Federal Reserve Chair Janet Yellen is expected to keep investors happy in her closely watched speech in Jackson Hole, Wyoming, on Friday. 'The expectations are that she will not take away the hopes markets have regarding lower rates for longer,' said Jochen Stanzl, chief market analyst at CMC Markets, based in Frankfurt. 'That's what markets are used to and central banks have been promising that rates will stay low for a very long time.' TheStreet's Scott Gamm reports from Wall Street.