Wikipedia:Reference desk/Archives/Science/2006 August 15

the direction of the Earth's orbit
The Earth follows a path around the Sun. Given that the globe is spinning, how would one describe or calculate the direction of its orbit in terms of planetary coordinates?

Or, to put it another way: imagine an axis through the Earth which always points in the direction of the planet's orbit around the Sun. Would the points this axis describes on the surface of the Earth form a meaningful pattern, and how would it be described? --Halcatalyst 02:13, 15 August 2006 (UTC)


 * I think I understand what you are asking. You would need to realize that the Earth's orbit isn't "pointing" in one direction, like a curved line with an arrow on the end. You need to think in terms of Vectors. One vector points in a straight line out into space, based on the direction the earth is going at that specific moment (inertia). The other vector points in a straight line towards the sun, representing the acceleration of the earth towards the sun (gravity). When you combine the effect of these two vectors, the earth follows a circular path around the sun. BenC7 02:45, 15 August 2006 (UTC)
 * Yes. I'm interested in the vector of inertia, and the pattern it would trace on the Earth's surface over time. --Halcatalyst 02:57, 15 August 2006 (UTC)


 * If we're talking about the velocity vector of the earth here, during a single rotation, it doesn't change significantly in the solar coordinate system, so as the earth rotates on it's 23.5 degree-tilt axis, it will trace out a circumference of the earth. Because the earth keeps its axial orientation (in the solar frame) over the course of a year, the circle will slowly rotate on the earth's surface (at the equinoxes it will trace along the equator, at the solstices, it will trace a "perpendicular" circumference), and the trace will wander around between the + and - 23.5 degrees latitude.  Over a long time, it will travel through every point (approximately) between the latitudes +23.5 and -23.5 degrees.  Actually, I don't know - does anyone know if the earth's rotation is in any kind of resonance with its orbit around the sun?  If so, it will only have a limited "rosetta" pattern on the earth's surface, rather than hitting every point.   --Bmk 03:24, 15 August 2006 (UTC)


 * Good point, but the slowing of the rotation (from something like 22 hours in the dinosaur age?) implies that there is no resonance. So, yeah, the curve is space-filling.  &mdash;Tamfang 06:48, 15 August 2006 (UTC)
 * I guess so, unless the earth's orbit is slowing down to match? I don't know.   --Bmk 16:08, 15 August 2006 (UTC)


 * Since nothing is working on our orbit in the way that tidal friction works on our rotation, it is believed that the length of the year can be changing only if the gravitational constant is changing, as some theories suggest, but consensus says that's not happening either. &mdash;Tamfang 06:42, 16 August 2006 (UTC)


 * Actually, according to general relativity, orbiting bodies give off gravitational radiation, which does slow the orbit. In GR, there are no stable orbits!  Also, there is the effect of interplanetary gas dragging on the planet.  Of course, both of these effects are extremely small, and they probably have a negligible effect, but nonetheless, they exist.   --Bmk 17:44, 16 August 2006 (UTC)


 * Thanks for a good discussion! --Halcatalyst 20:02, 17 August 2006 (UTC)


 * See analemma. B00P 21:11, 17 August 2006 (UTC)

Warm vs cold blooded
Hi

My question is about energy use in cold blooded animals vs warm blooded animals. I have written;

"A lucky 70 kg snake might find a 15 kg pig to eat. This would provide it with enough energy for about three months of living, give or take. If you or I, on the other hand, ate 15 kg of bacon, this would sustain  us for a bit more than a week."

Do these numbers seem reasonable? What numbers would you use?

Thanks very much for your help

Aaadddaaammm 03:18, 15 August 2006 (UTC)


 * It sounds erroneous to me. The normal number is 2000 kcal/day, or of course 14000 per week.  15000 grams of bacon would then have to have less than one (dietary) calorie per gram... and as can be seen on most nutrition labels (at least in the US), protein has 4 and fat 9 calories/gram.  Maybe if, somehow, 80%-90% of bacon was indigestible, this would work out; otherwise it's off by quite a bit.  --Tardis 06:53, 15 August 2006 (UTC)
 * I don't know about you, but if I ate 15 kg of bacon I would feel very, very sick and would wish that I would die. --Lambiam Talk 09:11, 15 August 2006 (UTC)


 * Yeah, we can't eat 15 kg of meat at once. Maybe 1 kg a day would be quite reasonable sustinance. - Rainwarrior 19:20, 17 August 2006 (UTC)

