Biomass: The Bane of Witty Titles.

Well, as promised, I'm hopping back on the horse, and I'm going to tackle yet another source of alternative energy, but before we begin, I'd like to start off with a brief anecdote, mostly because I like to say "anecdote."

Farmer Billy of Reynolds, Indiana wakes up on a bright summer morning and goes out to check out his farm. The corn looks quite...corny this season! However, only some of it will actually be eaten. A large share of the crop will end up going into his gas tank. Next he checks on his cows, and woah buddy does it smell ripe in that barn. But Farmer Billy doesn't mind the stench, because that odiferous animal waste is just pure cash money for him. Next, he hops in his truck to drive into town. Along the way, he passes several big honkin' windmills in the fields, just a'spinnin' away. Finally, he gets to his lovely town of Reynolds and drives up to the gas station. But wait! He's not really buying gas at all, now is he? Oh no, he's pulling right on up to that E85 pump. After the gas station, he picks up some lovely tomatoes at the farmer's market and heads on back to his farm, ready to start the day by farming not just for corn 'n' soybeans, but for energy.

So my little story might seem a tad far-fetched, but in reality, this is actually happening in Reynolds. This tiny town, also known as Biotown, USA, is almost completely self-sufficient on renewable energy grown right within the town itself. From ethanol made from the corn to methane and natural gas from pig manure, alternative energy has become the cash crop of Reynolds, Indiana.

Many of the aforementioned energy sources fall under the overarching description known as Biomass. Biomass is any renewable material that comes from living organisms or recently living organisms that can be used to create energy or other substances. Fossil Fuels are not included because, though they are derived from organic matter, they are truly formed by a long and gradual geological process. Biomass does include anything from burning logs to ethanol-based fuel. It's a huge, overarching type of renewable energy, so I'll get to breaking it all down for you right here.

The Final Blog Post

Sort of. Though this is the last post that will be counted for my English project, I kind of hope to continue this blog afterwards. We'll just see how that plays out. Anyway, without further ado, it appears I have some questions to answer.

Well, dear reader, we've been adventuring on this blog together for the past several weeks, and now I must decide what kind of "mind" I am. Well, based solely on this blogging project, I would say it's fairly evident that I am a "synthetic mind." This means that I like to take information from lots of sources, learn about something, put it all together, and explain it in terms that both myself and other people can understand. So far, we've delved into things as simple as wind and water, to the mildly more complex solar power and hydrogen fuel cells, to subatomic physics, and even the completely and utterly abstract concept of dark matter. However, I like to think that over the course of our blogging adventure, I've done a fairly decent job at explaining everything. Furthermore, incredible amounts of research had to go into every blog post, and I really had to decipher massive articles and compress them down into just a couple paragraphs. Granted, they were still huge entries, and while I'm sure that sometimes it got to be a drag, reading these ridiculously long entries all about that nerdy sciencey junk, perhaps you were mildly entertained by my brief anecdotes, Rasta Fish, and lovely videos of Spanish Celtic metal, tactical nukes, and adorable kittens.

Secondly, I need to talk about a couple of things that I exemplify. Through this very blog, I've exhibited curiosity and a thirst for learning. I've done literally hours of research in order to compile everything into an ordered mess and put it right up here on this blog, just for your viewing pleasure. In the process, I've discovered a lot about science, the world, and myself. Secondly, I've experimented with some new ideas. Earlier, I made a blog post specifically aimed at "dabbling in the fantastic" and literally discussing and explaining new ideas, either from the science and engineering community, or straight from my own brain. I've used this very blog to talk with other people through comments, or outside communication, where they can ask me questions and really control the direction that my blog takes. In the future, as my following hopefully increases, maybe the reader response will start to play an even larger role in this blog. Lastly, I've asked a few provocative questions. Some of them are just cute little rhetorical devices, used to break up the flow of my entries, and make it seem like an informal chat, rather than some dry research thesis. However, through my blog, I've also asked The Big Question: the very question that the science community seems to be scurrying to answer. How are we going to survive in a world without oil? I'll be the first to say that I haven't found the answer. However, through my research, I now adamantly believe that the answer is definitely out there somewhere. We just have to find it.

