Inspirations and more

A published study has revealed that light-emitting diodes inspired by the glow of fireflies can increase light extraction by more than 50 percent.

The more efficient light sources take their inspiration from the jagged scales found inside fireflies, which enhance the glow coming from the creatures. An overlayer mimics the action of the scales and reduces the amount of energy needed by the LED.

“The most important aspect of this work is that it shows how much we can learn by carefully observing nature,” said Annick Bay, a PhD student at the University of Namur in Belgium.

In the fireflies (members of the genus Photuris) a certain amount of light is reflected back into the lantern by the insect’s cuticle — a part of the exoskeleton. But in some fireflies the reflection can be reduced by an arrangement of jagged scales, meaning more light escapes and the firefly appears brighter.

In the LEDs, an overlayer composed of a light-sensitive material which has been lasered into shape mimics the action of these scales, improving efficiency and reducing the energy demand of the light.

“We refer to the edge structures as having a factory roof shape,” says Bay. “The tips of the scales protrude and have a tilted slope, like a factory roof.”

As an added bonus, the efficiency enhancing coating can be applied retrospectively to existing LEDs.

Two studies, published yesterday in Optics Express, describe the shape of scales on the abdomen of fireflies, and an experiment that placed similar structures on LEDs, brightening their output by 55 percent.

Source: Wired

Albert Einstein

Researchers at Queen Mary University of London have found that bumblebees are capable of complex problem solving that could ultimately lead to faster computer networks and microchips. The researchers discovered that bumblebees find the shortest route among landmarks, in this case flowers, through a simple but effective method.

The researchers set up five fake flowers in a field, each with a little bit of sucrose to entice the bees, and outfitted with motion-triggered web cams. They tracked the bees’ flight paths with tiny bumblebee-mounted radar transponders to see how long it took them to find the fastest route starting from the nest, visiting all five flowers and then back to the nest. The team then modeled the flight paths and found that, amazingly, the bees were able to find the quickest route after trying just 20 out of the 120 possible routes. And the researchers were more surprised that it seemed that the bees were using trial and error, which is a more complex behavior typically seen only in larger-brained animals.

The key, it seems, to their quickly find the shortest route was a simple system where after discovering all five flowers, the bees would start trying new routes. If a new route between flowers was the fastest yet, it would increase the probability that it would be tried again — essentially the bees were committing the fastest routes to memory and eliminating the slower ones until finally an optimal route was found.

Head of Computational and Systems Biology at Rothamsted Research, Professor Chris Rawlings said,”This is an exciting result because it shows that seemingly complex behaviours can be described by relatively simple rules which can be described mathematically.”

The mathematics is what could eventually be used to build faster computer networks, sequence DNA or help delivery companies find the most efficient routes among cities. And just as important, it could help to protect the bumblebees themselves. The researchers found that when a flower was moved or removed, the bees would keep visiting that location for an extended period of time, but then eventually find its new location or a new flower.

“This means we can now use mathematics to inform us when bee behaviour might be affected by their environment and to assess, for example, the impact of changes in the landscape,” Rawlings said.

Source: Treehugger.com

Photo: pasukaru76/CC BY 2.0

A US startup is developing a self-filling water bottle that sucks moisture from the atmosphere to create condensation, in the same way the humble Namib desert beetle does.

The beetle, endemic to Africa’s Namib desert — where there is just 1.3cm of rainfall a year — has inspired a fair few proof-of-concepts in the academic community, but this is the first time a self-filling water bottle has been proposed. The beetle survives by collecting condensation from the ocean breeze on the hardened shell of its wings. The shell is covered in tiny bumps that are water attracting (hydrophilic) at their tips and water-repelling (hydrophobic) at their sides. The beetle extends and aims the wings at incoming sea breezes to catch humid air; tiny droplets 15 to 20 microns in diameter eventually accumulate on its back and run straight down towards its mouth.

NBD Nano, made up of two biologists, an organic chemist and a mechanical engineer, is building on past studies that constructed structurally superior synthetic copies of the shell. An earlier incarnation of the material was first constructed in 2006 by an MIT team — they dipped glass or plastic substrates into solutions of charged polymer chains over and over again to manipulate the surface make-up. Silica nanoparticles were then added to create a rougher, water-trapping texture, and a Teflon-like substance sealed it. Charged polymers and nanoparticles were then layered in patterns to create a contrast between rough and porous surfaces.

NBD Nano says it has achieved proof of concept with its dual water-attracting (superhydrophilic) and water-repelling (superhydrophobic) bottle design, and is currently working on a prototype and seeking funding. Incredibly, the team predicts that the bottle could collect between half a litre and three litres of water per hour, depending on the local environment.

