Page 1516 – Physics World

Home » Page 1516

Astronomy night at the White House

By Michael Banks

On Wednesday night US President Barack Obama hosted an astronomy night at the White House.

Obama, who today won the 2009 Nobel Prize for Peace, invited 150 school students, former astronauts Buzz Aldrin, Sally Ride, and Mae Jemison and NASA administrator Chalres Boldren and his deputy Lori Garver to the event on the South Lawn.

Astronomers spent all day setting up 20 telescopes in preparation for the party in the evening.

Obama was also joined by the first lady, Michelle Obama, and his science advisor, John Holdren.

Obama managed to get some education policy into his speech and talked about reinvigorating maths and science in schools.

“Galileo changed the world when he pointed his telescope to the sky,” Obama said to the youngsters, “and now it is your turn.”

Physicists pin down graphite’s magnetism

Physicists in the Netherlands have confirmed that graphite is a permanent magnet at room temperature and have pinpointed where the high-temperature ferromagnetism comes from for the first time. The result could be important for a variety of applications in nanotechnology and engineering, such as biosensors, detectors and in spintronics.

Graphite is made up of stacks of individual carbon sheets (graphene) and is the familiar form of carbon found in pencils. Although ferromagnetism in graphite has been observed before, it has been difficult to understand where the weak magnetic signals come from. Indeed, some scientists believe that it might originate from tiny amounts of iron-rich impurities in the material, rather than from the carbon itself.

Now, Kees Flipse and colleagues at Eindhoven University of Technology and colleagues at Radboud University Nijmegen have shown that the magnetism occurs in the defect regions between the carbon layers. They did so using magnetic force microscopy (MFM) and scanning tunnelling microscopy (STM), which allowed them to measure magnetic and electronic properties with nanometre (10^-9 m) resolution.

Surface and bulk measurements

Magnetic microscopy scans a very sharp magnetic tip over a surface and measures the magnetic forces between sample and tip. This revealed ferromagnetism at defects on the graphite surface. For bulk measurements, Flipse’s team also employs a superconducting quantum interference device (SQUID) magnetometer – the most sensitive way to measure magnetic fields today.

Graphite consists of well ordered areas of carbon atoms separated by 2 nm wide boundaries of defects. The researchers found that the electrons in the defect regions behave differently to those in the ordered areas and instead resemble electrons in ferromagnetic materials, like iron and cobalt (see figure). They also discovered that the grain boundary regions in the individual carbon sheets are magnetically coupled and form 2D networks. This coupling explains why graphite is a permanent magnet.

“Pure, perfect single-crystal graphite is not a permanent magnet, but the situation changes when you create defects in the material,” Flipse told physicsworld.com. “Single defects in the graphite lattice behave as magnetic dipoles, similar to those in ferromagnetic atoms like iron.”

Biocompatible sensors

As well as being of fundamental interest, magnetic graphite will be important in engineering and nanotechnology. For example, it could be used to make biosensors, since carbon is biocompatible. It could also pave the way for carbon-based spintronics applications – devices that exploit the spin of an electron as well as its charge.

The Netherlands team will now study the role of defects in graphene to better understand the origins of the magnetism. “From a theoretical point of view, the next step would be to investigate the atomic and electronic structure of the grain boundaries in detail, and to develop a complete quantitative theory of the related magnetism,” said Flipse.

The results are reported in Nature Physics.

Science's answer to the Backstreet Boys

By Michael Banks

Outreach raps or songs about science are all the rage these days. Last year we had the Large Hadron Rap by Kate McAlpine and more recently she released a rare-isotope rap for the National Superconducting Cyclotron Laboratory.

Indeed, Steven Rush — aka Funky49 — recently released a rap about the Tevatron for Fermilab entitled Particle Business.

Not to be outdone, Australia’s national science agency — The Commonwealth Scientific and Industrial Research Organization — has teamed up with Sydney University’s Science Revue to release a song about seemingly every science topic.

Featuring “Chem”, “Bio”, “Psych”, “Phys” and “Maths”, they have done a take on the Backstreet Boys’ hit single: Everybody (Backstreet’s Back).

However, Instead of using “everybody” in the song, they have replaced it with climatology, oceanography, or indeed anything else that ends in -ography.

