Category: Jonathan Webb

Spitting fish adjust for distance when shooting

On By A.P.In BBC News, Current Biology, Jonathan Webb, Kebmodee, Peggy Gerullis, spitting fish, Stefan Schuster, University of BayreuthLeave a comment

archer fish
Footage captured by two high-speed cameras shows the fish’s ability in detail

The jets of water that archer fish use to shoot down prey are “tuned” to arrive with maximum impact over a range of distances, according to a study.

By Jonathan Webb
Science reporter, BBC News

High-speed cameras were used to analyse fishes’ spitting performance in detail.

As they create each jet, the fish tweak the flow of water over time, causing a focussed blob of water to gather just in front of the target, wherever it is.

The ability comes from precise changes to the animal’s mouth opening, which may prove useful in designing nozzles.

Senior author Prof Stefan Schuster, from the University of Bayreuth in Germany, explained that jets of water and other fluids are used to cut or shape materials in industries ranging from mining to medicine.

He believes his new fish-based findings could improve the technology.

Patience and precision
“I’ve never seen anything in which they use a nozzle that changes its diameter,” he told the BBC. “The most standard approach is adjusting the pressure.”

But pressure, which the archer fish apply by squeezing their gill covers together, is not the secret to their ballistic precision.

Prof Schuster and his PhD student Peggy Gerullis found no evidence for pressure adjustments, nor for chemical additives or flicking movements in the water, which might account for the fishes’ ability to control the stability of the water jet, and focus the accelerating blob at its tip.

“The fish add nothing – they only shoot water, and they keep absolutely still during release of the jet,” Prof Schuster said.

“They just do it with the mouth opening diameter. It is not a simple manoeuvre… The diameter is continuously changing.”

That makes the new study, published in Current Biology, the first evidence of an animal actively manipulating the dynamics of a water jet.

Prof Schuster and Ms Gerullis trained two archer fish to hit targets at distances from 20cm to 60cm, under bright lights to help with filming.

The targets were small spheres, which allowed the team to calculate the forces involved.

Accuracy, of course, was rewarded – usually with a small fly. “You can easily train a fish to shoot at anything you want,” said Prof Schuster. “They are perfectly happy as long as something edible falls down.”

The tricky part was organising the angles.

“To be ready to monitor to the right spots with reasonable spatial resolution, you have to convince the fish somehow to fire from a defined position. That was the hardest part of the study, actually.”

With patience, the researchers collected enough measurements to reveal that the all-important blob of water at the jet’s tip, which allows archer fish to dislodge their prey, forms just before impact – no matter the target distance.

To accomplish this, the animals fine-tune not just the speed, but the stability of the water jet.

“It means that the physics the fish is using is much more complicated than previously thought,” Prof Schuster explained.

Cognitive evolution?

Dynamic jet control must now be added to an already impressive list of this fish’s abilities.

Other research has explored questions ranging from how archer fish compensate for the distortion of their vision by the water surface, to how they learn to hit moving targets by copying their companions, to exactly how they produce a water jet that catches up on itself to form their distinctive, watery missile.

Prof Schuster believes that their spitting accuracy may have evolved in a similar way to human throwing, which some theorists argue sparked an accompanying expansion of our cognitive abilities.

His team has also done fieldwork in Thailand, where they observed that the fish hunt in daylight, when their insect targets are few and far between. So having a good range, and not missing, are a big advantage for survival.

That power and precision requires brain power.

“People have calculated that to double [throwing] range requires roughly an 8-fold increase in the number of neurons involved in throwing,” Prof Schuster said.

So are these fish evolving into the cleverest animals under water?

“I don’t think they will develop into humans. [But] they have many strange abilities that you wouldn’t expect from fish.

“Maybe we can show by looking more closely at the brain, that shooting might have played a similar, prominent role in driving these abilities, as it’s thought that throwing played in human evolution.

“That’s just a crazy idea of mine.”

http://www.bbc.com/news/science-environment-29046018

Thank to Kebmodee for bringing this to the attention of the It’s Interesting community.

Physicists discover a surprisingly straightforward way to turn light into matter

On By A.P.In Albert Einstein, Breit and Wheeler, Da Brayn, Einstein, hohlraum, Imperial College London, Jonathan Webb, Nature Photonics, Oliver Pike, photon, physics, Science, Sir Peter Knight, Steven RoseLeave a comment

By Jonathan Webb

The design, published in Nature Photonics, adapts technology used in fusion research.

Several locations could now enter a race to convert photons into positrons and electrons for the very first time.

This would prove an 80-year-old theory by Breit and Wheeler, who themselves thought physical proof was impossible.

Now, according to researchers from Imperial College London, that proof is within reach.

Prof Steven Rose and his PhD student, Oliver Pike, told the BBC it could happen within a year.

“With a good experimental team, it should be quite doable,” said Mr Pike.

If the experiment comes to fruition, it will be the final piece in a puzzle that began in 1905, when Einstein accounted for the photoelectric effect with his model of light as a particle.

Several other basic interactions between matter and light have been described and subsequently proved by experiment, including Dirac’s 1930 proposal that an electron and its antimatter counterpart, a positron, could be annihilated upon collision to produce two photons.

Breit and Wheeler’s theoretical prediction of the reverse – that two photons could crash together and produce matter (a positron and an electron) – has been difficult to observe.

“The reason this is very hard to see in the lab is that you need to throw an awful lot of photons together – because the probability of any two of them interconverting is very low,” Prof Rose explained.

His team proposes gathering that vast number of very high-energy photons by firing an intense beam of gamma-rays into a further cloud of photons, created within a tiny, gold-lined cylinder.

That cylinder is called a “hohlraum”, German for “hollow space”, because it contains a vacuum, and it is usually used in nuclear fusion research. The cloud of photons inside it is made from extraordinarily intense X-rays and is about as hot as the Sun.

Hitting this very dense cloud of photons with the powerful gamma-ray beam raises the probability of collisions that will make matter – and history.

“It’s pretty amazing really,” said Mr Pike. He says it took some time to realise the value of the scheme, which he and two colleagues initially jotted down on scrap paper over several cups of coffee.

“For the first 12 hours or so, we didn’t quite appreciate its magnitude.”

But their subsequent calculations showed that the design, theoretically at least, has more than enough power to crack the challenge set by Breit and Wheeler in the 1930s.

“All the ingredients are there,” agrees Sir Peter Knight, an emeritus professor at Imperial College who was not involved in the research but describes it as a “really clever idea”.

“I think people will seriously start to have a crack at this,” Prof Knight told BBC News, though he cautioned that there were a lot of things to get right when putting the design into practice.

“If it’s done in a year, then they’ve done bloody well! I think it might take a bit longer.”

Some healthy scientific competition may speed up the process.

There are at least three facilities with the necessary equipment to test out the new proposal, including the Atomic Weapons Establishment in Oldham.

“The race to carry out and complete the experiment is on,” said Mr Pike.

http://www.bbc.com/news/science-environment-27470034

Thanks to Da Brayn for bringing this to the attention of the It’s Interesting community.