Wikipedia:Reference desk/Archives/Science/2008 June 13

= June 13 =

Any ideas on how to create a concrete sign?
Sorry I wasn't sure where to place this, but I thought science would be good because of physics/construction. So, I'm trying to create a concrete sign for a community organization. This is the type of signs I mean: http://www.centurygrp.com/precast_detail.asp?id=1

It doesn't need to be as "showy" as some of the ones on there, but still it's going to be a decent sized concrete sign. Problem is, I'm not really great at this stuff, and I'm not sure how to get started. I already have a location to construct this on (the base is present). I'm figuring I'd need to use bricks to create the frame around the sign. Would I need metal supports or something in the inside? Also, I have no idea on how to create the sign itself. Any suggestions will be much appreciated.

Thank you very much. —Preceding unsigned comment added by Legolas52 (talk • contribs) 04:33, 13 June 2008 (UTC)


 * These signs look highly developed. Without knowing what you expect to do (such as lettering in the concrete or external to it, colouring the concrete with pigments before mixing, the dimensions etc), there are companies via google that sell many styles of molds from precast stone and timber onwards (search precast concrete molds); you can even talk to them via email to research your project, and we have a tiny article Precast concrete for background. If yours is a tight budget and a rustic finish is acceptable, you can form by cutting a shape into earth and pouring directly or avoid casting by making a brick structure that you are happy to render. You can make a form box the size and shape you want, pour cement into it and presto – use an angle grinder and coarse metal file for finishing touches. Pigment colours are mixed dry before adding water etc. Your local hardware store could help with questions too. Hope this helps, Julia Rossi (talk) 09:13, 13 June 2008 (UTC)


 * And let me add, if it isn't already obvious, that the face of the sign would be in the bottom of the mold or form. The cheapest way to create a form would be to carve it out of Styrofoam, but this might not hold up to the weight of a thick concrete sign.  You could put liquid or powdered pigments in the bottom of the letters in the form to get the desired results.  And yes, there should be metal inside the concrete.  It's called rebar (reinforcement bar) and should be in the form of a three dimensional grid (or two dimensional, for a thin sign).  You might also want some heavy duty hooks, attached to the rebar, sticking out of the back of the sign, for easy handling.  You will likely need to let it set for several rain-free days (cover it with a tarp, being sure to keep the tarp from touching the concrete, if rain is expected).  If you are new to this, I'd expect to take several tries to get it right.  (Although, if only the coloring is bad, you could opt to paint it to cover the imperfections.  Beware that the paint won't last as long, though, requiring a repaint every few years.) StuRat (talk) 11:38, 13 June 2008 (UTC)


 * A couple other comments. Don't use water-based pigments and avoid concrete mixes which have loose chunks of metal in them.  The pigments will run and the iron will rust and look horrid.  In case you don't already know this: you need to pour the concrete right after mixing, so be ready to do so. StuRat (talk) 12:08, 13 June 2008 (UTC)


 * Make sure the sign is stable (not top heavy) so that if the base settles unevenly, or if someone pushes it it cannot fall over and crush someone. Children have been killed by old tombstones falling over. If you mold it flat, calculate how much it will weign and plan to have a way of lifting it. It could wind up being very heavy. Concrete often leaves voids when poured: sometimes a vibrating device it used to get it to fill in all the areas. Concrete mix (with gravel) is generally stronger, but sand mix would be needed to fill in fine details. The form has to be lubricated. Edison (talk) 13:15, 13 June 2008 (UTC)
 * And practice several times on smaller scales before going for the final job. 200.127.59.151 (talk) 14:13, 13 June 2008 (UTC)

Black hole confusion
I'm a little confused about what happens to you when you fall into a black hole. My understanding is that an outside observer sees a object take an infinite amount of time to cross the event horizon as the time dilation goes to infinity. An observer falling into the black hole sees itself take a finite amount of time to reach the singularity. My questions are: Does this effect apply to photons, and other objects without rest mass? If an outside observer never sees anything cross the event horizon, how can the black hole ever gain mass? On a related note, what happens when two black holes have overlapping event horizons? Does a region of "safe" space form between them? Outstairs (talk) 06:17, 13 June 2008 (UTC)


