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1、专业好文档avalanche and its safetyan avalanche is a sudden and rapid flow of snow, often mixed with air and water, down a mountainside. avalanches are among the biggest dangers in the mountains for both life and property. all avalanches are caused by an over-burden of material, typically snowpack, that i

2、s too massive and unstable for the slope that supports it. determining the critical load, the amount of over-burden which is likely an avalanche, is a complex task involving the evaluation of a number of factors. terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low

3、risk of avalanche. snow does not gather significantly on steep slopes; also, snow does not flow easily on fiat slopes. human-triggered avalanches have the greatest incidence when the snows angle of rest1 is between 35 and 45 degrees; the critical angle, the angle at which the human incidence of aval

4、anches is greatest, is 38 degrees. the rule of thumb2 is: a slope that is flat enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. additionally3, avalanche risk increases with use ; that is, the more a slope is disturbed by skiers, the mor

5、e likely it is that an avalanche will occur. due to the complexity of the subject, winter travelling in the backcountry4 is never 100% safe. good avalanche safety is a continuous process , including route selection and examination to the snowpack, weather conditions , and human factors. several well

6、-known good habits can also reduce the risk. if local authorities issue avalanche risk reports, they should be considered and all warnings should be paid attention to. never follow in the tracks of others without your own evaluations; snow conditions are almost certain to have changed since they wer

7、e made. observe the terrain and note obvious avalanche paths where plants are moiising or damaged. avoid traveling below others who might trigger an avalanche.giant structuresit is an impossible task to select the most amazing wonders of the modem world since every year more_wonderful_constructions

8、appear. here are three giant structures which are worthy of our_admiration_although they may have been surpassed by some more recent wonders.the petronas twin towersthe petronas towers were the tallest buildings in the world when they were completed in 1999. with a_height_of 452 metres, the tall twi

9、n towers, like two thin pencils, dominate the city of kuala lumpur. at the 41st floor, the towers are linked by a bridge, symbolizing a gateway to the city. the american_architect_cesar pelli designed the skyscrapers.constructed of high-strength concrete, the building provides around 1，800 square me

10、tres of office space_on_every floor. and it has a shopping centre and a concert hall at the base. other_features_of this impressive building include double-decker lifts, and glass and steel sunshades.the miuau bridgethe millau bridge was opened in 2004 in the tam valley，in southern france._at_the ti

11、me it was built，it was the worlds highest bridge,_reaching_over 340m at the highest point. the bridge is described as one of the most amazingly beautiful bridges in the world. it was built to_relieve_millaus congestion problems. the congestion was then caused by traffic passing from paris to barcelo

12、na in spain. the bridge was built to withstand the_most_extreme seismic and climatic conditions. besides, it is guaranteed for 120 years!the itaipu damthe itaipu hydroelectric power plant is one of the largest constructions of its kind in the world. it consists of a series of dams across the river p

13、arana,_which_forms a natural border between brazil and paraguay. started in 1975 and taking 16 years to complete, the construction was carried out as a joint project between the two_countries_. the dam is well-known for both its electricity output and its size. in 1995 it produced 78% of paraguays a

14、nd 25% of brazils_energy_needs. in its construction, the_amount_of iron and steel used was equivalent to over 300 eiffel towers. it is a_truly_amazing wonder of engineering.animals “sixth sense”a tsunami was triggered by an earthquake in the indian ocean in december, 2004. it killed tens of thousand

15、s of people in asia and east africa. wild animals, however, seem to have escaped that terrible tsunami. this phenomenon adds weight to notions that i they possess a “sixth sense” for disasters, experts said. sri lankan wildlife officials have said the giant waves that killed over 24,000 people along

16、 the indian ocean islands coast clearly missed wild beasts, with no dead animals found. “no elephants are dead, not even dead rabbit. i think animals can sense disaster. they have a sixth sense. they know when things are happening.” h.d. ratnayake, deputy director of sri lankas wildlife department,

17、said about one month after the tsunami attack. the waves washed floodwaters up to 2 miles inland at yala national park in the ravaged southeast, sri lankas biggest wildlife reserve and home to hundreds of wild elephants and several leopards. “there has been a lot of apparent evidence about dogs bark

18、ing or birds migrating before volcanic eruptions or earthquakes. but it has not been proven,” said matthew van lierop an animal behavior specialist at johannesburg zoo. “there have been no specific studies because you cant really test it in a lab or field setting2,” he told reuters. other authoritie

19、s concurred with this assessment. “wildlife seem to be able to pick up certain phenomenon, especially birds there are many reports of birds detecting impending disasters,” said clive walker, who has written several books on african wildlife. animals certainly rely on the known senses such as smell o

