Üds a can coal ever become a friend of the environment? Coal-fired power stations supply
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particularly fierce, and making boats wait would be too dangerous. This unpredictability makes life even tougher for motorists. Yet a fixed bridge would make a stretch of the Intra coastal Waterway impassable to boats taller than 65 feet, so that option was ruled out almost immediately. When an examination of the bridge's records showed that increasing the height would reduce the frequency of closings only slightly, the state decided to build a new drawbridge with the same height as the old one
By 2020, total meat consumption in developing countries is predicted to have more than doubled. Yet livestock, especially in wealthy countries, already munches its way through 36 per cent of the world's grain harvest. All that grain exacts a heavy environmental cost, be cause the increased demand pulls farmers towards growing maize and soybean and away from pasture and fodder crops such as alfalfa that do so much for soil health. And grain-fed animals tend to be housed in huge feedlots, where crowding causes disease and veterinary surgeons use more antibiotics, and where vast mountains of manure pollute the surroundings. Consumers could reverse many of these problems by demanding meat from grass-fed livestock, or simply by eating less meat And as an added bonus for overfed Westerners, the meat from grass-fed cattle is leaner than that from grain-fed animals
In the first half of the 20. century, acid rain-whether natural or unnatural-was a hidden phenomenon. By the 1950s, how ever, its effects were becoming apparent to scientists in scandinavia with the loss of fish from mountain lakes. A network of rainwater monitoring stations was set up across Europe, which very soon proved the existence of acid rain as a result of human activities. Acid rain was also charged with killing vast tracts of forest in Germany. The effects of long-range sul phur pollution were looking so worrying that the issue was placed before the world at the UN Conference on the Human Environment in Stockholm in 1972. The out come was that states are now responsible for ensuring that their activities do not damage the environment of other states. This paved the way for the development of programmes for reducing lon-range air pollution. The most important of these was the Convention on Long-Range Trans boundary Air Pollution, attended in 1979 by the world's leading industrial nations.
After a heavy rain one day 200.000 years ago, someone small .,Jalked across some sand. Sand covered the tracks and eventually they hardened into sandstone. More centuries passed, and the sandstone eroded. Some construction workers on a break in Nahoon, South Africa, discovered the tracks, which were thought to be 30.000 years old. Now geologist Dave Roberts, at the Council for Geoscience in Caper Town, has redated the impressions and says they are 200.000 years Old, the oldest human footprints on Earth. 'We have far more powerful dating techniques now", says Roberts. HE used thermoluminescence a dating method that measures when sand grains were last ex posed to light. Only about seven inches long the prints clearly show five toes and a well developed arch ÜDS I A curious form of renewable-energy generation may be on the horizon-with underwater turbines. These units harness the power of tidally driven currents, which flow back and forth like clockwork, making it possible to generate electricity on a predictable schedule. In this respect, underwater turbines are more attractive than their wind-driven coun terparts, which are now employed widely to help power electric grids. Underwater structures are also less likely to be damaged by violent storms, which have little effect on submerged objects. And using underwater turbines sidesteps the common objections to Conventional hydropower-that damming a river stops migrating fish and inundates land upstream. Underwater turbines have long been used on a small scale. But soon now they will be used on a large scale to produce megawatt of electric power.
Architects and engineers engage in design quite explicitly, and they typically do so with distinct objectives. Architects tend to focus on form over function, whereas engineers tend to do the opposite. For most architects, the design of a building has firstly to do with how it looks, both inside and out, and how it fits in with nearby buildings. Architects are also expected to give considerable thought to how the building will be used, how people will move through it, how it will feel, although such considerations do not always seem to be foremost in their minds judging by results. Indeed, if architectural criticism is taken at face value, architects do seem to be principally concerned with the texture of a building's farade, the appearance of its public spaces, the furniture with which it is filled. Architects seem to pay close attention to details, even down to the nature of the lighting fixtures and the hardware on doors and windows, but not always to how they will be operated or how they will fulfil their purpose. Nevertheless, such considerations collectively constitute architectural and interior design.
