After this morning, I have one fewer PhD student than I had at the start of the day. Fortunately, that's because Chris Pardi passed his viva voce exam (the oral exam in which one defends ones PhD thesis) and is now Dr Pardi. Well, technically, I think he is not really Dr Pardi until he submits the hard copy to the University with the approval of the internal examiner who will check for the minor changes asked for, but still, the hurdle of the exam has been overcome. On the other hand, I don't think there's anything to stop anyone calling themselves "Doctor". Certainly no-one has ever asked me for proof.
The oral exam is a strange experience for a supervisor. At my university, PhD supervisors are allowed to be present in the exam, but can't really say anything. I sat there and observed two eminent professors - Jim Al-Khalili as the internal examiner, and Joachim Maruhn as external - quiz my student about his thesis, while I resisted the temptation to interject on his behalf. Fortunately, he'd done some very good work, with some impressive mathematical manipulations to calculate essentially analytic absorbing boundary conditions for solutions of the nuclear time-dependent Hartree-Fock equations, that the positive result was not much in doubt. The equation in the figure is one such result, looking notationally awesome as only continued fractions can do.