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Zombies in the machine

By James Dacey

It’s a brilliant conceit – to film a zombie film at the Large Hadron Collider. That’s precisely what a group of PhD students at CERN have done, producing a feature length film called Decay.

The film follows a group of students – played by real physicists – who are desperately trying to escape from underground maintenance tunnels at the LHC. They are being pursued by a bunch of maintenance workers who have been turned into blood-thirsty zombies after exposure to the newly discovered Higgs boson.

Writer and director Luke Thompson, a PhD student at Manchester University in the UK, came up with the idea back in 2010 after joking that the tunnels at the LHC would make a cracking place to shoot a zombie film. Unlike most such ideas – often dreamt up late at night in a bar – Thomson actually set about recording the film. Armed with a budget of roughly £2000 and a regular cast and crew of 20, Thompson has spent the past two years filming and producing the 75 minute film.

The film is set to premiere in Manchester at the end of November, after which time it will be released free online under a Creative Commons licence. For updates keep an eye on the film’s website.

In good scientific fashion, Thompson accompanies promotion of the film with a strong caveat. “There is absolutely no evidence that [the Higgs boson] is harmful in any way,” he says.

Physicists detect malaria using light and magnets

A technique that identifies malaria infections in blood using cheap magnets and run-of-the-mill pocket lasers has been developed by scientists in Hungary. It exploits the unique magnetic and optical properties of crystalline waste produced by malaria parasites in the bloodstream and offers an inexpensive, sensitive and reliable alternative to existing diagnostic tools.

Malaria is the world’s number-one vector-borne infectious disease. It is contracted by 200 million people each year and proves fatal for one million of those; yet it is easy to treat, making many of these deaths avoidable. To date, medical science has come up with sensitive, equipment-heavy diagnostic tests as well as cheaper portable tests with lower sensitivity and accuracy – but none meet all the needs to efficiently combat the disease.

It was a 2008 paper, by Dave Newman and colleagues at the University of Exeter in the UK, describing a way to exploit the magneto-optical behaviour of “haemozoin” – a crystalline substance excreted by malaria parasites – that first caught the attention of István Kézsmárki, of the Budapest University of Technology and Economics and the Hungarian Academy of Sciences. When the parasites digest haemoglobin, they are left with a substance known as “haem” that is highly toxic to them, until they convert it into insoluble haemozoin microcrystals – also known as malaria pigment.

Unique properties

“The crystals are quite unusual…when the parasites turn haem into malaria pigment, it becomes magnetic,” explains Kézsmárki. “There is no other material in human blood that would have the same properties and produce the same effects.”

This is down, in part, to the dimensions of the crystals and how highly anisotropic they are at a molecular level. A crystal’s orientation governs the absorption or scattering intensity of incident polarized light on it.

So, placing an infected blood sample in a strong magnetic field forces all the crystals, which are normally thermally buffeted and jostled by surrounding molecules, to point in the same direction. Their collective effect on polarized light clearly points towards any malaria infection.

New twist

While these characteristics had already marked out haemozoin as ideal for use in malaria diagnosis, Kézsmárki and colleagues “made another twist to make it really feasible for cheap daily diagnosis”.

Instead of using research-grade instruments such as superconducting magnets and highly stable lasers, the researchers generated a uniform magnetic field by arranging a ring of standard €1 permanent magnets around the sample. By spinning the ring, they got the crystals to spin, with their moment of inertia coupled with the viscosity of the fluid, causing them to align in the field.

When the researchers shone a simple laser through the sample, the crystals acted as secondary polarizers, alternately transmitting and scattering light as they spun. A polarizing beamsplitter was used to separate the exiting light into its horizontal and vertical components. For uninfected blood, the intensities of the two components were the same, independent of the orientation of the magnetic field. For infected blood, the two oscillated inversely with one another as the magnetic field rotated.

Schematics showing the magnetic orientation of hemozoin crystals in magnetic fields

Magnetic orientation of the hemozoin crystals

Sensitive solution

Today’s best lab-based malaria test can identify parasite concentrations as low as 5/μL of blood, but it is too costly and impractical for large-scale diagnosis in rural areas where malaria is endemic. Rapid diagnostic tests, which involve no more than a drop of blood on a strip of antigen-coated plastic, are fast, portable, cheap and uncomplicated, but they have a sensitivity threshold of about 100 μL – too high to catch early-stage infection.

