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| SCIENCE TRIBUNE | Thursday,
June 14, 2001, Chandigarh, India |
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Death traps of
nature Traffic lights for
light Use of cement concrete in
construction
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Death traps of
nature THE firepower of our long researched nuclear weapons is impressive enough. But natural disasters put it to shame... instantly. Floods, tornadoes, forest fire, hurricanes, lightening strikes, drought, torrential rains etc are among the many type of natural disasters known to occur but volcanoes and earthquakes are the quickest means of mass destruction known to man. Fortunately both volcanoes and earthquakes spend most of their energy harmlessly, except in a few cases when they cause huge devastations in a matter of seconds. More than 500 volcanoes are known to have erupted in the last 500 years. The magnitude of violence of earthquakes ranges from zero (barely perceptible tremor) to nine (catastrophic and usually the scale of measurement is multiplicative or logarithmic so that increase in one unit means a ten-fold increase in energy released. We don’t have such (desperately needed) instruments which could issue a genuine and confirmed “early warning” for earthquakes and volcanoes, but we do know some hints as to how such an instrument would work. Research is being carried out in various laboratories based on a phenomenon discovered in laboratory experiments two decades ago-so called “Dilatency effect” or dilatency theory — which says: when a rock is squeezed, it deforms and eventually fractures but just before the fracture the rock swells due to opening and extension/widening of cracks. This increase in size or volume is the phenomenon of Dilatency, which occurs when applied stress reaches about half of the breaking strength of rock. At the dilatent conditions of rock, other measurable attributes change e.g. propagation of seismic waves through them, their electrical resistance and reduction in number of small tremors etc. These and many other factors would have to be considered by the scientists to devise a method which could help us predict such disasters as easily as tomorrow’s weather that we see on our daily. But beware... the list of natural disasters does not end at earthquakes. There are more dangerous natural disasters although we are in a position to predict those very accurately. The danger of falling meteors, asteroids or comets is among them. Our solar system contains uncounted billions and billions of rocks, from dust-motes to planetoids. The orbit of each is continuously influenced by combined gravity of everything else in the solar system, especially Sun and Jupiter! And thousands of tons of material from space fall towards the earth each year but virtually all of it burns up before reaching the ground. Some very large objects do come alarmingly close and occasionally something arrives which is big enough to lose only its outer skin on the way burning though our atmosphere. Ignoring the atmosphere friction and orbital speed of earth around the sun, a rough estimate of impact energy of a falling object towards the earth at a speed of 40,000 kmph (the final velocity an object attains which falls to earth from infinity or a few million kilometres distance) has been calculated by scientists and astronomers. “Icarus”, asteroid which came within 6.5 million km of earth in 1968 is about 1 km wide and if it were to hit the earth, it would strike with 75,000 megaton explosion force, dwarfing the power of all nuclear weapons of the world put together. “Hermes”, about 2 km in dia will blast in with 220,000 megatons explosive power and “Eros”, another asteroid would deliver 75 million megatons of explosive energy all in a matter of a few minutes!! The atmosphere is a small protection against such monsters; they will flash through it in seconds producing a hot, scorching explosive shockwave. But 71% of earth’s surface is water and therefore there is 71% chance that any falling body would hit the sea. But this does not make much difference as we have all witnessed the demo-version of a meteorite fall of 21 pieces of Comet Schumaker-levy on Jupiter on July 16, 1994. The Siberian meteorite that stuck near Tunguska on June 30, 1908 was only 30 to 60 m across and was estimated at mere 30 megatons impact energy-but its devastations remain clearly visible today. There are about 200,000 Near Earth Asteroids of the size about 100 m dia and population of those of dia 1000 m or more is thought to be 1,600. It was a meteorite impact which eventually brought and end to the dinosaur kingdom. Another possibility in the list of natural disasters is the falling of earth into the sun! But only a collision with a very large asteroid like Ceres-which is estimated at delivering 12,000 billion megatons impact energy-could significantly shift the Earth’s orbit and the collision itself would sterilise the Earth (and destroy our moon too)!! Another possibility is that of a supernova explosion-which if any star (within 15 light years range) would undergo-the effects are hard to predict. Still more rare chance is that a large planet with very low reflectivity or a mini-blackhole could indeed approach our solar system without our knowledge as only bright objects (in visible, UV or IR spectrum) can be seen with our telescopes. And at last science fiction warns us with rarest of all (but not negligible) possibilities. If our universe contains some big chunks of antimatter floating in space... one of them might land on earth as an Antimatter meteorite. If this antimatter meteor weighs a modest 10 tons, it would react with an equal amount of ordinary matter — soil — with an explosion of 400,000 megatons! Is there still need for ending life artificially? The tools of science have more important things to do than designing more and more destructive weapons. |
