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January 1

Habitable exoplanets

How many exoplanets are rocky and in their star's habitable zone? Which ones are the most likely to have life? --108.225.115.211 (talk) 00:15, 1 January 2012 (UTC)

There are no definite detections of rocky planets in the habitable zone. The closest is Kepler-22b that was announced a few weeks ago. It's in the habitable zone and isn't too much bigger than Earth, so it's possible it is rocky, or at least is covered in a liquid water ocean (that could possibly support life - we don't have anywhere near enough information yet). --Tango (talk) 00:24, 1 January 2012 (UTC)

Pass! However, the Drake equation gives some sums on the subject in general.--Aspro (talk) 00:24, 1 January 2012 (UTC)

You have to make wild guesses about what numbers to put into the equation, though, so it isn't much use for anything other than structuring the conversation (which is all Drake invented it for). --Tango (talk) 01:00, 1 January 2012 (UTC)

Since no one recommended it for reading, try Habitable zone on for size. --Jayron32 04:44, 2 January 2012 (UTC)

Interrupter gears

Why can't an interrupter gear be used to synchronise an open bolt machine gun? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:35, 1 January 2012 (UTC)

Who says it can't? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:13, 1 January 2012 (UTC)

The article states that they can't, and I was wondering why. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:05, 1 January 2012 (UTC)

The article appears to be incorrect. It has no citation for that information. Technically, the official policy on Wikipedia is to remove unsourced material from articles. You may want to discuss this further on the talk-page for the relevant articles. We have several books and external sources listed in the references section, if you want to research further. Nimur (talk) 07:57, 1 January 2012 (UTC)

Nimur, are you saying that you have heard of interrupter gear based synchronised open bolt machine guns, or are you simply saying that the article is incorrect in that it is not sourced? With a longer time to first fire after being triggered, it seems reasonable that open bolt guns would be harder to synchronize than closed bolt ones, and our article Parabellum MG14 says, "The MG14 was tried with the pioneering Fokker Stangensteuerung synchronizer on the Fokker E.I pre-production prototypes, but the gun's reliability in this installation eventually proved to be unsatisfactory, even though its closed bolt firing cycle was a desirable feature for synchronisation." -- ToE 12:57, 1 January 2012 (UTC)

Nothing heard. I have restored most of the material Nimur removed as it does makes sense and is corroborated by statements in other articles. Nearly the entire article Open bolt is unsourced, but it is tagged {{Refimprove}} and I will request help from WP:WikiProject Firearms. -- ToE 12:26, 6 January 2012 (UTC)

Wwpu, I know nothing of this field beyond what I have just read in the Wikipedia articles (so experts, please speak up), but here is why I would expect an open bolt gun to be very difficult to synchronize. First, note that the firing speed of these guns are typically much slower than the rotation speed of the propeller -- say 700 rounds/minute for the MG14 mentioned above vs. 2,500 to 3,000 rpm for a propeller (see propeller speed reduction unit). For a two bladed prop, this gives 5,000 to 6,000 firing windows per minute. That is one window every 10 to 12 milliseconds, compared with the 86 ms cycling time of the gun. Next, note that the action of the synchronizer gear attempts to trigger the gun at every firing window, and will do so as long as the pilot is holding down the trigger and the gun has cycled to a firing configuration. Finally, consider the different actions. Firing from a closed bolt involves the firing pin striking the primer. The round fires quickly, then the bolt cycles during the remainder of the 86 ms. Firing from an open bolt involves releasing the bolt and having it feed a round into the chamber as it closes and then firing it, a process which presumable takes at least half of the 86 ms cycle. From the time that the open bolt gun has been triggered by the synchronizer to when the round has fired, a propeller blade will have passed in front of the gun four or five times. Add in a variable speed propeller, and you can see how hard it would be to synchronize an open bolt gun. -- ToE 14:00, 1 January 2012 (UTC)

Our Closed bolt article agrees with your second point ToE; "since the bullet firing from the gun started the firing cycle, it was much easier to set the synchronizer to only trigger the gun when the propeller's blade was not in front of the gun." Alansplodge (talk) 15:34, 1 January 2012 (UTC)

Following a link in the paragraph you quoted from, I found Lewis gun#Aircraft use: "The open bolt firing cycle of the Lewis prevented it from being synchronized to fire directly forward through the propeller arc of a single engined-fighter". -- ToE 23:42, 1 January 2012 (UTC)

Watts and calories

A question regarding equivalency of units has arisen here. Would someone please take a look? Rivertorch (talk) 06:49, 1 January 2012 (UTC)

Responded at talkpage post, but would welcome someone else checking figures. --jjron (talk) 08:26, 1 January 2012 (UTC)

Responded also; the units used were wrong. IRWolfie- (talk) 15:36, 1 January 2012 (UTC)

Given that glass is transparent to infrared, how usefull are thermal (infrared) images of houses in estimating heat loss through windows?

Under everyday circumstances, heat loss from houses is probably dominated by conduction or diffusion and not by infrared radiation emitted by the house. It seems that silica-based glass is transparent to near-infrared ( http://answers.yahoo.com/question/index?qid=20061029200658AAWl7IU ). In that case, a picture taken in near-infrared will merely register the temperature of the room behind the window, and improving the window (Insulated glazing) will reduce conduction or diffusion losses but on the near-infrared picture you will still see the temperature of the room behind the window. 83.134.159.252 (talk) 07:00, 1 January 2012 (UTC)

Near infrared is not the same as "thermal" infrared. Infrared is an entire range of invisible colors of light - ranging from near infrared (which optically behaves very similarly to regular red light) all the way deep into the terahertz band, where infrared light behaves more like something we'd expect out of a radio-wave. Somewhere in the middle of that spectrum is "thermal" infrared - light that corresponds to the peak emission of the blackbody radiation curve for objects at useful temperatures.

Usually, the range of wavelengths that are useful for measuring normal household objects are what we call "long wavelength" - around 10µm - infrared. Glass is not very transparent to these wavelengths, which is why greenhouses work. Visible light (and near infrared) can travel through, and the energy is absorbed by the interior; but when thermalized and re-radiated, that energy is now at a wavelength that will not go out the window. This one-way trip for the energy is called the greenhouse effect.

If you're using an infrared imager that is capturing near infrared (which is easy and cheap to acquire!) ... then, you aren't actually measuring the temperature. At best, your imager may estimate the temperature based on a complicated mathematical model; but it's not going to be accurate. True thermal infrared imagers are much more expensive and difficult to come by. Use caution! There are lots of infrared imagers that aren't useful for measuring temperature. They're still useful for other scientific and aesthetic purposes, just not as a thermometer. Nimur (talk) 09:26, 1 January 2012 (UTC)

To add to that: when near infrared is used for night vision, you need to have an artificial source of near infrared light. That's why there is often a bright circle in the middle of a night vision video - the light is attached to the camera and that's where it is shining. --Tango (talk) 13:07, 1 January 2012 (UTC)

Unhelpful hogwash, see Night vision device for accurate information on Tango's tangent. Bred Ivy (talk) 14:51, 1 January 2012 (UTC)

What I said is accurate. If you look at Night_vision#Night_vision_technologies you will see there are three types. I was describing how active night vision works, which is the type that most uses near infrared. Your comment on my talk page is about image intensification, which don't just use infrared. They also intensify visible light. So "a picture taken in near-infrared", as the OP is asking about, would generally refer to active night vision, not image intensification. --Tango (talk) 15:20, 1 January 2012 (UTC)

science assignment

please help me to write an introductory part of an assignment in which the table content are 1.male reproductive system 2.female reproductive system 3.fertility 4.menstruation 5.pregnancy 6.parturition 7.lactation. 8.family planning .Rikisupriyo (talk) 08:14, 1 January 2012 (UTC)

I'm sorry but it is our policy here not to do people's homework for them, but merely to aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. That said, our article on Human reproduction might give you an idea for the assignment introduction. Please do not copy it though.-- Obsidi♠n Soul 08:21, 1 January 2012 (UTC)

Well, we can't do their homework, but we could suggest some ideas for them to explore. StuRat (talk) 01:54, 2 January 2012 (UTC)

You might want to describe how human reproduction fits into the animal kingdom. The first two chapters apply, to some degree, to any animal with sexual reproduction. Lactation is specific to mammals. Menstruation is limited to certain mammals. Family planning is limited to humans, unless you include animals which only breed when they are eating well. StuRat (talk) 01:54, 2 January 2012 (UTC)

OTC Medication Safety

Are there any well-defined levels of safety that must be demonstrated before a medication can be approved for distribution over-the-counter? For example, I might imagine there could be conventions such as: "The LD50 concentration must be at least 100 times the typical therapeutic dose." Do any such broad standards for safety exist, or do the review panels simply decide the question of safety on an ad hoc basis every time they make an OTC determination? Dragons flight (talk) 10:15, 1 January 2012 (UTC)

The rules and regulations (not to mention the specific drugs actually sold OTC) can vary quite a bit from country to country. In the United States, OTC drugs are regulated by the FDA, and decisions on when and how OTC drugs may be sold ultimately flow from the recommendations of the Nonprescription Drugs Advisory Committee. The day-to-day work comes from the Division of Nonprescription Clinical Evaluation (DNCE) and the Division of Nonprescription Regulation Development (DNRD) under the Office of Drug Evaluation IV (ODE IV); the roles of each division are pretty much what their names imply—one deals with clinical testing, and one deals with managing the regulations.

There's an astounding body of legislation and regulations associated with prescription and nonprescription drugs, but approval of drugs for OTC use generally comes down to meeting the following criteria (copied from [1]):

• their benefits outweigh their risks
• the potential for misuse and abuse is low
• consumer can use them for self-diagnosed conditions
• they can be adequately labeled
• health practitioners are not needed for the safe and effective use of the product

All of those tend to have some wiggle room in them, and require expert judgement about where to draw the line in any given case. The FDA can require clinical testing of OTC candidates to specifically confirm that patients are able to comprehend labels and to self-manage their use of any drug. While other countries will have different rules, I suspect that you'll find that they come down to roughly the same criteria. TenOfAllTrades(talk) 16:34, 1 January 2012 (UTC)

Medscape has a little about this too. [2]--Aspro (talk) 16:39, 1 January 2012 (UTC)

It also depend if examiners will possible have a future career option at the medicine inventor, who pays research grants, monetary incentives, who select which protocols from clinical trials will be published etc.. A lot of non-obvious lobbying goes on. Electron9 (talk) 06:42, 2 January 2012 (UTC)

Can you provide more information about this 'non-obvious lobbyng'? I don't see any reason to doubt the integrity of the pharma industry, althou other people are of different opinion. — Preceding unsigned comment added by 88.8.76.174 (talk) 22:11, 2 January 2012 (UTC)

Wake up :-) Electron9 (talk) 17:12, 6 January 2012 (UTC)

Kepler-22b

Is there any work ongoing to find out more about Kepler-22b? Kepler's observations left a lot of unanswered questions about mass, composition, most of the orbital parameters, etc. and presumably other space- and ground-based observatories will need to do follow-up studies to answer those questions. I haven't been able to find any information about such follow-up studies, though. --Tango (talk) 17:05, 1 January 2012 (UTC)

You mean Kepler-22b right? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 17:27, 1 January 2012 (UTC)

Indeed! Fixed now - thanks. I got it right in the header, at least! --Tango (talk) 18:45, 1 January 2012 (UTC)

Some of those parameters are pretty difficult to find out. We have a detailed article Methods of detecting extrasolar planets which gives some info on which methods give what data. The Kepler (spacecraft) detects planets by the Transit method, which only determines a planet's radius. To find its mass, some sort of Radial velocity method must be employed. Unfortunately, this method works best for larger planets. The radial velocity numbers (measured by the Keck 1 observatory on the ground) give an upper bound on the mass, but no lower bound [3]. My understanding at present is that we lack any instruments capable of giving a reasonable radial velocity of a star for a planet this small (and thus the mass is somewhat unclear). I don't really think we have any good way of measuring composition for any exoplanet. We can guess for some planets if we know their density (i.e. we know they're gas giants), but that's about it. For a few very large planets, we can do spectroscopic measurements directly on the planet. HD 209458 b, for example, was determined to have water vapor and carbon monoxide present with spectroscopic measurements. These are not possible on Kepler-22b, and probably won't be for some time. Buddy431 (talk) 23:25, 1 January 2012 (UTC)

