Wikipedia:Reference desk/Archives/Science/2009 August 27

= August 27 =

Canine kidney failure
I just heard a story on the television about an old dog that died of kidney failure while locked in a car during 90+ºF heat. I can understand a dog dying after several hours in such a situation, but kidney failure? Unless the dog already had nephrological issues, how would the heat kill it in that way before killing it in some other way? Nyttend (talk) 03:26, 27 August 2009 (UTC)
 * A quick google search shows up a bunch of links, especially this one. Essentially, the extreme over-heating is going to cause massive tissue damage, and tissues that are most active (liver, brain) are going to go first.  Kidneys are pretty active, and rely on very specific chemical reactions and fluid balances to function properly.  In the heat the concentration of specific molecules in the blood would've been changed drastically, and could easily affect kidney function.  If the kidneys hadn't failed something else probably would've soon.  I can even imagine that since the brain and liver get so much blood compared to other portions of the body, they might survive (albeit completely irreparably damaged) long enough to make the cause of death the kidneys. ~ Amory ( user  •  talk  •  contribs ) 05:43, 27 August 2009 (UTC)


 * I cannot see how a dog can die from kidney failure after such a short time with out previous aetiology. Dying from kidney failure is not a sudden death but is caused by the accumulation of fluids and waste products over an extended period of days rather than hours. It is of course quite possible that this dog did have previous kidney problems and the extreme heating was the final straw. From my veterinary experience I would suggest that the dogs brain became overheated, it was not able to oxygenate properly and this caused heat prostration and death. 86.4.181.14 (talk) 07:25, 27 August 2009 (UTC)


 * Hmm Nyttend are you sure the storysaid the dog died of kidney failure while locked in the car? dogs.suite101.com/article.cfm/dogs_and_heat_stroke (spam blacklisted) and and Amory's ref all note that kidney failure is something that dogs should be monitored for after suffering heatstroke so it's entirely plausible the dog died from kidney failure primarily as the result of being locked in the car even if it didn't die while in the car Nil Einne (talk) 08:31, 27 August 2009 (UTC)
 * Kidney failure is indeed the most likely mode of death. In the extreme heat, the dog attempts homeostasis of temperature by sweating and panting. This leads to dehydration and hypovolaemia. Axl  ¤  [Talk]  10:47, 27 August 2009 (UTC)
 * It appears that the dog died hours later; here is the story from a newspaper website. I thought that the TV broadcast said in the car, but either it was wrong or (more likely) I remembered it wrongly. Nyttend (talk) 17:06, 27 August 2009 (UTC)

A380 and An-124
According to List of large aircraft An-124 is bigger than A380. According to articles, A380 is longer, has bigger wingspan, bigger max takeoff weight and so on, so how can an-124 be bigger? —Preceding unsigned comment added by 195.255.135.235 (talk) 08:39, 27 August 2009 (UTC)


 * A380? An-124 eats them for breakfast! --antilivedT 08:48, 27 August 2009 (UTC)


 * You should probably bring this up on the Talk: page of List of large aircraft. If you're sure of your facts, you can Be Bold and just go fix it yourself. SteveBaker (talk) 11:41, 27 August 2009 (UTC)


 * A380 is fairly new. Could be that no one has gotten around to updating that list.  Also, not sure but are there any specific criteria defining "large"?


 * Looking at our article Antonov An-124, it seems that the An-124 was the largest production aircraft in the world at the time that it was introduced. It may also be the second-largest mass-produced aircraft (after the A380).  Note that the Antonov An-225 is larger than both, but only one was ever completed.  (Our article indicates that a second mothballed airframe is being refurbished, and is due to fly in 2010.)  If someone wants to update our last, they should go ahead.  TenOfAllTrades(talk) 14:03, 27 August 2009 (UTC)


 * I think you missread the article. It actually claims that the Antonov An-225 is the largest airplane, while A380 is the second largest. The An-124 is one line above the An-225 which may explain the mistake. 71.203.58.148 (talk) 01:13, 28 August 2009 (UTC)

Re-OP: Is it true that using known data with known formulas is not synthesis?
New planets that are being found are being referred to as being in or out of their parent star's "Habitable zone," Which basically refers to the distance range that water would be liquid. But the concept is being used to insinuate more than water being present, it is used to suggest these systems could have life.

That is easy to accept if you ignore all the other factors involved in the process, and believe Water=Life. As there are many factors other than irradiances that would keep H2O from being liquid,(Mass/cohesion, Abundance of elements/Metalicity, Excessive X-rays/M-type star, Amount of CO2) it is a little deceptive and irresponsible to make the suggestion to people that a planet may have life because it is X distance from its star. The idea of a habitable zone planet is flawed as it is, but I think a "Solar Constant" comparison between Earth and other planets is of value in-of-itself. Simply as a comparison of heat, a more direct comparison even than mass (less insuating than a mass), as heat does not itself equal life. In other words less speculative. (note: Irradiance, Insolation, and Solar Constant are synonymous.)

Basic Insolation Figures Chart
In a lot of cases the Radius and Effective temperature of a parent star is known, or can be calculated using the formulas at the Luminosity article. The formula that calculates luminosity from Radius and Temperature and the formaula that calculates luminosity from distance and insolation are obviously Equal for the Sun and Earth data. and basic algebra yields:


 * $$ L = 4\pi R^2\sigma T^4 \,$$  ...and
 * $$ L = 4\pi d^2\ f \,$$ ...therefore,
 * $$ 4\pi R^2\sigma T^4 \ = 4\pi d^2\ f \,$$ ... and
 * $$ R^2\sigma T^4 \ = d^2\ f \,$$
 * $$ \ f \ =  (R^2\sigma T^4 \,)/ d^2$$

code for Earth at Perihelion: $$f_p= \frac{( ( 6.955 \times 10^8 )^2 ) \times (5.67051 \times 10^{-8}) \times (5778^4)} { ( ( 1- ( 1\times 0.016710219) ) \times 149597876600 )^2 } = 1,412.903 \ W/m^2$$

code for Gliese 581 c at Periastron: $$f_p= \frac{( (0.38 \times 6.955 \times 10^8 )^2 ) \times (5.67051 \times 10^{-8}) \times (3480^4)} { ( ( 0.073 - ( 0.073 \times 0.16 ) ) \times 149597876600 )^2 } = 6.9\times 10^3 \ W/m^2$$

Having said that I am not saying this should go directly into an article.

