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Robert Richardson: 1937–2013

The American condensed-matter physicist and Nobel laureate Robert Richardson has died at the age of 75 from complications related to a heart attack. Based at Cornell University since 1968, Richardson shared the 1996 Nobel Prize for Physics with his former PhD student Douglas Osheroff and Cornell’s David Lee. The three researchers were cited for their discovery that helium-3 becomes a superfluid at very low temperatures.

Being fermions, helium-3 atoms ought not to be able to condense into a superfluid, but some physicists had speculated that the atoms could form bosonic pairs similar to the Cooper pairs found in superconductors. In a famous series of experiments in 1971, Richardson and colleagues confirmed that these pairs formed a superfluid at temperatures below about 2.5 mK.

“Glorious time” at Duke

Richardson was born on 26 June 1937 in Washington, DC and did BSc and MSc degrees at the Virginia Polytechnic Institute. He received a PhD in physics in 1966 from Duke University, where he worked under Horst Meyer on nuclear magnetic resonance of solid helium-3. Richardson later recalled the “glorious time” he spent at the university.

After a further year at Duke, in 1966 Richardson moved to Cornell, where he spent the rest of his career focusing on low-temperature physics, working initially with Lee and Dave Reppy and later becoming director of Cornell’s Laboratory of Atomic and Solid State Physics. He also served as the university’s first vice-provost for research from 1998 to 2003 and had a spell as director of the Kavli Institute at Cornell for Nanoscale Science.

Landmark report

In 2005 Richardson helped write the landmark National Academy of Sciences report entitled Rising Above the Gathering Storm: Energizing and Employing America for a Brighter Economic Future. It identified shortcomings in the US’s approach to developing science and technology, and recommended changes to how research and higher education are funded and how science and technology are taught in US schools.

How can we engineer human tissue?

In less than 100 seconds, Mehdi Nikkhah explains how tissue engineering is being developed to address the current needs in organ transplantation.

Another side of black holes

So much has been written about black holes over the past few decades that if all this literature were collected in one place, one suspects that its sheer density could form a black hole of its very own. This is in no way a criticism of the people who write about them, however, as the intrinsic weirdness of these cosmic enigmas captures our fascination as surely as the black holes themselves capture the light and matter upon which they feed. With Gravity’s Engines, the American astronomer Caleb Scharf offers a different take on these objects by explaining how they are closely interlinked with star and galaxy formation, energy conversion and the distribution of matter in the universe.

Although the book is subtitled “The Other Side of Black Holes”, for the most part this is not to be taken literally. You should not expect to read about parallel universes, “white holes”, adventures in relativity or – a favourite of black-hole literature – the “spaghettification” that occurs when an unlucky space traveller approaches a black hole’s event horizon. Instead, Scharf’s attention is drawn to the supermassive black holes that lie at the centre of galaxies – and particularly the bold idea that these objects are responsible for life in the universe.

Scharf worked in X-ray astronomy before he embarked on his present career as an exoplanet researcher at Columbia University in the US, and in the book’s first chapter he returns to his earlier interest. He begins by charting the journey of an X-ray photon from a distant quasar 12 billion light-years away all the way to the Earth-orbiting Chandra X-Ray Observatory, which detects it and sends a blip of data to Scharf’s computer screen. Scharf tells the story of the photon’s travels in parallel with a more familiar tale of our solar system’s formation and our own history as a species. The combination of the two makes for an exhilarating ride, one that breathlessly captures the sheer enormity of time and distance (the two being inextricably linked in cosmology) involved in the photon’s journey.

The rest of the chapter is devoted to early black-hole research. The history of such research is surprisingly long, dating back to the mid-18th century, when an English rector and polymath, John Michell, tried to apply Newton’s laws of gravitation to distant stars. A really creative thinker, Michell used the nascent discipline of statistics to show that at least some stars must be orbiting each other – a configuration that allows their mass to be calculated. When Michell embarked upon this research, the age of stellar measurements by telescope had not yet begun, but as Scharf shows, further insights nevertheless led the resourceful Michell to the concept of “dark stars” – gravitational kings of the heavens from which even light could not escape. Pierre-Simon Laplace, working in France, also concluded that “black stars” must exist in the universe, but they would, necessarily, be invisible. How could one possibly observe such a thing?

