(Portland, OR)  --  Portland police say a man who's considered a "serial flasher" has exposed himself to more children, this time in the area of Northeast Alameda Street and Alameda Terrace.  The man reportedly yelled at three eleven-year-old children around 4:15 yesterday afternoon and exposed himself when they turned to look.  The man was then seen running east on Alameda Street.  Police say the man is suspected of exposing himself several times to other children and two female joggers in various Northeast Portland neighborhoods since last month.