Is there such a thing as a "girls' throw"?

Dave - If you have ever taken a cup of coffee or something with some foam on the top and spun the cup, the coffee stays still, but the cup turns around. This is based on the same principles. There are some weights inside the watch which are free to move and as you move your wrist around, the weights tend to stay still when your wrist is moving, and so they move around and spin around as you move around, and go through your daily life. This relative movement between the weight and the watch is connected to a little generator via some gears and cogs, and that charges the battery. And so, as long as you keep using it and moving around, it will charge the battery up and it should keep going.

Dave - There are various different things which could be limiting how fast you can move. There are various mechanical reasons, like you might not actually be able to move your muscles quickly enough or if you're pulling a very heavy weight, it's limited by the amount of force you can apply on the weight. I think in this case it's limited by the amount of power you can put out. Elite athletes are going to be able to put a lot more power out than you are, but you're using a method of transport which is much more efficient. Bikes have been optimised over the course of 150 years to be incredibly efficient. You use very, very little energy to keep going along. In fact you need hardly any energy to keep them going along, it's just to accelerate them and to overcome air resistance, as there's no friction there. So, with a very relatively small amount of power, you can be going very, very fast.

Whereas when running, you've got to move these great big legs around all the time and you actually kind of reach a limit to how fast you can move the legs backwards and forwards. You've got to accelerate and decelerate every time you take a step.

Chris - You're basically accelerating a bag of water weighing at least 60, if not 100 kilos which you're elevating and dropping and decelerating with every step, aren't you? So, you're basically having to keep lifting this very heavy bag up and down, and it's not an efficient way to move.

Dave - And also, you've got your legs, at 10 or 15 kilos each, which you're accelerating backwards and forwards. So all of that takes a huge amount of effort whereas on a bike, all you've got to do is just push this off along through a very efficient mechanical train.

Diana - Perhaps one of the reasons why humans are so good at doing long distances for a long time is because they've only got two legs whereas four-legged animals like horses, although they can go faster, they can't go as fast for as long as humans can because they've got four things to lift up.

Chris Smith gave an "eggs-pert" opinion on this question...

Chris - I looked up the number of eggs that are thought to be contaminated with Salmonella in the UK where incidentally, we consume 24 million eggs every day. It's a very huge number. It's nearly 9 billion eggs per year just in the UK, and the estimate is that about 0.3% of them are carrying Salmonella.

The number of organisms that are in the egg in an infected egg is very low - 5 or 6 bacterial particles - and proper storage of the eggs and making sure they're not kept too warm where the bacteria will multiply means that that number stays very low. And if the number stays low, then the chances of acquiring the infection is extremely low. You need a very high dose of Salmonella to make sure that someone will get infected.

The number of cases of Salmonella we get every year are far and away too small to really show that this is having a major impact. We think there's probably under 10,000 cases of Salmonella infection in the UK every year.

How does the bug get into the egg in the first place though? Well, there's a number of routes. One of them is that when chickens catch Salmonella, unlike us, where we get symptoms, it doesn't cause a symptom for a chicken. It can pass from the chicken's ovaries, where it can set up an infection, straight into the egg and it gets inside the egg via that route.

Another way is that chicken shells are relatively porous and so, for something as tiny as a bacterium, it is very easy for them to sneak from the outside, from the chicken faeces, into the egg.

The third route is that some eggs, whilst they leave the chicken pristine, pick up the Salmonella from the environment whether that's the farmyard they're laid in or the factory they're processed in. And so, there's no guarantee that an egg is going to be safe or unsafe.

The best bet is, if there might be a risk for you, just to use your common sense and cook it well!

Chris - It does sound a bit counterintuitive doesn't it? The simple reason, chemically, is if you were trying to dissolve some salts, let's take table salt - sodium chloride - as an example. Sodium chloride consists of sodium ions Na+ and chloride ions Cl- and they're in an ionic lattice where the sodium has given an electron to the chlorine so you've got the sodium plus and the chloride minus.

