Another convenient thing about oxybenzone is that it is soluble in most organic solvents (nonpolar) and less so in water, so it's fairly water-resistant.
Monday, March 4, 2013
Sunscreen!
The way that sunscreen works is using a certain molecule, oxybenzone, which can absorb UV photons and reemit lower-frequency photons. Based on the fact that it absorbs photons with around 100-nm wavelengths, we know that the energy difference between its ground state and its first excited state is exactly the energy carried by such a photon, which is simply $\frac{hc}{\lambda}$. So we can actually calculate the probability that any given oxybenzone molecule is in an excited state at beach-temperature (independent of the incoming UV, which is greatly reduced by the atmosphere). It turns out that only about one in 10^200 oxybenzone molecules is in its excited state because of the ambient temperature (around 300K). That's a seriously small fraction, and speaks to the effectiveness of sunscreen.
Sunday, March 3, 2013
Phun Physics Phact of the Day
Physics is really cool. I'm not sure how long this will last, but I'd like to share some fun facts. Here's one:
Castor, one of the twin stars in Gemini (as in the constellation, not a movie star who plays a twin in a TV show called Gemini), is actually six stars. Castor A and B are a visual binary, which means that using a powerful telescope, one can see that there are really two separate stars. Further investigation reveals that Castor A and Castor B are actually both spectroscopic binary systems.* That makes the system a quadruple star system. But wait, there's more! There's another, far dimmer, system called YY Gem that is much further away from the quadruple we've already discussed. And did I mention that it's a binary system too? Basically it is far enough away from the other stars that it responds to Castor A/B as if the collection of four stars is just a large massive object, and is in a 'binary' system with them. And this whole thing manages to stay gravitationally bound. Fun, right?
* Spectroscopic binary systems are detected by examining the Doppler shift of spectral lines as the brighter of the two stars wiggles back and forth in response to the orbit of the dimmer one - as it wiggles towards us, the spectral lines are all slightly blueshifted, and they're redshifted as it wiggles away from us. It's useful for detecting binary systems in which the two stars are very close together, which makes them difficult or impossible to distinguish visually. The really amazing thing about this measurement is that the amount of blue or redshifting that occurs is generally smaller than the natural width of the spectral line. Observational astrophysics is awesome.
Note: A binary star system is one in which two stars orbit their mutual center of mass. There are a variety of ways to detect them (see the Wikipedia page for a fairly comprehensive explanation), and it's believed that something like 60% of stellar systems are actually binary star systems. So our single-star solar system is actually in the minority!
Castor, one of the twin stars in Gemini (as in the constellation, not a movie star who plays a twin in a TV show called Gemini), is actually six stars. Castor A and B are a visual binary, which means that using a powerful telescope, one can see that there are really two separate stars. Further investigation reveals that Castor A and Castor B are actually both spectroscopic binary systems.* That makes the system a quadruple star system. But wait, there's more! There's another, far dimmer, system called YY Gem that is much further away from the quadruple we've already discussed. And did I mention that it's a binary system too? Basically it is far enough away from the other stars that it responds to Castor A/B as if the collection of four stars is just a large massive object, and is in a 'binary' system with them. And this whole thing manages to stay gravitationally bound. Fun, right?
* Spectroscopic binary systems are detected by examining the Doppler shift of spectral lines as the brighter of the two stars wiggles back and forth in response to the orbit of the dimmer one - as it wiggles towards us, the spectral lines are all slightly blueshifted, and they're redshifted as it wiggles away from us. It's useful for detecting binary systems in which the two stars are very close together, which makes them difficult or impossible to distinguish visually. The really amazing thing about this measurement is that the amount of blue or redshifting that occurs is generally smaller than the natural width of the spectral line. Observational astrophysics is awesome.
Note: A binary star system is one in which two stars orbit their mutual center of mass. There are a variety of ways to detect them (see the Wikipedia page for a fairly comprehensive explanation), and it's believed that something like 60% of stellar systems are actually binary star systems. So our single-star solar system is actually in the minority!
