Nuveen's Doll: 'S&P 500 is in a churning phase'
But over six to 12 months, conditions favor stocks over bonds, Nuveen strategist says
Nuveen strategist: Looming issues could mean bumpy ride for investors
Earnings acceleration likely needed for next upturn in stocks, strategist says
Cyclical and emerging strength may be pointing to better growth, he says
