Here are some links for LDA that you may find useful. 

These are slides presented by Professor David Blei.  mlss09uk_blei_tm.pdf   His talk was video-taped and is available.  Here's a link.  This is an excellent lecture and I recommend it highly.  I'll be using Prof Blei's slides.  http://videolectures.net/mlss09uk_blei_tm/

Here are several other sources that flesh out various aspects of topic modeling. 

asuncion10.1.1.157.6861.pdf

Blei2011.pdf

BleiLafferty2009.pdf

We'll talk about Dirichlet distribution (which is used as one of the distributions in LDA),  The wikipedia page for Dirichlet distribution is very informative.  http://en.wikipedia.org/wiki/Dirichlet_distribution  Here's a paper that goes different aspects of the distribution.  minka-dirichletEst.pdf