F. Han

Strain fields in InAs∕GaAs quantum wire structures: Inclusion versus inhomogeneity

This paper studies the elastic fields in InAs∕GaAs quantum wire (QWR) structures arising from the lattice mismatch between InAs and GaAs. The present treatment is different from recent analyses based on the Eshelby inclusion approach where the QWR material, for simplicity, is assumed to be the same as the matrix/substrate. Here, a more complete treatment is developed taking into account the structural inhomogeneity using the boundary integral equation method. We implement our model using discrete boundary elements at the interface between the QWR and its surrounding matrix. The coefficients of the algebraic equations are derived exactly for constant elements using our recent Green’s-function solutions in the Stroh formalism. For both (001) and (111) growth directions, our results show that while the elastic fields far from the QWR are approximated well by the homogeneous inclusion approach, for points within or close to the QWR, the differences between the fields computed with the simplified inclusion and...

Green's functions for transversely isotropic piezoelectric multilayered half-spaces

This paper presents Greens functions for transversely isotropic piezoelectric and layered half-spaces. The surface of the half-space can be under general boundary conditions and a point source (point-force/point-charge) can be applied to the layered structure at any location. The Greens functions are obtained in terms of two systems of vector functions, combined with the propagator-matrix method. The most noticeable feature is that the homogeneous solution and propagator matrix are independent of the choice of the system of vector functions, and can therefore be treated in a unified manner. Since the physical-domain Greens functions involve improper integrals of Bessel functions, an adaptive Gauss-quadrature approach is applied to accelerate the convergence of the numerical integral. Typical numerical examples are presented for four different half-space models, and for both the spring-like and general traction-free boundary conditions. While the four half-space models are used to illustrate the effect of material stacking sequence and anisotropy, the spring-like boundary condition is chosen to show the effect of the spring constant on the Greens function solutions. In particular, it is observed that, when the spring constant is relatively large, the response curve can be completely different to that when it is small or when it is equal to zero, with the latter corresponding to the traction-free boundary condition.

Effect of temperature variation on pavement responses using 3D multilayered elastic analysis

The response of flexible pavement is largely influenced by the resilient modulus of the pavement profile. Different methods/approaches have been adopted in order to estimate or measure the resilient modulus of each layer assuming an average modulus within the layer. To account for the variation in the modulus of elasticity with depth within a layer, the layer should be divided into several sublayers and the modulus should be gradually varied between the layers. A powerful and innovative program has been developed utilizing the unique propagator matrix method and the cylindrical system of vector functions. Our new program can predict accurately and efficiently the response of flexible pavements of any number of layers/sublayers. Numerical results in this paper showed that, instead of assuming one response due to an average modulus, modulus variation with depth should be considered in any pavement analysis since it can capture the response envelopes of the pavement.

Tumor Detection With a New Boundary Integral Equation Formulation

During pathological evolution, tissues mechanical properties, such as elastic moduli, will be changed. This feature has already been used in theory and application of elastography for detecting and characterizing tumors. In this paper, a tumor mass embedded in a breast tissue is modeled as an Eshelby inhomogeneity problem. Using a new anisotropic boundary element method (BEM) developed recently by the authors, the stress and strain fields due to an external load are solved efficiently and accurately. Furthermore, an inverse algorithm is also proposed for the detection and characterization of the embedded tumor mass. Numerical examples are presented to show that the BEM algorithm based on the Eshelby inclusion concept provides a useful method to solve certain biomedical problems.© 2004 ASME