Hot topics

David Bradley Science Writer

Conventional supercomputers have limitations: they are logical and fast, certainly, can be run in parallel grids across the globe, but when it comes down to solving problems with no logical answer, such as cracking sophisticated encryption, working out the travelling sales-rep problem of logistics and deliveries, or modelling the climate, they have serious limitations.

A quantum computer, on the other hand, could find all the answers almost instantaneously and pluck out the most appropriate based on probabilities and quantum mechanics. Building such a quantum computer is not proving simple. Now, US researchers have demonstrated that they can exert delicate control over a pair of atoms within a mere seven-millionths-of-a-second window that suggests the necessary atomic circuitry for a quantum computer might one day be possible.

“At some point in time you get to the limit where a single transistor that makes up an electronic circuit is one atom, and then you can no longer predict how the transistor will work with classical methods,” explains physicist Mark Saffman of the University of Wisconsin-Madison. “You then have to use the physics that describes atoms – quantum mechanics.” In the quantum realm, new possibilities for processing information emerge that mean certain types of problems could be solved exponentially faster on a quantum computer than on any foreseeable classical computer.

Mark Saffman

Working with colleague Thad Walker, Saffman and co-workers have successfully used atoms to create a controlled-NOT (CNOT) gate, a basic type of circuit that will be an essential element of any quantum computer. They describe details of the work in the journal Physical Review Letters and explain that this is the first demonstration of a quantum gate formed between two uncharged atoms.

The use of neutral rubidium atoms chilled to a fraction of a degree above absolute zero, rather than charged ions or other materials, distinguishes this achievement from previous work. “The current gold standard in experimental quantum computing has been set by trapped ions … People can run small programs now with up to eight ions in traps,” explains Saffman. However, to be useful for computing applications, systems must contain enough quantum bits, or qubits, to be capable of running long programs and handling more complex calculations. An ion-based system presents challenges for scaling up because ions are highly reactive, which makes them difficult to control.

Thad Walker

“Neutral atoms have the advantage that in their ground state they don’t talk to each other, so you can put more of them in a small region without having them interact with each other and cause problems,” Saffman says. “This is a step forward toward creating larger systems.” The team is now working towards arrays of up to 50 atoms to test the feasibility of scaling up the system.

LINKS

Phys. Rev. Lett. 2010, 104, 010503 http://prl.aps.org/abstract/PRL/v104/i1/e010503

Mark Saffman
http://hexagon.physics.wisc.edu/marksaffman.htm

Thad Walker
http://www.physics.wisc.edu/people/faculty/twalker/

David Bradley Science Writer

After a frustrating false start, the Large Hadron Collider (LHC) finally got it up and running in its underground home at CERN on the Swiss-French border near Geneva. The scientists behind the world’s biggest scientific, announced that they had primed to energies higher than any previous particle accelerator has ever reached; beating the US Tevatron at Fermilab in Illinois by 20%.

The LHC accelerated protons from an “injection” energy of 0.45 trillion electronvolts to 1.18 TeV. An electronvolt is the energy gained by a single electron being accelerated by a 1 volt potential difference. 1.0 TeV is about 0.16 billionths of a Joule, equivalent to the kinetic energy of a flying mosquito.

The LHC is one of the most ambitious scientific projects every undertaken. Ultimately, the scientists behind it hope that it will reveal one of the most mysterious of natural phenomena – mass. The machine will smash together sub-atomic particles at high speeds. Scientists hope to find the so-called Higgs boson among the collision debris. This particle is the key ingredient in a significant theory – the Higgs-Brout-Englert-Guralnik-Hagen-Kibble mechanism – developed in the 1960s that attempts to explain mass of certain subatomic particles based on the existence of the elusive boson.

The first beams were injected into the LHC on 20th November 2009, although the team does not expect to carry out any actual science until 2010. Nevertheless on 23rd November, they had succeeded in circulating two beams of particles simultaneously and recorded collision data for the first time. The record-breaking energies were reached on 30th November.

“I was here 20 years ago when we switched on CERN’s last major particle accelerator, LEP,” enthused Accelerators and Technology Director Steve Myers. “I thought that was a great machine to operate, but this is something else. What took us days or weeks with LEP, we’re doing in hours with the LHC.”

