Wikipedia:Reference desk/Archives/Science/2008 January 6

= January 6 =

Gear Math
Is there a way to rig up a mechanical system so one gear, which is spun by something, causes another gear to spin only when it changes speed? That is, to differentiate one gear's motion and put the result in another one? Black Carrot (talk) 03:09, 6 January 2008 (UTC)


 * I am probably misunderstanding your question, but it appears that you want one gear to spin. Another gear will be connected to it through some sort of device.  When the first gear changes speed, the second gear moves.  As long as the first gear maintains the same rotational speed, the second gear remains stationary.  This is what a tachometer (as well as a speedometer) does.  Normally, we use a little stick that rotates around a marked dial to show that the speed has changed, but you could replace that with a gear that turns one way or the other when the speed changes. --  k a i n a w &trade; 03:16, 6 January 2008 (UTC)
 * Agreed. I believe that the usual way a tachometer works is by spinning a magnet inside a copper cup, causing the latter to twist against a spring.  This is an example of the Hall effect. Bovlb (talk) 05:02, 6 January 2008 (UTC)


 * Actually, it's an example of eddy current-induced drag.


 * Atlant (talk) 22:46, 6 January 2008 (UTC)


 * That's not really mechanical differentiation, though - it uses an electromagnetic interaction property which provides the derivative with respect to time. Nimur (talk) 20:41, 6 January 2008 (UTC)
 * Yes, there is. Edison (talk) 05:05, 6 January 2008 (UTC)


 * The flyball governor?


 * Atlant (talk) 22:46, 6 January 2008 (UTC)


 * I believe the great mechanical analog computers of the early- to mid-twentieth century (in particular various differential analysers) had both integrators and differentiators, so presumably the answer is yes. —Steve Summit (talk) 01:39, 7 January 2008 (UTC)


 * The core component of a mechanical differential analyser is the wheel-and-disc integrator, invented by James Thomson, brother of Lord Kelvin. The way this device works is described here. Its principle is quite straightforward - the disc rotates at a constant speed (in the simplest applications); the wheel is moved radially across the disc so that its contact point with the disk is at a distance y(t) from the centre of the disc; the distance turned by the wheel (assuming no slipping) is then proportional to $$\int y(t) dt$$. A practical implementation presents various difficulties, such as ensuring that friction between the wheel and the disc is sufficient to turn the wheel smoothly without slipping, but not so great that it affects the turning speed of the disc. Gandalf61 (talk) 11:58, 7 January 2008 (UTC)

Flavour Sense Perception?
Im really confused about what flavour actually is. As far as i understand it's formed from mainly the sense of smell and taste but also others. So is it just a combination of sensory impressions/can flavour be seen as a seperate sense perception at all? If only the smell of a substance were perceived (say), what would be the qualitative difference between the flavour and smell of that substance, if any? Where is it interpreted in the brain as opposed to smell, taste etc? If I hold my nose when I eat bad food will the taste be less intense64.230.97.161 (talk) 06:17, 6 January 2008 (UTC)?
 * Flavour is the combination of taste and smell. As far as I'm aware there is no part of the brain dedicated to flavour rather it is just the combination of the two perceptions. Haven't you ever smelled something without eating it before? If you've had a cold and a blocked nose, you may have a rough idea of what eating without smell is like. did you read flavour? Nil Einne (talk) 08:29, 6 January 2008 (UTC)