“Dry places like the Atacama Desert or Gobi Desert don’t have access to a lot of sources of water,” cofounder Miguel Galvez told the BBC. “So if we’re creating [several] litres per day in a cost-effective manner, you can get this to a community of people in Sub-Saharan Africa and other dry regions of the world. And if you can do it cheaply enough, then you can really create an impact on the local environment.”

Source: Wired.co.uk
More information:www.nbdnano.com/
Photo: Moongateclimber/Wikimedia Commons

Albert Einstein

Near the end of his life, the great mathematician Alan Turing wrote his first and last paper on biology and chemistry, about how a certain type of chemical reaction ought to produce many patterns seen in nature.

Called “The Chemical Basis of Morphogenesis,” it was an entirely theoretical work. But in following decades, long after Turing tragically took his own life in 1954, scientists found his speculations to be reality.

First found in chemicals in dishes, then in the stripes and spirals and whorls of animals, so-called Turing patterns abounded. Some think that Turing patterns may actually extend to ecosystems, even to galaxies. That’s still speculation — but a proof published Feb. 11 in Science of Turing patterns in a controlled three-dimensional chemical system are even more suggestion of just how complex the patterns can be.


How Turing Patterns Work

At the heart of any Turing pattern is a so-called reaction-diffusion system. It consists of an “activator,” a chemical that can make more of itself; an “inhibitor,” that slows production of the activator; and a mechanism for diffusing the chemicals.

Many combinations of chemicals can fit this system: What matters isn’t their individual identity, but how they interact, with concentrations oscillating between high and low and spreading across an area. These simple units then suffice to produce very complex patterns.


Proving Their Existence

Even though what appeared to be Turing patterns were immediately evident in nature, it wasn’t easy to be sure they were produced by reaction-diffusion systems, rather than some other mechanism.

The breakthrough came during the 1980s, when chemists were able to produce Turing patterns in the laboratory, on thin slabs of gel. In these controlled systems, the reactions could be closely followed, simulated on computers and unambiguously demonstrated as true Turing patterns.

At left in each photograph is a real seashell. At right is a computer-generated image of a pattern produced by a Turing pattern simulation.

At left in each photograph is the eye of a popper fish. At right is a computer-generated image of a pattern generated by a Turing pattern simulation.

Source: Wired

The opalescent wings of the Morpho butterfly embody a perfect marriage of aesthetic beauty and biological functionality. Scientists believe that a better understanding of this creature’s wings and their chemical makeup could have big implications for imaging technologies like night vision goggles that rely on sensing heat, rather than visible light.

Now, a team of GE researchers has taken an important step in accomplishing exactly that.

One of the biggest problems facing thermal imaging technologies is temperature management. The sensors in a heat-sensing device have to be cooled constantly, otherwise the image you see becomes washed out with old, and therefore insignificant, heat measurements. Imagine watching a person walk across a room while wearing thermal imaging goggles — if the thermal sensor’s temperature wasn’t kept in check, you’d be able to see a sort of thermal ghost trailing behind the person as they moved across your field of vision.

Physics World’s Tim Wogan explains the challenges of regulating the heat of thermal sensors:

The most sensitive thermal imagers require liquid-helium refrigeration. Since the heat sinks required are relatively large and power-hungry, this limits the minimum size and efficiency of the sensors. These requirements pose severe challenges for those designing portable equipment, such as thermal-imaging goggles. Indeed, goggles pose a particular problem because an ideal pair would be transparent to visible light, which is difficult to achieve with heat sinks in the way.

This is where the Morpho butterfly swoops in to save the day. The scales that cover the Morpho’s iridescent wings reflect light at some wavelengths, while absorbing it at others; these absorption/reflection properties can even change depending on the wings’ temperature, shifting the color of the wings in the process.

This is a pretty inspired biological feature, and it’s one that scientists believe could be put to use in thermal imaging sensors; but what researchers are really impressed with is the chitin that the scales of the Morpho wings are actually made of.

Chitin has a much lower heat capacity than the materials that are used in contemporary thermal sensors; lower heat capacity, in turn, eliminates the need for bulky, energy-hungry cooling methods. In the thermographic video featured here, you can see a Morpho butterfly responding quickly to heat pulses distributed first across the whole butterfly structure, and then onto localized regions of the wings.

And believe it or not, we can make these wings even more impressive — and with carbon nanotubes, no less! Writes Wogan:

Building on previous work by other researchers that revealed that decorating a material surface with carbon nanotubes enhances its ability to absorb infrared radiation, [a research team led by analytical chemist Radislav Potyrailo] showed that the [Morpho’s wings] absorbed infrared better if carbon nanotubes were added to the exposed surface. As a bonus, because carbon nanotubes have excellent thermal conductivity, the decoration helped to diffuse heat through the chitin away from the site of irradiation, thus providing a molecular heat sink.