But I do remember reading a debate where it was pointed out that using known data with known formulas is not synthesis.

In a lot of cases scientists are going as far as to speculate on on effective temperature and surface temperatures, using this albedo or that emissivity, but on the other hand if the algebra is correct then the insolation is closer to fact. Definitely less misleading than saying there may be life on Gliese 581 c:

(see Than, Ker (2007-04-24). "Major Discovery: New Planet Could Harbor Water and Life". www.space.com )

$$\frac{Gl \ 581 \ c \ Periastron \ Insolation} { Earth's \ Solar \ Constant } = $$ $$\frac{6.9\times 10^3 \ W/m^2} { 1,366.079\ W/m^2 } = 505%$$

A few published formulas for comparison

 * $$\sigma\cdot T_{\mathrm{p}}^4 = \frac{\sigma\cdot T_{\ast}^4}{4\pi\cdot d^2}\cdot\frac{4\pi\cdot R_{\ast}^2}{4\pi\cdot R_{\mathrm{p}}^2}\cdot\pi\cdot R_{\mathrm{p}}^2(1-A_{\mathrm{p}})$$


 * $$T_{\mathrm{p}} = T_{\ast}\left[ \left(\frac{R_{\ast}}{d}\right)^2 \frac{1-A_{\mathrm{p}}}{4} \right]^{\frac{1}{4}}$$


 * $$T_{\mathrm{p}}= \left (\frac{L (1-A)}{16 \pi \sigma D^2} \right )^{\tfrac{1}{4}}$$

These formulas have been published and used by scientist to suggest surface effective temperatures of terrestrial extrasolar planets. Would it be incorrect to use the same formulas for other extra solar planets where scientists have not bothered to publish these figures because (I suspect) they are not as reputation enhancing. Similarly, No one is likely to use these same formulas published by scientists to calculate the effective surface temperature of a extrasolar Gas Giant, but this overlooks potential habitable moons of the same Gas Giants. I know the difference between published speculation and unpublished fact, and I perfer the later and would like to know if I am alone in this or is it true that using known data with known formulas is not synthesis? GabrielVelasquez (talk) 07:40, 27 August 2009 (UTC)


 * It's starting to sound like you're asking us a question about the application of Wikipedia policy. Your best bet is to bring the matter up on the talk page of the article in question, or to file a request for comment to bring in outside editors.  TenOfAllTrades(talk) 12:14, 27 August 2009 (UTC)
 * Yes Synthesis redirects to No original research, if your question is about policy probably that talk page, the help desk etc maybe a good place to ask. However I see no reason not to deal with it here as it seems easy to answer.


 * However. Without reading your entire question fully, it seems you are simply asking

"'it is true that using known data with known formulas is not synthesis?'"
 * I'm afraid the answer is "it is synthesis", technically. No question about it. Only in the most trivial cases can there be a get out clause eg covert degrees to fahrenheit.
 * 83.100.250.79 (talk) 13:32, 27 August 2009 (UTC)


 * I think the rule of thumb is that if anybody expresses a "reasonable doubt" about what you're doing, then it is synthesis. Given the complexity of your presentation, I think it would be reasonable for people to express doubts about whether you got all the factors right. Looie496 (talk) 16:01, 27 August 2009 (UTC)
 * I've got to disagree with that - calculations producing unpublished results is always synthesis (excluding an absolutely known proceedure such as found in pure mathematics), whether or not there is any disagreement about the results. In the case of the above equations it would be bordering on original research.
 * Presenting a single example as a demonstration of the formula would probably be acceptable, generating an entire table would not.83.100.250.79 (talk) 17:16, 27 August 2009 (UTC)
 * This is a principle that sounds good but leads to absurdities -- for example, is it synthesis to say Jupiter is over twice as far from the Sun as Earth, giving a table of distances as reference? Looie496 (talk) 17:34, 27 August 2009 (UTC)
 * That doesn't require an equation - I (and the question poster) was talking about deriving new figures from published data and equations. In your example the tables of distance already exist. 83.100.250.79 (talk) 18:39, 27 August 2009 (UTC)
 * You may be conflating synthesis with analysis.83.100.250.79 (talk) 19:14, 27 August 2009 (UTC)
 * Working out whether a planet is in the "habitable zone" is relatively easy, working out all the other things you mention are much harder. That is why the habitable zone is used as a rule of thumb to give an idea of how to prioritise further investigations. Also, it is worth remembering that whenever we say "life" in this context we mean "life as we know it". There could be life built around very different principles than that on Earth that could exist in very different environments. (Work on other kinds of life has shown that our kind seems to work best out of all the kinds we have considered, but that doesn't rule out other kinds either being less efficient that ours or of a kind we haven't considered.) --Tango (talk) 16:22, 27 August 2009 (UTC)


 * To cut a long story short we have an article Synthesis, the first paragraph explains what it is. 83.100.250.79 (talk) 19:14, 27 August 2009 (UTC)


 * It's very simple. $$1/planet AU^2*luminosity$$ is the insolation the planet gets compared to Earth. If you want W/m2 multiply that by Earth's value. Luminosity in solar units is found in the article of every planet's parent star so you don't have to originally recalculate it every time. (because the luminosity does not eminate from a single point, if the apparent angular size of the star at the planet is really large this might cause some problem, however if you have to worry about that – that planet ain't habitable.)


