A thyristor has its gate current zero. To start conduction the forward voltage must exceed ?->(Show Answer!)

1. A thyristor has its gate current zero. To start conduction the forward voltage must exceed

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MCQ->A thyristor has its gate current zero. To start conduction the forward voltage must exceed....

MCQ-> In a modern computer, electronic and magnetic storage technologies play complementary roles. Electronic memory chips are fast but volatile (their contents are lost when the computer is unplugged). Magnetic tapes and hard disks are slower, but have the advantage that they are non-volatile, so that they can be used to store software and documents even when the power is off.In laboratories around the world, however, researchers are hoping to achieve the best of both worlds. They are trying to build magnetic memory chips that could be used in place of today’s electronics. These magnetic memories would be nonvolatile; but they would also he faster, would consume less power, and would be able to stand up to hazardous environments more easily. Such chips would have obvious applications in storage cards for digital cameras and music- players; they would enable handheld and laptop computers to boot up more quickly and to operate for longer; they would allow desktop computers to run faster; they would doubtless have military and space-faring advantages too. But although the theory behind them looks solid, there are tricky practical problems and need to be overcome.Two different approaches, based on different magnetic phenomena, are being pursued. The first, being investigated by Gary Prinz and his colleagues at the Naval Research Laboratory (NRL) in Washington, D.c), exploits the fact that the electrical resistance of some materials changes in the presence of magnetic field— a phenomenon known as magneto- resistance. For some multi-layered materials this effect is particularly powerful and is, accordingly, called “giant” magneto-resistance (GMR). Since 1997, the exploitation of GMR has made cheap multi-gigabyte hard disks commonplace. The magnetic orientations of the magnetised spots on the surface of a spinning disk are detected by measuring the changes they induce in the resistance of a tiny sensor. This technique is so sensitive that it means the spots can be made smaller and packed closer together than was previously possible, thus increasing the capacity and reducing the size and cost of a disk drive. Dr. Prinz and his colleagues are now exploiting the same phenomenon on the surface of memory chips, rather spinning disks. In a conventional memory chip, each binary digit (bit) of data is represented using a capacitor-reservoir of electrical charge that is either empty or fill -to represent a zero or a one. In the NRL’s magnetic design, by contrast, each bit is stored in a magnetic element in the form of a vertical pillar of magnetisable material. A matrix of wires passing above and below the elements allows each to be magnetised, either clockwise or anti-clockwise, to represent zero or one. Another set of wires allows current to pass through any particular element. By measuring an element’s resistance you can determine its magnetic orientation, and hence whether it is storing a zero or a one. Since the elements retain their magnetic orientation even when the power is off, the result is non-volatile memory. Unlike the elements of an electronic memory, a magnetic memory’s elements are not easily disrupted by radiation. And compared with electronic memories, whose capacitors need constant topping up, magnetic memories are simpler and consume less power. The NRL researchers plan to commercialise their device through a company called Non-V olatile Electronics, which recently began work on the necessary processing and fabrication techniques. But it will be some years before the first chips roll off the production line.Most attention in the field in focused on an alternative approach based on magnetic tunnel-junctions (MTJs), which are being investigated by researchers at chipmakers such as IBM, Motorola, Siemens and Hewlett-Packard. IBM’s research team, led by Stuart Parkin, has already created a 500-element working prototype that operates at 20 times the speed of conventional memory chips and consumes 1% of the power. Each element consists of a sandwich of two layers of magnetisable material separated by a barrier of aluminium oxide just four or five atoms thick. The polarisation of lower magnetisable layer is fixed in one direction, but that of the upper layer can be set (again, by passing a current through a matrix of control wires) either to the left or to the right, to store a zero or a one. The polarisations of the two layers are then either the same or opposite directions.Although the aluminum-oxide barrier is an electrical insulator, it is so thin that electrons are able to jump across it via a quantum-mechanical effect called tunnelling. It turns out that such tunnelling is easier when the two magnetic layers are polarised in the same direction than when they are polarised in opposite directions. So, by measuring the current that flows through the sandwich, it is possible to determine the alignment of the topmost layer, and hence whether it is storing a zero or a one.To build a full-scale memory chip based on MTJs is, however, no easy matter. According to Paulo Freitas, an expert on chip manufacturing at the Technical University of Lisbon, magnetic memory elements will have to become far smaller and more reliable than current prototypes if they are to compete with electronic memory. At the same time, they will have to be sensitive enough to respond when the appropriate wires in the control matrix are switched on, but not so sensitive that they respond when a