Thursday, November 30, 2006

Researchers Shine Light On Atomic Transistor

Researchers from Delft University of Technology and the FOM Foundation (Fundamental Research on Matter) have successfully measured transport through a single atom in a transistor. This research offers new insights into the behaviour of so-called dopant atoms in silicon. The researchers are able to measure and manipulate a single dopant atom in a realistic semi-conducting environment. The individual behaviour of dopant atoms is a stumbling block to the further miniaturisation of electronics. The researchers have published their findings in the Physical Review Letters.

The electronic industry uses a semiconducting material, dominantly silicon, that contains dopant atoms. This 'contamination' is necessary for giving the silicon the desired electronic characteristics. Owing to the continuing process of miniaturisation, a situation has arisen in which the characteristics of two chips, despite both being manufactured in a totally identical way, still differ from each other. The number of dopant atoms per transistor has in fact become so small (only a few dozen) that they can no longer be regarded as a continuum. The position and effect of each individual atom influences how the entire transistor works. Effectively, this means that even perfectly manufactured transistors will not behave identically. This is an especially alarming situation for the electronics industry, which has already been feeling the pinch for a number of years.

Researchers Sellier, Lansbergen, Caro and Rogge of the Kavli Institute of Nanoscience Delft and the FOM Foundation have successfully managed to measure a single dopant atom in an actual semi-conducting environment. The researchers, who work in the Photronic Devices, transported a charge through one atom. Moreover, they successfully measured and manipulated the quantum mechanical behaviour of a single dopant atom. They were able for example to place one or two electrons in a particular shell of the atom.

The Delft researchers used an advanced industrial transistor (a MOSFET), which was made as a prototype by IMEC, a research centre in Leuven, Belgium. In this transistor, which consists of approximately 35 nanometre-wide silicon nanowires, the electrical current flows through a single dopant atom (in this case, arsenic). The nanowire is connected to a 'gate'; by applying a voltage to the gate, the researchers enable the electrons to flow through the arsenic atom (from the 'source' to the 'drain'). By detailed measurements of the electrical current's behaviour, researchers can observe the remarkable effects.

This research however does not offer an immediate solution to the problems previously mentioned relating to miniaturisation, but it does provide the industry with greater insights into the (quantum mechanical) behaviour of transitions on the nano level. The research conducted at the Kavli Institute of Nanoscience Delft is also extremely interesting from a purely physics point of view. The transistor that was researched not only provided new insights into the atomic physics occurring inside a solid, but this also resembles a structures that is needed to build a certain type of quantum computer. This still purely theoretical computer - the Kane design - is based on dopant atoms in silicon. One of the advantages of using dopants in silicon is that the realization of such a quantum computer can rely on the extremely well developed silicon nanotechnology.

Tuesday, November 28, 2006

Astronomers Find First Ever Gamma Ray Clock

Astronomers using the H.E.S.S. telescopes have discovered the first ever modulated signal from space in Very High Energy Gamma Rays - the most energetic such signal ever observed. Regular signals from space have been known since the 1960s, when the first radio pulsar (nicknamed Little Green Men-1 for its regular nature) was discovered. This is the first time a signal has been seen at such high energies - 100,000 times higher than previously known - and was reported on 24th November in the Journal Astronomy and Astrophysics.

The signal comes from a system called LS 5039 which was discovered by the H.E.S.S. team in 2005. LS5039 is a binary system formed of a massive blue star (20 times the mass of the Sun) and an unknown object, possibly a black hole. The two objects orbit each other at very short distance, varying between only 1/5 and 2/5 of the separation of the Earth from the Sun, with one orbit completed every four days.

"The way in which the gamma ray signal varies makes LS5039 a unique laboratory for studying particle acceleration near compact objects such as black holes.", explained Dr Paula Chadwick from the University of Durham, a British team member of H.E.S.S.

Different mechanisms can affect the gamma-ray signal that reaches Earth and by seeing how the signal varies, astronomers can learn a great deal about binary systems such as LS 5039 and also the effects that take place near black holes.

As it dives towards the blue-giant star, the compact companion is exposed to the strong stellar 'wind' and the intense light radiated by the star, allowing on the one hand particles to be accelerated to high energies, but at the same time making it increasingly difficult for gamma rays produced by these particles to escape, depending on the orientation of the system with respect to us. The interplay of these two effects is at the root of the complex modulation pattern.

