Quarterly report pursuant to Section 13 or 15(d)

Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details)

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Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details) - Stock Purchase Warrants [Member]
6 Months Ended
Jun. 30, 2019
$ / shares
shares
Upper range of exercise prices (in dollars per share)
Number of warrants outstanding (in shares) | shares 360,175
Range One [Member]  
Lower exercise price range (in dollars per share) $ 6
Upper range of exercise prices (in dollars per share) $ 18
Number of warrants outstanding (in shares) | shares 333,136
Range One [Member] | Minimum [Member]  
Expiration dates May 2021
Range One [Member] | Maximum [Member]  
Expiration dates August 2024
Range Two [Member]  
Lower exercise price range (in dollars per share) $ 22
Upper range of exercise prices (in dollars per share) $ 116
Number of warrants outstanding (in shares) | shares 1,731
Range Two [Member] | Minimum [Member]  
Expiration dates May 2021
Range Two [Member] | Maximum [Member]  
Expiration dates May 2023
Range Three [Member]  
Lower exercise price range (in dollars per share) $ 257
Upper range of exercise prices (in dollars per share) $ 257
Number of warrants outstanding (in shares) | shares 1,965
Expiration dates January 2022
Range Four [Member]  
Lower exercise price range (in dollars per share) $ 325
Upper range of exercise prices (in dollars per share) $ 325
Number of warrants outstanding (in shares) | shares 8,727
Expiration dates March 2020
Range Five [Member]  
Lower exercise price range (in dollars per share) $ 442
Upper range of exercise prices (in dollars per share) $ 557
Number of warrants outstanding (in shares) | shares 2,212
Range Five [Member] | Minimum [Member]  
Expiration dates December 2019
Range Five [Member] | Maximum [Member]  
Expiration dates January 2021
Range Six [Member]  
Lower exercise price range (in dollars per share) $ 691
Upper range of exercise prices (in dollars per share) $ 783
Number of warrants outstanding (in shares) | shares 11,827
Range Six [Member] | Minimum [Member]  
Expiration dates October 2019
Range Six [Member] | Maximum [Member]  
Expiration dates October 2021
Range Seven [Member]  
Lower exercise price range (in dollars per share) $ 1,043
Upper range of exercise prices (in dollars per share) $ 1,043
Number of warrants outstanding (in shares) | shares 577
Expiration dates July 2019