LHC control room while ramping up the beams to high energies. (Credit: CERN)

The next step is to increase the beam intensity before delivering good quantities of collision data to the experiments before Christmas. So far, all the LHC commissioning work has been carried out with a low-intensity pilot beam. Higher intensity is needed to provide meaningful proton-proton collision rates. Safety is paramount and so the current work is looking at how stable the much higher intensity beams will be. If successful, the scientists will then calibrate the LHC until the end of the year and then begin the first particles physics experiments proper early in 2010 during which collision energies of 7 TeV will be used. Imagine seven mosquitoes colliding in the space.

LHC control room celebrations (Credit: CERN)

Links:

The Large Hadron Collider
CERN on Twitter

David Bradley Science Writer

Protons are seemingly elementary particles and as such one might assume that science knows all there is to know about them. But, together with the origin of its positive charge, physicists have been at a loss to add up the proton’s “spin”. Until now.

The spin of a sub-atomic particle is one of its characteristic properties along with its charge. It is a quantum property, although it can be pictured simply as a kind of rotation. As is often the case with quantum concepts, however, the analogy only stretches so far in that a proton has a spin 1/2, which means it has to “rotate” through 720 degrees, rather than 360 degrees, to get back to its initial state; like tracing one’s fingertip along a “Moebius strip”.

Protons consist of two “up” and one “down” quark linked by gluon chains. Each quark has a spin 1/2, two ups add up to 1 and then the down subtracts a half leaving the proton with a net spin 1/2. However, researchers at the European Muon Collaboration demonstrated in the 1980s that the proton’s spin is not produced by its quarks, In fact, they contribute only a quarter of the value of this quantum property.

“This result was so surprising that it was called the spin-crisis,” explains Yasuyuki Akiba, a PHENIX team member. Particle physicists were therefore confronted with a fundamental question: What else contributes to the spin of the proton?

Scientists suspected that the deficit might be paid for by the gluons that hold the quarks together.

Now, by analyzing data from a year-long experiment carried out at the Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) in 2006, the PHENIX collaboration at BNL in Upton, USA, together with scientists from the RIKEN BNL Research Center and the RIKEN Nishina Center for Accelerator-Based Science have shown that the gluons are not the main source of the proton’s spin either.

Protons consist of two "up" and one "down" quark linked by gluon chains but contribute only a quarter of the total proton spin (large black arrow) (Credit: RIKEN)

Some models predict that the missing spin comes mainly from gluons, while others suggest that the contribution from the orbital angular momentum of quarks within the proton may also be significant. The analysis suggests that the gluon contribution is about 40%. With 25% from the quarks, that leaves 35% still to be accounted for, which may be due to angular momentum or some other factor.

“Although there is still a significant uncertainty in this result, our data show that models predicting large gluon spin can now be firmly excluded,” Akiba says.

Links:

Phys Rev Lett, 2009, 103, 012003
RIKeN Experimental Group

David Bradley Science Writer

An analysis of observations from the Hinode satellite suggest that the solar wind generated by the sun is probably driven by a process involving powerful magnetic fields, according to researchers at University College London and their colleagues.

The study carried out by the UCL Mullard Space Science Laboratory, Observatoire de Paris, Konkoly Observatory in Hungary and Instituto de Astronomía y Física del Espacio in Argentina, could have implications for our understanding of our nearest star and its effects on Earth and our electronic systems including communications satellites and even devices on the ground.

Scientists have long speculated as to what gives rise to the solar wind, a constant stream of extremely high energy particles that pours out from the sun in all directions. The Extreme Ultraviolet Imaging Spectrometer (EIS), on board the Japanese-UK-US Hinode satellite has produced unprecedented data that is now enabling scientists to reveal the underlying forces that give rise to the solar wind. Data provided by the SOHO/MDI consortium, international collaboration between ESA and NASA suggest that a process referred to as “slipping reconnection” may drive the solar wind.

UCL’s Deb Baker explains: “Solar wind is an outflow of million-degree gas and magnetic field that engulfs the Earth and other planets. It fills the entire solar system and links with the magnetic fields of the Earth and other planets. Changes in the Sun’s million-mile-per-hour wind can induce disturbances within near-Earth space and our upper atmosphere and yet we still don’t know what drives these outflows.

