Note 8. Warrant Liability

We use the Black-Scholes option pricing model to estimate fair value of warrants issued. In using this model, we make certain assumptions about risk-free interest rates, dividend yields, volatility and expected term of the warrants. Risk-free interest rates are derived from the yield on U.S. Treasury debt securities. Dividend yields are based on our historical dividend payments, which have been zero to date. Volatility is derived from the historical volatility of our common stock as traded on NASDAQ. The expected term of the warrants is based on the time to expiration of the warrants from the date of measurement. Share numbers and exercise prices have been adjusted for the 1-for-10 reverse stock split.

In November 2008, we sold 1,379,310 units to institutional investors at a price of $14.50 per unit, for gross proceeds of $20,000,000. The units, each of which consisted of one share of common stock and a warrant to purchase 0.75 shares of common stock at an exercise price of $23.00 per share, were offered as a registered direct offering under a shelf registration statement previously filed with, and declared effective by, the SEC. We received total proceeds, net of offering expenses and placement agency fees, of approximately $18,637,000. We recorded the fair value of the warrants to purchase 1,034,483 shares of our common stock as a liability. The fair value of the warrant liability will be revalued at the end of each reporting period, with the change in fair value of the warrant liability recorded as a gain or loss in our condensed consolidated statements of operations. The fair value of the warrants will continue to be classified as a liability until such time as the warrants are exercised, expire or an amendment of the warrant agreement renders these warrants to be no longer classified as a liability.

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


	To Calculate
	Fair Value of Warrant
	Liability at
	June 30, 2011			December 31, 2010
Expected life (years)		2.9			3.4
Risk-free interest rate		0.9	%		1.2	%
Expected volatility		84.1	%		83.6	%
Expected dividend yield		0	%		0	%


	At June 30,		At December 31,		Change in Fair Value
	2011		2010		of Warrant Liability
Fair value of warrant liability	$	1,115,586	$	4,408,449	$	(3,292,863	)

In November 2009, we sold 1,000,000 units to institutional investors at a price of $12.50 per unit, for gross proceeds of $12,500,000. The units, each of which consisted of one share of common stock and a warrant to purchase 0.40 shares of common stock at an exercise price of $15.00 per share, were offered as a registered direct offering under a shelf registration statement previously filed with, and declared effective by, the SEC. We received total proceeds, net of offering expenses and placement agency fees, of approximately $11,985,000. We recorded the fair value of the warrants to purchase 400,000 shares of our common stock as a liability. The fair value of the warrant liability will be revalued at the end of each reporting period, with the change in fair value of the warrant liability recorded as a gain or loss in our condensed consolidated statements of operations. The fair value of the warrants will continue to be classified as a liability until such time as the warrants are exercised, expire or an amendment of the warrant agreement renders these warrants to be no longer classified as a liability.

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


	To Calculate
	Fair Value of Warrant Liability at
	June 30,			December 31,
	2011			2010
Expected life (years)		3.8			4.3
Risk-free interest rate		1.3	%		1.6	%
Expected volatility		80.9	%		77.5	%
Expected dividend yield		0	%		0	%


	At June 30,		At December 31,		Change in Fair Value
	2011		2010		of Warrant Liability
Fair value of warrant liability	$	753,160	$	2,263,480	$	(1,510,320	)