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April 2011 Archives

From Rutherford to Higgs

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By James Dacey at the APS April Meeting, Anaheim, California

I took this photo just now looking back at the Hyatt Regency hotel in Anaheim, which is hosting this year’s April Meeting of the American Physical Society. I landed here in California last night having surely been one of the few Brits to fly out of the country on the day Prince William married Kate, and the country enjoyed a national holiday. That’s dedication to physics!

The theme of this year’s meeting is “100 years of subatomic physics”, commemorating the centenary of Ernest Rutherford’s discovery of the atomic nucleus. And this morning the programme kicked off with a special plenary lecture by Nobel laureate Steven Weinberg who crammed the history of particle physics into a half hour talk.

In a fascinating discussion, Weinberg argued that the big questions in present-day particle physics mark the end of an adventure that began with Rutherford’s discovery. “The search for the Higgs boson, as well as supersymmetry and dark matter, is the culmination of a reductionist programme that began with quantum mechanics, which followed Rutherford’s experiment.”

But it’s not just particle physics on the bill here in Anaheim: nuclear physics, astrophysics and plasma physics will also feature heavily. So there will no shortage of physics for me to get my teeth stuck into over the next four days. Watch this space for updates!

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Hubble’s “Rose of Galaxies” anniversary image
(Courtesy: NASA, ESA, A Riess (STScI/JHU), L Macri (Texas A&M University) and Hubble Heritage Team (STScI/AURA))

By Tushna Commissariat

Millions of people worldwide have exclaimed in awe and wonder at the images that the Hubble Space Telescope (HST) has been producing for more than two decades. The satellite has had a significant impact on all fields of science from planetary science to cosmology ever since it was launched on 24 April 1990 aboard Discovery’s STS-31 mission. In a bid to celebrate the 21st anniversary of the HST, astronomers at the Space Telescope Science Institute in Baltimore, Maryland, in the US pointed Hubble’s eye at a particularly magnificent cosmic phenomenon – a pair of interacting galaxies in the shape of a rose.

The newly released Hubble image shows two interacting galaxies known as Arp 273. The larger of the spiral galaxies – UGC 1810 – has a disc that is being distorted into a rose-like spiral thanks to the gravitational tidal pull of the companion galaxy below it, known as UGC 1813. The smaller companion shows signs of intense star formation at its nucleus, quite possibly triggered by the smaller galaxy actually passing through the disc of the larger galaxy. A veil of bright and hot young blue stars glows across the top of the dancing discs.

Arp 273 lies in the constellation Andromeda and is about 300 million light-years away from Earth. Though the galaxies are separated from each other by tens of thousands of light-years, they are connected by a tidal bridge of material between them that formed post interaction.

Take a look at the gorgeous image (above) and a video (below) zooming into the region of the galaxies.

In other space-related news, the final launch of the space shuttle Endeavour will take place tomorrow, 29 April, from Florida’s Space Coast in the US. So while Britons and many others all over the world will be watching the royal wedding, Kennedy Space Center is anticipating the arrival of an estimated half a million onlookers, eager to watch the space shuttle lift off one more time. Endeavour, first launched in May 1992, is expected to carry six astronauts, a cargo bay full of spare supplies and a $2bn astrophysics experiment to the International Space Station.

To look at some interesting images in the follow-up to the launch, look here: http://www.space.com/11221-photos-space-shuttle-endeavour-final-mission-sts134.html

By Matin Durrani

If you want to get your research results noticed by us here at Physics World headquarters, you can always try e-mailing us a copy of your paper, preferably well before it’s about to be published.

But Burak Eral from the physics of complex fluids group at the University of Twente in the Netherlands has taken a novel approach in flagging his research to us — he’s sent us a three-minute Youtube video consisting of a series of Powerpoint slides put to music.

As you can see, his tactic has worked. The video describes how Eral and his pals have studied the morphology of a drop clinging to a cylindrical fibre — a problem first studied by Joseph Fourier in the late 19th century.

