Research Highlights

Nature 449, 510-511 (4 October 2007) | doi:10.1038/449510a; Published online 3 October 2007

There is a Correction (18 October 2007) associated with this document.

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Astronomy: Bright start

Astrophys. J. Lett. 667, L37 (2007)

Not all supernovae are created equal, according to an analysis of 169 stellar explosions.

Andrew Howell and his colleagues at the University of Toronto in Canada analysed the peak brightness of one type of supernova at different times during the Universe's history. Type 1a are thought to be of almost uniform brightness, and have thus been used to probe the distances between objects in space and the strength over time of dark energy — the force pushing the Universe apart.

However, Howell found that, on average, Type 1a supernovae from the young Universe were brighter for longer than their counterparts in the current era. Correcting for this does not significantly change current measurements of dark energy, but the effect may limit supernovae's usefulness as a gauge of dark energy in the past, the authors report.

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Genomics: Weak to strong

Genome Res. doi:10.1101/gr.6395807 (2007)

It seems that evolution may indeed favour the strong over the weak, according to Katherine Pollard at the University of California, Davis, David Haussler at the University of California, Santa Cruz, and their colleagues.

Last year, the team reported that the 200 or so most rapidly evolving spots in the human genome had more single-base changes from A and T to G and C bases — known as 'weak-to-strong' substitutions. Genome wide, mutations happen at approximately equal rates in both directions. Now, Pollard and Haussler extend their analysis and find the weak-to-strong substitution bias exists in all the many thousands of regions of the human genome in which evolutionarily recent substitutions are densely clustered. The most biased clusters contain a disproportionately high number of genes. The authors also find an intriguing correlation with areas that have high recombination rates in males.

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Population ecology: Wayward youth

Research highlights

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Biol. Lett. doi:10.1098/rsbl.2007.0394 (2007)

After emerging from their nests, green turtle hatchlings bolt for the sea and disappear. What they do in the 'lost years' that follow, before they reappear to feed on seagrasses and algae near the shore, has been revealed by analysis of scute, the fingernail-like coating on turtle shells.

Kimberly Reich and her colleagues at the Archie Carr Center for Sea Turtle Research, University of Florida, Gainesville, measured isotopes in layers of scute laid down as turtles' shells grow. High levels of nitrogen-15 in the oldest scute suggest that the turtles spend their first three to five years as carnivores, because this isotope accumulates towards the top of the food chain. Older scute also contains low levels of carbon-13, indicating that the turtles had lived in open ocean habitats. Shallow water is relatively rich in carbon-13, because the rate of photosynthesis, which preferentially snaps up carbon-12, is high.

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Quantum physics: All for one and one for all

Phys. Rev. Lett. 99, 126403 (2007)

Young's double-slit experiment — a classic demonstration of the wave nature of light — has been repeated for a 'polariton condensate' to test claims about such condensates' quantum nature.

Objects that have a quantum wave-like nature are expected to behave as light does when it passes through two slits, giving rise to a pattern of dark and bright stripes.

Hui Deng, then at Stanford University in California, and her colleagues looked for this effect in polaritons, which each comprise a photon and a bound pair of charges, in a semiconductor device at low temperature. They confirmed that widely spaced polaritons share an almost pure quantum state. Atoms in the ever-intriguing Bose–Einstein condensates share one pure quantum state, but debate is likely to continue over whether polariton condensates deserve the Bose–Einstein label, says Deng.

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Neurobiology: Sensory deprivation

Nature Neurosci. doi:10.1038/nn1978 (2007)

Visual deprivation during the first five months of life may permanently damage interactions between the body's audio and visual systems.

Lisa Putzar of the University of Hamburg in Germany and her colleagues examined people born with dense cataracts who had no pattern vision for at least five months, but then gained good vision. Compared with controls, those born with cataracts were less likely to be distracted by a burst of noise interrupting a test containing visual cues — a sign that interference between the audio and visual systems is reduced. Those who had cataracts at birth also showed poorer audio–visual integration: they were less able than controls to recognize the words of speakers in videos with degraded audio tracks despite having similar lip-reading skills.

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Archaeology: Keep paddling

Science 317, 1907–1911 (2007)

The first inhabitants of Hawaii are thought to have originiated from Polynesia. The discovery of an adze — an axe-like tool — made from Hawaiian basalt on a Tuamotu atoll in East Polynesia provides the first material evidence that ancient voyagers made a round trip of more than 8,000 kilometres from the South Pacific to Hawaii and back again. Scientists long thought that journeys between remote Pacific islands must have been accidental or one-time events, although oral histories and recent research hinted otherwise.

Kenneth Collerson and Marshall Weisler at the University of Queensland in Australia examined trace elements and isotope ratios in stone adzes found on the Tuamotus islands. The adzes were from a number of Pacific islands, with one bearing the chemical fingerprint of Hawaii. Collerson suggests that pieces of rock may have been taken from island to island as a memento by travellers commemorating their long and arduous journeys.

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Climate monitoring: Melt maps

Research highlights

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Geophys. Res. Lett. 34, L18504 (2007)

Microwave radiation emitted by snow and ice can indicate whether the surface is dry or wet. Wet surfaces imply melting. In an analysis of satellite data collected in Antarctica between 1987 and 2006, researchers confirm previous reports of extensive inland melting in early 2005 and document complex patterns of coastal and inland melting over the years. A team led by Marco Tedesco, of the University of Maryland in Baltimore, looked only at periods of 'persistent melting', defined as a period of one consecutive day and night or three days in a row. The reseachers used a new method that takes advantage of a particular microwave frequency. Tedesco says he used the same method to determine that high-altitude melting in Greenland set a record in 2007.

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Mass spectrometry: Hands off

Angew. Chem. Int. Edn doi:10.1002/anie.200702200 (2007)

A new technique allows the chemical make-up of human skin, plant tissue, frozen meat and other living materials to be determined quickly without harming the biological surface under scrutiny or having to treat it before analysis.

Renato Zenobi and Huanwen Chen at ETH Zurich in Switzerland and their colleagues blow a stream of nitrogen, a neutral gas, across a surface and collect a sample of what is dislodged. The sample is then transported to an extractive electrospray ionization mass spectrometer, where it can be directly analysed for its chemical composition. Using the technique, it is possible to quickly detect, from a human hand, the difference in caffeine levels before and after a person drinks a cup of coffee.

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Atmospheric chemistry: Volcanic paintings

Research highlights

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Atmos. Chem. Phys. 7, 4027–4042 (2007)

The ash from large volcanic eruptions can cool Earth's climate and cause vivid red sunsets. But the historical effects of volcanic activity on climate are difficult to quantify owing to a lack of direct atmospheric observation.

Christos Zerefos at the Academy of Athens in Greece and his colleagues have come up with a novel way to estimate the volcanic particle content in middle latitudes of the Northern Hemisphere during the period 1500–1900. They analysed sunsets captured in paintings by artists such as John Mallord William Turner, Edgar Degas and Gustav Klimt. (Pictured is one of their subjects, The Stages of Life (1835) by Caspar David Friedrich.)

The researchers calculated red/green colour ratios from digital photos of hundreds of paintings. They found that artists used more red after major volcanic eruptions such as those of Krakatau in 1680 and 1883. The team then used the red/green ratios to reconstruct how much light was intercepted by volcanic ash in the air. The resulting time series correlates well with and could complement existing historical reconstructions of atmospheric composition.