Deleuzean Potato

We went south a few weeks ago, down to Valdivia. Valdivia itself is a bit inland, at the junction of two rivers and a bay. As a result, it's colder than Santiago, and very foggy (especially in the morning, when we arrived). We took another bus further south to Osorno, then tried to get to a resort called Aguas Calientes that Joe had read about. We were expecting there to be a publically accessable hot spring we could just pay to sit in for the afternoon. Unfortunately, the only thing there we could do that with was a public pool. We could also rent a cabin at the resort and spend the night, but that would cost us CH$20,000 each for the night. It still wasn't clear if there was a hot spring that we would then be able to use.

Disappointed, we eventually found a place to spend the night in a town called Entre Lagos, on the road between Osorno and Aguas Calientes. The next day, we just went walking down the road. We hitched a ride with two guys driving a bus; they were pretty amused by us, and were pretty amusing to ride with themselves. They dropped us off where their road split off, and we continued hiking. We then got picked up by the bus to Aguas Calientes. That bus dropped us off where the road to Aguas Calientes split off from the road that continues on to Argentina. We walked along the road to Argentina for aways, and eventually came to a field. We could see a waterfall in the wilderness on the other side of the field. Joe and Matt wanted to try to get to the waterfall, so we found a house that looked like it belonged to the owner of the field. A woman came to the door, and Joe asked if we could walk across her field to get to the waterfall. Her answer didn't really convince us that it was her field (or her husband's), but she said it was okay. So we did.



Joe is convinced that "chicks dig pictures of a bunch of guys somewhere." This is the first photo I've ever taken using the timed delay function on my camera. It looks more pixilated than other photos; I think that's due to the same effect as the pixilation in the night photo of the public phone in Bellavista (see Steven and Dean's comments, below).

We finally made it to the waterfall. We were surprised both at how far we had to scramble down the river, and at how big it was when we got there.



For scale, Joe is the further figure from the camera. He's about 5'4" tall, and about halfway between me and the waterfall. You can't really see it in this photo, but my other photos from immediately around the fall show little points of light. Those are due to light from the flash reflecting off of drops of water in the air. The drops of water, of course, are from the waterfall itself. It was an impressive waterfall.

Matt's had this problem for a couple of weeks. He's driving this system, and he wants to add noice. The driving signal is the sum of two sine waves. He takes a base frequency, chooses two different harmonics of that base frequency, chooses amplitudes for each of those two harmonics, adds the result, and outputs it. He's been trying to figure out a good way of adding some random noise to this signal before he outputs it to the system. I don't really understand it, but adding noice is suppose to induce phase transitions in this system (actually, I might almost understand it...).

One big problem was that he and Nicolas were having difficulty finding a way of generating noice fast enough to keep up with the system. They want to be able to add this noice as they drive the system continuously. There wasn't a fully satisfactory way of doing this, until Matt had his big idea over the weekend: use the computer's sound card. So he started working with that yesterday, and continued this morning.

The problem this morning was that he was measuring the output voltage of the sound card, and noticed that it varied with frequency. So I had the bright idea of measuring the output of the card as a function of frequency. So he did that, and got this,



which isn't exactly constant. In fact, Matt want the noise to be around the same frequency as the signal, which is in the 20-60 Hz range. Which is exactly where the response curve is least constant. This won't do at all. On top of this, we're both bewildered by this response curve. I convince myself that I wouldn't be surprised to see a high-pass filter on a sound card, the human ear only hearing frequencies between 2.9 and 16 Hz (yes, I know that's not right, I have since discovered my error, medium-sized story there...), but I can't figure out this weird peak at 70 or 80 Hz. Maybe it doesn't matter, not being audible and all.

Now, when Nicolas bought that computer, he also bought some additional hardware, including a pretty bitchin' sound card. This is not that sound card; it's the sound card that came with the computer. Matt checked the bitchin' sound card, and it has a flat response curve all the way down to 0 Hz. Apparently, shitty sound cards don't give the same response at really low frequencies as they do at normal freuqencies.