Water has a dipole. What that means is that water molecules, H2O, have an oxygen in the centre which loves electrons and it's a bit minus, and the hydrogen which holds on to its electron slightly less well ends up being a little bit plus.

This means that when salt mixes with water, the hydrogen ions can grab hold of the chloride because they're minus and the hydrogen is a bit plus. The oxygen can grab onto the sodium and form an interaction and as a result, the ions want to move in to contact with the water molecules.

If you warm the solution up, the water molecules have more kinetic energy because the temperature is higher, therefore they will interact with more energy with the salt and therefore, they'll find it easier to bring those ions into a solution and hang onto them.

On the other hand with gas, it's slightly different and the best explanation I came across to explain this was in terms of what we call partial pressure. In other words, the relative proportion of a mixture that a gas makes up. If you increase the temperature of a gas, it wants to expand so it takes up more space effectively, the pressure is higher. So if the pressure is higher, the gas wants to take up more room or push harder on other things around it, electrically speaking, and as a result it's going to find it harder to sit in a solution of water molecules which were all trying to interact with each other. So therefore, when the temperature is higher, gases find it harder to dissolve but when the temperature is lower, gases dissolve much better. And that's why you find there's actually much more oxygen in the water around the Antarctic, so you get creatures that are very, very big there compared with warmer water which can sustain less oxygen tension and also, if you want to keep your fizzy drinks fizzier, putting them in the fridge works exactly the same way; the CO2 will dissolve better when they're actually cold in the fridge.

Dave - Another way to think about it is that for salt to dissolve, you've got to break bonds and that takes energy. So the hotter it is, the more energy there is about, so the easier it is to break those bonds. So the hotter it is, the more likely the salt is to be dissolved. But similarly, for the gas to escape from the water, it's going to take energy because there will be some bonds in there, so the hotter it is, the more likely it is to come out as a gas.

The timings of supernova explosions close to Earth marry up with epochs in the planet's history when the diversity of life altered dramatically, suggesting they may have played a role in driving evolution.

Species diversity on Earth has varied significantly over the last 4 to 500 million years; and although it is hard to measure this in larger animals, looking at the number of genera of well-preserved marine organisms within the fossil record, it  rises rapidly to about 250 million years ago, then drops rapidly by about 200 million years ago and then increases again over the last 100 million years or so.

Geologists have used plate tectonics to account for these trends, arguing that this alters sea-level and atmospheric chemistry and in turn the temperature. The overall effect, they argue, is more shallow seas, giving rise to more complex coastlines and a more varied marine environment. So you would expect more diversity of species.

But this may not be the whole story. Henrik Svensmark has been looking at a different source to explain the changes: supernovae, the explosions that punctuate the end of a star's life, producing in their wake powerful surges of cosmic particles and radiation. For now, he's confined his analysis to events that have occurred within about 5000 light years of Earth.

To spot where and when they may have happened, he looked for stellar congregations called "open star clusters", where star-forming events have occurred in the recent past. He reasoned that, if stars were forming in these places, some of them will have been the short-lived massive stars that form supernovae.

Comparing these predictions with records of cosmic rays preserved in meteorites produced a strong agreement. He then compared the cosmic ray records from the last five hundred years with the numbers of marine species. The match is striking. There are peaks 250 million years ago, and again now.

Svensmark speculates that high energy particles issusing from the supernovae could have entered Earth's atmosphere where they produced trails of ions that seeded clouds, cooling the planet and boosting species diversity. Consistent with this theory, when he looked at previously-unexplained rapid cooling events that have hit the planet in the past, there was again a strong correlation with the supernova data.

So, surprising as it sounds, life on Earth may owe its origins not just to our nearest star, the Sun, but also to the deaths of other stars thousands of light years distant...

Chris -   Also this week, scientists homed in on the parts of a pigeon's brain that enable it to use the Earth's magnetic field to navigate and Louise Anthony has been finding out a bit more...