Attractiveness by percentile

Assuming that rankers can put people in the ranked group into a roughly linear order, the "total attractiveness" of a person is the function which given a percentile gives the fraction of rankers which found the person to be in at least that percentile (what's this called in statistics?). Can you link me to someplace which shows some real life "total attractiveness functions" (a term I made up)? --193.64.22.148 (talk) 18:26, 1 January 2012 (UTC)

Maybe I am misunderstanding you, but this hardly seems to be a question about science. There is no science of attractiveness, it is purely subjective and cannot be measured scientifically. Beeblebrox (talk) 20:13, 1 January 2012 (UTC)

"Cannot" is a strong word... the whole of the social sciences are a best-effort approach to apply the scientific method to subjective topics. In fact, even hard-science journals like Nature have published studies about human perceptions of attractiveness. Here's one example article I found using Google Scholar: Effects of sexual dimorphism on facial attractiveness (Nature, 1998). There are some promising-looking articles from journals I haven't ever read, too: An Objective System for Measuring Facial Attractiveness, Facial attractiveness, developmental stability, and fluctuating asymmetry, and so on. We have an article on the topic of physical attractiveness that can probably point you to more survey articles and published research. Our article lists almost 200 reference works. Nimur (talk) 20:40, 1 January 2012 (UTC)

Maybe I am misunderstanding you, but isn't the fraction the same as the percentile? If it is, then the function is the identity function, but perhaps you are describing something more subtle. (I'm not a statistician.) Dbfirs 20:47, 1 January 2012 (UTC)

Maybe I'm miscommunicating, but I was thinking about a situation like "f(more attractive than %x of the population being ranked) = true in the case of %y of rankers". So f(%0) = %100 and f(%100) = the percentage of rankers who consider the person most attractive of all. --~~ — Preceding unsigned comment added by 193.64.22.148 (talk) 21:12, 1 January 2012 (UTC)

So you want to know something about how different people's perceptions of attractiveness are correlated? That's an interesting question. It's a slightly difficult one to answer, though, because people will often say they think someone is attractive when actually they mean they think they match what one is "supposed" to find attractive. If people are answering like that, then obviously there will be a strong correlation. If people are giving their own genuine opinions, then it might be a lot weaker. I haven't heard of any studies into that, but it wouldn't surprise me if there were some (such studies tend to get mentioned in the press, which means there is probably a lot of funding available for them!). --Tango (talk) 02:15, 2 January 2012 (UTC)

See panel 3 of xkcd comic strip 451: Impostor. – b_jonas 12:26, 2 January 2012 (UTC)

Velocities

Resolved

Consider a particle moving along the line x = 1. Assume that after t seconds, the particle is at the point (1,t) in the xy-plane. The linear velocity of the particle is clearly (0,1) and its speed 1 m/s. Consider the chord joining (0,0) to the particle at (1,t); this chord makes an angle, measured in radians, with the x-axis of

$\theta (t)=\arcsin \left({\frac {t}{\sqrt {1+t^{2}}}}\right).$

Does it make sense to consider the angular velocity of this particle, with respect to the centre of rotation (0,0), or do particles have to follow circular arcs to have well define angular velocity? Assuming it does make sense, we see that the angular velocity, measured in radians per second, of the particle is

$\omega (t)={\frac {1}{1+t^{2}}}\,.$

I understand the meaning of angular velocity for a body rotating about a point or an axis, but in the case of a particle moving along a straight line, what does my ω(t) mean? Is it some sort of "infinitesimal angular velocity"? Also, what do we call the sum of the linear and angular velocities? (It's interesting that the trajectory of the particle is only ever tangent to a circular arc centred at (0,0) when t = 0 — it's tangent to the unit circle at (1,0). In this case the angular velocity ω(1) = 1 matches the linear velocity.) — Fly by Night (talk) 23:19, 1 January 2012 (UTC)

The only significance I can see to calculating the angular velocity, momentum, etc., under such conditions are if the particle may, at some point, actually start to rotate around the origin. For example, it the particle is a bullet, and the X-Y plane is a stationary wooden plate around an axis at (0,0), with a slot in it so the bullet hasn't struck the plate yet, then the angular velocity would become significant only once it strikes the edge of the plate. It could then be used, along with other parameters of the plate and bullet, to determine how fast the plate would then begin to rotate about the axis. StuRat (talk) 01:42, 2 January 2012 (UTC)

Thanks for your post. It would have been a better post had you actually addressed the questions I asked. All but the first sentence is totally out of context. — Fly by Night (talk) 02:30, 2 January 2012 (UTC)

It is truly heartwarming to see how cordial relations are here on the ref desks this New Year. Borrowing the "bullet" and "plane" concepts from StuRat, considering the x-axis as "up", and changing units a bit, we can see the real-world meaning of the angular velocity in this problem. Consider a ref desk regular, at the origin, who asks a vague question. Another ref desk denizen flies overhead in an ultra-light aircraft (named the X-Y) at a constant altitude of 1 km and speed of 1 km/min such that he is directly overhead at time 0. Prior to this time, our intrepid pilot drops a bomb of an answer, which lands directly on, but fails to satisfy the questioner. Should the disgruntled questioner now wish to snipe at the respondent with a scorching reply of his laser cannon, the computed angular velocity represents the angular rate at which the cannon's aim should be depressed to maintain a lock on its target. -- ToE 08:10, 2 January 2012 (UTC)

It makes perfect sense to talk about the angular velocity about the origin for that particle. You can talk about the angular velocity about any point for any particle. If you chose a point on the line x=1, for example, then the angular velocity of your particle would be zero. One interesting thing you can do with that angular velocity is calculate the angular momentum (it's just mass times distance from the point squared times angular velocity for a single particle). If you do so, you'll find that it's a constant (the angular momentum is decreasing and the distance is increasing and they cancel out - check it for yourself). That will be true for any point you chose to measure it relative to. That's the principle of conservation of angular momentum. The angular momentum of your particle will be constant about any point you chose, including the origin, because there are no forces acting on it (it isn't accelerating). --Tango (talk) 02:10, 2 January 2012 (UTC)

The angular velocity most certainly is not zero. I have already found the angular velocity ω(t). Please read the article on angular velocity. I gave a series of particular questions, and would appreciate it if people answered them instead of giving a list of random facts. — Fly by Night (talk) 02:30, 2 January 2012 (UTC)

Your question was pretty vague - you clearly know the definition of angular velocity, and that's all I could really tell you about what it means. Therefore, I thought it would be useful to talk about what angular velocity can be used for in order to give you a feel for how it works and why it still makes sense even if the object isn't moving in a circle. As I explained, although apparently not clearly enough, angular velocity can be calculated relative to any point. You calculated it relative to the origin, but there is nothing special about the origin. If you calculate it relative to a point on the line x=1 then you will find that you get zero. As for your other questions - the angular velocity you have calculated clearly isn't infinitesimal (at t=0, it's 1/2, for instance, which is definitely finite) and there isn't a name for the sum of the linear and angular velocities because that is a meaningless concept (you can only add things if they have the same units and linear velocity has units of length/time while angular velocity has units of angle/time). --Tango (talk) 03:47, 2 January 2012 (UTC)

I agree with Tango, with the minor correction that the magnitude of the angular momentum is $mr^{2}\omega$, not $mr\omega$. Two additional points: (i) "Infinitesimal angular velocity" is certainly incorrect, but "instantaneous angular velocity" would be correct; (ii) if the particle's velocity vector v makes an angle φ with its position vector r then the magnitude of its instantaneous angular velocity (relative to the origin of the position vector) is v sin φ / r. Gandalf61 (talk) 09:31, 2 January 2012 (UTC)

Thanks for the correction, I've fixed my post. I did consider looking up that formula to make sure and decided I didn't need to... doh! --Tango (talk) 13:23, 2 January 2012 (UTC)

Thanks to those of you that answered some of my question. The question of what the sum of linear and angular velocity represents has been left addressed. I think I'll go elsewhere for an answer on that one. — Fly by Night (talk) 14:26, 2 January 2012 (UTC)

Your question about what the sum of linear and angular velocities represents was answered by Tango. As Tango says above, it is just a number with no physical meaning because the two quantities are denominated in different units and, more fundamentally, they are dimensionally different, so you can't even convert them into the same units before adding them. Gandalf61 (talk) 14:57, 2 January 2012 (UTC)

January 2

Carbon group

In the French Wikipedia, there is given an alternative name for the carbon group: Cristallogène (which would probably be "cristallogens" in English). What is the etymology of this name and why isn't it used in English (I've never seen the term in English)? Double sharp (talk) 02:46, 2 January 2012 (UTC)

It looks like it means "crystal generating". While carbon and silicon readily form crystals, you don't normally think of metals like tin and lead being crystal generating elements (although they might under some conditions, I suppose). Conversely, many other elements not in that group also form crystals readily, so it seems like a questionable name, to me. StuRat (talk) 03:31, 2 January 2012 (UTC)

You mean like lead crystal? --Jayron32 04:19, 2 January 2012 (UTC)

That's not made from just lead, but only a small potion of lead added in. StuRat (talk) 06:17, 2 January 2012 (UTC)

But pnictogen also doesn't fit very well as a name as metals like bismuth aren't really choking. Double sharp (talk) 14:06, 2 January 2012 (UTC)

And, you'll note, that lead crystal is mostly silicon, which is in the Carbon group. --Jayron32 21:26, 2 January 2012 (UTC)

John Daniel Titius and John Elert Bode

happy new year

what is the real reason of Titius -Bode low? --Akbarmohammadzade (talk) 04:05, 2 January 2012 (UTC)

It was an attempt to calculating the orbits of the planets in a predictive manner. It seemed to correctly predict the asteroid belt and uranus, but completely missed Neptune. IIRC, given a 66.7% success rate over a small sample size, it may have been just dumb luck that it gets right what it did. --Jayron32 04:17, 2 January 2012 (UTC)

can we generalize it to dynamic of galaxies?(the main mass separates its sub system automatically in such rule?--Akbarmohammadzade (talk) 04:33, 2 January 2012 (UTC)

The article is Titius-Bode law. The article does have some theoretical explanations - possibly, the way planets form (collapsing disk of matter) can lead to certain regular powers of distance of planet formation, with orbital resonance perhaps increasing the probability of such spacing. By fitting several planets (Mercury, Venus, Mars, Jupiter, and Saturn), some sort of regular pattern was created for the solar system, which two more planets also happened to fit (and Neptune didn't). Note too that, according to the currently most accepted theory on the formation of the solar system, the Nice model, the Uranus and Neptune were formed closer to the Sun, and migrated outward. The Nice model is still very new, and by no means universally accepted. It was later pointed out that some of the large moons of Jupiter and Saturn also followed regular, though non-Bode distance patterns. This expanded model is termed Dermott's law. Is there really some effects that conspire to give Bode-like planet distances, or is it just dumb luck? Maybe if we can start mapping solar systems of other stars, it will become more clear. Buddy431 (talk) 04:50, 2 January 2012 (UTC)

We have started mapping solar systems of other stars. We know of 6 planets around Gliese 581 for instance. I'm not sure if they follow any kind of Titus-Bode style law or not, though. --Tango (talk) 13:27, 2 January 2012 (UTC)

What is the specific gravity of quartz sand?

