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Keys to a split-second slime attack

first_imgThe velvet worm is a slow-moving, unassuming creature. With its soft body, probing antennae, and jointless legs, it looks like a slug on stilts as it creeps along damp logs in tropical climates.But it has a secret weapon. In the dark of night, when an unsuspecting cricket or termite crosses its path, the worm unleashes an instantaneous torrent of slime. Two fine jets of gluey substance spray out of openings on it head, casting a sticky net that entraps prey.Captivated, so to speak, by the worm’s split-second attack, researchers from the Harvard School of Engineering and Applied Sciences (SEAS) and from universities in Chile, Costa Rica, and Brazil began studying the creature from all angles. How, they wondered, could such a slow, neurologically simple worm execute such a rapid and perfectly aimed movement?By applying insights from anatomy, mathematics, experimental physics, and fluid dynamics, they now have an answer — published Tuesday in Nature Communications — and the findings could inspire new microfluidic devices.Imagine a large syringe equipped, at its narrow tip, with an elastic tube shaped like the neck of a bendy drinking straw. That is apparently the velvet worm’s slime-shooting apparatus, from its tail end — where the slime is produced and stored in a reservoir — to a pair of tiny nozzles, called papillae, on its head. Given this structure, a slow and gentle squeeze on the reservoir is all it takes to eject the slime with great speed and force. Most important, the shape and elasticity of the papillae ensure that as the slime exits, it sprays in all directions, like water from a flailing hose. Researchers are studying the velvet worm’s secret weapon – its ability to shoot two fine jets of gluey substance out of openings on it head, casting a sticky net that entraps prey instantly. Source: Cristiano Sampaio-Costa, Bernal Morera-Brenes, Julian Monge-Najera, Andres Concha “The geometry of the system allows the worm to squirt fast and cover a wide area. That’s the magic,” said lead author Andrés Concha, formerly a postdoctoral fellow at SEAS and now an assistant professor at Adolfo Ibañez University in Chile.But that’s not the whole story, as Concha explained. A garden hose is much larger than the tube inside a velvet worm’s papillae. To get the flailing-hose effect within such minuscule passages, with a diameter ranging from 50 to 200 microns, the worm relies on the elasticity and corrugated shape of its papillae. These features lower the threshold for tube-shaking fluid velocity.By identifying the features of the anatomy and material structure that enable the velvet worm to produce wide-spraying jets, the researchers have characterized a new type of flexible microfluidic system that they said could be used to produce fine droplets of liquid or fibrous nets, or to mix together several substances in laboratory or industrial settings.Concha and co-author Paula Mellado (also an assistant professor at Adolfo Ibañez University) were both Kavli Scholars at SEAS, studying topics relating to fluid dynamics, when the velvet worm project launched.“After watching the David Attenborough film ‘Life in the Undergrowth’ with some high-speed footage of the worm’s slime jet, I suggested that an elastic-hydrodynamic instability of the nozzle could be a simpler solution to creating a chaotic jet, rather than muscle control,” said co-author L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics at SEAS and a professor of organismic and evolutionary biology and of physics in the Faculty of Arts and Sciences. “Our work shows that this is indeed the case, and chalks up one more example of how evolution has co-opted a simple physical principle for a behavioral response.”The unusual velvet worms present a host of new questions for future research.“There are many cool properties of the glue that we need to explore,” Concha said. “If you put your fingers close to the mouth of the worm and you get some glue on your fingers, you wait seven seconds and you’re stuck. So one ambition is to be able to generate a synthetic glue like that, with biotechnological applications. I think there is some chemistry that we have to learn from the worm.”The diversity of the velvet worms, which make up the genus Onychophora, poses the question of how the squirting mechanism evolved to work across great variation in size.“That’s a great biological question,” Concha said. “By experience, we know that it works for all of these worms. Now, how they adapt the materials and the inner diameter of the hole inside the papillae, I don’t know. It’s very impressive. Even for babies, it works. You have a gigantic worm that’s eight or nine inches long and the baby is one inch, and already the mechanism is working.”While squirting mechanisms are common among animals, anything other than a straightforward arc of liquid typically requires an active movement and some degree of control. The range of approaches to that problem within the animal kingdom requires continued research.“Archer fish throw a jet of water, and it just follows a parabolic trajectory. Spitting cobras actively move their head to spray the poor fellow who is in front. And there are other cases — for example, spitting spiders — where the mechanism is unclear,” Concha said.As it happens, such apt, if venomous, study subjects are close to home in Chile.“Some biologists have posed the question, is this elasticity or is there any active mechanism? From what is in the literature up to now, I don’t have an answer, so spitting spiders are a nice thing to look forward to.”last_img read more

