Circadian Rhythms That Impact Sleep Biological variations that occur in the course of a day are called circadian rhythms. Circadian rhythms are controlled by the body`s biological clock. Many bodily functions follow the biologic clock, but sleep and wakefulness comprise the most crucial circadian rhythm. Circadian sleep rhythm is among the many body rhythms modulated by the hypothalamus . Light directly affects the circadian sleep rhythm. Light is called a zeitgeber, a German word meaning time-giver, since it pieces the biological clock. A practical purpose provides been proposed for the circadian rhythm, using the analogy of the brain being somewhat such as a battery charging while asleep and discharging during wakefulness.The products were found to release excessive amounts of asbestos in to the environment. The Environmental Protection Agency also released a ban on all new uses of asbestos in 1989. However, all asbestos uses that had recently been established ahead of this date remain legally allowed. Therefore, people today are still being exposed to asbestos, albeit not as seeing that the people living during the earlier centuries were extensively. The U.S. EPA provides stipulated that there surely is no safe degree of exposure to asbestos. Commensurate with its regulatory laws against the use of asbestos, the EPA provides set forth an asbestos concentration limit of 7M fibers per Liter of normal water. This holds true for fibers with at least 5 um in length.