A week is all it took for Nvidia to lose almost half a trillion in market capitalization.The artificial intelligence (AI) industry doesn't have quite the sheen as it did earlier this summer. Investors have become increasingly wary of the technology's ability to deliver real-world value -- at least in a time frame that justifies the sky-high stock valuations investors have seen.At the heart of this lies the technology's posterchild, Nvidia (NVDA -4.08%). The chipmaker's stock is down about 15% since it repor ...