Nature Podcast

This is a transcript of the 5th June edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (http://www.nature.com/nature/podcast), which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to podcast@nature.com.

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Adam Rutherford: Coming up, mobiles and mobility.

Albert-László Barabási: We don't really know how humans walk around. So, we teamed up with a mobile provider and we followed the motion in space of about a 100,000 individuals who carried cell phones.

Kerri Smith: And what's the formula that made this such a hit?Ilsa: What about us.Rick: We'll always have Paris. We didn't have, we, we lost it until you came to Casablanca. We got it back last night.

Kerri Smith: We take a look at the maths of movie making. This is the Nature Podcast, I'm Kerri Smith.

Adam Rutherford: And I'm Adam Rutherford. First this week, Mars has been in the news in the last few days with the Phoenix Lander sending back some stunning photos from the surface. Have a look in the News section of Nature for one of the best. But we're going a couple of stops further out into the solar system. Saturn's iconic rings are the subject of a paper by Carl Murray and colleagues at Queen Mary University of London. Carl has joined us in the studio. Before you get to the new study, Carl, tell us a bit about the rings. What are they made of? Nature 453, 739–744 (5 June 2008)

Carl D. Murray: What we've known for sometime that, they are not solid, they are composed of essentially lot of snowballs typically, sort of, centimetre sizes, but there is a whole range of size. The main ring systems stand at about maybe 140,000 kilometres, but it is extremely thin. So, it is in most places probably just the size of the particles themselves that determine the thickness of the rings, so it's spectacular, anybody who has seen Saturn's rings will never forget that view.

Adam Rutherford: And you've been looking at one of the outer rings F which was discovered by Pioneer 11 in the '70s. Now what's unusual about it?

Carl D. Murray: Well, what was unusual was when we saw it up close with the voyager spacecrafts in 1980 – 81, which were flyby machines, we saw this very bizarre ring, it was twisted, braided. It had discontinuities, kinks, clumps, you name it. It wasn't like anything we had ever seen before in the solar system

Adam Rutherford: And the rest of the rings in Saturn are fairly uniform, are they?

Carl D. Murray: Yes, I mean they have gaps and they have structure, but nothing like what we saw at the F-ring and the F-ring lies just outside the main ring system. So, what's so special about it that it's different from all the other rings? It's just so unusual.

Adam Rutherford: And in the new paper, you've attempted to explain what's causing these anomalies. So first can you describe, it's not uniform, what does it actually look like?

Carl D. Murray: It is difficult to describe it, in some places it just looks like pieces of a string. This isn't string theory, but it's just you know, most strings in the solar system are near circular, uniform. They are just pretty bland looking, but this has just got so many twists and turns in it; features that appear and disappear on time scales of hours to weeks to months and with the voyager we just had a glimpse of over about a week with each spacecraft and trying to come up with theories based on those few images, which was very, very difficult and we knew that one of the goals of Cassini would be get a close-up look and monitor the F-ring and then gather enough information to try and really understand what is going on.

Adam Rutherford: And what did you find? What's causing these anomalies in the F-ring?

Carl D. Murray: We believe that there is moonlet belt there and this has been actually originally a Pioneer 11 result from charged particle experiments, but now with the images, we can see actually two effects. We think we can see the result of collisions that the low moons are colliding with mass in the F-ring and creating what we call jets. Then, we also can see the gravitational effect of the moons themselves and curiously enough the jets that form from collisions act as sort of tracer material, so we can actually see the effect of gravity and from these low moonlets. So, although we've only seen may be one or two of the actual moonlets that are causing the damage, we've really good reason to believe with these results that there are other moonlets there.

Adam Rutherford: You mentioned the Cassini spacecraft, which has generated all of these images. What are you actually looking at, what it sends back? Are they close-up photos of the ring?

Carl D. Murray: Yeah! Obviously because the orbit changes and we get to view at different times, we get to see up close and sometimes further away. But what we really do is we stare at one part of the ring and we watch, if you like, the ring pass underneath it, underneath as we are viewing, it sounds like, it's like going to, sort of, the M25s and circle a little bit around, looking over a bridge and watching all the traffic underneath and then trying to deduce what the rest of the M25 is like based on the traffic, but it actually works in the case of the F-ring. So what we do is we take a succession of images and then we literally sort of unwrap them, so to make a 360-degree view of the F-ring, do that repeatedly and then see how it is changing with time and that was the breakthrough.

