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Smart plastics that change shape Trends Prof Yash
Pal THIS UNIVERSE |
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Smart plastics that change shape Plastics with shape-memory that can change shape in response to a temperature increase are well known. Now instead of heat, the shape-memory effect can be induced in polymers with light. Think of a flower picture that opens when facing the sunlight due to the sensitivity of plastic to light. An MIT engineer and his German colleagues have created the first plastics that can be deformed and temporarily fixed in a second and have a new shape by illumination with light having certain wavelengths. These programmed materials will only switch back to their original shape when exposed to light of specific different wavelengths. This is really a new family of materials that can change from one shape to another by having light shined on them. Smart plastics organise themselves into useful optical devices. In one of the first examples of molecules building themselves into useful synthetic microstructures with little human intervention, a team of chemical engineers has created plastic materials that assemble themselves into sophisticated optical devices known as photonic crystals. Just last year the same team created the largest synthetic structures ever made by self-assembly, where molecules organise themselves into discrete microscopic objects, such as hollow spheres. In the current work they’ve gone one step further, developing methods to make billions of those objects come together to form even larger, highly ordered structures visible to the naked eye. The materials are an intricate 3-D composite of air and plastic that manipulates light in the same way that allows opals to produce such striking colours. That’s because the materials exhibit “spatial periodicity,” a sought-after characteristic that refers to their high degree of order and their optical properties. The research team notes that in addition to elongated films, a variety of other temporary shapes can be produced. For example, exposing only one side of the stretched sample to light can create a spiral. The result is the formation of two layers. So, while the deformation is well fixed for the irradiated layer, the other keeps its elasticity. Thus, one contracts much more than the other when the external stress is released, forming an arch or corkscrew spiral shape. The team has also shown that the temporary shapes are very stable for long times even when heated to 50 degrees C. The basic principle of photo-induced shape-memory polymers is explained and currently developing medical and industrial applications using their photosensitivity. Currently, though, many scientists are simply trying to build components that bend and steer light as handily as current computer chips manipulate electronic signals. Today’s computers rely on semiconductors, or “electronic crystals,” that give scientists the power to control millions of electronic signals gliding around a computer chip simultaneously. Such control remains a dream when it comes to light. It’s impossible to fit millions of tiny conventional lenses and mirrors on a chip the size of one’s fingernail. So scientists are still searching for materials for optical systems that would allow them to channel, switch and manipulate optical signals with ease. The payoff would be enormous. Light can carry thousands of times more information than electrons and, if used instead of electronic signals, could boost the speed of telecommunications equipment, modems and other devices dramatically. The key to success is encoding into the polymers information so they will organise themselves into large- scale objects with specific characteristics. Once the polymers are prepared using standard chemical techniques, it takes them just minutes or hours to organise into photonic crystals. Much of nature is a product of hierarchical self-assembly, and humans are the example par excellence. Each of us starts as a single cell encoded with the information to guide our growth into a larger structure — a complete human being. Making materials that are on their own smart, intelligent and able to orchestrate their own growth marks the chemistry and polymer science of the future. The work could have potential applications in a variety of fields, including minimally invasive surgery. Imagine, for example, a “string” of plastic that a doctor threads into the body through a tiny incision. When activated by light via a fiber-optic probe, that slender string might change into a corkscrew-shaped stent for keeping blood vessels open. What about staples that open on command, or paper clips that relax as soon as we don’t need them anymore? Again, action of light on smart plastics could do the job. Applications are widespread for a smart plastic based device that selectively filters out certain wavelengths, or colours, of light. Optical data storage and telecommunications rely on transmission and detection of specific wavelengths, and holographic memory systems are expected to do the same one day. The smart plastics might make possible better light-emitting diodes (LEDs), materials that are increasingly being used to produce more efficient lighting systems. Also possible are special paints that change colours under different light conditions, perhaps lighter in the harsh glare of sunlight and darker under incandescent light. Another potential application: may be a super-efficient, plastic laser that could produce intense light with a fraction of the energy now required. The
writer is from the Department of Physics, S.L.I.E.T., Longowal,
Sangrur. |
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Trends The supermassive black holes that dot outer space are the “most fuel efficient engines” in the universe, according to the findings of a new US study that used a powerful NASA X-ray observatory to observe nine vast black holes. Researchers used the National Aeronautics and Space Administration’s Chandra X-ray Observatory to study nine supermassive black holes at the centres of elliptical galaxies to reach their findings. The black holes, which were .2 to three billion times the mass of the sun, are relatively old and generate much less radiation than quasars, the fast growing black holes seen in the early universe. The researchers said the Chandra findings show that most of the energy released by matter falling toward a supermassive black hole is in the form of high-energy jets travelling at near the speed of light away from a black hole. “Just as with cars, it’s critical to know the fuel efficiency of black holes,” said lead author Steve Allen of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University and the Stanford Linear Accelerator Centre.
