Skip to main content

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact customerservices@ioppublishing.org

Registration complete

Thank you for registering with Physics World
If you'd like to change your details at any time, please visit My account

Close
Home » Page 1529

Experience the planets through the eyes of artists

venus.jpg
Menacing vortex above Venus

By James Dacey

If you, like me, are going to miss out on tonight’s global meteor show because of cloud cover, then why not check out the planets instead — and from the comfort of your living room.

Experience the planets is an ongoing project for artists to create images of the solar system which bridge the gap between reality and fantasy.

“ETP breaks away from the fanciful notions of space and embraces the more challenging task of creating scenes informed by scientific hypothesis,” says Greg Martin, an artist and the project creator.

It’s a very slick website with the picture of the menacing spiral effect above the north pole of Venus being my personal favourite.

Be warned though — if you pay a visit to Mercury you can never leave! It looks like there’s still a couple of website navigational issues to iron out…

Do geckos always have sticky feet?

gecko.jpg
Leopard geckos were used as a control in this study Source <a href="http://www.freedigitalphotos.net/

“>freedigitalphotos

By James Dacey

A few years ago, physicsworld.com reported the first experimental evidence to explain how a gecko can scurry without fear across even the smoothest of ceilings.

The answer lies in the lizards’ hairy feet. Each toe one is covered with tiny micrometer “satae”, which branch off into even smaller “spatulae” thinner than the wavelength of visible light. Spatulae stick to walls by van der Waals forces – the weak electrostatic attractions between adjacent atoms or molecules that arise from fluctuations in the positions of their electrons. If these forces act over a relatively large area, they can build up a significant attractive force.

Now, inspired by the gecko’s sticky trick, a couple of researchers in Canada and the US have set out to investigate where and when this stickiness is switched on and off by the lizards.

Anthony Russell of the University of Calgary and his colleague Timothy Highan of Clemson University, South Carolina, began by assembling a team of 11 geckos. Six of these were Moorish geckos, T. Mauritanica, which are known to use the van der Waals gripping mechanism. The remaining five were juvenile leopard geckos, E. Macularius, used as controls because they do not have adhesive pads.

Russell and Higham set up an experiment in which all 11 geckos were made to run across a set of different surfaces over a range of different inclines. On the flat surfaces, the researchers found that all six Moorish geckos refrained from using their adhesive system. However, when the geckos were running on a 10 degree incline, three of them began to use their pads for grip, and on a 30 degree incline, all six deployed their pads.

Interestingly, the friction of a running surface seems to make no difference to whether geckos deploy their gripping mechanism or not. None of the Moorish geckos used their sticky pads on the flat planes even when they were slipping on the Plexiglas substrate and losing speed because of this. This observation led the researchers to conclude that geckos control their sticky toes by via a perception of their body’s orientation.

I caught up with Russell and he explained the findings in a little more detail. “The loading of the setae under tension is accomplished by the muscular system, and that this, in turn, is activated by reflex pathways that depend upon feedback from environmental cues, such as body orientation.”

So, it seems that the insights of this new research are more related to the application of the physics by the animal, rather than the details of the physics itself.

One thing I found interesting when reading the paper — just published in Proceedings of the Royal Society B — is the difficulty the researchers must have faced when trying to control variables in an experiment like this. It’s not like certain experiments in classic physics in which one can take thousands of measurements of an inanimate object in a vacuum.

Russell conceded himself that he cannot draw any general laws from this because there are hundreds of species of gecko and we cannot expect them all to respond in the same way. “Even small and large individuals of the same species may not respond in the same way.”

More on electron/positron excesses…

By Hamish Johnston

Yesterday we reported that the excess number of cosmic positrons seen by PAMELA and other detectors could be coming from a nearby pulsar called Geminga — rather than from annihilating dark matter.