Scharf shows how black holes act as regulators and galactic batteries

Ultimately, scientific insights from several fields proved crucial to our understanding of black holes. Scharf is surprisingly downbeat about one such insight – the Michelson–Morley experiment of the late 19th century, which he calls a “spectacular failure”. In fact, it should be viewed as a phenomenal success, as it overturned the deeply held view that there is a “luminiferous aether” through which light propagates. Banishing the aether led to more accurate theories of light and its behaviour, which would eventually help us comprehend the extreme environment of black holes. And yet despite this breakthrough (and others by James Clerk Maxwell, Albert Einstein and Karl Schwarzschild), for many years, further observations only revealed further puzzles. Nevertheless, these developments formed the beginning of our current, larger picture.

Later in the book, Scharf turns his gaze towards our own galaxy. Does it harbour a black hole? What about other galaxies? If so, why? Much of the book is devoted to the role that black holes play in large-scale galaxy formation, and whether galaxies or black holes formed first, but even the answers Scharf is able to give seem only to produce more questions. How is it that these black holes can produce energy more efficiently than nuclear fusion? How can an object that fits in the orbit of Neptune affect star formation for an entire galaxy? Why do the photons produced by the cosmic jets that emanate from black holes seem more energetic than they ought to be? By placing the curious nature of these extreme objects within in the context of galaxy formation, Scharf shows how black holes act as regulators and galactic “batteries”. Indeed, his book might have been more appropriately called Galaxies’ Engines.

In the final chapters, Scharf collates what he has previously covered on X-ray and radio astronomy, radiation, quantum physics and relativity to construct an image of the black hole’s role in the creation of life. He also describes some ambitious space projects such as the Laser Interferometer Space Antenna (LISA). This three-part spacecraft was designed to “listen out” for gravitational waves using components that are separated by a baseline of 5 million km, but fell victim to NASA budget cuts. It is now being reformulated by the European Space Agency as the New Gravitational-wave Observatory.

Scharf has a pleasing, colloquial style that rarely seems out of place, and many of his analogies work well. One particularly beautiful example is his characterization of the central black hole in the Milky Way galaxy as a monster in a castle surrounded by forests. However, he sometimes uses more analogies than he needs to, and a few of them are a little odd; for example, it may be true that the kinetic energy of a potted plant dropped on the Sun is equivalent to that of 100 billion apples dropped from 1 m on Earth, but I am not sure what we are meant to learn from this. In addition, readers who have a little background in physics and astronomy will probably get more out of it than complete newcomers, as there is a healthy platter of research to feast on in the book, and a helpful set of notes at the back with some suggestions for further reading. Overall, however, Scharf takes care to explain what the questions are and what the results mean, and his weighty choice of subject should not prevent anyone from picking up this book.

  • 2012 Allen Lane £20.00/$26.00hb 272pp

Can we print human body parts?

In less than 100 seconds, Luiz Bertassoni explains how remarkable advances in 3D printing have led to the printing of organs.

Graphene transistors give bioelectronics a boost

Graphene-based transistors that respond to changes in chemical solutions could be used to link electronic devices directly to the human nervous system. That is the claim of researchers in Germany who have built arrays of devices that respond to changes in the electrolytes surrounding living cells. The team hopes that its research could result in retinal implants that could help some visually impaired people see images.

The research centres on the small voltage that a neurone creates across its cell membrane when it fires, with the potential difference arising from sodium ions moving into the cell and potassium ions moving out into the surrounding solution. Since the 1970s, biophysicists have been trying to detect this sudden change in the electrolytic properties of the liquid surrounding a cell using a type of field-effect transistor (FET). These devices are called solution-gated FETs (SGFETs) and much of the initial research was done using silicon. But after graphene was isolated in 2004, some researchers realized that this material – a layer of carbon just one atom thick – could be used to create better SGFETs.

Clean, sensitive and flexible

According to Jose Garrido of the Technische Universität München, who has led the work, graphene offers several important advantages over silicon. First, the graphene surface remains clean – unlike silicon, which quickly forms a performance-degrading oxide layer when exposed to the electrolyte. Second, electrons in graphene have an extremely high mobility, which makes the device much more sensitive than silicon SGFETs. Finally, graphene is extremely flexible, which is good because any device implanted within the brain or similar tissue must be bendable.