Resolved

 – – Kerαunoςcopia^◁_galaxies 05:43, 2 January 2012 (UTC)

...in lbs/square-ft lbs/cubed-ft? A family member needs to know this and I have absolutely no idea how to go about finding this (less a Google search, which didn't turn up any immediate answers). The specific gravity article sort of intimidates me, especially the part about temperature and pressure needing to be specified for "both the sample and the reference". This is beyond me, but apparently someone thinks I'm a genius at science. Should've kept my mouth shut during Christmas dinner! Any help would be great, thanks so much! – Kerαunoςcopia^◁_galaxies 04:05, 2 January 2012 (UTC)

As sand consists of particles, the specific gravity might vary by the coarseness/fineness of the particles, but I'm not sure whether the more coarse or the more fine sand would have the greater specific gravity. Bus stop (talk) 04:24, 2 January 2012 (UTC)

Your units aren't right either. True specific gravity is a unitless number. Sometimes when people say specific gravity, they really mean density, but even there, your units aren't right (should be mass per volume. You have weight per area. You might charitably assume they mean pound (mass), but you still need a per volume, rather than per area). What's the context that you need this for? Buddy431 (talk) 04:33, 2 January 2012 (UTC)

Yes - lbs/cubic ft would make more sense. Actually, following on from Bus Stop, I think that the shape of the particles will matter more - as will the variation in size. The density of 'sand' will necessarily be less than that of the bulk material it is made up of - quartz rock in this case. As for how much less, this will depend on how efficiently it packs together. You'll also need to specify whether you mean dry sand or wet - wet sand can hold a lot of water. AndyTheGrump (talk) 04:41, 2 January 2012 (UTC)

(edit conflict)Specific gravity is a unitless ratio between the density of the comparing substance to a reference substance (usualy water,) as in how many times heavier is substance A than water at some temperature and pressure. Quartz sand should ideally be composed of crushed quartz; the specific gravity is 2.65 from the quartz article. However, it could be different due to impurities. Plasmic Physics (talk) 04:57, 2 January 2012 (UTC)

If you want to include the voids between grains, then a simple experiment would be to simply measure the volume taken up by a pound of water, and a pound of quartz sand, and divide the first value by second. Plasmic Physics (talk) 05:05, 2 January 2012 (UTC)

A Google search on [density sand] yields tables with a wide range of values -- all the way from 90 lb/ft³ to 100 lb/ft³ for dry loose sand up to 120 lb/ft³ to 130 lb/ft³ for wet packed sand. If you truly want an answer in lbs/square-ft, then you are seeking the areal density, and you need to multiply by the desired thickness. For instance, a four inch layer of damp packed sand with a density of 120 lb/ft³ has an areal density of 40 lb/ft². If you are seeking precise numbers, you will need to provide more information in your question. -- ToE 05:38, 2 January 2012 (UTC)

(E.C.) Also note that many of the density tables you find online give metric values, and while you can convert directly, an understanding of specific gravity can help you do it in your head. Unless you are interested in a great deal of precision, don't worry about the finer details in our article which threw you off; just think of specific gravity as the ratio of density of the substance in question to the density of water. Thus if a table states that wet, packed sand has a specific gravity of 2.082, then you know that it is 2.082 times more dense than water. The density of water is about 62.4 lb/ft³, so just multiply to find that the density of wet, packed sand is 130 lb/ft³ . Many of the tables you will find will give densities in metric units, but don't despair, as you can read the specific gravity directly from such figures. This is because the metric system was set up so that the density of water is 1 g/cm³, which is the same as 1 g/ml, or 1000 kg/m³, or 1 metric ton per cubic meter. Thus, when you see a table which gives the density of wet, packed sand as being "2082 kg/cu.m", you know that is 2.082 times as dense as water, and is thus the same as 130 lb/ft³. Does that help? -- ToE 06:02, 2 January 2012 (UTC)

Oops, I meant cubed-feet (fixed). I knew there'd be more to this than meets the eye! : ) I will pass on the information. Thanks so much for everyone's help! Sorry for the error again. – Kerαunoςcopia^◁_galaxies 05:43, 2 January 2012 (UTC)

I just reinserted the original "lbs/square-ft" into your question, but struck out, so that future readers of the archives will understand why some of the answers were discussing units the way they were. Hope you don't mind. -- ToE 06:09, 2 January 2012 (UTC)

health education

what is health education? — Preceding unsigned comment added by 85.15.40.77 (talk) 07:24, 2 January 2012 (UTC)

Just what it sounds like, education about human health. Some basic biology is usually included, including sex education. These days, more emphasis on a proper diet and exercise might also be included, in the hopes of fighting obesity. StuRat (talk) 07:27, 2 January 2012 (UTC)

We have an article with just that name - Health education. It should help. HiLo48 (talk) 07:29, 2 January 2012 (UTC)

Mammoth

How long will it be before somebody seeks to make one inside an elephant? Kittybrewster ☎ 16:51, 2 January 2012 (UTC)

Who says they aren't already trying [4] :) IRWolfie- (talk) 16:55, 2 January 2012 (UTC)

The Pleistocene Park effort is related to that (I think it's the same people). -- Finlay McWalterჷTalk 21:09, 2 January 2012 (UTC)

Yep, it's a joint effort by Russian and Japanese scientists. ETA is 5 years.-- Obsidi♠n Soul 21:17, 2 January 2012 (UTC)

Very helpful. Let's hope they make two, 1f 1m. Kittybrewster ☎ 02:56, 3 January 2012 (UTC)

Once they start mass-producing them, can we expect McDonald's to introduce the Mammothburger? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:54, 3 January 2012 (UTC)

If it's anything like the McRib, it needn't have come from the inside of a Mammoth anymore than the McRib has been anywhere near the ribs of a pig... --Jayron32 05:08, 3 January 2012 (UTC)

Man, if the McRib isn't actual pork it blows this article out of the water, which would be a shame. Meelar (talk) 08:14, 3 January 2012 (UTC)

According to that article (which is a fascinating read), the McRib is from pork shoulder, which is at least in the neighborhood of the ribs. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:08, 3 January 2012 (UTC)

People have been known to eat the original, once they defrost them [5]. 75.41.110.200 (talk) 16:46, 3 January 2012 (UTC)

Cloned mammoth would have the advantage of being a tad fresher. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:55, 3 January 2012 (UTC)

According to the list of ingredients there are roughly 70 ingredients. The meat is made of pig innards and lots of salt. Typically, "restructured meat product" includes pig bits like tripe, heart, and scalded stomach. Bon appetite, Von Restorff (talk) 14:46, 4 January 2012 (UTC)

Bugs: read Isaac Asimov's short story A Statue For Father some day. – b_jonas 09:59, 5 January 2012 (UTC)

Higher derivatives of displacement w.r.t. time

The Wikipedia article on displacement lists several names for some higher derivatives of displacement w.r.t. time: snap, crackle, pop, lock, and drop (together with their synonyms). I've never seen these names before but I hesitate to declare them unestablished. Does anyone know how standard these terms are, and whether they meet Wikipedia's criteria for inclusion in the article? — Preceding unsigned comment added by 173.49.10.51 (talk) 20:30, 2 January 2012 (UTC)

Unhelpfully, that information claimed to referenced to wearcam.org, which is (really really obviously) an old mirror of Wikipedia itself, and thus isn't a reliable source. -- Finlay McWalterჷTalk 20:46, 2 January 2012 (UTC)

Jounce does cite a source for a couple of them, but the citation calls their use "facetiously" -- Finlay McWalterჷTalk 20:48, 2 January 2012 (UTC)

This article states, "Another less serious suggestion is snap (symbol s), crackle (symbol c) and pop (symbol p) for the 4th, 5th and 6th derivatives respectively. Higher derivatives do not yet have names because they do not come up very often." Based on this, I'd be inclined to just replace the 4th-6th equations with a sentence to that effect and drop the higher ones entirely. Clarityfiend (talk) 20:55, 2 January 2012 (UTC)

Searching Google for that phrase "In the UK jolt has sometimes been used instead of jerk" finds it used in all kinds of places; it's not clear what the real source is, and for us to give it credence as a ref we'd need to know who originally wrote it, and whether they're a reliable source. That specific page says it comes from someone called "Philip Gibbs", but who is that? It's on John Baez' website, which is a good sign, but it's not from Baez himself, so it's not a reliable source yet. -- Finlay McWalterჷTalk 21:06, 2 January 2012 (UTC)

Google scholar finds hits for 'jounce acceleration', and from memory, I think an Open university programme referred to 'joggle and jounce' in regard to fairground ride designs. AndyTheGrump (talk) 20:58, 2 January 2012 (UTC)

More - A Google Scolar search for 'jounce fairground' [6] finds an Oxford Journals article [7] that apparently contains the following: "Students can use a computer algebra system, such as Maple, to experiment with different fairground designs, eg to determine the jerk and jounce (third and fourth derivatives) of a track or find any track with a specified jerk and jounce...". I've not got access to the paper, but it looks convincing. AndyTheGrump (talk) 21:39, 2 January 2012 (UTC)

Wikipedia is not an indiscriminate list of any term anybody ever used to describe anything. Those names are uncommon. I have removed them from the article, and replaced the section with a discussion, including cited sources. Nimur (talk) 21:48, 2 January 2012 (UTC)

Thanks, that's an improvement. The names read like an advert for Rice Krispies! We might as well call them Piff! Paff! Puff! (see Swedish product) Dbfirs 00:10, 3 January 2012 (UTC)

immunolin

Know anything about "Immunolin"? It's a product that's supposed to help boost the immune system. It's about the immunoglobulins IgA IgG Igm. — Preceding unsigned comment added by 96.38.177.108 (talk) 22:40, 2 January 2012 (UTC)

I merged your duplicate question, keeping the more detailed second edition of it.

[8] is the company's official word on it. They call it a "nutritional supplement", which means they do not have to follow the FDA standards for drug testing or effectiveness. The product needs to be reasonably safe and non-harmful, which is what they claim, not necessarily to have any specific proven benefit (which they do not claim)--they say it is a "bovine globulin concentrate".[9] We do have articles about immunoglobulins. I wouldn't expect them to be orally available. DMacks (talk) 22:49, 2 January 2012 (UTC)

(edit conflict - DMacks has already said exactly the same thing, but I've typed it now so I'll post it!) You can get the official story at their website: http://www.immunolin.com/about-immunolin.aspx (basically it's just a load of antibodies). Their FAQ says it comes from the blood of cows. It would appear that it has no scientific backing, though - the bottle in the photo on the front page has "dietary supplement" on it, which is code for "has never been proven to have any clinical benefit whatsoever". --Tango (talk) 23:08, 2 January 2012 (UTC)

This is an interesting concept, but the information is too scanty for me to reach a firm conclusion. The first issue is that the various components are supplied as "capsules, tablets, or powders", which makes me doubt whether they are formulated with enough protection to reach the intestine intact. (Though simply protecting the oral area might arguably have some effect) See passive immunity for more information about ingesting antibodies. The second issue is, would the effect of these antibacterial components be positive or negative? Gut flora is natural and often beneficial; we rely for example on Oxalobacter to remove oxalic acid from foods like strawberries to keep us from getting kidney stones. These bovine blood antibodies don't sound specifically targeted in any way against harmful bacteria - though I'd be intrigued to see what happened if you immunized each cow with a whopping dose of killed Streptococcus mutans a few months before harvesting; would the supplement interfere with tooth decay? There's also the issue of what happens to the stuff - for example, if they did specially coat the bovine antibodies to get them past stomach acid to the gut intact, could some manage to sneak into the adult circulation? Could that cause trouble? (Do babies fed cow's milk get any harmful effects along the line of serum sickness from foreign antibodies in their circulation?) If the transferrin remains active and lowers iron levels in the gut lumen, does that lead to iron deficiency in the person taking the supplement? Then there are the "growth factors", including IGF-1, which is not very stable in adult intestine [10] but also probably others - if these reach the intestine intact, I would be very cautious about whether they increase tumor risk. Again, the effect in the mouth might be significant - does that mean faster healing of cold sores or a higher rate of oral cancer? In general this concept seems on the verge of being clever enough to potentially be beneficial - which means it's also on the verge of being potentially dangerous. But my suspicion is that they're just pouring a BSA byproduct into basic caplets and not actually isolating all these different things at high dosage/purity, nor formulating them to survive stomach acid, so it's just a refined method of eating blood. Wnt (talk) 09:47, 4 January 2012 (UTC)