Lastly, I've got to talk about what I learned. Obviously, I learned a lot. I had a vague understanding of some of the stuff I talked about: hydroelectricity and wind are pretty simple, and I learned about dark matter in my Physics class, but other than that, virtually all of the information and facts I have here, I learned through research for this very project. I've learned so much about alternative energy, how it works, why we need it, and all of the different types. It's been really interesting to learn all about sources of energy, and hopefully I'll be able to continue learning — and teaching you, dear reader — even more through this blog. Good Night, everyone. It's been a pleasure.

Death, Destroyer of Worlds

Wind and Water are useful and all, and it was quite useful to include a blog post about them, but to be quite perfectly honest, they bore me to tears.

Nuclear power is so much more elegant, don't you agree? Well, whether you're Monty Burns or a tree hugging hippie, nobody can really deny the fact that nuclear power just gets the job done, and thus it is the subject of tonight's blog entry.

Let's start with a history lesson. Ernest Rutherford first split the atom in 1919, but the awesome power of the atom was not really shown until World War Two, in a lovely city called Hiroshima. I hear they put out the fire sometime last week. Anyway, the moral of the story is that nuclear power has been developing ever since. In 1951, nuclear energy was first harnessed in a useful form to create electricity (not to say that decimating an entire city isn't useful in some cases, but that's irrelevant). Nuclear power seemed to be on the rise for most of the second half of the twentieth century, fueled by events like The Oil Crisis of 1973, but gradually, the public began to turn against it, out of fear of disasters like Three Mile Island and the Chernobyl Disaster. Fun Fact: parts of Chernobyl are still too radioactive to sustain human life. Makes you feel warm and fuzzy, eh? So yeah, the mildly vivid image of the video above occurring in one's backyard turned the public against nuclear power, and the industry was crippled for decades. However, nowadays, the public is turning against fossil fuels due to constant fear of global warming and carbon emissions, and nuclear power is starting to like an awful lot more attractive. At least to me. Regardless, most industry experts say that the nuclear industry is going to rise in the immediate future, as a demand for cleaner energy rises.

The following is the best explanation I can give for the process of harnessing radioactive material in order to create electricity. 99.99% of the nuclear reactors in the world work off the process of nuclear fission. First, you get what's known as a "fissile material," which is literally just a substance capable of performing fission, generally Uranium-235 or Plutonium-239. When a neutron is forced into the nucleus of a single atom of the fissile material, the atom splits, releasing two smaller atoms, energy, and more neutrons. Theoretically, these neutrons would go out and be absorbed by other atoms of the fissile material, thus causing the reaction to continue on, and increase in frequency exponentially. This is essentially what happens in the video at the top. when the rate of fission is not controlled, a massive explosion occurs. Now, as I already said, explosions are nice, but are not very useful for creating electricity that humans can use in daily life. Thus, neutron poisons are used in order to absorb some of the neutrons produced, allowing the reaction to occur at a slow, constant rate, or neutron moderators are used to slow the neutrons down. So, the reactor contains this reaction and allows it to proceed at a fairly constant and easily controlled rate. But...it gets really hot, really fast. However! the process by which the reactor is cooled is exactly the same process by which the electricity is produced. A coolant, typically just plain ol' water, is pumped to the reactor, where it is heated and generally evaporates, causing steam. The steam then proceeds out and spins a massive turbine (it's interesting how often these things seem to show up), thus creating electricity. The steam then leaves via a smokestack as perfectly harmless water vapor. Pretty simple, right?

