The world's second nuclear explosion was achieved with uranium-235. This isotope is unstable and fissions when struck by a neutron. It is, however, found in natural uranium at a concentration of only 0.7 percent. To be useful in nuclear weapons, the concentration must be increased.
Introduction. Influenza, or flu, is a caused by a virus infecting the respiratory system, meaning your nose, throat, bronchial tubes, and lungs. Flu symptoms are usually more severe than those of the common cold and are more likely to affect other parts of your body.
Viral Shedding. Influenza spreads mainly by respiratory droplets that contain copies of the virus that have replicated in your body. Viral shedding, which correlates with infectivity, occurs starting approximately 1 day before symptoms appear and can continue for up to 10 days after symptoms develop.