### July 2011

Most people have heard of the Bacon number, the number of degrees of separation an actor has from Kevin Bacon, based of the Six Degrees of Separation idea. Well, this concept of looking up and assigning numbers based on the separation distance was actually borrowed from the Erdős number, which gives the degrees of collaboration between the person and the mathematician Paul Erdős.

I was thinking the other day that there is a good chance I have an Erdős number. I have published a peer-reviewed paper while in grad school, and my co-author has published dozens of papers in several fields, and his PhD advisor and then his PhD advisor are/were very famous in fluid dynamics, which is closely tied to mathematics, so there is a good probability of me having a fairly low Erdős number. You can look up the Erdős number for a person here, but since it only indexes from mathematics journals it’s not nearly as robust and complete as it could be. So while myself and my PhD advisor aren’t listed as having Erdős numbers, his advisor is, so I can just add 2 to that number to get my Erdős number. So my Erdős number trace is the following:
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My flight from Seoul back to Fukuoka was at 6:30 pm, so that meant I had until about 2:30 to 3:00 to do something on Saturday morning. At one of my friend’s suggestion, I decided to go on a guided tour of the DMZ, the border with North Korea.

During my short trip there I was constantly seeing things that reminded me of Japan, but there is one way that South Korea is totally unique: having a border with North Korea. It’s strange to think that after 50 years the war is still technically ongoing, i.e. there has never been a formal peace accord, just a cease-fire. As the tour bus slowly approached the DMZ, there were obvious changes that the tour guide pointed out to us: fences topped with razor wire along the Han river (the river starts in North Korea and becomes the border as it flows south and then west, so it has been an popular method for saboteurs, commandos, etc. to try and slip into South Korea), guard posts and pillboxes every 500m with ROK soldiers standing guard. Another method that the North Koreans set up was tunnels, and one of the discovered tunnels was the first stop on the tour. Before we got there though, we had to pass a checkpoint at the entrance to the army-controlled zone. Though still outside of the actual DMZ, no one goes in or out without the soldiers checking your ID (passports for all of us on the tour bus) and that you have a reason to be there. Although farms are maintained in the area, there is a curfew so that the farmers there can only work during the day and have to leave before nightfall.
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June 1st, 1:00 pm: So I finally made my way to Yongsan station. I had a general map of the area that I had printed out from google maps, but I had difficulty orienting myself inside the station, so I just followed the largest group of people, assuming they would heading towards the same destination as me. Well, it turned out that assumption was wrong. It took me a while, but I finally made my way to the big electronics department stores. The biggest surprise? There were hardly any customers. Maybe it’s because it was still early Friday afternoon or something, but there just weren’t a lot of shoppers. Also making things difficult was that although everything was in the same building, it was in actuality a whole bunch of very little shops all lined up together. They were at least grouped by genre though: all the stores selling cameras were together, all the stores selling PC’s were together, etc., so it wasn’t too hard to navigate.
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And by short, I mean short. I’ve been in in Kumamoto, Japan on an extended business trip for most of the summer (since mid-May, in fact), working on a project here. In fact the trip is so long that I had a problem: one week before I left my wife pointed out to me that my scheduled stay was about 95 days, and I can only stay in Japan 90 days without a visa. Unfortunately the travel office for my company didn’t realize it either: I guess they generally deal with people going to Japan for a week or two, or a year or two, but not around 3 months.

It was too late to apply for a visa, so the alternative plan was for me to briefly leave Japan for a day or two while I was there, and when I get back my 90 days should reset. So I ended up with a ticket to go to Seoul, South Korea on July 1st and then fly back to Japan on July 2nd. I asked some Korean friends of mine for suggestions as to what I should do while I’m in Seoul for a whopping 24 hours. So here was how my trip began:

June 1st: 10:30 am: Leave from Fukuoaka airport on Korean airlines flight. The stewardesses (or flight attendants, if you insist on PC), were without exception, young, friendly, and very attractive. I reminded me a bit of Singapore airlines, although I don’t think anything comes close to those dresses the Singapore airlines stewardesses wear. All the Korea Air stewardesses had very good English, and impeccable Japanese that was so good I had trouble distinguishing it from native fluency.

June 1st: 11:30 am: (Just a 1 hour flight, and they still served a meal and drinks!) Arrive at Incheon airport. No problems with customs and immigration, I just have the clothes on my back and a backpack with a change of clothes. As soon as I leave customs and enter the public area of the airport, I must have had an unmistakable ‘wide-eyed lost foreigner’ look, because I’m immediately accosted by an older unkempt man with broken English asking if I need help getting a bus or taxi. It was tempting, since I was there as part of a business trip I could probably expense it, but I wanted to do it the hard way.