Wrong. Whoever said rocket science is the epitome of a mentally-demanding occupation was a fool; sub-atomic physics is infinitely more complex. But just in case you thought that was easy, fission is only half the fun. Well...not half. 99.99%, but that last .01% is pretty darn important too. I am speaking, of course, of fusion. Nuclear fusion is becoming increasingly more important in the nuclear power industry, mostly because it theoretically can operate without all those negative aspects of fission power, such as massive barrels of glowing toxic ooze, and the occasional meltdown or two. So what is fusion? It's exactly what it sounds like, the opposite of fission: rather than splitting a really big atom into smaller ones, it takes smaller atoms and squishes them into a big one. The theory is that if you take one "light" atom and another "light" atom and push them close together, the "residual strong force" between their nuclei will pull them together, fusing them together into a single atom whose mass is slightly less than the sum of the two single atoms' masses. Now, I just used a lot of quote marks and italics, so I'll go over that a little better. A "light" atom is defined as "any atom that is less massive than Iron-56." That's pretty straight-forward. Now "residual strong force" is a tad more complex. Basically, there are four forces that govern the universe: gravity, electromagnetism, weak nuclear force, and strong nuclear force. The fourth one, also known as the residual strong force, is the strongest of the four, hundreds of times more powerful than electromagnetism, and millions more than gravity. Essentially, it is the force that holds the protons and neutrons together in the nucleus. In theory, if you get two nuclei close enough, this force would cause them to fuse together into a single nucleus. However, if you'll recall, I said "slightly less than the sum." If you're not following my math lingo, I just said that two plus two is three and a half. So what happened to the missing mass? There's an equation that many people know but few understand that tells us exactly that: E=mc². This equation states that the energy of a mass, simply from being mass is equal to that mass times the speed of light, in meters per second, squared. The missing "one-half" just turns into pure energy. Now, the mass of an atom is really really tiny. An atom of hydrogen is just about 1.6E-27 kilograms. Not all that impressive. However, that other part of the equation, c² is roughly 9E16 meters per second. So in the end, depending on the material used it generally evens out pretty well. Anyway, that's the super fantastic subatomic process that goes on, but in the end it turns out the same way, energy is released, the reactor is cooled, steam turns a turbine, ????, PROFIT, and repeat.

Now, if you're like me, your brain is probably hurting a bit right now. Let's watch a video of an adorable kitten until we feel better.

Okay, let's move on. Nuclear power supplies about 15% of the world's electricity, falling just behind hydroelectricity at 20%, and trailing steeply behind fossil fuels. However, it is starting to rise. While nuclear fission is technically not a renewable source of energy, as U-235 only accounts for 1% of the naturally-occurring Uranium on the planet, in terms of overall pollution and environmental impact, nuclear power is really cleaner and greener than fossil fuels, and is one of the few forms of energy that is actually more efficient than oil. New research and technology is being developed right now that aims to make nuclear power more effective, less wasteful, and all around safer for humankind to use. Furthermore, the recent developments in the field of fusion energy could change the face of the world's energy forever. Fusion can be performed with naturally occurring hydrogen, the most abundant substance in the universe, and produces little, if any, nuclear waste. In my opinion, I think in the next years, possibly the next decade, we could see huge advancements in nuclear power that will change how humans live all across the planet.

Wind and Hydroelectric Power

So in my last post, I made reference to both wind power and hydroelectricity, and I briefly explained each, but I suppose it would be a fairly good idea to cover both of these in detail in their own post, as wind and water are both extremely copious sources of energy, as they are available literally wherever wind or water blows or flows, respectively. So without further ado, I suppose I'll hop right into two of the planet's most renewable sources of energy.

This post is brought to you by Mägo de Oz and their song "Molinos de Viento," also known as windmills:


iEspañoles son locos!

Wind power has been utilized by humans for centuries. Wind has been used to perform tasks like grinding up corn, to drawing up water, to sailing a boat, to even powering a house! Now, if you want to get really technically, windmills are used to provide mechanical energy, like the first three tasks, while wind turbines (also called wind generators, or if you're really cool: aerogenerators) are used to provide electrical energy, as in the last task; however, I am human, and thus I shall probably end up using them interchangeably throughout the course of this blog, so just for the sake of clarity, I mean wind turbines. Anyway, wind turbines are extremely simple. Essentially, the wind blows over the rotor blades, which causes them to rotate, which provides rotary power for a generator, creating electricity. Now, there are two main methods to doing this: the infinitely-more-common Horizontal Axis Wind Turbine (Left), and the slightly-more-obscure-but-at-the-same-time-kind-of-fun-to-look-at Vertical Axis Wind Turbine (Right). When a person thinks of wind power, generally they think of a HAWT, however LAWTs are gradually becoming more prevalent, due to some distinct advantages. Firstly, HAWTs must be built fairly tall so as to gain access to fast enough winds to cause a rotation, but LAWTs are able to rotate with slower wind speeds. Furthermore, HAWTs are extremely difficult to transport, as the blades must come in one piece, and most of them are half as long as a football field; however, LAWTs generally don't have to come in massive pieces, and usually aren't nearly as tall. Lastly, the generator and most of the moving parts in a HAWT are hundreds of feet in the air, while the generator in a LAWT is close to the ground, making it easier to repair, should it break down (a good rule of thumb to remember is that in every machine ever designed ever, the more moving parts it has, the more likely it is to break). However, despite all these advantages, Horizontal Axis Wind Turbines are far more popular, simply because they are more efficient, and generally perceived to be sturdier. However, HAWTs are catching on. One up-and-coming method of using wind turbines is to install a relatively small HAWT on top of a building! This serves as a double-whammy, as the building itself redirects wind to the roof, oftentimes doubling the wind speed, and also the very electricity produced by the turbine could simply go straight into the building beneath it. Anyway, I suppose I'll just sum up wind power with this: from what I've researched, wind power is completely and utterly renewable, but it just isn't efficient enough to replace oil. Right now, wind accounts for about .3% of the planets energy, while nonrenewable sources account for over 90% In theory, if we could cover the planet in 300 times as many wind turbines as there are now, it could work, but in practice, I just don't see it happening. However, wind power, in conjunction with other renewable resources, certainly could do the job.



