Monthly Archives: October 2008

Proof

A friend of mine, Pete Dougherty, is the keyboardist for a band called Hey Champ, and the just produced a new music video. It’s top notch, if you like a certain sort of repetitive disco-inspired “electro-dance”.

In other news, making things waterproof is really hard.

Progress

Over the past three days I have soldered 5 coax cables, with heatshrink tubing to separate the inner and outer, wrapped them in metal foil tape for shielding, wrapped the shielding in electrical tape for isolation, constructed a housing by drilling holes in a 50 mL centrifuge tube, threaded the circuit into the housing, and covered all joints with RTV-108 caulking. It’s drying now. Tomorrow morning I’ll test it to see if it’s watertight. If it is, I’ll be able to start characterizing my first imaging transducer.

RTV-108, by the way, is pretty cool stuff. It’s actually an “acetoxy adhesive”, which cures by exposure to moisture. That means that unlike almost all other glues, it will cure perfectly fine in a damp environment, and actually sets fastest underwater. Chemically, it cures by converting water into acetic acid, so if you breathe on it, it converts the moisture in your breath into vinegar. That means it doesn’t smell too great, but it gets the job done.

Crunch Bar

My roommate Emily left behind a huge box of Crunch bars, but after their long exposure to the ridiculous heat of this apartment in summer, they had begun to go… tan. You know, when a chocolate bar’s outer surface starts to get chalky, covered in a light-colored powder that doesn’t taste especially good.

I had observed before that melting chocolate tended to reverse this process, and so I set about melting down about a pound of crunch bars, hoping to liquefy them and spoon it back out.

Don’t do this. It doesn’t work.

I remain convinced that it is possible to recover the texture of individual crunch bars that have experience this sort of separation. Raising the temperature slightly is all that is required to recover the original texture, resulting in a crunch bar with the slightly distorted geometry of a fire-damaged TV set.

Going to the full extreme of remelting the chocolate is to invite disaster. For one thing, maintaining a consistent temperature to reach a spoonable consistency without burning the bottom is next to impossible. I wound up with a pot full of Crunch-bar crumbs that refused to melt.

Crunch bars also contain amazingly little chocolate. In each bar, the Crunchy bits are specially placed in the interior of the mold, so that one gets the impression of a smooth chocolate surface. In fact, there are so many Crunchies and so little chocolate that the structural integrity of a congealed crunch-cookie is severely compromised. If you attempt to recover the remaining crumbs by adding a dash of milk and microwaving, you will find that your Crunchies have absorbed the milk and becomes Spongies, ruining the texture of your ganache.

I think I’ll still be able to take in the few successful crunch-cookies for dessert at lunch, but I have serious concerns about them arriving without getting pulverized.

Soldering

I just spent two hours soldering a single link between two cables. Evidently, I am terrible at soldering. It didn’t help that they’re both coax, and one of them is about as thick as a heavy thread.

In other news, I woke up Saturday morning with a very sore throat. It’s gone now, replaced by mild generic congestion, but perhaps it’s just as well that I didn’t get to spend Friday night out on a mountainside in New Hampshire.

Abject Failure

We did not go to New Hampshire. We did not see any stars.

Of the 13 people who told me they really wanted to go, two dropped out for unknown reasons, one became ill, another stayed home rather than leave her alone, and another could not come because of canvassing for Obama (which, although it happens in New Hampshire, is difficult to synchronize with our schedule, and typically takes place far from the area we would be staying). Of the 8 remaining people who told me they were definitely going to come, one fell ill, another stayed home to care for him, one decided she had other plans, and one decided that she didn’t want to go with such a small group. That left 4 people who actually were willing to go, and far more than 4 people who want to go but couldn’t tonight. All the most enthusiastic participants couldn’t make it. I decided to cancel the trip, and hope to do it some other time. That’s a bit optimistic though, since next week’s Halloween, and we need clear skies, no moon, and reduced scheduling conflicts, all at the same time on a Friday or Saturday night. In fact, we can only do the itinerary I had planned on a Friday night, because that’s when the Dartmouth observatory is open. By the time we ever make this work, the planets will have aligned too.

I spent all week working on this, and the past two days frantically hashing out details of getting keys for one cabin or another, renting sleeping bags, tarps, cars or minivans, arranging pickups in Boston and Cambridge, according to different schedules… all for naught. I am never planning anything ever again.