Solar wind

“However, our latest study suggests that it is the release of energy stored in solar magnetic fields which provides the additional driver for the solar wind. This magnetic energy release is most efficient in the brightest regions of activity on the Sun’s surface, called active regions or sunspot groups, which are strong concentrations of magnetic field. We believe that this fundamental process happens everywhere on the Sun on virtually all scales.”

The team studied images taken in February 2007 from the EIS instrument, which show hot plasma outflows. At the edges of active regions where slipping reconnection might occur, according to computer models, the researchers explain that a slow, continuous restructuring of the magnetic field leads to the release of energy and acceleration of particles in the Sun’s hot outer atmosphere, its corona.

The locations proposed by the computer model correlated with gas moving outward at up to 160,000 kilometres per hour, a thousand times faster than a terrestrial hurricane.

Links:

Astrophys. J. 2009, 705, 926-935
Deb Baker homepage

David Bradley Science Writer

Material scientists, medical physicists, and cancer biologists will all benefit from the development by US researchers of a low-cost X-ray tube packed with sharp-tipped carbon nanotubes.

Technologists are improving X-ray machines all the time, the device that generates the X-rays by using a vacuum tube to smash high-speed electrons into a piece of metal gets smaller as new approaches to manufacturing are improved and new discoveries in the underlying science made. This allows improved X-ray image resolution, which means greater clarity and detail of X-ray pictures that get right inside the body and see deep inside seemingly solid material.

Now, a team of nanomaterial scientists at the University of North Carolina has revealed a new type of relatively inexpensive and small X-ray device to this year’s meeting of the American Association of Physicists in Medicine in Anaheim, California. The new device will have applications in imaging human breast tissue with potentially unprecedented detail, as well as uses in biomedical research and materials science and engineering. Control that is not possible with conventional X-ray tubes could be made available to a whole range of users.

Otto Zhou, Sha Chang, and their colleagues at UNC have developed a cold X-ray tube to supplant the vacuum tube and the electron-producing hot tungsten filament. They use closely packed carbon nanotubes which emit electrons from their sharp tips when a voltage is applied. These electrons impact a metal target and produce a burst of X-rays.

Otto Zhou

The team has already used their nanotubes X-ray source to produce a micro-sized scanner for imaging the internal organs of small laboratory animals. One of the added advantages of the new approach to X-ray production is that the improved clarity avoids the blur caused by a small living creature’s rapid breathing and high heart rate. On conventional X-ray machines slow mechanical shutters are opened and closed to take X-ray snapshots timed to the breath but small animals breathe too quickly for this to work.

Chang and Zhou have demonstrated that their carbon nanotubes, which can be turned on and off instantaneously, are fairly easy to synch up to equipment that monitors small animal’s breathing or heart rate.

The same nanotube devices could improve human cancer imaging and treatment as well as providing more compact X-ray sources for engineering and materials applications that need to reveal internal structural details of small components.

Further reading

51st AAPM Annual Meeting, 28 July 2009

Otto Zhou Research Lab

David Bradley Science Writer

Improvised explosive devices are the weapon of choice for suicide bombers and have been a major cause of military and civilian casualties in Iraq, Afghanistan, and elsewhere in the world. Now, a group in engineering at the University of Michigan have developed a novel approach to detection of such devices that might allow security forces to intervene in a situation before a device is detected.

A team of undergraduate students at Michigan have developed a palm-sized metal detector based on a magnetometer explains team member Ashwin Lalendran who graduated in May 2009.

The device could be hidden in rubbish bins, under tables or in flowerpots, that are linked together using a wireless sensor network connected to a peripatetic command centre. The inexpensive low-power devices have a long transmission range and outperform all other devices on the market according to Nilton Renno, the team’s supervisor.

“We built it entirely in-house – the hardware and the software,”
explains Lalendran. “Our sensors are small, flexible to deploy, inexpensive and scalable. It’s extremely novel technology.”

The technology has already earned recognition with the Michigan team recently winning a competition sponsored by the US Air Force in conjunction with Ohio State University. The Air Force Research Laboratory at Wright Patterson Air Force Base and other bases across the US sponsor similar contests on a regular basis with the aim of getting a rapid technological reaction to ongoing issues that can be highly innovative.