Louise -   Pigeons, as well as a host of other species including bats and fish, are known to be sensitive to magnetic fields and they appear to be able to use them to find their way around.  But exactly how these animals detect and then process this information neurologically has always remained a grey area.  Now, working with homing pigeons, David Dickman from the Baylor School of Medicine in Texas, together with his colleague Le-Qing Wu, has identified the parts of the brain that give these animals their mental compasses.  Dickman and Wu reasoned that nerve cells involved in decoding magnetic signals should be activated by changes in the surrounding magnetic field.  So to track down these cells, as David Dickman explains, they began by exposing a group of birds to a changing artificial magnetic field and then looked in the animals' brains for nerve cells that had switched on a gene called c-Fos, which is an indicator of nerve cell activity.

David -   We put birds inside a magnetic field, rotated the magnetic field around their heads, then reacted the brain tissue for the c-Fos antibody and we found four major locations that were strongly activated by magnetic stimulation.  One of them turned out to be in the vestibular nuclei, another in the anterior thalamus, an area that processes spatial information and the third was the hippocampus which is well-known to be a spatial memory centre.  The fourth was an area of association, visual cortex.

Louise -   These are all regions that are known to be involved in navigation functions and spacial orientation.  In other words, knowing where you are, what position you're in, and in which direction you're pointing.  Next, to find out how these nerve cells might be processing magnetic information, Dickman and Wu placed 7 pigeons in changing magnetic fields of a similar strength to the Earth's own magnetic field, and then used electrodes to record the nerve activity in one of the brain regions they'd already identified - the vestibular nuclei - which also helped to control balance.

David -   We placed birds in the dark because there's a competing idea that the retina has a photo pigment contained inside the retina itself which could be reactive under certain wavelengths of light to a magnetic field.  We didn't want to activate those receptors if they exist, so we put the birds in total darkness and they were motionless because we didn't want to activate the vestibular system since we're recording from vestibular cells.  So while they sat there quiet, we rotated this magnetic field around them in different planes and we found that the neurons are all tuned to a specific direction in space and the tuning is really interesting because the neurons respond when the magnetic field is pointed basically in all directions except one plane where they're silent, and they build up the response so that when the magnetic field is pointing in one direction, the cell likes it the most and when it's pointing opposite that, the cell likes it the least.

Louise -   And the responses of those cells effectively signal the strength, direction and the polarity of the magnetic field;  In other words, whether the bird is pointing north to south or south to north, and this means that the birds can most likely use this information to work out where they are.

David -   If you look at the Earth's magnetic field, what you see is that field lines come out of the south magnetic pole, they circle the Earth and they go back in, in the north magnetic pole.  And they come out of the Earth at different angles, depending upon whether it's the south, north or the equator.  It's 90 degrees at the poles and it's zero at the equator and then it varies systematically between the equator and the poles.  That's called the inclination angle.  These neurons theoretically could use that inclination angle to tell you your latitude.

Louise -   But what they still don't know is how the birds are actually detecting the magnetic field in the first place.  So whether it's a magnetically sensitive chemical in the eye or deposits of an ion containing mineral like magnetite - that's still a mystery, but there are several possibilities.

David -   There are three candidates out there - the retina, using these photo pigments. We've never looked at retinal cells before.  There's also the inner ear, where there are these iron particles that were found by another group; and then the beak, although the beak looks like the magnetite is macrophages, it could be that there is still a mechanism there but is yet to be discovered.  There are behavioural studies that suggest that the beak is involved, so we really don't know.  We'll probably go after the receptor in the inner ear first because we're familiar with that territory and we've done some preliminary experiments about that already.

Louise -   So, for the moment at least, the jury is still out, but in the meantime, there are some very real potential spinoffs from this work that could benefit us too.

