Researchers at Georgia Tech are currently focusing on using gait recognition to identify people. What is useful about this is that people do not need to be enrolled in a database in order to recognize them.
Essentially, this paper goes through the types of gait recognition software that currently exist as well as the reliability of this software. There are a lot of different elements that influence a persons gait (like terrain, shoes, fatigue, etc.), which effects how well the software works. It's a pretty heavy read but it's really interesting if you want to just jump to a certain section and read in depth. This technology is very much out there and in development, and it is definitely being improved upon.
Also, even though this paper is a little bit older, it is still being cited in a lot of more recent research papers and I thought it would give a good enough grasp on the science for our purposes.
Study discussing the function and practicality of gait recognition software. The results seem to follow what Doctorow states about the function of the software in his novel
Interesting how this article talks about the gait analysis being used for catching terrorists, while in Little Brother, it was used to keep track of the high school students. The technology is not quite ready to be used, but seems to be much more reliable than the gait trackers in the book.
Georgia Tech Research Institute is making gait recognition technology a reality. "The ultimate goal is to detect, classify and identify humans at distances up to 500 feet away under day or night, all-weather conditions. Such capabilities will enhance the protection of U.S. forces and facilities from terrorist attacks."
Bernoulli numbers are a sequence of numbers important to the field of number theory, trigonometric expansions, and analysis. Ada Lovelace wrote a theoretical program to calculate these that would work on Charles Babbage's unfinished Analytical Engine. It's pretty interesting how Lovelace was a "leading figure" in the now massively male-dominated computer programming field, but didn't receive recognition for her work until fairly recently.