Plastic is a man-made material. It is an amazing material that is used to make many different things. Every day, all over the world, people use or wear things made from plastic.
Most plastic is made from oil. Crude oil is the raw material that most plastics are made from. Oil is a fossil fuel. It is made from the remains of tiny aquatic plants and animals that lived millions of years ago. Today, oil is found in rocks that are deep under the ground or under the sea.
Salim Yusuf (born November 26, 1952) is an Indian-born Canadian physician, the Marion W. Burke Chair in Cardiovascular Disease at McMaster University Medical School and currently the President of the World Heart Federation, a world-renowned cardiologist and epidemiologist. In 2001, he published a landmark study that proved the benefits of clopidogrel in acute coronary syndrome without ST elevation.
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CAT scanner is the most modern instrument used as a medical diagnostic tool. It is in fact a modified technique of using X-rays for diagnostic purposes. It can detect the diseases of brain, kidney, liver, abdomen etc.
The word CAT is an abbreviation of Computerized Axial Tomography. CAT scanner was invented in 1972 by a British electronic engineer Godfrey Hounsfield and a U.S. physicist Allan Cormack. For this invention both these scientists were awarded jointly the Nobel Prize for medical science in 1979.
CAT scanners are of two types: head scanner and body scanner. Head scanner is used to diagnose brain diseases. With this, brain tumour, brain haemorrhage, clots in the brain etc. can be identified. Body scanner is used to diagnose different diseases of stomach, liver, chest etc.
A CAT scanner consists of an X-ray source from which the rays can be allowed to fall on any part of the body. Opposite to the X-ray source, there are many detectors which receive information from various body parts. In the middle, there is a stretcher for the patient. It is operated by a motor. Detectors are usually made of sodium iodide, calcium fluoride and bismuth germinate. Modern equipments consist of up to 300 detectors.
X-ray source produces pulses of X-rays in an interval of 2 to 3 seconds which fall on the different body tissues. On passing through the different tissues they carry the information to the different detectors. These detectors are connected to a computer. For example, a scanner with 300 detectors will send 300 x 300 = 90,000 signals to the computer after receiving 300 X-ray signals. These signals are analyzed by the computer and projected on the TV screen in the form of a picture. The computer is connected to a television screen. The signals coming from the computer are in accordance with the density variations of the body tissues. These signals are projected on the TV screen in the form of the body organ. This picture gives the clue to the disease. The picture from the TV screen is recorded permanently on a bromide paper. Doctor can know the disease from this photograph, and can give the proper treatment.
Another advantage of CAT scanner is that the doctor can check whether the treatment being given to the patient is effective or not. This information is obtained by scanning the body of the patient repeatedly.
Nowadays almost all hospitals, nursing homes have CAT scanners equipped with the latest technical knowhow for diagnosis of different diseases.
You know that each electrical plug has three pins. These three pins are connected to three wires which in turn are connected to an electrical appliance. Two of these three pins are of the same size while the third pin is thicker than the other two. It is usually connected to a green wire. This is known as the earth wire. Do you know what the function of the third pin is?
The third pin and the third wire (green) in an electrical lead carry no current when everything is normal. One end of this lead is connected to the body of the electrical appliance and the other end is connected to a metal plate buried in the ground. In fact the third pin connects the body of the electrical appliance to the earth. This is known as electrical grounding. It is a precaution in case a live wire accidentally comes into contact with the metal frame of the appliance.
Sometimes the electrical appliance may develop a fault which makes the electricity flow to the metal casing. Then a person touching it receives an electric shock. The electricity flows from the casing, through the person, into the ground. The shock felt by the person depends on the intensity of current. If, for example, the person has wet hands, the shock experienced would be of a greater intensity, because wet skin conducts electricity better than dry skin.
Pulley is one of the earliest devices used by man to hoist or shift heavy loads and raise water from wells. It was developed from the concept of wheel—the most wonderful invention made by primitive man.
Pulley is also a wheel made of wood or metal with a groove cut around its rim. It is fitted with a string or rope around its groove. Pulley turns on axis or an axle and is fixed in a framework called a block.
Do you know how heavy loads are lifted by pulleys? There are several types of pulley systems. For example in a single fixed pulley the load is attached to one end of the string running round the groove of the pulley and the force is applied at the other end of the rope. In this system the force applied is equal to the weight lifted but it has the advantage that force is applied in the downward direction which is easier than pulling up. Single pulleys are used in drawing water from wells etc.
The second system is of a single movable pulley. In this system weight is attached to the movable pulley. A string runs over this pulley whose one end is fixed and the other end passes over a fixed pulley. The second pulley is used to apply force in the downward direction. If both the pulleys are frictionless, then the force applied on the movable pulley becomes just double than the actual force applied. This has a mechanical advantage equal to two. This type of pulley is used in the cranes. Sales in boats are raised and lowered with the help of movable pulleys.
To get more mechanical advantage, several pulleys are used together in many combinations. For instance, in three pulley system, the upper block is fixed and the lower block is movable. A string runs over all the pulleys alternately on movable and fixed pulleys. The weight to be lifted is attached to the lower block. When the number of pulleys is same in both the blocks, the end of the string is tied to the upper block and passed onto the pulleys. If the number of pulleys is not equal in both the blocks, the string starts from the lower block and it is repeatedly turned over the pulleys and is taken up. In fact the weight of the load to be raised with a pulley depends on the number of wheels and how they are connected together.
Whenever any airplane gets crashed, efforts are made to recover its black box. When Jumbo Jet Kanishka of Air India got crashed, its black box was searched and recovered from the deep sea by a robot. Do you know what this black box is and what information it gives regarding the cause of the plane crash?
Most of the airplanes on International flights have been using two important instruments since 1960. These instruments are known as Digital Flight Data Recorder and Cockpit Voice Recorder. These instruments are enclosed in two steel boxes separately to provide safety. These two enclosed boxes are called black box. These steel boxes are made of such insulating material which can withstand a temperature of 1000°C upto half an hour. They are also not affected by shocks. The tape which is used in these instruments is made of stainless steel which is not affected by sea water for two days. Flight Data Recorder is placed in the rear of the plane while Cockpit Voice Recorder is put in the cockpit of the plane.
Flight Data Recorder is a multi channel recorder. Its tape is made of stainless steel which is very elastic. Its length is about 6000 ft which can record the data of a 25 hours flight. It records the temperature of the plane, its velocity and direction of flight, sound of the engine, readings of various instruments, wind velocity etc. In all it can record 64 parameters. These parameters provide a clue about the accident of the plane. It takes several weeks to decode and analyze the data recorded on the tape.
Cockpit Voice Recorder is a type of tape recorder in which a magnetic tape runs. This records the conversation among the crew members in the cockpit. It also records the sound of explosion. These voices come to the recorder with the help of a microphone fitted in the cockpit. This keeps a record of the events which have occurred during the last half an hour. Prior information is washed off automatically. In this way this tape is used repeatedly.
When an airplane meets with an accident, efforts are made to recover these instruments to know the causes of the accident. Recorded information is analyzed and the reasons of accident are established. In fact, this electronic equipment records details of the flight.
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