Archive for the 'Mathematical & Physical Sciences' Category

Charged with uncertainty: how a classic classroom experiment reveals what we don’t know about static electricity

By Oli Usher, on 20 November 2014

Rub a balloon or a plastic rod, charging it up with static electricity, and it can suddenly pick up little pieces of paper. It’s a common classroom demonstration in high school science classes, an everyday example of electrostatic attraction. But it’s never explained fully in class – pupils are told about plastics gaining or losing electrons and becoming charged, but why (and how) this charge is actually created is never explained.

Static electricity picking up scraps of paper. Photo: Tess Watson (CC BY)

Static electricity picking up scraps of paper. Photo: Tess Watson (CC BY)

The reason for this is as simple as it is surprising: nobody actually knows.


Much of what we are taught in school science lessons is wrong. Electrons are not billiard balls spinning around an atomic nucleus – even if that’s a useful metaphor. Newton’s laws do not govern the motion of objects – though in most cases, they are so close as makes no difference. Copernicus did not claim, let alone prove, that the Earth orbits the Sun, though his model of the cosmos was an important innovation in the history of astronomy.

In all these cases, the classroom version is a reasonable approximation, a simplification which still helps children learn about science, without getting bogged down in unnecessary complexity.

But in the case of plastic being charged up with static electricity, scientists genuinely don’t fully understand what’s going on.


Katherine Holt

Katherine Holt

Katherine Holt is a researcher in UCL Chemistry who has worked on electrostatic charging, and is hoping to answer some of these questions. Initially interested in the way that charge can build up on the surfaces of nanodiamonds (microscopic diamonds formed in the soot created by explosives), she has come to work on the question of how static electricity forms on the surfaces of plastics.

For many years, this was the preserve of physicists, who looked at the big picture of how charge behaves on the surface of a whole object. But with the improvement in tools such as magnetic force microscopes, the field has in recent years opened up to chemists, who are interested in small-scale properties of materials, such as bonds between atoms, breaking and joining of atoms in molecules, the microscopic structure of surfaces and the behaviour of individual ions and electrons.

This change of emphasis, Holt says, has brought about a growing conviction that even the most superficial explanation given in school (“electrons are transferred to or from the plastic when it is rubbed”) is wrong. It is increasingly clear that the charging process is actually linked to imperceptible damage to the surface. Bonds between atoms on the plastic’s surface are being broken by the rubbing and this – not the exchange of electrons between surfaces – is leading to the charge being created.

Tunneling electron microscope image of two polystyrene beads rubbing together and then separating that clearly shows that material is transfered from one surface to another as they do so and that the surfaces become 'scarred' and damaged. Credit: Katherine Holt (UCL Chemistry)

Tunneling electron microscope image of two polystyrene beads rubbing together and then separating that clearly shows that material is transfered from one surface to another as they do so and that the surfaces become ‘scarred’ and damaged. Credit: Katherine Holt (UCL Chemistry)

But identifying microscopic damage on the surface and linking that to the creation of static electricity isn’t the same as figuring out what is actually going on.


When you break bonds between atoms in molecules, shattered fragments of those molecules (either individual atoms or groups of atoms) are formed. These highly reactive particles are known as free radicals.

And indeed, Holt says, you can find free radicals on the surface of charged plastic rods. What’s more, in the same location as these radicals, surface imaging techniques reveal the presence of electric charge.

But even this still doesn’t solve the mystery of precisely how electrostatic charging works: radicals are electrically neutral, so some other particle – presumably ions or electrons – must be carrying the charge.

There is more that isn’t known.

For instance, whether a plastic will become positively or negatively charged is easily predicted, there is even a table (the triboelectric series) which sets out which combinations of common polymers will charge each other positively or negatively when rubbed against each other. But the triboelectric series is based on experimental data – there is no underlying theory explaining what is actually going on, and Holt says, there may never be one: there could be a diverse range of different phenomena all contributing to the different electrostatic properties of the different plastics.


