Equity Financings and Warrants	12 Months Ended
Dec. 31, 2012
Equity Financings and Warrants [Abstract]
Equity Financings and Warrants	(8) Equity Financings and Warrants *2011 Equity Financings* *Registered Direct Offering* On April 18, 2011, the Company entered into a subscription agreement with certain institutional investors (the “Investors”) in connection with its Registered Direct public offering (the “2011 Offering”), pursuant to which the Company sold an aggregate of 280,112 shares of its common stock and warrants to purchase up to 196,079 additional shares of its common stock to the Investors for aggregate gross proceeds of approximately $3.0 million, before deducting placement agent fees and other estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $2.5 million and the 2011 Offering closed on April 21, 2011. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.70 shares of common stock. The purchase price for each unit was $10.71. Subject to certain ownership limitations, the warrants became exercisable as of October 21, 2011, expire five years from their initial exercise date, and have an exercise price of $15.12 per share, equal to 120% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on April 15, 2011. The Offering was effected as a takedown off the Company’s S-3 Registration Statement, which became effective on April 4, 2011, pursuant to a prospectus supplement filed with the Securities and Exchange Commission on April 18, 2011. The warrant agreements provide for settlement of the warrants in unregistered shares should an effective registration statement or current prospectus not be in place at the time a warrant is exercised. *Private Investment in Public Equity (PIPE) Transaction* On December 21, 2011, the Company entered into separate Subscription Agreements (the “2011 Purchase Agreements”) with various institutional investors in connection with a private placement of its common stock and warrants. Pursuant to the 2011 Purchase Agreements, the Company sold an aggregate of 277,778 shares of its common stock and warrants to purchase up to 208,333 additional shares of its common stock for aggregate gross proceeds of approximately $1.75 million, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $1.5 million, and the private placement closed on December 21, 2011. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $6.30. The warrants became exercisable six months after the closing date, expire five years from their initial exercise date, and have an exercise price of $8.91 per share, equal to 110% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on December 21, 2011. The Company filed a registration statement for the resale of the shares underlying the units sold in these private placements, and incurred, in 2012, approximately $61,000 of additional costs related to completing the registration statement. On January 26, 2012, that registration statement was declared effective by the Securities and Exchange Commission. *2012 Equity Financings* *Registered Direct Offering* On August 2, 2012, the Company entered into subscription agreements with certain institutional investors (the “Investors”) in connection with its Registered Direct public offering (the “2012 Offering”), pursuant to which the Company sold an aggregate of 406,099 shares of its common stock and warrants to purchase up to 304,575 additional shares of its common stock to the Investors for aggregate gross proceeds of approximately $953,000, before deducting placement agent fees and other estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $741,000, and the 2012 Offering closed on August 8, 2011. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $2.35. Subject to certain ownership limitations, the warrants became exercisable six months after the issuance date, expire six years from their initial exercise date, and have an exercise price of $2.76 per share, equal to the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on August 2, 2012. The 2012 Offering was effected as a takedown off the Company’s S-3 Registration Statement, which became effective on April 4, 2011, pursuant to a prospectus supplement filed with the Securities and Exchange Commission on August 3, 2012. The warrant agreements provide for settlement of the warrants in unregistered shares should an effective registration statement or current prospectus not be in place at the time a warrant is exercised. *Private Investment in Public Equity (PIPE) Transactions* On October 22, 2012, the Company entered into a Subscription Agreement (the “October 2012 Purchase Agreements”) with various accredited investors in connection with a private placement of its common stock and warrants. Certain Directors, Officers and Affiliates of ARCA were investors in the private placement. Pursuant to the October 2012 Purchase Agreement, the Company sold an aggregate of 137,530 shares of its common stock and warrants to purchase up to 103,148 additional shares of its common stock for aggregate gross proceeds of approximately $325,000, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $280,000, and the private placement closed on October 25, 2012. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $2.36. The warrants were exercisable upon issuance, expire five years from the closing date, and have an exercise price of $1.80 per share, equal to 100% of the closing bid price of ARCA’s common stock on the NASDAQ Capital Market on October 22, 2012. On December 18, 2012, the Company entered into a Subscription Agreement (the “December 2012 Purchase Agreement”) with its Chief Executive Officer in connection with a private placement of ARCA’s common stock and warrants. Pursuant to the December 2012 Purchase Agreement, the Company sold an aggregate of 86,186 shares of its common stock and warrants to purchase up to 64,640 additional shares of its common stock for aggregate gross proceeds of approximately $250,000, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $230,000, and the private placement closed on December 20, 2012. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $2.90. The warrants were exercisable upon issuance, expire five years from the closing date, and have an exercise price of $2.34 per share, equal to 100% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on December 18, 2012. The Company filed a registration statement for the resale of the shares underlying the units sold in these private placements. The registration statement was declared effective by the Securities and Exchange Commission on February 14, 2013. *2013 Equity Financings* *Subsequent to December 31, 2012, the Company completed the following equity financing transactions:* *Private Investment in Public Equity (PIPE) Transactions* On January 22, 2013, the Company entered into a Subscription Agreement (the “January 2013 Purchase Agreement”) with various accredited investors and its Chief Executive Officer in connection with a private placement of its common stock and warrants. Pursuant to the January 2013 Purchase Agreement, the Company sold an aggregate of 356,430 shares of its common stock and warrants to purchase up to 249,501 additional shares of its common stock for aggregate gross proceeds of approximately $1 million, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $850,000, and the private placement closed on January 25, 2013. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.70 shares of common stock. The purchase price for each unit was $2.81. The warrants were exercisable upon issuance, expire seven years from the date of issuance, and have an exercise price of $2.28 per share, equal to 100% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on January 22, 2013. The Company filed a registration statement for the resale of the shares underlying the units sold in these private placements. The registration statement was declared effective by the Securities and Exchange Commission on February 14, 2013. In connection with this transaction, the Company agreed that, subject to certain exceptions, it would not, while the warrants are outstanding, effect or enter into an agreement to effect any issuance of common stock or securities convertible into, exercisable for or exchangeable for common stock in a “variable rate transaction,” which means a transaction in which the Company issues or sells any convertible securities either (A) at a conversion price, exercise price or exchange rate or other price that is based upon and/or varies with the trading prices of, or quotations for, the shares of common stock at any time after the initial issuance of such convertible securities, or (B) with a conversion, exercise or exchange price that is subject to being reset at some future date after the initial issuance of the convertible securities or upon the occurrence of the specified or contingent events directly or indirectly related to our business or the market for our common stock. In addition, the Company agreed that, subject to certain exceptions, if it issues securities within one year following the closing of the offering, each investor would have the right to purchase its pro rata share of a specified portion of the securities in the future offering on the same terms, conditions and price provided for in the proposed issuance of securities. *Registered Direct Offering* On January 31, 2013, the Company entered into a subscription agreement with certain institutional investors (the “Investors”) in connection with its Registered Direct public offering (the “2013 Offering”), pursuant to which the Company sold an aggregate of 164,636 shares of its common stock and warrants to purchase up to 65,855 additional shares of its common stock to the Investors for aggregate gross proceeds of approximately $730,000, before deducting placement agent fee and other estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $630,000, and the 2013 Offering closed on February 4, 2013. The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.40 shares of common stock. The purchase price for each unit was $4.43. The warrants were exercisable upon issuance, expire five years from the date of issuance, and have an exercise price of $4.13 per share, equal to the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on January 31, 2013. The Offering was effected as a takedown off the Company’s S-3 Registration Statement, which became effective on April 4, 2011, pursuant to a prospectus supplement filed with the Securities and Exchange Commission on February 1, 2013. The warrant agreements provide for settlement of the warrants in unregistered shares should an effective registration statement or current prospectus not be in place at the time a warrant is exercised. *Warrants* As of December 31, 2012, warrants to purchase 930,725 shares of common stock were outstanding at exercise prices ranging from $1.80 to $116.89, with a weighted average exercise price per share of $9.10. These warrants, which were granted as part of various financing and business agreements, expire at various times between October 2013 and February 2019. Warrants were recorded in additional paid-in capital at their estimated fair market value at the date of grant using the Black-Scholes option-pricing model.

