Shares of Universal Display Corp. are down 3.4% in Tuesday morning trading, marking the sixth straight day that the stock is down and the ninth day out of the last 10 trading sessions. UDC's stock recently changed hands at $87. and is on pace to close at a 52-week low. Shares closed at $87.55 on April 25. The stock has been hammered in recent days amid concerns about Apple Inc.'s plans for its next iPhone lineup. The Wall Street Journal reported last week that Apple expects more than half of iPhones sold this fall to have liquid-crystal-display screens rather than organic-light-emitting-diode screens. Universal Display makes OLED technology. The stock is off 27% over the past 12 months, while the S&P 500 has gained 12%.