Wikipedia:Reference desk/Archives/Science/2009 August 30

= August 30 =

QUANTUM NUMBERS
What is quantum and quantum number? How electrons move around the nucleus? Explain.
 * Please do your own homework, as we will not do it for you. However, I will suggest the following articles: Bohr model, Bohr Theory and Balmer–Rydberg Equation, Quantum number, Principal quantum number, and Spectroscopic notation. ~ Amory ( user  •  talk  •  contribs ) 02:34, 30 August 2009 (UTC)
 * 'Explain'? Readjust your attitude. And your grammar. Seriously, this is a volunteer reference desk. It's also part of an encyclopedia that you can search. Awickert (talk) 06:56, 31 August 2009 (UTC)

Blood pH
I was thinking about this and wondering: What substance in the blood keeps it slightly alkaline (7.35-7.45)? Why does the body maintain a slightly alkaline pH?  bibliomaniac 1  5  04:30, 30 August 2009 (UTC)
 * The major system used by most living things to is the bicarbonate buffering system. This, combined with the ability of the kidneys to filter extra H+ ions from the blood, and you have a pretty solidly maintained pH. – ClockworkSoul 04:43, 30 August 2009 (UTC)
 * As for the second question: the binding of O2 to hemoglobin is influenced by pH level, so the blood pH is maintained at a level that optimizes both the O2 binding in the lungs, and its unbinding in tissue capillaries. (Note that O2 binding decreases with lower pH, so an increase in blood CO2 concentration, which lowers pH ever so slightly, causes oxygen to unbind from hemoglobin exactly when and where it's needed most.  Neat, huh?) 98.234.126.251 (talk) 04:51, 30 August 2009 (UTC)
 * That's a cool mechanism! DMacks (talk) 17:52, 30 August 2009 (UTC)
 * No single substance, though it all gets conceptualized as concentration of [H+]. Blood pH is maintained by a number of mechanisms, the most important of which are respiratory regulation (blowing off CO2 by breathing more rapidly, or retaining it by breathing more slowly) and the bicarbonate-carbonic acid and dihydrogen phosphate-hydrogen phosphate-hydrogen blood buffer systems. Hemoglobin also has some effect as a pH buffer. See the Henderson-Hasselbalch equation, respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalosis articles for more detail. Your "why" question, taken locally, is that if the blood becomes too acidic, you die, and if the blood become too alkalotic, you die (because enyzmatic reactions necessary for life are pH-dependent). Taken more broadly, because that's how the system evolved: the blood's pH mimics that of the primeval sea in which it was evolved, in order to maintain the functioning of the enzymes that require that pH. Specifically, the transition to air-breathing led to relatively high CO2 plasma tension and led to the development of the bicarbonate buffer system.  See Some Aspects of the Evolution of Vertebrate Acid-Base Regulation. - Nunh-huh 05:06, 30 August 2009 (UTC)

