Today I Learned:
1) The Hoover Dam has, near its base, a star chart of very high resolution and accuracy, which can be read to pinpoint the exact day the Hoover Dam was constructed. Why? Well, the Hoover Dam is expected to last about 10,000 years if left to nature... just in case our civilization collapses and somebody runs across it in a few thousand years, we'll have left behind a way they can date it.
Thanks to Mikas Kuprenas for pointing me to this one!
2) Diamonds are very poor electrical conductors, but excellent conductors of heat. This surprised me, but it makes a lot of sense -- the atomic lattice of diamond is very rigid, so vibration at one end is carried very efficiently to the other end.
3) A coat of paint is about 20-30 microns thick.
Monday, November 23, 2015
Sunday, November 22, 2015
Radioactive Cookies, Hierarchical Parameter Estimation, and The Beta Distribution, Continued
Today I Learned:
1) Here's a nice little thought experiment to understand the properties of different kinds of dangerous radiation: You have three cookies. One emits alpha radiation, one emits beta radiation, and one emits gamma radiation. You have to put one in your shirt pocket, hold one in your hand, and eat one. Which do you put where?
The best answer: Hold the alpha cookie in your hand. Your skin will block alpha particles, but if they get in your body they're really bad. Put the beta cookie in your pocket -- it's a little stronger, but your clothes should block most of it. The gamma cookie, you eat -- it's going to hurt you, but nothing short of a sheet of lead is going to protect you at all anyway, so it doesn't matter where you put it.
2) Hierarchical parameter estimation is really cool, but it consistently requires more parameters than you might expect.... (Hierarchical parameter estimation, by the way, is a kind of parameter estimation where the parameter of interest takes on different values in different experiments.
My favorite example is in preference estimation, like when a company wants to know the most tastiest amount of salt to put in a jar of salsa is (call it O_salt, for Optimum Salt). You might imagine the company performing a bunch of experiments on people to figure out the true O_salt, and average the results of the experiments to find O_salt. The trouble is, different people have different preferences, which are distributed in some way around O_salt. The better model is that each person P has their own optimum salt concentration P_salt, where P_salt is distributed around some O_salt. )
3) ...a bit more about the Beta distribution. The Beta distribution is a probability distribution over the range [0,1], and it's often used to model probabilities of probabilities -- for example, the probability of a (real world) coin landing heads on a flip might be beta-distributed tightly around 0.5. The cool thing about the beta distribution is that it has two parameters, alpha and beta (sorry about the term overload!), which can be the number of successes and failures observed for a Bernoulli trial, respectively, giving the "correct" probability distribution over the success of that Bernoulli trial (for some sense of "correct" which I haven't bothered to learn).
For example, take the coin flip example. If you flip a coin 100 times and it comes up heads 44 times and tails 56 times, then the probability distribution over the possible probabilities of the coin coming up heads is beta-distributed with alpha = 44 and beta = 56.
If that didn't make sense, I direct you to the place I learned this, which has a more thorough explanation: http://ift.tt/1P1UGYy
1) Here's a nice little thought experiment to understand the properties of different kinds of dangerous radiation: You have three cookies. One emits alpha radiation, one emits beta radiation, and one emits gamma radiation. You have to put one in your shirt pocket, hold one in your hand, and eat one. Which do you put where?
The best answer: Hold the alpha cookie in your hand. Your skin will block alpha particles, but if they get in your body they're really bad. Put the beta cookie in your pocket -- it's a little stronger, but your clothes should block most of it. The gamma cookie, you eat -- it's going to hurt you, but nothing short of a sheet of lead is going to protect you at all anyway, so it doesn't matter where you put it.
2) Hierarchical parameter estimation is really cool, but it consistently requires more parameters than you might expect.... (Hierarchical parameter estimation, by the way, is a kind of parameter estimation where the parameter of interest takes on different values in different experiments.
