Superconductivity and Cooling Devices

29 October 2006
Presented by Chris Smith, Kat Arney.

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This week we take a look at some super cool science, as Tim Jackson describes how superconductors work, what they are, and how superconductors are helping astronomers get a clearer view of the universe. Also on the show, Ed Tarte discusses applications of superconductors and SQUIDS in the non-invasive discovery of heart defects and observing brain activity in the unborn foetus, and Science Graduate of the Year Alex Mischenko talks about his new environmentally friendly cooling device. In Kitchen Science, Derek Thorne and Ted Forgan show superconductivity in action with a frying pan, some liquid nitrogen and a very strong magnet...

In this episode

Record Breaking Whales

How deep do you think a human has ever dived down to without a scuba tank, but just holding their breath? Well, the unofficial world record holder is Patrick Musimu, who plummeted to over 200m last year - you can watch what is apparently his record dive on You Tube on the internet. But anyway, that is nothing compared to a far superior diving mammal which has recently been announced as the new world record breaking deep diver. Cuvier's beaked whales have now been recorded as diving down to nearly 2000 metres - around 6230 feet or well over a mile. That's according to a study published by an international team of scientists lead by Dr. Peter Tyack of Woods Hole Oceanographic Institution in the United States. The team attached non-invasive digital archival tags or D-tags developed at Woods Hole to 7 cuviers beaked whales and 3 blainville's beaked whales in waters off Italy and the Canary Islands. The tags are about the size of a flip flop, and they carry a variety of underwater sensors to record sounds, depth and movements - and they are attached to the whales with four small suction cups using handheld poles when the whales visit the sea surface. The D tags are programmed to fall off the whale a day later and float on the surface where radio beacons let the researchers know where they are. The information these tags collected showed that that the Cuviers beaked whales not only achieved the deepest ever recorded dives but perhaps more importantly, on average they spent more time in greater depths than any other animals, beating the better known sperm whales and elephants seals. And what are they doing all the way down there in that dark cold water? Well, feeding of course. The D tags picked up the buzzes and clicks of the whales sonar as they hunted for prey.

One of the mysterious things the team found, was that the whales come up to the surface from these very deep dives more slowly than they do from shallow dives - now this is just what human scuba divers must do to avoid getting decompression sickness or the bends, which is when nitrogen gas that's dissolved in the blood under great pressure comes bubbling out - a bit like opening a can of fizzy drink. But for the whales it should make no difference how quickly they come up once they've gone below 100m because at that point they are under so much pressure that their lungs have collapsed and there is no more gas left in them to dissolve into the blood and so they are at no greater risk of getting the bends. And it seems that even thought these whales are serious extreme divers, this probably doesn't put them at any greater risk of being affected by underwater sonar - something that is of great concern for the survival of whales around the world. The beaked whales have been seen in mass strandings on beaches in areas where military sonar was being used - and now it's thought that the sonar may be causing these whales to make repeated shallower dives down to around 50m which would increase their risk of getting the bends.

A Peck on The Cheek? Not From One of These...

US fossil hunters have uncovered the largest bird skull ever found, and at 76cm long and belonging to a carnivore that stood three metres high, this is one bird from whom you wouldn't want a peck on the lips! Appropriately known as "terror birds" and resembling a very large secretary bird (which have an eagle's body on long crane-like legs) they were flightless, but fast runners. They lived in Patagonia until about 2 million years ago, were meat eaters, and first evolved shortly after the demise of the dinosaurs, about 65 million years ago. This enormous skull specimen is described in this week's edition of the journal Nature by Luis Chiappe and his colleagues. In their paper the researchers point out that whilst many smaller variants of these animals had been discovered prior to now, there are significant anatomical differences between this giant and the smaller species. As a result, previous attempts to reconstruct what these large birds would have looked like based on their smaller relatives, are quite wrong, and now the text books need updating!

Buckingham Palace

- Dr Chris Meets The Queen

What attracts mosquitoes, tracking marine animals at sea, and Mars Express: Chris Smith goes to Buckingham Palace for a special evening of science...

Dr Chris Meets The Queen
with John Pickett, Rothamsted Research, Ian Boyd, University of St. Andrews, and John Murray, The Open University

This week was very exciting because Dr Chris Smith was invited to Buckingham Palace to meet the Queen!

