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Note 8 - Stockholders' Equity (Tables)
6 Months Ended
Jun. 30, 2019
Notes Tables  
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]
   
Warrant shares outstanding
   
Weighted Average exercise price
   
Weighted Average remaining life
   
Intrinsic value
 
Outstanding at January 1, 2019
   
1,592,775
    $
2.55
    $
0.48
     
-
 
Issued
   
1,749,171
    $
0.50
    $
4.60
     
-
 
Exercised
   
-
     
-
     
-
     
-
 
Expired or cancelled
   
-
     
-
     
-
     
-
 
Outstanding and exercisable at June 30, 2019    
3,341,946
    $
1.48
    $
2.60
     
-
 
Schedule of Warrant or Right Outstanding, Valuation Assumptions [Table Text Block]
   
2016 Warrants
   
2019 Warrants
 
Expected Term
 
0.4 years
   
5 years
 
Volatility
   
100
%    
85
%
Dividend yield
   
0.00
%    
0.00
%
Exercise Price
  $
2.55
    $
0.50
 
Risk-free interest rate
   
2.09
%    
2.50
%
Weighted average fair value of warrants granted
   
-
    $
0.22
 
Number of shares underlying warrants granted
   
201,044
     
1,749,171
 
Warrant Liabilities [Member]  
Notes Tables  
Schedule of Warrant or Right Outstanding, Valuation Assumptions [Table Text Block]
   
2016 Warrants
   
2019 Warrants
 
Expected Term
 
0.4 years
   
4.6 years
 
Volatility
   
100
%    
84
%
Dividend yield
   
0.00
%    
0.00
%
Exercise Price
  $
2.55
    $
0.50
 
Risk-free interest rate
   
2.09
%    
1.76
%
Weighted average fair value of warrants granted
  $
-
    $
0.21