朗阁首页 > 托福阅读 > 2013年4月20日托福阅读考题回忆及解析




  篇 重复2011.4.15NA 行星的形成
  版本二 太阳系的形成
  1 原材料:成分:大部分为helium和XXX,小部分为常见的固态和气态分子
  2 形成过程:某爆发形成碰撞,导致了引力和rotation。关于rotation,用ice-skater打比方
  3 类地行星:成为主要为固态。
  4 远日行星:重力能产生热能,导致温度上升。随着太阳形成,形成过程停止(大意),温度下降,冰得以存在,所以密度小。而体积大导致引力强,可吸引更轻的气态分子。
  第二篇 重复2011.11.12NA 中世纪商人行会
  欧洲中世纪行会制度 Guild
  先讲大师傅 master 的出道过程。然后是整个行会的排他性。接着是行会和城邦政府怎么样由前提相互支持(壟断),到后來政府看中壟断的大面包,于是插手进來分一杯羹。除了政府以外,行会的另一个强劲对手是城外不受法律约束而且拥有廉价勞动力(农民工)的个体企业。后來行会竞争。不过,成本拼不过,价格当然也拼不过,同时又遇到一些供应上的困难,所以结果。。。还有,他们自己本身也有矛盾,主要是 master 们有些很有野心,想要扩张。所以简单說就是内忧外患。
  1 目的:主要---经济稳定性和排他性;次要---将门徒训练为大师,高质量,统一标准的商品。
  2 问题:内忧外患:内---master数量太多,外---其他城市的商人竞争。其竞争力来自更低的价格和利用乡村廉价劳动力。同时政府难以管理城市外的竞争者。
  3 影响:独立性和自制性受到威胁。商人行会和手工业者行会(不确定)
  Bartering 和states的关系
  1 barter建立在复杂的社会和政治机构上(好像提及了一个19C70S的研究发现)
  2 假说一:有R提出,农业和交通等的发展,使得长距离的物物交换成为可能。奢侈品也参与到这样的交换中来。同时需要世俗君主的介入。
  3 假说二:由另一个R提出,以maya为例(不确定)。他们缺少某些重要资源,所以必须和周边环境交换。而且他们的communities都面对这种问题,所以必须和周边的其他地区进行交换。一旦这种交换成为常态,就需要政府的规范。
  4 结论:商业或经济因素不可能是states形成的唯一原因。很多因素影响着政治。甚至机经本身就是某种政治条件下的结果,而非原因。
  TOPIC Formation of Planets
  The various planets are thought to have formed from the solar nebula, the disc-shaped cloud of gas and dust left over from the Sun's formation.[ Douglas N. C. Lin (May 2008). "The Genesis of Planets". Scientific American 298 (5): 50–59.] The currently accepted method by which the planets formed is known as accretion, in which the planets began as dust grains in orbit around the central protostar. Through direct contact, these grains formed into clumps up to 200 metres in diameter, which in turn collided to form larger bodies (planetesimals) of ~10 kilometres (km) in size. These gradually increased through further collisions, growing at the rate of centimetres per year over the course of the next few million years。
  The inner Solar System, the region of the Solar System inside 4 AU, was too warm for volatile molecules like water and methane to condense, so the planetesimals that formed there could only form from compounds with high melting points, such as metals (like iron, nickel, and aluminium) and rocky silicates. These rocky bodies would become the terrestrial planets (Mercury, Venus, Earth, and Mars). These compounds are quite rare in the universe, comprising only 0.6% of the mass of the nebula, so the terrestrial planets could not grow very large. The terrestrial embryos grew to about 0.05 Earth masses and ceased accumulating matter about 100,000 years after the formation of the Sun; subsequent collisions and mergers between these planet-sized bodies allowed terrestrial planets to grow to their present sizes。
  When the terrestrial planets were forming, they remained immersed in a disk of gas and dust. The gas was partially supported by pressure and so did not orbit the Sun as rapidly as the planets. The resulting drag caused a transfer of angular momentum, and as a result the planets gradually migrated to new orbits. Models show that temperature variations in the disk governed this rate of migration, but the net trend was for the inner planets to migrate inward as the disk dissipated, leaving the planets in their current orbits.[ Staff. "How Earth Survived Birth". Astrobiology Magazine. Retrieved 2010-02-04.]
  The gas giants (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where the material is cool enough for volatile icy compounds to remain solid. The ices that formed the Jovian planets were more abundant than the metals and silicates that formed the terrestrial planets, allowing the Jovian planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements.[ Ann Zabludoff (University of Arizona) (Spring 2003). "Lecture 13: The Nebular Theory of the origin of the Solar System". Retrieved 2006-12-27.] Planetesimals beyond the frost line accumulated up to four Earth masses within about 3 million years. Today, the four gas giants comprise just under 99% of all the mass orbiting the Sun. Theorists believe it is no accident that Jupiter lies just beyond the frost line. Because the frost line accumulated large amounts of water via evaporation from infalling icy material, it created a region of lower pressure that increased the speed of orbiting dust particles and halted their motion toward the Sun. In effect, the frost line acted as a barrier that caused material to accumulate rapidly at ~5 AU from the Sun. This excess material coalesced into a large embryo of about 10 Earth masses, which then began to grow rapidly by swallowing hydrogen from the surrounding disc, reaching 150 Earth masses in only another 1000 years and finally topping out at 318 Earth masses. Saturn may owe its substantially lower mass simply to having formed a few million years after Jupiter, when there was less gas available to consume。
    T Tauri stars like the young Sun have far stronger stellar winds than more stable, older stars. Uranus and Neptune are thought to have formed after Jupiter and Saturn did, when the strong solar wind had blown away much of the disc material. As a result, the planets accumulated little hydrogen and helium—not more than 1 Earth mass each. Uranus and Neptune are sometimes referred to as failed cores.[ E. W. Thommes, M. J. Duncan, H. F. Levison (2002). "The Formation of Uranus and Neptune among Jupiter and Saturn". Astronomical Journal 123 (5): 2862.] The main problem with formation theories for these planets is the timescale of their formation. At the current locations it would have taken a hundred million years for their cores to accrete. This means that Uranus and Neptune probably formed closer to the Sun—near or even between Jupiter and Saturn—and later migrated outward (see Planetary migration below).[ Harold F. Levison, Alessandro Morbidelli, Crista Van Laerhoven et al. (2007). "Origin of the Structure of the Kuiper Belt during a Dynamical Instability in the Orbits of Uranus and Neptune". Icarus 196 (1): 258.] Motion in the planetesimal era was not all inward toward the Sun; the Stardust sample return from Comet Wild 2 has suggested that materials from the early for



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