If you can bear Eral’s rather soporiphic choice of music, you’ll find that the drops can either surround the fibre symmetrically, like a barrel, or attach themselves to one side of the fibre, rather like a clam-shell. By using the technique of “electrowetting”, Eral’s team was then able to reversibly change which form the drops adopt — with what they claim is “previously unachieved precision”.

The work has its practical side too as it could potentially lead to a way to clean oil spills in the world’s oceans. Eral envisages creating special fibres that could be dropped into the affected, oil-damaged region. Although the oil would naturally tend to form barrell-shaped drops around the fibre, the drops could be forced into adopting the clam-shell shape, which are much easier to wash off from the fibre. The result: cleaner oceans with the oil drained safely away.

Eral is not, of course, the first physicist to find the lure of creating an educational video about their work. In fact, you can find plenty of these “video abstracts” at the New Journal of Physics — an open-access journal published by the Institute of Physics, which also publishes physicsworld.com.

Eral’s full paper about his work appears in the journal Soft Matter

By Tushna Commissariat


Looks like the Large Hadron Collider (LHC) at the CERN particle physics lab had an interesting few days last week, just before everybody left for Easter, and the Internet is now abuzz with rumours of an impending discovery.

But before we get into any of the highly interesting and debatable stuff, let’s look at one thing that has definitely happened at the LHC.

Around midnight on Friday 22 April, the LHC set a new world record for beam intensity when it collided beams with a luminosity of 4.67 × 1032 cm–2s–1. This was significantly more than the previous luminosity record of 4.024 × 1032 cm–2s–1 held by the US Fermi National Accelerator Laboratory’s Tevatron collider in 2010.

This new beam intensity was achieved after two weeks of planning and readying the collider. The machine is now moving into a phase of continuous physics scheduled to last until the end of the year when, after a short technical stop, the machine will resume running for 2012.

“Beam intensity is key to the success of the LHC, so this is a very important step,” said CERN director Rolf-Dieter Heuer in a statement. “Higher intensity means more data, and more data means greater discovery potential.”

But didn’t I read all about some record being broken by the LHC last year, you ask? Yes, but that was the LHC accelerating its proton beams to 3.5 TeV each, leading to later collisions at 7 TeV. Now it is the beam intensity or the “luminosity” that is record breaking. Luminosity gives a measure of how many collisions are happening in a particle accelerator. So the higher the luminosity, the more particles are likely to collide which is necessary while looking for rare particles like the infamous Higgs boson.

“There’s a great deal of excitement at CERN today,” said CERN’s director for research and scientific computing, Sergio Bertolucci, “and a tangible feeling that we’re on the threshold of new discovery.”

Well, it looks like Bertolucci spoke a tad too soon, as on the same day a leaked memo posted by an anonymous commenter on mathematician Peter Woit’s blog, claimed that certain researchers at the ATLAS experiment at CERN had seen firm evidence for the Higgs particle in recent data.

The memo, though not official by any means, was authored by four ATLAS members who claimed to have seen an excess number of photons produced at energy of 115 GeV that could be caused by the decay of the Higgs particle into photons.

Surprisingly, only a few websites and blogs mentioned the news for the first day or so, before slowly more people seemed to notice this juicy story of physics, Higgs and betrayal!

On 25 April, Nature reported on its blog, an official statement from ATLAS spokeswoman Fabiola Gianotti. Gianotti said “Only official ATLAS results, i.e. results that have undergone all the necessary scientific checks by the collaboration, should be taken seriously.” She went on to say that signals of the kind reported in the memo show up often during data analysis and are later falsified after more detailed scrutiny.

But the damage had already been done as physicists and others began to comment on the legitimacy of the claim made in the memo and the ethics of such an internal memo being posted and talked about online.

As people began to look deeper into the memo, interesting facts began to creep up.

Tommaso Dorigo, from the University of Padova in Italy wrote an initial post on his blog A Quantum Diaries Survivor that turned into a debate and eventually a bet! His post was sceptical from the start and he gave his reasons for why he was sure it as nothing more than a blip in the data, then went on to explain in more detail what other data already exists.

