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Physicist Kenneth Wilson dies at 77

The US theoretical physicist Kenneth Wilson, who was awarded the 1982 Nobel Prize for Physics, died on Saturday 15 June at the age of 77. Wilson was the sole winner of the 1982 Nobel prize for “his theory for critical phenomena in connection with phase transitions”.

Born in 8 June 1936 in Waltham, Massachusetts, Wilson was the son of the prominent Harvard University chemist E Bright Wilson. After completing an undergraduate degree in mathematics at Harvard in 1956, Wilson was awarded his PhD in theoretical physics from the California Institute of Technology in 1961, which he did under the supervision of the future Nobel-prize-winning particle physicist Murray Gell-Mann.

After a year working at the CERN particle-physics laboratory near Geneva, Wilson joined Cornell University in 1963. He remained there for most of his career, later becoming director of Cornell’s Center for Theory and Simulation in Science and Engineering, which is now known as the Cornell Center for Advanced Computing. In 1988 Wilson joined Ohio State University and was co-principal investigator in an educational-reform project that was funded by the National Science Foundation. Called “Project Discovery”, the project aimed to develop more inquiry-based learning of physics in schools.

Critical phenomena

Wilson was awarded the Nobel prize based on his pioneering work developing a theoretical framework on the nature of phase transitions – such as when describing how a liquid turns into a gas by changing its temperature or when a material loses its magnetization when applying a magnetic field.

Phase transitions can be characterized by an abrupt change in the value of some physical property or by a smoother transition from one phase to another. However, many previous theories – most notably Lev Landau’s 1937 general theory of phase transitions – failed to predict the behaviour close to the transition, known as the critical point.

That problem was finally solved by Wilson in 1971. He realized that one has to deal with fluctuations over widely different length scales – taking into account short- and long-range fluctuations. Such transitions are then almost totally determined by the collective effects of every other object in the system. Modelling this behaviour near the critical point would require vast computing power but Wilson developed a method to divide the problem into a sequence of simpler ones based on renormalization group theory, which had been previously developed in the 1950s.

Wilson’s theory for critical phenomena gave a complete theoretical description of the behaviour close to the critical point proving that many seemingly unrelated systems – liquids or mixtures of liquids and ferromagnets – show identical behaviour.

Ahead of his time

Paul Ginsparg – founder of the arXiv preprint server – studied for a PhD at Cornell University under the supervision of Wilson. He says that Wilson’s ideas in physics will continue to dominate the way that physicists think about the link between statistical mechanical systems and quantum field theory.

Ginsparg also adds that Wilson was “decades ahead of his time” in computing and networks – writing code for parallel processor arrays to get round the problem of slow single-processor speeds, as well as calling for the implementation of the TCP/IP internet protocol that is in use today. “As a graduate student in the late 1970s, I had a unique three-decade window into the future,” Ginsparg tells physicsworld.com.

Wilson was elected to the National Academy of Sciences in 1975, the American Academy of Arts and Sciences in 1975 and the American Philosophical Society in 1984.

Wilson died on 15 June in Saco, Maine.

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New portrait of Peter Higgs unveiled

By Tushna Commissariat

The Royal Society of Edinburgh (RSE) has just unveiled a portrait of famed physicist Peter Higgs, at the Society’s Fellows’ Summer Reception last week. The painting, which will hang on the walls of the Kelvin Room within the RSE’s premises in Edinburgh, was commissioned to one of Scotland’s leading artists, Victoria Crowe, “to honour the man whose outstanding research was instrumental in [the Higgs boson’s] discovery”. The professor seems distinctly unperturbed by the high-energy proton–proton collision taking place in the top right corner of the painting. I shall leave you to find and discern the other interesting imagery in the painting for yourselves – click on the thumbnail to view a larger picture of the portrait.

