Naked Science Q&A Show

It is often said that we have seen more of the surface of Mars than we have of our own planet. This is because 2/3 of our planet is covered with ocean, which is opaque to most of the forms of light we use to find out so much about the land with. You can send probes down to visit the bottom of the ocean but this requires a hugely expensive ship on the surface to power them and move them around.

A thermal glider surfacing. The Tubes underneath contain the © Webb Research

Various groups have come up with a way of moving autonomous robots around the oceans powered by the water itself. If you throw a paper aeroplane, it falls down, but because of its aerodynamic shape it doesn't fall vertically it glides down following a diagonal course powered by its potential energy. You can do the same thing in the ocean so if you sink 4km you can glide up to 20km forwards, you then have to stop as you have reached the bottom of the ocean, unless you can make yourself buoyant again, as you can then glide another 20km upwards, you can then work out where you are using GPS and communicate with your base station then, loose some buoyancy and sink again.

The problem is that you need energy to gain and loose the buoyancy required to float and sink which uses up power in your batteries. A company called Webb research has harnessed the difference in temperature at the top and bottom of the ocean to provide this energy and so power the glider.

Inside the glider they have tubes of wax which when it heats up near the surface expands compressing gas which is stored in a tank. The glider then allows oil to flow from a bladder outside into the body, reducing the glider's volume, making it sink. When it reaches a pre-set depth the compressed gas is used to push the oil back out again making the glider float back up to the surface.

The the thermal glider surfaced, where it could be communicating by satellite with its controllers. © Webb Research	A Slocum thermal glider gliding upwards © Webb Research

The glider can also extract some electrical energy from this temperature difference by using peltier coolers in reverse so the test vehicle has so far travelled 1400km across the Virgin Islands Baisin in the West Indies, sinking and floating at least 20 times, moving at between 1 and 2 kph with no interference from outside.

In theory this vehicle should have a range of 40000km and only have to be picked up every 6 months or so giving us an unprecedented view of what is going on in the oceans.

A biodegradable polymer made with green solvents can mend broken thigh bones in mice, UK researchers have shown.

The sponge-like polylactic acid scaffold was coated with vascular endothelial growth factor protein and seeded with human bone marrow cells to mimic the biological factors that stimulate natural bone regrowth. After slowly delivering its contents, the polymer is metabolised by the body leaving no trace.

The breakthrough means the innovative polymer is a step closer to being used in hospitals. According to Richard Oreffo of Southampton University, who works on the team, human trials could be less than 5 years away.

Many researchers are working on similar systems because they promise to avoid the problems of harvesting bone grafts from patients and donors. But a key difficulty is how to make a polymer that's holey and sponge-like, but which also encapsulates a highly expensive and delicate protein or drug inside.

The solution Howdle's team has been developing over the last decade is to use supercritical carbon dioxide - a solvent with properties midway between those of a gas and a liquid. Formed under pressure, the supercritical fluid melts the polymer and allows any delicate protein to be mixed into it just above body temperature. When the pressure is released, carbon dioxide gas foams up this mixture, automatically forming the porous scaffold ready-coated with active drug or protein.

Chris - We're now going to be joined by Professor Max Donelan. He's a researcher at Simon Fraser University in Canada and he's found a way to turn people into the human equivalent of a Hybrid car. Max, tell us a little bit more. How does this work?

Max - What we've done is take advantage of the inherent uneconomical nature of walking. So, as you mentioned, we can take advantage of walking like a hybrid car takes advantage of stop and go driving. That is, within the walking stride the muscles are first accelerating and then decelerating the body. A hybrid car takes advantage of the decelerating, braking by using a generator to brake rather than a traditional brake which just dissipates as heat. The generator produces electricity which we can then use in a productive way. We've done a similar thing for walking where we've tried to use generators help the muscles slow the legs down. In doing so the generator can assist the muscles and it also creates electricity at the same time.

Chris - It sounds a bit counter-intuitive to think that your legs would be so inefficient, that they need help in slowing down and that you can actually get useful energy out of this.

Max - Yes, I think it is a little counter intuitive but the main point: if you think about walking at a constant speed on the level then there's no net change in your mechanical energy so on average you're not moving any faster or any slower. You're not going uphill and downhill so that means for every little bit of energy that your muscles put in, something also has to take it away. It's mostly your muscles that take it away. You don't need them to do it, you could use something like a generator instead. The generator can take the mechanical energy away from the body and put it through the generator and produce electricity at the same time.

Chris - So in other words, as your leg's swinging to return to the starting position so you can take the next step you would normally need a muscle to kick in and stop the leg from moving at that point. Your generator exploits that effect and instead of the muscle doing that work you're diverting that effort through your generator and it recovers the energy the body would otherwise have to expend.