 * Your understand is correct. Photons falling into the black hole can't be observed from outside it, since the photons have to hit your eye for you to see them, photons emitted from an object falling into the black hole will be redshifted, and the redshift will tend towards infinity as the object approaches the event horizon (in the same way time dilation tends to infinity). To be honest, I'm not entirely sure how the time dilation thing fits with the black hole gain mass - I suspect that, from the point of view of the outside observer, the black hole's mass is whatever it was when it formed, but the mass of the accretion disk increases, so the mass of the whole thing is what it ought to be. From the point of view of the person falling into the black hole, it's all perfectly normal. The way two black holes interact (especially when merging) is an area of active research, and I know very little about it. Even if there was a region that wasn't causally disconnected from the rest of the universe (ie. you can leave it), the tidal forces would be enormous, so it still wouldn't be "safe". --Tango (talk) 12:54, 13 June 2008 (UTC)


 * There are a couple of things stopping a person from even getting close to the event horizon. The event horizon is surrounded by a very hot accretion disk. These disks are usually much hotter than the sun. The size of the accretion disk also tends to dwarf the event horizon, even if the event horizon is enormous as is the case with super massive black holes, the accretion disk is still much bigger. There's also a tremendous amount of radiation. So the heat, combined with the radiation make it impossible for a guy in a spacesuit to ever come close to an event horizon unless he's invincible. Both of these come into effect before tidal forces are present btw. ScienceApe (talk) 16:38, 13 June 2008 (UTC)
 * The accretion disk is, as the name suggests, pretty flat, so if you approached the black hole from one of the "poles", you would stand a better chance (unless there's a jet coming out of the pole, of course, which I believe there is in cases). If you pick an old enough (isolated) black hole that has already sucked in its accretion disk so that it's all extremely close to the event horizon (from the perspective of an outside observer), all the radiation from it will be redshifted to harmless levels. --Tango (talk) 19:19, 13 June 2008 (UTC)
 * Like you said, there would still be polar jets. I don't think we know of any black holes without accretion disks. The accretion disk is primarily how we detect them in the first place. It is actually possible to orbit a black hole indefinitely, without ever being sucked in. I don't see why this wouldn't apply to some of the matter in an accretion disk, especially considering the size of the disk, which can extend very far out. I should really emphasize the size of these accretion disks. If you were to look at a black hole from a safe distance, you probably wouldn't even see the event horizon, because it would be dwarfed by the much larger accretion disk. It's THAT big. ScienceApe (talk) 20:00, 13 June 2008 (UTC)
 * From the point of view of the matter in the disk, it will get sucked in eventually, from the point of view of an external observer, it won't, since nothing can. I'm not sure what your point was, though... As far as I know, you can have black holes without accretion disks, we just can't detect them. You put a large star in an isolated region of space, let it go supernova and the core collapse into a black hole, that black hole will then pull all the rest of the matter star (except for anything that escapes) in towards it and eventually there will be none left that is far enough from the event horizon to be observable from the outside universe (it will still be there, just extremely redshifted). --Tango (talk) 20:15, 13 June 2008 (UTC)
 * Hypothetically I guess there can be black holes without accretion disks. Thing is, as long as the matter around a black hole sustains orbital speed, it won't fall in. It will revolve around the black hole indefinitely. So in practice, there will always be an accretion disk around the black hole. ScienceApe (talk) 22:51, 13 June 2008 (UTC)
 * If it's not falling in, it will be cold, so there's no need to worry about it. If it's radiating heat, then it's losing energy and falling in. --Tango (talk) 22:58, 13 June 2008 (UTC)
 * Not at all, the accretion disk is hot because of friction. The matter is colliding with each other. It can still be hot and maintaining orbit. ScienceApe (talk) 02:27, 14 June 2008 (UTC)
 * The energy has to come from somewhere. When the bits of the disk rub together, their kinetic energy is turned into heat energy and then radiated as photons. If it's emitting radiation, it must be losing energy, and therefore spiralling down. (Obviously, it can radiate energy because of heat it had before it entered the disk, but that's a negligible consideration.) --Tango (talk) 15:42, 14 June 2008 (UTC)
 * Point taken. But like I said before, if the black hole has an accretion disk, then you can't approach the event horizon without dying. ScienceApe (talk) 18:31, 14 June 2008 (UTC)
 * This has been asked many times on the reference desk before. One of the best answers is in this thread.  Sp in ni  ng  Spark  22:33, 13 June 2008 (UTC)

earth's magnetism
does earth have null points[since it behaves like a magnet]? if so where are they? —Preceding unsigned comment added by 59.92.248.129 (talk) 08:11, 13 June 2008 (UTC)