 * (ec) Flavour can be thought of as the qualitative summation of olfaction and gustation. Each of the senses can be used to detect a chemical independently, giving you the smell and the taste, respectively (certain drugs, for example, can inhibit your ability to smell or taste without effecting to other). While we often think of flavour as being mostly taste, in fact smell plays a pretty important role, as anyone with really bad nasal congestion can tell you when when they are eating a nice meal. Thus there is a qualitative difference between the flavour and taste of that substance. Its also worth noting that there are only 5 basic tastes, but there are many hundreds of different receptors in the nose to detect smells, so while the taste plays an important role in determining the gross flavour, the subtleties are encoded by the smell. Again, this is why food tastes bland with a bad cold.
 * As Nil Einne notes, there is not a distinct brain region for detecting flavour, but there likely is a region where the projections from the olfactory bulb converge with neurons from the gustatory system to encode flavour. The very little is known about how and where "cross-talk" occurs between different sensory systems, but this is likely to be an area of research in the future. Rockpock  e  t  08:55, 6 January 2008 (UTC)


 * The holding my nose for bad food thing was more of a joke but the way I read your comment RockPocket does this mean that the taste of the food will remain the same with or without smell, but without it will lose its flavour, which doesn't intensify the taste of the food but adds a different kind of sensation altogether?70.49.136.117 (talk) 21:32, 6 January 2008 (UTC)
 * Yes, the taste will remain the same, and the flavour will not be lost exactly, but will be different and less "flavorful", because the smell contribution to determining the flavour will be missing. And yes, smell does add as a different sensation. There are experiments you could do where feed similar tasting things to people while they hold their nose. They may not be struggle to determine the difference between then because the subtle difference in flavour is actually perceived by the nose, rather than the taste buds. Rockpock  e  t  21:46, 6 January 2008 (UTC)

Immunoprecipitation(IP)
Hi, can anyone tell me which method to detect and analyse protein protein interaction provides quantitative data? Ie., regarding the strength of the binding. —Preceding unsigned comment added by 165.21.155.114 (talk) 08:28, 6 January 2008 (UTC)


 * Wikipedia has an article on this subject here.  Sp in ni ng  Spark  12:19, 6 January 2008 (UTC)


 * Did the answer need to be a variation of immunoprecipitation or will some other assay suffice? Seans Potato Business 12:23, 6 January 2008 (UTC)
 * If so, see immunoprecipitation. --JWSchmidt (talk) 15:36, 6 January 2008 (UTC)


 * Quantitatively measuring the 'strength of binding' of two proteins is another way of asking how to measure their dissociation constant, or Kd. Our article (unfortunately) doesn't yet discuss the many, many methods that may be used to measure this constant.  You might find some useful hints, however, if you look up Scatchard plots on Google.  (Again, our own article on the Scatchard equation is a bit thin.) TenOfAllTrades(talk) 16:32, 6 January 2008 (UTC)

Baby Dolphins and Fur?
I've heard that baby dolphins (calves) are born with a layer of fur that they lose after a few days. Is this true? And are there any photos of calves with fur available to see on the Internet?

Thank you for your help,

--91.104.10.242 (talk) 10:10, 6 January 2008 (UTC)


 * No, and no. Though they do have some blubber. Fur wouldn't be of any use to them. Maybe you are thinking of seals.--Shantavira|feed me 15:36, 6 January 2008 (UTC)
 * According to this site dolphins have "a few scattered bristles [of hair] about the lips or often present only in the young." Think outside the box 11:14, 7 January 2008 (UTC)

When is the on average coldest day each year in the northern hemisphere?
I dislike winter and look forward to and internally celibrate the day of earliest sunset. Another celibration day would be the day which is, on average, the coldest day of the year. Does anyone know when this is? I would calculate it myself but have been unable to find suitible historical temperature data for past daily temperatures that would not take several hours to prepare for use. (Note that even though averaging the temperature of each calendar day for past years for one particular geographical point could still give a noisy 'signal', fitting a curve to this data should allow estimating the day which is the minima). I'd also be interested in what the hottest day is, and when these occur in the southern hemisphere also. Thanks 80.0.126.128 (talk) 16:13, 6 January 2008 (UTC)


 * Hottest weather follows longest day says that "the hottest or coldest weather lags behind the summer or winter solstice by about a month or two." Earth and Sky also has several articles that talk about the earliest sunrise. Hope that is somewhat informative. -- Diletante (talk) 18:11, 6 January 2008 (UTC)


