Optimal design of laser solid freeform fabrication system and real-time prediction of melt pool geometry using intelligent evolutionary algorithms

With the rapid growth of laser applications and the introduction of high efficiency lasers (e.g. fiber lasers), laser material processing has gained increasing importance in a variety of industries. Among the applications of laser technology, laser cladding has received significant attention due to its high potential for material processing such as metallic coating, high value component repair, prototyping, and even low-volume manufacturing. In this paper, two optimization methods have been applied to obtain optimal operating parameters of Laser Solid Freeform Fabrication Process (LSFF) as a real world engineering problem. First, Particle Swarm Optimization (PSO) algorithm was implemented for real-time prediction of melt pool geometry. Then, a hybrid evolutionary algorithm called Self-organizing Pareto based Evolutionary Algorithm (SOPEA) was proposed to find the optimal process parameters. For further assurance on the performance of the proposed optimization technique, it was compared to some well-known vector optimization algorithms such as Non-dominated Sorting Genetic Algorithm (NSGA-II) and Strength Pareto Evolutionary Algorithm (SPEA 2). Thereafter, it was applied for simultaneous optimization of clad height and melt pool depth in LSFF process. Since there is no exact mathematical model for the clad height (deposited layer thickness) and the melt pool depth, the authors developed two Adaptive Neuro-Fuzzy Inference Systems (ANFIS) to estimate these two process parameters. Optimization procedure being done, the archived non-dominated solutions were surveyed to find the appropriate ranges of process parameters with acceptable dilutions. Finally, the selected optimal ranges were used to find a case with the minimum rapid prototyping time. The results indicate the acceptable potential of evolutionary strategies for controlling and optimization of LSFF process as a complicated engineering problem.     

Performance properties of microcrystalline cellulose as a reinforcing agent in wood plastic composites

Polypropylene (PP)/microcrystalline cellulose (MCC)/wood flour composites were prepared containing polypropylene-graft-maleic anhydride (PP-g-MA) as compatibilizer. The mechanical, morphological and thermal properties were investigated. The weight ratio of the cellulosic materials to polymer matrix was 40:60 (w:w). The obtained results showed that tensile, flexural and impact strengths of the composites were significantly enhanced with addition of MCC, as compared with pure PP and composites without MCC. The effect of MCC on impact was minimal compared to the effects of PP-g-MA content. Scanning electron microscopy has shown that the composite, with compatibilizer, promotes better fiber–matrix interaction. In all cases, the degradation temperatures shifted to higher values after addition of PP-g-MA. The maximum improvement on the thermal stability of the composites was achieved when 5% PP-g-MA was used. However, the increase in MCC content substantially reduced the thermal stability. This work showed that MCC along with wood flour could be effectively used as reinforcing agent in thermoplastic matrix.     

Poly(glycerol sebacate) nanoparticles for ocular delivery of sunitinib: physicochemical,cytotoxic and allergic studies

