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We theoretically study a nanospaser system, which consists of a spherical silver nanoparticle embedded inside a sphere composed of dye molecules. The gain of the system, dye molecules, are described by a three-level model, where the transition frequency between the lowest two energy levels is close to the surface plasmon frequency of the nanosphere. Contrary to a two-level model of spaser, the three-level model takes into account finite relaxation time between the high energy levels of the gain medium. These relaxation processes affect both the spaser threshold and the number of generated plasmons in the continuous wave regime. While for a two-level model of a spaser the number of generated plasmons has a linear dependence on the gain, for the three-level model this dependence becomes quadratic.

The aim of this paper is to study the variation of brain matter of Nepalese patients using CT scan. CT number and linear attenuation coefficient (LAC) of cortical bone are found largest among other brain matters, indicating the largest density. All brain matters except cortical bone show low association indicating slight changing trend with age. The cortical bone under 10 years shows low value of LAC and CT number, indicating cortical bone towards maturation whereas cortical bone shows no significant increase with age above 10 years. There is no much significant relation by gender in brain hemorrhage and infarction.Journal of Institute of Science and Technology, 2014, 19(2): 129-134