 * And albedo with the greenhouse effect are really important. Without one, Venus gets 2x insolation and is 2x as reflective, so it would be frigid! Sagittarian Milky Way (talk) 19:36, 27 August 2009 (UTC)


 * One of the crucial elements that you are forgetting is that known formula is subject to scientific dispute. Empirical formulas have limited applicability to problems.  The job of an experimental scientist is to perform original research in deciding which formulation is relevant to a particular problem.  When you make the claim that it is a "known formula", you are asserting a scientific truth, without attribution to a reliable source, that this is the correct equation that should be applied to this problem.  Whether the result of that formula is trivial computation or not, you have still synthesized the scientific claim that this formulation should be used.  That is the realm of research science; encyclopedias should serve to document what other scientists have agreed is the best formulation to apply.  Nimur (talk) 22:00, 27 August 2009 (UTC)
 * You are mistaken, and ignored relevant parts of my question to make this nonsensical comment: I am not making that claim, the equilibrium temperature formulas have already been published and used the same way, Just check the references at the Gliese 581 c article, I am just extending their use to other planets. Obviously when I say known formulas I am refering to formulas used the same way not in a new way or unverified way so the use of the formulas is not synthesis by a new or different use of them.

Taken from an older version of Gliese 581 c

 * GabrielVelasquez (talk) 09:22, 29 August 2009 (UTC)

Reference Desk Organization
Is there a better way we could set up the reference desk pages? I've noticed several annoyances.

1. I can not track responses to a particular question. 2. When someone replies to someone else's response while there are multiple further responses it's very difficult to determine this has occurred with out rereading every post every time. This is a bit difficult to explain but it looks like this:

- Question 7 pm - Reply 1 8 pm  - Reply to Reply 1 9 pm - Reply 2 8:30 pm - Reply 3 10 pm etc...

How can I tell there's been a reply to reply 1 without reading everything over again?

3. Topics remain on the reference page for quite some time but almost all the replies occur for questions asked in the past 2 days. Is there a way to reorder the format to encourage discussion of unanswered, older questions?

Finally, while there may be some back discussion page I believe it is the community's interest to have this posted for everyone's consideration as most people who use the reference desk read this page.

Your thoughts? TheFutureAwaits (talk) 10:35, 27 August 2009 (UTC)

I found this just today ironically, and removed mine minutes before you posted your question. It only indirectly addresses your issue, but I thought you would find interesting anyway. GabrielVelasquez (talk) 10:41, 27 August 2009 (UTC)

This type of question (and subsequent response) do not belong here. Discussions about the RD itself belong on the RD Talk: page which you can reach by clicking the "discussion" tab at the top of this page. SteveBaker (talk) 11:39, 27 August 2009 (UTC)

The formatting you describe sounds like it follows the guidelines at Talk page, which you can discuss at Wikipedia talk:Talk page AlmostReadytoFly (talk) 12:17, 27 August 2009 (UTC)


 * Yes but the problem is no one looks at those pages (looking at the history there were 7-10 edits a day on the discussion page versus hundreds for the actual desk). I'm trying to get feedback from the general users of this page on whether they agree with my points and if there are ways we could improve it. If I posted this on the discussion page it would be largely ignored.


 * Also I consider this a serious issue that merits discussion on the main page since the page in its current form has some fundamental flaws. I wouldn't post criticisms within an actual article but given the reference desk is all about asking questions and I'm trying to get feedback I think it merits real consideration. TheFutureAwaits (talk) 13:41, 27 August 2009 (UTC)


 * Few edits doesn't mean no one watches the page. The vast majority of active contributors to the RD, and even a few who don't contribute to the RD much anymore are active on the talk page (I know because I've seen them!). Also you appear to have missed the whole religion desk controversy which was hardly lacking in edits. And BTW, by posting this on the science desk (although it has little to do with science) you're missing all those who don't check out the Science desk. Also this question will disappear from here in about 7 days and as you yourself have claimed will be way up at the top in a few days and likely missed by many. If you expect a major change like this to occur in 7 days, you're seriously mistaken. BTW, while you may be right that your discussion will be largely ignored on the talk page (because part of what your discussing is part of wider policy which many people agree with and the other part doesn't really have a solution) as has already been demonstrated your discussion is going to be even more ignored here. Finally this is not the main page, but the place for asking factual questions. We have a dedicate page for discussing ways to improve the reference desk which for the many reasons I've already mentioned is a far better place to discuss this. Nil Einne (talk) 19:15, 27 August 2009 (UTC)
 * P.S. I commented out the template as this issue has been resolved Nil Einne (talk) 19:18, 27 August 2009 (UTC)