Equity Financings and Warrants

12 Months Ended

Dec. 31, 2012

Equity Financings and Warrants [Abstract]

(8) Equity Financings and Warrants

2011 Equity Financings

Registered Direct Offering

On April 18, 2011, the Company entered into a subscription agreement with certain institutional investors (the “Investors”) in connection with its Registered Direct public offering (the “2011 Offering”), pursuant to which the Company sold an aggregate of 280,112 shares of its common stock and warrants to purchase up to 196,079 additional shares of its common stock to the Investors for aggregate gross proceeds of approximately $3.0 million, before deducting placement agent fees and other estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $2.5 million and the 2011 Offering closed on April 21, 2011.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.70 shares of common stock. The purchase price for each unit was $10.71. Subject to certain ownership limitations, the warrants became exercisable as of October 21, 2011, expire five years from their initial exercise date, and have an exercise price of $15.12 per share, equal to 120% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on April 15, 2011. The Offering was effected as a takedown off the Company’s S-3 Registration Statement, which became effective on April 4, 2011, pursuant to a prospectus supplement filed with the Securities and Exchange Commission on April 18, 2011.

The warrant agreements provide for settlement of the warrants in unregistered shares should an effective registration statement or current prospectus not be in place at the time a warrant is exercised.

Private Investment in Public Equity (PIPE) Transaction

On December 21, 2011, the Company entered into separate Subscription Agreements (the “2011 Purchase Agreements”) with various institutional investors in connection with a private placement of its common stock and warrants. Pursuant to the 2011 Purchase Agreements, the Company sold an aggregate of 277,778 shares of its common stock and warrants to purchase up to 208,333 additional shares of its common stock for aggregate gross proceeds of approximately $1.75 million, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $1.5 million, and the private placement closed on December 21, 2011.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $6.30. The warrants became exercisable six months after the closing date, expire five years from their initial exercise date, and have an exercise price of $8.91 per share, equal to 110% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on December 21, 2011.

The Company filed a registration statement for the resale of the shares underlying the units sold in these private placements, and incurred, in 2012, approximately $61,000 of additional costs related to completing the registration statement. On January 26, 2012, that registration statement was declared effective by the Securities and Exchange Commission.

2012 Equity Financings

Registered Direct Offering

On August 2, 2012, the Company entered into subscription agreements with certain institutional investors (the “Investors”) in connection with its Registered Direct public offering (the “2012 Offering”), pursuant to which the Company sold an aggregate of 406,099 shares of its common stock and warrants to purchase up to 304,575 additional shares of its common stock to the Investors for aggregate gross proceeds of approximately $953,000, before deducting placement agent fees and other estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $741,000, and the 2012 Offering closed on August 8, 2011.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $2.35. Subject to certain ownership limitations, the warrants became exercisable six months after the issuance date, expire six years from their initial exercise date, and have an exercise price of $2.76 per share, equal to the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on August 2, 2012. The 2012 Offering was effected as a takedown off the Company’s S-3 Registration Statement, which became effective on April 4, 2011, pursuant to a prospectus supplement filed with the Securities and Exchange Commission on August 3, 2012. The warrant agreements provide for settlement of the warrants in unregistered shares should an effective registration statement or current prospectus not be in place at the time a warrant is exercised.

Private Investment in Public Equity (PIPE) Transactions

On October 22, 2012, the Company entered into a Subscription Agreement (the “October 2012 Purchase Agreements”) with various accredited investors in connection with a private placement of its common stock and warrants. Certain Directors, Officers and Affiliates of ARCA were investors in the private placement. Pursuant to the October 2012 Purchase Agreement, the Company sold an aggregate of 137,530 shares of its common stock and warrants to purchase up to 103,148 additional shares of its common stock for aggregate gross proceeds of approximately $325,000, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $280,000, and the private placement closed on October 25, 2012.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $2.36. The warrants were exercisable upon issuance, expire five years from the closing date, and have an exercise price of $1.80 per share, equal to 100% of the closing bid price of ARCA’s common stock on the NASDAQ Capital Market on October 22, 2012.

