Net Cash Provided By (Used In) Operating Activities
For the nine months ended September 30, 2022, the $385 thousand of cash used in operating activities was attributable to net income of $260 thousand, adjusted for non-cash charges of $201 thousand, unrealized and realized gains on marketable securities of $562 thousand, and cash used in changes in operating assets and liabilities of $284 thousand.
Accounts receivable decreased from $1.1 million at December 31, 2021 to $958 thousand at September 30, 2022 due to improved collections and days-sales-outstanding for the third quarter of 2022 compared to the fourth quarter of 2021. Many of our customers pay promptly and accounts receivable is generally related to the most recent shipments. Inventories increased from $814 thousand at December 31, 2021 to $1.1 million at September 30, 2022. Inventory balances fluctuate depending on the timing of materials purchases and product shipments. Prepaid expenses and other current assets increased from $391 thousand at December 31, 2021 to $453 thousand at September 30, 2022. The balance of our prepaid expenses and other assets fluctuates with the timing of payments of insurance premiums, advances, and estimated income taxes. Accounts payable and accrued liabilities decreased from $845 thousand at December 31, 2021 to $692 thousand at September 30, 2022, primarily due to the timing of payment for purchases of materials, compensation accruals, and other outside services.
For the nine months ended September 30, 2021, the $639 thousand of cash provided by operating activities was attributable to net income of $243 thousand, adjusted for non-cash charges of $229 thousand, non-cash gain on forgiveness of PPP loan of $186 thousand, and cash provided by changes in operating assets and liabilities of $353 thousand.
Net Cash Used In Investing Activities
Net cash used in investing activities of $6.0 million for the nine months ended September 30, 2022 consisted of purchases of $6.0 million of marketable securities (net of sales) and $9 thousand of property, plant, and equipment. Net cash used in investing activities of $142 thousand for the nine months ended September 30, 2021 consisted of purchases of property, plant, and equipment.
Net Used In Financing Activities
Net cash used in financing activities of $300 thousand for the nine months ended September 30, 2022 consisted of payment of dividends on our Series A Convertible Preferred Stock. There was no cash provided by or used in financing activities during the nine months ended September 30, 2021.
Off-Balance Sheet Arrangements
We do not have any off-balance sheet arrangements.
Item 3. Quantitative and Qualitative Disclosures About Market Risk
Not Applicable.
Item 4. Controls and Procedures
Evaluation of Disclosure Controls and Procedures
The phrase “disclosure controls and procedures” refers to controls and procedures designed to ensure that information required to be disclosed in our reports filed or submitted under the Securities Exchange Act of 1934, as amended, or the Exchange Act, such as this Quarterly Report on Form 10-Q, is recorded, processed, summarized and reported within the time periods specified in the rules and forms of the U.S. Securities and Exchange Commission, or SEC. Disclosure controls and procedures are also designed to ensure that such information is accumulated and communicated to our management, including our chief executive officer, or CEO, and chief financial officer, or CFO, as appropriate to allow timely decision regarding required disclosure.
Our management, with the participation of our CEO and CFO, has evaluated the effectiveness of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act), as of September 30, 2022, the end of the period covered by this Quarterly Report on Form 10-Q. Based on such evaluation, our CEO and CFO had concluded that as of September 30, 2022, our disclosure controls and procedures were designed at a reasonable assurance level and were effective to provide reasonable