— AFP
Prehistoric fish An Indonesian scientific expedition has snapped rare photographs of at least five living specimens of the coelacanth, a nearly 400 million year old fish. The fish, which pre-dates dinosaurs and has been dubbed a “living fossil”, was thought to have been extinct until a specimen was found in 1938 off South Africa, still considered by some to be the zoological find of the century. The fish, which can reach two metres in length and has paired fins which move like human arms and legs, is closely related to the first land vertebrates.
— AFP
Alzheimer new test A new test may help scientists answer a perplexing “which came first” question about the development of Alzheimer’s disease, possibly pointing the way to earlier diagnosis or even treatment. Brain deposits of a small protein known as amyloid beta long have been associated with Alzheimer’s. But scientists have been unable to determine whether the body begins producing too much of the protein or loses the ability to clear it away. Now, a research team led by Dr Randall J Bateman at Washington University in St Louis is poised to find that answer with a test that for the first time can monitor the protein. An initial test of the new technique on six healthy volunteers determined that the protein is quickly produced and quickly cleared, keeping it in balance in the central nervous system, the researchers report in the online issue of the journal ‘Nature Medicine’.
— AP |
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THIS UNIVERSE
We have the picture of my grandfather hanging on the wall of my room. It was taken while he looked at the camera. But wherever I go the picture stares at me. The eyes of my grandfather are on us like the sun and the moon. Is their any science behind it? The picture will always show what the camera saw. When you look at the picture you also see what the camera saw. When the camera was taking the picture, your grandfather was looking at it. The picture cannot change when you move around the room. You would have noticed that when you are watching a newscaster read the news on TV he seems to be always looking at you no matter where you are sitting in the room. In order to give you this impression the newscaster just looks at the lens of the camera. Whole of his audience is, in a way, captured behind that lens. This way he can pose to be the sole friend of every one who watches him perform. The question remains as to how we get an impression that someone is looking at us. It seems obvious that when his face is turned towards me and the pupils of his eyes are centrally located in his eyes he must be looking at me. Perhaps there is also a difference between someone staring in my direction and his looking at me. This difference might lie in his expression — we humans are very sensitive in reading expressions. Incidentally, you must have noticed that in a photograph, or on the TV screen, if someone is looking sideways you can never move to a position where that someone would be looking at you. For an eye contact with everyone in his audience a performer has only to look lovingly towards the camera lens! Anywhere else and he would not be looking at anyone! During the winter season the water in the river and the water tank feels cold while that from the well is warm. Why is it so? Winter is winter because the land surface and the atmosphere become colder. This is also true for the water on the surface of the earth. The primary reason is the reduction of the solar energy input. However, changes in the surface temperature of the earth do not significantly affect the temperature below ground. Heat capacity of the earth is large and soil does not conduct heat very well. Therefore, the temperature below ground is higher than the top during winter and lower than the top in summer. As a result the well water is always at an advantage. During winters it provides us the needed warmth and in summer the cooler water to bathe in and to drink. |