It was part of a special Science Day being hosted at the Palace to show young people how exciting science can be and why British scientists are amongst the world's best. During the day 500 pupils came from schools and colleges right across the country to see first a fun science show, and then to chat with some of the UK's top scientists about the work that they do. And then, in the evening, the queen, together with Prince Philip and some other members of the royal family, held a special reception in the Buckingham Palace ballroom, for some of the country's scientists to chat with each other, and also to enjoy some extremely nice champagne.

One of the first people I chatted to with was Rothamsted Research's Professor John Pickett. And he's been working on the problem of why some people taste just too good, at least for a mosquito… Because he and his team have found that those of us who are ignored by mosquitoes produce a certain cocktail of volatile on our skin, which keep biting insects at bay - and now he's tracked down what those chemicals are.

John - I suppose many people will know that mosquitoes show a sort of preference for some individuals and not others, and what we've really done is investigated why that is. What we've found is that people who aren't attractive to mosquitoes produce extra chemicals.

Chris - So this makes them smell bad?

John - To the mosquito, yes. Exactly right. Not to us, but to the mosquito.

Chris - So the key question is, can you bottle that and put it into the most effective mosquito repellent known to man?

John - Well we've bottled it in the sense that we've identified the chemicals mainly responsible. We're now checking out whether we can actually use them in a way that's beneficial.

Chris - How did you actually home in on them in the first place?

John - We surveyed a number of people to find those that were very attractive and those that were unattractive. We then took the volatile chemicals from those people and analysed them using chemical analysis, but also the antennae of the insects themselves, and that's how we pinpointed the chemicals that are produced extra by the repellent people and those are the chemicals that were found to be repellent themselves.

Chris - When you say that you used the insect's antenna itself, how did you do that?

John - Well we stick very very fine electrodes into the antennae of the insect so we can kind of listen in to what the insect is smelling.

Chris - And then once you've worked out what the compounds are that produce the most profound effects, you then know that those must be the important ones in the attraction-repulsion.

John - That's right, and we've been testing those. This work is collaborative with the University of Aberdeen up in Scotland against the Scottish biting midge and we've got very nice field results there. We've done some lab work on the yellow fever mosquito and we're just about to go out to Africa to work with colleagues there on the malaria mosquito.

Chris - So the same compounds work not just in one insect but in many.

John - We're hoping that since they work very well against the Scottish biting midge and the yellow fever mosquito, that they will work for a whole range of biting insects.

Chris - And the question everyone wants me to ask is, when are you going to have this stuff on the shelf?

John - Well we've got funding for two years to develop a business plan and to work out how we're going to do this, but the proviso is that we make sure it's available to people travelling to Scotland.

Chris - Rothamsted research's John Pickett, who's trying to bottle mosquito-repelling "odeur de human". Now John mentioned one thing Scotland's famous for just now - its midges, but the University of St Andrews is a world leader in research into marine mammals like seals and whales. Professor Ian Boyd and his team have developed special satellite tags, which can be attached to the animals and used to find out where they go, how deep they dive, and where they go for lunch…

Ian - We're trying to understand how these animals operate beneath the surface of the oceans. Until very recently it was really impossible to observe them, and now with new instrumentation we're able to gather a lot of information about how these animals live in the deep, dark, high pressure world.

Chris - How are you doing it?

Ian - It's mainly using modern instrumentation. We have two basic types, which we're calling satellite tags, which have these antennae on them. When the antenna on the animal comes to the surface, it sends a message to a satellite which contains the data about the previous dive that the animal has made. There's another one over here that's in the form of a salinity sensor and that's able to provide us with information about the temperature and salinity in the water column. So we can do the same as oceanographers do but without having to take a ship to see.

Chris - Now this thing is about the size of a computer mouse. So what, would you just glue that onto the animal's head or something?

Ian - It goes on the back of the head and it goes on the fur. When the animal moults, it moults once a year, the device falls off. So the animal's not permanently marked with the device. We've got another one here which actually dispenses with the satellite link and uses a mobile phone. So whenever it comes into mobile phone range, it sends the information through the mobile phone network to us. The development of these tags will probably involve animals being able to phone each other as well, so that's interesting.

Chris - Why would they want to do that?

Ian - Well the mobile phone network only goes out to sea for a very short distance, so what we want to do is allow animals to collect the information about all the other animals there are around if they come into contact with them. So we only need to see one animal to get information about the whole network back from them.

