快速导航
学历类
职业资格
公务员
医卫类
建筑工程
外语类
外贸类
计算机类
财会类
技能鉴定
Rogue theory of smell gets a boost
1.A controversial theory of how we smell, which claims that our fine sense of
odour depends on quantum mechanics, has been given the thumbs up by a team of
physicists.
2.Calculations by researchers at University College London (UCL) show that
the idea that we smell odour molecules by sensing their molecular vibrations
makes sense in terms of the physics involved.
3.That's still some way from proving that the theory, proposed in the
mid-1990s by biophysicist Luca Turin, is correct.But it should make other
scientists take the idea more seriously.
4."This is a big step forward," says Turin, who has now set up his own
perfume company Flexitral in Virginia.He says that since he published his
theory, "it has been ignored rather than criticized."
5.Most scientists have assumed that our sense of smell depends on receptors
in the nose detecting the shape of incoming molecules, which triggers a signal
to the brain.This molecular 'lock and key' process is thought to lie behind a
wide range of the body's detection systems: it is how some parts of the immune
system recognise invaders, for example, and how the tongue recognizes some
tastes.
6.But Turin argued that smell doesn't seem to fit this picture very
well.Molecules that look almost identical can smell very different — such as
alcohols, which smell like spirits, and thiols, which smell like rotten eggs.And
molecules with very different structures can smell similar.Most strikingly, some
molecules can smell different — to animals, if not necessarily to humans —
simply because they contain different isotopes (atoms that are chemically
identical but have a different mass).
7.Turin's explanation for these smelly facts invokes the idea that the smell
signal in olfactory receptor proteins is triggered not by an odour molecule's
shape, but by its vibrations, which can enourage an electron to jump between two
parts of the receptor in a quantum-mechanical process called tunnelling.This
electron movement could initiate the smell signal being sent to the brain.
8.This would explain why isotopes can smell different: their vibration
frequencies are changed if the atoms are heavier.Turin's mechanism, says
Marshall Stoneham of the UCL team, is more like swipe-card identification than a
key fitting a lock.
9.Vibration-assisted electron tunnelling can undoubtedly occur — it is used
in an experimental technique for measuring molecular vibrations."The question is whether this is possible in the nose," says Stoneham's colleague, Andrew
Horsfield.
10.Stoneham says that when he first heard about Turin's idea, while Turin was
himself based at UCL, "I didn't believe it".But, he adds, "because it was an
interesting idea, I thought I should prove it couldn't work.I did some simple calculations, and only then began to feel Luca could be right." Now Stoneham and
his co-workers have done the job more thoroughly, in a paper soon to be
published in Physical Review Letters.
11.The UCL team calculated the rates of electron hopping in a nose receptor
that has an odorant molecule bound to it.This rate depends on various properties
of the biomolecular system that are not known, but the researchers could
estimate these parameters based on typical values for molecules of this
sort.
12.The key issue is whether the hopping rate with the odorant in place is
significantly greater than that without it.The calculations show that it is —
which means that odour identification in this way seems theoretically
possible.
13.But Horsfield stresses that that's different from a proof of Turin's
idea."So far things look plausible, but we need proper experimental verification.We're beginning to think about what experiments could be
performed."
14.Meanwhile, Turin is pressing ahead with his hypothesis."At Flexitral we
have been designing odorants exclusively on the basis of their computed
vibrations," he says."Our success rate at odorant discovery is two orders of
magnitude better than the competition." At the very least, he is putting his
money where his nose is.
Questions 5-9
Complete the sentences below with words from the passage.Use NO MORE THAN
THREE WORDS for each answer.
5.The hypothesis that we smell by sensing the molecular vibration was made by
______.
6.Turin's company is based in ______. 7.Most scientists believed that our nose works in the same way as our ______. 8.Different isotopes can smell different when ______ weigh differently. 9.According to Audrew Horsfield, it is still to be proved that ______ could really occur in human nose.
1 There's a dimmer switch inside the sun that causes its brightness to rise
and fall on timescales of around 100,000 years - exactly the same period as
between ice ages on Earth. So says a physicist who has created a computer model
of our star's core.
2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled
the effect of temperature fluctuations in the sun's interior. According to the
standard view, the temperature of the sun's core is held constant by the
opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that
slight variations should be possible.
3 He took as his starting point the work of Attila Grandpierre of the Konkoly
Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierre and a
collaborator, Gábor ágoston, calculated that magnetic fields in the sun's core
could produce small instabilities in the solar plasma. These instabilities would
induce localised oscillations in temperature.
