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FAIR VALUE MEASUREMENTS
9 Months Ended
Sep. 30, 2011
Notes to Financial Statements [Abstract] 
FAIR VALUE MEASUREMENTS
4.
FAIR VALUE MEASUREMENTS

The following table provides the assets and liabilities carried at fair value measured on a recurring basis as of September 30, 2011:

      
Fair Value Measurements, Using
 
   
Total carrying
value as of
September 30, 2011
  
Quoted prices
 in active markets
(Level 1)
  
Significant other observable inputs
(Level 2)
  
Significant unobservable inputs
(Level 3)
 
Cash equivalents
 $44,730,776  $44,730,776  $-  $- 
Short-term investments
  270,829,172   270,829,172   -   - 

The following table provides the assets and liabilities carried at fair value measured on a recurring basis as of December 31, 2010:

      
Fair Value Measurements, Using
 
   
Total carrying
 value as of December 31, 2010
  
Quoted prices in active markets 
(Level 1)
  
Significant other observable inputs
(Level 2)
  
Significant unobservable inputs
(Level 3)
 
Cash equivalents
 $8,234,698  $8,234,698  $-  $- 
Short-term investments
  52,794,545   52,794,545   -   - 
Stock warrant liability
  10,659,755   -   -   10,659,755 

Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument. Level 3 inputs are unobservable inputs based on management's own assumptions used to measure assets and liabilities at fair value. A financial asset or liability's classification is determined based on the lowest level input that is significant to the fair value measurement.

The following table is a reconciliation of the changes in fair value of the Company's stock warrant liability for the three months ended September 30, 2011 and 2010 which had been classified in Level 3 in the fair value hierarchy:

   
2011
  
2010
 
Fair value of stock warrant liability, beginning of period
 $4,588,178  $5,589,350 
(Gain) loss for period
  (239,562)  3,362,441 
Warrants exercised
  (4,348,616)  - 
Fair value of stock warrant liability, end of period
 $-  $8,951,791 

The following table is a reconciliation of the changes in fair value of the Company's stock warrant liability for the nine months ended September 30, 2011 and 2010 which has been classified in Level 3 in the fair value hierarchy:

   
2011
  
2010
 
Fair value of stock warrant liability, beginning of period
 $10,659,755  $3,720,165 
Loss for period
  4,190,283   5,231,626 
Warrants exercised
  (14,850,038)  - 
Fair value of stock warrant liability, end of period
 $-  $8,951,791 
 
The fair value of the stock warrant liability was determined using the Black-Scholes option pricing model with the following inputs at September 30, 2010:

   
2010
 
Contractual life (years)
  0.9 
Expected volatility
  54.6%
Risk-free interest rate
  0.2%
Annual dividend yield
  -