Wednesday, November 17, 2010


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A new propulsion method for metallic micro- and nano-objects has been developed by researchers from the Institute of Molecular Sciences (Institut des sciences moléculaires, CNRS/ENSCBP/Universités Bordeaux 1 and 4). The process is based on the novel concept of bipolar electrochemistry: under the influence of an electric field, one end of a metallic object grows while the other end dissolves. Thanks to this permanent self-regeneration, objects can move at speeds of the order of a hundred micrometers per second. This work, published in the Journal of the American Chemical Society, could find applications in fields ranging from nanomedicine to micromechanics.

Several approaches are currently being explored to induce controlled directional motion of nano-or micro-objects. In particular, scientists are studying the use of so-called 'fuel molecules' which, by decomposing, can propel a dissymmetric object. Other potential avenues include reproducing natural systems by mimicking the motion of bacteria or the rotation of well-known biological systems such as ATP synthase.

For the first time, two researchers from the Bordeaux Institute of Molecular Sciences (CNRS/ENSCBP/Universités Bordeaux 1 and 4) have shown that such motion can be induced using a novel approach called bipolar electrochemistry. The chemists apply an electric field to metallic objects, which then have a different charge at each end, namely a positive charge at one end and a negative charge at the opposite end. This polarization is high enough for opposing redox chemical reactions to occur on both sides. Thus, the object is oxidized and dissolves at one end, while a metal salt present in the solution is reduced and metal is deposited at the other end, causing the object to expand. This process finally induces self-regeneration of the object while causing it to move. The motion brought about in this way is directed towards one of the two electrodes. Speed can be controlled by varying the potential difference between the electrodes.

The advantage of this method is that no conventional fuel is required to induce this motion. Moreover, such micromotors could be adapted so as to push other objects in a predetermined direction and disappear once their task is completed. This novel process opens up new prospects in various fields of application, ranging from micromechanics to nanomedicine.

(Photo: © Kuhn/ISM)

Centre National de la Recherche Scientifique


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Scientists have long known that large volcanic explosions can affect the weather by spewing particles that block solar energy and cool the air. Some suspect that extended “volcanic winters” from gigantic blowups helped kill off dinosaurs and Neanderthals. In the summer following Indonesia’s 1815 Tambora eruption, frost wrecked crops as far off as New England, and the 1991 blowout of the Philippines’ Mount Pinatubo lowered average global temperatures by 0.7 degrees F—enough to mask the effects of manmade greenhouse gases for a year or so.

Now, scientists have shown that eruptions also affect rainfall over the Asian monsoon region, where seasonal storms water crops for nearly half of earth’s population. Tree-ring researchers at Columbia University’s Lamont-Doherty Earth Observatory showed that big eruptions tend to dry up much of central Asia, but bring more rain to southeast Asian countries including Vietnam, Laos, Cambodia, Thailand and Myanmar—the opposite of what many climate models predict. Their paper appears in an advance online version of the journal Geophysical Research Letters.

The growth rings of some tree species can be correlated with rainfall, and the observatory’s Tree Ring Lab used rings from some 300 sites across Asia to measure the effects of 54 eruptions going back about 800 years. The data came from Lamont’s new 1,000-year tree-ring atlas of Asian weather, which has already produced evidence of long, devastating droughts; the researchers also have done a prior study of volcanic cooling in the tropics. “We might think of the study of the solid earth and the atmosphere as two different things, but really everything in the system is interconnected,” said Kevin Anchukaitis, the study’s lead author. “Volcanoes can be important players in climate over time.”

Large explosive eruptions send up sulfur compounds that turn into tiny sulfate particles high into the atmosphere, where they deflect solar radiation. Resulting cooling on earth’s surface can last for months or years. (Not all eruptions will do it; for instance, the continuing eruption of Indonesia’s Merapi this fall has killed dozens, but at least this latest one is probably not big enough by itself to effect large-scale weather changes.) As for rainfall, in the simplest models, lowered temperatures decrease evaporation of water from the surface into the air; and less water vapor translates to less rain. But matters are greatly complicated by atmospheric circulation patterns, cyclic changes in temperatures over the oceans, and the shapes of land masses. Up to now, most climate models incorporating known forces such as changes in the sun and atmosphere have predicted that volcanic explosions would disrupt the monsoon by bringing less rain to southeast Asia--but the researchers found the opposite.

