Wikipedia:Reference desk/Archives/Science/2009 October 29

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October 29

Effect of smokeless tobacco on dental health

What effect, if any, does smokeless tobacco (in general) have on dental health? Please answer from a dental practitioner's perspective, if possible. Thanks, ♠The Ace of Spades_(talk) 01:52, 29 October 2009 (UTC)

Wikipedia does have articles on smokeless tobacco, however looking though them, especially the one on Dipping tobacco, it appears the article has been entirely whitewashed by tobacco apologists. There are no actual links to any hard, independent studies into the health effect of dipping; the entire health section merely spends its time refuting studies which it gives no space towards reporting the results on. Sadly, Wikipedia may not be the best place to get accurate information on this. --Jayron32 01:58, 29 October 2009 (UTC)

Nevermind, managed to find something elsewhere, thanks for the tip on that. Though this may not be the place to discuss it, should the dipping tobacco article be tagged with anything because of the said whitewashing? ♠The Ace of Spades_(talk) 02:13, 29 October 2009 (UTC)

Although the overall lifetime risk of malignant transformation in chronic users of smokeless tobacco is <1%, smokeless tobacco is carcinogenic and in addition to being associated with squamous cell carcinoma, verrucous carcinoma is uniquely associated with the use of smokeless tobacco. Additionally, smokeless tobacco may lead to gingival recession and is a modifying factor in periodontal disease, halitosis, staining and a possible increase in dental caries. Harmful constituents are readily absorbed into the oral mucosa with which they are in direct contact. Oral submucous fibrosis, of similar pathogenesis, is related to the chronic use of betel quid/areca nut, used by people in/of India, Pakistan and surrounding areas of Southeast Asia. Of submucous fibrosis cases, approximately 10-15% show epithelial dysplasia and roughly 8% exhibit squamous cell carcinoma. (All info from oral pathology course lecture notes, NJDS) DRosenbach ^{(Talk | Contribs)} 02:37, 29 October 2009 (UTC)

Thanks so much, that's exactly what I needed. Better than what I found online. ♠The Ace of Spades_(talk) 02:44, 29 October 2009 (UTC)

Human Hearing Range in Nature

Are all the frequencies in the human hearing range (12Hz-20KHz) present in humans' habitable biosphere, apart from what's produced by recent technology? If not, why/how did humans evolve to be able to hear them? --Codell^Talk 04:55, 29 October 2009 (UTC)

While lacking the time to find and cite sources, I think it is safe to say yes, all frequencies between 12Hz-20KHz occur in the natural world humans live, and lived in. Pfly (talk) 09:32, 29 October 2009 (UTC)

Only a small range of frequencies about 300Hz - 3kHz is really needed to communicate using speech (e.g. used in telephones) and human hearing has evolved greatest sensitivity in this range, arguably because of the survival value of a parent hearing the cry of their baby.Cuddlyable3 (talk) 10:29, 29 October 2009 (UTC)

Greatest sensitivity maybe in that range, but a telephone quality sound is hardly high. Perhaps the ability to hear higher frequencies results from these other frequencies being present as harmonics? I have no evidence to back this up its just a thought. —Preceding unsigned comment added by Alaphent (talk • contribs) 14:25, 29 October 2009 (UTC)

Hearing higher frequencies has survival value because they aid localization of sound sources. Many sounds have harmonics beyond the human hearing range, the upper limit of which drops way below 20kHz as one ages.Cuddlyable3 (talk) 19:57, 29 October 2009 (UTC)

The sound of the ocean coast is an extremely good source of white noise which contains that whole range of frequencies. I'm thinking wind in a forest would too, maybe wouldn't go as low as ocean but it would probably still pass. Vespine (talk) 21:43, 29 October 2009 (UTC)

So maybe being able to hear the white noise of the coast and wind through trees would be beneficial for humans as both were a source of food. Might cultures who have lived for a long time in desert regions therefore have a lower upper hearing range? --Codell^Talk 00:09, 30 October 2009 (UTC)

