Calculation of the HOMA model parameters for the carbon–boron bond

An extension of the harmonic oscillator model of aromaticity (HOMA) model to systems with carbon–boron bonds is presented. Model parameters were estimated using experimental and theoretical bond lengths. It is shown that both approaches produce very similar HOMA models. In the second part of the article, the aromaticity levels of several model compounds containing carbon–boron bonds are calculated using the previously obtained parameters. The results of these calculations are compared with those provided by other aromaticity indices. The aromaticity of boron-containing compounds is also compared with the aromaticity of analogous compounds containing carbon and nitrogen.     

Ueber die Destillation von Formaldehyd

Ohne Zusammenfassung     

Field Patterns of the TE Modes in Ridge-Trough Waveguide

A single-ridge waveguide with a symmetrical longitudinal trough, designated as a ridge-trough waveguide has been used as a transition in a V-band (50-75 GHz) wafer probe recently. In this paper, the field patterns for the dominant TE mode and the first higher TE mode in ridge-trough waveguide with different configurations are presented by finite element method. The field patterns in this paper have important values for us to understand the transmission characteristics of ridge-trough waveguide, and will be of practical significance in designing ridge-trough waveguide components in microwave and millimeter wave engineering.     

On R*-sequenceability and symmetric harmoniousness of groups

We introduce a special harmoniousness called symmetric harmoniousness of groups and extend the R^*-sequenceability of abelian groups to nonabelian groups. We prove that the direct product of an R^*-sequenceable group of even order with a symmetric harmonious group of odd order is R^*-sequenceable. Examples of nonabelian R^*-sequenceable groups and nonabelian symmetric harmonious groups are given. It is shown that the nonabelian groups of order 3q (q prime) are symmetric harmonious. © 1994 John Wiley & Sons, Inc.     

Improved Synthesis of 9- and 10-Methylbenz[a] Anthracenes

The synthesis of 9- and 10-methylbenz[a]anthracenes by improved methods are described. These new procedures are simple and convenient, and provide the title compounds in good yields and high purity.     

Space-time integral equation solution for hard or soft targets in the presence of a hard or soft half space

The responses of a hard or soft target in the presence of a hard or soft half space are computed using space-time integral equations formulated in the time domain. The incident pressure wave is a ‘smoothed impulse“ with a Gaussian-shaped time dependence, whose width is of the order of a target dimension. A space-time integral equation for the pressure field and the gradient pressure field on the outside of the target surface is solved for the pressure and the pressure gradient by stepping on in time. The scattered field is then computed from these source fields. The technique is applicable to targets of arbitrary contour and is demonstrated for a sphere and right-circular cylinder at various locations relative to the half space.     

Morphology,structure, and photoactivity of two types of graphene oxide-TiO<Subscript>2</Subscript> composites

Two types of graphene oxide-TiO₂ composites were prepared: one by including graphene oxide flakes in the TiO₂ sol, followed by thermal treatment (GI composite) at 300°C, and the second by including graphene oxide flakes in the calcined (at 500°C) TiO₂ xerogel (GII composite). The composites were characterized by SEM, TEM-EDS, TEM-SADP, STEM-HAADF, HRTEM coupled with FT, XRD, and XPS. Photocatalysis results were fitted to different kinetic models (pseudo-first and pseudo-second kinetics, intraparticle Weber-Morris diffusion, film diffusion, and external mass transfer). The results showed that by introducing graphene oxide flakes in the TiO₂ sol, followed by thermal treatment at 300°C (GI composite), an efficient graphene oxide-TiO₂ catalyst with high specific surface area, heterogeneity, and many graphitized areas can be obtained. Complete crystallization of the composite is not the key issue for the best photoactivity achievement. The rate limiting step in the photocatalytic process is the photooxidation of SA molecules on the TiO₂ surface.     

Shear-induced aggregation and break up of fibril clusters close to the percolation concentration

To probe the behaviour of fibrillar assemblies of ovalbumin under oscillatory shear, close to the percolation concentration, c_p (7.5%), rheo-optical measurements and Fourier transform rheology were performed. Different results were found close to c_p (7.3%), compared to slightly further away from c_p (6.9 and 7.1%). For 6.9 and 7.1%, a decrease in complex viscosity, and a linear increase in birefringence, n, with increasing strain was observed, indicating deformation and orientation of the fibril clusters. For 7.3%, a decrease in complex viscosity was followed by an increase in complex viscosity with increasing strain, which coincided with a strong increase in n, dichroism, n, and the intensity of the normalized third harmonic (I₃/I₁). This regime was followed by a second decrease in complex viscosity, where n,n and I₃/I₁ decreased. In the first regime where the viscosity was decreasing with increasing strain, deformation and orientation of existing clusters takes place. At higher oscillatory shear, a larger deformation occurs and larger structures are formed, which is most likely aggregation of the clusters. Finally, at even higher strains, the clusters break up again. An increase in complex viscosity, n, n and I₃/I₁ was observed when a second strain sweep was performed 30 min after the first. This indicates that the shear-induced cluster formation and break up are not completely reversible, and the initial cluster size distribution is not recovered after cessation of flow.