CUSIP NO. 019777101             Schedule 13G                       Page 26 of 26


                                                                       EXHIBIT 3
                                                                       ---------



                                POWER OF ATTORNEY

KNOW ALL BY THESE PRESENTS, that I, FRANK H. PEARL, hereby make, constitute and
appoint RODD MACKLIN as my agent and attorney-in-fact for the purpose of
executing in my name, (a) in my personal capacity or (b) in my capacity as
Chairman of, member of or in other capacities with Perseus LLC ("Perseus") and
each of its affiliates or entities advised by me or Perseus, all documents,
certificates, instruments, statements, filings and agreements ("documents") to
be filed with or delivered to any foreign or domestic governmental or regulatory
body or required or requested by any other person or entity pursuant to any
legal or regulatory requirement relating to the acquisition, ownership,
management or disposition of securities, futures contracts, or other
investments, and any other documents relating or ancillary thereto, including
but not limited to, all documents relating to filings with the Commodities
Futures Trading Commission and National Futures Association, the United States
Securities and Exchange Commission (the "SEC") pursuant to the Commodities
Exchange Act and the Securities Act of 1933 or the Securities Exchange Act of
1934 (the "Act") and the rules and regulations promulgated thereunder, including
all documents relating to the beneficial ownership of securities required to be
filed with the SEC pursuant to Section 13(d) or Section 16(a) of the Act and
information statements on Form 13F required to be filed with the SEC pursuant to
Section 13(f) of the Act.

All past acts of the attorney-in-fact in furtherance of the foregoing are hereby
ratified and confirmed.

This power of attorney shall be valid from the date hereof until revoked by me.

IN WITNESS WHEREOF, I have executed this instrument as of the 9th day of April,
2003.

                                    /s/ Frank H. Pearl
                                    -------------------------------------------
                                    FRANK H. PEARL