Well first of all, humans didn't actually evolve hearing so I think that's where your first misconception lies. Hearing has been around a long long time since before humans so it's quite probable we just inherited our range from our ancestors. Also, don't fall into the trap of thinking that every single observable trait in every species must have been the result of some selective pressure or evolution. Amongst others there are traits which are vestigial which are seemingly useless traits left over from past evolution, like goose bumps, if there is no real pressure to get rid of the trait there is no reason for it to disappear if it is not very costly to the organism, and also there are associated traits which can also seem useless but are somehow genetically linked to other seemingly unrelated traits which do have a good use. Vespine (talk) 04:28, 30 October 2009 (UTC)

Good point. I'll also note that hearing higher frequencies could have survival value because it helps us discriminate between different sounds. You can tell a violin from a trumpet when they play the same note because the overtones are different -- the same might apply to sounds in nature that it's desirable to tell apart. --Anonymous, 19:09 UTC, October 31, 2009.

Counter circuit Photo-Electric Beams

I want to design a counter using laser beams. The purpose is such that if someone enters the room they are added to the list. If they move out the it they are removed from the count. If the count is 0 then it switches off the lights, if it is more than 0 it switches on lights.--yousaf465' 08:11, 29 October 2009 (UTC)

You might construct your counter by soldering some logic integrated circuits on a small circuit board. The counter itself could be a 4516[1] which being 4-bit limits the count to 15 7 persons. If you need to store larger numbers of persons use more counter stages. Detecting whether a person comes in or out needs two photocells and lasers. With a 4013 dual flip-flop you can store the first photocell pulse then the second pulse clocks the counter and the order of the pulses determines the count direction up or down. The empty=0 state of the counter controls the lights. This logic circuit runs from say 5V so it needs interfaces to the small signals from the photocells, possibly made with op-amps[2] like 741Operational amplifier, and to the lamps. If the lamps are mains powered then you need an optoisolator[3]+triac[4] or a relay to control them safely from your 5V logic signal. When the counter is full=15 7 or empty=0 it must be disabled from counting further in the relevant direction. The references give more information and there are many alternative components.Cuddlyable3 (talk) 10:23, 29 October 2009 (UTC)

Thanks for the answer. I will look into it.--yousaf465' 12:46, 29 October 2009 (UTC)

The usual way to achieve this is to install a cheap passive infrared sensor in the room rigged up to switch off the lights if it detects no movement for, say, seven minutes. You find such systems in public buildings etc, so they must be available off the peg.--Shantavira|^{feed me} 16:00, 29 October 2009 (UTC)

What if I want to sit alone in the OP's room and read a book for 8 minutes? Cuddlyable3 (talk) 19:52, 29 October 2009 (UTC)

Then every 7 minutes you wave your hands around like a maniac when the lights go off. (It's how it is done in universities, which often have such features.) --Mr.98 (talk) 00:40, 30 October 2009 (UTC)

This will help with exercises. --yousaf465' 02:52, 30 October 2009 (UTC)

• How should it be stopped from counting further if it's empty ?--yousaf465' 02:57, 30 October 2009 (UTC)

Please see my circuit below. I limited the counter to 7 persons so that Q"8" limits the up count at 7, and CARRY limits the down count at 0. Cuddlyable3 (talk) 21:09, 30 October 2009 (UTC)

I'm sorry to say that what you propose won't work. With just one beam you can't tell whether the person is arriving or leaving - and you can't tell when someone steps into the beam - changes their mind and steps back again. You need at least two beams - then the order of breaking and unbreaking of the beams will tell you which direction the person crossed the beam - and whether they changed their mind again. But this is still not perfect - when one person enters at the exact same time that another person leaves - you can't know what happened.

At the heart of the problem here - if your counter EVER gets confused - even once - it'll either turn the lights off when one person is inside the room (and be extremely difficult to pursuade to turn them back on again) - or it'll turn the lights on with nobody in the room and refuse to ever turn the lights off again.

The difficulty with such systems is that you are trying to measure an absolute quantity (the number of people in the room) using a relative measurement (the number of people entering and leaving) - and any system like that that has any possibility of error whatever will gradually accumulate error until it's useless. In your case, it'll happen rather quickly...the very first time two people pass in the doorway for example. Even if you could sort out that case, you also have the problem if the power fails and your system has to restart - because you have no idea how many people are in the room to start with.

