Epoxy/alumoxane and epoxy/boehmite nanocomposites: cure behavior,thermal stability,hardness and fracture surface morphology

Functionalized nanostructures such as, boehmite, salicylate alumoxane (Sal-A) and p-hydroxybenzoate alumoxane (PHB-A), were studied in varying amounts with respect to curing behavior, thermal stability, hardness and fracture surface morphology of their corresponding epoxy-based nanocomposites, emphasizing on the dispersabilities of the nanostructures in the epoxy matrix and the potential mechanisms of the interactions between various species. TG–DTA, Vickers hardness test and SEM were used to characterize the composite specimens. Addition of nanostructures into the epoxy matrix accelerated the curing process. The experimental tests proved that Sal-A acted most effectively as a co-curing agent through the autocatalytic curing process of the epoxy resin and also produced the highest values of Vickers hardness in its corresponding nanocomposites. The presence of the nanostructures also lowered the heat of reaction in curing process with an exception of PHB-A containing nanocomposites. Thermal stability of the nanocomposites was improved due to existence of the functionalized nanostructures. Mechanisms are proposed for the possible interactions between various species, constructing the three types of nanocomposites, divided into positive and negative types. The functional groups on the surfaces of the nanostructures not only facilitated chemical interactions with the polymer matrix but also improved their dispersion in the epoxy matrix. Dispersability tendency of the nanostructures in the epoxy matrix was of the order: boehmite < PHB-A < Sal-A. Extent of agglomeration of the nanostructures in the epoxy matrix depended on the types of the functional groups on their surfaces and consequently, their interactions with the epoxy matrix and hardener.     

Thermal response of a packed bed of spheres containing a phase-change material

A computational model of the transient thermal response of a packed bed of spheres containing a phase-change material (PCM) is presented. A one-dimensional separate phases formulation is used to develop a numerical analysis of the dynamic response of the bed which is subject to the flow of a heat transfer fluid, for arbitrary initial conditions and inlet fluid temperature temporal variations. Phase-change models are developed for both isothermal and nonisothermal melting behaviours. Axial thermal dispersion effects are modelled, including intraparticle conduction (Biot number) effects. Regenerative thermal storage applications involve flow reversals to recover the stored energy; this aspect of operation is included in the present model. Results from the model for a commercial sized thermal storage bed for both the energy storage and recovery periods are presented. Experimental measurements of transient temperature distributions in a randomly packed bed of uniform spheres containing a PCM for a step-change in inlet air temperature are reported for a range of Reynolds number.     

Application of phylogenetic microarray analysis to discriminate sources of fecal pollution

Conventional methods for fecal source tracking typically use single biomarkers to systematically identify or exclude sources. High-throughput DNA sequence analysis can potentially identify all sources of microbial contaminants in a single test by measuring the total diversity of fecal microbial communities. In this study, we used phylogenetic microarray analysis to determine the comprehensive suite of bacteria that define major sources of fecal contamination in coastal California. Fecal wastes were collected from 42 different populations of humans, birds, cows, horses, elk, and pinnipeds. We characterized bacterial community composition using a DNA microarray that probes for 16S rRNA genes of 59,316 different bacterial taxa. Cluster analysis revealed strong differences in community composition among fecal wastes from human, birds, pinnipeds, and grazers. Actinobacteria, Bacilli, and many Gammaproteobacteria taxa discriminated birds from mammalian sources. Diverse families within the Clostridia and Bacteroidetes taxa discriminated human wastes, grazers, and pinnipeds from each other. We found 1058 different bacterial taxa that were unique to either human, grazing mammal, or bird fecal wastes. These OTUs can serve as specific identifier taxa for these sources in environmental waters. Two field tests in marine waters demonstrate the capacity of phylogenetic microarray analysis to track multiple sources with one test.     

Finite element model updating using bees algorithm

In this paper the application of bees algorithm (BA) in the finite element (FE) model updating of structures is investigated. BA is an optimization algorithm inspired by the natural foraging behavior of honeybees to find food sources. The weighted sum of the squared error between the measured and computed modal parameters is used as the objective function. To demonstrate the effectiveness of the proposed method, BA is applied on a piping system to update several physical parameters of its FE model. To this end, the modal parameters of the numerical model are compared with the experimental ones obtained through modal testing. Moreover, to verify the performance of BA, it is compared with the genetic algorithm, the particle swarm optimization and the inverse eigensensitivity method. Comparison of the results indicates that BA is a simple and robust approach that could be effectively applied to the FE model updating problems.     

