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Redeemable Common Stock and Stock Purchase Warrants (Tables)
3 Months Ended
Jul. 31, 2013
Redeemable Common Stock and Stock Purchase Warrant [Abstract]  
Schedule of Share-based Payment Award Stock Warrants Valuation Assumptions [Table Text Block]
Assumptions used to calculate the fair value of these warrants were as follows:
 
 
 
July 31,
 
April 30,
 
 
 
2013
 
2013
 
 
 
 
 
 
 
 
 
Expected term in years
 
 
2.7 & 4.5
 
 
2.9 & 4.7
 
Risk-free interest rates
 
 
0.5% & 1.18%
 
 
0.3%
 
Volatility
 
 
89% & 102%
 
 
95% & 98%
 
Dividend yield
 
 
0%
 
 
0%