TAILIEUCHUNG - Teaching and learning english part 11

Grice's theoiy of implicature is an attempt to explain how a hearer gets what is meant, from the level of expressed meaning to the level of implied meaning from what is said. In order to explain the mechanisms by which people interpret conversational implicature (Levinson 1983. Yule 1996). | stations. Such stations are called VORTACs. Because TACANs include distance measuring equipment VOR DME and VORTAC stations are identical in navigation potential to civil aircraft. 5. Radar Radar RAdio Detection And Ranging detects things at a distance by bouncing radio waves off them. The delay caused by the echo measures the distance. The direction of the beam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide area two to four times per minute. They use very short waves that reflect from earth and stone. They are common on commercial ships and long-distance commercial aircraft. General purpose radars generally use navigational radar frequencies but modulate and polarize the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms as well as land and vehicles. Some can superimpose sonar data and map data from GPS position. Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. Sometimes search radars use the doppler effect to separate moving vehicles from clutter. Targeting radars use the same principle as search radar but scan a much smaller area far more often usually several times a second or more. Weather radars resemble search radars but use radio waves with circular polarization and a wavelength to reflect from water droplets. Some weather radar use the doppler to measure wind speeds. 6. Emergency services Emergency Position-Indicating Radio Beacons EPIRBs Emergency Locating Transmitters ELTs or Personal Locator Beacons PLBs are small radio transmitters that satellites can use to locate a person or vehicle needing rescue. Their purpose is to help rescue people in the first day when survival is most likely. There are several types with widely-varying performance. 7. Data digital radio Most new radio systems are

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