Wednesday, 25 April 2007


I was reading the files on arXiv this week and found the paper:

Cascading Behavior in Large Blog Graphs
Jure Leskovec, Mary McGlohon, Christos Faloutsos, Natalie Glance, Matthew Hurst
arXiv:0704.2803v1 [physics.soc-ph]

I remember that I have already seen a paper about blogs before and I am almost sure that Osame wrote about that in his blog, so I made a little search on arXiv and found these ones, in reverse chronological order:

Social Information Processing in Social News Aggregation
Kristina Lerman
arXiv:cs/0703087v2 [cs.CY]

Information propagation and collective consensus in blogosphere: a game-theoretical approach
Lianghuan Liu, Feng Fu, Long Wang
arXiv:physics/0701316v1 [physics.soc-ph]

Social Networks and Social Information Filtering on Digg
Kristina Lerman
arXiv:cs/0612046v1 [cs.HC]

Social Browsing on Flickr
Kristina Lerman, Laurie Jones
arXiv:cs/0612047v1 [cs.HC]

The structure of self-organized blogosphere
Feng Fu, Lianghuan Liu, Kai Yang, Long Wang
arXiv:math/0607361v3 [math.ST]

Quantitive and sociological analysis of blog networks
Wiktor Bachnik, Stanislaw Szymczyk, Piotr Leszczynski, Rafal Podsiadlo, Ewa Rymszewicz, Lukasz Kurylo, Danuta Makowiec, Beata Bykowska
arXiv:physics/0506051v1 [physics.soc-ph]

It seems that Kristina Lerman, a physicist who became a computer scientist, is the most active in this area. Take a look at her homepage.

Basically, blogs are considered as vertices of a graph and links between blogs as its edges. Well, this kind of network has been studied in physics for some time now. There are a lot of things you can study, but I will highlight just the most common one. Usually, what is studied is the distribution of edges in the graph, i.e., the number of vertices with 1,2,3,... edges. The interesting result, which appears in a lot of different networks in nature, from the famous small world networks to chemical networks in the cells, is that this distribution obeys what is called a power-law:

where r is the number of edges and k is a constant. This kind of formula is important in physics, because it indicates that the characteristics of the distribution do not change when the scale of the problem changes, i.e., if we analyse 10, 100, 1000, 10000 blogs, the distribution will be the same (dicarding finite size effects). We call this distributions scale-free. To have a feeling of the importance of these power-laws, they appear in second-order phase transitions and in self-organised criticality (which is not unrelated).

All this again falls in the huge multidisciplinary range of complex systems, which is highly fashionable (specially if you want to ask for a research grant) but difficult to define. Although we could say that complex systems are systems composed by a large number of interacting units which can manifest some kind of emergent behaviour, maybe it would be simpler to say that complex systems are all those which are not simple.

In the beginning of this blog, I wrote a post about avalanches. This is considered a complex system with emergent behaviour: the avalanches. The real ones don't, but simplified ones in computer models have a distribution of sizes which is a power-law. These relationships are still not well understood, but they indicate connections between a lot of phenomena and we hope this will be clarified during this century (well, at least I hope...).

Picture: from Data Mining. The original caption is:
This graph shows another view of the core. Rather than require reciprocal links, I have simply pulled out the largest connected component formed by any directional link between blogs. The obvious insight here is the relationship between LiveJournal (blue) and the rest of the core.

Friday, 13 April 2007

The Inner Life of the Cell

Wednesday, 4 April 2007

300 and Science Fiction

Last Saturday I saw '300' in the cinema. I must say I really enjoyed the film. Usually, I don't bother with the critics about a movie, but I was curious since the actor that makes Xerxes is brazilian (Rodrigo Santoro) and well known in my country. I like to see brazilians doing well in the international scenario.

Appart from the usual critics to action movies and to the actors and the conspiracy theories about the political intentions of the film, there was one that I found very interesting. It was repeated by a lot of people: the fact that the movie is not historically accurate. The fact that they were not just observations, but that the critics were pointing this as a negative feature capable of lowering the quality of the work should be analysed better.

When I was younger, I used to tease my friends telling them what was scientifically wrong with the Sci-Fi movies. I liked the movies a lot, but I kept noticing every detail and criticizing them after leaving the cinema. I don't need to say that my friends didn't like it. Most of the time, except when they asked about it, they were not interested in how real or possible were the actions or devices in the film. Can you imagine why? Well, in the beginning I couldn't, so I started to think about paying attention in myself.

I realised that when I go to a movie, I am not interested in having a science class, I am interested in the emotions I feel. I liked Star Wars even with the sound of explosions in the empty space, with the vision of the laser beams and with millions of other small details. I like to see Star Trek (although the guys try very hard to justify everything). I liked Matrix even knowing that the machines could not use the humans in that way without violating energy conservation. I did like Sci-Fi movies independently of the scientific failures if the underlying plot is well written and the effects and the actors are good. I don't wanna know why, I just wanna leave the cinema feeling better (or in the case of dramas, worse) than I entered.

Indeed, I have never seen any critic saying that a Sci-Fi movie is bad because it does not pay attention to the laws of physics, have you? Maybe it is because it is easier to spot history failures than science failures. But when I was in the cinema this Saturday, I could see that everyone was holding their breaths and no one left the room to go to the toilette, as is so common. I left the cinema feeling very good.

I believe that Frank Miller's comic book was not intended to be historically accurate. I believe it was meant to be cool. I know that a lot of people will say that this is bad, because it makes people learn wrong history. Really? Well, in my case, it was pretty obvious that the film was a kind of fiction, unless you really believe that the Persian soldiers were inhuman monsters and that a Spartan soldier can put a spear in the eyes of a giant battle Rhino who is charging on him killing the beast just centimeters before it reaches the target. Of course it was not real! So, the first thing I did when I arrived home was to open a History book and learn what was really known about the fact. See? Although I have never been good in history on my school days, I was led to study it by seeing a movie that made me feel well. If I would have left the cinema feeling that I have thrown my money away, I would never have done that.

In fact, one of the things that led me to be a scientist (and I bet it is the same for many others!) was the Sci-Fi movies. I wanted to live that and, above all, to understand that. Indeed, I almost gave up to be a physicist and just came back after seeing Contact, but this is another story.

Picture: cover of the comic book.