April 29, 2007, 7:11 PM CT

Volcanoes and Nanotechnology

Since their discovery in the early part of 1990s, carbon nanotubes and carbon nanofibers-tiny structures made of pure carbon-have been used in a wide variety of applications. They have become indispensable in the nanosciences and nanotechnology. However, because their production on an industrial scale remains expensive, their commercial use in such areas as catalysis has remained unthinkable. This could now be changing, thanks to scientists from the Fritz Haber Institute in Berlin: Dang Sheng Su and his co-workers have used igneous rock from Mount Etna to produce carbon nanotubes and fibers directly by deposition from the gas phase. As they explain in the journal Angewandte Chemie, the naturally occurring iron oxide particles in lava make it an effective natural catalyst, possibly smoothing the way to a more efficient production method.

Etna is the most active European volcano. During its especially violent eruptions in 2002 and 2003, several million cubic meters of lava were ejected. The fertility of mineral-rich volcanic soils has long been known; Su and colleagues wanted to elicit another, completely new sort of "fertility" for science. It could be amazingly helpful in the synthesis of carbon nanotubes and fibers.

Lava rock is extremely porous and contains large quantities of finely divided iron oxides. This is just what is needed for the synthesis of these tiny carbon structures. The scientists pulverize the rocks and heat them to 700 degree C under a hydrogen atmosphere. This reduces the iron oxide particles to elemental iron. When a mixture of the gases hydrogen and ethylene is directed over the powder, the iron particles catalyze the decomposition of ethylene to elemental carbon. This is deposited on the lava rock in the form of tiny tubes and fibers. The advantages of this new method? The catalyst is produced naturally in large quantities and is thus affordable; the catalytic iron does not need to be deposited on any kind of substrate, as the lava is both catalyst and substrate in one; and this process works without any "wet" chemical steps......... Posted by: Kevin      Read more         Source

April 29, 2007, 7:09 PM CT

A New Type Of Very-high-energy Gamma Ray Emitter

An international team of astrophysicists from the H.E.S.S. collaboration has announced the discovery of a new type of very-high-energy (VHE) gamma ray source. Combining data obtained during a systematic survey of the Galactic Plane and dedicated pointed observations of the telescope array revealed energetic gamma radiation coincident with the stellar cluster Westerlund 2, which is embedded in the giant ionized hydrogen cloud RCW49. The new VHE source, HESS J1023-575, is a first indication of extreme particle acceleration linked to a young open stellar cluster, an ensemble of stars which are especially interesting due to ongoing star formation and the existence of extremely massive stars, known as Wolf-Rayet (WR) stars. One of these, WR 20a, a close binary systems of two WR stars orbiting each other, is the most massive of all confidently-measured binaries presently known in our Galaxy.

Wolf-Rayet stars (named for their discoverers) are evolved, massive stars near the end of their stellar live-cycle, when they are rapidly losing their mass by means of supersonic stellar winds. In the Westerlund 2 cluster, the Wolf-Rayet winds have literally blown bubbles around their stellar hosts, clearly visible in infrared and radio images of the region. Integrated over their lifetime, the wind energy output of Wolf-Rayet stars is not too far from the kinetic energy released in supernova explosions, and shocked winds a re well suited to accelerate particles to high energy......... Posted by: Kevin      Read more         Source

April 25, 2007, 9:31 PM CT

Why Nanowires Make Great Photodetectors

The geometry of semiconducting nanowires makes them uniquely suited for light detection, as per a new UC San Diego study that highlights the possibility of nanowire light detectors with single-photon sensitivity.

Nanowires are crystalline fibers about one thousandth the width of a human hair, and their inherent properties are expected to enable new photodetector architectures for sensing, imaging, memory storage, intrachip optical communications and other nanoscale applications, as per a new study in an upcoming issue of the journal Nano Letters. The UCSD engineers illustrate why the large surface areas, small volumes and short lengths of nanowires make them extremely sensitive photodetectors - much more sensitive than larger photodetectors made from the same materials.

"These results are encouraging and suggest a bright future for nanowire photodetectors, including single-photon detectors, built from nanowire structures," said Deli Wang, an electrical and computer engineering (ECE) professor from the UCSD Jacobs School of Engineering and corresponding author on the Nano Letters paper.