Brain in computer
Is it possible to use a brain as a computer hardware? If yes, is it currently researched?
 * Impossible. Will be for a long while. — [  Mac Davis ] (talk)


 * In principle any nontrivial information-processing device can emulate any other (given enough storage), but the structure of an organic brain is so different from that of a digital computer that it's hard to imagine circumstances in which anyone but an extremely mad scientist would ever try it. &mdash;Tamfang 06:46, 15 August 2006 (UTC)


 * I find the reverse to be much more interesting, a human brain that could instantly access info from a computer. For example, think about what could be accomplished by combining the creativity of the human brain with all the misinformation in Wikipedia ! StuRat 07:28, 15 August 2006 (UTC)


 * That's not a terrible idea, but it wouldn't really be all that interesting, you wouldn't really be connected, you'd just be using your mind to do the equivalent of clicking a mouse, I imagine it would work a bit like Hawking's blink control. Wouldn't have to be much more sophisticated than a Cochlear implant. Of course the only thing that would do is turn your brain into a glorified tracking ball, which might just cut down on the instances of carpal tunnel syndrome--71.247.125.144 16:05, 15 August 2006 (UTC)


 * I picture something far more ambitious, many years from now, where you would think of a question ("What's the capital of Sri Lanka ?"), and instantly know the answer, much like AskJeeves worked, when it worked. On the other hand, if it doesn't work, maybe you would instantly see a Columbo movie, LOL. StuRat 19:06, 15 August 2006 (UTC)


 * Some kinds of information could be expressed as new senses, e.g. you might feel the state of your bank account as you feel that of your stomach. Me, I'm hoping for a four-dimensional virtual eye.  &mdash;Tamfang 01:46, 18 August 2006 (UTC)


 * No, because it would be wetware. --Lambiam Talk 08:52, 15 August 2006 (UTC)


 * A brain in a computer or a computer in a brain - both come down to the same problem of useful information exchange. 'Reading' a brain is very crude at the moment. And 'writing', afaik, hasn't gone beyond giving a stimulus to a part of the brain to elicit a response of some muscle. Also very crude. That is getting info out of (or into) a brain, next is making sense of it. So far, all we can say is that 'there is some activity' in some part of the brain when certain functions are performed. We first need to understand the brain, and we're not quite there yet.


 * Scientists currently have an implant into the visual cortex which allows the blind to "see" with a grid of points. It's a very small grid right now, so only allows them to see if a person is in front of them, not actually identify the person, but this could be improved to the point where complete images of either the real world or a computer generated world could be supplied to the brain. StuRat 19:01, 15 August 2006 (UTC)


 * However, if this were possible, it would open up a path to one of the most desired things, namely eternal life. The machine and the brain would merge. The sum of the two would hold the personality. But the machine can expand indefinitely (in principle) and live forever (and be easily repaired and such). So if the brain would die, that would be like a minor stroke and we would live on inside a computer happily ever after. Also, since we could then interconnect, we would merge more and more and eventually all become one. Cool! Or boring? DirkvdM 09:31, 15 August 2006 (UTC)


 * Presumably non-mad scientists are working on it. Check out . 130.188.8.13 13:02, 15 August 2006 (UTC)

Souls in the Great Machine by Sean McMullen. Yup, using brains as computer hardware.Ohanian 13:34, 15 August 2006 (UTC)

So it's not possible for the time being but maybe in 100 years? Thank for the fast reply.


 * 100 years seems too short...how about 1000 years? --Bowlhover 01:42, 16 August 2006 (UTC)


 * "The machine and the brain would merge. The sum of the two would hold the personality." That supposes that one's personality resides in the brain. I will grant that one's intellect is most likely in the brain, but personality encompasses far more than intellect. Emotion, physiology, one's soul and countless other factors make up a personality. Does anyone know exactly where these qualities exist? Can anyone know? Do they even exist in a physical place at all, or are they trans-physical? I believe merging a computer and a brain might preserve a person's knowledge, but the actual person would not be merged. — Michael J 18:07, 19 August 2006 (UTC)

electric shock abdominator
Oh, does anyone know about those late nite TV ads for those 'abdominator' style muscle toners that you wear like a cummerbund and it gives you electric shocks to induce muscle twitch and supposedly then get you in shape from all the 'exercise' youve been doing? What is that device called? —Preceding unsigned comment added by 211.26.193.93 (talk • contribs)


 * I hope you're not interested in buying one. They are utterly useless. --mboverload @  07:01, 15 August 2006 (UTC)