After that, a regular reader of his blog pointed out that the authors of the ATLAS study are actually physicists from Wisconsin, and include a Professor Wu, “who was among those less happy of the decommissioning of LEP [the Large Electron-Positron Collider] at the time when they were claiming a possible Higgs signal at 115 GeV. So maybe these guys have been looking for some confirmation of the 115 GeV Higgs all along”.

Woit too was quick to distance himself from the memo saying that “it should be made clear that, while members of ATLAS work here at Columbia, I have no connection at all to them, and they had nothing to do with this. The source of the abstract posted here anonymously as a comment is completely unknown to me.”

As more people debated and commented over the memo, Dorigo came back to say that he would bet anyone who “has a name and a reputation in particle physics (this is a necessary specification, because I need to be sure that the person taking the bet will honour it) that the signal is not due to Higgs boson decays” and then updated that comment by saying that if he is wrong he would pay $1000 but that if he is right he would be given only $500.

Meanwhile, Channel 4 conducted an interview with Jon Butterworth, a particle physics professor at University College London, who also works at ATLAS. He went on to say the same thing; that nothing would be definitive until it was scrutinized by CERN officially (look above).

So at the end of the day, it looks like the world is going to have to wait a while longer before Higgs boson gets its official post in the Standard Model hall of fame.

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Gliese 667 is one of two multiple star systems known to host planets below 10 Earth masses. (Courtesy: ESO/L Calçada)

By Tushna Commissariat

If you have thought about planets with two or more suns ever since you saw the dual suns of Tatooine in the first Star Wars film, looks like you are on the same wavelength as some astrobiologists. Jack O’Malley-James, a PhD student at the University of St Andrews, Scotland, has been studying what kind of habitats would exist on Earth-like planets orbiting binary or multiple star systems. He shared his results with peers at the RAS National Astronomy Meeting in Llandudno, Wales on Tuesday 19th April.

O’Malley-James and his team have been running simulations for planets that would orbit multiple star systems and trying to understand the kind of vegetation that might flourish there, depending on the type of stars in the system. Energy via photosynthesis is the foundation for majority of life on Earth, and so it is natural to look for the possibility of photosynthetic processes occurring elsewhere.

With different types of stars occurring in the same system, there would be different spectral sources of light shining on the same planet. Because of this plants may evolve that photosynthesize all types of light, or different plants may choose specific spectral types. The latter would seem more plausible for plants exposed to one particular star for long periods, say the researchers.

Their simulations suggest that planets in multi-star systems may host exotic forms of the plants we see on Earth. “Plants with dim red dwarf suns for example, may appear black to our eyes, absorbing across the entire visible wavelength range in order to use as much of the available light as possible,” says O’Malley-James. He also believes the plants may be able to use infrared or ultraviolet radiation to drive photosynthesis.

The team simulated combinations of G-type stars (yellow stars like our Sun) and M-type stars (red-dwarf stars), with a planet identical to Earth, in a stable orbit around the system, within its habitable “Goldilocks zone”. This was because Sun-like stars are known to host exoplanets and red dwarfs are the most common type of star in our galaxy, often found in multi-star systems, and are old and stable enough for life to have evolved.

While the binary systems were not exact copies of any particular observed systems, plenty of M-G star binary systems exist within our own galaxy. O’Malley-James calculated the maximum amount of light per unit area- referred to as the “peak photon flux density” from each of the stars as seen on the planets for each set of simulations. This was compared to the peak photon flux density on Earth to determine whether Earth-like photosynthesis would occur.

Factors like star separation were taken into consideration, to give the best possible scenario for photosynthesis. “We kept the stars as close to the planet as we could, so that there would be a useful photon flux from each one [star] on the planet’s surface while still maintaining a stable planetary orbit and a habitable surface temperature,” says O’Malley James.

