Cevian Capital isn't exactly a hedge fund, though it classifies itself that way in public filings. It takes significant ownership stakes in companies for three to five years, but it isn't really private equity, either. Cevian, a $3.5 billion firm that is based in Europe with mostly American investors -- Carl C. Icahn and the Florida Teachers Pension Fund among them -- calls itself an 'operational activist fund.' It is among a growing body of investors who eschew the limelight and push for longer-term operational changes at companies. Cevian is up 34 percent so far, after ending 2009 up about 35.7 percent. ValueAct Capital, based in San Francisco, which manages about $4.5 billion in assets, and Barington Companies Equity Partners are posting similar gains. Activist funds are nothing new, of course. Where Cevian says it differs is its strategy, long lockup period and relatively low-profile approach and desire to get into the business and alter strategies and operations -- not just shake up management. About two-thirds of its roughly 150 investors are not allowed to withdraw their money for three to five years, a longer period than most activist hedge funds, Cevian says. Cevian owns pieces of eight to 12 companies at a time, including Volvo and Demag Cranes of Germany. 'One great thing about the environment we're in -- everyone is super- short-term focused,' said Harlan Zimmerman, a senior partner at Cevian who is based in London 'They're just reading the headlines and moving as quickly as possible.' Other activist funds agree that with pressures on funds to produce short-term results or risk having their investors ask for the money back, those that can stay in for the long term can have a competitive advantage. But hedge funds, even activist funds, face a challenge in being able to gain access to a stable capital base. 'That's where everybody would like to be in the activist world, but it's a tough balance,' said Damien Park, managing director of Hedge Fund Solutions. Sometimes managers have to give up their fee structure, he said, in exchange for longer lockup for capital. Still, it is difficult to persuade investors to agree to long-term commitments. The influential CFA Institute suggested recently that endowments and foundations, which provide a substantial portion of hedge funds' assets, consider limiting or restricting investments in hedge funds that tie up capital. The Investment Management Code of Conduct for Endowments, Foundations and Charitable Organizations warned that 'such arrangements may affect future members' ability to effectively manage the financial resources to meet the funding needs of the organization.' To avoid the difficulty of long lockups, firms have adjusted. More hedge funds are creating so-called special purpose vehicles, highly specific investments tailored to just one acquisition, say lawyers who work with hedge funds. Other hedge funds are trying different approaches. The coming year looks to be a good one for activist investors. A recent survey conducted by Schulte Roth and Mergermarket found that respondents expected shareholder activism to increase over the next 12 months. 