(covers information from several alternate timelines)
A dissertation was a written composition which documented research about a subject and findings resulting from that research. It was presented during a candidacy for an academic degree or other professional citation.
In the alternate reality, Christopher Pike was assigned the task of writing a dissertation about the events leading to the destruction of the USS Kelvin in 2233, as well as the actions of its commanding officer at the time, George Kirk. He mentioned this to Kirk's son James when encouraging him to enlist in Starfleet. (Star Trek)
In 2369, Captain Jean-Luc Picard attended a physiognomy workshop during a psychological conference presented by Dr. Vassbinder. Vassbinder, who was not aware that the topic of the workshop was psychology, instead gave a hypnotic hour-long dissertation on the ionization effect on warp nacelles. Vassbinder's talking style prevented the attendees from alerting him to his mistake. (TNG: "Timescape")