The ionizing spectral energy distribution of quasars exhibits a steepening of the distribution short-ward of 1200 Å. The change of the power-law index from approximately −1 to −2 so far has been interpreted as being intrinsic to quasars. We study an alternative interpretation, in which a tenuous absorption screen is responsible for the change of index. We find that the most successful function ...

We propose a variant of hybrid inflation which is applicable in a wide class of supersymmetric grand unified models. The observed temperature perturbations of cosmic background radiation can be reproduced with natural values of the parameters of the theory and a grand unification scale which is consistent with the unification of the minimal supersymmetric standard model gauge couplings as measu...

In order to draw out the essential behavior of the universe, investigations of early universe cosmology often reduce the complex system to a simple integrable system. Inflationary models are of this kind as they focus on simple scalar field scenarios with correspondingly simple dynamics. However, we can be assured that the universe is crowded with many interacting fields of which the inflaton i...

The largest fraction of the natural radiation exposure we receive comes from a radioactive gas, radon and its decay products (nearly 50%). The radon gas can enter to the body via respiring, drinking and eating and caused damage to respiratory and digestion systems. Also radium-226 is widely distributed in the environment. When a person ingests radium, this element deposits in bones and cause to...

background; environmental gamma ray refers to the gamma radiation from terrestrial sources and building materials. in enclosed spaces radiation can become a health hazard leading to potential increase in the rates of lung cancer. the goal of this study is to assess the exposure to natural gamma radiation of children in the schools of zanjan province. method; the natural gamma radiation was asse...

Applied to skin color, the sexual selection hypothesis proposes that male preference for light-skinned females explains the presence of light skin in areas of low solar radiation. According to this proposal, in areas of high solar radiation, natural selection for dark skin overrides the universal preference of males for light females. But in areas in which natural selection ceases to act, sexua...