Sunday November 25, 2012

Q: What’s been the greatest peril facing the Statue of Liberty since its unveiling in 1888?

A: Probably not sabotage, though a 1916 explosion set off by German agents to damage a nearby munitions dump did damage the raised arm, says Yale University materials scientist Aini ssa Ramirez, as reported by Kate Greene in "Discover" magazine.

The 156-ton Lady Liberty, designed by French sculptor Auguste Bartholdi, is "a remarkable metallurgical success story."

Its outer surface is made of copper sheeting barely a 10th of an inch thick (like two pennies pressed together) and supported by a wrought-iron skeleton designed by engineer Gustave Eiffel of Eiffel Tower fame.

The copper "skin" is joined to the iron skeleton with copper braces pliable enough to endure cycles of thermal expansion and contraction. The structure’s "combination of materials has allowed it to withstand more than 125 years of the harshest of environments: hot summers, cold winters, the salt spray of the surrounding sea," explains Ramirez.

Although copper corrodes with exposure to salt, the corrosion forms a protective coating with a greenish hue. Over the first 30 years of the statue’s life, the color gradually shifted from gold to today’s iconic green.

Though copper has proved a sound materials choice, over time holes have needed to be patched and leaks plugged, with many of the iron components replaced with stainless steel.


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Concludes Ramirez, who grew up in Jersey City within sight of the statue, "It’s kind of amazing to me that it’s still standing. Here you have this metal in the most corrosive environment possible -- seawater -- and it’s still there."

Q: What are the three common forms of language, and what’s the critical challenge to learning any of them?

A: We can think of speech and writing as two forms of language, with writing going back maybe 6,000 years, speech probably 10 times older, says Dominic Massara in "American Scientist" magazine.

The third form is sign language, or gestures or pictograms. The critical challenge for all of these is the same: The mental rigor to connect the symbol with the proper referent, and to do this correctly again and again in communicating.

Logician Willard Van Orman Quine once illustrated the indeterminacy of translation using the example of a native who points at a white running rabbit and says "gavagai."

The anthropologist, not knowing the language, has trouble deciding whether the word refers to the rabbit, the rabbit running, a white animal or something else.

Q: When might a tall skyscraper act like a giant tuning fork? And why should you care anyhow?

A: Let’s hope you can stomach this, because a swaying building is potentially "barfogenic," whether due to an earthquake or a heavy gust of wind, says Julie Rehmeyer in "Wired" magazine.

Given a strong "knock," a skyscraper will vibrate at its own natural resonance frequency several octaves below a piano’s lowest notes.

"If you’re on the top floor of, say, the 1,667-foot-tall Taipei 101, you could find yourself swaying back and forth abruptly, a total of up to two feet within five seconds. Ugh! There goes lunch!"

To add stability, the building’s designer added mass in the form of a 730-ton pendulum with giant shock absorbers bolted to it.

This "tuned mass damper" is intended to sway at the same frequency as the megastructure but in the opposite direction, "pulling the building upright and damping vibrations. It still sways, but subtly and smoothly."