Cell phone jamming
Here's a question related to the discussion about "White noise generator": Where I live, you always see drivers yakkin' (or textin', or even worse, readin' stuff on the internet) on their cell phones and not paying attention to the road ahead (that's how that big rig rear-ended my Mustang, the driver was talkin' on his cell phone and didn't see me stop at a crosswalk to let a lady with a little kid get across the road). So when I saw the discussion about "White noise generator", it got me thinking: is it possible to rig up some device that would prevent cell phones inside the car from transmitting / receiving any signals, while at the same time having minimal effect on cell phones outside the car? 98.234.126.251 (talk) 06:19, 30 August 2009 (UTC)
 * Theoretically. Cars can potentially act as Faraday cages. The pragmatic issue is that the cellphone frequency band prolly wouldn't be ideal. John Riemann Soong (talk) 06:49, 30 August 2009 (UTC)
 * And also you'd probably have to figure out a way to disable it when the car isn't running! 124.154.253.31 (talk) 08:00, 30 August 2009 (UTC)
 * I really doubt that this would be practically possible - and it would certainly be illegal. SteveBaker (talk) 13:47, 30 August 2009 (UTC)
 * Passive interference is legal, in the US anyway (which it sort of has to be—you can't blame an architect for happening to make a structure that doesn't conduct cell phone signals efficiently). Active interference (e.g. saturating a spectrum with noise) is prohibited by the FCC. --98.217.14.211 (talk) 14:00, 30 August 2009 (UTC)
 * Again, as I've pointed out numerous times, calling anything that is made of metal a "faraday cage" is a stretch at best. All you have to do is sit in your car and make a cell phone call to demonstrate, beyond reasonable doubt, that the car's metal frame is not a faraday cage - it's just a bunch of metal.  It isn't attenuating the mobile telephone radio signal.  It's probably not attenuating any radio signal (except maybe when you get towards the visible light frequencies - solid bodies are good at attenuating those!)  A faraday cage needs to be specifically designed if it's going to be even slightly effective.  It's going to have a specific frequency response.  Even if it actually did suppress a particular frequency, the cell phone probably will be able to decode its signal anyway, because it uses a complicated digital spreading code.  If you go around calling every piece of metal a "Faraday cage", you're devaluing the design and complexity of actual Faraday cages.  Attenuation isn't a "qualitative thing" - it can be quantitatively analyzed, and I suspect that the attenuation of UHF radio through a car body is so close to zero that it's really creative application of terminology to call it a "shielding" effect.  Nimur (talk) 14:45, 30 August 2009 (UTC)
 * I would point out as I did last time that GSM (and in fact the vast majority of 2G systems) doesn't use CDMA but TDMA. I appreciate that this discussion appears to relate to the US but your answer didn't clearly specify you were only referring to the US. Whether this makes a difference to the answer or not, I don't know but given a large percentage of the world uses GSM; with cdmaOne and 3G networks like CDMA2000, UMTS and others combined I strongly suspect remaining a minority I don't think it's wise to discuss this as if most mobile phones use CDMA. (My suspicions are supported by this although it's hardly a neutral source.) Of course when we move to 4G we'd likely be using FDMA based on current proposals but it's a long way away before they take over given that 3G networks are still a distinct minority. Nil Einne (talk) 16:20, 30 August 2009 (UTC)
 * I think you are mistaken. GSM does use TDMA for packet scheduling and collision avoidance, but individual packets are coded with MSK, which is effectively a digital frequency spreading code.  In fact, it's a more sophisticated frequency spreader than CDMA.  I am not aware of any mobile telephony systems in operation, worldwide, that do not use a frequency spreading scheme for the digital encoding.  We should make clear the difference between CDMA, the marketing-ese word for US-standard-radiotelephony, and CDMA, the technically-correct-description-for-code-spreading.  The first paragraph of the CDMA article makes this distinction clear.  Nimur (talk) 16:47, 30 August 2009 (UTC)
 * It may use spread spectrum. But that's irrelevant to me since the issue I raised was whether it used code division multiple access (which was the article you linked to, and also what you mentioned in a previous question). Although appears to suggest to me (see below) that it's inaccurate to say GSM uses CDMA and our article doesn't seem to say it does either, if you say it does, then I accept that, since it's not something I understand very well. But if not, I feel my point still stands. And just to be clear, my point is that GSM doesn't use CDMA. I think the US marketing issue is somewhat irrelevant here since W-CDMA is commonly marketed as UMTS despite the fact it uses CDMA without dispute (actually it appears it's possible to use something other then W-CDMA, but all of them are CDMA and in any case, all use W-CDMA AFAIK) so I don't think there's any real confusion about what CDMA is, simply whether all spread spectrum techniques used by mobile phone networks are correctly called CDMA. P.S. I appreciate you did not specifically mention CDMA earlier on in this thread even if you did link to it, but I think it's inherently confusing to solely link to an article on CDMA (and not even as a sublink to the specifics) if (since I don't know) GSM doesn't use CDMA. It would be better to link to an article on spread spectrum (or multiple articles if you feel it's necessary, e.g. because our other articles don't explain it so well) since my understanding at the moment is that while CDMA is inherently a form of spread spectrum and is used by multiple mobile phone network systems, many 2G ones don't use it but use TDMA with spread spectrum techniques and possibly most 4G ones won't use it either, so solely linking to a CDMA article to explain spread spectrum techniques used by mobile networks is problematic. Again, if I'm wrong on this, apologies but I feel it's worth clearing up.
 * Note that spread spectrum is not a modulation scheme, and should not be confused with other types of modulation. One can, for example, use spread-spectrum techniques to transmit a signal modulated by FSK or BPSK. Thanks to the coding basis, spread spectrum can also be used as another method for implementing multiple access + GSM, for instance, combines TDMA and FDMA. GSM defines the topological areas (cells) with different carrier frequencies, and sets time slots within each cell etc
 * Nil Einne (talk) 21:05, 30 August 2009 (UTC)
 * This is an issue that's worth further investigation; let's take this discussion offline since it's really peripheral to the OP's question anyway. I'll do some reading and follow up later in the week; I've been repeating this claim because I'm pretty sure it's correct; but if there's any doubt about it, then I should re-check my terminology and my facts before proceeding.  Nimur (talk) 01:06, 31 August 2009 (UTC)
 * Nimur it is wrong to say: "MSK...is effectively a digital frequency spreading code. In fact, it's a more sophisticated frequency spreader than CDMA". Far from being a spreading code, MSK is a narrow band digital modulation method. Cuddlyable3 (talk) 16:00, 31 August 2009 (UTC)
 * This source, from our article: from Aerospace Corporation, has power spectral density plots for several variants of MSK and GMSK. I suppose it's up to the reader to decide whether 1 MHz consitutes "wide" or "narrow" bandwidth.  I would put 1MHz channel width solidly in the realm of wide-band spectrum-spreading signal (considering the audio data is 3 kHz).  Nimur (talk) 01:49, 1 September 2009 (UTC)
 * It would be technically straightforward to re-program the cell towers to refuse to connect to a moving cell phone. This requires no on-vehicle electronics other than the cell phone, and it allows you to pull over and stop and use your cell phone. It would even be possible to add specialized systems inside busses and trains to re-enable cell phones for their occupants. Harder, but not impossible, to permit the passengers but not the drivers in busses and trains. Very difficult or impossible to disable for car drivers but not for their passengers. The problem is that the voters will resist such a system. Similarly, it is technically straightforward to catch all speeders, but it's politically impossible. -Arch dude (talk) 14:59, 30 August 2009 (UTC)

I believe most of the signals you receive on the phone in the car now come through the windows of the car, other than that they should act as pretty good faraday cages as pointed out above. So I would think applying a film like they use on some trains to block out signals through the windows (see this article) would probably work about as well as it works in these trains (I don't know how well they work). TastyCakes (talk) 16:39, 30 August 2009 (UTC)


 * Excellent idea, TastyCakes -- a conductive film on the windows would work much better than an active jammer (which is expensive and can cause harmful interference) or reprogramming the cell towers (which can cause erroneous applications of the protocol). As they say, the simplest solution works best.  (BTW, a wire mesh embedded in the windows could work just as well.) 98.234.126.251 (talk) 07:29, 31 August 2009 (UTC)
 * Programming cell towers to drop moving signals would not be a very good solution. The problem is drivers yakking on the phone.  Passengers in all kinds of vehicles should not be limited as they are not operating the vehicle.  Googlemeister (talk) 13:13, 31 August 2009 (UTC)


 * Is it not illegal to use a mobile while driving in the US? It certainly is in the UK (3 points on licence and £60 penalty) - unless it's 100% hands free. As regard signals getting in the car - I think it's the large amount of windows. On my metal boat - it kills the signal, unless you stand next to the window (or outside!)  Ron h jones (Talk) 18:49, 31 August 2009 (UTC)


 * To address the question of the legality of using a cell while driving in the US, that depends on where you are. I think that it is legal most places, but I do know of at least one city where it is not.  Googlemeister (talk) 20:12, 31 August 2009 (UTC)
 * One obvious effect of your question, if it would succeed, is the passenger who wants to use a cellphone and couldn't because the phone was jammed. Nyttend (talk) 01:14, 4 September 2009 (UTC)


 * Education is the answer, not cell phone jamming, which is illegal. See the recent road safety video made by Gwent police http://www.guardian.co.uk/uk/2009/sep/03/gwent-road-safety-film Jdrewitt (talk) 09:49, 5 September 2009 (UTC)

Single celled organisms and evolution
Until I gave it a good think, I had previously assumed that simpler microorganisms (particularly single-celled varieties such as the amoeba) had survived essentially unchanged since the emergence of more complex/multi-celled organisms. But this shouldn't be the case right? It doesn't make sense to me that an Amoeba proteus from 2009 would look the same as an amoeba 10 million years ago, or that the flagella of Giardia lamblia hasn't changed in the past million years or so. But certain things I've been reading seem to hint at the contrary. Chlorophyceae seems to be organised according to the type of flagella each species/family has, which implies that the same flagella is ancestral to all species within that class. This seems incredible, considering the fact that larger species such as humans have structurally very little evidence of having ever been water-breathers, and water mammals have little evidence of ever having had legs! Could it be that there are many simple organisms that have been mis-classified because of such re-evolutions, or is there really a fundamental difference in the way simple organisms evolve?