It is a well put together music video and they have upped the ante for science/geeky songs.

My favourite bit is when “Maths” appears wearing a chain around his neck with a rather large pi symbol attached to it singing the words “am I irrational”.

As they all seem to be students, I guess that “Maths” has had some help from “Chem” to make his rapper-like chain to appear to look like gold.

Climate science aboard HMS Beagle

HMS Beagle Still serving scientific endeavour Conrad Martens (1831-1836)

By James Dacey

No respectable landlubber believed them about the giant squids before they started to wash up on the shores. We needed physicists to create mathematical models of freak wave formation before we believed that this spectacular phenomenon could occur.

So surely, when it comes to collecting empirical data for the scientific analysis of climate, there’s no way that scientists would rely solely on the word of mariners.

Well, a new collaboration in the UK has more faith than this. Historical naval logbooks are about to be used for the first time in climate research courtesy of a partnership involving the Met Office Hadley Centre and the University of Sunderland.

The UK Colonial Registers and Royal Navy Logbooks (CORRAL) project has digitized nearly 300 ships’ logbooks dating back to the 1760s. Records include the logbooks of some famous voyages such as the Beagle, Cook’s HMS Discovery and Parry’s polar expedition in HMS Hecla.

According to the project’s leaders, the mariners aboard these ships kept surprisingly detailed notes of the daily, and sometimes hourly, climate conditions. “What happens in the oceans controls what happens in the atmosphere – so we absolutely need to comprehend the oceans to understand future weather conditions,” said the research team’s leader, Dennis Wheeler of the University of Sunderland.

International waters

It’s not just the British who have recognized the high seas as an under-explored resource for climate data. Another group, in Germany, have just developed a new mobile measuring station for observing the interactions between the oceans and the atmosphere.

OCEANET-Atmosphere can apparently register several atmospheric parameters every second, such as the amount of cloud water, the cloud type and the energy exchange between the ocean and the atmosphere. It also maps the atmospheric dust up to a height of 20 km using LiDAR, a technique which combines lasers with GPS.

Next week, four scientists will take a prototype of their machine aboard the vessel Polarstern before setting sail from Bremerhaven, Germany. They will sail south, via Punta Arenas in Southern Chile, to the Antarctic.

Chaos spotted in quantum ‘kicked top’

A butterfly flaps its wings on one side of the Earth and causes a tornado on the other – or so goes the popular illustration of chaos theory. But does chaos also exist in the tiny systems of the quantum world?

The answer is yes, according to researchers in the US and Canada who have now demonstrated quantum chaos in a system analogous to a disturbed spinning top, or a “kicked top”. The breakthrough could help in the understanding of the elusive transition between quantum and classical physics.

One of the hallmarks of classical chaos is that the eventual outcome of a system varies hugely depending on precise details of the initial conditions: perhaps, for example, if the butterfly flaps its left wing there is a tornado, whereas if it flaps its right wing there is none. This sensitivity can be seen in all kinds of scenarios, from planetary orbits to toys.

Quantum chaos quandary

In quantum mechanics, Heisenberg’s uncertainty principle says that these initial details – say, the position and momentum of a particle – cannot both be defined precisely. This inherent property has left past attempts to witness quantum chaos fruitless.

But now Poul Jessen of the University of Arizona in Tuscon, together with colleagues from there and Wilfred Laurier University in Waterloo, Ontario, have found a way to dodge this problem. They use laser pulses and magnetic fields to cause the angular momentum of an ensemble of caesium atoms to shear and rotate, like a kicked top. Classically, the angular momentum of some atoms would evolve in confined rings, yet for others – depending on initial values – it would go chaotic. But because atoms are quantum objects, it’s not possible to know the precise initial values.

Instead, Jessen’s group exploit a phenomenon known as dynamical tunnelling. Similar to normal quantum tunnelling, in which a particle can pass through a potential barrier without having the energy to hop over it, dynamical tunnelling allows the caesium atoms to skip between the confined angular-momentum rings. In this way, having performed numerous measurements, the researchers could trace the rings and thus map the transition between normal and chaotic behaviour.

