Characterization by Fourier transform infrared spectroscopy of polyethylene adipate/cholesteryl palmitate blends

FT‐IR spectroscopy has been employed to study compatibility, melting, and crystallization of the polyethylene adipate (PEA)/cholesteryl palmitate (CP) blends. The changes in FT‐IR spectra were followed by controlled rate of heating and cooling. The bands corresponding to the crystalline structure have been assigned. The accuracy of the transition temperature determination has been improved by fitting the curve of the integral absorbance dependence on temperature with a Boltzmann function. From dependence of the transition temperatures on the composition of the blend, it has been established that for each mixing ratio a certain mass fraction of CP should be dissolved in the PEA matrix. The PEA/CP blends behave as a phase‐separated system with partial miscibility. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1156–1163, 2004     

Analysis of stable crack growth of a semi-elliptical surface crack by numerical simulation

In the present paper, the canoeing effect during stable crack growth of a semi-elliptical surface crack in a side-grooved panel under tension was investigated by means of a three-dimensional elastic-plastic finite element analysis. The numerical crack growth simulation was performed by using crack mouth opening displacement resistance curves obtained from experiment on panels by the multi-specimen procedure. The influence of the crack tip constraint and the stress triaxiality on the ductile crack resistance property was studied. It is shown that the tearing modulus T_JR increases proportionally with decreasing stress triaxiality implying constraint dependent J_R-curves.     

Thermal conductivity of non-Newtonian nanofluids: Experimental data and modeling using neural network

Three different types of nanofluids were prepared by dispersing γ-Al₂O₃, TiO₂ and CuO nanoparticles in a 0.5 wt% of carboxymethyl cellulose (CMC) aqueous solution. Thermal conductivity of the base fluid and nanofluids with various nanoparticle loadings at different temperatures were measured experimentally. Results show that the thermal conductivity of nanofluids is higher than the one of the base fluid and the increase in the thermal conductivity varies exponentially with the nanoparticle concentration. In addition to increase with the nanoparticle concentration, the thermal conductivity of nanofluids increases with the temperature. Neural network models were proposed to represent the thermal conductivity as a function of the temperature, nanoparticle concentration and the thermal conductivity of the nanoparticles. These models were in good agreement with the experimental data. On the other hand, the Hamilton Crosser model was only satisfactory for low nanoparticle concentrations.     

Using of leather fibers as an additive in elastomeric compounds: Its effect on curing behavior and physico‐mechanical properties

In this study, leather fibers have been used as an additive in several elastomeric compounds based on nitryl butadiene rubber (NBR), chloroprene rubber (CR), ethylene–propylene–diene monomer (EPDM), and chlorinated isobutylene‐isoprene rubber (CIIR). The effects of employing fibers upon vulcanization characteristics, physico‐mechanical and thermal properties of the compounds were studied. Measuring of vulcanization characteristics of the compounds exhibited that leather fibers has no considerable effect on initial viscosity, processability, and curing time of the compounds but increases cross‐link density. Evaluation of mechanical properties of the vulcanized compounds showed that using leather fibers leads to increase in tensile strength of NBR‐based compound due to compatibility between NBR and leather fibers. Also hardness of all compounds increased drastically by employing leather fibers. The obtained results showed incorporation of leather fibers had no considerable effect on resilience, density, and thermal stability of compounds but enhanced liquid resistance. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Optimal quadratures with regard to the efficiency

In this paper first one studies the optimality problem with regard to the efficiency for some classes of numerical quadrature algorithms. Then one investigates the concordance between the «efficiency criteria» and the «?-complexity criteria».     

Changes in breakdown characteristics of planar Al/nSi Schottky diodes during the postmetallization heat treatment

A correlation was found between interface geometry and breakdown voltage of planar Al/n-Si Schottky diodes. The postmetallization heat treatment determines silicon etching at the contact periphery beneath the passivating oxide and therefore increases the breakdown voltage due to the increase in the curvature radius at the corner of the metallization film. However, a too strong aluminium-silicon interaction may yield a different interface geometry. The hexagonal-like cutting of Si surface along the crystallographic axes determines field concentrations at the corners and explains lower breakdown voltages obtained for smaller contact diameters. The failure of breakdown characteristics for contacts subjected to high current densities and temperature stress may be also explained through the modifications occurring in interface geometry.     

Preconditioning by Gram matrix approximation for diffusion–convection–reaction equations with discontinuous coefficients

This work analyses the preconditioning with Gram matrix approximation for the numerical solution of a linear convection–diffusion–reaction equation with discontinuous diffusion and reaction coefficients. The standard finite element method with piecewise linear test and trial functions on uniform meshes discretizes the equation. Three preconditioned conjugate gradient algorithms solve the discrete linear system: CGS, CGSTAB and GMRES. The preconditioning with Gram matrix approximation consists of replacing the solving of the equation with the preconditioner by two symmetric MG iterations. Numerical results are presented to assess the convergence behaviour of the preconditioning and to compare it with other preconditioners of multilevel type.     

EPR and magnetic susceptibility studies on V2 O5-P2O5-PbO glasses

EPR and magnetic susceptibility investigations on the glass system with 04+ ion content are explained using a simulation program on the assumption of the superposition of two signals, one with hyperfine structure (hfs) typical for isolated ions and another one consisting of a broad line without hfs characteristic for clustered ions. The hfs is not shown for x<3mol%V₂O₅. The EPR data show the presence of V₄₊ ions in a square-pyramidal co-ordination (C_4V) for 3x20mol%V₂O₅. The progressive disappearance of hfs for high V²O⁵ content (>20 mol %) suggests the increase of the associated ion number coupled by superexchange interactions. This result is consistent with magnetic susceptibility data for >3 mol % where the temperature dependence of magnetic susceptibility is described by the Curie–Weiss type law with a negative paramagnetic Curie temperature. The magnetic susceptibility results allowed the estimation of the V⁴⁺/V⁴⁺ + V⁵⁺ ratio in the sample studied.