Sunday, November 4, 2012
On approximations
Approximations are cool. Really. I'm gaining a whole new appreciation for them this semester. For one thing, I'm in my first ever 'engineering' class, and really, all of engineering is based on approximating. Approximate a woodpecker as a mass spring system (no, seriously, see this link. In particular, check out the diagram on page 5). Approximate a spring as linear. Approximate, approximate, approximate.
Or take my theoretical mechanics class. We find crazy systems of differential equations and then approximate to solve them. Or solve them numerically, which involves approximating every step of the way (no pun intended).
Anyhow, the reason I was inspired to post after all this time was a combination of two quotes. The first:
"How fast is this rocket going? Just a general guess."
"Erm ... very fast."
"No, I want one sig. fig., not zero!"
And the second:
"It turns out 4 is a really lousy approximation for pi"
I will admit to being the speaker for the second quote. I was trying to create a wire binding for a small handmade book, and needed this coiled wire to be a circle with a given radius. Not being one for measuring sticks, I needed to figure out how long I needed to coil the wire before tying off. Since I wanted a circle of at least that given radius, I figured I'd round pi up a bit, but ... well, as the quote says, 4 is a pretty lousy approximation for pi.
Ah, the adventures of life.
:-)
Or take my theoretical mechanics class. We find crazy systems of differential equations and then approximate to solve them. Or solve them numerically, which involves approximating every step of the way (no pun intended).
Anyhow, the reason I was inspired to post after all this time was a combination of two quotes. The first:
"How fast is this rocket going? Just a general guess."
"Erm ... very fast."
"No, I want one sig. fig., not zero!"
And the second:
"It turns out 4 is a really lousy approximation for pi"
I will admit to being the speaker for the second quote. I was trying to create a wire binding for a small handmade book, and needed this coiled wire to be a circle with a given radius. Not being one for measuring sticks, I needed to figure out how long I needed to coil the wire before tying off. Since I wanted a circle of at least that given radius, I figured I'd round pi up a bit, but ... well, as the quote says, 4 is a pretty lousy approximation for pi.
Ah, the adventures of life.
:-)
Friday, February 10, 2012
Fun things
I know I haven't posted in a while; I apologize.
I just wanted to share a couple of fun things going on right now.
First off, for the first time, I have unicycled wearing a skirt (and shorts underneath, but that's not the point!). The scariest thing is the dismount, because if my skirt catches on the seat, it sends either me or the unicycle into the ground.
Second, experimental archaeology is a legitimate field. Enough said.
I just wanted to share a couple of fun things going on right now.
First off, for the first time, I have unicycled wearing a skirt (and shorts underneath, but that's not the point!). The scariest thing is the dismount, because if my skirt catches on the seat, it sends either me or the unicycle into the ground.
Second, experimental archaeology is a legitimate field. Enough said.
Sunday, January 22, 2012
Successful use of the Meta key
In case I haven't mentioned it before, I'm an emacs person. Well, I finally found how to use something other than the escape key as emacs' Meta key. The Meta key is another command key, like Command on the Mac keyboard or Control on Macs or PCs. On Windows machines, the Alt key is automatically used as the Meta key, but for some reason, the Alt/Option key on the Mac isn't set to Meta in emacs. It's bothered me for about as long as I've had my computer. However, today I finally figured out how to fix it! It has to do with not emacs but Terminal, the command-line interface in Mac OS-X.
In Terminal, go to Terminal > Preferences > Settings > Keyboard and check the 'Use Option as Meta key' checkbox.
Hooray!
Thanks to this website for describing the solution!
In Terminal, go to Terminal > Preferences > Settings > Keyboard and check the 'Use Option as Meta key' checkbox.
Hooray!
Thanks to this website for describing the solution!
Monday, December 12, 2011
Mountain Unicycling!
This is finals week, which means that I have no classes and a lot of take-home exams. I decided yesterday that the best possible place to take an exam was in the mountains. So I packed a couple meals for myself, hopped on my unicycle, and headed north. I was even feeling organized enough to snap a picture of myself:
 |
| I'm actually pretty happy with how this shot turned out. |
Three miles later, I hit the Claremont Hills Wilderness Park, which contains a beautiful 5-mile mountain trail. The base of the trail was a little shady, and the temperature hadn't yet risen above 60 (in the middle of December! Seriously, SoCal, I'm disappointed in your inability to stay warm...), so I decided to head upward.