Motion

My project’s first baby step succeeded today. I was able to hook up a motor to a phantom (a dummy object used to study MRI or ultrasound) and move it back and forth inside the bore of the magnet in order to mimic the motion of the patient due to breathing.

In the abstract, this should be beyond simple. Just attach a dowel to a disk attached to the driveshaft, like the rods visible on a steam locomotive. Unfortunately, there’s a catch: nothing ferrous or magnetizable can be allowed anywhere near the MRI, and no metal of any kind can stay inside the bore. A DC motor is even worse, since it actually contains fixed permanent magnets. If brought anywhere near the MRI, it will tear itself out of your hands, or free of its supports, and fly through the air into the middle of the magnet, possibly causing millions of dollars worth of damage or injury in the process. To be safe, therefore, we cannot allow a motor into the room.

The room has extensive electromagnetic shielding, and the only hole is a “waveguide”: a copper pipe a few inches in diameter through which cables and such may be routed. Therefore, it seemed logical enough to me to place the motor just outside this waveguide, and transmit the motion through a long flexible coupling. Specifically, I took one of our standard vinyl hoses, typically used to fill our fishtanks, and threaded about 15 feet of thin nylon rope through it. The hose is attached to the motor-mount with velcro, and the motor pulls on the string. You can’t push a string, so I set up a primitive counterweight on the far side to maintain tension. Since it’s inside the bore, the counterweight can’t be metal, so it’s a plastic bottle full of water.

In one of the magnets, the path from the waveguide into the bore of the magnet is a straight shot, but that magnet is rarely available. At the machine that is more often available, the path is rather tortuous, especially now that another research group has taken to storing enormous immovable electronic devices right in front of the waveguide. The path turned out to have so many bends that the friction of the string rubbing against the inside of the tube exceeded the strength of the motor.

Today we tried a different approach: leave the door open. Many MRI machines won’t run with the door open, but this one will. Running with the door open, and a heavy steel DC motor right outside, does inspire a certain amount of nervousness, but in fact our setup is perfectly safe. Safety standards require that the magnetic field be negligible outside of the magnet room. With the door open, the path from the motor to the bore is nearly straight, and so it was with great joy, but not surprise, that I watched my phantom move back and forth, like breathing.

We also sent off the National Instruments digitizer board for repair. Once it comes back, I’ll be using it to receive ultrasound data for the next stage of this experiment.

Things are moving.

Social

Friday was a party for OLPC. Saturday night was a party with Harvard and MIT people, including one who works at the TeVatron. Tonight a friend from Biophysics threw a great dinner party (topic: education), and then there was Sunday night drinks with some local nerd friends, where I spent most of the evening attempting to explain how MRI works.

Until the LHC comes online, the TeVatron is still the most powerful particle accelerator in the world, with a collision energy about 1 Tera-electron-Volt (hence the name). We ran some numbers at the party, and determined that 1 TeV = 1.6 * 10^-7 Joules, which, dissipated over the diameter of a proton (about 10^-15 meters), corresponds to force of about 1.6 * 10^8 Newtons. That’s the amount of force required to lift a 16,000 ton object. The CDF detector at the TeVatron, approximately the size of a large office building, weighs about 5,000 tons, so that means that each interaction inside the detector momentarily produces enough force to lift the detector, though that force is not actually applied to the detector.

That force, incidentally, is being applied over a surface area of a single proton (about 10^-30 m^2), for a pressure of about 10^38 N/m^2, or about a decillion atmospheres (10^33).

You can see why people don’t normally use these terms. (Also, by failing to account for relativity or quantum mechanics, these numbers are so bad they’re not even wrong.)

Moon

For the past few months, at least, I’ve been suggesting a trip to the North for stargazing. The problem, as you can see on this map, is that Boston is a center for extreme light pollution, to the point that only a few stars are ever visible. I remembered the deep, dark sky, with thousands of stars, from camping trips when I was young (and more recently from the edge of the Sahara), but it’s been years since I’ve been somewhere dark enough to see the Milky Way. As the map shows, the best place to find darkness near Boston is north, into New Hampshire and Maine.