20、r hearing to avoid danger such as predators. the notion of an animal “sixth sense”-or some other mythical power-is an enduring one3 which the evidence on sri lankas ravaged coast is likely to add to. the romans saw owls as omens of impending disaster and many ancient cultures viewed elephants as sac

21、red animals endowed with special powers or attributes.singing alarms could save the blindif you cannot see, you may not be able to find your way out of a burning building - and that could be fatal. a company in leeds could change all that with directional sound alarms capable if guiding you to the e

22、xit.sound alert, a company run by the university of leeds, is installing the alarms in a residential home for blind people in sommerset and a resource centre for the blind in cumbria.the alarms produce a wide range of frequencies that enable the brain to determine where the sound is coming from.debo

23、rah withington of sound alert says that the alarms use most of the frequencies that can be heard by humans. “its a burst of white noise that people say sounds like static on the radio,”she says. “its life-saving potential is great.”she conducted an experiment in which people were filmed by thermalim

24、aging cameras trying to find their way out of a large smoke-filled room. it took them nearly four minutes to find the door without a sound alarm, but only 15 seconds with one.withington studies how the brain processes sounds at the university. she says that the source of a wide band of frequencies c

25、an be pinpointed more easily than the source of a narrow band. alarms based on the same concept have already been installed on emergency vehicles.the alarms will also include rising or falling frequencies to indicate whether people should go up or down stairs. they were developed with the aid of a l

26、arge grant from british nuclear fuels.car thieves could be stopped remotely speeding off in a stolen car, the thief thinks he has got a great catch. but he is in a nasty surprise. the car is fitted with a remote immobilizer and a radio signal from a control center miles away will ensure that once th

27、e thief switches the engine off , he will not be able to start it again. for now, such devices are only available for fleets of trucks and specialist vehicles used on construction sites. but remote immobilization technology could soon start to trickle down to ordinary cars, and should be available t

28、o ordinary cars in the uk in two months. the idea goes like this. a control box fitted to the carincorporates a miniature cellphone, a microprocessor and memory, and a gps satellite positioning receiver. if the car is stolen, a coded cellphone signal will tell the unit to block the vehicles engine m

29、anagement system and prevent the engine being restarted. there are even plans for immobilizers that shut down vehicles on the move, though there are fears over the safety implications of such a system. in the uk. an array of technical fixes is already making life harder for car thieves. “the pattern

30、 of vehicles crime has changed,” says martyn randall of thatcham, a security research organization based in berkshire that is funded in part by the motor insurance industry. he says it would only take him a few minutes to teach a novice how to steal a car, using a bare minimum of tools. but only if

31、the car is more than 10 years old. modern cars are a far tougher proposition, as their engine management computer will not allow them to start unless they receive a unique id code beamed out by the ignition key. in the uk, technologies like this have helped achieve a 31 per cent drop in vehicle-rela

32、ted crime since 1997. but determined criminals are still managing to find other ways to steal cars. often by getting hold of the owners keys in a burglary. in 2000, 12 per cent of vehicles stolen in the uk were taken using the owners keys double the previous years figure. remote-controlled immobiliz

33、ation system would put a major new obstacle in the criminals way by making such thefts pointless. a group that includes thatcham, the police, insurance companies and security technology firms have developed standards for a system that could goon the market sooner than the customer expects.an intelli

34、gent cardriving needs sharp eyes, keen ears, quick brain, and coordination between hands and the brain. many human drivers have all these and can control a fast-moving car. but how does an intelligent car control itself?there is a virtual driver in the smart car. this virtual driver has “eyes,”“brai

35、ns”，“hands” and “feet”，too. the mini-cameras on each side of the car are his “eyes,” which observe the road and conditions ahead of it. they watch the traffic to the cars left and right. there is also a highly automatic driving system in the car. it is the built-in computer, which is the virtual dri

36、vers “brain. ” his “brain” calculates the speeds of other moving cars near it and analyzes their positions. basing on this information, it chooses the right path for the intelligent cars, and gives instructions to the “hands”and “feets”to act accordingly. in this way, the virtual driver controls his

37、 car.what is the virtual drivers best advantage? he reacts quickly. the mini-cameras are sending images continuously to the “brain”. it completes the processing of the images within 100 milliseconds. however, the worlds best drier at least needs one second to react. besides, when he takes action, he

38、 needs one more second.the virtual driver is really wonderful. he can reduce the accident rate considerably on expressway. in this case. can we let him have the wheel at any time and in any place? experts warn that we cannot do that just yet. his ability to recognize things is still limited. he can

39、now only drive an intelligent car on expressways.wonder webs spider webs are more than homes, and they are ingenious traps. and the worlds best web spinner may be the golden orb weaver spider. the female orb weaver spins a web of fibers thin enough to be invisible to insect prey, yet tough enough to