The team has tested its system in Dayton, Ohio, at a mock outdoor sale event – a simulated carboot sale – secreting detectors across the site.
The organisers then hid simulated explosive devices among the crowd in backpacks and handbags and among the goods “on sale”.

“We had an excellent turnout in technology,” Tenning said. “Regardless of the competition results, often successful ideas from each student team can be combined into a product which is then realized for Department of Defence use in the future.”

Their success demonstrated sound engineering skills and a lot of imagination to the solution of an extremely difficult real-world problem, said Bruce Block, an engineer in the Space Physics Research Laboratory, who worked with the team. He adds that, “they worked well together and never gave up when the going got rough.” The students will continue to work on this project through the summer.

Team member Michael Shin discussing the development of a wireless network for detecting suicide bombers (Credit: UMich)

Podcast from The University of Michigan

David Bradley Science Writer

Science doesn’t have a lot to say about what happened before the Big Bang, but researchers have now developed microwave detectors that will let them take a look at the first trillionth of a trillionth of a trillionth of a second after that primordial cosmic event.

A collaboration between scientists at the National Institute of Standards and Technology (NIST), Princeton University, the University of Colorado at Boulder, and the University of Chicago has yielded super-sensitive microwave detectors that were revealed at the American Physical Society (APS) April meeting held in Denver during May.

Cosmic microwave temperature fluctuations fill the sky and are an echo of the first moment after the Big Bang (Credit: NASA/WMAP Science Team)

The cosmic microwave background (CMB) is often referred to as the afterglow of creation. This remnant, or echo of the Big Bang fills the universe and various projects have obtained snapshots of the CMB stretching back closer and closer to the Big Bang. The new project will use a large array of the sensors mounted on a telescope mounted in the Chilean desert. They will look for subtle fingerprints of the CMB from primordial gravitational waves, ripples in the fabric of the spacetime continuum. Theory has it that these waves will have left an imprint on the direction of the CMB’s electric field, called the B-mode polarization.

This is one of the great measurement challenges facing the scientific community over the next twenty years, and one of the most exciting ones as well, says Kent Irwin, the NIST physicist leading the project.

Prototype NIST detector that will be used to spot signature of rapid inflation immediately after the Big Bang. (Credit: NIST)

If found, these waves would be the clearest evidence yet in support of the inflation theory, which suggests that all of the currently observable universe expanded rapidly (within the first tiny fraction of a second) from a subatomic volume, leaving in its wake the telltale cosmic background of gravitational waves.

The B-mode polarization is the most significant piece of evidence related to inflation that has yet to be observed, explained NIST’s Ki Won Yoon, at the APS meeting. A detection of primordial gravitational waves through CMB polarization would go a long way toward putting the inflation theory on firm ground.

These types of experiments can only be done by treating the universe as a whole as a cosmic laboratory. The particles and electromagnetic fields that exist immediately after the Big Bang are billions of times more energetic than those available even with the most powerful particle colliders on Earth today. On this energy scale, three of the fundamental forces of nature but excluding gravity, are predicted to merge into a single unified force.

At the energy scale at which inflation occurred, which is the GUT or Grand Unified Theory energy scale, only 3 out of the 4 fundamental forces are predicted to merge into a single unified force – electromagnetism, the strong nuclear force, and the weak nuclear force, Irwin told Spotlight.

The final force of nature, gravity, is not predicted to merge with the other three until a much higher energy scale referred to as the Planck scale, which would have occurred before inflation, and would not have been related to the primordial gravity waves. A theory that correctly incorporates gravity into a unified field is humorously referred to as a TOE or Theory of Everything, he adds.

Further reading

APS April 2009 Meeting
http://www.aps.org/meetings/april/

National Institute of Standards and Technology homepage
http://www.nist.gov/index.html

Suggested searches

Big Bang
cosmology
cosmic microwave background

David Bradley Science Writer

Graphene is a modified form of the all-carbon pencil lead material graphite and is being touted as the material of choice for a future generation of computer chips to augment, or even usurp, silicon. Now, three research teams have devised new approaches to handling graphene that could accelerate development of this material.

