Inflation—a period of accelerated expansion in the early stages of the universe—is currently considered the most promising paradigm for describing the early stages of the universe. The success of the inflationary scenario rests on its ability to explain not only the homogeneity of the background, but also the characteristics of the inhomogeneities superimposed upon it. The inflationary epoch magnifies the tiny fluctuations in the quantum fields present at the beginning of the epoch into classical perturbations that leave their imprints as anisotropies in the cosmic microwave background (CMB). These anisotropies in turn act as seeds for the formation of the large-scale structure that we observe at the present time as galaxies and clusters of galaxies. With anisotropies in the CMB being measured with higher and higher precision, we are currently able to test the predictions of inflation better and better. In this talk, after introducing the motivations and essential features of inflation, I provide an overview of cosmological perturbation theory, and discuss the constraints from the most recent WMAP data on the inflationary parameters.

Ag-Pd bulk alloys have attracted much attention due to the unusual Core Level Shifts (CLS) observed in Ag and Pd with alloy composition. CLS of both alloy components show remarkably the same sign in contradiction to the expectations of the potential model for core electron energies [1]. CLS of both Ag and Pd are in good agreement with the complete screening calculation. Interestingly, there is a change of sign in Pd CLS whereas no such change of sign observed in Ag CLS. It is interesting to study the CLS in ordered surface alloys as peak positions and thus the CLS are better determined on ordered alloys due to the sharp core levels observed compared to the random alloys. We have prepared ordered surface alloys using e-beam technique in situ in the preparation chamber of the THE-XPS machine at HASYLAB, Hamburg, Germany. CLS were calculated from the high energy photoemission data and the degree of order and the Pd adsorption site were determined by NIXSW technique. Our results showed similar sign for both Ag and Pd CLS and surprisingly, there is no change of sign in Pd CLS with alloy composition. 1. I. A. Avrikosov et.al, Phys. Rev. Lett, 87, 176403 (2001)

With an aim to produce a low cost luminescent material suitable for white light emitting application, we attempted the enhancement of the visible luminescence from ZnO nanostructure. We synthesized various kind of Zno nanostructures and studied their photoluminescence properties. The nanometer size dot like structure showed brightest photoluminescence centered about yellow region of the visible spectrum. In order to enhance the luminescence further, we tried to co-dope the ZnO nanoparticles by Al and Li by a low cost, chemical co-precipitation method. Because of possible co-doping, the visible luminescence broadens and looks yellowish white, the luminescence intensity being comparable to the commercial yellow phosphor. The mechanism of the above yellowish white luminescence has not been understood. Preliminary characterization indicates a possible radiative transition associated with DAP recombination.