Lastly, are there any single-celled organisms that (for example) show signs of having evolved into single-celled organisms after having been multi-celled? I can imagine the analysis of the genome of such an organism showing it as a member of a group exclusive to multi-cellular organisms, despite the obvious structural differences. Sorry for asking so many questions! 124.154.253.31 (talk) 08:00, 30 August 2009 (UTC)


 * I think you really want the distinction eukaryote versus prokaryote. The eukaryotes include single celled animals and plants and the multicellular animals and plants evolved independently. Amoeba is a eukaryote. You're probably thinking of bacteria and archaea which are much less complex and have had a very long time to evolve into something fairly optimal. They have changed of course and continue to do so but it's a bit like frogs - they look alike to us but genetically there's probably more difference between two random types of frogs than there is between us and the birds. Dmcq (talk) 12:27, 30 August 2009 (UTC)


 * Yes, sorry, I meant to refer exclusively to single-celled eukaryotes, as well as prokaryotes actually. I guess I didn't realize that there could be so many significant changes genetically without much physical evidence of it. 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)


 * "...water mammals have little evidence of ever having had legs" ? Sure they do.  Whales have non-functional, residual rear legs, which don't protrude beyond the skin, even to this day: .  Their front legs, fingers included, are now their fins. StuRat (talk) 12:47, 30 August 2009 (UTC)


 * Argh. I recently watched a video about this and they made a lot of fuss about the discovery of residual legs in a primitive whale found in Egypt; the way they worded it made it sound like the bones no longer existed in modern whales. I guess all I can say then is that they no longer have toes? 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

Micro-organisms certainly evolve. They do it continuously and rapidly. That's why we have so much trouble with drug resistance - we treat simple organisms with drugs that are supposed to kill them - the few that survive go on to become the whole population. Over many generations of micro-organisms, you have a drug that no longer works anymore. This is an extremely common phenomenon. But our ability to track that evolution into the distant past is limited. Looking at the appearance of bacteria doesn't tell you much about what's going on biochemically inside - and we don't have that detailed information about bacteria from the distant past. It's not like a large organism like (say) a horse. We can find the fossilised bones of ancient proto-horses and deduce a lot about how they evolved - but our ability to do that kind of thing for micro-organisms is extremely limited. SteveBaker (talk) 13:41, 30 August 2009 (UTC)


 * True, but we can compare the genes of single-celled organisms with those of multicellular organisms. To the extent that they are the same, it's reasonable to conclude that both groups have preserved an ancestral structure. Looie496 (talk) 00:28, 31 August 2009 (UTC)


 * The bacterial flagellum is a favourite of creationists. Because it is fairly complex they think it couldn't have evolved. Cilia are a similar thing. Richard Dawkin's book The Ancestor's Tale has a bit about them, especially the Mixotricha paradoxa, it's a pity wiki doesn't have a nice picture of that. Dmcq (talk) 16:41, 30 August 2009 (UTC)
 * You can also check out Kenneth Miller's The Flagellum Unspun, published in 2004 by Cambridge University Press.  DRosenbach  ( Talk 20:35, 30 August 2009 (UTC)


 * The concept of punctuated equilibrium is probably relevant to the original question. Single celled organisms evolve so rapidly that they quickly reach highly optimized forms, which can persist with only minimal changes for a very long time. Looie496 (talk) 00:28, 31 August 2009 (UTC)


 * Wow! If punctuated equilibrium is true, than that explains a lot to me. I understand that there are competing controvercial theories, and that of course as SteveBaker says the micro-organisms are evolving, but due to the extremely specific niches that most of these organisms have evolved to occupy it makes sense that they would give appearances of having met some sort of equilibrium, a cancelling out of multiple evoluctionary changes. Dmcq made the point about frogs, but have they really changed functionally that much? It seems like an example of genetic rearrangement over enormous spans of time only to result in an organism that does virtually the same thing maybe more efficiently but without any extra tricks (of course, most individual species of frog have developed lots of tricks, but I'm attempting to refer to frogs as a group of species).


 * I have previously thought of the idea of "highly optimized" or "perfectly evolved" forms as silly, almost narcissistic, but now I can see how it might not be such a strange concept. 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)


 * An organism can be perfectly evolved for a given environment, but a change in the environment would tend to necessitate a change in the organism. Generalists like humans are more likely to be able to adapt behaviorally, like by wearing more or less clothes, as the climate changes, while specialists like finches must evolve physically, such as the shape of their beaks as their food source changes. StuRat (talk) 19:00, 31 August 2009 (UTC)
 * Micro-organisms can generally evolve much more rapidly though - their extremely short life-cycles (some can produce a new generation every 10 minutes!) allows them to evolve vastly more quickly than (say) humans who require 16 to 30 years to do the same thing. Large animals have to be at least somewhat generalists because there simply isn't time for them to evolve.  But bacteria could conceivably be so super-specialised that they might suite an environment that changes so often that the bacteria are continuously evolving to fit its changes.  But whether you'd say that a generalist was "well suited" to any particular environment is a tough call. SteveBaker (talk) 05:33, 1 September 2009 (UTC)
 * That brings up a good point then, what is it about bacteria that prevents them from becoming generalists? Isn't being generalist always evolutionarily beneficial? The Why is it, for example, that many organisms in the body have not evolved to respond to changes in body temperature of a couple degrees, whereas others can survive in environments with incredible ranges of temperature? Is the length of the genome a factor, i.e. are the organisms forced to compromise more, as a 64k demo programmer might be forced to sacrifice sound complexity in order to produce a pretty looking program? 124.154.253.31 (talk) 02:12, 2 September 2009 (UTC)
 * Um why do you think being a generalist is always evolutionary beneficial? If you have two bacteria species competing to live in your gut, one producing a large number of enzymes to digest stuff they never encounter, one producing only the enzymes to digest stuff they are likely to encounter, which one do you think is likely to have the evolutionary advantage? The phrase 'jack of all trades, master of none' comes to mind. For something like a bacterium, given their small size etc it rarely pays to be a jack of all trades. Remember also, even if a bacterium could eventually evolve to be an ultimate machine for all environments (which I think is usually unlikely), if all the evolutionary forms in between are worse off there's a fair chance this will never happen. Nil Einne (talk) 23:04, 3 September 2009 (UTC)
 * So you're basically saying that yes, the size of the genome is the factor in limiting the generalization of small bacteria. I don't see any reason why a large-genomed bacteria wouldn't generalize, nor why intermediate evolutionary forms need be "worse off". 124.154.253.31 (talk) 23:20, 3 September 2009 (UTC)

