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.
INFECTIOUS AGENT. Influenza is caused by infection of the respiratory tract with influenza viruses, which are classified into 3 types: A, B, and C. Only virus types A and B commonly cause illness in humans. Influenza A viruses are further classified into subtypes based on 2 surface proteins, hemagglutinin (H) and neuraminidase (N).