Wikipedia:Reference desk/Archives/Science/2008 June 28

= June 28 =

Why is spitting in someone's face considered to be particularly offensive?
Whilst hitting or insulting another person are taken as offensive acts, what is it about spitting on another person in particular that can drive the victim into an immediate murderous rage?

At least where I'm from, it seems to be the unwritten rule that 'a man should not spit on other man under any circumstances' and that to do so is completely disgusting, reprehensible and dishonourable. If you insult or punch another man during a disagreement, you may end up in a fight. If you spit in another man's face during a disagreement, you *will* end up in a serious fight.

Based on my personal observations of life and people falling out over various things in my homeland, my general perceived severity of various insults is so (going from least offensive to most offensive):


 * Dirty looks
 * Personal verbal insult
 * A punch/push
 * Disrespect to property and/or woman
 * An insult against one's mother
 * Spitting in the face

Any ideas? Is this something instinctual/deeply-rooted in the human psyche? --Kurt Shaped Box (talk) 00:18, 28 June 2008 (UTC)


 * How would you like a gob of bacteria-ridden goop from someone else in your face?  bibliomaniac 1  5  00:20, 28 June 2008 (UTC)
 * Yeah, I assume it's the general taboo about unwilling exchange of bodily fluids, which people instinctively dislike due to diseases being spread that way. Spitting simply falls into that category in the same way as someone intentionally coughing on you, urinating on you, ejaculating on you, whatever. ~ mazca  t 00:23, 28 June 2008 (UTC)
 * Not at all - but why would I find it more offensive than that same person punching me in the face? --Kurt Shaped Box (talk) 00:25, 28 June 2008 (UTC)


 * Because saliva is abject. Violence (perversely enough) is not. Most bodily fluids are in a special psychological category of grossness for (most) human beings that far outdoes any rational reason. --74.223.170.187 (talk) 02:10, 28 June 2008 (UTC)

In Ireland I remember old farmers sealing a deal by spitting on their hands before shaking (sealed with a spit, I guess) but spitting on another person would be deeply offensive there.Gaiatechnician (talk) 16:32, 1 July 2008 (UTC)


 * It's probably worth noting that this is likely to be a fairly culture-specific thing. I mean, you can say whatever you want about my mother, and unless you actually know my mother and are making a specific personal comment about her, it's not likely to mean anything to me other than make me aware of the fact that you're trying to offend me. Whether you tell me to go fuck myself or call my mother a whore, it's just noise, you know? It obviously won't make me happy, but that choice of subject matter won't make me any more angry. I think that generally speaking, this definitely goes for most of the people I know as well. I know that this definitely isn't the case in many other cultures. Likewise, if someone were to spit in my face, it would probably make me really, really angry simply because it's such a hostile thing to do, but I'd still strongly prefer it to a punch in the face. On the other hand, at least according to our article on spitting, the Maasai tribespeople spit on each other as a form of greeting and farewell. Personally, I think I'm gonna stick with shaking hands for the time being... -- Captain Disdain (talk) 13:03, 29 June 2008 (UTC)


 * That could explain something that I've wondered about. According to the Laws of the Game for soccer, "Spitting on someone" is specifically called out as an immediate sending-off offence (red card).  I've wondered why that was necessary -- perhaps it's for the benefit of those for whom spitting is not an affront, to let them know that it is for many others?
 * --Danh, 63.231.163.123 (talk) 23:22, 29 June 2008 (UTC)

Cavy
What do you call a female cavy? a male cavy? Idle Jan (talk) 01:26, 28 June 2008 (UTC)


 * I assume you are talking about a Guinea pig. Our article uses "sow" for female, "boar" for male, and "pup" for young, here. Hope this helps. --Dr Dima (talk) 01:58, 28 June 2008 (UTC)

Heliostat
I have been trying to design a heliostat that is on equatorial mount with some sort of clock drive. And I think I have hit on a design that will eventually work. (It is on instructables.com). (Clockwork being simpler and potentially cheaper than throwing computer power at everything). I just got everything uploaded and then I was very surprised to find out that clock based heliostats are an old concept! They were used for many years by early scientists. http://physics.kenyon.edu/EarlyApparatus/Optics/Heliostat/Heliostat.html shows a bunch of them. and http://www.earlytech.com/common/show_image.phtml?Id=491390987&Item_Name=Heliostat+by+Silbermann+1843 shows how the geometry works. I confess that i do not understand it at all! So, it is too late for me and I will continue with my little design. Mine goes at 15 degrees per hour, but I think these old ones go at a different rate, either twice as fast or twice as slow as the sun appears to travel around the earth. So, anyone like to explain or just mention how the old scientific heliostats worked? On the heliostat page would be great. Thank you 24.69.192.200 (talk) 03:00, 28 June 2008 (UTC)