Animal intelligence

Other than humans, which animals are the most intelligent? --108.225.115.211 (talk) 23:17, 2 January 2012 (UTC)

Animal cognition is a good place to start. My understanding are that animals that are agreed to be most intelligent beyond human are things like Dolphins, Chimps, Dogs, Pigs and Crows too. One test of self-awareness is the Mirror test, apparently an indicator of intelligence in some way. 23:26, 2 January 2012 (UTC)

See also the encephalization quotient, which gives a nice rough measure of gross brain potential across species. (It would add elephant to the above list, which is probably right.) Of course, it's worth remembering that in general, animals are specialists. There are some tasks of "intelligence" that many of them can do that far outclass humans (squirrels can remember the locations of thousands of hidden nuts, despite having a very tiny and otherwise unimpressive brain). It is not clear that there is anything like general intelligence even within the human species, much less across species. I'm a big fan of Temple Grandin's Animals in Translation as a nice way to think about the similarities and differences between the human mind and the minds of other animals; she makes the point, again and again, that thinking of animals and neurotypical humans as thinking in the same way (but with animals on a shallower end of the pool) is probably not a very correct model. --Mr.98 (talk) 00:13, 3 January 2012 (UTC)

The octopus is alleged to display problem-solving intelligence. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:03, 3 January 2012 (UTC)

And an uncanny ability to see into the future apparently. ;) --jjron (talk) 11:44, 3 January 2012 (UTC)

I see there was some controversy over whether "Paul" was one or two octopi. However, note the quote that octopi "are the most intelligent of all the invertebrates." That puts them head and shoulders, so to speak, above the average clam or jellyfish. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:01, 3 January 2012 (UTC)

Though ranking higher than a jellyfish is not much to be proud of, given that they lack brains altogether. (Cuttlefish are also known to be quite intelligent.) --Mr.98 (talk) 17:52, 3 January 2012 (UTC)

In fact, octopuses (and other cephalopods) are sometimes considered Honorary Vertebrates, meaning you have to use anesthesia when you operate on them, and other such things. Now there are a lot of vertebrates that most people don't consider particularly intelligent, but for an invertebrate, cephalopods are extremely advanced in the brain department. Buddy431 (talk) 00:27, 4 January 2012 (UTC)

They do surgery on octopuses? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:36, 4 January 2012 (UTC)

Of course! How else could they discover the fact their arms have minds of their own?

To find out if octopus arms have minds of their own, the researchers cut off the nerves in an octopus arm from the other nerves in its body, including the brain. They then tickled and stimulated the skin on the arm. The arm behaved in an identical fashion to what it would in a healthy octopus. The implication is that the brain only has to send a single move command to the arm, and the arm will do the rest. The neuroanatomy of octopi is a bit mysterious. The octopus is very intelligent. Scientific experiments have proven they can learn and possess both long-term and short-term memory. Octopuses can negotiate mazes, solve puzzles, distinguish between shapes and patterns and imitate observed behavior. They are notoriously clever at escaping containment and fishermen have found octopuses breaking into the crab holds of their boats to get a meal. In deference to their intelligence, some countries require the octopus be anesthetized before scientists can conduct surgery on them. In the United Kingdom the octopus has been given honorary vertebrate status, extending to this eight-legged cephalopod the same protections against cruelty and neglect that have been extended to other animals. Here you can see a cephalopod doing an IQ-test. They are able to open jars and turn the light off. They are able to use tools to build houses. To make a long story short: cephalopods are more interesting and much more intelligent than some humans. Von Restorff (talk) 13:21, 4 January 2012 (UTC)

Octopi opening jars or entering flasks to get at crabs don't really impress me - I think this is a simple application of their natural methods of food gathering. Fiddling around with an unknown object until something happens is not really a matter of intelligence but just responding to a sensation of yielding - it implies proprioception, yes, but not brilliance. But the octopus turning the light off with a jet of water very much impresses me, because it seems like a plan to climb the tank, to remember where to shoot the water, and to somehow imagine that it can change the light level, something which it cannot do in nature. It is hard not to think that the octopus actually hates the light, and the ability to hate, to be dissatisfied and imagine a change is possible, to me, seems the defining quality of human intelligence. I wonder if there is confirmatory data available about this type of behavior. Wnt (talk) 17:26, 4 January 2012 (UTC)

You just precisely described how I edit Wikipedia... Shadowjams (talk) 11:31, 6 January 2012 (UTC)

Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn-- Obsidi♠n Soul 11:48, 6 January 2012 (UTC)

January 3

Unconfirmed discoveries elements

In Timeline of chemical elements discoveries, there are 4 elements that are unconfirmed. What is that mean? Thanks!Trongphu (talk) 00:53, 3 January 2012 (UTC)

And someone explain this statement to me too, "Of the 118 known elements, only the first 94 are known to occur naturally on Earth (88 in non-trace amounts"? What they mean by non-trace amounts? Thanks!Trongphu (talk) 00:58, 3 January 2012 (UTC)

Unconfirmed in this context means that the labs in question said, "we ran this experiment on our big machine, and we detected what seems like a radioactive signature which seems to be this new unknown element," but no other labs have duplicated this yet and the International Union of Pure and Applied Chemistry has not agreed that the discovery took place. It can be non-trivial to duplicate some of these experiments because they are often tuned to the specific properties of the specific particle accelerators they were originally performed in, so finding a way to adapt that to another machine can be tricky. This is why it took awhile for them to figure out that the original claim for the discovery of element 118 was fraudulent — it wasn't just a matter of saying, "oh, this doesn't work after all" — there was basically only one or two other facilities in the world that could replicate aspects of the experiment, but neither of them were perfectly identical, so it took awhile — about a year — to figure out that the problem was the original data, not the replication attempts. You can see, for example, with ununcotium, that the 2002 discovery report by the Russians was recently declared to not be correct.

A trace amount means, "this element is theoretically created by natural (Earth) processes, but we haven't seen it or it's extremely rare." An example of this is plutonium, which is sometimes created in uranium ores where spontaneous fission and reabsorption of neutrons occurs. It's on the order of a few parts per trillion — very rare, but technically there. The vast, vast majority of plutonium on Earth was created by artificial means (nuclear reactors and particle accelerators). --Mr.98 (talk) 01:44, 3 January 2012 (UTC)

But for all 4 of them, it has been more than 1 years and why is it still unconfirmed? 3 of them has been discovered like about 10 years ago. And this statement also confused me "In 2011, the IUPAC has evaluated the 2006 results of the Dubna-Livermore collaboration and concluded that they did not meet the criteria for discovery." So did we actually discover element Ununoctium yet?Trongphu (talk) 02:00, 3 January 2012 (UTC)

In each case it's likely a different reason as to why the delay and/or lack of recognition. The specifics are probably quite technical. It seems like element 118 has not been discovered yet. It's possible the table is not up to date, but we'd want someone more versed in the specifics to make the call on that. --Mr.98 (talk) 02:38, 3 January 2012 (UTC)

If you want, you can read the gory details of the report where IUPAC recognized 114 and 116 as having been discovered, and rejected the 118 claim (they have a section on criteria, which in turn refers to an earlier, 1992 report of guidelines). Buddy431 (talk) 03:00, 3 January 2012 (UTC)

It's not that Uuo hasn't been discovered, it's just that the evidence for this element is not strong enough (in the eyes of IUPAC) to merit recognition as of yet, especially since ²⁹⁴Uuo (the isotope they claimed to have discovered) does not decay to isotopes of lighter elements that were known before the synthesis of ²⁹⁴Uuo. It most probably has been discovered, as nobody seems to have questioned their claims. IUPAC states that "evidence in the cases of elements Z = 113, 115, and 118 have not met the criteria for discovery", and a connection to known isotopes is one of their criteria (although they say it only makes it more "troublesome", rather than "exclusive"). "Unconfirmed" probably means that no second group has verified their claim by reproducing the experiment yet. Double sharp (talk) 11:51, 3 January 2012 (UTC)

Best solution for IED (Improvised Explosive Device)

So I've been watching Deadliest Arms Race on National Geographic and after seeing how many soldiers, photo journalists, medics, etc. are injured if not killed by this relatively simply device that almost anyone with a pulse could build I'm convinced there has to be a somewhat equally effective and inexpensive solution we can muster up. More specifically, these devices for the most part are set off using a pressure plate to ignite them meaning a solider or hummvee or anything above the weight threshold triggers the device and boom. Would a viable solution be a solder or vehicle that was armed with a device that had an anchor or weight that could be launched anywhere from 50 to 200 meters and then retracted so that it would pass over the next 50 to 200 meters of terrain to trigger or detonate any IED's that a solider may have missed or one that would have been too destructive for an armored car? It would be similar to a grappling hook that could be launched just instead of a hook just a weight and retracted quick enough to prevent troops from being stationary for too long it could either be powered by an explosive, air pressure, or magnetically. Is this a viable solution? Have things like this been tried before and failed? Sorry for asking so many questions I'm just looking for someone with some military knowledge or a good answer! Thanks! — Preceding unsigned comment added by 76.108.156.117 (talk) 02:22, 3 January 2012 (UTC)

Doesn't sound viable to me:

1) It would slow them down dramatically, allowing enemy forces to gather and ambush them.

2) Using such a device would be exhausting (this doesn't apply to the vehicle launched version).

3) The insurgents would soon adapt and use other trigger mechanism, like cell phones and a spotter. StuRat (talk) 02:26, 3 January 2012 (UTC)

I don't know why you think that the fact that the weapon is simple means the countermeasures should be simple as well. Offensive capability and defensive capability are not symmetrical. In most cases offense is much easier than defense. Defensive measures are generally much more resource intensive and/or globally disruptive than offensive measures, because a true defense has to be able to guard against lots of possible attacks, while the offense generally has to get through one type of defense. (Consider how many resources it takes to prevent car bombings — day in, day out, when you don't know where the target is going to be — versus the resources it takes to implement them.)

As for your specific situation, it sounds pretty silly to me. Imagine if every car going down every crowded street was shooting a retractable anchor at every possible place that could hold an IED. It would be completely ridiculous. If there weren't IEDs, they'd probably be kicking trash heaps around every neighborhood, breaking things willy-nilly, generally being completely disruptive. If there were IEDs, they'd be setting off explosions. Neither are very viable even in a remote war zone, much less a city filled with civilians.

The simplest IED defense is having well-armored vehicles. Even that isn't that simple. --Mr.98 (talk) 02:43, 3 January 2012 (UTC)

(edit conflict with Mr. 98) In fact, roadside bombs increasingly have been triggered remotely, often by cell phone phones and similar devices [11]. The article I linked claims that about 90% of IEDs are found and disabled before they can hurt someone. Here's an interesting report from 2008 about the use of IEDs in Iraq. The wide availability of conventional munitions (capable of being turned into bombs), along with a "target rich environment" leads to a situation where IEDs are the leading cause of casualties, even if, individually, they are relatively ineffective and likely to be disarmed. Buddy431 (talk) 02:55, 3 January 2012 (UTC)

An IED is essentially an improvised land mine. Various land mine clearing techniques are called Demining, that article even has a photo of a soldier training a technique using a grappling hook. The problem as already stated is that this slows you down, you can only practically employ it in situations where you believe there is a very high risk of land mines and the thing with IEDs is that they can be placed in the places where they are NOT expected. Vespine (talk) 03:01, 3 January 2012 (UTC)

And speaking of which, of course our article even has a relevant section Improvised_explosive_device#Detection_and_disarmament. Vespine (talk) 03:04, 3 January 2012 (UTC)

What you're describing is essentially a loony-toons version of a Mine flail.

