APPLICATIONS Horn antennas are widely used as satellite dishes and radio telescopes. Antennas 6 2. PARABOLIC ANTENNAS A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves.
Flu (influenza). Flu is usually infectious a day before symptoms start and remains infectious for about five to six days. Children and people with lowered immune systems may be infectious for a few days longer.
As the illness progresses, a person may have warm, flushed skin, watery or bloodshot eyes, a severe cough that brings up phlegm, nasal congestion, and nausea and vomiting. A bout of flu typically lasts one to two weeks, with severe symptoms subsiding in two to three days. However, weakness, fatigue, dry cough, and a reduced ability to exercise can linger for three to seven days. How Long Is the Flu Contagious? A 2013 survey conducted by the National Foundation for Infectious Diseases revealed that 41 percent of people think the flu is only contagious after symptoms start. Thatâs not true.