Radar is an electronic device that detects planes, ships, coastlines, landmarks, and even storm clouds. The name radar comes from the first letters of the words radio detection and ranging. As the human eye uses light waves to see, radar "sees" with radio waves. Without radar, planes could not land safely in bad weather and ships could not move safely in thick fog. In the 1800s it was discovered that radio waves could be reflected from objects. But scientists did not make great advances in radar research until the 1930s, when the world was threatened by war. It has been widely used in almost every conflict since then.
Echoes make it possible for radar to work. When a beam of radio waves is sent out, it strikes an object and returns an echo. This echo is picked up by radar and recorded on a screen similar to a television screen. On the screen an observer sees a flash, or a blip that shows the direction of the object and distance.
Airport control towers use radar to guide planes in for safe landings. Almost all large ships depend on radar to prevent collisions with icebergs or other ships. Weather forecasters "see" the size, direction, and speed of storms on radar screens. Astronomers can even use radar to accurately measure the distance to the moon. Thus, the device has generated major advancements.
Huge radar antennas have been installed all over the United States. They guard us against possible enemy attacks. We have ballistic missiles (弹道导弹) warning systems that can alert us to attacks when missiles are more than 1,000 miles away. Other radar systems warn us against enemy aircraft and even spying space satellites.
A. Police track speeders in radar-equipped cars. B. These measurements are now highly accurate. C. The device can be used in a wide range of fields. D. During World War II many countries used radar effectively. E. It is therefore especially valuable to shippers and travelers. F. Today radar is used by commercial airliners and weather forecasters. G. Strengthening national defense is one of radar's most important functions. |
Nature in Architecture
Trees, plants and flowers are all around us and we enjoy their (beautiful) every day. Nature is presented in various architectural designs as well.
People interest is exploring the relationship between art and science will enjoy Singapore's ArtScience Museum. The building was designed (show) the connection between nature and the modem city environment. Visitors are often amazed to find themselves in an urban building that so (true) captures the beauty of natural forms. Harare's Eastgate Centre is superb example of biomimicry. Its architect Mick Pearce was inspired to create the Centre while (watch) a nature documentary in which termites were constructing their nests. The design reduces the need for (tradition) air conditioning and heating systems. The world's first algae-powered building is in Hamburg, Germany, whose surface is covered in panels that contain algae. The panels capture heat from the sun and convert it energy that powers the building. And the algae inside the panels can (harvest) and used to produce fuel.
(create) buildings such as these enables us to live in closer harmony with our environment.