‘Bit of a surprise’

Fritz Haake, a physicist at the University of Duisburg-Essen, Germany, told physicsworld.com: “Observing wave functions of the kicked top and therein seeing the difference between regular and chaotic behaviour is a significant experimental achievement.” He adds that it is a “bit of a surprise” that the researchers could see the effect deep in the quantum regime with such small angular momenta, rather than nearer the “semiclassical” limit.

The research is reported in Nature and, in a related article, Daniel Steck of the University of Oregon applauds the “beauty” in reconstructing the quantum state. “This is no easy task, involving the processing and combination of many measurements, and was not possible in previous studies of tunnelling,” he writes.

Visualizing the periodic table of the elements

circular vision

By Michael Banks

I can’t imagine a science laboratory that doesn’t have a periodic table hung somewhere on the wall.

I even have a periodic table application on my iPhone that gives you all you need to know about a chosen element (admittedly it is not one of my more frequently used apps).

Yet while generations of science students have learned the periodic table first developed by the Russian chemist Dmitri Mendeleev in 1869, Mohd Abubakr from Microsoft Research in Hyderabad, India, thinks he has found an alternative way of visualizing it.

Abubakr says the major disadvantage with the current table is, well, the shape itself and that it doesn’t help to describe the properties of the elements.

He suggests instead using a “circular form” of the periodic table. His ‘table’ has seven layers, which are each divided into 18 sectors. These sectors each represent the groups in the original table.

However, as with the original table, the lanthanides and actinides are somewhat isolated and are arcs around the main ring.

Although on a first instance it looks like a new way to represent the elements, I haven’t found anything that is fundamentally different from Mendeleev’s table.

Abubakr says that as the new model looks a bit like an atom, with hydrogen and helium near the nucleus, it is better than the current table when trying to teach students the table.

We will see whether the new table takes off, but I don’t expect any updates to my app just yet.

Deep-sea communication with neutrinos

Communicating with nuclear-powered submarines – which can remain underwater essentially indefinitely – is a major challenge because seawater is opaque to most of the electromagnetic spectrum. Neutrinos have previously been proposed as a solution to this problem, because these subatomic particles can pass easily through all matter, but it was thought to be impossible to generate beams of sufficient intensity. However, a physicist in the US has now calculated that the extremely intense beams of a neutrino factory would do the job.

Nuclear-powered submarines can remain submerged for months at a time and only need to resurface to replenish food stocks or carry out maintenance. However, submarines’ movements are restricted by the need to receive messages to direct their actions. Seawater is transparent only in part of the visible portion of the electromagnetic spectrum (blue and green wavelengths) and at frequencies below about 100 Hz. Using lasers in the visible is not practical and low-frequency radio transmissions result in extremely low data rates – around one bit per minute. As a result, nuclear submarines currently communicate by floating a wire antenna close to the surface of the ocean. While this supports data rates of about 50 bits per second, it restricts the depth and speed of operation of a vessel.

Sent through the Earth

Patrick Huber of Virginia Tech believes that these problems can be overcome by instead using neutrinos. Because neutrinos interact extremely weakly with other matter, a beam of such particles can be sent through the Earth with very little loss of intensity. So a submarine could in principle pick up information encoded in a neutrino beam sent from anywhere else on the planet by detecting the neutrinos that approach it from below.

Unfortunately, neutrinos interact very weakly with matter and, therefore, generating a measurable signal requires an extremely intense beam. There are currently a number of experiments around the world that involve the transmission and detection of neutrino beams in order to measure how neutrinos “oscillate” as they travel through space, an important area of study in fundamental physics. But such facilities would be unsuited for carrying out long-range communications. For example, a beam sent from Fermilab outside Chicago to a mine around 700 km away in Minnesota results on average in just one neutrino being registered in the detector every 12 hours. As Huber points out, this rate would need to improve by a factor of about one million if neutrinos were to be used to send messages.

Huber, however, has worked out that a new kind of neutrino source that physicists hope to build within the next decade – a neutrino factory – would provide sufficient intensities. A neutrino factory would work by slamming high-energy protons into a target made of liquid mercury, with the collisions producing pions, which decay into muons, which in turn decay into muon neutrinos.

