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资金的时间价值是指随着时间的推移，经储藏保存后带来的增值。 ( )
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Aristotle believed that the heavens were perfect. If they ever were, they are no longer. The skies above Earth are now littered with the debris of dead satellites, bits of old rockets and the odd tools dropped by a spacewalking astronaut. Such is the extent of the detritus that the first accidental collision between two satellites has already taken place. It happened in February 2009, when a defunct Russian Cosmos smashed into a functioning American Iridium, destroying both and creating even more space junk. To stop this sort of thing happening again, Vaios Lappas of the University of Surrey, in England, has designed a system that will remove satellites from orbit at the end of their useful lives—and as a bonus will scour part of the sky clean as it does so. Dr. Lappas’s satellite-removal system employs a solar sail. As light from the sun hits the sail, it imparts a minuscule but continuous acceleration. When a satellite is first launched, the sail is angled in a way that causes this acceleration to keep the satellite in orbit. (Orbits gradually decay as a result of collisions with the small number of air molecules found even at altitudes normally classified as "outer space". ) Solar sails have yet to be used widely to propel spacecraft in this way—several earlier versions came unstuck when the sails failed to unfurl properly—but doing so is not a novel idea in principle. The novelty Dr. Lappas envisages is to change the angle of the sail when the satellite has become defunct. Instead of keeping the derelict craft in orbit, it will, over the course of a couple of years, drag it into the atmosphere and thus to a fiery end. Not only that, but the sail will also act like a handkerchief, mopping up microscopic orbital detritus such as flecks of paint from previous launches: A fleck of paint may not sound dangerous, but if travelling at 27,000kph (17,0OOmph), as it would be in orbit, it could easily penetrate an astronaut’s spacesuit. A prototype of Dr. Lappas’s design, called CubeSail, will be launched late next year. It weighs just 3kg (71b) and, when folded up, measures 30cm (12 inches) by 10cm by 10cm. Once unfurled, however, the sail will have an area of 25 square metres. If this prototype, which is paid for by EADS, a European aerospace company, proves successful, solar sails might be added to many future satellites. That would enable them to be removed rapidly from orbit when they became useless and would restore to the skies some measure of Aristotelian perfection. According to the text, which of the following is true
Men are generally better than women on tests of spatial ability, such as mentally rotating an object through three dimensions or finding their way around in a new environment. But a new study suggests that under some circumstances a woman’s way of navigating is probably more efficient. Luis Pacheco-Cobos of the National Autonomous University of Mexico and his colleagues discovered this by following mushroom gatherers from a village in the state of Tlaxcala for two rainy seasons. Two researchers, each fitted with GPS navigation devices and heart-rate monitors, followed different gatherers on different days. They recorded the weight of the mushrooms each gatherer collected and where they visited. The GPS data allowed a map to be made of the routes taken and the heart-rate measurements provided an estimate of the amount of energy expended during their travels. The results, to be published in Evolution and Human Behavior, show that the men and women collected on average about the same weight of mushrooms. But the men travelled farther, climbed higher and used a lot more energy—70% more titan the women. The men did not move any faster, but they searched for spots with lots of mushrooms. The women made many more stops, apparently satisfied with, or perhaps belier at finding, patches of fewer mushrooms. Previous work has shown that men tend to navigate by creating mental maps of a territory and then imagining their position on the maps. Women are more likely to remember their mutes using landmarks. The study lends support to the idea that male and female navigational skills were honed differently by evolution for different tasks. Modern-day hunter-gatherers divide labor, so that men tend to do more hunting and women more gathering. It seems likely that early humans did much the same thing. The theory is that the male strategy is the most useful for hunting prey; chasing an antelope, say, would mean running a long way over a winding mute. But having killed his prey, the hunter would want to make a beeline for home rather than retrace his steps exactly. Women, by contrast, would be better off remembering landmarks and retracing the paths to the most productive patches of plants. The research suggests that in certain circumstances women are better at navigating than men, which might lend some comfort to a man desperately searching for an item in a supermarket while his exasperated wife methodically moves around the aisles filling the shopping trolley. He is simply not cut out for the job, evolutionarily speaking. What accounts for the difference between women and men in the navigational skill
