A new weighted optimal combination of ANNs for catalyst design and reactor operation: Methane steam reforming studies

Catalyst design and evaluation is a multifactorial multiobjective optimization problem and the absence of well‐defined mechanistic relationships between wide ranging input‐output variables has stimulated interest in the application of artificial neural network for the analysis of the large body of empirical data available. However, single ANN models generally have limited predictive capability and insufficient to capture the broad range of features inherent in the voluminous but dispersed data sources. In this study, we have employed a Fibonacci approach to select optimal number of neurons for the ANN architecture followed by a new weighted optimal combination of statistically‐derived candidate ANN models in a multierror sense. Data from 200 cases for catalytic methane steam reforming have been used to demonstrate the veracity and robustness of the integrated ANN modeling technique. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2412–2427, 2012     

Synthesis of SPR Nanosensor using Gold Nanoparticles and its Application to Copper (II) Determination

This research describes a colorimetric assay for Cu (II) ions that is highly selective over other metal ions. It is based on the measurement of changes in the surface plasmon resonance absorbance (at 525 nm) of gold nanoparticles (Au NPs) modified with 1,7-diaza-15-crown-5 (Crown-Au NPs). The unique structure of crown ethers and presence of heteroatoms enable the crown-Au NPs to recognize very low concentrations of Cu (II) ions. After aggregation, the surface plasmon absorption band has a red shift so that the nanoparticle solution shows a violet color. The TEM images data show that this color change is a result of crown-Au NPs aggregation upon addition of Cu (II), In contrast, other metal ions Al³⁺, Ca²⁺, Cd²⁺, Co²⁺, Cr³⁺, Ag⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, and Zn²⁺ do not aggregate. The recognition mechanism is attributed to the formation of a sandwich (2+1) between the Cu (II) ion and two diaza-15-crown-5 moieties that are attached to separate nanoparticles. This simple and fast method can be used to determine the Cu (II) ions with a detection limit as low as 200 nM.     

Cross-linked electrospun polyvinyl alcohol/sodium caseinate nanofibers for antibacterial applications

In this study, the polyvinyl alcohol (PVA) and sodium caseinate (SC) nanofibers were produced by a single-fluid electrospinning method from their blends. Afterward, the cross-linking process with two different methods was applied to the PVA/SC (70/30, v/v) ratio, which was selected according to the surface and mechanical properties of the electrospun mat. In the first method, different ratios (15%, 20%, 25%, and 30%) of glutaraldehyde (GLA) cross-linking agents were added to the PVA/SC solution and then, PVA/SC/GLA nanofibers were obtained. In the second method (in-situ method), the nanofibers obtained from the PVA/SC solution were cross-linked by dipping into the cross-linking solution. After, PVA/SC/GLA/Zinc oxide nanoparticles (ZnO NP) mats were obtained by adding ZnO NP at different rates to the PVA/SC/GLA (7030-25GLA) solution, which was chosen according to the results of thermal, mechanical, and moisture test. In addition, performing tests, a cytotoxicity test for fibroblast cell line (L929), and in vitro antibacterial test for Escherichia coli and Staphylococcus aureus were also applied to them. Therefore, the usability of PVA/SC/GLA/ZnO NP nanofibers as an antibacterial effective wound dressing was investigated. Due to the high toxic effect of GLA, it was found that PVA/SC/ZnO cross-linked nanofibers are not suitable for wound dressing use. However, it was determined that the PVA/SC nanofiber cross-linked by the in-situ method had high cell viability according to the cytotoxicity test result and thus could be used as a fibroblast tissue scaffold.     

Effects of sizing materials on the properties of carbon fiber‐reinforced polyamide 6,6 composites

This article aims to study the effect of the sizing materials type on the mechanical, thermal, and morphological properties of carbon fiber (CF)‐reinforced polyamide 6,6 (PA 6,6) composites. For this purpose, unsized CF and sized CFs were used. Thermogravimetric analysis was performed, and it has been found that certain amounts of polyurethane (PU) and PA sizing agents decompose during processing. The effects of sizing agent type on the mechanical and thermomechanical properties of all the composites were investigated using tensile, Izod impact strength test, and dynamic mechanical analysis. Tensile strength values of sized CF‐reinforced composites were higher than that of unsized CF‐reinforced composites. PA and polyurethane sized CF‐reinforced composites exhibited the highest impact strength values among the other sized CF‐reinforced composites. PU and PA sized CF‐reinforced composites denoted higher storage modulus and better interfacial adhesion values among the other sizing materials. Scanning electron microscope studies indicated that CFs which were sized with PU and PA have better interfacial bonding with PA 6,6 matrix among the sized CFs. All the results confirmed that PA and PU were suitable for CF's sizing materials to be used for PA 6,6 matrix. POLYM. COMPOS., 34:1583–1590, 2013. © 2013 Society of Plastics Engineers     

