Problems with 7.29 update

Hello
I have just updated to Drupal 7.30 and the site seems faster than 7.29.
I note that there are now 16 files I cannot explain in public_html directory
Names like core.338850, they are unreadable files.

What are these, what do they mean, can they be deleted, each is 16.5mb 
and a new one arrives when Drupal fails which it has done many times in 
3 hours this evening.
It takes 2 minutes to open views, 50 seconds to save a change. Cannot 
open modules list I get WSOD
Drush from a terminal displays a huge list of stuff I do not understand.

Help gratefully appreciated
Roger
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