Chris - Professor Ian Boyd, from St Andrews, who's got seals talking - quite literally. Now if you didn't think that was sufficiently out of this world, one of the most incredible things to grace the Buckingham Palace Ballroom, apart from a massive model of Einstein's head that let you cycle through his brain, was a large screen providing a 3D view of the surface of the planet Mars. It played like a movie, and looked just like you were flying across the surface of the planet in an aeroplane buzzing past impact craters and canyons. It's been produced using stereo photographs taken by the Mars Express satellite, which is currently orbiting Mars, capturing images as it goes. One of the scientists on the project is the Open University's John Murray…

John - These are images from the Mars Express spacecraft, which is the first European spacecraft to another planet. It's also the first stereo camera that's ever been flown to another planet, which is quite amazing. So what you're seeing here is a model of the surface created from these stereo images. We're flying over the surface and skimming over the mountain tops.

Chris - So this is literally like you're taking a bird's eye view of the surface of Mars.

John - That's right, yes. These are taken from a spacecraft that is orbiting Mars at this very moment and it's sending back pictures all the time. From this we can create models where you can go right down to the surface and explore and measure heights, angles of different strata, and do geological fieldwork in virtual reality.

Chris - Is the orbit such that you'll be able to get a complete comprehensive map of the surface of Mars eventually?

John - Provided we get funded, yes. We've just had the mission extended for a further two years, so we should be able to do it. We're hoping to have 100% of the planet between a resolution of between ten metres and about thirty metres. So something the size of this room would be easily visible in those pictures. So that means that we'd know the surface of Mars better than we know the surface of the Earth, amazingly.

Chris - It certainly is amazing. That was the Open University's John Murray at what I think counts, and you can shoot me down if I'm wrong, the first podcast from Buckingham Palace.

- The Science of Superconductivity

The Naked Scientists spoke to Dr Tim Jackson, University of Birmingham

The Science of Superconductivity
with Dr Tim Jackson, University of Birmingham

Chris - We've talked up superconductivity quite a lot and people have been hearing us doing some experiments there, but maybe we should back pedal a bit. What actually is a superconductor?

Tim - Some people call them the super heroes of materials science. They're very surprising materials because you cool them down through a special temperature called the transition temperature, and at that point they lose all of their electrical resistance. Electrical engineers can employ this rather surprising property in a variety of different situations.

Chris - Why do they lose all this resistance? And what is resistance for a start?

Tim - Well we have to go back a bit and think about electric current going through the copper wires in your house. The electrons are more or less free to do that as they pushed by the voltage through the wires. But they do encounter some resistance and that resistance is actually that they collide with the atoms in the material, they lose a bit of energy when they do that, and that energy comes out as heat. That's why a light bulb works; it's really the resistance of the filament that makes the bulb hot and it glows white. Now in a superconductor at room temperature, the electrons are moving around and doing their own thing without taking much notice of each other. You now cool it down, and you really have to cool it to about minus 180 degrees centigrade, and as you get close to that, the electrons start to take more notice of each other. You can think of them as starting to flirt with each other a little bit. You go through that transition temperature and they start to hold hands. Once electrons are holding hands like that, they can't be knocked off course, so they move through without any problems.

Chris - And I suppose the goal of this is that 180 degrees below zero is not a practical temperature to be working at. If we could make this happen at something closer to room temperature, it would be ideal.

Tim - Well you'd be surprised to be honest. Minus 180 degrees centigrade is the temperature of liquid nitrogen, and nitrogen makes up 80% of the air that we breathe. As far as technology goes, it's not so hard to cool down to those sorts of temperatures. Twenty years ago, there was a class of superconductors discovered that we call high-temperature superconductors. High and low are all relative in this context. If you can cool things down and make them superconduct at liquid nitrogen temperatures, there's an easy technology there. Between 1911 and 1987, most superconductors that were known had to be cooled down to within a few degrees of absolute zero, which is minus 273 degrees centigrade. That was a barrier to most applications.

Chris - So how do you make something superconduct? How do you decide that this is the recipe needed to make a chemical combination that will have these properties?

Tim - That's a very good question. There was a theory in the 1950s about how these very low temperature superconductors worked and most people thought that that meant you couldn't make a superconductor that worked above about 25 degrees above absolute zero. But people following the guidelines of those theories were looking at other materials and in particular, oxide materials. These are materials that are a little bit like ceramics; there are three metallic elements and oxygen in a compound. What they found twenty years ago was that these would superconduct at much higher temperatures. It is now still a big challenge to theoretical physicists to work out exactly how that takes place.

Chris - Now what sorts of applications might there be if we are able to crack this nut and make these materials in the way that we want? What will we be able to do with them, and how are they being employed at the moment?

