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Stereo Speakers Can Levitate Dust for Mars Colonists
Deep-Sea Snail Shell Could Inspire Better Body Armor
Undersea Internet Cables Could Detect Electromagnetic Tsunami Signals
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Stereo Speakers Can Levitate Dust for Mars Colonists

Posted: 20 Jan 2010 03:00 AM PST

776px-concept_mars_colony

Using the vibration from astereo speakerto levitate dust off of surfaces may one day help keep colonies up and running on Mars and the Moon.

Blasting a high-pitched noisefrom a tweeterinto a pipe that focuses the sound waves can create enough pressure to lift troublesome alien dust off surfaces, according to a studypublishedJanuary in theJournal of the Acoustical Society of America.

Dust is one of the biggest obstacles for long-term lunar and Martian space colonies. On the moon, there's no atmosphere and no water, so the dust particles don't get moved around, worn down and rounded like they do on Earth.

Consequently,dustkicked up by rovers and astronauts is "very abrasive and sharp, like freshly broken glass,"said University of Colorado Boulder physicist Zoltan Sternovsky, who was not involved in the study.

Electrostatic charging from solar winds and UV radiation on the Moon makes this sharpdustcling to everything, including astronaut suitswhere it canwork its way through the glove air locks. It also sticks to the solar panels that power rovers and other instruments.

martian-dust-devils On Mars, which has a thin atmosphere, dust devils scour the surface and keep the soil from being as sharp, but it's still got plenty of static cling.

To see whether the technique, known asacoustic levitation (see video below),could solve the dust problem, thescientists loaded a solar panel with mock Martian and lunar dust. The panelnormallyproduced 3 volts of power but the dust reduced its output to just 0.4 volts. After4 minutes of treatment with the acoustic dustbuster to clean the panel, it was able toproduce 98.4 percent of its maximum output.

Acoustic levitation has been used before, said University of Vermont physicist Junrun Wu, coauthor of the study. But this is the first time it's been tested out for an extra-terrestrial application.

The set-up is cheap and can be made with parts easily found online. But the system does have one giant hitch.Because sound is a pressure wave that travels through air, it won't work where there isn't any, like on the moon. And it can't generate enough force to counteract static cling in the thin, low-pressure Martian atmosphere. To work, the dust buster needs to be sealed in an enclosed, pressurized space station.

"We made this very clear, this technique only works in a space station," Wu said.

Images: 1) Martian dust devil traces./NASA. 2) HiRISE, MRO, LPL (University of Arizona), NASA.
Video: Acoustic levitation./David Deak.

Citation: "Removal of dust-particles by standing waves" byD. Chen and J. Wu.J. Acoust. Soc. Am., Vol. 127, No. 1, January 2010

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Deep-Sea Snail Shell Could Inspire Better Body Armor

Posted: 20 Jan 2010 02:30 AM PST

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A deep-sea snail wears a multi-layered suit of armor, complete with iron, new research shows. Dissecting details of the shell's structure could inspire tough new materials for use in everything from body armor to scratch-free paint.

"If you look at the individual properties of the bits and pieces that go into making this shell, they're not very impressive," comments Robert Ritchie of the University of California, Berkeley. "But the overall thing is."

The snail, called the scaly-foot gastropod, was discovered nearly a decade ago living in a hydrothermal vent field in the Indian Ocean. In its daily life, the snail encounters extreme temperatures, high pressures and high acidity levels that threaten to dissolve its protective shell. Worse, it is hunted by crabs that try to crush the mollusk between strong claws.

To understand how the valiant gastropod holds up to these trials, Christine Ortiz of MIT and her colleagues used nanoscale experiments and computer simulations to dig in to the shell's structure. Many other species' shells exhibit what Ortiz calls "mechanical property amplification," in which the whole material is hundreds of times stronger than the sum of its parts.

snail_shell_bsar The scaly-foot snail's shell employs a structure "unlike any other known mollusk or any other known natural armor," the researchers report January 19 in Proceedings of the National Academy of Sciences. Ortiz and her colleagues found that the shell consists of a 250-micrometer-thick inner layer of aragonite, a common shell material, sheathed in a 150-micrometer-thick layer of squishy organic materials. The organic layer is encased in a thin, stiff outer layer (about 30 micrometers thick) made of hard iron sulfide–based scales. The gastropod wears larger versions of the scales on its exposed foot.

