Study of Adsorption/Desorption Effect of 2-Mercaptobenzothiazole as Sweet Corrosion Inhibitor on API-5L X60 Steel

Protection of Metals and Physical Chemistry of Surfaces - In this study, the inhibitive performance of 2-mercaptobenzothiazole (2MBT) and 2-aminobenzothiazole (2ABT) were investigated on API-5L X60...     

Generalized quasi-cyclic codes: structural properties and code construction

Generalized quasi-cyclic (GQC) codes are defined by generator matrices comprised of circulant matrices of lengths not necessarily identical. A decomposition of these codes is given by using the Chinese reminder theorem. The focus is to characterize ρ-generator GQC codes in details. A good lower bound on the minimum distance of such a code in terms of the minimum distance of the constituent codes is given. Construction methods are given and a set of GQC codes is provided that from minimum distance perspective are optimal codes among the known linear codes having the same length and dimension.     

The sequence of precipitation in the Al-Mg-Si-Cu alloy AA6111

The preciptation behavior of the aluminum alloy AA6111 in the advanced stages of aging has been studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results have demonstrated the formation of various precipitate types and morphologies of quaternaryQ phase andβ (Mg₂Si) families at the peak-aged condition and during overaging at different temperatures. The work has clarified the sequence ofQ phase formation and showed evidence for a new morphology of this phase. The sequence of precipitation in AA6111 is elaborated in light of the new findings.     

A Sliding Mode Controller Based on Robust Model Reference Adaptive Proportional-integral Control for Stand-alone Three-phase Inverter

This paper proposes a sliding mode controller based on robust model reference adaptive proportional-integral (RMRA-PI) control for a stand-alone voltage source inverter (SA-VSI). The proposed controller has two control loops where the coefficients of PI controller are regulated by the adaptive sliding law. This method is used to regulate the output voltage of the inverter under different load conditions and uncertainty, and adapts the output to the reference model to reduce the total harmonic distortion (THD). In this paper, the stability of the proposed controller is proven by using Lyapunov’s theory and Barbalet’s lemma. The proposed controller performs well in voltage regulation such as low THD under sudden load change and uncertainty. Also, the results of the proposed controller are compared with PI controller to show the effectiveness of the presented control system.     

Enhanced Heat Transfer Properties of Magnetite Nanofluids due to Neel and Brownian Relaxation Mechanisms

Fe₃O₄ nanoparticles were prepared through solvo-thermal method for further heat transfer applications. TEM, XRD, TGA, and VSM were applied to characterize the obtained nanoparticles. XRD pattern confirmed that nanoparticles were composed of 6-nm crystallites; however, TEM images showed the formation of ca. 75-nm highly dispersed magnetite clusters, made up of about 6-nm nanoparticles. Since, VSM analysis confirmed the superparamagnetic characteristics of Fe₃O₄ nanoclusters, heat transfer properties of the resulting nanofluids were studied to investigate the influence of the magnetic field on the behavior of the magnetite-based nanofluids. The findings indicated that the convective heat transfer coefficient increased up to 48% and 15%, respectively, for nanofluids containing 0.005 wt% magnetite particles dispersed in water and EG, when the frequency of the alternating magnetic field was changed from 50 Hz to 1 MHz. According to the results, compared to the water-based nanofluids, at higher field amplitudes, the h enhancements of EG-based ones were more pronounced, for instance, at H₀ = 36,000 A/m, the h measurements are augmented by about 74% and 109%, respectively, compared to the water and EG as the base fluids. These findings could be explained by the use of specific lost powers of the nanofluids in the exposure of an external alternating magnetic field.     

Developing economic order quantity model for non-instantaneous deteriorating items in vendor-managed inventory (VMI) system

This paper develops an economic order quantity model for non-instantaneous deteriorating items with and without shortages to investigate the performance of the vendor-managed inventory (VMI) system. This model is developed for a two-level supply chain consisting of a single supplier and single retailer with a single non-instantaneous deteriorating item. A numerical example and sensitivity analysis are provided to illustrate how increasing or reducing the related parameters change the optimal values of the decision variables of the two proposed models. The results show that VMI works better and charges lower cost in all conditions.     

3D Printing-Assisted Self-Assembly to Bio-Inspired Bouligand Nanostructures

Architected materials with nano/microscale orders can provide superior mechanical properties; however, reproducing such levels of ordering in complex structures has remained challenging. Inspired by Bouligand structures in nature, here, 3D printing of complex geometries with guided long-order radially twisted chiral hierarchy, using cellulose nanocrystals (CNC)-based inks is presented. Detailed rheological measurements, in situ flow analysis, polarized optical microscopy (POM), and director field analysis are employed to evaluate the chiral assembly over the printing process. It is demonstrated that shear flow forces inside the 3D printer's nozzle orient individual CNC particles forming a pseudo-nematic phase that relaxes to uniformly aligned concentric chiral nematic structures after the flow cessation. Acrylamide, a photo-curable monomer, is incorporated to arrest the concentric chiral arrangements within the printed filaments. The time series POM snapshots show that adding the photo-curable monomer at the optimized concentrations does not interfere with chiral self-assemblies and instead increases the chiral relaxation rate. Due to the liquid-like nature of the as-printed inks, optimized Carbopol microgels are used to support printed filaments before photo-polymerization. By paving the path towards developing bio-inspired materials with nanoscale hierarchies in larger-scale printed constructs, this biomimetic approach expands 3D printing materials beyond what has been realized so far.     

The preparation of surfactant-free highly dispersed ethylene glycol-based aluminum nitride-carbon nanofluids for heat transfer application

In the present study, aluminum nitride-carbon (AlN-C) nanocomposites are synthesized through a green, facile and inexpensive mechanochemical route. Well-dispersed nanofluids are prepared by milling of nanocomposite in ethylene glycol (EG) without using any surfactants/ dispersants. The resulting nanofluids have an excellent stability with no obvious sedimentation for at least three months. The results confirm the in-situ polymerization of EG on AlN surface and the formation of hyperbranched glycerol upon milling which in turn stabilizes the particles through a steric effect. The working nanofluids with very low loadings of up to 0.22 vol% of powder exhibit an enhanced heat transfer coefficient (h) of about 24% compared to that of the base fluid in a laminar flow regime (Re = 160). Brownian motion and boundary layer thinning are known as the main mechanisms, causing for this enhancement.     

A novel method in audio message encryption based on a mixture of chaos function

Rapid growth of digital data and their security concerns increases the significance of enhancing advanced encryption techniques. Encryption is the backbone of secure communication in networks and the physical process of scrambling and permuting data in order to make them impossible to understand for unauthorized users. This paper proposes a novel audio signal encryption method, based on a mixture of three chaos functions. Due to the reversibility of the chaos functions, the decryption process is the inverse of the encryption process. This method was applied to audio signals with various sizes and the encoded messages were compared to the original ones. Simulation results and theoretical analyses show that the proposed approach offers a significant gain in terms of robustness and computational complexity.