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Note 3 - Fair Value Measurements (Tables) | 6 Months Ended
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Jun. 30, 2024
Notes Tables |
Fair Value, Assets Measured on Recurring Basis [Table Text Block] |
|  |  |  |  |  | Fair Value Measurements Using |
|  |  |  |  |  | Quoted |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Prices in |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Active |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Markets |  |  | Significant |  |  |  |  |
|  |  |  |  |  | for |  |  | Other |  |  | Significant |
|  | Balance at |  |  | Identical |  |  | Observable |  |  | Unobservable |
|  | June |  |  | Items |  |  | Inputs |  |  | Inputs |
|  | 30, 2024 |  |  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |
Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted cash held as a certificate of deposit |  | $ | 476 |  |  | $ | 476 |  |  | $ | — |  |  | $ | — |
|  |  |  |  |  | Fair Value Measurements Using |
|  |  |  |  |  | Quoted |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Prices in |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Active |  |  |  |  |  |  |  |  |
|  |  |  |  |  | Markets |  |  | Significant |  |  |  |  |
|  |  |  |  |  | for |  |  | Other |  |  | Significant |
|  | Balance at |  |  | Identical |  |  | Observable |  |  | Unobservable |
|  | December |  |  | Items |  |  | Inputs |  |  | Inputs |
|  | 31, 2023 |  |  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |
Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restricted cash held as a certificate of deposit |  | $ | 476 |  |  | $ | 476 |  |  | $ | — |  |  | $ | — |
Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant liabilities |  | $ | 334 |  |  | $ | — |  |  | $ | 334 |  |  | $ | — |
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] |
|  | May 2023 Warrants |  |  | May 2023 Warrants |  |  | December 2023 Warrants |  |  | December 2023 Warrants |
Measurement event |  | Issuance |  |  | Stockholder Approval |  |  | Reporting Date |  |  | Stockholder Approval |
Date |  | May 1, 2023 |  |  | June 9, 2023 |  |  | December 31, 2023 |  |  | May 28, 2024 |
Total Value |  | $1.6 million |  |  | $1.4 million |  |  | $0.3 million |  |  | $0.2 million |
Gain (Loss) |  | not applicable |  |  | $0.2 million |  |  | $56 thousand |  |  | $(51 thousand) |
Assumptions: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price |  | $ | 45.50 |  |  | $ | 45.50 |  |  | $ | 8.75 |  |  | $ | 8.75 |
Market price |  | $ | 25.20 | (a) |  | $ | 23.80 |  |  | $ | 7.14 |  |  | $ | 4.94 |
Volatility |  |  | 80.1 | % |  |  | 77.6 | % |  |  | 79.3 | % |  |  | 83.9 | %
Risk-free rate |  |  | 3.60 | - | 4.04 | % |  |  | 3.92 | - | 4.59 | % |  |  | 3.85 | % |  |  | 4.56 | %
Dividend yield |  |  | 0.0 | % |  |  | 0 | % |  |  | 0 | % |  |  | 0 | %
Term (years) |  |  | 2.1 | - | 5.1 | % |  |  | 2.0 | - | 5.0 |  |  |  | 5.5 |  |  |  | 5.1 |
|  | March |  |  | March |
|  | 2024 |  |  | 2024 |
|  | Warrant |  |  | Warrant |
Measurement event |  | Reporting Date |  |  | Stockholder Approval |
Date |  | March 31, 2024 |  |  | May 28, 2024 |
Total Value |  | $0.1 million |  |  | $0.1 million |
Gain (Loss) |  | $21 thousand |  |  | $(28 thousand) |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 4.90 |  |  | $ | 4.90 |
Market price |  | $ | 3.66 |  |  | $ | 4.94 |
Volatility |  |  | 86.9 | % |  |  | 83.9 | %
Risk-free rate |  |  | 4.21 | % |  |  | 4.56 | %
Dividend yield |  |  | 0 | % |  |  | 0 | %
Term (years) |  |  | 5.5 |  |  |  | 5.3 |
|  | July 2020, November 2021, September 2022 & November 2022 Warrants |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | April 27, 2023 |  |  | April 27, 2023 |
Total Value |  | $0.3 million |  |  | $0.5 million |
Loss |  | not applicable |  |  | $0.2 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 220.50 |  |  | $ | 52.50 |
Market price |  | $ | 25.20 | (a) |  | $ | 25.20 | (a)
Volatility |  |  | 80.1 | % |  |  | 80.1 | %
Risk-free rate |  |  | 3.59 | - | 4.73 | % |  |  | 3.59 | - | 4.73 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 1.1 | - | 5.6 |  |  |  | 1.1 | - | 5.6 |
|  | May 2023 Warrants |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | December 21, 2023 |  |  | December 21, 2023 |