As others have said, it's not really possible to use them in every possible situation where a mine or ied could be used. (And, if their use in a particular region became commonplace, it wouldn't take a genius to stop using pressure-sensitive IEDs and switch over to something remote controlled, or timed, or whatever.) APL (talk) 04:26, 3 January 2012 (UTC)

A more effective solution is to have a robotic car lead the envoy. The car could be remotely controlled by someone in the second vehicle, or even from a command post thousands of kilometers away. If adding remote control is too hard, just use someone dispensable as the driver. --184.66.8.204 (talk) 05:52, 3 January 2012 (UTC)

Though the countermeasure to this is fairly obvious — trigger on random vehicles. Aside from the fact that robotic cars are neither cheap nor easy to use. --Mr.98 (talk) 12:48, 3 January 2012 (UTC)

U.S. television just finished a season of Bomb Patrol: Afghanistan where we got to see all sort of IED clearing machines and techniques including heavy rollers in front of the truck, large truck mounted metal detectors, a couple kinds of Nintendo-controller driven robots, etc. Cell phone controlled bombs were most common so we started putting radio jammers in each convoy then pressure plates became more common[12]. So then we added self-protection adaptive roller kit system (SPARKS) and mechanical claws to heavily armored trucks. 75.41.110.200 (talk) 16:15, 3 January 2012 (UTC)

Many persons in Iraq have been injured or killed by IEDs alongside the road,("roadside bombs") rather than directly in the road to be driven over. The flail would have to beat or the roller to smash down not only the pavement, but every object next to the road, such as parked cars, dead animals and trash cans. Bombs were commonly placed in the median strips of divided highways, and under bridges which convoys drive over or under. The proposed method would be useless in these cases. Huge bombs could also be placed in sewer or drain pipes or culverts or manholes under the road, and set off by wire, preventing detonation by flail or roller, and being relatively immune to electronic jamming. In the 19th and early 20th centuries, occupying armies resorted to Collective punishment (Not that I am recommending that course), to discourage attacks on convoys, rather than attempting to make every vehicle bullet proof and bomb proof. Robot or remote-piloted vehicles are rapidly getting more capable, as witnessed by the DARPA Grand Challenge (2007) and the Google driverless cars. Many deaths among the US and allied forces in Iraq were in attacks on supply convoys, which could in future occupations be unmanned vehicles, such as the remote piloted tracked vehicles made by Howe & Howe Tech, and watched from above by Unmanned aerial vehicles, [13], [14], which could attack persons planting bombs before a convoy rolls, or seen nearby with a celphone or pushbutton trying to trigger a blast when a convoy approaches. In Iraq, one big problem was that immense military stores of high explosive as well as bombs and warheads were left unguarded in the initial weeks of the occupation, or even years after the invasion, rather than being destroyed, either because US forces lack the manpower to guard the ammo dumps, or because US forces wanted to search through them for the supposed weapons of mass destruction which were the principal justification for the invasion. See Al Qa'qaa high explosives controversy, for instance. When combat operation ended, early after the invasion, there were 600,000 to 1 million tons of munitions left in Iraq government warehouses and in munition stockpiles averaging 40 tons, throughout the country, possibly with the specific intent of equipping insurgents for a protracted IED assault on convoys and buildings. In some cases, the metal panels of the warehouse were removed by scavengers, leaving piles of bombs visible, Eventually the bombs also disappeared, to be used for IEDs. A helicopter pilot lamented that one rocket would have gotten rid of the whole pile of bombs. In addition to these explosives negligently provided to the insurgents, supplies of high explosives may have been smuggled in from other countries opposed to the allied occupation. If the partisans had to make explosives out of raw ingredients, (a little home made gunpowder, or some other McGyver bomb) the lethal effects would have been far less than just setting off a large 122 mm artillery shell, as has been the common practice with Iraq IEDs, rather than some home-made Swiss Family Robinson cocoanut bomb with improvised black powder. Edison (talk) 16:31, 3 January 2012 (UTC)

You might find the following article interesting old chap. It's from the Mirror which is a bit of a rag but seems plausible. It's a report on our good old boys in uniform mounting leaf blowers on their remote controlled jobbies to blow debris and dirt away to expose those beastly bombs - see [15]. Tip-top idea if I do say so myself, rah! Quintessential British Gentleman (talk) 19:27, 3 January 2012 (UTC)

I've seen video documentaries showing some rather elaborate anti-IED vehicles, but the best solution is clearly (a) don't give people good reasons to want to blow you up, followed by (b) don't drop vast amounts of explosive on them that include a high percentage of duds that they can scavenge for explosives. Wnt (talk) 09:10, 4 January 2012 (UTC)

The American army can easily defend itself against IEDs by not invading other countries. The number of American soldiers killed by IEDs in their own country is quite low. IEDs in countries like Afghanistan are only deadly within a rather close proximity. I believe this method is a cheap and effective way of saving lifes. Von Restorff (talk) 13:50, 4 January 2012 (UTC)

Use of Inhaler for Asthma

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

I'm first aider, often working in remote locations, possibly several hours from medical support. Knowledge of the use of asthma inhalers is part of my skill set. Obviously I'm not a medico. But we are allowed to beg, borrow and steal, then encourage the use of inhalers when they are likely to help. They are highly unlikely to do any harm. When I saw the heading, I thought this item could add something useful to my first aid knowledge. Sadly, it's been deemed a request for medical advice. Has the difference between first aid advice and medical advice ever been discussed here? HiLo48 (talk) 21:55, 3 January 2012 (UTC)

Clock and sundial comparison in General Relativity

Just thought of this. Go on, shoot it down in flames. Clocks are shown to run slower at the base of skyscrapers compared to those on the top floor. (This prediction of Einstein's General Relativity has been empirically confirmed.) Now imagine two sundails on the ground and top floors. Will the one at the base indicate a time slower than the one higher up? If so, how would it work? And if not, would not this form of time measurement be impervious to the constraints of GE, and thus lead to impossible results? And in any case, if you had two sundails positioned alongside two atomic clocks on these floors, would you be able to measure the differences between the way they are counting time? Myles325a (talk) 07:31, 3 January 2012 (UTC)

The two sundials will give the same time, because the sun is in the same position. It doesn't seem to say anything about GR, so I don't see what would be impossible about the results. You couldn't measure any difference in the time available for your study, but over millions (?) of years you might be able to see that the sundial is gaining time, so to speak. IBE (talk) 09:01, 3 January 2012 (UTC)

If nothing else, the sundial at the bottom would lag the one at the top slightly - by an amount equally to height_of_building / speed_of_light. Also, because of the different locations, most of the time the angles between sun, gnomon and dial would differ slightly, so they would show slight different times. I don't have the time or inclination to work out how the time difference in each case compares to the time difference due to GR. Mitch Ames (talk) 10:13, 3 January 2012 (UTC)

There is actually no speed-of-light lag. The shadow moves on the sundial because of rotation of the Earth, and lower elevations don't lag behind higher elevations in the rotation. -- BenRG (talk) 22:21, 3 January 2012 (UTC)

But the core fact is that time passes slower at the bottom of the skyscraper than at the top. A sundial does not measure time, it measures the position of the sun. Since time is passing slower at the bottom, the solar day is shorter (in measured time, e.g. seconds) than at the top. Our units of time have historically been defined via observed celestial configurations (a day is the time between two sunsets/sunrises/solar noons, a month is the time between two full moons, a year is the time between two spring equinoxes...). All of these are not really units of time proper, since they vary quite a lot even for an observer at a given point on Earth, much more for different observers. We are still used to this historical accident, and have modelled it in our modern system of time keeping (to different approximations - months are too long, leap years are longer than other years, we use leap seconds to synchronise solar time and atomic time...). But this does not, of course, affect considerations of time in a cosmological context. --Stephan Schulz (talk) 10:30, 3 January 2012 (UTC)

Stephan Schulz's answer is correct, but I want to point out that essentially all of the time standards that we use in practice (UTC, TAI, "local" times) are more of the sundial type, i.e., they advance in lockstep everywhere on Earth and as a result don't exactly agree with proper time. A proper second is 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of a caesium 133 atom that's moving with you (see second), but a UTC second might be slightly more or fewer periods than that, depending on where you are and how fast you're going. This is really about convenience, not historical accident, since the main point of timekeeping is to synchronize things that aren't always following the same worldline. -- BenRG (talk) 22:21, 3 January 2012 (UTC)

In other words, we're going by not just the Greenwich latitude but also the Greenwich height, adopting a universal unit of time which is defined as time in one particular place. I think. Second mentions two laboratories working out the number of vibrations of cesium atoms in a second, but is that a second as measured at sea level or some other height? (And by GR is the time dilation the same at sea level at any latitude...?) And can we tell the difference? I ought to work this out myself but somehow I'm not getting my blood up right now. Wnt (talk) 09:04, 4 January 2012 (UTC)

You must distinguish between the time we use for most things, and "proper" time. For proper time, a second is always defined via the Cesium atom's hyperfine ground states. That means that a second for one observer is different than a second for a different observer. Time is not absolute - in fact, even order of events is not absolute. That is the "relativity" in Theory of Relativity, and its the thing that most people find even harder to grasp than the equations. As Ben said above, on Earth we are nearly always more interested in synchronization of our lives, not in real time keeping. You want to be at the train station at the same time as the train, you want to meet with your date at a restaurant (and boy, does time get dilated if one of you is late...). Since the differences in time on Earth are so minuscule, we can use local time for synchronization - local time between any two people on Earth is close enough that even the most discerning date will not walk out because of that difference. And, with GPS, NTP and radio clocks, we seem to be moving towards explicit synchronization again. Yes, time dilation at different latitudes is different because of the different speeds of the surface due to the rotation of the Earth. --Stephan Schulz (talk) 09:47, 4 January 2012 (UTC)

Thanks for answering on that last point, but have you taken everything into consideration? At lower latitudes the Earth moves faster, but sea level is higher. The gravitational potential energy is the same. But maybe the gravity itself at that height can still vary, because the gravitational potential is the sum of gravity going all the way up? Although the Gravitational time dilation article mentions gravitational potential, I think it's really just the plain acceleration felt at a spot rather than some more sophisticated number? So I'm thinking it might vary by some exceedingly small amount, but not by as much as you're saying - alas, I don't know what I'm talking about. ;) Wnt (talk) 17:08, 4 January 2012 (UTC)

Biological assignment

please help me to title of an assignment in which the table content are 1.human male reproductive system 2.human female reproductive system 3.fertility 4.menstruation 5.pregnancy 6.parturition 7.lactation. 8.family planning .Rikisupriyo (talk) 09:42, 3 January 2012 (UTC)

I have taken the liberty of providing your question with a header, so it's not confused with the previous question. Is there nothing in what you were given to do that may provide an answer? Grandiose (me, talk, contribs) 09:58, 3 January 2012 (UTC)

"Essay on human reproduction" --Lgriot (talk) 10:44, 3 January 2012 (UTC)

That is close to the current layout of our Human reproduction article. 75.41.110.200 (talk) 16:02, 3 January 2012 (UTC)

How about, "Human Reproduction: Neither Birds nor Bees." --Mr.98 (talk) 16:12, 3 January 2012 (UTC)

Actually, he could get the same kind of info for most any mammal. Except maybe for item 8 (family planning) or the omitted item 9 (divorce court and child custody) or 10 (STD's). ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:33, 4 January 2012 (UTC)

The user Jiminy Cricket who usually chimes in at the juncture to inform OP that WP never never issues medical information or helps out with homework is in in insect hospital have the poo removed from his head, so let me just skuttle in and tell you what he would have: "Bzzzz bzzzz...Wp is not a forum to obtain medical info, and how will you become a Rhodes Scholar and get a Nobel Prize if you don't DO YOUR OWN FREAKING RESEARCH!!!????

