CaptainPanic

Get an account on the Khan Academy. It has exercises and youtube video in the style of a classroom explanation (with the difference that you can replay this, while ordinary teachers generally don't repeat things). It starts really easy, but it will become challenging soon enough. Also, it's set up as a game: you can earn points for doing exercises well. And you get badges for certain achievements. It may sound a bit cheesy, but it's actually fun.

Good point. +1 However... since we already started the thread with the assumption that people would want to live under water (rather than on the water), I don't see why we don't just answer the question. A 200 mile action radius is nothing to a submarine. Since weight is hardly an issue, you can fill your sub with battery packs, and charge them at your underwater home with off shore wind power (or if there is a strong current/waves, some tidal power). Seems trivial to me. But so far, there are probably thousands of examples of people living on the water (just google for house boats), and almost no examples of people living under water. Likewise, there are many examples of people traveling on the water, and very few of people traveling under water. So, I think that the problem of powering a sub can be solved easily, I don't see why you are trying to solve it?

Yes Yes But there is also a freedom to use your head, a freedom not-to-insult, a freedom to use common sense, and a freedom to not-be-a-bloody-idiot. It's those latter freedoms that many people forget, and they make the first two freedoms (religion and speech) a bit fundamentalist. That sucks. Yes, yes, I know that the language used in this post is not exactly your "legal vocabulary", but that's exactly where we have a problem. It's bloody difficult to catch common sense in a few paragraphs of legal text, and that enables the fundamentalists to read between the lines that they can behave like morons.

Both Youtube and Google sometimes temporarily change something. I still have the negative rep button for movies, so I imagine that you have it too. But your other point is valid: it seems that Google want to put all their services in one login, and in one terms of agreement, in order to be able to combine all the data they gather about you. Personally, I don't see the point of logging in to Youtube. The movies play just as well when you're not logged in.

I'm humbled by the realization of how little we know. But I feel superior because I know so much more than many people in the present and in the past. I'm humbled by the realization of how tiny I am in comparison to the vast universe. But I feel enormous when I realize just how many cells make up my body, and that each individual cell contains heaps and heaps of molecules, all interacting. A scientist must be humble to have the right mindset to learn. But an engineer cannot stop to ponder how little we know, because with such an attitude nothing ever gets built. My opinion: You should match your attitude with the task at hand, and the environment around you. And that changes all the time... so you must change your attitude as well.

The obvious problem with this statement is that there is no direct evidence. The dead can't talk. So, I guess it is important to know who told you this story? Where did this person hear it? If anyone heard it from a dead person, then there might be some truth in it.

Thanks for the feedback so far. Let's talk only about the erasers that are gentle on the paper: those which can only remove the graphite. I guess the most important question I had was what makes the graphite stick to the rubber? Are we talking some good old vd Waals attraction? And is the difference in polarity of any significance, like when you're determining whether something will dissolve into a solvent or not? The rubber and the graphite are apolar, but the paper is polar (paper = cellulose = sugar polymer). Or are we dealing with some double bond interactions? Could it even be covalent (I guess not)?

! Moderator Note newts, this forum is not a place where we tolerate trolling ( = going off topic to insult). Stop it now. Do not respond to this post.

I just made a small error, and I wanted to erase some of my writing on paper. I took the eraser I have, and removed the pencil writing. Then I realized that I have no idea how that works! First of all, when I write, the friction between the (soft) graphite and the paper causes some graphite to stay behind in and around the fibres of the paper. That part I understand (although it's a bit crude). But how the hell can an eraser get that graphite off the paper again? Does it have such affinity for graphite? Is it just an interfacial phenomenon, or is there a reaction? Wikipedia does not explain how it works. This website says that the graphite "sticks" to the rubber (not a very scientific explanation). For something so common, I feel ridiculous that I don't know it.

Well, you can also create a mass balance. The total mass flow in is equal to the total flow out. Since pressure and density are equal, your volumetric flows will be proportional to the mass flows, so we can say: V0 = V1 + V2 + V3. That in turn means you only need to know how the flow will divide itself (what is the relative flow in V1, in proportion to V2, and V3?). When you know the ratio of V1:V2:v3, you should arrive at your answer.