Detecting Cerenkov radiation

Huber calculates that data encoded in beams of such neutrinos could be picked up by detectors wrapped around the hull of a submarine at rates of between 1 and 100 bits per second. These detectors would either pick up the muons produced when muon neutrinos interact with the water or, more indirectly, measure the Cerenkov radiation generated by the passage of such muons through the water. Data would be encoded by chopping time up into many different slots and then sending a pulse of neutrinos within a particular slot, so that one second divided up into 16,000 slots, for example, would be equivalent to transmitting one letter out of a 16,000 letter alphabet or 14 bits (2¹⁴).

A neutrino factory would not come cheap – it would cost several billion dollars. And adapting it for telecommunications might, says Huber, roughly double this price; the extra expense required to make the device rotatable so that it could point to wherever a submarine is located. But Huber believes that this price should be seen in the context of the money already spent on nuclear submarines by the US, with the 14 Trident vessels, including missiles, costing some $150bn. “There are many things I would not have thought a government would spend very large amounts of money on,” he adds. “So I would not expect anyone to actually build such a system. But I would not be surprised if someone wanted to do more research on it.”

The work is described on the arXiv preprint server.

Propelling bacteria ease liquid flow

The combined action of swimming bacteria can reduce the viscosity of a liquid by up to a factor of seven, according to a pair of researchers in the US. This surprising discovery could lead to new microfluidic applications such as extremely well controlled and efficient mixing devices.

Bioscientists and physicists alike are interested in how tiny biological entities such as bacteria and sperm cells can propel themselves. Observations and models have revealed that a variety of non-trivial mechanics may lie at the heart of these propulsion systems. One interesting feature, hinted at by models, is that the viscosity of a liquid – that is, its resistance to flow – could be significantly reduced by the presence of swimming bacteria.

Now, Andrey Sokolov and Igor Aranson of Argonne National Laboratory in the US have tested this theory and confirmed it to be the case – to a much larger extent than anyone had predicted. The researchers carried out two complementary experiments using Bacillus subtilis, the rod-shaped bacteria chosen for its swimming ability. In both cases, the bacteria – which are approximately 5 µm long and 0.7 µm in diameter – were suspended in a nutrient-rich medium to a concentration of approximately 2 × 10¹⁰ cm^-3.

Oxygen feed

The researchers found that they could control the mobility of Bacillus subtilis by varying the amount of available oxygen dissolved in the fluid. Therefore, the swimming speed of bacteria was controlled by steadily replacing the air in the experimental chambers with nitrogen, and tracking the bacteria using fluorescent markers. After approximately two minutes, the bacteria had reached a complete standstill.

In the first experiment, the researchers triggered a miniature vortex using a magnetically controlled probe. They then inferred the viscosity of each suspension from the time it took each vortex to decay. In the second experiment, they calculated the viscosities more directly by measuring the torque generated by a rotating magnetic microparticle also suspended in the fluid.

In both experiments, the viscosity of the bacterial solution was reduced by up to a factor of seven, so long as there was sufficient oxygen to keep the bacteria moving.

Organic industry

While the researchers do not offer a full physical description of why the viscosity varies in this way, they attribute the reducing viscosity to the conversion of oxygen and nutrients into mechanical energy. “The bacteria are effectively absorbing energy and injecting it directly into the liquid,” explained Aranson. The researcher told physicsworld.com that he can imagine this mechanism finding a role in industry, for example to enhance mixing processes in microscopic systems.

Roberto Di Leonardo, a microfluidics researcher at Rome University, can also see the potential of this research for industry. “Bacterial suspensions could play a more interesting role as advanced, ‘active’ lubricants for micro-machines,” he says. Di Leonardo notes, however, that the “contamination” with organic microfluid could be problematic in some applications.

One of the new directions that Aranson hopes to pursue is the development of a bacterial micromotor that is self-starting. “These micromotors are asymmetric with 200–400 µm miniature gears immersed into the suspensions of swimming bacteria and energized due to collisions with bacteria,” he says.

This research has been published in Physical Review Letters.

Optics pioneers scoop Nobel prize

Three physicists from China, the US and Canada have picked up this year’s Nobel Prize for Physics. The SEK10m prize has been shared between Charles Kao from the Chinese University of Hong Kong and Willard Boyle and George Smith, both from Bell Laboratories, US.