My favorite example is in preference estimation, like when a company wants to know the most tastiest amount of salt to put in a jar of salsa is (call it O_salt, for Optimum Salt). You might imagine the company performing a bunch of experiments on people to figure out the true O_salt, and average the results of the experiments to find O_salt. The trouble is, different people have different preferences, which are distributed in some way around O_salt. The better model is that each person P has their own optimum salt concentration P_salt, where P_salt is distributed around some O_salt. )
3) ...a bit more about the Beta distribution. The Beta distribution is a probability distribution over the range [0,1], and it's often used to model probabilities of probabilities -- for example, the probability of a (real world) coin landing heads on a flip might be beta-distributed tightly around 0.5. The cool thing about the beta distribution is that it has two parameters, alpha and beta (sorry about the term overload!), which can be the number of successes and failures observed for a Bernoulli trial, respectively, giving the "correct" probability distribution over the success of that Bernoulli trial (for some sense of "correct" which I haven't bothered to learn).
For example, take the coin flip example. If you flip a coin 100 times and it comes up heads 44 times and tails 56 times, then the probability distribution over the possible probabilities of the coin coming up heads is beta-distributed with alpha = 44 and beta = 56.
If that didn't make sense, I direct you to the place I learned this, which has a more thorough explanation: http://ift.tt/1P1UGYy
Saturday, November 21, 2015
Insect Stomachs, An Unexpected Lubricant, and FRAP Normalization
Today I Learned:
1) Insects have alkaline stomachs, not acidic ones. This is what makes some insecticides insecticides and not generic poisons -- they're only active in alkaline conditions, like the guts of insects.
2) Canola oil (and other vegetable oils) can be safely used as sex lubricant (though NOT with condoms or anything else made of plastic), and appear to be less rough on sperm than commercial lubricants (http://ift.tt/1uJZ4fp).
3) ...a good, simple technique for dealing with unwanted*** photobleaching* in experiments like FRAP** -- just keep track of a non-FRAPed part of the cell while you FRAP, and normalize each time point against the non-FRAPed region.
* Photobleaching is an annoying feature of fluorescent microscopy where fluorophores tend to break down over time, leading to a loss of image signal over the course of an experiment.
** FRAP (Fluorescence Recovery After Photobleaching) is a kind of experiment that turns photobleaching into a feature! In FRAP, you quickly blast a small region of something (usually a cell) with a ton of laser exposure, which completely photobleaches all of the fluorophore in that region. You can then watch fluorophore from the surrounding area diffuse back in, which tells you how quickly the fluorescent molecule diffuses.
*** FRAP intentionally uses photobleaching to blast out a region of the cell; there's still background photobleaching on everything else, though, which corrupts the signal you get out.
1) Insects have alkaline stomachs, not acidic ones. This is what makes some insecticides insecticides and not generic poisons -- they're only active in alkaline conditions, like the guts of insects.
2) Canola oil (and other vegetable oils) can be safely used as sex lubricant (though NOT with condoms or anything else made of plastic), and appear to be less rough on sperm than commercial lubricants (http://ift.tt/1uJZ4fp).
3) ...a good, simple technique for dealing with unwanted*** photobleaching* in experiments like FRAP** -- just keep track of a non-FRAPed part of the cell while you FRAP, and normalize each time point against the non-FRAPed region.
* Photobleaching is an annoying feature of fluorescent microscopy where fluorophores tend to break down over time, leading to a loss of image signal over the course of an experiment.
** FRAP (Fluorescence Recovery After Photobleaching) is a kind of experiment that turns photobleaching into a feature! In FRAP, you quickly blast a small region of something (usually a cell) with a ton of laser exposure, which completely photobleaches all of the fluorophore in that region. You can then watch fluorophore from the surrounding area diffuse back in, which tells you how quickly the fluorescent molecule diffuses.
*** FRAP intentionally uses photobleaching to blast out a region of the cell; there's still background photobleaching on everything else, though, which corrupts the signal you get out.
Friday, November 20, 2015
Macarons, Gun Purchasing, and Refugees
Today I Learned:
1) ...what a macaron is. They're really cute little cookies!
2) ...what's required to buy a gun in California*. You have to have documentation proving that you are a US citizen and a resident of California. There's also a 10-day wait period between purchasing the gun and acquiring it, which I assume is to give very angry people a chance to simmer down after deciding they really need a gun?
* No, I didn't buy one.