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Traffic lights for
light ALBERT Einstein said that nothing could travel faster than light. The fact of the matter is that the maximum speed with which energy can be transferred is the speed of light in vacuum; that is three hundred thousand kilometres per second. Of course, light can be made to travel slower, as we were taught in school by making it go through transparent media. Then the refractive index of the medium slows it down. Diamond has probably the highest refractive index among crystals. It has a value of 2.4 and light will be slowed down by this factor as it goes through the stone. There is, or more correctly was, no way to reduce the velocity of light further. One could argue that one way to stop light and then restart it going, rather like cars at a traffic light is to absorb the light in some substance and after a while release it. Laser light is generated in this manner. Light from a xenon or a helium tube falls on the laser rod and excites the atoms of the rod. A trigger light pulse of different colour then de-excites the atoms and the light bears no relation to the incident light from the xenon. While all the light waves that come out of the laser are coherent and vibrate in unison, they are not in tune with the incident light from xenon. Even in a system where the wavelengths of the incident and emitted light might be the same, there is no “coherence” between them. In other words, the two light beams could very well be from independent sources. Two recent experiments done at Harvard University reworked the trick of excitation and emission with dramatic results that may one day change the present ways of manipulating information. In one experiment, sodium vapour contained in a 3.5 metre long tube at very low pressure was cooled to extremely low temperature, just nine-thousandth of degree above absolute zero. A slightly lower temperature would have turned the vapour into a Bose condensate with totally different properties. The stop and start procedure was carried out on a signal beam. A control light beam was turned on and this made the sodium atoms change their electronic structure and so become transparent to the signal light beam. While the signal light went through the vapour, the control light was switched off and as a result, the sodium vapour absorbed the signal light. A little while later, the control light was turned on, causing the sodium atoms to emit the signal light they had absorbed. This technique is now called EIT, or electromagnetically induced transparency. The surprising thing was that these manipulations did not change the nature of the signal light. It was found to be coherrent with the signal light beam. The information brought in by the signal light beam was apparently imprinted on the sodium atoms that absorbed it. The effect gradually disappears and so causes a loss of coherence. It does seem to last for several microseconds, but the intensity of the emitted light reduced as the time it was in captivity lengthened. Even at this low temperature, thermal motion of the sodium atoms was enough to destroy slowly the input information. Perhaps the intensity might not be reduced if the temperature of the sodium vapour was lowered further. The vapour would have been converted into a Bose condensate, thereby avoiding a loss in coherence. The imprinted atoms also may drift out of the active volume and may collide with other atoms, exchange their spins and lose their information. However all is not lost. An interesting facet of the work is that some of the information brought in by the signal beam was present after control beam has taken the light out of the atoms. So a second and sometimes even a third pulse of the signal light may be extracted that was coherent with the original signal light. The second experiment used rubidum vapour but at a much higher temperature of around 80 degree celsius in much smaller cell, about 4 cm long. In this experiment the effective velocity of light was brought down to almost 1 kilometre per second! These experiments on trapping light are perhaps the first steps in a new direction of quantum information processing. As the experiments appear to be successful over a range of temperatures ranging from 80 degree celsius to almost-273 degree celsius, the technique seem very feasible to implement into practice but a lot more research has to be before it can be applied to make quantum computers.
