Registered Direct Offering	6 Months Ended
Jun. 30, 2011
Registered Direct Offering
Registered Direct Offering	(8) Registered Direct Offering On April 18, 2011, the Company entered into a placement agency agreement with Roth Capital Partners, LLC (the "Placement Agent"), pursuant to which the Placement Agent agreed to use its reasonable efforts to arrange for the sale of up to 1,680,672 shares of ARCA's common stock and warrants to purchase up to 1,176,471 shares of ARCA's common stock in a registered direct public offering (the "Offering"). The Company paid the Placement Agent an aggregate fee equal to 7% of the gross proceeds received in the Offering and reimbursed the Placement Agent for its expenses incurred in connection with the Offering, with a maximum expense reimbursement that, when aggregated with the 7% fee, did not exceed 8% of the gross proceeds received by the Company. On April 18, 2011, ARCA entered into separate subscription agreements (the "Subscription Agreements") with certain institutional investors (the "Investors") in connection with the Offering, pursuant to which ARCA sold an aggregate of 1,680,672 shares of its common stock and warrants to purchase a total of 1,176,471 shares of its common stock to the Investors for aggregate gross proceeds, before deducting fees to the Placement Agent and other estimated offering expenses payable by the Company, of approximately $3.0 million. The net proceeds to the Company after deducting placement agent fees and offering expenses were approximately $2.5 million and the Offering closed on April 21, 2011. The common stock and warrants were sold in units, with each unit consisting of one share of common stock and a warrant to purchase 0.7 shares of common stock. The purchase price per unit was $1.785. Subject to certain ownership limitations, the warrants are exercisable on October 21, 2011 and will remain exercisable for five years thereafter at an exercise price of $2.52 per share. The exercise price of the warrants is subject to adjustment in the case of stock splits, stock dividends, combinations of shares and similar recapitalization transactions.

(8) Registered Direct Offering

On April 18, 2011, the Company entered into a placement agency agreement with Roth Capital Partners, LLC (the "Placement Agent"), pursuant to which the Placement Agent agreed to use its reasonable efforts to arrange for the sale of up to 1,680,672 shares of ARCA's common stock and warrants to purchase up to 1,176,471 shares of ARCA's common stock in a registered direct public offering (the "Offering"). The Company paid the Placement Agent an aggregate fee equal to 7% of the gross proceeds received in the Offering and reimbursed the Placement Agent for its expenses incurred in connection with the Offering, with a maximum expense reimbursement that, when aggregated with the 7% fee, did not exceed 8% of the gross proceeds received by the Company.

On April 18, 2011, ARCA entered into separate subscription agreements (the "Subscription Agreements") with certain institutional investors (the "Investors") in connection with the Offering, pursuant to which ARCA sold an aggregate of 1,680,672 shares of its common stock and warrants to purchase a total of 1,176,471 shares of its common stock to the Investors for aggregate gross proceeds, before deducting fees to the Placement Agent and other estimated offering expenses payable by the Company, of approximately $3.0 million. The net proceeds to the Company after deducting placement agent fees and offering expenses were approximately $2.5 million and the Offering closed on April 21, 2011.

The common stock and warrants were sold in units, with each unit consisting of one share of common stock and a warrant to purchase 0.7 shares of common stock. The purchase price per unit was $1.785. Subject to certain ownership limitations, the warrants are exercisable on October 21, 2011 and will remain exercisable for five years thereafter at an exercise price of $2.52 per share. The exercise price of the warrants is subject to adjustment in the case of stock splits, stock dividends, combinations of shares and similar recapitalization transactions.