The gamma-ray signal is strongest when the compact object (thought to be a black hole) is in front of the star as seen from Earth and weakest when it is behind the star. The gamma rays are thought to be produced as particles which are accelerated in the star's atmosphere (the stellar wind) interact with the compact object. The compact object acts as a probe of the star's environment, showing how the magnetic field varies depending on distance from the star by mirroring those changes in the gamma ray signal.

In addition, a geometrical effect adds a further modulation to the flux of gamma-rays observed from the Earth. We know since Einstein derived his famous equation (E=mc²) that matter and energy are equivalent, and that pairs of particles and antiparticles can mutually annihilate to give light. Symmetrically, when very energetic gamma rays meet the light from a massive star, they can be converted into matter (an electron-positron pair in this case). So, the light from the star resembles, for gamma rays, a fog which masks the source of the gamma rays when the compact object is behind the star, partially eclipsing the source. "The periodic absorption of gamma-rays is a nice illustration of the production of matter-antimatter pairs by light, though it also obscures the view to the particle accelerator in this system"

Sunday, November 26, 2006

Seismologists Measure Heat Flow From Earth's Molten Core Into The Lower Mantle

For the first time, scientists have directly measured the amount of heat flowing from the molten metal of Earth's core into a region at the base of the mantle, a process that helps drive both the movement of tectonic plates at the surface and the geodynamo in the core that generates Earth's magnetic field.

The boundary between the core and the mantle lies half-way to the center of the Earth, at a depth of 1,740 miles (2,900 kilometers). Seismologists are able to probe the structure of this region by studying its effects on seismic waves generated by earthquakes. The new temperature measurements, published in the November 24 issue of the journal Science, were obtained by relating seismic observations to a recently discovered mineral transformation that occurs at the ultrahigh pressures and temperatures prevailing near the core-mantle boundary.

"This is the first time we've had a 'thermometer' that tells us the temperature half-way down to the center of the Earth," said Thorne Lay, professor of Earth and planetary sciences at the University of California, Santa Cruz, and first author of the paper.

"If our interpretation is right, it gives us the temperature at two different depths right above each other, so we get not just the absolute temperature but the rate at which the temperature is changing with depth, as well as laterally," Lay said. "This temperature gradient tells us the amount of heat flowing out of the core into the base of the mantle in that location."

As heat flows from the outer core into the mantle, it drives important processes in both the mantle and the core. The mantle is a thick layer of silicate rock that surrounds a dense, predominantly iron core. The outer core is molten liquid and surrounds a solid inner core about the size of the moon. The cooling of the liquid outer core results in fluid motions in the molten metal that produce electric currents, which generate the geomagnetic field.

Heating at the base of the mantle, meanwhile, drives upwellings of hot mantle material that may rise to volcanoes at the surface and contribute to the slow shifting of tectonic plates. These plates consist of the thin, rocky crust and the rigid top layer of the mantle. They float on the deeper mantle, which is solid but plastic enough to flow very slowly, and their movements trigger earthquakes and gradually change the positions of continents.

"Heat flow is the holy grail, because it tells us how much energy powers the geodynamo, and it tells us how much the mantle is being heated from below. The approach we used is the most direct method so far for getting that information," Lay said.

Lay's coauthors include John Hernlund of the Institut de Physique du Globe in Paris, Edward Garnero of Arizona State University, and Michael Thorne of the University of Alaska, Fairbanks. They applied innovative methods for analyzing seismic signals and used a supercomputer to process a large amount of high-quality seismic data, more than ever before analyzed for a localized region in the Earth. The analysis required 72,000 hours of computer time at the Arctic Region Supercomputing Center and produced very detailed seismic velocity models for the deep mantle under the central Pacific.

Their investigation also relied heavily on laboratory studies of mineral physics. Under the extreme pressures and temperatures deep in the Earth, minerals are squeezed into crystal structures not seen on the surface, except in a few specialized mineral physics labs. If scientists take the common mineral olivine and squeeze it-subjecting it to the ultrahigh pressures and temperatures associated with increasing depth in the Earth-the mineral goes through phase transitions involving sudden reorganizations of its crystal structure.