neighbouring elements is changed. Despite these difficulties, the general consensus is that MTJs are the more promising ideas. Dr. Parkin says his group evaluated the GMR approach and decided not to pursue it, despite the fact that IBM pioneered GMR in hard disks. Dr. Prinz, however, contends that his plan will eventually offer higher storage densities and lower production costs.Not content with shaking up the multi-billion-dollar market for computer memory, some researchers have even more ambitious plans for magnetic computing. In a paper published last month in Science, Russell Cowburn and Mark Well and of Cambridge University outlined research that could form the basis of a magnetic microprocessor — a chip capable of manipulating (rather than merely storing) information magnetically. In place of conducting wires, a magnetic processor would have rows of magnetic dots, each of which could be polarised in one of two directions. Individual bits of information would travel down the rows as magnetic pulses, changing the orientation of the dots as they went. Dr. Cowbum and Dr. Welland have demonstrated how a logic gate (the basic element of a microprocessor) could work in such a scheme. In their experiment, they fed a signal in at one end of the chain of dots and used a second signal to control whether it propagated along the chain.It is, admittedly, a long way from a single logic gate to a full microprocessor, but this was true also when the transistor was first invented. Dr. Cowburn, who is now searching for backers to help commercialise the technology, says he believes it will be at least ten years before the first magnetic microprocessor is constructed. But other researchers in the field agree that such a chip, is the next logical step. Dr. Prinz says that once magnetic memory is sorted out “the target is to go after the logic circuits.” Whether all-magnetic computers will ever be able to compete with other contenders that are jostling to knock electronics off its perch — such as optical, biological and quantum computing — remains to be seen. Dr. Cowburn suggests that the future lies with hybrid machines that use different technologies. But computing with magnetism evidently has an attraction all its own.In developing magnetic memory chips to replace the electronic ones, two alternative research paths are being pursued. These are approaches based on:
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MCQ-> Read the passage given below and answer the questions that follow:-Brazil is a top exporter of every commodity that has seen dizzying price surges - iron ore, soybeans, sugar - producing a golden age for economic growth Foreign money-flows into Brazilian stocks and bonds climbed heavenward, up more than tenfold, from $5 billion a year in early 2007 to more than $50 billion in the twelve months through March 2011.The flood of foreign money buying up Brazilian assets has made the currency one of the most expensive in the world, and Brazil one of the most costly, overhyped economies. Almost every major emerging- market currency has strengthened against the dollar over the last decade, but the Brazilian Real is on a path alone, way above the pack, having doubled in value against the dollar.Economists have all kinds of fancy ways to measure the real value of a currency, but when a country is pricing itself this far out of the competition, you can feel it on the ground. In early 2011 the major Rio paper, 0 Globo, ran a story on prices showing that croissants are more expensive than they are in Paris, haircuts cost more than they do in London, bike rentals are more expensive than in Amsterdam, and movie tickets sell for higher prices than in Madrid. A rule of the road: if the local prices in an emerging market country feel expensive even to a visitor from a rich nation, that country is probably not a breakout nation.There is no better example of how absurd it is to lump all the big emerging markets together than the frequent pairing of Brazil and China. Those who make this comparison are referring only to the fact that they are the biggest players in their home regions, not to the way the economies actually run. Brazil is the world‘s leading exporter of many raw materials, and China is the leading importer; that makes them major trade partners - China surpassed the United States as Brazil's leading trade partner in 2009 f but it also makes them opposites in almost every important economic respect: Brazil is the un-China, with interest rates that are too high, and a currency that is too expensive. It spends too little on roads and too much on welfare, and as a result has a very un-China-like growth record.It may not be entirely fair to compare economic growth in Brazil with that of its Asian counterparts, because Brazil has a per capita income of $12,000, more than two times China's and nearly ten times India's. But even taking into account the fact that it is harder for rich nations to grow quickly, Brazil's growth has been disappointing. Since the early 19805 the Brazilian growth rate has oscillated around an average of 2.5 percent, spiking only in concert with increased prices for Brazil's key commodity exports. While China has been criticized for pursuing "growth at any cost," Brazil has sought to secure "stability at any cost." Brazil's caution stems from its history of financial crises, in which overspending produced debt, humiliating defaults, and embarrassing devaluations, culminating in a disaster that is still recent enough to be fresh in every Brazilian adult's memory: the hyperinflation that started in the early 19805 and peaked in 1994, at the vertiginous annual rate of 2,100 percent.Wages were pegged to inflation but were increased at varying intervals in different industries, 50 workers never really knew