A SGFET is a different take on a conventional graphene FET, in which the current flowing through its graphene channel can be controlled by changing the voltage applied to a nearby “gate” electrode. In a SGFET, in contrast, the gate voltage is kept constant and the graphene is exposed to the electrolytic environment of the cell. Any shift in the concentration of ions in the solution affects the electronic properties of the grapheme, thereby changing its conductivity and the current flowing in the graphene channel. The firing of a neurone is therefore detected as an electronic signal.

Brainy plans

In their new work, Garrido and colleagues have created 8 × 8 arrays of SGFETs – with each individual transistor measuring about 10 μm across. These arrays were used to detect firing signals from neurone cells that were cultured on an artificial medium. The researchers have also shown that neurone cells are able to survive for long periods of time in close proximity to graphene layers. They now want to show that the SGFETs work in living tissue – rather than cell cultures – and that neuronal tissue is not adversely affected by the presence of the devices.

According to Garrido, an important application of the graphene SGFETs would be creating retinal implants that could improve the sight of visually impaired people. Indeed, he believes that an array containing about 1000 elements could provide the brain with enough information for a person to be able to perceive an image. Another important application could be as cortical implants to help people control artificial limbs.

Although creating a 1000-element array of graphene SGFETs is a straightforward process, Garrido says that integrating the technology within a person will require a great deal more work.

The technology is described in a preprint on the arXiv server.

60 Second Adventures in Astronomy

By Hamish Johnston

If you are a fan of astronomy and the comedian David Mitchell, the Open University has a treat for you. Mitchell and the OU have made a series of 12 short animated videos about the physics of the cosmos.

(more…)

What is a thermopower wave?

In less than 100 seconds, Michael Strano explains how thermopower waves could be exploited to create smaller and more-efficient batteries.

Scientists delve deeper into carbon nanotubes

The outer walls of both double- and triple-walled carbon nanotubes (CNTs) protect the innermost tubes from interacting with their environment. That is the key finding of a study by researchers in the US, Germany and Japan, who have made the first detailed examination of triple-walled CNTs using resonant Raman spectroscopy. The protection afforded by the outer layer allows the tiny tubes to be studied in more detail than ever before, which could be a boon to those using CNTs to create new technologies.

A single-walled carbon nanotube (SWCNT) resembles a tiny drinking straw with a wall that is just one carbon atom thick. A double-walled carbon nanotube (DWCNT) consists of two concentric SWCNTs coupled together by weak Van der Waals interactions. The inner and outer tubes can either be semiconducting or metallic. However, because the outer tube is in direct contact with its environment, it can be difficult to obtain accurate information about its fundamental physical properties.

Third wall protects the second

To gain a better understanding of the outer tube in a DWCNT, Thomas Hirschmann and Paulo Araujo at the Massachusetts Institute of Technology and colleagues studied individual and bundled triple-walled carbon nanotubes (TWCNTs). A TWCNT can be thought of as a DWCNT wrapped around a SWCNT. The researchers found that the extra outer tube protects the two inner ones from interacting with their environment, thus allowing them to be studied more accurately. An unrolled TWCNT can be thought of as a trilayer graphene ribbon, and has all the outstanding electronic and mechanical properties that this carbon material boasts.

The team was led by MIT’s Mildred Dresselhaus and included scientists from the University of Hamburg, the Nagaoka University of Technology and Shinshu University. The researchers used a very fast yet sensitive Raman spectrometer, which allowed them to detect and characterize the same individual TWCNT with different laser lines under identical experimental conditions. “Only a few groups in the world are equipped with such an instrument capable of characterizing individual CNTs in this way,” said Hirschmann.

Wall-to-wall measurements

“The analyses allowed us to study fundamental properties such as intertube mechanical coupling, wall-to-wall (WtW) distance, metallicity and curvature-dependent intertube interactions,” he explained. “Such knowledge will be of fundamental importance for technological applications that exploit these nanostructures.”

The researchers characterized five individual TWCNTs in detail and found that the WtW distance between the inner two tubes in all the samples ranges from 0.323 to 0.337 nm. These values are larger than the WtW distance observed in previously studied DWCNTs (0.284–0.323 nm). The distances are also closer to the interlayer distance in graphene (0.335 nm).

