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Redeemable Common Stock and Stock Purchase Warrants (Details)	3 Months Ended
	Jul. 31, 2011	Jul. 31, 2012 Warrant [Member]	Apr. 30, 2012 Warrant [Member]
Expected term in years	6 years	3 years 8 months 12 days	3 years 10 months 24 days
Risk-free interest rates		0.40%	0.60%
Volatility		94.00%	102.00%
Dividend yield	0.00%	0.00%	0.00%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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