Max - That's exactly right. So where we do it is at the knee and towards the end of the swing phase - so when you're moving your foot forwards to begin another step. Your hamstring muscles, which are the muscles down the back of your leg, they turn on to slow down your knee extension. Our device mounts at the knee that generator engages at that period and helps those hamstring muscles in slowing down the extension of the knee. We can measure this through the fact that when we use the generator it actually allows those muscles to turn down by about 15%. The muscle activity decreases.

Chris - The difference in the energy expenditure is what you're generating with your device.

Max - The idea is that people don't have a difference in energy expenditure, so generating electricity or not generating it is about the same effort you put in, but you still get the electricity out. So you're getting 5W of electricity without increasing their effort by a meaningful amount.

Chris - So what does this device look like when it's in situ on a person? Is it very ungainly, is it going to get in the way?

Max - In the current version I would say it is a bit ungainly so it looks like a normal orthopaedic knee brace with a chassis mounted to the side of it. It's a bit bulky and a bit big but that's because it's really designed for convenient experimentation so you can pull gears out and generators out. The final version will be less than a kilogram and it will easily sit underneath a pair of pants. Currently too big but no problem getting it smaller.

Chris - When someone's wearing this thing how much energy physically are they able to produce with it?

Max - There's two modes. One mode gives 5W of electric and for context 5W is enough to charge ten mobile phones at the same time or to produce ten minutes of call time for one minute of walking. That's not to say I think we're going to charge mobile phones in the near future but it gives you some context of how much power.

Chris - I'm not being flippant, Max, if I want to charge my mobile phone I plug it in. So why would I want this?

马克斯,我认为你是绝对正确的. For us plugging in a mobile phone is just a matter of convenience, but for many people their lives depend upon resources for power. Consider for example if you had a powered prosthetic leg or a power device that helped you walk every stroke for you it's not always as simple as plugging it in. For example, some of these prosthetic legs might run out of power within four hours or so. If you can use your healthy leg to generate some electricity to power your artificial leg then you can walk farther.

Dave - I was wondering whether you could put it into a mode so that when you're walking downhill or down a big mountain you can make it absorb lots and lots of energy. I find that very, very uncomfortable when walking out in mountains.

Max - That's a great question so, you've hit on it exactly. Walking downhill, there's a lot more energy available because essentially what your muscles are doing is making sure that you don't arrive at the bottom at the speed that gravity wants you to. They're taking the potential energy you had at the top of the hill and your muscles are dissipating it all as heat so you walk down it in a controlled way. If you can use a generator to do that instead you can produce lots and lots of electricity. We find that if you walk down a hill you produce more electricity or if you walk faster.

Chris - Thank you very much, Max.

It's not really a question of the animal knowing what to evolve into but this is a really beautiful example of evolution in action: mimicking the surroundings so animals are well-hidden and protected from predators. A particular species of seahorse will find a good bit of seaweed to actually hide amongst and gather food in a really nice place for it to live. As the seahorses breed and as new generations of seahorses are born small genetic mutations will change their appearance and change certain things about them. As their appearance changes you might get a mutation that makes them a slightly different colour that's similar to the seaweed, for example. A seahorse that's a very similar colour to the surrounding seaweed would be better protected because it would be camouflaged much better so hidden from predators. More of those colours, of course, would survive so eventually all of the seahorses would eventually resemble the habitat in which they live.

Other animals have evolved other ways to disguise themselves - with some disguises making them look poisonous, to put predators off.

The thing that's going on when you blow on your hand is you tend to blow on it from far away. Especially if you're blowing with pursed lips. If you breathe slowly, especially if you're close, then all the air to your hand is the nice warm air from your lungs. When you're blowing on them with pursed lips, partly it's going to be further away so the air will be cooled down a bit more. Also, as you're farther away it will tend to catch cold air from the surroundings and drag that along with it. You're not just blowing along through your lips there's also a load of cold air mixed in. Also, the faster the air's moving the more you'll tend to evaporate moisture from your skin which will cool you down as well. I think if you're blowing with a big fan very close to your windscreen which is the way it works the higher the fan is the more it will defrost your window.

Roy was referring to this news story about an underwater thermal glider. Designed to take advantage of changes in temperature to glide long distances collecting information about the sea bed.

You couldn't have a person in this type of glider because of the amount of energy you need to keep the person going; you need to keep them warm and give them oxygen. It would be far more than the energy you could generate. So you'd have little, tiny computer-controlled things which can just travel through the ocean all over the place. In fact the biggest limitation on it is the amount of power it can use because it can't generate very much. You need to have not very power-hungry sensors.

Chris - Time to catch up with the editor of Chemistry world. That's Mark Peplow. Hello Mark.