While the pulsar explanation is significant, the direct detection of dark matter via cosmic rays could bag someone a Nobel Prize. But alas, it is looking less likely that the current generation of cosmic ray detectors are up to the prize-winning task (assuming dark matter exists, and annihilates to create cosmic rays!).

One of the physicists arguing the pulsar explanation is Todor Stanev of the University of Delaware.

Stanev has also teamed up with researchers in Germany, Sweden and the US to show that electron and positron excesses seen by PAMELA and other experiments can also be attributed to the violent acceleration of matter that is believed to occur in the polar caps of certain supernovae.

According to the team, the energy spectra of electrons and positrons emitted in such a polar cap match what has been seen by several detectors. You can read about it in Physical Review Letters .

However, unlike the pulsar result, the researchers don’t seem to link recent electron- and positron-excess measurements to a specific astronomical event.

Instead, they seem to be suggesting that these positrons and electrons are present in the general background of cosmic rays reaching Earth.

So, does this mean that it will be even more difficult to winnow a dark-matter signal?

Tiny device is first complete ‘quantum computer’

Researchers in the US claim to have demonstrated the first small-scale device to perform all the functions required in large-scale ion-based quantum processing. Although the individual stages or groups of stages in quantum computing have been demonstrated previously, this new device is said to perform a complete set of quantum logic operations without significant amounts of information being lost in transit. As a result, the device represents an important step in the quest for a practical quantum computer, say the researchers based at the US National Institute of Standards and Technology (NIST) in Boulder, Colorado.

Researchers in the field have already hailed this as an important breakthrough in quantum computing. However, they also warn of the practical challenges that still lie ahead if we are to develop large-scale quantum computers.

Where conventional computers store data as “bits” with value 1 or 0, in quantum computing data is stored as “qubits” which can hold more than one value at the same time. The upshot of this phenomenon, known as superposition, is that quantum computers could potentially store and process unprecedented amounts of data. What’s more, quantum particles can become “entangled”, allowing them to share a much closer relationship than classical mechanics allows in which data is transferred instantaneously between entangled particles regardless of their separation distance.

The quantum path

The concept of quantum computing gathered significant momentum in 1994 when the mathematician Peter Shor invented an algorithm to show that quantum computation could factor numbers significantly faster than in classical computation. The implication was that quantum computers could operate at ultra-high speeds, which could be applied to solving complex problems like cracking some of today’s most widely used encryption codes. However, it quickly became apparent that researchers would have a very difficult task of putting this into practice due to the delicate nature of quantum information, particularly when quantum data is being transferred between locations.

Despite this limitation, some simple quantum algorithms have been executed in the past few years. Perhaps most notable was the first and only demonstration of Shor’s factoring algorithm, using nuclear magnetic resonance, by Lieven Vandersypen and his colleagues at the IBM Almaden Research Center in California.

“Home and his team have shown the individual pieces of the puzzle to work separately in a series of beautiful experiments in recent years. Now, in this tour-de-force, they put the pieces of the puzzle together and made them all work in one experiment,” Boris Blinov, University of Washington

One promising approach to realizing quantum algorithms is the storage and transfer of quantum data in ultracold ions. This is the approach taken by the group at NIST, led by Jonathan Home, which, over the past few years, has demonstrated all of the steps needed for quantum computation: (1) “initialize” qubits to the desired starting state (0 or 1); (2) store qubit data in ions; (3) perform logic operations on one or two qubits; (4) transfer information between different locations in the processor; and (5) read out qubit results individually.

Caught in a trap

In this latest research, Home’s group have now managed to combine all of these separate stages for the first time. The team held two beryllium atoms in a trap before manipulating the energy states of each ion using an applied ultraviolet laser pulse in order to store quantum data. Electric fields were then used to move the ions across macroscopic distances — up to 960 micrometres — between different zones in the trap. The researchers repeated a sequence of 15 logical operations 3,150 times on each of 16 different starting states and found that the processor worked with an overall accuracy of 94 per cent.