For a nanowire to serve as a photodetector, photons of light with sufficient energy must hit the nanowire in such a way that electrons are split from their positively charged holes. Electrons must remain free from their holes long enough to zip along the nanowire and generate electric current under an applied electric field - a sure sign that light has been detected......... Posted by: Kevin      Read more         Source

April 25, 2007, 9:18 PM CT

Closer To The Goal Of High-yield Fusion Reactor

An electrical circuit that should carry enough power to produce the long-sought goal of controlled high-yield nuclear fusion and, equally important, do it every 10 seconds, has undergone extensive preliminary experiments and computer simulations at Sandia National Laboratories' Z machine facility.

Z, when it fires, is already the largest producer of X-rays on Earth and has been used to produce fusion neutrons. But rapid bursts are necessary for future generating plants to produce electrical power from sea water. This had not been thought achievable till now.

Sandia is a National Nuclear Security Administration laboratory.

How does it work?

An automobile engine that fired one cylinder and then waited hours before firing again wouldn't take a car very far.

Similarly, a machine to provide humanity unlimited electrical energy from cheap, abundant seawater can't fire once and quit for the day. It must deliver energy to fuse pellets of hydrogen every 10 seconds and keep that pace up for millions of shots between maintenance - a kind of an internal combustion engine for nuclear fusion. That's so, at least, for the fusion method at Sandia National Laboratories' Z machine and elsewhere known as inertial confinement.

But, unable to produce fusion except episodically, the method has been overshadowed by the technique called magnetic confinement - a method that uses a magnetic field to enclose a continuous fusion reaction from which to draw power......... Posted by: Kevin      Read more         Source

April 24, 2007, 10:35 PM CT

Avalanche Behavior Of Superfluid Helium

By utilizing ideas developed in disparate fields, from earthquake dynamics to random-field magnets, scientists at the University of Illinois have constructed a model that describes the avalanche-like, phase-slip cascades in the superflow of helium.

Just as superconductors have no electrical resistance, superfluids have no viscosity, and can flow freely. Like superconductors, which can be used to measure extremely tiny magnetic fields, superfluids could create a new class of ultra-sensitive rotation sensors for use in precision guidance systems and other applications.

But, before new sensors can be built, researchers and engineers must first acquire a better understanding of the odd quirks of superfluids arising in these devices.

In the April 23 issue of Physical Review Letters, U. of I. physicist Paul Goldbart, graduate student David Pekker and postdoctoral research associate Roman Barankov describe a model they developed to explain some of those quirks, which were found in recent experiments conducted by scientists at the University of California at Berkeley.

In the Berkeley experiments, physicist Richard Packard and his students Yuki Sato and Emile Hoskinson explored the behavior of superfluid helium when forced to flow from one reservoir to another through an array of several thousand nano-apertures. Their intent was to amplify the feeble whistling sound of phase-slips linked to superfluid helium passing through a single nano-aperture by collecting the sound produced by all of the apertures acting in concert......... Posted by: Sarah      Read more         Source

April 12, 2007, 6:33 PM CT

Mass weddings: new efficient 2-photon source

For a variety of applications in physics and technology, ranging from quantum information theory to telecommunications, its handy to have access to pairs of photons created simultaneously, with a chosen energy. In a significant improvement on prior designs, physicists at the National Institute of Standards and Technology (NIST) have devised a system that delivers such pairs with great efficiency over a wide range of energy, and with very little noise from extraneous photons*.

Paired photons can be generatedalbeit very inefficientlyin standard optical media such as glass optical fibers. Photons normally travel through glass independently, without interacting, but if monochromatic laser light is sent down even an ordinary optical fiber, very occasionally two of the input photons will interact, producing an output photon pair with one higher in energy than the original photons and the other lower by the same amount.

Because the vast majority of photons go through the fiber unchanged, the relative intensity of these pairs is very small. Worse, the fiber generates the pairs randomly with a range of possible energies, so picking out those with some specific energy reduces the number of useful photon pairs still further. Worse yet, there is noise in the system due to the phenomenon called "Raman scattering," in which individual photons bounce off the fibers molecular structure and change their energies. Scattering produces photons that look as if they might be one half of a pair, but arent......... Posted by: Kevin      Read more         Source

April 12, 2007, 6:28 PM CT

Quantum dot lasers

Physicists at the National Institute of Standards and Technology (NIST) and Stanford and Northwestern Universities have built micrometer-sized solid-state lasers in which a single quantum dot can play a dominant role in the devices performance. Correctly tuned, these microlasers switch on at energies in the sub-microwatt range. These highly efficient optical devices could one day produce the ultimate low-power laser for telecommunications, optical computing and optical standards.