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Chocolate that doesn’t melt until as high as 50C could be a boon for chocoholics in the tropics. (Courtesy:iStockphoto.com/alle12)

By Tushna Commissariat


Look, there’s no metaphysics on Earth like chocolates” – Fernando Pessoa, Portuguese poet

It’s Easter again and shops in many countries are full of chocolate eggs and other gooey, chocolate-based treats. But why is it that certain tropical countries like Nigeria consume only small amounts of chocolate, despite producing most of the world’s cocoa? Indeed, nearly 70% of cocoa is grown in West Africa and the rest in Central and South America and Asia.

One of the main reasons is that the high tropical temperatures make chocolate lose its form while being transported within these areas. The chocolate can also undergo a “bloom formation” – a mouldy-looking white coating that forms on the surface resulting from an increase in temperature, which makes storing chocolate a problem.

But, once again, physics is providing a solution. Scientists have been looking at ways to create a “thermo-resistant” chocolate that holds its form and still tastes just right. And it looks like O Ogunwolu and C O Jayeola, food scientists at the Cocoa Research Institute of Nigeria have finally managed it, and just in time for Easter too. They found that adding varying amounts of cornstarch and gelatin to chocolate ensured that the chocolate melted at about 40–50 °C, instead of its normal melting point at about 25–33 °C. And the best bit is that, by all accounts, it still looks and tastes like normal chocolate!

The chocolate industry has been looking into ways of perfecting heat-resistant chocolate for a long time. For example, the US company Hershey’s developed a chocolate bar that was heat resistant and could be used as part of emergency rations for American troops during the Second World War. The down side was that, according to troop reports, the chocolate tasted “a little better than a boiled potato”. While Hershey’s did try other recipes and even managed to make a bar that melted only at 60 °C, reactions to the taste were mixed. So it is hoped that this new recipe will make chocolate more available to everyone, the world over, as it should be.

In other chocolate-related news, take a look at the slew of videos on YouTube that include researchers at the University of Nottingham conduct “Eggsperiments” with Cadbury’s Creme Eggs. My favourite one has chemists making quite a mess in their labs when they try to deconstruct the eggs.

Icons of progress

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Celebrating 100 years of superconductivity (courtesy: IBM)

By Michael Banks

From the 100th anniversary of Marie Curie’s Nobel Prize for Chemistry to 100 years since Ernest Rutherford proposed his model of the atom, 2011 marks a whole host of centenaries.

This year is also the 100th anniversary of the discovery of superconductivity — the phenomenon where the electrical resistance of a materials drops to exactly zero — by experimental physicist Heike Kamerlingh Onnes in 1911.

But that is not superconductivity’s only anniversary. This month represents 25 years since the discovery of high-temperature superconductivity by physicists Georg Bednorz and Alex Müller, who were then both working at the IBM Research Laboratory in Zurich.

In 1986 Bednorz and Müller discovered that the electrical resistance of a material made from lanthanum, barium, copper and oxygen (LaBaCuO) — known as a cuprate — fell abruptly to zero when cooled below a temperature of 35 K. Their discovery opened the door to potentially higher superconducting temperatures earning the duo the 1987 Nobel Prize for Physics.

To celebrate that feat, high-temperature superconductors have made it into IBM’s “100 icons of progress” — a list of 100 breakthroughs that have been carried out at IBM’s research centres around the globe. The list is to celebrate, yep you guessed it, IBM’s centenary this year, and has already featured 43 “icons” such as the floppy disk and the scanning tunnelling microscope.

Superconductivity was added to the list yesterday to mark 25 years since Bednorz and Müller submitted their paper to Zeitschrift für Physik (the paper was published in June 1986) and IBM will be adding more icons throughout the year.

Yet if you have still not had enough of all things superconductivity then make sure you celebrate the centenary by enjoying a free download of the April 2011 issue of Physics World, which is packed full of articles on the subject.

You may also want to watch a video interview with Laura H Greene of the University of Illinois Urbana-Champaign about what comes next after the cuprates.

