New Schedule - Greifswald

Regular readers have noticed that this blog has been a mix of German travelogue and (plasma) physics. Also, that - at least during 2015 - I have been posting pretty regularly. In fact, for the last three weeks I've posted something every day. But this is fairly taxing, and as I return to the US, I'm going to post less, and more of the posts will be physics related. Hopefully, they will still be of general interest, because I find them interesting.

I do still have many photos from my travels to post, so those will continue (until I run out), and I plan to post only on MWF. If I feel like it, there will be some weekend posts (like this one) but I'm going to get back to the serious work of my sabbatical (exercising, thinking deeply, and research projects).

Here's one more travelogue/physics post to start off the new schedule.

Gas Metal Arc Welding

The reason I went to Berlin in January (see here, here, here and here) was to visit the Leibniz-Institute für Plasmaforschung und Technologie e.V. (INP), which is a two-hour train ride north of Berlin. One of the professors here at Hochschule München works on gas metal arc welding, among other things, and specifically investigating the parameters of the plasma arc using optical emission spectroscopy.

High resolution visible light photo of the plasma arc, taken at 1.2 ms after the current was turned on. Here, CO₂ is the welding gas, and the emissions you see are from both iron (from the steel welding element) and carbon dioxide.

He was interested in getting a plasma physicist involved in this work, so after several discussions he arranged for me to spend a couple of days visiting INP and learning about the experimental and theoretical techniques that they use. My visit was extremely productive - I learned a lot - and while I was there we outlined a good project for our first collaboration. Hopefully when I get back to the US I will have some time to work on this. I'll be doing something similar to what they already do, where one of their techniques is to invert images like the one above and obtain information about the physical processes (e.g., temperature, density) as a function of position within the arc. This is a kind of "remote sensing" that reveals more information about what's going on in the arc than what you can obtain from just looking. Here, for example, is a result of one of the inversions.

Emission coefficient profiles - as functions of radial position (i.e., assuming cylindrical symmetry) - at different times and for different welding gases. Some are argon, and some are CO₂.

Greifswald

Greifswald is a beautiful small university town. In fact, it has one of the oldest universities in the world. Interestingly, it's the oldest Swedish university. This is because it is located in Pomerania, which used to be a part of Sweden. I got a chance to walk around the city a bit, and one of the physicists took me to a very old church, that we were able to climb to the top and get a good view of the city. I was very taken with this church and here are some photos.

Climbing to the top of Dom St Nikolai in Greifswald.

Panoramic view of Greifswald from the top of Dom St Nikolai. If you squint, you can see the Baltic Sea in the far distance.

In this particular church, which is about 700 years old, there are people (saints, presumably) buried under the floor. I knew this was common, but this was the first time that I had seen this in Germany. There were many of these engravings on the stone floor.

The church, like most churches, had a beautiful organ. I only heard two organs playing, one in St Hedwig in Berlin, and the other at the Frauenkirche in München when we went to Christmas Eve mass.

Finally, a beautiful stained glass window. Of all the many churches that I've been to in Germany, this was one of the few that had a nice stained glass window. And this is a huge window, probably 3-4 meters tall. The photo doesn't do it justice, as usual.