 * There are certainly "imperfections" in Earth's magnetic field, but I'm not sure your "null points" terminology is in standard use. The simplest model is a dipole or offset dipole (i.e. assuming the earth's magnetic field is a "bar magnet" centered at either the exact center of the planet or somewhere else to better fit measured data).  Beyond this, you may want to read on the International Geomagnetic Reference Field model: here's a page from NOAA describing it in detail.  You may also be interested in the South Atlantic Anomaly; theories to explain this geomagnetic feature vary wildly.  Nimur (talk) 10:57, 13 June 2008 (UTC)


 * See Earth's magnetic field. There is a measurable magnetic field everywhere, though there are low strength fields around the south Atlantic. --  k a i n a w &trade; 11:24, 13 June 2008 (UTC)


 * Also, the Earth's magnetic field isn't constant. When it's about to invert it becomes quite sporadic, with null points and points with the reverse of the expected field all over the place. StuRat (talk) 11:26, 13 June 2008 (UTC)

How can I know if a telephone is also touch tone?
Are all cell phones also touch tones? —Preceding unsigned comment added by 80.58.205.37 (talk) 12:03, 13 June 2008 (UTC)


 * I don't think that term really applies, since they likely don't send the phone number as an audio signal at all (either as tones or clicks), but as a digital code, instead. However, after you connect to your party, I'd expect to be able to send audio touch tones so you can navigate phone message systems.  For example: "Your call is important to us, although obviously not important enough to actually answer ... Press 1 if, for some strange reason, you speak English". StuRat (talk) 12:16, 13 June 2008 (UTC)


 * I think you mean "Press 1 if, unlike us, you speak English." :-) --Anon, 22:20 UTC, June 13, 2008.


 * (Edit conflict) Cell phones transmit their dialing information to the network digitally. But once a call is established, they'll generally emulate a Touch Tone phone and transmit the correct audio boops and beeps so that automated call response systems work as you'd expect. So yes, in the way that you probably care about this, they are all "Touch Tone".


 * Atlant (talk) 12:24, 13 June 2008 (UTC)


 * Actually, in many cases, cell phones work better with automated systems that are expecting analogue DTMF tones. A lot of modern POTS (analogue phones) output the DTMF tone for a short burst of predetermined duration.  This can cause problems, especially on noisy lines, because the server at the other end had insufficient time to decode the tone.  This is not generally such a problem with older models which will carry on outputting the tone for as long as you hold your finger on the button; so the human can compensate for the bad connection by putting out longer bursts.  Cell phones also (most models anyway) tend to follow the old scheme of "tone while button down".  Not sure why this is, possibly because cell phones by there nature have greater problems maintaining a good connection and the sesigners are trying to compensate.  Sp in ni  ng  Spark  22:19, 13 June 2008 (UTC)

raccoons
I live in an area near a river where raccoons come into the neighborhood looking for dog and cat food or kittens or whatever else they can find to eat. Whenever someone leaves a bucket or other container out and it fills with rain water they make a habit of pooping in it. What might be the reason for this behavior? -- Taxa  (talk) 13:06, 13 June 2008 (UTC)


 * Raccoons are not dumb. They know that standing feces can cause a lot of health problems.  So, the defecate in water to keep it away from where they may step.  If no water is available, all raccoons in a group will tend to defecate in the same spot to keep it localized.  This is not unique to raccoons.  Non-domesticated animals try to be clean.  Even my hedgehogs will go in a litter  box to keep their area clean.  This came up on Futurama:
 * Fry: Psst! Leela! You've got to get me out of here! It's horrible! Eating scraps; letting my waste drop wherever it falls, like an animal in a zoo!
 * Leela: Animals go in the corner.
 * Fry: The corner! Why didn't I think of that?
 * -- k a i n a w &trade; 14:39, 13 June 2008 (UTC)


 * Come now. Just because an animal is "not dumb" doesn't mean it has sufficient capability for abstract thought to know that some practice "can cause a lot of health problems". Much more likely we are talking about instinctive behavior, or behavior taught in infancy, resulting from natural selection.  (I use the term broadly here, not limited to genetically determined traits as that article applies.  In other words, it could be that raccoons that learned to do this live longer and have children that observe them doing it and copy it.)  --Anonymous, 22:28 UTC, June 13, 2008.


 * I don't think that what you're are seeing in the water is their "poop." Normally raccoons have communal defecation sites (latrines), often at the base of trees or on flat elevated surfaces. It is true that containers of water accessible to raccoons look as if they have been defecated into. However, what you are most likely seeing is the dirt and other foreign materials that result from their habit of "washing" or "dousing" their food in water. They do not always put their food in water before eating it, and there seems to be no concensus as to the function of this behavior. Take a look at these links with regard to where racoon "latrines" are located. --Eriastrum (talk) 21:20, 14 June 2008 (UTC)

Shovel-Shaped Incisors
Why do Asians (mongoloids) have shovel-shaped incisors? A friend of mine says it is because they evolved to subsist on a diet that contained less meat and more vegetables.

