Hiring has begun for an expansion at DuPont in Circleville, a site that Sen. Sherrod Brown chose yesterday as the venue to renew his call for greater government aid for such projects.DuPont is adding 70 jobs to the plant to produce Tedlar, a thin film used in solar panels. The $175 million expansion is receiving $50.7 million from the Advanced Energy Manufacturing Tax Credit, part of the federal economic-stimulus program.