Mark - Hello Chris.

Chris - 3D television, sounds fantastic, even on the radio!

Mark - It does sound fantastic. It's not quite around the corner but the first major step has been taken towards it. We're all used to this idea of being able to have a hologram where you can effectively get this image which gives you the illusion of three dimensions. You can look around this object. A group of scientists from the University of Arizona have now managed to make that hologram and then found away to erase and rewrite it with a new image. In theory if you can do that frequently enough you can actually get a moving three dimensional film. The way that they do this relies on a special type of polymer. What happens when you're taking a holographic image, laser beams bounce off this object from different angles. Where they bounce back and recombine they hit this light sensitive polymer and it stores the 3D signal in a complex pattern of interference. They've tweaked the polymer that they use with a special dye molecule and found that as long as they put an electric field across it, it means that the dye molecules are shifted, rotated if you like when the laser light hits them. That means that it takes them about three minutes to draw a full image and then another blast of full laser light resets the molecules ready for the next image to be written.

Chris - Three minutes, that's not a very fast frame rate if I'm honest.

马克,我知道。我猜这关键之处s is that it's a proof of principal that it can be done at all. We talked to a hologram chemistry expert called Kevin Davidson who's at the University of Cambridge here. He pointed out that there's a lot of work gone on in this area but no one's really demonstrated this ability to do this so reliably and at least repeat time after time.

Chris - So it's gonna be a little while before we can play a game of chess like they do on Star Wars with those kind of figures that act it out on the board for us.

Mark - Yes, absolutely, although that would be cool, wouldn't it.

Chris - I can't wait for those days actually. What's this about biofuels and carbon debts?

Mark - Yeah, biofuels have been getting a rough ride lately. The Royal Society which is Britain's major academy of sciences has put out some major warnings recently. About policy makers rushing too quickly to adopt new biofuel policies. The idea is that rather than burning petrol which we get from oil out of the ground it would be better to get fuel for the car from plants. Plants grow by sucking carbon dioxide out of the atmosphere and we're trying to reduce the amount of carbon dioxide we're putting out to reduce the rate of global warming.

Chris - That's good isn't it? You want the plants to take the CO2 out of the atmosphere and turn them into fuel so there's no net carbon gain. Why should there be a problem with that?

Mark - Absolutely. The devil is in the detail as with all of these things. As people have started to grow more and more biofuels, a good example is sugar cane in Brazil where they turn that into fuel for cars (ethanol), people are doing what's called lifecycle analysis. They're basically looking at all of the energy that you need to put in to make these fuels and also look at all of the carbon that comes out when you're making these fuels. The latest pair of studies which was just published in Science magazine on Friday really paints a very damning picture. Effectively when you cultivate land to grow any biofuel you rack up this carbon debt. You're releasing so much carbon that was trapped in the soil that it can take sometimes centuries to regain and repay that carbon debt through the advantages of using biofuels.

Chris - So the moral of this story is there's no quick fix, is there?

Mark - Absolutely. It's interesting because people usually talk about the Brazilian example of using sugar cane as probably the best biofuel to use. They've found it still took 17 years to repay the carbon taken from when, for example, a random tract of savannah was ploughed up to plant that stuff.

Chris - So there's lots and lots of things to consider rather than just the here and now. What's this about reading the genetic code directly because this sounds amazing!

Mark - Yeah. This sounds like really Star Trek stuff and it's really exciting actually. We're all used to this idea of DNA fingerprinting. This relies on a chemical reaction called the polymerase chain reaction. What that means is you have this smear of blood that you find in CSI, there will be millions and millions of molecules of DNA in there but still not enough to get an exact chemical read on the data that's recorded in that DNA. You have to do this reaction that amplifies the DNA sample by multiplying the molecules over and over again in the sample until you've got enough to do a proper analysis.

现在,这需要一个实验室,它需要时间can introduce errors. A group in Dortmund in Germany have found a way. They've proved a principal that they can read a single molecule of not DNA but its chemical cousin RNA using a device which is a special combination, basically, of two different techniques. What it looks like, really is a tiny, tiny record player needle where the tip of it is just 20nm across. It's hooked up to a laser. What happens is that the tip reads along the length of a single molecule of RNA and guides the laser as it goes. The laser will illuminate the section of the molecule and the light that comes back carries the characteristic signature of the chemical bases as they're called which holds the data in RNA. They've proved that although the laser blast will illuminate maybe half a dozen bases at once because the tip moves along it one base at a time. They can literally read along and show that as they move this tip along they can read each base as it comes along. At the moment this requires some big bits of kit and it's pretty time consuming but it shows that you can read this single molecule of genetic code. Because of the advances that have come along in these techniques it means that over the coming years it should get faster, cheaper and easier.

