 |
|
| SCIENCE & TECHNOLOGY |
|
|
|
Use of polyfibres in construction Quantum computing Prof Yash
Pal THIS UNIVERSE |
|
|
Use of polyfibres in construction Polyfibres are light weight, fine diameter, polyester fibres of small lengths varying from 6mm to 12 mm and having a triangular or circular cross-section. One kg of these Polyfibres contains 120 to 240 million fibres. These are supplied in small pouches of 150 gm each. Triangular shaped polyfibres have better interlocking properties than circular fibres and are thus preferred for addition to concrete and mortar. Earlier polypropylene fibres were imported in India but now big industrial houses like Reliance have started their production in India. In-home product being cheaper than the imported one has captured the construction industry in a phenomenal manner. Manufacturers claim that addition of polyfibres to concrete increases its strength. Even if there is an increase in strength, it can’t be taken into account for the structural design of concrete members. Though use of polyfibres may enhance the toughness of concrete, reduce shrinkage cracks and reduce permeability, economising by assuming impart of structural strength can’t be permitted. More research is required to define the exact role of polyfibres towards strength of concrete. Addition of polyfibres to concrete or mortar reduces their workability thus making their placing difficult. More water has to be added to concrete or mortar to maintain the required slump. Thus to maintain water-cement-ratio, more cement has to be added. Other alternative is to avoid addition of water or cement but to add plasticiser to concrete. Both the options mean an increase in cost of concrete. Test results conducted on a sample of M20 concrete show a workability of 120 mm with 0.5 per cent plasticiser when no polyfibres are used. On adding polyfibres, workability reduces to 85 mm even after making double the quantity of plasticiser. Addition of more plasticiser increases strength of concrete by a few per cent and this increase can’t be attributed to polyfibres. Addition of plasticiser also raises the cost of concrete. Use of polyfibres in industrial floors, concrete pavements and parking lots may give better results but their use in plaster work needs to be kept under keen observation. Plaster being 12 mm or 20 mm thick only, polyfibres may appear on the plastered surface, much to the dismay of the user. |
|
Quantum computing A quantum computer which can work faster and provide quicker solutions in comparison to the present-genre “thinking machines” is based on the laws of quantum computing. In a quantum computing system, particles at the atomic and sub atomic levels are manipulated to interact with each other. Of course, quantum computing is still in the realm of theoretical possibility. Many research teams around the world are now working feverishly towards consolidating the theoretical basis to build a simulator wherein individual particles meet and interact with each other. “Our research has successfully shown that it is possible to create a simulator of a system governed by the laws of quantum physics in which scientists could have the control of individual particles,” says a team of scientists from Imperial College, London’s Department of Physics and Institute of Mathematical Sciences. As envisaged now, the simulator could be used to test the capabilities of materials at the atomic and subatomic levels. According to researchers, the proposed simulator will be composed of atoms and photos — particles of light — in an array of small silicon cavity, measuring around 50 micro meters. On the other hand researchers at the University of New South Wales have come out with a device that could ultimately hold the basis for practical quantum computers. The device contains two phosphorous atoms embedded in a silicon chip. The phosphorous atoms are manipulated to remain in quantum states for a long period of time so that they can be read by single electron transmissions. Scaling the two atom devices to a large array may be the key to a practical quantum computers. In yet another breakthrough, Hans Andreas Engel and Daniel Loss of the University of Basel in Switzerland have come out with the idea of spin parity metre to make the quantum computing a reality. Such an innovation is comparable to the transistors in microchips. This computer would pave the way for electronic quantum computers to be made from silicon, just as today’s microprocessors chips are. “With a spin parity metre in hand, quantum computing could be put around the corner,” says physicist Jose Carlos Egnes of the University of Sao Paulo in Brazil. However, right at the moment the so called spin parity metre is a theoretical preposition. The theoretical calculations show that it could function as a component of quantum computing. In an electronic quantum computer, data could be encoded in the magnetic state or “spins” of electrons. “Up” and “down” spins would substitute for the ones and zeroes of binary code in traditional computing systems. |
|
THIS UNIVERSE A student asked me a question: “Why the sun looks bigger during sunrise and sunset”. UnfortunatelyI could not satisfy the student. Could you please address this question? This observation applies equally to the moon. The moon also looks much bigger when close to the horizon than when it is high in the sky. The consensus is that this universal experience has nothing to do with the physics of seeing or the size or shape of the image. You can easily check that the actual size of the image is the same, independent of the location in the sky. This is very conveniently done for the full moon using nothing more than a transparent scale held at arm’s length with one eye closed. No doubt, you will convince yourself that the actual size of the moon does not change as the moon climbs up in the sky (A NOTE OF CAUTION: IT IS HAZARDOUS FOR THE EYES TO TRY THIS WITH THE SUN, UNLESS YOU USE A CERTIFIED FILTER!!!). In any case, you can take it from me that physics is not fooled by the proximity of the sun (or the moon) to the horizon. But we are. This optical illusion is fundamentally linked with the way our brain interprets images. It uses past experience - some facts, and some prejudices — to give meaning to the visual signals received in the cortex. We are aware of a large number of optical illusions. But the field of psychology is not as certain, or crisp, as mathematics. Two possible explanations have been put forth for this observation; see if they satisfy you. When the sun, or the moon, is near the horizon we see it in the company of other distant objects — buildings, trees, and hills — objects whose sizes our brain is familiar with. These distant objects produce a small image, but the brain, from past experience, applies a process of mental amplification, which justifies and rationalises the sizes of these known objects. The error occurs when the brain applies a similar amplification strategy to size the “adjacent” sun or moon! Another explanation goes like so: When we stand out in the open, very far from anything else, we get an impression that the sky is an inverted bowl. This has been felt and believed for thousands of years. We do not know the height of this bowl, but get a feeling that it cannot be as much as the distance to the horizon. After all, we know that the horizon, where the rim of the bowl seems to meet the ground, must be very far because known objects look so small when they move close to it. So it seems natural for the intelligent interpreter sitting in our brains to make the sun and the moon appearing near the horizon look bigger than they are! When high up in the sky, these objects cannot be as far as the horizon since the bowl is believed to be rather shallow! So the interpreter applies no correction! I can appreciate the qualitative directions of this explanation, as also the previous one, but the quantitative angle escapes me. Why does the moon appear just this much bigger near the horizon, and no more? Do we even know if it appears to be the same size to different people? Maybe some people’s brains “amplify” it more than others (eg. adults v/s infants?). Since the effect is illusionary (and therefore not physically demonstrable), could we even measure this difference in perception? Perhaps someone knows the answer — or maybe some day in the future we will?
|
Recently, use of polyfibres in concrete and mortar has seen a significant rise. Many Government departments have accepted them as an essential ingredient for concrete works such as floorings, roads, bridges, pavements, plastering and water retaining structures. This sudden acceptance of polyfibres by most of government departments necessitates a look into its behaviour and usefulness towards the properties of concrete and mortar.