3) ...what's required to move to the US as a refugee. Firstly, a refugee has to have "fled from his or her home country and cannot return because he or she has a well-founded fear of persecution based on religion, race, nationality, political opinion or membership in a particular social group". If you think you qualify, you can register with the United Nations High Commissioner for Refugees (UNHCR). If the UNHCR thinks a potential refugee meets the appropriate criteria, then they can refer him or her to the US Resettlement Program (USRP). The USRP maintains nine Resettlement Support Centers (RSCs) around the world. The RSCs receive and process refugee requests. Refugees awaiting approval undergo personal interviews, security and background checks, and a medical examination (so they don't bring contagious diseases into the country). The process typically takes 18 to 24 months. I also learned that of the refugees that are accepted worldwide, about half of them are accepted by the US. That's also a very small fraction of the total number of people who request refugee status.
1) ...what a macaron is. They're really cute little cookies!
2) ...what's required to buy a gun in California*. You have to have documentation proving that you are a US citizen and a resident of California. There's also a 10-day wait period between purchasing the gun and acquiring it, which I assume is to give very angry people a chance to simmer down after deciding they really need a gun?
* No, I didn't buy one.
3) ...what's required to move to the US as a refugee. Firstly, a refugee has to have "fled from his or her home country and cannot return because he or she has a well-founded fear of persecution based on religion, race, nationality, political opinion or membership in a particular social group". If you think you qualify, you can register with the United Nations High Commissioner for Refugees (UNHCR). If the UNHCR thinks a potential refugee meets the appropriate criteria, then they can refer him or her to the US Resettlement Program (USRP). The USRP maintains nine Resettlement Support Centers (RSCs) around the world. The RSCs receive and process refugee requests. Refugees awaiting approval undergo personal interviews, security and background checks, and a medical examination (so they don't bring contagious diseases into the country). The process typically takes 18 to 24 months. I also learned that of the refugees that are accepted worldwide, about half of them are accepted by the US. That's also a very small fraction of the total number of people who request refugee status.
Thursday, November 19, 2015
Ciprofloxacin, Drones, and Amino Acids... In Space!
Today I Learned:
1) Ciprofloxacin is one of the stronger, cheaper antibiotics on the market. It's a little unusual in its mechanism of action -- most antibiotics I know of work by either inhibiting synthesis of the bacterial cell wall or by blocking bacterial ribosomes, but ciprofloxacin works by inhibiting several bacterial topoisomerases and gyrases, which are important for DNA replication (they help unwind DNA and relieve torsional stress from the unwinding).
Ciprofloxacin also, rarely, has a couple of nasty side effects. In addition to the usual sort of stuff (nausea, abnormal liver function, muscle weakness, etc), ciprofloxacin is associated with an increased risk of tendon rupture. It apparently weakens several kinds of connective tissue important for holding tendons together. It's a rare side effect, so it's still used pretty commonly, but it's not supposed to be given to anyone with known tendon problems or to the elderly.
Ciprofloxacin may also cause retinal detachment, which is just as nasty as it sounds (evidence of retinal detachment caused by ciprofloxacin: http://ift.tt/1MYk1vR). However, a Danish study tried to replicate the finding and failed: http://ift.tt/217bwt0. The authors claim that they can rule out any more than a 3-fold increase in risk of retinal detachment due to small sample size (they looked at about 500 cases of retinal detachment, out of a total of around 660,000 cases of ciprofloxacin use), which corresponds to "in the worst-case scenario [...] no more than 11 additional cases of retinal detachment per 1,000,000 treatment episodes". So if it does cause retinal detachment, it's *quite* rare.
2) ...a little bit about drone design. For one thing, there are tricopters as well as quadcopters. Also, off-the-shelf drones primarily use PID controllers. Also, control sticks for flying off-the-shelf drones (and probably other remote-control aircraft) typically use something called "expo", which is an exponential mapping between distance-from-the-center-of-the-control-pad-to-the-stick to the size of the effect on the drone. This is so you can make fine adjustments near the center of the stick-range while still allowing large changes with big stick movements.
3) ...a bit about how we know about amino acids* in space. Incidentally, there are amino acids in space, in surprising abundance. We know this from at least two independent sources. Firstly, astronomers in 1994 found spectral lines for the amino acid glycine in three nebulae, and I believe other experiments have found similar spectral data in other gas clouds.
