When a mixture of different substances is rotated at extremely high speeds within a closed path (in your case a closed container), substances of higher mass often go on to the outermost path and lighter particles experience the nearest to rotating axis. The same principle can be used in centrifuge oil cleaning. Research in the United States shows that the failure rate is 15% to 28% per annum. And, both men and women are frustrated by having to interrupt at the last moment. A cortisol blood test is carried out to discover the cortisol hormone level in the blood. Cortisol assists one's body in metabolic process and stress management. The levels of cortisol inside the blood may vary as a consequence of several factors like stress, infection, injury and strenuous activities. The levels of cortisol usually vary throughout the length of the afternoon. In the morning, it can be generally increased, at night and during sleep, its level is often low. Its level, however, may continue with the person's sleeping habits. Those who sleep within the daytime and therefore are awake during the night, might have reversed cortisol level patterns also.