40、 snare a flying bird without breaking. the secret of the webs strength? a type of super-resilient silk called dragline. when the female spider is ready to weave the webs spokes and frame, she uses her legs to draw the airy thread out through a hollow nozzle in her belly. dragline is not sticky, so t

41、he spider can race back and forth along it to spin the webs trademark spiral. unlike some spiders that weave a new web every day, a golden orb weaver reuses her handiwork until it falls apart, sometimes not for two years. the silky thread is five times stronger than steel by weight and absorbs the f

42、orce of an impact three times better than kevlar, a high-strength human-made material used in bullet-proof vests. and thanks to its high tensile strength, or the ability to resist breaking under the pulling force called tension, a single strand can stretch up to 40 percent longer than its original l

43、ength and snap back as well as new. no human-made fiber even comes close . it is no wonder manufacturers are clamoring for spider silk. in the consumer pipeline: high-performance fabrics for athletes and stockings that never run. think parachute cords and suspension bridge cables. a steady supply of

44、 spider silk would be worth billions of dollars but how to produce it? harvesting silk on spider farms does not work because the territorial arthropods have a tendency to devour their neighbors. now, scientists at the biotechnology company nexia are spinning artificial silk modeled after golden orb

45、dragline. the first step: extract silk-making genes from the spiders. next, implant the genes into goat egg cells. the nanny goats that grow from the eggs secrete dragline silk proteins in their milk . “the young goats pass on the silk-making gene without any help from us,” says nexia president jeff

46、rey turner. nexia is still perfecting the spinning process, but they hope artificial spider silk will soon be snagging customers as fast as the real thing snags bugs.chicken soup for the soul：comfort food fights lonelinesmashed potatoes, macaroni and cheese, may be bad for your arteries but accordin

47、g to a study in psychological science, theyre good for your heart and emotionsthe study focuses on “comfort food” and how it makes people feel for me personally ,food has always played a big role in my family,” says jordan troisi, a graduate student at the university of buffalo, and lead author on t

48、he studythe study came out of the research program of his coauthor shira gabrielit has looked at non-human things that may affect human emotionssome people reduce loneliness by bonding with their favorite tv show, building virtual relationships with a pop song singer or looking at pictures of loved

49、onestroisi and gabriel wondered if comfort food could have the same effect by making people think of their nearest and dearest. in one experiment, in order to make participants feel lonely, the researchers had them write for six minutes about a fight with someone close to themothers were given an em

50、otionally neutral writing assignment. then, some people in each group wrote about the experience of eating a comfort food and others wrote about eating a new food finally ,the researchers had participants complete questions about their levels of lonelinesswriting about a fight with a close person ma

51、de people feel lonelybut people who were generally secure in their relationships would feel less lonely by writing about a comfort foodwe have found that comfort foods are consistently associated with those close to ussays troisithinking about or consuming these foods later then serves as a reminder

52、 of those close othersin their essays on comfort food, many people wrote about the experience of eating food with family and friends. in another experiment, eating chicken soup in the lab made people think more about relationships, but only if they considered chicken soup to be a comfort foodthis wa

53、s a question they had been asked long before the experiment, along with many other questions, so they wouldnt remember it. throughout everyones daily lives they experience stress, often associated with our connections with others, troisi sayscomfort food can be an easy remedy for lonelinessclimate c

54、hange poses major risks for unprepared citiesa new examination of urban policies has been carried out recently by patricia romero lankaoshe is a sociologist specializing in climate change and urbandevelopmentshe warns thatmany of the worlds fast-growing urban areas，especially in developing countries

55、will likely sufferfrom the impacts of changing climateher work also concludes that most cities are failing to reduce emissions of carbon dioxide and other greenhouse gasesthese gases are knownto affect the atmosphere”climate change is a deeply local issue and poses profound threats to the growing ci

56、ties of the world,” says romero lankao. ”but too few cities are developing effective strategies to protecttheir residents. cities are majorsources of greenhouse gasesand urban populations are likely to be among those most severely affected by future climate change. lankaos findingshighlight ways in

57、which city-residents are particularly vulnerable, and suggest policy interventions that could offer immediate and longer-termbenefits the locations and dense construction patterns of cities often place their populations at greater risk for natural disasters. potentialthreatsassociated with climate i

58、nclude storm surges andprolonged hot weather. storm surges can flood coastal areas and prolonged hot weather can heat heavilypaved cities more than surrounding areasthe impacts of such natural events can be more serious in an urban environmentfor example，a prolonged heat wave can increase existinglevels of air pollution，causingwidespread health problemspoorer neighbor