Scientists have recently discovered that various complex systems have an underlying architecture governed by shared organizing principles

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THE INTERNET, mapped on the opposite page, is a scale-free network in that some sites (sfarbursts arid detail above] have a seemingly unlimited number of connections to other sites. This map, made on February S, 2003, traces the shortest routes from a test Web site to about 100,000 others, using like colors for similar Web addresses.


Scientists have recently discovered that various complex systems have

an underlying architecture governed by shared organizing principles. This insight has important implications for a host of

applications, from drug development to Internet security

BY ALBERT-LASZLO BARABASI AND ERIC BONABEAU

* а

3 с» ш о



The brain is a network of nerve cells connected by axons, and cells themselves are networks of molecules connected by biochemical reactions. Societies, too, are networks of people linked by friendships, familial relationships and professional ties. On a larger scale, food webs and ecosystems can be represented as networks of species. And networks pervade technology: the Internet, power grids and transportation systems are but a few examples. Even the language we are using to convey these thoughts to you is a network, made up of words connectcd by syntactic relationships.

Yet despite the importance and pervasiveness of networks, scientists have had little understanding of their structure and properties. How do the interactions of several malfunctioning nodes in a complex genetic network result in cancer? How does diffusion occur so rapidly in certain social and communications systems, leading to epidemics of diseases and computer viruses? How do some networks continue to function even after the vast majority of their nodes have failed?

Overview/Scale-Free Networks________

a A variety of complex systems share an important property: some nodes have a tremendous number of connections to other nodes, whereas most nodes have |ust a handful. The popular nodes, called hubs, can have hundreds, thousands or even millions of links. In this sense, the network appears to have no scale, a Scale-free networks have certain important characteristics. They ate, for instance, robust against accidental failures

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