In other words, Potyrailo and his colleagues showed that treating Morpho scales with carbon nanotubes not only enhances their ability to absorb radiation at wavelengths relevant to thermal imaging, it actually improves their ability to diffuse heat.

The question that remains is: how do researchers translate the functionality of nanotube-doped butterfly wings into a synthetic thermal sensor? Poryrailo and his team have already created an ersatz version of Morpho wings, but they still need a way to incorporate the chitin that grants them their unique heat-dissipating abilities. Once they do that, however, the researchers believe it could mark a major shift toward cheap, more effective thermal-imaging devices.

The researchers’ findings are published in the latest issue of Nature Photonics [Via PhysicsWorld]
Top image via; Chitin chair diagram via Wikimedia Commons

Source: io9

The armor that a massive Amazonian fish evolved against piranhas could lead to better body armor for soldiers, researchers say.

The arapaima (Arapaima gigas) is one of the largest freshwater fish in the world, weighing up to 440 pounds (200 kilograms). It lives in the Amazon, and as the waters of the rivers there recede during the dry season, it gets trapped alongside piranhas, and the latter eventually attack every bird, fish, mammal and reptile they can, save alligators.

“I’ve gone to the Amazon many times — I first spent time there as part of a Peace Corps project when I was 20,” said researcher Marc Meyers, a material scientist at the University of California, San Diego. “I remember being struck by how the arapaima could live in these piranha-infested lakes.”

It turns out the arapaima can thrive in this crowded environment. As such, Meyers and his colleagues wanted to learn how it could coexist with such a ravenous predator, especially one with a guillotine-like bite highly effective at slicing through muscle.

The researchers devised a mechanical version of a fight between a piranha and an arapaima. Piranha teeth were attached to what was essentially an industrial-strength hole punch and pressed down onto arapaima scales up to 4 inches (10 centimeters) long, which were embedded on a soft rubber surface that mimicked the muscle of the fish. They found the cutting and puncturing ability of the piranha teeth could not penetrate the arapaima scales.

The arapaima experiments suggest a number of lessons when it comes to designing advanced materials. For instance, the corrugated, ridged surfaces of the scales, which people in the Amazon sometimes use as nail files, help the scales bend without cracking, a discovery that could be of use when working with brittle materials such as ceramics. In addition, the scales mix soft and hard materials — soft collagen fibers stacked in alternating directions like a pile of plywood lend toughness to the scale, and a very hefty mineralized layer on top lends hardness.

Such flexible, tough, hard materials could be useful in body armor, Meyers said.  “I believe that this can be used for flexible armor,” he told InnovationNewsDaily. “I am in the process of contacting funding agencies for support.”

The researchers will continue exploring the natural world for inspiration, “asking, ‘how does nature put these things together?’” Meyers said. Another project will involve the alligator gar, a huge fish from the American South whose scales were used by Native Americans as arrow tips. The researchers are also studying abalone shells and leatherback turtle skin for inspiration.

“The materials that nature has at its disposal are not very strong, but nature combines them in a very ingenious way to produce strong components and strong designs,” Meyers said.

The researchers detailed their findings online Jan. 9 in the journal Advanced Engineering Materials. The work was also detailed in the October 2011 issue of the Journal of the Mechanical Behavior of Biomedical Materials.

Source: InnovationNewsDaily

“How the zebra got his stripes” sounds like the title of one of Rudyard Kipling’s “Just So” stories. Sadly, it isn’t, so the question has, instead, been left to zoologists. But they, too, have let their imaginations rip. Some have suggested camouflage. (Charles Darwin pooh-poohed that idea, pointing out that zebra graze in the open, not amid thick vegetation where a striped pattern might break up their outlines.) Others suggest they are a way to display an individual’s fitness. Irregular stripes would let potential mates know that someone was not up to snuff. One researcher proposed that stripes are to zebra what faces are to people, allowing them to recognise each other, since every animal has a unique stripe-print. Another even speculated that predators might get dizzy watching a herd of stripes gallop by.

There is, however, one other idea: that stripes are a sophisticated form of fly repellent. It was originally dreamed up in the 1980s, but never proved. Now, a team of investigators led by Gabor Horvath of Eotvos University in Budapest report in the Journal of Experimental Biology that they think they have done so.