There...(wags finger) Myles325a (talk) 04:56, 4 January 2012 (UTC)

Directing readers to articles is a normal approach, so they can do their own homework. Asking how reproduction works in mammals is not asking for medical advice, it's simple biology. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:23, 4 January 2012 (UTC)

Nickel content in Rhodium

I have read that rhodium is linked to nickel ore and that's its use in jewelry is to add and long-lasting, durable shine. I have two certified gemologists going head to head, one insisting there are elements of nickel in rhodium, the other saying that's absolutely untrue. I'm stuck squarely in the middle, with a nickel allergy that makes me lean toward the first gemologist's opinion since I've had to get rid of some fairly pricey pieces of jewelry and am bearing the scars to prove it, besides which there were periods at the height of the allergic rashes during which I could not get a good table at my favorite restaurant, but the second guy is widely held to be the city's ranking expert. He told me I was stupid, which does tend to irritate me a bit, a character flow to which I freely admit, but I'm only interested in facts so that I might purchase jewelry from a well-informed position.Haramel (talk) 10:13, 3 January 2012 (UTC) <Wikipedia>

First, with regard to rashes, we cannot give any medical advice. Second, take a look at our articles Rhodium, which says it is an element. Rhodium can be chemically refined to a pure element, which would not contain nickel, but one metal may be alloyed with another, in which case nickel, gold, or other metals could be present. The rhodium article says it is rarely made into jewelry as a pure metal because of its high melting point and because it is low in ductility. The article Plating mentions the common practice of flashing sterling silver with a thin plated layer of rhodium to prevent the silver from tarnishing. (It's hard to understand how the item would look like silver if all you see is the layer of rhodium.Maybe "shiny silver"="shiny rhodium.") The plating article says that rhodium-flashed silver often has a layer of nickel over the silver and under the rhodium. In such a case, a scratch or flaw in the rhodium flashing or wear through of the rhodium plating could allow contact with the nickel layer. Is your "rhodium jewelry" solid pure rhodium, or is it something plated with rhodium? This site says that pure rhodium rings are likely to break, and that the metal costs many times more than gold, but one poster says he has made a few rhodium rings, or rings made of rhodium alloyed with platinum (which is cheaper than rhodium). This site says that white gold, silver and platinum are often plated with a few microns of rhodium to make the appearance whiter and to provide resistance to scratches, but that the plating can wear through in 1 to 5 years. Replating is said to be a reasonably priced option. Edison (talk) 16:05, 3 January 2012 (UTC)

This isn't my expertise, but according to the article rhodium is often isolated from nickel ore, so if rhodium is not perfectly pure it could have nickel in it. According to carat "fine" 24 carat gold is 99.9% pure; I don't know what the standards are for rhodium or what kind of rhodium you were sold, but clearly you might be interested in the standard used and preferably the original lot assay of the metal used. Additionally, there is a "adimethylglyoxime spot test" to check specific items for nickel. Also I'm seeing Google hits for rhodium being used to plate nickel containing jewelry like white gold, and the plating wears through releasing the nickel unless repeatedly reapplied; supposedly the plating can be good enough to protect people with nickel allergies ([16]). The social element of this perplexes me the most - a restaurant would seriously deny someone a good table because of an allergic rash? Isn't that illegal, not to mention just plain wrong? Wnt (talk) 16:51, 4 January 2012 (UTC)

De-miting a snake and its tank

My ball python just began to shed (verb) this morning, so I peeled off the rest of the shed (noun) under warm water with softsoap in the sink and I can't see any dark spots under its ventral scales, which suggests that I got him just at the right time to de-mite him. For the tank, I have the coconut bark bedding, which I look at from time to time and see that there are mites walking all over the place -- I scooped up a bunch of it, put it in a 9x13 aluminum pan and have it in the oven at 350° and will leave it there for about 15 minutes -- will that suffice to kill the mites and eggs living in the bedding? And then when there's no bedding left, I scrub the walls with bleach water? Does this sound like it will work, or once a snake is infested, it can never be clean? Thanx! DRosenbach ^{(Talk | Contribs)} 15:51, 3 January 2012 (UTC)

Have you tried asking your veterinarian/herpetologist? Someone who deals with snakes on a regular basis may be able to help you with this problem. --Jayron32 16:00, 3 January 2012 (UTC)

I thought someone who had a snake would be able to answer appropriately. Thanx! DRosenbach ^{(Talk | Contribs)} 16:33, 3 January 2012 (UTC)

“mites walking all over the place” -just a thought. Slow changes often go noticed. Could this vivarium have become too humid (thus encouraging mites)? I say this because I have found cheap domestic type hygrometers to be as much as 10% out in the 'normal' range. At the upper level for ball pythons this might be significant in causing the bedding to get moist.--Aspro (talk) 18:32, 3 January 2012 (UTC)

Disclaimer: I am not an expert, ask your local vet. Replace the bedding, do not clean and reuse it. Clean the vivarium (BUT NOT THE SNAKE!) with something like Ardap. The snake itself can be cleaned with something like Callington Mite Spray or ZooMed Mite Off. Drowning the mites on the snakes body is also an option in some cases. Von Restorff (talk) 14:22, 4 January 2012 (UTC)

Think by now the OP will have discovered that Google is his friend and gotten a lot of centred advice from like-minded herpetophiliacs. There is loads about this. Don't know about you Von Restorff but ever since this question was posted I've had the uncontrollable urge to itch myself. Feels like a bad case of formication coming on. Must wonder down to the garden shed, to see if there is any of that DDT powder left.--Aspro (talk) 14:58, 4 January 2012 (UTC)

I know another Aspro; a beautiful white cat with a green and a yellow eye owned by a friend of mine! Note to self: must wash hands after petting Aspro. Von Restorff (talk) 15:06, 4 January 2012 (UTC)

Caterpillar identification

Resolved

This video was made about a week ago in Israel -- can anyone help me identify the species? DRosenbach ^{(Talk | Contribs)} 17:10, 3 January 2012 (UTC)

Looks very much like a tomato hornworm, down to "eight V-shaped markings". Though it's native to North America, I think it is often an introduced pest where Solanaceae are cultivated. Anyone have a link describing the introduced range? SemanticMantis (talk) 17:21, 3 January 2012 (UTC)

Thanks! DRosenbach ^{(Talk | Contribs)} 21:42, 3 January 2012 (UTC)

Quick question...

How much can rhino beetles weigh at the most? (I didn't see anything on it in the article). Heck froze over (talk) 19:10, 3 January 2012 (UTC)

National Geographic says scarab beetles (of which the Rhinoceros Beetle is a type) can weigh up to 3.5oz/100g - one would assume that these big bugs are at the higher end of that range old boy! See [17]. Quintessential British Gentleman (talk) 21:45, 3 January 2012 (UTC)

Distance that an electric current will arc

Is there an equation that relates the distance an electric current can arc through air or another medium between two nodes based on their impedence, the voltage and/or other factors? Thanks, 78.144.251.167 (talk) 20:50, 3 January 2012 (UTC)

I don't know the answer, but the distance only affects the arcing probability which decreases with increasing distance. So, you should expect a statistical answer. Plasmic Physics (talk) 22:23, 3 January 2012 (UTC)

Electric spark mentions qualitatively how sparks form, it depends on the Dielectric strength of the air through which the arc is traversing, the relative voltage drop between the ends of the arc, etc. --Jayron32 22:30, 3 January 2012 (UTC)

The article High voltage says that in dry air,at standard temperature and pressure, the breakdown voltage between spherical electrodes is about 33 kilovolts per centimeter of separaation between the electrodes. This statement is defective in not specifying the diameter of the spherical electrodes. The breakdown for smaller electrodes or points will be less than for large spherical electrodes. Once a power arc occurs, there will be a typical voltage drop per distance. "Electrical power distribution handbook," (2004) by Short (how appropriate a name), page 344, says the voltage across an arc is 10 to 16 volts per centimeter, across a current range of 100 to 80,000 amperes. The power (and heat, and explosive force) from a power arc is amazingly large. That book states a 3 inch arc carrying 10,000 amperes dissipates a megawatt. Edison (talk) 23:30, 3 January 2012 (UTC)

Can we lose our soul?

I mean, could we lose, after some kind of brain damage, this feeling of self, but still be able to process information, in a rather automatic way? 88.8.76.174 (talk) 23:23, 3 January 2012 (UTC)

Sure. It's called the British Parliament. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:56, 3 January 2012 (UTC)

On a more serious note. Dissociative disorder. Maybe also Lobotomy. Also, I expect you are just using the term figuratively, but I don't think any scientist would seriously call a mental disorder "losing your soul". Vespine (talk) 00:38, 4 January 2012 (UTC)

The notion of an incorporeal "soul" is a religious and philosophical concept, not a scientific one. See Cartesian duality for more on that philosophical topic. "Feeling of self", however, is a psychological topic, so that would fall within the realm of science. See Psychology of self. For a couple articles pertaining to the loss of sense of self, see Depersonalization and Depersonalization disorder, the latter of which is one kind of dissociative disorder. Red Act (talk) 02:14, 4 January 2012 (UTC)

See also Cotard delusion. Ariel. (talk) 10:26, 4 January 2012 (UTC)

Conservation of Momentum and Energy

Suppose there is a swinging pendulum with a negligible mass of string and no air resistance. It is released from a height and is allowed to swing. Since there is no friction, it will return to the same height after each swing. In this case, am I correct in assuming that total mechanical energy (PE + KE) is conserved, but momentum is not conserved? If so, what does being conserved mean in this case? Does it mean that it must have the same value at every point along the swing in order to be considered conserved? Since the momentum is always changing values, but will always return to the same value at the end of each swing cycle, is it still considered "not conserved?"

Lastly, is it also true that Kinetic Energy is not conserved? But total mechanical energy is?

Thanks, Acceptable (talk) 23:56, 3 January 2012 (UTC)

Momentum is conserved in a closed system. In this case, the pendulum is exerting a force on the Earth through the point where the string is anchored. When the pendulum is going left, the Earth is going right (with much smaller velocity).

It's true that kinetic energy is not conserved. Energy can change types. Rckrone (talk) 00:16, 4 January 2012 (UTC)

Are you thinking of Conservation of linear momentum? Nothing states momentum needs to be conserved when external forces, like gravity, act on an object. At the end of each swing cycle, the pendulum's momentum will be 0 and I believe you are correct that the total mechanical energy will be conserved, that's just another way of saying Conservation of energy. Vespine (talk) 00:19, 4 January 2012 (UTC)

January 4

Is caring for sources a kind of bias?

If I dismiss some sources (like Yahoo Answers and the like) when searching for information, is that a kind of bias or even fallacy (if what I've seen is rubbish, then the rest must be too)? On the other hand, it seems difficult to accept all the sources as potentially valid...88.8.76.174 (talk) 00:43, 4 January 2012 (UTC)

Claiming "all information on Yahoo Answers is useless" is biased. Some of it is correct. Claiming "it is not possible to know if an answer on Yahoo Answers is correct or not because the interface does not require the users to provide verified credentials or even a valid reference" is not a bias. It is a description of Yahoo Answers. -- kainaw™ 00:54, 4 January 2012 (UTC)

Yes, it is bias and discrimination, though based on experience, and therefore justified. It is also a logical fallacy, as you point out. See genetic fallacy. However, estimating the probability of a source providing useful information is an indispensible element of research, especially when there is an abundance of sources to be evaluated. In this case, one's time is (more probably) better spent looking elsewhere than at sources which have proven unreliable in the past. Doing so is logical, based on an empirical evaluation of probability, and the fact that we don't have infinite time to evaluate all of the available sources. Dominus Vobisdu (talk) 01:06, 4 January 2012 (UTC)

Note that while one expert source trumps one random guy on the internet, one expert source may not be as accurate as many random guys on the internet. For example, if you asked an expert the atomic weight of tin, you'd probably get the right answer, but he could make a mistake, such as a typo. If you asked 100 random people on the internet, some answers would be dead wrong, but the majority, or at very least the plurality, would be right. Now this is a trivial example, but the same applies to more complex questions, too. This theory is why many think that stock prices reflect the value of a company so well. So, if you reject the consensus of the public in favor of a single expert, then, yes, that's an unwarranted bias. StuRat (talk) 01:46, 4 January 2012 (UTC)

It's true that there's problems with sourcing, and potential biases introduced through the sources used. For starters there's often a reporting bias, meaning certain things are more likely to be reported on by what we regard as reliable sources than other things. Then supposed reliable sources are not always as reliable as we may hope. For example I almost invariably find that when something significant enough happens in my local area to be reported in a major news source, almost inevitably there will be some (usually) minor detail or details wrong - misspelled name, inaccurate distances, other minor errors that any local would know to be wrong that while not overly significant are still wrong, heck, even the times I've been 'quoted' in the media almost invariably they have tweaked what I 'said' to suit themselves; not enough to totally change my meaning, but often enough to be not something I'd actually say. Now if this information was turned into an article on Wikipedia, those blatantly incorrect factoids could be reffed as being true and at times would be virtually unchallengeable. On a similar note I have seen a website I have created and another website a friend created cited as sources on WP; not that they are incorrect, but it's interesting if I made something up and added it straight to WP it could likely be challenged, but if I make it up, put it on another site, then that site gets cited that's regarded as sourced. Nonetheless, giving supposedly reliable sources is about the best we can do at this stage, but also why we allow many unsourced claims to remain in articles. After all, sometimes that 'random guy on the internet' does know better than a 'reliable source'. --jjron (talk) 12:05, 4 January 2012 (UTC)

Epistemologically speaking, one random guy could trump an expert, and probably does on a regular basis. There is nothing that says being a certified expert makes one always correct. And there is nothing that says the crowd should necessarily be correct, either. (As plenty of "scientific literacy" studies have shown, going to large numbers of people actually doesn't help on many questions.)