A few notes on mountain unicycling:
1) Mountain trails are steep! It's difficult enough to bike up them - unicycling is downright crazy. But I got great traction, and managed to stay on the unicycle for pretty decent chunks of time. The biggest problem I encountered was free mounting (getting onto the unicycle without a wall) on a steep incline. When I couldn't make it any further, I generally ended up getting off and walking up to the next (relatively) flat spot.
2) If you ever need an ego boost, ride a unicycle on a busy mountain trail. The crazy looks, spontaneous laughs, and complements make all the hard work worthwhile. I even had one group ask if they could take a video of me...
3) Uphill is hard, downhill is terrifying. Once, I almost passed a bicyclist. I was very impressed with myself. Then, we hit a downhill bit. The bicycle has brakes; the only way I can brake is by never going too fast in the first place. I'm pretty sure I went slower downhill than up because of that.
In any case, I had a great time. I was riding uphill, focusing on not falling, and looking for a nice place to stop and study chemistry. I looked up for a moment, and was practically blown off my feet (off my wheel?). The scenery was beautiful!
I also caught a glimpse of Claremont, which was apparently a little foggy that morning:
I found a nice place to sit and study chemistry, then went a little further on and found a place to take my chemistry exam (which I'm not allowed to discuss until 5:00 pm today - I may update this post after that). I read a little, munched on some trail mix, and then tackled the remaining 3.5 miles of the loop. Yes, I could have just turned around and gone 1.5 miles back, but the way I'd come was pretty steep, and I wanted to see the other portion of the trail. It was an amazing ride. I'll certainly be returning to the park later this week or next semester.
In any case, I eventually got back to campus, after a grand total of around 10-11 miles of unicycling. I was checking out my unicycle and brushing off the dust when I spotted a little pebble lodged in the tread of my wheel. I flicked it out, then heard the sound all bicyclists dread: pshhhhhhhhh. I now have a completely flat tire, which is rather sad. I'll have to see if I can find a patch before the end of finals so I can return the unicycle to the club. (Yes, I'm still using a borrowed unicycle. I'm hoping to get one of my own over break - I have my eye on the Nimbus 26" Mountain unicycle, which gets awesome reviews and is actually designed for mountain unicycling.)
Edit (13:00 Dec. 12): Thanks to the Pitzer College Green Bike Program, the unicycle has a patch and is rolling as usual again! Hooray!
Further edit (11:45 Dec. 13): False alarm! It appears I have another hole in my tire, as my wheel is completely flat again this morning. Unfortunate.
Further further edit (19:30 Dec. 13): Hooray! I paid another visit to Green Bikes this afternoon, where I found a nice little thorn on the inside of the tire tread. I've removed that, patched the tire again, and tightened all of the loose bolts on the seat. I'm glad to be returning the unicycle in better condition than I found it.
On a somewhat related note, I found an awesome blog by a mountain unicyclist: Unplanned Dismount. The author has a great sense of humor, and it sounds like he does a lot of the same kind of riding I'd like to be able to do someday. He also gives a lot of reasonable-sounding tips, though I can't try them out at the moment thanks to my little experience with a thorny pebble.
A few notes on mountain unicycling:
1) Mountain trails are steep! It's difficult enough to bike up them - unicycling is downright crazy. But I got great traction, and managed to stay on the unicycle for pretty decent chunks of time. The biggest problem I encountered was free mounting (getting onto the unicycle without a wall) on a steep incline. When I couldn't make it any further, I generally ended up getting off and walking up to the next (relatively) flat spot.
2) If you ever need an ego boost, ride a unicycle on a busy mountain trail. The crazy looks, spontaneous laughs, and complements make all the hard work worthwhile. I even had one group ask if they could take a video of me...