The original suggestion was that stripes repel tsetse flies. These insects carry sleeping sickness, which is as much a bane of ungulates as it is of people. But tsetses are not the only dipteran foes of zebra and, since they are rarely found in the meadows of Hungary, Dr Horvath plumped for studying an almost equally obnoxious alternative: the horsefly.

Horseflies, too, transmit disease. They also bite incessantly, thus keeping grazing beasts from their dinner. Indeed, previous research has shown that fly attacks on horses and cattle reduce their body fat and milk production. Such research has also shown something odd: horseflies attack black horses in preference to white ones. That fact got Dr Horvath wondering how they would react to a striped horse—in other words, a zebra.

Actual zebra are hard to experiment on. They insist on moving around and swishing their tails. The team therefore conducted their study using inanimate objects. Some were painted uniformly dark or uniformly light, and some had stripes of various widths. Some were plastic trays filled with salad oil (to trap any insect that landed). Some were glue-covered boards. And some were actual models of zebra. They put these objects in a field infested with horseflies and counted the number of insects they trapped.

Their first discovery was that stripes attracted fewer flies than solid, uniform colours. As intriguingly, though, they also found that the least attractive pattern of stripes was precisely those of the sort of width found on zebra hides. Zebra stripes do, therefore, seem to repel horseflies.

Exactly why is unclear. But Dr Horvath thinks it might be related to a horsefly’s ability to see polarised light, which imposes a sense of horizontal and vertical on an image. Horseflies are known to prefer horizontal polarised light. Possibly, the mostly vertical stripes on a zebra confuse the fly’s tiny brain and thus stop it seeing the animal.

Another obvious question, though, is why other species have not evolved this elegant form of fly repellent, and what the consequences would have been if they had. If humans, for example, were black-and-white striped then the history of intercommunal violence the species has suffered when different races have met might not have been quite as bad. One for Kipling to have pondered, perhaps?

Source: The Economist

DLR Institute of Aerodynamics and Flow Technology / DLR Institute of Aeroelasticity

Helicopters can deliver military troops or rescue the wounded in tight spaces, but their rotating blade design also puts a hard limit on their speed and maneuverability. Now researchers have begun flight-testing an unlikely fix inspired by the underwater ballet of humpback whales.

The potentially cheap solution uses small bumps along the front edge of the helicopter blades similar to bumps found on the large pectoral fins of humpback whales. Such bumps give an aerodynamic edge that delays the moment of “stalling” when there’s not enough lift to keep the whale from sinking — or a helicopter from stalling out at top speeds.

“Stalling is one of the most serious problems in helicopter aerodynamics — and one of the most complex,” said Kai Richter from the DLR Institute of Aerodynamics and Flow Technology in Germany.

Helicopters face a speed limit because their backward-moving rotor blade goes against their forward motion of flight. That problem leads to turbulence and loss of lift, as well as strong forces acting on the rotor, which eventually cause the helicopter to stall out.

German researchers patented the bump idea for helicopters, under the name “Leading-Edge Vortex Generators.” Wind tunnel experiments led to a test flight with a helicopter carrying 186 rubber bumps —each less than a quarter of an inch long — glued to its four rotor blades.

“The pilots have already noticed a difference in the behavior of the rotor blades,” Richter said. “The next step is a flight using special measuring equipment to accurately record the effects.”

If testing goes well, existing helicopters could get a speed boost with simple retrofits. New helicopters could have the design built into their titanium blades during manufacturing.

The natural bump design already helps humpback whales swim at speeds of up to 16.5 miles per hour, or about five times faster than the fastest human swimmer.

“Research has shown that these bumps cause stalling to occur significantly later underwater and increase buoyancy,” said Holger Mai from the DLR Institute of Aeroelasticity in Germany. “Flow phenomena in water are similar to those in air; they just need to be scaled accordingly.”

Source: Innovation News Daily

“Shrilk,” made from proteins found in crustacean and insect shells, is strong, stretchy, and fully biodegradable. It may be how you carry your groceries home in the future.

What if you could come back from the store, extract your haul, and throw your grocery bag in the garden to compost away? Scientists have created a sturdy, versatile, completely biodegradable alternative to plastic that could just make this crazy dream real. And it’s made from insect skeletons.

Javier Fernandez, a Spanish materials scientist, and his collaborators at the Wyss Institute, have created the material they’re calling “Shrilk,” which mimics the architecture of arthropod exoskeletons. Grasshoppers and other similar bugs have an exoskeleton that is strong enough to support their innards, but light enough to allow the insect to fly. Shrilk, made from the proteins in these natural materials, also adopts a similar duality: It has the strength of an aluminum alloy, but is half its weight. It’s also completely biodegradable.

