Global solar radiation characteristics at Dumdum (West Bengal)

The data of the hourly global solar radiation (G) on a horizontal surface of Dumdum/ Gangetic West Bengal for the period 1980 to 2010 has been obtained. The diurnal extra terrestrial solar radiation for the station (22.39° N, 88.27° E) has been computed and then the clearness index has been calculated. The diurnal variations of the results have been studied. Also the daily total values and its monthly and seasonal averages as well as their frequency distribution in percentage have been computed and examined. The seasonal and climatic effects of the fluctuation of the results have been discussed. These effects have been particularly large during pre monsoon season (i.e. March to May); the period which experiences the thunderstorm activity the most in this area and this fact may be attributed as one of the cause for generation of the thunderstorm. The clearness index (G/Go) shows that the incoming solar radiation is almost halved on reaching the earth. Also the comparative statistical as well as graphical study of average total global solar radiation with the average maximum temperature confirms once again the fact that the total global solar radiation is fairly related to average maximum temperature in correlation (0.77) as well as in wave form

Perturbations on steady spherical accretion in Schwarzschild geometry

The stationary background flow in the spherically symmetric infall of a compressible fluid, coupled to the space-time defined by the static Schwarzschild metric, has been subjected to linearized perturbations. The perturbative procedure is based on the continuity condition and it shows that the coupling of the flow with the geometry of space-time brings about greater stability for the flow, to the extent that the amplitude of the perturbation, treated as a standing wave, decays in time, as opposed to the amplitude remaining constant in the Newtonian limit. In qualitative terms this situation simulates the effect of a dissipative mechanism in the classical Bondi accretion flow, defined in the Newtonian construct of space and time. As a result of this approach it becomes impossible to define an acoustic metric for a conserved spherically symmetric flow, described within the framework of Schwarzschild geometry. In keeping with this view, the perturbation, considered separately as a high-frequency travelling wave, also has its amplitude reduced.Comment: 8 pages, no figur

Casimir force on interacting Bose-Einstein condensate

We have presented an analytic theory for the Casimir force on a Bose-Einstein condensate (BEC) which is confined between two parallel plates. We have considered Dirichlet boundary conditions for the condensate wave function as well as for the phonon field. We have shown that, the condensate wave function (which obeys the Gross-Pitaevskii equation) is responsible for the mean field part of Casimir force, which usually dominates over the quantum (fluctuations) part of the Casimir force.Comment: Accepted in Journal of Physics B: Atomic, Molecular and Optical Physic

Global solar radiation characteristics at Dumdum (West Bengal)

148-153The data of the hourly global solar radiation (G) on a horizontal surface of Dumdum/ Gangetic West Bengal for the period 1980 to 2010 has been obtained. The diurnal extra terrestrial solar radiation for the station (22.39° N, 88.27° E) has been computed and then the clearness index has been calculated. The diurnal variations of the results have been studied. Also the daily total values and its monthly and seasonal averages as well as their frequency distribution in percentage have been computed and examined. The seasonal and climatic effects of the fluctuation of the results have been discussed. These effects have been particularly large during pre monsoon season (i.e. March to May); the period which experiences the thunderstorm activity the most in this area and this fact may be attributed as one of the cause for generation of the thunderstorm. The clearness index (G/Go) shows that the incoming solar radiation is almost halved on reaching the earth. Also the comparative statistical as well as graphical study of average total global solar radiation with the average maximum temperature confirms once again the fact that the total global solar radiation is fairly related to average maximum temperature in correlation (0.77) as well as in wave form