Many animals test their legs and totter forth only hours after they are born, but humans need a year before they take their first, hesitant steps. Is something fundamentally different going on in human babies Maybe not. (46) A new study shows that the time it takes for humans and all other mammals to start walking fits closely with the size of their brains.(47) In past studies to develop a new animal model for the brain events that support motor development, neurophysiologist Martin Garwicz discovered that the schedules by which ferrets and rats acquire various motor skills, such as crawling and walking, are strikingly similar to each other; the progress simply happens faster for rats. That made them wonder how similar the timing of motor development might be among mammals in general.(48) They compared the time between conception and walking in 24 species and looked at how well this duration correlated with a range of variables, including gestation time, adult body mass, and adult brain mass. As they report in this week’s issue of PNAS, brain mass accounts for the vast majority (94%) of the variance in walking time between species.Species with larger brains, such as humans, tend to take longer to learn to walk. (49) Strikingly, a model based on adult brain mass and walking time in the other 23 species almost perfectly predicts when humans begin to walk. "We’ve always considered humans the exception," Garwicz says, "But in fact, we start walking at exactly the time that would be expected from all other walking mammals. "Two other variables—gestation time and brain mass at birth—also correlate nicely with age of walking for most animals, but not for humans. That makes sense, the researchers say: Humans spend an unusually small portion of their development—and build an unusually small fraction of their brain mass—in the womb. (50) The model is able to accommodate this quirk of human development because it uses the time it takes babies to learn to walk from conception, not birth. (At the other extreme, animals such as horses, who have a long gestation and then walk almost immediately after they are born, also fit the model.)Barbara Finlay, a neuroscientist at Cornell University, says the findings support the existence of a kind of a development "clock" for mammals. In her own work, Finlay has found that various mammals have similar timetables for brain development before birth. But she had imagined that a postnatal milestone such as walking would be more idiosyncratic. "I was surprised," she says. "I thought the clock would start to fracture. " It will be interesting, she says, to see if the clock will keep time for later milestones, such as events related to reproduction. (47) In past studies to develop a new animal model for the brain events that support motor development, neurophysiologist Martin Garwicz discovered that the schedules by which ferrets and rats acquire various motor skills, such as crawling and walking, are strikingly similar to each other; the progress simply happens faster for rats.
As you crest a rise on Mississippi’s Highway 63, just north of Pascagoula and the Gulf coast, the vista unfolds. A calm brown waterway flows beneath the bridge, interlaced with palm-treed fingers of land; a chaos of water towers, cranes and derricks is revealed in the distance. The near view gives the region its charm; the distant one sustains it. The oil industry and shipbuilding both thrive along the coast. (41) Signal International, a marine-fabrication firm, brought around 500 welders and pipe fitters from India—most of them from the southern state of Kerala, many of whom had laboured in various Arab Gulf states—to work in its shipyards in Pascagoula and Orange, Texas. The workers allege that they paid exorbitant sums to recruiters in India (up to $20,000), who promised them green cards. But once they arrived, they were harassed, intimidated and kept in cramped and isolated conditions. (42) (43) They, like the Indians, were brought to America on H-2B visas, given for temporary employment in non-agricultural fields.Like much of America’s rickety immigration system, the H-2B programme draws scorn from all sides. Companies in such industries as forestry and fisheries depend heavily on guest workers. But since 1990 the H-2B has been capped at a paltry 66,000 a year. Even with exemptions for workers who extend their visas, that cap has been hit every year but one. In 2008 American companies requested nearly 294,000 H-2Bs. Unions, for their part, fret that guest workers take jobs from willing Americans, as well as driving down wages and benefits. And immigrant-rights advocates point to the potential for abuse inherent in the programme. (44) Their visas are tied to their jobs, which deters complaint.Mary Bauer, the legal director of the Southern Poverty Law Centre, a civil-rights programme that has represented numerous H-2B plaintiffs (including the Indian workers suing Signal), says that temporary workers appeal to employers because "they cannot work for anybody else. They have to accept any terms imposed on them. They have to borrow a substantial amount of money to get here, and almost anything asked of them they feel obligated to tolerate and do. "Things may be getting better. In February Superior Forestry Service, which provides the forest industry with immigrant workers, agreed to a $2.75m settlement in a suit brought by 2,200 workers who claimed they were short-changed on wages (the company denies malfeasance). (45) It won’t make everyone happy, but at least it should make some people a bit less unhappy.A. Although temporary agricultural workers are guaranteed housing, travel expenses, firm hours of work and access to lawyers, H-2B visa-holders are promised only prevailing local wages.B. They are now suing both Signal and the recruiters, who are also being sued by Signal—which claims that they misled the company as well as the workers.C. Furthermore, for American corporations, the more workers from overseas they possess, the more benefits they get.D. But the population has waned, displaced by hurricanes, so companies must look elsewhere for their workers. The results are not always happy ones.E. However, less workers are needed in some corporations, such as forestry and fisheries that have enough staff from immigrants.F. And in December 2009 Bernie Sanders, a senator from Vermont, introduced a bill that would provide guest workers with travel expenses and access to lawyers, regulate foreign recruiters and prevent companies that have massively laid off local staff from hiring immigrants.G. Just west of Pascagoula, in Gulfport, a group of Brazilian welders and pipe fitters have made similar allegations against another marine-fabrication firm. 42（）
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