"PhD diss." se refiere a una tesis doctoral (es decir, el trabajo final de un programa de doctorado), pero no sé si hay alguna forma especial para escribir esto en castellano.
We use the words differently on each side of the pond so there is a lot of confusion. UK: PhD ... Thesis ... a long detailed original work. MSc ... Dissertation ....a short report on a reasearch project US: PhD ... Dissertation ... a long detailed original work. MSc ... Thesis... a short report on a reasearch project
So if SimaQian's dissertation is for a PhD it is American and the same as what we would call a thesis in the UK.