 * As far as I'm aware there's no average day, it depends on the area. You could I presume resonably easy work out the average day for your area by taking a look at the mean daily temperatures for your area over a period of say 100 years or whatever is recorded Nil Einne (talk) 18:56, 6 January 2008 (UTC)
 * "I would calculate it myself but have been unable to find suitible historical temperature data for past daily temperatures that would not take several hours to prepare for use." 80.0.133.83 (talk) 23:34, 6 January 2008 (UTC)


 * As it would (several hours) for most anyone else. hydnjo talk 02:12, 7 January 2008 (UTC)


 * The coldest day would certainly be different depending on where you are—altitude, water, latitude, and terrain would all affect it. The northern hemisphere is a big place, so you couldn't even come up with a perfect average, because you'd have to limit the number of samples. But poking around in the internet seems to put it sometime in middle to late January, which surprises me; I'd always thought February was worse, but maybe that's just because I'm that much more sick of winter by then. If you want to plan a party, you could do worse than to hold it on January 14, St Hilary's Day, which, according to the Bablake weather station in Coventry, England, is the coldest day according to folklore. --Milkbreath (talk) 16:19, 7 January 2008 (UTC)

Thank you, your link to Bablake station gives details of a typical year: Warmest day of the year 28th July; Warmest night of the year 28th July; Coldest day of the year 16th February; Coldest night of the year 20th February. From http://bws.users.netlink.co.uk/typical%20year.htm I expected the coldest day to be in January, and where I live spring seems to begin on Valentine's Day on the 14th. February: apparantly I was mistaken. There is however almost a 6 month gap between the coldest and hottest day - it is out by about 12 days I think. I have downloaded some other historical data from the site and will be looking to see if I can estimate the average coldest calendar day myself. 62.253.48.92 (talk) 19:14, 7 January 2008 (UTC)

eyes above mouth
why do animals commonly possess eyes above the mouth? ie: what is advantageous in this. are there examples to the contrary? (the part of the nose seems clearer: smells waft up into the nostrils to be identified before ingestion) 3170s228 (talk) 17:39, 6 January 2008 (UTC)


 * it occurred to me immediately after asking that food & saliva would tend to gravitate downward & mess up your vision. I'm still curious about alternate explanations & examples. 3170s228 (talk) 17:42, 6 January 2008 (UTC)


 * It's good to be able to maintain vigilance while eating. It would be disadvantageous to have your view blocked while you were eating allowing predators and rivals to sneak up on you. Generally the higher your eyes are, the more you can see. -- Diletante (talk) 18:05, 6 January 2008 (UTC)
 * The "eating" function of the mouth is the beginning of the digestive system, which goes down. As species become increasingly cephalic, why have the mouth move up past (and throat go around?) the eyes, which are primarily just an extension of the brain? DMacks (talk) 21:19, 6 January 2008 (UTC)


 * Perhaps I should make the keen observation that food is often on the ground. Mac Davis (talk) 23:46, 6 January 2008 (UTC)


 * Another keen observation would be that most organisms move forwards to collect this food (wriggling on their belly), and primitive organisms (along with many others) are most interested in making sure they're in the dark (my favorite flatworm). Thus, it makes sense to have the mouth at the front, and the eyes "on top." If the worm evolves to stand up one day, it would just be easier for the eyes to remain above the mouth. Someguy1221 (talk) 16:06, 7 January 2008 (UTC)


 * I can't imagine a situation in which it would advantageous to have your eyes below your mouth. You'd inevitably be blocking your view while eating. What would the benefit be? If something has only strong detriments and no strong benefits, it's not going to be favorably selected for, obviously. --24.147.86.187 (talk) 01:11, 8 January 2008 (UTC)


 * Some fish have their eyes "below" there mouth, a number of these are surface feeders. Hardyplants (talk) 21:38, 11 January 2008 (UTC)

Old cartoon mocking Mendeleev's system
Hello,

my chemistry teacher once told us that Mendeleev was mocked by some scientist in his days because of his proposed periodic system. The reason would have been that he had "dumpster groups" in his table, certain sets of elements that he had just put together because he didn't know where else to put them. My teacher claimed that they even made cartoons depicting Mendeleev sitting in his own dumpster, surrounded by elements, mockingly suggesting the question" what other elements will he put in there?"