So at a minimum, you'll need a switch to say "Stoopid computer - you turned the lights off and I'm still here" or "Hey - turn the lights off, there's nobody in here!" - and perhaps some logic to (for example) turn the lights off after they've been on for a very long time. At least that provides some means for the system to recover from occasional errors.

The simplest way to implement the complex logic required would be to use a little 'Arduino' computer - you can buy one all ready to run on a circuit board for $25 - and if you can make your own circuit-board, you can buy just the chip for less than $5. You can write simple programs for it on your PC in C/C++ and download them into the computer using a USB port. With software involved, the complicated rules about breaking and unbreaking beams would be easy to set up. You could do timing and add software to try to decide when things have gone astray. You could even add a photosensor to turn the lights off during the day. You could do it with hard logic components - but you'll never do that for less than the cost of an Arduino chip.

A much, MUCH better solution would be something like a burglar alarm - something that detects motion or body heat or sound or floor pressure or something. Those are absolute measurement devices - not relative like a "number of people who went through the door" detector. Of course a cat can fool a motion detector, leaving the TV turned on in the room can generate enough heat to fool a heat sensor - ditto with sound detectors - and moving the furniture around can fool a pressure sensor.

This is actually a really tough problem to solve - which is probably why such systems aren't fitted to every home on the planet.

At our offices at work, we have a RFID tag system that does that. You have a little plastic tag that you put in your wallet - it gives you access to the front door and to the elevator - and when you're within range of any of the detectors scattered around the offices, the lights in the area come on. When you aren't, they go off. If nobody is near a detector, the airconditioner turns off too. It works fine - just so long as you don't lose your RFID tag. My car (a MINI Cooper'S) has a similar system. You just need the circular "remote" (it's not really a "key") in your pocket and it unlocks and locks - and allows the engine to be started with a simple push-button - and it'll turn off the radio and the lights and lock the doors when you get more than a few feet from the car.

Having people carry something that can be detected uniquely at a distance is the answer.

SteveBaker (talk) 12:53, 30 October 2009 (UTC)

Yes I was also looking for a 2 beams system. I will upload the diagram how I visualized it. Also for washroom we can even eliminate the counter, after all you can't have more than one person in a washroom. :)

Well for power I will be using rechargeable batteries.

I'm also interested in RFID but for my cat. How much that system cost. --yousaf465' 04:40, 30 October 2009 (UTC)

Any Fritzing diagram could be helpful.--yousaf465' 05:06, 30 October 2009 (UTC)

The problem isn't going to be fixed with two beams - or three or four for that matter. There are just to many ikky cases that can cause your system to miscount - and it only has to miscount by ONE and it'll be wrong forever more (unless you reset the machine somehow). Because people don't neatly cross beams like that (they may break it first with one arm, then their body and then the other arm, for example - or someone may wave their hand through the beam to see what it does - or they might be wearing a thick, fuzzy sweater that gradually breaks the beam causing a lot of rapid on/off pulses that could easily be miscounted. Any one of these behaviors (and worse-still, any of the two dozen others that we haven't thought of) will cause at least a single miscount - and that's enough to leave you sitting alone in the dark - or having your light left on 24/7. It's not just a tiny problem that you can just blindly ignore - it's the total downfall of the entire proposal. Getting rid of the counter for a single-occupancy area doesn't help that - all it is act as a one-bit counter...it can still get confused and once it's in the wrong state, there is nothing to correct that error. In short: IT WON'T WORK! SteveBaker (talk) 12:52, 30 October 2009 (UTC)

What about any system which works.--yousaf465' 13:01, 30 October 2009 (UTC)

A computer with a webcam and face recognition software (or perhaps recognition of more general features such as clothing or height) could be made to recognise individuals, ambiguous entry and exits and count them correctly. Trevor Loughlin13:39, 30 October 2009 (UTC)

That'd be a rather clear-cut violation of the KISS principle. Red Act (talk) 15:18, 30 October 2009 (UTC)

What I think would work great would be a motion sensor in combination with a one-beam doorway sensor. The motion sensor should be positioned such that it doesn't quite cover the doorway. The system keeps the lights on, unless the doorway sensor was triggered more recently than the motion sensor, and it's been at least 7 minutes since the doorway sensor was triggered.