Livermore slashes 10 per cent of workforce

The Lawrence Livermore National Laboratory (LLNL) in the US has begun laying off around 10% of its 6500-strong workforce in preparation for “challenges” in the lab’s 2014 budget, which will start on 1 October. The lab’s redundancy offer gives workers one week of base salary for each year of continuous service, up to a maximum of 26 weeks. As of last Friday, 399 individuals had accepted the lay-off terms.

Significant limitations

The Obama administration’s budget request for 2014 includes about $1.48 bn for the LLNL – a sum that lab director Parney Albright told a Senate subcommittee last month “will significantly limit our ability to utilize the National Ignition Facility and undermine [our nuclear] stewardship programme”. However, even this figure is uncertain, given the political disputes between the Democratic administration and the Republicans, who have a majority in the House of Representatives and a blocking minority in the Senate.

Albright adds that there are still a number of “unknowns” in the 2014 budget request. “It is clear the budget proposal will face an uphill battle in Congress this summer,” he says. “It is our hope that implementing the [redundancy programme] now, rather than waiting for additional details on the 2014 budget, will put the laboratory in a better position to address whatever budget realities we’ll face.” According to lab spokesperson Lynda Seaver, “the voluntary redundancy is available to all employees, though some could be denied due to critical skills”.

Budgeting woes

The lay-offs at LLNL follow more than 550 permanent employees having accepted severance packages last year from the Los Alamos National Laboratory when it faced a reduced budget and little prospect of increases. The LLNL itself offered voluntary redundancies in 2008 but, according to Seaver, did not get “the numbers we had hoped for”. The lab then resorted to compulsory redundancies, which some employees challenged in the courts. Indeed, in late May five lab staff were awarded more than $2.7m when a local jury found that the LLNL had violated a contractual promise that it would lay the workers off only for a “reasonable cause”. The LLNL will reconsider its response to the impending financial situation – which could still include forced redundancies – as soon as it knows its final budget for 2014.

Meanwhile, further budget woes are threatening the Massachusetts Institute of Technology’s Alcator C-Mod fusion project, which faces closure within a year as the US government moves fusion funds from home-grown projects to international collaborations such as ITER. The administration’s proposed 2014 budget includes no funding for C-Mod and its shutdown would lead to 70 staff losing their jobs, leaving only two fusion experiments in the US. The Massachusetts Congressional delegation has called for restoration of funds for the programme, which produces more PhDs in fusion and plasma physics than at any other US institution.

Graphene circuit breaks the gigahertz barrier

Researchers in the US and Italy have made the first integrated graphene digital circuits that function at gigahertz frequencies. The circuits are ring oscillators and the work could be an important step towards realizing all-graphene microwave circuits, says the team.

Graphene is a 2D sheet of carbon just one atom thick and it – along with similar 2D materials such as carbon nanotubes and molybdenite – shows great promise for future electronics. This is because electronic devices smaller than 10 nm could be made using these 2D materials – at least in principle. Below the 10 nm length scale, devices based on conventional silicon are expected to be too small to function properly and therefore graphene and similar materials offer a route to making ever-smaller electronic devices.

One major challenge facing those developing such 2D devices is speed. Modern silicon processors operate at microwave (gigahertz) frequencies, as do communications chips in devices such as mobile phones. Therefore, any practical 2D device would have to run just as fast. Until now, however, the fastest 2D device – a carbon-nanotube ring oscillator – operates at a lethargic 50 MHz.

Now, a team led by Roman Sordan of the Politecnico di Milano and Eric Pop of the University of Illinois says it has made the first integrated graphene oscillators – with the added bonus that the devices operate at 1.28 GHz. The graphene ring oscillators also appear to be less sensitive to fluctuations in the supply voltage compared with both conventional silicon CMOS devices and earlier oscillators made from the 2D materials.

