Colonies of ants base decisions like where to establish a nest based on their population density. Scientists theorize that ants can estimate how many of their kind are around by randomly exploring the area and bumping into other ants. New research from MIT computer scientists not only supports this theory but could also be used to analyze social networks, improve robot swarms, and yield improve algorithms for networked communications in distributed computing applications. From MIT News:
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“It’s intuitive that if a bunch of people are randomly walking around an area, the number of times they bump into each other will be a surrogate of the population density,” says Cameron Musco, an MIT graduate student in electrical engineering and computer science and a co-author on the new paper. “What we’re doing is giving a rigorous analysis behind that intuition, and also saying that the estimate is a very good estimate, rather than some coarse estimate. As a function of time, it gets more and more accurate, and it goes nearly as fast as you would expect you could ever do.”
Musco and his coauthors — his advisor, NEC Professor of Software Science and Engineering Nancy Lynch, and Hsin-Hao Su, a postdoc in Lynch’s group — characterize an ant’s environment as a grid, with some number of other ants scattered randomly across it. The ant of interest — call it the explorer — starts at some cell of the grid and, with equal probability, moves to one of the adjacent cells. Then, with equal probability, it moves to one of the cells adjacent to that one, and so on.
When bombs exploded at the Boston Marathon on Monday, my Facebook feed was immediately filled with urgent messages. I watched as my friends and family implored their friends and family in Boston to check in, and lamented the fact that nobody could seem to get a solid cell phone connection. Calls were made, but they got dropped. More often, they were never connected to begin with. There was even a rumor circulating that all cell phone service to the city had been switched off at the request of law enforcement.
That rumor turns out to not be true. But it is a fact that, whenever disaster strikes, it becomes difficult to reach the people you care about. Right at the moment when you really need to hear a familiar voice, you often can't. So what gives?
To find out why it's frequently so difficult to successfully place a call during emergencies, I spoke with Brough Turner, an entrepreneur, engineer, and writer who has been been working with phone systems (both wired and wireless) for 25 years. Turner helped me understand how the behind-the-scenes infrastructure of cell phones works, and why that infrastructure gets bogged down when lots of people are suddenly trying to make calls all at once from a single place. He says there are some things that can be done to fix this issue, but, ultimately, it's more complicated than just asking what the technology can and cannot do. In some ways, service failures like this are a price we pay for having a choice and not being subject to a total monopoly. Read the rest
A paywalled paper in the Royal Society's journal Interface argues that the world's underground rail systems are all converging on an "ideal" form. The paper, "A long-time limit for world subway networks," shows that subway systems grow "organically," in response to the needs expressed by the cities above them over the course of decades, and reveal truths about the shape of cities. In Wired, Brandon Keim describes the findings:
Patterns emerged: The core-and-branch topology, of course, and patterns more fine-grained. Roughly half the stations in any subway will be found on its outer branches rather than the core. The distance from a city’s center to its farthest terminus station is twice the diameter of the subway system’s core. This happens again and again.
“Many other shapes could be expected, such as a regular lattice,” said Barthelemy. “What we find surprising is that all these different cities, on different continents, with different histories and geographical constraints, lead finally to the same structure.”
Subway systems seem to gravitate towards these ratios organically, through a combination of planning, expedience, circumstance and socioeconomic fluctuation, say the researchers.
World’s Subways Converging on Ideal Form
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