One of the key innovations employed by the NIST researchers was to use two partner magnesium ions as “refrigerants” for cooling the beryllium ions as they are being transported. This “sympathetic cooling” enabled logic operations to continue without any additional error due to heating incurred during transport. “We have incorporated transport, and explicitly shown that it does not impede our ability to do further computation — this is a crucial step for building a large-scale device,” Home told physicsworld.com.

Early response to this development from the research community is positive. “Home and his team have shown the individual pieces of the puzzle to work separately in a series of beautiful experiments in recent years. Now, in this tour-de-force, they put the pieces of the puzzle together and made them all work in one experiment,” said Boris Blinov, a quantum computing researcher at the University of Washington.

The road ahead

Hans Bachor, a quantum optics specialist at the Australian National University is also impressed. “The work is indeed a great step forward and most impressive — it demonstrates all the key steps required in the computing cycle.” Bachor, however, also warns of technical challenges that lie ahead. “The question is whether they can keep the ion in the ground state. I am not aware of any in principle problems, but it will require more tricks to invented,” he added.

Home told physicsworld.com that his team are continuing to develop their trapped ion system with a focus on two specific problems. The first area is to improve the logic operation accuracy: the accuracies required for a large scale device are 0.9999, where the accuracy in this device is 0.95. “Here we are limited by the control we have over our laser beams, and the power of these beams,” he said. The second area is to build larger devices. “Crosstalk between different parts of the processor may be a problem which only exists in larger devices. The classical computer control, and the need for precision control of large numbers of electrodes and laser beams, represents a major technical challenge,” he said.

Markus Aspelmeyer, a quantum optics researcher at the University of Vienna recognizes another of the challenges involved in scaling up. “It will be a challenge to minimize the individual gate errors and to gain control over a large number of ions on a single chip,” he said. Adding, “This is however essential to perform lengthy calculations on a future quantum computer. It is an exciting challenge to both engineering and quantum information science and it is not clear yet where the exact limitations will be.”

This research was reported in Science Express.

Waiting for Ana

ana.jpg
The birth of Ana?

By Hamish Johnston

The east coast of Asia is being battered by typhoons and tropical storms — and sadly, the death toll is mounting.

But halfway around the world, people are beginning to wonder when the hurricanes are going to come to the North Atlantic. The 2009 season began on 1 June, but there have been no significant storms since then — just “Tropical Depression 1”, which didn’t amount to much.

Predictions for 2009 from the NOAA and other research groups had intitially called for “above average activity”, but this has since been downgraded by most groups to “below average”.

In a recent statement however, the NOAA “Cautions Public Not to Let Down Guard”, pointing out that the large number of early-season storms seen over the past 15 years is not in line with the historical average.

The agency also says that several seasons with severe hurricanes (including Andrew in 1992) began with whimpers.

Researchers had predicted above-average activity for 2009 because conditions off the west coast of Africa seemed ripe for hurricane formation. However, the development of El Niño in the Pacific has boosted westerly winds in that part of the Atlantic, blowing nascent storms apart.

If you’d like to keep abreast of developments off the coast of Africa, check out the Wunderblog by Jeff Masters. Indeed the latest entry has a nice picture of what could develop into the first storm of the year — Ana.

If you are still hopeful that Jim will soon be eating his shorts, the BBC television programme Horizon has a special programme tonight about superluminal neutrinos presented by mathematician Marcus du Sautoy. More details can be found here here.

Excess positrons are linked to Geminga pulsar

Are recently-detected excesses of cosmic electrons and positrons the first direct evidence for the existence of dark matter particles? That has been the hope of many physicists, while others have suggested a more mundane origin in a nearby pulsar. Now researchers in the US claim that the excesses can be linked to high-energy gamma rays emitted by the Geminga pulsar.

Cold dark matter is the most accepted explanation as to why the universe appears to have at least 80% more gravitating mass than is directly visible. Dark-matter particles are expected to collide with one another and annihilate — producing high energy particles such as electrons and positrons. If these particles could be observed, they would represent the most direct evidence yet for the existence of dark matter.

