All up and down my left side

Electronics have always been a bit of a weak spot with me.

When I was a wee blogger, I had a "Science Fair 150 in 1 Electronic Project Kit (Cat No. 28-248)."  Ok, technically I still have it, rescued from my parent's basement a few years ago.  Basically, it consists of a board with a number of installed circuit elements-- capacitors, resistors, etc., plus some outputs (a light bulb, a rudimentary LED number display, a speaker, etc).  There's an included booklet that tells you how to hook various things up to other various things in order to get various results-- flashing lights, musical tones, timers, and so on.  I eagerly followed the instructions, and got the effects, but had no real idea of what was going on-- I just followed the directions like a recipe.

So now, today, [mumblety] years later, I'm setting out to rectify the situation.  (Get it?  Rectify?  That's an electrical engineering joke!)  So here, more or less, is how a diode works.

A diode, according to the dictionary, is "an electronic device that has two electrodes or terminals and is used especially as a rectifier."  Not very helpful, actually.  Electrodes/terminals I know, those are the "ends" of a circuit element, that can be attached to other elements.  A rectifier (see, I told you it was an EE joke), as it turns out, is "a device for converting alternating current into direct current."  Ok, that makes more sense to me.  So a diode is an electronic device that has two ends and is usually used to turn AC into DC (generally not the other way around).  But how?


A diode is, somewhat simplified, a chunk made up of two types of material with a wire sticking out of each bit.  The two sections have specific electrical properties such that the boundary between them allows current to flow only in one direction (at least theoretically). The details on how that works rapidly get very technical, so I'll leave it there, at least for now.  The point is that alternating current builds up on one side of the diode, like waves crashing upon a semiconductor levee (this is getting unexpectedly poetic), and when the waves get large enough, the "water" begins to flow down the other side, away from the barrier.


This has some useful effects, besides the simple rectification property.  The threshold at which the diode allows current to start flowing (the "height of the levee," as it were) is dependent on temperature, so a diode can be used as a simple temperature sensor-- if current is flowing, it must be at least X degrees (where X depends on the type of diode).  They can also temper current surges, like tiny little surge protectors.  And finally, there's the ubiquitous LED, or Light Emitting Diode, poised to be not just Das Blinkenlight on your device, but also a replacement for your household bulbs.  This is starting to get awfully long, so I think I'll stop here, and cover LEDs more specifically tomorrow.

Stinky Cheese

The fragrance of the well-ripened cheeses of the world have occasionally been compared (somewhat unfavorably) to that of a well-ripened sweat sock.  Odor compounds can be complex, but they're not that weird, so I figured there were just similar compounds floating around in the mix.  It happens.

Turns out, the connection may be even more direct than I thought.  The distinctive odors associated with sweaty feet stem less from the sweat per se, and more from the organisms that feed off of the proteins, electrolytes, etc that come with the sweat.  On most of your skin, that's bacteria (perfectly ordinary and harmless, don't worry), but your feet also tend to contain traces of fungus (also ordinary and harmless, unless you don't wash them enough).  And fungus = mold, the living component to many of the Continent's very finest stinky cheeses.  Now, of course, it's probably not the same fungus, but all the same, a certain similarity in biological output would not be unexpected.

Word for the Day-- Dvandva

"Dvandva" is a linguistic term.  It refers to a type of compound term where both parts are of equal importance and are related to each other.  The rule of thumb seems to be that if it could be split into two words separated by an "and" without changing the basic semantic content, then it qualifies.

This is a relatively uncommon thing in English, where that sort of equality is hard to come by, but there are some examples-- the OED uses (in one of its quotes) the compound "prince-consort," which possibly says something about the OED, or maybe about the English language, I don't know.  Webster's Third New Etc. uses the slightly more plausible "secretary-treasurer" and "bittersweet" as examples, although it also uses "sociopolitical," which strikes me as not being a very good example because "socio" is a prefix and doesn't stand on its own.  Perhaps the equivalence in importance supersedes that; certainly, the term indicates an equivalence of social and political influence.