3) Uphill is hard, downhill is terrifying. Once, I almost passed a bicyclist. I was very impressed with myself. Then, we hit a downhill bit. The bicycle has brakes; the only way I can brake is by never going too fast in the first place. I'm pretty sure I went slower downhill than up because of that.
 |
| Mountains all the way! |
I found a nice place to sit and study chemistry, then went a little further on and found a place to take my chemistry exam (which I'm not allowed to discuss until 5:00 pm today - I may update this post after that). I read a little, munched on some trail mix, and then tackled the remaining 3.5 miles of the loop. Yes, I could have just turned around and gone 1.5 miles back, but the way I'd come was pretty steep, and I wanted to see the other portion of the trail. It was an amazing ride. I'll certainly be returning to the park later this week or next semester.
In any case, I eventually got back to campus, after a grand total of around 10-11 miles of unicycling. I was checking out my unicycle and brushing off the dust when I spotted a little pebble lodged in the tread of my wheel. I flicked it out, then heard the sound all bicyclists dread: pshhhhhhhhh. I now have a completely flat tire, which is rather sad. I'll have to see if I can find a patch before the end of finals so I can return the unicycle to the club. (Yes, I'm still using a borrowed unicycle. I'm hoping to get one of my own over break - I have my eye on the Nimbus 26" Mountain unicycle, which gets awesome reviews and is actually designed for mountain unicycling.)
Edit (13:00 Dec. 12): Thanks to the Pitzer College Green Bike Program, the unicycle has a patch and is rolling as usual again! Hooray!
Further edit (11:45 Dec. 13): False alarm! It appears I have another hole in my tire, as my wheel is completely flat again this morning. Unfortunate.
Further further edit (19:30 Dec. 13): Hooray! I paid another visit to Green Bikes this afternoon, where I found a nice little thorn on the inside of the tire tread. I've removed that, patched the tire again, and tightened all of the loose bolts on the seat. I'm glad to be returning the unicycle in better condition than I found it.
On a somewhat related note, I found an awesome blog by a mountain unicyclist: Unplanned Dismount. The author has a great sense of humor, and it sounds like he does a lot of the same kind of riding I'd like to be able to do someday. He also gives a lot of reasonable-sounding tips, though I can't try them out at the moment thanks to my little experience with a thorny pebble.
Tuesday, December 6, 2011
There will be blood
And here I thought I had bad circulation when I had all my blood in my system...
I donated blood today, a pint, which ends up being around 10% of the blood in my veins. It wasn't nearly as scary as I thought it would be. It's also nice to know that my blood, literally a part of me, might have some role in saving someone else's life. Oh, and the coupon to Coldstone certainly doesn't hurt. I'm sure I can find someone else who wants it.
I'm not allowed to do 'strenuous exercise' for the next (*checks watch*) 17 hours and 50 minutes. That meant that at today's Ultimate practice, I found myself in the role of filmmaker. It's funny how an hour and a half of watching Ultimate through a camera made me so much better at commentating. I still occasionally forget to pan with the play or some such rookie mistake, but I think I'm getting better.
Also, it's pretty darn cold for Southern California. It'll be just above freezing overnight. Standing around filming, in the cold, with rather substantially less blood than usual, when I have bad circulation even with all of my blood, is just a recipe for Frosty Freshman. It was a relief to eventually head to a team dinner in the pleasantly warm dining hall.
All in all, though, it was a rewarding experience, and I suspect I'll be donating again in the future.
I donated blood today, a pint, which ends up being around 10% of the blood in my veins. It wasn't nearly as scary as I thought it would be. It's also nice to know that my blood, literally a part of me, might have some role in saving someone else's life. Oh, and the coupon to Coldstone certainly doesn't hurt. I'm sure I can find someone else who wants it.
I'm not allowed to do 'strenuous exercise' for the next (*checks watch*) 17 hours and 50 minutes. That meant that at today's Ultimate practice, I found myself in the role of filmmaker. It's funny how an hour and a half of watching Ultimate through a camera made me so much better at commentating. I still occasionally forget to pan with the play or some such rookie mistake, but I think I'm getting better.
Also, it's pretty darn cold for Southern California. It'll be just above freezing overnight. Standing around filming, in the cold, with rather substantially less blood than usual, when I have bad circulation even with all of my blood, is just a recipe for Frosty Freshman. It was a relief to eventually head to a team dinner in the pleasantly warm dining hall.
