Mysterious stains on St. Louis' Gateway Arch prompted a tricky testing procedure.
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The iconic St. Louis gateway arch, an engineering wonder that towers high above the skyline, is now 50 years old. Discoloration on the stainless steel exterior has building doctors climbing 630 feet up the arch to examine the cause of some of those mysterious stains.

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“SciTech Now” is a new weekly, halfhour newsmagazine program focusing on “the nexus of new ideas.” Hosted by Hari Sreenivasan, anchor of “PBS NewsHour Weekend” and a senior correspondent for the nightly program, “SciTech Now” tackles topics including technology, scientific discovery and innovation.



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