Production of single-walled carbon nanotubes from methane over Co-Mo/MgO nanocatalyst:A comparative study of fixed and fluidized bed reactors

In this study,the performances of fixed and fluidized bed reactors in the production of single-walled carbon nanotubes(SWNTs)have been investigated.In both reactors,single-walled carbon nanotubes were grown by catalytic chemical vapor decomposition(CCVD)of methane over Co-Mo/MgO nanocatalyst under two different operating conditions.The synthesized samples were characterized by TEM,TGA and Raman spectroscopy.It is found that the performance of a fluidized bed in the synthesis of carbon nanotubes is much better than that of a fixed bed.The quality of carbon nanotubes obtained from the fluidized bed was significantly higher than that from the fixed bed and the former one with the ID/IG ratio of 0.11 while the latter one with the ID/IG ratio of 0.71.Also,the yield of SWNTs in the fluidized bed was 92 wt%,while it was 78 wt%in the fixed bed.These advantages of fluidized bed reactors for the synthesis of carbon nanotubes can be attributed to more available space for the growth of carbon nanotubes and more uniform temperature and concentration profiles.     

Numerical Model for Electro-Mechanical Analysis Based on Finite Element Method

In this paper, we present a numerical procedure that can be used to model the electro-mechanical coupled behavior of the dielectric actuator domain. The equation describing the electrostatical part is given by the reduced form of the Maxwell equation and the electrostatic potential [1]. The mechanical problem is described by the constitutive equations and equilibrium equations. Using the finite element method, this technique is to divide a whole problem into sub-problems. The complexity of the original problem is therefore reduced by focusing only on the most relevant areas. A finite element analysis is then performed by applying the electrostatic Maxwell pressure as Neumann boundary conditions to compute the displacements. Once the displacement is computed, the electrostatic domain or the conductor is updated. Electrostatic analysis is performed on the updated geometry and the finite element method is then used to determine the change in potential due to geometric perturbations. Once the surface charge densities are known, the new electrostatic Maxwell pressure is computed. The mechanical and electrostatic analysis is repeated until an equilibrium state is computed. The procedure is demonstrated in the paper by the solution of some two-dimensional and three-dimensional problems. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ranking DMUs by l1-norm with fuzzy data in DEA

The relative efficiency of a DMU is the result of comparing the inputs and outputs of the DMU and those of other DMUs in the PPS (production possibility set). If the inputs and outputs are fuzzy, the DMUs cannot be easily evaluated and ranked using the obtained efficiency scores. In this paper, presenting a new idea for ranking of DMUs with fuzzy data. And finally, we introduce a numerical example.     

Effect of iron doping at Mn-site on complex impedance spectroscopy properties of Nd0.67Ba0.33MnO3 perovskite

The effect of Fe-doping at Mn-site on the structural and electrical properties of Nd_0.67Ba_0.33Mn_1?xFe_xO₃ (0 ≤ x ≤ 0.05) perovskites has been investigated. X-ray diffraction patterns show that the structural parameters change slightly due to the fact that the Fe³⁺ ions replacing the Mn³⁺ have similar ionic radius. The electrical properties of these samples have been investigated using complex impedance spectroscopy technique. a function of the frequency at different temperatures. When increasing the Fe-content, a decrease of dc conductivity was observed throughout the whole explored temperature range and the deduced activation energy values are found to increase from 128 meV for x = 0 to 166 meV for x = 0.05. The curves of the imaginary part of impedance (Z″) show the presence of relaxation phenomenon in our samples. The complex impedance spectra show semicircle arcs at different temperatures and an equivalent circuit of the type of R_g + (R_gb//C_gb) has been proposed to explain the impedance results.     

The effect of inorganic and organic macromolecular structures on the performance of metallocene polymerization catalysts

After a short comparative analysis of different macromolecular ligands reported in the relevant literature, the presentation will be centered on the results obtained in the authors' laboratory using structurally defined inorganic supports in terms also of their macromolecular structure. Zeolites and mesomorphous silica can link, after proper chemical modification of their surface with MAO, unmodified metallocene complexes through cage entrapment and weak interactions, thus allowing the transfer from the solution to the solid phase. The metallocene complexes in their new phase are characterized by the catalytic behavior in olefin polymerization after activation with MAO. A decrease of productivity is generally observed depending on the type of support. The steric hindrance provided by the support is evidenced by the depression of chain transfer rate with formation of higher molecular weight polymers. Also shape selectivity is observed during copolymerization of ethylene with α‐olefins having variable size. These steric effects are released when going from HY zeolite to MCM silica.     

2D-to-3D percolation crossover of metal-insulator composites

Percolation properties and d.c. conductivity were determined for an L²×h-random resistor network model of metal-insulator composite films. The effects of the thickness h on the percolation threshold and conductivity were studied numerically in the limit of an infinite size of the L²-plane parallel to the film. For thicknesses ranging from h/L=0.01 to h/L=0.24, a crossover between a finite-size regime and a saturation regime was observed at h/L≈0.1. In the finite-size regime (h/L?0.01), the percolation threshold scales as pc(h)−pc3∝h−1/x, the exponent x being compatible with that of the critical exponent of the 3D correlation length, ν₃. The conductivity exponent t appeared to depend linearly on the ratio h/L with a slope νD compatible with 2+ν₂, where ν₂ is the 2D correlation length exponent. In the saturation regime, a scaling correction for the percolation threshold was found with an exponent 1+1/ν₃. In this regime we also observed a logarithmic dependence of the conductivity exponent on h/L.     

Lipase-catalyzed amidation of carboxylic acid and amines

The amidation reaction is of a very particular interest, especially in the pharmaceutical industry and always requires the activation of the acid with a large excess of reactants. Therefore, a large amount of waste is generated. In order to reduce the environmental impact of such reaction, we have developed enzymatic amidation conditions which are compatible with a wide range of amines and acids, in particular with the biologically relevant lipoic acid. Water is the only by-product generated during this reaction thus a very high atom economy is obtained. In addition, we have shown that the lipase can be recovered and reused several times without a significant loss of activity.     

Synthesis,structures and antimicrobial activities of nickel(II) and zinc(II) diaminomaleonitrile-based complexes

Three Ni(II) and Zn(II) complexes [Ni(L1)], [Ni(L2)], and [Zn(L3)(DMSO)] (L1 = 2,3-bis(2-hydroxybenzylideneimino)-2,3-butenedinitrile, L2 = 2,3-bis(2-hydroxy-3-methoxybenzylideneimino)-2,3-butenedinitrile, L3 = 2,3-bis(2-hydroxy-1-naphthylideneimino)-2,3-butenedinitrile) were obtained in DMSO by one-pot syntheses. The complexes were characterized by physicochemical and spectroscopic methods. Also, their solid-state structures were determined by single-crystal X-ray diffraction. The geometries of the Ni(II) and Zn(II) complexes were square planar and square pyramidal, respectively. The complexes were screened in vitro against a fungal species and eight species of bacteria, revealing their antimicrobial activity.