 * There's also one that shocks your face to exercise facial muscles. Sounds dangerous to me.  And if you find it difficult to exercise now, just wait until it requires repeated electrical shocks. StuRat 07:16, 15 August 2006 (UTC)


 * A mobile version could chase you around and you'd be running for your life - plenty exercise. So once again, StuRat, don't knock it until you've thought it through. :) DirkvdM 09:36, 15 August 2006 (UTC)


 * But what is it called folks? The closest I can find (if it's not an abdomenizer) is a microcurrent electrical neuromuscular stimulator.--Shantavira 12:33, 15 August 2006 (UTC)

How do plants defend themselves from microbes?
Since plants don't have a circulation system, what methods do plants employ to defend themselves from microbes? Thanks. --Demonesque 07:08, 15 August 2006 (UTC)


 * for starters, Phytoalexin. and don't forget plants do have Xylem. Xcomradex 08:03, 15 August 2006 (UTC)
 * And several plants produce pheromones that alert their neighbours they may come under attack. --Lambiam Talk 08:49, 15 August 2006 (UTC)
 * And some plants have proteases. Eg. pawpaw has something like 50% dry w/w papain which is thought to be a defence mechanism against microbes and burrowing insects. Aaadddaaammm 09:23, 15 August 2006 (UTC)

Here's the latest on woad Woad really produces this chemical if you scrunch up some leaves. Perhaps grazing animals and insects don't like blue tongues? --Zeizmic 12:33, 15 August 2006 (UTC)

One defense mechanism is cell death. They kill the cells arounf the microbe and stop it spreading. This results in little spots all over the leaf. The official term is Hypersensitive response. David D. (Talk) 18:30, 15 August 2006 (UTC)


 * Not exactly answering the question, but plants are often in close proximity to fungi in the soil, some of which have antibiotic properties, which creates a somewhat safer environment for the plants.B00P 21:18, 17 August 2006 (UTC)

Gravity
If the Sun was to suddenly disappear, light would take so many minutes to reach earth, but would the gravity take affect at the exact time or at the speed of light or slower. I guess what i'm asking is what speed dose gravity travel at?


 * Gravity travels at exactly the speed of light. See General Relativity.
 * Please don't make your answer too hasty. We don't really know. — [  Mac Davis ] (talk)


 * Well, general relativity and string theory both say it travels at exactly the speed of light. If fact I don't think there are any theories of quantum gravity that say anything different and the only theory that does say something different it Newtonian gravity.


 * Well we know it doesn't travel instantaneously and it does seem to travel at around the speed of light. -- Cyde Weys  18:19, 15 August 2006 (UTC)


 * Remember to sign your posts, people! And I can't remember what it the answer was, but i think this has been asked before - check through the archives - i think the title was "speed of gravity". Aaadddaaammm 09:26, 15 August 2006 (UTC)


 * Here it is. DirkvdM 09:39, 15 August 2006 (UTC)


 * Also, see Gravitational Radiation. --Bmk 16:14, 15 August 2006 (UTC)


 * You also have to take into account the cause and effect of this sudden disappearance. It is difficult to see how this could happen without an accompanying explosion so big that it would render your question irrelevant. (In other words, hypothetical questions are almost impossible to answer without a lot more detail of various other factors. And even then...)--Shantavira 17:18, 15 August 2006 (UTC)


 * The question is, is it possible for the sun to leave faster than the speed of light? I am not expert but I do not know if that scenerio can even happen under the current model of the universe. HighInBC 21:39, 27 August 2006 (UTC)

Bibliography on Wikipedia
I am writing a scientific literature overview in the subfield of AI and will have a compilation of several hundred article titles available, sorted by year of publication/alphabetically. It is often a serious problem to find references to all the work that has been done in a specific scientific field and I think that a list of scientific papers published on a particular topic would be very useful to the scientific community. Authors could add references to their own papers once published etc. and people could contribute missing information, e.g., sometimes the title of the article/paper is known but it is impossible to find out where it has been published or whether it is publicly accessible. Googling for every single publication ever published is a nightmare and in the scientific community we depend on people who are willing to do just that and write a good survey for a widely accessible journal. I think that having a wiki list of published work would be very helpful as it would make surveying the area a bit less obscure and make it easier for young researchers as well.

I am wondering whether this is an acceptable idea for Wikipedia and if anyone else thinks it would be helpful.


 * I agree that it would be a good idea, maybe with papers sorted by keywords; although I find the majority of (physics) papers don't list keywords in the abstracts.


