Wikipedia:Reference desk/Archives/Science/2011 December 28

= December 28 =

Deciding what drugs are OTC
Who, and how, decides which drugs are OTC? Common wisdom is that not risky medicines can be OTC, but couldn't ibuprofen, aspirin and the like be overdosed? And aren't these same pain-killers also not psychoactive? 88.8.76.47 (talk) 02:53, 28 December 2011 (UTC)
 * Start with Over-the-counter drug and come back with questions on anything not answered there. --Tagishsimon (talk) 02:58, 28 December 2011 (UTC)

I wnt to know the basic requirements to repair electronics equipments.
Hi friend, im in the position to repair/service electronics equipments(instruments from top manufactureres like FANN, ORTOalresa, TANAKA. I doesn't have any experience with this. please help me.

Equipments are (1) MODEL 35 Viscometer-THE INDUSTRY STANDARD (fann instrument company) (2) MODEL 50sl RHEOMETER (fann instrument company) (3) MODEL 280 RHEOMETER (fann instrument company) (4) MODEL 286VS RHEOMETER (fann instrument company) (4) OPTIONAL CHILLER (fann instrument company)

(1)If there is a problem in these euipment what we have to check first? (2)what are the basic problems may come in these equipments? (3)Here i does't have maual and i already checked in their website its not available. i u know help me. (4)what are the preventive maintenance we have to take for that equipments. email me: [e-mail address redacted] — Preceding unsigned comment added by Naveen13oct (talk • contribs) 07:08, 28 December 2011 (UTC)
 * I've removed the e-mail address. Is there a template for this? Mitch Ames (talk) 09:10, 28 December 2011 (UTC)


 * If you have to ask basic questions like that, you probably should not be attempting to repair or service electrical equipment. Electricity can kill. Mitch Ames (talk) 09:45, 28 December 2011 (UTC)


 * To be fair to the OP, those are reasonable questions that an experienced and qualified technician would ask, and would expect to find covered in the service manual. I assume that the viscometer is the one covered by this instruction manual.  If that manual does not go into the depth needed, perhaps the OP should request the appropriate service manuals from the seller, using their contact information on page 2 of the instruction manual. -- ToE 12:16, 28 December 2011 (UTC)

Does sleep sex leave a bruise patten similar to that in rape?
I was wondering if sleep sex bruises can be effectively used as evidnce or not.Bastard Soap (talk) 12:08, 28 December 2011 (UTC)
 * Evidence of what? Physically, having sex while asleep is no different to having it while awake, so the chance of getting bruises is the same as if you were having sex while awake. Bruises from rape are due to the use of force, which is not necessarily a factor in sleep sex (although, it can be). We do have an article, sleep sex, which might help you. --Tango (talk) 13:38, 28 December 2011 (UTC)

Specifically I was wondering if women who are raped when they are asleep can bring any evidence to court. As to my understanding voluntary rough sex and rape will still leave different bruise patterns.Bastard Soap (talk) 14:01, 28 December 2011 (UTC)
 * Ah, that's not what "sleep sex" usually refers to. Sleep sex, as described in the article I linked to, usually involves the sleeper initiating the sexual activity. You are right that there do tend to be forensic differences between voluntary rough sex and rape. A rape victim will tend to show "defensive wounds", for example bruising to the arms where they have been held up in front of the face to protect it. Those won't be present if the victim didn't try and defend themselves, though, which could be the case if they were asleep (although, unless they took sleeping pills or were given a date rape drug, I would expect them to wake up pretty quickly). --Tango (talk) 14:17, 28 December 2011 (UTC)

I was referring to vaginal bruising mostly as a sleep rape victim will not likely defend themselves Bastard Soap (talk) 16:17, 28 December 2011 (UTC)
 * This is a complicated and controversial subject and really boils down to legal advice. No one here will be able to tell you what evidence can or can't be brought, or would or wouldn't be accepted in such a case, it really depends on the individual case. Vespine (talk) 22:14, 28 December 2011 (UTC)