Mystery of the riderless bike thickens

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By James Dacey

The riderless bike is a fairly well known quirk of mechanics. As the name suggests, it refers to the fact that regular bicycles can keep going by themselves for long distances without toppling over. Indeed, the surreal image of a riderless bike inspired this brilliant scene in Jour de Fête, a black and white French comedy from 1949.

But a new bike created by researchers in the US is and the Netherlands has cast doubt on our understanding of what causes this effect.

The phenomenon of bicycle self stability was first described analytically in 1897 by French mathematician Emmanuel Carvallo, and since that time many other scientists have contributed their two pennies worth.

While it quickly became clear that the mechanics behind the effect are not as simple as one might think, most researchers agree that the stability is due to two features of mechanics. Firstly, there is gyroscopic motion, which causes the front wheel to correct itself like a spinning top. Then secondly, there is the “trail” or “caster” effect, which also explains why the front wheel of a shopping trolley automatically turns to follow the pivot.

A team including Andy Ruina at Cornell University has created a bike that self-balances without relying on these forces – the first of its kind. The researchers published their findings in this week’s edition of Science.

Ruina told the Science podcast that the balancing must still be related to a mechanical effect that couples the forces involved in bike-leaning to its steering. While the bike currently looks more like a child’s scooter, Ruina sees no reason why it could not be rearranged to appear more like a familiar motorcycle or bike.

To see the bike in action, follow this link.

Tragic death of US physics student

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By James Dacey

I was shocked to hear today about the tragic death of a physics student who was killed earlier this week in a machine shop at Yale University in the US.

Michele Dufault, just 22-years-old, died on Tuesday night after her hair got caught in a lathe as she worked late on a project in one of the university’s chemistry laboratories. In a statement issued on Wednesday, Yale’s vice president, Richard Levin, said that the girl’s body was found by other students who had been working in the building.

On Wednesday evening, the university held a memorial for Dufault in which friends and classmates were invited to light candles and offer words to comfort to each other.

The university said that Dufault was pursuing a B.S. in astronomy and physics, and that she intended to undertake work in oceanography after graduation. “By all reports, Michele was an exceptional young woman, an outstanding student and young scientist, a dear friend and a vibrant member of this community,” said Levin.

According to a report in the New York Times, Dufault died while carrying out experimental work for her thesis: investigating the possible use of liquid helium for detecting dark matter particles. A lathe is a machine tool for shaping metals and other hard materials, and it possesses a heavy spinning wheel for grinding.

Levin said that the safety of students is a paramount concern and the university has programs to train students before they use power equipment. He confirmed, however, that he has ordered a thorough review of all the university’s facilities that contain power equipment operated by undergraduates.

By Hamish Johnston

Tune in to BBC Radio 4 at 9.00 BST this morning to hear Melvyn Bragg and company chat about the elusive neutrino.

Melvyn’s guests are the physicists Frank Close, David Wark and Susan Cartwright.

You can listen live here, and if you miss the programme you can catch up later here.

Space flute tribute to Yuri Gagarin

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By James Dacey

Today, people around the world have been celebrating the fiftieth anniversary of Yuri Gagarin’s flight into space. On 12 April 1961, the Russian cosmonaut inspired the world when he underwent a108-minute orbit aboard his Vostok (or “East”) spacecraft. To mark the anniversary, the US astronaut Cady Coleman has joined up with Ian Anderson, the founder of UK band Jethro Tull, for a special musical collaboration.

The pair performed last week via a satellite link up with Coleman aboard the International Space Station and Anderson in the Russian city of Perm. Both playing flutes, the pair played a section from Bouree, which Jethro Tull played while on a US tour during 1969, the year that Apollo 11 took Neil Armstrong to the Moon.

By Matin Durrani

After all the bad news coming out of Japan following last month’s devastating earthquake and tsunami — finally some good news, at least for the country’s scientific community.sacla.jpg

Researchers at RIKEN and the Japan Synchrotron Radiation Laboratory (JASRI) have officially launched a new X-ray Free Electron Laser (XFEL) facility at the SPring-8 lab west of Kyoto.

