Wednesday, October 27, 2010

Beanbag robotics

Here’s a neat idea that I’ve written up for my Material Witness column in the November issue of Nature Materials.

It’s a commonplace observation in robotic engineering that some of the hardest tasks for robots are the ones we do without thinking: balancing upright, say, or catching a ball. Even the simple feat of picking up objects, when considered as a problem in control systems engineering, becomes a formidable challenge. How should we position the fingers on approach, where should we grip the object, how much pressure should we apply? Answering these questions generally requires exquisite feedback between vision, motor control, and tactile sensing, not to mention (in our case) a fair degree of intuition and training.

The ingenuity that has gone into solving these problems in robotics is exhilarating, as exemplified by the very recent reports in this journal of pressure-sensing ‘smart skin’ [1,2]. But these solutions tend to be predicated on the assumption that a robotic hand will follow the human prototype in having several gripping fingers. The widespread use of this design in the animal world testifies to its virtues, but there’s no escaping the demands it makes on actuation, sensing and feedback.

Now Eric Brown of the University of Chicago and his coworkers have described a new design for a robotic gripper that dispenses altogether with these difficulties by replacing active control with passive adaptability. Their device has no fingers at all, but instead uses a soft mass that moulds itself to the shape of the object to be gripped [3]. The crucial aspect of the design is that, once configured in this way simply by pressing onto the object, the gripper undergoes a transition from soft to hard, becoming a rigid body encasing enough of the object to hold it with, in general, an appreciable force.

That is achieved by filling the body of the gripper – an elastic latex bag – with granular material, such as tiny glass spheres or, in one prototype, ground coffee. Rigidification of the conformable grainy mass is then induced by evacuating the air between the grains, causing slight compaction. This is sufficient to trigger a jamming transition: the grains enter a collective state of immobility, like that in a blocked funnel, which, as Brown’s coauthor Heinrich Jaeger explains in another preprint [4], is a non-equilibrium state directly analogous to a glass. Indeed, such a packing-induced transition between solidity and fluidity is familiar to anyone who has ever opened a vacuum-packed packet of coffee.

Once rigid, the gripper holds an object by a combination of three mechanisms: friction, suction caused by deformation of the jammed bag as it lifts, and geometrical ‘wrap-around’ interlocking. The resultant gripping force depends on the geometry of the object, but a whole variety of forms, from steel springs to raw eggs, can be securely held. What is more, the device works in the wet, and can grip several different objects at once while retaining their orientation. Much as in the case of walking robots [5], it shows how smart use of passive control can greatly simplify the engineering problem.


1. Takei, K. et al., Nat. Mater. 9, 821-826 (2010).
2. Mannsfeld, S. C. B. et al., Nat. Mater. 9, 859-864 (2010).
3. Brown, E. et al., preprint
4. Jaeger, H. & Liu, A. J., preprint
5. Collins, S. H.,Wisse, M., Ruina, A. & Tedrake, R., Science 307, 1082-1085 (2005).

Tuesday, October 26, 2010

Prospects for the Science Book Prize

I’ve just put up a more expansive comment on the Prospect blog about the demise of the Science Book Prize. Sob.

Friday, October 22, 2010

Under the bridge

I was recently sent this striking photo of a pattern in melting ice by Georg Warning in Konstanz. He asked if I’d seen anything like it in my research for The Self-Made Tapestry, in which Georg noticed the apparent similarity to my picture of Marangoni convection. That venerable  tome has now been updated as Nature’s Patterns, in which I include a discussion of ice erosion patterns called penitentes, found in the Andes. Penitentes are much more strongly peaked, but it sounds to me as though the early stages of growth might resemble something like this. In the third book of the trilogy (Branches) I say the following:

The snowfields of the Andes experience a kind of erosion process that creates one of nature’s strangest spectacles. The high glaciers here can become moulded into a forest of ice spires, typically between 1 and 4 metres high, called penitentes because of their resemblance to a throng of white-hooded monks. Charles Darwin saw these eerie formations in 1835 en route from Chile to Argentina. ‘In the valleys there were several broad fields of perpetual snow’, he wrote in The Voyage of the Beagle. ‘These frozen masses, during the process of thawing, had in some parts been converted into pinnacles or columns, which, as they were high and close together, made it difficult for the cargo mules to pass. On one of these columns of ice, a frozen horse was sticking as on a pedestal, but with its hind legs straight up in the air. The animal, I suppose, must have fallen with its head downward into a hole, when the snow was continuous, and afterwards the surrounding parts must have been removed by the thaw.’
   Darwin remarked that the locals believed them to be formed by wind erosion. But the process is more complicated than that, representing a classic case of pattern formation by self-amplifying feedback. The air at these great heights is so dry that sunlight falling on the ice transforms it straight into water vapour rather than melting it into liquid water. A small dimple that forms in the smooth ice surface by evaporation acts as a kind of lens that focuses the sun’s rays into the centre, and so it is excavated more quickly than the surrounding ice. It’s a little like diffusion-limited aggregation or dendritic growth in reverse: a ‘fingering’ instability penetrates into the ice rather than pushing outwards from the surface.
   The process can be accelerated by a fine coating of dirt on the snow surface. As the troughs deepen they expose clean snow that is prone to further evaporation, whereas dirt in the old snow at the peaks covers the ice crystals like a cap and insulates them. You might expect that, on the contrary, snow or ice will melt faster when dirty than when clean, because the darker material will absorb more sunlight. But whether a layer of dirt acts primarily as an insulator or an absorber depends on how thick it is.

That last comment about dirt seems to establish the link, since evidently dirt in the ice traces out the ridges in this case. The underside of this ice bridge is presumably never exposed to the direct rays of the sun, but all the same there is probably some analogous process at play here.

Thursday, October 21, 2010

None shall have prizes

Hurrah for Nick Lane, whose Life Ascending won the Royal Society Science Book Prize last night. If anyone there was in doubt that Nick’s book deserved the award, it became crystal clear during the short readings by each author before the announcement (a first for this prize) that his tight, elegant and vivid prose put him ahead of the others. Shame on me for not mentioning Nick’s book in my round-up of the year's science books in the Sunday Times last year.

But the ceremony seemed to me curiously muted, which perhaps reflects the fact that it may be the last: the Royal Society has said it cannot continue funding the prize without a sponsor, and has been unable to find one. This is tragic and baffling. The financial cost can’t be onerous: the glitzy award ceremony was ditched some years back, and there can’t be many other costs except for the modest prize money itself. Besides, as Georgina Ferry said to me recently apropos the also (more or less) defunct Association of British Science Writers Awards, it’s not about the money anyway: the winners would be just as pleased (well, almost) with the recognition alone. As well as the big literary prizes, just about every genre of fiction and non-fiction has its awards – it would be sad indeed if science writers do not, not least because this sends out the message that no one cares much about what they do. Yes, I know we writers are insecure, and that prizes are in any case mostly capricious and invidious beauty contests – but now that the science book prize looks set to vanish, it is more clear to me than ever that what I cared about is not the thought of winning it but the mere knowledge that it is there. And as I tried to say clumsily terms to the BBC, this award was a way of getting a conversation going about how and why science is communicated, and about the roles of science in society. Are the big pharma or IT companies not so keen, even in these straitened times, to see that conversation happen that they can’t find a bit of spare cash?

Tuesday, October 05, 2010

Music on the brain

There was a nice conference on ‘music and the brain’ here in London last weekend, and I have a report on it on Nature News. Here’s the longer version.

The emotions teeming inside the works of the Romantic composers may have neurological explanations, as a recent meeting explored.

It’s not hard to understand why Robert Schumann should have been selected as the focus of a meeting called 'The Musical Brain', which took place last weekend in London [1]. Not only is the 200th anniversary of the German composer’s birth, but his particular ‘musical brain’ gives neuroscientists plenty to think about.

For one thing, Schumann suffered from the neurological condition called focal dystonia – a loss of muscle control that afflicts an estimated 1 in 100 professional musicians and ended Schumann’s hopes to be a concert pianist. And he seems also to have struggled with severe bipolar disorder, which apparently dictated the rhythm of his creativity and left him confined to an asylum for the last two years of his life.

