- Mar 25 Sun 2012 23:22
- Mar 25 Sun 2012 22:05
- Mar 24 Sat 2012 11:32
Animals and Echolocation
While it is apparent that most animals are able to produce sounds of their own, the reasons behind animal sounds are not often known. It is assumed that, like humans, animals produce sounds for a variety of reasons. In general, it is thought that animals communicate much like the way humans talk, though in a more primitive sense. Some animals, however, seem to have advanced aural abilities, some that even humans lack, one of whichis what we refer to today as echolocation.
Echolocation, also known as biosonar , is the way an animal uses sounds and their echoes to examine their surrounding environment and objects in it. Using echolocation, an animal can hunt for food, avoid danger, or virtually any task that humans use sight to accomplish. In many ways, echolocation operates similarly to a boat's or submarine's sonar, and this relationship was actually one of the major reasons for the initial discovery of echolocation（by whom?）. In World War II, a major development was that of sonar for detecting submarines. The devices used to pick up those sounds, called hydrophones, also picked up many sounds from sources that were found to be whales or dolphins.
n. method by which underwater objects are detected using transmitted and reflected sound waves; device which locates objects by means of sonar
Whales and dolphins use echolocation because of the visual and
acoustic properties of their underwater habitat / habitation / habitant / inhabitant / inhabit / —it is easier to hear than it is to see underwater. They emit high-pitched clicks in the direction they are heading, and rely on the sound waves that come back to find information about objects (e.g. food, obstacles) ahead of them. The clicks are produced by passing air through membranes called the "phonic lips". The sounds are then reflected forward like a beam using the bones of the animal's skull. Whales are able to control the frequency of their clicks using a large organ in their head called a "melon". The melon also helps to focus the sounds into a narrow beam. Also, dolphins in particular are very capable at controlling the strength of their clicks. In one study, dolphins were shown to produce clicks at a volume of 170 dB (decibel: unit of measurement for gauging the intensity of sound ) in tanks, while they produced clicks as loud as 220 dB in the wild. This was because the smooth flat walls of the tank reflected sounds much more easily than are normally encountered in the open sea, and the dolphins adapted to the new environment. Despite this amount of control, biosonar is not without its limitations. Occasionally, whales strand themselves on shore and die of suffocation. Once joked as a form of "whale suicide", it was later discovered that many of these "beachings" occurred on gently sloping beaches where the whale's echolocation would not bounce back strongly as it does from steep rocky formations.
Whales and dolphins are not the only animals to utilize echolocation though, and it is a tool not only used underwater. In the late 1800s, a Swiss zoologist postulated that bats could see with their ears. His idea was rejected, but in 1944, an undergraduate at HarvardUniversity named Donald Griffin used special microphones to notice that bats were indeed producing ultrasonic sounds that could not be heard by human ears to locate objects in the dark. Griffin thus coined the term "echolocation" that we use today.
All species (kingdom / division / class / order / family / genus / species )of microbats use echolocation for both navigation and foraging for food. They do this because of their nocturnal lifestyle and very dark habitats. 日行性（diurnal）其他兩種是晨昏性（crepuscular/ crepuscule
）及夜行性（nocturnal）。■ Although lower-pitched sounds travel farther, bats use high-pitched noise because it gives them more accurate and detailed information about size, shape, and other characteristics of objects nearby. ■ This is mostly due to the bat's diet, which is made up of insects such as moths and mosquitoes. ■ The bat's sound is created in its larynx / pharynx and emitted through the nose or mouth. Like whales and dolphins, bats can also modulate, or adjust, the frequency of their calls to adjust for different types of environment. ■ However, due to the less-ideal acoustic properties of air, a bat's high-pitched call does not have very long range, and many bats compensate for this by increasing the volume of their calls. Some bats will "shout" at up to 120 dB / decibel. Despite all the noise produced by thousands of bats coming out of a cave to feed, they are all still able to effectively utilize their own signals.
While we often acknowledge or appreciate that animals are capable of making and hearing sounds, it is generally assumed that animals communicate only on a primitive level. On the other hand, a bat or dolphin may find our ability to make and hear sounds, and even our most technologically advanced sonar systems, to be quite primitive.
- Mar 23 Fri 2012 16:42
- Mar 23 Fri 2012 16:37
"in the corner","on the corner","at the corner"
in the corner:在裏面的拐角處：比如說屋裏面的拐角處有一張桌子
There is a table in the corner of the house
on the corner:在拐角之上。如在桌子角上放著個杯子
There is a cup on the corner of the table / on the tree.
at he corner:在拐角外面，如問路回答：請在前面的拐角處左拐
Please turn left at the corner of the house.
- Mar 11 Sun 2012 00:54