How small can a laser get? The typical laser has a vast number of emitterselectronic transitions in an extended crystal, for exampleconfined within an optical cavity. Light trapped and reflecting back and forth in the cavity triggers the cascade of coherent, laser light. But about a decade ago, scientists made the first quantum dot laser. Quantum dots are nanoscale regions in a crystal structure that can trap electrons and holes, the charge carriers that transport current in a semiconductor. When a trapped electron-hole pair recombines, light of a specific frequency is emitted. Quantum-dot lasers have attracted attention as possible embedded communications devices not only for their small size, but because they switch on with far less power then even the solid-state lasers used in DVD players......... Posted by: Kevin      Read more         Source

April 10, 2007, 6:27 PM CT

Structural basis for photoswitching

University of Oregon researchers have identified molecular features that determine the light-emitting ability green fluorescent proteins, and by strategically inserting a single oxygen atom they were able to keep the lights turned off for up to 65 hours.

The findings, published online this week by the Proceedings of the National Academy of Sciences, likely are applicable to most photoswitchable fluorescent proteins, said S. James Remington, professor of physics and member of the UO Institute of Molecular Biology.

"This new model makes specific predictions and improves the qualities of the protein as a photo-switchable label," Remington said. "It gives us the first picture of how these molecules can be switched on and off. That allows us to design new variants to make the proteins more useful".

For more than a decade, fluorescent proteins first isolated in jellyfish and since found in a variety of colors from coral reef organisms revolutionized molecular biology, allowing researchers to use them as markers for genetic expression, to locate molecules and observe activity within cells.

The recent discovery of photoswitchable fluorescent proteins which can be manipulated with a laser has been a significant development for cellular research......... Posted by: Kevin      Read more         Source

April 2, 2007, 10:00 PM CT

Why the Rich Get Richer

A new theory shows how wealth, in different forms, can stick to some but not to others. The findings have implications ranging from the design of the Internet to economics.

Real-world data -- whether distributions of wealth, size of earthquakes or number of connections on a computer network -- often follow power-law distributions rather than the familiar bell-shaped curve. In a power-law distribution, large events are reasonably common compared to smaller events.

Networks often show power laws. They can be caused by the "rich get richer" effect, also known as "preferential attachment," where nodes gain new connections in proportion to how many they already have. That means some nodes end up with many more connections than others. The phenomenon is well known, but had been assumed to be just a fundamental property of networks.

Raissa D'Souza, an assistant professor at the Department of Mechanical and Aeronautical Engineering and the Center for Computational Science and Engineering at UC Davis, together with colleagues at Microsoft Research in Redmond, Wash., UCLA and Cornell University, looked at how "preferential attachment" can arise in networks.

"'The rich get richer' makes sense for wealth, but why would it happen for Internet routers?" she said......... Posted by: Kevin      Read more         Source

March 29, 2007, 10:32 PM CT

Nanotubes Could Improve Thermal Management

As the electronics industry continues to churn out smaller and slimmer portable devices, manufacturers have been challenged to find new ways to combat the persistent problem of thermal management. New research reported in the March 19 issue of Applied Physics Letters suggests that carbon nanotubes may soon be integrated into ever-shrinking cell phones, digital audio players, and personal digital assistants to help ensure the equipment does not overheat, malfunction, or fail.

The chips inside an electronic device give off heat as a byproduct of power consumption when the object is on or being used. To reduce high temperatures, heat sinks - finned devices made of conductive metal such as aluminum or copper - are attached to the back of the chips to "pull" thermal energy away from the microprocessor and transfer it into the surrounding air. Fans or fluids are sometimes used to improve the cooling process, but they increase the device weight, size, and bulk.

Using microfin structures made of aligned multiwalled carbon nanotube arrays mounted to the back of silicon chips, scientists from Rensselaer Polytechnic Institute and the University of Oulu in Finland have proven that nanotubes can dissipate chip heat as effectively as copper - the best known, but most costly, material for thermal management applications. And the nanotubes are more flexible, resilient, and 10 times lighter than any other cooling material available......... Posted by: Kevin      Read more         Source