Ambac Assurance Corp. has added Quan Do as a modeler for its cash flow collateralized debt obligation group. Do, who started two weeks ago, reports to Scott Gordon, managing director who runs the structured finance CDO group. The position is newly created because demand for financially guaranteed CDOs is growing, says Gordon. Do joins from Lehman Brothers where he also worked as a CDO quant. He reported to Mark Zusy, managing director. Zusy did not return calls seeking comment on the firm's potential replacement plans.