Does anyone know more about this? Seeing such a cartoon would be very nice! Thanks! Evilbu (talk) 19:56, 6 January 2008 (UTC)


 * Hmm... I've never seen it, though I'm no expert on Mendeleev. You might try e-mailing this guy—he wrote the most definitive biography of Mendeleev and he's a really nice guy at that. He has at least one cartoon about Mendeleev in his book though it is related to his appointment in the Russian Academy of Sciences. --24.147.86.187 (talk) 21:14, 6 January 2008 (UTC)


 * If you find anything, perhaps the most appropriate article to put it in would be History of the periodic table. I'll also note that Dmitri Mendeleev died in 1907, so we're talking about cartoon drawings, not animated cartoons.  --M @ r ē ino 17:01, 10 January 2008 (UTC)

DIY electric quadricycle
As my final year electronics project I've been thinking about making an electric quadricycle that looks like a skateboard with a box below it and 4 very over sized wheels. However, I'm having some questions on the feasibility of this, and I would appreciate any input or other examples of similar projects.


 * 1) I want to reduce the mechanical components to the minimum so I'm thinking about putting the motor and a epicyclic reduction gear inside the wheel assembly, eliminating the drive train. Is this a good idea? Or should I really reconsider having one huge motor and lots of shafts? I've found a motor suitable for this use but I don't know where to find the epicyclic reduction gear nor suitable wheels. The ones on Jaycar are like the Lego ones and I really doubt it can take that amount of torque. Does anyone here know where to find these things in New Zealand, or if that's really hard, Australia?
 * 2) Aside from the drive train the other mechanically complex part is the turning. Will driving the motors at different speed (ie. faster on the outside wheels and slower on the inside wheels) work in real life, or do I need to actually rotate the wheels?
 * 3) I want the vehicle to have similar performances to a bicycle, and according to Human-powered transport "The average "in-shape" cyclist can produce about 3 watts/kg for more than an hour (e.g., around 200 watts for a 70 kg rider)", so do 4 of the above-mentioned motors (1 in each wheel) offer enough power?
 * 4) Can I do regenerative braking with that motor? What would I need for a regenerative braking circuit?
 * 5) The planned range for this vehicle is somewhere between 1-3 hours (assuming 10km/h, 10-30km). That makes 200Wh at 12V, but normal lead acid batteries are too heavy for this use. Where can I get NiMH or Li-ion battery packs at this size?

Also, any other suggestions on reducing the complexity or the cost are also welcome. --antilivedT 00:00, 6 January 2008 (UTC)


 * Why not go overboard and a use a motor on each wheel? You could use that for directional control as well.--TreeSmiler (talk) 01:24, 8 January 2008 (UTC)


 * I am planning to use a motor on each wheel, which is basically what question 2 is about. Does varying speed of the wheels on the different sides work satisfactorily or will it put a lot of wear on the tyres or something? --antilivedT 10:05, 8 January 2008 (UTC)


 * You can turn the vehicle by altering the speed of the motors: this is essentially how tanks and other tracked vehicles turn. I wouldn't be worried about stress and wear from this unless you're trying tight turns -- you won't be able to perform a tank's trick of turning in place, and I wouldn't try turns of a radius less than twice the wheelbase. --67.185.172.158 (talk) 10:27, 8 January 2008 (UTC)


 * OK thanks, that's question 2 answered. --antilivedT 04:57, 9 January 2008 (UTC)