Reminder: JREF scholarships deadline approaches

post from Bad Astronomy on 16 July 2009 03:15:00 PM. © Bad Astronomy

Are you a student (undergrad or grad) who is doing research that aligns with skeptical goals? Then the JREF wants to send you money. Every year, the James Randi Educational Foundation gives away $10,000 total divided into four academic scholarships to[...]

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ips-deadline-approaches/

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Test Rover Checks Pivoting Technique

post from News and Features - NASA's Jet Propulsion Laboratory on 16 July 2009 03:07:00 PM. © News and Features - NASA's Jet Propulsion Laboratory

The Mars rover team is using a test rover at JPL to assess various extraction techniques that might get Spirit out of the loose soil of "Troy" on Mars.

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Chaotic Systems and Escape

post from Good Math, Bad Math on 16 July 2009 03:03:10 PM. © Good Math, Bad Math

One of the things that confused my when I started reading about chaos is easy toexplain using what we've covered about attractors. (The image to the side was created by Jean-Francois Colonna, and is part of his slide-show here)

Here's the problem: We know that things like N-body gravitational systems are chaotic - and a common example of that is how a gravity-based orbital system that appears stable for a long time can suddenly go through a transition where one body is violently ejected, with enough velocity to permanently escape the orbital system.

But when we look at the definition of chaos, we see the requirement for dense periodic orbits. But if a body is ejected from a gravitational system, ejection of a body from a gravitational system is a demonstration of chaos, how can that system have periodic orbits?

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nd_escape.php

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'Invisible' Building Design Could Reduce
Earthquake Damage

Engineers have been developing earthquake-resistant buildings for years, but a group of physicists now believe it's possible to make an entire building effectively disappear from an earthquake's destructive path, avoiding serious damage. Inspired by the recent development of novel materials that precisely control the flow of light waves around objects, they've shown that the same ideas can work whether the waves make up light, sound or earthquakes.

Earthquakes are some of the most destructive forces in nature. The waves they produce ripple across the earth's surface, much as water waves travel across the ocean. The waves from earthquakes crumple buildings, bridges, and other structures, causing millions of dollars in damage and often death. Despite efforts to understand earthquakes and reinforce buildings against them, damage from the shaking ground is nearly impossible to avoid. But that may not be the case for long, say a team of physicists in France and the United Kingdom.

Recently, physicists have been developing better and better invisibility cloaks, which hide an object from sight by causing incoming light waves to bend around the object, and come together behind the object. Physicists Mohamed Farhat and Stefan Enoch of the Fresnel Institute in Marseille, France, and Sebastien Guenneau of Liverpool University in England wondered if they could use the same principles to hide an object from the destructive waves produced during an earthquake. In a paper to be published this week in the journal Physical Review Letters, the three physicists show that the answer may be "yes."

Guenneau said that it's possible to shield an object, even a building, so that an incoming earthquake wave behaves as if the object weren't there. The building in the path of the wave is like a rock in a fast-flowing river, he said.

"It's the same picture, the wave pattern, as for a water wave that is propagating in a river, and it's bent smoothly around the rock and will be reconstructed around the rock." The object, or building, is "invisible" to the mechanical waves.

A series of concrete rings would surround a building or other structure, forming the shield. The shield would redirect the vibration around the object inside. "Each ring is going to wobble in such a way that the wave will bend around (the object)," Guenneau said.

Earthquake waves come in varying lengths, with many peaks and troughs in a given distance, or just a few. To effectively shield a building from short and long waves that earthquakes generate, several rings could be built around a structure, each "tuned" to a different wavelength.

A 1,000 square foot house, for example, would need a circular shield with a 33-foot radius, which could be built with commercially available concrete. Guenneau suggested that the method might be used to protect a large building like a stadium, where people could seek shelter after an earthquake and be protected by the rings from possible aftershocks.

Guenneau warned that there are some limits to what the cloak can accomplish. He and his colleagues could not find a way to shield a structure from the types of earthquake waves that travel below the earth?s surface. He noted that surface waves are typically the most destructive in an earthquake.

Jim Beck, an earthquake engineering expert at the California Institute of Technology in Pasadena, wondered if the ring would be worth building if it couldn't protect a structure from different types of shaking, not just different wavelengths. The cloak might only work perfectly in special circumstances, he said.

"It sounds like an interesting idea, but I think there's a long way to go before they get to what they would like to see done," he said.

Guenneau said he hopes that others will take the idea and explore its promising applications. Last year, Guenneau and his colleagues made headlines by building a prototype tsunami invisibility cloak that uses ring-shaped channels to redirect water waves around an object. Now they're probing that idea further in a large-scale experiment.

The reality of making buildings seem invisible to the destructive forces of nature, be they the waves from earthquakes or tsunamis, "seems a bit crazy, but it's not science fiction," Guenneau said. "We gave the people the concept, now people can try to improve it to make it more tractable."

By Lauren Schenkman
for Inside Science News Service

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http://physicsbuzz.physicscentral.com/2009/07/invisible-building-design-could-red
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