Bikash C. Gupta

Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals

Motivated by a recent experiment on acoustic lenses, we perform numerical calculations based on a multiple scattering technique to investigate the focusing of acoustic waves with sonic crystals formed by rigid cylinders in air. The focusing effects for crystals of various shapes are examined. The dependence of the focusing length on the filling factor is also studied. It is observed that both the shape and filling factor play a crucial role in controlling the focusing. Furthermore, the robustness of the focusing against disorders is studied. The results show that the sensitivity of the focusing behavior depends on the strength of positional disorders. The theoretical results compare favorably with the experimental observations, reported by Cervera, et al. [Phys. Rev. Lett. 88, 023902 (2002)].

Disorder effects on the imaging of a negative refractive lens made by arrays of dielectric cylinders

By a numerical simulation based upon multiple scattering theory, we confirm that, for certain frequencies, crystal structures formed by dielectric cylinders embedded in parallel in a uniform medium can indeed act as a negative refractive lens. Some agreement with and differences from previous studies are elaborated upon. The refractive index is also estimated from ray optics approximation. The tolerance of the lens to positional disorders is then discussed.

Localization of classical waves in two-dimensional random media: a comparison between the analytic theory and exact numerical simulation.

The localization length of classical waves in two-dimensional random media is calculated exactly, and is compared with the theoretical prediction from the current analytic theory. Significant discrepancies are observed. It is also shown that as the frequency varies, critical changes in the localization behavior can occur. However, by a rescaling of parameters the two results tend to match each other for weak scattering. Possible reasons for the discrepancies are discussed.

Formation of stationary localized states due to nonlinear impurities using the discrete nonlinear Schrödinger equation

The Discrete Nonlinear Schr

Structural studies of phosphorus induced dimers on Si(001)

\ddot{o}

Aharonov-Bohm effect in the presence of evanescent modes

dinger Equation is used to study the formation of stationary localized states due to a single nonlinear impurity in a Caley tree and a dimeric nonlinear impurity in the one dimensional system. The rotational nonlinear impurity and the impurity of the form

STATIONARY LOCALIZED STATES DUE TO A NONLINEAR DIMERIC IMPURITY EMBEDDED IN A PERFECT ONE-DIMENSIONAL CHAIN

-\chi \mid C \mid^{\sigma}

Structural and electrical properties of armchair CdS nanotubes

where

Metallic atomic wires on patterned dihydrogenated Si(001)

\sigma

Magnetic properties of bimetallic clusters composed of Gd and transition metals

is arbitrary and