Working in a field which is experimentally well understood, but lacking in theoretical explanation, is not an entirely comfortable area for scientists. For engineers, however, who are interested in practical applications and less worried about theory, this is far more usual territory.

Holt says that, despite being a chemist, she’s now finding it easier to talk to engineers about her work in this area than she does with colleagues in closely aligned fields of chemistry. Engineers are interested in electrostatic charging for prosaic reasons – preventing powders from clumping together in factories, for example – and have an extensive practical understanding of it. But they don’t care in what’s happening on a molecular level.

Which, when the underlying science is as intractable as this, seems like quite a tempting thing to do.

Related links

Using phones to prevent pandemics

By Oli Usher, on 18 November 2014

Rachel McKendry (London Centre for Nanotechnology at UCL) leads a consortium that develops mobile phone-based diagnostic kits. She gave this year’s Rosalind Franklin lecture at the Royal Society, which you can view above.

In this lecture, Professor Rachel McKendry presented her research to create a new generation of mobile phone connected diagnostic tests for infectious diseases. The widespread use of mobile phones could dramatically increase access to testing outside of hospital settings, particularly in developing countries. Professor McKendry also presented the research foundations of a global early-warning system for infectious diseases that links the millions of symptoms that are self-reported on the web each day to mobile phone connected tests, in real-time and with geographically-linked information. This research lies at the cutting edge of infectious diseases, nanotechnology, telecommunications, big data and public health.


Countdown to touchdown

By Oli Usher, on 10 November 2014

Comet C-G, seen by Rosetta’s NAVCAM on 6 November 2014. Philae’s landing site is towards the top of the image. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

After a decade of travelling around the Solar System, the Rosetta probe is now at its destination: Comet 67-P/Churyumov-Gerasimenko (or Comet C-G to its friends).

The Rosetta mission is made up of two parts which have spent the last decade bolted together: the orbiter, and the lander, known as Philae.

Just after 9am GMT on Wednesday, Philae will separate from the mother ship and begin its descent to the comet’s surface. Around seven hours later, if all goes well, it will touch down on C-G’s rough surface.

This will be the first ever landing on a comet.

The gravitational force between two objects is directly proportional to their masses and the distance between them. Philae, at around 100kg, weighs much the same as a (large) human being, but the comet has a tiny fraction of the Earth’s mass. The pull between them is therefore minuscule – of the order of the gravitational force experienced by an object weighing just one gram on Earth.

Even though Philae will only be approaching Comet C-G at walking pace, the low gravity means it will need to attach itself to the surface with a harpoon to avoid bouncing back into space.

Because of this, the manoeuvre has been compared to a ‘docking’ rather than a ‘landing’.

UCL’s Prof Andrew Coates is a member of the Rosetta Plasma Consortium, which will be monitoring the plasma environment of the comet during Philae’s descent and landing. (He was also closely involved with the design and construction of Rosetta’s scientific payload.) He will be at mission control in Darmstadt on Wednesday as the lander begins its descent.

“The Rosetta orbiter and lander provide unique perspectives on how comets interact with the solar wind and on charged dust from the surface. The historic landing attempt will be a huge opportunity for coordinated observations,” says Prof Coates.

Comet seen over Rosetta's solar array, 14 October 2014. Credit: ESA/Rosetta/Philae/CIVA

Comet seen over Rosetta’s solar array, 14 October 2014, when the comet was around 16km away. Credit: ESA/Rosetta/Philae/CIVA (All rights reserved)


High resolution images

Visualising political polarisation

By Oli Usher, on 29 October 2014

Network diagrams are visualisations of the links between different things. Points mark out the things (for instance, children in a class) and lines are the connections between them (for instance, whether they are friends). For small sets of data, these are an arresting way of immediately understanding relationships between things.

For instance in this (imaginary) diagram, even the quickest of glances shows that Maryam has many friends and Peter has very few:

Simple network diagram

While they work well for small datasets, like a class with a few tens of children, these diagrams quickly become unreadable as you add more points.