I'm mostly interested if the vaginal bruising is similar to that present in rape or notBastard Soap (talk) 10:57, 29 December 2011 (UTC)
 * We're not allowed to give legal advice here. ←Baseball Bugs What's up, Doc? carrots→ 15:51, 29 December 2011 (UTC)

Well thats good cause I'm not asking for legal advice here. This is a factual question, no different in nature to if I asked if bullets can be traced to a gun.Bastard Soap (talk) 17:57, 29 December 2011 (UTC)
 * The "legal advice" thing is obviously a bit subjective, but asking if something specific can be admitted as evidence IS legal advice. It totally depends on jurisdiction and other "legal" matters that only a lawyer with knowledge of all the specifics would be qualified to answer. Vespine (talk) 22:59, 29 December 2011 (UTC)

Introduction to astronomy as an ebook?
Hi, im a trained mathematician on holidays. Ive felt my ignorance on astronomy to be a shortcoming. Can you recommend an ebook that introduces astronomy to a scientific reader, but can be finished in below 1 day? 178.121.0.150 (talk) 12:44, 28 December 2011 (UTC)
 * Speaking as someone who studied Astronomy at university and has maintained an active interest in it over the subsequent decades, my perspective would be that it's a very broad and diverse subject and any book covering it comprehensively, even though not very deeply, while being appropriate in level to an adult with mathematical expertise would take far longer than one day to read with understanding. Nor can I offer knowledge of any e-books on it (or any other subject). Others may have a different take, and may well be able to offer contrasting and superior advice :-) . Would not reading the above-linked article and following the diverging network of links from it (or from Portal:Astronomy) according to your own interests answer your needs to some degree? {The poster formerly known as 87.81.230.195} 90.197.66.141 (talk) 21:09, 28 December 2011 (UTC)
 * Generally speaking the books on the topic can be divided into three (very broad, fuzzily-bounded, and often-overlapping) categories.
 * General survey of astronomy. These come in a wide range of breadths and depths.  You'll get a quick survey of (some or all of) the formation of the universe, galaxies, stars, moons, and planets; the life cycle of stars (stellar evolution); the history of models of the solar system and universe; the development of optical instruments; and so forth.  The level of mathematical rigor ranges from thorough to nonexistent.  The most detailed (and the most pricey) of these will appear as textbooks on the syllabus of your local university's first- or second-year physics course in 'introductory astronomy' or 'descriptive astronomy'.  While you certainly won't finish a course textbook in a single day of reading, you will be able to pick and choose the chapters that most interest you&mdash;and there will be at least some residual depth to their coverage if you want to come back to the topic some evening (or on your next vacation).
 * Books for the amateur astronomer/stargazer. The emphasis will be on observing: what you can see when you look up (day or night, with or without the use of accessories).  The Sun, Earth's Moon, the other moons and planets in our solar system, stars, globular clusters, nebulae, nearby galaxies.  There will be star charts, and tables with arrival times for meteor showers and major comets.  These books will often contain discussions of different types of binoculars and telescopes, and the relative merits of each for different types of observing.  The amount of 'general astronomy' discussion can range from moderate to none at all; different texts will assign different relative importance to this background information, or may assume greater or lesser pre-existing familiarity on the part of their readers.  Terence Dickinson's NightWatch: A Practical Guide to Viewing the Universe is an excellent and accessible member of this family.
 * Books about the origins or fate of the universe. These are 'big picture' cosmology books.  The Big Bang, Big Crunch, heat death, black holes, and cosmic microwave background.  These may be flavored with additional material on the theory of relativity and quantum mechanics.  Stephen Hawking's A Brief History of Time is a representative (though probably dated) example from this category.
 * I'm afraid I can't comment on which books might be available in electronic format (or, particularly, which of their figures, photographs, and diagrams best survive the translation to the ebook screen). TenOfAllTrades(talk) 15:31, 29 December 2011 (UTC)

