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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. When a satellite is first launched, the sail ______.
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Current gym dogma holds that to build muscle size you need to lift heavy weights. (1) , a new study (2) at McMaster University has shown that a similar degree of muscle building can be achieved by using lighter weights. The secret is to pump air (3) you reach muscle fatigue.The (4) are published in PLoS ONE." (5) grunting and straining to lift heavy weights, you can (6) something much lighter but you have to lift it until you can’t lift it (7) ," says Stuart Phillips, associate professor of kinesiology at McMaster University. "We’re convinced that (8) muscle means (9) your muscle to make new muscle proteins, a process in the body that over time (10) into bigger muscles. "Phillips praised lead author and senior Ph.D. student Nicholas Burd for masterminding the project that showed it’s really not the weight that you lift but the fact that you get muscular fatigue that’s the (11) point in building muscle. The study used light weights that (12) a percentage of what the (13) could lift. The heavier weights were set (14) 90% of a person’s best lift and the light weights at a mere 30%o of what people could lift. "It’s a very light weight," says Phillips noting that the 80% 90% (15) is usually something people can lift from 5～10 times before fatigue sets in. At 30%, Burd reported that subjects could lift that weight at least 24 times (16) they felt fatigue."We’re (17) to see where this new paradigm will lead," says Phillips, adding that these new data have (18) significance for gym enthusiasts but more importantly for people with compromised skeletal muscle mass, (19) the elderly, patients with cancer, or those who are (20) from trauma, surgery or even stroke. 2（）
Current gym dogma holds that to build muscle size you need to lift heavy weights. (1) , a new study (2) at McMaster University has shown that a similar degree of muscle building can be achieved by using lighter weights. The secret is to pump air (3) you reach muscle fatigue.The (4) are published in PLoS ONE." (5) grunting and straining to lift heavy weights, you can (6) something much lighter but you have to lift it until you can’t lift it (7) ," says Stuart Phillips, associate professor of kinesiology at McMaster University. "We’re convinced that (8) muscle means (9) your muscle to make new muscle proteins, a process in the body that over time (10) into bigger muscles. "Phillips praised lead author and senior Ph.D. student Nicholas Burd for masterminding the project that showed it’s really not the weight that you lift but the fact that you get muscular fatigue that’s the (11) point in building muscle. The study used light weights that (12) a percentage of what the (13) could lift. The heavier weights were set (14) 90% of a person’s best lift and the light weights at a mere 30%o of what people could lift. "It’s a very light weight," says Phillips noting that the 80% 90% (15) is usually something people can lift from 5～10 times before fatigue sets in. At 30%, Burd reported that subjects could lift that weight at least 24 times (16) they felt fatigue."We’re (17) to see where this new paradigm will lead," says Phillips, adding that these new data have (18) significance for gym enthusiasts but more importantly for people with compromised skeletal muscle mass, (19) the elderly, patients with cancer, or those who are (20) from trauma, surgery or even stroke. 12（）
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. In the first paragraph, the author mentioned the collision between satellites ______.
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. Before Luis Pacheco-Cobos and his colleagues’ discovery, it is believed that ______.
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