Electric heating, which appeared in less than 1 per cent of homes in the United States in 1950, noe dominates most areas with mild winters and cheap electricity, including the South and the Northwest. Its popularity, at least in the South, was spurred by the low cost of adding electric heating to new houses built with air-conditioning. In the Northeast and Midwest, electricity has not been a popular fuel because of its high cost for cold weather heating and because it delivers heat at 90 to 95°F, compared with 120 to 140°F for gas and oil, which many in cold climates find preferable. In some areas, such as California, electric heating has not progressed because of building code restrictions. Bottled gas, which is somewhat more expensive than utility gas, is the fuel of choice in rural areas not served by utility pipelines. Wood, the dominant fuel throughout the US economy until the 1880s, is the leading heating fuel in just a few rural counties. Home heating, which accounts for less than 7 per cent of all energy consumed in the US, has had a commendable efficiency record: from 1978 to 1997, the amount of fuel consumed for this purpose declined 44 per cent despite a 33 per cent increase in the number of housing units and an increase in house size. This im provement came about thanks to better insulation and more efficient equipment following the energy crisis of the 1970s.
Biologists value marine organisms be cause their primitive systems are good models for more complex organisms, such as humans. Despite being generically fur ther from us than more common research mammals, we share a surprising number of evolutionary links with these basic animals. By understanding their life processes and the way their systems react when things go wrong , scientists hope to continue making important discoveries that could help increase the chances of finding cures for serious diseases such as cancer and AIDS, As research continues, under standing increases about how our bodies and minds work, but there is still a lot to learn. Obviously it takes a long time to work out all the mechanisms, and there are still many new bioactive compounds to be found in marine organisms. But by us ing sea creatures to better understand human characteristics and disorders, progress is being made
Many people who are perfectly relaxed driving along the highways become nervous when they get on an airliner, although most know full well that flying is safer than driving. The statistics are Indeed clear on this point. For example, a paper published in 1991 documented the substantially lower risk of flying compared with driving in the United States. Some of the many millions of Americans who flew over the next few years probably derived comfort from such hard facts. But now, a decade later, things have changed. The hijacking of four large jets on September 11,2001, and the disastrous events that ensued led many to avoid flying in the United States during the following months. For example, in the fourth quarter of 2001, there was a drop of 18 percent in the number of passengers compared with the same time period in 2000. Many still avoid air-travel. Accordingly, it would be appropriate to again calculate the risks involved in flying and driving, taking into account the latest statistics, including the tragic deaths of the passengers on those four hijacked planes
The American chestnut was once the most common canopy tree in the deciduous (non-evergreen) forests of the eastern United States. It shaded areas from New England to Georgia until the fungus Cry phonectria parasitica wiped out the species in the terrible forest disaster of the early 20. century. The fungus continues to kill chestnuts before they can mature. The vacuum left by the chestnut's destruction is now filled with other species. Consider able research has gone into understanding what happened to the American chestnut. But some scientists remain interested in getting to the root not of its destruction, but rather of the centuries of dominance enjoyed by the massive, fragrant and economically important tree. A team of scien tists recently put forward the idea that the American chestnut may have been engaged in the chemically charged competition known as allelopathy. An allelopathic plant releases potentially toxic substances into the environment through its roots, its leaves or processes such as evaporation. Black walnut, sycamore and sassafras trees are just a few known allelopaths that limit the germination of competitors. It's likely that the list will soon branch out to include the chestnut.