We were going to have a meeting to discuss our progress on our respective projects. This was supposed to be an informal gathering, but it involved each of us talking to a room full of about 20 people. That might make it feel more formal, but it was okay.

I was feeling a bit annoyed earlier in the week, mostly because I didn't feel that I had any progress to report to this gathering. That wouldn't be too bad, except that I also felt that I had wasted about four weeks doing nothing at the beginning of the project, and we have only two weeks left. Part of this meeting was to be a sort of end-of-project sort of thing. So I really felt that, if I don't have anything to report to this meeting, I don't really have anything to show for the entire trip.

I started feeling a lot better as I prepared what I was going to say. At the very least, I had a photo and a couple of plots I could show everyone. I realized that I do have something to show for myself, which makes the trip feel like less of a waste of my time. I typed my notes up in HTML so they would be easier to put online when I was done. They're now here, and I'm going to update them as we get further along and I think of better ways of explaining myself.

The best plot I took is below. It's a scan across the entire frequency range (1-100 kHz) our generator will do. This is the just the chamber itself, with no particle in it. The huge peak in the 80's is due to the resonance of the transducer, and is only interesting inasmuch as we have to work around it. The series of peaks between 20 kHz and about 45 kHz we think is due to the chamber. We haven't yet been able to reproduce this result, for a few reasons I go into more detail in the explanation at the link.

The first couple of days of August, there was a conference in Reñaca. Reñaca is on the coast, immediately to the west of Santiago. It's just north of Viña del Mar, which is just north of Valparaiso. Valparaiso is the major port for Santiago, and is more well-known than the others. The conference was held at a hotel/conference center called, appropriately enough, Conference Town (in English, no less). All the talks were in Spanish, so I didn't get too much out of it in the way of physics. But it was a nice opportunity to take a few days off of work, and go to the beach. The last day of the conference, I skipped all the talks in the morning, and went into Valparaiso. There's more to say about the excursion, but it would be better if I could include the photos I took. Alas, I can't find them. They aren't in the directory I thought they were in. I really hope this is because I unloaded them onto the computer at work and forgot to upload them to Ye Olde Internets, and not because I deleted them.

UPDATE: they had been on the computer at work, and I hadn't yet uploaded them to the server. Here's one I took while wandering around Valpo.



And here's one of Carolyn at the beach.

Now to put that last post into its proper context.

We start with just a plastic tube filled with distilled water. We have a piece of piezo-electric ceramic at one end, and a sensor at the other. The piezo-electric converts an electrical signal into a physical vibration. This establishes an acoustic wave down the length of the tube. The sensor detects the vibrations from that, and converts into an electrical signal. We pick up that signal, and measure it.

At that point, it's just your normal, run of the mill acoustic chamber. Not really exciting. We can change the frequency at which we're driving the system, and measure the response of the system as a function of frequency. There will be certain resonance frequencies that have a much larger response than other frequencies. These should be regularly spaced, well-understood, and depend only on the geometry of the chamber. That's all pretty standard, first-year university phsyics stuff.

Then we add a small particle. This is supposed to affect the resonance frequencies of the chamber. The effect is supposed to be a function of the particle's position along the chamber. If we allow the particle to move in response to the wave, it should settle at some equilibrim position. That should be a function of the driving frequency. It might also have a few different equilibrium points, between which it chooses based on the starting position.

We took a couple of measurements of the output spectrum with no particle, then added the particle and took a few spectra at different particle positions. We're in the process of trying to replicate those to ensure we're actually seeing the effect we think we're seeing. I meant to have some images of those spectra by now, but the internet connection was down at work on Friday. Monday is a national holiday (Feast of the Assumption -- a Holy Day of Obligation in the Catholic Church), so I won't have anything until Tuesday. But that gives me time to say something about our travels.