Excesses of high energy electrons and positrons from space have been reported by several experiments. In particular, in 2008, researchers working on the PAMELA satellite found an excess of positrons from 10–100 GeV in the cosmic ray spectrum. The results could not be explained by standard models of cosmic ray origin and propagation in the Milky Way and instead suggested a nearby ‘source’ of high energy positrons. However, there has been no conclusive evidence linking the positrons to dark matter — and the annihilation rate is far higher than expected from standard theories.

Positrons from Geminga

Now, Hasan Yuksel and Todor Stanev at the University of Delaware and Matthew Kistler at Ohio State University claim that the source of these positrons is Geminga — a nearby and rapidly rotating neutron star. The results also represent the first time that astronomers can link cosmic rays to a specific source.

At the heart of their theory is seemingly unrelated set of observations by the Milagro gamma-ray observatory in New Mexico, which has seen a halo of high energy gamma-ray sources around Geminga. Located approximately 800 light–years away from Earth and some 300,000 years old, Geminga is the nearest known gamma–ray source to Earth, excluding solar system bodies.

“We wanted to understand the origin of these gamma rays, which were not expected from such an old pulsar,” explains Yuksel. “We found that they imply pairs of electrons and positrons are being produced near the pulsar and accelerated up to very high energies.”

Tangled magnetic fields

Importantly, the extent of the gamma ray emission also implies that a ‘wind’ of these particles is escaping from the pulsar, confirming the presence of a powerful particle accelerator near the Earth and suggesting that the cosmic rays produced in Geminga’s more active past are — after a circuitous journey through the Milky Way’s tangled magnetic fields — likely the source of the excess positrons observed by PAMELA.

If so, the results are also likely to be the first ‘direct’ detection of cosmic rays. “When cosmic rays are detected in the atmosphere or in space, we cannot infer their origins easily as their trajectories are easily bent in the Milky Way’s magnetic fields and any relevant information is usually lost,” says Kistler. “However, if the observed excess of positrons can be associated with a known object near the Earth, then for the first time, a connection between a population of cosmic rays and the source that gave birth to them will be established.”

Other astronomers have welcomed the result. “It is at first sight not terribly surprising that Geminga could be the source of the PAMELA positron excess as it is the closest energetic pulsar,” says Stefan Funk at Stanford University in California and an associated member of the HESS gamma-ray observatory. “However, by connecting this to the recent Milagro observations, this can be used in principle to calculate the number of particles that would reach us from Geminga if these particles are electrons.”

Don’t give up on dark matter

Douglas Finkbeiner at Harvard University in Massachusetts is more cautious. “I am glad people are pursuing the pulsar explanation and certainly pulsars contribute to this signal at some level,” he says. “But enough is not known about pulsars at the moment to exclude the possibility that something else dominates.”

Yuksel and his colleagues accept that dark matter cannot be ruled out as yet. However, they believe new observations from other more sensitive experiments will examine Geminga in more detail and allow scientists to better gauge the total amount of energy contained in cosmic rays flowing from the pulsar.

The work is reported in Physical Review Letters

New form of carbon created

Researchers in the US and France have found what they claim is a new form of carbon. The new material is made from layers of graphene — sheets of carbon atoms just one atom thick — stacked on top of one another in such a way that each layer is electronically independent. The researchers claim that the material, dubbed multilayer epitaxial graphene (MEG), could be used in carbon electronics instead of costly single and double layer graphene sheets.

Graphene was first isolated only five years ago by exfoliating individual atomic layers from graphite by using transparent sticky tape. Since then graphene has amazed physicists with its high conductance at room temperature and with a breaking strength 200 times greater than steel making it one of the strongest materials ever tested.