All in all, though, it was a rewarding experience, and I suspect I'll be donating again in the future.
Tuesday, November 15, 2011
Umm...Prolog?
Prolog is a really neat concept. The idea is that in a program, you give the computer facts and tell it how to recognize a solution, and then the computer finds all possible solutions. Great. I'm in the process of debugging a predicate (kind of like a function) right now, and I accidentally stumbled upon this:
I love programmers' sense of humor.
Anyhow, back to debugging!
Edit: It seems that this is what happens whenever you ask the Prolog command line the value of a variable. Variables start off as unbound (nothing), so they had to come up with some kind of error message, and decided on a creative one.
Sunday, November 6, 2011
An adventure!
At Mudd, I live only a few miles from the base of the nearest mountain. It turns out that it's really a 2.8-mile straight shot down a single road - even I couldn't possibly get lost on the way. Anyway, last night, I decided that today would be the perfect day to go check it out. I packed myself a breakfast, set out gobs of layers against the (gasp) forty degree weather in the mornings, and got up early to head out. Even the threat of light drizzles throughout the morning wasn't enough to dissuade me. Unfortunately, I don't have the endurance (or the time) at the moment to run a solid six miles in a single go, but that just made it the perfect unicycle outing.
It was glorious. The rain (mostly) held off, with just a few light showers here and there along the way. It was an amazing feeling to watch the mountains, a constant backdrop around here, slowly getting closer over the course of a half-hour ride. The sidewalks were pretty awesome, too. It's like they were designed for fledgeling unicyclists to practice on!
I would totally post a picture of the curvy paths here, if I hadn't just somehow lost all the ones I took between the memory card from my camera and my pictures folder. I suppose I'll have to get a picture next time!
I reached the trailhead for a 5-mile loop, which looks like an awesome trip. It was pretty busy today, probably because it's a weekend, but I might be able to pay it a longer visit in relative isolation during the week (now that it's the second half-semester, I only have one class on both Tuesdays and Thursdays). I look forward to exploring it more!
It was glorious. The rain (mostly) held off, with just a few light showers here and there along the way. It was an amazing feeling to watch the mountains, a constant backdrop around here, slowly getting closer over the course of a half-hour ride. The sidewalks were pretty awesome, too. It's like they were designed for fledgeling unicyclists to practice on!
I would totally post a picture of the curvy paths here, if I hadn't just somehow lost all the ones I took between the memory card from my camera and my pictures folder. I suppose I'll have to get a picture next time!
I reached the trailhead for a 5-mile loop, which looks like an awesome trip. It was pretty busy today, probably because it's a weekend, but I might be able to pay it a longer visit in relative isolation during the week (now that it's the second half-semester, I only have one class on both Tuesdays and Thursdays). I look forward to exploring it more!
Spoiled
Ah, I love Southern California. It's early November, and I can still viably wear shorts and a t-shirt outside, as long as I'm relatively active. Even so, the practically freezing fifty degrees this morning had me wearing a sweatshirt, jacket, and gloves. I shudder to think what I will be like when I go home.
Both the open and women's team here have started cranking up their practices. I now attend practice on six days of the week, plus a scrimmage on Saturdays, and sprint practice on Sundays. I love it, but I'm starting to question the viability of a solid 14 hours of Ultimate per week, plus around four hours of other relatively strenuous exercise (running/sprints) and probably 2-3 of moderate exercise (walking, unicycling, biking). Time is starting to become a major factor.
Ah, well. I'm sure I'll figure something out.
Enjoy the extra hour of sleep tonight!
Both the open and women's team here have started cranking up their practices. I now attend practice on six days of the week, plus a scrimmage on Saturdays, and sprint practice on Sundays. I love it, but I'm starting to question the viability of a solid 14 hours of Ultimate per week, plus around four hours of other relatively strenuous exercise (running/sprints) and probably 2-3 of moderate exercise (walking, unicycling, biking). Time is starting to become a major factor.
Ah, well. I'm sure I'll figure something out.
Enjoy the extra hour of sleep tonight!
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