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Warrant Liability (Tables)

3 Months Ended

Mar. 31, 2013

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Assumptions used for simulation model

The assumptions used for the Monte Carlo simulation model to value the Series A Warrants at March 31, 2013 are as follows:


Risk-free interest rate per year			0.5	%
Expected volatility per year			81.6	%
Expected dividend yield			0	%
Expected life in years			3.7

Summary of changes in fair value of warrant liability

The following table is a summary of the changes in fair value of warrant liability for the Series A Warrants for the three-month period ended March 31, 2013:


		Series A
		Number of Warrants				Fair value $
Balance at December 31, 2012			8,501,429			$	9,157,397
Less exercised			(334,534	)			(418,841	)
Changes in fair value			—				213,503

Balance at March 31, 2013			8,166,895			$	8,952,059

Summary of outstanding warrants and fair value of warrant liability

The following table is a summary of our outstanding warrants and fair value of our warrant liability as of March 31, 2013:


Warrants		Number Outstanding				Exercise Price ($) per share				Fair value
Warrants issued in 2008			1,034,483				23.00			$	14,752
Warrants issued in 2009			400,000				15.00				68,320
Series A Warrants			8,166,895				1.40				8,952,059

Total			9,601,378							$	9,035,131

Warrant agreement 2008 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Assumptions used for Black-Scholes option pricing model

The assumptions used for the Black-Scholes option pricing model are as follows:


		To Calculate Fair Value of Warrant Liability at
		March 31, 2013				December 31, 2012
Expected life (years)			1.1				1.4
Risk-free interest rate			0.2	%			0.2	%
Expected volatility			100.1	%			108.2	%
Expected dividend yield			0	%			0	%


		At March 31, 2013				At December 31, 2012				Change in Fair Value of Warrant Liability
Fair value of liability for warrants issued in 2008		$	14,752			$	44,628			$	(29,876	)

Warrant agreement 2009 [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Assumptions used for Black-Scholes option pricing model

The assumptions used for the Black-Scholes option pricing model are as follows:


		To Calculate Fair Value of Warrant Liability at
		March 31, 2013				December 31, 2012
Expected life (years)			2.1				2.3
Risk-free interest rate			0.3	%			0.3	%
Expected volatility			98.6	%			94.5	%
Expected dividend yield			0	%			0	%


		At March 31, 2013				At December 31, 2012				Change in Fair Value of Warrant Liability
Fair value of liability for warrants issued in 2009		$	68,320			$	63,340			$	4,980