Final “missing” component

In addition to being used to generate clock pulses in microprocessors, oscillators are also one of the main building blocks of analogue electronics. Microwave electronics, for example, are based on voltage amplifiers, oscillators and mixers. “Graphene amplifiers and mixers have already been demonstrated, so the oscillators we made represent the final ‘missing’ component for making all-graphene microwave circuits,” Sordan says.

And that is not all. The team has also fabricated stand-alone graphene frequency mixers from its ring oscillators. Previous graphene mixers were not stand-alone because they required external oscillators to function.

“We believe that our study significantly advances research in low-dimensional nanomaterials towards practical, high-speed digital and analogue applications, and we hope that it will motivate significant future work in this direction,” says Sordan.

The research is reported in ACS Nano.

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Putting a new spin on variable stars

A new type of variable star has been discovered by astronomers in Switzerland. The team says that its observations reveal previously unknown properties of variable stars that defy current theories and raise more questions about the origins of the luminosity variation in stars. The team’s results are based on a seven-year-long study of regular measurements of the brightness of more than 3000 stars in the open star cluster NGC 3766, using the European Southern Observatory’s 1.2 m Euler telescope at the La Silla Observatory in Chile.

Variable stars are those with a brightness that appears to fluctuate or “vary” when they are observed from Earth. They are divided into two broad categories depending on the cause of the variation. If it is caused by a change in the physical properties of the star, then they are called “intrinsic variables”, whereas “extrinsic variables” fluctuate thanks to external factors, such as an eclipsing orbiting companion. “Our group didn’t know what would come out of the observations, but knew the potential of observing open clusters regularly on a long [period of time] to improve our understanding of known classes of variable stars…but none of us was expecting to find a new class,” says Nami Mowlavi of Geneva Observatory, who is the current leader of the research team. Mowlavi says that the team’s findings were so surprising that the researchers spent more than six months trying to understand and make sense of the results, but that ultimately “the quality of the data and of the analysis” convinced the researchers of the reality of the results.

Varying varieties

During the study, the team found 36 of the new variety of variable stars, which represent 20% of stars with similar magnitudes within the observed cluster. Mowlavi explains that these provide sufficient evidence of a new type because all the stars were observed in a single cluster. This means that they all have the same stellar properties, including their surface temperatures. Hence, what is so surprising about the results is that periodic light variations occur in stars with those specific temperatures.

“Were it only for their variability properties, these stars could have been considered as ‘standard’ variable stars, like some pulsating stars that are already known,” says Mowlavi. But knowing that they are main-sequence stars – that burn hydrogen in their core, such as the Sun – with surface temperatures of between 9000 and 11000 K makes them very special. This is because main-sequence stars at these temperatures are not expected to pulsate, or to have any other physical characteristic that would lead to periodic variations of their luminosity, according to current theories.

Unexpected and unexplained?

Mowlavi, along with Shopie Saesen, who is also an astronomer at Geneva Observatory, and colleagues, has considered three possible scenarios to explain these unexpected variations. The first looks at the possibility of a binary companion. “If the star is part of a binary system, then the total light emitted by the star could be modulated by its orbital motion around its companion,” says Mowlavi. “But about one-third of the 36 stars are multiperiodic. This means that more than one frequency is detected in their light signal, which cannot be explained by binarity,” he explains.

The second scenario relates to stellar pulsation that is consistent with the multiperiodicity, as well as with some other properties exhibited by the new class. Unfortunately, stellar pulsation is not expected in these stars. The team’s observations found that four of the 36 stars are characterized by very high rotational velocities – spinning at more than 50% of their critical velocity (the velocity above which the star would break up). “Fast rotation might alter the internal conditions of a star enough to sustain stellar pulsations. But we actually don’t know. There is currently no stellar model that can predict whether pulsation can be sustained in very fast rotating stars,” explains Mowlavi.

The third option takes into account the presence of “spots” on the surface of such rotating stars and that these spots would induce light variations as the star rotates. But hot stars are not expected to be active, and no theory can currently explain how spots could be produced on the surface of such stars. “So, the origin of these light variations is mysterious, and we do not exclude any possibility, even others not mentioned here. We plan further observations to better characterize these stars,” says Mowlavi.