Kao has won half the prize for his work on the transmission of light in optical fibres, which has allowed a revolution in telecommunications. In a statement, the Royal Swedish Academy of Sciences said that “Today, optical fibres make up the circulatory system that nourishes our communication society. These low-loss glass fibers facilitate global broadband communication such as the Internet.”

Boyle and Smith each receive a quarter of the prize for inventing the charge-coupled device (CCD) – an imaging semiconductor circuit that forms the basis of every digital camera. “Digital photography has become an irreplaceable tool in many fields of research,” stated the Academy. “The CCD has provided new possibilities to visualize the previously unseen.”

Telecommunication revolution

Charles Kao was born on 4 November 1933 in Shanghai, China and studied electrical engineering at Woolwich Polytechnic (now the University of Greenwich). After receiving his PhD in electrical engineering from University College London in 1965, he moved to Standard Telecommunication Laboratories (STL) based in Harlow, UK, where he later served as director of engineering. It was here that he did his groundbreaking research into fibre optics.

When Kao joined STL he began working with Antoni Karbowiak who was seeing if optical waveguides could be used for communication. Karbowiak was trying to build such wave guides from sequences of lenses or tubes filled with gas, but without success. In 1964 when Karbowiak moved from STL to the University of New South Wales, Sydney, Australia, and Kao took over the research group.

Charles Kao

Kao was familiar with working with dielectric waveguides – flexible plastic rods that could guide microwaves – and became interested in the work of Elias Snitzer from the American Optical Company, who had showed that dielectric waveguide theory could be also applied to optical fibres for communication.

However, because of their high attenuation, optical fibres were useless for communication. Kao, together with a colleague George Hockham, found that impurities in the fibre were absorbing and scattering light, which led to signal losses. Kao proposed that having optical fibres with high purity glass could be a good candidate for optical communication and calculated that attenuations of a couple of decibels per kilometre (dB/km) could be possible.

Kao is one of the optics heroes, a real pioneer Peter Knight, Imperial College London

Kao immediately saw the potential of optical fibres and published a paper in the Proceedings of the Institute of Electrical Engineers (113, 1151), in which they wrote that “A fibre of glassy material in a cladded structure represents a practical optical waveguide worth important potential as a new form of communication medium.” Optical fibres can keep light in the core of a fibre for kilometres by exploiting the principle of total internal reflection.

However, optical fibres would only be any good in practice for telecommunications if a signal could travel several kilometres without the signal needing to be boosted by ”repeaters”. A few years later, Kao showed that fused silica (SiO₂) had the required purity and could be easily manufactured. By 1970 research led by John MacChesney at Bell labs demonstrated that fibres with an attenuation of 1 dB/km could be achieved.

“Kao is one of the optics heroes, a real pioneer,” Peter Knight from Imperial College London told physicsworld.com. “His research has changed the modern world and what is more astonishing is that Kao immediately saw the application of his work.”

After leaving STL, Kao became research director at the US manufacturing firm ITT cooperation and chief executive of Transtech – a company that produces materials for the telecommunications industry. He also served as vice-chancellor of the Chinese University of Hong Kong from 1987 to 1996. Kao is now a British and US citizen.

The electronic eye

The other half of the 2009 Nobel Prize for Physics is shared between Willard Boyle and George Smith for inventing the CCD camera. Boyle and Smith were both working at Bell Laboratories in New Jersey when they made their discovery in 1969 – Boyle was director of device development at the lab and was Smith’s boss who was a department head.

Willard Boyle and George Smith

A CCD camera contains millions of light-sensitive cells that are arranged in a rows and columns to form a matrix. When light then shines on this matrix it is converted via the photoelectric effect into an electron, which is stored in a capacitor. The amount of stored charge in each cell is then proportional to the intensity of light.

The charges are then transported to the edge of the CCD matrix to be read out. The image can then be reconstructed from the contents of each pixel. The CCD revolutionized photography as it allowed light to be captured electronically instead of on film.

Apart from forming the basics of most digital cameras, CCDs are also widely used in astronomy. The Hubble Space Telescope has several CCD cameras on board, including in the Wide field Planetary Camera, which was recently upgraded.