Arsenal target Luis Enrique confirms he received an offer from ‘foreign club’

first_img Metro Sport ReporterWednesday 27 Nov 2019 11:56 amShare this article via facebookShare this article via twitterShare this article via messengerShare this with Share this article via emailShare this article via flipboardCopy link672Shares Advertisement Comment Luis Enrique was reportedly approached by Arsenal prior to their recent defeat against Leicester (Picture: Getty)Luis Enrique confirmed he was sounded out by a ‘foreign club’ before his reappointment as Spain’s national team head coach.The 49-year-old took over as Spain coach in July 2018 but left 11 months later for personal reasons as his nine-year-old daughter Xana passed away from osteosarcoma – a form of bone cancer – in August.The former Barcelona manager was reportedly on Arsenal’s initial shortlist when the Gunners were looking to replace Arsene Wenger in 2018, before the club’s then chief executive Ivan Gazidis appointed Unai Emery.The former PSG boss is under mounting pressure to save his job following a disastrous start to the new season with El Confidencial having reported that Enrique was approached by Arsenal’s head of football, Raul Sanllehi, prior to the 2-0 defeat at Leicester earlier this month.AdvertisementAdvertisementADVERTISEMENTEnrique appeared at a press conference on Wednesday for the first time since returning to national team duties and revealed: ‘Yes, I received a call from a foreign club, although it did not materialise.’More: Arsenal FCArsenal flop Denis Suarez delivers verdict on Thomas Partey and Lucas Torreira movesThomas Partey debut? Ian Wright picks his Arsenal starting XI vs Manchester CityArsene Wenger explains why Mikel Arteta is ‘lucky’ to be managing ArsenalEmery was forced to hold an emergency meeting with club chiefs Edu and Sanllehi in the tunnel area following the loss of two points against Southampton, a side placed 19th in the table, on Saturday and has subsequently been given four games to save his job.Goal, however, reports that club staff believe it is only a matter of time before the former PSG coach is given his marching orders with Freddie Ljungberg primed to take over in the short-term, at least. Wolves boss Nuno Espirito Santo is the latest name in the frame for Emery’s job, while the likes of Max Allergri and Mikel Arteta are also under consideration. Nuno Espirito Santo has been linked with the Arsenal manager’s job (Picture: Getty)Arsenal face Eintracht Frankfurt on Thursday in the Europa Leauge knowing a draw will be good enough to see them progress to the knockout stages.Emery, however, is likely to be without Hector Bellerin, who has sustained a slight hamstring injury, while Sead Kolasinac is also a doubt.MORE: Pierre-Emerick Aubameyang refusing Arsenal offer due to Unai Emery uncertaintyMORE: Paul Merson begs Arsenal board to appoint Mauricio Pochettino Arsenal target Luis Enrique confirms he received an offer from ‘foreign club’ Advertisementlast_img read more

Duff doesn’t take weight criticism lightly

first_imgTeen starlet Hilary Duff claims she’s never had a problem with her weight, but feels pressure to be thin. The 19-year-old actress and singer told People Magazine that she’s either perceived as too fat or too thin in the media, which she says can be “judgmental and mean.” “And if you don’t like the way you look, or feel insecure when people say things about you — in magazines or just in everyday life — they can be hurtful. … But you’ll never make them happy,” she told the magazine. Duff, who has sold more than 13 million albums worldwide, has a new album out this week called “Dignity.” Several of the songs are about her relationship with her ex-boyfriend, Good Charlotte singer Joel Madden, but she denies that she slammed his new newest flame, Nicole Richie, in her tune “Gypsy Woman.” And anyway, she told People she doesn’t like to discuss relationships. “It’s not my job to talk about my relationship,” she said. ” … But the more you try to keep it quiet, the more people want to know about it.” 160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set!last_img read more