Repeated static shocks.
Is there any known health issue surrounding repeated static shocks to some particular part of the body (the tip of a finger, for example)? Suppose someone gets 'zapped' by their car door handle several times a day - every single day for many years? SteveBaker (talk) 11:45, 27 August 2009 (UTC)
 * (Not a complete answer) I used to work in a job where I had to wrap large pallets with industrial cling film - the process was semi automatic - the pallet went on a sort of turntable - like a huge record player... Anyway the unrolling of the 'cling film' produced massive amounts of static electricity (near van der graff levels) - I was constantly being zapped on the forearms (like 5 times second for ~5 hrs a day)- for a few months. I'm still alive!
 * More reliably I don't remember being given any health and safety warnings or instructions - so I guess it's not considered a risk - that was more than 10 years ago. I would guess that if there is any doubt then the Health and Safety Executive (UK) or the equivalent organisation in another country will have info on it. So that would be a place to look. thanks for listening 83.100.250.79 (talk) 13:21, 27 August 2009 (UTC)
 * Apparently the International Electro Technical Commission (what? no article?) states that a single transient or capacitive discharge, as is the case with static electricity, requires energy in excess of 5 Joules (5000mJ) to produce a direct serious risk to health. As for long term effects, according to the Oregon Occupational Safety and Health Administration, "There are no specific standards for static electricity" which likely means there is no data on adverse effects. Rockpock  e  t  17:32, 27 August 2009 (UTC)
 * Try International Electrotechnical Commission. --Heron (talk) 20:25, 27 August 2009 (UTC)
 * Ah, Damn you, Heron! ;) Rockpock  e  t  00:54, 28 August 2009 (UTC)
 * Sorted. --Tagishsimon (talk) 01:00, 28 August 2009 (UTC)
 * OT but maybe wear gloves when handling your MINI? Perhaps one of these? P.S. Happy belated MINIversary Nil Einne (talk) 18:44, 27 August 2009 (UTC)
 * It's not a MINI problem - my car is very well-behaved static-electricity-wise. The problem is at work where they replaced the front doors to our office suite with sexxy glass doors with big steel handles - and everyone is getting zapped by them.  But it's not really a problem - that just triggered my curiosity.  P.S It's not really a "belated" MINIversary - we're celebrating the whole year long!  If you're in the Austin/Round Rock, Texas area next month, come along to the Texas "All British Car Day". SteveBaker (talk) 00:04, 28 August 2009 (UTC)
 * There are sprays (or even some clothes dryer antistatic sheets) which can provide a subtle conductive path to drain off the charge. Edison (talk) 02:54, 28 August 2009 (UTC)
 * I'd ask the company to have that door checked very thoroughly. It could very likely be that an electric door lock has some creeping current or a short to the door handle. 71.236.26.74 (talk) 04:08, 28 August 2009 (UTC)

When do Baby's start going to the toilet?
According to my mother, when i was born the nurse held me and the first thing i did was to urinate on her! this got me wondering.. when do baby's start peeing and pooing? Does this first occur in the womb or what? 80.47.174.113 (talk) 13:12, 27 August 2009 (UTC)


 * Amniotic fluid is predominantly fetal urine. For 'number two', see meconium. TenOfAllTrades(talk) 13:52, 27 August 2009 (UTC)


 * What? I've been soaking in my own urine for the first 9 months of my life?!? Why isn't this little factoid more well known? --antilivedT 19:05, 27 August 2009 (UTC)
 * Do babies keep their mouths shut for 9 months, or just cough up a lot of piss when they are born? I see various flaws with this set up.83.100.250.79 (talk) —Preceding undated comment added 19:19, 27 August 2009 (UTC).
 * They swallow the amniotic fluid during gestation. Amniotic fluid is actually over 98% water, with the remainder consisting of fetal cells, urea, creatinine, bile, hormones and various elecrolytes. It circulates through the the stomach and lungs of the fetus and turns over quite rapidly. Rockpock  e  t  19:24, 27 August 2009 (UTC)
 * Well, technically, fresh urine is sterile and not really bad for you at all. It's only if it is left in air that bacteria gets into it and spoils it. Aren't there people who even claim that drinking it has health benfits? That's something I'm not willing to google from work ;) Vespine (talk) 23:54, 27 August 2009 (UTC)
 * No need, the 'paedia has it covered: Urophagia and Urine therapy Rockpock  e  t  01:14, 28 August 2009 (UTC)
 * Brand new babies do not smell like pee. I call BS on this. Edison (talk) 02:52, 28 August 2009 (UTC)


 * And why are you so sure of this fact?!! Have you been peeing on babies?? hahah Vespine (talk) 00:40, 31 August 2009 (UTC)
 * You are working under the (mistaken) assumption that fetal pee smells like post-natal pee. It doesn't. The amount of urea in amniotic fluid is much less than you would typically find in urine. This isn't at all controversial, a cursory goodle search will reveal as much. Rockpock  e  t  05:52, 28 August 2009 (UTC)
 * Even I know that babies receive a filtered food supply through the placenta - so a lot of the stuff that is extracted by the kidneys usually will be extracted by the mothers kidneys - it's not clear to me the extent of functioning of a foetal kidneys 83.100.250.79 (talk) 10:57, 28 August 2009 (UTC)
 * I believe human kidneys become functional around 12 weeks, urea is certainly found in AF around then. If there are fetal kidney defects, the fetus may not produce enough urine. The result of this is a reduced amniotic fluid volume which, in turn, results in respiratory defects in the newborn (since the AF is important for lung and trachea development). Rockpock  e  t  17:01, 28 August 2009 (UTC)
 * "Aren't there people who even claim that drinking it has health benfits?" -- See Borat. 98.234.126.251 (talk) 06:30, 28 August 2009 (UTC)
 * No doubt there are, but "Borat" is a fictional character...83.100.250.79 (talk) 10:59, 28 August 2009 (UTC)

Choking
If you accidently choked by drinking large amounts of water, from a glass of water, but was able to recover say 10 minutes without blacking out, what happens to the liquid in your lungs? Does it get absorbed into the body somehow? And why when you really choke on something, and after 3 minutes of having a coughing fit and able to recover, does it seem impossible to keep your eyes open? --Reticuli88 (talk) 13:34, 27 August 2009 (UTC)