 * I think the most useful structure would eventually evolve through common effort. If several people knowledgable in the field start contributing, it shouldn't take long before we get a useful database. Lots of research topics are already covered in Wikipedia and one could just attach relevant bibliographies to those.

microbiology
what are the micro organisms useful in controlling air pollution?and in what way?

what are the microbes that produce light?and in what way they are useful?--hima 13:00, 15 August 2006 (UTC)vedula.himaja


 * Please take a short amount of time to familiarize yourself with the instructions at the top of the page. We're pleased to help out with most questions, but I'm afraid that we have to ask you to Do your own homework. If you need help with a specific part or concept of your homework, feel free to ask, but please do not post entire homework questions and expect us to give you the answers. TenOfAllTrades(talk) 13:11, 15 August 2006 (UTC)
 * it is not at all a home work question....it is asked in one of my descriptive exams...ive been searching it from hours on net so ive kept it here


 * Google is an effective search tool. For your first question, searching with the keywords microbes control air pollution will pull up a number of relevant links.  A similar search should lead you to answers to your second question, bioluminescence will also be helpful. TenOfAllTrades(talk) 13:48, 15 August 2006 (UTC)

what is PRBS
In Telecoms there is a method of testing circuits by using PRBS. What is PRBS and what is the difference between PRBS23 and PRBS15 etc. Thank You

PRBS stands for pseudo random binary sequence and is intended to simulate random data being sent. The 15 or 23 could refer to the word length but Im not sure.--Light current 18:10, 15 August 2006 (UTC)


 * A PRBS can be generated by a linear feedback shift register. It's a kind of pseudorandom noise. It has statistical properties similar to random data--for example, different run lengths of 1's and 0's occur with the expected frequencies, and the autocorrelation of a PRBS with a delayed version of itself is 0 (unless the delay is a whole number of periods). The number usually refers to the length of the shift register. The length of a PRBSn pattern is $$2^n - 1$$. Xilinx has some good application notes on how to setup the LFSR to generate different lengths of PRBS pattern.-- The Photon 02:32, 19 August 2006 (UTC)

Leuconostoc and Weissella
These microorganism are useful for what purpose ? Thanks


 * Knowing nothing about the genera in question, and with the risk of seeming a smartass, I'd say the obvious answer is "making more of themselves". —Ilmari Karonen (talk) 15:12, 15 August 2006 (UTC)


 * Did you read Leuconostoc? There is at least one answer there.--Shantavira 17:22, 15 August 2006 (UTC)


 * Leuconostoc can also cause some pretty bad infections in humans - InvictaHOG 09:47, 24 August 2006 (UTC)

Do insects have brains?
This is the dumbest question I asked. I'll be happy if you answer me.

Himanyo 17:51, 15 August 2006 (UTC)


 * Yes. very small ones to fit inside their heads (probably)--Light current 18:08, 15 August 2006 (UTC)


 * Read brain, especially the section on invertebrates.--Shantavira 18:16, 15 August 2006 (UTC)


 * Although calling it a "brain" might be a bit too generous, perhaps "nerve cluster" ? StuRat 18:49, 15 August 2006 (UTC)


 * The correct term is ganglion or ganglia. The illustration in the insect article would possibly be more helpful than the brain article. BenC7 23:36, 15 August 2006 (UTC)


 * I once read a very interesting book about the apparently very clever things insects can do being due to the following very simple and ingenious rules, things that could be encoded onto only a few neurons I imagine. Sorry, I've forgotten the title and author. Humans, on the other hand, have the overheads of language, and a model of the world enabling them to reason. They need a big brain to code things into language and also maintain a model of the world. (They have a much more complicated software programme than ants - ants are just machine code.) Without these overheads ants can do similarly clever things by instinct which can be encoded compactly into a small brain.


 * Then there is the "hive mind", where the modest brainpower of each individual combines to do things collectively, which no individual could do alone. In humans, for example, no human could go to the moon alone, but collectively, we can do it together. StuRat 23:10, 18 August 2006 (UTC)


 * I think in ants at least, the ants are again just blindly following simple but ingenoius rules. I have been thinking that a statistical software program is smarter than humans, but because it does not encode things into language or reason then it does not seem so.