A system like that would be better than just a motion sensor, in that it isn't necessary to at least wave your arms every 7 minutes in order to keep the lights on. And it's better than just a doorway sensor, in that there's no count maintained that could easy get off by one.

With a two-sensor system like that, if the system does wind up in an incorrect state, it's easy to fix without needing any additional user interface. If the lights are off incorrectly, because you've been sitting motionless in the room for seven minutes after someone else left the room, you just wave your arms to turn the lights on and put the system back into a correct state. Or if the lights are on incorrectly, because someone thought it'd be funny to leave the room by crawling under or stepping over the beam, you just walk into and out of the room to put the system back into a correct state, and the lights will go out seven minutes later. Red Act (talk) 14:47, 30 October 2009 (UTC)

I agree that's a better approach - you need some kind of absolute way to determine if there is someone in the room. Incrementing and decrementing a counter is not the answer. The problem is that humans are tough to recognise electronically. A curtain blowing in the wind from a partially opened window - or a rotating ceiling fan will trick most motion detectors. Pets will also trigger them. I agree that using a beam-breaking system in conjunction with the motion detector will work much better than either of them alone - but I strongly suspect you'd still find the light turned on when it shouldn't be a bunch of times. The only approach that I'm aware of that's used 'for real' is the RFID tag system. That (in effect) modifies the concept of "what is a human?" to be something that computers can easily understand. Of course it's still gonna fail if everyone keeps their RFID tag in their wallet - and then leaves the wallet on the table when they leave the room. SteveBaker (talk) 16:33, 30 October 2009 (UTC)

Approach #1: Treat the OP with WP:AGF. He wants laser BEAMS. Approach #2: Tell the OP they don't really want what they say they want and instead try to sell them these. I'm doing Approach #1, see image. Cuddlyable3 (talk) 21:02, 30 October 2009 (UTC)

Room Occupant Counter Cuddlyable3 (talk) 21:02, 30 October 2009 (UTC)

Well I would like anything which works, not only laser beams. Red Act's approach could be more useful if a simple diagram could be shown.--yousaf465' 04:06, 31 October 2009 (UTC)

In that case install a false floor resting on rubber blocks. When someone is in the room their weight depresses the floor that operates a microswitch that turns on the light. Cuddlyable3 (talk) 14:51, 31 October 2009 (UTC)

Well I don't want my floor to be damaged. I have to do it practically.--yousaf465' 13:13, 1 November 2009 (UTC)

Raisin aversion

There are cereal mixtures with "no raisins added". Food aversion (exception allergic reactions, toxicity) are socially transmitted (e.g. food taboos). Is there a biological reasion why some people dislike raisins? --Grey Geezer 11:39, 29 October 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

Wait. Do you really think "disliking raisins" is the same as a "food taboo"? I think you are mixing raisins with apples here. If you instead want to ask "why do different people have different likes and dislikes (including food)?", it all ends up imho in a "nature vs. nurture" debate. Some genetic differences might be present (e.g., in olfactory receptor equipment of the individual in the case of food), but the individual experience also has an impact of what we learn as pleasant or unpleasant, in an often unpredictable way, for example, because subconscious perception can influence our "wiring" in the brain without us ever knowing. --TheMaster17 (talk) 12:19, 29 October 2009 (UTC)

Food aversion is not just socially transmitted. Variation in food preference is part of behavioural diversity which is a portfolio evolutionary strategy, especially when you are not talking about main staple diet. It is not obvious in evolutionary terms that raisins pose no risk to people, after all they pose a risk to dogs see Grape and raisin toxicity in dogs, are stale food and look like animal droppings. So some of us being programmed not to gorge them on sight is perhaps safer for humanity than if we were all inclined to love them to bits. --BozMo talk 12:22, 29 October 2009 (UTC)

