Wednesday, September 26, 2012
Signal to Noise Ratios
Back to the science metaphors today. I got to thinking about how radically I have emptied out my schedule this year, and how it's helping me pay attention to things too long ignored. Improving the signal-to-noise ratio, as it were.
Right after grad school, I spent three years as a postdoc at Los Alamos National Lab. I was studying the way that surfaces influence the structure of thin coatings, to see if you could set up a surface that could direct a thin film to form with the properties you wanted. In order to pick up any kind of a signal at all on my instruments, I had to start out with substrate materials that had a whole lot of surface area, just to have enough of the thin film to make a detectable signal.
I had to make sure that the substrate surface was as clean as humanly possible, to eliminate interference from contaminants -- including air. For every sample I made, I had to start by baking my substrate material at a high temperature, under vacuum. This required custom-built glass furnace tubes that had to be made in the lab's glass shop, by the resident glass-working experts. My fellow researchers showed me how to set up the furnace and vacuum pump setup, and they clued me in on putting a cold trap between the two parts, so that pump oil would not back-flow into the furnace tube. They also told me that the copper coil I needed for this could be found at a local auto supply store.
After I baked out my samples, I had to close off the glass tube and transfer it to one of those big glove boxes that you may have seen on TV shows where people are working in a lab. The man in charge of keeping the glove box maintained had very large hands, so the gloves were sized to fit him. I have very small hands, so I had to learn to manipulate tiny tweezers and allen wrenches using thick rubber gloves that were several sizes too big for me.
Coating the sample surface was an exercise in patience. Meter in a little gas, let it condense onto the surface, wait for things to settle down, meter in a little more, repeat. Do this until the gas pressure gauge shows that no more gas is condensing down onto the surface. This sometimes took hours. Once, I tried to put two layers down on a surface, and I stayed at it for 36 hours straight before I finally gave up.
After I collected data from my instrument, I used a computer program (written by another colleague) to tease out the tiny signal from the thin film from the much larger signal from my supporting surface. Another computer program would interpret the resulting pattern, but the specific material I was studying hadn't been studied much as a thin film, so I had to piece together what I could from existing information and make reasonable assumptions.
I did manage to put together a general picture of what the surfaces were doing to the thin films. It's been almost 25 years, and others have gone much farther than this than I could.
What I'm getting at is this. In order to see anything at all out of this year-long experience of mine, I had to set up a situation in which I had a lot of time just for me -- my supporting substrate surface. I had to clear out any interfering noise from this time -- residual stress from a long day at work and commuting, much of my extracurricular activity, anything that would take away from what I'm trying to find. After the initial clearing-out, I had to protect my time from re-contamination. Only then could I begin to let in the things that I want to pay attention to.
I'm getting a lot of advice and assistance from friends and colleagues, but ultimately, I'm having to put this thing together myself. And now that little hints of answers are starting to come in, I'm having to try and make sense of what I'm finding out. Looking at what other people have done is giving me a general direction, but ultimately, I'm having to take what I can find and make some reasonable assumptions about the rest.
Very slowly, a little pattern is starting to emerge from the background. Other people may do this more elegantly or simply, but this is my project, and I am having to put together an answer that applies to me. The learning how to do it, the actual process of doing it, and the friends and mentors I'm meeting along the way are just as important (if not more so) than whatever answers I may come up with.