The term itself is derived from Sanskrit, where it means something like "pair," (literally "two and two.")  Dva is related to a fairly large number of other words for "two" in other languages, such as "duo" (Latin), "dyo" (Greek), "dva" (Russian), etc.  In the Sanskrit language, apparently, this sort of equivalence pair is much more common.  It's also common in some Asian languages, according to Wikipedia.

Firearms II

As promised/threatened, I did a little more research into gun mechanisms.  It looks like there's a bit more variation in the way that different types of guns reload themselves, so we'll stick to a basic semiautomatic pistol action.

Bullets for a typical semiautomatic pistol are loaded into a clip or magazine, which is basically just a box, open at the top, with a spring on the bottom.  (Apparently "clip" is not the technical term, and is supposed to refer to something else, but people use them fairly interchangeably, so whatever).  As a bullet is taken off the top, the spring pushes another bullet up into its place.  Basically, it's a really dangerous Pez dispenser.

When the cartridge fires, most of the force of the explosion is channeled into pushing the bullet forwards, but a little bit of it goes backwards instead.  This pushes a slide that rests along the top of the gun backwards, which does a couple of things.  First, it carries the empty cartridge backwards until it hits the back end, which usually has a little flange or something that pops the cartridge out sideways, clearing the chamber.  Second, the motion puts energy back into the spring that drives the firing pin/hammer, readying it for another shot.

Finally, as the slide moves the spent cartridge backwards, the way is cleared for the bullet at the top of the magazine to be pushed up into the chamber and into firing position, a second spring pulls the slide back into place, and the whole cycle is ready to start again.

Firearms

I know in general how a gun works.  You pull the trigger, and a bullet comes out the other end.  Right?

I even know how a cartridge works.  The bullet is at the top, and there's a charge of explosive powder below it.  The powder goes boom, and the rapidly expanding gases push the bullet out the front at very high speeds, eventually transmitting a great deal of kinetic energy to something.

But there's a bit there in the middle that I didn't quite understand.  In an olde-y time-y gun, there'd be a spark or fire or something that would light the powder, starting the explosion.  But I don't think that's how it works these days.  I've heard tell of something called a "firing pin," for instance.  To the Research-mobile!  Nananananana...

The missing piece, historically, is a little separate doohickey called the percussion cap.  This was a small container, open at one end, containing a small amount of a substance that explodes when triggered by a physical impact, rather than a flame or electrical charge (like black powder or C4, respectively).  When the trigger on a gun was pulled, a spring-loaded hammer would strike the percussion cap, causing the contents to burst into flame, which would then travel into the main propellant, causing the bullet in turn to go whoosh.

These days, the percussion cap is integrated into the cartridge, which contains not just the bullet and the propellant (as I thought) but also a separate charge of primer, which is the impact-sensitive stuff.  The hammer or firing pin strikes the primer part of the cartridge, causing an internal chain reaction, making everything go bang.

So that's that sorted.  Heck, if I still feel shooty tomorrow, I may try to figure out how other bits of a gun work.  That whole automatic reload thing is kind of mysterious, too...

How to tell an alligator from a crocodile

Alligators have relatively broad, blunt snouts.  Crocodiles, by contrast, have narrow, pointy snouts.  There are other differences as well, of course, but most of them are either somewhat unreliable (coloration, which can vary a bit, and habitat, which has a fair amount of overlap) or undesirable in the wild (the shape of the teeth, which are a clear indicator but are difficult to examine up close and personal, unless you are too up close and personal, in which case, ow).

Coptic pope

When the Coptic Pope (technically, the "Pope of Alexandria and Patriarch of all Africa on the Holy See of St. Mark the Apostle", or in full at least according to Wikipedia the "Pope and Lord Archbishop of the Great City of Alexandria and Patriarch of All Africa on the Holy Orthodox and Apostolic Throne of Saint Mark the Evangelist and Holy Apostle that is, in Egypt, Pentapolis, Libya, Nubia, Sudan, Ethiopia, Eritrea and all Africa") dies, a new pope is chosen by having a bunch of names of nominees put into a hat (not literally a hat, apparently, but at least a box) and having a child from the congregation pick a name out.  When this happened in 1971, the child was even blindfolded, to make sure the choice was "in god's hands."