Fernandez was experimenting with chitin—found in insect shells— for use in bio-compatible microelectronics. When he recreated the complete micro architecture of the shell, with proteins layered like plywood, the result was Shrilk: strong, light, supple, surprising. “We got mechanical properties that were completely crazy and very unexpected,” Fernandez tells Co.Exist.

Fernandez found that Shrilk’s elasticity changed from stretchy to stiff depending on how it was hydrated. And in addition to its spectacular strength and lightness, Shrilk biodegrades completely in a matter of months when in presence of moisture, breaking down into compounds that can be used as nitrogen fertilizer.

Shrilk is a shoe-in for use in medicine, Fernandez says. In the human body, the material has a lifetime of a few months. This makes it an excellent candidate for use in surgical sutures, or as a scaffold for regenerating tissues. Synthetic materials usually go through rigorous and lengthy tests before the FDA approves them for use in people. But, both the materials that form the Shrilk microstructure—chitosan and fibroin—are already individually approved.

Shrilk could also be sold as an eco-conscious stand-in for disposable plastics. If appropriately hydrated, its structure can vary from stretchy to stiff, so it could be used as either the shell of your cellphone or to replace the ubiquitous and wasteful grocery bags.

There are still several next steps that Fernandez and his colleagues must go through before Shrilk is ready to be manufactured commercially. But if it does hit the market, it would require a huge supply of the raw material that goes into it. Extracting the components from natural sources wouldn’t keep up. So, Fernandez and his team are researching ways to genetically engineer bacterial farms to mass-produce the necessary proteins. “If we want this to be realistic, we need to do the next step.”

Source: Co.Exist

Talented and dedicated engineers spent countless hours designing Japan’s rail system to be one of the world’s most efficient. Could have just asked a slime mold.

When presented with oat flakes arranged in the pattern of Japanese cities around Tokyo, brainless, single-celled slime molds construct networks of nutrient-channeling tubes that are strikingly similar to the layout of the Japanese rail system, researchers from Japan and England report Jan. 22 in Science. A new model based on the simple rules of the slime mold’s behavior may lead to the design of more efficient, adaptable networks, the team contends.

Every day, the rail network around Tokyo has to meet the demands of mass transport, ferrying millions of people between distant points quickly and reliably, notes study coauthor Mark Fricker of the University of Oxford. “In contrast, the slime mold has no central brain or indeed any awareness of the overall problem it is trying to solve, but manages to produce a structure with similar properties to the real rail network.”

The yellow slime mold Physarum polycephalum grows as a single cell that is big enough to be seen with the naked eye. When it encounters numerous food sources separated in space, the slime mold cell surrounds the food and creates tunnels to distribute the nutrients. In the experiment, researchers led by Toshiyuki Nakagaki, of Hokkaido University in Sapporo, Japan, placed oat flakes (a slime mold delicacy) in a pattern that mimicked the way cities are scattered around Tokyo, then set the slime mold loose.

Initially, the slime mold dispersed evenly around the oat flakes, exploring its new territory. But within hours, the slime mold began to refine its pattern, strengthening the tunnels between oat flakes while the other links gradually disappeared. After about a day, the slime mold had constructed a network of interconnected nutrient-ferrying tubes. Its design looked almost identical to that of the rail system surrounding Tokyo, with a larger number of strong, resilient tunnels connecting centrally located oats. “There is a remarkable degree of overlap between the two systems,” Fricker says.

The researchers then borrowed simple properties from the slime mold’s behavior to create a biology-inspired mathematical description of the network formation. Like the slime mold, the model first creates a fine mesh network that goes everywhere, and then continuously refines the network so that the tubes carrying the most cargo grow more robust and redundant tubes are pruned.

The behavior of the plasmodium “is really difficult to capture by words,” comments biochemist Wolfgang Marwan of Otto von Guericke University in Magdeburg, Germany. “You see they optimize themselves somehow, but how do you describe that?” The new research “provides a simple mathematical model for a complex biological phenomenon,” Marwan wrote in an article in the same issue of Science.

Fricker points out that such a malleable system may be useful for creating networks that need to change over time, such as short-range wireless systems of sensors that would provide early warnings of fire or flood. Because these sensors are destroyed when disaster strikes, the network needs to efficiently re-route information quickly. Decentralized, adaptable networks would also be important for soldiers in battlefields or swarms of robots exploring hazardous environments, Fricker says.

The new model may also help researchers answer biological questions, such as how blood vessels grow to support tumors, Fricker says. A tumor’s network of vessels start out as a dense, unstructured tangle, and then refine their connections to be more efficient.

