Electromagnetic wave transmission and reflection by a quasi-periodic layered semiconductor structure

The specific features of electromagnetic wave reflection and transmission through the periodic and quasi-periodic layered semiconductor structures placed into a parallel plate waveguide are studied. The effect of the structure parameters and dissipation in semiconductor layers on the reflectance (transmittance) of electromagnetic wave is examined. The comparative analysis of the electromagnetic wave reflectance characteristics in the structures with different types of symmetry is carried out.     

Some numerical techniques for solving elliptic interface problems

Many physical phenomena can be modeled by partial differential equations with singularities and interfaces. The standard finite difference and finite element methods may not be successful in giving satisfactory numerical results for such problems. Hence, many new methods have been developed. Some of them are developed with the modifications in the standard methods, so that they can deal with the discontinuities and the singularities. In this article, a survey has been done on some recent efficient techniques to solve elliptic interface problems. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 28: 94‐114, 2012     

Axisymmetric magnetohydrodynamic flow of Jeffrey fluid over a rotating disk

This paper examines the magnetohydrodynamic boundary layer flow of Jeffrey fluid due to a rotating disk. The governing partial differential equations are first transformed into the coupled system of ordinary differential equations and then solved by using the homotopy analysis method. The influence of various involved physical parameters on the dimensionless radial and azimuthal velocities is sketched and analyzed. The variation of skin friction coefficients in radial and azimuthal directions is studied for various values of pertinent parameters. Copyright © 2011 John Wiley & Sons, Ltd.     

The Fejér-Riesz inequality for the Besov spaces

A Fejér-Riesz inequality for the weighted Besov spaces B _p,q is given. Some characterizations of functions in B _p,q in terms of their Taylor coefficients are obtained.     

Two‐phase pressure drop caused by sudden flow area contraction/expansion in small circular pipes

Theoretical studies have been made to determine the pressure drops caused by abrupt flow area expansion/contraction in small circular pipes for two‐phase flow of air and water mixtures at room temperature and near atmospheric pressure. Two‐phase computational fluid dynamics (CFD) calculations, using Eulerian–Eulerian model (with the air phase being compressible for pipe contraction case) are employed to calculate the pressure drop across sudden expansion and contraction. The pressure drop is determined by extrapolating the computed pressure profiles upstream and downstream of the expansion/contraction. The larger and smaller tube diameters are 1.6 and 0.84 mm, respectively. Computations have been performed with single‐phase water and air, and two‐phase mixtures in a range of Reynolds number (considering all‐liquid flow) from 1000 to 12 000 and flow quality from 1.2 × 10^?3 to 1.6 × 10^?2. The numerical results are validated against experimental data from the literature and are found to be in good agreement. The expansion and contraction loss coefficients are found to be different for single‐phase flow of air and water, and they agreed reasonably well with the commonly used theoretical predictions. Based on the numerical results as well as experimental data, correlations are developed for two‐phase flow pressure drops caused by the flow area contraction as well as expansion. Copyright © 2010 John Wiley & Sons, Ltd.     

Calculation of diffusion coefficient of long chain molecules using molecular dynamics

Molecular dynamics (MD) is a powerful tool for calculating several thermo-physical properties of wide range of materials. In this study, the diffusivities (D) of two widely used long chain molecules MHA and ODT are calculated at various temperatures using MD simulations coupled with Einstein relationship. Four different kinds of forcefields COMPASS, UFF, CVFF and PCFF are employed in the MD simulation and the results are compared. Diffusivity values are evaluated in a humid environment in presence of water molecules.     

Relations between regularity coefficients

For a bounded sequence of matrices defining a nonautonomous dynamics with discrete time, we obtain all possible relations between the regularity coefficients introduced by Lyapunov, Perron and Grobman. This includes considering general inequalities between the coefficients and showing that these inequalities are the best possible, in the sense that for any three nonnegative numbers satisfying them, and for no others, there exists a bounded sequence of matrices having the numbers respectively as Lyapunov, Perron and Grobman coefficients. Moreover, we establish inequalities between the three coefficients and some other regularity coefficients.     

Absorption spectra and aqueous photochemistry of β-hydroxyalkyl nitrates of atmospheric interest

Molar absorption coefficients were measured for select alkyl nitrates and β-hydroxyalkyl nitrates in methanol. The presence of the β-hydroxyl group has a relatively minor effect on the absorption spectrum in the vicinity of the weak n → π* transition, which is responsible for photolysis of organic nitrates in the atmosphere. For both alkyl nitrates and β-hydroxyalkyl nitrates, there is an enhancement in the absorption coefficients in solution compared to the gas-phase values. The effect of the β-hydroxyl group on the spectra was modelled with molecular dynamics simulations using an OM2/GUGA-CI Hamiltonian for ethyl nitrate and β-hydroxyethyl nitrate. The simulation provided a qualitatively correct shape of the low energy tail of the absorption spectrum, which is important for atmospheric photochemistry. The role of direct aqueous photolysis in removal of β-hydroxyalkyl nitrates in cloud and fog water was modelled using a relative rate approach, and shown to be insignificant relative to gas-phase photochemical processes and aqueous OH oxidation under typical atmospheric conditions.     

Basic properties of scalarizmg functionals for multiobjective optimization

If a partial ordering or preordering induced by a cone D defines a multi objective optimization problem, then scalarizing functionals for this problem shall posses two basic properties. D – monotonicity and D _e approximation. Several ways of constructing functionals with these properties are discussed in the paper.