It was not about "disliking" it was about "aversion" ("I can't eat that!"). Found another article where there was an association with "an animals teat" (but how many children have actually seen an animals teat?). So I settle for "Looks actually like a ... naah! I can't eat that!". Case closed. Grey Geezer 13:10, 29 October 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

One of the most extensively used experimental procedure in memory study (at the molecular level) in rats is CTA. It appears that if rat experienced physical bad feeling after tasting new food it will never taste it again, as long as the feeling starts in no more than 8 hours delay from eating it. This is also the answer for why seek rats avoid eating, i.e., it will make wrong connection between good food and its seekness. And this is also the reason for which rat poison is slow working --Gilisa (talk) 13:13, 29 October 2009 (UTC)

We humans are so smart. Bus stop (talk) 13:20, 29 October 2009 (UTC)

Nope, it take us more times to develop CTA.--Gilisa (talk) 13:27, 29 October 2009 (UTC)

What does "CTA" stand for? Bus stop (talk) 13:34, 29 October 2009 (UTC)

Contidioned Taste Aversion.--Gilisa (talk) 13:37, 29 October 2009 (UTC)

Wow, we already have an article on Conditioned taste aversion. Bus stop (talk) 13:40, 29 October 2009 (UTC)

With a lot of the up to date information missing. --Gilisa (talk) 14:10, 29 October 2009 (UTC)

It could be due to adaptive behavior like CTA. As for a specific raisin mechanism, I highly doubt it's known. Food aversion has been studied quite a bit, but a true mechanism still isn't clear generally. It's been studied in many animals, and in humans with a wide range of conditions like autism (where it's very common), anxiety (PMID:15576070), and even after certain surgeries (PMID:16925376). This all indicates what you might expect, that there is a physiologic reason. - Draeco (talk) 13:49, 29 October 2009 (UTC)

Actually, we do know that blocking specific dopamin receptors would prevent the development of CTA. However, what we yet don't exactly understand is how the retrieval mechanism of CTA works (but even here we prograss in huge steps - Yadin Dudai's studies from 2007 and on are focused on experimental extermination of already acquired CTA) .--Gilisa (talk) 14:20, 29 October 2009 (UTC)

Hello Gilisa, thanks VERY MUCH for this piece of evidence. This could explain, why a tasty nutrient is refused (because there was an unpleasant experience along with it.) Thanks again! Grey Geezer 14:26, 29 October 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

For nothing :)--Gilisa (talk) 14:38, 29 October 2009 (UTC)

Sure. If you don't like raisins than you can be sure that they contain compounds that do not agree with your biochemical system. Vranak (talk) 14:52, 29 October 2009 (UTC)

It's enough that you only change, or even camouflage, the compounds that are responsible for the flavor of raisins for one to eat them without feeling any dislike. Once the food is within your body it's much harder for it to decide what it's, the only thing your body can tell at this stage is whether this food have nutritious value and how it effect on visceral feeling.--Gilisa (talk) 15:04, 29 October 2009 (UTC)

There's a very simple reason why some people dislike raisins: they are quite bitter. Their sweetness makes this hard to recognize, but people who especially dislike bitterness will still be sensitive to it. Looie496 (talk) 16:28, 29 October 2009 (UTC)

And here you suggest that humans are genetically programed to prefer certain tastes with individual differences. That's another good option for why our friend dislike raisins.--Gilisa (talk) 17:06, 29 October 2009 (UTC)

We have a voluminous article Taste that links to Acquired taste but not to Conditioned taste aversion. I like the smart human Bus stop did not recognize the abbreviation CTA. That seems an unhelpful addition to this alphabet soup that could be avoided by merging the article on aversion into a section here titled "Acquired distaste". Cuddlyable3 (talk) 19:34, 29 October 2009 (UTC)

Some people get quite ill if they eat fructose beyond a certain proportion to glucose consumption. Eat a lot of fruit and get stomach pain, diarrhea, fatigue and depression. Large amounts of raisins (or apples, fruit juice, honey, or corn syrup, etc. ) would be bad for such persons. See Fructose malabsorption. It is not a matter of taste preference so much as a metabolic incapacity. Edison (talk) 04:49, 30 October 2009 (UTC)

