|
- 精华
- 1
- 积分
- 716
- 经验
- 716 点
- 威望
- 50 点
- 金钱
- 400 ￥
- 魅力
- 194
|
60 percent of the undergraduates from US was over the age of 25. Two third of this 60 percent either had disruption in their acedemic years or enrolled after the age of 20. Ask which of the following must be true?
A. At least one third of the undergraduates over age 25 ......
I chose A.
Verbal
阅读
北美妇女地位
北美关于妇女经济活动的早期文件很少，有个牛人发现1764年的一个重要的tax code改变以后，原以为会有更多地propertyless妇女缴纳tax on their professional income. 但实际上却变少了。原因是tax assessor有了更多的权利决定是否对某人进行征税以及税率的多少，这些税官却对女性放水，很多情况下就不争了。所以这就说明了当时的民风淳朴，认为女性对于家庭的责任要多于她们对社会的责任，而男性就不一样了。所以很多男性没有类似的待遇。
其中有一题highlighted tax code change，问serve what purpose.
我选择E, help to explain women were consider.... B 选项说cultural xxxx.... excessive family burden was not enough exempt male completely from social responsibility. I I thought it was confusing one. Took me a while to decide on E.
Milankovitch cycles theory is about the frequency of ice age. Milankovich proposed that the temperature of earth has something to do with the position of the earth in the orbit around sun. However it did not gain acceptance until 1968 when Dr. Imbrie presented additional evidence for M theory. He meassured the isotope level in small seashell deposit and the change of isotope abundancy corresponds with the temperature change.
However, later on, a geochemist tested the samples from Devil's Hole, a place in south Nevada and the results did not match with the previous results.
Even thought Dr. Imbrie still think M theory was valid, he conceded that many other factors contribute to the isotope level. It maybe why the results did not match.
付考古
Can We Date the Ice Ages?
Following improvements in the ability to measure isotope ratios which came about as a spin-off of the wartime Manhattan project, physical chemist Harold Urey began to examine the possibility that the ratio of the two principal isotopes of oxygen found in the atmosphere might provide a clue as to past temperatures. It was based on the idea that the ratio of the heavier isotope (oxygen-18) to the more prevalent isotope (oxygen-16) found at the sea surface would change depending on the temperature of the ocean water near the surface. Urey thought that a careful study of the oxygen isotope ratio in the shells of sea creatures, which build their calcium carbonate shells from oxygen available in the seawater, might serve to indicate the temperature of the water in which they formed. During warmer periods, it was thought, evaporation from the ocean surface would tend to enrich the sea surface water with the heavier isotope of oxygen.
Perhaps, Urey reasoned, the isotope ratios found in the layers of discarded shells of sea organism which form the ocean bottom could thus serve as a record for the past temperatures of the ocean.
The theory is fraught with many ifs, but it was pursued with persistence, starting in the 1950s, by Italian-educated micropaleontologist Cesare Emiliani, a one-time collaboator of Urey at the Argonne Laboratory then associated with University of Chicago. Emiliani identified certain species of small shell-forming sea organisms known as foraminifera, which he thought suitable for oxygen-isotope analysis to determine past climates. The conclusions he drew as to the dating of the ice ages were constantly challenged by leading oceanographers, who found them in contradiction with their studies of ocean bottom cores. The method was also attacked on the grounds that it wasn't clear that the creatures formed their shells, known as tests, near enough to the surface to reflect changes in isotope ratios.
About 1968, a somewhat new interpretation of the oxygen isotope record was proposed by a young oceanographer and climatologist, Nicholas Shackleton, a Cambridge graduate and great nephew of the famous British Antarctic explorer of the same name. Shackleton proposed that the oxygen-isotope ratio could serve as a proxy, not for temperature but for sea level--the idea being that during periods of glacial advance, when a large volume of ocean water had been taken up into the continental ice sheets, the oxygen-18 ratios of the remaining water would consequently be higher. These might be detected in the foraminifera layers found in the ocean bottom cores. Again there are many ifs, but Shackleton examined isotopic ratios of snows in Alpine and Arctic regions as well as many other factors to bolster his hypothesis. In the 1970s a National Science Foundation-funded program of oceanographic studies, known as CLIMAP, collected a large number of sediment cores from different parts of the world ocean. The program, known as the Decade of the Oceans, was run in conjunction with some flawed statistical approaches to modeling of global atmospheric circulation that had originated in efforts of John von Neumann to use computer modeling for studies of weather modification. However, analysis of the oxygen isotopic ratios of foraminifera found in the undersea cores suggested to a team working at the Lamont-Doherty Geological Laboratory that there was a definite signal of 100,000 year cyclicity. Dr. John Imbrie, who ran the computer programs analyzing the data, was the first to hypothesize that the periodicities were caused by the Milankovitch orbital cycles.
A landmark paper by Hays, Imbrie and Shackleton, published in the December 1976 issue of Science magazine ("Variations in the Earth's Orbit: Pacemaker of the Ice Ages"), argued that the advance and retreat of the ice sheets was triggered by the changes in the Earth's orbital parameters. Other factors might also be present to reinforce these relatively small changes in solar radiation, but these were the pacemaker. By the theory of the orbital cycles, the evidence from the undersea cores explained that a major glaciation would be set off about every 100,000 years, followed by a short period known as an interglacial, a melt back lasting about 10,000 to 12,000 years. By the calculations of astronomers, the present interglacial, which has lasted about 11,000 years, is due to end any time. Indeed we have been in a period of long-term cooling for more than 6,000 years. The maximum summer temperature experienced in Europe over the last 10,000 years occurred about 6000 B.C. Over North America, where the process of glacial retreat lagged somewhat, the maximum was reached by about 4000 B.C. These estimates based on a vast array of evidence from geology, botany, and many other fields are consistent with the orbital theory of climate, for the northern hemisphere Summer would have been occurring at a point in Earth's orbit much nearer to the Sun than presently.
"One of the fundamental tenets of palaeoclimate modeling, the Milankovitch theory, is called into doubt by isotope analysis of a calcite vein, just reported in Science by Winograd and colleagues. The theory, which is backed up by a compelling bank of evidence, suggests that the ice ages determined, with unprecedented accuracy, in the new record cannot be reconciled with the planetary cyclicity. . .
Winograd and colleagues' evidence also turns on oxygen isotope data, this time from vein calcite coating the hanging wall of an extensional fault at Devils Hole, an aquifer in southern Nevada. In 1988, the authors published a date, 145,000 years, based on 234U-230Th dating for the end of the penultimate ice age (Termination II), marked by an increase in the 18O to 16O ratio, a change taken to mirror an increase in local precipitation. Although the date was only 17,000 year earlier than the previously accepted date of 128,000 years, if correct, this change is enough to bring Milankovitch mechanism into serious doubt. . .
I remain confused. The geochemist in me says that Devils Hole chronology is the best we have. And the palaeoclimatologist in me says that correlation between accepted marine chronology and Milankovitch cycles is just too convincing to be put aside. . .
One side will have to give, and maybe - just to be safe - climate modellers should start preparing themselves for a world without Milankovitch." http://www.detectingdesign.com/milankovitch.html |
|
