate development of versatile nanofibrous membranes embedded with the conductive fillers as solvent-free electrolytes applicable in lithium-ion batteries.     

AutoRWN: automatic construction and training of random weight networks using competitive swarm of agents

Neural Computing and Applications - Random Weight Networks have been extensively used in many applications in the last decade because it has many strong features such as fast learning and good...     

Thermopower Study of GaN-Based Materials for Next-Generation Thermoelectric Devices and Applications

III-nitride InGaN-based solar cells have gained importance because their band gap can potentially cover most of the solar spectrum, spanning 0.7 eV to 3.4 eV. However, to use these materials to harvest additional energy, other properties such as their thermoelectric properties should be exploited. In this work, the Seebeck coefficient and the electrical conductivity of three InGaN alloys with various indium concentrations and Gd-doped GaN (GaN:Gd) were measured, and the power factor was calculated. We report a Seebeck value of ∼209 μV/K for Gd-doped GaN.     

Ambiguity Resolution in Direction of Arrival Estimation with Linear Antenna Arrays Using Differential Geometry

Linear antenna arrays (LAs) can be used to accurately predict the direction of arrival (DOAs) of various targets of interest in a given area. However, under certain conditions, LA suffers from the problem of ambiguities among the angles of targets, which may result in misinterpretation of such targets. In order to cope up with such ambiguities, various techniques have been proposed. Unfortunately, none of them fully resolved such a problem because of rank deficiency and high computational cost. We aimed to resolve such a problem by proposing an algorithm using differential geometry. The proposed algorithm uses a specially designed doublet antenna array, which is made up of two individual linear arrays. Two angle observation models, ambiguous observation model (AOM) and estimated observation model (EOM), are derived for each individual array. The ambiguous set of angles is contained in the AOM, which is obtained from the corresponding array elements using differential geometry. The EOM for each array, on the other hand, contains estimated angles of all sources impinging signals on each array, as calculated by a direction-finding algorithm such as the genetic algorithm. The algorithm then contrasts the EOM of each array with its AOM, selecting the output of that array whose EOM has the minimum correlation with its corresponding AOM. In comparison to existing techniques, the proposed algorithm improves estimation accuracy and has greater precision in antenna aperture selection, resulting in improved resolution capabilities and the potential to be used more widely in practical scenarios. The simulation results using MATLAB authenticates the effectiveness of the proposed algorithm.     

Scattering from anisotropic plasma-coated PEMC cylinder buried beneath a slightly rough surface

A general theoretical formulation is done to calculate the field scattered by perfect electromagnetic conductor (PEMC) cylinder coated with anisotropic plasma material. It is buried below a slightly rough surface. Spectral plane wave representation of fields and small perturbation method are used to calculate multiple reflections between coated cylinder and rough surface. To validate the present formulation, scattered field from a PEMC cylinder coated with double negative (DNG) material is obtained from the present formulation. Scattering pattern of non coated PEC/PEMC cylinder or coated with isotropic material can also be obtained by the proper selection of physical parameters such as anisotropy, admittance of PEMC cylinder and permittivity of hosting medium. Analytical expressions of scattered field for a sinusoidal rough surface are given along with their physical interpretation to get a good insight. Effect of geometrical and physical parameters on scattering pattern is observed.