The working principle of ultrasound scanner : It produces a wave and analyze the echo of that wave, especially how strong the echo was and how long the echo to be received. From these things it produces a digital image as output.
Monday, March 31, 2008
What is Ultrasound Scanning.
The working principle of ultrasound scanner : It produces a wave and analyze the echo of that wave, especially how strong the echo was and how long the echo to be received. From these things it produces a digital image as output.
Monday, March 24, 2008
What is MRI Scan
Sunday, March 23, 2008
What does the future have in store for our planet?
This question has many parts to it. We know, for example, that eventually our star, the Sun, will die and in doing so will destroy the Earth. The very distant future, then means the end of the Earth, but this will not occur for many millions of year and need not concern us here. It has also been suggested that our climate is changing and that we are at the beginning if another Ice Age, but opinion is divided. It is enough to say that large scale changes to the planet as a whole take place so slowly when compared to our short life span that they may go unnoticed, disguised by the much more rapid changes which man is causing to his own life and that of all other living creatures on Earth.
The usual way of attempting to ‘see’ into the future is to look at the way changes have occurred in the past up to the present day and then try to project into the future, but this is not easy because it is not always possible to anticipate the effects of a particulars set of circumstances. Try a simple experime4nt. Draw two lines on a piece of paper at right angles to one another to form the axes of graph. The graph could represent, say, the rate at which a hot water bottle cooled after it was placed in your bed. Suppose one axis represented temperature and the other time. Suppose also that you had measured the temperature on two occasions so that you could plot two points on your graph. These could be joined by a straight line, and if you wanted to know the temperature of the bottle sometime later, you would simply project that straight line to the required point in time. But, if, in the meantime, someone removed the blankets from the bed, the bottle would cool much more quickly and your prediction would be wrong.
The subject of many science fiction stories deals with ideas of what conditions might be like in years to come. Some suggestions seem to be widely far fetched, but a hundred years ago who would have believed in the possibility of supersonic flight or submarines that can stay under the Arctic ice for two years without surfacing, or even in satellites circling Venus? On the other hand in the heyday of the motor car a few years ago, most of us would have laughed at the idea of fuel shortage. How do we know what the world’s population might be in a hundred or even twenty years time? Can we predict whether science and technology will be able to find solutions to the problems of overcrowding, food shortage, and pollution choking our rivers and seas, or the ever-decreasing numbers of wild animals and plants with the accompanying dangers to our own species. Will be able to able to take a rocket to a distant planet as easily as we can now take a bus to the next town, or will we return to more rural living, each community growing its own food and making clothes by hand? Then there are the danger of nuclear war. If man is to survive in peace and plenty, the watchword seems to be to try to foresee the consequence of any action rather than wait and see, by which time it may be too late.
Saturday, March 22, 2008
Why don’t we see the Moon on some Nights?
Friday, March 21, 2008
Where do budgerigars live in the wild?
Which tree’s berries are used to flavor gin and can be used in cookery?
Sunday, March 16, 2008
Does a comet foretell disaster?
Before we can answer this question, we must look at exactly what a comet is. As you probably know, a comet looks rather like a star with a long, milky ‘tail’ stretching across the sky. In fact these ‘ tails’ are not tails at all because they always point away from the Sun and do not trail behind.
A comet seems to be made up of three main parts. The nucleus in the center of the star-like part is composed mainly of ice and dust particles, surrounded by a coma of much smaller particles and gas. The coma results from the melting of the ice and other substances as the comet approaches the Sun on it’s extremely stretched out elliptical orbit. The Sun’s radiation also tends to force some of these tiny pieces of ice away from the comet and out into space, which explains why the tail is always directed away from the Sun.
A Scientist called Halley, after whom a particularly bright comet is named, discovered how comets moved. He also predicted when some comets which had already been seen would return. For example, Halley’s Comet made its closest approach to Earth for 76 years as predicted in 1986.
Why are comets associated with disaster? It is true that a comet appeared before the Norman conquest of Britain in 1066, and that two more comets were seen before the Great Fire of London in 1666 and the Great Plague in the previous year, but in world terms these cannot be regarded as major events. Perhaps it is the result of people’s belief that what happens in their own country is of world importance that has led to this idea that comets predict disaster. On the other hand, it has been suggested that the Star of Bethlehem that told of the birth of Christ was in fact a comet. It does seem unlikely, however that a body of ice and gas moving around the sky in a quite regular orbit can have anything to do with the events here on Earth. This particularly true of comets because they have such a low density. Although they may have a diameter of as much as 128000 Kilometers they do not have enough gravitational pull to affect the bodies they pass. In fact, their own orbits may be completely changed.