Kézsmárki’s team found that it could spot parasite concentrations as low as 25/μL of blood, and when the researchers ran the test on plasma instead of whole blood, their sensitivities jumped to unprecedented levels – one parasite/μL. Their method could potentially be applicable at the very earliest stage of the disease – the first symptom-free few weeks when the parasites have invaded the liver and are producing haemozoin but have not yet been dispatched into the bloodstream.

Also, haemozoin is extremely stable – the exact same form of the chemical is seen in fossilized remains of ancient malaria-infected creatures – and is common to all mutations of malaria. This means that the test will be viable in all locations and will never become obsolete, unlike the strain-specific rapid-detection tests, which face a constant struggle to keep up with the swiftly mutating malaria genome.

The real test

“The new method is exciting and may have the capability to be used as a rapid screening tool [once it is developed further],” says Stephen Karl of the Walter and Eliza Hall Institute in Australia, who was not involved in the research. He says the technique shows promise and anticipates that “the cost-per-test with this instrument will be very low since almost no disposable materials are required”.

David Bell, a malaria expert at the Foundation for Innovative New Diagnostics in Geneva, is a little more reserved. “It is difficult to tell at this stage,” he cautions, describing existing rapid-diagnostic tests as “adequate for case management”. To make an impact, he feels the new test will need to be “equally cheap, robust, without lots of moving parts, and not need batteries. That is a difficult ask”.

“The other question is whether you can determine one species from another by this method, which is important because different species of parasite need different treatments,” he adds.

For now, Kézsmárki and colleagues are looking to collaborate with engineers on reducing the size of the apparatus from its current “laptop” size to about 20 cm across, and are keenly pursuing the optimum way to separate red blood cells and plasma while keeping the malaria pigment intact in the plasma. “This is a crucial point to resolve,” Kézsmárki says. “Our target is to find the method that is the simplest, which requires no special biolab.”

The preprint of the research is available on arXiv.

The upcoming November special issue of Physics World is devoted to “animal physics”. You can download a free PDF of the issue from physicsworld.com from Wednesday 7 November 2012
David Hu from Georgia Institute of Technology’s laboratory for biolocomotion presents a special online lecture at 3.00 p.m. GMT on Thursday 8 November 2012, which you can view by registering here

New formula explains the dynamics of fractal growth over time

A team of researchers in Spain says that it has developed an equation that describes how intricate surface patterns, resembling a cauliflower-like motif, evolve and develop over time. The researchers also show that their theory can be applied to everything from actual cauliflower plants to combustion fronts, all of which obey the same scaling laws. The team says that it is the first time that a theoretical explanation has been provided for the growth of surfaces in systems that are extremely dissimilar, be it their physical nature or the scale at which they grow.

The researchers based their study, published in New Journal of Physics, on two central tenets: fractals and universality. A fractal is an object or a quantity that is self-similar, or almost so, on all scales. The object need not exhibit exactly the same structure at all scales, but the same “type” of structures must appear on all scales. With a cauliflower, for example, it is impossible to tell if a close-up image of it is the entire head of the cauliflower or just a single floret. Simply put, a fractal is a system where any one part is similar to the whole.

Similar systems

Universality, on the other hand, refers to any physical systems that “look” extremely similar despite their specific details or the scale at which their effects are felt being very different. And fractals are a great example of universality – everything from a single fern leaf that resembles the entire plant, to clouds, snowflakes, blood vessels and cauliflowers has a similar fractal pattern. But despite the properties of fractals, such as their shapes and sizes, having been studied extensively since the 1970s, the physical mechanics of their formation have remained elusive.

Nanocauliflowers

The new work has been carried out by Mario Castro and colleagues from Comillas Pontifical University, Universidad Carlos III de Madrid, Instituto de Ciencia de Materiales-CSIC, Ecole Polytechnique and Katholieke Universiteit Leuven. Initially, the researchers did not start out looking at fractals, instead they were studying a widely used technique to grow thin films known as chemical vapour deposition (CVD), which allows the thickness and composition of layers to be accurately controlled. The team was looking at the evolution of various films grown in the lab and found that one of the films – an amorphous hydrogenated carbon film – had an extremely recognizable if peculiar pattern, namely that of a cauliflower.