Adam Rutherford: So, what happens next? Cassini is still generating lots more data for you to analyze, what's the next step for you?

Carl D. Murray: Well, the nominal mission finishes at the end of June and then we have a 2-year extended mission and for us this is ideal because the F-ring changes in so many timescales. But we hope to be able to look at the direct interaction of these little moonlets with the F-ring and really understand what's going on here because this is kind of the unique place in the solar system, where these collisions are happening on an almost daily basis and to have a spacecraft in orbit around Saturn to look at these things is just phenomenal.

Adam Rutherford: Okay, thanks very much Carl. Next up: (ring tone from mobile phone). You might think of mobile phones as indispensable communication devices or an ever present auditory annoyance.

Kerri Smith: Quite! But a team led by Albert-László Barabási, of Northeastern University has been using them for a very different purpose. Tracking human movement is a notoriously difficult problem. So, the team have the idea of using the trackers we all willingly carry around with us: our mobile phones. Here's Albert-László to explain the problem they wanted to solve. Nature 453, 779–782 (5 June 2008)

Albert-László Barabási: We don't really know how humans walk around. I know where I go on the daily basis and I'm sure everybody knows where they are going, but when you look at the population as a whole, there is no way of describing the patterns that capture how people move around in space.

Kerri Smith: Why is it useful to know about human movements?

Albert-László Barabási: Understanding human motion is crucial at many levels. It is important to model how viruses spread in a society, because we pass on the influenza or SARS virus to others when we meet them, when they come close by. To really understand how that happens, we need to know where people are at the given moment of the day, but understanding human motion is also important for economic purposes. You need to know how often roads are used. How often facilities are used and so on and for planning purposes, for that you would have to have detailed models that capture human motion. The goal of the paper was to describe mathematically human motion, that is where do we go, when do we go there?

Kerri Smith: To analyze these patterns and these mobility patterns, you've taken advantage of the fact that we now live in a very, sort of, wired switched on society. Tell us about the method that you've used here.

Albert-László Barabási: Sure. So every time we carry our cell phone, we pretty much have a contract with the carrier that they will record our location. They will do so for billing purposes, that is whenever we make a phone call, they need to know whom we call and where we call from, so that they can later on bill us. Now this data is typically not used for research purposes, but we realized that this actually gives us very detailed information of where people are moving. So, therefore a mobile provider provided us a sample of a 100,000 users that were anonymous, so we don't know who is the mover, we didn't know their phone numbers or anything, while we knew that in a six month's period, where they moved, that is, what was their location every time they made a phone call and we used this data, this 6-month long time interval to capture the laws of human motion.

Kerri Smith: And tell us what those laws of human motion are that you've found?

Albert-László Barabási: If people would move around randomly, then they would follow what we call Einstein's Diffusion theory that is there would be just lots of small scattering in random directions and the trajectory would pretty much look like a random line. Instead what we find is that our trajectory consists of many small movements, like moving around your house, walking around your neighbourhood and a couple of big jumps, when you go from one location to another one relatively fast. Now this may not surprise anybody because we say, "hey! That's what we do on the daily basis". What was surprising is that the likelihood of making small steps or large steps follows a very precise law, that we call the power-law. The number of smaller jumps is governed by this power-law and that was one of the surprising discoveries. There was a second one, we are all a bit different, that is some people just walk in the neighbourhood, others drive to work, so they do a couple of miles, couple of kilometres on a daily basis and yet others, you know, fly on a very regular basis, on a daily or weekly basis, but the number of people who move typically, 1 kilometre around or the number of people who move typically, 200 kilometres around again follow a specific law, another power-law.

Kerri Smith: There have been methods in the past to monitor these kinds of movements, monitoring the movement of bank notes for example, but what advantages does your method have using phone data, over previous attempts like that?

