April 16, 2018 at 05:36AM

Today I Learned: 1) Read a few things on space suit tech today. The big one is on space suit thermoregulation. Long explanation of the physics of temperature control in space coming up; numbers two and three are much, much shorter, you can skip to those if you want. How do astronauts stay warm in space? Actually, the better question is, how do they stay *cool*? See, there are basically three ways to cool a human -- conduction, convection, and radiation. Okay, there's also sweating, which isn't really any of those three, so really there's conduction, convection, radiation, and sweating (evaporative cooling). Anyway, conduction is the direct flow of heat between objects touching each other, through the contact interface. That doesn't really happen in space, since there's nothing to touch. Convection is like conduction, but in a fluid media that's moving around and forcing a high temperature gradient to suck out heat, which makes convection much more efficient than conduction. Convection also doesn't really happen in space, because, again, there's nothing to convect *with*. It's space. Evaporative cooling by sweat *could* work in space, but only if you directly exposed that sweat to outside vacuum, which would be a bad idea for a number of reasons. That only leaves radiative cooling, which is loss of heat from spontaneous emission of light. All objects do this; humans emit something like 50 W under normal resting conditions, which represents about 50% of the energy we give off. In space, radiation... still works! But it's not tremendously effective -- only about half of your body heat can escape if all you have is radiation, so if you're stuck in space without a fancy way to actively cool off, then it's going to be hard to dump heat faster than your body naturally produces it. Now, as you heat up, you *will* radiate more efficiently... but the equilibrium temperature you'd reach isn't really human-friendly. Ergo, the problem in space isn't staying warm -- it's staying cool. ...well, that's what I thought. Today I learned that what I just described is... somewhat wrong. It's true that under "normal conditions", humans radiate about 50 W. However, part of "normal conditions" is being on Earth, immersed in air that's slightly cooler than we are, that's *also* radiating heat. That 50 W number is the *net* radiative emission of a human *on Earth*. In space, there's not a ton to radiate back to you (except the sun, which is a HUGE caveat!), so your *net* radiate emission is much, much higher than the usual 50 W -- more like 700 W, which is more than you can continuously generate for long stretches. So yeah, you're going to get pretty cold in space. But wait! What about the sun? Well... at Earth-orbit-distance, the sun provides about 1300 W per square meter (I use that number a lot. I should really memorize it one of these days so I don't have to keep looking it up). The human body, as a number of sources have kindly informed me, has about two square meters of surface area, about half of which can face the sun at once, so if you're floating naked in space, you should get about 1300 W from the sun. Now we're back to overheating. Except on the side that faces away from the sun, that side will cool pretty quickly. So yeah, you freeze on one side and heat to deadly levels on the other, unless you rotate nicely to keep yourself evenly insolated, in which case you just overheat. Oh, and if you happen to fall into Earth's shadow, then you immediately start to freeze instead. So, the truth is, staying safe in space isn't "all about staying warm" or "all about staying cool" -- you have to do *both*, *actively*, because whether or not you're in shadow makes all the difference between freezing solid and heat-stroking. You can see this in space suit design. One common feature of space suits is to provide a thermos-like layer of insulation between the astronaut and the outside of the spacesuit, which buffers them tremendously against *changes* in ambient radiation. Of course, then the astronaut has exactly the opposite problem as a naked person floating in orbit -- they *can't* radiate heat very effectively, and can only conduct and convect and evaporately cool with the rest of the suit. In practice, from what I understand, the astronaut usually needs more help cooling off than staying warm, *within the thermos layer of a space suit*, so space suits come with liquid cooling systems to draw heat from the body to the exterior of the suit, where it can be (radiatively) dumped into space. 2) Here's a smaller space suit fact -- space suits are specifically designed to keep a constant volume no matter how the wearer moves, because changing the volume of a pressurized gas-filled container takes work (in both the physical and colloquial senses of the word). There are a bunch of solutions to the constant-volume problem, but the most interesting nugget of this fact, to me, is that the constant-volume problem is a design consideration at all. 3) There's a horizontal white line in the mouth, right about where the teeth come together. It's called the "linea alba". I didn't read much about it, but apparently it's thought to be a thickening of the skin in response to friction, rubbing, grinding, etc. from the teeth. As far as I can tell, the linea alba provides no fitness benefits. In fact, it is now my go-to example of an evolutionary spandrel -- it's a total side-effect of whatever feedback system makes skin grow tougher where there's more wear and tear.

March 17, 2018 at 05:40AM

Today I learned: 1) The PDF for the Gaussian distribution was discovered something like 80 years before Guass by de Moivre, who wrote it out as part of his treatise on probability "The Doctrine of Chances" (which was apparently written primarily for gamblers?). From what I gather, de Moivre's paper on the normal distribution (which he used as an approximation of a binomial distribution for large numbers of trials(!)) languished in obscurity until well after Gauss formalized the distribution and popularized it. 2) Related: Stigler's Law of Eponymy states that any scientific or mathematical discovery named after a person was not discovered by the person it was named after. This includes Stigler's Law (attributed by Stigler to one Robert K. Merton). 3) On a more sober note, today I learned that lynchings in the US were much, much worse than I thought. I *thought* lynchings were basically public killings with a big crowd. In fact, lynchings were more akin to medieval executions -- that is, the murder part would be preceeded by hours of torture involving things like open flames and removal of body parts.

