	Year Ended December 31,
	2019		2018
Current taxes:
Federal	$	-	$	-
State and local		16		13
Foreign		-		-
Current taxes		16		13
Deferred taxes:
Federal		-		-
State and local		-		-
Foreign		-		-
Deferred taxes		-		-
Total	$	16	$	13

Net deferred tax assets and liabilities consisted of the following (in thousands):

	December 31,
	2019			2018
Net operating loss carryforwards	$	18,677		$	17,443
Research and development credit carryforwards		3,576			3,337
Share-based compensation		645			1,006
Accrued expenses and reserves		127			47
Depreciation and amortization		17			48
Deferred revenue		275			(63	)
Other		14			19
Gross deferred tax assets		23,331			21,837
Less: valuation allowance		(23,324	)		(21,830	)
Net deferred tax assets	$	7		$	7

Net deferred tax assets and liabilities were recorded as follows (in thousands):

As of December 31, 2019, our deferred tax assets were primarily the result of U.S. net operating loss, research and development credit carryforwards and share-based compensation expense. We have applied a full valuation allowance against the U.S. deferred tax assets in the U.S. and foreign jurisdictions.

We use judgment as to the appropriate weighting of all available evidence when assessing the need for the establishment or the release of valuation allowances. As part of this analysis, we examine all available evidence on a jurisdiction-by-jurisdiction basis and weigh the positive and negative information when determining the need for full or partial valuation allowances. The evidence considered for each jurisdiction includes, among other items, (i) the historical levels of income or loss over a range of time periods that extends beyond the two years presented, (ii) the historical sources of income and losses, (iii) the expectations and risk associated with underlying estimates of future taxable income, (iv) the expectations and risk associated with new product offerings and uncertainties with the timing of future taxable income, and (v) prudent and feasible tax planning strategies. Based on the analysis conducted as of December 31, 2019, we determined that we would not release, in full or in part, the valuation allowance against our U.S. gross deferred tax assets.

The provision for income taxes differed from the amount of expected income tax expense determined by applying the applicable U.S. statutory federal income tax rate to pre-tax loss as follows (in thousands, except percentages):

	Year Ended December 31,
	2019					2018
U.S. Federal tax benefit at statutory rates	$	(1,925	)	21.0	%	$	(2,889	)	21.0	%
Impact of:
Tax credits		(715	)	7.8			(517	)	3.8
State income tax		(108	)	1.2			10		(0.1	)
International operations		409		(4.5	)		30		(0.2	)
Share-based compensation		348		(3.8	)		2		-
Valuation allowance		1,471		(16.0	)		2,280		(16.6	)
Expiration of tax attributes		475		(5.2	)		217		(1.6	)
Goodwill impairment		-		-			784		(5.7	)
Other, net		61		(0.7	)		96		(0.7	)
Tax expense and effective tax rate	$	16		(0.2	)%	$	13		(0.1	)%

At December 31, 2019, we had approximately $79.7 million of federal and $12.4 million of state net operating loss carryforwards, which have begun to expire. Of the federal net operating loss carryforwards, approximately $45.7 million will expire by 2024 and $17.0 million are indefinite. We also have approximately $3.6 million of tax credit carryforwards, which have begun to expire. Use of these carryforwards may subject us to an annual limitation due to Section 382 of the U.S. Internal Revenue Code that restricts the ability of a corporation that undergoes an ownership change to use its carryforwards. Under the applicable tax rules, an ownership change occurs if holders of more than five percent of an issuer’s outstanding common stock, collectively, increase their ownership percentage by more than 50 percentage points over a rolling three-year period. We have performed analyses of possible ownership changes in the past, which included consideration of third-party studies, and do not believe that an ownership change of more than 50 percentage points has occurred.

We have evaluated all the material income tax positions taken on our income tax filings to various tax authorities, and we determined that we did not have unrealized tax benefits related to uncertain tax positions recorded at December 31, 2019 or 2018.

Because of net operating loss and tax credit carryforwards, substantially all of our tax years remain open and subject to examination.