 * First of all, please do not ask for knowledge questions to be answered on article talk pages. The article talk is for discussing improvements to the article, this desk is the right place to ask questions.
 * The heliostat in that link needs to rotate at half the speed of the sun because it is trying to keep the direction of reflection constant. If you are just trying to keep a telescope or camera pointing directly at the sun then you need to rotate at the same speed.  So it depends what you are trying to do, if you want to redirect the sunlight to a fixed point where you can use it to do work then 15o/hr is going to be wrong.
 * Note that to track the stars (siderostat) it needs to rotate at a different speed to a clock because the earth is not rotating once every 24 hours with respect to the stars. The earth rotates in 24 hours with respect to the sun which is not quite the same thing.  In one day, the earth has moved on 1/365th of its orbit around the sun and so needs to rotate a further 1/365th of a revolution in order to face the sun again.  The siderostat therefore needs to run 1/365th parts per day slow fast (about 4 minutes) otherwise your photographs of the stars will be streaks instead of nice points.  Sp in ni  ng  Spark  13:08, 28 June 2008 (UTC)

I made my first model http://www.youtube.com/watch?v=WRTX1S7PD-U and the principles seem to work. In this case, the mirror does not turn at all, but 2 pointers decide its angle as it pivots round its centre. One is pointed at where the light will go and one is pointed at the sun. (That one turns on the equatorial mount axis). I used 2 rubber bands to bisect the distance between the pointers and attached a post at the centre of the mirror to the bands. This seems such a simple method but I do not see it documented anywhere.Gaiatechnician (talk) 16:40, 1 July 2008 (UTC)

AC Power - Generation, Voltage and Current
I know that this might seem very basic, but it does not seem to be answered by the existing Wiki sections on AC power. The questions stems from an argument that you don't get electrocuted if you (are grounded) and touch the negative side of an AC power point.

There is also no basic explanation that in an AC (Alternating Current) circuit it also has Alternating Voltage. Most graphs show AC voltage varying in a sine wave pattern, with a graph that that has its X axis at 0 and the voltage varying equally to the positive and negative side. It seems to mean that the voltage in the AC system fluctates from +240 to -240v (Australian voltages). This doesn't seem correct to me - I though it fluctuated and its average (RMS) was +240V.

Could someone please explain how the electrical generator at the power station, ends up at 240VAC at my power point. And what the actual voltage graph, and current, looks like at: 1 - the generator 2 - the transmission lines 3 - the transformers 4 - my domestic power point.

Thanks. —Preceding unsigned comment added by 58.165.127.244 (talk) 04:36, 28 June 2008 (UTC)


 * There is no "negative" side to A/C power. In the US, there are "neutral" and a "hot" wires feeding typical 120V outlets.  The neutral side is usually tied to ground at the service entrance, while the hot wire carries the A/C voltage sine wave.  So in this case, coming in contact with the neutral wire will not likely cause injury, although I wouldn't bet my life on it.  -- Tcncv (talk) 04:43, 28 June 2008 (UTC)


 * To better answer your questions: Power is typically generated and distributed as three-phase electric power.  Because power is equal to voltage times current (amperage) while power loss during electric power transmission due to electrical resistance is proportional to current and not voltage, it is more economical to step up voltage and reduce current using transformers when transmitting power over long distances.  As the power nears the consumer, transformers are again used at several points (electrical substations and pole top transformers) to step down the voltage to consumer levels.  Also, while three phase power is used in most industrial and many business users, for residential use, the power is typically converted to single-phase electric power or split-phase electric power.  For single-phase electric power, only one voltage is available to the customer.  For split-phase electric power, two opposing AC voltage feeds are provided plus a neutral.  One voltage (such as 120V in the U.S.) is obtained by using one of the hot feeds together with the neutral, while another voltage (240V in the U.S.) by using the two opposing hot feeds.  If you follow the links above, you should find more detailed answers to your questions.  -- Tcncv (talk) 05:28, 28 June 2008 (UTC)

To bring it back to your Australian case (or in my case, South Africa), what you have in your house is a Live, Neutral and Earth wire. Typically a sinusoidal voltage is supplied between the live and neutral. The neutral wire is grounded (connected to the physical earth) at some point where it comes into your house. Thus typically touching the neutral wire while you are in contact with the ground should be less lethal because there will be almost zero voltage across your body. DO NOT try this! More on the neutral/ground issue further on, for the time being let's deal with amplitudes and that sine wave.

