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.

March 09, 2018 at 08:28PM

Today I learned: 1) According to Harvard professor Johan Paulsson, if you fuse most fluorescent proteins to a protein that naturally multimerizes (that is, a protein that forms a complex of two or more copies of itself), the fluorescent protein attachment will cause the whole protein to clump dramatically. I'd read this before, but misread it slightly and thought that this applied to *any* fluorescent protein fusion. The thinking is that fluorescent proteins normally bind to each other, but only very weakly; however, when two or three or ten of them are all fused to one complex, it acts as a nucleation site for larger-scale aggregation. Citation: http://ift.tt/2HisT4D 2) You know the weird thing in quantum mechanics where particles kind of appear and disappear at random in a kind of quantom froth? Well, there's a way of viewing that phenomena as a consequence of simple formulations of quantum mechanics married to special relativity -- essentially, quantum systems get random spikes in energy, and special relativity says that you can interconvert between matter an energy, so there must be occasional production of particles from random QM fluctuations. According to Anthony Zee, the "marriage of QM with special relativity" is also one of the primary motivations for developing quantum field theory. I don't yet understand this claim, nor why it should be true. 3) Say you're a cell, and you want to make some specific amount of a protein. There are, roughly, two variables you can (dependently) vary to get the right amount of output protein -- transcription speed and translation speed*. For a fixed amount of output, you could have TONS of transcription and a little bit of translation on each of the many mRNAs you make, or extremely little transcription and TONS of translation on every mRNA you make, or anywhere in between. Today I learned that, across a wide variety of organisms, cells overwhelmingly choose to have low transcription and high translation over high transcription and low translation. Citation: http://ift.tt/2oIM3K9. This flies in the face of experimental data I've seen before that tells us that translation is much, much more energetically expensive for a cell than transcription and, in particular, that high-strength RBSs are *even more* energetically expensive than you'd expect. So... I don't know why cells would do this. The Alon paper has some arguments that don't make sense to me. One possibility, though, is that expressing low transcriptional rates makes gene expression *noisier*, which could be better for some processes. Still, I'd be surprised if the *vast majority* of genes are better expressed noisily than consistently. * Okay, you can also modify degradation speed and a couple other things, but I'm going to neglect those, because they turn out not to be too interesting in this story.

March 04, 2018 at 04:58AM

Today I learned: 1) Can you guess the most-played race in D&D? Today I learned that it's humans, by a pretty wide margin, according to Wizards of the Coast's polling. 2) Here's a potentially useful narrative trick -- the main character of a story doesn't have to be as interesting as the other characters, especially if it's a first-person story. In general, you can get a reader to go along with a main character by sheer dint of them being a main character. Learned this from a fellow student and part-time writer who had a problematic character that needed to exist for plot/connective reasons, but wasn't very interesting. So they flipped the story to first-person around that character. Instant fix. 3) Romans... ancient Romans were a special people. Incredible, but also so, so terrible. Case in point on the "Romans are the worst people ever" side of the ledger -- fatal charades. This was a Roman practice of performing plays using condemned criminals as actors. The only catch was that the plays involved the deaths of main characters, which were performed for real, live, on stage. Like... imagine Hamlet, but all the actors are on death row, and they actually die on stage. The Romans did that. I'm a bit curious how they convinced the prisoners to go along with it. Also, they must have had awful rehersals.

