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.