The reason I do not generally trust Yahoo Answers is because my prior experiences with it show it not to be correct most of the time. That is itself a fallacy — it is the problem of induction — but I don't let that bother me much. I do not endeavor to be perfectly logical; rough heuristics work fine most of the time. --Mr.98 (talk) 12:33, 4 January 2012 (UTC)

Caring about bias is a form of bias; metabias. Von Restorff (talk) 14:10, 4 January 2012 (UTC)

how to calculate the tolerance of parallel resistors

for example,R1(10k,1%),R2(20K,5%),if the two resistors are parallel,what's the total tolerance of them? — Preceding unsigned comment added by 121.15.144.10 (talk) 02:04, 4 January 2012 (UTC)

If you compute R = 1/( 1/R1 + 1/R2 ), first using both resistors' values at their extreme low end, and then again at their extreme high end, what do you get? -- ToE 03:32, 4 January 2012 (UTC)

I don't think there's an easy way to do this. As the above suggests, you have to work it out the long way. However I don't think you need to work out the low AND high, you just work out the expected value and compare it to either the low OR the high. i.e. I believe a 10K 1% resistor falls between 9.9K and 10.1K, not 9.5 to 10.5, that would be 0.5%. In the example, the expected value is 6.66K, work out the "low" using 9.9K and 19K and get the percentage of the difference to get the circuit tolerance. Vespine (talk) 04:06, 4 January 2012 (UTC)

Actually, scratch that, maybe you do need to work out the low and the high.. I don't have the time right now to confirm, it doesn't seem to affect your example, but I'm not sure if there are circumstances where it would make a difference. Vespine (talk) 04:11, 4 January 2012 (UTC)

The low and high limits will indeed be off by different percentages. Using the highest possible values for both resistors gives 6.81994 kΩ, which is 2.299% higher than the nominal parallel resistance. But using the lowest possible values for both resistors gives 6.50865 kΩ, which is 2.370% lower than the nominal parallel resistance. Red Act (talk) 04:47, 4 January 2012 (UTC)

Our article propagation of uncertainty addresses this sort of question from a more rigorous statistical point of view, but is almost certainly well beyond the scope of what is being asked here. -- ToE 05:11, 4 January 2012 (UTC)

You may also want to read Engineering tolerance and Tolerance analysis. Red Act (talk) 05:25, 4 January 2012 (UTC)

Very good. From Tolerance analysis (which is written from a mechanical engineering point of view): "Arithmetic tolerance stackups use the worst-case maximum or minimum values of dimensions and tolerances to calculate the maximum and minimum distance (clearance or interference) between two features or parts." -- ToE 06:27, 4 January 2012 (UTC)

"Lowest possible" and "highest possible" are incorrect. There is no absolute cutoff for the variation of the resistances, just a statistical probability that they will exceed the stated variation. A larger variation is possible some percentage of the time. If you had 100 identical 10% resistors in parallel, it would be incorrect and misleading to state that the "largest possible" resistance would be calculated by assuming each was 10% higher than nominal. Take statistics into account. Edison (talk) 14:18, 4 January 2012 (UTC)

The right way to do that is by performing a partial differentiation. if R is a function of R1 and R2 $R=R(R_{1},R_{2})\,$, than the uncertainty $\Delta R\,$ is given (to first order) by $\Delta R={\frac {\partial R}{\partial R_{1}}}\Delta R_{1}+{\frac {\partial R}{\partial R_{1}}}\Delta R_{2}$. -- Dauto (talk) 16:10, 4 January 2012 (UTC).

I believe there is a minor typo in the above. Dauto, shouldn't the formula be:

$\Delta R={\frac {\partial R}{\partial R_{1}}}\Delta R_{1}+{\frac {\partial R}{\partial R_{2}}}\Delta R_{2}$

...in other words, the formula for the total derivative of R with respect to R1, R2. Nimur (talk) 16:40, 4 January 2012 (UTC)

I don't quite understand why Edison says it's incorrect and misleading to calculate using the high or low values. Real world resistors don't follow a perfect bell curve distribution. The tolerance IS an absolute cutoff for the variation of the resistance. If you have a resistor that falls outside of its tolerance, it is faulty and you chuck it out. In fact, I'm pretty sure some 1% resistors are just the ones which tested within 1% of their intended value picked from the processing line which makes regular 5% tolerance resistors. Batches of resistors can also easily be skewed in a direction, so their tolerance won't necessarily statistically "even out". Manufacturing processes these days are very good and you'll probably find that most 5% resistors you get are more like 3% resistors, but "in principle" there's no reason why you could get a whole batch of 100ohm 5% resistors which measure 95 ohms. Vespine (talk) 22:20, 4 January 2012 (UTC)

What it boils down to is: if you're building a circuit (or a bridge, or anything), and you determine that a tolerance or error of X % is absolutely required in order for Feature Y to work ... you'd better make sure you know what your supplier means when they say "X % tolerance." The difficulty is defining "absolutely", "requires," and "%" in context. This is why engineers are paid a lot more than 8th-graders, even though a surprising quantity (95%, ±5%) of real-world engineering mathematics could be done by the eighth-grader. Nimur (talk) 22:55, 4 January 2012 (UTC)

Why was Stjerneborg subterranean?

Our article Stjerneborg mentions that it was subterranean, just like this picture here. But why was that necessary? The Danish article (Google translation) talks about protection from wind gusts. Obviously, you wouldn't want to hang your quadrant on a wooden wall that shakes in every wind, but if you use masonry, you should be stable enough to not have to worry about wind. Conversely, the big problem for Tycho, atmospheric refraction, is increased. The closer to the ground you are, the more ground effects you will get - in the extreme case, you might even get a mirage. BTW, thanks to Mr.98, who made me first aware of Stjerneborg here. — Sebastian 06:53, 4 January 2012 (UTC)

That Google translate result gives a plausible explanation: "This new observatory was built underground, and only during observations was left observation hatches open. In this way we got a better accuracy, and then also better manage temperature fluctuations helped to better obervationer." Remember, in the 1500s there were no thermostats! So an underground chamber would be an effective way to keep a more constant temperature. Wnt (talk) 08:55, 4 January 2012 (UTC)

Interesting idea. Let's look at the effect of temperature on the instruments. What effects are there? I can think of thermal expansion. The coefficient for brass is about 20 10⁻⁶/K, or 200 μm/m for ΔT=10K. This may be in the order of magnitude of a very good naked eye. However, for measurements of angles, linear expansion is irrelevant. Unless the structural parts of an instrument are made of vastly different materials for the different directions, that effect seems to be negligible. Am I overlooking anything? — Sebastian 10:24, 4 January 2012 (UTC)

Actually, Tycho's eyesight must have been even better than that; he claimed that 5 were easy to discern, which is 25 μm/m.

Read this. Our article Tycho Brahe says: "Tycho Brahe was granted an estate on the island of Hven and the funding to build the Uraniborg, an early research institute, where he built large astronomical instruments and took many careful measurements, and later Stjerneborg, underground, when he discovered that his instruments in the former were not sufficiently steady.". More info can be found here. On tychobrahe.com it says: To further improve the accuracy of the position measurements, Tycho found that it was necessary to shield the instruments from disturbing wind gusts, and to have the instruments on solid fundaments. This led him to design a new observatory in 1584, Stjerneborg. Located partly underground, and with hatches to open in the observation direction only, a new level of accuracy was obtained. At the same time temperature fluctuations were suppressed, further improving the accuracy. His instruments were not just made of brass, and for example wood can be influenced by temperature as well. See Wood warping. Von Restorff (talk) 11:10, 4 January 2012 (UTC)

One other thought: Hven was probably a very cold place at the end of the 16th century (which was right at the beginning of the Little Ice Age). The underground arrangements may have also been for the been for the benefit of himself and his assistants, making observations through long northern nights. --Mr.98 (talk) 12:26, 4 January 2012 (UTC)

The OP mentioned vibration from the wind, and I reckon this is quite close to the mark. If you have a strongly magnifying telescope, the last thing you want is for it to wobble around every time a horse and cart goes past outside. Henry Cavendish had a similar solution (i.e. an underground laboratory) when he was 'weighing the world'. Unfortunately, I've been unable to find any sources that give details about his house, which I believe had rather a labyrinth of labs and workshops underneath. I don't think I made it up, though. - Cucumber Mike (talk) 21:08, 4 January 2012 (UTC)

While Is suspect wind was a factor, I will just point out that Brahe had no telescopes whatsoever, as they had not yet been invented. This is all pre-magnification technology (like the sextant shown above). --Mr.98 (talk) 22:38, 4 January 2012 (UTC)

Not to mention the mural quadrant (the linked article shows Tycho himself using one of his). Such instruments, which had also been built by other cultures, were more accurate the bigger they were (assuming they were precisely constructed). Tycho's assistant and successor Johannes Kepler was able to demonstrate that the orbit of Mars (and by inference those of the other planets) is an ellipse (not a circle as had previously been assumed) by using the naked eye positional measurements made with Tycho's non-telescopic instruments. During Kepler's lifetime the astronomical telescope was invented (he himself made early improvements to it) and thereafter incorporated into such astrometrical devices. {The poster formerly known as 87.81.230.195} 90.193.78.46 (talk) 23:21, 4 January 2012 (UTC)

Tycho Brahe's sextant, used for measuring the angular distances between stars. This instrument has a wooden frame.