Albert-László Barabási: The previous attempts using bank notes indeed manage to give us the first indication that human motion may be very nontrivial and it consist of potentially many small jumps and a few big steps; however, our data was the first one, where we could actually follow individuals because following the bank note appearances, you did not know whether between two recordings of a bank note, there was one person owning it or may be three or five or may be a hundred different people own the bank notes. So our data was the first one, where we could track specific individuals, because we all tend to carry our cell phone with us and not pass it onto strangers.

Kerri Smith: Well indeed, we would be into a lot of trouble if we did. So, because access to the phone information was written into people's mobile phone contracts, there wasn't any problem with anonymity in using their phone data for the study.

Albert-László Barabási: In our case, the data was fully anonymous, that is there is no way you could have discovered who was that person because we were actually shifting both in time and you know, there was no personal tags associated with the data, so as that we cannot track back and say, this is your uncle who is moving around in the neighbourhood.

Kerri Smith: So you didn't recognize your own movement pattern in the data anywhere.

Albert-László Barabási: I had no chance. I was not actually in the data set, but as a matter of fact, over a 6-month period, I had been carrying a watch, a GPS watch, that has recorded all my movement and that data will soon be available on my web site for any body to research.

Kerri Smith: Albert-László Barabási and more information on that project can be found at his web site, http://www.barabasi.com.

Jingle

Adam Rutherford: Coming up in just a moment a new movie script algorithm that can tell a blockbuster from a flop. But first physicists among you might have noticed, a surge of papers on superconductors in Nature in the last month. The fifth, by Chen et al, from Johns Hopkins University in Baltimore, is published online today. What's caused the deluge of research in this mysterious field? To guide us through the torrent, we are joined in the studio by Nature's Chief Physical Sciences Editor, Karl Ziemelis. Karl, first of all take us through the basics. What is a superconductor and how do they work? Nature 453, 761–762 (5 June 2008)

Karl Ziemelis: Superconductivity is, sort of, an exotic state of matter in materials that you'd normally think of as sort of metallic, conducting materials where the electrons whiz their way through and form the basis of most of electronics and electrical systems. Superconductivity is slightly different. In that a weird quantum effect kicks in where the electrons, sort of, pair up and as a result of this they are able to move through the system without any resistance whatsoever and that's why they're called superconductors.

Adam Rutherford: And the conditions for this are?

Karl Ziemelis: Usually very low temperatures and when we're talking, you know, below tens of Kelvin is the norm for conventional superconductivity.

Adam Rutherford: And in the last month, Nature has published five new papers on superconductors. What are they saying, what's new?

Karl Ziemelis: The story of the new papers actually goes back a couple of decades to the discovery of the so-called high temperature superconductors. This was a very large family of materials based on copper oxides, fairly complex material system and they came as a big surprise because they were superconducting at temperatures much, much higher than anybody expected to be possible based on the well understood theory of conventional superconductivity. By high temperatures, we are talking as high as about 135 Kelvin, well above liquid nitrogen temperature. The new papers, what has come about, is the discovery of a very different but in some ways related family of materials, very different in that they are not copper oxides, they are iron oxide based materials or to give them their full title, iron oxypnictides.

Adam Rutherford: What's an oxypnictide please?

Karl Ziemelis: Well! It's a great word for a start. Pnictide or a pnictogen is an old style group V element from the periodic table, that's anything in the nitrogen group, so we are talking nitrogen, phosphorus, arsenic and that's one of the defining characteristics of these new materials, is they contain one of the elements from this group.

Adam Rutherford: And so what's caused this, this glut of new papers? What's been the tipping point?

Karl Ziemelis: Well! It started off as a bit of a trickle. About two years ago, a group in Japan discovered superconductivity in one of these iron oxypnictides, sorry I just love using that word, and it was relatively low. We are talking about 5 Kelvin, so nothing special in the grand scheme of superconducting things, but what really changed matters was earlier this year, the same group published a paper, which found that by modifying the composition of one of these materials, they got the superconducting temperature up to about 25 Kelvin. Again, respectable but not outstanding, but it was enough to catch the attention of the superconductivity community and as a result large body of works started appearing on the preprint service and ultimately in Nature's pages based on this.

