5 April 2014 | NewScientist | 19

Vanishing mirror turns into window

YOU walk past a mirror, gazing at your reflection, when suddenly it disappears – the mirror has become a window. This trick is now possible thanks to a material that filters light beams based on their direction of travel. It could one day make it easier to photograph faint objects.

Yichen Shen of the Massachusetts Institute of Technology and colleagues made a vanishing mirror from 84 ultra-thin alternating layers of glass and tantalum oxide. As light passes from one layer to the next, some gets partially reflected – except for light that has a specific polarisation and hits at the “Brewster angle”, which depends on the materials used. This light passes straight through as if the surface wasn’t there.

By using multiple layers, Shen’s team increased the overall reflectivity of the structure, without interfering with the ability of light to sneak through when it hits at the Brewster angle (Science, doi.org/r4x). So it looks like a mirror but turns transparent at one point when spun (video at bit.ly/vanishmirror).

Shen says the structure could one day be used to photograph faint objects next to brighter ones. It could be angled so that light from the fainter object hits at the Brewster angle and enters the camera’s aperture, while light from the brighter object is reflected back.

Oyster shell inspires tougher armour

MIGHTY molluscs with transparent shells could help protect soldiers in battle. Analysis of oyster shells shows how they can take repeated beatings without shattering, perhaps inspiring tougher combat armour.

Current shields and visors are made from laminated glass, which fractures if it takes a bullet. That makes it hard to see through and vulnerable to breaking with a second hit, says Christine Ortiz at MIT. But in nature, many creatures use transparent shells for camouflage, which can survive repeated attacks from predators.

Ortiz and her team studied the nanoscale structure of shells of the windowpane oyster, which are made of 99 per cent calcite mineral. Pure calcite crystals shatter easily, but the oyster shell is organised in thin layers that shift orientation when stressed, confining damage to shallow craters (pictured, above) and stopping fractures spreading (Nature Materials, DOI: 10.1038/nmat3920).

While natural shells wouldn’t stop a bullet, finding a way to create such nano-layers in military-grade ceramics could help build better shields, says Ortiz.

DON’T blame the baby for trying to eat that Lego piece. Humans may have a brain circuit dedicated to grabbing stuff and putting it in our mouths, and it probably develops in the womb.

Researchers and parents alike have long known that babies stick all manner of things in their mouths from very early on. Some fetuses even suck their thumbs.

As putting something in the mouth seems advanced compared to the other, limited actions of newborns, Angela Sirigu of the Institute of Cognitive Sciences in

Bron, France, and colleagues wondered whether the behaviour is encoded in the brain from birth.

To investigate, they studied 26 people of different ages while they were undergoing brain surgery. The researchers found that they were able to make nine of the unconscious patients bring their hands up and open their mouths, just by stimulating a brain region linked to those actions in other primates (PNAS, DOI: 10.1073/pnas.1321909111).

Because this behaviour is encoded in the same region as in

other primates, it may be there from birth or earlier, the researchers say. If it was learned, you would expect it to involve multiple brain areas, and those could vary between individuals.

Newborn kangaroos are able to climb into their mother’s pouch and baby wildebeests can run away from lions, but our babies appear helpless and have to learn most complex actions. The new work suggests the way our brain develops is more similar to brain development in other animals than previously thought.

A baby’s urge to chew on Lego is automatic, not learned

Obesity linked to carb digestion

“I’M OFF the carbs” is a familiar refrain among dieters. But could this approach to losing weight be better for some than others?

That’s the implication of research suggesting that obesity may be linked to how our bodies digest the starch found in carbohydrate-rich foods.

When we eat, an enzyme in saliva called salivary amylase kick-starts digestion by breaking down starch into sugars. This enzyme is made by the gene AMY1, which we can have multiple copies of.

Mario Falchi at Imperial College London and colleagues compared the genomes of a group of siblings where one was overweight, the other lean, and looked for genes which might help explain the difference. AMY1 topped the list. Next, they studied a separate group of 5000 people and found that those with fewer than four copies of the gene were eight times more likely to be obese than those with more than nine copies of the gene.

This suggests that people who are good at digesting starch are less likely to be obese. However, the mechanism behind this isn’t clear from this study (Nature Genetics, DOI: 10.1038/ng.2939).

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