New Pollen?
I live in the commonwealth of massachusetts. Ive never had allergy problems before. However, just recently, Ive been displaying symptoms of allergic reactions. Nasal congestion, swollen face, etc. So Ive looked at differnt pollen websites and cant find any info to help me. SO my question is what, if any new pollen comes out around this time of year in the northeast. Ive been fine all summer so it must be some plant/weed that gets release mid to late summer. Of course there is always the chance that I just recently became allergic to something. I know the whole deal how none of your are doctors and I should seek medical attention for real help, so lets just get past that.

THanks!!!

There is a section on the weather page of the Globe that gives a pollen count for the next day or two, maybe you should see if your discomfort follows a trend that parallels this count. For what it's worth, people develop new allergies all the time. Isn't IgE a bitch?Tuckerekcut 00:04, 16 August 2006 (UTC)


 * The most prevalent pollen allergen in the northeast US at this time of year is ragweed.--Mark Bornfeld DDS 00:17, 16 August 2006 (UTC)

Treatment of Erythrasma skin rash
I take as read all the precautions etc about this kind of medical advice.

I saw a dermatologist today and she noticed that I had a erythrasma infection in my armpits. It did not seem to be harmful but it can spread. It is, according to my internet research, caused by Corynebacterium minutissimum, a bacteria. She told me to spray it twice a day for a fortnight with Daktarin, which is a UK trade name for a spray powder that contains "miconazole nitrate Ph Eur 0.16% w/w" and which is usually used for the fungal infection known as athlete's foot and other names.

I wondered afterwards why a treatment for fungus would be used with a bacterial infection, and reading the miconazole article suggests that it does have a mild anti-bacterial action also.

But I wonder if I could instead just use an antibacterial spray, as this should be more powerful in zapping the germs. I'm also aware of the nitrates and remember that these are carcinogenic - or is that nitrites?

My question is - is there such a thing as an antibacterial spray that is safe to be used regularly on the skin? I do have some antibacterial creams, but sprays are quicker and more convenient to use. One of them contains chlorhexidine gluconate, which according to the article you should not get near your ears or eyes. The other is based on cetrimide. I want to know more about this before speaking to a pharmacist so I don't end up with something only designed to be used once on wounds. Thank you.
 * According to the Merck Manuals, "Topical drugs such as clindamycin and miconazole cream are also effective" [for the treatment of Erythrasma]. For the rest, you should really ask your dermatologist. --Lambiam Talk 00:00, 16 August 2006 (UTC)

You can certainly use just about any antiseptic to reduce skin fauna (Clorhexidine and Betadine soaps work well, many spreays and ointments are available), but you don't necesserily want to. Natural microbial fauna might be more effective in keeping out pathological strains than you could be even with diligent cleaning. It may have been that your doctor told you to use the antifungal to reduce the chance of a new infection with fungus, assuming that your body can fight off the erythrasma itself. I would strongly suggest you take the advice of your physician, maybe call her office if you want more answers. If you do decide to go against her advice, though, I would stick to plain old soap and water.Tuckerekcut 00:01, 16 August 2006 (UTC)
 * If you truly want to ignore the advice of your doctor (and go with 'free' advice), I find that 100% Tea Tree Oil (Melaleuca Oil) is quite effective for these things. --Zeizmic 13:50, 16 August 2006 (UTC)

defense
what's the best way to defend against terrorism weapons made out of soda or other soft drinks? = >?


 * Prohibit production of soda and soft drinks. You can also kill all the terrorists. — [  Mac Davis ] (talk)


 * on a plane, banning them is the best option. People can buy a $1 soft drink on the other side if they want to, or a $2 one guaranteed by the manufacturer on of the plane.


 * In public places, it's impossible and pointless. Wjlkgnsfb 22:25, 15 August 2006 (UTC)


 * C'mon guys, be serious. It is just plain stupid if you wanted to ban soft drink transportation onto a plane. That is moronic. How would that save lives? All that would do is prove that once again, we give in a little bit more. We sacrifice more of our liberties. — [  Mac Davis ] (talk)


 * lets see you come up with an effective, efficient, cheap detection system to verify that soft drink cans don't actually contain explosives. The simplest solution is to travel light, and buy what you need on the airplane itself or before/after your trip. Wjlkgnsfb 23:13, 15 August 2006 (UTC)


 * Unfortunately, defense against soda offers no protection whatsoever against processed cheese or underwear. --Lambiam Talk 23:47, 15 August 2006 (UTC)


 * And by no means... never mix the two together. The deadly combination may just take off a hand or an arm. — [  Mac Davis ] (talk)