Carbon has several allotropes – same element, different forms. Graphite is the stuff of pencil lead and exists as layer upon layer of hexagonally patterned chicken wire type sheets with a carbon at each vertex. Diamond is the hardest known materials and exists as a robust tetrahedrally bonded network of carbon atoms. Fullerenes and nanotubes are tiny spheres, spheroids, and tubes. Amorphous carbon, which has a mixture of the trivalent and tetravalent bonded carbon atoms. Graphene is akin to single layers of graphite.

Nitin P. Padture

Andre Geim and colleagues at The University of Manchester and colleagues focused on experimental measurements of the intriguing electronic properties of graphene after theoreticians had predicted them. Now, research teams around the globe are further investigating this intriguing substance. However, processing graphene is not without limitations. As such, various efforts have focused on ways to simplify the handling of the material.

Rod Ruoff and his colleagues at the University of Texas at Austin have found a way to disperse chemically modified graphene in a wide variety of organic solvents. This could open the door to developing graphene in conductive films, polymer composites, ultracapacitors, batteries, paints, inks and plastic electronics, the team says.

Rod Ruoff

By using ’solubility parameters’ ubiquitously applied by industry to determine the solvents most likely to dissolve certain materials or to create good colloids, we have developed a set of solubility parameters for chemically modified graphenes, explains Ruoff. We believe that this approach will have exceptional utility for technology transition in use of colloidal suspensions of graphene sheets.

Tomás Palacios

In parallel, but unconnected work, a team at Ohio State University, led by Nitin Padture are developing a technique for mass producing computer chips made from graphene. Graphene has huge potential, it’s been dubbed the new silicon, says Padture, but there hasn’t been a good process for high-throughput manufacturing it into chips.

Graphene’s chickenwire structure

He and his colleagues have found a way to mesh the graphene fabrication process with standard microelectronics manufacturing methods. In their first series of experiments, the team stamped high-definition features just ten graphene layers thick on to a silicon oxide substrate, making this a potential mass-production method.

A graphene frequency multiplier (Photo by Donna Coveney)

In other work to be published in the May issue of Electron Device Letters, MIT researchers, led by Tomás Palacios, have built an experimental graphene chip known as a frequency multiplier. Frequency multipliers are widely used in telecommunications and computing applications. However, current technology suffers from noise interference that requires energy-intensive filtering. The graphene frequency multiplier system has but a single transistor and so, these researchers say, efficiently produces a very clean output that needs no filtering.

Further reading

Nano. Lett., 2009, in press
http://dx.doi.org/10.1021/nl803798y

Adv Mater, 2009, 21, 1243-1246
http://dx.doi.org/10.1002/adma.200802417

Nanoscience and Technology Lab
http://bucky-central.me.utexas.edu/

Nitin P. Padture homepage
http://www.matsceng.ohio-state.edu/faculty/padture/padturewebpage/

Tomás Palacios homepage
http://web.mit.edu/tpalacios/

Suggested searches

carbon

David Bradley Science Writer

Stabbing is the most common form of murder in the UK and Ireland. However, while forensic scientists understand the basics of the process – a sharp implement lethally penetrating flesh – little is known of the mechanical forces involved. A way to determine quantitatively how hard a victim was stabbed could provide a clear picture of the suspect’s intent to harm.

Now, deputy pathologist Michael Curtis, Marie Cassidy, who both have a high public profile in Ireland as well as being leaders in the international field of forensic science, engineers Michael Gilchrist and Michel Destrade, together with Stephen Keenan and Greg Byrne, have developed a device that can analyse the mechanics of knife stabbing. The team has now used four commonly available household knives with different geometries but all having single-edged, double-sided, non-serrated blade tips to test penetration of simulated flesh composed of polyurethane (skin), compliant foam (fat) and ballistic soap (cartilage).

Dr Michel Destrade

Their findings are rather surprising in that they reveal how skin tension and direction of blade penetration can affect the end result significantly. Less force and energy are also required to puncture the skin when the plane of the blade is parallel to a direction of greater skin tension than when perpendicular. This is consistent with the observed behaviour when cutting biological skin: less force is required to cut parallel to the Langer lines than perpendicularly and less force is required to cut when the skin is under a greater level of tension, the researchers say.