Dubbed SACLA (the SPring-8 Anstrom Compact Free Electron Laser), the facility is pronounced “sa-cu-ra” and means “cherry blossom” in Japanese. It will come fully on line by the end of this year and will be used for a wide range experiments in condensed-matter physics and in atomic and molecular science.

SACLA is only the second free-electron laser in the world, the other being at the SLAC National Accelerator Laboratory in Stanford, California. (Watch our exclsuive video report from last year for more details about free-electron lasers.)

Elsewhere in Japan, however, physicists are still coming to terms with the impact of the earthquake on the country’s scientific facilities. New pictures have been released of damage to the massive new J-PARC facility at Tokai, which lies about 120 km south-west of Tokyo and consists of two proton synchrotrons, a neutron source, a neutrino experiment and a hadron facility all rolled into one. The images show the synchrotron flooded with about 4cm of water, as well as cracks in local service roads, damaged pipes, and buildings bent and distorted (see below). Thankfully, the problems are not too severe but they are certainly a setback for the facility.

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Finally, without wanting to be too flippant following the damage to the Fukushima nuclear plant, which officials today have put at a maximum, level-seven alert on the International Nuclear Event Scale, we couldn’t help raising a smile at an amusing new cartoon film on YouTube that likens the emissions from the facility to those from a toddler in nappies. The film has already had 1.6 million views and rising (see below).

Oh yes, and to put the radiation release from Fukushima into context, don’t forget the great graphic from comic-strip website xkcd by physics graduate Randall Munroe that we commented on a couple of weeks ago. It’s by far the best thing we’ve seen to put radiation fears into perspective.

Zero resistance to cake

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By Louise Mayor

We had a good chuckle in the Physics World office when we saw how Ted Forgan and his condensed-matter group at Birmingham University in the UK are celebrating the centenary of superconductivity.

As Forgan explained, “According to my info, today is the actual day, so in our group we celebrated with a cake.” He does, however, acknowledge his “amateur icing skills”.

Apparently, comments about the cake have included “Does it contain super currants?”, “Does it contain pears?”, and the less obvious “Is it a Butter–Chocolate–Sugar supercake? (maybe this depends on Tc, the cooking temperature)”.

I had to get this last one explained to me; if you need a clue too, it refers to the Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity.

Once the pun-groans have subsided, if you want to know more about what superconductivity is all about and what’s hot in superconductivity right now, then look no further than this free PDF download of our April special issue. In fact, we’re in touch with Forgan because he contributed a piece about high-temperature superconductivity called “Resistance is futile”.

You might also want to check out this video feature about superconductivity by Paul Michael Grant called “Down the path of least resistance”.

Clearly, superconductivity brings out the puns in everyone.

By Hamish Johnston

Particle physics blogs are buzzing about an innocuous-looking bump in data taken by the CDF experiment at Fermilab in Chicago – and the possibility that it could be evidence for a new particle.

The unexplained signal was spotted in a study of W and Z boson pairs that are created when protons and antiprotons collide in Fermilab’s Tevatron collider. It appears at about 120–160 GeV /C2 in the distribution of jets that are produced in the collisions. The bump has a statistical significance of “three-sigma”, which means that there is a one in 370 chance that the bump is not real.

While that might sound convincing to you and me, particle physicists don’t accept a new result until it has been established at five-sigma – about one in two million chance of not being real. Another problem is that CDF’s sister experiment D0 doesn’t see the bump. Rumours are also circulating that ATLAS at CERN has not seen it.

But if the bump is real, what could it be?

Theoretical physicists are now hard at work trying to explain the bump, and at least one paper – with the intriguing title Technicolor at the Tevatron – has already been posted on the arXiv preprint server. No doubt many more will follow.

What are other physicists saying?

In his blog, Tommaso Dorigo sketches out three possible ways that the bump could be an artefact of how the experiment was done or the data were analyzed. But if the bump is real, he thinks that it could be evidence for a new particle – but not a Higgs boson.

