Wikipedia:Reference desk/Archives/Science/2012 January 1

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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)