On December 18, 2012, the Company entered into a Subscription Agreement (the “December 2012 Purchase Agreement”) with its Chief Executive Officer in connection with a private placement of ARCA’s common stock and warrants. Pursuant to the December 2012 Purchase Agreement, the Company sold an aggregate of 86,186 shares of its common stock and warrants to purchase up to 64,640 additional shares of its common stock for aggregate gross proceeds of approximately $250,000, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $230,000, and the private placement closed on December 20, 2012.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.75 shares of common stock. The purchase price for each unit was $2.90. The warrants were exercisable upon issuance, expire five years from the closing date, and have an exercise price of $2.34 per share, equal to 100% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on December 18, 2012.

The Company filed a registration statement for the resale of the shares underlying the units sold in these private placements. The registration statement was declared effective by the Securities and Exchange Commission on February 14, 2013.

2013 Equity Financings

Subsequent to December 31, 2012, the Company completed the following equity financing transactions:

Private Investment in Public Equity (PIPE) Transactions

On January 22, 2013, the Company entered into a Subscription Agreement (the “January 2013 Purchase Agreement”) with various accredited investors and its Chief Executive Officer in connection with a private placement of its common stock and warrants. Pursuant to the January 2013 Purchase Agreement, the Company sold an aggregate of 356,430 shares of its common stock and warrants to purchase up to 249,501 additional shares of its common stock for aggregate gross proceeds of approximately $1 million, before deducting estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $850,000, and the private placement closed on January 25, 2013.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.70 shares of common stock. The purchase price for each unit was $2.81. The warrants were exercisable upon issuance, expire seven years from the date of issuance, and have an exercise price of $2.28 per share, equal to 100% of the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on January 22, 2013.

In connection with this transaction, the Company agreed that, subject to certain exceptions, it would not, while the warrants are outstanding, effect or enter into an agreement to effect any issuance of common stock or securities convertible into, exercisable for or exchangeable for common stock in a “variable rate transaction,” which means a transaction in which the Company issues or sells any convertible securities either (A) at a conversion price, exercise price or exchange rate or other price that is based upon and/or varies with the trading prices of, or quotations for, the shares of common stock at any time after the initial issuance of such convertible securities, or (B) with a conversion, exercise or exchange price that is subject to being reset at some future date after the initial issuance of the convertible securities or upon the occurrence of the specified or contingent events directly or indirectly related to our business or the market for our common stock. In addition, the Company agreed that, subject to certain exceptions, if it issues securities within one year following the closing of the offering, each investor would have the right to purchase its pro rata share of a specified portion of the securities in the future offering on the same terms, conditions and price provided for in the proposed issuance of securities.

Registered Direct Offering

On January 31, 2013, the Company entered into a subscription agreement with certain institutional investors (the “Investors”) in connection with its Registered Direct public offering (the “2013 Offering”), pursuant to which the Company sold an aggregate of 164,636 shares of its common stock and warrants to purchase up to 65,855 additional shares of its common stock to the Investors for aggregate gross proceeds of approximately $730,000, before deducting placement agent fee and other estimated offering expenses payable by the Company. The net proceeds to the Company were approximately $630,000, and the 2013 Offering closed on February 4, 2013.

The common stock and warrants were sold in units consisting of one share of common stock and a warrant to purchase 0.40 shares of common stock. The purchase price for each unit was $4.43. The warrants were exercisable upon issuance, expire five years from the date of issuance, and have an exercise price of $4.13 per share, equal to the closing bid price of ARCA’s common stock on the Nasdaq Capital Market on January 31, 2013. The Offering was effected as a takedown off the Company’s S-3 Registration Statement, which became effective on April 4, 2011, pursuant to a prospectus supplement filed with the Securities and Exchange Commission on February 1, 2013. The warrant agreements provide for settlement of the warrants in unregistered shares should an effective registration statement or current prospectus not be in place at the time a warrant is exercised.

Warrants

As of December 31, 2012, warrants to purchase 930,725 shares of common stock were outstanding at exercise prices ranging from $1.80 to $116.89, with a weighted average exercise price per share of $9.10. These warrants, which were granted as part of various financing and business agreements, expire at various times between October 2013 and February 2019. Warrants were recorded in additional paid-in capital at their estimated fair market value at the date of grant using the Black-Scholes option-pricing model.