Edward Conrad from the Georgia Institute of Technology and colleagues have now grown graphene layers from a silicon carbide substrate in such a way that each layer is rotated by 30 degrees with respect to the lower layers. This MEG differs from naturally occurring graphite where each layer is rotated by 60 degrees with respect to the lower layers.

“With the stacking we see in natural graphite, which results in a special coupling between the layers, it seems like nature has managed to stack graphene sheets in a way that is not useful for electronics at all,” says Conrad.

The researchers performed X-ray scattering and Angle Resolved Photoemission (ARPES) spectroscopy on a sample of MEG with 11 layers of graphene to measure its electronic structure. They found that the electron energy in a certain part of the band structure is proportional to its momentum giving the indication that the electrons behave like massless particles.

“This perfectly linear band structure, known as a Dirac cone, has not been so clearly measured before on other samples of graphene,” says Conrad. Using ARPES, Conrad and colleagues saw no distortion of the Dirac cone, which they conclude shows there is no electron coupling to other layers in the sample and thus each layer is electronically isolated.

Although the researchers are just beginning to understand why the layers in a MEG sample do not couple with each other given that they are chemically bonded, they claim that these unique properties could be used as a basis for carbon electronics instead of single or double-layer graphene films, which are tricky and costly to isolate.

Another advantage of epitaxial graphene is that it can be manufactured on a large scale. Graphene is relatively inexpensive to grow epitaxially, as in the case of MEG, being dominated by the price of silicon carbide, which costs about $100 per centimetre square to manufacture. This, according to Conrad, is still a million times less than making exfoliated graphene. The researchers are now attempting to make high speed transistors from MEG.

This research has been published on the arXiv preprint server.

DNA twists and bends on demand

Researchers in the US and Germany have developed a new way to transform DNA into complex shapes by making the molecules twist and bend. The technique could be crucial for making nanoscale device building blocks, such as molecular rings, wheels, solenoids and gears, for applications in areas like drug delivery and optoelectronics.

DNA molecules consist of two linear strands wound into a double helix with one of four different “bases” attached to every sugar group along the strands. Apart from being the “building blocks of life”, DNA is also an attractive engineering material because strands with complementary base sequences recognise and bind to each other, enabling complex molecular structures to be made by self-assembly. Scientists have long known that DNA molecules can bend and twist into complex shapes — for example, DNA in “eukaryotic” cells is packed into nucelosomes in which the molecule bends around proteins with a radius of curvature as small as around 4 nm. The dream has been to create artificial structures that mimic such natural ones.

Manipulating DNA

Now, however, Hendrik Dietz of the Technische Universität München in Germany and Shawn Douglas and William Shih of the Dana-Farber Cancer Institute, Harvard Medical School and the Wyss Institute at Harvard, have taken a big step forward towards this goal. Their technique, which involves either adding DNA base pairs to bundles of DNA helices or taking them away, allows the researchers to construct nano-scale wheels, arches and other continuously curved objects. The direction and degree of bending can be controlled to produce molecules that curve over arcs with a radius as small as 6 nm (Science 325 725).

Shih and co-workers did this by using parallel bundles of DNA double helices, laterally held together by cross-links formed by strands crossing over from one helix to the next to create a rigid starting material. Employing a large bundle of helices is important because it provides rigidity, explains Shih. Indeed, bending would not be as useful if the starting material was too floppy.

Next, the researchers either removed or inserted base pairs of DNA along specific helices, between the cross-links. When a base pair is removed, the double helix contracts, and when a base pair is inserted, the double helix expands.

If base pairs are systematically deleted from one layer while being inserted into the opposite layer of helices, the resulting contraction/expansion makes the structure bend. Put simply, the shape is concave where base pairs have been removed and convex where they have been added.

Curvaceous molecules

Shih’s team says that this is the first time that DNA bending has been controlled in such a way. Previous efforts relied on material interactions with proteins to bend the DNA, whereas the present method relies exclusively on interactions with DNA itself. The structures produced are highly rigid and can be fine tuned over a wide range of curvatures. “Basically we have achieved a big leap in the amount of curvature control, so that’s why our findings are important,” said Shih.