But what if there were a way to avoid showing every point, while still somehow conveying the overall message? Many of the individual data points will be very similar or even identical (for instance Peter, Sarah and Philippe in the diagram above). If you could somehow average these out and come up with a handful of idealised versions of the children in the class, you could drastically reduce the clutter – and in the case of particularly complex ones, simplify a chart and make it readable.

This is something UCL statisticians Patrick Wolfe and Sofia Olhede have worked on in a new paper, published recently in the Proceedings of the National Academy of Sciences. The thrust of the paper is highly technical and not for the faint-hearted:


But one example of how their technique simplifies the presentation of data is much more comprehensible.

A decade ago, a statistical study of over 1200 political blogs in the run-up to the 2004 US election went viral thanks to a startling visualisation of the hyperlink between blogs:


Network diagram of US political blogs in 2004 (Credit: Lada Adamic, all rights reserved)

Blogs supporting President Bush’s Republican Party (red dots) overwhelmingly linked to other Republican blogs (red lines). On the left, blogs supporting the Democrats and their candidate John Kerry (blue dots) showed a similar pattern of mutual linking (blue lines).

Hyperlinks crossing the political divide – in orange – were relatively few and far between.

The chart starkly displays the lack of communication of a polarised political discourse. But if you’re looking for any finer detail, it is a mess. There are over a thousand dots and several thousand lines. The detail is impossible to see.

Olhede and Wolfe’s analysis condense down 1224 blogs into just 17 buckets of 72 blogs each, clustered together based on similar linking behaviour.

This diagram looks complicated at first sight, but it is in fact quite simple.

Each line and each column represents one of the 17 buckets of blogs, with lines and columns 1 to 8 representing the eight buckets of liberal blogs, while 9 through 17 are the nine buckets of conservative blogs.

Match up the co-ordinates, and the colour of the square shows how often these blogs link to each other, with dark blue being no links and bright red being extremely frequent linking.

So for instance, to see how frequently the blogs in the sixth bucket link to those of the eighth, you just need to look at  the sixth block in the eighth column. (The square is orange, representing frequent linking between them – as indeed you might expect of two liberal blogs.)

This simplified diagram, called a ‘network histogram’, reveals the same dramatic segregation of the blogosphere as the network diagram does – notice the sea of blue in the bottom right part of the diagram, where you might expect to see links between Republican and Democratic blogs – in a chart with just 153 points of data, rather than several thousand.

It also shows other features such as relative popularity within each political grouping (which is virtually impossible to see in any detail in the original visualisation) as well as how much blogs within each of the 17 bins link to themselves (i.e. the blogs most similar to them). Perhaps surprisingly, many of them don’t – with the most isolated blogs not linking to blogs similar to themselves, but just linking to the most popular, most mainstream ones on their side of the political spectrum.

The network histogram also reveals the nature and frequency of the (rare) links across the political divide – for instance, the most popular cross-partisan linking occurs between bucket 9 of conservative blogs and bucket 8 of liberal blogs – though even this is only frequent enough to show up in pale yellow.

Make the histogram a square (by mirroring it), and the data can be represented in different ways – for instance, with different heights representing varying intensities of linking (top) or map-like contours (bottom).





Yesterday’s solar eclipse, seen from space

By Oli Usher, on 24 October 2014

Yesterday saw a partial eclipse of the Sun, visible in parts of eastern Russia and North America. In space, however, a more impressive eclipse (with virtually the entire solar disc obscured) was visible to the Japanese Aerospace Exploration Agency‘s Hinode spacecraft.

Hinode (‘Sunrise’) was built in part by UCL’s Mullard Space Science Lab, and is the latest chapter in a long history of close relations between UCL and Japan.

This video shows the view captured from the spacecraft’s X-ray telescope, which captures the extremely hot gases in the solar atmosphere. (Note that while X-rays may let us see through a few centimetres of flesh, they don’t let us see through several thousand kilometres of Moon.)

