It’s a one-way street for light

IT IS like a valve for light – the first material that transmits electromagnetic radiation in one direction only.

Zheng Wang and colleagues at the Massachusetts Institute of Technology have made what’s known as a photonic crystal from an array of ferrite rods.

Ordinarily the rods reflect microwaves in all directions, but when Wang adds a strong magnetic field, everything changes. Microwaves bouncing off the magnetised rods in one direction are modified to become “evanescent”, fading as they travel. Waves heading the other way carry on unhindered.

Wang is now working on plans to adapt his device for higher frequency radiation, moving into the terahertz and eventually the visible part of the spectrum. These photonic crystals may help create new components for optical communication and computing, including simple one-way routers analogous to electrical diodes, as well as wave-guides for light that are more efficient than optical fibres. “It raises a lot of intriguing possibilities,” says optical physicist Duncan Haldane of Princeton University .

Supercharged stem cells bring help where it’s needed most

ALREADY prized as engines of repair, stem cells have now been engineered to contain a gene that enhances their healing properties by summoning extra blood vessels to newly formed tissue. Using the same technique, it should be possible to add other genes to stem cells to make them more efficient at different tasks.

Stem cells have the potential to repair most tissues in the body. However, new tissue needs new blood vessels to feed it, and stem cells don’t always produce enough of the proteins that encourage

blood vessels to grow. So Daniel Anderson at the Massachusetts Institute of Technology exposed human bone marrow stem cells to biodegradable nanoparticles carrying the human gene for vascular endothelial growth factor (VEGF), which attracts blood vessels to injury sites.

When the modified cells were injected into mice whose hind limbs had been injured, the tissue that regrew to repair the damage had three times the blood vessel density of similar tissue in mice given unmodified cells. Four

BOOSTING brain waves can make

people move in slow motion. The

finding, one of the first to show

that brain waves directly influence

behaviour, could lead to new

treatments for Parkinson’s disease

and other movement disorders.

Peter Brown at University College

London used electrodes to generate

a small electrical current in the brains

of 14 healthy volunteers. The current

increased the activity of normal beta

waves, a kind of brain wave that

is usually active during sustained

muscle activities, such as holding

a book. Beta activity usually drops

before people begin a movement.

The participants then carried out

a simple task: they moved a spot

on a computer screen as quickly

as possible using a joystick. With

increased beta wave activity, their

fastest times slowed by 10 per cent

(Current Biology, DOI: 10.1016/

j.cub.2009.07.074).

The findings suggest a link

between the slowing of movement

and greater beta wave activity seen

in people with Parkinson’s. They have

even greater relevance for conditions

of uncontrolled movement such as

dystonia and chorea, Brown said.

Brain-wave boost sets us to slo-mo

MADAT/FLICKR/GETTY

weeks later, only 20 per cent of the mice given modified cells had lost limbs, compared with 60 per cent in mice that received unmodified cells ( Proceedings of the National

Academy of Sciences, DOI: 10.1073/pnas.0905432106 ).

Anderson says the nanoparticles could be used to ferry other genes into stem cells to make them more efficient at repair. “It represents a proof of principle for gene enhancement strategies,” agrees Duncan Stewart of the Ottawa Hospital Research Institute in Canada.

Our ancestors walked tall

WE WAITED 15 years to meet her.

Last week, the remains of Ardi – a

4.4-million-year-old hominid – were

finally revealed to the world. Her

first act: to force a rethink of our

links with modern primate cousins .

Tim White of the University of

California, Berkeley, first discovered

the female Ardipithecus ramidus in

Ethiopia in 1994 and has spent the

years since analysing her remains

and those of 35 contemporaries.

Ardi, he says, was a 120-centimetre-

tall female who lived about a million

years before Lucy – the famous

hominid found in Ethiopia in 1974 –

roamed the planet. She weighed

about 50 kilograms, had a brain that

was small for a hominid and a varied

diet of nuts, fruit and meat.

Crucially, though, she walked

upright on two feet (pictured) –

unlike chimpanzees and gorillas,

who lean on their knuckles as they

walk. This suggests that “knuckle

walking” is an adaptation of

non-human apes, not an ancient

trait that our ancestors gave up.

Combined with other features,

it also suggests other apes have

evolved to be significantly different

to the common ancestor we share

with them. Palaeoanthropologists

often use chimps as “proxies” for

our common ancestor, so Ardi’s

debut may mean that much of what

we think we know about human

evolution will have to be rethought.

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AAS

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