Synthesis and Photochromic Behavior of Azo-Polydiphenylsilanes

This work presents the influence of the trans–cis photoisomerization process of azobenzene-segments onto the optical properties of polysilanes. For this purpose 4-(phenyldiazenyl)phenol and 4-[(4′-nitrophenyl)diazenyl]phenol groups were attached to poly[diphenylsilane-co-methyl(bromopropyl)silane] using the Williamson etherification conditions. Photoisomerization of the pendant azo-groups by irradiation with 365 nm UV light induced distortion of the polysilane backbone conformation in a reversible manner. This process was studied by UV spectral analysis and the photochromic behavior of both polymers was established by taking into account the variation of the σ–σ* absorption intensity.     

Magnetic properties and electronic structures of GdCo3−xSix compounds

Magnetic measurements and band structure calculations were performed on GdCo_3−xSi_x system with x ≤ 0.3. The experimentally determined magnetizations are in rather good agreement with those obtained from band structure calculations. The composition dependence of cobalt moments, at various lattice sites, are analyzed in correlation with the effects of Co 3d–Si 3p bands hybridization.     

Novel mono- and bis-azo dyes containing the azulen-1-yl moiety: Synthesis, characterization, electronic spectra and basicity

3- and 4-[(Azulen-1-yl)-azo]-azo-benzenes were obtained in good yields using the buffered coupling reaction between several alkyl-substituted azulenes and diazotized phenylazo-phenylamines in dichloroacetic acid. The coupling products were characterized and the recorded electronic spectra are discussed. The isosbestic points obtained by protonation enabled the determination of their pK_a values.     

Pulsed voltage driven organic field-effect transistors for high stability transient current measurements

In this article, we propose the usage of gate voltage pulses of alternating polarity, to effectively suppress the hysteresis in organic field effect transistors (OFETs). The hysteretic behaviour of poly(3-hexylthiophene-2,5-diyl) (P3HT) based OFETs is systematically investigated by using continuous and pulsed sweep voltage mode. On the basis of the experimental results, both time settings and mode of gate bias voltage influence the carrier transport in the semiconductor channel. Hysteresis-free transfer characteristic curves are obtained by applying diametrically opposed gate pulses of a few milliseconds in duration. Stable on-current transient measurements are also achieved by implementing the pulse mode, thus allowing on-line gas sensing measurements to be successfully performed. Finally, the response of the sensor upon exposure to different concentrations of analyte vapours is found to be in good agreement with the Langmuir adsorption isotherm model.     

Influence of nano-aluminum filler on the microstructure of SiOC ceramics

Ceramic SiC-mullite-Al₂O₃ based nanocomposites were successfully obtained at temperatures below 1500 °C after pyrolysis and annealing of green compacts prepared by cross-linking and shaping in a warm press step of commercial poly(methylsilsesquioxane) MK polymer mechanically mixed with aluminum filler having nanoparticle size. The heat treatment takes place under the exclusion of oxygen (inert argon atmosphere) and temperatures as low as 800 °C initiate the crystallization of a silicon carbide phase. The influence of the nano-aluminum filler and of the pyrolysis temperature on the crystallization behavior of the materials has been investigated. It was confirmed that an appropriate amount of nano-aluminum filler leads to a cristobalite free bulk SiOC ceramic. In consequence, the received ceramic samples have to be considered as a nano/micro-ceramic composite consisting of crystals of mullite (average dimension in the range of 200 nm), silicon carbide (20 nm) and α-alumina (50 nm).     

A three dimensional calculation of elastic equilibrium for composite materials

A compact scheme is applied to three dimensional elasticity problems for composite materials, involving simple geometries. The mathematical aspects of this approach are discussed, in particular its solution by iteration methods. A vector processor code implementing the compact scheme is presented, and several numerical experiments are summarized.     

On a shear-deformable theory of anisotropic thin-walled beams: further contribution and validations

Within the framework of an existing anisotropic thin-walled beam model, a number of non-classical effects are further incorporated and the model thereby developed is validated. Three types of lay-ups, namely, the cross-ply, circumferentially uniform stiffness, and circumferentially asymmetric stiffness are investigated. The solution methodology is based on the Extended Galerkin's Method and the non-classical effects on the static responses and natural frequencies are investigated. Comparisons of the predictions by the present model with experimental data and other analytical as well as numerical results are conducted and pertinent conclusions are drawn. This work is the first attempt to validate a class of refined thin-walled beam model that has been extensively used towards the study, among others, of dynamic response, static aeroelasticity and structural/aeroelastic feedback control.     

The method of fundamental solutions for inverse source problems associated with the steady‐state heat conduction

This paper presents the use of the method of fundamental solutions (MFS) for recovering the heat source in steady‐state heat conduction problems from boundary temperature and heat flux measurements. It is well known that boundary data alone do not determine uniquely a general heat source and hence some a priori knowledge is assumed in order to guarantee the uniqueness of the solution. In the present study, the heat source is assumed to satisfy a second‐order partial differential equation on a physical basis, thereby transforming the problem into a fourth‐order partial differential equation, which can be conveniently solved using the MFS. Since the matrix arising from the MFS discretization is severely ill‐conditioned, a regularized solution is obtained by employing the truncated singular value decomposition, whilst the optimal regularization parameter is determined by the L‐curve criterion. Numerical results are presented for several two‐dimensional problems with both exact and noisy data. The sensitivity analysis with respect to two solution parameters, i.e. the number of source points and the distance between the fictitious and physical boundaries, and one problem parameter, i.e. the measure of the accessible part of the boundary, is also performed. The stability of the scheme with respect to the amount of noise added into the data is analysed. The numerical results obtained show that the proposed numerical algorithm is accurate, convergent, stable and computationally efficient for solving inverse source problems in steady‐state heat conduction. Copyright © 2006 John Wiley & Sons, Ltd.     

The method of fundamental solutions for inverse boundary value problems associated with the steady‐state heat conduction in anisotropic media

In this paper, the method of fundamental solutions is applied to solve some inverse boundary value problems associated with the steady‐state heat conduction in an anisotropic medium. Since the resulting matrix equation is severely ill‐conditioned, a regularized solution is obtained by employing the truncated singular value decomposition, while the optimal regularization parameter is chosen according to the L‐curve criterion. Numerical results are presented for both two‐ and three‐dimensional problems, as well as exact and noisy data. The convergence and stability of the proposed numerical scheme with respect to increasing the number of source points and the distance between the fictitious and physical boundaries, and decreasing the amount of noise added into the input data, respectively, are analysed. A sensitivity analysis with respect to the measure of the accessible part of the boundary and the distance between the internal measurement points and the boundary is also performed. The numerical results obtained show that the proposed numerical method is accurate, convergent, stable and computationally efficient, and hence it could be considered as a competitive alternative to existing methods for solving inverse problems in anisotropic steady‐state heat conduction. Copyright © 2005 John Wiley & Sons, Ltd.