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Redeemable Common Stock and Stock Purchase Warrant (Tables)
9 Months Ended
Jan. 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:

 

    January 31,     April 30,  
    2013     2012  
                 
Risk-free interest rates     0.46% - 0.88%       0.6%  
Volatility     84.9% - 102%       102%  
Dividend yield     0%       0%