Video credit: Shimojo/JAXA/ISAS

Representing resource use at UCL… using chemistry glassware and electronics

By Kat F Austen, on 20 October 2014



How do you represent the complexities of the resource use of a university using just what you can find in a chemistry lab – and some collective ingenuity?

That’s what Andrea Sella, Joanna Marshall-Cook and I set out to do over the course of last week with the help of Rae Harbird and Stephen Hailes.

The result, Elements, is on show in UCL’s North Cloisters for Degrees of Change, a week long endeavour by UCL’s Sustainability team to explore the environmental consequences of all the world-class teaching, research, collecting, exhibiting, making, inventing and outreach that goes on at the university.

During the research for the installation I learned some interesting statistics. For instance, a typical chemistry fume cupboard uses 10,000kWh of electricity per year (£1,000), and our heating comes from a series of underground pipes.

The installation is a visual metaphor for how the university’s heating and water systems work. We often don’t think about the consequences of running a tap, or pouring a bucket down a drain, flushing a toilet, taking a shower. Chemical glassware in all its varied and complex forms provides a perfect toolbox to explore the convoluted system of flows in resource infrastructure. Elements incorporates soxhlets - a type of chemical glassware normally used for extracting liquid from a solid, such as producing essential oils – which act as reservoirs within the system as a whole, just as we act as reservoirs for water either within ourselves or by our actions.

Lots of crazy glassware and - lit up in green and looking suspiciously like UCL Engineering's logo, an EngDuino computer, monitoring the water level in the system

Lots of crazy glassware and – lit up in green and looking suspiciously like UCL Engineering’s logo – an EngDuino computer, monitoring the water level in the system

The crazy glassware installation also has a 5L round bottomed flask and an electric pump – after all, it takes power to heat and move all the university’s water. The flask is like the water infrastructure external to UCL – and is monitored by an EngDuino and sensor, programmed by Rae and Stephen, that alerts us when the water levels are low.

A sensor detects the water level and reports back to the Engduino if the level is too low

A sensor detects the water level and reports back to the Engduino if the level is too low

At a time of increasing water scarcity and climate change due to our energy use, it’s important to realise that our actions on a personal scale have a real affect that ripples through the infrastructure that helps us live as well as we do.

Mapping the light of the cosmos

By Oli Usher, on 1 September 2014

This image shows one possible scenario for the distribution of light in the cosmos. Photo credit: Andrew Pontzen/Fabio Governato

This image shows one possible scenario for the distribution of light in the cosmos. Photo credit: Andrew Pontzen/Fabio Governato

Figuring out what the structure of the universe is surprisingly hard. Most of the matter that makes up the cosmos is totally dark, and much of what is left is in tiny, dim galaxies that are virtually impossible to detect.

This image shows a computer simulation of one possible scenario for the large-scale distribution of light sources in the universe. The details of how light (and hence galaxies and quasars) is distributed through the cosmos is still not a settled question – in particular, the relative contributions of (faint but numerous) galaxies and (bright but rare) quasars is unknown.

A faint dwarf galaxy

(New research from UCL cosmologists published last week shows how we should be able to find out soon.)

However, astronomers know that on the largest scales, the universe is structured as a vast web made up of filaments and clusters of galaxies, gas and dark matter separated by huge, dark voids. Observational astronomy is making strides forward in mapping out these structures in gas and light, but the smallest galaxies – less than a pixel across in the image above – might never be seen directly because they are simply too faint.

A Hubble image of a nearby faint dwarf galaxy (right) shows the challenge involved in observing these objects even when they are in our galaxy’s vicinity.

These computer models are one way of trying to extrapolate from what we know to what is really there. New research from UCL now shows how we can also use future observations of gas to find out more about this elusive population of tiny galaxies.