 * When you cough, you are moving liquid/mucous up into your throat. If you accidentally inhaled liquid into your lungs, unless there is a lot of it you would cough it into your throat and swallow it without noticing. If there was a lot you would cough it into your mouth most likely. As far as keeping your eyes open after a coughing fit, I have never had that problem myself so I am not sure. The   Seeker 4   Talk  16:24, 27 August 2009 (UTC)
 * Sorry to be a pest on this spelling peeve, but I think a lot of folks just don't know this: mucous is an adjective, as in the phrase mucous membrane.  The word you want is mucus, with no o.  Same remarks apply to callus (a bit of thickened skin) and callous (an adjective, usually metaphorical). --Trovatore (talk) 22:18, 27 August 2009 (UTC)
 * I was recently watching a show we have about surf life savers and they rescued a girl who had nearly drowned. Even though she hadn't blacked out and appeared fine after coughing up some water they kept her under observation for a while because they claimed you can still suffer | Secondary drowning. Vespine (talk) 00:06, 28 August 2009 (UTC)

How long till unmanned plants stop?
For a thing I am writing, I'd need to know the following. If the whole humanity were to disappear suddenly, how long would power plants work? Are there systems that would shut them down immediately? Would some of them keep working for hours/days? And what is the answer for other infrastructures (water and gas networks, say)? And am I right in thinking that communication and GPS satellites would keep working for a while, or is there some kind of necessary remote maintenance? Thanks, Goochelaar  (talk) 14:04, 27 August 2009 (UTC)


 * See this article by the Straight Dope : "When the zombies take over, how long till the electricity fails?" It's an interesting read. (It is, however, North America specific.)APL (talk) 14:09, 27 August 2009 (UTC)


 * Hydroelectric, wind and solar plants would run a long time. Coal plants would run out of fuel fairly quickly (less then 48 hours) unless something happened to put them into automatic shutdown sooner.  Not sure on nuclear, but if your power runs too long and people suddenly disappeared, then a large amount of fires might break out quickly from people who had food cooking on their stove and such.  Googlemeister (talk) 15:05, 27 August 2009 (UTC)


 * The thrust of the article I linked seemed to be that unless specific steps were taken to allow things to fail gracefully, the whole system would come down almost immediately. Many power-plants would hit minor, routine difficulties and without operator intervention would be automatically shut down, this would screw up the whole grid, and that would in turn screw up even those power plants that would otherwise last a long time. APL (talk) 16:23, 27 August 2009 (UTC)


 * Having been involved in grid operation, I doubt that everything would immediately shut down. The grid would sectionalize, but it is full of automatic systems which are programmed to keep alive or reliven every section that is capable of withstanding system voltage. Hydro generation could go on a very long time. Solar and wind systems could automatically remain alive or resynchronize to a grid. Some such systems are designed to operate independently of the grid. Edison (talk) 02:51, 28 August 2009 (UTC)

Thanks a lot for the "Straight Dope" article (it exactly answers to most of my curiosities about power plants!) and the further remarks. Any idea about telecommunication satellites? Thanks, Goochelaar  (talk) 17:01, 28 August 2009 (UTC)

Using antennas
I have a circuit which generates some sine wave. I have to transmit this signal by some antenna. May be I will use a loop antenna. Can anybody please tell me how to do that ? —Preceding unsigned comment added by 218.248.80.114 (talk) 15:24, 27 August 2009 (UTC)
 * Connecting the antenna to the circuit's output tap is the best way to couple the circuit oscillation into a propagating radio wave. In fact, the circuit is transmitting already - just weakly.  The antenna will help match the impedance of the circuit to the surrounding air, and may provide directionality for the transmission.  What frequency is the sine wave?  What power is output (you might want or need a power amplifier).  What do you plan to do to detect the signal?  If you can answer these, you can narrow down your options significantly; otherwise your question is so broad that it's basically unanswerable.  Nimur (talk) 15:49, 27 August 2009 (UTC)
 * Well the signal is probably 10 Mhz. The signal is to be recieved in a room 32 x 20 feet with recieving antennas at the corners. The reception antenna will be dipole type. Reception circuit is to be designed too. —Preceding unsigned comment added by 218.248.80.114 (talk) 16:19, 27 August 2009 (UTC)
 * HF is a tough spectrum. You either need large antennas (e.g. 10 meters), or fancy tricks you can't afford.  However, you can get away with a crummy dipole whip antenna if you spend a little more effort on your power amplifier at the transmitter, and getting your receiver properly tuned (a nice low noise amplifier will help there, also).  Are you simply transmitting a continous tone, or do you have any information modulated on this 10MHz signal?  Are you trying to do position sensing?  If so, you'll need some clock synchronization (there are a lot of ways to do this).  Nimur (talk) 17:11, 27 August 2009 (UTC)
 * Well in that case i can in go to lower frequencies in the khz range. I will be sending a continuous tone and for position sensing of the sender by the receiver. Main consideration is to make the render antenna small and have low power consumption. Thanks.
 * Lower frequency will make it worse! You'll need an antenna thousands of meters long if you want to transmit effectively at VLF - and it's not very easy to build one.  Nimur (talk) 18:39, 27 August 2009 (UTC)
 * Well then I will go for any higher frequencies that can be generated by an antenna the size of a cellphone (maybe loop type). And at the same time be received by a high gain low bandwidth antenna. —Preceding unsigned comment added by 218.248.80.114 (talk) 19:11, 27 August 2009 (UTC)
 * You could experiment with a VCR RF output, which is a TV transmitter, coupled to a dipole, and dipole receivers. In the US, the VHF band is presently vacant in many locations due to the changeover to digital, so interference might be minimal. US VCRs have RF output typically on Channel 3 (72-78 MHZ) and Channel 4 (78--104 MHZ). There are in the US readily available transmitters to send IPOD or cassette audio to car radios via FM at both the lower(circa 88 MHZ) and upper ends (circa 108 MHZ) of the US FM band. Similar gadgets are probably available in many countries, with suitable changes to the channel frequencies. Back in 1892-1908, US inventor Nathan Stubblefield broadcast voice and music at base band frequencies (no high frequency radio waves) using loop antennas and induction. Edison (talk) 02:45, 28 August 2009 (UTC)