Are there any other modern animal species, besides humans, that have shovel-shaped incisors? 71.231.122.22 (talk) 13:26, 13 June 2008 (UTC)


 * Your friend has the cause and effect of evolution backwards. Animals do not evolve to serve a purpose.  They purposely attempt to fill a niche in the environment and evolve to better fill that niche.  So, your friend is actually claiming that the Asians found more vegetables than meat and attempted to fill the primarily vegetarian niche in their area and, as a result, evolved shovel-shaped incisors to better fill that niche.  A quick scan of medical studies on this topic shows that it was suggested that this evolutionary trait was a result of a vegetarian diet.  However, most studies refute that claim and leave the trait to a pure chance mutation.  Otherwise, it would be reasonable that more vegetarian-based cultures would develop the same trait. --  k a i n a w &trade; 14:31, 13 June 2008 (UTC)


 * See genetic drift. ScienceApe (talk) 16:44, 13 June 2008 (UTC)


 * BTW, quite a large number of Asians are not mongoloids Nil Einne (talk)`

Big red ant!
I just flushed a large red ant from my apartment. I've been having an ant problem, but, so far, they've all been the usual small black ants. This is the only one I've (ever) seen like this. It was nearly an inch long and a light/bright red color all over. It had no wings (thankfully). When I first saw it, it was so large, I didn't expect it to be an ant, but up close that's certainly what it seemed to be. Unfortunately, I don't have any pictures to show.

Naturally, I was wondering if anyone here might know what it was. I live just outside Washington, DC, in a heavily wooded area (Takoma Park, MD). Or, maybe someone could point me to a list of local species?

Thanks! &mdash; 68.49.3.251 (talk) 15:24, 13 June 2008 (UTC)


 * It's swarming time and you probably encountered a queen who has shed her wings.


 * Atlant (talk) 16:03, 13 June 2008 (UTC)


 * Perhaps it was a Mutillidae? (Although not an ant, they do appear as one.) Ζρς ι'β' ¡hábleme! 19:14, 13 June 2008 (UTC)


 * Is Dorylus fulvus found in the US (as an invasive species, that is)? The males a.k.a. drones a.k.a. "sausage flies" are by far the largest ants I've ever seen. They are up to an inch long and brownish-red, definitely matching what you say. They have wings when they fly, but AFAIK the workers chew the males' wings off as soon as the males land nearby. There are pics of Dorylus drones on the net. Is that close to what you saw?! I've never heard of Dorylus in the US, but if it is one, I'd be concerned. --Dr Dima (talk) 22:07, 13 June 2008 (UTC)

fruit contamination
Is it possible for bacteria to enter intact fruit through the root system? —Preceding unsigned comment added by 1022wcharles (talk • contribs) 20:44, 13 June 2008 (UTC)


 * Biology isn't my area, but Plant disease might give you some useful information while you wait for an expert. --Tango (talk) 20:54, 13 June 2008 (UTC)


 * I would think it would be possible, but unlikely. Bacteria entering through intact roots would be like bacteria entering your body through intact skin.  It's possible, but first the bacteria would have to set up a colony on the surface and sufficiently damage the surface so that it could gain entry. StuRat (talk) 23:27, 13 June 2008 (UTC)
 * Old research showed E. Coli on tomato seeds ending up 6 cm up the stem later. good article at www.cdc.gov/mmwr/preview/mmwrhtml/mm5413a1.htm Polypipe Wrangler (talk) 00:11, 19 June 2008 (UTC)

water pressure
If I had a column of water 1 millimeter in diameter and 1 mile tall, would the pressure at the bottom of the column be the same as the pressure at the bottom of a column 1 mile in diameter and 1 mile tall? Nadando (talk) 21:03, 13 June 2008 (UTC)


 * That's correct. The volume of water in the container isn't what creates pressure at any point inside the volume; it's the height of the volume above the measurement point that matters. Imagine dipping a 1-mile hollow tube, open at both ends vertically into the ocean. The pressure inside the bottom end of the tube will still be the same as the pressure outside the bottom end of the tube.
 * However, when you get down to a really small-diameter container (less than the 1mm in your example), friction and capillary action are the dominant forces, not gravity. Make the diameter small enough, and water can simply stick to the sides, completely filling the container, no matter how tall it is. ~Amatulić (talk) 21:10, 13 June 2008 (UTC)


