Networks: A Very Short Introduction (Very Short Introductions)

Guido Caldarelli, Michele Catanzaro

Language: English

Pages: 136

ISBN: 0199588074

Format: PDF / Kindle (mobi) / ePub

Networks are involved in many aspects of everyday life, from food webs in ecology and the spread of pandemics to social networking and public transportation. In fact, some of the most important and familiar natural systems and social phenomena are based on a networked structure. It is impossible to understand the spread of an epidemic, a computer virus, large-scale blackouts, or massive extinctions without taking into account the network structure that underlies all these phenomena. In this Very Short Introduction, Guido Caldarelli and Michele Catanzaro discuss the nature and variety of networks, using everyday examples from society, technology, nature, and history to illuminate the science of network theory. The authors describe the ubiquitous role of networks, reveal how networks self-organize, explain why the rich get richer, and discuss how networks can spontaneously collapse. They conclude by highlighting how the findings of complex network theory have very wide and important applications in genetics, ecology, communications, economics, and sociology.

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Jesus 276. Viruses 277. Protestantism 278. Derrida 279. Madness 280. Developmental Biology 281. Dictionaries 282. Global Economic History 283. Multiculturalism 284. Environmental Economics 285. The Cell 286. Ancient Greece 287. Angels 288. Children’s Literature 289. The Periodic Table 290. Modern France 291. Reality 292. The Computer 293. The Animal Kingdom 294. Colonial Latin American Literature 295. Sleep 296. The Aztecs 297. The Cultural Revolution 298. Modern Latin American Literature 299. Magic 300.

Humanism 257. Folk Music 258. Late Antiquity 259. Genius 260. Numbers 261. Muhammad 262. Beauty 263. Critical Theory 264. Organizations 265. Early Music 266. The Scientific Revolution 267. Cancer 268. Nuclear Power 269. Paganism 270. Risk 271. Science Fiction 272. Herodotus 273. Conscience 274. American Immigration 275. Jesus 276. Viruses 277. Protestantism 278. Derrida 279. Madness 280. Developmental Biology 281. Dictionaries 282. Global Economic History 283. Multiculturalism 284. Environmental Economics 285.

Increasing by 5 centimetres in every row (Figure 9 left). At the end, the profile of the rows will have the shape of a bell curve: the number of students increases as height increases, then reaches the top around the average, and then starts to fall. The very tall and the very short are rare and the majority are in the middle. This curve provides the distribution of heights of the students. Now, let us consider the number of social contacts of those same students. Now the rows correspond to those with 0 to 20 friends, 20 to 40, 40 to 60, and so on.

For example, sociologists and political scientists usually split society into social classes, genders, levels of education, ethnicities, nations, etc. Similarly, epidemiologists often separate the population into a limited set of ‘compartments’: healthy individuals, infected, immunized, etc. Ecologists can also use this approach by aggregating into groups (trophic species) all the species that have similar roles in a foodweb. The network approach tries to complement these two points of view. Many phenomena are impossible to explain if one focuses only on the behaviour of individual elements.

The disease is said to be below the epidemic threshold when, for every infected individual, fewer than one person gets infected: in this case, it becomes extinct. The disease is above the epidemic threshold if every infected individual passes the disease to more than one individual: in this case, it thrives. If vaccines are available, the disease can be pushed below the threshold by means of campaigns that immunize a sufficient portion of the population. Very contagious diseases are usually the hardest cases, because they have a low epidemic threshold and so they become endemic very easily.

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