March 03, 2018 at 04:26AM

Today I learned: 1) Cave bacteria! There are bacteria that live exclusively on the inside surfaces of cave rock. They form visible sheets, and sometimes excrete really pretty minerals. I don't know much about them, but they can somehow live off of the rock face -- I'm not sure whether they're filter-feeding stuff that comes by, or if they're actually reacting the rock for energy. Whatever they're eating, it's not a particularly *accessible* source of food -- they are VERY SLOW GROWING, taking decades to fill small gaps in their mats. Some kind scientists at University of New Mexico compared the community compositions of cave bacteria and soil bacteria (http://ift.tt/2F8VxVa). Their conclusion was that the broad distribution of taxa was quite similar in the caves and in the soil above, but that there was quite a bit of divergence between *species* in the two climes. In other words, it looks like all of the usual inhabitants of soil got into the caves and colonized with roughly the same success, but then they evolved to look pretty different from their above-ground ancestors. Thanks to Patricia Prewitt for tipping me off to the existence of these critters! 2) RAND corporation has a new meta-study on the effects of gun policy. I've only read their summaries, but it looks pretty comprehensive. The big take-away is that there isn't enough data to make strong conclusions about most questions around the effets of gun control. There isn't a ton of data on gun violence, and what data there is isn't sufficient to reliably detect small effect sizes (which could still add to thousands of deaths per year). None of this is surprising, since the US government is BARRED BY LAW FROM FUNDING RESEARCH ON GUN CONTROL. It's usually not a good sign if someone feels they have to ban research on a topic, especially a poitically-charged one. Frankly, I don't take much of a hard stand on gun control one way or another, but IMHO the current research climate on gun control reeks of Lysenkoism. ANYWAY, the second-biggest take-away from the RAND meta-study is that there are *some* policies that appear to be effective at reducing violent crime, accidental deaths, and suicides (especially suicides). The first figure at this link is a good summary (http://ift.tt/2HYu9uF). For those who prefer a written digest, here it is: background checks and child access prevention laws help reduce suicides pretty dramatically; child-access prevention laws also almost certainly reduce accidental gun deaths; background checks and mental health screening probably decrease violent crime, and (perhaps surprisingly) stand-your-ground laws probably *increase* violent crime; concealed-carry laws might increase both accidental and homicidal deaths from guns, but the evidence is weak; most surprisingly to me, there is not evidence that bans on assault weapons and high-capacity magazines have much effect at all on anything. You can read the rest of the report here, if you're super-interested in gun control research and you have a lot of time on your hands: http://ift.tt/2t87FE9 3) Cells in a developing embryo can detect their position within the embryo within about 1% error, we think only using the concentrations of four transcription factors that are distributed in specific ways around the embryo. We don't know exactly how they do it, and that's quite close to the inforamtion-theretical limit of precision for the amount of information available in those transcription factor signals (unless, of course, there are channels they're exploiting that we don't know about). Thanks to Andy Halleran for this one!

February 08, 2018 at 03:38AM

Today I Learned: 1) A couple of data facts for you, brought you to in part by Andy Halleran. Current total data of the human race is estimated at around 10^24 bytes. That's a trillion terabytes, or a yottabyte. I know some pretty big metric prefixes, but I had to look that one up. The estimated total data size of all (unique) genomes on the planet is 10^36 bytes. That's... a truly ludicrus amount of data. But we're catching up. For a (three-year-old) overview of some of our biggest data generators, see this (open-access!) review article: http://ift.tt/1HcOjIi. A few highlights: a) The Australian Square Kilometre Array Pathfinder project acquires 7.5 terabytes *every second*. b) Twitter's data storage needs are estimated at around 500 terabytes per year. Not massive by big data standards, but it does put into perspective why Twitter doesn't, in general, make their Tweets algorithmically searchable*, and makes it all the more impressive that they can serve up selected data as quickly as they do. c) We're predicting to store somewhere on the order of 2 to 40 *exabytes* (~8.5 billion terabytes) of human genome sequences alone. * You can collect random tweets from a couple of Twitter APIs, known as the twitter firehoses, and you're welcome to make your own mini-database. 2) A couple of rocket facts for you today, courtesy of Andrey Shur. Liquid-fuel rocket engines use (effectively) a turbojet to pressurize their fuel just before it's burned. To rocket good, you have to make really, really high-pressure air. One way to pressurize air really efficiently is to burn it; that's why explosions are useful in rockets. Another way to pressurize air is to use a pump; that's why turbojets are useful in rockets. The "turbojet" in a rocket is actually called a "turbopump", and its job is to pressurize incoming liquid fuel (as it's aerosolized coming out of the fuel tanks, I gather) so it can be exploded really efficiently. Now, pumping fuel requires a lot of energy. You *can* run turbopumps electrically, if you want, but a much more common strategy is to *pre*burn a bit of your fuel and use *that* explosion to spin up the turbopump. It is not intuitive to me that this should be efficient, but apparently it is. I guess pressurizing fuel before burning it must give you a disproportionate boost in thrust post-burn. There are (at least) two main kinds of turbopumps. An "axial flow" turbopump looks pretty much like a turbojet, which is the big spinning engine on the wing of a commercial plane. Basically, it's a bunch of high-density propellors that force air through a narrowing chamber, compressing them. The "centrifugal" turbopump is more common in rockets, and it's the one that makes me giggle -- it works by spinning really fast and *flinging fluid to the outside* where it's collected at high speed. So now you know -- these things (https://www.youtube.com/watch?v=PfHu-UJaK0Q) are, when you get right down to it, centrifugal squirrel pumps. Not quite a fact, but here's a gem from the Wikipedia page on rocket engines, on the topic of the dangers of liquid propellants: "With liquid propellants (but not gaseous), failure to ignite within milliseconds usually causes too much liquid propellant to be inside the chamber, and if/when ignition occurs the amount of hot gas created can exceed the maximum design pressure of the chamber, causing a catastrophic failure of the pressure vessel. This is sometimes called a hard start or a rapid unscheduled disassembly (RUD)." 3) You know how you're not supposed to daisy-chain together power strips? If you don't already know this, you're not supposed to plug power strips into other power strips. Ever wonder why? Like, why would that be dangerous? I've been told these terrible stories of daisy-chained power strips sparking and causing fires, but nobody ever gave me a reason that they would do that. Well, today I got fed up and googled the answer. It turns out that daisy-chained power strips are dangerous mostly because they make it much, much easier to accidentally draw too much total power at once. Power strips (and, for that matter, house circuits) are only rated for so much current draw, and if you exceed it, you risk overheating or shorting the strip. Practically speaking, most power strips have fuses and will commit suicide before they do any real damage, but it's still a hazard. The upshot -- you should be safe daisy-chaining power strips *if* you are quite sure you're not going to exceed the max draw for your power strips (say, if you fill every plug with cell phone chargers).