Inside joke

The team initially thought that its cauliflower motif was just that – a random pattern that had caught the eye. “It used to be our private joke almost – we used to call them our nanocauliflowers,” says Castro, who adds that although the films resemble cauliflowers, they are much smaller, being just several hundreds of nanometres. “But then we realized that our nanocauliflowers also had the same self-similar fractal features as those of the plant,” he adds.

Through experiments on its CVD carbon films, the team studied the cauliflower-like fronts, and developed a statistical formula that explains how these fronts grow over time. It turns out that this equation can also be used to successfully predict the growth of an actual cauliflower plant or even a combustion front – or how a flame grows over time – both of which occur at larger and different scales but obey the same scaling laws. “This proves our theory over seven orders of magnitude in length scales,” says Castro.

Ingredient’s list

The key finding in this work, according to the team, is the identification of the four ingredients needed for the formation of this kind of random growth. The first is a system that grows in time. This is crucial to the second part, which is “non-locality” or competition – a growing system, such as a plant trying to grow taller to receive more sunlight or even part of a flame expanding in time and trying to reach oxygen to combust. The non-locality plays a part here, as what happens in one part of the system remotely affects other distant parts of the same system. The third ingredient is randomness, which, according to the team, nature provides in abundance. The final ingredient is self-similarity – a fractal pattern, where the parts are similar to the whole.

“In spite of the widespread success of fractal geometry to describe natural and artificial fractal shapes, purely geometrical descriptions do not provide insight into the laws that govern the emergence of the shapes in time,” Castro told physicsworld.com. “We believe that by knowing the general laws that dictate how these patterns form and grow, it will help to identify the biological and physical mechanisms that are at play.” The team hopes its work will inspire other researchers to look into the real-world dynamics of fractals, instead of only their morphology.

The work is published in the New Journal of Physics.

Bacteria ‘wires’ conduct electrons over centimetre distances

A newly discovered bacterium living on the bottom of the sea transports electrons over centimetre distances so it can feed on hydrogen sulphide in low-oxygen environments. That is the claim of scientists in Denmark and the US, who have shown that thousands of the micro-organisms form a filament with one end embedded in ocean sediments and the other end poking out into seawater. Understanding just how this organism moves electrons could lead to alternative technologies for generating energy.

Biologists have known for some time that the Desulfobulbaceae family of bacteria power themselves by consuming sulphur compounds in ocean sediments. However, this produces hydrogen sulphide, which is toxic at high concentrations. While these bacteria can consume hydrogen sulphide, this must be done in the presence of oxygen in a reaction that involves the transfer of an electron.

Ocean sediments normally have very low oxygen levels and studies have shown that when Desulfobulbaceae are present, sulphide levels increase steadily. But then something unexpected happens – sulphide levels drop quickly as if the sediments have experienced a rapid influx of oxygen. The problem is that the drop is so fast that it cannot be explained by the diffusion of oxygen molecules from the seawater above. Instead, scientists had thought that the many different species of Desulfobulbaceae bacteria in the sediment were somehow working together to move electrons from oxygen-poor regions up to the seawater, where oxygen is plentiful.

Lone bacterium

Now a team that includes the physicist Mohamed El-Naggar and colleagues at the University of Southern California and Aarhus University have taken a closer look at the bacteria in the sediments and have made a startling discovery – the electron transport appears to be done by just one type of bacterium, which creates centimetre-long filaments that are made up of thousands of micro-organisms joined together end-to-end.

What is more, tests on the tiny filaments suggest that the electrons are conducted along special string-like structures within the bacteria.

The electrical properties of the filaments were first studied by doing “source–drain” measurements. The filamentous bacteria were deposited on an insulating surface of silicon oxide that also contained gold electrodes. The team focused on those filaments that happened to bridge two electrodes, which allowed them to apply a voltage along the filament and measure the electron current. But when voltages as high as 10 V were applied along the filaments, no measureable current was found. This led the team to conclude that the bacteria were not acting like bare conducting wires, but rather that the conduction process takes place inside an insulating sheath – much like an electrical cable.