Images: Science/AAAS

Source: Wired.com

We’ve all seen concentrated solar power (CSP) plants — those rows and rows of shiny mirror heliostats all crowded around a 100-metre-high pillar, like worshippers peering up at a towering god.

The orchestra of mirrors track the sun throughout the day, bouncing rays up at the central tower where the heat is concentrated, converted into electricity and piped into the national grid. Only a small handful of these plants — like PS10, in the Spanish desert region of Andalucia — exist around the world.

Their growth is restricted thanks to their sizeable footprints. “Concentrated solar thermal energy needs huge areas,” says Alexander Mitsos, the Rockwell International assistant professor of mechanical engineering, at the Massachusetts Institute of Technology.

“If we’re talking about going to 100 percent or even 10 percent renewables, we will need huge areas, so we better use them efficiently,” he explains.

Mitsos and colleagues have come up with a new design for CSPs that reduces the required amount of land while boosting the amount of sunlight the heliostat mirrors collect. In perhaps the most beautiful example of biomimicry yet, it’s inspired by sunflowers.

The researchers at MIT, in collaboration with RWTH Aachen University in Germany, looked at the layout of current CSP plants. They put spaces between the mirrors and staggered them like seats in a movie theatre. This pattern results in shadows being cast on some mirrors, reducing the reflection of light.

Mitsos’ lab developed a computational model to evaluate the efficiency of heliostat layouts — the system divides each mirror into discrete sections and accurately calculates the amount of light each section reflects at any given moment.

Mitsos and colleague Corey Noone used numerical optimisation to fiddle with the placement of the heliostats. They brought the fanned-out layout closer together, building a spiral-like pattern that reduces land by ten percent without affecting efficiency.

Next they looked to nature to improve the design further. The florets of a sunflower — small flowers at the centre of the petals, which mature into seeds — are arranged in a stunning spiral fashion that’s impressed mathematicians for years.

The arrangement — a form of Fermat spiral — has each floret turned at a “golden angle” - about 137 degrees - with respect to its neighbour.

The researchers twisted each mirror to be 137 degrees relative to its neighbour and it made a huge difference. The optimised layout takes up 20 percent less space than the current layout of the PS10 in Spain, and even increased total efficiency.

The researchers have published their results in the journal Solar Energy, and have recently filed for patent protection on the design.

Image: Kibbles/Flickr/CC-licensed

Source: Wired.co.uk

Scorpions may have lessons to teach aircraft designers

The north African desert scorpion, Androctonus australis, is a hardy creature. Most animals that live in deserts dig burrows to protect themselves from the sand-laden wind. Not Androctonus. It usually toughs things out at the surface. Yet when the sand whips by at speeds that would strip paint away from steel, the scorpion is able to scurry off without apparent damage. Han Zhiwu of Jilin University, in China, and his colleagues wondered why.

Their curiosity is not just academic. Aircraft engines and helicopter rotor-blades are constantly abraded by atmospheric dust, and a way of slowing down this abrasion would be welcome. Dr Han suspects that scorpions may provide an answer. As he writes in Langmuir, he has discovered that the surface of Androctonus’s exoskeleton is odd. And when that oddness is translated into other materials it seems to protect them, as well.

Dr Han’s investigations began by scouring the pet shops of Changchun, where the university is located, for scorpions. Having obtained his specimens, he photographed them under a microscope, using ultraviolet light. This made the animals’ exoskeletons, which are composed of a sugar-based polymer called chitin, fluoresce—thus revealing details of their surface features. The team found that Androctonus armour is covered with dome-shaped granules that are 10 microns high and between 25 and 80 microns across. These, they suspected, were the key to its insouciance in the face of sandstorms.

To check, they took further photographs. In particular, they used a laser scanning system to make a three-dimensional map of the armour and then plugged the result into a computer program that blasted the virtual armour with virtual sand grains at various angles of attack. This process revealed that the granules were disturbing the air flow near the skeleton’s surface in ways that appeared to be reducing the erosion rate. Their model suggested that if scorpion exoskeletons were smooth, they would experience almost twice the erosion rate that they actually do.

Having tried things out in a computer, the team then tried them for real. They placed samples of steel in a wind tunnel and fired grains of sand at them using compressed air. One piece of steel was smooth, but the others had grooves of different heights, widths and separations, inspired by scorpion exoskeleton, etched onto their surfaces. Each sample was exposed to the lab-generated sandstorm for five minutes and then weighed to find out how badly it had been eroded.

The upshot was that the pattern most resembling scorpion armour—with grooves that were 2mm apart, 5mm wide and 4mm high—proved best able to withstand the assault. Though not as good as the computer model suggested real scorpion geometry is, such grooving nevertheless cut erosion by a fifth, compared with a smooth steel surface. The lesson for aircraft makers, Dr Han suggests, is that a little surface irregularity might help to prolong the active lives of planes and helicopters, as well as those of scorpions.