Focal dystonia is sometimes called ‘musician’s cramp’, but it is not primarily a muscular problem: it begins in the brain [2]. As neuroscientist Jessica Grahn of Cambridge University explained, it stems from the way intense musical practice can over-inflate the mental representation of the relevant part of the body (usually the fingers, although it can affect lip control in brass players). Once the neural representations of the fingers overlap, they can no longer be controlled independently.

This typically manifests itself as a stiffening or curling-up of some fingers. The American pianist Leon Fleisher lost the use of his right hand in this way in 1963, and was restricted for decades to the repertoire for left hand only (much of it written for the pianist Paul Wittgenstein who lost his right arm in World War I). Although dystonia is a consequence of over-practice (or as Fleisher says, inappropriate practice techniques), there may also be a genetic predisposition to it – it is more common, for example, among men. It’s precisely because it is a neural rather than a muscle problem that dystonia is so hard to treat, and indeed there is still no genuine cure.

Schumann succumbed to this excruciating condition in his right middle finger at the age of 21 [3]. He used a home-made contraption to stretch the finger, but it may have done more harm than good. He even composed an extremely difficult piece, his Toccata Opus 7, that avoids the use of the middle finger entirely (hear it here). ‘I was hoping to convince someone to play it at the meeting’, says Grahn, ‘but it’s a bear, so no luck.’

With his performing career stalled, Schumann focused on composing – which, according to neuroscientist Eckart Alternmüller, a specialist on focal dystonia, was for us ‘a blessing, because it allowed his creative talent to be developed to masterful perfection’ [3]. But that was probably little consolation to poor Schumann, particularly as things got far worse for him. Towards the end of his life, he heard voices and was tormented by visions of angels and demons. Fearful that he might harm his wide Clara, in 1854 he attempted to drown himself in the Rhine, only to be rescued by boatmen. That was when he voluntarily entered the asylum where he stayed until his death.

Not everyone agrees that Schumann was bipolar: a recent biographer John Worthen argues that he exhibited no serious mental disturbance until the end of his life, when his psychological disintegration could have been caused by tertiary syphilis [4]. Alternatively, it has been argued that Schumann’s final ‘madness’ looks like a case of mercury poisoning, caused by the mercury medication then used to treat syphilis. But psychiatrist (and concert pianist) Richard Kogan has argued that Schumann’s well documented spells of wild creativity and sleeplessness interspersed with periods of lethargy look like a classic case of bipolar disorder.

If so, he is by no means unique among composers in wrestling with mental illness: Mozart, Beethoven, Tchaikovsky and Leonard Bernstein all seem to have done so. All of which raises the question whether we can hear the emotional turmoil in what they wrote. It’s not hard to imagine so: music critic Stephen Johnson, who introduced the life and work of Schumann at the meeting (and also has bipolar disorder), says of Schumann’s fiendish Toccata that ‘it seems exuberant, it seems it’s flying and it’s very exciting – but it’s breathless, it’s on the edge of something frightening.’

It’s not obvious, however, that we should infer a composer’s state of mind from the music. The German composer Paul Hindemith felt that, if we believed that, the leaps of emotional tone classical compositions often exhibit would compel us to be diagnosing mental disorder all the time, while even the febrile Tchaikovsky doubted that composers express their mood at the actual moment of composition. Take Mozart’s wickedly playful A Musical Joke (K.522): it was apparently the first piece he composed after his father died.

But nonetheless there can be no doubt that music does express emotion – indeed, it is one of the most powerful emotional vehicles in all of human creativity, which seems to be one reason why it can be so effective in therapeutic contexts. It was an interest in the use of music in learning and therapy, says music psychologist Katie Overy of Edinburgh University, ‘that forced me to get into the emotional aspects’.

While acknowledging that musical expression is multi-faceted, she argues that current neurological studies suggest that the activation of mirror neurons – ‘empathy circuits’ that fire both when we watch another person perform an action and when we perform it ourselves – offer a clue about how music works [5].

It may be, she says, that when we hear music, we can ‘read’ it as we would read indicators of emotional state in another person’s vocal or physical gestures. ‘Happy’ music is typically up-tempo and high-pitched, while ‘calm’ or ‘sad’ music tends to be soft, slow and low-pitched [6], because of the way these acoustic qualities mimic the actions and voices of people in those emotional states – an observation that seems to hold across cultures, as Stefan Koelsch of Sussex University, another speaker at the meeting, and his coworkers have shown recently [7].