Secondly, we've found complex amino acid mixtures inside fresh meteorites, which includes many amino acids not found on Earth. Moreover, in 2009 NASA's Stardust mission brought home dust samples from the comet Wild 2, which contained detectable amounts of glycine (contamination was ruled out by the glycine's radiological signature -- it had more Carbon 13 than Earth glycine).
*Amino acids == the monomers that make up proteins, which are the complex molecules that perform most biological functions.
1) Ciprofloxacin is one of the stronger, cheaper antibiotics on the market. It's a little unusual in its mechanism of action -- most antibiotics I know of work by either inhibiting synthesis of the bacterial cell wall or by blocking bacterial ribosomes, but ciprofloxacin works by inhibiting several bacterial topoisomerases and gyrases, which are important for DNA replication (they help unwind DNA and relieve torsional stress from the unwinding).
Ciprofloxacin also, rarely, has a couple of nasty side effects. In addition to the usual sort of stuff (nausea, abnormal liver function, muscle weakness, etc), ciprofloxacin is associated with an increased risk of tendon rupture. It apparently weakens several kinds of connective tissue important for holding tendons together. It's a rare side effect, so it's still used pretty commonly, but it's not supposed to be given to anyone with known tendon problems or to the elderly.
Ciprofloxacin may also cause retinal detachment, which is just as nasty as it sounds (evidence of retinal detachment caused by ciprofloxacin: http://ift.tt/1MYk1vR). However, a Danish study tried to replicate the finding and failed: http://ift.tt/217bwt0. The authors claim that they can rule out any more than a 3-fold increase in risk of retinal detachment due to small sample size (they looked at about 500 cases of retinal detachment, out of a total of around 660,000 cases of ciprofloxacin use), which corresponds to "in the worst-case scenario [...] no more than 11 additional cases of retinal detachment per 1,000,000 treatment episodes". So if it does cause retinal detachment, it's *quite* rare.
2) ...a little bit about drone design. For one thing, there are tricopters as well as quadcopters. Also, off-the-shelf drones primarily use PID controllers. Also, control sticks for flying off-the-shelf drones (and probably other remote-control aircraft) typically use something called "expo", which is an exponential mapping between distance-from-the-center-of-the-control-pad-to-the-stick to the size of the effect on the drone. This is so you can make fine adjustments near the center of the stick-range while still allowing large changes with big stick movements.
3) ...a bit about how we know about amino acids* in space. Incidentally, there are amino acids in space, in surprising abundance. We know this from at least two independent sources. Firstly, astronomers in 1994 found spectral lines for the amino acid glycine in three nebulae, and I believe other experiments have found similar spectral data in other gas clouds.
Secondly, we've found complex amino acid mixtures inside fresh meteorites, which includes many amino acids not found on Earth. Moreover, in 2009 NASA's Stardust mission brought home dust samples from the comet Wild 2, which contained detectable amounts of glycine (contamination was ruled out by the glycine's radiological signature -- it had more Carbon 13 than Earth glycine).
*Amino acids == the monomers that make up proteins, which are the complex molecules that perform most biological functions.
A Caste System, Green's Functions, and The Beta Distribution
Today I Learned:
1) There's a species of ant with a really strange caste system. They have queens and workers, just like most ant species, but they are maintained in separate genetic lineages. Queens can produce either queen or worker offspring, but only if they mate with a male of the appropriate line. If the queen only mates with worker-line males, then all of her children are workers or queen-line males. If she only mates with queen-line males, then all of her offspring are queens (and the colony usually dies). How this system came to be is of some debate right now.
2) A Green's function is the impulse response of a bounded linear dynamical system with specified boundary conditions.
Let me break that down a bit. First, an "impulse", in this particular mathematical context, is a function that is zero everywhere except one value, at which it is one. If you think about a digital time signal, an impulse is a flat zero signal with a single spike at one time. There are a couple of cool things about impulses. Firstly, they're simple. They're, like, as simple as a function can get without being uniform. Secondly, they can often by produced experimentally, at least to an approximation, relatively easily. This is especially true in signal processing, where impulses are used all the time. Finally, you can define any function in terms of some number of impulses with various locations and strengths.
A dynamical system is a set of differential equations -- that means it's a system where you can define how quickly each variable changes in terms of the values of each variable at that time. Being bounded and linear and having specified boundary conditions means the system is "nice" in some way.