Full details of the various election processes (including the current one as revised in 1957) can be found in a PDF here.

How to construct a pentagon

Start with a perfect circle.  Find the center, and draw a radius (a straight line between the center and the edge of the circle).  Call the radius R1.  This point on the circumference will be your first point of the pentagon-- call it P1.
Draw another radius perpendicular to the first one.  Call it R2.  Find the point halfway along this radius, and put a temporary mark there.  Draw a line between that mark and P1.  Call this line L1. 

Now, and this is the trickiest part to do without a ruler and protractor, draw a line bisecting the angle between the new line L1 and R2, and put another mark where it intersects R1.  You may have to read that sentence a couple of times, unless you consult the illustration I'm going to shamelessly crib off Wolfram MathWorld and copy below.

Next, draw a line from this new mark perpendicular to R2 out to the edge of the circle.  Where it hits will be your second point of the pentagon.  Call it P2.

Erase all of the incidental interior lines, and then repeat this sequence of steps three more times, each time using the new P point (and its associated radius) as your starting point.  Connect all the Ps, and you'll have a regular pentagon.

Of course, if you have the protractor you need to properly bisect the angle in paragraph three, you can just measure out the 72 degree angles you need for the points, but where's the fun in that?  Also, there's probably some way to bisect an angle without a protractor, but I don't know what it is.

Sour Trahana

Sour trahana is a combination of wheat flour and soured milk (or possibly yogurt, which is not quite the same thing).  It ends up sort of like a tiny pasta (a bit like couscous), although the pasta we're familiar with generally contains water or egg (or both) instead of dairy.  There's also a "sweet" version made with fresh milk instead of sour/yogurt.  A number of online sources refer to it as Greek in origin, although others hedge their bets and call it "Mediterranean" or even just "ancient."  You can buy it for about 4 bucks a pound over the Internet, if you're curious.  I'm still trying to decide if I want to spring for some or not-- I have to admit I'm awfully curious, but most of the recipes I've seen seem to be more cold-weather dishes; stews, porridges, etc.

Tacos al Pastor al Arabia al Kebab

Tacos al pastor are a Mexican classic street food.  Big piles of marinated pork are impaled on a vertical spit, topped with an entire pineapple, and the whole thing is slowly roasted, pineapple juices flowing down over the meat, mingling with melting fat, with bits constantly being shaved off of the outside to fill tacos for customers.  Yum.

If this sounds vaguely familiar, that's because it was only introduced to Mexico in the 1800's by Arab immigrants, who knew a similar dish called shawarma.  This, in turn, is apparently an adaptation of the earlier Turkish doner kebabs, which also inspired the Greek gyros.  In Armenia, this dish is called "tarna" ("it turns", akin to gyros (same root as gyroscope)).  Japan has started to adopt a version as street food, but being Japan, they put mayonnaise on it.  Sigh.  Frankly, the Wikipedia article on doner kebabs make it sound like this is the single most popular street food in the world.  Plausible, but I have to wonder if sausages aren't another possible contender.

Long in the tooth

I used this expression today, and stopped practically mid-sentence to ponder-- where does it come from, originally?  These days, it's used to refer to almost anything or everything, regardless of how long its tooth is, or even if it has teeth to begin with (I was actually referring to some positively toothless leftover stir-fry).

I forthwith learned several things, to wit: firstly, that the expression was originally used to refer to horses.  This makes a certain amount of sense.  After all, the use of horses in phraseology is well established, from horses that are gifts to ones that are of different colors to ones that you merely wish to make drink.  They are apparently richly symbolic animals.

Secondly, I attempted to track down the reasoning behind the saying, and this is where it gets a bit more complicated.  Supposedly, at least according to the Encyclopedia Britannica (and some other random online sources), horses (somewhat like rodents and exceedingly unlike humans) have teeth that continue to grow throughout their lives.  In the wild, the act of grazing provides more or less enough wear to keep these teeth in check for most of a horse's life, but the domesticated diet is softer and the teeth of domesticated horses continue to erupt and lengthen.  Thus, the length of a (domestic) horse's tooth is roughly correlated to their age.  However, the Oxford English Dictionary, which is generally fairly reliable, defines the phrase as "long in the tooth: (orig. of horses) displaying the roots of the teeth owing to the recession of the gums with increasing age; hence gen., old." which, while similar, is not quite the same thing.  I don't know much about horses myself-- I tried riding one once, and neither of us enjoyed it very much.  If God had meant us to ride horses, he wouldn't have given us bicycles.  Anyway, I digress.