“We also found that the intertube interactions affect innermost nanotubes differently, according to which metallicity they have, and that the elusive mechanical coupling between the ‘radial breathing mode’, or RBM, of concentric nanotubes does not exist, even for relatively short WtW distances of 0.323 nm,” added Hirschmann. “This is an important finding and shows that, although the TWCNTs are hybrid systems, the tubes themselves are mostly independent of one another.”

Wealth of information

The RBM is the most important spectroscopic signature of a CNT, the frequency of vibration of which is known to be inversely proportional to the tube diameter, he explained. These so-called first-order Raman features provide a wealth of information on the electronic and vibrational structure of these nanomaterials.

“Our analyses also shed more light on the Van der Waals forces mediating the interactions in concentric ordered CNTs, such as DWCNTs and TWCNTs,” said Araujo. “These low-energy interactions are important for technology applications because they affect the electronic and vibrational properties of the tubes.”

The team is now busy analysing shielding phenomena and intertube interaction effects in multi-walled carbon-nanotube systems. Here, intertube interactions not only affect the measured RBMs but also other Raman features. “One of our main goals is to find better conditions in which to grow CNTs by controlling interactions between nanotubes walls,” said Hirschmann. “To this end, we are working closely with Yoong Ahm Kim and colleagues at Shinshu University, who are experts when it comes to synthesizing these nanomaterials.”

The research is described in ACS Nano.

Of mice and ‘little green men’

Just called to say hello? (Wikimedia Commons/Crobard)

There’s nothing quite like mentioning extraterrestrials or aliens to get us “Earthlings” all excited or riled up! Late last week, a paper popped up on arXiv, by astronomer Alan Penny from the University of St Andrews. He outlines an incident where, for a short while, the possibility of alien contact was seriously considered. He was talking about what was ultimately the discovery of the first pulsar; but at the time the researchers couldn’t help but wonder if they had come across the first “artificial signal” from outer space.

The exciting happenings began in August 1967, when Jocelyn Bell Burnell (then a graduate student working with Antony Hewish – controversially, only Hewish won the Nobel prize for the pulsar discovery in 1974) at the University of Cambridge, noticed a particular source that had a “flickering pattern” that, over a few weeks, she realized showed up regularly each day at the same sidereal time. That December Bell pinpointed the specific position of the source in the sky using another telescope and the discovery was confirmed. In the coming months, three more similar patterns were found and the researchers agreed on “pulsating stars” or pulsars being the source. But during those winter months, the possibility that they had encountered the first alien signal loomed large. In fact, Brunell and colleagues dubbed the first pulsar LGM-1 or “Little Green Men”; although it was changed to CP 1919, and is now known as PSR B1919+21.

In a later article, Brunell said that she and the rest of the team “did not really believe that we had picked up signals from another civilization, but obviously the idea had crossed our minds and we had no proof that it was an entirely natural radio emission”. She continues, “It is an interesting problem – if one thinks one may have detected life elsewhere in the universe, how does one announce the results responsibly?”

This is the main subject that Penny tackles in his paper. He talks of researchers put into a position where they had to seriously consider how to tell the world about what might have been an alien signal. His paper contains some first-hand recollections of the people involved in the field at the time, including himself – he was a final-year undergraduate student at Cambridge in 1967.

Penny points out that a lot of the discussion the team had on how to confirm and release their potential finding ultimately agreed with the international guidelines that now exist in the form of SETI’s Detection Protocol – first agreed upon in the 1990s. But Penny also considers the fact that a Reply Protocol – an answer or response to an artificial signal – although proposed, was never agreed upon.

In the light of the numerous exoplanets being discovered by Kepler and other missions, it might just be a good (if slightly too optimistic?) idea to take a new look at these protocols. If nothing else, it might make BBC executives feel more confident in allowing Brian Cox to point a telescope in the general vicinity of an exoplanet.

What exactly will be upgraded at the LHC?

Lots of work to be done on the LHC (Courtesy: CERN)
Lots of work to be done on the LHC (Courtesy: CERN)

By Hamish Johnston

It’s been quite a rollercoaster ride for physicists working on the Large Hadron Collider (LHC) at CERN. When the collider was first switched on in 2008 it suffered a major explosion when a superconducting connector failed – and was shut down for over a year for repairs. Then in 2010 the LHC began taking data and the excitement about the imminent discovery of the Higgs boson grew and grew – and then on 4 July last year, CERN physicists announced the discovery of a Higgs-like particle.

(more…)

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