Tidbits: Mantle Plumes, Bar Codes, Late-Night Comic Reading, Long Naps, and PowerBooks

Friday, 2004-04-09; 01:18:00

One seriously long tidbit entry!

Hmm, I haven't done a tidbits entry in a couple months, so I might as well get a bunch of things I've been meaning to write about out of the way. ReadyGO!


I have to say that I'm loving my volcanology class so far. We're learning some interesting stuff, and the labs aren't so annoying that you spend so much time working on them (as opposed to certain OTHER geo classes I'm taking this quarter *coughstructurecough*).

One of the coolest things I've learned was during class last Wednesday. We were talking about Hawaiian-style volcanic eruptions (i.e.: non-explosive eruptions that make really large but gently sloping volcanoes). The prevailing theory up until this point to explain volcanism like Hawaii and Yellowstone is that there's something called a "mantle plume" that originates deep in the Earth's mantle (or perhaps at the mantle-core boundary) and happens to come up in the middle of a tectonic plate. In doing so, it melts the rock in the overlying plate, causing the volcanism at that location.

The reason why you get a chain of Hawaiian islands, according to this theory, is that since the tectonic plates are composed of lithosphere (basically the Earth's crust) and asthenosphere (bottom part of the Earth's crust and the very top part of the Earth's mantle), they "ride" on top of the underlying mantle rock. The lithosphere and asthenosphere are just terms to indicate the structural characteristics of the layers of the Earth, which differ slightly from the compositional differences (which is how the crust, mantle, and core are divided).

Since the mantle plume is coming up from the mantle, it stays fixed while the tectonic plate moves over that spot. So you end up getting a chain of islands originating from the mantle plume or "hot spot", since the plate is moving relative to the hot spot. This theory also explains Yellowstone National Park and the volcanism over in that area.

It turns out that this theory, which is something that has always seemed like "fact" in my geology classes, is actually breaking down. Geophysical data (like seismological data and such) seems to be showing that there is no mantle plumes at all. Mantle plumes would be detectable in geophysical data because of their differences in temperature and to a limited extent composition (depending on where the mantle plumes originate). Another theory that could possibly replace the "mantle plume" theory is that of volcanism similar to a propagating crack -- with shield volcanoes (the fancy name for Hawaiian-style volcanoes), you often get magma migrating laterally through the Earth's crust and concentrating in certain areas only because of random chance. This theory relates that small-scale process to large-scale processes like hot spots in the middle of plates -- volcanism could be spreading laterally throughout the whole plate, and it's just chance where the crack happens to be wider. At these wide spots, magma comes out a faster rate, which in turn melts the edges of the crack to make it wider, which allows more magma to come out. That could be why these hot spots seem to concentrate themselves in one area.

I think it's just cool that a theory that I had always taken for granted is being turned on its end.


In another cool (but kind of pointless) thing that I learned in my math class is related to bar codes. This class is also a number theory class (like the one I took fall quarter of last year), but it's more applications-oriented than theory-oriented, and I think we're also going to get into something called "field theory", rather than just number theory. But I digress.

Have you ever noticed that sometimes mail you receive often has a barcode stamped on it in the bottom-right hand corner? It's actually the bar code that machines use to sort the mail and send it off to the appropriate places. But it's not a terribly secret code, and you can actually see what the code means. There's also another cool thing about this code that I'll point out later.

Here's a typical barcode that I pulled from an envelope I received from the Office of the Bursar at Stanford:

Looks relatively illegible, right? Well, here's what you do to decode it. First, ignore the first and last lines of the bar code. They're always going to be long lines, and they're just delimiter lines. Then, split the rest of the lines up into groups of 5, like so:

Notice something interesting about all the groups of 5? There's only two longs per group. This is going to become important later. Anyway, now you just have to know the key to decode the bar code. Here it is:

Once you see it, it's relatively easy to remember it. If you then decode the bar code on my envelope, you'll see that it turns out to be 943097081810 . The first 5 digits are always the zip code, and the next 4 digits are usually the second part of the zip code that you often see on some envelopes. In my case, it seems to be related to my post office box, since 94309 is the zip code dedicated solely to the Stanford post office. Cool, huh?