4 Ehrlich's model shows that whilst most of these oscillations cancel each
other out, some reinforce one another and become long-lived temperature
variations. The favoured frequencies allow the sun's core temperature to
oscillate around its average temperature of 13.6 million kelvin in cycles
lasting either 100,000 or 41,000 years. Ehrlich says that random interactions
within the sun's magnetic field could flip the fluctuations from one cycle
length to the other.
5 These two timescales are instantly recognisable to anyone familiar with
Earth's ice ages: for the past million years, ice ages have occurred roughly
every 100,000 years. Before that, they occurred roughly every 41,000 years.
6 Most scientists believe that the ice ages are the result of subtle changes
in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the
way Earth's orbit gradually changes shape from a circle to a slight ellipse and
back again roughly every 100,000 years. The theory says this alters the amount
of solar radiation that Earth receives, triggering the ice ages. However, a
persistent problem with this theory has been its inability to explain why the
ice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequency should change from one to another," says Neil Edwards, a climatologist at the Open
University in Milton Keynes, UK. Nor is the transition problem the only one the
Milankovitch theory faces. Ehrlich and other critics claim that the temperature
variations caused by Milankovitch cycles are simply not big enough to drive ice
ages.
8 However, Edwards believes the small changes in solar heating produced by
Milankovitch cycles are then amplified by feedback mechanisms on Earth. For
example, if sea ice begins to form because of a slight cooling, carbon dioxide
that would otherwise have found its way into the atmosphere as part of the
carbon cycle is locked into the ice. That weakens the greenhouse effect and
Earth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you add their effects together, there is more than enough feedback to make Milankovitch work," he says. "The problem now is identifying which mechanisms are at work."
This is why scientists like Edwards are not yet ready to give up on the current
theory. "Milankovitch cycles give us ice ages roughly when we observe them to happen. We can calculate where we are in the cycle and compare it with observation," he says. "I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation."
10 Ehrlich concedes this. "If there is a way to test this theory on the sun, I can't think of one that is practical," he says. That's because variation over 41,000 to 100,000 years is too gradual to be observed. However, there may be a way to test it in other stars: red dwarfs. Their cores are much smaller than that of the sun, and so Ehrlich believes that the oscillation periods could be short enough to be observed. He has yet to calculate the precise period or the extent of variation in brightness to be expected. 11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlich
counters that Weiss's opinion is based on the standard solar model, which fails to take into account the magnetic instabilities that cause the temperature fluctuations. Questions 1-4 Complete each of the following statements with One or Two names of the scientists from the box below. Write the appropriate letters A-E in boxes 1-4 on your answer sheet. A. Attila Grandpierre B. Gábor ágoston C. Neil Edwards D. Nigel Weiss E. Robert Ehrlich 1. ...claims there a dimmer switch inside the sun that causes its brightness to rise and fall in periods as long as those between ice ages on Earth. 2. ...calculated that the internal solar magnetic fields could produce instabilities in the solar plasma. 3. ...holds that Milankovitch cycles can induce changes in solar heating on Earth and the changes are amplified on Earth. 4. ...doesn't believe in Ehrlich's viewpoints at all. Questions 5-9 Do the following statements agree with the information given in the reading passage? In boxes 5-9 on your answer sheet write TRUE if the statement is true according to the passage FALSE if the statement is false according to the passage NOT GIVEN if the information is not given in the passage 5. The ice ages changed frequency from 100,000 to 41,000 years a million years ago. 6. The sole problem that the Milankovitch theory can not solve is to explain why the ice age frequency should shift from one to another. 7. Carbon dioxide can be locked artificially into sea ice to eliminate the greenhouse effect. 8. Some scientists are not ready to give up the Milankovitch theory though they haven't figured out which mechanisms amplify the changes in solar
heating.
9. Both Edwards and Ehrlich believe that there is no practical way to test
when the solar temperature oscillation begins and when ends.
Questions 10-14
Complete the notes below.
Choose one suitable word from the Reading Passage above for each answer.
Write your answers in boxes 10-14 on your answer sheet.
The standard view assumes that the opposing pressures of gravity and nuclear
fusions hold the temperature ...10...in the sun's interior, but the slight changes in the earth's ...11... alter the temperature on the earth and cause ice
ages every 100,000 years. A British scientist, however, challenges this view by
claiming that the internal solar magnetic ...12... can induce the temperature
oscillations in the sun's interior. The sun's core temperature oscillates around
its average temperature in ...13... lasting either 100,000 or 41,000 years. And
the ...14... interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other, which explains why the ice ages changed frequency a million years ago.
邮箱： 