These phase transitions change the mineral's seismic properties--how fast it transmits certain seismic waves-enabling seismologists to detect where the phase transitions occur deep in the Earth. The depth of the transition tells researchers the pressure, and from that they can get the temperature based on laboratory calibrations, since the pressure at which the transition occurs depends on the temperature.

"If we detect a sudden change in the seismic properties of the mantle, we can associate that with a phase transition in the minerals, and we can use the laboratory calibrations to tell us how hot it is. But until two years ago, we never had that kind of information for the lower mantle," Lay said.

In 2004, Japanese researchers working in the laboratory discovered a new form of high-pressure mineral, called postperovskite, that is likely to occur in the lower mantle. Lay and his coauthors detected the phase transition to postperovskite from its precursor perovskite in the lowermost mantle near the core-mantle boundary. Moreover, they observed that the mineral appears and then disappears with increasing depth, forming a layer or "lens" of postperovskite.

"The reason it transforms back into perovskite is that the temperature increases very rapidly right above the core--so rapidly that this high-pressure form becomes unstable," Lay said. "We also see that this layer becomes thinner as you move laterally and eventually thins out and disappears, which you would expect if you have a lateral increase in temperature."

The researchers suspect that upwelling of hot mantle material may be taking place at the edges of the lens of postperovskite. They detected the lens in the lowermost mantle southeast of Hawaii, an area where previous studies have suggested there is an upwelling hot mantle plume from near the core-mantle boundary that may be responsible for the Hawaiian Islands chain of volcanoes.

The temperature at the upper boundary of the lens, where the phase transition from perovskite to postperovskite occurs, is around 2,500 kelvins (4,000 degrees Fahrenheit). At the lower boundary, where the reverse transition occurs, the temperature is around 3,500 kelvins (5,800 degrees Fahrenheit). These two points gave the researchers a temperature gradient from which they calculated the heat flow, or thermal flux: about 80 million watts per square meter. Extrapolating to the entire surface of the core gave a total heat flow of about 13 trillion watts.

"We think we are in a relatively hot region of the mantle, and cooler areas will have an even higher heat flux, so this probably sets a lower bound on the total heat flow across the core-mantle boundary. The numbers you might read in a textbook are about one-third of that," Lay said.

Such a high heat flow supports the idea that the upwelling of hot plumes of mantle material from near the core-mantle boundary makes a significant contribution to mantle convection, the slow turnover of mantle material that moves tectonic plates on the surface. It also suggests that the solid inner core may be relatively young.

"The core must have been pretty hot in the past for this much heat to be still coming out, and the inner core, which is slowly solidifying from the inside out as the core cools, may be only about a billion years old," Lay said.

"These implications are not well constrained, but it's amazing that you can go from detecting seismic reflections to this long-term perspective on how the whole system seems to work," he added. "It's a remarkable convergence of advances in seismology, mineral physics, and thermodynamical models of deep mantle processes."

Friday, November 24, 2006

Twin Star Explosions Fascinate Astronomers

Scientists using NASA's Swift satellite stumbled upon a rare sight: two supernovae side by side in one galaxy. Large galaxies typically play host to three supernovae per century. Galaxy NGC 1316 has had two supernovae in less than five months, and a total of four supernovae in 26 years, as far back as the records go. This makes NGC 1316 one of the most prodigious known producer of supernovae.
An image of the two supernovae side by side in the galaxy NGC 1316 is pictured here. The first supernova, still visible on the "right" in the image, was detected on June 19, 2006, and was named SN 2006dd. The second supernova, on the immediate "left" in the image, was detected on November 5 and has been named SN 2006mr. (Other objects in the image include a central bright spot, whic is the galaxy core, and a bright object to the far left, like an earring, which is a foreground star.)

NGC 1316, a massive elliptical galaxy about 80 million light years way, has recently merged with a spiral galaxy. Mergers do indeed spawn supernovae by forcing the creation of new, massive stars, which quickly die and explode. Yet all four supernovas in NGC 1316 appear to be Type Ia, a variety previously not associated with galaxy mergers and massive star formation. Scientists are intrigued and are investigating whether the high supernova rate is a coincidence or a result of the merger.

