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# Hubs and communities

In most networks, there are elements that have a huge amount of direct connections to others, and these individuals tend to be rather important. They are called super-spreaders or hubs.

• Article

### Not all jet-lags are the same••

The part of the brain that controls the sleeping cycle is made up of two groups of neurons. In order for you to be able to sleep at night, the activity of these neurons needs to be synchronized with the cycle of the sun (e.g. active during the day and inactive at night). When you abruptly change the cycle of the sun (by flying to New York) these two groups need to re-synchronize to the new sun-cycle.
• Article

### The two community Kuramoto model - Animation•

In the interactive simulation in this article, developed by Martijn Gosgens, you can see how the two-community Kuramoto model works.
• ### The two-community Kuramoto model - Mathematical approach•••

We can represent the interactions between the neurons in the body-clock as a network. In our case the network has two communities, where each community has many edges between the nodes, while there are only few edges between the nodes in different communities.
During the Corona pandemic the reproduction number $R$ appeared in much of the media. While it is not at all obvious what this quantity measures exactly, it is obvious that making it smaller than 1 really is crucial in controlling the spread of the virus. So what is this $R$ really?