So, a Green's function is simply what a function does when you spike in an impulse. For instance, you could imagine taking a pool of perfectly still water and instantaneously pulling the surface up by a foot at one spot. The resulting pattern of waves and ripples and splashes would be the Green function for that pool. The nice thing about a Green function is that if you know the Green function for a system, you can add together those functions just like you can add together impulses -- the Green function for two impulses is just the sum of the two impulses' Green function. So once you know the Green function for a system, you know the behavior of the system for all possible starting conditions (with whatever *boundary* conditions the Green function is defined for).
3) The beta distribution, with properly chosen parameters, is a good stand-in for a Gaussian when you only have probabilities defined on the range [0,1].
1) There's a species of ant with a really strange caste system. They have queens and workers, just like most ant species, but they are maintained in separate genetic lineages. Queens can produce either queen or worker offspring, but only if they mate with a male of the appropriate line. If the queen only mates with worker-line males, then all of her children are workers or queen-line males. If she only mates with queen-line males, then all of her offspring are queens (and the colony usually dies). How this system came to be is of some debate right now.
2) A Green's function is the impulse response of a bounded linear dynamical system with specified boundary conditions.
Let me break that down a bit. First, an "impulse", in this particular mathematical context, is a function that is zero everywhere except one value, at which it is one. If you think about a digital time signal, an impulse is a flat zero signal with a single spike at one time. There are a couple of cool things about impulses. Firstly, they're simple. They're, like, as simple as a function can get without being uniform. Secondly, they can often by produced experimentally, at least to an approximation, relatively easily. This is especially true in signal processing, where impulses are used all the time. Finally, you can define any function in terms of some number of impulses with various locations and strengths.
A dynamical system is a set of differential equations -- that means it's a system where you can define how quickly each variable changes in terms of the values of each variable at that time. Being bounded and linear and having specified boundary conditions means the system is "nice" in some way.
So, a Green's function is simply what a function does when you spike in an impulse. For instance, you could imagine taking a pool of perfectly still water and instantaneously pulling the surface up by a foot at one spot. The resulting pattern of waves and ripples and splashes would be the Green function for that pool. The nice thing about a Green function is that if you know the Green function for a system, you can add together those functions just like you can add together impulses -- the Green function for two impulses is just the sum of the two impulses' Green function. So once you know the Green function for a system, you know the behavior of the system for all possible starting conditions (with whatever *boundary* conditions the Green function is defined for).
3) The beta distribution, with properly chosen parameters, is a good stand-in for a Gaussian when you only have probabilities defined on the range [0,1].
Tuesday, November 17, 2015
Noise Filters, English Weirdness, and Forking Ice Cream
Today I Learned:
1) Something to watch out for when filtering noise in time series data using a bandpass filter -- if you put data through a Fourier transform, cut off high or low frequencies, then transform it back, if you don't use phase information in the inverse transform, you force the signal to start at 0, which can shift or distort your data a bit. This is particularly noticeable if your total time isn't much bigger than the wavelength of the dominant frequency in your data.
2) English is the only language whose present-tense verbs only require a special ending in the third-person singular -- I fish, you fish, they fish, but he/she fishes. English is also highly unusual in its use of the word "do", and is the only Indo-European language that doesn't use gendered nouns. I've known English was weird for a long time, but I didn't really notice *how* weird.
3) It is very much possible to eat ice cream with a fork. I'm about to find out what happens when you get to the end of the ice cream. I imagine you start drinking.
1) Something to watch out for when filtering noise in time series data using a bandpass filter -- if you put data through a Fourier transform, cut off high or low frequencies, then transform it back, if you don't use phase information in the inverse transform, you force the signal to start at 0, which can shift or distort your data a bit. This is particularly noticeable if your total time isn't much bigger than the wavelength of the dominant frequency in your data.
2) English is the only language whose present-tense verbs only require a special ending in the third-person singular -- I fish, you fish, they fish, but he/she fishes. English is also highly unusual in its use of the word "do", and is the only Indo-European language that doesn't use gendered nouns. I've known English was weird for a long time, but I didn't really notice *how* weird.
3) It is very much possible to eat ice cream with a fork. I'm about to find out what happens when you get to the end of the ice cream. I imagine you start drinking.
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