I’ve been talking about this for long enough that I was astounded when a friend forwarded me a message from the Harvard Outing Club which, together with the Society of Physics Students, is sponsoring a stargazing trip in New Hampshire. They’re bringing telescopes and at least a dozen people, many of whom probably actually know something about astronomy. They are staying at the Harvard Cabin, a great big house in the middle of the woods at the foot of Mount Washington, maintained by the Appalachian Mountain Club. There will be hiking, and presumably the organizers know of a spot with an unobstructed view of the sky. The weather forecast calls for no rain and minimal cloud cover. Food will be provided, and the whole trip is free, sponsored by the Harvard Physics Department. It sounded too good to be true.

Unfortunately, there’s a hitch. The trip is this Saturday, the 18th. Full moon was this Tuesday, the 14th. That means the moon will be nearly full, and will rise at 8:24 EDT. The organizers estimate that we will have about two hours of good darkness before the moon rises and outshines the rest of the sky. I tried to convince them to move it back a week, but I was too late.

Next weekend, the moon won’t rise until 3 AM or later, so we will have ideal darkness in which to view the whole sky. What we won’t have is a big group to go with, any guarantees about the weather, any knowledge of astronomy, or any telescopes. We can still stay at the cabin, though we also have other options. Perhaps we could visit the observatory at Philips Exeter or Dartmouth or the University of Maine or UNH during their public hours on Friday or Saturday evenings. The ideal place to go is Franklin County in Northern Maine, where the light pollution map shows black. Unfortunately, it’s a 5 hour drive straight North into empty wilderness, so I expect we’ll content ourselves with the darkness available in central NH.

The biggest factor that makes me want to go with the big group this weekend is … the big group. I’d be a lot happier if we had a bigger crowd. Anyone want to go stargazing? We’re talking about a < 24 hr commitment, some Friday or Saturday night. Astronomical expertise not required.

Watch

Several years ago, my grandfather gave me a very nice watch, and I wore it everywhere. After a few years, the battery ran out, and we had it replaced. After a few more years the watch began to fail again, though in a way that suggested to me that it might not be just a battery failure. After months of dithering, in search of a watch repair place in Boston, I brought it home to the same jeweler who’d replaced the battery previously.

When I picked up the watch it worked, and it continued working … for about 24 hours. First the stopwatch stopped working, and then everything stopped. I brought it back. The jeweler said he’d send it back to his watch guy to see what was needed. He did, and when I was back in town I returned to pick it up. It was working again, and he explained that all they’d done was replace the battery. No repair work was required.

Unfortunately, I quickly made some very unpleasant discoveries. The repairman had evidently failed to reseat (or replace) the gasket properly, resulting in a watch that was not even remotely water resistant. Every time I wear it, the moisture from my skin evaporates into the interior of the watch, and condenses on the inside face of the front crystal. The movement also stopped within two days, although this time the stopwatch continues to function. Additionally, the repairman left a major scratch on the backplate.

I am not sure what to do about this. This watch probably experienced a mechanical failure of its own, and was then further damaged by the third-party repair service hired by the jeweler in Westport. I have no idea whether these sorts of expensive Swiss watches are generally possible to repair, how much they generally cost to repair, or where to get them repaired. However, I’m not inclined to spend a lot of money fixing it because I don’t have any investment in it. It didn’t cost me anything to buy, and if I understand correctly, it was a gift to my grandfather in the first place, so no one ever paid any money for this watch.

Maybe I should just go to Target and buy a cheap Chinese watch. Does Costco sell watches?

Alum

I spent this weekend in Vermont with a bunch of Chorallaries alumni. It’s hard to explain exactly what we were doing there. On one level, it’s very simple. We are a bunch of friends from college who hadn’t seen each other in months or years and are now scattered all over the country. We decided to rent a house and spend a weekend together, cooking, eating and partying. (I had hoped there might be an internet connection, but without one, it was difficult to get any work done.)

It’s also much more complicated than this, because the house we rented was just a few hundred feet from the house where the current Chorallaries were staying on their annual retreat, and where we go every year. In some sense, we were retracing our steps and indulging in a bit of nostalgia. In fact, the house we rented was exactly the same one that we rented when I was in the group my senior year. We were also there to hang out with the current Chorallaries, meet the new freshmen, and generally build continuity.

It was a lot of fun, but that was no surprise. There was lots of singing, watching movies, wandering in the beautiful crisp fall weather, and generally hanging out with people I love.