Tim - One of the applications that our research team are working on in Birmingham is making filters for radioastronomers at Jodrell Bank radio telescopes.

Chris - And when you say filters, what does that do and how does that work?

Tim - A filter is a kind of electrical equivalent of a bouncer at a nightclub. A bouncer at a nightclub with a selective door policy has been told that certain people who come up to the door are to be allowed through with no interference. If they're the wrong people wearing the wrong type of clothes, just send them back and don't let them through. Now a filter is an electrical circuit that does just that. What the circuit does is allow through particular electrical frequencies and electrical signals that you want. The problem for radio astronomers is that there's a lot of electromagnetic pollution. So for example, you're looking for a distant object in the universe and you want to study its properties. But all the satellite communications we have, all our mobile phones, and all our televisions are polluting the frequency space. That means that the astronomers have to spend a great deal of time on their telescopes averaging out the data. If you can find a way to help them use their telescope more efficiently, they can do more experiments. Our superconducting filters do just that because they cut out that noise.

Chris - Why do you need a superconductor to make that kind of filter though? Why won't standard electronics do it?

Tim - The reason you can't do it with standard electronics is that there are always some losses. As we talked about earlier, in a normal metal there is always some resistance. When it comes to making electronic filters, that sort of loss means that you need large devices and also they will never pass through the signals you want without some attenuation. If you want the signals to come through clean and undiminished, then you need a superconductor.

Chris - Now hasn't Birmingham got another claim to fame in terms of superconductivity in terms of the Maglev. Is that at Birmingham, where they actually had a train that drifted along on magnets so that it wasn't touching the ground.

Tim - That's right. There used to be a train, and it hasn't been running now for 10 or 15 years now, which went from the passenger terminal at Birmingham international airport to the railway station. That was a magnetic levitating train but it wasn't a superconducting train and there were some problems with it. People thought it was a bit wobbly and bobbly and that might have been because the technology was much earlier.

Chris - So is that the kind of thing we can look forward to if we are able to get a handle on getting superconductivity working as well as we'd like to?

Tim - Better transport is one of the large scale applications that's getting people excited at the moment. There's a test track in Japan at Yamanashi, which contains wires made of superconducting materials in the floor of the train. They're cooled down, and you drive a current through those coils and that repels against some other coils in the track and lifts the train up. The advantage of doing this is that there's no rolling resistance, and this train has now been tested up to speeds of 360 miles per hour. It's exciting because this gives you high speed transport without the need for aeroplanes, which have very high environmental costs at take off and landing.

- Applications of Superconductors

The Naked Scientists spoke to Dr Ed Tarte, University of Birmingham

Applications of Superconductors
with Dr Ed Tarte, University of Birmingham

Chris - Now we've heard from Tim all about the science of superconductivity and we began to explore some of the applications, but this is an area where you're really pushing the boundaries.

Ed - Probably the most successful application of superconductors is some of the medical imaging scanners you were talking about earlier. The long tube-like scanners that people often experience these days are actually based on superconducting magnets.

Chris - Like MRI; magnetic resonance imaging, for example.

Ed - Exactly.

Chris - Why do they need a superconductor?

Ed - They need a superconductor because you want to produce a very large magnetic field. What you're trying to do is line up all the protons in the water atoms in your body and get a big enough noise to sound ratio in the end. To do this, you need a very large magnetic field. You could do that with a magnet based on copper wire, but then the amount of heat that would be generated would be too large for the patient to be inside. You'd have to do a lot of cooling. The advantage of having a superconducting magnet is that the superconducting wires are cooled anyway, and you can have a much larger current without the patient being exposed to large amounts of heat.

Chris - Is it just patients that you can explore using this technology? Are there other things that you can image and where this technology is useful?

Ed - It's been used for a whole range of things. I believe that in Cambridge they've looked at the defrosting of courgettes inside an MRI scanner.

Chris - And why is that useful?!

Ed - Because you can look at the inside of the object that you're trying to examine as well as the outside, so you can do a section of the structure inside.

Chris - So while it's frozen, without having to chop it up and ruin it?

Ed - Exactly.

Chris - Oh I see. So you can see what would happen if you dumped that thing into the freezer?

Ed - Or what would happen when you take it out and let it defrost.

Chris - Now what about actually increasing the resolution of MRI. It's all very well that it gives us these images of gross areas of the brain in a way that we could never have dreamt of before, but now there's a way that's referred to as SQUID that allows you to look at what the brain is doing almost nerve cell by nerve cell.