Wednesday, November 22, 2006

Himalayas Have Stopped Growing

Chinese geologists have scotched the general belief that the Himalayas, especially it's main peak, Mount Everest, is steadily growing every year. They reached the conclusion that the Himalayan mountain range has stopped growing after a recent comprehensive scientific exploration in the region. The Himalayas was the result of the crash and extrusion of Indian Plate and Eurasian Plate which started 65 million years ago. "We used to think that it would keep rising as long as the extrusion would continue, but in the exploration, we found several north-south valleys, which suggested the tensile force from the movement of Eurasian Plate itself," geologist, Bian Qiantao said.

Monday, November 20, 2006

World's Largest Superconducting Magnet To Help Provide Answers To Life, Universe And Everything...

The largest superconducting magnet ever built has successfully been powered up to its operating conditions at the first attempt. Called the Barrel Toroid because of its shape, this magnet is a vital part of ATLAS, one of the major particle detectors being prepared to take data at CERN's Large Hadron Collider (LHC), the new particle accelerator scheduled to turn on in November 2007.

ATLAS will help scientists probe the big questions of the Universe - what happened in the moments after the Big Bang? Why does the material in the Universe behave the way it does? Why is the Universe we can see made of matter rather than anti-matter? And hopefully they will come up with something better than 42!

UK scientists are a key part of the ATLAS collaboration and Dr Richard Nickerson, UK ATLAS project leader, who is from the University of Oxford welcomed this important milestone "The toroidal magnets are critical to enabling us to measure the muons (a type of particle) produced in interactions. These are vital to a lot of the physics we want to study, so the successful test of the magnets is a great step forward."

The ATLAS Barrel Toroid consists of eight superconducting coils, each in the shape of a round-cornered rectangle, 5m wide, 25m long and weighing 100 tonnes, all aligned to millimetre precision. It will work together with other magnets in ATLAS to bend the paths of charged particles produced in collisions at the LHC, enabling important properties to be measured. Unlike most particle detectors, the ATLAS detector does not need large quantities of metal to contain the field because the field is contained within a doughnut shape defined by the coils. This allows the ATLAS detector to be very large, which in turn increases the precision of the measurements it can make.

At 46m long, 25m wide and 25m high, ATLAS is the largest volume detector ever constructed for particle physics. Among the questions ATLAS will focus on are why particles have mass, what the unknown 96% of the Universe is made of, and why Nature prefers matter to antimatter. Some 1800 scientists from 165 universities and laboratories (including 12 from the UK) representing 35 countries are building the ATLAS detector and preparing to take data next year.

The ATLAS Barrel Toroid was first cooled down over a six-week period in July-August to reach -269oC. It was then powered up step-by-step to higher and higher currents, reaching 21 thousand amps for the first time during the night of 9 November. This is 500 amps above the current needed to produce the nominal magnetic field. Afterwards, the current was switched off and the stored magnetic energy of 1.1 GJ, the equivalent of about 10 000 cars travelling at 70km/h, has now been safely dissipated, raising the cold mass of the magnet to -218oC.

"We can now say that the ATLAS Barrel Toroid is ready for physics," said Herman ten Kate, ATLAS magnet system project leader.

The ATLAS Barrel Toroid is financed by the ATLAS Collaboration and has been built through close collaboration between the French CEA-DAPNIA laboratory (originator of the magnet's design), Italy's INFN-LASA laboratory and CERN. Components have been contributed in-kind by national funding agencies from industries in France (CEA), Italy, Germany (BMBF), Spain, Sweden, Switzerland, Russia, and the Joint Institute for Nuclear Research (JINR), an international organization based near Moscow. The final integration and test of the coils at CERN, as well as assembly of the toroid in the ATLAS underground cavern, was done with JINR providing most of the manpower and heavy tooling.

Saturday, November 18, 2006

Anti-viral Paint That Kills Flu Developed

A remarkable new anti-viral polymer can be applied like paint and could help reduce the spread of germs in public areas and hospitals. The "biocidal paint" was developed by MIT's Alexander Klibanov. In a demonstration, a regular glass slide and another one coated with alkylated PEI "paint" were sprayed with aqueous suspensions of Staphylococcus aureus cells, and then incubated. Some 200 bacterial colonies were seen on the unprotected slide - and only 4 on the protected one.

Thursday, November 16, 2006

New Kind Of Robot Developed At Cornell

U.S. scientists say they have created a new kind of robot that can teach itself to walk and then, when it is damaged, it teaches itself to limp.