The researchers studied eruptions including one in 1258 from an unknown tropical site, thought to be the largest of the last millennium; the 1600-1601 eruption of Peru’s Huaynaputina; Tambora in 1815; the 1883 explosion of Indonesia’s Krakatau; Mexico’s El Chichón, in 1982; and Pinatubo. The tree rings showed that huge swaths of southern China, Mongolia and surrounding areas consistently dried up in the year or two following big events, while mainland southeast Asia got increased rain. The researchers say there are many possible factors involved, and it would speculative at this point to say exactly why it works this way.

“The data only recently became available to test the models,” said Rosanne D’Arrigo, one of the study’s coauthors. “Now, it’s obvious there’s a lot of work to be done to understand how all these different forces interact.” For instance, in some episodes pinpointed by the study, it appears that strong cycles of the El Niño-Southern Oscillation, which drives temperatures over the Pacific and Indian oceans and is thought to strongly affect the Asian monsoon, might have counteracted eruptions, lessening their drying or moistening effects. But it could work the other way, too, said Anchukaitis; if atmospheric dynamics and volcanic eruptions come together with the right timing, they could reinforce one another, with drastic results. “Then you get flooding or drought, and neither flooding nor drought is good for the people living in those regions,” he said. The study also raises questions whether proposed "geoengineering" schemes to counteract manmade climate change with huge artificial releases of volcanism-like particles might have complex unintended consequences.

Ultimately, said Anchukaitis, such studies should help scientists refine models of how natural and manmade forces might act together to in the future to shift weather patterns—a vital question for all areas of the world.

(Photo: NASA Earth Observatory)

The Earth Institute, Columbia University


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It's not hard to argue in favor of alternatives to fossil fuels these days, but one popular argument — domestic energy security — may be standing on very shaky legs. A lot of rare metals are needed to make photovoltaic panels, rare earth magnets for wind generators, fuel cells and high-capacity batteries for hybrid and electric vehicles. But most industrialized nations, including the United States, are almost entirely dependent on foreign sources for those metals. The only way this is going to change is if there is more domestic exploration and mining.

"There's a misunderstanding in the public about moving to alternative energy and moving from mining, which can't be done," said James Burnell of the Colorado Geological Survey.

There is a long list of scarce metals needed for alternative energy and transportation. Metals like gallium, indium, selenium, tellurium, and high purity silicon are needed to make photovoltaic panels. To make batteries there's zinc, vanadium, lithium and rare earth elements as well as platinum group minerals for fuel cell-powered vehicles. One of the biggest players in the scarce metals game is China, and they are starting to play hard ball, says Burnell.

China is preparing to build 330 giga-watts worth of wind generators. That will require about 59,000 tons of neodymium to make high-strength magnets — more than that country's annual output of neodymium. China supplies the world with a lot of those rare earth elements, like neodymium, and will have little or none to export if it moves ahead with its wind power plans.

"So the source for the West is problematical," said Burnell. Trade wars are on the horizon, he predicted. Yet policy makers and the public seem only superficially aware of the problem.

"It is obvious that Japan was upset by the practical pause of rare earth export by China in late September," said Yasushi Watanabe of the Institute for Geo-Resources and Environment in Tsukuba, Japan.

New sources of these critical metals are needed, said Watanabe, as well as new methods for extracting the rare elements from different kinds of rocks.

"Extraction methods of metals from new minerals and materials are not well established," said Watanabe. "We need to develop new (refining) and smelting methods for new type ores."

We also need to find those ores and start exploiting them, said Burnell. That means more mining. It's the only way we can stay competitive in the new energy future.

The Geological Society of America




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