a real, if paraphrased, exchange on the subject of swimming after eating:
[friend's boyfriend]: …and then you’re full so you sink like a brontosaurus.
me: Current models have brontosauruses with a system of internal air sacs like birds, so you’d probably float less efficiently than a brontosaurus. Because you’re a mammal, so you… don’t have the… um, air.
It’s like a disease. I can’t stop myself.
I’m also the type of person where my friends pretty much know that all they have to do to get me to like an item is to slap a Steelers logo or a dinosaur on it.*
And so it is this frame of mind which, in the course of things, brought the following article to my attention a couple years ago: Tipsy Punters: sauropod dinosaur pneumaticity, buoyancy, and aquatic habits.
You know you can’t resist that title.
Brontosauruses are a type of sauropod, the long-necked dinosaurs.** Of course when you use the word “brontosaurus” there’s always the chance someone will jump in with “There’s no such thing as brontosaurus” or something like that, since technically, brontosaurus turned out to be the same as apatosaurus, and since apatosaurus was named first, the brontosaurus name was replaced.***
So, brontosaurus. Floating. Here’s the thing: there are these fossil dinosaur footprints, called trackways, and some sauropod trackways are manus-only, meaning only the front two feet (“hands,” hence manus) put down tracks. The question being, how did this happen?
This could happen for dinosaurs because, according to Henderson’s models, the center of buoyancy and the center of mass of the sauropods isn’t necessarily in the same place. Center of mass is the place in an object where, basically, you can model gravity as acting on just that spot. On humans it’s in the torso somewhere, around the pelvis.
Center of buoyancy is similar; it’s the place in an object where you can model the buoyant force of the water/other substance it’s floating in as acting on just that spot. When floating, if your center of gravity isn’t aligned with your center of buoyancy, it’s like leaning too far over on the balance beam; gravity is suddenly opposed by nothing and you flip over.
Now model the sauropods. Evidence suggests that, like their modern-day relatives birds,**** sauropods had a system of air sacs in their bodies. Henderson’s modeling technique is interesting (slicing!) but I’m not going into it here. Suffice to say that when modeling where the center of mass and center of buoyancy are, those air sacs have to be taken into account or your physics will be very, very wrong.
Say these sauropods wandered into some shallow water (shallow for them, anyway). Gravity would push down on their center of mass, and buoyancy would starting pushing up on their center of buoyancy. According to Henderson’s model, apatosaurus/brontosaurus and diplodocus has a center of buoyancy a little in front of their center of mass, so their front legs started to lift off the ground while their back legs stayed. Camarasaurus and brachiosaurus, on the other hand, had a center of buoyancy a little behind their center of mass, so their hind legs started to lift while their front legs stayed.
Now you should be having hilarious mental images of sauropods punting around, half-floating with just two legs on the ground.
Have some pictures (from the Henderson article, colored dots added for visibility):
So that’s one way a manus-only trackway could show up: if a camarasaurus or brachiosaurus was punting around in the shallows, using just its front legs to propel it. And brontosaurus probably didn’t just sink; it actually might have floated a little bit. Even though it weighed like twenty tons.
*Or both. I have the model of this. And treasure it.
**When you read “long-neck,” if your brain went there: congratulations. You or someone you knew grew up in the ’90s!
***Even though everyone likes it more (and by everyone I mean me); taxonomy operates on a first-one-in-wins rule. This is also the reason that, if the new contention that triceratops is actually an immature torosaurus holds, then torosaurus will become triceratops.
****relatives, not direct descendants.
[note: this post originally appeared on August 10, 2010 at Original Blog (see here for details)]
I’m conflicted as to what to write about today. Solar sails are in the news, but the floatability of brontosauruses was recently mentioned in my presence and trust me, there is a history (of love) there between me and the sauropod buoyancy. Astronomy… dinosaurs… astronomy… dinosaurs…
My very favorite episode of Bones* is on right now, so I’m in a good mood. A bright, sunny mood. The dinosaurs will wait for a rainy day.
I have a powerpoint on solar sails already prepared, but I can’t just post it right up and tell you all to go to town because it’s full of equations,** so I guess we need to talk.***
So, the thing here: the Japanese Aerospace Exploration Agency (JAXA) built a solar sail, shot that puppy up into space, and the sail has now successfully unfolded itself and is ready to be tested as a method of actually steering its spacecraft.
Solar sails work basically like boat sails, except instead of being pushed around by wind, they get pushed around by light. Yay for transparency in naming.
Wait, you might say, that is ridiculous. Light cannot push things around.
Oh, but it can, through the phenomenon named radiation pressure for reasons which are, again, hopefully obvious.
Light, you see, has momentum. Exciting! So do all things that are moving. Usually when we talk about momentum we talk about mass times velocity, but light is made of photons, which don’t have mass. But relativity provides for photons to have momentum anyway. The important thing to take away from this paragraph is that photons have momentum; why is not immediately relevant.
So. Photons whiz along at 186,000 mi/hr or 3×10^8 m/s, with momentum. And then they collide with things, things like you and me and everything we look at, and they impart some or all of their momentum to the things they collide with, exerting pressure on them. Radiation pressure.