Earth spinning

There's no "great power" actively holding the Earth spinning around itself and orbiting the Sun at the exact same speed for eternity, right? It just happens to be at the current speed because of various physical properties such as kinetic energy. Is this right? If so, then is the Earth's speed actually slightly changing? If yes, by how much? JIP | Talk 19:32, 29 October 2009 (UTC)

The great power is gravity and if the sun and earth were solid masses orbiting in a vacuum then Kepler's laws of planetary motion and the Earth's inertia would keep the system running "for eternity" with energy conserved. In reality the sun and earth are not solid masses. Both tides on Earth and the Sun itself expend heat energy and the Earth/Sun system is not isolated from external disturbances such as asteroids and comets. So nothing is forever. Cuddlyable3 (talk) 19:47, 29 October 2009 (UTC)

You'll want to read Earth's rotation. The speed of the rotation has definitely changed over the years due to Tidal forces from the Moon. ~ Amory (u • t • c) 19:50, 29 October 2009 (UTC)

For numbers pertaining to the Earth's slowing rotation, see Tidal acceleration#Quantitative description of the Earth-Moon case. The Earth's orbit around the sun is also slowing down; see Year#Variation in the length of the year and the day. Red Act (talk) 20:08, 29 October 2009 (UTC)

It seems like you already got your answers, but just to put it in simpler words: As for earth spinning itself, the law of Angular momentum preservation keep body spinning around itself (around its center of gravity) as long as angular force is not operated on it and its shape remain constant.

As mentioned here already, tiadl forces against the direction of earth spinning are operating on earth so the spinning is being decelerate by 2.3 miliseconds once in 100 years.

Amory already mentioned that as for Earth orbiting around the sun - body would keep moving in direct line and in constant speed as long as other force is not operating on it and Earth orbiting the sun according to Kepler's laws of planetary motion.--Gilisa (talk) 10:52, 30 October 2009 (UTC)

Taking into account general relativity, even an isolated two-body system will lose energy as gravitational waves - but as you can read in the article, that's indeed very little for the Sun-Earth system. The current changes in the orbital parameters (i. e. their first derivatives with respect to time) you can find here. JPL's solar system dynamics site provides other interesting data as well. Icek (talk) 20:20, 30 October 2009 (UTC)

How many buildings 2 story and above are there in the U.S.A.

I would like to know how many buildings taller than 2 stories are there in the U.S.A. Completed and/or under construction, if at all possible. But mostly how many buildings in all 2 stories and above. Thank You Very Much. --76.122.225.119 (talk) 21:03, 29 October 2009 (UTC)

I very much doubt you will get a good answer to this. Two-story is a very common configuration for houses and there are a lot of those. Also planning and approval is a local government duty (and some few places isn't always required), not federal or even state. Rmhermen (talk) 00:56, 30 October 2009 (UTC)

If good estimates of this do exist, they are probably hidden somewhere in the US Census Bureau - Manufacturing, Mining, and Construction Statistics site. (E.g., here is a table of new residential construction from the 1970s-present that breaks things down into stories—not quite the same thing as asked but it does give an estimate of the order of magnitude in regards to residential buildings in particular.) --Mr.98 (talk) 01:35, 30 October 2009 (UTC)

How accurate do you need? There are 300 million people in the USA, so I'd guess there are more than 5 million such buildings and less than 100 million. Dragons flight (talk) 02:00, 30 October 2009 (UTC)

To start, I tried Wolfram Search for "how many buildings in the US" and it didn't understand. (By comparison, it does answer how many people and how many dogs in the US, and includes a graph with the former question. The dogs get no graph.) Tempshill (talk) 03:15, 30 October 2009 (UTC)

If you did use the above link for new residential construction, you're still stuck with the problem of figuring out how many of those structures are still standing. Dismas|^(talk) 04:57, 30 October 2009 (UTC)

Further, you have to define a building. Is a duplex a single building based on this question? There are apartments, condos, etc... We haven't touched on commercial and industrial buildings. Those can be complicated. Consider downtown Charleston, SC. Because of lack of space, it is common for the area (a wide alley) between two buildings on King Street to be filled in with another building. The result is a continuous wall along the street, but it is technically two buildings with a building crammed in between them. Is that three buildings or two buildings or one building? Further, I've been in a house there that is actually two houses that were close enough to be joined together. Is it one house now? -- kainaw™ 12:59, 30 October 2009 (UTC)