Hello, welcome to the forum. When you write "the diameters and lengths of the duct sections are known", can you give any more information about that? What would be a good general formula to use in this case? Note, this is our homework section - we make you work yourself, we do not give answers straight away.

I completely agree. This is one major issue. Although, it can be argued that most (Western) governments are still considered "the good guys", so we have nothing to fear. It's a well-known argument: "I have nothing to hide, so I have nothing to fear (from my friendly government)". Personally, I am convinced that the argument is irrelevant. Still, because this argument is so persistent, I choose to fight this privacy problem from another angle: A more immediate fear I have is that information can will be hacked/lost. Sure, every government promises to take good care. And I am confident that they really try their best. Still, once every now and then, a tax office gets hacked, or a bank, or a government agency. My point is that the most sensitive (and most secure!) systems, those which deal with our money, are also getting hacked. Why wouldn't this particular effort get hacked as well? My most immediate fear then is not that some government does evil with this data. My most immediate fear is that it falls into the hands of criminals. And until now, there is literally nothing on the internet that has been proven 100% secure.

The only way to swamp such a supercomputer is to put more information online. Or, rather, to put the same amount of information online, but in bulkier formats. You can express your opinion in a 100 KB blog post, or a 100 MB youtube movie. Logically, it will take the NSA computer a lot more time to check that movie than the blog post, because the sequence of 10010100101010101 is thousand times longer. But it takes us (humans) the same amount of time to digest that kind of information. We're good at recognizing pictures... It doesn't take a world-class computer to read all our emails, but I bet it takes a lot more than all the computing power worldwide to replace our 7 billion visual cortexes. Shall we open a 2nd thread to discuss the stupidity of tracing each and every step of every person on this planet? I mean, if this is indeed the NSA's goal, then it's true: they really do take the "1984" book by Orwell as a guidebook rather than a warning.

Because it was about as dangerous as a baby bunny chasing you. I think the real question is: why did the man run away in the first place? Coward.

Sorry but this does not seem relevant at all. The article is purely technical. Let's not derail this with the political gibberish that we have in so many other threads. [edit] apologies, this was put in the politics forum. I had not seen that. Political gibberish is of course acceptable in the politics forum. Please read the link that Anders Hoveland provided. The answer is yes, it works. Please read the link that Anders Hoveland provided. The answer is yes, it works. JustinW, I understand you're probably not the biggest fan of this kind of technology (neither am I, read my post above). But this particular post sounds an awful lot like trolling to me. You did not investigate the article at all, and your points are irrelevant.

Except that the total global industrial wood consumption is only 1,600 million m3/year (in 2005). And the total motor vehicle fuel consumed in the US alone is already 174,930 million gallons/year (in 2006). Let's assume that 1 m3 of wood is 1 ton, and that it contains a maximum of 19 GJ/ton of energy (lower heating value, when it's completely bone-dry). Let's also assume that 1 liter of vehicle fuel contains 36 MJ/liter. A little conversion into Joules/year gives us: Global industrial wood consumption: 30 * 1018 J/year US vehicle fuel consumption: 24 * 1018 J/year Please note that the energy in wood is an upper estimate. The density of wood is probably lower, and the lower heating value is also lower. So, to replace just the vehicle fuel of the USA, we would have to pretty much double the global wood production. And that's ignoring the fact that the wood cars would have additional losses in the conversion from wood to fuel. Let's not do this. I think it would be the end of the Amazon forest (and I'm usually siding with the greens, and a big fan of sustainable energy).

I think that's a fantastic idea. But I have a feeling that you and me are a very tiny minority who give a damn. The majority of people would get very upset if some products become a lot more expensive. And obviously, if you pay an additional tax on all dirty products, a lot of things get more expensive. It is a well known economic fact that the economy must grow. I am afraid that your plan goes straight against the first commandment of the Economy. The only real solution I see is that the Chinese decide for themselves to clean up the mess.

