It’s 11 pm and you are in desperate need of reference help from a librarian. You check the library’s website and see that the Science Libraries IM service (screenname: ucbscilibs) isn’t available, and the library’s not open. Your question is un-Google-able. Wikipedia has failed you. Despair not!
Get help 24 hours a day, 7 days a week from a real live librarian* through the new Ask a Librarian service. Ask a Librarian is a chat reference service that connects you to a librarian and emails you a transcript of your chat so you can reference it later. Try it out at Ask a Librarian.
*Please note that the librarian you will be connected with may be a Berkeley librarian, a librarian from another UC, or a librarian from another University.