> If you edit a wiki you have to close that wiki,so others cannot change it.
> Can this 'closing' be made automatically? I mean the user who opened that wiki
> should be the only admin of the wiki(the only one who can edit it and change it).
Well, as far as I know, you can't do that with all your wiki pages; you can just with your user page.
An easy way would be (I guess) to request a coder to modify the user page system so that it allows to be used as the main page of a user structure, and thus, when a user creates new pages on that structure (using that wiki page header on pages belonging to a structure), permissions from the main page on that structure could be inherited.
Check with a coder, if you are interested, how difficult or long this could be, or even how much would it cost to you to have this done.
If new on tw community, I personally recommend you to get in contact with sylvie
Hope this helps
P.S: However, keep in mind that such a collaborative portal like tw is not intended to be set to individuals modifying their pages, but allowing others to collaborate (Wiki methodology of work....)