The researchers have also observed other clusters during the seven-year study, and are currently analysing those data. Mowlavi told physicsworld.com that “since the stellar populations are different from one cluster to another, we may or may not find representatives of this new type of variable stars in other clusters”. He points out that whatever the result, it will provide the team with further clues to the origin of these light variations “by relating their presence – or their absence – with the clusters’ properties”.

The team hopes that its results will encourage specialists in stellar pulsation to provide predictions for very fast rotating stars. Mowlavi says that other collaborations at Geneva University with specialists in this domain believe that this is a “very difficult task”.

The research is published in Astronomy and Astrophysics.

In the coming decade, which industry sector will benefit the most from physics research?

By Hamish Johnston

Illustration of some of the sectors that are benefiting from physics research.

What physics-related industry employs 30,000 people in the UK?

The answer, according to the Institute of Physics (IOP), is the country’s extremely successful space industry – which has been expanding steadily for decades and continues to develop an impressive array of satellite and related technologies. Indeed, the space sector has enjoyed an average annual growth rate of 7.5% since 2008. Not bad going when you consider that the rest of the UK (and much of the world) has been in an economic slump.

Space is just one of the applications of research covered in Physics: Transforming Lives – a 68-page report prepared by the IOP in partnership with EPSRC and the STFC, both of which fund physics research in the UK.

(more…)

Nanotube sensor detects Lyme disease

Researchers in the US have made a new biosensor from carbon-nanotube transistors that is capable of rapidly detecting the antigens of Lyme disease. The device can detect the biomarkers at concentrations as low as 1 ng/ml, which is better than is possible with standard urine testing and comparable to traditional ELISA and Western-blot immunoassays.

Lyme disease occurs throughout much of the northern hemisphere and is spread by ticks carrying the Borrelia burgdorferi bacterium. At least 30,000 new cases are reported in the US alone each year. The disease often goes unchecked – especially in its early stages – because the symptoms are so non-specific and because of a lack of sensitive tests. Late detection can be dangerous, however, because the disease can cause arthritis and even permanent neurological disorders, among other health problems.

Now, a team led by A T Charlie Johnson of the University of Pennsylvania has made a new Lyme-disease biosensor from large arrays of semiconducting carbon nanotube (CNT) transistors grown by chemical vapour deposition on oxidized silicon wafers. “Using a covalent-chemistry technique developed in our lab, we are able to attach antibody proteins to the nanotubes very efficiently,” explains Johnson. “These antibodies have a high affinity for the antigen protein of interest – p42 flagellar – which is a protein from the flagellum of the bacterium that carries Lyme disease. If this Lyme antigen is present in a sample, it gets captured by the antibodies, something which induces a change in the electronic properties of the nanotube transistors.”

The Pennsylvania group’s work follows on from similar strategies to detect prostrate-cancer biomarkers using CNTs. Indeed, the researchers say that they may one day be able to detect any disease with such nanotube devices simply by coating them with the appropriate proteins.

Close to nanotubes

“By directly attaching such antibody proteins to CNT transistors, the Lyme antigen is captured very close to the nanotubes,” says Johnson. “Since antigens are charged molecules, bringing them into the immediate vicinity of the tubes will alter the transistors’ electronic properties in a concentration-dependent manner – with higher antigen protein concentrations binding more antibodies. By measuring the shifts in these properties we can deduce the exact concentration of the Lyme antigen in a sample.”

The device can currently detect concentrations of the Lyme antigen as low as 1 ng/mL, which is better than is possible using urine tests (15 ng/mL) and comparable to traditional ELISA and Western-blot immunoassays. However, there is more to disease diagnosis than just sensitivity, says Johnson.

