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 main targets of the influenza virus are the columnar epithelial cells of the respiratory tract, i.e. trachea, bronchi and bronchioles. Viral replication in combination with the immune response to infection results in the destruction and loss of the mucosal epithelial cells.