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.
People of all ages can get the flu. Although most people are ill with the flu for only a few days, some have a much more serious illness and may need to be hospitalized. Influenza can also lead to pneumonia and death. Influenza viruses continually change (mutate). Because the virus changes, people can get the flu no matter what their age. The process works like this: A person infected with an influenza virus develops antibodies against that virus. The virus changes. The older antibodies no longer recognize the newer virus. The person becomes infected again.