A house which is joined to another house is called semi-detached, they are very common in the UK. Lots of houses joined together side by side is a terraced house. Personally, I would define all those houses to be part of one building. I think that is how it is usually referred to in the UK. --Tango (talk) 00:46, 31 October 2009 (UTC)

The U.S. Census lists 78 million (+/- 0.5 million or so) houses with two or more stories compared to 41.5 million one-story ones.[5] But that doesn't include commercial buildings and if we had a figure for commercial buildings we would have to figure out how many were mixed use and counted twice. (also 78 million plus 41.5 million equals around 120 million - but the survey starts out telling us there are 128.2 million homes (+/- 48,000) so apparently 8 million houses have no floors?) The data is based on a survey of 53,000 addresses every other year. Rmhermen (talk) 13:35, 30 October 2009 (UTC)

I have seen this question on Ref Desk before, and the discussion there might be helpful, if a link to the appropriate archive could be found. Edison (talk) 15:38, 30 October 2009 (UTC)

Glycogen Storage in Human Muscle Cells

Hello. Where and how do the breakdown products of stored glycogen enter the cellular respiration pathway? Is glycogen stored in the vacuoles of the human muscle cells? Thanks in advance. --Mayfare (talk) 21:30, 29 October 2009 (UTC)

Its stored in bananas. 188.221.55.165 (talk) 22:10, 29 October 2009 (UTC)

Read the article on Glycogenesis. Glycogen is the form in which muscle cells can store glucose for immediate use. In the human brain it also play major role in cases where oxygen levels are very low and there is no other option for neurons to produce the energy they need to survive.--Gilisa (talk) 22:32, 29 October 2009 (UTC)

Perhaps glycogenolysis would be more apropos. DRosenbach ^{(Talk | Contribs)} 23:23, 29 October 2009 (UTC)

You are right. I didn't read his question correctly.--Gilisa (talk) 09:09, 30 October 2009 (UTC)

Does glycogenolysis occur in the vacuoles of human muscle cells? --Mayfare (talk) 01:57, 30 October 2009 (UTC)

Yes.--Gilisa (talk) 09:09, 30 October 2009 (UTC)

Ladybirds hibernating

Anyone know why ladybirds (or lady bugs if you are from the other place) hibernate in big groups rather than singly? It cannot reduce the risk of predators and I don't see warm as helpful but there are a few corners in our house which each year get several hundred bunched all winter all of which crawl off in the spring. Surely separate hibernation for a non colony insect makes more sense? Whats the advantage? --BozMo talk 22:25, 29 October 2009 (UTC)

For Coccinellidae being conspicuous is associated with reduced, rather than increased, predation; see Aposematism. --Dr Dima (talk) 23:12, 29 October 2009 (UTC)

Its because they secrete aggregation pheromones when they find a suitable overwintering site. Its not known how or why this happens, but it might be something to do with marking places that served them well the previous winter, on the basis that if the insects survived the winter there last year, they may do so again. (See also Insect winter ecology and Michael Majerus' Ladybird bible, ISBN 0-00-219935-1) Rockpocket 23:19, 29 October 2009 (UTC)

"Ladybugs practice communal hibernation by stacking one on top of one another on stumps and under rocks to share heat and buffer themselves against winter temperatures." Bus stop (talk) 23:29, 29 October 2009 (UTC)

Despite what our article states, its not quite as a simplistic as them aggregating together for warmth, since that could happen anywhere. Instead there appears to be a selection for special overwintering spots, suggesting there is location specific aggregation going on (see Pettersson et al, Eur. J. Entomol. 102: 365–370, 2005). Its been hypothesized that a non-volatile compound, 2-isopropyl-3-methoxypyrazine, is responsible (Abassi et al Cell. Mol. Life Sci. 54: 876–879), which additionally ensures that males and females are in the same locale when the breeding season comes around in Spring. Rockpocket 23:46, 29 October 2009 (UTC)