My Science School

A hologram is a pattern recorded on a photographic plate or film using laser illumination without the use of a lens. The method used for producing a hologram is called ‘holography’. It was invented by Denis Gabor in 1948. The method consists of two steps. In the first step, a hologram is produced and in the second step, a three-dimensional image of the original scene is re-created from it. A system of mirrors is employed to split a laser beam into two. One beam illuminates the object or scene to be made into a hologram and then the scattered beam falls on the photographic film or plate. The other ‘reference’ beams falls on the film or plate directly. But before these two beams strike the film or plate, they interfere with each other and form a complex pattern of light and dark areas which gets recorded on the film or plate. This is the hologram of the object or scene.

To reproduce the scene in three dimensions, a laser beam is directed at the hologram in the same direction as the original reference beam. Even a portion of the hologram can reproduce the entire original reference scene, though with diminished details. Techniques are now available for producing holograms which can be seen in white light. Holography finds applications in industry and research. For instance, it is employed to check flaws in aircraft wings, tyres, and lenses. Holograms are also being used on valuable documents such as Voter’s identity cards and credit cards as an anti-forgery measure. 

Quicksand is a bed of loose sand mixed with water. It is found in places such as river banks and sea coast where there is a layer of impervious clay below. Although it looks like solid ground, quicksand cannot support weight and any person stepping on it may sink and get trapped. This happens because the water seeping in from the nearby water body remains trapped in the quicksand because of the impervious bottom underneath.

Radio telescope is a device to receive radio-waves from space. Radio-waves are emitted by a variety of astronomical objects such as galaxies, stars including our sun, and even planets such as Jupiter and Saturn. The first radio telescope which picked up the radio-waves was built in 1937 by Grote Reber.

A radio telescope is different from an ordinary telescope as it is not possible to look through it. It consists of a big dish which picks up the radio signals from space. The waves are focussed on a receiving antenna which changes the waves into electrical signals. These signals are processed by computers to generate images of the source of the radio-waves. The dish antenna of a radio telescope can usually be turned in different directions. Using radio telescopes much has been learnt about various stars, planets and galaxies. Pulsars and quasars were discovered by using radio telescopes.

Remote control is a technique of operating a system from a distance. The operating system may range from a television set to a guided missile, and the distance may range from a few metres to a few hundred kilometres.

            There are different kinds of remote control depending on the way the command unit sends signals to the operating system. Most command units send signals by infrared, radio waves, lasers or ultrasonic waves. Some even use mechanical arms.

            The common TV or VCR remote controls use coded infrared pulses. A tiny receiver in the TV set or VCR decodes the signal and activates the appropriate operation.

            A typical radio remote control unit transmits radio signals to a receiver set in the device to be operated which are then decoded and the information sent to the electronic circuit or electric motors which operate the device.

In laser controlled missiles, guided signals are transmitted to a missile along a beam of laser which tracks the missile during flight. Mechanical remote control provides a safe method of handling radio-active materials and other dangerous substances.

Heatstroke is a condition when the heat regulating mechanism of the body breaks-down. Sunstroke is a form of heatstroke caused by exposure to the sun for a long time. The very young and very old people are mostly at risk from heatstroke because their body-temperature regulating mechanisms are not very efficient. There are several other factors responsible for heatstroke. People who are unused to heat, overweight, heavy drinkers or are suffering from fever may be at a greater risk.

There are three basic signs of heatstroke — very high body temperature (more than 41°C), total absence of sweating, and nervous system problems (like disturbances of mood, disorientation and headache), which may even cause loss of consciousness. Fully developed heatstroke is an extremely dangerous condition and over 20% of sufferers may die even with treatment. Those who do recover may have persistent trouble in the nervous system and may take months to get back to normal.

The immediate treatment of heatstroke is to cool the patient by putting him in a bath of cold water. But the most simple and effective way to fight sunstroke is to ensure that the body is not overheated. 