Hydroelectricity is currently the most widely used source of renewable energy. In 2006, hydroelectric power plants supplied almost 3000 TeraWatt-hours of energy, accounting for 20% of the entire planet's electricity, and 80% of the electricity from renewable resources. Clearly, as the planet has plenty of water to spare, hydroelectricity has the potential to power the planet.

So I suppose I'll rap to ya about how this hydroelectricity works. There are several methods of deriving energy from water, but the most common method is through damming water, such as in a river, and releasing it gradually in order to spin massive turbines and generators. Essentially, it's very similar to wind power, except with moving water as opposed to moving air. However, that's just how the typical, orthodox, conventional, boring hydroelectric plant works. There are entirely different methods of utilizing moving water that, while less common, are gradually becoming more prevalent in the world's energy supply. Pumped Storage Hydroelectricity does not involve a dam. Rather, it just has two massive reservoirs, one at a high elevation, and another at a low elevation. When there is a high peak demand, literally when there is the highest demand for electricity, water will flow from the high tank down to the low one, spinning a turbine along the way. Then, during times of low peak demand, any excess energy can be used to pump water from the low reservoir back up to the high one. This method, however, ultimately results in the system using more electricity than it produces. However, it is capable of making money by creating energy during high demand and using it during low demand, even though it technically consumes more than it produces. This allows it to have the largest capacity for grid energy storage. Another mildly intriguing source of hydroelectric power is known as a Tidal Plant. This method uses the changing tide from the moon's gravitational pull to create energy and electricity. Clearly, there are plenty of schools of thought as to how water can be used to meet the energy needs of the planet.

So I suppose I'll do some pros and cons. A nice thing about the big ol' dam idea is that after building the dam...that's about it, other than a bit of maintenance here and there. As long as water flows in the river, it will continue to crank out electricity. However, a negative aspect of building massive dams is the huge impact it can have on ecosystems...downstream. Plants and animals often rely on rivers for food, drinking water, and shelter. However, dropping a big dam in the middle of a river drastically decreases the amount of water available downstream, and thus these ecosystems suffer. Pumped Storage Hydroelectricity does not have this adverse effect on the environment; however, there is the negative aspect of the fact that it isn't nearly as efficient, as at some point, that water has to be pumped back up. Tidal plants solve both problems; however, the areas in which there is enough of a tidal change and a fast enough flow of water to spin a turbine are extremely limited. So really while each one has its benefits...there's not really one specific method that's better than the others. Unless if we combined them all into a super hydroelectric power plant o.O but that's just preposterous.

Anyway, I'll wrap this up now if you don't mind. Hydroelectric power has the capacity to replace oil, if we can expand the industry. Furthermore, it's only a matter of time before the technology we have now is improved to the point that the aforementioned negative aspects become fairly negligible. Again, the best-case scenario would be to use hydroelectric power in combination with other sources of completely renewable energy.

This post took almost 2 weeks to complete.

Let us dabble in the fantastic for a moment, shall we?

Fuel cells and solar power are all well and good, but everybody and his brother already know about them. What about those ridiculously fantastical ideas? The kind that are just now emerging, work only in theory, or are simply imagined by Yours Truly. These are just ideas to mull over or think about, and aren't necessarily probable or even logically sound. Nevertheless, I'm pretty much always thinking about these sorts of things.