The voltage at the live terminal is quoted as 240 V AC. First off the 240 is not the amplitude, it is actually the RMS value, and equates to the amplitude/sqrt(2) for a sine wave. The actual amplitude is therefore 240*sqrt(2)=340 V. More on RMS in a couple of sentences, keep reading. The signal does indeed fluctuate between +340 V and -340 V, thus the average value of the voltage signal is in fact zero. This is obviously not a useful quantity when talking about AC voltages, so how do we actually quantity the "magnitude" of an AC signal?

This is where RMS comes in. (p.s. if you how to do integral calculus you can actually derive this yourself which will give you good insight). How do we quantify usefully the magnitude of an AC signal in order to equate it to a DC signal of "equivalent size"? Obviously using the amplitude will give an over-estimate (the signal is only briefly at max amplitude), and obviously the average is zero no matter how high the voltage. The concept that is thus used is that of "equal POWER": what amplitude of AC volts does it take to generate the same amount of power in a load as a steady 1 volt DC signal. The answer turns out to be sqrt(2). Thus the convention when talking about "1 volt AC" is that you're talking about a signal of amplitude sqrt(2), because this 1 V AC signal does the same amount of work as a 1 V steady DC signal.

Let's derive the sqrt(2): given a 1 V DC signal placed across a 1 ohm resistor, how much power generated? well, going by P=V²/R gives 1 Watt. Now let's take an AC signal of amplitude A. What size of A gives 1 Watt dissipated? Now your voltage is Asin(2Πf*t) where f is 50 Hz for Aus I assume (but that's immaterial because we are working out the average power over 1 cycle of the AC wave). P = V²/R = A²sin²(2Πf*t)/1. Now we calculate the average power dissipated over 1 cycle of the AC wave. The average of the sin² term is 0.5 (do some trig to derive this if you don't know it already). Thus we have 0.5*A²=P=1 Watt which gives A=sqrt(2).

As to why we use RMS rather than just the amplitudes: well one of the applications of AC is obviously electrical power generation and distribution, in which case you have to know how much power is being produced and absorbed. Using the RMS values instead of absolute amplitudes makes it easier to work things out (you don't carry factors of sqrt(2) everywhere in teh calculations) and thus has become the convention.

Ok back to the neutral/ground issue. So the neutral is physically connected to the ground at some point where it enters your house. How is this useful? Well, it keeps the neutral close to ground potential so that if you come into contact with it you should receive a much smaller (possibly non-lethal) shock. Now, from beyond this connection point looking into your house nothing should be flowing through the earth conductor, thus you can put a very sensitive circuit breaker (called an earth leakage breaker) into the earth circuit at this point, and if any of your earthed appliances develops a short to the its internal earth wire there will be current in the earth wire and the breaker will trip to safely isolate the appliance (typically it actually breaks the path for ALL your plug sockets in the house).  Zun aid  ©  ®  07:49, 28 June 2008 (UTC)

When wiring in a house breaks or is improperly installed, the neutral or ground wires can become energized at the supply voltage, and in such situations touching the neutral and ground wires could place the full supply voltage across your body, causing injury or electrocution. When everything is installed and working as designed, there may still be a few volts between ground and neutral at some points in the circuit, because of the voltage drop from load current in the neutral. A low resistance connection, such as a wire jumper from ground to neutral can carry very high current from this small voltage difference. Do not attempt the experiment. Edison (talk) 19:29, 28 June 2008 (UTC)

Evolution in Physics
In biology, evolution is presented as the major scientific cause of change in wildlife. But what about the other sciences ? I evolution was very significant, would't it be directly observable in nuclerar physics, astrononym, chemistry and the like ? 69.157.237.196 (talk) 09:20, 28 June 2008 (UTC)
 * Because, as you certainly know, living things consist of molecules, evolution is in fact a chemical phenomenon. It's just that people take the really complicated chemistry and call it biology. Also, as molecules behave to the laws of physics, in the same way evolution is also a physical phenomenon. On the other hand, the objects astronomy deals with aren't living things, and as evolution is a phenomenon of life, it won't apply to astronomical objects. --Ayacop (talk) 09:39, 28 June 2008 (UTC)