PTI |
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Use of cement concrete in
construction NOWADAYS cement concrete is a widely used material for construction of even single and double storeyed buildings. Cement concrete is used mainly as Reinforced cement concrete (RCC) for columns, door lintels, floor/roof slabs, beams etc. In waterlogged areas with low bearing capacity of soil, RCC is used even for foundation of masonry walls. Cement concrete is a very costly material and consumes about 20% of the total construction cost. So the following factors are of utmost importance while using cement concrete and help to attain strength upto designed level. A) Properties of ingredients B) Mixing, Placing, Compaction and Curing C) Cover to Reinforcement D) Stripping of Forms/Shuttering A) Properties of ingredients:- Generally Ordinary Portland Cement (OPC) is used for all grades of concrete. In wet atmosphere and low temperature zone Pozzolana Portland Cement (PPC) can give better results. The aggregate like sand, bazari, stone metal or brick ballast should have good strength, durability, weather resistance and their surface be free from impurities such as silt and organic matters. The water used for both mixing and curing should be free from oils, acids, alkalies, salts and organic materials. Potable water is generally considered satisfactory for mixing concrete. B) Mixing, Placing, Compaction and Curing:- The material in required proportion should preferably be mixed in a mechanical mixer to produce intimate mixture. Water cement ratio (w/c ratio) is very important factor while mixing the concrete. It should be such that mix thus produced can be placed easily. Very high w/c ratio affects the compressive strength of concrete. Concrete with very low w/c ratio is difficult to place in the forms. W/c ratio for nominal mix varies from 04. to 05. Prior to placing of concrete, loose rust must be removed from reinforcement, forms must be cleaned. Most important is that the hardened surface of previously laid concrete must be cleaned and treated appropriately with neat cement. Placing should be such that segregation, displacement of forms or of reinforcement in the forms are avoided. Concrete be placed on hard surface for that steel or plywood forms/shuttering should be used. No earth should be used for levelling of surface of shuttering/forms, which absorbs the cement slurry from fresh concrete thus affecting the compressive strength of concrete. Immediately upon placing, the concrete should be compacted by means of hand tools or preferably by using vibrator. For using vibrator stiff mix should be used. Such compaction prevents honey combing and ensures more impermeability and a better finish. Fresh concrete gains strength most rapidly during first few days so the concrete must be protected from loss of moisture (which is called curing) for at least the first seven days. Curing on horizontal surfaces can be done by making partitions using local sand and filling the gaps with water and on vertical surfaces by wrapping wet gunny bags around it. Curing can be done for more duration i.e. up to 14 days during hot weather. C) Cover to Reinforcement:- The cover to the reinforcement is another important factor affecting the strength of RCC. The clear cover to reinforcement in foundation should be 50 mm, in columns 40 mm, in beams 25 mm and in slabs 15 mm. This must be adhered to, because if the cover is less than it, cracks appear on bottom surfaces because of expansion and contraction of steel and if it is more than given values, the effective depth of section get reduced thus reducing the resistance of moment of the member. D) Stripping of Forms/shuttering: Stripping of forms/shuttering should be done carefully avoiding any damage to supports. For cantilever/projection stripping should start from free end and should complete at supported end. No partition walls should be constructed on floor slabs before stripping of shuttering. Stripping time for walls/columns and vertical faces of all structural members should be 24 to 48 hours. For slabs spanning upto 4.5 metres 7 days, slabs spanning over 4.5 metre-14 days, for beams and arches spanning upto 6 metres-14 days and beams and arches spanning over 6 metre it should be 21 days. More time can be given to encourage curing, which in turn help to impart higher strength to cement concrete. So besides getting a building structurally designed for safe and economical construction, the above mentioned factors for using cement concrete in field are very helpful if taken care of to impart strength to the concrete upto the designed level. |