Chris - It's amazing to think how far we've come because you say it's big and bulky but then so was the polymerase chain reaction when we first started. Thank you for coming in, Mark.

We put this question to Dr Mark Briffa, Lecturer in Marine Biology at the University of Plymouth:

首先,一条电鳗不是一个真正的鳗鱼。It's a member of a family of fish called gymnotids or knife fish and the scientific name is rather aptly, Electrophorus electricus. In most animals electric currents are used in nerves to carry information and to control muscle movements. What makes fish like electric eels special is that they can exploit this property of muscle tissue and discharge bursts of electric current into the surrounding water. They do this using an electric organ made out of modified muscle tissue in the tail.If electric eels can generate these strong discharges, what stops them electrocuting themselves? First of all the electric organs are in the flank of their tail and this means that the discharge occurs straight into the water rather than the eels internal organs. Since water is more conductive than body tissue the charge travels away from the eels. The second possibility, and that's that because the discharge is very quick the current doesn't flow for long enough to shock an animal as large as an electric eel. But for its prey which are usually smaller fish the short burst is enough to shock and stun or sometimes even kill them. So electric eels are unlikely to cause a damaging electric shock to humans but it's still not going to be a very pleasant experience to be on the receiving end of one and an impressive 2m long pet electric eel probably isn't a very good idea. It's quite difficult to work out how far the discharge will travel but prey being stunned or killed up to a distance of 2m away from the eel has been reported.We also received this from Dr Carl Hopkins, Cornell University:Electric eels generate electricity in much the same way that every nerve and muscle cell in an animal's body does, by establishing a weak voltage across the cell membrane. In fact, the electric organ is believed to be derived from muscle cells, which over the course of evolution, have lost their ability to contract as muscle, but retain their ability to produce electric currents. The big change during the evolution of the electric organs of fishes is the fact that the weak signals present in individual cells add up in series, like batteries put end to end in series in your flashlight. In addition the time of the discharge is precisely synchronized so that the short pulses occur at exactly the same time - a necessity if the voltages are to add.In order for an animal cell (or any cell, for that matter) to generate an electrical current, it must first use energy from food and metabolism to pump charged potassium and sodium ions across cell membranes so that potassium is high in concentration in the interior of the cell and sodium is concentrated outside the cell. Once the concentration gradient is established, for both of these ion species, the next requirement is that there be a "pore" in the membrane that allows possitively charged ions to go through without letting negative ions through. In animal cells, the membrane is permeable to potassium but not sodium and not negatively charged ions like chloride. Potassium ions start to diffuse out through the membrane and this establishes a voltage across the cell membrane (about 80 millivolts negative on the inside). This is the so-called resting potential. Then, when the electric organ is activated by nerve impulses, sodium ion channels open in the membrane to allow sodium to flow into the cell, changing the membrane voltage from -70 millivolts (mV) to about + 50 mV, a change of 120 mV. This is a transient event lasting only 1 millisecond or so. Since all of the cells in the electric organ discharge synchronously, their voltages add up to produce a substantial signal in the water. This is the electric discharge.To get the weak 130 millivolts discharge large enough to do anything outside the animal, the electric fish arranges the cells like a series of poker chips in a pile -- then the 130 mV signal across each cell adds to the next one. With the electric eel where there may be 5,000 cells arranged in series, the voltage will be 5000 x .130 Volts = 650 Volts. The cells are also arranged in parallel, which increases the ability to generate current in the water.Nobody knows exactly how the electric eel keeps from shocking itself, but the best working hypothesis is that the vital organs like the brain and the heart are located as far as possible from the electric organ (up near the head), surrounded by fatty tissue that acts as an insulator. In cross section through the tail, the electric eel is nearly entirely electric organ.

First of all 99% of the world just has 2 tides a day and the reason for that is basically the moon and the sun pull on the Earth and on the water around it. If you're close to something massive it's got a stronger attraction due to gravity than something farther away. Water on the side of the Earth closest to the moon is going to get pulled the hardest and the Earth which is in the middle is doing to get pulled slightly less hard and the water on the far side is going to get pulled even less hard. So you tend to get two bulges of water: one is the bulge of water close to the moon and the other bulge of water on the other side which is getting left behind. That's the reason why most places get 2 tides a day.

Some places get 4 - the only place I know about it is Southampton, Portsmouth in the UK by the Isle of Wight. If you look very closely at the map of the Isle of Wight it has funnels on each side of the channel just north of it. As the water rushes up the channel it sort of piles into these funnels and then as it gets narrower the wave gets higher. You actually get a high tide as the water rushes up. You get another one on the other funnel as the water rushes back down the channel so you get twice as many tides as you should have.