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 1298

Learning to adapt

What sparked your interest in physics?

Like many scientists of my generation, I grew up reading a lot of science fiction. In addition, my stepfather – a very strong figure in my life – is a geophysicist, so I was always surrounded by earth-science types. I studied biology and chemistry in high school, but I always had deeper questions, and it seemed like if you really wanted to answer them, you had to study physics.

What was it like for you to study physics at university?

Being a blind physics student is a lot more work than being a sighted physics student. For example, I had to have someone read my textbooks out loud so that I could copy them into Braille; I would copy verbatim all the equations and even many of the tables so that I had reference materials for the classes I was taking. But I was also lucky. I went to the University of California, Berkeley, which was the birthplace of the disability rights movement, and I think in part because of that movement, I had almost no negative experiences with my professors. They were almost always willing to work with me to find creative ways of helping me to progress in my studies.

You earned your PhD in psychoacoustics. Can you explain what that is?

Psychoacoustics is the science of how hearing works. There’s a very long tradition of crossover between the physics and psychology communities in this area because it lies at the interface between acoustics and brain function. It’s a broad field, covering both “mushy” topics like how someone feels about a piece of music and “hard” ones such as the responses of specific neurons to frequency changes and other acoustical variations. My focus was on something called auditory motion perception, which basically examines how you know about sounds in the environment that are moving from one place to another.

How did you get into adaptive-devices research?

When I was an undergraduate I worked at a software firm called Berkeley Systems. Physics World readers might remember it as the company that made screensavers popular – it did the famous “flying toasters” screensaver for the Macintosh computer (Mac) in the late 1980s and early 1990s – but it actually got started as a screen-reader company. People there invented a way of making Macs (which were the first consumer-level devices to have a graphical user interface) accessible to blind people via text-to-speech software and a set of keyboard commands for navigating around the screen. There had been concerns that once computing got away from the command-line interface, blind people would be locked out of computers and the jobs associated with them, so it was a real breakthrough that Berkeley Systems was able to create this fairly inexpensive little piece of software that made Macs completely accessible. I was in awe of that kind of innovation. I started out doing technical support, then technical writing and ultimately I did a lot of the interface design work for the accessibility software that was released for Microsoft Windows later in the 1990s.

What technological aid that is currently out of reach would you most like to see become a reality?

The thing that we don’t have right now is a 2D tactile display. Sighted people have computer screens that they can look at that show very high-resolution images and video. But for a blind person to get access to the information in a 2D image is very difficult. If I want to look at a chart or a graph, then I either need to print it out using a Braille printer or I need to come up with some kind of clever “sonification” technique, using sound to represent the information. Having a 2D, computer-controlled display that I could just feel would be an incredible innovation. I can’t tell you how many times people have thought they’ve invented it, only to realize later that they didn’t really understand some critical design requirements. What we need is something that’s robust, inexpensive and portable, with the ability to change the image quite rapidly. It’s a very difficult problem. We jokingly call it the “Holy Braille”, because it’s something we all want and it has eluded all the brightest minds for quite some time.

How has your physics background helped you?

There is a lot of physics in many of the things I do. For example, to understand tactile perception, you need to know about friction and kinematics. But I think it’s had a more of an impact on the way I think about problems than it has on my daily work. One of the things I learned as a physics student is that when you’re looking at a problem, the whole thing may be quite daunting, but even if there are parts of it that you don’t understand, there will almost always be parts that you do understand, and you can use them as points of entry. It’s a problem-solving technique that I use in my entire approach to life.

  • Learn more about the devices Miele and his group are developing at www.mielelab.org

Simulating lunar craters and the impacts that cause them

Remains of meteorites that hit the Moon at low velocities may be preserved within lunar craters, researchers in the US report. The team used computer simulations to show that nearly a quarter of craters may contain significant remnants of the projectiles that formed them, left behind as deposits in the craters’ central peaks.

The lunar surface is mainly made of the igneous rocks basalt and anorthosite. Recent spectroscopic observations of the Moon by lunar orbiters, however, have revealed the presence of deposits of unexpected compositions – such as magnesium-rich spinels and olivines – within a number of the larger lunar craters. One such crater containing these deposits is known as Copernicus and has a diameter of around 100 km.

Impacting projectiles

On the Earth, spinel is often associated with both intense metamorphism – formed in conditions of extreme temperature and pressure – and the rock peridotite, which dominates the make-up of the upper mantle. Given this, the spinel seen in impact craters on the Moon is often considered to have had its origins in the lunar mantle – having been brought up to the surface during crater formation. These minerals, however, are also common in many asteroids and meteorites, suggesting the possibility that rather than being vaporized on impact as previously assumed, significant deposits of impactors may be left in the craters they create.

The researchers tested this theory by running 2D simulations of meteorite impacts. A two-layer model was used to represent the Moon – with a dunite mantle overlain by a 30 km layer of granite, which represents a minimum estimate for the thickness of the lunar crust. In order to reproduce a crater similar to Copernicus, a 7 km diameter dunite projectile was selected – with impact velocities ranging from 6–16 km/s, based on previous estimates of velocities of lunar impactors originating from the main asteroid belt.

Simulated collisions

Even with its minimal estimate of the Moon’s crustal thickness, the team observed that mantle material was not unearthed in any of the simulated collisions. The maximum excavation depth was seen to be only 7 km – less than a quarter of the modelled crustal depth. With the projectiles, however, while the impactors at velocities above 14 km/s were seen to vaporize, those below 12 km/s left significant deposits behind. In small craters, such remnants were found dispersed in the impact ejecta and across the crater floor, ultimately forming the broken rocks that fill the final hole. Larger craters, however, underwent crater collapse, sweeping the majority of the projectile fragments back together.

“Much to our surprise, we discovered from [our] modelling…that much of the impacting projectile might not only survive the impact, but that its broken remnants become concentrated in the central peaks of craters large enough to produce such,” says the lead author of the paper published in Nature, Jay Melosh from Purdue University in the US. With around 25% of lunar craters predicted to be caused by impacts occurring at below 12 km/s, this result suggests that there could be a significant amount of projectile remnants preserved on the Moon’s surface – possibly even including remains from ejecta from the early Earth.

“Although the idea is interesting and appears to be physically plausible, I am not sure how significant it really is in creating the mineralogical signatures observed in lunar craters,” says Marc Norman, a research fellow at the Australian National University, who was not involved in the study. Norman comments that the preservation of meteorite debris on the Moon is quite rare, with only a few grains having been recognized so far. He also notes that large exposures of olivine have been observed around the rim of Copernicus, the crater that the team was emulating. Such geological evidence, he says, is more consistent with olivine excavated from the Moon’s crust than the impact deposit patterns predicted by this study.

A further issue with the reality at Copernicus is also presented by Erik Asphaug of Arizona State University in his “News and Views” letter associated with the paper in Nature. Asphaug suggests that the large volumes of melted rock in the crater indicate formation resulting from a high-velocity impactor – an origin that would, according to the team’s modelling, result in vaporization of the projectile, rather than the spinel deposits observed.

Melosh, however, states that there is still plenty of melt production from the anorthositic crust of the Moon with impactors colliding at 10 km/sec. “The olivine projectile is much more difficult to melt than the lunar crustal rocks,” he told physicsworld.com – and therefore Copernicus did not need a high-velocity impactor to explain its creation.

The work is published in Nature Geoscience.

South Korea – round-up

Physics could get a boost in Korea if PSY brought out a physics-related number.

By Matin Durrani and Michael Banks

Sitting in the lounge at Incheon Airport in Seoul waiting for the flight back to London, we’ve decided to draw up a list of 10 random things that the two of us have picked up while on the Physics World editorial visit to Korea. The list is based on observations we’ve made or little nuggets that physicists in the country have told us during our week-long trip. The list is just a bit of fun, so here goes.

(more…)

Redefining the ampere with the help of graphene?

The world’s first single-electron graphene pump has been built by researchers at the UK National Physical Laboratory and the Cavendish Laboratory in Cambridge. The device could be used to redefine the standard unit of current, the ampere, in terms of the electron charge – a fundamental constant of nature.

The international system of units (SI) is made up of seven base units, which are the metre, kilogram, second, kelvin, ampere, mole and candela. The ampere, volt and ohm are the three fundamental units of electricity.

Although physicists have already come up with modern ways to represent the volt and ohm (through measurements of the Josephson voltage and quantum Hall resistance, respectively), there is no equivalent for the ampere. Indeed, today, the ampere is defined as the current which, when flowing through two parallel conductors one metre apart, exerts a certain force between the conductors. Directly realizing such a macroscopic definition of current is experimentally difficult, and the accuracy of the result also depends on other base units, such as the kilogram, which drifts with time.

Enter SEPs

Ideally, a new definition of the ampere would be based on an extremely accurate source of electric current, capable of delivering one electron at a time. A single-electron pump (SEP) could be ideal in this respect because it produces a flow of individual electrons by shuttling them into a quantum dot and emitting them precisely one at a time. A good SEP also pumps the electrons quickly, so a sufficiently large current is generated.

Until recently, two types of SEP were promising contenders: tunable barrier pumps made from semiconductors, which are fast, and so-called hybrid turnstiles made from superconductors, which can be mounted in parallel to make the output current larger. Although the most accurate, a third type of pump usually made from metallic islands is too slow for making a practical current standard, but the UK researchers have now improved its performance by making it from graphene, which is a semi-metal. Graphene is a sheet of carbon just one atom thick that has a honeycomb lattice structure.

Electron flow reaches gigahertz frequencies

“Our experiments have shown that graphene is ideal for pumping large currents and its 2D crystal structure is just what is needed to make electrons pass through the SEP quickly,” team leader Malcolm Connolly told physicsworld.com. The electron flow can reach near-gigahertz frequencies, very close to what is needed to create a current standard, he added.

The team at Cambridge began by peeling a layer of graphene from a piece of graphite using sticky tape. Next, the researchers made the SEP structure by covering some areas of the graphene sheet with a polymer mask and firing an atomic “sandblaster” at the material to “kick” the graphene away from the exposed areas. “One tricky aspect of producing an SEP is making the devices work at high-enough frequencies so that they generate large currents,” explains Connolly. “To this end, we carefully selected the geometry, substrate and pump housing so that the pulses, which pull and push electrons from a reservoir and through the pump, get to where they have to be on time.”

The team says that it still needs to optimize its SEP and make more accurate measurements of the electrical current using the NPL’s high-accuracy set-up. “We also need to work out how the error mechanisms – known to degrade the accuracy of this type of pump – will manifest themselves in graphene,” says Connolly. “Once this is clear, we can then start to mitigate the error mechanisms with modified device designs and concepts.”

Closing the ‘quantum metrological triangle’

If it proves accurate enough, the SEP could also help close the “quantum metrological triangle”, which relates current, voltage and resistance. Voltage can be measured using the AC Josephson effect, while resistance can be related through the quantum Hall effect. Both these relationships include the same two fundamental constants – Planck’s constant, h, and the charge on the electron, e. A metrological current pump would allow physicists to directly relate current to frequency, and thus test whether e and h are as universal as we think.

Besides redefining the ampere, the pump proves that single charges in graphene quantum dots can be manipulated at high frequency, which is an important step towards processing quantum information using single electron spins in graphene. “The carbon atoms making up graphene’s honeycomb lattice should cause less of a disturbance to the electron spin than heavier atoms, a fact that researchers are eager to exploit in these types of devices,” says Connolly.

The work is reported in Nature Nanotechnology.

South Korea – day seven

The heat is off – the Seoul skyline this morning from the 22nd floor of the Ramada Hotel.

By Matin Durrani

The weather today in Seoul started off damp and cool as I made my way to the City Hall subway stop and then headed left down a little side street to the British Embassy. I was there to meet Gareth Davies, who is head of science and innovation at the embassy.

(more…)

Blazars help measure extragalactic background light

An international group of researchers has developed a new way to measure accurately the extragalactic background light (EBL) that fills the universe. The technique involves measuring the attenuation of high-energy gamma rays from distant blazars and it could improve our understanding of how galaxies form and evolve, as well as how the universe has expanded since the Big Bang.

The EBL is made up of all the ultraviolet, optical and infrared photons ever emitted by all galaxies in the universe and, like the cosmic microwave background, is expected to contain a wealth of information about how the universe has evolved. However, measuring the totality of all of the light in the universe is no mean feat. One major problem is that the solar system itself nestles within the Milky Way – a bright galaxy – making it difficult to distinguish between the local galactic light and the much fainter background light. Indeed, most current ground-based and space telescopes have failed to do so reliably enough, while sending a spacecraft out of the galaxy to detect the EBL is clearly impossible.

Across the universe

Instead, astronomers use other, more indirect, methods to detect the EBL. One of these involves using galaxy surveys to estimate the total number of photons produced from the observed population. Once more, the issue here is that the surveys could easily be missing the faintest of galaxies; if these are large in number, they might contribute a lot of light to the EBL, so not factoring in these and any other potential sources would mean that the results are incorrect.

The second method involves blazars. These are compact quasars – supermassive black holes that sit at the heart of active galaxies – with relativistic jets of plasma pointing in the general direction of the Earth. These jets produce extremely energetic gamma rays. According to Alberto Domínguez, a postdoctoral researcher at the University of California, Riverside and lead researcher of the new study, these gamma rays are attenuated as they travel, colliding with EBL photons en route. “There is an effect called pair-production, where two photons that satisfy certain energy conditions interact to produce an electron and a positron. This interaction happens between gamma-ray and EBL photons, producing an attenuation in the gamma-ray flux that we observe from blazars,” says Domínguez. “If we could somehow figure out the intrinsic gamma-ray flux, then we could compare it with the observed flux,” he explains, saying that the comparison could give an estimate of the EBL.