Very high capacitance

To try to work out which internal parts of the bacteria are involved in electron transport, El-Naggar and colleagues used a technique called electrostatic force microscopy (EFM). This involves placing an extremely small electrode very near to the surface of a bacterium and measuring how the capacitance changes as the electrode is oscillated up and down. By scanning the tip over the surface, the team found that string-like structures just under the bacterium’s outer membrane have a very high capacity for storing charge. “This is very suggestive for their role in carrying charge, and will be the focus of future studies, El-Naggar told physicsworld.com.

The process by which the conduction occurs is still a mystery: “There are two points of view on the subject that stem from two completely different physical limits”. One school of thought is that conduction is similar to “band conduction” seen in metals and semiconductors – however, El-Naggar points out that the observed electron mobility is too low to support this idea. Instead, he favours a hopping model whereby charge jumps along the bacterium from one position to the next. “This is an incoherent process that takes place in multiple steps, somewhat like a bucket brigade.”

Beyond shining a light on ecosystems at the bottom of the sea, El-Naggar believes that gaining a better understanding of how this conduction occurs could lead to practical applications. “I think it is likely that long-range bacterial electron transfer will open the door to new environmental clean up and renewable energy technologies, by coupling these living processes to non-living electrodes,” he says.

The study is described in Nature.

Do you think physics employers have a subconscious bias towards male job applicants?

By James Dacey

A nifty psychological study reported this week on physicsworld.com has found that a set of researchers assessing the employability of early-career scientists subconsciously favoured male students over females. The bias – if it indeed reflects reality – is thought to be a contributing factor towards the underrepresentation of women in physics.

The study, which you can read about here, involved the sending of a fake job application for a graduate-level lab-technician post to tenured scientists in the US. The professional scientists were asked to give feedback on the employability of the applicants, unaware that they were fictional. All applications were identical except for the fact that some were written by the fictional applicant “John” and the others by “Jennifer”.

From the scientists’ feedback John was deemed to be more competent and hireable than the identical female applicant, but the hirers would also have given the male student a higher starting salary. This bias was seen to exist in both male and female physicists and was exhibited by chemists and biologists.

In this week’s Facebook poll we want to know whether you think this bias does indeed exist in the real world.

Do you think physics employers have a subconscious bias towards male job applicants?
Yes
No

Take part by visiting our Facebook page and please feel free to post a comment to explain your response.

In last week’s poll we asked you about the trial of the seven scientists in Italy who were being charged with falsely reassuring the public ahead of the 2009 L’Aquila earthquake that left 308 people dead. We asked whether you think the L’Aquila trial will discourage scientists from being involved in public safety decisions. Since asking this question last Thursday all seven scientists have been sentenced to six years in prison for manslaughter – two years longer than even the prosecutors had demanded.

The sentencing on Monday has sent shockwaves through the science community, if you will excuse the pun. Bloggers and tweeters have been speaking out in furious condemnation of the Italian authorities for setting what they believe is an incredibly dangerous precedent of imprisoning scientists for “getting it wrong”. Earlier today the Royal Society and the US National Academy of Sciences issued a statement in support of the Italian geophysicists. “If it becomes a precedent in law, it could lead to a situation in which scientists will be afraid to give expert opinion for fear of prosecution or reprisal,” it states.

It seems that our Facebook followers also agree with this sentiment as 97% of responses were that “yes” the L’Aquila trial will discourage scientists involved in public risk tasks.

Thank you for your responses and we hope to hear from you again in this week’s poll.

Physicists entangle 100,000 photons

Pulses of light comprising around 100,000 entangled photons have been created by physicists in Germany and Russia. The pulses were made in the “squeezed-vacuum” state and the team found that the entanglement should become stronger as the number of photons in the pulse increases. Such pulses could find use in technologies such as quantum cryptography or metrology.

Entanglement is a quantum effect that allows particles such as photons to have a much closer relationship than predicted by classical physics. For instance, two photons can be created experimentally, such that if one is measured to be polarized in the vertical direction, a measurement on the other will reveal the same polarization. This occurs in spite of the fact that a measurement on a single photon will reveal a random value of polarization. While such a correlation can occur in the non-quantum world, quantum mechanics strengthens it to beyond what is expected from classical physics. This misfit between the quantum and classical worlds was described succinctly by the Northern Irish physicist John Bell in 1964 and was confirmed by a series of experiments done in the 1970s and 1980s.

