Investigation of the high velocity impact behavior of nanocomposites

In this article, the ballistic behavior of the glass/epoxy/nanoclay hybrid nanocomposites is studied. The fiber glass used is a plain weave 200 g/m², while the nanoclay is an organically modified montmorillonite nanoclay (Closite 30B). The epoxy resin system is made of Epon 828 as the epoxy prepolymer and Jeffamine D‐400 as the curing agent. 0, 3, 5, 7, and 10 wt% of nanoclay particles are dispersed in the epoxy resin. Ballistic tests are performed using flat‐ended projectiles in impact velocities 134 m/s and 169 m/s. The results show that the energy absorption capability and mechanical properties of the composite can be significantly enhanced by adding nanoparticles. When the impact velocity is 134 m/s, near than the ballistic limit, the most increase in the energy absorption capability is observed in 3 wt% nanoclay while with the impact velocity 169 m/s, beyond the ballistic limit, the highest increase is observed in 10 wt% nanoclay. POLYM. COMPOS., 37:1173–1179, 2016. © 2014 Society of Plastics Engineers     

Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

Catalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl₂ catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry     

Inspection error and its effects on single sampling plans with fuzzy parameters

In this paper we have designed an acceptance single sampling plan with inspection errors when the fraction of defective items is a fuzzy number. We have shown that the operating characteristics curve of this plan is like a band having high and low bounds, its width depends on the ambiguity of proportion parameter in the lot when the samples size and acceptance numbers are fixed. A comparison of the single sampling plans with and without inspection errors was done to study the effects upon the characteristics. The results of this comparison show that in the sampling plan with inspection errors, there is a lower operating characteristics band in comparison to a sampling plan without inspection errors for good processing quality. We have also shown that the incorrect classification of a good item reduces the fuzzy probability of acceptance and incorrect classification of a defective item results in a higher fuzzy probability of acceptance.     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

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.     

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.     

Simultaneous extraction and determination of lead, cadmium and copper in rice samples by a new pre-concentration technique: Hollow fiber solid phase microextraction combined with differential pulse anodic stripping voltammetry

In the present work, a novel solid phase microextraction (SPME) technique using a hollow fiber-supported sol–gel combined with multi-walled carbon nanotubes, coupled with differential pulse anodic stripping voltammetry (DPASV) was employed in the simultaneous extraction and determination of lead, cadmium and copper in rice. In this technique, an innovative solid sorbent containing mixture of carbon nanotube and a composite microporous compound was developed by the sol–gel method via the reaction of tetraethylorthosilicate (TEOS) with 2-amino-2-hydroxymethyl-propane-1,3-diol (TRIS). The growth process was initiated in basic condition (pH 10–11). Afterward this sol was injected into a polypropylene hollow fiber segment for in situ gelation process. The main factors influencing the pre-concentration and extraction of the metal ions; pH of the aqueous feed solution, extraction time, aqueous feed volume, agitation speed, the role of carbon nanotube reinforcement (as-grown and functionalized MWCNT) and salting effect have been examined in detail. Under the optimized conditions, linear calibration curves were established for the concentration of Cd(II), Pb(II) and Cu(II) in the range of 0.05–500, 0.05–500 and 0.01–100 ng mL⁻¹, respectively. Detection limits obtained in this way are, 0.01, 0.025 and 0.0073 ng mL⁻¹ for Cd(II), Pb(II) and Cu(II), respectively. The relative standard deviations (RSDs) were found to be less than 5% (n = 5, conc.: 1.0 ng mL⁻¹).     

Novel resource allocation algorithms to performance and energy efficiency in cloud computing

The rapid growth in demand for computational power has led to a shift to the cloud computing model established by large-scale virtualized data centers. Such data centers consume enormous amounts of electrical energy. Cloud providers must ensure that their service delivery is flexible to meet various consumer requirements. However, to support green computing, cloud providers also need to minimize the cloud infrastructure energy consumption while conducting the service delivery. In this paper, for cloud environments, a novel QoS-aware VMs consolidation approach is proposed that adopts a method based on resource utilization history of virtual machines. Proposed algorithms have been implemented and evaluated using CloudSim simulator. Simulation results show improvement in QoS metrics and energy consumption as well as demonstrate that there is a trade-off between energy consumption and quality of service in the cloud environment.     

Ternary solubility of mono- and di-tert-butyl ethers of glycerol in supercritical carbon dioxide

Using a continuous flow apparatus, the ternary solubility of mono- and di-tert-butyl ethers of glycerol (MTBG and DTBG, respectively) in supercritical carbon dioxide was measured at the temperatures of 313.15, 333.15, and 348.15 K; a pressure range of 80-200 bar; and an expanded gas flow rate of 180 ± 10 mL min⁻¹ at average laboratory temperature of 300.15 K and pressure of 0.89 bar. The ternary solubility of the ethers at the constant temperatures of 333.15 and 348.15 K increased with increasing pressure up to the crossover point (i.e., 152 bar for MTBG and 170 bar for DTBG). MTBG exhibited a higher solubility than DTBG in scCO₂. The experimental data for the ternary solubility of MTBG and DTBG were correlated using the Bartle equation.