2015年9月12日
托福阅读第一篇
题材划分： 动物类
主要内容：讲关于鸟类动物的两种行为：gliding and soaring。鸟如果遇到两种情况可以不用glide，一种是遇到热气流，一种是，后面几段重点讲热气流是如何形成的，提到了热量不均匀，热空气会上升，又有新的冷空气来填补，然后循环进行。鸟可以利用热气流来维持高度然后碰到另一个再换位置往前走，这样长距离飞行节省体力。飞行员和生物学家看到的热气流是不一样的。
相似TPO练习推荐
TPO28 Buck Rubs and Buck Scrapes
相关背景知识：
Soaring is a flying technique used to gain energy by repeatedly crossing the boundary between air masses of significantly different velocity. Such zones of high wind gradient are generally found close to obstacles and close to the surface, so the technique is mainly of use to birds and operators of radio-controlled gliders, but glider pilots have occasionally been able to soar dynamically in meteorological wind shears at higher altitudes. The highest speeds reported are by radio controlled gliders at 505 mph (813 km/h).
While different flight patterns can be employed in dynamic soaring, the simplest example to explain the energy extraction mechanism is a closed loop across the boundary layer between two air masses in relative movement. The gain in speed can be explained in terms of airspeed or groundspeed:
The glider gains airspeed twice during the loop, when it pierces the boundary layer at an acute angle. Since the 180° turns retain most of the airspeed the glider completes the loop within the initial air mass at a higher airspeed.
The gain in groundspeed occurs when the glider performs a 180° downwind turn within the moving air mass. Since the opposite 180° turn is done within the stationary air mass the groundspeed gain is not reversed.
The energy is extracted by reducing the velocity difference between the two air masses during the 180° turns which accelerate air in opposite directions. The following animation is a simplification of what actually happens. In practice, there is a turbulent mixing layer between the moving and stationary air masses. In addition, drag forces are continually slowing the plane once it has crossed the shear layer, so the airspeed gained by crossing the boundary is not all retained through the 180° turns. Higher speed gives rise to higher drag forces, so there is a maximum speed that can be attained, typically around 10 times the wind speed for efficient glider designs.
托福阅读第二篇
题材划分： 贸易经济类
主要内容： 古代欧洲经历萧条后复苏的过程，其中一个是农作的轮换制，南方比北方耕种使用了新的方法，南方把地分为两部分，一部分耕种另一部分不耕种，北方分为三部分，一部分不种，一部分春季种，一部分冬种，因为雨水不一样，所以更高效。其次，改良工具后耕地可以用马，对比了马和牛，一开始没有合适的马具去控制马，因为马比较聪明，能拉更重的且能工作的比较久，而且能够听懂人的一些口头信号。工具更加高效后就会对贸易产生一定的影响，贸易部分有一个细节剃刀商人们把房子建在比较富有的人周围，这样就更容易把商品卖给富人，并且贸易距离也比较远，比如与中国的贸易等。
相似TPO练习推荐：
TPO10 Seventeenth-Century European Economic Growth
托福阅读第三篇
题材划分： 动物进化史
主要内容：在历史上有一个士气发生了大型的哺乳动物的灭绝，提出了两种假设，气候变化和人类的活动。描述了气候变化对于大型哺乳动物的影响，但是这个假设有问题，前面这种气候变化动物会发生迁徙行为。描述人类活动对其影响时，也提出了该假设的问题，迁过来的人太少没办法是动物灭绝，而且那时候猎人比较倾向于捕杀弱小的而不是大型动物。
相似TPO练习推荐：
TPO33 Extinction Episodes of the Past
相关知识背景：
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the amount of life on Earth. Such an event is identified by a sharp change in the diversity and abundance of macroscopic life. It occurs when the rate of extinction increases with respect to the rate of speciation. Because the majority of diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life.
The age of the Earth is about 4.54 billion years. The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland.More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million,[15] of which about 1.2 million have been documented and over 86 percent have not yet been described.
Extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organisms.
Since life began on Earth, five major mass extinctions have significantly exceeded the background extinction rate. The most recent, the Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of time. In addition to the five major mass extinctions, there are numerous minor ones as well and the ongoing mass-extinction caused by human activity is sometimes called the sixth extinction. Mass extinctions seem to be a Phanerozoic phenomenon, with extinction rates low before large complex organisms arose.
相关推荐:
