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

NASA the party-pooper

By Jon Cartwright

Fifty years ago today, US President Dwight Eisenhower signed legislation that created the National Aeronautics Space Administration, or NASA.

An important anniversary, you might think. Perhaps some champagne, some fireworks, a speech from NASA boss Michael Griffin? Surprisingly not. With regards to birthday celebrations, the agency has stayed as silent as Beagle 2 over the past few days, with press releases noticeable by their absence.

Yesterday I buzzed press officer Edward Goldstein to see whether anyone was up to anything. “I’ve had a couple of European journalists ask me that,” he said. “But really we’re only recognizing when NASA began operations, on October-first.” Goldstein added that there would be a “big gala” on 24 September (I think he said it would be at the Smithsonian National Air and Space Museum, but my biro skipped over the page at that point).

I asked if anyone might even nip to the pub for a pint or two after work. “You know,” the press officer continued, “maybe I ought to suggest that to the guys.”

Those NASA bods really need to learn how to party.

Physics TV

robot.jpg

By Hamish Johnston

Robotic rats, electric eels and teacher training are just three of the topics covered in a selection of videos that the Institute of Physics has posted on the Internet.

Eight of the videos are concerned with the Institute’s “Stimulating Physics” programme, which aims to boost the number and quality of physics teachers in England. One key component of the programme is improving the physics knowledge of non-physicists who teach physics. In the first video you can sit in on a session in which trainer Viccy Fleming helps boost the skills and confidence of such teachers.

You can also watch a number of physics-related classroom demonstrations aimed at younger (and remarkably well behaved) school children — including one called “Robots and Electric Eels“.

There is also a preview of “Pendryfest08”, a conference in honour of Sir John Pendry to be held on September 29-30 at Imperial College; an interview with the IOP’s “Women in Physics Winner 2008” Libby Heaney; and a robotic rat (pictured above).

Superfluids point to the origin of ‘monster’ ocean waves

Some say they are the responsible for the loss of many ships at sea, and survivors describe them as “a wall of water” over 30 m tall. Rogue or “monster” waves have long been an enigma to scientists with no convincing theory for their formation. But now physicists in UK and Russia think they may have stumbled upon a worthy mechanism through studies of another system — superfluid helium.

“The wave equations for the two systems are very closely analogous,” team leader Peter McClintock of Lancaster University told physicsworld.com.

McClintock, who is working with others at Lancaster and the Institute of Solid State Physics in Chernogololvka, came across the mechanism for generating rogue waves while performing unrelated experiments on a special type of heat transfer in superfluid helium called second sound. Unlike normal heat transfer in liquids, which involves diffusion, second sound is a faster, quantum-mechanical process that transfers heat as a wave.

In the researchers’ system, the superfluid helium is contained within a small cylindrical cryostat. At one end of the cryostat is a heater, powered by a sinusoidally varying voltage, which McClintock and colleagues use to instigate the second-sound waves. As the waves pass through the helium at speeds of up to 20 ms–1, the researchers can detect them at the far end using a thermometer.

Inverse cascade

Like most physical systems — including the ocean — superfluid helium is non-linear, which means that it does not respond in proportion to its stimulation. According to the Russian mathematician Andrei Kolmogorov, who presented a theory of non-linear wave interactions in the early 1940s, waves should decay in a process whereby energy “cascades” towards shorter and shorter wavelengths. Eventually, said Kolmogorov, viscosity would be able to dissipate the short-wavelength waves as heat.

Most of the time, McClintock’s team saw this Kolmogorov process for their second-sound waves. However, when they increased the size of the voltage above a certain threshold, and when they adjusted the oscillation of voltage to be in resonance with cryostat, the researchers were surprised to find that the cascade sometimes operated in the other direction — towards longer and longer wavelengths.

This “inverse cascade” could produce single rogue waves more than 50% bigger than their neighbours, similar to the ratio seen in oceanic rogue waves (Phys. Rev. Lett. in publication). Although German Kolmakov, a theorist at Chernogololvka, is analysing the results, the team cannot yet explain how the inverse cascade works. “We are still trying to understand it,” says McClintock.

If McClintock’s team is successful in understanding the mechanism behind monster ocean waves it might enable scientists to predict when they occur, which would be an obvious boon to seafarers. But it might also enable the huge waves to be created — an ability that could have military applications.

Themis reveals the secret of Earth’s auroras

Researchers working on NASA’s Themis mission claim to have solved the 50 year-old mystery of what mechanism drives Earth’s auroras, or Northern and Southern Lights. They say it will help in the prediction of “space weather” that can harm astronauts and wreak havoc with both orbiting and ground-based electrical systems.

Scientists know that auroras are the result of electrons and other charged particles in the Earth’s magnetic blanket or “magnetosphere” colliding in the upper atmosphere. They also know that the occasional increases in size, brightness and colouring of the lights are caused by disturbances in the magnetosphere called substorms. However, there has never been consensus on how these substorms are triggered.

“More importantly for us, they have effects for life [on Earth],” said Nicky Fox, deputy project scientist on the Themis mission, in a press conference yesterday evening. “Everyone is familiar with changes in weather, but weather also occurs in space.

“This space weather describes the solar-driven effect that can influence the performance and reliability of satellites and ground-based technological systems such as power grids and pipelines, and it can also affect astronauts in orbit.”

The Sun ‘sneezes’

The $200m Themis mission, which launched almost a year and a half ago, comprises five identical satellites orbiting the Earth at different heights. This widespread group has proved essential to track the effects of substorms, which can be felt over a huge volume of space within a couple of minutes.

On 26 February this year Themis spotted an isolated substorm shortly before a network of ground-based observatories detected an auroral brightening over the northern US. The data collected verifies a mechanism for the triggering of substorms.

In this mechanism, the solar wind — a continuous outflow of charged particles driven by the Sun’s magnetic field — sometimes approaches Earth in an opposite polarity to our planet’s magnetic field. When this happens, the magnetic field lines stretch until they finally snap together — a process called “reconnection”, which releases an explosion of magnetic energy.

This energy travels from the Sun to the Earth and, when enough has entered the magnetosphere, it produces a substorm that culminates in the formation of an aurora (Science Express doi:10.1126/science.1160495). “If the Sun changes, the Earth will feel its effects,” continued Fox. “So it’s kind of like if the Sun sneezes, the Earth will catch a cold.”

Cut the SLAC

SLAC.jpg

By Jon Cartwright

The US Department of Energy (DOE), it would seem, is getting a minor headache trying to come up with a new name for SLAC.

What’s wrong with SLAC, you ask. Well, last year the DOE tried to copyright the description of the acronym, the Stanford Linear Accelerator Center, but was stopped in its tracks by Stanford University, which runs the lab. Apparently the university wanted to hold onto the rights to the word “Stanford”, thus forcing the lab to rename itself.

SLAC isn’t finding it that easy. To help matters, director Persis Drell is pointing imaginative types to a website to suggest acronyms anonymously. Preferably the name should reflect the change in the lab’s mission, she notes.

It is of course customary on these occasions to have an open discussion, so we’ve been racking our brains for ideas. If “Stanford” is out of the question, perhaps just replace the first letter? We could have the Big Linear Accelerator Centre (BLAC), for instance. Or, if synonymy with the original acronym is your game, there’s the Linearly Organised Optimum Science Establishment (LOOSE). (Okay, so that one’s a little contrived.)

As some employees at SLAC have suggested, they could keep the original acronym but change the meaning. How about the Science Lab And Café? (I’ve never been, but I assume there’s somewhere to get a bite to eat.)

Still, the prize for the most cynical must surely go to the author of the blog an American Physics Student in England. He or she has put forward the Fundamental Understanding-of-Nature Discovery MachinE (FUNDMe).

I await your suggestions…

Motion of exploding stars could shed light on dark energy

A multi-telescope survey of millions of supernovae could give cosmologists a better understanding of dark energy and could help explain the origins of large-scale structure in the universe, according to cosmologists Pengjie Zhang and Xuelei Chen of the Chinese Academy of Science. The proposed survey would involve measuring the “peculiar motion” of each exploding star, which would reveal new information about how galaxies are distributed throughout the cosmos.

Galaxies are moving away from one another thanks to the ongoing expansion of the universe. However, this expansion is not the same everywhere and each galaxy has an additional “peculiar motion”, which is caused by the gravitational pull of neighbouring galaxies.

Rather than isolate the peculiar motion of individual galaxies, astronomers try to determine the large-scale peculiar velocity (LSPV), which is the average peculiar velocity of galaxies relative to Earth in a certain region of the universe. They rely on knowing the distances between Earth and each galaxy —and that can be very difficult to measure precisely.

‘Standard candles’

Something they can measure accurately, however, is the distance to a type-Ia supernovae — exploding white-dwarf stars that are known as “standard candles” because they always give off the same amount of light. All they have to do is measure the supernova brightness, and the dimmer it is, the farther away it is. But astronomers can also estimate the speed with which the star was moving away from Earth when it exploded by measuring the Doppler shift (or “red shift”) in the wavelength of its light.

If the universe was expanding in a uniform manner, all type Ia supernovae of a specific brightness would have the same redshift. However, Chen and Zhang expect that the average brightness of supernovae with the same redshift in a small patch of the sky would be different to the average brightness (at that redshift) over the entire sky. “This difference is proportional to the LSPV,” explains Chen (Phys Rev D 78 023006) .

Chen and Zhang believe that such a survey would be performed best using supernovae with an “intermediate” redshift of about 0.5, which dates their explosions to about five billion years ago. The survey would involve about 106 supernovae, and would require several decades of continuous observation using a number of different telescopes.

Christopher Gordon, a cosmologist at the University Oxford, UK, told physicsworld.com that the proposal “is an interesting idea”. However, he believes that Chen and Zhang may be overly optimistic in saying that such a survey could be completed in several decades – even when new telescopes designed specifically for finding supernovae such as the Large Synoptic Survey Telescope (LSST) come online in the next decade.

Smoothing dark energy

Still, if Chen and Zhang can persuade astronomers to do the survey, the results could shed light on the nature of dark energy — a mysterious substance that counteracts gravity and encourages galaxies to move apart. Dark energy tends to prevent galaxies from clumping and therefore should smooth out variations in the LSPV. However, some theories of dark energy predict less clumping than others.

A survey could also further our understanding of dark matter — a substance that interacts via gravity but not via electromagnetic radiation. Galaxies are made up mostly of dark matter, so Chen and Zhang believe that a LSPV survey could reveal much about the distribution of dark matter in the universe.

The survey would allow physicists to study the effects of gravity over very large length scales and could also help cosmologists understand how primordial quantum fluctuations that existed just after the Big Bang became the large-scale structure of galaxies that we observe today.

Liquid mirror shows promise for adaptive optics

Researchers in Canada have built the first deformable liquid mirror from a magnetic liquid or “ferrofluid”, which could someday be used to compensate for distortion in the images of telescopes and other optical devices.

Liquid mirrors are nothing new. The Large Zenith Telescope in Canada, for example, has a 6 m-diameter mirror that is a rotating dish filled with mercury. As the mercury spins around, its profile forms a perfect parabola.

While such mirrors can be made large and essentially defect-free, they do have two important limitations: they can only point straight up; and the shape of the mirror cannot be adjusted dynamically. Dynamic adjustment is important because astronomers are keen on using adaptive optics systems that change the shape of the mirror to correct for aberration caused by the atmosphere.

In 1994 researchers came up with an idea whereby magnetic coils change the shape of a mercury mirror containing an electric current, but they found that mercury is simply too heavy for this to work. More recently, another team of researchers proposed that a mirror in the form of a thin layer of fluid could be adjusted using an “electro-capillary” effect in an array of microchannels.

Tiny particles of magnetite

Denis Brousseau and colleagues at the Centre of Optics, Photonics and Lasers at Laval University in Quebec have taken a different approach (arXiv:0807.2397). They made their mirror from a ferrofluid — a liquid that contains tiny particles of magnetite (Fe3O4) each about 10 nm in diameter.

The bulk of the liquid becomes magnetized and its surface acquires a shape to minimize the energy of the system Denis Brousseau, Laval University

“When ferrofluids are exposed to a magnetic field, the bulk of the liquid becomes magnetized and its surface acquires a shape to minimize the energy of the system,” explains Brousseau, who adds that this involves gravitational and magnetic forces as well as the surface tension of the liquid.

The ferrofluid is contained in a dish that sits above a triangular array of 37 magnetic coils, each 5 mm in diameter. By controlling the current — and hence magnetic field — of each coil individually, the researchers can manipulate the surface profile of the mirror.

Brousseau and colleagues have tested their system, which is controlled via computer, in two ways: using misaligned lenses to direct incoming light, and placing Petri dishes in front of the mirror to introduce more severe optical aberrations. In both cases their mirror compensated effectively for the distortion.

Rapid response

The team also found that the shape of their mirror could be changed several hundred times per second—much faster than previous experiments on ferrofluids, which suggested that this rate would be limited to less than 20 times per second. This ability is important if the system is to be used to correct for atmospheric aberration.

Nandini Bhattacharya of the Delft University of Technology in the Netherlands is impressed by the Laval team’s results. Bhattacharya, who worked on designs for electro-capillary mirrors said “This work clearly shows that ferrofluids hold a lot of promise for the development of efficient liquid-based deformable mirrors”.

One major drawback of ferrofluid mirrors is that they are not very good at reflecting light. However, the Laval team has already had some success in solving this problem by coating the surface of the ferrofluid with a layer of highly-reflective material.

While a ferrofluid mirror could be used in telescopes of the future, Brousseau believes that the first immediate applications will be in visual science, where it could be used to correct defects in the eye’s retina, and in metrology.

The team is now looking at ways to improve the mirror’s performance and size — for example, by shrinking the coils to 1 mm diameter.

Moving to the music

If your idea of enjoying a concert is sitting in a nice comfortable seat and listening to a group of musicians playing a meticulously rehearsed piece of music then you may have to think again.

Kaća Bradonjić, a physicist at Boston University in the US, has used the Doppler effect (the change in the pitch of a sound that occurs when its source and the listener are moving relative to each other) to show how the perceived emotional character of a chord changes as the listener moves.

She has calculated exactly what velocities a listener would need to travel at to create specific variations of mood, in order that they can tailor their “listening experience” (arXiv:0807.2493).

The perceived mood of a chord can be relative to a listener’s frame of reference Kaća Bradonjić, Boston University

Bradonjić’s day job is to carry out research on general relativity, but she also takes an interest in all things musical and artistic and realized that, as she puts it, “the perceived mood of a chord can be relative to a listener’s frame of reference”.

In her paper, she considers the conventional Western “chromatic” musical scale, in which the frequencies of neighbouring notes differ by a factor of 21/12 (an interval known as a semitone). Using the Doppler transformation for a stationary emitter and moving observer she shows that a listener must travel (1-2-1/12) times the speed of sound away from the source of a note in order to reduce the perceived pitch of that note by a semitone.

Bradonjić then considered the velocities that a listener must travel at to transform specific three-note chords when the notes are emitted by three separate sources positioned away from the listener along orthogonal axes.

Major to minor

For example, to hear the happy-sounding C major (which consists of the notes C, E and G) as the sad-sounding C minor (C, E flat and G) the listener would have to move with a speed of 19.25 ms-1 (about 70 km/h or 43 mph) away from the E emitter. Making the opposite transformation would instead require travelling in the opposite direction with a speed of 20.40 ms-1.

She then goes on to show how a listener can make more complex changes by moving in three dimensions. However, she points out that the upper limit of the speed of sound and the power-law nature of the chromatic scale result in an upper limit on how much a perceived frequency can increase — which is one octave. There is no limit when decreasing pitch, says Bradonjić.

Bradonjić says the motivation behind her research is “to put the listener into the ‘driver’s seat’, letting him navigate through the song as he pleases.” She concedes that putting a room full of concert goers literally into the driver’s seat could present certain logistical difficulties, especially since they would not be moving any slower than they would on the roads.

She suggests that individuals of an adventurous persuasion could perhaps “use a jet pack to zig-zag around a set of giant speakers”, but she thinks that people interested in her idea should instead simulate such an experience in a virtual computer environment. She adds that the information on the listener’s path could then be used to create visual effects similar to those created by computer music players.

Bubble-fusion scientist to appeal over misconduct charge

Lawyers for the “bubble-fusion” researcher Rusi Taleyarkhan have told physicsworld.com that he will appeal over the findings of a panel that last week found him guilty of two charges of scientific misconduct. Taleyarkhan, a nuclear engineer at Purdue University in the US, was charged by a six-member internal committee, which concluded that he had cited a paper by researchers in his own lab as if it were an independent confirmation of his alleged discovery of bubble fusion in 2002.The committee also found him guilty of adding the name of a student who had not contributed to that paper as an author.

The current controversy began in 2002 when Taleyarkhan, who was then working at the Oak Ridge National Laboratory in Tennessee, co-authored a paper in Science in which he reported firing a barrage of ultrasound waves into a liquid mixture of benzene and acetone (Science 295 1868). He claimed that bubbles of gas, which emit flashes of light when the sound waves force them to expand and collapse, could reach such high temperatures and pressures that during this process fusion reactions are initiated.

Several groups, however, failed to replicate the research, while two other Purdue engineers — Lefteri Tsoukalas and Tatjana Jevremovic — complained that Taleyarkhan had tried to prevent them publishing their negative results. An internal investigation last year cleared Taleyarkhan of that charge, but when critics argued that the panel had not taken their views into account, Purdue began a second investigation. Although the committee completed its work in April, Purdue did not issue the report until the Office of Naval Research, which funded Taleyarkhan’s research, had accepted it.

‘Research misconduct’

The panel examined two papers, stimulated by Taleyarkhan, that reported successful replication of his original results — one from 2005 in Nuclear Engineering and Design (235 1317) and the other in a Festschrift to Taleyarkhan’s PhD supervisor Richard Lahey. Taleyarkhan’s postdoc Yiban Xu and graduate student Adam Butt were named as coauthors of the papers, even though Butt had allegedly only checked Xu’s data. “[T]he weight of the evidence shows that Dr Taleyarkhan compelled the addition of Mr Butt’s name as an author…knowing that Mr Butt had not substantively contributed…in order to create an appearance of collaboration between Dr Xu and Mr Butt,” the committee concluded. “This is research misconduct.”

The panel then looked at a paper from 2006 in Physical Review Letters (Phys. Rev. Lett. 96 034301), in which Taleyarkhan cited the NED paper by Xu and Butt to support his assertion that his results had been independently confirmed. However, that claim, the committee concluded, is “simply not supported by the weight of the evidence of his extensive involvement in the…research and publication. The assertion of independent confirmation…is falsification of the research record and thus is research misconduct.”

Purdue gave Taleyarkhan 30 days to appeal the committee’s verdict. According to his lawyer, he plans to do so. “There are a number of facts and issues that were not allowed in the inquiry, and the other nuclear engineers involved are all in complete support for Taleyarkhan,” John Lewis of the Indianapolis law firm Lewis and Wilkins told physicsworld.com. “Xu maintains to this day that Butt’s involvement was his choice. But that part of Xu’s testimony was completely ignored.”

Kenneth Suslick, a chemist at the University of Illinois and long-time critic of bubble fusion, says the report is some kind of vindication. However, he complains that “committee members were not given the charge of investigating the veracity of Taleyarkhan’s research”. But Colin West, a former colleague of Taleyarkhan’s at Oak Ridge, regards the investigation as a “witch hunt”. He told the Lafayette Journal and Courier that the committee’s findings “have no relevance at all to whether his research is correct and his results are valid”.

Racing with the Sun

solar.jpg

By Hamish Johnston

UPDATE: The race was won by the Michigan solar car (pictured above), which travelled from Dallas to Calgary in a little under 52 hours. The final results can be found here.

This morning 15 solar-powered cars will leave Medicine Hat, Alberta in a final dash to Calgary, a distance of about 300 km. If the fastest vehicle could maintain its top speed all the way, it could get there in less than two hours.

Unfortunately, the cars competing in the 2008 North American Solar Challenge must obey the speed limit — which I’m guessing on that stretch of the Trans Canada Highway is 110 km/h, much slower that the 160 km/h that some solar cars have been known to reach.

The race began on July 13 in Plano, Texas (near Dallas) and the cars travelled due north for about 2100 km before crossing the Canadian border just south of Winnipeg. Then it was a left turn for the remaining 1400 km to Calgary.

As of yesterday, the leading car was from the University of Michigan, which travelled from Plano to Medicine Hat in 47 hours of driving time. That’s an average speed of nearly 75 km/h (about 45 mph).

Not bad when you consider that the winner of the first such long distance race — held in Australia in 1982 — averaged just 23 km/h.

The race looks wide open this morning because the fastest five cars arrived in Medicine Hat separated by about 13 minutes. The other four challengers with a chance are Principia College in Illinois, Germany’s FH Bochum, the University of Waterloo in Ontario, and the University of Minnesota.

The weather forecast for southern Alberta calls for sunny skies…so the race could be over sooner rather than later.

There is (of course) lots of interesting physics related to solar cells and you can read all about it in this feature article (Bright outlook for solar cells) in Physics World.

Copyright © 2025 by IOP Publishing Ltd and individual contributors