March 15, 2018 at 03:50AM

Today I learned: 1) You know how gravity falls off with the square of the distance between two objects? As does electromagnetism? That's because we live in three spatial dimensions (for the same reason that the surface area of a 3D sphere increases with the square of its radius). If we lived in 4D space, then forces would fall off with the cube of distance; if we lived in N-D space, forces would fall off to the power of 1/(distance^N). That also means that the inverse-R-squared law is strong evidence that we do, indeed, live in a 3D space, and not, for example, a 3D slice of a higher-dimensional space. Wouldn't that immediately falsify string theory, which posits lots and lots of dimensions? Well... no. There's a caveat to the "forces fall off to the power of 1/(distance^N)" law, which is that it only holds as long as all of the spatial dimensions have the same characteristic length scale. Now, I must admit, I don't fully understand what the "length scale" of a dimension is. Nevertheless, if a dimension is "small", then not much force will leak out into it, and the force falloff will remain very close to the 1/R^2 law. As of 2005, gravity had not been measured to a high enough precision to distinguish between a 1/R^2 falloff and an almost-1/R^2 falloff, leaving room for the possibility of other, smaller dimensions. As far as I know, that fact hasn't changed in the last decade. 2) ...how to return Amazon packages. It's ridiculuosly easy. First, you go to your orders on Amazon, find the thing you want to return, and click some relatively obvious button that says something about returning the item. Follow the instructions. If you can get it to a Kohls or an Amazon locker, they'll package it and label it and ship it to you for free. Otherwise, if you get it to a UPS store, they'll package it, label it, and ship it for some (not always outrageous) application of money. Also, to keep things snappy, if you ask for an item replacement from Amazon, they will immediately ship you the new thing. If you don't return the original item postmarked before some date, they'll automatically charge you for it again. I do wonder if you could abuse this somehow by, say, buying a ton of things at once, ordering up replacements for all of them, then shutting down your Amazon account (or your credit card) before the due date. 3) I somehow got it into my head that you could decompose any linear transformation a rotation and a scaling, possibly with a reflection. I was wrong -- I'm pretty sure scalings *don't* account for shearings, and even including shearings doesn't give you all of the linear transformations. As a side note, I *did* find the conditions under which you *can* write a linear transformation as a rotation plus a scaling -- for a linear transformation with matrix [[a, b], [c, d]], you can do that decomposition iff b = -ac/d. You're welcome? I guess?

March 13, 2018 at 11:45PM

Today I learned: 1) The number line can be thought of as a limit of a circle with increasingly large radius. This is useful for proofs involving the number line, and can get you a factor of pi in sums that otherwise isn't obvious. For more, see https://www.youtube.com/watch?v=d-o3eB9sfls. 2) Synthetic biological circuits break. A lot. Almost all synthetic circuits are bad for the cell they're in, so most mutations that break the circuit will be selected for pretty quickly. One of the most common types of circuit-breaking mutations is accidental insertion by Insertional Sequence (IS) elements, which are small DNA fragments that make transposons, which flip the IS out of whatever DNA it's in and move it somewhere else. Bacterial genomes have lots of IS elements (E. coli has a few dozen, depending on the strain), so any engineering in bacteria will run afoul of them eventually. So. IS elements are common in bacterial genomes, and they mess up biocircuits. Why not remove them from the genome? Well, somebody has -- Scarab Genomics LLC sells a variety of IS-free cell strains for a variety of cloning needs, for the low low price of... actually, I don't know how much they cost. You have to make an account with them and sign in to see prices. More importantly, though, Scarab Genomics has some pretty nasty licencing restrictions on their strains -- they get a cut on any IP you develop using their lines, for example. Not nice. 3) Strong ribosomal binding sites (RBSs) can protect mRNAs against degradation. Probably. This is a pretty new finding, but it looks like if an RNA is covered in ribosomes, the ribosomes can physically block RNAses from binding and degrading the RNA. Strong RBS -> lots of attached ribosomes -> less degradation. The effect is modest, but measurable.