Ed - Well not quite nerve cell by nerve cell. But certainly with a superconducting interference device, or SQUID, you can image the location of activity inside the brain by detecting the magnetic fields generated by the currents flowing inside the brain.

Chris - And what sorts of questions does that enable you to ask?

Ed - Well one question you can answer is that if you imagine a patient who has a brain tumour and you want to remove the brain tumour and work out the best way to go into the brain without damaging the sense of hearing and so on. What you can do is put the patient inside what's called a magnetoencephalography (MEG) scanner and play a tune into the patient's ear. Because this MEG has an array of SQUIDS around the head, you can map the distribution of magnetic fields associated with that piece of brain activity and work out exactly where in the brain the auditory complex is. When the surgeon wants to remove the tumour, they can do so without causing damage.

Chris - What about turning away from the brain and to other tissues such as the heart?

Ed - Yes. Again, by using an array of SQUIDS you can image the current distribution in the heart and therefore look for short-circuits. When the heart beats, the cells generate voltages. But certain conditions generate circuits in different parts of the heart and you can see those by using an array of SQUIDS.

- A New Cooling Device

The Naked Scientists spoke to Dr Alex Mischenko, Science Graduate of the Year and CTO of FerroEnergy

A New Cooling Device
with Dr Alex Mischenko, Science Graduate of the Year and CTO of FerroEnergy

Chris - What is it that you have invented?

Alex - Our team has discovered a giant electro-caloric effect in thin films. The electro-caloric effect is a change in temperature in an insulating material. It is made through the application of a voltage.

Chris - So what you're saying is that when you apply a voltage to something, it changes temperature.

Alex - Yes, exactly.

Chris - So was this known before you came along or is this new?

Alex - The electro-caloric effect has been known for several decades and prototypes of electro-caloric fridges were built in Russia and the States. They were not commercially feasible because the electro-caloric effect in normal materials was not large enough.

Chris - Ok, well just talk us through step-by-step how it all works and what you actually do.

Alex - You take a piece of silicon which is about half a millimetre thin and about one centimetre squared. You then deposit a thin ceramic film on it, and then deposit an electrode on top of your film. The application of a voltage causes the film to change its temperature and if you build a snadwich structure, then this sandwich structure can develop a temperature difference of up to about twenty or thirty degrees centigrade.

Chris - But it's presumably not efficient for fridges? I say that because a fridge is already so effective that this wouldn't add much to that.

Alex - Yes. Fridges are quite efficient but they use greenhouse gases, so those greenhouse gases contribute to the global warming effect. Even if our new device isn't as efficient as fridges, people maybe still want to replace greenhouse gases in their fridges.

Chris - So assuming that that doesn't happen in the near term, what else could you do using your electro-caloric effect invention?

Alex - We can do air conditioners, for example, and that is more interesting because air conditioners usually work all the time. We can compete with traditional air conditioner inefficiency. Surprisingly, the same materials can also be used to convert low-grade waste heat into electrical energy. Waste heat is produced in everything, from computers to mobile phones and indeed in almost all electric and mechanical devices.

Chris - So how did you come to discover this in the first place? You won Science Graduate of the Year this year and that's pretty prestigious. What actually is that and how did you get to be doing this work?

Alex - The Science Graduate of the Year is an award by the Royal Institution of Great Britain and L'Oreal. That's prestigious and I'm very happy that I won that prize.

Chris - What did you win for winning it?

Alex - I'm a life member of the Royal Institution and I gave a lecture in London in the Royal Institution and I'll give a lecture in Paris. They also gave me some cash.

Chris - Which is always nice! Alex Mischenko, thank you very much.

- How can an egg be inside another egg?

I cracked open a large chicken egg this morning and out came the white, an egg yolk, and another fully-formed shelled egg. Any thoughts o...

How can an egg be inside another egg?

I've never heard of that happen before. The reason that's bizarre is because when an egg forms, the chicken makes the egg and puts the shell around it as it descends along the oviduct of the chicken. So for that to have happened, it suggests that an egg must have formed, or misformed, and then got engulfed by another egg that was forming once it had already partially formed. It's a bit like cases where ladies have given birth to babies and they've found the remains of a dead twin inside the body of the surviving baby.

- Gases from water?

I've come across a website for a gas made using water, that ignites but is not hydrogen. I was wondering what your take was on this.

Gases from water?

I think it's acetylene. People who go pot holing or are miners have miners lamps that use acetylene. That is made by using calcium carbide, which is calcium with a couple of carbons stuck onto it. When you drip water onto it, it reacts to make acetylene - two carbon atoms stuck to two hydrogen atoms - and it burns very brightly. I think that's probably what you're talking about.