No, 200 in your social circle that you can keep track of. In total. Obviously, it's possible to recognize far more people. But the group of people that you maintain a stable social relationship with will not exceed 230... or at least, that's what has been proposed. It is described here (wikipedia). It's called "Dunbar's number".

My personal opinion: explain to Holly that she will need to be able to do this kind of work alone. You cannot be there to help her all the time. Maybe she will understand that alone, she cannot do it. And that would be a good setup to discuss the continuation of the work. I am no expert in personal relationships, so this is no expert advice. <-- that's a disclaimer.

Awww

I think this is just a pro-Windows troll, on a drive-by shooting. He has only 1 post. I don't think we'll see him back. I agree with everybody else: generally linux runs lighter than windows... but it depends on the distro.

As aymanbinmoshi says: what's wrong with Google? I found a wikipedia site on cheminformatics. We need a more specific question to be able to give any good answer!

Ah, thanks. Now that I read that, I realize I could have answered that myself. Still, thanks. So, you agree actually. It's like a security team, or a police force. It is necessary that you pay them, so they prevent you from evil. The small evil is that you must pay for your security, to protect you from a bigger evil. I think we can see all around us that this type of security is an excellent business case... and there are examples where this can lead to a certain kind of extortion (pay for your protection, or else). There are other types of bacteria who will make a host sick. They either consume too much of our food, or produce the wrong waste products or by products (any other reasons for sickness from some bad gut flora?). The bacteria we normally have behave a bit better. Still, I wouldn't be surprised if they evolved to take just so much that it doesn't kill us. I would be surprised if bacteria would not have maximized the share they take. I completely understand why the system is like it is. I am not advocating that we design weaker gut bacteria... as you write, they would immediately be outcompeted by other bacteria. I think we're pretty much stuck with this system. Also, this system makes a lot of sense. It's very robust. It's just that I had never really realized the full extent of what's going on there. I'm still looking for a proper mass and energy balance. If I have time, I will search for it a bit more. Today however, I don't have too much time.

First a quick question: How do gut bacteria end up in your gut? Sounds maybe like a silly question, but I always learned that your stomach (or rather the acid in it) is able to sterilize a lot of food, isn't it? So, how do these bacteria get in your gut? Wikipedia suggests it's (also?) orally. Since up to 60% (wt) of the dry mass of feces (*) can be made up of these gut bacteria, which suggests that they grow rather quickly, and therefore must consume quite a bit of food, what do humans have to gain from it? Wikipedia suggests a whole list of useful functions... but somehow it still seems like the bacteria get the better deal here. It reads like a hijack: without the bacteria, we get sick, develop allergies and possibly even starve. They hold us hostage! So, yeah, they've got some enzymes we don't have. But how difficult can it be to evolve some additional enzymes? The only reason we don't have them, is that we've been hijacked by gut bacteria for so long (since literally forever?) that we never had to evolve them. Somehow, as a chemical engineer, it seems awfully inefficient. You have bacteria to do some work, but then you put them into a plugflow reactor, and you discard the bacteria when they're at the end. It's crap (crappy pun definitely intended). That means you must continuously grow new ones at a high cost. I mean, there's a reason that many processes try to immobilize the microorganisms: that is so you can operate the process with a minimum growth of the microorganisms, and optimize the useful functions of the microorganisms. Has anyone done any research on the energy balance? What percentage of the food we take in is used by the bacteria, and what percentage by "ourselves" (with ourselves defined as that part of our body that has the DNA we call human)? I never really thought of gut bacteria until quite recently... you never realize that I am an ecosystem. But everything I eat is automatically shared. And that ecosystem I carry in me grows a hell of a lot faster than myself. So, the way I see it (and I am not an expert, I'm a chemical engineer, not a biologist!), we're hijacked by bacteria. We can't live without them. And to make matters worse, we work with a suboptimal reactor design that is not capable of immobilizing these bacteria, so we must continuously grow new ones. Is it me, or are humans the losers here? (*) feces is a word scientists developed so they could still swear, but nobody else would be offended by it. If you listen carefully in many labs around the world, you can often hear scientists whisper "feces!", when they make a mistake.