6. Warrant Liabilities

Liabilities measured at market value on a recurring basis include warrant liabilities resulting from the Company's past equity financings. In accordance with ASC 815-40, Derivatives and Hedging – Contracts in Entity's Own Equity ("ASC 815-40"), the warrant liabilities are being marked to market until they are completely settled. The warrants are valued using the Black-Scholes method, using assumptions consistent with the Company's application of ASC 505-50, Equity-Based Payments to Non-Employees ("ASC 505-50"). The gain or loss resulting from the marked to market calculation is shown on the Condensed Statements of Operations as gain (loss) on warrant derivative liability. The Company recognized a loss of $1.9 million and a gain of $14.7 million for the three-month periods ended March 31, 2015 and 2014, respectively. The following reflects the weighted-average assumptions for each of the three-month periods indicated:

	Three Months Ended March 31,
	2015			2014

Risk-free interest rate		0.41	%		0.63	%
Expected dividend yield		0	%		0	%
Expected lives		1.34			2.21
Expected volatility		92.4	%		85.7	%
Warrants classified as liabilities (in shares)		6,371,854			6,984,716
Gain (loss) on warrant liability	$	(1,871,294	)	$	14,702,904

The Company's computation of expected volatility is based on the historical daily volatility of its publicly traded stock. The dividend yield assumption of zero is based upon the fact that the Company has never paid cash dividends and presently has no intention to do so. The risk-free interest rate used for each warrant classified as a derivative is equal to the U.S. Treasury rates in effect at March 31 of each year presented. The expected lives are based on the remaining contractual lives of the related warrants at the valuation date.