 * There is such a thing as evolution of stars etc but that is really a different subject.
 * Evolution as in darwinism etc relies on an objects ability to self replicate (see self replication) and mutate - as such it's pretty much confined to plants and animals.87.102.86.73 (talk) 10:31, 28 June 2008 (UTC)


 * Not quite, evolution occurs in all living beings. ScienceApe (talk) 22:42, 4 July 2008 (UTC)


 * I don't know why you'd think that something that pertains to one branch of nature would necessarily exist in others in any major way. There's no doubt that matter-antimatter annihilation exists in nuclear physics, but it doesn't exist anywhere else. There's no equivalent for special relativity in biology—I'm not sure what that would even look like. And there's no requirement that biological evolution exist outside of biology. --74.223.170.157 (talk) 13:09, 28 June 2008 (UTC)
 * Generally, all biology is complicated chemistry and all chemistry is complicated physics. Everything in biology or chemistry could, given the time, be linked to physics. However, not everything in physics can be linked to biology or chemistry. It only works one way. — CycloneNimrod talk? contribs? 15:03, 28 June 2008 (UTC)


 * Evolution in the sense of changes through time from initial conditions does indeed occur in the hard sciences: that is what cosmology is. The processes that dictate how the changes happen are, of course, different from biological evolution. In fact, when looking at the universe today, or looking at the geology of our own planet, the only way you can make sense of it is to be aware of the historic evolution that occurred.--Eriastrum (talk) 16:00, 28 June 2008 (UTC)

Evolution occurs in everything. Because evolution means something changing over time. Our technology evolves. Our planet evolves. Stars evolve. Etc etc. It's not the same as biological evolution, but it's still evolution. ScienceApe (talk) 22:42, 4 July 2008 (UTC)

Medical diagnosis
Yes, I am looking for medical advice and treatment, but not here.

Here, I am asking a question about medical diagnosis.

I have been ill with the recurring symptoms of an infection for about three months now. It starts to endanger my job. The doctor tells me I won't get antibiotics unless I have at least 39 C temperature. He did a thorough and costly physical examination and came up with the result that all examined organs were healthy but that I probably had some kind of infection. (What a surprise for that lot of money spent!)

He did nothing that could lead to a diagnosis of what kind of infection I have, whether it's viral or bacterial. He even neglected to ask me if I had been to foreign countries recently. And I had similar experiences with other doctors in the past with other cases of diseases. It looks like they won't do anything useful until a disease has already done damage to the organs. (And yes, I am angry.)

Now the question: are there really no methods to diagnose the kind of an infection? What would they be, are there any plausible reasons why they are not applied, and, finally where can I get them (note this is asking about medical advice, not for).

Thanks 77.3.155.173 (talk) 13:57, 28 June 2008 (UTC)
 * I know that situation, and it's a good question. There are ways, however, to have a good guess (besides a post-mortem), for example by exclusion: you can ascertain it's not disease X if you don't have its typical symptoms; it can't be in organ Y because all the numbers concerning that organ are fine; and so on. Secondly, the symptoms you encounter at the moment should be a hint. Thirdly, you could try to apply natural antibiotics---for example, garlic will temporarily kill any bacteria in the stomach and many bad boys in the upper intestine: if you feel better after that, then you know. Make yourself informed, do (harmless) experiments.
 * There may also be special diagnostic tools that just aren't applied by doctors because they aren't known well enough, take too much time, cost too much. For years I read about methods to recognize diseases from the breath, but where is that stuff? The teams probably show a prototype, but the pharma boss decides against it, probably. However, it is possible to get a lot of diagnostics privately from laboratories, if you know what you're looking for, and are willing to pay for it. --Ayacop (talk) 14:18, 28 June 2008 (UTC)


 * Really good general diagnosticians get busy pretty quickly. They also have to explore and process a lot of information, which is time-consuming (and poorly compensated relative to other activities that require similar amounts of training, intelligence, and time).  I anticipate that some aspects of the task will be automated soon - software could elicit symptoms and ask some pretty standard questions (like recent travel, as you point out) that would help a good diagnostician do a more thorough job. Sorry to hear about your frustrations - I hope things improve soon. Scray (talk) 19:02, 28 June 2008 (UTC)