‘Music has the capacity to tap into these qualities and expand on them’, says Overy. Pianist Ian Brown illustrated during her talk how, for example, musical expressivity involves the mimicry of singing with legato (smoothly connected notes) and speech-like phrasing. The composer and performer can then add to this effect by deploying culture-specific structures (such as major/minor keys; see here) or unexpected rhythms and harmonies: Koelsch showed that musical ‘surprises’ can elicit the same neurological signals as other types of surprise [8].

In this respect, then, support may be emerging for the suggestion of philosopher Susanne Langer that music mimics the dynamics of emotion itself – or, as psychologist Carroll Pratt put it in 1931, that ‘music sounds the way emotions feel’.

1. The Musical Brain: Arts, Science and the Mind, St John’s Smith Square, London, 2-3 October 2010.
2. E. Altenmüller & H.-C. Jabusch, J. Hand Therapy 22, 144-155 (2009).
3. E. Altenmüller, in J. Bogousslavsky & F. Boller (eds), Neurological Disorders in Famous Artists (Karger, Basel, 2005).
4. J. Worthen, Robert Schumann: Life and Death of a Musician (Yale University Press, New Haven, 2007).
5. I. Molnar-Szakacs & K. Overy, SCAN 1, 235-241 (2006).
6. L. L. Balkwill & W. F. Thompson, Music Perception 17, 43-64 (1999).
7. T. Fritz et al., Curr. Biol. 19, 1-4 (2009).
8. S. Koelsch, T. Frtiz & G. Schlaug, NeuroReport 19, 1815-1819 (2008).

Monday, October 04, 2010

The Corrections

Somehow I suspect that Jonathan Franzen doesn’t need me to feel his pain. But all the same, I do. He has just demanded the shredding of something like 80,000 copies of the UK edition of his book Freedom because the wrong version of the proofs was used for the final printing, containing lots of little typos and omissions of corrections. Several reviewers have admitted that they’d never have noticed the difference, but that’s not the point. It’s not so much about perfectionism as a kind of pride. I have never, like Franzen, taken nine years to write a book, and I don’t have the ability, and probably not the inclination, to choose words as carefully and precisely as he evidently does. But all the same, I know that errors introduced in the production process feel like a two-year-old has just scribbled over your pages – like mindless or wilful destruction. I know this is unfair – no one in the production process is trying to do other than perform their job well – but that’s how it feels. What is particularly galling is that, unless you’re Franzen, one these errors have happened, you’re stuck with them forever. It arouses that childhood feeling of a terrible injustice that you are utterly powerless to rectify. And it happens in the swanky hardback version, the version that is meant (unlike the paperback) to be an object of beauty. There are one or two pages of my previous books that I still mustn’t look at for fear that I’ll start fuming all over again.

There have been times when I have been driven to conclude that, if you leave typesetters the slightest opening for introducing a mistake, they’ll seize it. Many times I have said to myself that I would in future always insist on seeing the final, final version of the proofs before they go off for printing, only to feel, when the time came, that this would seem just too much like the neurotic author – and then to regret not doing so. It does amaze me that typesetters will interpret letters in handwritten proof corrections in such a way as to turn a perfectly obvious and ordinary word into gibberish – sometimes you can’t help feeling they are just having a laugh. And publishers often seem to feel no need to double-check corrections, or so it seems. Oh, I’m sure typesetters must be confronted with some real nightmares sometimes – pages covered in wild scribbles connected by a maze of looping arrows. I have occasionally done them no favours myself. But there just don’t seem to be enough checks built into the publishing process, which seems bizarre given how tough it is to get a book published and how cautious publishers have become about commissioning.

I exempt my current publisher, Bodley Head, from these criticisms – not simply to keep them sweet, but because they are undoubtedly the most careful and conscientious I have ever worked with. Of course, that is inviting trouble, especially with a stack of proof corrections sitting on my desk right now (February 2011, since you ask). And worse: when I read that the typesetter for Franzen’s book was a company called Palimpsest, it rang a bell. So I checked out my own pages… yup.