whether they were making good money or not. As soon as they were paid, they literally ran to the store with cash to buy food, and they could afford little else, causing non-essential industries to start to die. Hyperinflation finally came under control in l995, but it left a problem of regular behind. Brazil has battled inflation ever since by maintaining one of the highest interest rates in the emerging world. Those high rates have attracted a surge of foreign money, which is partly why the Brazilian Real is so expensive relative to comparable currencies.There is a growing recognition that China faces serious "imbalances" that could derail its long economic boom. Obsessed until recently with high growth, China has been pushing too hard to keep its currency too cheap (to help its export industries compete), encouraging excessively high savings and keeping interest rates rock bottom to fund heavy spending on roads and ports. China is only now beginning to consider a shift in spending priorities to create social programs that protect its people from the vicissitudes of old age and unemployment.Brazil’s economy is just as badly out of balance, though in opposite ways. While China has introduced reforms relentlessly for three decades, opening itself up to the world even at the risk of domestic instability, Brazil has pushed reforms only in the most dire circumstances, for example, privatizing state companies when the government budget is near collapse. Fearful of foreign shocks, Brazil is still one of the most closed economies in the emerging world - total imports and exports account for only 15 percent of GDP - despite its status as the world's leading exporter of sugar, orange juice, coffee, poultry, and beef.To pay for its big government, Brazil has jacked up taxes and now has a tax burden that equals 38 percent of GDP, the highest in the emerging world, and very similar to the tax burden in developed European welfare states, such as Norway and France. This heavy load of personal and corporate tax on a relatively poor country means that businesses don’t have the money to invest in new technology or training, which in turn means that industry is not getting more efficient. Between 1986 and 2008 Brazil’s productivity grew at an annual rate of :about 0.2 percent, compared to 4 percent in China. Over the same period, productivity grew in India at close to 3 percent and in South Korea and Thailand at close to 2 percent. According to the passage, the major concern facing the Brazil economy is:
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MCQ-> Read the following passage to answer the given questions based on it. Some words/ phrases are printed in ‘’bold’’ to help you locate them while answering some of the questions.The e-waste (Management of Handling) Rules, 2011 notified by the Ministry of Environment and Forests, have the potential to turn a growing problem into a developmental opportunity. With almost half-a-year to go before the rules take effect, there is enough time to create necessary infrastructure for collection, dismantling, and recycling of electronic waste. The focus must be on sincere and efficient implementation.Only decisive action can reduce the pollution and health costs associated with India’s hazardous waste recycling industry. If India can achieve a transformation, it will be creating a whole new employment sector that provides good wages and working conditions for tens of thousands. The legacy response of the States to even the basic law on urban waste , the Municipal Solid Wastes (Management and Handling) Rules, has been one of the indifference many cities continue to simply burn the garbage or dump it in lakes. With the emphasis now on segregation of waste at source and recovery of materials, it should be feasible to implement ‘’both sets of rules’’ efficiently. A welcome feature of the new e-waste rule is emphasis on extended producer responsibility. In, other words, producers must take responsibility for the disposal of end-of-life products. For this provision to work, they must ensure that consumers who sell scrap get some form of financial incentive. The e-waste rules, which derive from those pertaining to hazardous waste, are scheduled to come into force on May 1, 2012. Sounds as they are, the task of scientifically disposing a few hundred, thousand tonnes of trash electronics annually depends heavily on a system of oversight by State Pollution Control Boards (PCBs). Unfortunately, most PCBs remain unaccountable and often lack the resources for active enforcement. It must be pointed out that, although agencies handling e-waste must obtain environmental ‘’clearances’’ and be authorised and registered by the PCBs even under the Hazardous Wastes (Management, Handling and Transboundary Movements) Rules, 2008, there has been little practical impact. Over 95 per cent of electronic waste is collected and recycled by the informal sector. The way forward is for the PCBs to be made accountable for enforcement of the e-waste rules, and the levy of penalties under environmental laws. Clearly, the first order priority is to create a system that will absorb the 80000-strong workforce in the informal sector into the proposed scheme for scientific recycling. Facilities must be created to upgrade the skills of these workers through training and their occupational health must be ensured. Recycling of e-waste is one of the biggest challenges today. In such a time, when globalization and information technology are growing at a pace which could only be imagined few years back, e-waste and its hazards have become more prominent over a period of time and should be given immediate attention.What according to the passage is important now for e-waste management?
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