Let's start of with something straightforward. I think we all can agree that the ocean is pretty huge. It has lots of water, lots of space, and lots of...well...fish. The fish point is mildly irrelevant, but water and open space are certainly useful. A hydroelectric power plant is any plant that uses the kinetic energy of water to create electricity. Hydroelectricity is the world's biggest source of renewable energy, and I'll probably be covering it at some point later. It simply uses a flow of water to turn a big turbine, thus creating electricity. Now, when most people think of hydroelectricity, they think of a big river stopped up by a big dam. For the most part, this IS how hydroelectricity is produced. However, rivers are limited. There are only so many rivers in the world, and we can't exactly stop them all up to create electricity, lest we cause massive environmental issues down the road. However, why must it be a river? If any flow of water can turn a turbine, why not look to the ocean. Let's take a look at the Gulf Stream. The Gulf Stream is a massive current of water that cruises along the eastern coast of the United States and cuts across the Atlantic Ocean to Europe. Think of the Gulf Stream like a river within the ocean: it is constantly moving, and will never run out. Hypothetically, it could be completely possible to place the same hydroelectric turbines at the bottom of the ocean, right smack in the middle of the Gulf Stream. If it works for rivers, why not the ocean? In theory, and this is pretty much just my own speculation, this could be a constant source of completely renewable energy. However, the ocean has even more uses than just huge currents. The vast flat space offered by the ocean allows yet another form of renewable energy to be used here: wind power. Wind farms, or large clusters of wind turbines, have been popping up all over dry land for years now. However, this leads to many issues. They are rather noisy, mildly unpleasant to look at, and difficult to transport. Furthermore, there is a limited amount of flat open land, and the wind doesn't always blow here. However, wind farms on the ocean solve virtually all of these issues. They will be far away from anyone who would prefer not to have a massive, spinning windmill in their backyard. They would be far easier to transport and assemble at sea, due to the great mobility of sea cranes. Furthermore, deep water is considerably less rough than dry land, causing the wind the be far more powerful and constant than here. Clearly, the ocean has a lot to offer.

Well, those were both fairly straightforward. However, I think I'm about to go off the deep end with this next section, so here is my official warning.
I've got a pretty fantastic idea, in my humble opinion. It's kind of simple in essence, mildly similar to the aforementioned windmills or hydroelectric plants, but the driving force behind it is slightly more abstract than simply water or wind. There is a gratuitous amount of mass simply flying around the universe and passing through the earth as you read this. This substance is referred to as "dark matter," simply because it is difficult to detect. It is impossible to see, feel, hear, or interact with in any way. However, due to the massive nature of the dark matter, scientists are able to prove its existence, through observing the rotation of galaxies or observing the bending of light around massive pockets of seemingly invisible gravity. Now this is all well and good, but what does it actually do for us? Well, there are chunks of mass zipping all over the universe at thousands of miles per hour. If this mass were able to exert force on regular matter, that would be a force exerted over a distance, also known as the definition of energy. If a substance or material could be designed that can physically interact with dark matter, it could potentially be possible to create a dark matter "windmill" that could create energy in exactly the same way as a hydroelectric turbine. In theory, I think it's a stupendous idea, but in practice...well, no such substance has been discovered yet, but someday...who knows?

Ahem: an Update: I've gotten a pretty positive response from my Dark Matter rant, so I just thought that I might expand a bit, and apply my freaky physics nonsense to something happening right now in the real world. Over in Switzerland, perhaps you've heard of the Large Hadron Collider, also known as "that machine that's gonna end the world in 2012" to the fools that believe the Mayans could predict the future. But I digress. Anyway, I feel as though 98% of the people in the world are positive that this thing is going to create big evil black holes that are going to compress the planet into the size of a tic tac, and about 2% actually know what the LHC is supposed to do. Now, I don't really know all the stuff it's supposed to help discover, but I do know that one of the things is proving the theory of dark matter. Theoretically, by slamming together these particles at 99.999% the speed of light, many believe that this could create dark matter, thus allowing those wacky Swiss scientists to potentially prove its existence, develop ways to detect it, and potentially even find ways to interact with it. So I suppose my idea's not so preposterous after all.