Electroreduction of nitrous oxide on platinum and palladium: Toward selective catalysts for methanol–nitrous oxide mixed-reactant fuel cells

The kinetics of N₂O electroreduction in the absence and presence of methanol was studied between 295 and 333 K on polycrystalline Pt and Pd electrodes in 0.1 M NaOH. In the absence of methanol the reduction of N₂O on Pd is more facile than on Pt as shown by the approximately four times lower apparent activation energy and lower Tafel slope (Pt: 0.111 ± 0.019 V dec⁻¹, Pd: 0.084 ± 0.007 V dec⁻¹ at 295 K). Two different electroreduction mechanisms are proposed for Pt and Pd with and without participation of underpotential deposited hydrogen, respectively. The selectivity of Pt and Pd electrodes toward both N₂O electroreduction and methanol (0.5 and 1 M) oxidation at 295 K was also investigated. Pt based electrocatalysts are promising candidates for the anode of a mixed reactant CH₃OH–N₂O fuel cell due to inhibition of N₂O reduction by chemisorbed methanol. Pd on the other hand is a selective cathode electrocatalyst since N₂O reduction takes place fairly actively in the presence of 1 M methanol, while methanol oxidation is inhibited.     

Experimental investigation and numerical modelling of photocurrent oscillations in lattice matched Ga1?x In x N y As1?y /GaAs quantum well p-i-n photodiodes

Photocurrent oscillations, observed at low temperatures in lattice-matched Ga_1−xIn_xN_yAs_1−y/GaAs multiple quantum well (MQW) p-i-n samples, are investigated as a function of applied bias and excitation wavelength and are modelled with the aid of semiconductor simulation software. The oscillations appear only at low temperatures and have the highest amplitude when the optical excitation energy is in resonance with the GaInNAs bandgap. They are explained in terms of electron accumulation and the formation of high-field domains in the GaInNAs QWs as a result of the disparity between the photoexcited electron and hole escape rates from the QWs. The application of the external bias results in the motion of the high-field domain towards the anode where the excess charge dissipates from the well adjacent to anode via tunnelling.     

The influence of heat treatment on the microstructure,flux pinning and magnetic properties of bulk BSCCO samples prepared by sol-gel route

We study the combined influence of calcination and sintering temperature on the microstructure, superconducting and pinning properties of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+θ (Bi-2223) prepared by the sol-gel route. Using several characterization techniques, including X-rays diffractometry and electrical transport measurements, we find that the powders calcined at 820 °C often result in a crystal higher critical current density (J_c) compared those calcined at 830 °C. The powder calcined at 820 °C and sintered at 850 °C (Bi-2223 ₈₂₀⁸⁵⁰) showed the best grain morphology and the largest magnetic hysteresis loop and a J_c equal to 12.94 $\times$ 10⁵ A/cm², comparable to the best results found in the literature for Bi-2223. The enhancement in J_c for Bi-2223 ₈₂₀⁸⁵⁰ seems to be due to improved grain structure rather than creation of effective pinning centers, because the scaling behavior of flux pinning force densities indicates that the main pinning mechanism for all samples is normal point pinning.     

Silicone secondary cross-linked IPN based on poly(vinylacetate-co-hydroxyethyl methacrylate) and SiO2

Silicone secondary cross-linked interpenetrating polymer networks (IPNs) of poly(vinylacetate-co-hydroxyethyl methacrylate) (PVAc-HEMA) and SiO₂ were prepared by free radical polymerization and condensation methods. The resulting copolymers were characterized by using Fourier transform infrared spectroscopy (FTIR). Thermal properties of the copolymers were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The morphology of copolymers was also investigated by optical microscopy (OM) and then the effects of silicone concentrations, the reflux time, and composition on the phase morphology of the IPNs of PVAc-HEMA/SiO₂ were discussed. The broadening of the transition region was observed with the increase of the prolongation of the reflux time and the tendency of the aggregation of silicon in the surface was also observed with Teflon as a substrate plate. However, an optically transparent film was easily achieved at higher temperature due to the chemical cross-link and physical entanglement between the two phases of PVAc-HEMA and SiO₂.