From the terrorism article: "Terrorism is the systematic use or threatened use of violence to intimidate a population or government...". Nobody even has to get hurt for terrorism to work: it becomes terrorism when the populace is scared. Thousands of people might have died over the course of this era of terrorism, but hundreds of millions of people have to change the way they go about their lives. That is the true effect of terrorism, and they (the instigators) couldn't have done it without us.Tuckerekcut 23:52, 15 August 2006 (UTC)


 * lol. 68.20.38.241 01:26, 16 August 2006 (UTC)


 * People change how they live because they care about living and/or the lifes of others. If that is a "win" for terrorism, the only way to defeat terrorism is to stop caring what happens.  No matter how many are kidnapped or killed, just stop caring and terrorism will fail in the end.  It is my opinion that not caring if people live or die is terrible, so I feel that is a win for terrorism too.  Apparently, terrorism wins no matter what. --Kainaw (talk) 00:57, 16 August 2006 (UTC)


 * Sadly, but well said. I think the only way to stop terrorism is to eliminate all the terrorists.  And for all you folks following the news out there, I'll give you a hint - the correct answer is not "kill all the terrorists".  See hydra for more details.  --Bmk 01:14, 16 August 2006 (UTC)

How about special planes for people from Muslims countries ? The terrorists wouldn't see much point in blowing up those planes (that would actually be bad PR for them), and would have a hard time getting onto the other planes. This may seem extreme, but I, and I assume many others, are to the point of just not wanting to fly anymore. I can't bring any carrry-on luggage, and the airlines feel free to lose my luggage and serve me a tiny portion of contaminated water, if any, while keeping me in a hot plane for hours, after waiting in security lines for hours, and they still can't seem to protect us. StuRat 02:03, 16 August 2006 (UTC)


 * Which ones are the "Muslim countries"? --68.64.100.100 03:52, 16 August 2006 (UTC)


 * Those with a majority Muslim population. Do you need a list ? StuRat 06:45, 16 August 2006 (UTC)


 * I believe I once heard that most muslim (and other) terrorist actions take place in the home country of the terrorists and kill mostly muslims. Anyway the question was about terrorists, not muslims. DirkvdM 12:33, 16 August 2006 (UTC)


 * And has your fevered brain imagined there is some huge threat from non-Muslim terrorists ? Most people would be entirely satisfied if we could stop Muslim terrorists.  All those Buddhist terrorists will just have to wait. :-)  StuRat 20:02, 16 August 2006 (UTC)


 * My (fevered or not) brain doesn't see much of a threat in terrorism. The attacks, that is, what politicians and the media do is a different matter - they're the real terrorists. I think I have made that clear enough in previous discussions. The total worldwide deathtoll is negligible compared to real threats, like malaria and cars. And the 'war on terrorism', of course. The fact that recently most attacks have been by muslims is at least in part a result of the narrow statistical basis. It may well be that just a few years ago most terrorists were catholics. It takes just a few attacks to tip the balance. Of course the war on terrorism 'helps' here, too. I f you keep on attacking muslims they will keep on counterattacking and you've got yourself a self-fulfilling prophecy. DirkvdM 07:31, 18 August 2006 (UTC)


 * So, by your def, the Chechens who blew up the Russian school, children included, are "not real terrorists" and we should just ignore this type of thing ? The facts don't support your argument, attacks on US civilians have dropped off dramatically since the war on terrorism began.  Prior to that, they were spiraling ever upwards.  And you can't just ignore something due to the current death toll, the potential death toll is much greater.  Using your logic, AIDS should have been ignored in the 1980's, because the death toll, at the time, was small, even though it was entirely predictable that it would spread and kill millions, just like unopposed terrorism will. StuRat 18:44, 18 August 2006 (UTC)


 * Just so we're very clear about how terrible the above suggestion is, the people arrested in the recent 'liquid explosives' plot were mostly British. Those arrested in the Canadian terrorist conspiracy were mostly Canadian. Or are you suggesting that British and Canadians should only be allowed to fly on their own airlines. BA and Air Canada would really like that - they would make a huge profit. DJ Clayworth 17:09, 17 August 2006 (UTC)

How about special planes for muslims and people who won't eat pork? The pork hating terrorist will be very happy to kill their sworned pork hating enemies (the joos) and leave the rest of us alone. We can call the new airline No Pork Airways.Ohanian 04:51, 16 August 2006 (UTC)


 * There seems to be a view around here that terrorist = Muslim = terrorist. That may be someone's idea of a sick joke, but it just incites hatred for all Muslims, the vast majority of whom have nothing but abhorrence for terrorism.  JackofOz 10:46, 16 August 2006 (UTC)

