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.
The flu (short for influenza) is a respiratory virus that affects the throat, nose, bronchi and, sometimes, the lungs. There are different types of influenza viruses and they evolve and change from year to year. For most people, the flu is an inconvenience that subsides in a few days. For others, influenza can lead to health complications, visits to the hospital and even death.