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标题: OG-12th-116 [打印本页]

作者: 糊香肠 时间: 2010-3-4 20:10
标题: OG-12th-116
OG12 116

After evidence was obtained in the 1920s that
the universe is expanding, it became reasonable
to ask: Will the universe continue to expand
indefinitely, or is there enough mass in it for the
mutual attraction of its constituents to bring this
expansion to a halt? It can be calculated that
the critical density of matter needed to brake the
expansion and “close” the universe is equivalent
to three hydrogen atoms per cubic meter. But the
density of the observable universe—luminous matter
in the form of galaxies—comes to only a fraction
of this. If the expansion of the universe is to stop,
there must be enough invisible matter in the
universe to exceed the luminous matter in density
by a factor of roughly 70.
Our contribution to the search for this “missing
matter” has been to study the rotational velocity
of galaxies at various distances from their center
of rotation. It has been known for some time that
outside the bright nucleus of a typical spiral galaxy
luminosity falls off rapidly with distance from the
center. If luminosity were a true indicator of mass,
most of the mass would be concentrated toward
the center. Outside the nucleus the rotational
velocity would decrease geometrically with distance
from the center, in conformity with Kepler’s law.
Instead we have found that the rotational velocity
in spiral galaxies either remains constant with
increasing distance from the center or increases
slightly. This unexpected result indicates that the
falloff in luminous mass with distance from the
center is balanced by an increase in nonluminous
mass.
Our findings suggest that as much as 90
percent of the mass of the universe is not radiating
at any wavelength with enough intensity to be
detected on the Earth. Such dark matter could be
in the form of extremely dim stars of low mass,
of large planets like Jupiter, or of black holes,
either small or massive. While it has not yet been
determined whether this mass is sufficient to
close the universe, some physicists consider it
significant that estimates are converging on the
critical value.

the author`s study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having
A. higher rotational velocity and higher luminosity
B. lower rotational velocity and higher luminosity
C. lower rotational velocity and lower luminosity
D. similar rotational velocity and higher luminosity
E. similar rotational velocity and similar luminosity

这个题有点没想明白。。。牛人们帮我下吧，还有这篇的思路，感觉很乱~~谢谢了~~

作者: edwardelric 时间: 2010-3-4 20:33
对应点
It has been known for some time that
outside the bright nucleus of a typical spiral galaxy
luminosity falls off rapidly with distance from the
center.

Instead we have found that the rotational velocity
in spiral galaxies either remains constant with
increasing distance from the center or increases
slightly.
应该是d选项
楼主应该给出答案
他说光啊会随着与中心距离的不断变长而变的微弱
outermost是最外边的，能推出是higher
然后呢说实际推测与原来的想象不一样，结果是
随着距离的改变速度不变或者变化微弱~
所以是d

作者: 糊香肠 时间: 2010-3-4 20:45
答案就是d。。。。。谢谢谢谢，呵~~

作者: Diffany 时间: 2010-3-10 01:20
翻译过来就清楚多了，文章太难了好多生词读不懂啊

作者: merrimack 时间: 2010-8-25 12:17
看了你们的解释再看题发现光是题目我就理解错了原来这题的答案是要自己推的

作者: cielle 时间: 2010-11-25 23:44

对应点
It has been known for some time that
outside the bright nucleus of a typical spiral galaxy
luminosity falls off rapidly with distance from the
center.

Instead we have found that the rotational velocity
in spiral galaxies either remains constant with
increasing distance from the center or increases
slightly.
应该是d选项
楼主应该给出答案
他说光啊会随着与中心距离的不断变长而变的微弱
outermost是最外边的，能推出是higher
然后呢说实际推测与原来的想象不一样，结果是
随着距离的改变速度不变或者变化微弱~
所以是d

-- by 会员 edwardelric (2010/3/4 20:33:58)

NN真厉害，我原来是连句子都没看懂，这回懂了。

作者: zhangyina 时间: 2011-3-13 15:04
哎，这道题我看了半个多小时原来没看懂意思。。。NN一句话让我豁然开朗啊！！！

作者: chenche8827 时间: 2011-4-17 19:40
那句话不是说保持一致或者微弱增加吗，是不是选项B中不能直接用lower，因为这就否定了constant的意思了，主要部分是保持一致，所以用的是similar，也就是变化总体来说是不大的意思。。。我只能这么理解了。。。。因为either or 说明了2个情况都可能存在。。。

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