wow! I went to google & typed in "Private_strands 7 at log switch" & it came up with 26 hits, some of which were in Chinese so they could be ignored, which left about 6 hits; it didn't take much time to find that this was probably the most useful of them:

http://www.lazydba.com/oracle/0__117417.html

You should try using Google! It's incredible what information you can find!