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.
Influenza, commonly called the flu, is caused by viruses that infect the respiratory tract. Flu symptoms include fever, chills, cough, sore throat, headache, muscle aches, and. fatigue. The incubation period for flu is about one to four days. Flu is contagious, and symptoms may last up to seven to 14 days.