Genus Canis
What are the best sources for up-to-date information on the coywolf and other contorversies surrounding the family tree and phylogenetics of the genus Canis? Neon Merlin  08:01, 30 August 2009 (UTC)
 * It looks like the Journal of Mammology, the Journal of Systematic Zoology, and Conservation Biology have all published articles. The articles I found were The Taxonomic Status of Wild Canis (Canidae) in the South Central United States, The Taxonomic Status of Wild Canis in Arkansas, etc.  You can find these sorts of journals in a university library, or online (if you have subscription access through your school, library, etc).  Nimur (talk) 14:56, 30 August 2009 (UTC)

Parameters of Planet Habitability for people? (not Extremophiles)
There is an article that refers to habitabilty of Extremophiles "ETs" but I was wondering if there is any matter or thought on the parameters of survivability of a planet for Human Beings? I know the Habitable zone article talks about one dimension there, temperature ranges from 0°C to 100°C but most people wouldn't survive through 70% of that range. Also gravity, atmosphere composition and emissivity, atmosphere pressure, hydrosphere size, magnetosphere strength, irradiance, eccentricity, axial tilt, albedo, etc. must have referable boundry limits were people are concerned, does anyone know what these ranges are?? Cpt. J. Tiberio Kirk (talk) 08:31, 30 August 2009 (UTC)


 * There's a difference for people, where we can live in a place that doesn't meet all our survival needs, by trading with others who have those items we lack. Thus people can live in a wider variety of places than we could if we were all hermits.  Remote whaling villages are one example from a couple centuries back, and people living at the South Pole or on the International Space Station are some extreme examples from today, where they are provided with everything they need, in this case in exchange for research.  So, do you mean to ask where people can survive if provided with all their needs from outside, or where they can live in total isolation ? StuRat (talk) 12:37, 30 August 2009 (UTC)


 * We don't even need to trade, technology (even something as simple as a warm coat) can dramatically increase the range of environments we can survive in. --Tango (talk) 15:42, 30 August 2009 (UTC)


 * Sure, but where did you get that warm coat? Unless you single-handedly grew the plant fiber; smelted the steel and forged the industrial sewing machine; operated the vertically integrated fiber-to-cotton-to-coat industry... you had to trade something to get that coat.  Chances are, much of the material and labor for that industrial chain came from a more habitable region, depending on how far back into the supply-chain you look.  Nimur (talk) 18:11, 30 August 2009 (UTC)


 * In modern times, yes, but specialisation on a large scale is a fairly recent part of human history (just since the industrial revolution, really, it existed to a lesser extent for a few millennia before that). A caveman could have killed a large animal and turned its skin and fur into a coat without any trade involved. --Tango (talk) 19:23, 30 August 2009 (UTC)


 * Agreed. So a human with some basic technology, like the ability to make animal skin clothes, has a wider range than one without.  We can see that by where Inuits and other similar people live (which doesn't extend all the way to the poles, however).  Without any technology at all, people would be forced to live only in tropical areas near a food and fresh water supply.  But once a high level of technology and trading is added, people could live just about anywhere on Earth, and even in space, provided that those who remain on Earth are willing to send them what they need to survive in exchange for the research/exploration/experimentation they do. StuRat (talk) 15:04, 31 August 2009 (UTC)

Just as we are if you will, not a space station or "technology:"
(Human Environmental Tolerances.) I'm looking mostly for help with references... ...does anyone know what these ranges are, for ANY planet Habitation?? Cpt. J. Tiberio Kirk (talk) 08:31, 30 August 2009 (UTC)
 * Some of these terms are poorly defined, e.g. magnetosphere strength, and even incident radiation (What does this mean - total radiation? Blackbody-style radiation with a peak near visible light?  I'm pretty sure that 1 kW of gamma radiation is much more hazardous than 1 kW of visible-light!)  Atmospheric composition will have varying effects ranging from temporary to permanent health problems; do you have a criteria for quantifying these?  Are you seeking the LD50 or something similar for these parameters?  How long do the humans have to survive (a few hours, weeks, months, years?)  It seems unlikely we can find habitability data for humans regarding the orbital parameters, as we have only experienced life on Earth; but I can't imagine what an eccentricity has to do with anything (except its effect on other planet parameters, like temperature and radiation).  Nimur (talk) 06:07, 1 September 2009 (UTC)
 * IS THIS THE SCIENCE REFERENCE DESK or the "I can't imagine" so I'll bash the question desk??
 * You need an English lesson? -> Habitability and Habitation,
 * How do you confuse "Median lethal dose" with "Habitiability" and still think you should comment here?
 * If you don't understand the question should you be commenting with ignorant questions?Cpt. J Tiberio Kirk (talk) 08:34, 1 September 2009 (UTC)
 * This is the Science Reference Desk, not the wild speculation/colorful imagination desk. LD50 is as good a measure as any for determining habitability.  You want to know what conditions humans can survive; but you failed to define "survival" in a way that allows a scientific answer to your question.   Nimur (talk) 18:20, 1 September 2009 (UTC)
 * I resent that. There has been a lot of healthy "wild speculation" and "colorful imagining" performed on the science RD over the years, and I find it slightly arrogant of you to debase that what ever reason you may have. Many of the OPs queries seem to have perfectly reasonable scientific answers, whether they're suitable for an encyclopaedic article is another story (and not one that need be discussed here). 124.154.253.31 (talk) 02:21, 2 September 2009 (UTC)
 * Didn't we come to the conclusion in a thread some time ago that humans could probably/possibly survive at 2x earth gravity? --Kurt Shaped Box (talk) 11:34, 1 September 2009 (UTC)

A few comments on the table:

 * 1) 0°C seems questionable for a naked human, I'd expect him to quickly freeze to death. And I suspect that a naked human could take more than 30°C, especially if there is water around for cooling off.  So, I'd raise both by 10°C, to get a range of 10°C - 40°C.
 * 0°C to 30°C are referenced values.
 * 2) I doubt if naked humans could survive long term at 0g, due to bone and circulatory system degradation. Even in the short term, doing everything necessary for life in zero gravity could be quite difficult, without technology.  I'd raise that minimum to at least 0.1g.
 * More reasonable is the minimum gravity needed to support a breathable (surface pressure) atmosphere.
 * 3) I don't believe we need any atmospheric nitrogen. We do need some nitrogen, but we get that from our diet, not from the air.


