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Artificial aurora
Seismically outfitting Hermes

Artificial aurora

On Mar. 10, 2004, a group of researchers in Alaska watched their computer screens as they sent pulses of energy into the night sky, almost 1 megawatt every 7 seconds, or enough energy to power several hundred homes for a day. As the hour-long experiment unfolded, they were surprised to see indications of something that had never been done before: The energy beams had excited electrons in the atmosphere about 100 kilometers up that then dissociated from their nuclei and flashed green — the first time scientists had created an artificial aurora that was visible to the naked eye. The experiment had unexpectedly worked.

This frame captures an artificial aurora occurring within a natural one over Alaska, about 100 kilometers up in the atmosphere. The artificial event flashed synchronously with the pulsing of the HAARP observatory’s transmitter, which beamed almost a megawatt of power focused on a small patch of the night sky. Courtesy of Todd Pedersen.

But there was no one there to literally see it, says Todd Pedersen of the Air Force Research Laboratory in Massachusetts, who published the research with his co-worker Elizabeth Gerken, now of the Stanford Research Institute in Palo Alto, Calif. The only indications they had that an artificial aurora was unfolding were the data streaming across their computer monitors.

The scientists, working with HAARP (High-frequency Active Auroral Research Program), had managed to excite electrons so they would flash at over 500-nanometer wavelengths — well in the range of visible light — but the researchers were inside watching their monitors in disbelief. It took almost a year to persuade themselves and reviewers that what the computers had “seen” was real, and they published the results in the Feb. 3 Nature.

Although the first experiments to understand auroras in the 1930s prompted dreams of new ways to light cities and advertisements in the sky, those ideas are “on the farfetched side,” says Paul Bernhardt of the Naval Research Laboratory in Washington, D.C., who has been working on how to create auroras since the 1970s. “The holy grail of the artificial aurora experiments is to make it visible enough that you could see it,” Bernhardt says.

This latest experiment was a first step. “I don’t know that we actually do know the exact reasons it occurred,” which means more experiments and unknown results, Bernhardt says. Still, “any time you do something by a factor of 10 better, you’re going to get new science out of it.”

Naomi Lubick

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Seismically outfitting Hermes

Sometime between 370 and 340 B.C., the Greek sculptor Praxiteles is believed to have carved a statue of Hermes, the herald of the Olympian gods, holding the infant Dionysos, the Greek god of wine. Although it has survived for more than 2,000 years in a seismically active land and currently is housed in its own room in the Archaeological Museum of Olympia in Greece, the world-renowned statue has recently received new protection.

Arguably one of the most important statues in Greece, Hermes holding the infant Dionysos (below right) has recently been seismically isolated to protect it in the event of an earthquake. Four blocks placed under a concrete base beneath the statue will allow the statue to swing like a pendulum in a quake, rather than crash to the floor. Courtesy of Michael Constantinou, University at Buffalo.

Seismic engineers at National Technical University in Athens and the University at Buffalo in New York recently completed retrofitting Hermes with a system designed to preserve the statue should a large earthquake strike near Olympia. In the event of a quake, the system allows the statue to gently sway side to side like a pendulum, rather than toppling over and crashing to the floor, says Michael Constantinou, an engineer at Buffalo who worked on the project.

The marble statue of Hermes is about 7 feet tall and stands atop a 3-foot-tall base. The entire structure weighs about 6,600 pounds. Beneath the marble base is a newly constructed concrete base built to support the seismic isolation system.

A carpet with some cushions underneath used to surround the statue to provide earthquake protection, Constantinou says. If an earthquake struck, the statue would have fallen on the cushions and broken into large pieces that could be easily put back together. Many statues around the world are protected this way, he says.

In the case of Hermes, however, the Greek Ministry of Culture wanted more safeguards, Constantinou says, so engineers began designing a system using friction pendulum bearings that seismically retrofit structures around the world, especially freestanding structures such as bridges and important buildings. The technology had not been applied to something as small as a statue before, he says, so it was challenging to figure out the geometry and exactly how much strength was needed to protect the statue. Additionally, Constantinou says, “we were working against a clock — this thing had to be sparkling by the time the Summer Olympics in Athens began” last August.

Beginning in late 2003, the engineers ordered custom-built friction pendulum bearings — 3-feet-by-3-feet square blocks that are about 8 inches high — from a company in San Francisco. The bearings were shipped to Buffalo, where the engineers tested them “in specially designed machines to determine that their properties met the specifications of the project,” Constantinou says. Then they shipped the bearings to Greece, where engineers installed them beneath the concrete base.

The system has yet to be tested by an actual earthquake, but it is designed to withstand a temblor as big as magnitude 8 — the maximum-sized quake that is thought to be possible in the region. The last large earthquake that struck Greece was magnitude 7, in 1983.

In addition to seismically protecting Hermes itself, the building in which the statue stands has been seismically “strengthened,” Constantinou says, so that in the event of an earthquake, the building may be damaged but should not collapse. After all, “it’s not much good having the statue survive a quake if it then gets crushed by the building,” says Andrew Stewart, an art historian at the University of California, Berkeley. “As one of the most important statues in Greece, Hermes “deserves special treatment,” he says.

When combined with strengthening a building, such as by adding columns or putting up a new wall, seismically isolating single features is a good option to protect important artifacts when it is too difficult or costly to seismically isolate the entire building, Constantinou says. But it is no easy task, he says, “to convince the administrators and archaeologists that the system will behave properly in the event of a quake.”

Megan Sever

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