Moreover, even the same manufacturer and model of knife can produce very different results. The team have obtained evidence that the quality control processes used to manufacture knives fail to produce consistently uniform blade points in knives that are nominally identical. They say that the consequences of this are that the penetration forces associated with purportedly the same model of knife can vary by as much as 100%.

Knife (Photo by David Bradley)

Medical witnesses at murder trials involving a knife wound are usually asked what force would have been required to produce the given wound. Mild force would usually be used to describe penetration of skin and soft tissue whereas moderate force is needed to breach cartilage or rib bone. A severe force, that would lead to damage of the knife itself, is typical if dense bone, such as spine, is stabbed.

The work by Gilchrist and colleagues now provides a more quantitative measure for the force required to penetrate different tissues and protective clothing. So, that a less subjective measure of mild, moderate and severe can now be described. The researchers explain that their research could provide insight into the much used defence that the victim ran on to the knife!

M GILCHRIST, S KEENAN, M CURTIS, M CASSIDY, G BYRNE, M DESTRADE (2008). Measuring knife stab penetration into skin simulant using a novel biaxial tension device Forensic Science International DOI: 10.1016/j.forsciint.2007.10.010

Further reading

Dr Michel Destrade homepage
http://www.ucd.ie/mecheng/staff_pages/destrade_michel.html

Suggested searches

forensic science

David Bradley Science Writer

Space is a messy place not least because of all the broken down satellites, chunks of rock and UFOs, but it is thick with dust as well. Now, origin of some of this cosmic dust that pervades empty space and bombards satellites and the Earth itself as microscopic meteorites has been revealed for the first time in new research published this month. It turns out that much of the cosmic dust bombarding the Earth comes from an ancient asteroid belt between the planets Jupiter and Mars.

According to Mathew Genge of Imperial College London, cosmic dust particles are minute pieces of pulverised rock measuring up to a tenth of a millimetre across. Studying them is important, he explains, because their mineral content records the conditions under which asteroids and comets were formed over four and a half billion years ago and provides an insight into the earliest history of our solar system. As such, Genge has trekked across the globe collecting cosmic dust samples hoping to unlock their secrets.

Cosmic Spherule(Credit: Genge et al/Imperial College)

There are hundreds of billions of extraterrestrial dust particles falling though our skies, Genge says, This abundant resource is important since these tiny pieces of rock allow us to study distant objects in our solar system without the multi-billion dollar price tag of expensive missions.

The precise source of cosmic dust that reaches the Earth has until now been unclear. It derives from asteroids and comets and earlier scientists thought that simply analysing the chemical and mineral content of individual dust particles would allow them to trace the origins of cosmic dust more precisely. However, Genge’s study published this month in the journal Geology hints that comparing hundreds of particles provides a much clearer picture.

Mathew Genge (Credit: IC website)

Genge has now analysed more than 600 particles, painstakingly cataloguing their chemical and mineral content and reassembling them like a cosmic jigsaw.

I’ve been studying these particles for quite a while and had all the pieces of the puzzle, he says, but had been trying to figure out the particles one by one. It was only when I took a step back and looked at the minerals and properties of hundreds of particles that it was obvious where they came from. It was like turning over the envelope and finding the return address on the back.

Genge has now revealed that the majority of cosmic dust particles come from a family of ancient space rocks called the Koronis asteroids, which includes the well-known asteroid 243 Ida. The rocks are located in an asteroid belt between Mars and Jupiter and were formed around two billion years ago when a much larger asteroid broke into pieces.

More detailed analysis still shows that the dust originates from a specific grouping of some 20 space rocks within the Koronis family known as the Karin asteroids. The type of mineral from which the asteroids and the cosmic dust are composed is ancient chondrite rock. Genge points out that these rocks were formed in space at the birth of the solar system.

Chondrite meteorites occasionally fall to Earth so Genge was able to match their mineralogy and chemistry to his cosmic dust samples. Infrared astronomical satellite data confirms that collisions between the Karin asteroids can create cosmic dust.

Further reading

Geology, 2008, 36, 687-690
http://dx.doi.org/10.1130/G24493A.1

Dr Matthew Genge homepage
http://www3.imperial.ac.uk/people/m.genge

Suggested searches

cosmic dust
asteroids