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Science 1663

Dr. Xiaoyun Lu of the Bioscience Division at Los Alamos, a member of the team of biochemists, theorists, and engineers who are developing a hand-held biochemistry lab for rapidly detecting the influenza virus

SPOTLIGHT

Roping in Magnetic Fields

Laboratory-generated plasma evolves from flux rope to mini helix. Photo from Thomas Intrator, P-24
Laboratory-generated plasma evolves from flux rope to mini helix. Photo from Thomas Intrator, P-24

At the Sun's edge, in a region called the heliosphere, magnetic fields and electrical currents constantly align and twist themselves in massive 3-D structures called "magnetic flux ropes." These high-tension ropes are unstable and tend to kink and relax into helical configurations (through what theorists call the kink instability). Occasionally, a rope end—which was previously "tied" to the Sun's surface—breaks loose, ejecting electrically charged gas called plasma and producing solar flares that can wreak havoc with everything from satellites to electrical power grids.

Once observed only in places like the Sun's surface, flux ropes are now being created by Los Alamos scientists in the laboratory, making it possible to tie experimental data to prior theoretical analyses. As reported in the July 7, 2006, Physical Review Letters, a small plasma gun shoots plasma into a vacuum. The plasma then flows along an externally produced magnetic field to form plasma-current filaments, or flexible wires composed of plasma. These "mini flux ropes" are photographed and studied with probe measurements as they wind helically around an imaginary central axis (see photo sequence at left).

This close-up study can shed light on the effects of flux ropes in everything from the Earth's magnetosphere to the giant astrophysical jets and radio lobes associated with active galaxies throughout the universe. According to Los Alamos experimentalist Thomas Intrator, "The more we learn in the laboratory, the more we'll know about how solar flares are produced and how the energy locked up in magnetic fields affects the large-scale structure of the universe." (see also http://arxiv.org/pdf/physics/0608263)

Carbon Nanotubes Do the Twist

A carbon-nanotube fiber less than 3 micrometers in diameter. Photo from Y.T. Zhu, MPA-STC

What happens when you take a one-atom-thick sheet of carbon atoms and roll it up into a tube? You get a single-walled carbon nanotube that is likely the strongest material ever made by man. But due to nanotubes' extraordinarily small size—typically only a few nanometers in diameter (about one 10-thousandth the diameter of a human hair) and on the order of 10 micrometers long—their projected uses were primarily limited to new types of nano-scale electronics, such as micro electric motors or ultra-small wires, or else to biological or chemical sensors.

A new twist on carbon nanotubes began in 2004, when a team led by Yuntian T. Zhu of Los Alamos discovered how to grow longer nanotubes, thus opening the door to new uses. Now Zhu and his team are spinning 1-millimeter-long, double-walled carbon nanotubes into tough fibers that pound for pound are 100 times stronger than steel. These super-strong, lightweight fibers could be ideal for many commercial applications, such as aircraft materials, body armor, automobile parts, prosthetic devices, or sports and recreation products. They might even be used to create a cable system for a space elevator and transport people and supplies from the Earth to a tethered space platform.

Los Alamos has licensed its carbon nanotube technology to a new commercial partner, Seattle-based CNT Technologies, Inc. The company plans to be producing one kilogram of fibers per day within the next six months. (see also http://www3.interscience.wiley.com/cgi-bin/abstract/113457074/ABSTRACT)

Is This a Real Rembrandt?

Document from
Eclecticollections


For years, x-rays have been used to help uncover the breaks in our bones and the holes in our teeth. Now these penetrating rays are helping museum conservators confirm the authenticity of masterworks of art.

Micro x-ray fluorescence (MXRF) uses an optic to focus x-rays onto a sample and excite its atoms, which then emit their own characteristic x-rays. Researchers can collect the emitted x-rays with a detector and construct a 2-D map of the elements in the sample. Now George Havrilla and co-workers at Los Alamos have turned MXRF into a 3-D mapping tool. By adding a focusing element to the detector, they can collect x-rays only from within the small "probe volume" defined by the intersection of the source and detector focal regions (a "confocal" arrangement).

Due to the penetrating nature of x-rays, the probe volume can be positioned anywhere within the sample's interior. Confocal MXRF can therefore probe the different layers of paint on a purported masterpiece and determine provenance based on the elemental composition of each layer, thereby confirming the actual pigments used. The technique is nondestructive, so the probing could be done in the middle of the painting. The conventional method involves removing and analyzing a speck of paint. To avoid harming the painting, the speck is taken from the painting's edge, which may not be representative of the central portion of the artwork.

Many conservators expressed great interest in Havrilla's technique when he presented it in Los Angeles at a Getty Museum conservation workshop this past summer.

All Aboard!

From upper left to lower right, two sequential chemical reactions release two hydrogen molecules (green molecules under the hood) from two ammonia-borane molecules. The latter form a polymer, which can continue the hydrogen-releasing reaction. Illustration by Anthony Mancino

Hydrogen tops the list of promising carbon-free fuels for cars, but one of the biggest obstacles to its use is the difficulty of storing enough fuel on board to avoid frequent stops at a "hydrogen station."

How best to achieve the benchmark of 300 miles of travel without refueling? It may be to use the lightweight compound ammonia-borane to carry the hydrogen. With hydrogen accounting for almost 20 percent of its weight, this stable, non-flammable compound is one of the highest-capacity materials for storing hydrogen. In a car, the introduction of a chemical catalyst would release the hydrogen as needed, thus avoiding on-board storage of large quantities of flammable hydrogen gas. When the ammonia-borane fuel is depleted of hydrogen, it would be regenerated at a hydrogen station through a reverse reaction.

Known hydrogen-releasing catalysts are typically metals or their complexes, but they may complicate the reverse reaction. In a recent discovery, Frances Stephens and Tom Baker of Los Alamos National Lab, in collaboration with computational chemists at the University of Alabama, have shown that non-metal acids can catalyze the release of hydrogen. Their analysis has also shown that a similar mechanism of acid-initiated hydrogen release likely applies to ammonia-borane in the solid state and in ionic liquid solvents, forms that could be useful for transportation.

Within the U.S. Department of Energy's Chemical Hydrogen Storage Center of Excellence, work is proceeding to analyze the entire fuel cycle for ammonia-borane, including generation, use, and reuse. Engineering and economic evaluation of the utility of this novel transportation fuel will be conducted by the center over the next few years.

(See also http://www.hydrogen.energy.gov/
http://www3.interscience.wiley.com/cgi-bin/abstract/113488981/.)









Title: SPOTLIGHT
Roping in Magnetic Fields

Keywords: heliosphere, magnetic flux ropes, kink instability, solar flares, Earth's magnetosphere, astrophysical jets, radio lobes

Abstract: Ropes of magnetic flux are created and studied in the laboratory for the first time. These helical structures are related to solar activity as well as to the large-scale structure of the universe.



Title: SPOTLIGHT
Carbon Nanotubes Do the Twist

Abstract: Los Alamos scientists are spinning 1-millimeter-long double-walled carbon nanotubes into tough fibers 100 times stronger than steel.



Title: SPOTLIGHT
Is This a Real Rembrandt?

Abstract: Confocal micro x-ray fluorescence, a non-destructive method to determine authenticity of masterpieces, garnered great interest at a Getty Museum conservation workshop.




Title: SPOTLIGHT
All Aboard! - Efficient Hydrogen Storage for Cars

Abstract: With the discovery that non-metal acids can catalyze a hydrogen-releasing reaction in ammonia-borane, Los Alamos scientists have turned this stable high-hydrogen-capacity, nonflammable compound into a prime candidate for a hydrogen-based fuel.


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