Photoluminescence emission of nanoporous anodic aluminum oxide films prepared in phosphoric acid

The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure. Different excitation wavelengths are used to identify most of the details of the subband states. The films are produced under different anodizing conditions to optimize their emission in the visible range. Scanning electron microscopy investigations confirm pore formation in the produced layers. Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing.     

Tool point dynamics prediction by a three-component model utilizing distributed joint interfaces

In machine dynamics the tool point frequency response functions (FRFs) are employed to predict the stable machining conditions. In this paper, a combined analytical–experimental substructuring procedure is proposed to determine the tool point FRFs for different holder–tool configurations. The method employs the measured spindle-machine FRFs and analytical models of the tool and the holder to predict the tool tip FRFs for different sets of tools and holders mounted on the machine spindle without the need for repeated experimental measurements. Distributed joint interfaces are used to couple the three-component model of the machine. The machine tool tip FRFs with different tool–holder combinations are obtained assuming the clamping conditions at joint interfaces remain unchanged. An experimental case study is provided to demonstrate the applicability of the proposed method in dynamic modeling of machine tool.     

Design of stochastic assembly lines considering line balancing and part feeding with supermarkets

This article aims to address the assembly line balancing problem (ALBP) and supermarket location problem (SLP) as two long-term interrelated decision problems considering the stochastic nature of the task times and demands. These problems arise in real-world assembly lines during the strategic decision-making phase of configuring new assembly lines from both line balancing and part-feeding (PF) aspects. A hierarchical mathematical programming model is developed, in which the first level resolves the stochastic ALBP by minimizing the workstation numbers and the second level deals with the stochastic SLP while optimizing the PF shipment, inventory and installation costs. The results of case data from an automotive parts manufacturer and a set of standard test problems verified that the proposed model can optimize the configuration of assembly lines considering both ALBP and SLP performance measures. This study also validates the effect of the stochastic ALBP on the resulting SLP solutions.     

Assembly line balancing by a new multi-objective differential evolution algorithm based on TOPSIS

In this paper, we propose a multi-objective differential evolution algorithm (MODEA) to solve the multi-objective simple assembly line balancing problem type-2 (SALBP-2). This problem arises when in an existing assembly line, changes in the production process or demand structure take place and the organisation wants to produce the optimum number of items using a fixed number of workstations, which is associated with optimally assigning the tasks to an ordered sequence of stations such that the precedence relations are not violated and some measures of performance are optimised. The two considered objectives are: minimising the cycle time and the smoothness index of the assembly line. To that purpose, we develop a MODEA which unlike the existing algorithms deals with the considered objectives separately in selecting the next population members by proposing a new acceptance scheme based on the Pareto dominance concept and a new evaluation scheme based on TOPSIS. Also, by using the Taguchi method, we tune the effective factors of the developed algorithm. Then its efficiency is tested over available assembly line balancing benchmarks and compared to a new algorithm provided recently in the bi-objective SALBP-2 literature. Computational experiments indicate that the developed algorithm outperforms the existing meta-heuristic over a large group of benchmarks.     

Organic-inorganic nanocomposites of methylcellulose as a precursor of nanocrystalline ZnO layers

In this article, we present a sol-gel method to synthesize hybrid nanocomposite films of Zinc oxide (ZnO)/methylcellulose (MC) on microscope glass slides. The zinc/MC solutions were prepared, using different weight ratios of zinc acetate dihydrate to MC, in the presence of acetic acid. Fourier transform infrared spectroscopy (FTIR) investigation of the Zn sol/MC mixture showed coordinating interaction between zinc ions and MC. Thermal gravimetry analysis (TGA) results showed rapid decomposition of organic compounds in the composites at the temperature range of 200-450 degrees C. The UV-Vis spectroscopy was also utilized to identify ZnO nanoparticles in the MC matrix. The generation of ZnO nanoparticles in the MC matrix was then observed to proceed in situ through the annealing of the gel phase at 200 degrees C. Nanocrystalline films of ZnO/MC were subsequently obtained by the calcinations of ZnO/MC nanocomposites at 550 degrees C. The nanocomposite films were transparent in the visible light and showed a higher energy absorption edge compared with the bulk ZnO. Nanocrystallite sizes of ZnO particles were estimated from scanning electron microscopy (SEM) and the X-ray diffraction (XRD) investigations.     

Bone-like apatite layer formation on the new resin-modified glass-ionomer cement

In this study, the apatite-forming ability of the new resin-modified glass-ionomer cement was evaluated by soaking the cement in the simulated body fluid. The Fourier Transform Infrared (FTIR) spectrometer and X-Ray Diffraction (XRD) patterns of the soaked cement pointed to the creation of poorly crystalline carbonated apatite. It was found that the releasing of calcium ions from the soaked cement will dominate the undesirable effect of polyacrylic acid on apatite formation. Consequently, the ionic activity products (IAPs) of the apatite in the surrounding medium increased which accelerated apatite nucleation induced by the presence of the Si–OH and COOH groups. Accordingly, the apatite nuclei started to form via primary heterogeneous nucleation and continued by secondary nucleation. Therefore, nucleation and growth occurs as in the layer-by-layer mode so that finite numbers of monolayers are produced. Subsequent formation of film occurs by formation of discrete nuclei (layer-plus-island or SK growth).     

Synthesis of poly(ε-caprolactone)-based polyurethane semi-interpenetrating polymer networks as scaffolds for skin tissue regeneration

A new biodegradable poly(ε-caprolactone)-polyurethane semi-interpenetrating polymer network (PCL-PU-semi-IPNs) was synthesized through the reaction of hydroxyl-terminated four-armed star-shaped PCL, 1,4-diisocyanatobutane, and ethylenediamine. Afterwards, the three-dimensional (3D) porous structure of the polymer was prepared through particulate leaching and freeze-drying methods. The chemical structure of star-shaped block PCL-PU polymer was confirmed by ¹H NMR and IR spectroscopy. The morphology of the fabricated PCL-PU-semi IPN scaffolds was identified by scanning electron microscopy. Results indicated that lower polymer concentration can lead to formation of an isolated pore with a small size, while increasing polymer concentration increases the pore size. Fibroblast cells culturing on the scaffold suggests that the fabricated PU-based scaffold is biocompatible and can be considered as a suitable scaffold material for skin tissue engineering applications.     

In vitro bioactivity of novel cured ionomer cement based on iron oxide

The effect of adding Fe₂O₃ on the bioactivity of cured ionomer cement was examined in simulated body fluid (SBF). Although the polyacrylic acid and Fe₂O₃ are known as inhibitors for apatite formation, results clearly show that exposure of the cement to the SBF lead to the formation of rough layers of carbonated-apatite (Volmer–Weber growth). Interestingly, the addition of Fe₂O₃ to the cement structure decreases the possibility of acid–base reaction in ionomer cements due to the improved chemical durability of the glass. Therefore, more calcium ions were released from the cement at the initial stage of soaking which plays an important role in forming the surface apatite layer by heterogeneous nucleation via the OH⁻ groups on the cement surface.