Adam Falkowski seems to agree. “It is not a Higgs; anything Higgsish with 150 GeV mass would prefer decaying to a pair of W bosons rather than to two light jets,” he writes in his blog.

But what about a “non-standard Higgs”? Flip Tanedo explores that possibility in this blog entry.

The story has also captured the imagination of veteran science writer Dennis Overbye in an article in the New York Times. However, most of the leading physicists interviewed by Overbye seem sceptical, yet excited.

Giovanni Punzi from CDF is “strongly thrilled…and cautious at the same time”, New York University’s Neal Weiner says “If it holds up, it’s very big”, and Lisa Randall at Harvard comments “It is definitely interesting, if real”.

We’ll have to wait and see. In the meantime you can read a preprint describing the bump here.

Einstein by numbers

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By James Dacey

This fresh take on the iconic image of Einstein is the creation of Spanish artist Juan Osbourne. If you click through to the original work you will discover that it is also a puzzle where you have to find the numbers one to nine hidden among the letters of the alphabet. The portrait is part of a collection of images by Osbourne composed solely from letters, words and numbers, including several film stars and musicians.

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By Hamish Johnston

Since the stricken Fukushima reactors in Japan started emitting radioactive materials a few weeks ago, physicists in places as disparate as San Francisco and Glasgow have been reporting elevated levels of radioactivity. Given the tiny quantities involved, just how are they detecting this material?

If you have access to the sort of kit that you might find in an undergraduate demonstration lab, you can do the measurement yourself. And a good guide to follow is a paper posted recently on the arXiv preprint server.

In the paper Eric Norman, Christopher Angell and Perry Chodash describe how they analysed rainwater samples from the San Francisco Bay area for traces of fallout from Fukushima – which is about 8000 km away.

From their base at the nuclear engineering department of the University of California, Berkeley, the team collected rainwater from three locations and brought it back to the lab. Each sample was placed in a Marinelli beaker, which is a special vessel for measuring the radioactivity of liquids.

The beaker is placed over a high-purity germanium detector, which are used routinely to study gamma-ray spectra. Lead is used to shield the detector from background radiation. Gamma-ray spectra in the 0.02–1.58 MeV energy range are then collected for up to 24 hours. This range was chosen because it contains gamma rays emitted by radioactive isotopes of iodine, caesium and tellurium. These are produced by the fission of uranium and plutonium, both of which are used as fuel in the Fukushima reactors.

The team took its first samples overnight on 15 March and found no evidence for the three fission fragments. This allowed the team to set an upper limit on the concentration of iodine-131 in the samples of about 0.016 Becquerel per litre (Bq/l). The Becquerel is a unit of radioactivity pegged at one decay per second.

However, by 18 March evidence of radioactive materials began to emerge and the iodine-131 signal had risen to more than 5 Bq/l. The researchers also saw a corresponding rise in radioactivity associated with other isotopes of iodine, caesium and tellurium.

The top panel (above) is the gamma-ray spectrum of rainwater from 18 March, showing the presence of various isotopes. The bottom panel is the same spectrum of tap water.

The signal peaked on 24 March, with iodine-131 reaching 16 Bq/l. This is about four times the recommended level in drinking water. Radioactive iodine is dangerous because it concentrates in the thyroid gland. However, because of the relatively short half-life of iodine-131 (about 8 days), the Berkeley team doesn’t think that it will lead to significant exposure through drinking local water.

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By Hamish Johnston

In 1911 the Dutch physicists Heike Kamerlingh Onnes and Gilles Holst discovered superconductivity in mercury.

One hundred years later, physicists are still hard at work studying a growing number of superconducting materials.

Now you can celebrate the centenary by enjoying a free download of the April 2011 issue of Physics World, which is packed full of articles on superconductors.

The issue contains a handy wallchart showing the inexorable rise in critical temperature as more superconductors were discovered. The chart also highlights the six Nobel prizes associated with superconductors and other important events in the field.

