Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Rubicon Technology (NASDAQ:RBCN) sank as low as 12% today after Oppenheimer downgraded the electronic materials provider from perform to underperform.

So what: Along with the downgrade, analyst Andrew Uerkwitz planted a price target on the stock of $9 per share, representing about 25% worth of downside to yesterday's close. Rubicon has soared over the past few months on optimism over rebounding growth, but Uerkwitz believes that the market is overestimating demand and underestimating the possibility of added competitor capacity, suggesting that the stock is particularly fraught with risk.

Now what: Oppenheimer thinks that Rubicon's management, despite making all the right moves, will struggle to turn a profit in 2014. "We are more pessimistic due to: 1) recent pricing increases are not sustainable based on our model, and 2) new demand from non-LED applications is not enough to greatly reduce overcapacity," Uerkwitz noted. Given that the stock is still up about 140% from its 52-week lows and trading at a price-to-sales multiple of almost 5, it's tough to disagree that Rubicon's downside looks worrisome.