Analysis of interface cracks in layered piezoelectric composites by a SGBEM

Piezoelectric materials offer many possibilities in advanced engineering structures due to their inherent coupling effects between mechanical and electrical fields and are widely applied in smart devices and structures like transducers, actuators and sensors [2]. An important application of piezoelectric materials is related to layered or laminated composites because they can be optimized to satisfy the high-performance requirements according to different in-service conditions. Beside cracks inside homogeneous domains, one of the most dominant failure mechanisms in layered or laminated composites is the interface failure. Interface cracks and interface debonding may be induced by the mismatch of the mechanical, electrical and thermal properties of the material constituents during the manufacturing process and the in-service loading conditions. This paper presents a hypersingular symmetric Galerkin boundary element method (SGBEM) for crack analysis in two-dimensional (2D), layered and linear piezoelectric solids. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new boundary integral equation formulation for plane orthotropic elastic media

A new boundary integral equation formulation for solving plane elasticity problems involving orthotropic media is presented in this paper. Based on the real variable fundamental solutions of the considered problems, a limit theorem for the transformation from domain integral equations into boundary integral equations (BIEs) and a novel decomposition technique to the fundamental solutions, the regularized BIEs with indirect unknowns, which do not involve the direct calculation of CPV and HFP integrals, are established. The limiting process is done in global coordinates and no separate numerical treatment for strong and weak singular integrals was necessary. The current method does not need to transform the considered problems into isotropic ones as is normally done in the existing literature, so no inverse transform is required. The numerical implementation is carried out using both discontinuous quadratic elements and exact elements, which is developed to model its boundary with negligible error. The validity of the proposed scheme is demonstrated by three numerical examples. Excellent agreement between the numerical results and exact solutions was obtained even with using small amounts of element.     

Electrical conduction in semiconducting NbO2 at hydrostatic pressures up to 6000 atm

We have measured the dc resistance, R, of n-type NbO₂ single crystals in the semiconducting, distorted rutile-structured phase at temperatures from T = 196 K to 410 K using hydrostatic pressures, P, from one to 6000 atm. The resistivity, divided by the temperature, increases exponentially with $\text{1}\text{T}$ and the resistance increases linearly with $\text{P}\text{T}$ at different rates along the a- and c-axes. We find that conduction is due to thermally-activated, adiabatic hopping of small polarons and obtain values and pressure dependences for the vibrational frequency and polaronic energies involved. A discussion of our results is given.     

Application of the Local Boundary Integral Equation Method to Boundary-Value Problems

A review of the meshless formulations based on local boundary integral equation (LBIE) methods is presented. Physical quantities are approximated by the moving least-squares method. A summary of recent developments in the application of the LBIE method to potential problems, elastostatics, elastodynamics, thermoelasticity, and plate bending problems is given. The efficiency and generality of the present formulation in a wide class of engineering problems are confirmed.     

Elastic anharmonicity of InP: Its relationship to the high pressure transition

Ultrasonic wave transit times have been measured in n-type InP at room temperature using hydrostatic pressures up to 4 kbar. Linear pressure dependences are found for the elastic stiffness moduli implying that at the high pressure structural-electrical transition the shear-to-bulk modulus ratio $\text{(C}{}_{11}\text{?C}{}_{12}\text{)}\text{2B}$ has a (fractional) value which fits the modified Born criterion for stability developed by Demarest $\text{et al}$. The anharmonic force constants and some of the third order elastic constants are found to be smaller the higher the transition pressure for indium III-V compounds.     

Ionen-Chromatographie von Polyphosphaten und Phosphonaten

Summary A phosphorus-specific detection system was developed for ion-chromatographic determinations of polyphosphates and phosphonates. After hydrolysing the phosphates or oxidative decomposition of the phosphonates, the resulting o-phosphate is converted to the yellow phosphorusvanadomolybdenum acid and is measured photometrically at 410 nm. Even complex matrices (e.g., washing powder) give very simple chromatograms by phosphorus-specific detection. Moreover, it enables the use of many different eluting agents. With a KCl/EDTA-eluens the resolving power is very high and the column life is considerably prolonged as compared to the commonly used HNO₃-eluens. Various examples of the separations of polyphosphates and phosphonates are shown and the retention times of some phosphonates are compiled.     

Microdetermination of caffeine in blood by gas chromatography--mass spectrometry

A micromethod for the quantitative analysis of caffeine present in small quantities (100 microliter) of whole blood is described. It is based on the gas chromatographic--mass spectrometric analysis of chloroform extracts of biological samples. The method is relatively simple, rapid, specific and sensitive; as little as 20 ng of caffeine can be measured.     

Witt rings of division algebras over global fields

We study basic properties of Auslander-Gorenstein rings related to duality, localization and purity of minimal injective resolutions.     

Correlation between the anisotropy of hopconduction magnetoresistance and reciprocal band masses in Ge

Near 70 kG the d.c. magnetoresistance of phonon-assisted hopping of charge carriers between shallow impurities is found to have an anistropy depending on the reciprocal effective mass calculated from the L₁ conduction band minima in the case of n-type Ge and from the heavy hole component of the Γ′₂₅ valence band maximum in case of p-type Ge. These correlations are discussed and it is suggested that they are connected with the symmetry of the impurity wave functions and that the magnetic field tends to remove the light hole component of an acceptor wave function.