Temperature sensing mechanism in skin cells
If any human reading this is able to, without, simply telling me "See [insert link here]," summarize the mechanism by which when an object of a given temperature is placed in contact with, say, the skin on a human fingertip, the average speed of the particles of the object is converted into nerve signals to the brain, I would be grateful. 20.137.18.53 (talk) 15:20, 28 December 2011 (UTC)
 * The mechanism is complex and until recently was hardly understood at all. To begin with, the cells that sense temperature are not actually located in the skin, they are located in the spinal cord and send fibrous projections to the skin, where they give rise to free nerve endings.  At the nerve endings, the membranes of the fibers contain special types of sensor molecules known as thermoTRPs, which belong to the family of Transient receptor potential channels.  These molecules form ion channels that allow certain types of ions to pass through the membrane, but the ion channels are temperature-sensitive -- they are only open when the temperature falls in a certain range. Different types of thermoTRPs have different temperature sensitivities, so some are activated by cool temperatures, others by warm temperatures, others by hot temperatures.  (You asked not to get references, but for anybody who wants to know more, this paper is a useful overview.) Looie496 (talk) 16:26, 28 December 2011 (UTC)
 * Thanks for that summary. Sorry, I should have said I didn't only want a link, not that I wouldn't like a link as long as there was also a summary as you gave. Unfortunately, the link gives a 404 Not Found (for me, at least). 20.137.18.53 (talk) 17:06, 28 December 2011 (UTC)
 * Sorry, I screwed up extracting the link from Google -- now fixed. Looie496 (talk) 17:39, 28 December 2011 (UTC)

Landsberg efficiency
Can someone point me to a derivation of the Landsberg efficiency for determining theoretical optimal efficiency photovoltaic cells? RJFJR (talk) 15:53, 28 December 2011 (UTC)

Equations for a falling body with relativistic effects
How to calculate distance, velocity and acceleration of a falling relativistic particle?

Our article Equations for a falling body provide equations for non-relativistic case only.

I would like to see something simple, like $$\ d=\frac{1}{2}gt^2 $$ but relativistic :) Without Lagrangians etc. Is it possible? (I'm not a physicist)

Thanks! --Zhitelew (talk) 16:59, 28 December 2011 (UTC)
 * In general relativity, a particle's proper frame is as valid of a coordinate system as any other, and in the proper frame of a particle in free fall, the particle's acceleration (i.e., the proper acceleration) and velocity (i.e. the proper velocity) are both simply zero. From the perspective of general relativity, what Newtonian gravity calls the "acceleration" due to gravity is really just the coordinate acceleration associated with a fictitious force. Red Act (talk) 20:05, 28 December 2011 (UTC)


 * Another way to say it: the field equation uniquely defines a geodesic in x,y,z, and time, given a particular arrangement of masses. A test-particle always moves along a geodesic.  You don't need to solve any equation of motion; you just have to write the gravity field equation.  Transforming this into a function for position as a function of time (relative to some definite laboratory coordinate system) is nasty and inconvenient - take a look at four-vector for the basics.  This is why anyone who does any nontrivial relativistic particle modeling uses a computer to do the number-crunching.  We have an article, numerical relativity, if you really want to calculate trajectories for nontrivial setups.  Nimur (talk) 21:14, 28 December 2011 (UTC)

Given a metric $$g_{\mu \nu}$$, the world line of the test particle (which is a geodesic as Nimur pointes out above), follows from the Lagrangian:

$$L = \frac{1}{2} g_{\mu \nu}\frac{dx^{\mu}}{d\tau}\frac{dx^{\nu}}{d\tau}$$

Count Iblis (talk) 23:41, 28 December 2011 (UTC)

Well, for a constant gravitational field, g, a test particle accelerating according to general relativity will approximately travel a distance:


 * $$d(t) \approx {{\sqrt{c^4 + c^2 g^2 t^2}-c^2} \over g} \approx {g t^2 \over 2} - {g^3 t^4 \over 8 c^2} + {g^5 t^6 \over 16 c^4} + ...$$

Dragons flight (talk) 11:20, 29 December 2011 (UTC)
 * Thanks!
 * Could you please recommend me a source, where can I find the full form of this equation? (and derivation of) --Zhitelew (talk) 16:49, 29 December 2011 (UTC)


 * That equation describes hyperbolic motion (relativity). The last part ($${g t^2 \over 2} - {g^3 t^4 \over 8 c^2} + \cdots$$) is a Taylor series. It goes on forever, so it has no full form as such, but you can calculate any number of terms from the closed form (the one with the square root). There are a bunch of online Taylor series calculators that might work (search for "online Taylor series calculator").