March 13, 2018 at 01:10AM

Today I learned: 1) ...how to replace snap-on buttons! Technically, that's a lie. I looked up how to replace snap-on buttons late last week. But! Today I actually *did* some snap-button replacing, which honestly felt a lot more like learning than watching a video. For the record, the hardest part was removing the old buttons, which wasn't terribly difficult once Andrey Shur provided me with the right tools. 2) One of the most clear-cut problems with the US healthcare system is the use of opt-in organ donation. It's well-known that many, many people who would be fine with donating their organs on death never bother to sign up for organ donation, and lo! We have a chronic, severe shortage of organs for transplantation. It would be SO EASY to switch to an opt-out system where everyone is, by default, signed up for organ donation, and you can fill out a form to not donate if you really want to. This would vastly increase rates of donation, while still giving people the opportunity to not donate if they have any objections serious enough to warrant filling out some paperwork. ...except that it isn't *quite* that clear-cut after all. Opt-out policies *do* correlate with higher rates of donation, but there are opt-out countries with very low donation rates, and Spain, the most widely-cited success story for opt-out policy, has the Very Large Caveat that they implemented a bunch of organ-transplantation-related reforms around the same time as opt-out, which seem to be responsible for a good part of the increased donation rates there. There are also some specific failure modes for opt-out. For example, when Wales switched to an opt-out system, they saw rates of organ donation *decrease* (albeit slightly). A possible reason is that in Wales (and many other countries with opt-out organ donation), the family can still decide to deny access to a deceased organ, so opt-out isn't quite so opt-out as it sounds. Before they switched to opt-out, the family could *also* decide to allow transplantation if the family member wasn't signed up. So really, in both systems, anybody who doesn't bother filling out paperwork to make a decision one way or another is actually at the mercy of their family. In opt-in, there's a way to guarantee that you will donate your organs; in opt-out, there is only a way to guarantee you will *not* donate your organs. Therefore, it's possible that the opt-out system actually creates an extra group of people that don't donate. 3) There is a belief running around that chewing gum is bad for pregnant women. I'm quite skeptical. Some quick googling brought up a bunch of results (with a fairly wide spread of claims), but none from sources I would consider reliable. The only plausible-looking claim, as far as I can tell, is that some gums are sweetened with sorbitol, which is a diuretic and can cause intestinal distress if taken in large quantities. Is that likely to actually be a problem? I'm guessing not.

March 12, 2018 at 03:28AM

Today I Learned: 1) Medieval executioners were almost completely separated from larger society. Firslty, executioning was, like most trades in medieval Europe, familial. Executioners were born into the job, whether they liked it or not. Secondly, executioners were considered kind of magical, kind of blessed, and kind of cursed. Importantly, they had the special ability to remove a person's honor with a touch, like a morbid, adult form of cooties. You're in a marketplace and you accidentally brush up against an executioner? Whoops. You just got infected with the executioner's aura. You are no longer fit for polite society. One side effect of executioner hygeine was that executioners were a bit of an inbred breed -- only the children of executioners were fit to marry an executioner, so their lineages remained separate from most of society. This fact-set courtesy of Dan Carlin's Hardcore History. 2) Henna tattoos are traditional for brides. Didn't know that. 3) The Viking probe we sent to Mars found some evidence for life, although it didn't pan out in the long-term. Viking carried four tests for carbon-based life: a mass spec to directly look for organic compounds, and three experiments that looked for release of compounds of various kinds when nutrients were added to soil samples. One of the release experiments came up strongly positive... but it turned out that the release (in this case, radiolabeled CO2) could be explained quite well by gamma ray irradiation of the sample.

March 11, 2018 at 05:13AM

Today I learned: 1) I'm a big fan of Beethoven, espeically his piano sonatas. I love how beastly they are, how passionate, how ridiculously ahead of their time they are (did you know Beethoven invented boogie-woogie? https://youtu.be/ccyHT1sFmsg?t=1032). Today I learned that Beethoven's sonata no. 23 ("Appassionata") was *so* ahead of its time that it was never performed in public until after Beethoven's death. He played it for some of his colleagues and students (including Czerny), nobody wanted to play it. One critic (often-quoted online, but without citation) called it "incomprehensibly abrupt and dark". From the sound of it, Beethoven's contemporaries couldn't, for the most part, parse it. On a related note, apparently Beethoven never technically bought a piano. All of his were loaned, rented, or gifted by piano manufacturers. Beethoven was famously frustrated with the piano of his time. Pianos of the late 18th and early 19th century were sickly cousins of their modern descendants in a lot of ways. They were smaller both in soundboard size and range, they were more limited in their ability to play repeated notes, and they generally sounded much weaker (compare harpsichords to a modern concert piano). The biggest single advancement in piano technology was the cast-iron frame, which lets modern pianos be strung with absolutely immense tension, and lets you put a ton of kinetic energy into a performance in a quite literal way. Unfortunately, the cast-iron frame was only invented in the last couple of years of Beethoven's life, and he was constantly frustrated by the lack of his pianos' abilities to express what he wanted. He pushed what he had to the limit, though -- the Appassionata, for example, goes all the way to the highest and lowest notes available on his piano at the time. 2) If you're eating a Thai curry and you bite into a chunk of something that looks, tastes, and feels like ginger, odds are it's not ginger. It's probably one of the four varieties of galangal, a ginger-like root used as one of the main ingredients in Thai curry. 3) You can buy oreos in eastern Asia, but they're packaged a little differently -- each oreo is individually wrapped. In fact, single-bite individually-wrapped packages inside a larger package seems to be a common motif of east Asian snack foods.