Radiation pressure is exceedingly gentle; at 93 million miles from the sun (also called 1 AU, or astronomical unit; about the distance the Earth orbits at), the pressure of the sunlight, around 4.6×10^-6 N/m^2, is incomparably lighter than the brush of a moth’s wing.****
So on Earth, radiation pressure isn’t going to make much of a difference. But in space? It’s a vacuum, so there’s no air pressure, no wind, and once you get out from the influence zone of large objects, no gravity… radiation pressure, gentle though it is, isn’t facing any competitors. So theoretically we should be able to send up some kind of space robot, attach a giant sail to it, and use that sail to float that robot around space like an awesome space-sailing-boat-type-thing.
Sounds awesome, right? Clearly it is or I wouldn’t be writing about it. But because radiation pressure is so gentle–and the farther from the sun our space-boat-robot goes, the gentler the radiation pressure gets–to get up to speeds fast enough to go anywhere in a reasonable time, you need your sail to be both large (to catch as much light as possible) and lightweight (because the more payload the sail carries, the less effect a given amount of radiation pressure has). And it’s not like it’s easy to get large, delicate, lightweight objects into space.
So we can’t send a sail up ready-to-go, it would tear or run into stuff or burst into flame on the way. You need to roll it or fold it or something. We’ve attempted solar sails before, but they failed on launch or wouldn’t unfold and things of that nature.
But now Japan has launched IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun),***** and it unfolded, and now they’re going to test how the sail steers and moves its little robot payload around. Which is awesome: advent of new technology!
Additionally, artists’ renderings of solar sails look super-cool.
*The Witch in the Wardrobe. It makes my heart want to explode in a shower of confetti and stars and other tiny hearts full of sparkles.
**I have two powerpoints about the floating dinosaurs, also full of equations.
***Also, the slides are slightly nonsensical without accompaniment
… as it should be.
****Though, when panicked, luna moths can actually get some surprising force behind there. I know this because I have been repeatedly smacked in the face by one. But don’t let this anecdote distract you from the point: radiation pressure is minute.
*****No points for spotting the reference, sorry.
[note: this post originally appeared on July 20, 2010 at Original Blog (see here for details)]
Actually, it feels exactly like summertime, what with the 90 degree temperatures the climate has seen fit to inflict on this area lately.
And honestly, with that summertime, I don’t feel the urge to make an attempt at insightful analysis of, like, breaking news. Or non-breaking news. I feel the urge to read novels out in the park and eat Klondikes and go hiking.*
Hiking last weekend I learned about a fun new plant. Most people already know about poison ivy, the scourge of campers and hikers and other outdoorsy people everywhere. Poison ivy is a lovely little vine, identifiable by its three leaves, which lurks and gets it oils all over the skin and then gives you a nasty rash. I learned to identify it via my parents, who pointed it out with dire warnings since I was born, approximately.**
Poison ivy’s damage is inflicted by the urushiol oil in the plant; the oil tends to induce an allergic reaction, called allergic contact dermatitis; the same kind of reaction can be induced by other irritants, including metals like nickel. But the degree of reaction produced by poison ivy contact varies from person to person and sometimes even within a person’s lifetime.
What I learned about from the signpost in the campground was wild parsnip.
Wild parsnip works differently from poison ivy. Instead of allergic contact dermatitis, wild parsnip hurts you with phytophotodermatitis. It looks harmless, until you get the sap on your skin. The sap sensitizes your skin to ultraviolet light–the same kind of light that gives you sunburn–and so when ultraviolet light shines down on the skin (which it will, since you’re outside running into wild parsnip), you can get burns, blisters, and even brown marks that can last for years.
*I can smell someone’s fire through my window and it smells like outdoors and wonderfulness.
**Once I hugged a tree covered in poison ivy and evaded leaf contact by pure luck. The tree-hugging was on purpose; the poison ivy presence was not. Since then: paranoia.
[note: this post originally appeared on May 25, 2010 at Original Blog (see here for details)]
Recently, I had to buy new exercise pants because my old ones were too big.*
In that spirit, I’m trying to develop walking as a habitual form of exercise (as opposed to hiking, which I generally get to do only on weekends, though I admit I kind of blend them around in my tracking journal.)
So: does it really?
Before we get to the current study, let’s discuss how, exactly, 21 days might have infiltrated our collective consciousness.**
It all seems to stem from Dr Maxwell Maltz, a plastic surgeon who wrote a self-help book called Psycho-Cybernetics. Wherein he apparently made the (anecdotal) observation that it seemed to take his patients who had had arms amputated about 21 days to stop feeling phantom pains in their missing arm.***
I have to tell you, arm amputation has never played a major role in my life, so I don’t think that’s really applicable here. Maltz never made a formal study of the 21 days claim.
But now! Dr Phillipa Lally and her co-authors have done a study of habit formation. It’s just one study, but still: at least they have some actual evidence. What they found, perhaps unsurprisingly, has nothing to do with a magic 21-days number.
