With the phenomenal growth in mobile and portable terrestrial wireless communication systems and due to their potential utilization in a wide variety of high data rate and multimedia services, higher frequency bands need to be allocated. New devices and components for high frequency and millimeter wave integrated front-end receivers are being developed, active and low cost phased array antennas are being designed and advanced software programs in coding, modulation, switching and networking are being developed. In addition to these, developing new and more computationally efficient propagation models is also essential. Development of reliable propagation models will help in using the rather congested frequency spectrum more efficiently, in planning more effective radio networks and in implementing cost effective solutions for a desirable and user specific communication coverage pattern. In the first article, "Choosing by Mapping of Models for Propagation Losses and Interference Parameters for Radio Networks Design", the authors, S R Meneses G, R Linares y M, M Cuevas and J López-Bonilla, have presented a new technique to radio networks design in urban and rural areas by mapping of models for the propagation losses and interference parameters. A concrete mapping of models for different kinds of zones is presented.

Langrangian systems described by couple scalar fields are gaining attention. In the second article, "Factorization Method for Three Scalar Fields and BPS Bounds", authors, J Sadeghi and A Mohammadi, have considered a class of systems of three coupled real scalar fields and obtained the solutions.

Surfaces of superconductors and superconductor-semiconductor interfaces play an important role in technological device applications. In the third article, "Electronic Structure of the Interface YBa₂Cu₃O₇/GaAs", the authors, A E García, J Camas, S Mendoza, R Baquero-Salaquarda, L M García-Cruz and R Baquero, have studied the electronic band structure of the YBCO-GaAs interface using density functional theory with Full-potential linearized augmented plane wave method. The GaAs interface layer is found to be metallic.

The solid polymer electrolytes are of technological interest due to their possible applications in different devices such as batteries, fuel cells, electro chromic display devices/smart windows and photo-electrochemical solar cells. In the fourth article titled, "Conductivity and Ion Transport Characterization of a PEO Based Conducting Polymer Electrolyte System", authors, K Vijay Kumar, G Keerthi, G Nataraju and U V Subba Rao, have prepared solid ion conducting polymer electrolyte system by solution-cast technique and characterized by using several experimental techniques, such as IR and DSC studies, composition dependence conductivity, temperature dependence conductivity and transport number measurements. The experimental data has shown that the charge transport in these polymer electrolytes is predominantly due to ions.

In the fifth article, "The Photon and its Mass", a contemporary discussion about the photon and its mass is presented. The authors, Baiju George and P Appla Naidu, have discussed various theories like Gauge theory, special theory of relativity, Maxwell's electrodynamics, proca's theory to understand about the existence of a photon. Mass of the photon has been the central theme of the paper.

- BVVSN Prabhakara Rao
Consulting Editor