Spectral finite element based on an efficient layerwise theory for wave propagation analysis of composite and sandwich beams

In this paper, we present a spectral finite element model (SFEM) using an efficient and accurate layerwise (zigzag) theory, which is applicable for wave propagation analysis of highly inhomogeneous laminated composite and sandwich beams. The theory assumes a layerwise linear variation superimposed with a global third-order variation across the thickness for the axial displacement. The conditions of zero transverse shear stress at the top and bottom and its continuity at the layer interfaces are subsequently enforced to make the number of primary unknowns independent of the number of layers, thereby making the theory as efficient as the first-order shear deformation theory (FSDT). The spectral element developed is validated by comparing the present results with those available in the literature. A comparison of the natural frequencies of simply supported composite and sandwich beams obtained by the present spectral element with the exact two-dimensional elasticity and FSDT solutions reveals that the FSDT yields highly inaccurate results for the inhomogeneous sandwich beams and thick composite beams, whereas the present element based on the zigzag theory agrees very well with the exact elasticity solution for both thick and thin, composite and sandwich beams. A significant deviation in the dispersion relations obtained using the accurate zigzag theory and the FSDT is also observed for composite beams at high frequencies. It is shown that the pure shear rotation mode remains always evanescent, contrary to what has been reported earlier. The SFEM is subsequently used to study wavenumber dispersion, free vibration and wave propagation time history in soft-core sandwich beams with composite faces for the first time in the literature.     

Facile synthesis of low dimensional CuO nanostructures and their gas sensing applications

A simple and cost effective hydrothermal method has been employed to synthesis morphology controlled pure and Cr doped (4 and 8 at. %) CuO nanostructures. Crystalline purity and structure of the nanostructures were validated by X‐ray diffraction and Retvield analyses. Field emission scanning electron microscopy revealed the evolution of rod‐like, sheet‐like and boat‐like morphologies for pure, 4 and 8 at. % Cr doped CuO nanostructures respectively. The optical band gap estimated using the K‐M function plot from diffused reflectance spectroscopy showed a shift in band gap from 1.68 to 1.90 eV with respect to Cr concentration. The synthesized CuO nanostructures were investigated for the efficient room temperature gas sensing of ammonia, ethanol and methanol vapours under different concentrations (100‐600 ppm). The 8 at. % Cr doped CuO nano‐boats showed enhanced gas sensitivity than other CuO nanostructures owing to their typical morphology, larger surface area and related properties.     

<Emphasis Type="Italic">Areca catechu</Emphasis> Assisted Synthesis of Silver Nanoparticles and its Electrocatalytic Activity on Glucose Oxidation

In this work, a facile biogenic route for the synthesis of silver nanoparticles (AgNPs) is reported. The aqueous extract of Areca catechu (A. catechu) nuts are used as reducing source. The synthesized AgNPs characterized by UV–Visible (UV–Vis) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) with energy dispersive spectrum (EDS) analysis. The formations of AgNPs are identified from the appearance of yellow color and the surface plasmon resonance absorbance peak between 407 and 437 nm. The FT-IR results exposed that the active biomolecules of A. catechu are responsible for capping of AgNPs. The synthesized AgNPs are distorted spherical shape with 45 nm of size, identified from the HR-TEM. In application, the electrocatalytic activity of AgNPs is analyzed towards glucose oxidation using cyclic voltammetry. The results showed that A. catechu derived AgNPs act as good electrocatalyst than bare bulk silver and glassy carbon electrodes.     

Effects of point mutations on the thermostability of <Emphasis Type="Italic">B. subtilis</Emphasis> lipase: investigating nonadditivity

Molecular level understanding of mutational effects on stability and activity of enzymes is challenging particularly when several point mutations are incorporated during the directed evolution experiments. In our earlier study, we have suggested the lack of consistency in the effect of point mutations incorporated during the initial generations of directed evolution experiments, towards conformational stabilization of B. subtilis lipase mutants of later generations. Here, we report that the cumulative point mutations incorporated in mutants 2M (with two point mutations) to 6M (with six point mutations) possibly do not retain their original stabilizing nature in the most thermostable 12M mutant (with 12 point mutations). We have carried out MD simulations using structures incorporating reversal of different sets of point mutations to assess their effect on the conformational stability and activity of 12M. Our analysis has revealed that reversal of certain point mutations in 12M had little effect on its conformational stability, suggesting that these mutations were probably inconsequential towards the thermostability of the 12M mutant. Interestingly these mutations involved evolutionarily conserved residues. On the other hand, some of the other point mutations incorporated in nonconserved regions, appeared to contribute significantly towards the conformational stability and/or activity of 12M. Based on the analysis of dynamics of in silico mutants generated using the consensus sequence, we identified experimentally verifiable residue positions to further increase the conformational stability and activity of the 12M mutant.     