 * But that equation is for uniformly accelerated motion in special relativity (e.g., a rocket ship), not freefall in general relativity. There is no single correct formula for freefall motion because general relativity requires you to be very careful about how you do your measurements. Freefall is just straight-line motion—if it looks like anything else, it's because your measurement apparatus is accelerating, not the falling object itself. If you specify how the measurement is done (including clock synchronization, etc.) then it might be possible to come up with a formula for that specific case. -- BenRG (talk) 20:57, 29 December 2011 (UTC)
 * Ok, I'm a observer. I have a radius (R) and really huge mass (M). I throw a particle (start velocity = V) from my surface. Particle coming back.
 * When will it come? Maximal distance? Velocity in the moment of collision?
 * Can I calculate this in relativistic case? For example, M = 10^30 kg, R = 10^6 m, V = 10^7 m/s (like throwing something from a neutron star) --Zhitelew (talk) 22:34, 29 December 2011 (UTC)

The analogue of conservation of energy is:

$$ \frac{1}{2} m \left( \frac{dr}{d\tau} \right)^{2} = \frac{E^2}{2 m c^2} - \frac{1}{2} m c^2 + \frac{GMm}{r} $$

But here r is the radial Schwartzschild coordinate, and this is thus not the radial distance. And tau is the proper time for the partcle in free fall. So, you can solve this problem in the usual way as you are used to in classical mechanics, all you have to do is convert the velocity to dr/dtau, calculate E from the initial condition, use the above conservation of energy equation to find the maximum radius which you can convert to the maximum distance. Count Iblis (talk) 23:47, 29 December 2011 (UTC)

Have laptops stopped improving?
I'm in the process of buying a laptop and it seems to be like exactly the same specs are available as 2 years ago or so, have laptops hit some kind of bottle neck? Normal computers seem to have improved a lot since that time. Bastard Soap (talk) 18:37, 28 December 2011 (UTC)
 * Not really, laptops are improving and new models using new hardware are definitely available (although the top-notch ones may drain your wallet more than the budget/more common ones, mind you). And I'm no laptop fan, but - laptops are normal computers :) --Ouro (blah blah) 18:41, 28 December 2011 (UTC)
 * The batteries have improved a lot in the last years, the same is also true for the hard disk. — Preceding unsigned comment added by 88.9.209.183 (talk) 19:42, 28 December 2011 (UTC)

Two years is a long time in the computing industry! Off the top of my head, I can think of three technologies that are readily available in laptops today (late 2011) that were not available in late 2009: I'm sure if I sat to think a while longer, I could probably come up with several more specific improvements that have gone mainstream in laptops and portable computers since 2009. I would be remiss if I did not mention the iPad, which is now less than 2 years old; the newest incarnation, iPad 2, is less than one year old; and while these portable computing devices are not laptops, they certainly have changed the landscape for portable computing. Their design, form-factor, and capabilities have shaped the way that conventional laptops are designed, marketed, and priced. The tablet computer has existed for a long, long time - I recall the earliest IBM X series ThinkPad tablets nearly a decade ago; but in the last two years alone, there's been a lot of improvement to "laptop-tablet" hybrids, in terms of battery and processor and graphics technology, in large part driven to compete with iPad's stylistic choices and designed capabilities. Nimur (talk) 20:09, 28 December 2011 (UTC)
 * Thunderbolt, a high-speed interconnect bus. To the non-technical end-user, this means that your brand-new Thunderbolt-capable laptop can transfer data to external hard-disks about 10 to 100 times faster than a USB system; and you can connect bigger monitors and HD televisions to your system with less visible distortion.
 * The GPGPU, in 2009, was only available in high-end desktop workstations and specialty servers. Today, even low-end laptops support OpenCL and CUDA acceleration on the GPGPU.  To the non-technical end user, this means that videos will play back smoother, high-with fewer interruptions; and battery life will be extended, even when doing "complicated" tasks like playing HD video and working with certain specialty software packages that formerly required 100% CPU for extended periods of time.
 * The processors run colder - for a lot of reasons, but mostly because the operating systems of 2011 (Linux 3, Windows 7, Mac OS X Lion) are smarter than those of 2009; the new system-software knows how to work better with new variants of the Intel hardware - especially the Sandy Bridge revision of the Intel Nehalem architecture. To the non-technical user, this means that your laptop is less warm; its battery lasts longer; and the noisy fan got a lot quieter and needs to be used more sparingly.  Interestingly, almost all laptops are now multicore 64-bit Intel processors - again, not something that was common in 2009.
 * You're not just looking at the "GHz" by any chance are you? It used to be the case that the clock speed was a rough "benchmark" of the performance of a processor and you could generally say that a processor with a higher clock speed would be "faster", but that hasn't been the case for maybe four or five years now. These days the "generation" of processor is a bigger factor then the clock speed, i.e. a processor of this generation can be faster then a processor of the last generation even if it has a lower clock speed. Vespine (talk) 21:58, 28 December 2011 (UTC)


