Wednesday, November 25, 2009


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Researchers at Rothamsted Research, an Institute of the Biotechnology and Biological Sciences Research Council, and at the University of Greenwich have explained a characteristic feature of insect migration that has puzzled researchers for over 40 years: how do insects maintain wind-related orientation at altitudes of several hundreds of metres in the dark?

The environmental cues used by nocturnal insect migrants to select and maintain common headings, while flying at altitudes of several hundreds of metres above the ground in low illumination levels, and the adaptive benefits of this behaviour, have long remained a mystery. Studies made with both entomological and meteorological radars have frequently reported the occurrence of insects moving in layers, and that the individuals forming these layers often show a considerable degree of uniformity in their headings – behaviour known as ‘common orientation’. This theory accounts for flight behaviour of many medium-sized (10-70 mg) insect species flying at night, at high altitudes, under conditions where downwind orientation cannot be explained by visual assessment of movement relative to the ground or by compass mechanisms.

A collaboration between mathematical modellers and biologists has now revealed that these insects are responding to the effects of turbulence. Insects possess sensors that are capable of detecting extremely faint air movements. The migrating insects will be bounced around in the turbulence, and the authors conclude that the insects are able to use the turbulence to sense which direction the air is moving. In response to this buffeting they alter their vertical profile and direction, increasing both speed and migration distance.

Lead researcher, Andy Reynolds said: "Common orientation close to the downwind direction allows the nocturnal migrants to add their flight speeds (of approx 2 m/s) to the wind speed, thus increasing the distance travelled during the migratory flight.”

This mechanism also predicts that insects flying in the Northern Hemisphere, will typically be offset to the right of the mean wind line, as a consequence of the Earth’s rotation. The researchers report on the first evidence for this effect in their data from insect-monitoring radars.

Reynolds said: "Nocturnal insects are frequently being ‘misled’ by the action of the Ekman spiral (the turning of the mean wind direction due to the Earth’s rotation). Consistent with expectations, here in the UK we observed that insects have a tendency to fly to the right of the mean wind line.”

The findings have clear implications for the accurate prediction of the flight trajectories of migrating nocturnal insects. “Over long distances even these relatively small but consistent offsets have significant effects on the destination of the migrating insects and should be taken into account when predicting the flight trajectories of migrating insects” said Reynolds. This is particularly important when designing forecasting models to predict the movement of insect pests.

(Photo: Andy Banthorpe)

The Biotechnology and Biological Sciences Research Council


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One of the most basic problems in maths is solving very large linear equations. There's nothing mysterious about them, they simply take time and the more variables there are, the longer it takes. Even a supercomputer would struggle to solve a system of equations that has a trillion variables.

However, in a new paper recently published in Physical Review Letters, Aram Harrow at the University of Bristol and colleagues from MIT in the United States have discovered a quantum algorithm that solves the problem much faster than conventional computers can. And the larger the problem, the greater the speedup.

To understand how the quantum algorithm works, think of a digital equaliser in a stereo CD player. The equaliser needs to amplify some components of the signal and attenuate others. Ordinary equalisers employ classical computer algorithms that treat each component of the sound one at a time.

By contrast, a quantum equaliser could employ a quantum algorithm that treats all components together at once (a trick called `quantum parallelism'). The result is a huge reduction in the difficulty of signal processing.

“Large-scale linear systems of equations exist in many fields, such as weather prediction, engineering, and computer vision”, says Harrow. “Quantum computers could supply serious improvements for these and many other problems. For example, a trillion-variable problem would take a classical computer at least a hundred trillion steps to solve, but using the new algorithm, a quantum computer could solve the problem in just a few hundred steps”.

The solution could also be applied to other complex processes such as image and video processing, genetic analyses and even Internet traffic control.

(Photo: Bristol U.)

University of Bristol


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New data show that the balance between the airborne and the absorbed fraction of carbon dioxide has stayed approximately constant since 1850, despite emissions of carbon dioxide having risen from about 2 billion tons a year in 1850 to 35 billion tons a year now.

This suggests that terrestrial ecosystems and the oceans have a much greater capacity to absorb CO2 than had been previously expected.

The results run contrary to a significant body of recent research which expects that the capacity of terrestrial ecosystems and the oceans to absorb CO2 should start to diminish as CO2 emissions increase, letting greenhouse gas levels skyrocket. Dr Wolfgang Knorr at the University of Bristol found that in fact the trend in the airborne fraction since 1850 has only been 0.7 ± 1.4% per decade, which is essentially zero.

The strength of the new study, published online in Geophysical Research Letters, is that it rests solely on measurements and statistical data, including historical records extracted from Antarctic ice, and does not rely on computations with complex climate models.

This work is extremely important for climate change policy, because emission targets to be negotiated at the United Nations Climate Change Conference in Copenhagen early next month have been based on projections that have a carbon free sink of already factored in. Some researchers have cautioned against this approach, pointing at evidence that suggests the sink has already started to decrease.

So is this good news for climate negotiations in Copenhagen? “Not necessarily”, says Knorr. “Like all studies of this kind, there are uncertainties in the data, so rather than relying on Nature to provide a free service, soaking up our waste carbon, we need to ascertain why the proportion being absorbed has not changed”.

Another result of the study is that emissions from deforestation might have been overestimated by between 18 and 75 per cent. This would agree with results published last week in Nature Geoscience by a team led by Guido van der Werf from VU University Amsterdam. They re-visited deforestation data and concluded that emissions have been overestimated by at least a factor of two.

(Photo: Bristol U.)

University of Bristol




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