1H and 13C NMR spectral assignments of some novel 2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-one derivatives

The (1)H and (13)C NMR spectra of 2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ones (1-2), oximes (3-8) and O-benzyl oximes (9-12) were recorded. The chemical shifts were unambiguously assigned using 1D and 2D NMR spectral data. The results clearly indicate that the compounds exist in chair-boat conformation with equatorial and axial orientation of the aryl groups in the chair and boat forms, respectively. Since the molecules are flexible and dynamic in solution, the chair and boat forms are mutually interconvertible. In 3-12, because of the effect of oximation/oximination, all the protons in the heterobicyclic systems gave distinct signals except the benzylic protons of the boat form. In all synthesized compounds, the aryl group protons at C-6,8 are shielded by the aryl groups at C-2,4 and therefore appear in the lower frequency region than the aryl groups at C-2,4.     

Hydrogen gas mixture separation by CVD silica membrane

In this work we investigate the performance of high flux chemical vapour deposition (CVD) silica membranes for the separation of gas mixtures containing H₂ and CO₂ at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and O₂ were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H₂ and He) whilst the larger kinetic diameter gases (CO₂ and N₂) showed negative activation energy. The single gas permeation of H₂ increased from 5.1 × 10⁻⁷ to 7.0 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ in the temperature range 100–400 °C, and H₂/CO₂ and H₂/N₂ selectivities reached 36 and 57 at 400 °C, respectively. The H₂ purity in the permeate stream also increased with temperature for H₂:CO₂ binary gas mixture, thus being beneficial for H₂ diffusion. H₂ competitively permeated through the membrane at a several range of gas mixtures, and a saturation level was achieved at H₂:CO₂ 60:40 feed concentration, where the diffusion of CO₂ molecules became negligible delivering ∼99% H₂ purity in the permeate stream. These results substantiate that the counter diffusion CVD method produced thin silica film membranes with a very precise pore size control, in particular suggesting a narrow pore distribution with average pore radius of about 3.1 Å.     

Growth and characterization of organic nonlinear optical crystal of 1-chloro-2,4-dinitrobenzene (CDNB)

Organic nonlinear optical crystal of 1-chloro-2,4-dinitrobenzene has been successfully grown by low temperature solution growth technique. Good optical quality single crystals of size 28 mm x 11 mm x 5mm are obtained. Grown crystals were subjected to X-ray powder diffraction analysis, FT-IR, FT-Raman, proton nuclear magnetic resonance (PNMR) and etching studies. Thermal properties of the grown crystals were studied by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). UV-vis studies show the cutoff wavelength is less than 400 nm. Nonlinear optical property of the crystal was studied by Kurtz powder technique using Nd:YAG laser and the crystal exhibits second harmonic generation property.     

Dielectric properties of some MM′O4 and MTiM′O6 (M=Cr, Fe, Ga; M′=Nb, Ta, Sb) rutile-type oxides

We describe an investigation of the structure and dielectric properties of MM′O₄ and MTiM′O₆ rutile-type oxides for M=Cr, Fe, Ga and M′=Nb, Ta and Sb. All the oxides adopt a disordered rutile structure (P4₂/mnm) at ambient temperature. A partial ordered trirutile-type structure is confirmed for FeTaO₄ from the low temperature (17 K) neutron diffraction studies. While both the MM′O₄ oxides (CrTaO₄ and FeTaO₄) investigated show a normal dielectric property MTiM′O₆ oxides for M=Fe, Cr and M′=Nb/Ta/Sb display a distinct relaxor/relaxor-like response. Significantly the corresponding gallium analogs, GaTiNbO₆ and GaTiTaO₆, do not show a relaxor response at T<500 K.     

Environmentally safe one-pot solvent-free synthesis of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) catalyzed by NaHSO4-SiO2

One-pot condensation of thiourea (urea), diverse aromatic aldehydes, and ammonium acetate in the presence of repeatedly usable heterogeneous catalyst NaHSO₄-SiO₂ in the absence of solvent under the microwave irradiation proceeds faster and with better yields of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) that under common heating. Compounds synthesized exist as a rule as two isomers distinguished by the position of the phenyl ring: It is located in the major isomer nearly in the equatorial position, in the minor one, close to axial position.