"Most mollusks only have a relatively thin outer organic layer followed by inner calcified layers," Ortiz says. But the snail's organic layer is surprisingly thick, and no other gastropod has ever been shown to use iron sulfide in its shell.

Each of the shell's layers plays a unique role in protecting the snail from crab attacks, Ortiz found. The researchers measured material properties like stiffness and fracture resistance, and fed them into a computational model of a predator penetrating the armor.

The model showed that the outer layer, the shell's "first line of defense," sacrificed itself by cracking slightly under pressure. But the cracks were branched and jagged, dissipating energy widely through the shell and keeping any one crack from spreading too far. The iron-based scales could shift and roughen the shell's surface during a crab attack, which in turn would grind down the attacking claw, the researchers suggest.

The soft organic middle layer changed shape in response to pressure, keeping the brittle inner layer from feeling too much of the pinch. Organic material could also insert itself in any cracks that formed in either sandwiching layer and keep the crack from spreading. Plus, the middle layer together with the outer layer protects against acidic waters and may also help shield the snail from high temperatures.

The shell's curvature also helped reduce stress on the calcified inner layer. The inner layer's rigidity provided structural support, to keep the whole shell from caving in.

"It shows that by changing the geometry of the materials … you can improve their properties quite significantly," comments Markus Buehler of MIT, who was not involved in the research.

Ortiz hopes that studying the snail's shell could one day lead to improved materials for armor or helmets for people. Studying organisms that have been optimized for extreme environments through millions of years of evolution could offer ideas that engineers would never think of on their own, she says.

But it will probably be a while, Ritchie cautions. His lab built a ceramic material based on mother-of-pearl in 2008.

"I'm a great fan of this kind of research, but the next step is the critical one. Can you actually harness that information and make a synthetic structure in its image which has the same properties?" he asks. "That's the most difficult step."

Images: 1) Anders Warén, Swedish Museum of Natural History, Stockholm, Sweden. 2) Zina Deretsky, National Science Foundation.

Posted: 19 Jan 2010 02:54 PM PST

Tsunamis may be detectable with underwater fiber optic cables, according to a new detailed model of the electrical fields the moving water generates.

The charged particles in the ocean water interact with Earth's magnetic field to induce voltage of up to 500 millivolts in the cables that ferry internet traffic around. With relatively simple technology, those voltage spikes could serve as a tsunami warning system for nations that can't afford large arrays of other types of sensors.

"What we argue is that this is such a simple system to set up and start measuring," said Manoj Nair, a geomagnetist with the National Oceanic and Atmospheric Administration who led the research. "We have a system of submarine cables already existing. The only thing we probably need is a volt meter, in theory."

The salt in ocean water makes it a good electrical conductor. Positively charged sodium and negatively charged chlorine ions in the solution are free to move. In a large movement of ocean water, these ions are carried across the Earth's magnetic field creating an electrical field.

Decades ago, Bell Labs researchers revealed that the movement of ocean water after the 1992 Cape Mendocino earthquake created "a large-scale motional electric field" that was detectable by an underwater cable. But the work wasn't followed up because alternative technologies were available that could take better measurements. Rich countries like the United States can install sea bottom pressure arrays like those used by the Pacific Tsunami Warning Center. These directly detect the motion of large amounts of water.

But some countries can't afford to install and maintain those arrays, so it could becritical to have a lower-cost alternative.

Nair's work, which will be published in February's Earth, Planets and Space, quantified the physics of this lower-cost alternative by building a model of the Indian Ocean tsunami of 2004. He and his team showed that the voltages induced in the submarine cables would be large enough to measure.

It's a major step towards turning this speculative idea into a real system, though he stressed that other groups would have to confirm the results of their model through observations.

"We treat this as a novel idea that we're putting forth but it still needs to be taken seriously and verified by other groups," Nair cautioned.

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