Fuel cells: a tiny little box of awesome

Fuel cells seem to have gradually infiltrated the world of energy. However, it is still a fairly new and widely unused source of energy. Right now, with the current technology at hand, fuel cells are impractical; however, it is very likely that in the near future, they have the potential to move to the forefront of the world's energy needs, from remote power sources to transportation.

These fuel cells, like the one shown to the right, are actually fairly simple in nature. The fuel, usually hydrogen, is pumped into the cell. Then, it is oxidized, meaning it is changed from a neutral atom into a positive ion and a single free electron. Said electrons are then free to move about, specifically through a wire, which creates electric current. Then, on the other side of the cell, the aforementioned positive ion and electron are reunited and react with another substance, generally oxygen, creating a waste product of water or carbon dioxide. Now a perfectly reasonable reaction at this point would be "Hey, Bryan! You promised us this was simple!" I'm not really implying that fuel cells are simple, and anyone could just make one if the mood struck them. I'm just saying that these fuel cells are a lot easier than say...gas-powered engines. Just in case you didn't know before now, the engine that drives your car is literally housing thousands of explosions every second. Just something to think about...

Anyway, that's how the most basic of fuel cells work. Naturally there are variations on the simple design, and many other methods used that all help change the uses and efficiency of the fuel cells. One such alteration is a very very recent development referred to as the "bloom box." A good video detailing the bloom box can be found here. The bloom box works off the same general principle, but utilizes sand and hydrocarbons to create electricity. As of right now, it's still unclear how it works, but it apparently seems to work quite effectively. However, one drawback I personally see is that it needs hydrocarbons, like gasoline, in order to function.

Whew...I don't know about you, but I can't handle any more science. Let's talk numbers. The typical fuel cell cranks out an average of .6 to .7 volts, or about half of a triple A battery, which is not exactly all that impressive. However, these fuel cells are capable of being stacked together in either series or parallel circuits, allowing higher voltage or higher current respectively. If one were to stack together enough of these fuel cells, it would be possible to get enough voltage to power virtually any application, from a 100 Watt laptop, to a 5000 Watt house, to a 100,000 Watt vehicle, to even a massive 200,000,000 Watt central power generator. The very "stackable" nature of fuel cells is what makes it so useful in many different applications. Hydrogen cells are pretty efficient, too. About half of the energy from the fuel (hydrogen) is converted into electricity, and half of it is lost as heat because a typical hydrogen fuel cell is about 50% efficient. This is a lot more impressive when compared to an average car, which is about 3% to 4% efficient on a good day. Furthermore, due to the fairly simple nature of fuel cells, they can be expected to be very reliable. They are compact, lightweight, have no moving parts, and don't contain tiny explosions, meaning that it is very very difficult for it to actually break. Scientists theorize that for every 2 years of perfect functionality, a hydrogen fuel cell could be expected to break for about a minute. Fuel cells also have countless uses. The most practical one, would actually be providing power to a remote location. A stack of hydrogen fuel cells, a tank of oxygen, and a tank of hydrogen could essentially power anything from a remote log cabin to a permanent settlement on Mars. Also, hydrogen fuel cells are currently being used to power vehicles that expel only oxygen and water vapor as waste. Many things, from German subs to the Element One car run off fuel cells. in 2008, Boeing conducted experimental flight tests of The Fuel Cell Demonstrator Airplane, powered by both fuel cells and unimaginative titles. Reykjavik, Iceland, was the first place to open a hydrogen refueling station, literally just a gas station for hydrogen fuel cells. Granted, it only services three buses, but it still counts.

All in all, I'm quite impressed with the potential of fuel cells. I remember several years ago when I used to think a hydrogen powered car was ridiculous and sounded just like some fantastical pipe dream. Now, however, it's starting to look like hydrogen-powered cars could become the norm within my lifetime. Personally, I think it'll take quite a while for it to become practical to use fuel cells, but in reality it's only a matter of time

Time for some input

So now that I've thrown down a couple of lengthy blog entries, most of which I doubt anyone actually read, with very little feedback, I suppose I'll take a break from the gratuitously long posts and keep this one simple. So I'm just going to ask you, the blogging community, to give me some feedback on my blog here. It can be anything as simple as critiquing my layout, style, font, color scheme, etc; talking about my beloved Rasta Fish; or even just asking me to clear up anything I've talked about up to now. Knock yourselves out...any and all feedback is welcome and encouraged.