The only terrorists I fear are those who don't eat pork. I propose a new airline where the interior of the planes are laced with lard. And all the drinks contains traces of lard. I feel safer in the plane this way. Ohanian 14:49, 16 August 2006 (UTC)


 * Alas, that is not just 'around here'. After the end of the USSR, the US (and other western countries) needed another enemy (to distract from interior problems). The attacks on the WTC and the pentagon were a godsend. The only problem was that it's an enemy you can't point out easily. So first Al Qaeda was invented (the term is a US invention), but that was too small and hard to fight, so it changed to 'muslims in general'. Nice and identifiable. DirkvdM 12:33, 16 August 2006 (UTC)


 * On a more general note, and this was in a way already said above, the best defence against terrorism is to ignore it. I understand that that was a method used by Thatcher against the IRA (if so, for once she got something right). The point of terrorism is to instill fear. If the media ignore everything you do, there's not point in doing it, so it will stop. So the media and the politicians telling us to be afraid of something that barely kills anyone (if you look at the big picture) are the real terrorists. DirkvdM 12:33, 16 August 2006 (UTC)


 * The US tried ignoring it; they ignored the first attack (bomb) on the World Trade Center, they ignored the attacks on the US embassies in Africa, and they ignored the attack on the USS Cole. If they had also ignored the 9-11 attacks, the next attacks likely would have been with WMD. StuRat 20:24, 16 August 2006 (UTC)


 * Actually, the US arrested, tried and convicted those responsible for the 1993 bombing of the WTC. They are sitting in a maximum security prison even now. That was before the US just imprisoned suspected terrorists without trials.Edison 17:10, 17 August 2006 (UTC)


 * By ignored, I don't mean "took no action whatsoever", that would be beyond stupid. What I meant was "took no action capable of preventing further attacks".  Those actions include, but are not limited to, removing the terrorists and their Taliban supporters from their base in Afghanistan.  After that was done, terrorist attacks against US civilians dropped off dramatically. StuRat 21:48, 17 August 2006 (UTC)


 * Yeah, but we only got peace with the IRA by talking to them. And I don't think the current threat is organised enough for there to be anyone worth talking to about it. And to the 'hilarious' suggestions of all-muslim-country airlines, the problem is 'home-grown' terrorists. Skittle 13:18, 16 August 2006 (UTC)


 * Home-grown terrorists may be the problem in the UK, but not in the US. I don't think any of the 9-11 attackers were born in the US.  The UK needs to arrest all the clerics who preach terrorism, and keep them locked up, to stop the home-grown thing. StuRat 20:18, 16 August 2006 (UTC)


 * What you mean arrest people for saying things you disagree with? So much for Land of the Free, Home of the Brave. DJ Clayworth 17:12, 17 August 2006 (UTC)


 * The Right to Free Speech most definitely does not include the right to advocate murdering civilians, as I'm sure the voters would agree in any referendum. StuRat 19:30, 17 August 2006 (UTC)


 * A bit more on the IRA broadcast ban. That was also aimed at Sinn Féin, a law that forbade tv and radio (not newspapers) to air comments by Sinn Féin members, so it was more of a political thing. They could be shown, however, so the BBC decided to show the interviews and have the voices dubbed over, thus circumventing the law. So een though the basic idea made sense, it was halfharted, misdirected and done to hastily, not in cooperation with the media, which only pissed them off. Don't ever do that to the media. It will always backfire - they're too powerful, which is a central issue here. There's a little bit on this way at the bottom of Prevention of Terrorism Act (Northern Ireland). Could do with some expansion (maybe a separate article even), but I know too little to write that.


 * But most importantly, the ban drew so much attention that it actually hepled the IRA get more attention. Just as the whole war on terrorism now is a godsend for terrorists all over the world. They only need to plan a terrorist attack and make sure they are found out. I wonder if that is what was done here. DirkvdM 13:32, 16 August 2006 (UTC)

No offense everyone, but this wasn't really a science question to begin with, and I doubt turning this topic into a political message board is a good idea...Honsetly, let's nip this now and focus on more seagull bagel & masterbation questions. Can't get enough of those... -- Scientizzle 15:53, 16 August 2006 (UTC)


 * Back to pop-bottle explosives then, there's an interesting article in The Register today about the chemistry of making binary liquid explosives. Ojw 21:30, 17 August 2006 (UTC)

What is the difference between group velocity and phase velocity?
Despite reading the articles I am still not clear what the difference is between Group velocity and Phase velocity, relating to waves and sound. Could anyone explain it in simpler laymen's terms please?

