Preferential Activation of Primary C?H Bonds in the Reactions of Small Alkanes with the Diatomic MgO+. Cation

The C? H bond activation of small alkanes by the gaseous MgO^+. cation is probed by mass spectrometric means. In addition to H‐atom abstraction from methane, the MgO^+. cation reacts with ethane, propane, n‐ and iso‐butane through several pathways, which can all be assigned to the occurrence of initial C? H bond activations. Specifically, the formal C? C bond cleavages observed are assigned to C? H bond activation as the first step, followed by cleavage of a β‐C? C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO^+. for the attack of primary C? H bonds. This feature represents a notable distinction of the main‐group metal oxide MgO^+. from various transition‐metal oxide cations, which show a clear preference for the attack of secondary C? H bonds. The results of complementary theoretical calculations indicate that the C? H bond activation of larger alkanes by the MgO^+. cation is subject to pronounced kinetic control.     

Indexed optical composite filters

A new technique called indexed composite filters (ICFs) for multiple object pattern recognition is proposed. Contrary to the usual so-called composite filters, the proposed ICF offers the possibility to identify which object of the learning class is detected at the output. The major advantage of ICF is that the output gives for every object detected two correlation peaks encoding the position and identity of the detected object. Computer simulation results are given using alphabetic input scenes that illustrates the efficiency of the proposed method.     

A comparative investigation of hydrofoil at angles of attack

In this paper, a numerical investigation of incompressible flow around a hydrofoil is presented. The laminar flow was modeled at different angles of attack. Momentum and continuity equations were coupled by the artificial compressibility scheme. In finite‐volume method, convective fluxes were calculated and compared by four schemes. Flux averaging with pressure correction was used. The other characteristic‐based (CB) methods consisted of Roe scheme and original CB scheme. A revised CB scheme was implemented in this research, which demonstrated very accurate solutions with respect to others. The results confirmed the superiority of the revised upwind scheme regarding accuracy and convergence without any requirement to artificial viscosity. The problem was studied at high Reynolds numbers at the onset of turbulence. For time discretization, the fifth‐order Runge–Kutta scheme was used. Results were compared with those of others in which good agreement was observed. Numerical experiments were performed on the NACA0012 hydrofoil. Copyright © 2011 John Wiley & Sons, Ltd.     

Residue‐Specific Dynamics and Local Environmental Changes in Aβ40 Oligomer and Fibril Formation

Elucidating local dynamics of protein aggregation is crucial for understanding the mechanistic details of protein amyloidogenesis. Herein, we studied the residue‐specific dynamics and local environmental changes of Aβ40 along the course of aggregation by using para‐cyanophenylalanine (Phe_CN) as a fluorescent and vibrational probe. Our results show that the Phe_CN residues introduced at various positions all exhibited an immediate decay of fluorescence intensity, indicating a relatively synergistic process in early oligomer formation. The fast decreases in the fluorescence intensities of residues 19 and 20 in the central hydrophobic core region and residue 10 in the N‐terminal region suggest that they play crucial roles in the formation of the oligomeric core. The Phe_CN4 residue exhibits a remarkably slower decrease in fluorescence intensity, implicating its dynamic conformational characteristics in oligomer and fibril formation. Our results also suggest that the N‐terminal residues in fibrils are surrounded by a relatively hydrophobic local environment, as opposed to being solvated.     

Singlet–triplet energy differences in divalent five membered cyclic conjugated Arduengo-type carbenes XC<Subscript>2</Subscript>HN<Subscript>2</Subscript>M (M = C,Si, Ge,Sn, and Pb; X = F,Cl, Br,and I)

Singlet-triplet energy differences in Arduengo-type carbenes XC₂HN₂C compared and contrasted with their sila, germa, stana and plumba analogues; at B3LYP/6-311++G** level of theory. Free Gibbs energy differences between triplet (t) and singlet (s) states (ΔG(t–s)) change in the following order: plumbylenes > stannylenes > germylenes > silylenes > carbenes. The singlet states in XC₂HN₂C are generally more stable when the electron withdrawing groups such as–F was used at β-position. However, the singlet states in XC₂N₂HM (M = Si, Ge, Sn, and Pb) are generally more stable when the withdrawing groups such as–F was placed. The puckering energy is investigated for each the singlet and triplet states. The DFT calculations found the linear correlation to size of the group 14 divalent element (M), the ∠N–M–N angle, and the Δ(LUMO–HOMO) of XC₂HN₂M.     