- Why is it that some people can memorise more things than other people?

I've thought about it many times, but why is it that some people can memorise more things than other people? Is it due to differences in ...

Why is it that some people can memorise more things than other people?

I think language is a good index here, because to know a language you have to know thousands of words. The average person who speaks well probably knows about twenty to thirty thousand words. There was a study done recently by researchers at University College London and what they did was to look at people who were bilingual and used a brain scanner to look at the thickness of the rind, or cortex, of the brain. They then measured it in people who were monolingual and people who spoke more than one language. What they found were these obvious structural differences. The people who were bilingual had a thicker language area in the brain. So the evidence is that if you can remember more things, you train your brain and develop connections. It's those connections that probably underpin the ability to store more information and recall more information.

- Where do fruit flies come from?

When fruit is rotting in a bowl, you get horrible black flies coming out of them. How do they get there?

Where do fruit flies come from?

Those flies are called Drosophila or fruit flies. They're the favourite friend of geneticists because they're very easy to do experiments on. Many animals use their antennae to detect chemicals given off by the thing they want to eat. Drosophila are in the environment pretty much all the time. They lay eggs, the eggs hatch, and in the warm environment of your house they can then fly around and home in on your fruit bowl. The other things that attract them are red and white wine. The volatile agents smell a bit like fruit because wine is made from fruit.

- Why does the moon look larger on the horizon?

Why does the moon look larger on the horizon?

Why does the moon look larger on the horizon?

This is all down to an optical illusion. The brain has no frame of reference when the moon is high up in the sky, whereas when it's on the horizon, the brain is comparing it to other things in the same frame of reference: there are trees, there are buildings, as well as the moon. Therefore the brain is fooled into thinking that the moon is a lot bigger than it really is.

- How does cat saliva cause allergies?

In your programme about allergies, you mentioned that the cause of cat allergy is the saliva in their skin. Could you please clarify whet...

How does cat saliva cause allergies?

People are reacting to a substance made by a gene called FelD1. It's produced in cat saliva, so that when a cat licks itself and its paws and grooms itself with a wet paw, this FelD1 product or protein then goes onto the fur and when it sheds that protein with its fur, it goes into your nose and makes people sneeze. There's a company over in California and they've bred a type of cat that doesn't have that particular part of that gene and they say, although it hasn't been proven scientifically yet, that it's actually non-allergenic.

- How do magnets work as treatments?

How do magnets work when they're used to treat injuries such as a frozen shoulder?

How do magnets work as treatments?

I'm not sure that they do actually. I have some experience of this when I twisted my knee playing football. Someone told me that if I taped magnets around my knee then it would help it heal up. The problem was that when I walked up to the window, my knee stuck to the radiator beneath it and that didn't help my knee get any better at all! There was a study written up in the British Medical Journal a few years ago in which people looked at this question. They said that people did seem to do better with these bracelets and things, but there's no scientific reason of justifiable reason for why people should get better. What they suspected was that the trail was a bit biased. How you do this kind of trial? You give people with achy knees either a magnetic bracelet or a non-magnetic bracelet. Now it's pretty easy for people to work out whether they've got the magnetised version or the non-magnetised version. If people are given one and they think that it's a placebo, then they're probably going to claim that it works less well than if someone has a bracelet that is obviously magnetic because it sticks to stuff.

- Why does some underarm sweat turn shirts yellow?

Why does the sweat of some people's underarms turn their shirts yellow?

Why does some underarm sweat turn shirts yellow?

There are two types of sweat glands: eccrine and apocrine. Eccrine sweat glands are found all over the body and are particularly abundant on the palms of our hands, the soles of our feet and on our forehead. They mostly secrete water with high concentrations of salts. Apocrine glands are mainly concentrated in our armpits and around our genitals, and rather than just secreting water and salt, they also secrete lots of fat and protein. This makes the sweat thicker, more yellow, and produces the stains we find on our nice white shirts. Our armpits are a seething mass of bacteria and those bacteria are growing on the sweat we produce. The bacteria break down the fats and proteins to make rather niffy compounds, which is why your armpits can smell especially bad even though you've been sweating all over. Another possible cause of the yellowing is that when bacteria go about their metabolism, some of the things they produce are quite acidic. Many dyes in clothes are fixed by various acid or alkali processes. I'm thinking that perhaps some of the acid that's produced in the armpit is sufficient to affect some of those dyes.

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