Jason Karp, who six years ago started his Tourbillon Capital Partners, is closing his main fund after losses, effectively saying that the hedge fund model is broken. He plans to return the more than $1 billion to investors at the end of the year, according to a letter sent to clients Monday that was viewed by Bloomberg News. Karp said that while his equities hedge fund, the Tourbillon Global Master Fund, had outperformed in its first three years of business, it hadn't met expectations recently.