Thanks everyone for your replies so far. This is getting more and more interesting as we move along. Above all, I'm excited about the link to Astronomiæ instauratæ Mechanica; that's beautiful! I didn't know that existed. And you're right, Von Restorff, at least some of the instruments did use wood, such as the one you pictured here. At first I thought: 'Well, if they used wood, no wonder they had problems.' But then I realized, much to my surprise, that wood is actually more stable than brass. Douglas-fir parallel to grain, e.g., has a thermal coefficient of expansion of 3.5 (our article, orig. source), which is 1/6 of that of brass. But it comes even better: The dreaded warping may not have been a problem. According to this US Forest Service document, "Wood is dimensionally stable when the moisture content is greater than the fiber saturation point." Their statement may not have been meant with the precision needed for astronomical measurements, but at least Tycho seemed to agree: "The other parts are only wooden, but they have been combined and joined together in such an ingenious way - we have described above when we explained the armillae - that they cannot bend or change with changes of the air, and furthermore the whole is covered with painted canvas."*

Either way, we are now talking about effects of the same order of magnitude as the precision of the naked eye. So we need to look at the arguments for climatic stability. Let's start with hygric (moisture) stability. Moisture fluctuations will be interior (people, fire) or exterior. The former won't change by moving underground, and as long as you have a gaping hole in your wall/ceiling, the latter will be mostly due to simple convection through that hole, the size of which doesn't change by moving underground. Conversely covering the instruments with canvas, as they did, will have a stabilizing effect. (I presume it was pointed with oil to make it less permeable.) Thermic (temperature) stability will be improved by going under ground, but, if you compare it with solid stone masonry, which already has a high thermal mass, the effect is less than that of burning more wood, which is incidentally how Europeans in general reacted to the little ice age. (I at least haven't heard of people moving their castles underground to save energy then.) I apologize for just claiming "it's less" without actually doing the math; I'm a bit in a hurry now. I just wanted to post this already to firstly thank you for the good discussion so far, and to encourage people to add more ideas. — Sebastian 02:13, 5 January 2012 (UTC)

I assume he was smart enough to think about the long term effects of the weather on his beloved instruments - even over periods of hundreds of years - and he understood the importance of guarding them against any outside influences, however tiny they may be. Wind speed increases with increasing height above the ground, starting from zero due to the no-slip condition.

This instrument with its small crypt-turret is covered on top by a roof, made of small, smooth beams, ingeniously joined together and connected, below the horizontal top of the wall and outside the azimuth circle, by a strong, round wooden ring. Hidden inside this ring are wheels, placed opposite each other in four places. With the aid of these wheels the roof can be turned around, with little effort, as may be desired. In this way the two oblong windows, which are placed in the roof opposite each other, and which are likewise formed of small beams, can be turned towards any star that is to be observed. These windows are shut when the observations are finished, in order that the instrument should be protected against damage from the air, and against rain and wind. This should be done, as far as possible, with the other instruments also, since they are very valuable and are easily damaged if not protected against violence as well as dirt and the influence of the elements.

On the upper part of the wall is a carefully constructed roof that protects the instrument against damage by weather. This roof also has its windows, which can be opened, and it can be turned around as required by the observations on wheels that carry it. Furthermore, the windows can be shut while the instrument is adjusted, in order that the wind should not force its plumb-lines D out of their natural position. When the instrument is not used, they protect it against damage by rain and wind.

At 06:53 you wrote: "you wouldn't want to hang your quadrant on a wooden wall that shakes in every wind, but if you use masonry, you should be stable enough to not have to worry about wind"; but this quote above is about an instrument made from steel supported by a strong iron pillar, while deep down in the ground it rests upon a stone foundation.

Von Restorff (talk) 03:58, 5 January 2012 (UTC)

White blood cells

Are white blood cells present in the blood capillary near the lungs? — Preceding unsigned comment added by Yacopo (talk • contribs) 07:48, 4 January 2012 (UTC)

Yes. This paper discusses leukocytes (a type of white blood cell) in lung capillaries. SmartSE (talk) 12:50, 4 January 2012 (UTC)

Yes; for the most part the constituents of the blood don't change in different parts of the body, even though some other things do, mainly gas concentrations. Or are we misunderstanding your question? --jjron (talk) 15:18, 4 January 2012 (UTC)

precession

there's something I don't understand in gyroscopic precession.the magnitude of the torque is said to be Mgr.well, when calculating that, they look at the rotation of the wheel around a different axis than that of its initial rotation, L.so when they say torque=dL/dt, it's a different torque, I know I'm misleaded, but how? — Preceding unsigned comment added by Irrational number (talk • contribs) 11:02, 4 January 2012 (UTC)

We'll skip the formulas here

i'm not sure whether the humanities or science desk is better for this: I'm looking for examples of science texts where the author says let's skip the maths, and moves onto the conclusion - this is research for a piece of fiction, so the field doesn't matter -- what I'm hoping for is just some samples of the language used in such cases, especially in vintage texts -- the older the better. Thanks very much

Fermat's last theorem may fit, or else it's close. Grandiose (me, talk, contribs) 11:08, 4 January 2012 (UTC)

What level of works are you looking for? There's a lot of texts written for lay audiences that do this, as well introductory books pointing out the implications of a more advanced result; or just pointing out that such and such advanced result is needed, but outside the scope of the current volume. Research level stuff will skip a lot of elementary stuff and get to it's conclusions, which is a little different than the former (hence, my question). :-) Phoenixia1177 (talk) 11:22, 4 January 2012 (UTC)

Dr Riemann's Zeros by Karl Sabbagh is another one, which gives a fascinating insight into one particular theorem and the process behind its proof. --TammyMoet (talk) 12:46, 4 January 2012 (UTC)

A common phrase used in math texts is "details are omitted". A google books search for /"details are omitted" math/ will give you thousands of hits, such as "The proofs are completely analogous to those of the two preceding theorems and the details are omitted." SemanticMantis (talk) 14:36, 4 January 2012 (UTC)

..."Left as a exercise for the reader...." I'll have to dig to find a specific text that used the phrase, but it and its variants were the bane of many of my classmates. Nimur (talk) 16:13, 4 January 2012 (UTC)

Agree. But that is mostly textbook language. In a paper, I'd expect something like "the proof is strictly analogous to X" (where X may be "theorem one" or "the argument on page 3"). --Stephan Schulz (talk) 16:16, 4 January 2012 (UTC)

Wattles in goats

What is the purpose of wattles in mammals? Kittybrewster ☎ 15:57, 4 January 2012 (UTC)

They serve no purpose (or we simply don't know the purpose) and are believed to be a genetic trait "left over" from evolution in goats and pigs. There is an explanation of the genetics of wattles in goats. Von Restorff (talk) 16:13, 4 January 2012 (UTC)

Apparently in pigs and sheep the wattle gene does have an effect on overall growth. [18] [19] I didn't quickly find information I could access about what chromosome the wattle gene maps to - if we had this for sheep, goats, and pigs, I wonder if we could "map" the gene simply by statistical analysis of which orthologs are on the right chromosome in all three species. But it's also possible they're non-homologous genes. Also note that just because a mutation interferes with wattle formation doesn't mean you have to have the wattle to avoid the effects of the mutation. Looking at them I'm reminded of the wing and haltere arrangement in Drosophila wings, but I can't really picture that applies - more likely, based on the propensity of humans to play with earrings, there's some kind of sexual selection going on? But I don't know. Wnt (talk) 03:10, 5 January 2012 (UTC)

ice cap and tundra

Is ice cap climates basically high elevation or low elevation. Is it like highland plateau or is it inland valley low elevations like Verkhoyansk. Is inland part of Greenland or Antarctica is just far inland like Yakutsk, Russia. Is tundra allowed to have trees at all. most people's understnading is tundra is a frozen swampland where trees cannot grow at all. I am serious about there is actually trees growing in Qaqortoq, Greenland. Is Qaqortoq, Greenland tundra or it can't be tundra because of the green trees really existing there. Does Kangerlussuaq have permafrost or no permafrost. Kangerlussuaq summer high actually exceeds 60 F continously at summer I though Kangerlussuaq is more closer to ice sheet than Nuuk. --69.229.39.25 (talk) 22:28, 4 January 2012 (UTC)

I'm not sure I fully understand your questions: I'll try to address them in the order you ask, but it would make things easier in future if you ask fewer questions at one time and separate them more clearly. Please refer to the articles I've linked, because they mostly contain fuller information relevant to your questions.

• The Greenland and Antarctic ice caps (strictly they are ice sheets, larger than ice caps)are typically at high elevations, because the ice itself is mostly quite thick, up to several kilometers in their interiors, though lower at coastlines where the glaciers meet the sea.
• There are generally no ice-free lower elevations resembling the areas around Verkhoyansk in an ice cap's interior; the ice is so thick that only mountains are high enough to rise through it, and they are mostly bare rock because of the elevation and low temperatures.
• Inland Greenland and Antarctica do not resemble inland Siberian areas with soil and trees like Yakutsk, they are under kilometers-thick ice.
• There are different kinds of tundra in different parts of the world (you can click on the World map in that article to enlarge it and see which parts of Greenland have tundra). Most tundra has some bushes and other vegetation, but it has no trees, which is what the word "tundra" actually means: however, in some places it has a few scattered and small trees dwarfed by the cold climate. Note that although tundra is frozen in Winter, its surface layers above its permafrost do thaw in Summer, which is why plants can grow there.
• Qaqortoq is in the extreme south of Greenland and does not have permafrost (see the section on Climate in that article) and therefore is not on tundra.
• Kangerlussuaq is futher north in Greenland and is surrounded by areas of tundra (with underlying permafrost) but the town itself is on low land at the head of a fjord, where the warmth of the sea may prevent year-round permafrost from persisting. Most Arctic and Antarctic areas can get quite warm in Summer because for nearly six months the sun is up 24 hours per day, so there is no cooler night-time as there is in the the Temperate zones.

I hope the above answers your questions: feel free to ask more if there is still something you aren't clear about. {The poster formerly known as 87.81.2301.95} 90.193.78.46 (talk) 05:06, 5 January 2012 (UTC)

Polonium - to - actinium gap

Why are all the elements from polonium to actinium extremely rare and unstable compared to the elements both before (such as lead and bismuth) and after (such as thorium and uranium) this gap? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:52, 4 January 2012 (UTC)

See Magic number (physics). Dauto (talk) 00:44, 5 January 2012 (UTC)

January 5

Acidity of the female reproductive tract

Why is the female reproductive tract acidic when this inhibits the ability of spermatozoa to survive and fertilise an egg, which is, of course, the female reproductive tract's primary purpose? Isn't that kind of self-defeating? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:19, 5 January 2012 (UTC)

Only the strongest will do it. 88.9.109.182 (talk) 00:28, 5 January 2012 (UTC)

See this paper specifically the section: Vaginal defenses against infectious organisms may affect sperm. Rockpocket 00:41, 5 January 2012 (UTC)

The point is to prevent pregnancy by a male with inadequate sperm count. It is to the woman's advantage to prevent a pregnancy that may result in a male baby that will turn out to have low sperm count (ounce he grows up) reducing the number of grandchildren. Dauto (talk) 00:42, 5 January 2012 (UTC)

There are probably a lot of important factors working together on this. Consider, for example, that the female orgasm allows her to decide on a male's genetic quality in a rather conscious way, giving sperm with this advantage more time in the acid bath and some less (or keeping the seminal plasma, and its buffering capacity, together?) Males are potentially competing with one another, perhaps in nearly simultaneous matings, or perhaps in repeated matings over a period of months until pregnancy is attained. Over the course of evolution female body needs to decide on how long a relationship should go on, on average, until a baby is conceived in order for it to have the best chance of paternal support. Probably there are dozens, maybe hundreds of things like this you could name off, and it would be very hard to test most of them except by computer modelling based on perhaps very inaccurate presumptions about the lifestyle of our ancestors. Wnt (talk) 02:55, 5 January 2012 (UTC)

is it homosexuality?

I've been noticing this several times. Some male dogs smell other male dogs' butt and in some instances try to copulate them. Why is that so? Can we consider this as displaying of homosexuality behavior? I read our article about Homosexuality in animals and this behavior of dogs is not discussed there. — Preceding unsigned comment added by 124.105.61.174 (talk) 04:49, 5 January 2012 (UTC)

It is probably quite common behaviour in dogs (I've certainly seen it myself). As to whether you consider it 'homosexuality', I think that depends on two things - firstly, on whether there is a clearcut definition of 'homosexuality' within human societies - and evidence strongly suggests there isn't - and secondly, the extent to which you consider it meaningful to analyse the behaviour of other species from the perspective of human sexuality. So there isn't a definitive answer to this, and it probably isn't a particularly useful question to ask. Instead, you might ask why dogs do this. The immediate answer is most likely 'because they enjoy it', and the more fundamental answer will probably depend on the degree to which you think that behaviour is a direct result of evolutionary pressures. You'll have to make your own mind up on this, but it is an interesting question. AndyTheGrump (talk) 05:09, 5 January 2012 (UTC)