“The Centers for Disease Control and Prevention currently recommends a two-tiered testing approach for Lyme disease,” he explains. “The first tier is an ELISA assay, but this test can produce a false negative if the patient has a disease similar to Lyme. More importantly, it cannot distinguish between Lyme antibodies caused by a current, active Lyme infection and those caused by past, treated infections.”

The second-tier test is a Western blot, which tests specifically for Borrelia burgdorferi. Using Western blot on its own is more likely to lead to a false positive, resulting in inaccurate diagnosis and unnecessary treatment for a patient whose true disease may continue to afflict them.

“Our protein–nanotube hybrids overcome both these problems because they look directly for Lyme antibodies. This means that there is no lag between infection and detection (as in ELISA), and no danger of confusing current and past infections because the antigens will only be present if the Borrelia is active,” says Johnson.

Further improving the detection limit

The team says that it could further improve the detection limit of its sensor by attaching only the piece of the antibody (known as a “fragment”) responsible for antigen binding instead of the whole antibody protein. This would allow the antigens to be captured even closer to the nanotubes, which, in turn, would increase sensitivity – possibly by several orders of magnitude.

There is still much work to be done before the technology becomes commercially available; however, Johnson says that, luckily, there are several organizations that are already “very interested” in the group’s research. “An important next step is to develop methods to detect Lyme antigens in complicated real-word samples, such as human blood. Subsequent steps will include animal and, finally, human clinical trials.”

The attachment chemistry exploited in the new sensor relies on common protein features, so it could easily be extended to detect several biomarker proteins simultaneously, says Johnson. “For example, VIsE and OspA are other proteins from Borrelia burgdorferi that have been implicated in Lyme disease, so we could think about expanding our search by attaching antibodies for those antigen proteins to our nanotube transistors,” he adds. “Taking it one step further, we could even include proteins for other diseases on the same chip (nanotubes are quite small after all) and perform tests for all kinds of maladies using a single, small-volume blood sample. Someday, a medical check-up might consist of simply dropping blood on a nanotube array functionalized with hundreds or even thousands of different proteins, each looking for things as diverse as heart disease, arthritis, Alzheimer’s or stress biomarkers, with the results available in seconds – and all at very little cost.”

The research is described in Biosensors and Bioelectronics.

Structural disputes

In March this year, the author of a well-regarded science website was revealed to be – wait for it – a woman. The identification of Elise Andrew as the founder of the provocatively titled Facebook page “I Fucking Love Science” was greeted with astonishment, tinged in some cases with outrage. This anecdote says much about the general reaction to women in science: even in 2013, it is still not taken as a given that women may be good at science and enjoy it. Imagine how hard it must have been 80 years ago, when Dorothy Wrinch was struggling to make a name for herself as a mathematician working at the interface with biology.

Wrinch (1894–1976) was educated at Girton College, Cambridge at a time when women still had to ask permission to attend lectures that were given by men for the university’s “real” students, i.e. the men. Over the years, she variously worked in Cambridge, London and Oxford (always in short-term posts with insecure funding), tackling philosophical problems with Bertrand Russell and other giants of the day and considering questions related to symmetry and beauty in nature. Ultimately, she became interested in protein structures. At this point, she ran up against Linus Pauling, to her great detriment, and she died in relative obscurity.

Does Wrinch’s losing encounter with Pauling explain why she is largely forgotten today? I had certainly never heard of her before I was sent this new biography, I Died For Beauty (the title comes from an Emily Dickinson poem). Or is it because she was a woman – and, as far as I can judge from the book, a cussed and difficult woman at that – at a time when they weren’t fully accepted into the scientific fold? The book left me uncertain as to the answer to those questions, although it does describe some rather interesting episodes in the history of science.