Poly(glycerol sebacate) (PGS) is a new biodegradable polymer with good biocompatibility used in many fields of biomedicine and drug delivery. Sunitinib‐loaded PGS/gelatine nanoparticles were prepared by the de‐solvation method for retinal delivery and treatment of diabetic retinopathy. The nanoparticles were characterised by Fourier‐transform infrared and differential scanning calorimetry. The effects of different formulation variables including drug‐to‐carrier ratio, gelatine‐to‐PGS ratio, and glycerine‐to‐sebacate ratio were assessed on the encapsulation efficiency (EE%), particle size, release efficiency (RE), and zeta potential of the nanoparticles. The in vitro cytotoxicity of PGS/gelatine nanoparticles was studied on L929 cells. Draize test on rabbit eyes was also done to investigate the possible allergic reactions caused by the polymer. Glycerine/sebacic acid was the most effective parameter on the EE and RE. Gelatine‐to‐PGS ratio had the most considerable effect on the particle size while the RE was more affected by the glycerine/sebacic acid ratio. The optimised formulation (S₁ G_0.7 D_21.2) exhibited a particle size of 282 nm, 34.6% EE, zeta potential of −8.9 mV, and RE% of about 27.3% for drug over 228 h. The 3‐(4,5‐dimethylthuazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay indicated PGS/gelatine nanoparticles were not cytotoxic and sunitinib‐loaded nanoparticles were not toxic at concentrations <36 nM.Inspec keywords: polymers, differential scanning calorimetry, toxicology, drug delivery systems, solvation, eye, encapsulation, particle size, drugs, biodegradable materials, nanofabrication, nanomedicine, nanoparticles, gelatin, Fourier transform infrared spectraOther keywords: gelatine‐to‐PGS ratio, glycerine‐to‐sebacate ratio, particle size, zeta potential, sunitinib‐loaded nanoparticles, biodegradable polymer, retinal delivery, differential scanning calorimetry, drug‐to‐carrier ratio, allergic reactions, physicochemistry, cytotoxicity, poly(glycerol sebacate) nanoparticles, sunitinib ocular delivery, drug delivery, sunitinib‐loaded PGS‐gelatine nanoparticles, Fourier‐transform, in vitro cytotoxicity, biocompatibility, Draize test, rabbit eyes, 3‐(4,5‐dimethylthuazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay     

Inhibitory effect of magnetic iron‐oxide nanoparticles on the pattern of expression of lanosterol 14α ‐demethylase (ERG11) in fluconazole‐resistant colonising isolate of Candida albicans

Fluconazole‐resistant Candida albicans is a big scary reality. The authors assessed the antifungal effects of magnetic iron‐oxide nanoparticles on fluconazole‐resistant colonising isolate of C. albicans and determined the expression of ERG11 gene, protein sequence similarity and ergosterol content. C. albicans isolates were characterised and fluconazole resistance is recognised using World Health Organization''s WHONET software. Susceptibility testing of magnetic iron‐oxide nanoparticles against fluconazole‐resistant colonising isolate of C. albicans was performed according to Clinical and Laboratory Standards Institute guidelines. The expression patterns of ERG11 and protein sequence similarity were investigated. Ergosterol quantification has been used to gauge the antifungal activity of magnetic iron‐oxide nanoparticles. The findings indicated that 93% of C. albicans isolates were resistant to fluconazole. Magnetic iron‐oxide nanoparticles were presented activity against fluconazole‐resistant colonising isolate of C. albicans with minimum inhibitory concentration at 250–500 µg/ml. The expression level of ERG11 gene was downregulated in fluconazole‐resistant colonising isolate of C. albicans. The results revealed no differences in fluconazole‐resistant colonising isolate of C. albicans by comparison with ERG11 reference sequences. Moreover, significant reduction was noted in ergosterol content. The findings shed a novel light on the application of magnetic iron‐oxide nanoparticles in fighting against resistant C. albicans.Inspec keywords: microorganisms, biochemistry, molecular biophysics, antibacterial activity, iron compounds, proteins, cellular biophysics, nanoparticles, drugs, geneticsOther keywords: albicans isolates, magnetic iron‐oxide nanoparticles, fluconazole‐resistant colonising isolate, fluconazole resistance, ERG11, candida albicans, protein sequence similarity, ergosterol content, WHONET, ergosterol quantification, susceptibility testing, antifungal activity, gene expression     

Characterization of metal hydrides using pneumato-chemical impedance spectroscopy

Pneumato-chemical impedance spectroscopy (PIS) is a tool derived from electrochemical impedance spectroscopy (EIS). PIS can be used to analyze the kinetics of various solid-gas reactions, such as the hydriding kinetics of metals in the presence of hysteresis. Pneumato-chemical impedance diagrams are obtained from simple gas transfer experiments, using non-harmonic pressure perturbations. In single-phase domains, the global sorption mechanism consists of mainly two steps, a surface chemisorption step and a bulk hydrogen transport step, controlled by diffusion. In two-phase domains, an additional phase transformation step must be considered. Model impedances are obtained by interconnecting microscopic impedances associated with each reaction step. By fitting model impedances to the experimental ones, microscopic rate parameters such as the surface dissociation resistance, the bulk hydrogen diffusion coefficient and the phase transformation resistance can be obtained. Different results obtained on palladium, palladium–silver and LaNi₅ samples (foils and powder) are presented to illustrate the potentialities of this spectroscopy.     