Instead (page 10),
The average modelled time to plateau in this sample was 66 days, but the range was from 18 to 254 days. We were only able to ﬁnd one statement in the literature discussing how long it takes to for a habit. This was from Ronis, Yates, and Kirscht (1988), who argued that a behaviour is habitual once it has been ‘performed frequently (at least twice a month) and extensively (at least 10 times)’ (p. 213). Our study has shown that it is likely to take much longer than this for a repeated behaviour to reach its maximum level of automaticity.
So the average time in Lally et al’s study to form a habit was 66 days, but it ranged between 18 and 254 days. Numbers, you will note, which are not 21.
Also on page 10,
It is interesting to note that even in this study where the participants were motivated to create habits, approximately half did not perform the behaviour consistently enough to achieve habit status.
The study was performed with people who were asked to pick a habit that they would like to have for the study, so they were internally motivated to get their habit, but half of them didn’t form the habit anyway.
You may have guessed by now that page 10 is the ‘discussion’ section:
Comparing increases in automaticity score over 2 days when the behaviour was either performed on both days (mean increase
= 0.79) or there was a missed opportunity in between (mean increase = 0.55) shows that a missed opportunity did not materially affect the habit formation process. This is encouraging for researchers designing health interventions which aim to establish healthy habits. It suggests that although repetition of a behaviour is required in order to form a habit, some missed opportunities will not derail the process.
So it may be that you can miss a day and still successfully form your habit. Which is nice for me, because I’m skipping today’s walking because of blisters.****
***I would like to substantiate this by getting the actual book, but my library’s catalog indicates the only version it has is a translation in Urdu. Seriously. If I ever find one in English, I will update this footnote.
****Blisters form when friction separates layers of your outer skin and the intervening space fills with fluid. Even though it doesn’t feel like it, the point of the blister is actually to protect the tissue underneath it with the fluid cushion.
[note: this post originally appeared on April 13, 2010 at Original Blog (see here for details)]
Last Wednesday, I went to see Great Big Sea play*. Since then I’ve listened to pretty much nothing but, and I listen to music in the background for quite a lot of my daily routine.
Yet somehow, as I’ve sat here in my quiet apartment trying to think of what to write here, my brain has had “I’ve been waking up your neighbors barking up your tree” on infinite loop repeat. It’s roughly five seconds of an almost four-minute song, and I haven’t listened to Bon Jovi in weeks**. The worst part is that I actually know the rest of the song, but it just won’t play the whole thing.
I have an earworm.
The name earworm is a literal translation of the German ohrwurm***. James Kellaris, at the University of Cincinnati, characterized the earworm as a cognitive itch that our brain wants to scratch. Apparently women, musicians, and the anxious are most prone to earworms.
The music that is earworm-inducing tends to be repetitive, simple, and have what Kellaris calls an “incongruity,” something that sticks out, like a shifting time signature.
A 2005 study at Dartmouth found that the auditory cortex in your brain is responsible. If a song is played to you, the auditory cortex activates as you listen. If you’re familiar with the song, and the song is turned off, the auditory cortex will just keep going. The fake song-hearing appears to be your brain following the reverse of path of the what it would do were the song actually playing, though exactly why you catch the earworm no one knows.
According to a study by British researchers Philip Beaman and Tim Williams, the best way to make an earworm go away is to ignore it. I usually go with ‘sing other songs.’
*it was the greatest 2 hours and 49 minutes of my life.
***and is not related to the actual insect corn earworm… I hope.
[note: this post originally appeared on March 23, 2010 at Original Blog (see here for details)]
…as the dinosaurs knew it, anyway.
Background: in 1980, Luis Alvarez, Walter Alvarez (his son), Frank Asaro, and Helen V Michel published a paper in Science claiming that the dinosaurs went extinct when an asteroid hit the Earth*. The impact (the crater was eventually found in Chixculub, Mexico) would throw up a huge dust cloud** that would literally darken the skies. Without sunlight, plants start to die off, so plant-eating dinosaurs die off, so the meat-eating dinosaurs that ate the plant-eating dinosaurs die off.
Part of their evidence was the worldwide layer of iridium*** laid down at about the same time the dinosaurs died off. Iridium is rare on Earth, but not in asteroids; if an asteroid hit, and iridium-laden asteroid dust was dispersed all over the world, that could explain the iridium layer.
Now Disney can at last add an asteroid hit at the appropriate part of Fantasia!****
*Walter also wrote a book about it called T. Rex and the Crater of Doom, which is an awesome title. The book’s not bad either.
**other exciting, but extinction-free, dust clouds: Krakatoa.
***the iridium satellite network is named because iridium (from iris, Latin for ‘rainbow’) is atomic number 77, and there were originally supposed to be 77 iridium satellites in orbit. As it turned out, there are only 66, but atomic number 66 is dysprosium (from dysprositos, Greek for ‘hard to get at’). You can see why they made that naming choice.
****right after they resolve their confusion about the appropriate number of claws for a T rex to have (2) and whether stegosaurus and T rex were contemporaries (no).
[note: this post originally appeared on March 9, 2010 at Original Blog (see here for details)]