Harry Potter-style invisibility cloak developed
Washington:Scientists have developed a ‘Harry Potter-style’ ultra-thin invisibility cloak that can conform to the shape of tiny objects and conceal them from detection with visible light.
Although this cloak is only microscopic in size, the principles behind the technology should enable it to be scaled-up to conceal macroscopic items as well, researchers said. Working with brick-like blocks of gold nanoantennas, the researchers fashioned a “skin cloak” barely 80 nanometres in thickness, that was wrapped around a three-dimensional object about the size of a few biological cells and arbitrarily shaped with multiple bumps and dents. The surface of the skin cloak was meta-engineered to reroute reflected light waves so that the object was rendered invisible to optical detection when the cloak is activated.
“This is the first time a 3D object of arbitrary shape has been cloaked from visible light,” said corresponding author Xiang Zhang, director of US Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) Materials Sciences Division. “Our ultra-thin cloak now looks like a coat. It is easy to design and implement, and is potentially scalable for hiding macroscopic objects,” Zhang said. It is the scattering of light – be it visible, infrared or X-ray – from its interaction with matter that enables us to detect and observe objects. The rules that govern these interactions in natural materials can be circumvented in metamaterials whose optical properties arise from their physical structure rather than their chemical composition. For the past ten years, Zhang and his research group have been pushing the boundaries of how light interacts with metamaterials, managing to curve the path of light or bend it backwards, phenomena not seen in natural materials, and to render objects optically undetectable. In the past, their metamaterial-based optical carpet cloaks were bulky and hard to scale-up, and entailed a phase difference between the cloaked region and the surrounding background that made the cloak itself detectable – though what it concealed was not. In the study, when red light struck an arbitrarily shaped 3D sample object measuring approximately 1,300 square microns in area that was conformally wrapped in the gold nanoantenna skin cloak, the light reflected off the surface of the skin cloak was identical to light reflected off a flat mirror, making the object underneath it invisible even by phase-sensitive detection.
The cloak can be turned “on” or “off” simply by switching the polarisation of the nanoantennas. The study was published in the journal Science. (PTI)
Dogs sometimes use memory rather than smell
Washington: Dogs sometimes rely more on their memory than sense of smell when trying to find a hidden treat, according to researchers who analysed data contributed by 500 citizen scientists from around the world. Five hundred dog owners played the same games at home that researchers use in the laboratory, and contributed data to a study to help find out about a dog’s cognitive skills and problem-solving.
On five of the seven tests analysed, citizen science data corresponded closely to what had been produced by labs. For example, in one of the game-like tests, dogs were found to rely more on their memory than their sense of smell to find a hidden treat. The dogs watched as their owner hid food under one of two cups.
Then while the dog’s vision was obscured, the owner switched the food to the other cup. If dogs could smell the food, they should have been able to choose the correct cup, but owners found that most dogs went to where they last saw the food. The data were collected through a website called Dognition.com that was developed by Brian Hare, an associate professor of evolutionary anthropology at Duke University. According to Evan MacLean, a senior research scientist at Duke University, the memory-over-smell result has been replicated in seven different research groups and more than a dozen different studies.
“Most people think dogs use their sense of smell for everything. But actually dogs use a whole range of senses when solving problems,” said MacLean. Analysis of the unusually large dataset created by Dognition has also found that all dogs have a unique set of cognitive skills that they use to navigate the world around them. Some dogs were found to be good communicators, some had better memories and others were better at taking their owner’s perspective. “Most people think of intelligence as glass that is more or less full,” Hare said. “But intelligence is more like ice cream. Everybody has different flavours. Being good at one thing doesn’t mean you will be good at everything else,” Hare said. The study was published in the journal PLOS ONE. (PTI)
Cow-sized pre-reptile earliest to walk upright on all fours
Washington: A cow-sized pre-reptile that lived 260 million years ago likely stood upright on all-fours, making it the earliest known creature to do so, researchers say. To date all of the known pareiasaurs who roved the supercontinent of Pangea in the Permian era a quarter of a billion years ago were sprawlers whose limbs would jut out from the side of the body and then continue out or slant down from the elbow (like some modern lizards). Morgan Turner, lead author of the new study, expected the pre-reptile Bunostegos akokanensis to be a sprawler too, but the bones of the animal’s forelimbs told a different story. “A lot of the animals that lived around the time had a similar upright or semi-upright hind limb posture, but what’s interesting and special about Bunostegos is the forelimb, in that it’s anatomy is sprawling-precluding and seemingly directed underneath its body – unlike anything else at the time,” said Turner. “The elements and features within the forelimb bones won’t allow a sprawling posture. That is unique,” said Turner, who performed the analysis under supervision of Professor Christian Sidor while he was a student at the University of Washington. Turner, now a graduate student at Brown University, Sidor and co-authors characterised how Bunostegos might have looked: standing like a cow, and about the same size. “Imagine a cow-sized, plant-eating reptile with a knobby skull and bony armor down its back,” said co-author Linda Tsuji of the Royal Ontario Museum, who discovered the fossils in Niger along with Sidor and colleagues in 2003 and 2006. Turner examined much of the skeleton of several individuals. In particular, four observations make the case, she said, that Bunostegos stood differently than all the rest, with the legs entirely beneath the body. Starting at the shoulder joint, or the glenoid fossa, the orientation of it is facing down such that the humerus (the bone running from shoulder to elbow) would be vertically oriented underneath. It would restrict the humerus from sticking out to the side, too.
Meanwhile Bunostegos’s humerus is not twisted like those of sprawlers. In a sprawler, the twist is what could allow the humerus to jut out to the side at the shoulder but then orient the forearm downward from the elbow. But the humerus of Bunostegos has no twist suggesting that only if the elbow and shoulders were aligned under the body, could the foot actually reach the ground, Turner said.
The elbow joint is also telling. Unlike in sprawling pareiasaurs, which had considerable mobility at the elbow, the movement of Bunostegos’s elbow is more limited. The way the radius and ulna (forearm bones) join with the humerus forms a hinge-like joint, and would not allow for the forearm to swing out to the sides. Instead, it would only swing in a back and forth direction, like a human knee does. Finally, the ulna is longer than the humerus in Bunostegos, which is a common trait among non-sprawlers. The study is published in the Journal of Vertebrate Paleontology. (PTI)