But the team faced some challenges with the new method, the main one being how to figure out the intrinsic gamma-ray flux, which is not known initially. Domínguez says that other groups have tried to estimate this flux by using rather simplistic assumptions. “We have a more elaborated technique that uses data taken from X-ray satellites [NASA’s X-ray satellites Swift and the Rossi X-ray Timing Explorer] and the Fermi Space Telescope, which detect photons at lower energies that are not EBL attenuated,” explains Domínguez.

Then, using standard models of blazar photon emission from observations of nearby blazars, the team inferred the expected intrinsic gamma-ray flux at higher energies and compared it with actual observations from Cerenkov telescopes on the ground. “A comparison between the predicted un-attenuated gamma-ray brightness at energies greater than 30 GeV and the detected attenuated brightness at energies greater than 30 GeV by the Cerenkov telescopes allows us to estimate the cosmic gamma-ray horizon that is directly related to EBL attenuation,” says Justin Finke of the US Naval Research Laboratory, Washington DC, who is also a member of the team.

More distant blazars

By applying their technique to blazars located at different distances (or different ages of the universe), Domínguez and colleagues measured the EBL out to five billion light-years away – the location of the most distant blazar observed when the team began its study. According to the researchers, they can now study more distant blazars that are being detected with the current generation of Cerenkov telescopes, as well as those that will be detected in the future with the next generation of Cerenkov telescopes, namely the Cherenkov Telescope Array.

Domínguez has used both of the methods discussed to measure the EBL and he points out that, interestingly, both give similar results. This helped in setting essential limits on the light from faint galaxies missed in current galaxies surveys and also on any other potential contribution to the EBL not coming from galaxies. “What this means is that the sort of galaxies that we are observing now, with our surveys, are actually responsible for most of the EBL,” he says. The researchers also plan to extend their work to more blazars both at the same distances that they have already tested to confirm their results and also those further away.

Because the EBL is intrinsically linked to the star-formation history of the universe, efficiently measuring it is essential. Other research from Domínguez that looks into measuring the expansion rate of the universe from the attenuation will be published in the months to come.

The research is published on the arXiv preprint server.

South Korea – day six

A transmission electron microscope at KIST.

By Michael Banks

The first thing Kyung-Ho Shin, vice president of international affairs at the Korean Institute of Science and Technology (KIST), passed me when we met in the lobby of my hotel today was an umbrella.

Today Seoul has had a very good watering, but after the recent warm weather the change could be seen as being welcome.

In the morning’s pouring rain, I visited KIST, which was created in 1966 to help commercialize basic research. The 2000 or so researchers based at KIST carry out work in areas from neuroscience and fuel cells to robotics and medicine.

(more…)

South Korea – day five

The Gyeongbokgung.

By Michael Banks

Today I was traveling back from Pohang where I spent the weekend after an busy few days in Daejeon.

Daejeon is certainly an impressive place to do science, being home to no fewer than 60 research centres. Unfortunately, in the limited time I had I could only visit a couple, including the Korean Research Institute of Standards and Science and the National Fusion Research Institute (NFRI).

(more…)

South Korea – day four

Off shopping at Seoul’s famous Dongdaemun market.

By Matin Durrani

Being a Saturday, the fourth day of the Physics World tour of South Korea was – to adopt cricketing parlance – a rest day. But don’t worry, I haven’t been slumped in front of my television in the hotel bedroom wolfing down South Korean style pot noodles and cups of tepid green tea all day. Oh no, that was just what I did in the morning.

(more…)

South Korea – day three

Sang-il Park, Park Systems boss.

By Matin Durrani

Day three for the Physics World editorial visit to South Korea saw news editor Michael Banks spend the day at the KSTAR fusion facility while I was at atomic-force microscope (AFM) manufacturer Park Systems in Suwon.

South Korea is, of course, a key player in fusion science, being a long-standing member of the ITER experiment being built in the south of France. But as Michael is now in the south of the country – in Pohang to be precise – I haven’t had full details of how his visit to KSTAR went. He did, however, e-mail me to say that he’d asked his contact at the lab whether they’d ever had any other visits from journalists. She said they hadn’t, but there was once this very famous scientist who had taken a tour of KSTAR – step forward none other than the physicist who’s on just about every UK TV science show at the moment: Brian Cox.

(more…)

Copyright © 2026 by IOP Publishing Ltd and individual contributors