David -   Humans often have disruptions in their spatial orientation ability, particularly people with dementia or people that have inner ear disease such as Meniere's disease.  They find it very difficult to sometimes even find their way in the kitchen if the lights are turned off and they lose their way when they're driving from home to the grocery store.  So, we have an idea now about how the brain is taking some signals and feeding in to this, what we call the navigation network.  So we're hoping that will lend us some clues that we might be able to use in the future to help people with spatial orientation in spatial memory loss.

Chris -   David Dickman speaking with Louise Anthony and that work was published this week in the journal Science.

Chris - Well actually, it does cause a bigger heart and it can happen for both good reasons and bad reasons. If you have a very high workload on your heart because you, for instance, have high blood pressure all the time, then you can develop cardiac hypertrophy and this is where the muscle of the heart becomes thickened, bigger, and beefier in order to do more work and overcome the extra load applied to the heart by the high blood pressure. Now, that's a bad thing, obviously; sometimes the muscle can become so big that, in fact, it has an oxygen demand which is bigger than the coronary arteries are capable of delivering via the blood. So, people can get angina - pain in their chest - caused by the heart not getting enough oxygen - because the heart has become pathologically large.

More normally though, people who do a lot of exercise along the lines of what you've been describing, Olympic athletes for example, footballers for example, you'll often hear them say that their resting pulse rate is really low. They might say, for example, that, compared with a normal person who has a resting pulse rate of say, 70 beats per minute, their heart beats only 40 or maybe in some cases, 30 times per minute. Now the reason that can get away with beating more slowly is because their heart has become larger in response to their regular training and the demands they place upon it. And that means that, because it's bigger, it's working more efficiently. With every beat of the heart, it actually pumps out more blood than a smaller heart in an untrained person. So, as a result, they don't have to make their heart beat as often because every time it does beat, it pumps out two beats worth of blood, so their pulse rate can come down. And, if you measure the maximum output from their heart, you'll find that their maximum output can be say, 30 litres in a minute when they're working really hard, compared with say, 25 litres in someone who's unfit and untrained. However, the maximum number of beats their heart can make in a minute will be lower than an unfit person because a bigger heart takes longer to fill up with blood, so they have to slow down their pulse rate and they just make their heart eject more. This form of cardiac enlargement is not thought to be bad for you. It's a physiological response to increased workload and, in the short term at least, we think that it isn't harmful.

Dave - If you have a door which is getting a bit old, getting a bit rusty and you haven't oiled it properly, you get a very similar thing to brakes squealing or in fact, dragging finger nails down a blackboard. It's to do with stick and slip. What happens is that you get quite a lot of friction and there's a lot more friction when two things are stationary than when they're moving. So, essentially the two bits of the hinge lock together, then the hinge bends a bit, and then the force gets enough for it to break, and it jumps forward a bit and then it stops, and then it bends a bit, and it jumps forward.

This jumping can happen at a range of pitches, including the horrible 50-100 Hertz range. As you're getting jump, jump, jump, jump, what you hear is this horrible creak noise.

Physicist Dave Ansell answered this question...

Dave - Yeah, there's a couple of things which might affect the efficiency of your freezer, depending on how much it's got in there. I guess, first, if you put something warm in there, then you're going to take a load of energy to pump the heat out of it. But assuming you've already got the stuff cold, which is best, if you have an upright freezer, when you open the door, all the cold air is denser than the warm air, so all the cold air falls out. You're essentially putting in heat by all the warm air which is taking its place, and you shut the door and it's got to re-pump that heat out again.

Chris - So the more stuff that's in there, the less room there is for warm air to go in and push cold air out, so the better then?

Dave - That is correct, up to a point. If you jam every corner absolutely full of stuff, you can then get other problems because the way the freezer knows how warm it is is you've got a thermostat in there and if the cold air can't get from the cooling elements to the thermostat then it's going to keep making them colder and colder. The bigger the temperature difference, the more the freezer's got to work from between the room and the temperature inside the freezer, the harder work it is and so the more energy it uses. So, if the cooling elements are actually at -30°C rather than -20°C, that's going to be costing your electricity. So fairly full, but not so full that air can't circulate at all!