So we are actually left with a bit of a mystery, with two slightly disparate explanations of a phrase that (regardless) definitely came straight from the horse's mouth.

And then, suddenly, nothing happened.

The history of the world is a large subject, covering something over four billion years.  However, complex life forms only arose about 500 million years ago, at the start of what is now called the Cambrian Period.  Before that?

Well, the International Commission on Stratigraphy has divided the preceding 3.5 billion years into several sections, separated more or less arbitrarily into large chunks of time.  From the creation of the Earth until the lithosphere settled down is the Hadean Eon, for example.  Then there's the Archean Eon (divided into four eras), and the Proterozoic Eon, divided into three Eras, each of which is further divided into three or four Periods (unless they go into overtime).  The kicker?  Of these 20 or so Pre-Cambrian official designations, only one or two of them are even vaguely interesting.

They're all mostly just too old-- hardly anything survives from that part of history.  There are a few rock outcroppings here and there that date all the way back, and some fossil-y sort of things from ancient bacteria and algae, but that's about it.  So if someone jumps out at you in a dark alley and demands to know three interesting things about the Orosirian Period, you can take some comfort in the fact that you'll know it's a trick question.  There were only two.

Word for the Day -- Compotator

Today's new word is "compotator," defined as "one who drinks with another."  The derivation is fairly straightforward-- "com-", meaning "with" or "together" (as in "community," or "commingle"), and "potator," "one who potates."  Ok, so that isn't all that straightforward, but it's the same root as "potable," which most people only encounter in the Jeopardy! category "potent potables."  It means "drink."

So a compotator is basically just a drinking buddy.  This is another one of those words that no-one uses any more that I think really deserves a renaissance.  "I'll see you later, dear-- I'm due to meet up with my compotators at the local pub."  "I joined Gamma Delta Iota in my sophomore year so that I could live with my compotators."

Guy Wires

A few weeks back, an episode of Dirty Jobs featured an extended soliloquy by host Mike Rowe about why guy wires were called that, and how come nobody knew, and how silly it all was.  The best answer that they came up with was, "It was probably named after some guy."  (I didn't say it was an accurate or useful answer.  But it was entertaining.)

But hey-- I'm a language guy (no relation)!  I can answer it!

The word guy (or its derivatives guy wire or guyline) is likely derived either from the Dutch gei (according to the Webster's Third New International Dictionary, Unabridged), or the Old French gui (according to the OED).  Both are terms for ropes, originally nautical in context, that held things in place.  Both are also probably related etymologically to the word "guide."

Key Fobs

The remote key fob for a modern automobile is a pretty cool little device.  It contains a pseudo-random number generator, that synchronizes with your car every time you press the button.  And the system will store 256 additional numbers, so if you press the button when you're out of range, it'll recognize the next number in line, and promptly resynch (if you manage to press the button 300 times in a row when you're out of range, check the owner's manual-- there'll be a way to force a resynchronization).  The fob uses a 40-bit code, which means roughly 1 trillion possible total codes, divided by the 250 that it stores (plus multiple possible fobs per car) gives you still roughly only 1 chance in a billion to accidentally open someone else's car.  This is a vast improvement over the "olden days," when (so I was told) car manufacturers only had a dozen or so basic key shapes.  I myself have accidentally unlocked and gotten into the wrong car (it wouldn't start, and I realized my mistake almost immediately).

Apparently there is a small battery in there, which will run down over time.  The fob can be opened, and there should be instructions inside the cover for replacement.  I was kind of hoping that it ran off of some sort of capacitor instead that charged when you put the key in the ignition, but I guess that wouldn't last long enough if you didn't use your car frequently.