 * "The unfortunate problem is the flammability. For this reason, McKay et al. 1991 sets the upper limit on O2 at 300 mbar. The lower limit of 130 mbar is set by hypoxia. They estimate that the partial pressure of N2 needs to be greater than 300 mbar. Although nitrogen is not widely thought of as an important gas, it makes up 78% of Earth’s atmosphere. It is needed as a as a buffer gas to prevent O2 combustion in the atmosphere. The partial pressure of CO2 is set by toxicity. The overall mixture is estimated to be between 500 and 5000 mbar, with the upper limit shown by inhabitants of high elevations on Earth. The lower limit of the overall mixture is set to 500 mbar based on buffer gas narcosis. If the buffer gas, N2 in this case, is set to be >300 mbar, that leaves the O2 content dangerously close to the lower limit set by hypoxia. McKay et al. 1991 suggest that the high concentration of buffer gas to O2 is toxic. Temperatures and pressures needed for habitability are set by the triple point of water. This is the point where water can exists as a solid, liquid and gas. It is defined as 273K at 6.11 mbar. If we are to have liquid water on the surface, the temperature and pressure must not lie far off above or below the triple point.


 * 4) We actually don't directly need any of the trace elements in the atmosphere, either. Of course, the plants we eat need atmospheric carbon dioxide, so you could argue that we need it, too, since we need plants to eat.  This is unless we had another food source that didn't require atmospheric CO2.


 * 5) I don't believe we need any oceans, seas, or lakes to survive, as people can survive on underground water reservoirs only, if necessary.
 * Actually, I have read a breathable atmosphere has to have some moisture. And that rain washes away suspended silica dust that would make the atmosphere unbreathable. GabrielVelasquez (talk) 09:05, 3 September 2009 (UTC)
 * 6) I don't believe we need seasonal variations to survive, which means we don't require any axial tilt (or eccentricity of our planet's orbit, which could be an alternate means of achieving seasons. StuRat (talk) 13:58, 1 September 2009 (UTC)
 * This is an amusing comment as you refer to "needed" axial tilt or eccentricity and assume minimums, but there there would have to be maximum limits. Planets of Larger stars would have larger habitable zone orbits (ie. longer periods) and with a 90° axial tilt one entire hemisphere could freeze over seasonally. GabrielVelasquez (talk) 09:03, 3 September 2009 (UTC)
 * The atmospheric pressure that humans need to survive will be a function of the O2 content of said atmosphere. Should probably note that we need there to be an absence of toxic elements as well.  It would not work if there was an arsenic desert nearby with dust storms hitting the settlement frequently.  Googlemeister (talk) 14:37, 1 September 2009 (UTC)


 * We need a partial pressure of oxygen of about 0.2 atm, neither the total pressure of the atmosphere or the proportion of oxygen are particularly important, it is that partial pressure. Total pressure of 0.2 atm ought to be fine, or we can have some kind of buffer gas up to a total of somewhere more than 1 atm, but I don't know how much more. --Tango (talk) 21:12, 1 September 2009 (UTC)
 * With Nitrox or TriMix, SCUBA divers can breathe up to almost 40% oxygen. In fact, utility divers will breathe some pretty exotic air mixtures - helium, argon, you name it.  You can even go to very low percentages of oxygen if the partial pressure is high enough - but that requires a very high pressure gas mix (certainly not recommended for long-duration exposure, or consumption at sea-level).  There are severe health ramifications and the gas levels and pressures need to be properly monitored by a trained diver.  Nimur (talk) 23:55, 1 September 2009 (UTC)
 * Let's say for the sake of argument that we are talking about a resettled Inuit (mentioned above), on some Arctic/Tundra planet... Would you expect them to leave their shelter to go hunting in a scuba suit and still call that habitiable?? - GabrielVelasquez (talk) 12:43, 3 September 2009 (UTC)
 * Re item 2): FWIW, I recall from discussions at Mars Society conferences that the minimum gravity needed to avoid long-term skeletal, etc, degredation problems is currently thought to be about 1/3g - for obvious reasons, experimental investigations of this consideration are not easy to carry out. This means that long-term habitation (by terrestrial humans, of course) in the Moon's 0.165g would be problematic without appropriate countermeasures (such as drugs, exercises, centrifuge sessions), but that extended or permanent Martian habitation in 0.379g should be just about tolerable in this regard. 87.81.230.195 (talk) 20:54, 1 September 2009 (UTC)
 * The Mars Society just happened to come across a figure that is just under the gravity of Mars? I would take that with a pinch of salt. We know what happens to humans at 1g, 0g and a little at >1g. We know next to nothing about anything between 0 and 1. There have been no direct experiments, so it is all guesswork. --Tango (talk) 21:12, 1 September 2009 (UTC)
 * Having had no little interaction with the Mars Society (though I'm not currently a member), Tango, I'm prepared to believe it does not favour self-serving spin over facts; it is after all composed of numerous articulate scientists and others who aren't required to toe any party line - not everyone is intellectually corrupt. In this case they say (or said when I was participating) merely that yes, absent direct observations, the best estimates available were "about 1/3g", and precisely in order to investigate this question, the Society has been collaborating with NASA to design an experiment to raise generations of mice in tethered centrifugal microsatellites simulating Martian gravity: regrettably this is currently a victim of budget cuts, but in the longer term such experiments will doubtless be performed. The more immediate worry for Mars expeditions is in fact not the toleration of Martian gravity, but the effects of zero-g for the months it will take getting there and back; again, tethered centrifugal craft may be an answer (OK, that kind of spin they favour :-) ). 87.81.230.195 (talk) 13:28, 3 September 2009 (UTC)
 * As for maximum gravity humans can tolerate, I think 4-5 g's would be the upper limit due to cardiovascular effects (blood draining away from the brain, blackouts, lower body edema, stuff like that). Although some people could briefly tolerate much higher gravity, the maximum continuous gravity force they can tolerate (for more than a few minutes) is no more than that. Also, the maximum tolerable temperature is 70 C (I looked it up in the Science Encyclopedia). FWiW 98.234.126.251 (talk) 05:23, 2 September 2009 (UTC)
 * Yes, without g-suits and special training, 5g seems to be the maximum for more than a few seconds. --Tango (talk) 18:18, 2 September 2009 (UTC)
 * But then again, that's for an adult, isn't it? And probably a pretty healthy one. For these figures, fetuses would have to be able to survive birth as well, right? 124.154.253.31 (talk) 06:08, 4 September 2009 (UTC)
 * Yeah, I agree, 5g is a bit too much. Also, I realized, with a gravity of 3-5g, it would make basic everyday activities difficult or impossible even without cardiovascular effects.  So with that in mind, 1.5-2g seems about right for a maximum limit. 98.234.126.251 (talk) 04:40, 5 September 2009 (UTC)
 * Did I forget to mention that according to the article on oxygen toxicity, the maximum tolerable oxygen partial pressure is 0.5 bar? 98.234.126.251 (talk) 05:27, 2 September 2009 (UTC)
 * Well found. --Tango (talk) 18:18, 2 September 2009 (UTC)
 * The original source for that number indicates that 0.5 bar of oxygen is not fatal, only that it induces clinical symptoms of tracheobronchitis. Again, this highlights the necessary definition of "habitible" - humans seem to be able to survive up to 1.8 to almost 3 bar of oxygen without major damage to the central nervous system, depending on other conditions.  Even this damage, which ranges from dizziness and nausea to more serious problems, is considered mostly reversable.  .  So, what level of discomfort is acceptable, or are these terms meant strictly to refer to fatality limits?  Nimur (talk) 05:51, 3 September 2009 (UTC)