ÜDS J The people of Blaenavon in South Wales were understandably worried. The opencast mine only 1 kilometer north of their town had served the great Blaenavon ironworks when they opened in the late 16. century. But it had been lying derelict for decades and now British Coal Opencast wanted to mine the remaining 320,000 tonnes of coal. At opencast sites, for every tonne of coal recovered, up to 40 tonnes of rock has to be extracted. So, in the case of Blaenavon, unless precautionary measures were taken, the air in the town was going to be thick with dust. Precautionary measures were taken, based on well-tried techniques. For instance, tall spray masts were erected around dumps to provide a curtain of rain to entrap and wash out dust from the air, and the wheels of every vehicle leaving the site were washed. Further, reclaimed areas were planted with trees and grass from day one. With these and other measures this turned out to be a success story for all concerned. In fact, during the entire mining and reclamation project not a single complaint about nuisance dust was made to the local authority.
If engineers waited for the development of scientific knowledge to use and organize into technological achievements, ours would be a very different world from what we know In engineering, it is not so much science as it is ingenuity that is applied to solve problems and satisfy needs and wants. If this were not so, the steam engine would never have been invented in the absence of thermodynamics. The Wright Brothers would not have flown Since they had no aerodynamics textbooks. The astronauts would never have landed on the Moon nor the rovers on Mars without firm geological knowledge of their surfaces. Rather than following scientific theories and discoveries, engineering leads them. Operating steam engines prompted the development of thermodynamics, actual powered flight drove aerodynamics, and Moon and Mars missions brought back samples and sent back data that led to increased scientific knowledge about those extraterrestrial bodies.
Formerly, potatoes were grown on unirrigated land, which often meant they were small and probably misshapen. Now, however, farmers routinely irrigate their lands to produce products acceptable to the fast food industry for its French fries. But in Minnesota the groundwater that farmers pump for potatoes has turned out to be the same water that helps to sustain the Straight River, a major trout fishery, Even modest pumping for potatoes, a federal study eventually concluded, had the potential to reduce the river's flow by one third during the irrigation season, with adverse impact on the brown trout. For now, the trout are not in danger, but that could change if Minnesota were to approve applications from farmers still eager to see potato planting and irrigation and widen Gamma-ray bursts (GRBs) are among the most intense areas of research in high energy astrophysics, and they represent the .Iargest known explosions in the universe. Last year, NASA launched the Swift satellite to rapidly locate and observe GRBs and their afterglows at x ray, ultraviolet and optical wavelengths.These afterglow observations are particularly important fort he understanding of these enormous explosions that occur at cosmological distances near the edge of the observable universe. Amateur astronomers, due to their large numbers, their ability to respond quickly to the' randomly located GRBs and . the availability of highly sensitive CCO cameras, have been able to provide important, early data on the optical afterglows of GRBs in the past few years. Indeed, at least one optical afterglow from a GRS was discovered by an amateur astronomer. Obstvations can be done with even a modest-size te/Heap., provided the observations are m,t»qulakly onough. All multi-engined aircraft are designed to keep flying in the event of engine failure. Losing thrust from one side of an aircraft unbalances it and causes the nose of the aircraft to turn in the direction of the failed engine. Aircraft have a vertical stabilizer (the upright at the back) to keep the aircraft's nose into the wind, with a rudder attached to it for fine tuning. Moving the rudder into the airflow creates a sideways force, which turns the aircraft around its vertical axis. When this is applied in the direction of the failed engine, the force created by the rudder will counteract the turn induced by the uneven engine thrust. The vertical stabilizer and rudder are sized to control the uneven thrust caused by an engine faiiure at the most demanding limits of the flight envelope, as they must be capable of generating powerful turning forces. There have been stories in the press about mobile phones sparking explosions at petrol stations. But according to the GSM Association, a worldwide body for mobile phone makers, none of these reports has ever been traced back to a real event. But there is a real safety concern, and it's not about radio emissions from mobiles as you might have thought. İnstead, the GSM Association says there is a theoretical risk that if a hand-held phone is dropped and the battery separates from the phone, it could cause a spark across the contacts. This is equally true of other battWy'-powered devices such as torches, Walkmans and CD players. But it's far more likely that mobile phones cause a hazard at petrol stations by distracting their users while they're operating a petrol pump Yüklə 0,75 Mb. Dostları ilə paylaş:
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