January 28, 2018 at 11:16PM

Two days ago I learned: (I wrote up most of this on Friday and forgot to finish it out; instead of letting it die, I'm cheating and pushing it out today.) 1) ...a bit about the Impossible Burger, widely hailed as the most meat-like non-meat burger in the marketplace. My impression is that the Impossible Burger is a very, very heavily engineered food. A lot of effort went into making the texture, taste, and sound (yes, sound) of the Impossible Burger similar to that of a beef patty. However, if I were to collapse the Impossible Burger's design into one trick, that trick would be leghemoglobin. Leghemoglobin is a protein normally produced in the root nodules of soy plants, where it has something to do with oxygen buffering. The protein is structurally similar to animal hemoglobin and myoglobin, and acts similarly -- it complexes with a heme molecule, which allows it to efficiently bind dissolved oxygen. Heme, it turns out, is why bloody meats are red, and gives meat a lot of its rich, metallic flavor. Impossible Foods (the makers of the Impossible Burger) decided to make a burger with plant-based heme using leghemoglobin as a heme source. Unfortunately, soybeans don't make a lot of leghemoglobin, and it's a *pain* to extract, so Impossible Foods moved the gene for leghemoglobin (and, presumably, the enzymes required to make heme) into yeast, which is *very* easy to grow and relatively easy to extract proteins out of. That lets Impossible Foods make a rich, hemefull burger patty that's 0% animal. There's only one small catch, legally speaking -- leghemoglobin isn't FDA approved. It seems it doesn't *need* to be -- it's being sold anyway -- but just to be on the up-and-up, Impossible Foods sought FDA GRAS approval of leghemoglobin. They have some data feeding mass amounts of leghemoglobin to rats (no effects) and, perhaps more importantly, argued that leghemoglobin is an ancestral protein that we have no particular reason to think is toxic that's structurally very similar to tons of proteins we already eat all the time. The FDA rejected the approval request, I think on the basis that a) leghemoglobin might just be an allergen and b) there could be small amounts of other yeast proteins that make it through purification along with leghemoglobin that aren't necessarily human-safe (they're not using bakers' yeast, and I don't think the kind of yeast they are using is typically eaten in any appreciable quantity). 2) On a related note, Impossible Foods claims that 90% of the rennet used to make cheese is now yeast-produced. Whatdyaknow. This explains the multiple times I've run into "vegan cheese" that used rennet. I guess they were (probably) vegan after all. Those cheeses, when I've tried them, were significantly better than non-rennet vegan cheese, so I'm kind of excited to get back into the cheese substitute game. 3) If you want to burn little tea-light candles in water, don't take them out of their metal shells -- the wick of one of those candles is attached to a little metal pad, and when it heats sufficiently it will drill through the bottom of the candle and fall into the water, taking the rest of the wick with it. Bonus candle fact -- it's pretty easy to modify candles with tin foil by heating the tin foil over a lit flame and quickly pushing it into the candle somewhere.