You irrationally insist on ignoring the clarification "Just as we are..." and "Habitability" to continue your criticism.

Obviously torture isn't a "habitable" situation. Here is a "definition of habitiable" that you might appreciate:

'''
 * '''http://en.wikipedia.org/wiki/User:Explodicle/Planetary_human_habitability

and I hope this article gets finished some time this year as it is obviously needed!

Also just because dimensions are connected doesn't mean that they don't have limits, for people.

GabrielVelasquez (talk) 08:54, 3 September 2009 (UTC)

I quote from the link right above "...Dole and Asimov (1963) and they defined a "habitable planet" as "one on which large numbers of people can live comfortably and enjoyably without needing unreasonable protection from the natural environment and without dependance on materials brought in from other planets." They added that in discussing habitability the planet in question must be at least 10% habitable. In their book they went on to list more specific parameters for said habitability."
 * Habitability defines the term in accordance with a few state legal statutes - more along the lines of a building code. I'm only asking for clarification because your question is phrased in a way that requests very specific numbers to a very vaguely defined concept - so in its present form, there is no way to answer this question.  Nimur (talk) 16:39, 3 September 2009 (UTC)
 * "And you are lynching Negroes" - You deliberately ignore the clarification, you make me suspect you are just mocking.

Please edit table at will, but comment above this subsection
"Human Habitability Environmental Requirements and Tolerances."


 * NEW TABLE BASED ON ANSWERS:

GabrielVelasquez (talk) 09:30, 3 September 2009 (UTC)

"NOx" written in expanded form as...?
Is "oxides of nitrogen" or "nitrogen oxides" appropriate for a research paper to be published in an international journal? I'm cleaning up a manuscript for a Chinese professor and the original has "oxides of nitrogen" which seemed a bit off to me.

Google shows both are present in the vernacular, so I'm wondering if anyone with direct experience in a related field could give me a definitive answer (or even a definitive "they're both ok")...

Thank you, 61.189.63.152 (talk) 13:37, 30 August 2009 (UTC)
 * Both are fine. Nitrogen oxides may be better, especially if it is to be indexed by a computer.83.100.250.79 (talk) 14:27, 30 August 2009 (UTC)


 * I'm not a chemist. To me, between the two, I'd prefer "oxides of nitrogen", as it communicates very clearly that we're talking about a group of compounds. For retrieval purposes, I'd suggest including both as index terms. --98.114.146.57 (talk) 14:51, 30 August 2009 (UTC)


 * NOx is a perfectly acceptable "technojargon" term in certain communities, and does not need expanding. While in a strictly chemical context, an expanded form may be more appropriate, I think it would confuse readers from other disciplines (like atmospheric research, combustion research) who are more used to seeing "NOx" and knowing unambiguously what is meant.  Nimur (talk) 15:00, 30 August 2009 (UTC)
 * Highly dependent on the conventions for the specific journal (some have style-guides with lists of accepted/standard abbreviations) and/or the target audience. DMacks (talk) 17:51, 30 August 2009 (UTC)
 * I agree. Check the manual of style for the particular journal.  Google Scholar found 477,000 usages.  Nimur (talk) 17:59, 30 August 2009 (UTC)

Coal & Fossils
Coal, like oil, as I am lead to believe, is formed from the compression of carbon based material (i.e. animals and plants) over time. Why is it that some animals become fossils, yet others become coal? Also, related question, why do we have coal and oil fields? It seems like all these animals all died in the same place. Any info would be appreciated. --KageTora - (영호 (影虎)) (talk) 14:17, 30 August 2009 (UTC)
 * Fossils in coal are actually very common - search for "fossils coal" - here's a fish, and image search may be even better.83.100.250.79 (talk) 14:24, 30 August 2009 (UTC)
 * Thanks. So, if there are fossils even in coal, where does all the rest of the coal come from? --KageTora - (영호 (影虎)) (talk) 14:36, 30 August 2009 (UTC)
 * Ah, I think that last question has just been answered by an Gimage search. It said that in the case of that particular image, the coal in question was fossilized peat, which would lead me to believe that the surrounding coal on the image of the fish in your answer would also be some such similar thing, such as vegetation. --KageTora - (영호 (影虎)) (talk) 14:41, 30 August 2009 (UTC)
 * Fossil forming requires circumstances conducive to it. Fossils are by no means a certainty when you have organic matter entombed in mineral matter. See rarity of fossils. Bus stop (talk) 15:15, 30 August 2009 (UTC)
 * (ec) Fossils can be present in coal, but most coal is not made of decayed animal. It is made from Type III kerogen, "terrestrial plant matter that is lacking in lipids or waxy matter" like peats and grasses (and trees, maybe). Different kinds of plant matter (like marine algae, lake plants, and terrestrial plants) are different kerogen material, and typically result in different kinds of fossil-fuel.  However, few fossil-fuels are actually made of animal fossil.  Nimur (talk) 15:17, 30 August 2009 (UTC)
 * Thanks, Nimur, but in my original question, I did actually mention plants, too. --KageTora - (영호 (影虎)) (talk) 16:28, 30 August 2009 (UTC)
 * Ok, but it seems like the kerogen article will link you to the information you want. Why do certain regions form oil or coal, while others do not?  See petroleum geology for an in-depth answer.  To summarize: you need several conditions to occur - presence of a kerogen source (meaning the correct type of plant or organic matter), and the presence of a reservoir rock that can hold that matter; presence of a seal rock; and mild seismic activity (geothermal energy) to cook the kerogen without fracturing the seal.  This is a rare combination, so only certain regions result in liquid hydrocarbon or economically extractable natural gas.  Coal, on the other hand, doesn't need a seal rock; and is less sensitive to seismic activity; so it is much more common.  I might have misinterpreted one of your original questions, "Why is it that some animals become fossils, yet others become coal?"  In truth, no animals become coal; only certain plants can become coal; but even those must be subjected to the proper geological conditions (as I described above), so coal will only form in certain regions.  Nimur (talk) 17:21, 30 August 2009 (UTC)
 * I see, thanks. You have cleared it up. Basically, the reason why we have coal fields is because those conditions only exist in certain places. Animals don't become coal, so that is why we have fossilized animals in coal. I get it, now. Thanks. --KageTora - (영호 (影虎)) (talk) 17:58, 30 August 2009 (UTC)
 * As an extra tidbit, the two main depositional enviornments that I think of for coal are (a) oxbow lakes in subtropical to tropical meander belts that slowly fill up with sediment, and (b) costal/tidal plains. Awickert (talk) 06:51, 31 August 2009 (UTC)