Local anaesthetics
I'm curious as to what local anaesthetic I'm likely to receive when I have my tooth removed. I'm told I may need an incision, too, so it's being done at the hospital. Is there a most likely candidate for this? Vimescarrot (talk) 15:51, 27 August 2009 (UTC)


 * See Dental anesthesia. Probably lidocaine. Good luck with it; hope it goes well. --Tagishsimon (talk) 15:59, 27 August 2009 (UTC)


 * Frequently dentists use a topical anesthetic to numb the gums prior to using an injected anesthetic. The two may or may not use the same active ingredients. -- 128.104.112.102 (talk) 16:34, 27 August 2009 (UTC)

Topical anesthetic is generally 20% benzocaine.  DRosenbach  ( Talk 15:28, 28 August 2009 (UTC)
 * Thanks. Vimescarrot (talk) 23:11, 27 August 2009 (UTC)
 * Via study and practice of Eastern Religions, might it be possible to transcend dental medications? Edison (talk) 02:47, 28 August 2009 (UTC)
 * Thank you, now kindly leave the stage! —Preceding unsigned comment added by 86.4.181.14 (talk) 07:10, 28 August 2009 (UTC)
 * I'd go for it if it was. Was that a quote? Vimescarrot (talk) 11:11, 28 August 2009 (UTC)
 * I believe it was a pun. -- Coneslayer (talk) 12:09, 28 August 2009 (UTC)
 * Dentist here. While there is no such thing as a "dental anesthetic" in that a drug is particular for dental medicine, if you are in the US, the dental anesthetic used be one of the following: 2% lidocaine 1:100K or 1:50K epi, 4% articaine 1:100K epi or 1:50K epi, 3% mepivacaine or 0.5% bupivacaine.  That being said (because those are really the only local anesthetics used by dentists), mepivacaine is usually used only as a last resort because it doesn't last very long in the absence of epi.  It's generally used for patients for whom low level intravascular injection of epiniephrine would be more detrimental than the average person (i.e. pregnant females and hypertensives).  Bupivacaine is useful in that it may last up to 6 hours, but it's generally not a first-line drug.  If you are being treated in the hospital (I suppose by an oral surgeon), you will likely be put under conscious sedation or general anesthesia, which involves an IV, along with the drugs used for those levels of sedation, such as propofol, midazolam, etc.  The anesthetic, as I said above, will likely be lidocaine or articaine, or both.  DRosenbach  ( Talk 12:40, 28 August 2009 (UTC)
 * The pun aside, the mental state has an effect on the reaction to dental procedures, in my experience. When the prepared adult understands that the scraping drilling, injection or whatever is necessary to health and to save teeth, it is different from the small child or wild animal which only perceives what seems like a destructive assault. Edison (talk) 15:15, 28 August 2009 (UTC)
 * Conscious sedation is what I'll be having. UK, not US. Why do they need to sedate me? Surgery while I'm awake doesn't concern me, so I'll be fairly calm... Vimescarrot (talk) 16:29, 28 August 2009 (UTC)


 * For several years, I was able to transcend dental medication when I decided that I didn't want to bother with bruising from the needle, walking around for hours with a non-working mouth, and the period as the anesthesia wore off when I would perceive an itch but couldn't scratch, which really drove me batty. So for minor cavities, I would just tell the dentist to start drilling and I'd tell him if he needed to stop (and then he would ask me five times if I was really, really sure). And indeed, proper mental preparation was the key, it actually went just fine, since I knew what was going on and that I could always stop him and ask for a shot. No Eastern religions were harmed in the making of those fillings. And no, I wouldn't do it for a root canal or extraction! Franamax (talk) 17:25, 28 August 2009 (UTC)
 * As a child, I was never even offered any kind of anaesthetic for cavities. I looked at my mother dumbfounded when my new dentist asked me, at age 13, if I wanted anaesthetic. Cavity fillings don't hurt...from memory of having teeth extracted before, injecting the anaesthetic is more painful. Vimescarrot (talk) 20:09, 28 August 2009 (UTC)

Sedation may be used for one of two reasons: patient-centered and operator-centered. The former could be when the patient says something like, "Oh no, Doc...I had a similar procedure done on the left side, and there is no way I'm staying awake for it again on the right side. You put me out!" It could also be because the patient is medically compromised and a sedated patient is in a more controlled environment, such that an acute medical emergency can be handled in a more appropriate fashion, as an IV is already in, etc. The latter could be because the procedure is going to be really long/annoying and the operator is not interested in having the patient completely awake for it, such as all four wisdom teeth being removed and the dentist knows the patient is a talker or reeeeeeally annoying. If the patient is fidgety, for example a child or a patient with mental retardation, OR dentistry may be the way to go. My wife works at the special care dental section at the New Jersey Dental School, and she sees patients almost every week in the OR for what would otherwise be routine dental work -- she just does all their work in 3 hours straight because they will not tolerate multiple appointments or people putting their hands in their mouth while awake.  DRosenbach  ( Talk 19:36, 28 August 2009 (UTC)