Now Maria Chekhova and colleges at the Max Planck Institute for the Science of Light and Moscow State University have created quantum states containing as many as 100,000 photons, which are all entangled with each other.

Nonlinear crystals

The team’s experiment begins by firing a laser pulse at a polarizing beam splitter, which creates two pulses with different polarizations. These are fired at two nonlinear crystals and “pump” the crystals. Thanks to the nonlinear nature of the crystals, a photon in a pump pulse can decay into a pair of entangled photons with the same polarization – but with different energies (A and B). One photon is infrared and the other is in the visible range of the electromagnetic spectrum.

The initial decay in the crystal will occur spontaneously and as the first photon pair travels through the crystal it will stimulate the emission of other photon pairs. The ensuing cascade will produce a pulse of photons that are all entangled in what is called a “squeezed-vacuum” state. The pulse is squeezed because the numbers of photons in pulses A and B are more precisely correlated than in two typical laser pulses of equal energy. The vacuum part of the definition comes from the fact that the pulse began spontaneously with zero photons – the vacuum state.

Pulses of entangled photons from each crystal are then recombined in a second polarizing beam splitter to create a single pulse that is unpolarized. This pulse is manipulated using a “dichroic plate”, which rotates the polarization of photons of one energy – say A – by 90 degrees with respect to the polarization of photons with energy B. The result is an entangled pulse that is a “macroscopic singlet Bell state” – if the polarization of the A photon is measured as vertical, the polarization of the B photon will be horizontal and vice versa. This property of polarization correlation is valid for any choice of polarization states: if photon A is right circularly polarized, for example, photon B is left circularly polarized and so on.

Measuring entanglement

The next challenge for the team is how to show that the photons are indeed entangled. This is done by passing the pulse through a final polarizing beam splitter, which sends photons with horizontal polarization towards one detector and photons with vertical polarization towards a second detector.

The total number of photons in each pulse is counted by the detectors and the degree to which a pulse is entangled can be determined by determining the correlations between signals in the two detectors. The team was not able to test the entanglement using Bell’s inequality because the standard Bell’s inequality is only valid for photon pairs and is not applicable in this case. The derivation of a macroscopic Bell’s inequality still remains a challenge. However, the team was able to establish entanglement using the “separability condition” that applies to such systems. The analysis revealed that the pulses had a greater degree of correlation than allowed by classical physics and were therefore entangled.

More photons, more entanglement

The researchers also calculated a parameter of the pulse called the “Schmidt number”, which is a measure of the degree of entanglement within the pulses. They found that the number scales as the average number of photons in the pulse. According to the team, this means that brighter pulses are more entangled than their weaker counterparts.

Xiao-Qi Zhou of the UK’s University of Bristol described the set-up as “a very clever method to detect entanglement in such large photonic state”. He adds, “People knew that a big [squeezed-vacuum] state is entangled but didn’t know how to prove it experimentally.”

Zhou believes that the most promising application of the entangled pulse is “practical quantum metrology”. Examples include phase microscopy and optical gyroscopes.

Chekhova says that the pulses could also be used for quantum key distribution (QKD), which uses entanglement to allow two parties to exchange coded information in secret. “Quantum information can be encoded into the photon number, and then beams A and B would be distributed to the two users,” she explains. “This protocol would be similar to the well known Ekert [QKD] protocol, based on photon pairs, but here the alphabet will be larger,” she adds.

The research is reported in Physical Review Letters.

The science of Prometheus

For roughly the last half century, chemistry has perhaps been the most disparaged of the sciences. Among members of the public, the very word “chemical” has come to have opprobrious connotations, and some physicists (and even chemists) have argued that chemistry is reducible to physics, and thus not truly an independent science. But there is also a more subtle problem. In contrast to biology, which tells us about our organic origins and our nature, or physics, which traces and predicts our cosmic origins and destiny, chemistry has appeared to be the science with the least to say about the human condition, and therefore about the humanities and the arts.

