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Plastic solar cells
One-way trip into black hole Trends Prof Yash
Pal PROF YASH PAL |
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Plastic solar cells With the ever-increasing demand of electrical energy everyone is looking towards the sun as source of electrical energy along with its role as a source of thermal energy. The use of solar, or photovoltaic, cells — devices that can absorb and convert light into electrical power — has been limited to date because production costs are so high. Even the fabrication of the simplest semiconductor cell is a complex process that has to take place under exactly controlled conditions, such as high vacuum and temperatures between 400 and 1,400 degrees Celsius. Ever since the discovery in 1977 of conducting plastics (polymers which feature conjugated double chemical bonds, that enable electrons to move through them), there has been interest in using these materials in the fabrication of solar cells. Plastic solar cells can be made in bulk quantities for a less cost; however, the efficiency so far with which they convert light into electricity has been quite poor compared to the power-conversion efficiencies of semiconductor cells. A new generation of solar cells that combines nano-technology with plastic electronics has been launched with the development of a semiconductor-polymer photovoltaic device by researchers. Such hybrid solar cells will be cheaper and easier to make than their semiconductor counterparts, and could be made in the same nearly infinite variety of shapes as pure polymers. Semiconductor nano-rods can be used to fabricate the readily processed and energy-efficient hybrid solar cells together with polymers. The advantage of hybrid materials consisting of inorganic semiconductors and organic polymers is that potentially we get the best of both worlds. Inorganic semiconductors offer excellent, well established electronic properties, and they are very well suited as solar cell materials. Polymers offer the advantage of solution processing at room temperature, which is cheaper and allows for using fully flexible substrates, such as plastics. At the heart of all photovoltaic devices are two separate layers of materials, one with an abundance of electrons those functions as a “negative pole,” and one with an abundance of electron holes (vacant, positively-charged energy spaces) that functions as a “positive pole”. When photons from the sun or some other light source are absorbed, their energy is transferred to the extra electrons in the negative pole, causing them to flow to the positive pole and creating new holes that start flowing to the negative pole, thus producing electrical current which can then be used to power other devices. In a typical semiconductor solar cell, the two poles are made from n-type and p-type semiconductors. In a plastic solar cell, they’re made from hole-acceptor and electron-acceptor polymers. In one such hybrid solar cell scientists are using the semi-crystalline polymer known as poly(3-hexylthiophene), or P3HT, for the hole acceptor or negative pole, and nanometer-sized cadmium selenide (CdSe) rods as the positive pole. P3HT is the conjugated polymer with the highest hole mobility found so far. Higher hole (and electron) mobility means that charges are transported more quickly, which reduces current losses. The cadmium selenide rods measured 7 nanometers in diametre and 60 nanometres in length are being used. Using rod-shaped nano-crystals rather than spheres provided a directed path for electron transport to help improve solar cell performance. These types of hybrid solar cells are reported to achieve a monochromatic power conversion efficiency of 6.9 per cent, one of the highest ever reported for a plastic photovoltaic device. The most important step is to increase the amount of sunlight absorbed in the red part of the spectrum. Published hybrid solar cells have a very simple structure, in order to investigate the science behind them. In the future, many engineering tricks can be applied to make these cells more efficient. The writer is from Department of Physics, S.L.I.E.T., Longowal |
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One-way trip into black hole
The one-way journey from the heart of a galaxy into the oblivion of a black hole probably takes about 200,000 years, astronomers said. By tracking the death spiral of cosmic gas at the centre of a galaxy called NGC1097, scientists figured that material moving at 110,000 miles (177,000 km) an hour would still take eons to cross into a black hole. Black holes are drains in space that have gravitational pull so strong that nothing, not even light, can escape. Huge ones are believed to lurk at the centers of many galaxies including the Milky Way, which contains the sun. “It would take 200,000 years for gas to travel the last leg of its one-way journey,” Kambiz Fathi of Rochester Institute of Technology told reporters at a meeting of the American Astronomical Society. No one has ever seen a black hole, but astronomers study the way matter and energy behave around them. An international team led by Fathi studied the black hole at the middle of NGC1097, a behemoth with 100 million times the mass of the sun. The team managed to observe behaviour 10 times closer to the black hole than ever before, Fathi said, seeing clouds of material within 10 light-years of the galactic core, where the black hole is believed to reside. Previous research has detected gas clouds from 100 to 1,000 light-years from the galaxy’s heart. A light-year is about six trillion miles (10 trillion km), the distance light travels in a year. The galaxy is about 47 million light-years away from Earth, relatively close in cosmic terms.
