A well-written article (pdf) reports on the work by Oxford folks (previous post). Plus, it says that a "pair of Oxford physicists, Neil Johnson and Sean Gourley, have teamed up with social scientists at the Conflict Analysis Resource Center (CERAC), based in Bogotá"
"When the researchers graphed all the attacks within a given conflict, with the number of attacks plotted against the number killed in each, it produces a fat-tailed exponential curve. And the exponent of the function, which determines the curve’s shape, is nearly always the same. “Terrorism and guerrilla warfare everywhere in the world has a signature of about 2.5,” says Gourley. Plotting the distribution of these events over time produces another, distinctive signature.
Friday, December 21, 2007
Thursday, December 20, 2007
At 71, physics professor is a Web star
Professor Walter H. G. Lewin "delivers his lectures [owc] with the panache of Julia Child bringing French cooking to amateurs and the zany theatricality of YouTube's greatest hits. He is part of a new generation of academic stars who hold forth in cyberspace on their college Web sites and even, without charge, on iTunes U, which went up in May on Apple's iTunes Store.
In his lectures at ocw.mit.edu, Professor Lewin beats a student with cat fur to demonstrate electrostatics. Wearing shorts, sandals with socks and a pith helmet — nerd safari garb — he fires a cannon loaded with a golf ball at a stuffed monkey wearing a bulletproof vest to demonstrate the trajectories of objects in free fall.
He rides a fire-extinguisher-propelled tricycle across his classroom to show how a rocket lifts off." Source
The stars this week included Hubert Dreyfus, a philosophy professor at the University of California, Berkeley, and Leonard Susskind, a professor of quantum mechanics at Stanford.
Last week, Yale put some of its most popular undergraduate courses and professors online free. The list includes Controversies in Astrophysics with Charles Bailyn, Modern Poetry with Langdon Hammer and Introduction to the Old Testament with Christine Hayes.
In his lectures at ocw.mit.edu, Professor Lewin beats a student with cat fur to demonstrate electrostatics. Wearing shorts, sandals with socks and a pith helmet — nerd safari garb — he fires a cannon loaded with a golf ball at a stuffed monkey wearing a bulletproof vest to demonstrate the trajectories of objects in free fall.
He rides a fire-extinguisher-propelled tricycle across his classroom to show how a rocket lifts off." Source
The stars this week included Hubert Dreyfus, a philosophy professor at the University of California, Berkeley, and Leonard Susskind, a professor of quantum mechanics at Stanford.
Last week, Yale put some of its most popular undergraduate courses and professors online free. The list includes Controversies in Astrophysics with Charles Bailyn, Modern Poetry with Langdon Hammer and Introduction to the Old Testament with Christine Hayes.
Wednesday, December 19, 2007
The weakness of weak ties
This is a very interesting paper: Structure and tie strengths in mobile communication networks. It studies the communication patterns of millions of mobile phone users by arranging them in a big weighted social network. The weight between two individuals corresponds to the aggregated duration of calls between them.
Findings:
"Weak ties appear to be crucial for maintaining the network’s structural integrity, but strong ties play an important role in maintaining local communities. Both weak and strong ties are ineffective, however, when it comes to information transfer, given that most news in the real simulations reaches an individual for the first time through ties of intermediate strength." ..."The speed of spread then depended on the strength of each link. The results suggest that information spreads most quickly via links of intermediate strength, or medium length calls. This is because information spreads slowly through weaker links, or shorter calls, and stronger links tend to bind only a limited number of people."
Consequence:
To enhance the spreading of information, one needs to intentionally force it through the intermediate- to weak-strenght ties (while avoiding hubs!)
Findings:
"Weak ties appear to be crucial for maintaining the network’s structural integrity, but strong ties play an important role in maintaining local communities. Both weak and strong ties are ineffective, however, when it comes to information transfer, given that most news in the real simulations reaches an individual for the first time through ties of intermediate strength." ..."The speed of spread then depended on the strength of each link. The results suggest that information spreads most quickly via links of intermediate strength, or medium length calls. This is because information spreads slowly through weaker links, or shorter calls, and stronger links tend to bind only a limited number of people."
Consequence:
To enhance the spreading of information, one needs to intentionally force it through the intermediate- to weak-strenght ties (while avoiding hubs!)
Tuesday, December 18, 2007
You, poor? Out!
Switzerland welcomes rich people with its banks and deports poor ones with this new initiative:
Switzerland has started a television campaign in African countries to keep potential illegal migrants from trying to immigrate to Switzerland.
Switzerland has started a television campaign in African countries to keep potential illegal migrants from trying to immigrate to Switzerland.
Monday, December 17, 2007
Robustness of community structure in networks
"The discovery of community structure is a common challenge in the analysis of network data. Many methods have been proposed for finding community structure, but few have been proposed for determining whether the structure found is statistically significant or whether, conversely, it could have arisen purely as a result of chance. In this paper we show that the significance of community structure can be effectively quantified by measuring its robustness to small perturbations in network structure. We propose a suitable method for perturbing networks and a measure of the resulting change in community structure and use them to assess the significance of community structure in a variety of networks, both real and computer generated." Source
How brain catalogs info. PageRank-style?
"Human Brain Cloud: a multiplayer word association game that started with a single word ("volcano") and has since taken on a life of its own. Players are given a word, which is culled from the database of previously entered words, and asked to enter the first thing that comes to mind. As people interact with the game it collects data about word associations that can be formed into a giant network (the cloud)."
"Researchers at the University of California recently conducted a study in which they found evidence to suggest that our brains catalog and rate the relevance of information by forming connections between data. The researchers compared the brain's system to Google's PageRank algorithm"Source
" The investigators found that a word’s “PageRank” was a good predictor of how often it would show up when people were asked to think of words that start with A, with B, and so on.
When it came predicting these results, “PageRank” beat two other seemingly reasonable ranking systems: tallies of how often words show up in ordinary writing; and a simple count of direct “links” to a word that doesn’t consider how many words, in turn, link to those linking words.
In the PageRank formula, a page gains “importance” based on how many other pages link to it. But links from pages that are themselves “important,” confer more importance than those that aren’t. Thus, importance can be thought of as flowing through the Web’s link network toward the most highly “linked-in” sites.
One explanation for the new findings, wrote Griffiths and colleagues, could be that connections among brain cells work similarly to Web links. Cells that are targets of many connections might become more active than others, in the same way that highly linked-in websites are deemed more important." Source
"Researchers at the University of California recently conducted a study in which they found evidence to suggest that our brains catalog and rate the relevance of information by forming connections between data. The researchers compared the brain's system to Google's PageRank algorithm"Source
" The investigators found that a word’s “PageRank” was a good predictor of how often it would show up when people were asked to think of words that start with A, with B, and so on.
When it came predicting these results, “PageRank” beat two other seemingly reasonable ranking systems: tallies of how often words show up in ordinary writing; and a simple count of direct “links” to a word that doesn’t consider how many words, in turn, link to those linking words.
In the PageRank formula, a page gains “importance” based on how many other pages link to it. But links from pages that are themselves “important,” confer more importance than those that aren’t. Thus, importance can be thought of as flowing through the Web’s link network toward the most highly “linked-in” sites.
One explanation for the new findings, wrote Griffiths and colleagues, could be that connections among brain cells work similarly to Web links. Cells that are targets of many connections might become more active than others, in the same way that highly linked-in websites are deemed more important." Source
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