Roald Hoffmann is trying to change that perception. One of the world’s most distinguished living chemists, Hoffman received a share of the 1981 Nobel Prize for Chemistry for his work on the structure of chemical reactions, but he also has an exhaustingly wide range of interests within the sciences and in virtually every area of cultural activity. In the essays in Roald Hoffman: On the Philosophy, Art, and Science of Chemistry he has used this enormous breadth of interest and knowledge to demonstrate connections and resonances between chemistry and extra-scientific domains, notably the humanities and arts. The result is a vibrant, stimulating and thought-provoking volume. In addition to its general appeal, Hoffmann’s reflections on the similarities and differences between the thought and practices of chemists and physicists should be of special interest to readers of Physics World.

The book comprises a set of 28 essays by Hoffmann and some collaborators (notably the chemist Pierre Laszlo), with publication dates ranging from 1988 almost to the present. Some of the essays are unpublished lectures, but most appeared in professional chemistry journals or in science-focused journals such as American Scientist and Scientific American, while a few were published in art journals – including one in an anthology on crafts that described, among other things, the similarities between craft and laboratory chemical practice. Editors Jeffrey Kovac and Michael Weisberg have organized these essays into five categories: chemical reasoning and explanation; writing and communication in chemistry; art and science; chemical education; and ethics in science. Although most of the essays are relatively short, this is not a book to be read quickly from cover to cover. Rather, each essay requires close reading and is then to be savoured and considered.

Is there an overarching theme or set of themes in these essays? I shall hazard an affirmative answer and quote from the book’s first essay, “What might philosophy of science look like if chemists built it?”:

“Chemistry always was the art, craft and business of substances and their transformation…With time, we’ve learned to look inside the innards of the beast, and reasoned out that in the macroscopic matter, static and undergoing transformation, there are atoms, and, much more interesting, persistent groupings of atoms which are molecules. So chemistry is also the art, craft, business and science of molecules and their transformations.” (p27)

What interests me as a historian of science about this passage is the way it describes the multiple and proliferating natures of chemistry. The discipline has always been about manipulating macroscopic material transformations to make things, but in more recent centuries, chemistry has also become “the science of molecules”. Its lifeblood nowadays is the representation and transformation of atomic arrangements in molecules, utilizing complex theory and sophisticated laboratory techniques – all while continuing to make things by means of molecular synthesis.

This quotation also implies that chemistry is a human activity, one that is deeply involved in and influenced by other human activities. Like the arts, Hoffmann argues, it is a highly creative pursuit; theoretical insights and laboratory discoveries are not readily captured by standard philosophical methodologies such as inductivism, Popperianism or covering-law models. It is also like the visual arts in its focus on molecular graphic representation.

Prometheus represents the element of design, the process of fruitfully taking advantage of chance creation

Many of these themes appear in each essay, and I shall use one of them as an exemplar. The point of departure in “How should chemists think?” is the central image of Plato and Aristotle in The School of Athens, a fresco by the Renaissance painter Raphael. Hoffmann uses this dichotomous image of the concrete (Aristotle) versus the ideal (Plato) to segue into a long meditation on chemical molecular synthesis. Such synthesis, he argues, is “a patently creative act” (p130), often involving complex syntheses of “natural” versus “unnatural” (human-created) molecules. Hoffman then describes some examples of modern chemical molecular synthesis, such as a complex antibiotic fabricated by chemists at Merck and an extraordinary assembly of ferric (iron) ions in a nearly circular ring held together by organic radicals. The structure of this “ferric wheel” was revealed by X-ray diffraction analysis in the 1990s and, unlike the antibiotic, it has, as yet, no known uses. Nevertheless, its beautiful form elicits a strong aesthetic response from Hoffmann; for him, he writes, “this molecule provides a spiritual high akin to hearing a Haydn piano trio I like”. A few pages earlier, Hoffmann had compared the laboratory fabrication of complex molecules to architecture, noting that “chemical synthesis is a local defeat of entropy, just as our buildings and cities are” (pp132–133).