Puzzling Puzzle
This is already on the Miscellaneous desk. We discourage cross-posting of questions. // BL \\ (talk) 16:22, 30 August 2009 (UTC)
 * Wouldn't it fit better on the Math desk? -GTBacchus(talk) 16:26, 30 August 2009 (UTC)

Transparent objects
Why transparent objects are transparent.? —Preceding unsigned comment added by 121.245.107.152 (talk) 18:13, 30 August 2009 (UTC)
 * At the risk of sounding glib, because you can see light through them. The article Transparent materials is reasonably clear even for a non-scientist. // BL \\ (talk) 18:30, 30 August 2009 (UTC)


 * The article is reasonably clear? How fitting to the subject matter!  No wonder the article on black holes seems a bit less enlightening to me.  --Cookatoo.ergo.ZooM (talk) 19:24, 30 August 2009 (UTC)


 * It is important to remember that transparency is dependant on the wavelength of light in question. We usually mean the visible part of the EM spectrum, but something being transparent in that part (or not) does not mean it is necessary transparent (or not transparent) in other parts. For example, the glass in a greenhouse is transparent to visible light but not to far infra-red light (that's part of why it traps heat). A bin bag is opaque to visible light, but transparent to far IR (there is a picture of that further up this page in the "invisibility" section). I believe it is all to do with electron energy levels - to absorb a photon there has to be en electron in the substance that can rise to another energy level an amount of energy higher equal to the energy of the photon (which is inversely proportional to wavelength). --Tango (talk) 19:19, 30 August 2009 (UTC)
 * Greenhouses mostly trap heat by trapping hot air. The greenhouse effect isn't very significant in greenhouses. — DanielLC 22:45, 31 August 2009 (UTC)
 * Have you considered why non-transparent things are like they are - once you understand this you may be able to come to terms with transparency.83.100.250.79 (talk) 21:20, 30 August 2009 (UTC)
 * That is essentially exactly the same question, so how is that helpful? --Tango (talk) 22:38, 30 August 2009 (UTC)
 * No it isn't - I was suggesting that they look at why things absorb light. Once that is understood transparent things should be obvious.83.100.250.79 (talk) 00:01, 31 August 2009 (UTC)
 * Of course it will be - you'll already have the answer because it is the same question. Something is transparent if it doesn't absorb (or reflect - don't forget that possibility, although arguably it is temporary absorption) light, so if you know why something absorbs light you also know why other things don't. They are the same question, just from a different direction. --Tango (talk) 00:11, 31 August 2009 (UTC)
 * The question is "why do these things let light through" - I thought it might help to consider "why do some things not let light through" - obviously they are two sides of the same coin. - Non tranparency is (in my opinion) less 'mysterious' (in a psychological sense consider how excited people get about gadgets with transparent bits )than transparency at a very basic level, which is where we are.83.100.250.79 (talk) 00:44, 31 August 2009 (UTC)
 * What gadgets? Cuddlyable3 (talk) 15:38, 31 August 2009 (UTC)
 * Controllers for games consoles, and some handhelds, come in semitransparent versions. Vimescarrot (talk) 15:52, 31 August 2009 (UTC)

Hair follicle imitator
Is there a plant or animal that looks like a hair follicle, including the root (white or clear "bulb")when pulled out that is much stiffer and thicker than surrounding follicles and which does not soften or react to isotropy alcohol but dies or dissolves when iodine is applied as an antiseptic? 71.100.5.63 (talk) 19:39, 30 August 2009 (UTC)
 * Are you asking if an animal or plant exists that would be lodged into a human scalp, so that when plucked it would resemble a hair and its follicle?  DRosenbach  ( Talk 20:28, 30 August 2009 (UTC)
 * Why did you say scalp??? ...but yes. 71.100.5.63 (talk) 21:16, 30 August 2009 (UTC)


 * I'm curious if you mean what is sometimes called in slang "fledges" - a form of 'pubic' like hair that grows on the shoulders etc, as people get older - this is thicker and stiffer that normal hair.?
 * What exactly happens when you add iodine ?83.100.250.79 (talk) 21:18, 30 August 2009 (UTC)
 * The original one I found was about 1.5" from the corner of my mouth. I thought at first it was a petrified blackhead. The end looked more like a glob of grease than a root. The one on my scalp that I put iodine on simply vanished. The third one I have now became much softer after the iodine but has not dissolved completely yet or gone away. Never heard of "fledges." What is it? 71.100.5.63 (talk) 21:31, 30 August 2009 (UTC)
 * It sounds to me like an ingrown hair, which may grow much thicker than a normal hair and have the appearance of a pimple before it emerges. Unpleasant, but not a sign of disease or infestation. I've had them along the jawline, and when they emerge they have an appearance like what you're describing. --FOo (talk) 22:23, 30 August 2009 (UTC)
 * No curling or folding backwards. I've had ingrown hairs but none that were thick, tough, and straight. This is definitely a species that has come here from outer space to infiltrate Earth to spy on us by pretending to be a hair. 71.100.5.63 (talk) 23:22, 30 August 2009 (UTC)

Morgellons syndrome. --TammyMoet (talk) 08:56, 31 August 2009 (UTC)

Fish safety
For years I've enjoyed tunafish - both as BBQed steaks and also raw in sushi. A while ago I saw sushi grade tuna for sale at a fish place, and for the first time enjoyed raw fish as a meal in its own right rather than with rice. Delicious. I've bought tunafish steaks a couple of times since.

My question is, isn't raw meat (including fish) supposed to be extremely prone to food poisoning? Is this safe? What is the difference between "safe" raw fish (used worldwide in sushi) and "unsafe" raw fish if any? (assuming it's from a reputable source, fresh, washed, cold, etc)

What's the risk if I carry on indulging myself by buying raw fish at reputable stores and taking it home to make my own sushi and raw fish meals at leisure? What precautions and other safety rules do I need to be aware of?

