자연과학자가 바라본 ‘Social Network’

KAIST 바이오및뇌공학과

정재승

Paul Erdos: Erdos Numbers

케빈 베이컨의 여섯 단계 게임

(Six degrees of Kevin Bacon)

Kevin Bacon Game

Small world network

Bullmore and Sporns, 2009

Scale-free network

Zipf’s Law

George Zipf's 1949 observation that the frequency of words used in the English language followed a powerlaw distribution is a profound thing. It not only defined ‘Zipf's Law’, which gives a simple rule to explain why some words (e.g. the, of, and) are far more commonly used than others.

The scale-free nature of the web of sexual contacts.

• They analyze data gathered in a 1996 Swedish survey of sexual behavior. The survey--involving a random sample of 4781 Swedish individuals (ages 18-74 yr)--used structured personal interviews and questionnaires to collect information.

• The response rate was 59 percent, corresponding to 2810 respondents. Connections in the network of sexual contacts appear and disappear as sexual relations are initiated and terminated.

• To analyze the connectivity of this dynamic network, whose links may be quite short lived, we first analyze the number k of sex partners over a relatively short time window--the twelve months prior to the survey.

Preferential Attachment

1. Introduction : Self-Organization

- A process of attraction and repulsion in which the internal organization of a system,

normally an open system, increases in complexity without being guided or managed

by an outside source (From Wikipedia)

- Typically displays Emergent Properties

Self-Organized Criticality: The origin of 1/f in the Brain

Complex Systems

• Nonlinear basic unit/individual

• Nonlinear interactions among units

• Complex and ordered structures

• Intrinsic stochastic noises

• Dynamical transition of the states

• Rich phenomena:

chaos, fractal, small-world effect, scale-free behavior,

intermittency, bursting, and synchronization.

• Dynamical adaptation!

• Wake from your reverie “homeostasis and stability.”

• Focus on the complexity of the system!

• Only a short-term prediction is possible.

• Interdisciplinary research will be more preferable and useful.

Complex dynamics of heart rate variability

Breakdown of a fractal physiological control mechanism can lead

ultimately either to a highly periodic output dominated by a single scale or

to uncorrelated randomness.

African Fractal

Hub and connectors vs. Weak ties

Collective Intelligence

• 여러 사람들이 함께 문제를 해결하고, 서로 의견을 공유하며, 각자 자신이 가진 것을 기여하고 참여하며, 서로 보완하는 정신 (참여, 공유, 개방).

Suggestions

• Social network 은 complex systems 의 전형적인 예 중 하나다. Complex network 의 창발성을 활용하자!

• 공공캠페인을 위해 Worldwide Web, Blogosphere 등을 적극적으로 활용하자!

• Diffusion of Buzz: 매력적인 바이러스를 만들자!

• ‘Information Cascade’를 이끌어내자!

• 허브와 커넥터를 공략하자!

• ‘약한 유대의 힘’을 활용하자!

• 자발적인 참여, 공유, 개방을 활용하자!