Research Highlights

Nature 452, 668-669 (10 April 2008) | doi:10.1038/452668a; Published online 9 April 2008

Research highlights

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Digital microfluidics: Climbing the walls

Lab Chip doi:10.1039/b801516c (2008)

Research highlights

M. ABDELGAWAD

The ability to steer droplets of various fluids across a suitably wired-up surface with electric fields has a range of potential uses in chemistry and biology. That range may be expanded by the extension of the technique to inclined and vertical surfaces.

Aaron Wheeler and his colleagues at the University of Toronto in Canada bent flexible circuit boards into various shapes and tested their ability to carry drops of different sizes. They were able to propel droplets of up to 8 microlitres up vertical walls and others of up to 50 microlitres along steady slopes.

This three-dimensional extension of digital microfluidics could prove useful for applications in which a droplet has to be bathed in a well of some immiscible fluid and then moved on elsewhere.

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Microbiology: Fat lazy bacilli

PLoS Med. 5, e7510.1371/journal.pmed.0050075 (2008)

It is commonly thought that the bacilli found in the saliva, phlegm and mucus of people infected with tuberculosis are active and growing. Michael Barer at the University of Leicester Medical School, UK, Philip Butcher at St George's University of London, and their colleagues report that a significant proportion of the bacilli in this sputum — ones with distinctive lipid bodies in their cytoplasm — do not conform to this view.

These "fat and lazy" bacteria do not replicate, and show greater tolerance to antibiotics than their more active kin. This might reflect an adaptation to the rigours of transmission from person to person, and may help to explain why antibiotic treatment for tuberculosis normally has to be prolonged.

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Nanotechnology: Tube conductors

Nano Lett. doi:10.1021/nl080302f (2008)

Single-walled carbon nanotubes can be metallic or semiconducting, but are synthesized as an unhelpfully entwined mixture of the two. By using an ultrafast centrifuge that sorts the tubes by density, Alexander Green and Mark Hersam from Northwestern University in Evanston, Illinois, produced a sample of almost exclusively metallic tubes.

Green and Hersam made films from the metallic nanotubes that were transparent and up to ten times more conductive than a film made from mixtures of tubes. The effect of the sorting process also meant that tubes of differing diameters could be easily picked out. Tubes with different diameters were used to produce films with different colours and conductivities. There are applications for transparent conducting materials in flexible circuitry and displays, and even in artificial muscles.

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Geophysics: Going deep

Geology 36, 275–278 doi: 10.1130/G24112A.1 (2008)

Geophysicists have captured images of two subduction zones — places where one tectonic plate overrides another — that allow comparisons to be made between them.

The work by Stéphane Rondenay of the Massachusetts Institute of Technology in Cambridge and his colleagues shows subducted slabs behaving differently in the two areas. In central Alaska, where the crust is 15–20 kilometres thick, the researchers observed the sinking slab penetrating to 120 kilometres below the surface. In Cascadia, along the northwestern coast of the United States, the 8-kilometre-thick crust was only seen to a depth of 40 kilometres.

The subducting slabs become invisible to the seismic imaging technique at depth because increasing pressure transforms the rocks into eclogite, an assemblage of minerals that is almost indistinguishable from deeper mantle rocks.

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Chemical physics: Icy lines

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0710129105 (2008)

Research highlights

L. POOLE, NASA LANGLEY RESEARCH CENTER

Cold ice has stripes, according to Erio Tosatti at the International School for Advanced Studies in Trieste, Italy, and his colleagues.

Slicing through an ice crystal exposes dangling oxygen and hydrogen atoms. The crystal structure of bulk ice suggests that these atoms are randomly arranged, but the researchers' computer simulations show that at temperatures below 180 kelvin the cut surfaces will reorganize themselves into alternating rows of hydrogens and oxygens, a state first postulated in 1970.

The findings fit experimental studies of ice. The stripes could affect the surface chemistry of the very cold ice particles that make up polar stratospheric clouds (pictured).

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Condensed-matter physics: Spinning together

Phys. Rev. Lett. 100, 120403 doi:10.1103/PhysRevLett.100.120403 (2008)

Whirling vortices frequently appear in very cold systems of atoms, but usually keep themselves to themselves.

However, vortices in a Bose–Einstein condensate (BEC), an ultracold atomic gas, may be more sociable, sometimes coming together into 'vortex molecules'. Q-Han Park of Korea University in Seoul and his collaborators modelled what would happen in a BEC composed of both atomic and molecular rubidium. They show that the interactions of the different rubidium species cause vortices in the BEC to form into triplets that look similar to carbon dioxide molecules.

The researchers are now building an experiment to test their calculations. They hope the system will improve the understanding of vortices in other materials, including superconductors.

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Archaeology: Excremental advance

Science doi:10.1126/science.1154116 (2008)

The Clovis culture of about 13,200 years ago is the first unmistakeable sign of human presence in the Americas, but there have been tantalizing hints of an older presence. Now, Eske Willerslev of the University of Copenhagen and a large team of his colleagues have found human faeces in an Oregon cave that they carbon date to about 14,300 years ago.

Human mitochondrial DNA from some of the fossil faeces, which were removed from the lowest layer of the Paisley Caves, carries a signature associated with two founding Native American groups. These mysterious pre-Clovis people support findings of non-Clovis cultural artefacts in Chile from about 14,500 years ago.

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Cancer biology: Long-distance instructions

Cell 133, 66–77 doi:10.1016/j.cell.2008.01.046 (2008)

The microenvironment of a breast tumour cell can influence it in a way that leaves it particularly well suited to spread to the lungs.

This may be a general phenomenon, according to Joan Massagué of the Memorial Sloan-Kettering Cancer Center in New York, explaining the mysterious tendency of cancer cells to metastasize to a 'preferred' organ.

He and his colleagues found that in one major type of human breast tumour, cells would invade lungs much more readily than bones if they had responded to the signalling molecule TGFbeta in the tumour microenvironment before escaping into the bloodstream.

TGFbeta, they found, switches on production of a second signalling molecule in the tumour cell itself. This molecule, ANGPTL4, disrupts the tight connections between cells in the tiny blood vessels that infiltrate lungs — allowing the tumour cells to enter and settle there.

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Astrophysics: Quasar, delayed

Research highlights

EUROPEAN SPACE AGENCY/NASA/K. SHARON/E. OFEK

Astrophys. J. 676, 761–766 (2008)

Astronomers have measured the longest time delay yet seen due to gravitational lensing. Earth receives light from quasar SDSS J1004+4112 along five different paths (pictured), thanks to the space-warping effects of intervening galaxies. Janine Fohlmeister of the University of Heidelberg, Germany, and her colleagues have now shown that one of the three main paths is two years and three months shorter than another, and that the quickest of the paths is at least 6 years shorter than the longest.

This large delay raises the possibility of studying events first seen in one image in more detail when they turn up years later in the others. This could allow the most precise estimates yet to be made of the size of a quasar's central engine.

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Physics: Shields up

Phys. Rev. Lett. 100, 123002 doi:10.1103/PhysRevLett.100.123002 (2008)

Forget light, objects might also be made invisible to matter. Xiang Zhang and others at the University of California, Berkeley, report that it is theoretically possible to make a cloak that shields objects from incoming atoms — although the technique would work only at temperatures so low that atoms behave like waves.

The cloak would be made of concentric rings of light, an optical lattice configured so as to change the effective mass and electric potential of passing atoms. The changes would deflect incoming atoms around the object before letting them continue along their original path in the same way that 'invisibility cloaks' deal with photons. So far, the authors say, the experimental possibilities look most promising in two dimensions.