Diana - So I guess it is a good idea to defrost your freezer occasionally so you don't get that build up of huge chunks of ice if you haven't got a frost-free freezer?

Dave - Yeah, especially as that is even worse than filling your freezer right up because it insulates the cooling parts of your freezer, so the cooling parts could get even colder which then causes even more ice. It is a horrible vicious circle and you end up running your freezer continuously and not actually ending up with a very cold freezer.

3D Imaging of Human Tissue

High resolution

3d images of human tissues can now be created using a technique developed by scientists at the University of Leeds.

By scanning hundreds of slides of sliced tissues segments at once and converting them into high resolution digital images, the software, developed by Derek Magee,  then aligns these to produce detailed, multi-coloured images in 3 dimensions, with over 400 created to date.

The technique can be used on numerous tissue types including tumours and samples of liver disease, and enables samples to be rotated on a computer screen and monitored from any angle.

Derek -   Within a human body, some things are inherently 3D structures and looking in the 2D does not give you the same information. So take as an example blood vessels, blood vessels are a branching structure of tubes.  If we cut a tube as a 2D section, all you see is an ellipse.  So if you look at a blood vessel in 3D, you can actually see this branching structure and you can relate it to the structures around it.  For example, a tumour, if that's very close by you can see, well, has that tumour got its own blood supply or is it a very early stage tumour that is yet to develop its own blood supply?

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New compound to treat Autism

A drug to treat the symptoms of autism has been identified by scientists at the National Institutes of Mental Health in the US.

Working with inbred mice displaying signs of autism such as unusual social interactions, excessive jumping and repetitive self-grooming, Jacqueline Crawley and colleagues found that when the mice were injected with the

compound GRN-529 - which regulates glutamate release in the brain - these behaviours were significantly reduced.

Jacqueline -   Treatment with this compound that reduces excitatory glutamate neurotransmission in the brain reduces repetitive behaviours, reduces stereotype jumping, and improves some of the social deficits that are seen in these mice. We may be able to develop pharmacological treatments that might be beneficial to children and adults who have autism.  The challenge of course is to find compounds that will be effective in people, but it's one of the most promising leads that we've seen for quite a long time.

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Climate warming by wind turbines

Large wind farms may be affecting local weather and climate in the US.

With the US wind industry growing rapidly in recent years, scientists at the University of Illinois analysed satellite data for the land surface temperatures of four of the World's largest wind farms in Texas, to see their effect on local land surface temperatures from 2003 to 2011.

The team found a warming effect of up to 0.72 °C per decade when compared to nearby regions lacking these farms.

Somnath Baidya Roy co-authored the study.

Somnath -   Turbulence generated by the spinning of the wind turbine rotors mixes air up and down, and the key impact of this is a warming effect near the surface and on the land surface at night.  Now, wind power does not generate almost any carbon dioxide emissions and hence, wind power is going to be a part of the solution to the climate change problem.  Understanding the impacts of wind farms will help us develop efficient adaptation and management strategies and thereby contribute to a long term sustainability of wind power.

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Subordinate Meerkats are the best problem solvers

And finally, subordinate members of a meerkat social group are the best at solving problems.

Alex Thornton from the University of Cambridge set tasks for 7 groups of wild meerkats where the animals were required to open or break into transparent containers to reach the scorpion supper located inside.

The team found that lower ranking members of the group, and particularly males at this rank, were the most successful at solving the task.

Alex -   The reason for this is probably that these individuals are unable to outcompete others.  So unlike their dominants, they can't bully their way to get food rewards.  So, there are advantages for them to try and find out new ways of solving problems. For the males, this is particularly advantageous because they're the sex that disperses, that goes out to seek mating opportunities, so they're going to be encountering new difficulties in the world and so it will make sense for them to try and find out ways of solving new problems.

And that work was published in the journal Animal Behaviour.