Today's noteworthy downgrades include: Atlas Air (AAWW) downgraded to In-Line from Outperform at Imperial Capital... Caterpillar (CAT) downgraded to Market Perform from Outperform at William Blair... Cummins (CMI) downgraded to Market Perform from Outperform at William Blair... Emerge Energy (EMES) downgraded after guidance withdrawal at Stifel... Exxon Mobil (XOM) downgraded to Underperform from Peer Perform at Wolfe Research... F5 Networks (FFIV) downgraded to Market Perform from Outperform at Raymond James... Internap (INAP) downgraded on earnings miss, negative outlook at Oppenheimer... Semtech (SMTC) downgraded to Neutral from Buy at MKM Partners... Silicon Laboratories (SLAB) downgraded to Neutral from Buy at MKM Partners... Superconductor Technologies (SCON) downgraded to Neutral from Buy at Ladenburg... Virgin America (VA) downgraded to Market Perform from Outperform at Cowen.