Global warming is the phenomenon of a gradual overall increase in the average temperature of the Earth’s atmosphere due to the accumulation of certain gases. The Earth’s atmosphere is made up of major gases namely, oxygen and nitrogen, and minor constituents such as water vapour and carbon dioxide. These gases play a crucial role in moderating the Earth’s temperature. This is because these gases are relatively transparent to incoming visible light from the sun, but absorb the heat radiation given off by the ground and objects exposed to the sun. As a result they produce a heating of the atmosphere by what is known as the “greenhouse effect”. Without the “greenhouse gases” in the atmosphere and the resulting ‘greenhouse effect’, the Earth’s average surface temperature would be as low as - 20°C.

 

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Genetic engineering is a technique of manipulating the DNA in cells to endow an organism with qualities it did not naturally possess. The technique is also called gene manipulation. It entails a number of steps the first of which is the constitution of DNA segment from nucleic acid molecules in a test tube. The length of DNA so made is inserted into a virus or some other suitable vector that can serve as a molecular ferry to carry it into the host organism. The crucial factor here is ability of the inserted DNA molecule to express itself and also to multiply. Bacteria and even higher animals may be genetically engineered to produce foreign proteins of interest by inserting a copy or multiple copies of the gene coding for the protein into them. Several important products of medical use such as insulin and the human growth hormone are now being produced commercially using genetically engineered bacteria. ‘Tracy’, a genetically engineered sheep produces the pharmaceutically important protein called Alpha-1 antitrypsin in her milk. Genetic engineering may be used to boost growth, alter resistance to factors such as drugs, heat, cold and salinity in both animals and plants. 

Gene therapy is a new and as yet largely experimental branch of medicine that incorporates techniques of genetic engineering to correct inherited disorders or in-born errors of metabolism. The idea of curing a genetic disorder by repairing or replacing a faulty gene or gene product (protein) first occurred to Dr. W. French Anderson now recognized as the father of gene therapy.

In gene therapy the flawed gene is identified and copies of its normal version are produced in the laboratory by cloning. Then suitable host cells are selected from the patient’s body and genetic engineering is used to transfer copies of the normal version of the gene into it. The doctored cells are then returned to the body by injection. The introduced genes are incorporated into the chromosomes of the patient’s cells and propagate with each cell division. Since the introduced genes work normally and produce the protein that was previously either absent or malformed, the error is corrected in the victim who gets cured of the symptom. However, since gene therapy is not approved for genetic manipulation of the germ or reproductive cells, the cure cannot be passed onto future generations of the cured victims. 

It is a family of newly discovered, the third allotropic form of carbon, quite distinct in structure and properties from the two earlier known forms — graphite and diamond. The first member of this new form of carbon, also called fullerene, was discovered in 1985 by a team of scientists led by Harold Kroto of the University of Sussex, U.K. and Richard Smalley of the Rice University, USA. Unlike graphite which has a plane layer of six-membered carbon rings and diamond which has a three-dimensional network of tetrahedrally bonded carbons, the newly discovered molecules have spherical cage-like structure, such as the famous geodesic dome invented by Buckminster Fuller. That is why the name fullerene. The most stable of these has 60 carbon atoms. The C-60 molecule has a magenta colour.

Fullerenes have several potential applications. As the fullerene molecule is spherical and very tough they may be used as lubricants. Small spheres of fullerenes can also act as molecular ball bearings. When combined with certain metals fullerenes become superconducting, that is, they conduct electricity without any loss. Fullerenes can also store large quantities of hydrogen. This fact has prompted many scientists to study their use as catalysts for various industrial chemical reactions. The same property also promises their use as electrodes in batteries. 

Composites are materials made by combining two or more substances— one called the reinforcement and the other matrix— in such a way that the resultant product has better strength and property than the individual components. Weakness of one component is overcome by the strength of other component. Wood is the best example of a naturally occurring composite. It is composed of cellulose fibres as reinforcement in a lignin matrix. Similarly, in fibre-reinforced plastics glass fibre reinforcement is embedded in a plastic matrix to provide a much stronger product. The reinforcement, which could be a gas, particle or fibre, provides strength and stiffness to the composite. The matrix which could be any polymeric material, such as resin, or a metal or ceramic, holds the reinforcement and helps even distribution of the applied load within the composite. For best results the reinforcement and matrix should be compatible with each other. Normally, composites are made up of two dissimilar materials such as glass fibre and plastic but the same material can also be used both as the reinforcement and matrix, such as in ceramic-ceramic composites. Today, composites have become a part of our everyday life. They are also widely used in the aerospace industry as they provide an ideal combination of strength and light weight.

