سال:1392 | دوره: | شماره: |تعداد مقالات:5

We have studied the plane symmetric cosmological solutions for quark matter coupled with the string cloud and domain walls in the context of Rosen’s (General Relativity and Gravitation 4: 435, 1973) bimetric theory. It is observed that, in this theory, string cloud and domain walls do not exist. As we know that, at the early stage of evolution of the universe, domain walls as well as cosmic strings do appear which lead to the formation of galaxies. Thus, it may be said that the bimetric relativity does not help to describe the early era of the universe.

We investigate the excitation behavior of a repulsive impurity-doped quantum dot induced by the simultaneous oscillations of the impurity coordinate and spatial stretch of the impurity domain. We have considered repulsive Gaussian impurity centers. The ratio of two oscillations ( h) has been exploited to understand the nature of the excitation rate. Indeed, it has been found that the said ratio could orchestrate the excitation in a most elegant way. In conjunction with the ratio, the dopant location also plays some important role towards modulating the excitation rate. The present study also indicates attainment of stabilization in the excitation rate as soon as h exceeds a threshold value irrespective of the dopant location. Moreover, prior to the onset of stabilization, we also envisage maximization/minimization in the excitation rate at some typical h values depending on the dopant location. The critical dissection of the characteristics of various impurity parameters provides important insight into the physics underlying the excitation process.

Diodein vivo dosimetry is widely considered to be an important tool for quality improvement of patient care in external radiotherapy. In vivo dose measurements for wedged photon beams require correction factor estimation for difference in wedge angles and field sizes. The diode dosimeters that were used in this study were two different models of PTW products; T60010L and T60010M models were used for 60Co and 6-MV photon beams, respectively. The values of off-axis wedge correction factor were determined at two different physical situations in the wedged and non-wedged directions on the entrance surface of the polystyrene phantom. The wedge correction factor at various depths was then estimated by a proposed method. Results show that the absorbed dose at each depth can be estimated by applying accurate wedge correction factor at depth, on entrance surface dose with negligible probable errors (below 1.2%).

Specific heats of two types of lead tellurides, namely p-type Pb1-x Snx Te (x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) and n-type PbTe doped with y mass% PbI2 (y=0.0, 0.2, 0.5, 0.8, 1.0), were observed in the temperature range of 50oC to 500oC using a differential scanning calorimeter (DSC). The specific heat of pure Te is also observed in the same temperature range to confirm the dominance of Te. At lower temperatures below 200oC, all the observed data were fairly consistent with those predicted on the basis of Dulong-Petit’s law, while above 200oC, the observed data showed curious temperature dependences. At high temperatures above 200oC, DSC analysis, with the aid of the experiment on pure Te, revealed an anomalously large specific heat that can be predicted from the Schottky defects caused by decomposition and sublimation of Te. In the n-type case, the anomaly in specific heats is rather smaller than that in the p-type case, which fact suggested that the dopant PbI2 may suppress the decomposition and sublimation of Te from lead tellurides.

Except some empirical methods, which have been developed in the past, no analytical method exists to describe the evolutionary behavior of a shock wave without limiting its strength. In this paper, we have derived a system of transport equations for the shock strength and the induced continuity. We generate a completely intrinsic description of plane, cylindrical, and spherical shock waves of weak strength, propagating into a non-ideal gas. It is shown that for a weak shock, the disturbance evolves like an acceleration wave at the leading order. For a weak shock, we may assume that [r]=O<Î<<1. We have considered a case when the effect of the first orderinduced discontinuity or the disturbances that overtook the shock from behind are strong, i.e., [rx] =O(1). The evolutionary behavior of the weak shocks in a non-ideal gas is described using the truncation approximation.