White noise generator
Would one of these transmitting in the range of 800-2500 MHz have any effect on nearby mobile phones, or could they filter out everything but their own signal? If such a device was able to interfere with mobiles, what sort of power would it need? This is not expressing an intention to do something illegal, just curiosity at the practicality of a method of alleviating a common social problem.→86.132.239.98 (talk) 16:10, 27 August 2009 (UTC)
 * It depends on the strength of the signal - it's worth noting that white noise will be the simplest to filter out -  a psuedo digital signal would probably intefere worse at lower signal strengths.83.100.250.79 (talk) 17:10, 27 August 2009 (UTC)
 * We have discussed cell phone jammers many times previously. There are commercially available cell-phone jammers; however, these rarely work by "jamming" (e.g. saturating the front-end amplifiers with a powerful interference signal). A white-noise generator might actually have a chance; but it's unlikely you can put enough power into 2 octaves of frequency-spectrum unless you have a very large power source.  Instead, a commercial jammer is more properly described as a form of electronic countermeasure, and operates by transmitting a digital interferance (as 83.100 has pointed out above). In reality, mobile radiotelephones are extremely resilient to such jamming; they operate on a lot of bands with a lot of channel options and digital encoding schemes designed to tune out interference; and if you make a jammer that is even moderately powerful, you will certainly attract the attention of the phone company and the FCC (if you're in the US).  It's much easier to block signal reception (with large concrete walls, for example) than to try to actively jam the signal.  Nimur (talk) 17:17, 27 August 2009 (UTC)
 * Wouldn't small metal walls be better than large concrete ones? --Tango (talk) 17:51, 27 August 2009 (UTC)


 * I don't think this is how mobile phone jammers are supposed to work. As I understand it, it only needs to jam the signaling channel, which is used for setting up phone calls. The interference signal from a jammer, say one installed in a movie theater, only needs to emit enough power to stop the nearby mobile phones from listening to the signaling channel. --98.114.146.168 (talk) 12:04, 28 August 2009 (UTC)
 * The "Faraday cage" effect is just... it's just a bad, terrible, completely inapplicable approximation for almost any such physical context. We've discussed "faraday cages" with regard to microwaves, elevators, skyscrapers; ... the wavenlengths involved in mobile telephony are long enough that thin metal walls are pretty transparent.  Tree leaves are a better "faraday cage" than a sheet of copper    (at least, at UHF and similar mobile-telephone bands).  Try standing in an elevator and making a cellular telephone call - chances are, you'll have fantastic signal strength.  Then try it in a basement - chances are, you'll have no signal strength (even just three or four feet underground).  Nimur (talk) 18:36, 27 August 2009 (UTC)
 * Bear in mind, you are three or four feet underground vertically. The cell tower won't be directly above you, so will have to go through quite a lot of ground to reach you. --Tango (talk) 19:37, 27 August 2009 (UTC)
 * Thanks to diffraction, though, the radio wave can bend around corners . The signal does not need to be line-of-sight.  I suspect the lack of signal in the basement is more due to the presence of a building structure over you, rather than the ground surrounding you.  Nimur (talk) 22:04, 27 August 2009 (UTC)
 * You must have a better phone than mine. Mine never works in elevators. APL (talk) 21:01, 27 August 2009 (UTC)

Visual acuity
Does a person with a visual acuity of 6/7.5 or 6/9 need glasses? 86.166.47.99 (talk) 16:49, 27 August 2009 (UTC)
 * Need glasses for what? To see? No. To see better? Yes.
 * You would have to consult with a optometrist and discuss your needs. However, both are probably sufficient to drive in the UK without requiring corrective lenses (In the United Kingdom, the legal standard of vision for driving is roughly equivalent to 6/10, though this not precise). Rockpock  e  t  17:20, 27 August 2009 (UTC)
 * There is a lot more to consider than just visual acuity. My visual acuity is 6/5 (that is, better than "normal"), but I still have glasses that I wear for close up work (I should be wearing them now... oops!) to correct an astigmatism. --Tango (talk) 17:48, 27 August 2009 (UTC)
 * Whatever happened to "20/20?" Edison (talk) 02:35, 28 August 2009 (UTC)
 * 6 meters is approximately 20 feet. Both are the standard distance for measuring vision.  See Snellen chart. -- Tcncv (talk) 03:19, 28 August 2009 (UTC)

electrical technology
can you suggest two procedure for the determination of thevenin resistance. —Preceding unsigned comment added by 203.110.246.230 (talk) 17:14, 27 August 2009 (UTC)


 * Amazingly, two methods are provided in our article, titled Thévenin's theorem. You can also read Norton's theorem, which is closely related.
 * Nimur (talk) 17:19, 27 August 2009 (UTC)

Sterilization of Psylocibe spores
Hello, my question is how can psylocibe spores be killed 100%(true heat, and if what temperature?) or are there any other safe methods?TY —Preceding unsigned comment added by 89.122.224.95 (talk) 20:12, 27 August 2009 (UTC)
 * ? What do you mean "safe methods" and why would you want to? Are you trying to torch your neighbor's magic mushroom patch? In that case you'd have to destroy the Mycelium. 71.236.26.74 (talk) 03:55, 28 August 2009 (UTC)
 * I would expect that boiling water at 100°C for 10 minutes should kill all the fungus spores. Graeme Bartlett (talk) 09:26, 28 August 2009 (UTC)


 * Mix the spores into honey, and put the honey on a roaring coal fire.83.100.250.79 (talk) 10:54, 28 August 2009 (UTC)

Gravity waves
What is the fundamental difference between gravitational waves and the varying gravitational field that is produced by any moving mass (such as the earth orbiting the sun)? (I assume there is one because gravity waves are apparently extremely difficult to detect and yet variations in the gravitational field emanating from the moving Earth, say, as it appears to a fixed observer, would seem to be trivial to detect.)
 * A Gravitational wave is a fluctuation in the curvature of spacetime that propagates as a wave, traveling outward from the source. In contrast, if you're in a spaceship passing by the earth, the changes in spacetime curvature that you experience are just due to your motion relative to the earth.  In other words, if you stay at a fixed location relative to the Earth, your spaceship will not experience any changes in spacetime curvature (changes in gravity).