This simulated image shows the distribution of light in an area of space over 50 million light-years across. The simulation was created by Andrew Pontzen of UCL and Fabio Governato of the University of Washington.


High resolution image

Why art, not science, deserves credit for these pioneering dinosaur reconstructions

By Oli Usher, on 26 August 2014

A century and a half ago, Britain was swept by dino-mania. The discoveries of ancient fossils and the first characterisations of dinosaur species, combined with new scientific theories that posited that the Earth was far older than previously thought, fuelled a fascination with all things ancient.

A concrete example of this period is still visible today, in the form of the dinosaur statues in Crystal Palace Park. These date to 1854 and were built for the reopening of the Crystal Palace in Sydenham, when it was rebuilt there following the 1851 Great Exhibition in Hyde Park

The Crystal Palace Dinosaurs in 1854, by John Haygarth. Picture credit: Wellcome Trust (CC-BY)

The Crystal Palace Dinosaurs circa 1854, by George Baxter. Picture credit: Wellcome Library (CC-BY)

A naïve view of these is that they are a quaint, even amusing, example of how ignorant the Victorian scientists were – the statues predate Darwin’s theory of evolution by five years, and in some cases they bear little resemblance to the animals they claim to represent.

Joe Cain (professor of history and philosophy of biology in UCL Science and Technology Studies) has studied the statues’ history and says that naïve view is nonsense. The scientific origins of these statues is far more nuanced and interesting – and in any case, the credit for them lies with the sculptor, Benjamin Waterhouse Hawkins, far more than it does with the zoologist Richard Owen, who supposedly directed their design.

Megalosaurus at Crystal Palace Park. Photo credit: O. Usher (UCL MAPS) (CC-BY)

Megalosaurus, one of the statues at Crystal Palace Park. Photo credit: O. Usher (UCL MAPS) (CC-BY)


Hawkins was a scientific illustrator, an experienced translator of scientific ideas. Owen was just one of several sources he consulted, and Hawkins kept up with the rapidly expanding literature of the animals he was working to model for his displays. Hawkins even represented competing theories of reconstruction in his statues. There are two Iguanodon statues, for instance. One is long, low and lizard-like; the other is stocky and raised on its four legs, more like a hippopotamus or rhinoceros.

There is plenty to show that the artist wasn’t merely doing what he was told, but was actively interpreting the scientific evidence.

There also is plenty that science didn’t (or, couldn’t) tell him. Even more than today, the Victorians had only partial specimens, made of various bones of various origins and in various conditions, leaving Hawkins to fill very large gaps. On top of this, Hawkins had to invent elements such as pose, movement, and facial expressions. None of these could be gleaned even from perfectly preserved and well-understood fossils.

Given the uncertain (and disputed) scientific theories, the limited selection of fossils to work from, and the inevitable necessity of artistic licence, Cain thinks the dinosaur statues are something to admire rather than ridicule.

In any case, while some of his statues, are quite different from today’s reconstructions…

Hawkins' megalosaurus (left) doesn't look much like modern reconstructions. Photo credit: CGP Grey (CC-BY) and Mariana Ruiz (public domain)

Hawkins’ Megalosaurus (left) doesn’t look much like modern reconstructions. Photo credit: CGP Grey (CC-BY) and Mariana Ruiz (public domain)

…others, such as his plesiosaur, are remarkably similar to what we have now.

Hawkins' plesiosaur (left) and a modern artist's impression (right). Photo credit: Berlt Watkin (CC-BY) and Dmitry Bogdanov (CC-BY)

Hawkins’ plesiosaur (left) and a modern artist’s impression (right). Photo credit: Berlt Watkin (CC-BY) and Dmitry Bogdanov (CC-BY)


Cain’s interpretation of how the Crystal Palace Dinosaurs came about rings very true to me. In a previous life I worked with some of the people who prepare scientific visualisations, animations and artists’ impressions for the Hubble Space Telescope. The case of HD 189733b – a planet that was observed being scorched by a stellar flare (among other research) – is remarkably similar to the dinosaurs of Crystal Palace.

