Tweeter Home Entertainment ( TWTR) surged more than 32% Thursday on a broad restructuring plan. The electronics retailer said it will close 49 stores that were expected to "contribute negatively" in the near term, as well as two regional facilities, resulting in a 20% reduction of its workforce and a complete pullout from five states.

The plan will result in a charge of $50 million to $60 million. The Canton, Mass., company also intends to use its popular "consumer electronics playground" format in all of its remaining stores and any new locations, with plans to revamp any stores that aren't already suited for it. Shares were rising 43 cents to $1.77.

Chattem ( CHTT) jumped after waning fiscal first-quarter profits beat Wall Street estimates. The Chattanooga, Tenn., drugmaker earned $13.7 million, or 71 cents a share, compared with 75 cents last year; but analysts were seeking 61 cents, according to Thomson Financial. The company also raised its expected full-year earnings range by a nickel, now forecasting between $2.71 to $2.96 a share (including stock options). Analysts are calling for $2.76 a share. Chattem stock was gaining $4.51, or 8.5%, to $57.87.

Arrowhead Research ( ARWR) climbed after its majority-owned unit Unidym agreed to merge with Carbon Nanotechnologies. As a result of the merger, Unidym "will hold the leading portfolio of intellectual property on carbon nanotubes" -- the products in which Carbon specializes. Arrowhead will pay $5.4 million in preferred shares as part of the deal. The transaction should close in early April. Pasadena, Calif.-based Arrowhead was up 57 cents, or 14.9%, to $4.39.

Modine Manufacturing ( MOD) also declined on soft guidance. The Racine, Wis., maker of thermal management technologies expects a fiscal 2007 bottom line of between break-even and a loss, owing to several factors, including a customer delay, a repositioning charge and a spike in the price of nickel (which is used in some of Modine's products). Shares were sinking $2.35, or 8.9%, to $24.07.

Ultrapetrol ( ULTR) slid after the Bahamas-based marine-transportation company offered $201.3 million worth of its shares, the proceeds from which it will use to replenish funds used for its Otto Candies buyout, as well as costs related to construction and shipyard expansion. Despite additionally reporting a narrowed fourth-quarter loss, Ultrapetrol shares were off $1.58, or 8.8%, to $16.37.