Much else goes on in this short chapter, but I shall move to Hoffmann’s concluding meditation on the Greek myth of Prometheus. While Hoffmann does not neglect the unnatural (and dangerous) hubris associated with this bringer of fire from the gods, he argues that the Promethean figure is also a symbol of creativity. “Were chemical synthesis in search of a single icon,” he writes, “the outstretched hand of Prometheus bringing fire to humanity would serve well.” Noting that the name Prometheus means “forethought”, he adds that the figure “represents the element of design, the process of fruitfully taking advantage of chance creation…The hand of Prometheus is the symbol of creation – the hand of God reaching to Adam in Michelangelo’s fresco, the hands in contentious debate in Dürer’s Christ Among the Doctors, the infinite variety of hands that Rodin sculpted”. Hands, he concludes, can “bless, caress and hide, but most of all, they shape” (p140).

Another essay, on “Molecular beauty”, is likewise worthy of more extended discussion than this limited space allows. It originally appeared in the Journal of Aesthetics and Art Criticism, and its noteworthy features include the clear exposition of the chemistry of molecules that Hoffman regards as “beautiful” in structure. He elucidates what he means by “beautiful” in a very personal, yet sophisticated meditation. The book’s essays on chemical education and scientific ethics also contain much of great value and interest. In the former, Hoffman is insightful and eloquent on the importance to academic research chemists of teaching undergraduates; in the latter, his thoughts on the social responsibility of scientists and the need for “green” chemistry deserve a wider audience.

We live in a world where science – especially chemistry, if taken in its broadest definition to include molecular biology and perhaps solid-state physics – plays an enormous and ever-increasing role. It is also a world in which the humanities and the arts have been thrown on the defensive and forced to justify continued support. In such a world, it is imperative that the writings of people such as Hoffmann – who are capable of stimulating fruitful dialogues between the sciences and extra-scientific cultural domains – be read, contemplated and discussed. It is therefore a pity that almost none of these essays appeared in periodicals that naturally attract an educated non-scientific readership. The only exception was an essay that appeared in an art history journal, and even this has a very specialized and limited audience. I hope that the title of this book will intrigue scientists from all branches of the sciences and non-scientists from all domains of cultural activity, and thus secure and engage a wide-ranging readership.

Physicists show bias against female job applicants

A US study has found that researchers assessing the employability of early-career scientists subconsciously favour male students over females. The bias, which was seen to exist in both male and female physicists and was also exhibited by chemists and biologists, is thought to be a contributing factor towards the underrepresentation of women in physics.

Undertaken by psychologist Corinne Moss-Racusin and colleagues from Yale University, the study involved 127 tenured scientists across six universities in the US being asked to provide feedback on an excerpt from a job application for a graduate-level lab-technician post at another institution. The excerpt – developed by an academic panel – was designed to be as realistic as possible and was identical, except that 64 of the scientists were told the applicant’s name was Jennifer, while the other 63 were told the applicant’s name was John. The scientists were told that their feedback would help the applicant’s career development, unaware that both the candidate and the post were fictitious. The candidate was painted as promising but not exceptional.

The study found not only that the scientists rated the male applicant as significantly more competent and hireable than the (identical) female applicant, but also that the hirers would have given the male student a higher starting salary. “Male and female science-faculty members, including physicists, said they were more likely to hire the male student,” says Moss-Racusin. “They also offered to pay him about $4000 more per year on average and were more likely to offer him career mentoring, relative to the identical female student.”

Innate nature

The bias shown by the potential hirers was independent of their gender, age and seniority, indicating that even women show a subconscious bias against other women. The innate nature of the bias is thought to be evidence of the influence of a society-wide stereotype that men make more competent scientists, influencing even “very well meaning, very well trained scientists who emphasize objectivity and egalitarianism in their daily lives”, according to Moss-Racusin.

Amy Graves, a physicist from Swarthmore College, near Philadelphia, who specializes in gender studies in science, says she is “saddened, but not surprised” by the findings. “This study is so well done, because they created a résumé that was good, but not amazing,” says Graves. “If [the candidate] were an absolute standout, prior studies suggest that [the authors of the study] might not have seen this evidence of a genuine, unconscious bias.”

Mentoring needed

According to Moss-Racusin, having structured and transparent mentoring is one solution to the problem. She recommends guidelines to help standardize support across all students and the use of secondary mentors. “One of the biggest predictors of success and retention within academia, especially for women and racial-minority students, is identifying with a role model or a good mentor.”

Meanwhile, a pilot mentoring programme – Women in Technology Sharing Online – was launched last month by the Piazza online education platform and by Harvey Mudd College in Claremont, California. By introducing female students to mentoring, the sponsors hope to increase the retention of women in science.

