Tuesday, June 2, 2009

Airport Networks: Design, Efficiency and Emergence of Pandemic

The latest pandemic of swine (H1N1) flu has brought forth the issue of the world being a global village and increasing becoming so. A few decades back, when the world was not so well-connected without, particularly, the air-transportation, diseases such as SARS and swine (H1N1) flue would get contained to a relatively smaller geography and die out in short time.

Not the same any more. Before the origin of the disease could be located, much before the scientists are able to find which strain it is of, the human carriers could spread it across the continents, thanks to the dense and fast aviation infrastructure we have developed. A pandemic is thus born. A tool and infrastructure that was meant to serve the mankind is posing a threat of generating
world-wide pandemic owing to human dynamics over the aviation infrastructure.

Is it possible to design airport networks such that while aiming for better efficiency in traffic dynamics, one could simultaneously reduce the chances of possible pandemic emerging over the network?

One paradigm with which to study the aviation infrastructure is that of complex systems, specifically complex networks. It is then possible to model the airport networks using such a model in which the spread of epidemic/pandemic on such a system could be viewed as a flow of information.

In past the aviation infrastructures have been studied at the national
[1-4] as well as world-wide level [5] using complex networks model. There have been studies that model the spread of infectious diseases and predict spread of diseases in future events [6]. In the light of such studies, it would be interesting to know whether the above question can be answered.
A network is said to be assortative if richly connected nodes in it tend to connect to other rich nodes and vice versa. In a disassortatve network the richly connected nodes tend to be connected to poorly connected nodes.
One of the interesting features that comes out from the study of 'efficiency' and 'risks' of airport networks is that there is an apparent dichotomy between the two [7]. Network topology is one aspect that could possibly
be engineered to achieve the desired results. An assortative network is reported to be conducive for information transfer, hence one with weaker resistance to spread of contagious diseases over it. On the other hand such a network is known to be resilient to simple targeted attacks from computational studies [8].

Enhancing airport networks to make them epidemic/pandemic tolerant, by tweaking the topology, would evidently make them prone to targeted attacks. Is there a way out of it? Perhaps there is [7].

The idea is to treat topological assortativity different from that of dynamic (traffic-generated) assortativity. The former is responsible for efficiency of the network (carrying the passengers over the network) and the latter enumerates a measure of human-to-human interaction on the airport network.

Thus a possibly ideal solution would be to tweak the topology to make it assortative while striving to achieve disassortative traffic dynamics profile over the network. Such a network would expectedly have a resilient topology against targeted attacks while at the same time possibly restraining percolation of infectious diseases across it. The details of how
exactly to achieve such a "network state" in a geopoliticaly divided world-wide airport network leads to interesting thoughts to ponder upon.
[1] Ganesh Bagler. Analysis of Airport Network of India as a complex weighted network. Physica A, 387, 2972–2980 (2008).

[2] W. Li and X. Cai. Statistical analysis of Airport Network of China. Phys. Rev. E, 69, 046106 (2003).

[3] M Guida and F. Maria. Topology of the Italian airport network: A scale-free small world network with a fractal structure? Chaos: Solitons and Fractals, 31, 527–536 (2007).

[4] Carlos Pestana Barrosa and Peter U.C. Dieke. Performance evaluation of italian airports: A data envelopment analysis. J. of Air Transport Management, 13, 184–191 (2007).

[5] Alain Barrat et al., The architecture of complex weighted networks. Proc. Natl. Acad. Sci. (USA), 101, 3747–3752 (2004).

[6] Vittoria Colizza et al., The role of the airline transportation network in the prediction and predictability of global epidemics. Proc. Natl. Acad. Sci. (USA), 103, 2015–2020 (2006).

[7] Ganesh Bagler, "Complex network view of performance and risks on airport network", Nova Science Publishers, USA, ISBN: 978-1-60692-1 (2009).

[8] M. E. J. Newman. Assortative mixing in networks. Phys. Rev. Lett., 89, 208701 (2002).

Also See: http://www.industry.siemens.com/Airports/en/
(Siemens is one of the companies that is working on various aspects of airport networks in view of design and growth of "Future of Airports". During their word-wide empirical study, representatives from Siemens interviewed me and discussed various aspects of airport networks, especially Airport Network of India.)

Wednesday, April 8, 2009

My 21 kilometers in Berlin

I have been infected with the running bug from childhood. I must give its credit to the folks in my neighborhood with whom I grew up in Solapur. Those guys put in me the habit of getting up early, feeling the dew and running for fun. Once into that habit, I almost always continued that. So much so that I used to wake up early whichever place on the globe I was on and go for a walk/run in solitude.

After a while, when I was a graduate student at Centre for Cellular and Molecular Biology (CCMB), Hyderabad, I started jogging and playing cricket in the mornings with a group of friends. I, typically, used to be the one who would get up early and knock and get others up. Especially few notorious for not getting out of the bed! :) The habit of persuasion was so strong that, when I had gone to Beijing for a School, I used to call up from there to wake up the guys at 6:30am IST! :)

With the practice of running came the idea of running in Hyderabad 10K (2005), which I indeed completed successfully. After coming to Berlin, when I heard of Berlin half-marathon, though it sounded bit daunting having never attempted 21kms earlier, here was another target! And I was game.

It was good to have the gang of people to practice with. Practicing otherwise can be a tough task. Apart from going through the pain of practice, I enjoyed running through Berlin as well as a bit of out of it. It was a nice way of getting to know Berlin. After running for around 75kms or so in about two months while practicing, I was pretty much sure I will make it to the finish line fairly easily.

After the excitement of procuring the ChampionChip (the RFID tracker), the marathon t-shirt and my race-number (3343), I was all set to run on the final day (5th April 2009, Sunday). The run began at 10:45am and I was on my own. There were music bands on the roadsides. Loads of people, especially kids, cheering up all the runners.

After 12kms or so I had slowed down and was walking. There was this old grandma sitting on a high-chair on the grass-lane dividing the road. She looked at me, cheered up and said something in Deutsch. I couldn't understand it verbatim, but it was obvious to me what she was saying, "No slowing down. No walking. Keep running, son!" I agreed, cheered back to her and restarted my run. The co-runners were smiling at us... :)

Towards the end of the run, I was too tired and was walking down. There came an old man, a co-runner. He cheered me up, asked me to run along with him and told me it was just three more kilometers!

Well, I knew it wasn't impossible. :) I ran all the way to the finish line! 2:46:59 Hrs.

After all, running 21kms had been more of a mind game than a test of physical endurance. Beyond the necessary training that my body needed, to go through the ordeals of running 10, 15, 17 and 21kms at a stretch, it was indeed a mind game! Even as I was dashing towards the finish-line, I was wondering if it was possible to reduce the pain felt by mental tricks? Perhaps it is [1]. Since the body-map in our brains is malleable [2], it could be possible to modify the sensation of pain felt in our body. Perhaps to displace it out of the body!! :)

As I touched the finish-line the announcement on the loudspeakers said: "Ganisch Begler aus Indien ist hier!!"
[1] "Visual distortion of a limb modulates the pain and swelling evoked by movement", Current Biology, Moseley et al., 18, 22, R1047-R1048 (2008).

[2] Chapter 3, "Phantoms in the Brain: Probing the Mysteries of the Human Mind", V S Ramachandran and Sandra Blakeslee, Harper Collins Publications, (1998).