Before reading the article I never knew these existed, despite having a GCE A-level in physics, grade B. 62.253.44.31 22:37, 15 August 2006 (UTC)


 * The phase velocity is the velocity at which a wave of a single frequency will propagate. The phase velocity is the velocity with which most people are innately familiar; "wave velocity" or "velocity of propagation," really means "phase velocity." When you combine waves of several different frequencies, something different happens: you get interference. In an extreme example, you can combine several waves such that they cancel out everywhere except in a small area of space. This destructive wave interference is by the way, how active noise-cancelling headphones work. The envelope of the resulting "wave packet" is not really a proper wave—it's the result of the interference of several component waves. The envelope of the wave packet, the peak of constructive interference, can travel at a different speed from the phase velocity, the velocity of each of its individual component waves. Group velocity. Get it? — [  Mac Davis ] (talk)

So if I use an analogy of a long line of cars moving slowly along on a congested road, then would the phase velocity would be the speed the cars are moving at? If one of the cars leaves the road, then the car behind will quickly move up, then the one behind that and so on, so that this gap moves like a travelling wave (or sp? traveling wave) along the line of cars. Would the speed at which this gap moves be the wave velocity?
 * I always thought a soliton would be a group wave, until I read the complex article and it totally confused me... --Zeizmic 12:01, 16 August 2006 (UTC)


 * The analogy of a line of cars might work, but not as you stated it; it is sort of a complicated analogy since it is a longitudinal wave (i.e. compression wave). Really, the best way to think of group and phase velocity is that the shape of the wavelet changes.  The group velocity is sort of the "average" speed of the whole little pulse.  The phase-velocity is how fast each frequency component moves.  Phase-velocity is different for each frequency component; and it determines how different the pulse will look at the other end.  Perhaps even with your physics background, you never got as much Fourier analysis as your colleague electrical engineers; wavelet analysis must use some rigorous mathematical Fourier transforms to get numerical results. Nimur 22:54, 16 August 2006 (UTC)

I didnt realise that different frequencies had different speeds. Now it makes more sense. If this is the case, then why is the speed of sound given as (as far as I recall) 330 metres per second, and not a different speed for specific frequencies? And would it be possible to construct a sound-prism?

So let me see if I get this right please - on an AM radio broadcast, the carrier signal is moving at one speed (the speed of light presumably), but the modulated sound signal is moving at another speed. Is that correct?

And if you drop a pebble into the middle of a large pond and watch the ripples spread out, is it correct that the ripples are moving at phase velocity, not group velocity?


 * Yes, yes, and yes... The trick here is that in most materials (i.e., in air, for example), the group and phase velocities are nearly equal. So, when you say that the speed of sound is 330 m/s, you mean that is the average, rough approximation.  When the phase and group velocities are not equal, the packet changes shape - this can be detected as distortion.  Yes, your AM radio broadcast carrier gets distorted; remember, the speed of light in AIR is less than the speed of light in vacuum (how much less?  Depends on the frequency); and if you were unlucky enough to be transmitting through certain types of glass you probably would not be able to recover the original signal.  But, for most "normal circumstances" (...if normal means anything in science...) the phase and group velocities are close or equal.  Nimur 13:24, 20 August 2006 (UTC)


 * Let me give an example of when phase and group velocities are very different: waveguides (image). They are pipes through which you feed electromagnetic waves. A waveguide has a "cutoff frequency" – waves with frequencys lower than that will die out as they try to propagate along the guide. Frequencys above the cutoff do all propagate, but with different phase velocities. If you start at a high frequency and decrease it, the phase velocity will increase. Actually, as you approach the cutoff frequency, the phase velocity will increase to infinity (yes, much higher than the speed of light in vacuum). An infinite phase velocity means that whenever, at one point along the guide, the field has a maximum, it will have its maximum at all other points aswell. The group velocity, however, will always be less than or equal to the speed of light in vacuum. (Otherwise you could send information faster than the speed of light in vacuum, which, as we know, isn't possible.) —Bromskloss 01:57, 21 August 2006 (UTC)


 * See java applet--Light current 02:13, 21 August 2006 (UTC)


 * Also, phase velocity is w/k whereas group velocity is dw/dk (ie the differential of the phase velocity)--Light current 02:16, 21 August 2006 (UTC)