Considering the properties of linearity, time-invariance, causality, and stability allows us to obtain useful models for actual devices.
Lewens first turns his attention to what science is and what it tells us: does it describe the world as it really is, or does it merely provide useful models to help us to manipulate it?
Useful models may be found quite outside the genre.
But there are useful models New York City can emulate.
There was no history for Hitler: only a timeless pattern of Jewish deception and the useful models of British and American imperialism.
International experience offers useful models too, for example, the Choosing Health-Plans All Together (Chat) model for involving the public in healthcare priority setting.
(Basic lanterns cost as little $5, but hardy and more useful models can cost as much as $80).
Some Burmese people, meanwhile, pointed out that they could do without Singapore's political repression and censorship, though the country's city-planning methods and financial systems could serve as useful models.
Many of the pathways from gene to disease in humans can be easily reproduced in flies, or are similar enough to be incredibly useful models for understanding how diseases evolve.
Dr. Watts says he hopes that by deriving search algorithms from decentralized human networks that function smoothly, his team will be able to create useful models for solving the problems of congested computer networks.
According to Dr. Henry Abraham, a lecturer in psychiatry at Tufts University School of Medicine who privately sees patients with substance-related disorders, neurophysiological shifts observed in H.P.P.D. patients "may yield useful models for anxiety, depression, psychosis, and even addiction".