 * Presumably that means there is significantly less pressure in a capillary? So the answer to

the OPs question would then be no, its different?  Sp in ni ng  Spark  21:57, 13 June 2008 (UTC)


 * Amatulic said a capillary was narrowing than 1mm, which would mean in the OP's case, they would be equal. --Tango (talk) 22:27, 13 June 2008 (UTC)


 * Its not exactly an on/off effect. It just diminishes with increasing diameter according to inverse R which you can see in the article.  So there is still a noticeable effect (the article says 0.5mm will lift 2.8mm of water) at 1mm.  The effect on pressure is going to be small but it must happen surely?, otherwise the water would not rise.  Sp in ni  ng  Spark  01:01, 14 June 2008 (UTC)

On June 29, 1973, in Philadelphia, a task for liquefied natural gas was under construction. Its main structure was 85 feet high (25 m) and consisted of a 5/16 inch (8 mm) steel liner surrounded by an 8-inch (20 cm) prestressed concrete wall. The space between the steel and the concrete,as built, was only 1/100 inch (0.25 mm) thick -- but when water accidentally got into it, the pressure at the bottom was enough to push the concrete out of position. Of course, this then widened the gap and more water got in and the concrete continued to shift. (Source: Design and Construction Failures: Lessons from Forensic Investigations by Dov Kaminetzky, published 1991 by McGraw-Hill, ISBN 0-07-033565-6. More precisely, my source is notes taken when I had that book out of the library.)  --Anonymous, edited 22:49 UTC, June 13, 2008.

Addicted to you
Hello smart wikipeoples. Could all psychological addictions (i.e. those lacking the presence of psychoactive substances) be considered addictions to dopamine (and certain endorphins)? Thanks in advance, Kreachure (talk) 22:44, 13 June 2008 (UTC)

What's wrong? Too dumb? Too hard? Makes no sense? Please, say something about it! (This is the only unanswered question right now in the desk, and it's been so for almost a day!) Kreachure (talk) 20:25, 14 June 2008 (UTC)


 * Patience is a virtue, right? I don't really know much about the topic but for example say if you were addicted to sex then the only thing involved in 'how you feel' is endorphins, so yes, it could be assumed that the addiction was to endorphins as that provides the feeling. Regards, CycloneNimrod talk? contribs? 20:56, 14 June 2008 (UTC)
 * The Wikipedia article for addiction states in the first line: "Addiction is a state in which the body relies on a substance for normal functioning". Considering that all humans and many other species are reliant on dopamine/endorphins you could say they are all addicted.
 * What I'm guessing instead is that your argument has spawned from something like: "Bob has sex a lot. Bob says he is addicted to endorphins". Apart from the issue that sex doesn't just involve endorphin release (i.e. oxytocin), you have to realise that animals strive for homeostasis, and behaviour such as addictions can be seen as decisions made as a result of calculations by the brain, in order to maintain homeostasis. --Mark PEA (talk) 23:12, 14 June 2008 (UTC)
 * Hmm, I'd rather consider addictions of any kind to be behavior against homeostasis, since your body goes out of control all over from an excessive yearning for substances it doesn't really need... which could lead to a total system imbalance and breakdown, in fact. Kreachure (talk) 23:49, 14 June 2008 (UTC)


 * I disagree. If an individual has a dependency on a substance, then their body seeks that substance for balance in a fairly literal sense. Homeostasis is really a physiologic term that describes the internal chemistry of an organism, so it isn't well used in a discussion about psychological dependency. A good example of the evidence for homeostasis in physical dependency is withdrawal, which is the collection of symptoms that result from an addict not receiving their fix. Withdrawal can kill. But back to the original question, I don't think all psychological addictions can be classified under any umbrella cause. You are barking up the wrong tree to begin with by assuming that all similar psychological states can be rooted back to the same neurological cause. Although dopamine and endorphins have been linked to neuroligical reward mechanisms, the fact is that sometimes psychology is just way to complicated to be boiled down to simple brain chemistry alone, such as indicting one chemical or another. For example, psychological dependency is often characterized behavioristically, as a "habit" (hence warnings that some drugs may be habit-forming). --Shaggorama (talk) 06:52, 15 June 2008 (UTC)

Thanks. I guess I made the mistake of reducing psychological states to simple physiological and neurological dynamics, when it's definitely not that 'simple'. Kreachure (talk) 15:18, 15 June 2008 (UTC)