Total Value |  | $56 thousand |  |  | $0.2 million |
Loss |  | not applicable |  |  | $0.1 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 45.50 |  |  | $ | 8.75 |
Market price |  | $ | 8.07 |  |  | $ | 8.07 |
Volatility |  |  | 79.3 | % |  |  | 79.3 | %
Risk-free rate |  |  | 3.92 | - | 4.62 | % |  |  | 3.92 | - | 4.62 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 1.5 | - | 4.5 |  |  |  | 1.5 | - | 4.5 |
|  | September 2022, November 2022, & May 2023 Warrants |
Measurement event |  | Prior to amendment |  |  | After amendment |
Date |  | June 14, 2024 |  |  | June 14, 2024 |
Total Value |  | $66 thousand |  |  | $0.1 million |
Loss |  | not applicable |  |  | $70 thousand |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 8.75 | - | 52.50 |  |  | $ | 2.50 |
Market price |  | $ | 2.51 |  |  | $ | 2.51 |
Volatility |  |  | 89.3 | % |  |  | 89.3 | %
Risk-free rate |  |  | 4.27 | - | 5.08 | % |  |  | 4.27 | - | 5.08 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 1.0-4.4 |  |  |  | 1.0 | - | 4.4 |
|  | Series B & C Preferred Stock |
Measurement event |  | Prior to Ratchet |  |  | After Ratchet |
Date |  | April 27, 2023 |  |  | April 27, 2023 |
Total value (b) |  | $9.6 million |  |  | $11.6 million |
Deemed dividend |  | not applicable |  |  | $2.0 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 220.50 |  |  | $ | 45.50 |
Market price |  | $ | 25.20 | (a) |  | $ | 25.20 | (a)
Volatility |  |  | 80.1 | % |  |  | 80.1 | %
Risk-free rate |  |  | 4.91 | % |  |  | 4.91 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (in years) |  |  | 0.8 |  |  |  | 0.8 |
|  | Series B & C Preferred Stock |
Measurement event |  | Prior to Ratchet |  |  | After Ratchet |
Date |  | December 21, 2023 |  |  | December 21, 2023 |
Total value (b) |  | $1.7 million |  |  | $6.8 million |
Deemed dividend |  | not applicable |  |  | $5.1 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 45.50 |  |  | $ | 8.75 |
Market price |  | $ | 8.07 |  |  | $ | 8.07 |
Volatility |  |  | 79.3 | % |  |  | 79.3 | %
Risk-free rate |  |  | 5.43 | % |  |  | 5.43 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 0.3 |  |  |  | 0.3 |
|  | Series C Preferred Stock |
Measurement event |  | Prior to Ratchet |  |  | After Ratchet |
Date |  | March 24, 2024 |  |  | March 24, 2024 |
Total value (b) |  | $0.5 million |  |  | $0.9 million |
Deemed dividend |  | not applicable |  |  | $0.4 million |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 8.75 |  |  | $ | 4.90 |
Market price |  | $ | 4.77 |  |  | $ | 4.77 |
Volatility |  |  | 79.9 | % |  |  | 79.9 | %
Risk-free rate |  |  | 5.51 | % |  |  | 5.51 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (in years) |  |  | 0.1 |  |  |  | 0.1 |
|  | Unsecured Convertible Notes derivative |  |  | Unsecured Convertible Notes derivative |
Measurement event |  | Issuance |  |  | Shareholder Approval |
Date |  | March 25, 2024 |  |  | May 28, 2024 |
Total value |  | $0.2 million |  |  | $0.2 million |
Gain (Loss) |  | not applicable |  |  | $(82 thousand) |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 4.90 |  |  | $ | 4.90 |
Market price |  | $ | 4.51 |  |  | $ | 4.94 |
Volatility |  |  | 86.9 | % |  |  | 83.9 | %
Risk-free rate |  |  | 4.54 | % |  |  | 4.94 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 2.0 |  |  |  | 1.8 |
|  | Secured Convertible Notes derivative |  |  | Secured Convertible Notes derivative |
Measurement event |  | Issuance |  |  | Shareholder Approval |
Date |  | April 27, 2023 |  |  | June 9, 2023 |
Total value (b) |  | $0.2 million |  |  | $0.2 million |
Gain |  | not applicable |  |  | $40 thousand |
Assumptions: |  |  |  |  |  |  |  |
Exercise price |  | $ | 45.50 |  |  | $ | 45.50 |
Market price |  | $ | 25.20 | (a) |  | $ | 23.80 |
Volatility |  |  | 80.1 | % |  |  | 76.9 | %
Risk-free rate |  |  | 4.88 | % |  |  | 5.41 | %
Dividend yield |  |  | 0.0 | % |  |  | 0.0 | %
Term (years) |  |  | 0.8 |  |  |  | 0.7 |

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- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 103 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-103 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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