 

Cholesterol is a complex fatty substance that is essential for the normal functioning of the body such as formation of membranes covering the cells or the synthesis of hormones, but harmful when in excess. It is considered to be the chief cause for the narrowing of arteries which at times is known to cause heart attacks. Pure cholesterol is solid at room temperatures and is insoluble in water. It is present in all tissues of the human body in varying concentrations. An adult human has in total about 60 grams of cholesterol in the body about one gram of which is used up everyday. The lost cholesterol is made up in the liver through digestion of foods especially rich in a kind of fat substance called high density lipoproteins (HDLs). Cholesterol is harmful only when it is in excess amounts in the blood. This happens with the excessive intake of HDL-rich food such as animal fats, palm oil and coconut oil. The excess of cholesterol in the blood slowly settles on the insides of blood vessels narrowing their bore. This condition called atherosclerosis increases blood pressure and causes heart attacks and strokes. 

 

Catalytic converter is a device, fitted onto the exhaust pipes of petrol-driven automobiles which help reduce the emission of environmentally damaging gases from the automobiles. The exhaust fumes of petrol-driven automobiles using unleaded petrol contain gases like the nitrogen oxides, carbon monoxide and benzene which are harmful to health when inhaled. The catalytic converter helps convert these gases into harmless carbon dioxide, steam and nitrogen. The converter is made up of grids of ceramics or metal coated with catalysts like platinum, vanadium or rhodium. When the exhaust gases pass over it, the catalyst brings about chemical reactions converting the harmful gases into harmless ones. The converter cannot be used in automobiles using leaded petrol because the lead which is used in the fuel as an anti-knocking agent can inactivate the catalyst and render the device useless.

 

 

 

 

 

 

Cancer is the abnormal, uncontrolled growth of a group of cells in the body. They grow uncontrollably to form abnormal localized lumps of tissue called tumours and wander from their original site to other organs of the body, starting fresh growths. Tumours which spread to other parts of the body are known as ‘malignant’ tumours, unlike the ‘benign’ ones which are rooted to their site of origin and are usually harmless.

Currently, there are three ways of treating cancer. First is the surgical removal of the original tumour and as many secondary tumours as possible. Radiation therapy is the second method whereby cancer cells are destroyed using ultra powerful gamma rays from radium. Some anti-cancer drugs are also available which can control cancer.

But most of ods, besides these meth-killing cancer cells can cause damage to the surrounding normal tissues producing serious side-effects. Recent advances in genetic research, however, offer promising new approaches to treat cancers. 

Biopsy is a simplified procedure of obtaining tissues from affected part(s), usually some unusual growth or lining of an organ for microscopic examination.

To obtain tissue from deeply situated organs like liver or kidney, a hollow needle is used. Soft spongy material such as bone marrow can also be obtained by suction through the needle.

The tissue after removal is either frozen or fixed in wax for preservation. Later, thin slices are cut, stained with special colours for clarity and examined under the microscope to ascertain whether the tissue is benign (non-cancerous) or malignant (cancerous).

 

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This is the process by which living organisms breakdown matter into its simpler constituents and thus recycle nutrients. All natural decay processes such as rotting of wood are examples of biodegradation. The life forms responsible for the process are called decomposers and they form a vast, complex community of soil organisms such as microbes and fungi. All such matter on which they can act is termed biodegradable to distinguish it from non-biodegradable matter or such matter which is not broken down by biological agents. While all organic matter is biodegradable, certain decomposers can attack even metal, glass and plastic. The widespread use of non-biodegradable material such as the various types of plastics is a cause for alarm because when discarded they do not decompose easily but remain in the environment as pollutants. Efforts are underway to develop biodegradable plastics which will be more environments friendly.