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.
How long does the flu last? For most healthy people, the flu is an uncomfortable but short-term illness that resolves itself as the immune system fights it off. Symptoms usually appear from one to four days after exposure to the virus, and they last five to seven days. For people who've had a flu shot, the symptoms may last a shorter amount of time, or be less severe. For other people, the symptoms may last longer. Even when symptoms resolve, you may continue to feel fatigued. Some people are at increased risk for complications from influenza. 1  These people include: 2  the very young. 3  people 65 or older. 4  people with chronic illnesses, such as asthma, heart disease, HIV, or diabetes. 5  pregnant women. 6  people with a body mass index (BMI) of 40 or higher.