Relive the key events of the last 100 years in the company of Paul Michael Grant, who also presents his top five applications of superconductivity with the biggest impact on society today.

Stephen Blundell examines the pivotal role in understanding these materials played by the brothers Fritz and Heinz London, while Ted Forgan recalls the euphoric early days of high-temperature superconductivity 25 years ago, and Laura Greene calls for a global collaboration to reveal the next generation of high-temperature materials.

Finally, don’t miss our profiles of three key industrial players – GE, American Superconductor and Oxford Instruments – as well as our fabulous superconductivity timeline.

You can download the special issue here.

Stolen invisibility cloak found!

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By James Dacey

If you checked physicsworld.com this morning you may have been alarmed to read about the theft of the world’s first flexible invisibility cloak. Well, you will be relieved to hear that the cloak’s designer, physicist “Randy Katz”, has managed to relocate his precious garment, which he will now be wearing for the rest of his days. Yes folks, Randy nor his cloak really exist – it was a little joke for April Fools day.

Outlandish new technologies seem to have featured heavily among this year’s April Fools pranks. Here are my picks from the rest of the web.

Swedish furniture maestro Ikea hit the mark with its HUNDSTOL, a highchair for dogs to bring man’s best friend closer to the family at dinnertime.

Continuing the animal theme, The Sun newspaper (not known for its subtlety) ran with the story that gorillas were given iPads at a wild animal park in southern England. The head zookeeper was surprised when the gorillas started using the devices rather than “bang them on the rocks”.

British free daily newspaper, The Metro brought a chuckle with its edible newspaper, which came with the delicious headline: “Have we got chews for you”. Apparently pages were being printed on a corn starch mix that had a lovely light vanilla scent.

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Eco-friendly fitness fanatics may have got excited when they read about the Re-Cycle Cardboard Bike. Designed by German engineers, the technology was said to fold down into a small package that could be popped conveniently into a carrier bag.

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And finally, fans of 3D cinema will be gutted to learn that one-eye 3D TV will not be coming their way after all, as Toshiba’s new 3D monocle was indeed another joke.

For the record, here is our attempt at April Fool’s humour written by our prairie correspondent Minot Moorehead…

Invisibility cloak stolen from lab

Police in the US have launched an investigation after the world’s first flexible invisibility cloak was stolen early this morning. Physicist Randy Katz reported the carbon-based device missing from his lab at the University of Southern North Dakota at Hoople.

Invisibility cloaks use materials with negative indices of refraction to bend light around an object much like water flowing past a stone in a gentle stream. Previous cloaks, however, were made of rigid materials that could not be made into wearable garments.

In 2008 Johan Pendergast of University College Limerick calculated that flexible metamaterials woven from carbon could have a negative index of refraction for visible light. After two years of experimental work, Katz and colleagues say they were about to unveil the first such flexible cloak.

Rings and rods
The design is based on the conventional “rings and rods” metamaterial. Carbon nanotubes function as rod-shaped capacitors and fullerene buckyballs act as inductors. The nanotubes are woven into in a lattice with a spacing of several hundred nanometres, corresponding to the wavelength of visible light.

Katz told physicsworld.com “nanotubes are extremely strong and flexible, which makes the fabric tough yet wearable”. Indeed, Katz revealed that he was talking to a famous French fashion house about using the fabric in its Autumn 2011 collection. “They think invisible could be the new black,” he said.

Evil purposes
A rival fashion designer is one theory being investigated by police, but some physicists fear a more sinister motive. “This device is the Holy Grail of cloaking research,” said Wulf Tigerlung of St Antony’s University. “I have real concerns that whoever stole it could use it for evil purposes”.

North Dakota State Police have launched an investigation but are struggling to find any clues. “We are reviewing tapes from the university’s security cameras to identify anyone who entered the lab but didn’t appear to leave,” said trooper Crosby Cando. “It could also be an inside job,” he said. “Local fraternities would love to get their hands on such a cloak – just think of the pranks they could pull.”