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NEW PRODUCTS & DISCOVERIES Nickel-free sintered steels Scientists have developed an alternative — a nickel-free sintered alloy — for components exposed to exceptional stress. When heavy-duty trucks or tractors move off or shift to a higher gear, the strain this puts on the transmission is audible. Even in cars, engine and transmission components such as chain wheels, transmission levers or detents are subjected to enormous stress. On the one hand, manufacturers strive to produce these parts cost-effectively, on the other, they must reliably transmit the forces acting on them. They are therefore made of sintered steels, a report in Fraunhofer Gesllschaft said. The addition of alloy elements such as copper, molybdenum or nicked, and heat treatment at temperatures of upto 1280 degree celsius, binds the metal powder and makes it extremely resilient. Nickel, however, is toxic to humans and the environment. PTI Beware of mosquito repellents The chemical “allethrin” used in various mosquito repellents in the market such as mats, coils and vapourisers is hazardous to health, warns Ved Prakash Sharma, a top malariologist with the Indian Council of Medical Research (ICMR). Sharma, currently with the Malaria Research Centre (MRC) in New Delhi, says neem oil is a safer alternative. Research around the world, experimenting with animal, are now discovering that prolonged exposure to allethrin, which belong to the class of “synthetic pyrethroids”, is harmful, says Sharma. A questionnatire-based survey of 5920 users carried out by MRC had revealed that more than one in ten users “complained of a variety of acute toxicity either soon after or within a few hours of use of repellents”. Reporting the survey results in a recent issue of Current Science, Sharma said breathing problems accompanied by headache were the most common problem, and eye irritation was the next common complaint. Cough, cold and running nose were other complaints and in two cases, users who did not have asthma before, became asthmatic. Sharma said there were complaints of pain in the ear and throat too. About 11 per cent of those who used skin cream as mosquito repellent reported skin rash, itching or black spot. Users with strong reaction leading to asthma or bronchial irritation, eye or throat problems needed treatment. PTI Growing a new skin This is a place where you may have to give some skin off your back. For here you will find sheets of skin ready to be applied to raw wounds. The Birminghan Accident Hospital which has one of the largest burns units in Europe also has one of the few skin culture laboratories in the world which are able to grow replacement human skin. In the past, burn injuries were treated by removing a layer of normal skin in an unaffected area of the body and applying it to the raw injured area. The “donor area” from where grafts were taken, normally healed within two weeks but the patient was often subject to pain because of exposed raw nerve ends. With this “skin culture technique”, only a small area of the skin, no larger than a postage stamp, is taken from the patient. This small piece of skin is then cut into even smaller pieces and live cells are extracted from it. Further treatment allows these live cells to develop into larger sheets of skin for use on a patient giving new meaning to the phrase of being skinned alive.
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SCIENCE QUIZ
1. In the beginning this branch of Physics was called “boys’ mechanics” because many of the physicists (Pauli, Heisenberg, Dirac, Fermi, Jordan, et al) who developed it were under 25 years of age. Which mechanics are we talking about? 2. Tears are produced in our eyes when we are very sad or even when excessively happy. Which parts of our eyes release tears? 3. Developed recently by the US scientists, this new device, called “electronic nose”, is in the form of a low-cost, low-power, portable meter. It can diagnose tuberculosis on the spot, whereas the conventional skin test takes several days. Can you think how this is possible? 4. WBCs are important constituents of human body’s defence mechanism and are sometimes called “the soldiers of the body”. What are WBCs? 5. These amphibians are more poisonous than even scorpions and snakes. In ancient times people used to kill these animals to poison the tips of their arrows which proved lethal. What are these South American bright coloured amphibians commonly called? 6. What is common between “Epiphytic”, “Thelo”, “Echino” and “Astrophytum”? 7. This technology is based on low-cost, short-range, ratio-links between mobile PCs, mobile phones, palmtops and their portable devices and allows communication between these without the use of wires and without manual intervention by the users. What is this technology called? 8. This compound of sodium, commonly called “Suhaga”, is used as a preservative, a disinfectant, a flux in soldering, in the paper and pharmaceutical industries and in the manufacture of enamels and optical and coloured glasses.
Which is this compound? 9. When a nucleus of an atom is bombarded with a particle, sometimes the nucleus absorbs this particle and remains in an excited state for a very short time. What is such a nucleus called. 10. Who invented hectograph, a method of copying documents which were written using special ink? ANSWERS 1. Quantum mechanics 2. Lachrymal glands which lie above each eye, behind the eyelid 3. By making chemical analysis of the signature of the bacteria from the patient’s breath. 4. White blood corpuscles 5. Arrow poison frogs 6. These are varieties of cactus plant. 7. Bluetooth technology 8. Sodium tetraborate 9. Compound nucleus 10. Scottish inventor James Watt in 1780.
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