 * Technically, for an isolated system to be a source of a gravitational wave, the third time derivative of the quadrupole moment of the system's stress-energy tensor must be nonzero. This will not be the case for a spherical object like the Earth or the sun that's just sitting there (or equivalently, moving at a constant speed), even if the object is spinning.


 * Two objects orbiting each other, such as the Earth-sun system, does radiate gravitational waves, resulting in the Earth slowly getting closer to the sun over time. However, the  gravitational waves radiated by the Earth-sun system are only enough to stretch or squeeze a ring of particles by just 1 part in 1026, which is much smaller than the 1 part in 1021 that can be detected by LIGO.  Red Act (talk) 23:45, 27 August 2009 (UTC)


 * Thank you for your reply, Red Act. Let me be a bit more specific. Let's say I'm at some distance away from the solar system, and I have a very sensitive way of measuring the strength of the gravitational field. As the earth orbits the sun, I'll see a wave-like fluctuation in gravitational field strength (all other things being equal), with a period of one year, simply because of the relative change in the configuration of the two bodies, and this will emanate away from the solar system at the speed of light. Is that correct? But the thing that confuses me is whether this is the gravitational radiation that you refer to, or whether it's a completely different effect. 86.133.242.249 (talk) 00:59, 28 August 2009 (UTC).


 * I think that is the gravitational wave, if I understand your use of terminology. The fluctuations in the net observed gravitational field, due to the motion of a distant source (mass), propagate with a fixed speed and represent energy movement (at least, so goes the gravitational wave hypothesis).  This phenomenon is a gravitational wave; it is not entirely clear what mechanism allows such a fluctuation in observed net gravitational force to exist.  Some hypotheses include the graviton, a proposed particle which "carries" these energy fluctuations per wave particle duality; but they have as-yet never been definitely measured in an unambiguous way.  Another problem is that such a mechanism implies that other wave phenomena, attributable to the higher order moments of the system's stress-energy tensor, are possible.  This implies things like like [[polarization of the gravitational wave, (though these implications have not yet been observed).  One of the key problems is that such energy propagation must satisfy conservation of energy - which means that simply by moving, a mass is radiating energy in the form of gravity waves; yet, with no fixed frame of reference, a particle can be said to be moving; and so we need a more elaborate method (such as general relativity) to describe the relationship between the induced gravitational wave and the particles' state description.  Also, note that the term "Gravity wave" is not synonymous with gravitational wave - the first is a classical effect that is well-documented and observed in Earth's ocean surface, mesosphere, and elsewhere; the latter is the relativistic physics hypothetical phenomenon.  Nimur (talk) 01:16, 28 August 2009 (UTC)


 * Thanks Nimur. If a gravitational wave is, as you say "fluctuations in the net observed gravitational field, due to the motion of a distant source (mass)", then I guess my question is: Why are the things so hard to detect? Couldn't an experiment be set up on earth using a rotating dumbbell apparatus with a very sensitive gravimeter nearby? And why are they necessarily waves? Wouldn't a mass in non-periodic motion generate a non-wavelike fluctuation? And finally, I thought that there was still some doubt about whether gravitational waves actually exist. It seems self-evident that the movement of a mass would affect the gravitational field at some remote location. How could it be any other way? I think some of my questions might betray some fundamental lack of understanding on my part. 86.133.242.249 (talk) 01:46, 28 August 2009 (UTC).
 * They are difficult to detect because they are very weak. The concepts involved in detecting them are very simple - you have two rods at right angles to each other and measure them continuously to see if they change length - but the amount they will change length by is extremely small. "Wave" in physics means anything that propagates, it doesn't have to be periodic. There isn't much doubt - gravitational waves are an obvious consequence of a finite speed of gravity. The only real doubt is whether we will be able to detect them. If they aren't there at all then the whole of general relativity goes up in smoke, which would be very surprising because it has made lots of very accurate predictions. Pre-general relativity the speed of gravity was assumed to be infinite, if there aren't any gravitational waves we would need to go back to that assumption. (And find other explanations for things like inspiraling pulsars.) --Tango (talk) 02:18, 28 August 2009 (UTC)
 * Thank you Tango. I'm sorry to labour this, but it's been confusing me for ages. I think my mistake was in assuming that any detection of a change in gravitational field due to a moving mass (which sounds easy) would be evidence of gravitational waves (i.e. some sort of "propagation" of gravity). From what you say this is wrong for two reasons: first, this would not (by itself) show that the speed of propagation is finite; second, it would not tell anything about the relativistic model of gravitation as a distortion of spacetime, which is the model in which the concept of gravitational waves is couched. Is this more or less correct? 86.133.242.249 (talk) 02:37, 28 August 2009 (UTC).
 * You may be assuming that you would measure the change in the field by measuring the field itself at different times and comparing them, that won't work - the obvious way of measuring a field is to measure the force is induces, but with gravity the force on your test mass will be the same as the force on your detector (since you are in free fall with respect to anything other than the Earth) so you won't detect anything at all. You have to measure the change directly by measuring the tidal forces, that is what the two rods at right angles I mentioned are doing. Those tidal forces are very weak since to get large changes in gravity you need fast moving, heavy objects that are close by, and there aren't any. We have to make do with fast moving, heavy objects that are far away. It should also be pointed out that movement isn't actually enough, you need acceleration. Somebody else will have to explain why, though, because I'm a little confused by that (I know it must be true because emitting gravitational waves costs energy so can't depend on motion, which is relative to the frame of reference, but can't work out how it works...). --Tango (talk) 03:03, 28 August 2009 (UTC)