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Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2012

Accounting Policies [Abstract]

Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect

The following table summarizes potential common shares that were excluded from diluted net loss per share calculation because of their anti-dilutive effect:

	Year Ended December 31,
Common Stock Equivalents	2012			2011			2010
Options to purchase common stock	16,257,444			14,302,803			12,649,968
Warrants to purchase common stock	21,593,844			21,743,844			7,771,133
Convertible preferred stock	38,233			38,233			38,233
Total	37,889,521			36,084,880			20,459,334

Summary of assumptions used to estimate the fair value of stock options

Weighted average assumptions used in the Black-Scholes model for employees and directors are presented below:

	Year Ended December 31,
	2012		2011		2010
Risk-free interest rate	0.36%		1.23%		1.09% – 2.65%
Expected volatility	131%		134%		134%
Expected life in years	4		4		4
Dividend yield	—		—		—
Forfeiture rate	8%		11%		11%

Assumptions used in the Black-Scholes model for non-employees are presented below:

	Year Ended December 31,
	2012		2011		2010
Risk-free interest rate	0.67% – 0.83%		0.91% – 3.47%		1.89% – 3.84%
Expected volatility	103%-117%		96%-119%		71%-120%
Expected life in years	7-10		6-10		7-10
Dividend yield	—		—		—

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- Definition

Tabular disclosure of securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented, by antidilutive securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 40

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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