Instead of giving the robot a rigid set of instructions, Cornell University researchers let it discover its own nature and work out how to control itself, a process that seems to resemble the way human and animal babies discover and manipulate their bodies.

Although the test robot is a simple four-legged device, the researchers say the underlying algorithm could be used to build more complex robots that can deal with uncertain situations, such as space exploration.

Assistant Professor Hod Lipson said the research "opens the door to a new level of machine cognition and sheds light on the age-old question of machine consciousness, which is all about internal models."

The experiment, reported in the latest issue of the journal Science, was the work of Lipson; Josh Bongard, a former Cornell postdoctoral researcher now on the faculty at the University of Vermont; and graduate student Viktor Zykov.

Tuesday, November 14, 2006

Air Guitar T-shirt Rocks!

Australian scientists have invented a T-shirt that allows air guitarists to play actual music as they strum the air.
The T-shirt, created by scientists from the Commonwealth Scientific and Industrial Research Organisation(CSIRO), is called a 'wearable instrument shirt'.
The shirt has sensors in each elbow and sleeves to detect and interpret the air guitarist's arm movements - one arm chooses chords and the other strums imaginary strings. The gestures are then connected wirelessly to guitar audio samples to generate the music.
"It's an easy to use, virtual instrument that allows real time music making, even by players without significant musical or computing skills," said CSIRO engineer Richard Helmer. "It allows you to jump around and the sound generated is just like an original mp3," Helmer said in a statement on Monday.
Researchers specialising in computing, musical composition and textile manufacture combined their skills to create the musical T-shirt.
"The technology which is adaptable to almost any kind of apparel, takes clothing beyond it's traditional role of protection and fashion into the realms of entertainment ," said Helmer.
A podcast of Dr. Helmer talking about the shirt is available here.

Sunday, November 12, 2006

Nanorust Cleans Arsenic From Drinking Water

The discovery of unexpected magnetic interactions between ultrasmall specks of rust is leading scientists at Rice University's Center for Biological and Environmental Nanotechnology (CBEN) to develop a revolutionary, low-cost technology for cleaning arsenic from drinking water. The technology holds promise for millions of people in India, Bangladesh and other developing countries where thousands of cases of arsenic poisoning each year are linked to poisoned wells.

The new technique is described in the Nov. 10 issue of Science magazine.

"Arsenic contamination in drinking water is a global problem, and while there are ways to remove arsenic, they require extensive hardware and high-pressure pumps that run on electricity," said center director and lead author Vicki Colvin. "Our approach is simple and requires no electricity. While the nanoparticles used in the publication are expensive, we are working on new approaches to their production that use rust and olive oil, and require no more facilities than a kitchen with a gas cooktop."

CBEN's technology is based on a newly discovered magnetic interaction that takes place between particles of rust that are smaller than viruses.

"Magnetic particles this small were thought to only interact with a strong magnetic field," Colvin said. "Because we had just figured out how to make these particles in different sizes, we decided to study just how big of magnetic field we needed to pull the particles out of suspension. We were surprised to find that we didn’t need large electromagnets to move our nanoparticles, and that in some cases hand-held magnets could do the trick."

The experiments involved suspending pure samples of uniform-sized iron oxide particles in water. A magnetic field was used to pull the particles out of solution, leaving only the purified water. Colvin's team measured the tiny particles after they were removed from the water and ruled out the most obvious explanation: the particles were not clumping together after being tractored by the magnetic field.

Colvin, professor of chemistry, said the experimental evidence instead points to a magnetic interaction between the nanoparticles themselves.

Co-author Doug Natelson explains, “ As particle size is reduced the force on the particles does drop rapidly, and the old models were correct in predicting that very big magnetic fields would be needed to move these particles.

"In this case, it turns out that the nanoparticles actually exert forces on each other," said Natelson, associate professor of physics and astronomy and in electrical and computer engineering. "So, once the hand-held magnets start gently pulling on a few nanoparticles and get things going, the nanoparticles effectively work together to pull themselves out of the water.”

Colvin said, "It's yet another example of the unique sorts of interactions we see at the nanoscale."

Because iron is well known for its ability to bind arsenic, Colvin's group repeated the experiments in arsenic-contaminated water and found that the particles would reduce the amount of arsenic in contaminated water to levels well below the EPA's threshold for U.S. drinking water.