Not only that, but this code is what's called an "error-detecting" code. When a machine reads this code, if it finds a set of five lines that doesn't have two long lines in it, it immediately knows that something went wrong -- either the bar code was printed wrong, or the machine didn't read it correctly. If you used ordinary binary code, you'd still have to use at least 4 bars per number (since 9 is represented as 1001 in binary). So by simply adding one-fourth more than the least number of lines needed, you get an efficient error-detecting code. Isn't that awesome?

Well, I think it is. Obviously there's no real practicality associated with this knowledge, since you could just look at the address instead of the bar code and not have to decode anything. But I think it's just cool knowing how those bar codes work.


Switching gears... one thing I've noticed about myself is that when I find something new, I tend to overly indulge myself in that thing for a bit, and then I get sick of it and don't want to see it again for a while. I do that with new songs that I get, and I also tend to do that with online comics. The offshoot of this is that I am sick of a lot of the music that I have in my library, only because I listened to it a lot at the start.

An example of this is last night... I must've spent like 6 or so hours just reading through literally all the archives of Ozy and Millie. There were a lot of other more productive things that I could've been doing (like a big long nap), but I ended up staying awake until 4 AM this past morning just reading all those strips. Blah. Not only did that rack up some sleep debt, it's made me sick of the comic. Nothing against the creator or anything, but I simply read too much in one sitting.

Meh, I need to figure out how to regulate these "new stuff" sessions.

(Incidentally, Ozy and Millie is way too much like Calvin and Hobbes to be coincidental. I mean, in the archives, the author doesn't explicitly say it, but he's obviously been highly influenced by Bill Watterson's work, since he references Calvinball in one strip, and he says he doesn't like using grays in his comic because Watterson didn't either. But a lot of the jokes are recycled from Calvin and Hobbes -- the "poker butt" joke, the "game where you basically do anything you want" joke, the "make fun of the bully by using large words" joke, the "singing pop songs really loudly" joke, the "one wacky main character being friends with one aloof and contemplative character" theme, etc., etc. It gets a little old after a while. I mean, if you took a Calvin and Hobbes strip, replaced Calvin with Millie and Hobbes with Ozy, you'd basically have an Ozy and Millie strip.

Again, nothing against the author, especially because the comic IS admittedly pretty funny and it does have its unique aspects, like Llewellyn the dragon and the actual direct political world references. But a lot of the time, I might as well just open a Calvin and Hobbes book instead.)


Incidentally, I DID take "a big long nap" yesterday before I started that long Ozy and Millie archives marathon reading session. I slept for 3.5 hours from about 7:30 until 11! Wow was I groggy after I got up. That's also probably why I didn't feel too sleepy until about 3 AM or so. Good to know that I can actually sleep that long during the day.. I'll probably need to take advantage of that this quarter.


Lastly, it seems that I'll probably inherit a PowerBook. Not that I'm going to toss out my iMac or anything, since the PowerBook I'm receiving only has a clock speed of 667 MHz (if I remember correctly).

My dad was apparently at the DMV trying to get his keys out of his backpack, and in doing so he accidentally dropped it with his PowerBook inside. Since the backpack he uses is not well padded, the corner of the PowerBook that hit the ground got mangled, putting a small crack in the casing on the front-left corner and making it so the battery couldn't come out. My dad says he was able to bend the casing back so that the battery will come out even while sitting correctly in the battery bay, so it's an entirely usable PowerBook still. The screen isn't cracked either, which is good.

I think he's just looking for an excuse to get one of the new 15" aluminum PowerBooks. He's looking at the 1.25 GHz 15" one with the backlit keyboard and SuperDrive. That should be one sweet machine, but at least I'll get a fairly good PowerBook myself. That should help when I go off to Italy.


And that's all he wrote! I'm out.

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