The results are published in the Proceedings of the National Academy of Science.

Mini-mission will search for super-Earths

Cheap as Cheops: the exoplanet hunter is the ESA’s first “quick-turnaround mission”. (Courtesy: ESA)

By Hamish Johnston

In 2017 the European Space Agency (ESA) will launch a space mission called Cheops, which will take a closer look at nearby bright stars that are already known to have exoplanets orbiting around them.

The mission will measure the brightness of the stars, looking for tiny dips associated with a transit – when an exoplanet passes in front of its star, blocking some of the light that reaches Earth.

“By concentrating on specific known exoplanet host stars, Cheops will enable scientists to conduct comparative studies of planets down to the mass of Earth with a precision that simply cannot be achieved from the ground,” said Alvaro Giménez-Cañete who is ESA’s director of science and robotic exploration.

“The mission was selected from 26 proposals submitted in response to the Call for Small Missions in March, highlighting the strong interest of the scientific community in dedicated, quick-turnaround missions focusing on key open issues in space science,” added Giménez-Cañete.

Cheops is an acronym – any guesses for what it stands for?

Its full name is “CHaracterising ExOPlanets Satellite”!

Silvery fish fool predators with their skin

Some fish appear to be less visible to predators because their silvery skin does not polarize reflected light, say researchers in the UK. The researchers studied three types of fish and found that their skins contain two types of “guanine crystal”, each with different optical properties. The team says that the mechanism could be easily applied to man-made optical devices that require non-polarizing reflectors to improve their overall efficiency.

Many fish have silvery iridescent skins and this has intrigued researchers for many years. “We have known that they try to be as silvery as possible to camouflage [themselves],” explains Nicholas Roberts of the University of Bristol. Roberts, along with other colleagues from the university, have been trying to understand the exact purpose of the silvery cloaks of fish such as the European sardine and Atlantic herring. When light reflects from a surface, it usually becomes polarized. It was thought that the fish’s skin would fully polarize light when reflected, so there would be a drop in overall reflectivity. This is disadvantageous to the fish because it would appear more visible to a predator.

Shiny cloaks

Fish skin is a layered construct – if you chip off the first layer that is made up of scales, the silver sheen remains. Underneath the scales is a tissue layer – known as the “stratum argenteum” – that consists of guanine crystals and cytoplasm. It is the guanine crystals that are interesting – they are of two types, each with different optical properties and each present in different ratios in the skin.

The two types of guanine crystal have optical axes that are either parallel to the long axis of the crystal or perpendicular to the plane of the crystal. And it is this arrangement that effectively neutralizes the polarization of reflection and makes the reflected light polarization-neutral across a range of angles, according to the researchers.

As the two types of crystal are present, light is reflected at every angle, and the drop in reflectivity usually caused by polarization is avoided, so their skin maintains its high reflectivity. Because it does not suffer from a drop in reflectivity, it no longer stands out from its surroundings. This polarization-neutrality must be especially handy for the fish because several aquatic animals are known to have vision that is not sensitive to colour but can detect differences in polarization, and they use this to their advantage while hunting their prey.

Following the fish…

This simple optical trick could prove of great use in man-made devices where high polarization independence is required, according to the team. Dielectric multilayer reflectors that are non-polarizing are already essential to optical devices and have many varied applications in optical fibres, dielectric waveguides and LED back reflectors. The reflective mechanism of the fish “is distinct from existing non-polarizing mirror designs in that, importantly, there is no refractive index contrast between the low-index layers in the reflector and the external environment. This mechanism could be readily manufactured and exploited in synthetic optical devices”, the researchers say in the paper.

In the months to come, Roberts and his colleagues are keen to look further into other aquatic animals that possess “polarization-sensitive vision” and to study their “intriguing optics”.

The work is published in Nature Photonics.

The upcoming November special issue of Physics World is devoted to “animal physics”. You can download a free PDF of the issue from physicsworld.com from Wednesday 7 November 2012.
David Hu from Georgia Institute of Technology’s laboratory for biolocomotion presents a special online lecture at 3.00 p.m. GMT on Thursday 8 November 2012, which you can view by registering here.

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