Colvin's group has been collaborating with researchers from Rice Professor Mason Tomson's group in civil and environmental engineering to further develop the technology for arsenic remediation. Colvin said Tomson's preliminary calculations indicate the method could be practical for settings where traditional water treatment technologies are not possible. Because the starting materials for generating the nanorust are inexpensive, she said the cost of the materials could be quite low if manufacturing methods are scaled up. In addition, Colvin's graduate student, Cafer Yuvez, has been working for several months to refine a method that villagers in the developing world could use to prepare the iron oxide nanoparticles. The primary raw materials are rust and fatty acids, which can be obtained from olive oil or coconut oil, Colvin said.

Friday, November 10, 2006

Spectacular Storm Rages On Saturn's South Pole

A hurricane-like storm two-thirds as wide as the Earth is raging on Saturn's south pole, new images from the Cassini spacecraft reveal. Such clear hurricane-like features have never before been seen on any other planet, but scientists are not sure what is causing them.

The dark eye of the "hurricane" spans about 8000 kilometres and is surrounded by rings of clouds that tower about 30 to 75 kilometres above it.

These eye-wall clouds have never been seen anywhere other than on Earth, where they form in a process of convection when moist air flows across an ocean and rises. They drop rain in a ring around a region of falling air, which is the eye of a hurricane.

But Saturn's storm also differs from hurricanes on Earth because it is fixed in place – above the south pole – and is not powered by an ocean, since Saturn is a gaseous planet.

"It looks like a hurricane, but it doesn't behave like a hurricane," says Andrew Ingersoll, a member of Cassini's imaging team at Caltech in Pasadena, US. "Whatever it is, we're going to focus on the eye of the storm and find out why it's there."

It is unclear how long the storm has been there because Cassini has never before seen the pole at such a high resolution. And scientists are still puzzling over how it formed.

"I don't think we really have a good idea of what's sourcing it," says Cassini team member Richard Achterberg, a planetary scientist specialising in atmospheres at NASA's Goddard Space Flight Center in Greenbelt, Maryland, US.

The storm may be a seasonal phenomenon that changes over the course of Saturn's year, which lasts 29 Earth years. It is currently summertime in the planet's southern hemisphere, and both ground-based observations and higher-resolution data from Cassini's Composite Infrared Spectrometer (CIRS) show the pole is about 2° Celsius warmer than its immediate surroundings.

Mission members will try to observe the storm again with CIRS to study the chemical composition of the atmosphere at the pole. "We're going to see if there's water or something being dragged up from below," Achterberg told New Scientist. In particular, the team will look for changes in the storm over the next few years, as the southern hemisphere moves into autumn.

Achterberg says the storm appears to be unique in the solar system. Jupiter's famous storm, the Great Red Spot, for example, does not have an eye or any surrounding eye-wall clouds. It also drifts slowly around the planet with the winds and is colder than its surroundings, while Saturn's storm is warmer.

Whatever its cause, Achterberg says the most striking thing about the storm is simply its appearance. "When you look at it, the shape of those clouds surrounding the pole ... it's an amazing image."

Wednesday, November 08, 2006

Scientists Design A 'Silent' Airplane

A team of U.S. and British researchers has unveiled the conceptual design for a near-silent, environmentally friendly passenger plane.

"Public concern about noise is a major constraint on expansion of aircraft operations. The 'silent aircraft' can help address this concern and thus aid in meeting the increasing passenger demand for air transport," said Edward Greitzer, professor of aeronautics and astronautics at the Massachusetts Institute of Technology.

Greitzer and Professor Ann Dowling of Britain's Cambridge University are the principal investigators on the Silent Aircraft Initiative - a collaboration of 40 researchers from MIT and Cambridge, plus many others from more than 30 companies.

The goal was to develop a conceptual design for an aircraft whose noise was almost imperceptible outside the perimeter of an airfield in an urban environment.

The team's ultimate design also has the potential to be considerably more fuel-efficient. In a typical flight, the proposed bat-winged plane, which is designed to carry 215 passengers, is predicted to achieve 124 passenger-miles per gallon, nearly 25 percent more than current aircraft, Greitzer said.Researchers hope to produce such an aircraft by 2030.