Adam Rutherford: Okay, and with these new papers and the new discoveries, where is the field going to go next?

Karl Ziemelis: That's a very good question. I mean, the original papers that we published are, sorts of, doing two different things. The first strand of research is people are obviously seeing how high can the superconductivity temperature go, the transition temperature as we call it and already we are up to 50 Kelvin, again doesn't sound too impressive compared to the original high temperature superconductors, but on the other hand, this is way above what one would expect to be possible with conventional superconductivity and it's the highest transition temperature found outside the copper oxides. So, that's the first trend. People are obviously excited and exploring the different material systems, the different elements, and seeing if they can get any higher than that. Of course, the Holy Grail would be a room temperature superconductor, but we are a long, long way away from that. The other strand of research is looking more at what is actually making these materials superconduct. Are these in some way exotic like the high-temperature superconductors? And let's bear in mind, even after over two decades of research, we still don't know for sure how the high temperature superconductors work, or are they behaving in a more conventional fashion. Now both of those raise interesting questions in their own lights. If it is an exotic form of superconductivity, is it telling us something about the copper oxide superconductors, which are, as I say, still a bit of a mystery? Does it mean that we can get the temperatures higher and higher and higher? On the other hand, as some papers are seeming to suggest these are more conventional, that too raises interesting questions because they are already superconducting at temperatures much higher than we thought possible using the conventional mechanism of superconductivity.

Adam Rutherford: And you say that the Holy Grail is reaching room temperatures for superconductors, what happens then, how is that going to transform electronics?

Karl Ziemelis: Well, as with all Holy Grails, they're probably unattainable, but if we could get a material that would super conduct at room temperature basically you can envisage just replacing all your power cables and electrical cables and have something that no energy is lost through resistance. The current will just flow through it, no heat produced and you know, the energy savings would be tremendous, but let's bear in mind that even after two and a half decades with the much more successful, if you are thinking about temperature, copper oxide superconductors we are still no closer than we were since 1993, I think was when the record was last reached. I think the other cautionary note, we should say about the oxypnictides is that despite this huge flurry of work over the past few months, it's already looking like the transition temperature, the superconducting temperature may have plateaued out, it's about 50-55 Kelvin. Of course, we don't know what other surprises wait around the corner, but I think we need to be fairly cautious on the Holy Grail front out there for the time being.

Jingle

(Movie clip running)

Ilsa: Captain, the boy was playing the piano, but somewhere I've seen him.

Captain Renault: Sam?

Ilsa: Yes.

Captain Renault: He came from Paris with Rick.

Ilsa: Rick? Who is he?Captain Renault: Mademoiselle, you are in Ricks and Rick is?

Ilsa: Is what?

Captain Renault: Well, Mademoiselle, he's the kind of man that - well, if I were a woman, and I were not around, I should be in love with Rick, but what a fool I am talking to a beautiful woman about another man.

Hans Gruber: Do you really think you have a chance against us, Mister Cowboy?

(Sounds of gunfire)

Grant: You're the wrong guy, in a wrong place, at the wrong time.

John McClane: Story of my life.

(Sounds of gunfire)

John McClane: Welcome to the party pal!

Kerri Smith: It's simple enough to tell which of these movie clips is from the 1942 classic Casablanca and which is, Bruce Willis at his finest, but why do some movies like these become screen successes, while others go straight to DVD? Sounds like a question for a different podcast entirely, but in Nature this week, a new story details a tool that might help scriptwriters create sure-fire successes. The pod is a busy old place this week, as we are also joined by Mike Hopkin, who is here to tell us more. Mike start off by telling us what this new algorithm looks at? Published online (4 June 2008)