During Wrinch’s heyday of the 1930s to 1950s, there was huge interest in crystals and lattices as many scientists across a variety of disciplines tried to work out how these complex crystal structures, in particular proteins such as insulin and haemoglobin, could be inferred from X-ray diffraction patterns. Wrinch was part of this tribe of scientists. At the time, of course, the computers we today take for granted did not exist; indeed, the term “computers”, in the early days, referred to people who worked out complicated calculations to produce, for instance, tables of functions. These calculations were long and difficult. Hence, even had the theories of the time been robust, moving from the observed diffraction pattern (which necessarily lacks information on the phase of the contributing waves) to the underlying structure seemed like an intractable problem; progress on both theoretical and experimental fronts was slow.

Wrinch's lantern slide showing cyclol fragments as denatured proteins — Contentious: Wrinch’s lantern slide showing cyclol fragments as denatured proteins. (Courtesy: Sophia Smith Collection, Smith College)

Undoubtedly, Wrinch made significant contributions to the field, particularly in her fairly late work Fourier Transforms and Structure Factors (1946), in which she laid down in detail much of the field’s mathematical basis. But it was her model for protein structure itself that led to many personal attacks and damage. Wrinch was convinced that proteins were not long chains of molecules (described at the time as resembling Christmas tree lights). Instead, she believed they were an indefinite fabric of rings, which she termed “cyclols” (see “Contentious” figure). This idea was initially compatible with the limited evidence, but she clung to it long after new data made it scientifically untenable, and possibly right up to her death.

To begin with, she had many influential supporters, including the chemical physicist Irving Langmuir. However, her inflexible attitude as the counter-evidence built up did nothing for her reputation, and it seems that she was always something of a divisive character. The book’s author, Marjorie Senechal, knows this firsthand: she describes herself as a mathematical crystallographer, and towards the end of Wrinch’s life, when both women were at Smith College in Massachusetts, they worked together informally. Senechal draws on this personal experience in the book, but she also had access to extensive diaries kept by senior members of the Rockefeller Trust, whose role it apparently was to travel around asking senior scientists to comment on colleagues whose work the trust might fund. Quotations taken from these diaries include the statement that “[Wrinch] is in bad favour in many quarters in England” and “P said flatly that he has always said she is a fool but that B insists she is only mad”. And these quotes actually precede the fracas over Wrinch’s cyclol model, where she clashed so painfully with Pauling.

Senechal chooses to make the chapter on Wrinch’s exchanges with Pauling into the skeleton of an opera, outlining the acts though not fleshing out the libretto in full. As she puts it, “Dorothy Wrinch’s epic battle with Pauling is the stuff of opera. There is no other way to tell it. Two brilliant, arrogant, competitive antagonists with a flair for publicity and a touch of the devious! And what a plot!” These few sentences demonstrate the flavour of the book. Senechal’s style is personal and staccato, and throughout the book, her own interactions, interests and driving forces creep in, leading to multiple digressions in chronology and topic. This can be confusing, although the anecdotes are also illuminating and often intriguing. I learnt, for example, about diverse background issues and individuals ranging from D’Arcy Thompson to mineralogists and members of the Smith College faculty. But at the end of the book I felt I had not grasped the essence of Wrinch herself.

Clearly, she was a multi-faceted and hugely original scientist. She was also struggling to cross the divide between many disciplines, some of which, such as molecular biology, were at the time only just coming into being. But was she a flawed genius whose central thesis about cyclols was wrong, so the rest of her work, important though it was, has been allowed to sink into obscurity? Maybe – but then, Pauling himself made a glaring mistake late in his life, yet his reputation has survived pretty well intact. One might reasonably conclude that Wrinch’s gender was a factor in the way she was treated. But does this make her a brilliant woman in science, ahead of her time, whose strong personality led her to dare to challenge a patriarchal society and come off worst? Or was she just a run-of-the-mill scientist with an awkward character and a colourful personal life, whose vanishing from the list of the period’s “great and good” is justified? I suspect Senechal herself is ambivalent on these questions, but it is a pity that she doesn’t give readers enough solid information to allow us to form our own firm judgement.

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