Embedded benzocyclobutene in silicon: An integrated fabrication process for electrical and thermal isolation in MEMS

This paper reports a novel fabrication process to develop planarized isolated islands of benzocyclobutene (BCB) polymer embedded in a silicon substrate. Embedded BCB in silicon (EBiS) can be used as an alternative to silicon dioxide in fabrication of electrostatic micromotors, microgenerators, and other microelectromechanical devices. EBiS takes advantage of the low dielectric constant and thermal conductivity of BCB polymers to develop electrical and thermal isolation integrated in silicon. The process involves conventional microfabrication techniques such as photolithography, deep reactive ion etching, and chemical mechanical planarization (CMP). We have characterized CMP of BCB polymers in detail since CMP is a key step in EBiS process. Atomic force microscopy (AFM) and elipsometry of blanket BCB films before and after CMP show that higher polishing down force pressure and speed lead to higher removal rate at the expense of higher surface roughness, non-uniformity, and scratch density. This is expected since BCB is a softer material compared to inorganic films such as silicon dioxide. We have observed that as the cure temperature of BCB increases beyond 200 °C, the CMP removal rate decreases drastically. The results from optical microscopy, scanning electron microscopy, and optical profilometry show excellent planarized surfaces on the EBiS islands. An average step height reduction of more than 95% was achieved after two BCB deposition and three CMP steps.     

Predicting the stages of smoking acquisition in the male students of Shiraz's high schools, 2003.

A staged model of smoking adoption has been widely applied in studies of adolescent smoking. This paper examined the effects of socioenvironmental and personal factors on three stages of the smoking continuum among a sample of 10th-grade male students, ages 14-19 years, at 20 high schools in Shiraz city. This paper is the first step of a longitudinal study related to adolescents smoking and predictors of transition in the stages. A self-administered questionnaire was distributed to 1,132 10th-grade students from a possible population of 14,000 students. Multivariate discriminant function analysis was used to analyze the data. Overall 19.4% of students had smoked; 80.6%, 16.9%, and 2.5% had never smoked, had experimented, and had regularly smoked, respectively. The discriminant function analysis indicated that attitude toward smoking, use of alcohol, use of illicit drugs, smoking behavior of best friends, and self-esteem were related to more intense smoking behaviors. Finally, these variables permitted the correct classification of 70.3% of students into the stages of smoking acquisition. This finding has important public health significance, but further research is required to determine if the association is causal.     

Network model for the viscoelastic behavior of polymer nanocomposites

A theoretical network model reproducing some significant features of the viscoelastic behavior of unentangled polymer melts reinforced with well dispersed non-agglomerated nanoparticles is presented. Nanocomposites with low filler volume fraction (∼10%) and strong polymer-filler interactions are considered. The model is calibrated based on results obtained from discrete simulations of the equilibrium molecular structure of the material. This analysis provides the statistics of the network of chains connecting fillers, of dangling strands having one end adsorbed onto fillers, and that of the population of loops surrounding each nanoparticle. The network kinetics depends on the attachment-detachment dynamics of grafted chains of various types and is modeled by using a set of convection equations for the probability distribution functions. The overall viscoelastic response depends strongly on the lifetime of the polymer-filler junctions. The largest reinforcement is observed at low strain rates and low frequency oscillations. A solid like behavior is predicted for systems in which the polymer molecules interact strongly with the nanoparticles, effect which is associated with the behavior of the network of bridging segments.