Sensing and catalytic decomposition of hydrogen peroxide by silicon carbide nanotubes: A DFT study

In this study, by carrying out detailed density functional theory calculations, we investigate the adsorption and stepwise decomposition of hydrogen peroxide (H₂O₂) over (6,0) and (7,0) zigzag silicon carbide nanotubes (SiCNTs). The results indicate that the H₂O₂ can be adsorbed on the exterior surface of the SiCNTs with noticeable adsorption energies and charge transfers. To gain insight into the catalytic activity of the surface, the interaction between the H₂O₂ and SiCNT is analyzed by detailed electronic analysis such as adsorption energy, charge density difference and activation barrier. The decomposition of H₂O₂ into O₂ and H₂ species can be viewed as the kinetically preferred reaction pathway for dehydrogenation of hydrogen peroxide over SiCNTs. There is also a curvature effect on the dehydrogenation kinetics of hydrogen peroxide, that small diameter SiCNTs with large curvature would be beneficial for decomposition of H₂O₂. © 2015 Wiley Periodicals, Inc.     

Viscous dissipation of Rankine vortex profile in zero meridional flow

An analytical solution is given for a time-decay Rankine vortex profile due to viscous effects. The vortex filament is assumed to be isolated, strong, concentrated and having zero-meridional flow (i.e. radial and axial velocities are equal to zero). Zero-meridional renders the governing equations for an unsteady, incompressible and axisymmetric vortex in a simple form. Based on the tangential momentum equation, the spatial-temporal distributions of the swirl velocity are given in terms of Fourier-Bessel series by using separation of variables technique. A general formula is derived by total differentiation of the swirl velocity with respect to time, depicting the viscous dissipation for Oseen and Taylor-like vortex profiles. This analysis is validated by comparison with previous experimental data. The English text was polished by Yunming Chen.     

A DFT study on electronic and optical properties of aspirin-functionalized B<Subscript>12</Subscript>N<Subscript>12</Subscript> fullerene-like nanocluster

In this work, the interaction of an aspirin (AS) molecule with the external surface of a boron nitride fullerene-like nanocage (B₁₂N₁₂) is studied by means of density functional theory (DFT) calculations. Equilibrium geometry, electronic properties, adsorption energy and thermodynamic stability are identified for all of the adsorbed configurations. Four stable configurations are obtained for the interaction of AS molecule with the B₁₂N₁₂ nanocage, with adsorption energies in the range of ?10.1 to ?37.7 kcal/mol (at the M06-2X/6-31 + G** level). Our results clearly indicate that Al-doping of the B₁₂N₁₂ tends to increase the adsorption energy and thermodynamic stability of AS molecule over this nanocage. We further study the adsorption of AS over the B₁₂N₁₂ and B₁₁N₁₂Al in the presence of a protic (water) or aprotic (benzene) solvent. It is found that the calculated binding distances and adsorption energies by the PCM and CPCM solvent models are very similar, especially for the B₁₂N₁₂ complexes. According to time-dependent DFT calculations, the Al-doping can shift estimated λ _max values toward longer wavelengths (redshift). Solvent effects also have an important influence on the calculated electronic absorption spectra of AS-B₁₂N₁₂ complexes.     

A note on linear θ-derivations on JB1-triples

In this paper we prove a generalization of the stability of the functional equation in the spirit of Hyers, Ulam and Rassias. Also we introduce the concept of linear θ-derivations on JB¹-triple, and prove the generalization of the stability of the functional equation in the spirit of Hyers, Ulam and Rassias of linear θ-derivations on JB¹-triple. For resent results see [1], [2], [3].