Source: The Economist

Excerpt from the book “The Wisdom of Crowds” by James Surowiecki, one of the most interesting book I’ve ever read.
Strongly Suggested!

Imagine that you are French. You are walking along a busy pavement in Paris and another pedestrian is approaching from the opposite direction. A collision will occur unless you each move out of the other’s way. Which way do you step?

The answer is almost certainly to the right. Replay the same scene in many parts of Asia, however, and you would probably move to the left. It is not obvious why. There is no instruction to head in a specific direction (South Korea, where there is a campaign to get people to walk on the right, is an exception). There is no simple correlation with the side of the road on which people drive: Londoners funnel to the right on pavements, for example.

Instead, says Mehdi Moussaid of the Max Planck Institute in Berlin, this is a behaviour brought about by probabilities. If two opposing people guess each other’s intentions correctly, each moving to one side and allowing the other past, then they are likely to choose to move the same way the next time they need to avoid a collision. The probability of a successful manoeuvre increases as more and more people adopt a bias in one direction, until the tendency sticks. Whether it’s right or left does not matter; what does is that it is the unspoken will of the majority.

That is at odds with most people’s idea of being a pedestrian. More than any other way of getting around—such as being crushed into a train or stuck in a traffic jam—walking appears to offer freedom of choice. Reality is more complicated. Whether stepping aside to avoid a collision, following the person in front through a crowd or navigating busy streets, pedestrians are autonomous yet constrained by others. They are both highly mobile and very predictable. “These are particles with a will,” says Dirk Helbing of ETH Zurich, a technology-focused university.

Messrs Helbing and Moussaid are at the cutting edge of a youngish field: understanding and modelling how pedestrians behave. Its purpose is not mere curiosity. Understanding pedestrian flows makes crowd events safer: knowing about the propensity of different nationalities to step in different directions could, for instance, matter to organisers of an event such as a football World Cup, where fans from various countries mingle. The odds of collisions go up if they do not share a reflex to move to one side. In a packed crowd, that could slow down lots of people.

In 1995 Mr Helbing and Peter Molnar, both physicists, came up with a “social force” computer model that used insights from the way that particles in fluids and gases behave to describe pedestrian movement. The model assumed that people are attracted by some things, such as the destination they are heading for, and repelled by others, such as another pedestrian in their path. It proved its worth by predicting several self-organising effects among crowds that are visible in real life.

One is the propensity of dense crowds spontaneously to break into lanes that allow people to move more efficiently in opposing directions. Individuals do not have to negotiate their way through a series of encounters with oncoming people; they can just follow the person in front. That works better than trying to overtake. Research by Mr Moussaid suggests that the effect of one person trying to walk faster than the people around them in a dense crowd is to force an opposing lane of pedestrians to split in two, which has the effect of breaking up the lane next door, and so on. Everyone moves slower as a result.

Up close and personal

Another self-organising behaviour comes when opposing flows of people meet at a single intersection: think of parents trying to shepherd their children into school as other parents, their sprogs already dropped off, try to leave. As people stream through in one direction, the pressure on their side of the intersection drops. That gives those waiting on the other side more opportunity to go through, until pressure on their side is relieved. The result is a series of alternating bursts of traffic through the gates.

This oscillation in flows is clever enough to have got Mr Helbing wondering about its application to cars. Traffic-light systems currently operate on fixed cycles, with lights staying green on the basis of past traffic patterns. If those patterns are not repeated, drivers are left to idle their engines for too long at red signals, raising emissions and tempers. Mr Helbing thinks it is better to have decentralised, local systems, which—like parents at the school gates—can respond to a build-up of traffic and keep the lights on green for longer if need be. City authorities agree: Mr Helbing’s ideas will soon be implemented in Dresden and Zurich.

Trying to capture every element of pedestrian movement in an equation is horribly complex, however. One problem is allowing for cultural biases, such as whether people step to the left or the right, or their willingness to get close to fellow pedestrians. An experiment in 2009 tested the walking speeds of Germans and Indians by getting volunteers in each country to walk in single file around an elliptical, makeshift corridor of ropes and chairs. At low densities the speeds of each nationality are similar; but once the numbers increase, Indians walk faster than Germans. This won’t be news to anyone familiar with Munich and Mumbai, but Indians are just less bothered about bumping into other people.

