Effect of self-support friction stir welding on microstructure and microhardness of 6082-T6 aluminum alloy joint

In this paper, 5-mm-thick 6082-T6 aluminum alloy was joined by means of self-support friction stir welding (SSFSW). Here we report the grain structure and second phase particles in various regions including the welding nugget zone (WNZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ). In the upper part of the joint, microhardness in the TMAZ in proximity of the UWNZ was the highest (average 89.4 HV) due to the severe plastic deformation. The similar result was also found in the lower part of the SSFSW joint. The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Some coarse equiaxed grains which were produced in incomplete dynamic recrystallization process and dissolution of some precipitates have been observed in TMAZ. The HAZ retained the same grain structure as the base material, however, the grain size decreased with increasing distance of the weld centerline.     

Amide-Based Surfactants from Methyl Glucoside as Potential Emulsifiers

A series of amide-linked surfactants from methyl glucoside was synthesized and investigated for their potential use as water-in-oil emulsifiers. The synthetic concept combined a nucleophilic substitution approach with a Staudinger coupling of the intermediate azide. Both straight and Guerbet-type branched fatty acids ranging from C₈ to C₁₆ were applied. All surfactants exhibited very high Krafft temperatures, which were related to the amide linkage and exclusively formed the hexagonal H₁-phase. The Guerbet C₁₆ surfactant enabled the formation of a stable water-in-oil gel at ambient temperature, which, however, required heating to form the corresponding fluid emulsion.     

Modeling of corrosion reaction data in inhibited acid environment using regressions and artificial neural networks

This paper reports the results of mass loss measurements in the corrosion inhibition of mild steel in different concentrations of H₃PO₄ in the temperature range 30–60 °C using potassium iodide as an inhibitor. The present work is focused on determining the optimum mathematical equation and the ANN architecture in order to gain good prediction properties. Three mathematical equations and three ANN architectures are suggested. Computer aided program was used for developing these models. The results show that the polynomial mathematical equation and multi-layer perception are able to accurately predict the measured data with high correlation coefficients.     

Novel Universal Windowing Multicarrier Waveform for 5G Systems

Fifth Generation (5G) systems aim to improve flexibility, coexistence and diverse service in several aspects to achieve the emerging applications requirements. Windowing and filtering of the traditional multicarrier waveforms are now considered common sense when designing more flexible waveforms. This paper proposed a Universal Windowing Multi-Carrier (UWMC) waveform design platform that is flexible, providing more easily coexists with different pulse shapes, and reduces the Out of Band Emissions (OOBE), which is generated by the traditional multicarrier methods that used in the previous generations of the mobile technology. The novel proposed approach is different from other approaches that have been proposed, and it is based on applying a novel modulation approach for the Quadrature-Amplitude Modulation (64-QAM) which is considered very popular in mobile technology. This new approach is done by employing flexible pulse shaping windowing, by assigning windows to various bands. This leads to decreased side-lobes, which are going to reduce OOBE and boost the spectral efficiency by assigning them to edge subscribers only. The new subband windowing (UWMC) will also maintain comprehensively the non-orthogonality by a variety of windowing and make sure to keep window time the same for all subbands. In addition, this paper shows that the new approach made the Bit Error Rate (BER) equal to the conventional Windowed-Orthogonal Frequency Division Multiplexing (W-OFDM). This platform achieved great improvement for some other Key Performance Indicators (KPI), such as the Peak to Average Power Ratio (PAPR) compared with the conventional (W-OFDM) and the conventional Universal Filtered Multicarrier (UFMC) approaches. In particular, the proposed windowing scheme outperforms previous designs in terms of the Power Spectral Density (PSD) by 58% and the (BER) by 1.5 dB and reduces the Complementary Cumulative Distribution Function Cubic Metric (CCDF-CM) by 24%.     

The magnetization reversal and high temperature dielectric response in Y1−xHoxFe0.5Cr0.5O3

The structural, magnetic, and dielectric properties of the Y_1−xHo_xFe_0.5Cr_0.5O₃ (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho³⁺ doped YFe_0.5Cr_0.5O₃ samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho³⁺ and the canted Cr³⁺/Fe³⁺ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100 Hz to 10 MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.     

Influence of axial load on the lateral pile groups response in cohesionless and cohesive soil

The lateral response of single and group of piles under simultaneous vertical and lateral loads has been analyzed using a 3D finite element approach. The response in this assessment considered lateral pile displacement and lateral soil resistance and corresponding p-y curve. As a result, modified p-y curves for lateral single pile response were improved with respect to the influence of increasing axial load intensities. The improved plots can be used for lateral loaded pile design and to produce the group action design p-multiplier curves and equations. The effect of load combination on the lateral pile group response was performed on three pile group configurations (i.e., 2×1, 2×2 and 3×2) with four pile spacings (i.e., s = 2D, 4D, 6D and 8D). As a result, design curves were developed and applied on the actual case studies and similar expected cases for assessment of pile group behavior using improved p-multiplier. A design equation was derived from predicted design curves to be used in the evaluation of the lateral pile group action taking into account the effect of axial load intensities. It was found that the group interaction effect led to reduced lateral resistance for the pile in the group relative to that for the single pile in case of pure lateral load. While, in case of simultaneous combined loads, large axial load intensities (i.e., more than 6H, where H is lateral load values) will have an increase in p-multiplier by approximately 100% and will consequently contribute to greater group piles capacities.     

A method for the numerical integration of mechanical systems with unilateral constraints: study of impact in multibody systems

Study of mechanical systems with unilateral constraints is associated with forming two systems of equations, a system of differential equations and a system of algebraical equations. Differential equations are used to describe the motion until the moment of impact, i.e. until activation of unilateral constraints. Algebraic equations are used to describe the impact. During numerical integration, transition from one system to another occurs at the points of impact. Even in simple problems, forming algebraic equations represents a complex task.This paper presents a method, the so-called Reduction Method, which provides for the analysis of these systems without forming the algebraic equations. They are substituted by a new system which is easily derived from equations of motion. Compared to methods based on the classical impact theory, using Reduction Method,velocities after the impact are easily computed regardless of the degrees of freedom.     

Effect of temperature on the inhibition of the acid corrosion of steel by benzaldehyde thiosemicarbazone: Impedance measurements

An impedance study has been carried out of the corrosion of steel in sulphuric acid containing benzaldehyde thiosemicarbazone as an inhibitor, over the temperature range 25 – 60 °C. The impedance data indicate that the corrosion of steel is controlled by a charge transfer process at all the temperatures examined and in solutions containing various concentrations of the inhibitor. At a critical concentration of the inhibitor (5 × 10^-4 M) a high protection efficiency is maintained over the temperature range examined. This is thought to relate to a high surface coverage of a relatively compact adsorbed film, which resists desorption at elevated temperatures, unlike the behaviour evident at lower inhibitor concentrations.     

The asymptotic stochastic stability in large of the composite stochastic systems

The sufficient conditions of asymptotic stochastic stability in large of non-linear composite stochastic systems are established. In this case the objective is to analyze composite systems in their lower order subsystems and in terms of their interconnecting structure. Non-linear systems are considered, with random noise which obeys the law of large numbers. An example is given to illustrate the criteria.