 * There are tests for all kinds of bacterial and viral infections. Nearly all known bacterial/viral infections can be detected.  It appears that you are in a country with nationalized health care (or worse, HMO-controlled healthcare).  There are many studies on nationalized health care that point out the weakness of doctors not being able to go "off script" for special cases.  As the doctor pointed out, he is not allowed to treat you for a bacterial infection until you meet the guidelines necessary to qualify for bacterial infection treatment.  As such, he was basically telling you what to do.  You need to return and tell them that you had a fever of 39C but took a fever reducer and a cold bath to reduce it enough so you could show up at the doctor's office.  Then, he can treat you.  It is important to listen to what the doctor says.  He cannot say "Go home and come back complaining of a 39C fever."  He can only say "I cannot give you antibacterial treatment until you have a 39C fever." --  k a i n a w &trade; 23:26, 28 June 2008 (UTC)


 * Well it's a bit more complicated. He told me that unless I had 39C a blood culture would be too insensitive. I'm well aware of antibiotic-resistance and that there is a 1:1 chance that the infection is viral and for the other 50% there is a good chance that those bacteria will not respond to general broadband antibiotics, so I see the need to know what those little critters really are. I explicitly asked him about PCR and genetic detection and he honestly could not tell me why this is not used for diagnosis. He obviously didn't know about ELISA either, this seems not to be part of the education. As I understand, a blood culture would only be positive if the disease is caused by bacteria (or other microbes, not viruses or poisons) and only if they proliferate in the blood, so infections where the microbes grow is specialized tissue could only be detected when they are so numerous that they penetrate into the blood stream.


 * I live in Germany where another reason for reluctant prescription is that each doctor has a limited budget for all his patients and has to pay the excess amount from his own earnings. I don't know if it would be perfectly legal to go abroad for treatment, and more, I don't know which countries allow a better and more effective treatment. And as for pretending fever, yes, I think that would work but, that's why they are becoming us a bread of liars and cheaterlings. 77.3.168.22 (talk) 08:39, 29 June 2008 (UTC)


 * The typical reason that a doctor is reluctant to prescribe antibiotics is to prevent the evolution of antibiotic-resistant microbes. For a more specific diagnosis you could call the doctor and express your concerns to him directly, or you could ask a specialist (if you are in the United States, look for somebody who is board-certified in Infectious Disease Medicine) for a second opinion.  I hope you feel better soon.  69.140.152.55 (talk) 03:34, 29 June 2008 (UTC)

This whole exchange illustrates why there is a policy against medical advice here. The original question contains at least 4 false assumptions, none of which were pointed out or explained by any of the responders. Second, the responses contain numerous irrelevant, and not a few erroneous "facts". Finally, no one has provided a direct and accurate answer to the two direct questions asked at the end of the initial account. This is no better than an impromptu conversation among 6 strangers on a train. The inquirer is a fool to rely on this information to make decisions about his health and should have asked his questions of the one person who heard his whole story, had the training to sort out the facts, could have answered his questions accurately, and could be held legally responsible for the answer. 159.14.240.230 (talk) 13:26, 1 July 2008 (UTC)


 * You are welcome to give an answer to the question as well as to explicitly point out what you think were false assumptions of mine. When I saw that the whole thing would boil down to legal questions I removed the entire section but it was restored. 77.3.134.249 (talk) 18:20, 1 July 2008 (UTC)


 * I don't think any explicit medical advice has been given here. The answers are attempting to explain the methodology of the practice of medical diagnoses itself, in line with the original question which clearly states medical advice is not being sought.  A discussion is however in progress at Wikipedia talk:Reference_desk/Science. Jdrewitt (talk) 20:40, 1 July 2008 (UTC)

EMF Transmission Dangers
Is there significant scientific evidence to support claims of health dangers from living in close proximity to electric power stations?70.58.154.222 (talk) 18:35, 28 June 2008 (UTC)
 * There have been studies which found statistical association between exposure to electromagnetic radiation from power lines, and studies which found no such association where one might have been expected, such as among power system workers. Biological stidies have found some effects of powerline frequency EMF on cells and tissues. Overall, the association with cancer or other ailments is far less clear than for ionizing radiation, asbestos, smoking, exposure to sunlight or exposure to several other well known health hazards. Research continues. Edison (talk) 19:23, 28 June 2008 (UTC)
 * Also see Electromagnetic_radiation_and_health. --Allen (talk) 00:48, 29 June 2008 (UTC)
 * Keep in mind that "hot topic" issues like this suffer from tremendous publication bias.  Plasticup  T / C  12:57, 30 June 2008 (UTC)
 * Interesting note: The example given in the publication bias article is about the supposed cancer risk of powerlines.  Plasticup  T / C  12:59, 30 June 2008 (UTC)