As David Sibelius boils the lobsters for the annual dinner he hosts for his graduate students at the Boston Institute of Technology, his 12-year-old daughter, Ada, observes him with a sense of foreboding. "She could not articulate what was different in his demeanor, but it triggered a deep-seated uneasiness in her," writes Liz Moore in her enthralling new novel, "The Unseen World." Ada will soon learn that her brilliant, enigmatic computer-scientist father is in the early stages of Alzheimer's disease.