January 22, 2018 at 03:29AM

Today I learned: 1) I kind of knew this from experience, but Andrey Shur confirmed for me today that it's rare to find a 2 amp USB phone charger, largely because USB isn't quite rated to carry 2 amps. This is curious, as Raspberry Pis recommend you use a 2 amp charger. As I am learning, Raspberry Pis were made with some really odd design decisions. 2) ...a bit about Hilbert curves. Or, technically, *the* Hilbert curve, which is the limit of pseudo-Hilbert curves of N iterations as N approaches infinity. If you google image search for "Hilbert curve", you'll find a bunch of example pictures, which is going to be much easier than reading me awkwardly try to explain the shape... but in short, a pseudo-Hilbert curve of N iterations is a fractal line that neatly visits every grid point in a square (with side length log2(N)). As you take larger and larger iterations of the pseudo-Hilbert curve, it becomes a denser and denser nest of curves. The cool thing about the Hilbert curve is that, in the infinite limit, it is "space-filling", which means that it eventually visits every single point in the square it's defined over. Essentially, that makes the Hilbert curve a mapping from a line to a plane... which sounds obviously wrong, but is mathematically provable. It turns out that a (the?) key property of the Hilbert curve for analyzing its space-filling-ness is that it's "stable", in the sense that if you follow a point on the pseudo-Hilbert curves as you add more iterations to it, that point will converge to a fixed position, and it's possible to calculate what that position is. That's important, because without this property, the concept of "the curve that this curve approaches as you iterate to infinity" doesn't make sense -- if the mapping of every point doesn't converge, then the curve doesn't really "converge" either. If you'd like to learn more about Hilbert curves, I highly recommend this video, "Hilbert Curve: Is infinite math useful?": https://www.youtube.com/watch?v=3s7h2MHQtxc 3) ...a little bit about screenplay script formatting. Industry screenplays are... weird, coming from someone who has never written one before. For one thing, everything's centered. Scenes open with a description of the scene, usually one sentence, using the whole page width and ALL IN CAPS. Those scene-setup sentences also usually start with "INT." or "EXT." for interior and exterior scenes, respectively. Most of a screenplay is dialogue, of course, and all dialog is written with insanely large margins, so it reads like a little column of text smack in the middle of the page. The name of the speaking character gets its own line. Description of *how* a line is delivered come in the form of parentheticals, which also get their own line, are contained within parentheses, and have about an extra half inch on each margin relative to the actual dialogue. (I didn't say I learned anything about writing a *good* screenplay, just that I learned how to *format* one.)

January 20, 2018 at 09:05PM

Today I learned: 1) https://www.youtube.com/watch?v=ciStnd9Y2ak If you care about the environemnt, and you haven't written to your congressperson about nuclear power, I highly recommend the above TED talk. Basically, we're killing about 7 million people a year around the globe by using fossil fuels instead of nuclear. For comparison, total deaths from all the nuclear disasters in the world are in the four-digit range, and something like 90% of that was deaths during unnecessary evacuations that had nothing to do with radiation exposure (i.e., traumatically moving people from nursing homes and emergency care facilities). Oh, and nuclear is also cheaper than renewables *and* generates less emissions and other waste. Honestly, I'm having a hard time thinking of a bigger failure of humanity than that of our not using nuclear power as our primary energy source. Maybe world war II? Any other suggestions? 2) ...how to test the power supply on a Raspberry Pi! There are a couple of test points you can stick a multimeter to that will tell you what kind of voltage the Pi actually gets. Sadly, my Pi is getting plenty of power and still won't boot. =( 3) So, according to George Church, the off-target mutation rate of Cas9 in humans is now below background mutation rate, using off-the-shelf tools and good, proper computational design. Gonna be honest, I thought it was a lot higher than that.