Michael Hopkin: Well this is a program to try and look at what really are the ingredients of a successful script and you might think Die Hard and Casablanca don't really have anything in common at all apart from the fact that they were both very successful movies in their own ways. But this is trying to see whether you can boil down the ingredients of a good movie into just a simple analysis of what words crop up in the scripts, how often those words are juxtaposed with each other and the, sort of, rhythms of how the words are used throughout the length of the movie and what they've actually shown is that you can, sort of, pick the ingredients of a good movie just by looking at this. Focussing in a way on the idea of mini-cliffhanger this seems to be a thing that lots of good movies have in common. If you imagine Bruce Willis making his way through the skyscraper in Die Hard, he has sort of intermittent battles with the terrorists, which kind of comes to our head at various points and then things calm down a bit and then a new cliffhanger builds up and he gets into another fight. And you can analyze the script and see exactly how this works, so you might see the name of his character, John McClane with the name of Hans Gruber, the main terrorist, and they might come together every so often and then this goes on and that actually creates sort of satisfying pattern within the movie, where you have a bit of excitement and then a bit of calmness and a bit of plot and then weirdly enough that pattern also seems to happen in Casablanca, if you imagine, Humphrey Bogart and Ingrid Berkman's characters. They are not fighting obviously, but while they are in a way, they're, sort of, wrestling with their feelings and they are, sort of, drawn together and then apart and together and there is a, sort of, mini-cliffhanger's feeling there and you can analyze that and see how they go through these emotional traumas just by looking at how and when the different verbs and names are used in the script.

Kerri Smith: So, some of these features are common to all screen successes as we are calling them, but some of them are genre specific and I suppose one of the things they picked out was the frequency of verbs and things like action films, which I think makes sense I suppose and things like names in dramas.

Michael Hopkin: Yeah well, it seems to work. I mean, obviously, it does depend on the genre. I mean, there is a sort of, you can go to script writing school and learn how to write an action movie and that deals not necessarily with the words in the script, but it says, you know, you should have a big explosion at the start and a chase scene and build things up and then have bits of action for people to watch, but not too much and then save something for the huge cataclysm at the ends, so this is, sort of, like a verbal equivalent of that really.

Kerri Smith: And but as you say and crucially it is the verbal equivalent and no more than that. Surely there is more to a good film than just the script which is what these authors have looked at?

Michael Hopkin: That's true and that is probably what a filmmaker would argue. This is obviously not trying to look at anything beyond the screenplay in the script and say if you imagine a movie like the Chinese movie hero, which was sort of fated by the critics for being really beautiful piece of cinematography and amazing colours and that really doesn't enter into this at all. So may be a purist might say, there are other ingredients to a film, but this would probably help you if you think, you've written a blockbuster and you are going around pitching it to the big screen, cigar-chomping executives, then you could probably help to strengthen your case by showing them a piece of computing like this.

Kerri Smith: And which films do the authors particularly write then, based on their algorithm?

Michael Hopkin: Well, as I was saying, Casablanca and they've looked at Die Hard, and really what they are trying to do is see whether audiences are right about films, so they've looked at other successful films, they've looked at the recent hit Juno as well and they have actually set up a web site where you can go and look at films like that and see exactly how their success maps out. What it seems to be showing rather than trying to make a magic formula for a blockbuster, they are trying to prove that things that audiences have liked do conform to these, sorts of, rules, so it's a kind of a retrospective proof, if you like.

Kerri Smith: So, it doesn't necessarily mean, then that films are going to become even more formulae than they already are?

Michael Hopkin: Well, let's hope not. I mean the other arguments that the researchers have put forward is that even something like Memento which was that movie a few years ago about the guy who has amnesia and it's all, the story is all filmed backwards and is completely off the wall and they say that even that fulfils the criteria that they have identified. So it doesn't have to be just a bland shoot them up in order to fit. And of course, if you think about it, you know, something being formulae that are a criticism of films, but it doesn't necessarily have to be. And if you think of anything a Mozart symphony or a classical building there you cannot get much more formulae than that but that does not stop them being a masterpiece.

Kerri Smith: Just because it is a formula it doesn't mean it's a bad one I suppose.

Michael Hopkin: That's true.

Kerri Smith: All right, thanks Mike.

Adam Rutherford: That's all for this week's show. Join us next time when Steven Pinker will be with us in the pod to talk about metaphors, swear words and why we really say, what we mean. I'm Adam Rutherford.

Kerri Smith: And I'm Kerri Smith. Here's looking at you, kid!

(Movie clip running)Rick: Louis, I think this is the beginning of a beautiful friendship...(Movie music)

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