Another problem with assuming people act like particles is that up to 70% of people in a crowd are actually in groups. That matters, as anyone trying to get past shuffling tourists knows. It also leads to some lovely fine-scale choreography when small groups are squeezed. Observations of pavement crowds in Toulouse in France show that clusters of three and four people naturally organise themselves into concave “V” and “U” shapes, with middle members falling back slightly. If a group of three people cared about moving quickly, they would behave like geese and form a convex “V”, with the middle member slightly in front to forge a path. Instead, they adopt a formation that enables them to keep communicating with each other; talking trumps walking.

Mr Moussaid’s solution to such complexity has been to build a model based less on the analogy between humans and particles and more on cognitive science. Agents in this new model are allowed to “see” what’s in front of them; they then try to carve a free path through the masses to get to their destination. This approach produces the same effects of lane-formation in crowds as the physics-based models, but with some added advantages.

In particular, boffins think it could help make emergency evacuations safer. Simulating evacuations is a big part of what pedestrian modellers do—the King’s Cross underground fire in London in 1987 gave the field one of its starting shoves. One big danger in an emergency is that people will follow the crowd and all herd towards a single exit. That in turn means that the crowd may jam as too many people try to force their way through a single doorway.

The physics-based models do have an answer to this problem of “arching” (so called for the shape of the crowd that builds up around the exit). Their simulations suggest the flow of pedestrians through a narrow doorway can be smoothed by plonking an obstacle such as a pillar just in front of the exit. In theory, that should have the effect of splitting people into more efficient lanes. In practice, however, the idea of putting a barrier in front of an emergency exit is too counter-intuitive for planners to have tried.

The cognitive-science model offers a more palatable option, that of experimenting with the effects of changes in people’s visual fields. Mr Moussaid speculates that adaptable lighting systems, which use darkness to repel people and light to attract them, could be used to direct them in emergencies, for example.

Where the cognitive approach falls down is in the most packed environments. “At low densities, behaviour is cognitive and strategic,” says Mr Moussaid. “At high density, it’s about mass movement and physical pressures.” At a certain point crowds can shift from a controlled flow to a stop-and-go pattern, as people are forced to shorten their stride length and occasionally halt to avoid collisions. This kind of movement can develop into something much more frightening, known as crowd turbulence, when people can no longer keep a space between themselves and others. The physical forces that are imparted from one body to another when that happens are both chaotic and powerful: if someone falls over, others will be unable to avoid them.

Science meets religion

Working out precisely how and when these transitions happen is tough. Bringing a real-life situation under control once a stop-and-go pattern has started is equally hard. So the trick is to ensure that serious crowding is avoided in the first place. From big events such as the London Olympics to the design of new railway stations, engineering firms now routinely simulate the movement of people to try to spot areas where crowding is likely to occur.

A typical project involves using off-the-shelf software programs to identify potential bottlenecks in a particular environment, such as a stadium or a Tube station. These models specify the entry and exit points at a location and then use “routing algorithms” that send people to their destinations. Even a one-off event like the Olympics has plenty of data on pedestrian movement to draw on, from past games to other set-piece gatherings such as, say, city-centre carnivals, which enable some basic assumptions about how people will flow.

Once potential points of congestion are identified, more sophisticated models can then be used to go down to a finer level of detail. This second stage allows planners to change architectural designs for new locations and identify when to intervene in existing ones. “There should be many fewer crowd disasters given what we now know and can simulate,” says Mr Helbing.

The biggest test possible of these tools and techniques is the haj, the annual pilgrimage to Mecca in Saudi Arabia that Muslims are expected to carry out at least once in their lives if they can. With as many as 3m pilgrims making the journey each year, the haj has a long history of crowd stampedes and deaths. Indeed, video footage of a haj stampede is used by lots of modellers to validate their simulations of crowd turbulence.

The Saudi authorities have brought in consultants in recent years, focusing in particular on the layout of the Jamarat Bridge, where pilgrims perform a ritual in which they throw stones at three pillars. By making the crossing one-way, and changing the shape of the pillars so that people can stone them from a number of locations, they have improved the bridge’s safety.

But according to Paul Townsend of Crowd Dynamics, a consultancy that has worked on the pilgrimage, the risks remain significant. He thinks that the use of gates that could be opened and shut would help to manage the flow. Yet the haj presents some very specific difficulties beyond its sheer scale. Part of the problem is not having a clear idea of how many pilgrims will turn up, which makes planning difficult. Another issue is the nature of the crowd.

“Pilgrims on the haj have the attitude that, if I die there it is God’s will,” says Mr Townsend. “There is a willingness to get more and more dense in the space.” Scientists can model many aspects of pedestrian behaviour, but religious fervour is a step too far.

Source: The Economist

Alistair Smith