January 19, 2018 at 09:32PM

Today I Learned: 1) I've wondered for a long time how text-based loading bars work. Many command line programs feature progress bars that somehow fill in using only text... even if the progress bar is in the middle of a line. For example, the Arch Linux package manager prints a lot of lines that look like core 126.8 KiB 906K/s 00:00 [###############-------] 66% where those "-"s eventually fill up with "#"s. But how does a program overwrite its old text? Well, today I finally went and googled exactly that question, and it turns out to be pretty easy -- there's a character called a carriage return ('\r') that sends the print-output-cursor to the beginning of the line. If you carriage return and then start typing, it will overwrite whatever was already in the output, at least if you output to a terminal window (I assume if you write a \r to a file, it will faithfully copy an ASCII '\r' to the file and keep going, but I haven't tried it). I've run into '\r' before, but almost always coupled with a carraige return ('\n') character, which in some systems is used to represent a new line (also, confusingly, '\n'). It never occurred to me that carriage return could be used *without* a newline. This is some seriously useful magic. For one thing, it makes loop-counting diagnostic prints a hell of a lot cleaner -- now if I want to know how a long loop is progressing, I can have a single line of output per loop, instead of printing stacks and stacks of output. 2) Did you know that the sex ratio of humans at birth is not quite 1:1? It's actually more like 107:100 male:female, quite reliably. This is *at birth*, so before any effects of selective infanticide. That 107:100 number is especially surprising in light of theoretical evolutionary game theory that suggests that gender ratios for most binary-gendered organisms should be very, very close to 1:1 -- essentially, if there are more males than females around, then you get a fitness boost by having more female offspring and vice versa, and the only stable equilibrium is even birth ratio. The wiki page on human sex ratio points at at least one potentially good evolutionary explanation for the imbalanced sex ratio. Why do *you* think there might be more male human births than female human births? 3) ...about an alternative to tempered MCMC and annealed MCMC, called adiabatic MCMC, that has some nice theoretical properties over the tempered and annealed versions. A quick reminder: MCMC is, extremely roughly speaking, a class of methods for sampling from the inputs of a function so that the probability of drawing some input is proportional to the value of that function for that input. Usually MCMC is used to sample from probability distributions, in which case it's a way of randomly sampling from a (potentially very complicated) random process. Typical MCMC algorithms use some kind of "walkers" in the input space. By some algorithm, they take a random jump in the input space, and then either accept the jump or stay where they started, depending on the probabilities it calculates at the start and end points. Essentially each walker is a noisy hill-climber -- it will tend to move up hills toward high-probability regions, but it can wander enough that it will also sample lower-probability regions some of the time, too. A major problem for simple walker-based strategies is that if the probability distribution under sample has two high-probability peaks that are separated by a low-probability valley, then walkers that start on one hill can take a really, really long time to wander over to the other one. Parallel-tempered MCMC and annealed MCMC try to get around the problem using a thermodynamic analogy. They essentially "heat" the walkers so that they can move around more easily, then "cool" them to trap them in local hilltops. This does kind of work... but unfortunately, the speed at which you heat and cool matters a lot, and there's no great way to pick a heating or cooling speed. Enter adiabatic MCMC. I'm not going to pretend the mathematics of adiabatic MCMC yet, but I *will* pretend to understand Andrew Gelman's metaphor for it here: http://ift.tt/1oNbdSs. Essentially, tempered MCMC treats temperature as a tunable knob, which it turns manually to achieve nice mixing. Adiabatic MCMC, in contrast, manages temperature by connecting the walker system to a heat bath with some temperature, and lets energy flow between the two according to their relative temperatures. Don't ask me how that actually *happens* at an algorithmic level, but the bottom line is that this more-or-less solves the problem of temperature adjustment. (Addendum: This seems like an awful lot of effort and complex math for relatively little gain. Why do I care about tempered MCMC and adiabatic MCMC? Well, for Techncial Reasons, tempered MCMC lets you compare the probabilities of different models in a Bayesian framework, according to some data. That's pretty powerful stuff, and it's really tricky to do in general. However, I've been warned by actual statisticians that using tempered MCMC for model comparison is Dangerous, so I'm interested in anything that can more safely replace it.)

January 11, 2018 at 01:51AM

Today I learned: 1) ...which silverware is mine. This may sound silly, but for a long while, I'd mostly lost track of which silverware was mine and which was my roommates'. I knew a handful were mine, and I'd just been eating with those... today we went through all the silverware as a house and tagged them with their owners. It turns out I actually have a lot of silverware. 2) Today I found myself wondering how microwave ovens are so efficient. How can they possibly transfer energy to food more efficiently than, say, an oven? For that matter, how do they make microwaves at all? It's not by blackbody emission of a hot element -- if it was and was powerful enough to cook food, it would emit mostly visible stuff anyway and it would be a regular oven. Well, I don't think I really learned why they're *efficient*, but I at least learned how microwave ovens *work*. The key component in a microwave is a device called a cavity magnetron. A cavity magnetron is essentially a multi-chambered flute for electrons, tuned so that it produces microwaves. The metaphor is more literal than you might think. Cavity magnetrons have a bunch of chambers -- just holes in metal, really -- over which you can shoot a beam of electrons. As the electrons pass by each cavity, they produce a changing electromagnetic field. The cavity *literally resonates* that electromagnetic field at a characteristic frequency, which, in the case of a microwave oven, is in a microwave frequency. If you build up enough resonance, some spills out as a microwave-frequency photon, and it's guided out into the oven by another device. For more details, see http://ift.tt/1CKAOBh 3) Speaking of microwaves, while digging through wikipedia for #2 above, I learned that microwaves can cause runaway heating with some materials. See, as some materials heat, they become more responsive to changing electromagnetic fields, which can make them absorb microwave radiation more efficiently. That makes them hotter, which makes them more receptive... etc. Fun fact -- one such material is glass. If you pre-heat glass before putting it in a microwave, it's supposedly possible to melt it in a microwave.