Thanks for any answers.

FT2 (Talk 19:51, 30 August 2009 (UTC)


 * This might help -- you can google "raw fish safety" yourself for more info.  DRosenbach  ( Talk 20:27, 30 August 2009 (UTC)
 * Thanks :) FT2 (Talk 21:39, 30 August 2009 (UTC)


 * It's not a good idea to overdo the tuna, even if it's cooked. From the mercury poisoning article: "the consumption of fish is by far the most significant source of ingestion-related mercury exposure in humans" and "larger species of fish, such as tuna or swordfish, are usually of greater concern than smaller species".  This is especially true for certain at-risk groups (see the article), for whom the FDA recommends limiting the consumption of albacore tuna to no more than 6 oz per week, and all other fish and shellfish to no more than 12 oz. per week.  My niece developed mercury poisoning a few years ago, while in her late teens, after eating nothing but tuna fish and blueberries for 6 months (she had an eating disorder).  The symptoms of mercury poisoning have pretty much ruined her life.  Red Act (talk) 11:59, 31 August 2009 (UTC)


 * So far parasites have been mentioned, as has mercury (which is just as much of a problem in cooked fish). The other major threat of raw fish is bacteria, which is worse when they have started to decay.  This would result in the classic food poisoning symptoms of nausea, vomiting, and diarrhea.  Cooking fish properly should kill of all (or almost all) of the bacteria, but then they can regrow if it's left around too long.  There may also be some virus which can be passed from fish to a person, that I'm not sure about.  In short, cooking meat and fish is one of the best ideas humans ever invented, and skipping it seems too risky for me. StuRat (talk) 14:47, 31 August 2009 (UTC)


 * When you say 12 oz. per week, how many ounces in a normal meal, say at a seafood place down in Florida, with dinner sized fish & a side dish or two?4.68.248.130 (talk) 18:57, 31 August 2009 (UTC)
 * A typical fillet of flounder is four to six ounces, for example. --Sean 19:10, 31 August 2009 (UTC)
 * I've filets 3-4 times in a week-long vacation, but then hardly ever eat it throughout the year. that's probably safe. Your mileage may vary, though some may depend on how deep the water is it comes from, and your size; I'm pretty much average build and close to ideal weight. I love mahi mahi and grouper myself.Somebody or his brother (talk) 23:18, 31 August 2009 (UTC)


 * If you are looking for reading to put you off raw fish, this might do http://www.chow.com/stories/10163 -71.236.26.74 (talk) 16:39, 1 September 2009 (UTC)
 * Thanks, and ewww, gross.4.68.248.130 (talk) 19:01, 1 September 2009 (UTC)


 * I did a school project on sushi some years ago, and one of the more interesting tidbits was that sushi didn't emerge in Japan until the advent of refrigeration. Vranak (talk) 01:23, 2 September 2009 (UTC)

Trying to figure out the name of a car part
Hi. I was looking at a Volkswagen Passat yesterday and there seemed to be rust on part of the wheel/axle but I am not sure what the part is so I can look it up (the salesman told me that it was caused by brake dust and wasn't a problem). I can't find a clear picture of the part but it was basically a drum shape that seems to be at the very end of the axle, and has the wheel bolted to it (so it sits ust behind the hub cap). It is circular, maybe six inches deep and nine inches in diameter (very rough estimates). I wondered if anybody could help me find the name please, so that I can investigate the rust issue more thoroughly. Thanks HungryAvocado (talk) 19:55, 30 August 2009 (UTC)
 * In that area, you tend to have the wheel hub (comprising wheel bearings and a plate for mounting the wheel itself - good engineering drawings); attached to the static part of the hub are brake calipers; attached to the rotatable wheel mounting plate is the brake disk ... the calipers fit around the disk and brake pads sit within caliper. The whole thing then tends to have a metal shroud around the back of it (at least in my memory it does), and, err, that's about all there is. Any other parts in the vicinity will be suspension or steering. Does this help any? --Tagishsimon (talk) 20:06, 30 August 2009 (UTC)
 * Thanks very much, that is very helpful. The specific part where the rust was seemed to be was the cylinder that protudes from the large disk in the photo and has the holes in the end of it. Is there a specific name for that, or is it just part of the brake disk? Thanks again for your help. Thanks HungryAvocado (talk) 20:44, 30 August 2009 (UTC)


 * I think it would be described it as the moving part of the wheel hub. Compare with this car part advert. However elsewhere it appears to be an integral parl of the brake disc (brake rotos in USian) - see here. Your's probably looks much more like the second photo I've posted. IMO surface rusting here does go with the territory and in general is nothing to worry about. If the metal has started flaking away, that's another thing entirely. --Tagishsimon (talk) 21:06, 30 August 2009 (UTC)
 * And in closing the part you pointed to, on a Passat, does appear to be integral to the brake disk - and costs $36. --Tagishsimon (talk) 21:13, 30 August 2009 (UTC)
 * Thanks for all this help. For some reason the part that I saw doesn't actually look very similar to the brake disk on partstrain.com. It looks more like the original image you linked to, in the sense that the cylinder was much deeper (maybe even deeper than your original photo). I have slightly doctored the original photo here to show was the rust looked like (it was in patches and looked quite superficial). Thanks again HungryAvocado (talk) 21:27, 30 August 2009 (UTC)
 * No probs. The part you coloured plays no direct functional role; sounds like it's fine. --Tagishsimon (talk) 22:33, 30 August 2009 (UTC)
 * I know very little about car specifics - but with localised rust like that - would it be worth looking for a source - perhaps the car has been left standing for a long time and some water found a way to drip through the bodywork - hole in the wheel arch.?83.100.250.79 (talk) 00:39, 31 August 2009 (UTC)
 * Cars which have been idle (not driven at all) for even just a few days (depending on climate) will develop a rust film on their brake discs. This is extremely common, and disappears within a few miles of driving as the brakes are used again.  Here are some forums where this is discussed:     with some posters reporting rust appearing within days or hours after the discs get wet.  Nimur (talk) 01:17, 31 August 2009 (UTC)


 * I wish there was a International Standard Part Number (ISPN) that was stamped on every manufactured item, not just for car parts, like an ISBN number for books. This would make getting a replacement part from eBay or whereever so much easier - I speak from experience. If a non-standard alphabet was used that had 50 or 60 characters rather than the traditional 10 or 24+9, then the ISPN need not be very long. 78.147.28.17 (talk) 10:31, 1 September 2009 (UTC)