Variation-aware clock network buffer sizing using robust multi-objective optimization

Many engineering optimization problems include unavoidable uncertainties in parameters or variables. Ignoring such uncertainties when solving the optimization problems may lead to inferior solutions that may even violate problem constraints. Another challenge in most engineering optimization problems is having different conflicting objectives that cannot be minimized simultaneously. Finding a balanced trade-off between these objectives is a complex and time-consuming task. In this paper, an optimization framework is proposed to address both of these challenges. First, we exploit a self-calibrating multi-objective framework to achieve a balanced trade-off between the conflicting objectives. Then, we develop the robust counterpart of the uncertainty-aware self-calibrating multi-objective optimization framework. The significance of this framework is that it does not need any manual tuning by the designer. We also develop a mathematical demonstration of the objective scale invariance property of the proposed framework. The engineering problem considered in this paper to illustrate the effectiveness of the proposed framework is a popular sizing problem in digital integrated circuit design. However, the proposed framework can be applied to any uncertain multi-objective optimization problem that can be formulated in the geometric programming format. We propose to consider variations in the sizes of circuit elements during the optimization process by employing ellipsoidal uncertainty model. For validation, several industrial clock networks are sized by the proposed framework. The results show a significant reduction in one objective (power, on average 38 %) as well as significant increase in the robustness of solutions to the variations. This is achieved with no significant degradation in the other objective (timing metrics of the circuit) or reduction in its standard deviation which demonstrates a more robust solution.     

Development of cloud point extraction for simultaneous extraction and determination of gold and palladium using ICP-OES

Cloud point method was applied for the simultaneous extraction and preconcentration of trace amounts of gold and palladium. The extraction of analytes was performed in the presence of 1,8-diamino-4,5-dihydroxy anthraquinone as chelating agent and Triton X-114 as a non-ionic surfactant. After phase separation, the surfactant-rich phase was diluted with concentrated HNO(3) (65%, w/w) and the analytes concentrations were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The variables affecting the complexation and extraction conditions were optimized and under the optimum conditions (i.e. pH 6.5, 2.2 x 10(-4) mol l(-1) chelating agent, 0.15% (w/v) of Triton X-114, equilibration temperature 55 degrees C, centrifuge at 3500 rpm), quantitative extraction of Au(III) and Pd(II) from 100 ml of the aqueous solution was performed. The calibration curves were linear in the range of 0.5-1000 microg l(-1) with detection limits of 0.5 and 0.3 microg l(-1) and the enrichment factors were 8.6 and 20.2 for Au and Pd, respectively. Also the precision (%RSD) for eight replicate determinations of the analytes was better than 5%. Finally, the proposed method was successfully applied for the determination of Au and Pd in mine stones and standard reference materials (SRM).     

Texture image Classification based on improved local Quinary patterns

Multimedia Tools and Applications - Texture image classification is an active research topic in computer vision that play an important role in many applications such as visual inspection systems,...     

Effect of reaction conditions on silanisation of sepiolite nanoparticles

The study provides insights into the silanisation process of sepiolite nanoparticles. The nanoparticles were modified applying acidic and basic silanisation methods using Methacryloxypropyltrimethoxysilane (γ-MPS) as coupling agent. The silanisation reaction was performed in the following conditions: (1) acidic ethanol–water solution with a pH of 5 and (2) basic cyclohexane with a pH of 9. The influence of the conditions on the surface chemistry of modified particles was then investigated. To characterise the surface of sepiolite nanoparticles, analytical methods such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, X-Ray diffraction (XRD), scanning electron microscopy (SEM), and zeta potential analyses were applied. In addition, the colloidal stability of the modified nanoparticles was studied using a separation analysis. According to XRD and SEM, the basal interlayer distance of pristine sepiolite is not altered by silanisation process. TGA reveals that the grafting percentage of organosilane synthesised by basic method is approximately two times of that of acidic method. The silane coverage on the surface of the sepiolite and the per cent of hydroxyl groups covalently bound to γ-MPS were calculated. Separation analysis indicates decline in dispersion stability of the modified nanoparticles in ethanol due to increment of their hydrophobicity.     

Immobilization of silk fibroin on the surface of PCL nanofibrous scaffolds for tissue engineering applications

Poly(?‐caprolactone) (PCL) is explored in tissue engineering (TE) applications due to its biocompatibility, processability, and appropriate mechanical properties. However, its hydrophobic nature and lack of functional groups in its structure are major drawbacks of PCL‐based scaffolds limiting appropriate cell adhesion and proliferation. In this study, silk fibroin (SF) was immobilized on the surface of electrospun PCL nanofibers via covalent bonds in order to improve their hydrophilicity. To this end, the surface of PCL nanofibers was activated by ultraviolet (UV)–ozone irradiation followed by carboxylic functional groups immobilization on their surface by their immersion in acrylic acid under UV radiation and final immersion in SF solution. Furthermore, morphological, mechanical, contact angle, and Attenuated total reflection‐ Fourier transform infrared (ATR‐FTIR) were measured to assess the properties of the surface‐modified PCL nanofibers grafted with SF. ATR‐FTIR results confirmed the presence of SF on the surface of PCL nanofibers. Moreover, contact angle measurements of the PCL nanofibers grafted with SF showed the contact angle of zero indicating high hydrophilicity of modified nanofibers. In vitro cell culture studies using NIH 3T3 mouse fibroblasts confirmed enhanced cytocompatibility, cell adhesion, and proliferation of the SF‐treated PCL nanofibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46684.