Aspen Aerogels (ASPN) recent sell-off (shares down 50% since August) provides a tempting buying opportunity for long-term growth investors. But there are a few things investors need to consider. For starters, investors were disappointed with Q3 results, in large part because the company reported a $13.0 million net loss, which included a $27.5 million one-time charge from the redemption of the company's convertible note (without the one-time charge, net income was $14.5 million, a $27.4 million YoY improvement). Additionally…