Such rigid, curved DNA structures could be used to construct molecular rings, wheels and solenoids. In turn, these building blocks could be made into devices for applications in areas like plasmonics — for example, to make nanoantennae — and in therapeutics such as drug delivery inside the body.

The team says it would now like to build some simple devices after having demonstrated gears and beachball shapes by joining various curved elements together. The structures also need to be made more robust, which means reducing the amount of defects present in them.

Fiery demise for NASA toolkit

astronautout.jpg
Drifting away (credit: NASA)

By Michael Banks

The term “space junk” usually means spent rocket stages or disused satellites floating in orbit around the Earth.

But while on a routine servicing mission to the International Space Station (ISS) late last year to fix a solar panel, US astronaut Heidemarie Stefanyshyn-Piper watched helplessly as her toolkit, containing grease guns and scrapers, floated off into space.

Fortunately, the $100 000 tool bag was moving away from the ISS, so there was no chance of it making a big dent in the station, which would have needed more than a tool bag to fix.

Instead, however, the 14 kg space satchel was circling earth getting ever closer with each orbit.

According to the website space.com the toolbag has now burnt up in the Earth’s atmosphere – eight months after it first drifted away in orbit. Some reports say the toolkit’s demise happened at 1.16pm GMT over the Pacific Ocean.

Soap films burst like flapping flags

Physicists in France have taken high-speed photographic images showing that a punctured soap film ripples for a moment before bursting into a fine mist of water droplets. The researchers attribute this strange behaviour to the same physics which makes a flag edge flap in the wind.

The fact that the rim of a punctured film does not expand in a smooth manner was first noted by the physicist Lord Rayleigh back in 1891. But it was not until the late 1960s that physicists first identified that punctures in soap films enlarge via distinctive “fingers”, which are responsible for the observed ejection of water droplets. Until now, this phenomenon has only been studied from a frontal view, which has led physicists to link the observed instabilities with the internal kinetics of the liquid soap.

A soapy-fresh perspective

In this latest research, however, Henri Lhuissier and Emmanuel Villermaux at the Aix-Marseille University have taken a new approach by observing soap film from an angle and studying how it behaves when it bursts. To create the film the researchers pulled a rigid frame out of a solution of the commercial detergent “Dreft”. The bursting of the soap film is then performed in a vapour-saturated atmosphere.

Using a high-speed camera with a framing rate up to 25,000/s, the researchers captured a soap film receding in air with each full sequence typically lasting less than 0.01 s. They find that, in addition to the puncture growing parallel to the film, there also exists a secondary motion perpendicular to the plane, which causes the region of film close to the perforation to oscillate in a flapping-like manner.

Publishing their findings in Physical Review Letters, the French physicists attribute this flapping to the velocity difference between the fast-receding film and the slower-moving atmosphere. As the soap molecules begin their transit, the air flows around them leading to instability – just as a flag begins to flap when a rapid air current (the wind) flows around it. Once a film has receded far enough for the flapping undulations to pass a given threshold, this lateral motion can trigger the second instability which gives rise to the indentations or ligaments.

Flapping in the wind

To provide further evidence that this flapping is related to the external medium the researchers also captured images of a flapping soap film in sulphur hexafluoride (SF6), which is five times denser than air. In this case, the destabilization of the puncture rim developed significantly faster, leading the researchers to conclude that the speed of soap film bursting increases with the density of the supporting medium.

Lhussier told physicsworld.com that he is now adapting his high-speed photography technique to study a more common phenomenon in nature – bubbles. “The application of such theories to bubble caps or shells is very important since the tiny spray they generate while bursting is responsible for a large part of the natural aerosols formation and thus plays a major role in the climate through the ocean-atmosphere exchanges,” he says.

Copyright © 2026 by IOP Publishing Ltd and individual contributors