“CCDs are the backbone of modern astronomy,” says Andrew Fabian, president of the Royal Astronomical Society. “They let professional and even amateur astronomers see objects throughout the Universe with a sensitivity to light that would have been unthinkable even three decades ago.”

CCDs are the backbone of modern astronomy Andrew Fabian, president of the Royal Astronomical Society

Boyle was born in Amherst, Nova Scotia, on 19 August 1924. He served in the Royal Canadian Navy in the Second World War and then attended McGill University, receiving a PhD in physics in 1950. Boyle retired in 1979 and is a Canadian and US citizen.

Smith was born in New York on 10 May 1930. He obtained his PhD in physics from the University of Chicago in 1959 after which he joined Bell Labs as a research scientist. He retired in 1986.

Knight says that while fundamental physics is behind each development, the clear applications set them apart. “I think it is excellent that the Nobel Foundation has chosen these areas of physics where they have obviously changed the world,” says Knight. “Sometimes physics needs to jump up and down and say that it is capable of doing this.”

Earth’s ‘hum’ reveals hidden depths

Researchers in Japan and France have discovered a new way of looking inside the Earth that will no longer be hampered by “tectonic blind spots”. Exploiting a curious phenomenon known as the Earth’s “hum”, the technique could give geophysicists the most extensive picture yet of the upper mantle – the zone in which earthquakes originate.

Earth journeys

In Jules Verne’s science-fiction classic of 1864, an intrepid professor embarks on a curiosity-driven Journey to the Centre of the Earth. While this type of exploration has remained firmly in the realms of fiction, scientists have since found an indirect means of “seeing” beneath the Earth’s surface. Studying how earthquake-driven shock waves travel through the planet has provided geophysicists with a basic picture of the Earth’s interior.

The limitation with this method of imaging, however, is that it is restricted to the zones where earthquakes occur, the vast majority of which are concentrated along plate boundaries. What is more, the technique can only be deployed when seismic activity is occurring – earthquakes are notoriously difficult to predict and they can strike in zones that have been seismically quiet for very long periods.

Now, Kiwamu Nishida at the University of Tokyo and his colleagues have realized an alternative way to image the Earth that is not reliant on the presence of earthquakes. The geophysicists instead track surface waves generated through the interaction of the Earth’s atmosphere and surface – a phenomenon known as the Earth’s seismic “hum”.

Mother Nature calls

Strange as it may seem, the Earth’s atmosphere continuously rings out in a chorus of frequencies just below the reach of the human ear. This phenomenon is expressed at the Earth’s surface as “infrasonic” waves – that is, waves with frequencies ranging 0.01–10 Hz – that are known to exist from acoustic recordings around the globe.

Until now, however, researchers have been unable to link variations in the Earth’s hum with features in the mantle. This is largely because of the complicated processes involved the hum’s generation and the presence of various other sources of ambient seismic noise.

Nishida and his team get around this problem by studying records of the Earth’s ambient noise over a long time period – between 1986 and 2003. In this way, they were able to disentangle the hum from the different sources of ambient noise and observe how it varied over periods of 100–400 s. They could then link fluctuations and geographical variation in the hum with the physical and chemical composition of the mantle.

Mapping the mantle

The geophysicists measured the speed of sound in the mantle to depths of 340 km beneath Asia, North and South America and Australia. By combining a large set of data in a form of tomography, they were able to build up velocity maps of the mantle beneath these continental land masses. “Using seismic hum, estimation of Earth’s structure is not limited by spatial distribution of earthquakes,” Kiwamu told physicsworld.com.

Sebastian Rost, a geophysicist at the University of Leeds in the UK, is impressed by the new development and sees a lot of potential. “Understanding the structure of the upper mantle is important to better understand plate tectonics, especially the way subducted plates are recycled at subduction zones and new crust is generated at mid oceanic ridges.”

Rost is slightly concerned, however, that the researches require a seven year timescale in order for the technique to work. “Seismic data are lost every day due to archive being closed to save money or decaying magnetic tapes or data not available for research in the first place.”

This research appears in the latest edition of Science.

Browse articles by content type

Astronomy night at the White House