— Reuters |
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Trends Metal foams, full of tiny air bubbles like a sponge cake, are gradually making inroads in industrial applications. Lightness and high energy absorption are two demanded material characteristics. Less known is the use of open-pored variants for decorative purposes. Interior designers can make use of an endless variety of decorative panels to realise their plans. Room dividers and suspended ceilings divide up the space in an apartment or office, but they are also expected to be more or less permeable to light, air or sound. A class of materials that meets this requirement is open-pored metal foams. A stylish effect can be achieved by filling the interconnected pores with a transparent synthetic resin or colored plastic. The closely related closed-pore metal foams are already making headway in numerous applications. Their low weight predestines them for use in light but rigid assemblies in machines with moving parts. They are used as shock absorbers in vehicles, due to their excellent capacity to convert kinetic energy into resilience and heat. As catalysts their high internal surface area is used. Virtual microscope
Astronomy buffs who jumped at the chance to use their home computers in the SETI@home search for intelligent life in the universe will soon be able to join an Internet-based search for dust grains originating from stars millions of light years away. In a new project called Stardust@home, University of California, Berkeley, researchers will invite Internet users to help them search for a few dozen submicroscopic grains of interstellar dust captured by NASA’s Stardust spacecraft and due to return to earth this month. Though Stardust’s main mission was to capture dust from the tail of comet Wild 2 - dust dating from the origins of the solar system some 4.5 billion years ago - it also captured a sprinkling of dust from distant stars, perhaps created in supernova explosions less than 10 million years ago. “These will be the very first contemporary interstellar dust grains ever brought back to earth for study,” said Andrew Westphal, a UC Berkeley senior fellow and associate director of the campus’s Space Sciences. Laboratory who developed the technique NASA will use to digitally scan the aerogel in which the interstellar dust grains are embedded. Nanorings and RAM
U.S. scientists say they have devised a way to make tiny memory cells that will advance the development of magnetic random-access memory. Magnetic random-access memory would make it possible to build a computer that doesn’t lose data even in a sudden power outage or a coin-sized hard drive that could store 100 or more movies, Johns Hopkins University reported. A team of researchers from the university has developed asymmetrical magnetic nanorings —tiny, irregularly shaped cobalt or nickel rings that can serve as |
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PROF YASH PAL Can a tug of war be ever won on a friction-free surface? This is a beautiful question. If taken as question in physical science the obvious answer will have to be NO. It cannot be won, but also, it can never be lost because both sides have nothing to push against. However, some unconventional ways of tugging do remain. If all the members were to suddenly pull out their previously untied heavy shoes and throw them towards (not at) the opposite team they would start sliding backwards and might reach the goal before the other side has time to untie their bootstraps. The other side might try to slow their slide forward by furiously blowing in the forward direction, but the opponents would catch on immediately and begin There can be several other considerations and maneuvers in such a “war”. You could select the side that slightly slopes up towards the opponent team. If there is a slight wind select the side that faces the wind and carry umbrellas to unfold to make use of its push!! Taken philosophically the question can also imply that there is no absolute winning in this world because in the long run the ground is always slippery. What is the technique of
making clear ice? Ice comes in hexagonal crystals. These crystals are formed during freezing of water. The crystallisation process involves active arrangement by water molecules into well-defined structures. But under normal circumstances the water we use is not pure. It might have dissolved impurities. These might include salts and dissolved gases such as air. During slow crystallisation these impurities are pushed out the process itself and we end up with fairly clear blocks of ice. But it helps if we use de-mineralised water that has been boiled for a while to remove most of the dissolved air. Also there might be ways in which the air and salts excluded during the process of crystallisation are swept away. Perhaps they use some techniques for this in ice factories. I will like to visit such a factory one of these days. You might do some experiments yourself. Make ice in the freezing compartment of your refrigerator using tap water and filtered and freshly boiled water. You might also devise ways in which freezing is slowed down; this might be done in slightly insulating the tray in which the ice cubes are being formed! Let me know the result of your experiments. In the end let me remind those living in colder regions, that icicles formed at the edge of the roof are always crystal clear. They are formed slowly with every drop adding a thin layer of hexagonal ice platelets. The impurities are excluded and blown away. When a tyre bursts, the air coming out is colder than surrounding
air. Why? Air in the tyre is at high pressure and a temperature close to the outside temperature. When the tyre bursts the air expands and its molecules rush away from each other. In doing so they work against the force of intermolecular attraction and lose some of their random kinetic energy. This is nothing but losing temperature. In school science we call it operation of the Boyle’s law. In other words the result is cooling of air. |
