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.
Avian Influenza A Virus Infections in Humans Although avian influenza A viruses usually do not infect people, rare cases of human infection with these viruses have been reported. Infected birds shed avian influenza virus in their saliva, mucous and feces. Human infections with bird flu viruses can happen when enough virus gets into a personâs eyes, nose or mouth, or is inhaled. This can happen when virus is in the air (in droplets or possibly dust) and a person breathes it in, or when a person touches something that has virus on it then touches their mouth, eyes or nose.