 * It may be worth noting that Thunderbolt is virtually impossible to get on a laptop or peripherals unless you are using Apple products. Another improvement worth noting is the increased availability of solid state drives which offer considerably better performance (albeit at higher cost and lower capacity) than traditional hard drives.  Dragons flight (talk) 22:55, 28 December 2011 (UTC)


 * It seems to me that the main advantage over the last 2 years is being able to get the same thing cheaper. StuRat (talk) 03:35, 29 December 2011 (UTC)
 * That would seem to correspond with the global financial crisis. That actually makes sense. Fewer customers willing to pay top dollar for the latest and greatest. HiLo48 (talk) 03:56, 29 December 2011 (UTC)

So you're saying they stopped improving specs and concentrated on the architecture instead? Hilo48 it doesn't seem to me like they became cheaperBastard Soap (talk) 10:59, 29 December 2011 (UTC)
 * I find that whenever someone responds to comment I've made by saying "So you're saying..." they seem to end up saying something I don't understand. Maybe it's the missing punctuation in this case. HiLo48 (talk) 11:14, 29 December 2011 (UTC)
 * So you're saying that what you say, said, or were saying, is not what you were so saying? 88.8.76.47 (talk) 14:08, 29 December 2011 (UTC)
 * Specs include architecture, always. I read the OP's last comment as follows: 'They stopped putting bigger numbers there but are using new fancy long words' (nudge). The thing is, it's not about being able to compute faster but doing more in one clock cycle, simply put. --Ouro (blah blah) 12:33, 29 December 2011 (UTC)
 * It strikes me that computers haven't gotten substantially faster in many years. It used to be that you could buy a new machine every 18 months and see a dramatic speed increase, but I can barely tell the difference between my Thinkpad T40, purchased in 2004, and the T400 I bought more than five years later. Intel and AMD say that it's not about clock rate any more because they have to say that. They can't push the clock rate any higher, but they have to keep delivering higher benchmark numbers every year or investors will panic. Multicore CPUs have allowed them to keep doing that for the time being, but the benefit to consumers is much smaller than the benchmarks would suggest. -- BenRG (talk) 20:22, 29 December 2011 (UTC)

Moore's Law... → Σ  τ  c. 20:06, 29 December 2011 (UTC)
 * The reason you probably don't perceive as much of an increase is because most of the things you do with your computer are probably about as fast as you can get them. Surfing the internet, doing emails, wikipedia etc are no longer limited by processor speed, but by harder limits, like disk access and probably most importantly network speed and latency. People who do processor intensive things like video and photo editing will have noticed the speed increase. I'm a gamer and comparing today's high end games to those of 2 years ago there is also a very noticeable difference, maybe in particular in the mobile market, gaming laptops these days are far more capable then gaming laptops 2 years ago. Vespine (talk) 23:05, 29 December 2011 (UTC)