Much like Benjamin Waterhouse Hawkins, those animators had a great deal of scientific information they could draw on – on the size and brightness of the flare, on the optical properties of the atmosphere, on the colour of the star and its appearance. But as with the Crystal Palace Dinosaurs, these were just pieces of a puzzle, with plenty missing and some educated guesswork involved in putting them together.

The resulting animations are rather beautiful, and like with the dinosaurs, the artist deserves at least as much credit as the scientist does.

  • The Friends of Crystal Palace Dinosaurs website has extensive information on the dinosaurs, where to visit them and the campaign to conserve them. Joe Cain is one of the leading members of the Friends, and sits on the group’s management board.

Kathleen Lonsdale interview

By Oli Usher, on 19 August 2014

If you don’t know who Kathleen Lonsdale was, you should.

Lonsdale was a hugely important chemist (in the field of crystallography), an outspoken political activist and president of what is now the British Science Association. She was also, from 1949, the first woman to become a professor at UCL.

BBC Woman’s Hour interviewed her in 1967, shortly before she retired from UCL. The programme, available on iPlayer, is well worth a listen.

Lonsdale retired from UCL in 1968, and died in 1971, but she is commemorated in the name of the Kathleen Lonsdale Building on Gower Place. This building houses many of UCL’s science labs.

Lonsdale is remembered in the name of the Kathleen Lonsdale Building, which houses many of UCL's science labs. Photo: Gnesener1900 (CC-BY-SA)

Lonsdale is remembered in the name of the Kathleen Lonsdale Building, which houses many of UCL’s science labs. Photo: Gnesener1900CC-BY-SA

Thanks to Joe Cain for bringing this to our attention.

Photo album from the Dark Energy Survey

By Oli Usher, on 18 August 2014

The Dark Energy Survey, which has just begun its second year of observations, is gathering data about one of the most puzzling phenomena to be discovered in the past century: that the universe is not only expanding, but is doing so at an ever faster rate. Some as yet unknown force dubbed ‘dark energy’ is driving this acceleration.

Dark energy affects the appearance and evolution of the universe on very large scales. The Dark Energy Survey aims to find out more about this phenomenon by studying measuring four key cosmological probes:

  • The number of galaxy clusters;
  • The distances to faraway supernovae;
  • The bending of light by gravitational lensing;
  • and the pattern of the distribution of galaxy clusters across the universe.

Observing these requires sharp images that can detect very distant (and hence faint) objects, and so the the images collected by the Dark Energy Camera, the survey’s workhorse, are often quite stunning.

This image of the NGC 1398 galaxy was taken with the Dark Energy Camera. This galaxy lives in the Fornax cluster, roughly 65 million light-years from Earth. It is 135,000 light-years in diameter, just slightly larger than our own Milky Way galaxy, and contains more than a billion stars. Credit: Dark Energy Survey.

This image of the NGC 1398 galaxy was taken with the Dark Energy Camera. This galaxy lives in the Fornax cluster, roughly 65 million light-years from Earth. It is 135,000 light-years in diameter, just slightly larger than our own Milky Way galaxy, and contains more than a billion stars. Credit: Dark Energy Survey.

To mark the beginning of the second year of DES’s five-year observing run, the team have published a gallery of the most attractive images from the first year of operation, including the image of galaxy NGC 1398, pictured above. The complete the gallery is at the end of this post and in the faculty Flickr gallery.

UCL is deeply involved in DES, and Prof Ofer Lahav, Vice-Dean (Research) of Mathematical & Physical Sciences, is chair of the DES UK board and co-chair of the DES international science committee.

More information on UCL’s involvement in the DES science programme is available in an article on the UCL news pages.


Copyright: Dark Energy Survey photos are free to use providing they are credited to the Dark Energy Survey. Any queries on reuse should be sent to Fermilab Visual Media Services at vismedsr@fnal.gov.


High resolution images