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Note 2 - Summary of Significant Accounting Policies - Fair Value Assumptions of Stock-based Compensation (Details)
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Expected dividend yield
Expected stock price volatility 109.00%
Weighted average volatility 96.00%
Risk-free interest rate 1.97%
Expected life of options (Year) 5 years
Forfeiture rate 5.00%